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TRENDS IN THE DEVELOPMENT OF ADVANCED METALS WITH REGARD TO ENVIRONMENTAL COMPATIBILITY

PART I: TECHNICAL SOLUTIONS WITH THE AID OF ADVANCED METALS

Heinz F. Voggenreiter, Rolf Homann Munich, Germany

For United Nations Industrial Development Organization UNIDO, Vienna Dept. New Technologies

October 1995 Content

1 Introduction

2 Fundamentals

Application-based solutions

Production-process-based solutions

3 Objectives of the Study

4 Tendencies in Technical Solutions for Ecological Compatibility

4.1. Light-weight structures

4.1.1. Ground transportation systems

General Aspects of Light-Weight Construction in Ground

Transportation Systems

Ground transportation systems - Materials Overview

4.1.2. Aerospace Applications

General Overview

Aerospace Applications - Materials Overview

4.2 Efficiency of Thermal Engines

4.2.1 Automotive Engines

4.2.2 Industrial Gas Turbines and Aeroengines

5 Materials and Processes

5 .1 Ferrous Alloys

5 .1.1 High-strength steels

5.1.2 Bake-hardening steels

5.1.3 Tailored Blanks

5.3 Intermetallic Alloys

5.3.1 Aluminides

TiAl (y)-based alloys

Ti3Al (a2 )-based alloys Ni3Al

NiAl

5.3.2 Silicides

Al-Mg2Si and Mg-Mg2Si

Molybdenum Disilicide MoSi2

5.4 Dispersion Strengthened Alloys

Oxide Dispersion Strengthened-Aluminium Alloys

Oxide and Carbide Dispersion Strengthened Al Alloys

ODS Nickel Base Alloys

ODS NiAl Alloys

ODS Iron Base Alloys

5.5 Light-weight Alloys

5.5.1. Aluminium Alloys

Aluminium-Lithium Alloys

High-Strength Aluminium Alloys

5.5.2. Magnesium Alloys

5.5.3. Reinforced Light-weight Alloys Production processes

Properties of Reinforced Aluminium Alloys

Reinforced Titanium

Reinforced Magnesium

6 Summarizing Discussion

6.1 Materials For Light Weight Structures

6.2 Materials For Increased Efficiency of Thermal Engines References

Figures

Abriviations TRENDS IN THE DEVELOPMENT OF ADVAN CED METALS WITH REGARD TO ENVIRONMENTAL COMPATIBILITY

PART I: TECHNICAL SOLUTIONS WITH THE AID OF ADVANCED METALS

Heinz F. Voggenreiter, Rolf Homann

Munich, Germany

However, ecological studies and current Introduction activities on the modelling and prediction of global warming and its negative effects lead to Ozone thinning, the greenhouse effect, global industrialized countries calling for a reduction in warming, lack of drinking water - these are the energy consumption. In the course of alarming keywords which are found all over the industrialization the semi-industrialized world predicting an ecological collapse caused countries counteract this positive development by intensive environmental pollution. The main by their increasing energy demands, especially reason for most of the polluting reagents is the for current generation and industry, insisting on generation of energy and the consumption of the use of their own local fossil energy natural resources for the different needs of the resources. Nevertheless, at present the human race. In most cases energy is generated industrialized countries are the dominant by firing fossil resources such as oil, coal and initiators of air pollution. Figure 1 shows the natural gases, thus affecting the environment USA, the former USSR and China at the top of through the emission of gaseous reagents. The the list of the percentage share in the worldwide energy consume for heating, cooling, transport, emission of greenhouse gases of the different industry and the generation of current rises from countries [3]. year to year due to the progressive tendencies in global industrialization, increasing prosperity, Consumption of fossil energy sources and and finally due to the exponential growth rate of therefore greenhouse gas emission can be the human race. Thus the emission of so-called assigned mainly to the four sections greenhouse gases and aerosols is additionally heating/cooling, transport, industry, and current increased. Table 1 summarizes the main generation. In 1991 the total global energy reagents affecting the global climatic situation, consumption amounted to about 11 billion of their mostly man-made sources and their coal equivalents [I]. stability in the atmosphere [ 1]. Current results of mathematical modelling predict a severe Because of the impossibility of reducing of increase of the surface air temperature of up to global energy consumption, the consequence of 2.5°C in the year 2040 based on the effect of this environmental situation should be to both greenhouse gases and aerosols [2]. This develop alternative energy resources. Studies by must be seen in conjunction with the ongoing K.-P. Molier [1] show the technical feasability thinning of the ozone layer. of switching energy-consuming processes to alternative energy sources, avoiding 75% of Application-based solutions C02 but merely doubling the specific energy price. However, international and • reduction of weight for all kinds of intercontinental economic competition makes vehicles and for the moving parts of such a step virtually improbable. Thus, only engines competition-compatible, conventional technical solutions are practicable which promise a • improvement of the energy efficiency of stepwise reduction of the emission of harmful thermal, engine-driven machines reagents. • Applications based on natural raw materials 2 Fundamentals Production-process-based solutions Future-orientated solutions to satisfy the demand of mankind for energy are based mainly • optimization of the production processes on the search for alternative energy resources. A • Recycling of materials lot of investigations are being conducted on energy production through fuel cells or solar­ WEIGHT REDUCTION can be realized by based processes such as photovoltaics, solar new, light-weight designs in addition to the use plants, solar collectors, etc. By using solar of advanced materials such as modified plastics, processes or hydroelectric power plants , water metal alloys and natural materials such as is broken down into hydrogen and oxygen to be cotton, coco fiber and natural rubber. The light­ used as fuel components for thermal engine­ weight effect is mainly based on the following dri ven machines. This reduces greatly the materials properties: particle and reagents emission. However, this technique necessitates the development of • specific weight hydrogen storage and adapted motor concepts. A further solution for transportation is the use of • Young's modulus (stiffness) electric motors based on future current generation with solar plants or photovoltaics. • strength Also fuel cells, using hydrogen and oxygen as reagents or the Molten Carbonate Fuel Cell Lower material specific weight will directly (MCFC), are thought to be good candidates for reduce the application weight. However, automotive engines. All these developments are materials with low specific weight but medium-term or even long-term solutions and insufficient stiffness and strength only must be carried out with priority. Taking into contribute moderately to the reduction of account the rapid increase in energy and raw weight. In general, the required application materials consumption, caused by the prosperity performance limits the admissible elastic of the industrialized countries and the increasing deformations caused by operational loads. Thus, industrialization of the developing countries, the stiffness of the material used must be high short-term solutions are necessary. The main enough to meet the tolerances required. Stiffness demand is the systematic decrease in the is the mathematical product of Young's consumption of fossile resources and raw modulus and the moment of resistance against materials. bending, respectively torsion. As the moments of resistance depend on the part's dimension, Solutions are fundamentally based on the too low a Young's modulus must be following technical approaches, mainly driven compensated for larger dimensions in order to by the demand for fuel and raw materials saving attain the required stiffness. This means partial (fig. 2): or complete compensation of the specific weight-induced light-weight effect. The situation that low-specific weight materials 2 commonly show a low Young's modulus is the THE TOT AL EFFICIENCY of thermal, engine­ driving force for materials researchers to invent driven systems is based on the efficiency of the new modified material composites featuring thermodynamical process itself and the both low specific weight and high stiffness. dissipation of energy caused by friction between articulating machine parts. Thus, the total High strength at room temperature as well as efficiency can be improved by at elevated temperatures is a requirement for weight-optimized structures. High material • optimizing of the thermodynamic process strength permits the appropriate reduction of of the thermal engine application dimensions. However, many low­ specific weight materials, plastics or metal • increasing the admissible rate of alloys show insufficient strength at low revolutions by reducing the weight of temperatures and severe creep effects under load oscillating engine parts at elevated temperatures. As a consequence, the reduction of stress by enlargening of the part's • reducing friction between moving parts dimensions results in an increase of weight. This This study focuses on the first two topics. fact shows the necessity of developing of new plastics and alloys as well as modifiying of the The efficiency of the thermodynamic process existing materials with secondary phases in is dominated by the level of the entrance order to improve the material strength temperature of the gaseous medium. Efficiency corresponding to the operational and weight increases at higher temperatures. Additionally, a requirements. higher admissible gas temperature m combustion chambers improves the In summary, the results of the above completeness of the chemical reaction. This paragraphs, i.e. low material specific weight in leads to an increase in efficiency and combination with both high stiffness and high consequently to a reduction of pollutants. strength, are necessary to reduce application Depending on the type of thermal engine, weight. temperatures from 600°C up to 1400°C are Additionally, the weight-saving potential of discussed. materials with low specific weight, high Higher process temperatures require new stiffness and high strength is limited by the advanced metal and ceramic materials matching materials' formability. This leads to critical the complex thermal-mechanical load situation. design limits in forming processes such as The main demand concerning mechanical casting, forging, milling, etc .. Thus, in order to properties is an improved resistance to fatigue gain maximum weight saving, two materials and creep at elevated temperatures in addition to development approaches are being pursued: a sufficient degree of ductility. This postulates a • the development of new advanced microstructure which is thermodynamically materials or material compounds with low stable at the required temperatures over an specific weight, high stiffness and high economically useful period of time. Depending strength on the operation environment (corrosive, inert medium, etc.) an additional acceptable • appropriate processes for optimum resistance of the material to high-temperature formability of the above-mentioned light­ corrosion and oxidation is inevitable. Since weight materials in order to make there is no steady state for microstructure and maximum use of their weight-reduction corrosion, respectively oxidation, at elevated potential. temperatures, intensive efforts are being made to modify materials in order to prolong the period Both material cost and process cost must be of these changes. Concerning the mechanical compatible with the competitive situation. properties, optimizing of the material's chemical

3 composition and solutions based on material must be carefully compared with the predicted composites is being pursued. Corrosion, technical and environmental benefits of the new respectively oxidation behaviour, is improved material. by defined adaption of the chemical composition or by appliying of protective RECYCLING is a key target for all standard coatings. However, in most cases the first materials and new advanced materials used in "intrinsic" solution exhibits contrary effects on mass production. The main goals are saving the mechanical properties and oxidation/corrosion raw materials resources and primary energy for resistance. materials production and to reduce waste. The best example is the virtually complete material The demand for increased rates of r~volution loop circuit for steels. However, for many for oscillating or rotating engine components materials the main problems are founded on the leads to the necessity of materials with low fact that recycling the same base material but specific weight in order to reduce the mass with different chemical additives leads an forces. For components used at room deterioration of the materials quality. temperature and slightly above or below, the Additionally, research activities over the past technical problem is comparable with that of the years have been based more and more on above-discussed light-weight structures. adapting materials properties to the technical However, the combination of low specific requirements by means of materials composites weight and high mechanical and thermal loads and compounds. Metal-polymer compounds, for postulate more advanced materials properties. instance, are thought to combine the New materials such as intermetallic alloys are advantageous properties of both these different being developed in order to close the gap materials. However, separating of these different between standard metal alloys and ceramics for materials for recycling is a severe problem. This high-temperature, light-weight applications. shows that the production of tailor-made materials often counteracts recycling OPTIMIZED PRODUCTION PROCESSES are requirements. necessary to reduce energy consumption during material and component manufacturing. High­ A new approach to environment compatible performance computer systems for process materials is the use of natural materials. This control and new processes provide a powerful concept is commonly named Design for feature for this objective. Also "old" material­ Environment (DFE). Advantage of natural production processes, such as steel production, materials is, that they can easily be diposed by have to adapt to the new requirements. Process emitting exactly that quantity of C02 they steps like ore drying, coke production, etc. must consumed during growth. Thus ecological be dicussed critically. New knowledge in balance is guaranteed. Typical representatives of materials science and chemistry offer a baseline such materials are cotton, coco fiber, natural for new developments. Investigations on the rubber etc.. They are up to one fifth of the ecological harmfulness of chemical reagents weight of metal or polymere materials. Typical necessary for materials production lead to a applications are automotive parts such as door better understanding of the interaction of covers, head restraints and insulating parts. industry and environment, necessarily bringing Even composite materials are thought to be about a partial reorientation of the industry. produced by replacing glas fiber by flax fiber in glas fiber reinforced plastics. The future could However, advanced high-performance even be the replacement of oil-based plastics by materials, such as metal/metal and metal/non­ tree resin. metal composites, dispersion-strengthend materials and materials of high purity are based To SUMMARIZE the above-mentioned aspects, on new, sometimes exotic processes. Increased the complexity but also the potential of energy demand and production expenditure material-based solutions for reducing the

4 em1ss1on of reagents are obvious. Current resultant development of new or modified metal research in the field of materials engineering alloys is described and discussed. These results clearly shows the path towards tailor-made provide the necessary baseline for the further materials for the specific operating conditions, parts of the study and for the last and most applying material composites and compounds. important part, the global view of the life cycle However, in many cases the structure of such pollution of new materials-based solutions. This tailor-made materials is not completely comprises an estimation of the total consumed compatible with the requirements for a energy and emitted harmful reagents of a recycleable material. Thus, the development f technical component, including raw material new advanced materials will always featuren the production, transport, processing, recycling conflict between ecological, economic and and/or waste disposal. Only in the context of technical aspects. this final global view can the real degree of benefit of new materials solutions for the reduction of environmental pollution be defined 3 Objectives of the Study within statistical limits. In this study a global overview is given of current and future technical research with the 4 Tendencies in Technical Solutions f aim of reducing the ecological incompatibility or Ecological Compatibility of critical technologies such as heating/cooling, current generation, industry, transport. Focussing on the emission of reagents and 4.1. Light-weight structures sparing energy and raw materials, solutions from the materials research point of view are 4.1.1. Ground transportation systems pointed out, referring to the above paragraphs. In ground transportation systems (cars, trains With respect to the above paragraphs and the and trucks), weight reduction is one of the most wide field of researches into metal, ceramic and important research fields. Reduced structural polymer materials, a complete study of new weight is necessary to just keep the level of fuel advanced materials and their environmental consumption constant because of the weight­ compatibility must be subdivided into the intensive security devices such as airbags, ABS following seven sections: and so on. In trains, the requirements for comfort (airconditioning, kitchen) are weight­ Part I: Metal Alloys intensive but necessary components of modem train systems. Trucks virtually need to have a Part II: Ceramic Materials low structural weight, as they must carry as Part III: Polymeres much freight as possible.

Part IV: Natural Materials General Aspects of Light-Weight Construction in Ground Transportation Systems Part V: Production Processes Weight saving is (in most cases) an Part VI: Recycling expensive thing. Often it is necessary to use new machining and joining technologies. Further, Part VII: Global View on Life Cycle every material has its own "rules of Pollution construction" which have to be learned. All these things are expensive and risky, especially In the following Part I of the study, in public transportation systems - and thererfore tendencies concerning metal-based solutions for new light-weight constructions will be light-weight structures and the increased established only when there is a significant efficiency of thermal engines are indicated. The 5 marketing advantage. This advantage could be new locomotive contammg high amounts of an improved environmetally benign product. In plastics and light metals in combination with a the European automotive industry an additional new aerodynamic design [5]. An example of expense of 6-8 U.S.$/kg weight reduction is light-weight lorry construction concepts can be accepted due to the fact that 100 kg weight seen in (fig. 4 [5]). In future many parts of both reduction effects 0.3 - 0.6 Ill OOkm fuel saving. street and rail-guided systems will be based on light metal and plastic materials. There are different philosophies in light­ weight construction. The first and apparently Ground transportation systems - Materials easiest method is to optimize the conventional Overview steel construction principles. The use of high­ strength steels, bake-hardening steels, tailored The major light-weight materials used for blanks, and laser-beam welding technologies automotive and train applications are aluminium will allow saving about 20 kg in a car body of and magnesium alloys. At the moment (1995) 400 kg raw weight. The weight reduction interest in magnesium is increasing, although in increases with the amount of light metals. A the past quite a lot of magnesium was even pure aluminium car (same raw body weight) used, especially in automotive systems. Because will be about 130 kg lighter than a conventional of this fact, the emphasis of this part of the steel body - but nearly 40 % more expensive, study focusses on the basic magnesium see fig. 3 [4]. For example, the new BMW 5 technology and the major differences between series is equipped with an aluminium chassis, magnesium and aluminium in terms of the rest of the structure consists of conventional fundamental technological properties. An steel. The automotive and especially the overview of aluminium technology is given in commercial vehicle market is very sensitive to the section "Aerospace Technology: Materials the cost/benefit ratio [4]. The tranportation Overview". industry (trains and trucks) is very interested in low operating costs because of the long MAGNESIUM for automotive mass-production distances that goods have to be carried in was first introduced in the Volkswagen "Beetle" modern times. Although fuel consumption is in 1936. It contained more than 18 kg of only one part of the operating costs it is still a magnesium when it went into production after big one - and in future the fuel price may World War II. The main reason for the extensive increase because of new, environmentally use of magnesium in those times was the benign tax systems. At the moment discussions remaining stock of magnesium from war plane are under way in the European Union to production. At the end of Beetle production in increase the taxes for environment-polluting 1980, the entire amount of magnesium used was products such as fuel or some chloride-based about 345.000 t [6]. Magnesium offers a whole chemical products. From this point of view it is number of advantages for the automotive a necessity for the industry to develop products industrie. featuring low energy consumption. Some • Highly developed technical processes politicians in Germany demand a fuel price of 3,30 U.S. $/1 (exchange rate: 1$ = 1,50 DM) in • High castability the year 2005. Today we have a price of 1 US$/l. If only half this demand is be followed, • Nearly unlimited resources (seawater) we will have a fundamentally new situation in the European industry. • Stable prices

Today there are developments in progress in • Not traded on the commodity exchange all parts of the transportation system industry to obtain competitive products for the next Magnesium with a specific weight of p=l,7 millennium. For example, AEG has developed a g/cm3 offers a very high structural efficiency.

6 This means the ratio between the load it can material satisfies all functional and crash-energy support and its weight. It is defined as PN p, management requirements because of its where P is the load, V is the volume of the part toughness and high elongation. A new alloy and p is the specific weight of the material. The development is the alloy AE42. This alloy range of this ratio is shown in fig. 5a [6]. It is contains 2% rare earth metals and has a high obvious to see that magnesium offers creep resistance. Its operating temperature up to competitive properties in comparison with the 175 °C (the maximum for AM and AZ alloys is other materials. 135 °C) makes it very interesting for light­ weight drive-train applications. Although not Another important property of an engineering yet qualified, the material is being considered material is its stiffness. The stiffness is relating for applications such as automatic transmission to the elastic deflection of a part (for example a housings [7]. beam) under load. The higher the stiffness, the lower is the deflection. The values for Young· s All current magnesium applications at the big modulus are given in fig. 5b [6] for the most automakers are die castings. Some applications important structural materials. At first glance it in die-cast magnesium are shown in fig. 6 [8]. seems that magnesium has the lowest stiffness Because of the relatively large investment of all the metals. But from the point of view of necessary for production dies, much of the light-weight construction, the ratio between preliminary design and test work is often done stiffness and weight is of greater interest (fig. using plaster - or sand-cast prototypes [6]. Sc). With regard to strenght, magnesium offers ALUMINIUM and magnesium technology meet • Nearly the same stiffness I weight ratio at this point. Many structural parts made of as magnesium were constructed as aluminium parts and then - depending on the actual cost • Higher strength I weight ratio ratio between aluminium and magnesium raw material - die-cast in the same dies with the than aluminium and steel. cheaper material. Therefore a magnesium­ optimized construction to take advantage of the The major problems in the usage of excellent properties ( castable to thinner wall magnesium are its about two times higher price thickness than aluminium) is often not possible. compared to aluminium and from the technical In past years, aluminium often won the cost point of view the contact corrosion. Magnesium competition. Aluminium has many advantages exhibits contact corrosion to every other metal for structural applications. Its high availability of engineering interest. This matter has to be in combination with low and relatively stable considered in every construction containing prices makes aluminium a very interesting magnesium. Furtheron, exposing magnesium to engineering material. Aluminium offers high elevated temperatures in the range of 120°C stiffness, low weight (p=2, 7 g /cm3) and good and higher effects creep problems. castability. In contrast to magnesium, the In recent years many classical steel products shavings of aluminium are virtually in the automotive industry have been replaced inflammable. The corrosion resistance of by magnesium because of its high­ aluminium is in the order of magnitude of strength/weight ratio and its good castability. magnesium, but it has a smaller tendency to For example, alloy AM60 replaces steel in a van galvanic corrosion. The main poblem in seat component. The reduction of weight in this magnesium is often its poor creep resistance. At special application is from 4kg (steel elevated temperatures (> 120 °C) aluminium is component) to 1kg (magnesium component). often the better choice. The part is, like nearly all magnesium parts, die­ From the recycling point of view it has to be cast. Alloy AM 60 is also used for instrument considered that aluminium alloys are divided panels and steering wheel armatures. The

7 into two basic alloy types: The wrought alloys alloys and titanium-based alloys. These alloys, and the cast alloys (magnesium cast and based on the AlMg-system (2xxx) and AlZn­ wrought alloys are also subdivided - but system (7xxx) and TiAlV alloys offer the best magnesium is only used in the automotive compromise between all the requirements of industry as a casting alloy). The problem is that aerospace engineering. in the recycling process of aluminium (melting of scrap metal), a casting alloy - which often A study by Lockheed Ind., although written contains high amounts of silicon and copper - for a military plane, is of general interest [ 11]. It does not have to be mixed with a wrought alloy. says that if weight is to reduced by 10%, the When such mixing happens, the result is an density must also be reduced by 10%. In this alloy with poor castability and - as a wrought case the strength has to be increased by 35%, product - with low strength and ductility [9]. the stiffness by 50% and the fatigue tolerance Sometimes the combination of cast and wrought indeed by 100%. This strongly underlines the alloys in the same product is of great advantage position of light-weight metals in aerospace and then the mechanical engineering demands applications. Aluminium is - because of its counteract the recycling point of view. In lower price - always the first choice. Only when spaceframe structures for cars, the combination special demands (corrosion resistance, strength of extruded profiles with cast knots is the or creep resistance) require special properties, is preferred solution. The necessity to take apart expensive titanium used [10]. the knots and the rest of the structure makes the recycling process expensive. Aerospace Applications - Materials Overview The question for the aerospace engineer is to 4.1.2. Aerospace Applications find the best compromise between cost, safety and weight (fig. 7). In the next paragraph of the General Overview study, a general overview about the most important development approaches and a short For aircraft, light-weight construction is a description of the "state of the art" will be fundamental assumption to guarantee the provided. function and the economic efficiency of an aeroplane. Every kg of weight reduction In past years the content of light metals, increases the payload and decreases the fuel especially of aluminium, has decreased in consumption. In contrast to the situation on the aeroplanes. The reason is simple: The automotive market, the accepted cost-increasing development of advanced plastics. Fig. 8 [12] per kg weight reduction for aeroplane shows the increase of the content of plastic­ applications is about 600 - 800 U.S.$ [10]. composite materials and the decrease of Further, the production period of a type of aluminium from more than 70% (A300) to aircraft is significantly longer than that of about 65% in the new Airbus A340. On the automotive systems. An aircraft type will be other hand, the content of new Al alloys in the produced over a period of 15 and more years. planned Airbus 2000 will be about 10-15%. The development costs must be regained in this These new alloys such as AlLi or AlMgSc must time. be discovered or developed over the next 5-10 years. In aerospace construction, not only the weight is a matter of interest. The fatigue In 1994 Alcoa developed a new AlLi alloy behaviour and the strength-to-weight ratio play with reduced specific weight due to lithium. It an important role in the selection of materials. features a 200% higher fatigue-crack-growth Therefore the major alloy systems for structural resistance than AA7075-T651 (AJZn-based and application are not aluminium and magnesium heat treated). It is also reported to have 35 % cast alloys, as for trains and street-guided higher fracture toughness than AA 7075. A transportion systems, but aluminium wrought potential application for this new alloy might be 8 the vertical stabilizer and tailplanes for the interest only. Whiskers are said to cause cancer, Boeing 777 or Airbus 330/340. Investigations and the benfit of the properties of the composite on the resultant weight reduction show that, is relatively low compared to the other using the new alloy, weight savings of about reinforcement materials. 12% could be realized fpr the above-mentioned parts (related to conventional aluminium alloy). The main effect of the reinforcement is an The cost per kg weight reduction is 480 U.S.$ increased Young's modulus and therefore a [ 13] and therefore in an acceptable range. higher stiffness of the material. The maximum tensile strength does not increase by particulate­ Table 2 (12] shows the typical application reinforcement, although the strain-hardening fields for the two major aluminium alloy groups rate and the yield strength will increase. This 2xxx and 7xxx. Metals are always the first effect is called the stain-hardening effect and is choice when excellent fatigue resistance in based on the increasing internal stress caused by combination with high ductility are needed to dislocation movement. In reinforced metal fulfill the safety requirements. Especially the matrices, the dislocations cluster at the particles alloy series 2xxx, based on the AlCuMg-system, or fibre boundaries and strengthen the material. is known to be very damage-tolerant. Therefore one of the main application fields for this alloy One problem m all reinforcement type is sheets for the outer skin. The high­ technologies is the significant decrease in strength alloys of the 7xxx series are often used ductility and fracture toughness, caused by the for forged parts and extruded sections. Typical above-mentioned effect. The damage tolerance properties of the 7xxx-series alloys are given in will also decrease. Because of the last­ Table 3. Although there are corrosion problems mentionened reasons, the usage of MMC's in in ground transportation systems as well the aerospace applications as well as in automotive requirements for aerospace materials are much applications did not yet reach the status of serial higher. Therefore many of the alloys used in production. Research on improving ductility and aeroplanes must be of high purity to secure damage tolerance is still in progress. Some minimum stress crack corrosion sensitivity. applications of SiC long-fibre-reinforced titanium are under development in the United Today, and probably in future, the States to improve the propulsion capability of development of aluminium alloys plays and will military aircraft, see fig. 9 (15]. The continue to play an important role in materials development in continuous-fibre-reinforced research. For example, in past years a new alloy aluminium matrices is also continuing. In recent - AA6013 (AlMgSiCu) - has been developed years the company 3M developed an alumina and is under practical examination. Its major fibre with excellent properties (16]. The benefit is good weldability and lower cost m composite features a very high Young's contrast to AA2024 (AlCuMg) (12]. modulus in fibre direction and is therefore suited for stiffness- and bending-sensitive Because of the high stiffness demands in applications such as the service panels of an aerospace applications, reinforced metals (MMC aeroplane, see fig. 10 (16]. Metal Matrix Composite) have been developed. The reinforcement usually consists Summarizing the above-mentionend aspects, of high-modulus ceramics like silicon carbide a general catalogue of the properties of new

(SiC) or alumina (Al20 3) in long-fibre, short­ aeroplane materials can be drawn up to include: fibre or particulate form (14]. Usually aluminium and titanium are used as the matrix • Low density material. In future, the particulate and long-fibre reinforcement of magnesium alloys will be of • High strength increasing interest. Other forms of • High fracture toughness reinforcement such as whiskers are of little

9 • High stiffness of the combustion bowl and the piston ring groove. Therfore replacing the material locally • High damage tolerance ( epecially for the at the failing points by alloys with better high­ wings) temperature capabilities is necessary. One solution which has already been transferred into • Good weldability the series prodution of trucks is the local reinforcement of the critical points by • Reproducability of material's properties aluminium matrix composites (MMC) [17] or, None of these requirements can be fulfilled as is under investigation, by titanium aluminides by one material. But not every part has to (fig. 11). On the other hand, new composite combine all these properties. alloys with improved high-temperature properties and additional reduced specific weight are being investigated. Such new alloys 4.2 Efficiency of Thermal Engines produced by the conventional squeeze-casting process are SC-(Mg2Si)30Al70 or SC­ 4.2.1 Automotive Engines (Mg2Si)20Mg80 [18, 19]. These alloys offer mechanical properties comparable to the Research on automotive engines concerning standard piston Al alloys but with less CTE, the efficiency of the thermal engine focuses higher stiffness and a 10% (Al-base alloy) to predominantly on oscillating, light-weight 30% (Mg-base alloy) lower mass. components. Materials with low specific weight but high strength and stiffness allow the A further potential for fuel saving consists in reduction of oscillating masses. This results in a the reduction of friction in the valve mechanism. higher number of revolutions and therefore a Energy loss due to friction is mainly caused by fuel saving, a decrease of reagent emission, and the the valve tappet sliding on the cam of the additionally a reduced noise level. Typical cam shaft [20]. It is evident that high valve oscillating parts are pistons, valves, con rods, spring forces increase friction between the cam etc. However, new materials for this purposes and the valve tappet. As the valve spring force is may not or only slightly exceed the component a function of the moved mass of valve and valve cost of the conventionally manufactured spring (fig. 12, 20) the spring force and thus component. Therefore titanium alloys with friction can be drastically reduced by decreasing excellent mechanical properties have not been the mass moved. A reduction of fuel directed towards light-weight applications in consumption up to 4% in the ECE cycle is commercial vehicles. achieveable (fig. 13). Fig. 14 shows the light­ weight potential of titanium alloys and ceramics In the past few decades a lot of work has compared to the steel version of the valve. From been done on the introduction of special Al the metals point of view, titanium alloys are alloys to the piston technology of cars and hopeful candidates for the less thermally loaded commercial vehicles. Decisive materials inlet valves. For exhaust valves working in the properties for Al alloys applicable for pistons temperature range of 700°C to 900°C, the are fatigue resistance, form stability (stiffness) intermetallic NiAl alloy is a possible material and resistance to thermal fatigue in combination solution due to ist superior oxidation resistance. with a low coefficient of thermal expansion Whether ceramics or titanium or alumindes are (CTE). The latter is mainly important for high­ used for valves in automotive engines in future performance diesel engines. A typical standard depends in the final resort on the manufacturing light-weight alloy designed for pistons is the Al­ costs and the reliability. As mentioned above, base cast alloy AlSil2CuMgNi. However, the the valve spring mass also contributes up to thermo-mechanical loads of high-performance 50% to the moved masses in the valve system. diesel engines with high combustion pressure With the use of a cold-formable and age­ involve fatigue failure of the material at the rim hardenable beta titanium alloy Ti13V11Cr3Al,

10 mass can be drastically reduced by 130% Critical engine components with regard to the compared to the steel version at the same load demand for higher turbine inlet temperatures are level. Additionally, the natural frequency and in general the nozzle guide vanes and the thus the possible operational frequency is rotating turbine blades mainly in the first turbine increased by up to 50% [20]. stage (fig. 16). In the following sections, only the main demands for these critical engme The development and application of high­ components are briefly sketched. temperature metal alloys is limited to some few motor components such as catalysts or the Nozzle guide vanes direct the hot combustion combustion areas of high-performance diesel gases into the rotating stage of the turbine. engines. Direct injection systems as have been Adequate service life requires active cooling introduced to reduce fuel consumption and and thus a complex design only achievable by particle emission require high-temperature metal casting technology. Due to mechanical loads alloys. The main demands are excellent caused by thermal gradients and aerodynamical resistance to high-temperature corrosion and forces, thermal fatigue resistance and creep high strength at temperatures up to 1300°C [21]. strength are defined as the main requirements. As ferritic Fe-base oxide-dispersion­ Oxidation and corrosion resistance are realized strengthened (ODS) alloys can be treated by by intrinsic material resistance and protective conventional production processes, they are coatings. Thus, for new materials withstanding privileged candidates for use in the pre-chamber higher temperatures, thermal fatigue resistance of diesel engines. A typical ferritic ODS alloy is and creep strength have to be improved. Incoloy MA 956 (Fe20Cr4,5Al0,5%Ti + Y203 Standard alloys used in the past decades are cast dispersoids ). CoCrNi base alloys, and NiCrCo base alloys due to their very good mechanical properties 4.2.2 Industrial Gas Turbines and Aero­ and their good to excellent oxidation and engines corrosion resistance.

Gas turbines can generally be divided into Rotating turbine blades extract energy from aero-engines and industrial gas turbines. The the combustion gases, transforming it into main components for the cycle process are the mechanical energy to drive the compressor compressor stage, combustor, and turbine. In (aero-engine) or the generator (industrial aero-engines the working fluid expands to some engine). Additionally to thermal fatigue and extent in the turbine and largely in an additional creep effects, high cycle fatigue is critical due to jet nozzle. The dominant factor for the the vibration phenomena and centrifugal loads. efficiency of the Brayton cycle of gas turbines is Since wrought nickel base alloys are mainly the gas temperature at the turbine inlet. Figure used in industrial turbines y'(Ni3Al)-hardening 15 demonstrates that the efficiency of an cast NiCrCo base alloys are widely used in aero­ industrial gas turbine increases with the turbine engines. New casting technologies such as inlet temperature [22 I 23 I 24 I 25]. This means directional solidification and singl-crystal that a further improvement in the gas turbine casting led to an overall improvement in efficiency is mainly attainable by increasing the mechanical properties. With these techniques, temperature of the combustion gas at the turbine grain boundary stabilizing elements such as C, inlet. As a consequence, materials used in the B and Zr could be removed. Thus, the turbine are exposed to higher temperatures. temperature of incipient melting and Typically, a gas temperature of about 1400°C consequently the operating temperature of the leads to a temperature of the first-stage rotating alloys were increased. turbine blades of about 800°C, down to about However, high operating temperatures of 650°C for the last stage (industrial gas turbine about 80% to 85% of the solidus temperature FMW 701F, [22]). lead to fast changes in microstructure and thus

11 to the decrease in mechanical properties. properties, processing capability, and the Moreover surface degradation occurs due to complexity of the component, such as an corrosion and oxidation. Since Cr has to be actively cooled turbine blade. New metal alloys reduced in order to allow higher amounts of y' - such as ODS alloys pose some difficulties in hardening elements like Al, Ti and Nb, a further producing turbine blades with complex cooling increase of mechanical properties in general systems. Therefore some alternative research counteracts the oxidation and high-temperature aims at increasing of the high-temperature corrosion behaviour. mechanical properties by improving the purity of cast alloys for directional or single crystalline Thus, for higher operating temperatures, new solidification. The main topic of this work is to metal composites are investigated. They are avoid impurities caused by chemical reactions mainly based on oxidation and corrosion­ of the alloying elements with the crucible wall. resistant alloys (Ni-base, Fe-base and Typical new melting processes are current­ intermetallics) provided with finely dispersed, induction skull crucible casting and electron thermal stable second phases like oxides or beam casting. carbides, which induce the strengthening effect. The best known and most investigated alloys of this category are the so-called oxide-dispersion­ 5 Materials and Processes strengthened alloys (ODS). They promise improved creep resistance and higher structural 5.1 Ferrous Alloys stability at elevated temperatures [25]. Ongoing developments in non-ferrous light­ As the specific weight of nickel and cobalt weight and high-temperature materials force the base alloys is high, new intermetallic high­ steel industry to flexibly adapt of their product temperature, light-weight alloys with qualities to customer's demands. Up to now the appropriate mechanical properties and intrinsic standard blast furnace processes for making iron good oxidation behaviour are under limited the flexibility to meet market variations investigation. Titanium alloys were developed due to the demand for maximum productivity in showing good microstructural stability up to order to be competitive. The development of 650°C (IMl834). But application at this new production processes for ferrous semis, temperature level was rejected due to the beginning with the ironmaking process and detrimental oxidation and corrosion behaviour. extending to the fabrication of the semis, allows Promising candidates are alumindes of titanium new flexibility in producing custom-made and (TiAl, Ti3Al, and alloys) and nickel (NiAl, application-tailored components [26]. Thus, the Ni3Al, and alloys) due to their temperature base is provided for new ferrous alloys or semis. potential and up to 50% less weight compared to Processes under development such as the Ni-base alloys. Smelting Reduction Process (SRP), the Cyclone Converter Furnace (CCF) and the Jupiter Superior resistance to high-temperature Process permit dispensing with coke production corrosion and thermal fatigue and low specific and iron ore sintering, and facilitate weight makes silicides of molybdenum and simplification of the process, therfore helping to titanium (M0Si2, TiSi2, Ti5Si3) into applicable avoid or reduce polluting emittant output. New high-temperature alloys. Fig. 17 and table 4 [24] computer technologies have permitted of recent summarize the possible applications in gas developments in the continuous casting of turbines and the admissible operating ferrous alloys [26]. Casting strips with temperatures. thicknesses down to 1 to 3 mm should be achieved. This technique allows remarkable However, the development of applicable savings in raw materials and energy and thus ODS and intermetallic alloys takes place in a lower em1ss1on of harmful reagents. situation of conflict between materials Additionally, a new potential method for the

12 development of new steels is available, which Phosphorus and micro-alloyed steels are could not be produced by the conventional mainly applied to crash structures due to their rolling route [27]. high strength but difficult drawability. Bake­ hardening steels are used for auto body sheets. Because of the high Young's modulus of The weight saving potential for these groups of 2 about 210,000 N/mm in addition to high yield steel is documented in fig. 18 [29]. strength, steels are excellent candidates for light-weight structures. Improved strength, cold Figure 19 shows the increasing demand for drawability and high energy absorbtion in crash high-strength steel strips on the part of the situations for automotive bodywork sheets, automotive industry in the past ten years [30]. which are the basis for steel-based, light-weight structures, are achieved by manipulating of the 5.1.1 High-strength steels microstructure with the aid of advanced materials treatments. Additionally, new alloys In the automotive industry, high-strength are under development in order to match the steels have been used for years with a share of required demands, especially those of the about 20% of the structural steels [29]. The automotive industry. So-called tailored blanks demand for steels with higher strength led to the provide a new way of using the properties of development of micro-alloyed (MA) steels with different steel types. This combination of laser­ a yield strength of 260 - 420 N/mm2 and welded blanks offers simpler production of phosphorus-alloyed (PA) steels with a yield components and necessitates simultaneous strength of 220 - 300 N/mm2 [29]. The engineering between steel makers and the strengthening mechanisms of MA steels are manufacturing industry. Nevertheless, a weight­ mainly fine-grain hardening and hardening saving potential of about 25% and more through precipitation of TiN, NbC, respectively compared to today's weight of a car could be (Nb,Ti)(C,N) [31]. Strengthening PA alloys is attained by substituting 50% standard steels by based on solid-solution hardening. An additional new high-strength steels and tailored designs rise in strength is attained through [28]. Estimations of the fuel-saving effect show thermomechanical treatment (TMT) of V, Ti that reducing fuel consumption by about 0.3 l and/or Nb-alloyed alloys. The minimum yield per 100 km and 100 kg are possible. A strength extends from 340 up to 690 N/mm2 consequent transfer of the light-weight potential depending on the alloy composition and the of high-strength steels could thus lead to a fuel TMT. The properties and chemical composition saving of about 346· l 06 liters per year in of a typical high-strength, hot-rolled steel, western Europe [29]. micro-alloyed with Ti and V, are summarized in table 5. The effect of Ti and V comprises the Developing of high-strength steels with good adjustment of a fine-grain structure and cold drawability began in the seventies. After an precipitation hardening [31]. initial delay due to the lack of experience in drawing processes with these new steels, they The drawback of the increased strength is the began to be applied in the automotive industry reduced cold formability. Thus, MA and PA [30]. The main high-strength steels developed steels are mainly used in structural, crash­ over the last 25 years are: critical parts. Investigations on the energy dissipation of high-strength steels show that the • micro-alloyed steel above-mentioned high-strength steels commonly exhibit an improved energy • phosphorus-alloyed steel consumption at high strain rates. Figure 20 shows the energy consumption per volume of • pot-galavanized high-strength sheets typical high-strength steels (hot-rolled • bake-hardening steel QStE500TM, bake-hardening ZStE180BH, interstice-free, pot-galvanized alloy IF (HS))

13 compared to the classical deep-drawing steel 225 s-1, which corresponds to a crash velocity FeP04 and the aluminium alloy Al5182 of 50 kmph, extends increasing energy (Al4,5Mg0,4Mn). In all cases the high-strength absorption with increasing strain rate [31 ]. steels show equal or better energy consumption compared to the standard alloy FeP04 [31]. The Bake-hardening steels have now reached a low values of the aluminium alloy, investigated state where they can increasingly be used in the for automotive structural applications, reveals mass production of auto bodywork structures. the problematic crash behaviour of Al-based They are a powerful alternative material to Al structures. alloys with respect to the reduction of weight and thus fuel consumption of automotives as well as of production energy. 5.1.2 Bake-hardening steels

The main demand for auto body coverings is 5.1.3 Tailored Blanks the buckling resistance, which depends mainly on stiffness and the yield strength of the steel. Tailored blanks were introduced onto the Additionally to the metallurgically increased automotive market by Thyssen Inc. Germany in yield strength and the rise in strength by cold the late eighties. A tailored blank is the working, bake-hardening steels harden during combination of steel sheets of different quality, baking-enamelling. The metallurgy of these surface coating and thickness by laser beam steels is conditioned such, that hardening occurs welding (fig. 23). This procedure offers the at temperatures above l 20°C, due to controlled possibility of combinating the different sheet carbon aging. This offers good cold drawability properties section-wise and thus the local in the unaged condition and an increase in adaption of stiffness and strength to the required strength of the final structural component, such structural demands. This provides an excellent as doors, fenders, and hoods. Yield strengths of chance to reduce the weight of structural bake-hardening (BH) steels commonll extend components. Yielding, easily deformable steels from 190 N/mm2 up to 330 N/mm, tensile types can be used in crush sections, while sheet 2 2 strength from 300 N/mm to 440 N/mm • sections with higher strength and thickness are Strength is adjusted by alloying with used in load-bearing sections of the structure. phosphorus [31]. In order to attain minimum C Fig. 24 shows the examples of tailored blanks content, BH steels are decarburized by vacuum for auto components. The sheet thicknesses are annealing. The chemical composition of a adapted to the necessary local stiffness of the typical representative of the BH steels (ZStE respective component [32]. Fabrication of a car 180 BH) is given in table 6. door, for example, by using tailored blanks leads to a weight reduction of about 0,8 kg per The drawability of typical bake-hardening door [32]. A tailor-made wheel housing shows a steels is comparable to the deep-drawing steel higher life time additionally to the decrease in St14, as is shown in fig. 21 [29]. Compared to weight. phosphorus-alloyd or micro-alloy steels, BH steels offer higher elongation and therefore A supplementary benefit of the use of better drawability. The extent of the tailored blanks in addition to the great weight strengthening effect depends on the process reduction potential is the reduction of finishing parameters strain, temperature and bake steps, the decrease in parts and in transportation. hardening time [28]. Figure 22 documents an increase of the BH effect with both increasing Tailored blanks are currently approaching use temperature and time for the non-deformed state in mass production. and the 2%-deformed state. An improved crash behaviour of BH steel ZStE 180 BH compared to standard cold-draw sheets results of high­ strain-rate tensile tests with strain rates up to

14 5.2 Nickel Base Alloys solidification (SCS) are applied. During DS and SCS, the melt-containing mould is moved from As mentioned earlier, Ni-base alloys are the a heating zone into a cooling chamber providing current standard candidates for high-temperature a nearly axial temperature gradient and thus applications such as turbine blades and turbine axial solidification. With the DS process, grain vanes. Their potential is the ability to harden by boundaries are also directed in axial direction. precipitating the y'(Ni3Al)-phase in addition Grain boundaries running into the casting with good oxidation resistance. However, surface are therefore minimized, avoiding crack coatings are necessary when using these alloys initiation sites. A next step is the formation of a at temperatures above 1000°C in oxidizing single crystal using special casting starters ("pig atmosphere. As will be described in the tail"). A higher thermal gradient by using liquid subsequent chapters, oxide-dispersion­ metal cooling improves the microstructure strengthened (ODS) Ni-based variants offer (smaller dendrite spacing) and minimizes higher strength and fatigue resistance. The element segregation and the formation of drawback of ODS-Ni alloys is the limitation in porosity (fig. 26) [23]. For SCS the probability design due to the powder production route. For of more than one grain forming is reduced. gas turbine blades it is necessary to design complex cooling channels [22]. Experience in The development of new Ni-base alloys tends gas turbine development shows that the to reduce chromium content in order to attain advantages in strength and fatigue of ODS the maximum solubility of y'(Ni3Al)-forming alloys are offset by the absence of efficient elements. An increase in y' -precipitation in cooling structures due to the reduced processing addition to directional solidification allows capability. Based on this fact, new casting improving both thermal fatigue and creep processes and Ni-base alloys are currently under resistance. Alloys of the third generation owe development for turbine blades or vanes in order their improved creep behaviour to the addition to meet the requirements for improved thermal of refractory elements like rhenium and fatigue and creep strength at high temperatures. tungsten. However, the severe segregation behaviour counteracts this effect. Thus, a Developments in the casting process focus on directional solidification process with a high the purity of the alloys used. The main point is thermal gradient is necessary to exploit to avoid impurities and the impoverishing of maximum creep resistance at high temperatures. reactive elements such as Cr, Nb, Ti, etc. caused Fig. 27 shows the possible increase in by the interaction between the ceramic crucible temperature capability with decreasing Cr and the molten alloy. This problem is content. The values are related to conventional aggravated if new alloys with highly reactive cast alloy 738 (CC). A rise in operating elements such as Y, Hf, etc. are used [23]. Thus temperature of about 110°C seems to be new melting technologies are under possible by using Cr-poor alloys in addition to investigation with the aim of trying to avoid the SC process [33]. However, the poor direct contact of the melt with the crucible wall. chromium content requires coatings that protect In the Current Induction Skull Crucible (CISC) from hot corrosion attack. and the electron casting process, which utilize a water-cooled copper crucible, a thin skin of the 5.3 Intermetallic Alloys molten alloy solidifies on the crucible surface separating the melt from the crucible surface (fig. 25). Thus a high degree of purity can be 5.3.1 Aluminides achieved. Ordered alloys of intermetallic constitution Additionally to the improved melting based on aluminium are called aluminides. The process, higher thermal gradients during most representative alloy systems are those of directional solidification (DS) and single-crystal titanium aluminides (TixAl) and nickel aluminides (NixAl) with their low-alloyed 15 variants. They are mainly produced by resistance to creep and oxidation is insufficient conventional casting routes or powder processes for application. Oxidation behaviour is (PM/HIP) and subsequent extruding. In general, dominated by the formation of the Ti02/Al203 high specific stiffness and ultimate tensile layer. The lack of Al leads to the formation of strength are the advantages, while brittleness at Ti3Al, which causes embrittlement by room temperature and poor creep resistance dissolving up to 20% of oxygen. (except TiAl) of the monolithic alloys are the negative aspects of these alloys. The main Ti3Al (a2 )-based alloys disadvantage of these alloys is their lack of ductility at low and medium temperatures The most preferred alloys are Ti 3Al alloyed caused by their ordered lattice structure and the with Nb, V and/or Mo for enhanced ductility. lack of active slip systems [34]. The best known and most promising is alloy Super-alpha-2 alloy Ti62Al26Nb 1OMo1. TITANIUM ALUMINIDES are the light-weight Unfortunately, this alloy lacks acceptable aluminides and can principally be divided into formablity and is susceptible to hydrogen two main alloy types, TiAl and Ti 3Al. embrittlement [35]. Two phase az-y alloys, stabilized by additions of Cr, V, Mo and/or Nb TiAl (y)-based alloys (e.g. Ti59Al40V), show that the most promising mechanical properties, yield strength and room TiAl consists of a major matrix of TiAl with temperature fracture toughness are superior to Ti3Al second phases. The specific weight is those of TiAl (fig. 29). Processes to enhance about 3.9 g/cm3. The alloy systems investigated room temperature fracture toughness by grain up to now are Ti + 46-52 at% Al + 1-10at% of refining are similar to those of TiAl alloys. the elements V, Cr, Mn, W, Mo, Nb,or Ta. Fig. Application of Ti3Al alloys is limited to 28 documents the lower ductility by comparing temperatures equal to or below 650°C, due to the fracture toughness of TiAl and Ti3Al-based insufficient oxidation and strength [24]. alloys with the Ni-base alloy In738LC and the However, further research activities show that near-a titanium alloy IMI834 [24]. Alloying alloying with Si up to 8,5% leads to the with elements such as Cr, Nb, Mn and Si (e.g. formation of an eutectic alloy system T3Al­ Ti48Al2Cr2Nb) enhances ductility and high­ Ti5Si3 with improved mechanical properties temperature strength by forming a two-phase and oxidation behaviour [36]. A comparison of microstructure (y (TiAI) and a 2 (Ti3Al)). the oxidation behaviour of Ti3Al alloys with Furthermore, a complex thermo-mechanical TiAl and other Ti alloys is given in fig. 30 [3 7]. treatment (TMT) increases the yield strength and ductility of Ti-aluminides by resulting in Due to the above-mentioned inherent fine equiaxed grain and a flaw-free structure material problems, TixAl-based alloys are still [20]. Appropriate processes to achieve fine grain under development and not yet applied are isothermal forging, extrusion or powder commercially site. A further problem is the very processing [22]. The resulting excellent specific limited reproducibility of properties of materials yield strength (strength/weight) compared to Ni­ from different suppliers and different batches base alloys and near-a titanium alloys up to [38]. Current activities on alloy development 700°C is shown in fig. 29 [19]. However, focus on the further improvement of room­ specific yield strength is lower than that of the temperature fracture toughness, formability and Ti3Al-based alloy. Fatigue strength of defect­ high-temperature creep strength. Recently, free material is very high at 80% to 90% of the orthorombic titanium aluminides based on yield strength. Micro-pores and notches Ti2(AlNb) were investigated and exhibited significantly reduce life time. Applying of TiAl excellent ambient-temperature formability and alloys is possible up to 750°C and thus offers a high-temperature mechanical properties. A cold by about 100°C temperature potential higher reduction of 40% to 80% and a specific strength than Ti3Al [24].At higher temperatures, 50% to 75% greater than Inconel Alloy 718 at

16 700°C is reported [35]. TiAl alloyed with 0.3% toughness through the formation of second Sb and 0.5% Hf exhibits superior high­ phases [41, 42]. A typical alloy is NiAl-Cr. The temperature strength of about 280 N/mm2, with formation of eutectic phases of NiAI-Cr and specific gravity only rising from 3.8 to 3.9 processing with directional solidification or g/cm3. The lack of sufficient creep strength of powder metallurgy routes improves high­ both types of alloys TiAl and Ti3Al at elevated temperature strength and ductility. Figure 31 temperatures above 600°C makes resarchers documents the increase of 0.2% proof stress apply the method of oxide dispersion with the rise in Cr content and its temperature strengthening to aluminides. behaviour [36]. Unfortunately, the increasing Cr counteracts oxidation resistance [36]. Processing NICKEL ALUMINIDES can mainly be divided the alloy greatly influences strength and fracture into the two alloy groups NiAl and Ni3Al. In toughness due to microstructural effects such as contrast to the Ti aluminides, Ni aluminides, grain size, second phase distribution, etc.. Fig. beside low room temperature ductility feature 32 reports on the difference in elongation and insufficient strength and creep resistance at high fracture toughness depending on processing temperatures [39]. However, with densities of (HIP resp. HIP and extrusion). about 5.9 g/cm3 (Ni3Al) to 7.7 g/cm3 (NiAl), they exhibit a weight reduction potential of up The above-mentioned facts give distinct to 25% compared to Ni-base superalloys. picture of the situation, namely that the main problems of Ni aluminides that have to be Ni3Al solved are the low room-temperature ductility and the high-temperature creep resistance. An Despite the sufficient room temperature approach for solving the brittleness at ambient ductility attained of about 10-15% for boron­ temperatures is the concept of ductile phase doped Ni3Al, this type of alloy was mainly toughening. By dispersing ductile particles of, rejected in the investigations. This is due to low for instance, Cr and Nb in the brittle material, creep resistance at elevated temperatures and the the crack resistance should be enhanced, leading embrittlement at 600°C to 700°C [24]. Thus, to a quasi-ductile material behaviour [43]. investigations are focussing on the Ni aluminide Investigations on NiA1+5%Cr and NiA1+5% Nb type NiAI. particles show that there is an toughening effect, but it is only metastable. After exposure to NiAI temperatures higher than 1000°C Nb and Cr NiAl exhibits an excellent oxidation and particles become as brittle as the NiAl matrix corrosion behaviour up to 1300°C. Additional due to solid-solution reactions [43]. This means advantags compared to Ni-base superalloys are a limit to operating temperature well below a 4-times higher thermal conductivity, a lower 1000°C. However, research in the fields of coefficient of thermal expansion (CTE), and the ductile phase toughening is continuing. A reduced specific weight. A further benefit is the promising solution for the creep problem is to better resistance to thermomechanical fatigue. strengthen the matrix by adding oxide However, high-temperature strength of about 40 dispersoids (see chapter on ODS alloys). Ntmm2 at 1000°C , creep strength at elevated temperatures and room temperature fracture 5.3.2 Silicides toughness are poor [40]. To improve this situation, NiAl is alloyed with elements and Low densitiy and the oxidation resistance of with metallic, respectively intermetallic phases. silicides due to the formation of a protective However, enhancing strength by solid solution Si02 scale on the surface makes silicide a strengthening with alloying elements like Cr and potential candidate for light-weight components Nb will only be mediocre because of the low operating at moderate temperature in an solubility of Cr and Nb. Alloying with Cr, Mo, oxidizing environment. Possible applications W, Ta and Nb enhances strength and fracture are, as mentioned above, oscillating masses like 17 pistons. However, silicides lack room­ fraction of Mg-Mg2Si, as is shown in fig. 34 for temperature ductility, like all intermetallic Al-Mg2Si. Additionally the CTE of Al-Mg2Si phases. Therefore most research activities are is lower than that of the AlSi alloy. This offers driven by the demand for improved room­ the possibility of reduced piston play. temperature ductility and easy processing. In the following paragraphs, some engine-component­ The above-described properties of the Al­ related alloys and their advantages and resp. Mg-Mg2Si alloys show that the specific disadvantages are described. strength is superior to that of the standard piston alloy. This means a weight reduction of the piston of about 10% with Al-30%Mg2Si and 30% with Mg-20%Mg2Si. Additional benefits The search for new piston alloys with high are the lower CTE and the good processing thermal stability, good high-temperature capeabilities. However, these types of alloys strength and low specific weight points toward have been under investigation up to now and the intermetallic phase Mg2Si. Due to the have not yet been incorporated in prototypes and inherent room-temperature ductility Mg2Si, mass production. utilizing the monolithic intermetallic is not possible. Thus, with respect to ceramic-fibre or Molybdenum Disilicide MoSi 2 particle-reinforced materials (MMC's), a composite of Mg2Si with either an Al matrix or M0Si2 is commonly known as an an Mg matrix was produced and investiagted intermetallic alloy for use as an oxidation [18,44]. protection coating for high-temperature applications and is produced by vacuum plasma Both alloys are produced by squeeze casting, spraying (VPS). However, there are multiple grain refined by the addition of 1wt% possibilities for using of this type of alloy for phosphorus. A maximum of about 30vol% high-temperature components in turbines or Mg2Si can be achieved by the casting process. combustion chambers [45]. The most promising Both alloys offer the advantages of lower processes are hot isostatic pressing (HIP) with thermal conductivity, a moderate CTE and a optimized pressure and temperature control, lower specific weight compared to the die-cast metal injection moulding (MIM) with type-true standard piston alloy Al Si 12CuMgNi. Ductility sinter additives and SHS (self-propagating high­ is only sufficient with high amounts of Mg, temperature synthesis) [46]. All these process respectively Al. Following the mixture rule, Al­ routes aim to produce near-net-shape parts. Mg2Si exhibits a higher Young's modulus than the AlSi-based alloy. The Young's modulus of M0Si2 offers excellent corrosion and Mg-Mg2Si is lower compared to the standard oxidation behaviour in oxidizing atmosphere at AlSi piston alloy, but consequently higher than temperatures up to 1600°C, due to the formation that of alloy MgY5.2RE3Zr0.7 (WE54). Fig. 33 of a dense Si02 surface layer. Under continuous shows a lower drop in Young's modulus with thermomechanical load, a maximum operating increasing temperature compared to the standard temperature of about 1200°C is achievable [45]. piston alloy [44]. The behaviour of the yield Due to the covalent-metallic bond, M0Si2 strength of Mg-Mg2Si is documented in fig. 33. exhibits high thermal conductivity (24.1 W/mK In the temperature range of about RT to 270°C, at 1200°C) and sufficient room-temperature the Mg-Mg2Si alloy shows a significantly lower strength of about 320 MPa. However, as with yield strength compared to the standard piston every intermetallic ordered phase, the covalent alloy and alloy WE54 [44]. At T > 270°C the atomic bond component causes low ductility Mg composite is superior. A comparable below the ductile-brittle transition temperature behaviour of tensile strength and fatigue (DBTT). The fracture toughness at room strength is reported for the Al-Mg2Si alloy [18]. temperature is about 4.7 MPa..Jm. Due to the The CTE is reduced with increasing volume influence of the microstructure on the

18 mechanical properties of MiSi2 alloys, thermomechanical treatment adjusts the required oxidation stability is based to a very great micro structure. extend on microstructure and porosity. Spalling of the Si02 surface layer and severe surface Different DS alloys are investigated degradation are observed in a temperature range extending from pure aluminium, respectively of about 600°C-700°C. Hence, careful aluminium alloys, to y' -hardenable Ni-base processing is necessary to take full advantage of alloys, Fe-base alloys and finally to the above the alloy's oxidation resistance. mentioned Ni-aluminides.

Since investigation of bulk M0Si2 materials Oxide Dispersion Strengthened-Aluminium is just starting, only few data are available. But Alloys investiagtions on second-phase strengthened alloys such as MoSi2-WSi2, respectively Oxide-dispersion-strengthened (ODS) MoSi2-SiC, are under way [45]. aluminium is produced by milling pure Al powder with Al203 particles under cryogenic conditions with liquid nitrogen. The volume 5.4 Dispersion Strengthened Alloys ratio of the oxides is 3 vol%. The resultant ODS DS alloys consist of a matrix of an alloy or a powder is subsequently treated by PM/HIP pure metal with finely dispersed, insoluble and processes and/or extruding. thermal stable second-phase particles (mainly This ODS aluminium shows some very good carbides or oxides) some ten nanometers in size. high-temperature properties. The result of The reason for developing these alloys is to tensile tests is a higher UTS of the ODS-Al improve strength and creep resistance at high compared to that of alloy Al74 75-T6 l at a test temperatures by up to 90% of the alloy's temperature above about 200°C (Fig. 35) [47]. melting point, compared to 40% for strain­ Creep tests show that when subjected to a load hardened alloys and 60% for precipitation­ of 160 MPa a strain threshold of about 0.3% is hardened alloys. Recent inverstigations show reached at a proof temperature of 275°C (Fig. that the dominant strengthening mechanism is 36). This behaviour is caused by grain pinning the attraction of the dislocations to the particles by the oxide particles and nanocrystalline and a resultant partial relaxation of the stress aluminium oxynitrides formed in situ [47). The field produced by the dislocation [25]. A elastic modulus changes only moderately with maximum strengthening effect is attained, the volume content of the second phase fraction. reducing the diffusion-controlled creep by producing microstructural texture. Oxide and Carbide Dispersion Strengthened Al Alloys DS alloys are produced by mechanical alloying. A certain ratio of powders of the Typical alloys of this type are summarized in reinforcing oxide and the matrix alloy are mixed table 7. and subjected to Jong-term milling in a ball mill or an attritor mill. During this process the Dispersion strengthening is based on the metallic particles are strongly deformed, cold­ formation of both Al4C3 and Al203 during the bonded, including the second-phase particles, mechanical alloying process [48, 49]. Optimum and crushed. The constituents of the original mechanical properties are attained without powder mixture are thereby dispersed subsequent heat treatment after the extrusion submicroscopically. Temperature and gaseous process. Room-temperature tensile strength medium (Ar, N1, vacuum, etc.) in the mill reaches about 400 MPa, depending on the depend on the materials processed. The resulting matrix alloy and the volume fraction of composites are commonly processed by cold dispersoids. However, increasing strength is isostatic pressing (CIP), hot isostatic pressing accompanied by a drop in elongation and thus (HIP) and extruding. In some cases ductility (fig. 37) [50]. Fig. 38 shows the

19 superior strength of DS Al alloys at mentioned above, oxidation protection coatings temperatures above l 50°C compared to a are necessary for such high operating conventional piston Al alloy AlSi 12CuMgNi. A temperatures. specific phenomenon is the drop in elongation with increasing temperature. A severe decrease ODS NiAI Alloys in tensile strength with increasing temperature is reported to appear above 400°C JSOJ. Fatigue As attempts to strengthen NiAl-based strength of about 80 to 95 N/mm at 350°C is matrices by solid solution hardening or reported, which is superior to that of standard Al precipitation hardening mechanisms failed for alloys. Reduced crack initiation and growth low strain rates and high temperatures [51, 52], during thermal cycling leads to superior thermal new approaches are being pursued concerning fatigue resistance compared to standard piston oxide dispersion strengthening. ODS-NiAI and Al-alloys [50]. Up to now no mass-production NiFeAl alloys are reported to be produced by application of this type of alloy is known, but mechanical alloying with 1% to 2% Y203 components like pistons, con rods and cylinder dispersoids. The experiments on mechanical head inserts have been tested. alloying and hot isostatic pressing (HIP) show the possibility of producing materials with a fine However, contary to the Ni-base ODS alloys grain in the micrometer range [53]. The exhibiting operating temperatures of about 90% influence of the oxide disperoids on creep of their melting point Ts. ODS-Al alloys just behaviour is currently under investigation. reach temperatures of about 50% Ts [25]. The interest in new "high-temperature" Al alloys for ODS Iron Base Alloys structural applications calls for further ODS alloys based on ferritic Cr steel have inverstigations on ODS-Al. been developed for high-temperature ODS Nickel Base Alloys applications. The reason for such development was the above-mentioned mediocre oxidation Based on the first classical Ni alloy TD resistance of high-strength Ni-base casting nickel (pure nickel with 2 vol% thoriumoxide), alloys and ODS Ni-base alloys. Conventional new alloys like MA 754 and MA 6000 were ferritic steels with a high content of chromium developed. The alloys are produced by posses excellent oxidation behaviour. Thus, mechanically milling the Ni base alloy with ferritic ODS Fe-base alloys like MA 956 and Y 203 particles and subsequent PM 2000 were developed consisting of thermomechanial treatment like HIP or Fe20Cr4,5Al0,6Ti (MA 956), respectively extruding in order to attain an optimum Fe20Cr6Al0,6Ti (PM 2000) and 0,5% finely microstructure. Contrary to the strengthening y' dispersed Y203 particles [54]. The alloys are particles, the oxides do not dissolve in the alloy generally produced by mechanical alloying, matrix at elevated operating temperatures. compaction, deformation and final Additionally, grain growth is hindered by the recrystallization. These alloys exhibit excellent inherent oxides due to grain boundary pinning. oxidation and corrosion resistance up to However, in alloy MA 6000 both strengthening temperatures of about 1250°C by forming of mechanisms, oxides and y' hardening, are used adherent, stable Al203 oxide films [55]. in order to attain maximum creep strength at However, the creep strength of MA 956 high temperatures. Fig. 39 shows the 1OOOh amounts to about 60% of the values attained creep strength for alloy MA 6000 to be superior with Ni-ODS alloy MA 754 at temperatures to that of the classical Ni-base alloys [21]. between 1000°C and 1100°C, but extends up to Because of the thermal stability of the inert 1350°C [21]. The maximum operating time in oxide particles, the alloy is applicable at a combustion gas atmosphere for MA 754 is about temperature up to 1100°C -1150°C, which is 7500 hours at 1250°C [55]. PM 2000 shows near the melting point of the alloy. But, as better oxidation resistance, due to the higher Al

20 content and very good creep behaviour at The aluminium wrought alloys are of temperatures up to 1250°C. For both types of increasing interest even for the automotive Fe-ODS alloys, production and the resulting industry. They offer high strength and microstructure significantly influences the final toughness, often in combination with good high-temperature properties. Fig. 40 compares weldability. On the other hand, cast alloys are the creep strength of both alloys with Ni- and much cheaper because they do not have to be of Co-base alloys and with the Ni-ODS alloy MA such high purity and processing is easier. So the 754. The Ni-ODS alloy exhibits higher creep wrought alloys are only used when they are resistance, but ferritic Fe-ODS is applicable up really needed. to 1250°C. Note that Ni-ODS alloys must be coated for operating temperatures from 1000°C Aluminium-Lithium Alloys to 1100°C. Aluminium-Lithium alloys offer advantages Alloy PM 2000 is currently about to be such us low density and high modulus. Lithium applied to some thermally loaded components of is the lowest-density metallic element (p=0.534 3 automotive engines in mass production. g/cm ). Therefore alloying with lithium will lead to a reduced density of the alloy gained in this Nevertheless, world-wide investigations on way. For example, a lithium content of 2.5% ferrous ODS alloys are continued. Japanese leads to a weight reduction of about 10% [57]. researchers have report on the production of a In the past 15 years much research work has particle-dispersed steel with the highest been focused on these alloys, but their impact Young's modulus ever reached for steel of about on the aerospace market has fallen short of 265 to 285 GPa [56]. This Fe,13-16Cr,1-3Al, initial expectations. Part of the reason is the 0.5(Y203+Yb203)-based steel is produced by lower fracture toughness and stress-corrosion three-stage processing consisting of mechanical resistance of the actual AlLi alloys compared alloying with the above-mentioned oxides, hot with conventional aerospace-quality aluminium extrusion and subsequent heat treatment at alloys [58]. 1200°C to 1400°C. Yield strength is about 600 MPa to 900 Mpa and UTS about 700 MPa to New technologies (vacuum refining) are 900 MPa. The alloy can be fabricated as bars, under development to obtain high-purity alloys pipes or sheets. with high lithium contents of up to 3.3%. It seems that aluminium-lithium alloys are very sensitive to impurities, especially hydrogen and 5.5. Light-weight Alloys alkali metals. Fig. 41 [58] shows the increase in the purity of the alloys and the improvement in 5.5.1. Aluminium Alloys fracture toughness. As mentioned earlier, the fracture toughness is an important factor for Developments in aluminium technology are aircraft engineering. very rapid. Today's major research fields are the optimizing and modification of known alloys High-Strength Aluminium Alloys and the development of new process technologies to increase productivity and The high-strength aluminium alloys are properties in one step without higher costs. The undergoing continuous development. Especially casting technology is a good example of the the alloys of the 7xxx series are of great interest last-mentioned development line. New casting because of their excellent fatigue behaviour and technologies like thixoforming or thixomolding their high-strength. Table 8 gives a are approaching large-scale production. The die­ classification of the currently used high-strength casting process today allows nearly pore-free aluminium alloys in aerospace applictions. manufacturing of castings in extremely short In the development of high-strength time cycles. aluminium alloys, the powder metallurgical

21 route offers one of the most interesting ways to • Lowprice obtain even higher strength in combination with increased fracture toughness than today. Rapid • High ductility in the as-cast condition solidification technologies lead to a combination of different hardening mechanisms because of • Excellent castability in sand-, permanent the supersaturation of the solidified material. mould- and die-casting processes The volume content of the particles containing Zn-Mg-Cu in AlZnCuMg alloys of the 7xxx 5.5.2. Magnesium Alloys group could be increased. This leads to an improved precipitation hardening effect. The The use of magnesium alloys is, as addition of elements like Zr, Mn, Cr, Fe or Ti mentioned before, growing continously. In fig. leads to the formation of intermetallic phases 42 [60] the North American magnesium die cast and therefore to additional strengthening. With alloy consumption is to be seen. If this course is the next step in powder metallurgical processes, followed in coming years, in future the mechanical alloying, it is possible to alloy importance of magnesium will increase greatly. elements which are not soluble in any thermodynamic state (e.g. alloying of graphite The magnesium alloys can be divided into three major groups: and aluminium without getting Al4C3) [57]. The adavantages of PM-aluminium alloys are • Standard casting alloys, based on the obvious when compared to conventional ingot MgAlZn system (Azxx alloys) and its alloys (table 9). The alloy 7093 is a PM alloy related systems MgAlMn (AMxx) and based on the aluminium-iron-cerium system MgAlSi (ASxx). [59]. • The higher-strength alloys, based on The powder metallurgy processes have the MgZnREZr, MgAgREZr and MgZr. These disadvantage of high cost. On the other hand, materials contain rare earth metals and some light-weight or high-temperature problem partly offer unusually high damping areas cannot be solved without the use of such performance materials. In future, the need for highly developed, advanced powder aluminium • The creep-resistant Mg cast alloys products may increase. Until now none of PM MgZnREZr, MgAgREZr and MgYREZr processes are of any use for big parts like whole can reach operating temperatures up to 150 engine blocks. - 300 °C

From the above it is possible to derive the The yttrium-containing alloy is the most demands that have to be fulfilled by future creep-resistant light-metal alloy in the group of aluminium wrought and cast alloys as well as magnesium and aluminium alloys [61]. PM products: Fig. 43 [61] shows the mechanical properties • High-strength of some selected magnesium alloys compared to selected aluminium alloys. The high­ • High fracture toughness temperature tensile strength of the above­ mentioned yttrium-containing alloy is obvious. • High crack-corrosion resistance It should be mentioned that the last two alloy • Low density groups are very expensive wrought alloys. A • High Young· s modulus look at the utilization trend for magnesium alloys shows that the market relates mainly to and especially for cast alloys: cast alloys of the first group (Mg-Al­ Zn=>AZxx, Mg-Al-Mn=>AMxx, Mg-Al-

22 Si=>ASxx). Because of their better properties than their matrix materials alone, and tailorable (corrosion and strength), the AM alloys will physical properties. Particulate composites can increase in importance, see fig. 44 [60]. be fabricated using a variety of low-cost, net­ shape processes. Continuous-fibre composites A property catalogue for new magnesium offer low density, high-strength, and stiffness at alloys can be derived from the above: elevated temperatures [63]. The three most important light-weight alloy systems • Excellent die-castability aluminium, magnesium and titanium are suitable for reinforcement. An overview over • Creep-resistant up to 150 °C (minimum) these three groups is given in table 10. • Fracture toughness and ductility must The most interesting MMC's are those that fulfill safety requirements for automotive consist of fibres or particles in a common matrix applications material. They have significant advantages over • A recycling market for magnesium has to monolithic metals and polymer matrix be established composites (PMC's). Compared with monolithic metals, they have a higher • Corrosion resistance m the order of strength/density and stiffness/density ratio. They aluminium alloys offer tailorable CTE, electrical and thermal conductivity and they resist wear better than the • High availability (because main market is matrix material alone. The creep resistance is the automotive industry) also increased [63].

• Stable and low price (whole production Because of their anisotropic structure, the process for the part does not have to be long-fibre reinforced metals feature an more expensive than with aluminium) anisotropic property profile. The particulate MMC's, when not extruded, are isotropic. Some fundamental assumptions have to be guaranteed for the production of the raw The mam parameters influencing a material magnesium. A lot of electric energy is particulate-reinforced MMC' s properties are needed and therefore the price of the magnesium given in table 11. When it is possible to control produced and the resultant pollution of the the effects of these parameters, the MMC's environment are determined by the availability might really be called "Tailored Materials". The of cheap and clean elelctricity. problems in long- and short-fibre-reinforced MMC' s are comparable. Magnesium offers many economic and ecological advantages when in the producing Production processes area: The following process technologies were all • Electricicty generated through water, solar, developed for aluminium matrix systems. Today or wind energy ... most of the MMC' s are based on an aluminium matrix, although many of the process • Seawater ... technologies can be transferred to magnesium, too. are available [62]. The main disadvantage of MMC' s is the 5.5.3. Reinforced Light-weight Alloys complex solidification process in production and machining. Essential is a strong connection Metal matrix composites (MMC's) have between particle and matrix. This interface tremendous potential for the future. These should be in thermodynamical balance to obtain materials provide better mechanical properties a stable microstructure at elevated temperatures. 23 The major production processes for particulate intermetallic phases or oxides is a great problem reinforced MMC's are [64]: in this technology as well as chemical reactions between fibre and the melt. The infiltration time IN POWDER METALLURGICAL PROCESSES, a is usually about I second per mm2 infiltration pre-consolidated green body consisting of the cross section [66]. In most of the process types a metal matrix and the reinforcement is sintered or defined atmosphere (Ar, N2) is necessary due to hot isostatically pressed (HIPed). Sometimes a oxidation. One of the most important infiltration mechanical alloying process is carried out processes today is the squeeze-casting process. before solidification. The high pressures in squeeze-casting (up to 1000 bar) are necessesary to obtain a pore-free By the use of mechanical alloying it is material. Another approach in infiltration possible to alloy non-soluble elements due to technologys is the use of low-pressure the fact that alloying is carried out at investment-casting to infiltrate bundles Al20r temperatures below the solidus-temperature. fibres. The mechanical alloying process is a long term process, where usually mixing times between 2- In SPRAY DEPOSITION (OSPREY-PROCESS) a 4h are necessary. Normally the particles have liquid aluminium melt is atomized by an inert dimensions of 1-3 µm. The optimum size of the gas. The melt is over-heated to about 750 - matrix powder is about 2 times that of the 800°C, the reinforcement particles are fed reinforcement. Coarse matrix powders (>50µm) directly into the beam of molten metal after the lead to the formation of large particle free zones nozzle. The goal of the process is to produce in the composite [65] and therefore to materials with a grain-size between that of melt­ inhomogenuous material properties. metallurgical and powder metallurgical products. The molten particles are solidified on The next step in the solidification process is 3 a cooled substrate, cooling rates of about I 0 - pressing. Due to the poor thermal conductivity I 05K/s can be reached - in comparison PM the powders have to be cold pressed firstly. offers a cooling rate of about I 08 K/s. In the as­ Pressures in the order of magnitude of 500-600 sprayed condition, the density of the material is MPa are used in this step. Then the powders about 95 - 98%, therefore the pre-solidified have to be encapsulated and degased to 5 material has to be extruded before use because pressures of about 10- mbar. Afterwards of its porosity and low ductility [see 65]. sintering or hot isostatic pressing is carried out at temperatures up to the solution treatment In comparison to powder metallurgical temperature of the material. In the HIP process products the oxygen content of the solidified pressures of up to 1000 bar are used. The PM material is, in the case of aluminium, I 0 - 20 products are usually reported to be fine-grained times lower. Currently (1995) the sprayed bulks and homogeneous [65]. At the moment they have a diameter of up to 300mm, a length of lm deliver the best available metal matrix and a weight of about 400kg and only two composite products. A description of the production plants producing aluminium MMC' s process technology is given in figure 45 [65]. are known.

INFILTRATION PROCESSES are used to produce The major economical problem in the Osprey particulate- or fibre reinforced MMC's by process is the so-called overspray. Usually 30 - infiltration of pre-forms with liquid metal. 50% of the melt are of no use for the production Usually, mm1mum reinforcement volume process because it does not hit the cooled contents of 45% are necessary due to the substrate. mechanical stability of the preform. The infiltration can be carried out under high THE IN-SITU PROCESS features the advantage pressure or under gravity. The process is usually that the reinforcement (e.g. particles) is not a long-term process and therefore formation of supplied to the melt but formed in the melt by a

24 chemical reaction. An example is the formation Properties ofReinforced Aluminium Alloys of TiB2 in a aluminium (AA 6061) melt. The in­ situ process technology is very sensitive to One of the most important benefits of impurities in the basic alloy and the process reinforcement is, as mentioned before, the parameters. In future, the importance of in-situ increase of Young's modulus. When using long­ MMC's may increase because of their specific fibres the strength in fibre orientation direction properties. They offer also increases. In 50 vol.% alumina fibre (diameter 100 µm) reinforced AlZn alloy, • Small particle sizes ( <3 µm; common produced by investment casting infiltration particle sizes in other MMC's are> 15µm) process, a Young's modulus of more than 130 GPa and a maximum bending stress up to 900 • Thermodynamic stable interface MPa was measured. particle/matrix and The reinforcement by the use of particles • Low price, because most of the process is causes an isotropic change in the properties, the same as in conventional wrought although the strength does not increase product fabrication. significantly. Only sometimes the yield strength increases a little, depending on the production For the scale of clarification, the smaller the process. The increase of elastic modulus at particles, the better is the fatigue behaviour of constant tensile strength can be seen in fig. 4 7 the composite. "Big" brittle particles, as in the [65]. It can be seen that the yield strength is in most common particulate-reinforced aluminium the case of PM material lower than in the alloys, lead to low ductility and fracture conventional wrought alloy. Typical properties strength. Research and development in these of some advanced PM-aluminium MMC's are areas are being pursued increasingly at the given in table 12 [59]. The most important moment. If these materials can keep what they property of these alloys are the high elongation promise, a big market will grow for these combined with high modulus and yield strength. materials over the next few years. This combination of properties is only available with particulate reinforced aluminium when it is THE MELT METALLURGICAL PROCESS is the produced by the use of powder metallurgy. Note cheapest solidification process for aluminium­ that the CTE is a function of the particle volume based MMC' s. The best known process is the content. Unreinforced aluminum has a CTE of Duralcan process: A conventional cast alloy like 23xl 0-6 the reinforced alloys offer a CTE in the AA357 or AA380 (AlSi-base alloy group) is ' -6 order of magnitude of 16-18x10 [59]. used and the particles (SiC is always used in an AlSi matrix due to thermodynamical The improved wear resistance of particulate­ necessities) are supplied to the melt. The reinforced AlSi alloys makes it possible to use particles are distributed under vaccum by the material in brake systems. The high thermal mechanically stirring the melt. The stirring conductivity of aluminium (4 times that of grey process is usually carried out for a time of up to cast iron) keeps the temperature in the operating 70min. The so obtained MMC's can be cast in range of the matrix material. This is the first conventional moulds and therefore they are large-scale application for reinforced cheap. Currently the price of 1kg is about two aluminium. Fig. 48 shows the improvement in times that of a conventional AlSi cast alloy. wear resistance caused by ceramic particles Typical properties of cast MMC in comparison [68]. to the unreinforced matrix are shown in fig. 46 [67]. This type of MMC may allow large-scale In companson to other materials of light­ production in the automotive industry. weight engineering interest, long-fibre reinforced aluminium alloys offer excellent properties due to theire high strength and

25 stiffness in fibre orientation direction. Fig. 49 These material group will be an approach to [69] shows this type of composite in comparison lower structural weight and offer a great field of to other light-weight construction materials. applications. Especially in the aerospace industry, where the amount of magnesium Reinforced Titanium products is relatively low, these improved properties may increase the use of magnesium. Titanium is usually reinforced with SiC in continuous fibre form. The fibres are coated by Currently the company MEL in Great Britain electron-beam deposition with high-purity Ti- is developing a SiC particle reinforced 6Al-4 V in a controlled atmosphere [70]. The magnesium alloy to reach higher operating cross-section of a typical Ti6Al4V/SiCfibre temperatures for the use of magnesium in gear composite is to be seen in fig. 51. The core in housings and engines of automotive systems. the middle of the white SiC fibres consists of The volume content of the reinforcement is in tungsten. A tungsten core is necessary in the the range of I 0-20%, typical particle size is production process of SiC monofilament fibres. about IO - 15µm [71]. After coating with Ti-alloy the fibres are consolidated applying the HIP process. As with aluminium, the reinforcement of titanium leads 6 Summarizing Discussion to higher operating temperatures and to higher strength in fibre orientation direction. Therefore 6.1 Materials For Light Weight the material is useful in landing gear Structures applications or as a fan-blade structure in modern turbine engines. The research and development activities for new Al alloys and Mg alloys show, that there is It should be mentioned that currently the cost a growing demand for weight reduction in both of this group of reinforced metals is extremely the aerospace industry and automotive industry. high (up to I 000 US$/kg). One reason for this is the high price of the fibres, developments Favorite Al alloys are the AlLi alloys with concerning the production process of SiC-fibres reduced specific weight and increased specific are in progress. In future it may be that the stiffness due to Li, or the aluminium magnesium major market for titanium-matrix composites scandium alloys which prove to combine high will be enlarged from advanced military jet strength and weldability with excellent fatigue applications to civil applications and therefore behaviour. Especially in high performance parts to a wider market. like automotive engines an increasing amount of high strength PM aluminium powder products Reinforced Magnesium may be used.

The reinforcment of magnesium by the use of The development of creep resistance particles or fibres is one of the most interesting magnesium alloys with good die-castability will parts in future material development. be on of the most important fields in the development of new Mg alloys. Although today The disadvantages of Magnesium like the usage of magnesium for parts working at elevated temperatures in the range of up to • low creep resistance 150°C, for example in gear housings, is not • low stiffness possible due to the poor creep-resistanceof the material, in future these application fields will • low wear resistance be of growing interest for the automotive industry. New alloys containing rare earth can be increased significantly by metals provide well creep-resistance combined reinforcement. with high damping performance.

26 The use of reinforced light-weight alloys will aided designing, including computer simulation, increase in the same rates, that cheap process allows engineers to take maximum use of the technologies (like the Duralcan-process) will be steel properties. These tendencies and the use of available. The tailorable properties of the tailored blanks and steel types with higher material offers an on-the-problem-oriented strength offer a excellent base for new light design and therefore a high weight/stiffness or weight structures in all ground transportation weight/strength ratio. Especially the industry. Comparison of steel based solutions of development of long-fibre and particulate light weight structures with the development of reinforced magnesium is a very important Al-based solutions (e.g. Audi spaceframe) show development route. The disadvantages of that steel is a strong competitor. magnesium (low stiffness and poor creep­ resistance) can be managed with this approach. The advantage of the steels is the nearly The usability of magnesium will increase and 100% recycling in Europe and North America. therefore new application fields can be reached. This means a primary energy and raw materials saving production. Calculating the whole energy It does not have to be forgotten, that bilance of the production process, the use of intermaterials competitions are won or lost not secondary Al-alloys must be increased from only on the basis of raw material price, but also actually 35% (Germany) to 70% in to order to on the base of total lifecycle economics of compete with the steel solution in environment finished systems, as shown in fig. 50 [72]. compatibility and cost [73, 29]. Therefore, for instance, airplanes are made of aluminium rather than steel, not because 6.2 Materials For Increased Efficiency of aluminium is a cheaper raw material or costs Thermal Engines less to fabricate, but rather because the lifecycle cost of aluminium aircraft is less than that of The Ni-base alloys are commonly the work­ steel aircraft. For the same reason, most car horses of high temperature materials. However, bodies are currently made of steel sheet rather the demand for higher temperatures above than aluminium. In automotive applications, 1000°C involves problems like oxidation, lifecycle economics are very different from transformation of the microstructure and those in airplanes; however the same principles resulting creep. One way to solve these of material selection apply [72]. problems is the mechanical alloying of the Ni­ base matrix with oxides of yttrium. This leads to The recycling problems and the high primary a creep resistance superior to that of the energy consumption of the Al-alloy production unreinforced alloy and a maximum operation are critical aspects delaying the introduction of temperature of about l 150°C. However, these Al-alloys into automotive mass production of temperatures necessitate coatings in order to structural components. However, research in avoid oxidation and hot gas corrosion. automotive Al-structures pushes the steel Drawback of this ODS alloys is the reduced makers to develop new steels and processes for possible complexity of the component design. steel based light weight structures. Due to high For turbine blades, the excellent creep properties strength, excellent crash behavior, low energy are counteracted by reduced cooling demand for steel production and the nearly functionality. Thus, new casting technologies closed recycling loop, steels are excellent for pure y' -hardening Ni-base alloys with higher candidates for light-weight structures. New purity are under development. They offer the processing routes offering flexible reactions to full design field of cast components with the changing demands of steel processing improved high temperature properties. industries give a new perspective for the "old" However, precipitation hardening is only a metal steel. The new processes also allow a temporary strength effect due to the much more easier development of new alloys thermodynamical instability of the precipitations and accelerate steel research. New computer at high temperatures.

27 High specific weight and thus weight of Ni (pesting) and the difficult processing of bulk base alloys involves investigations on materials necessites further detailed research aluminides for high temperature applications. work. Because of the poor room temperature Background is the reduction of mass and thus ductility of silicides MgSi2 is used as a mass forces of oscillating parts in addition to reinforcing second phase in Al and Mg, operation at high temperatures. The specific produced by an in-situ reaction. The use of Al­ yield strength of both types of aluminides TixAly MgSi2 and Mg-MgSi2 alloys for automotive and NixAly are superior to that of the Ni-base pistons provide a weight saving potential of up alloys and the titanium alloys at temperatures to 30% compared to the standard piston alloys. from 700°C (Ti-aluminides) up to 1000°C (Ni­ This means an improved efficiency of the aluminides). However, drawbacks like inherent engine and thus reduced reagant and particle room temperature brittlness, the difficult emission. Additional benefits are the higher formability, the very limited reproducability of stiffness, contributing to the weight saving, mechanical properties (TixAly) and the lack of reduced CTE, higher thermal conductivity and sufficient creep resistance delay their use in high efficient production by the casting route. temperature applications. A lot of investigations Because of their properties and their cost are done to solve the problem of brittlness by efficient production route they have good the addition of alloying elements or second chances to be used in serial production. phase ductilization. Recent investigations on Tii(AlNb) show very prom1smg results Besides oxidation behavior and concerning formability and room temperature thermodynamical stability of the microstructure, properties. However, in some cases alloying for creep resistance is the most dominating factor improved mechanical properties counteracts the for high temperature materials. Creep occures at oxidation resistance. To improve the creep 150°C for AI- and Mg-alloys as well as at behavior, the process of oxide dispersion temperatures above 1000° for Ni-base and Fe­ strengthening is applied to aluminides, base alloys. Oxide dispersion strengthening by especially to Ni-alurnindes. The fine dispersed, inherent, thermodynamically stable oxides thermodynamically stable oxides should avoid reduces creep. Some ODS-Al alloys show grain boundary migration. However, mechanical excellent creep behavior and strength at alloying and the subsequent powder metallurgy temperatues up to 300°C. However, drawback route is complex and expensive. Up to now, non of these alloys is the reduced room temperature of the described aluminides has been transfered ductility and damage tolerance. Nevertheless, to mass production. A lot of further ODS-Al alloys are excellent candidates for light investigations on metallurgy, processes and weight structures for elevated operation quality control have to be done in order to attain temperatures. More research work is necessary the required materials properties. to increase the operation temperature of now 50% of the alloy's solidus temperature up to Comparable with the alurninides, 90%. intermetallics based on silicium (silicides) offer the advantage of a hughe weight saving ODS-variants of Ni-base alloys and Fe-base potential (MgSi2) and high operation alloys feature operation temperatures up to 90% of their solidus temperature without creeping. temperatures (MoSi2). Unfortunately silicides show the same poor ductility at room However, Ni-base alloys need oxidation temperature as the alurninides due to the ordered protection coatings at temperatures exceeding lattice structure. MoSi2 as a structural material 1000°C. Fe-base, ferritic alloys show the offers operation temperatures up to 1200°C with superior oxidation behavior up to 1250°C but sufficient strength and excellent oxidation lower admissible loads compared to Ni-base resistance due to silica layer formation. ODS. Nevertheless, both types of ODS-alloys However, room temperature brittlness, sever posess a high potential for the improvement of oxidation in the temperature range of 600°C the efficiency of thermal engines. The drawback 28 for high temperature applications is the limited properties. Metal matrix composites (MMC) design potential compared to cast components exhibit higher stiffuess and thus an advantage in due to the mechanical alloying and PM/HIP weight, but low fracture toughness and damage route. Nevertheless, the Fe-base alloy PM2000 tolerance. Ductile phase toughening of brittle is now used for serial high temperature aluminides is only metastable du to the components of automotive engines. Research thermodynamical instability of the metal second work is continued in order to improve phases at high temperatures. processing and material properties. In some cases, material combination 7 Conclusions counteracts the demands for recycling due to the problems in materials separation. For a global The results of the study show that there are a ecological effect of the technical components lot of research activities in the fields of metal produced, this fact must be carefully taken into alloys in order to improve the ecological account. situation of man-made technology. However, driving forces of these developments are a Besides the problems in combining different mixture of political, economical and ecological types of materials, the process of materials factors. Main research and development combination is more complex compared to cast domains are the reduction of weight for and wrought alloys. The production of ODS­ transportation systems on ground and in air, the alloys for instance consists of high energetic increase of efficiency of thermal engines for milling of the matrix alloy and the oxides with transport or current generation and the reduction subsequent hot isostatic pressing and extrusion. of energy and raw materials consumption in This means a cost, time and energy intensive industrial production. However, improved production process. That could in fact technical components do not only need counteract the aimed effect of the technical generally improved materials. With increasing solution for improved environmental technical demands for the components, tailor compatibility. On the other hand, too high made materials for the special applications are materials or product costs affect the necessary. In general materials do not meet all competi tivness. the requirements of the special technical solution. The higher the requirements, the more The above-mentioned results show, that in diversified the materials properties have to be. many cases an appropriate materials solution for Besides standard solutions like alloying, new the respective technical problem can be processes exceeding the limits of achieved in long term. However, the effect of thermodynamical equilibrium such as this special technical solution on fuel saving and supersaturation of alloys by rapid solidifications thus on the decrease in reagents emission or raw are investiagted in order to get new alloys with materials consumption must be carefully new properties. An example is the Li­ compared to the energy and materials supersaturated AJLi-alloy with decreased consumption during production process. For a specific weight. On the other hand, more global estimation of the effect of technical complex loads like the combination of thermal, solutions with improved materials a calculation mechnical and chemical load in addition to the of all energy and mass fluxes, beginning at the light-weight demand lead to the necessity of raw materials mining and transportation to the special designed materials compounds complete production process is undoubtly consisting of different materials types. However, necessary. the combination of different materials often produces drawbacks in materials properties and processing. E.g. oxide dispersion strengthening improves the creep behaviour at elevated or high temperatures, but deteriorates room-temperature

29 References 17 Sick G., Essig G - Aluminium, 67. Jahrgang 1991, 9, S 880, in German Bild der Wissenschaft, DV A, 2/1994, p. 68, in German 18 Schmid E.E- 2. Syrnposinum Materialforschung des Bundesministeriums filr Forschung und 2 NATURE, Vol 374, april 1995, p. 487 Technologie, Projekttragerschaft Material- und Rohstofforschung (PLR),S 899, 1991, in German 3 Silddeutsche Zeitung, Silddeutscher Verlag, 418195, in German 19 Kumpfert J. et al - Proceedings of the 7th World Conference on Titanium, San Diego, USA 1992 4 Daimler-Benz HighTechReport 4 I 1994 20 Bartels et al - Proceedings of the 13th 5 Daimler-Benz HighTechReport 4 I 1994 international Plansee Seminar 1993, Vol.3, pp 564 ff 6 Thomas J. Ruden and Darryl L. Albright - Magnesium Castings for Auto Applications - 2 l Hedrich H.D - VDI Berichte Nr. 600.4, 1987, S Advanced Materials & Processes 6/94 S. 28 - 32 401, VDI-Verlag, in German

7 Technical Note - Advanced materials and 22 Campo E. and Lupine V.- in "Innovative processes 4/95, p. 10 Materials, Prospects and Problems in a Competitive Industrial Context", Edited by P. 8 Alfred Frisch - Zukunft der NE-Metalle in der Vincenzini, Techna Sri, 1993 Automobilindustrie - Metall 3/95 p. 166- 167 23 Singer R.F - VDI-Bericht Nr. 1151, 1995, VDI­ 9 A. Koewius - Aluminium, Automobil und Verlag, in German Recycling - einige grundsatzliche Aspekte Aluminium 3/95 S.276 - 281 24 Smarlsky W., Sinheiser L.- VDI Berichte Nr. 1151, 1995, VDI-Verlag, in German lO M. Peters und W.A. Kayser - Das Potential metallischer Leichtbauwerkstoffe in der Luft- 25 E.Arzt -2. Symposinum Materialforschung des und Raumfahrt - VDI Berichte nr.1080, 1994, s. Bundesministeriums filr Forschung und 483 - 506 Werkstofftag 1994, VDI-Gesellschaft Technologie, Projekttragerschaft Material- und W erkstofftechn ik Rohstofforschung (PLR), S 103, 1991, in German 1 I J.C. Ekvall, J.E. Rhodes, G.G. Wald - Methodology for evaluating weight savings from 26 R. Bruno - Innovative Materials edited by P. basic material properties - Design fo fatigue and Vincenzini, Techna Sri, 1993 fracture resistant structures, p. 328-341, ASTM- STP 761, ASTM Philadelphia, 1982 27 C. Hendricks - VDI Berichte Nr. 1080, 1994, p. 3-16, VDI-Verlag, in German 12 E.Loechelt - Obersichtsvortrag: Leichtbau in der Luft- und Raumfahrt - VDI Berichte nr.1080, 28 L. Hamm - International Iron and steel Institute, 1994, s. 461 - 471 Werkstofftag 1994, VDI­ Brussels, 1993 Gesellschaft Werkstofftechnik 29 8. Engl und E.-J. Drewes - VDI Berichte Nr. 13 Technical Note - Advanced Materials & 1080, 1994, p. 35-54, VDI-Verlag, in German Processes , 8/94 p. 9 30 W. Bleck, K. Blilmel and W. Prange -VDI 14 B. Reuter- Diplomarbeit Metallische Berichte Nr. 1080, 1994, p. 25-34, VDI-Verlag, Verbundwerkstoffe mit Aluminium-Matrix", in German 1989 31 D. Stark-Seuken, W. Bleck und W. Dahl - VDI­ 15 Information on the TMCTECC Program - Berichte Nr. 1151, 1995, p. 503-513, VDI­ Contact: Fred Polhemus, United Tech. Corp. Verlag Deutschland, in German Pratt &Whittney, West Palm Beach, USA 1994 32 W. Prange, C. Schneider - VDI-Berichte 16 Product Information on aluminium composites - Nr.1021, 1993, p. 45-52, VDI-Verlag, in German 3M, 1995

30 33 R.F. Singer in D. Coutsouradis et al. (editors), 50 Hummert Klaus, PEAK Werkstoff GmbH, Materials of Advanced Power Engineering, Part Germany, in German II, Kluwer Academic Publishers, Dordrecht 1994, S. 1707-29 51 J.D. Whittenberger, R.K. Viswanadham, S.K. Mannan, K.S. Kumar -Journal of Materials 34 Lipsitt H.A. et al. - Metal Transactions A, Vol Research 4, 1989, p. 1164 6A (1975), pp 1991-1996 52 R.S. Polvani, Wen-Shian Tzeng and P.R. Strutt, 35 Tuominen S. and Wojcik C. - Advanced Metal Transactions A, 7 A (1976), p. 33 Materials and Processes, Vol 147, No. 4, April 1995,p.23-26 53 K. Z~ltzer - Proceedings of the 13th International Plansee Seminar, Eds H. Bildstein and R. Eck, 36 Sauthoff G - 2. Symposinum Materialforschung Metallwerke Plansee, Reutte (1993), Vol. 3, p. des Bundesministeriums filr Forschung und 528-536 Technologie, Projekttrligerschaft Material- und Rohstofforschung (PLR),S 877, 1991, in German 54 Korb G. et al. -Proceedings of the 13th International Plansee Seminar 1993, Vol.I, pp 37 Peters M., Winkler P.-J. - Metall, 46. Jahrgang, 130 ff Heft 12, Dec. 1992 55 N. Wood, Q. Mabbutt, J. Wonsowski and F. 38 U. Herold-Schmidt, S. Schwantes, G. Broden - Starr - The long-term oxidation behaviour of iron Advanced Materials and Structures from based ODS-alloys - Proceedings of the 13th Research to Application, edited by J. Brandt et International Plansee Seminar 1993, Vol.I, pp al., SAMPE European Chapter 1992 115 ff

39 Sauthoff G., lntermetallische Phasen, in: 56 Advanced Materials and Processes 7/94, Vol. Symposium Materialforschung 1988, KFA-PLR 146, No.I, p.7, ASM International Jillich 1988, S.399-414 57 M. Peters und W.A. Kayser - Das Potential 40 Rudy M., Sauthoff G., Creep behaviour of the metallischer Leichtbauwerkstoffe in der Luft­ ordered intemetallic (Fe,Ni)Al phase, in: High­ und Raumfahrt - VDI Berichte nr. I 080, 1994, s. temperature ordered intermetallic alloys, C.C. 483 - 506 Werkstofftag 1994, VDI-Gesellschaft Koch, C.T. Liu and N.S. Toloff, MRS, Werkstofftechnik Pittsburgh 1985, p.327-333 58 Donald Webster - Advanced Materials & 41 Walter J.L. and Cline H.E. - Metallurgical Processes 5/94pp. l 8ff Transactions I ( 1970) 1221-1229 59 Thomas B. Gurganus - Aluminium Powder 42 Sauthoff G. und KleinekathMer W. - VDI Applications - Advanced Materials & Processes, Bericht Nr. 1151, VDI-Verlag 1995, in German 8/1995, p. 57-59

44 Beer St., Frommeyer G., Schmidt E. und Helbig 60 D.L. Albright, T. Ruden - Magnesium utilization H. - VDl-Berichte Nr. 1080, 1994, p89, VDI­ in the north american automotive industry - Verlag, in German Hydro Magnesium 4/1994

45 F. Jansen, E. Lugscheider - VDI-Berichte Nr. 61 N. Zeumer, Dr. H. Fuchs - Einsatz von 1151, 1995, VDI-Verlag, in German Aluminium- und MagnesiumguB im Leichtbau VDI Berichte Nr. 1021, 1993 p. 241-254 46 R. Scholl, B. Kieback - Proceedings of the PM Worl Conference, Vol. 2, 1994, Paris 62 H. Grabert Magnesium: das leichte Leichtmetall - technik heute 3/1979 p. I - 11 47 Publication Raufoss 63 Carl Zweben - Materials engineering 2000 and 48 Jangg G., Kutner F., Korb G.; Aluminium, 51, beyond: Metal Matrix Composites - Advanced 1975,641 Materials & Processes 1/1994 p. 28-30

49 Jangg G., Kutner F., Korb G., Powder Metall. 64 B. Reuter Diplomarbeit "Metallische Int., 9( 1), 1977 ,24 Verbundwerkstoffe mit Aluminium-Matrix", 1989

31 65 Rainer Rauh - Dissertation "Einsatzpotential und Beanspruchungsgrenzen partikelverstlirkter Aluminiumlegierungen auf der Basis einer metallkundllichen Bewertung", S. 6ff

66 B36 J.A. Black - Shaping Reinforcements for Composites, Advanced Materials and Processes, 19888, Metall Process 3

67 Technical Note - Aluminium 4/95 p 420-421

68 R. Mehrabian, F.M. Hosking, F.F. Portillo, R. Wunderlin Structure and deformation characteristics of rheocast metals - Dep. of metallurgy and mining engineering, Univ. of Illinois, Final report DAAG46-76-C-0046

69 M.F. Ashby - Materials Selector Data -

70 Product Information on titanium composites - 3M, 1995

71 MEL Product Information, 1995

72 John Busch - Materials compete in recycling alternatives; 1 I 1995; Advanced materials & processes, p. 25-26

73 Liedke Christa - Wuppertal-Institut, in Bild der Wissenschaft, 9/1995, Deutsche Verlagsanstalt GmbH, S. 27, in German

32 Tables

Hothouse gases Ejection of hothouse gases Mean existence Share in additional relative hothouse time hothouse effect in % potential" Carbondioxid Fire clearing of tropical rain 50 - 200 years 50 l forest, of fossile C0 combustion 2 energy resources (heating, traffic)

Methan CH4 Fire clearing of tropical rain 10 yeras 13 58 forest, rice fields, dumps

Ozon03 traffic 2 -3 months 7 1800

Dinitrogenoxide manure, combustion of fossile 130 - 150 yeras 5 206 energy resources N20

FCCH CCl3F fuel gas 65 years 5 3970

• compared to an eqmvalent mass of co2 m kg Souroe: Bild der W1ssenschaft, DV A, 2/1994, p68

Table 1: Greenhouse reagents and sources

R,,. RdO,l A5 SRK Dichte ~O,l Kc 3 (MPa) (MPa) (MPa) (%) (MPaVm) (MPa) (g/cm > 7075 1'7351 490 390 400 7 - 290 2,80 7075 1'7651 490 415 435 6 - 172 2,80 7075 T651 525 476 455 7 28 69 2,80 7050 1'7651 525 455 440 9 28 172 2,82 7150 T6151 580 540 530 9 22 69 2,82 7150 T651 570 525 - 8 - - 2,82 7150 T7751 580 540 530 8 22 172 2,82 7055 T7751 615 595 594 7 24 103 2,85

Table 2: Typical properties of 7xxx (AIZn-based) series alloys 2xxx alloys 7xxx alloys 2024,2324,2224 7075, 7475, 7050/7010, 7150

fuselage planking fuselage extruded stringer stringer milled ribs ribs seat components window frames

wmg planking/stringer wmg planking/stringer (bottom side) (top side) slat ribs girders

Table 3: Typical application fields of 2xxx and 7xxx series alloys in aircraft

Component Intermetallic Temperature High-pressure compressor TiAI 650°C • housings Ti3Al 600°C • blades TiAl 100°c Combustion chamber • housings TiAl 750°C • shingles NiAl 1300°C M0Si2 1600°C High-pressure turbine • gaskets NiAl 900°C • liner NiAl 900°C • vanes NiAl 1300°C M0Si2 1400°C Low-pressure turbine • housings TiAl 750°C • blades TiAl 750°C NiAI 900°C

Table 4: Applications of intermetallics in gas turbines alloyin2 elements in wt% c N Mn p Al Nb v 0,07 0,006 1,3 0,01 0,04 0,045 0,045

mechanical properties

YS UTS e~m 612 671 25

Table 5: Chemical composition and properties of a hot-rolled, micro-alloyed high-strength steel (QStE500TM)

elements in wt% c Si Mn p s Al Cu Fe 0,00 0,02 0,22 0,04 0,00 0,06 0,01 bal 8 7 8 4

Table 6: Chemical composition of bake-hardening steel ZStE 180 BH

alloying elements Al Si Fe c 0 bal. 12-20 0-5 0.5-4 0.5

Table 7: Variation of alloying elements in dispersion strengthened aluminium alloys Alloy Type AA No. Specific Property Al-Cu-X 2024,2014,2090,2091,2219, Damage-tolerant, Al-Li, Creep-resi- 2618 Stant Al-Mg-X 5091 MA (AL-905XL) Al-Mg-Si-X 6013, 6061 Corrosion-resistant Al-Zn-X 7075, 7475, 7010, 7050, 7055 High-strength Al-X 8009, 8019, 8090, 8091 Creep-Resistant (Powder Metallur- gical), Al-Li Table 8: Classification of High-strength Aluminium Alloys

Aluminum alloy, 7093, 7075, 7075, 7050, 7055, condition T-7E92 T-6 T-73 T-74 T-77 Room temp. properties, longitudinal direction Tensile strength, MPa (ksi) 607 (88) 572 (83) 503 (73) 517 (75) 593 (86) Yield strength, MPa (ksi) 579 (84) 503 {73) 386 (56) 462 (67) 558 (81) Elongation,% 14 11 13 15 11 Density, g/cm3 (lb/in3) 2.85 2.80 2.80 2.83 2.85 (0.103) (0.101) (0.101) (0.102) (0.103) Specific tensile strength 854 821 723 735 835 Fracture toughness, MPa·m112 (ksi·in.112) 53 (48) 29 (26) 34 (31) 38 (35) 33 (30) Modulus, GPa (Msi) 75(10.8) 72(10.4) 72(10.4) 72(10.4) 70(10.2)

Corrosion properties Generali A c A-B B B Exfoliation2 p EC EA EB EB Stress corrosion cracking, MPa (ksi) »310 (45) 55 (8) 276 (40) 241 (35) 207 (30)

1 - Ratings A through E are relative ratings in decreasing order of merit, based on exposure to sodium chloride solution by intermittent spraying or immersion. 2 - Accelerated exfoliation corrosion test per ASTM G34. P =pitting. least exfoliation; EA =superficial; EB = moderate; EC = severe; ED = very severe.

Table 9: Prealloyed PIM 7093 vs. ingot alloys

Material Common Reinforcement Approach Type Aluminium & Particles Stiffhess, Strength, Wear- Magnesium Long-fibres resistance (particles), Creep- Short-fibres resistance Titanium Long-fibres High-temperature strength

Table I 0: Overview of reinforced light-weight alloys Table 11: Influencing Parameters on an Particulate Reinforced MMC' s Properties

Alloy, v/o SiC particulates, X2080, X2080, 6113, condition lSv/o, T-4 20v/o, T-4 2Sv/o, T-6 Tensile strength, MPa (ksi) 483(70) 517 (75) 4%(72) Yield strength, MPa (ksi) 365 (53) 393 (57) 437 (63.5) Elongation, % 7.5 6 3 Density, g/cm3 (lb/in.3) 2.82 2.85 2.82 (0.102) (0.103) (0.102) Modulus, GPa (Msi) 100(14.5) 110 (16.0) 120 (17.5) Coefficient of thermal expansion, x1()6 18 16 Thermal conductivity at R.T., W /m-·c 105 103.4

•Extrusions

Table 12: Typical properties of PIM MMC's (extruded) Figures

Greenhouse Effect - Comparison of Initiators Share in worldwide ejection of greenhouse gases (C02, Melhan, FCCH)

fumcr 1.ESR 13.6 Great BriL 24 "".'. IJC''"'5-...-.­ Fnnc:e 1.6 Germany 3.8 r.:'~--~: Italy 1.7

'°"""'' Siiddeu•die Zcilung 8.4.9S

Figure 1: World wide initiators of green house gases Heating/Cooling

D Technical Solutions for Reduction of Fnvironmental Hann

Reduced Raw Material Consumption

Reduction of Weight of Vehicles Reduced Energy Consumption and Moving Components for Manufacturing Processes

Reduction of Friction Loss

Advanced Processes

Recycling

Figure 2: Factors for environmental harm and technical approaches for short or mean term solutions secondary savings(%)

' cell structure r ( l Cl.) "' drive train rt/ . '> ' +id ~u .s gears wz== ~ 0 u chassis LllJ2£iliillillill2fil±28Efillt±filillEl]illl@ additional hn ; rd 0 3 6 9 12 15 auto weight sharing .§ -30+-~~~l--3\.,---~-+~~~-+~~-----4 ~ cell structure e -60+-~~~1--~--"'~~~~-+~~--j 47% ~ -90-t-~~~~~~-t-~~-+-~~~ ~ chassis 23%

liquids electronics I 4,5% 3,5% -ISO~'~~~~~~~~~~~'--~~---'

Figure 3 : Reduction of weight and cost development Light-weight construction Truck

rnr waD Al-foam sandwich

cab Fiber structures

-Is Polyester fibre fleece

inside rquipmmt Thcrrnoplast sandwich

air intakr fibre compound

joining ttthniqur Al~sings/SP-profile

am componenta fibre compound qht-welght brw system crash structutt MMC-Al brake rotor fibre compound cab floor Al-foam sandwich

------·~ ------

Figure 4: Light-weight construction concepts for a lorry Available range

Magnesium Engineering Aluminum Steel plastics

30 (b) .. (207) !:2"" -;; 0.. b 20 :. (138) :;" "'O Q E 10 -~-;; (69) u:;..

Magnesium Engineering Aluminum Steel plastics

1.25 (c) Q =:? ,;: ·o;OD it A 0.75 ,),., .. 0.5 ~.. => 0.25 ...... c:

Magnesium Engineering Aluminum Steel plastics

Figure 3 : Property efficiency attributes of magnesium compared to those of selected other structural materials for auto applications. a) Relative strength-to-weight ratio. b) Eastic modulus. c) Relative stiffi1ess-to-weight ratio. Knee Bolster Steering Column Support Rconforcemenl Panel. Bracket. AZ910 AM608

Cellular Telephone Engine Accessory Housing. AZ910 Brackets, AZ91 D

Bench Seaf Stanchion. Automotive Wheel. AM70 AM608

Figure 6: Typical magnesium applications Fig. 7: Material choice in light-weight structures

100%

80% ·a; 'E Cl! 60% 15 (ii .::t: Ci> 40% ~ 20%

0% A300 A310-200 A320-200 A340 Airbus 2000 Flugzeugmuster Iii Aluminium I!§ neue Al-Leg. • Verbundwerkstoff • Titan lil Stahl [] Andere

Figure 8: Content of different materials in aeroplanes Nozzle, compressor and fan components

Figure 9: Components made by the use oflong-fibre reinforced titanium

Figure 10: Aircraft panel- a typical appliction for long-fibre reinforced aluminium ~max = 3QQOC

~max = 220°C

.:1max :: 1sooc

Figure 11: Critical piston sections [17]

~ 900"t------t------~---::;~ § cE .§ 600+------+--:;;;;lll'C. Q. "'

o--~~~~~'T-~~~~~--~~~~__, 50 100 150 200 moving mass [g]

Figure 12: Required spring force of serial motors (related to the nominal rate ofrevolutions 6250 I/min) [20] 5 c ·.c0 Q. E ~ 18 ...... structure optimized 8~ concept Q) .a 2,5 ....o.!? - § u '£ Y' maximum ~ u.;i concept ""8 ... "-"&:l 0 0 20 40 60 reduction of spring force [%]

Figure 13: Reduction of fuel consumption with decreasing valve spring force (ECE-cycle) [20]

steel ::§ ~60 titanium E ~40+------.,..~ ceramic ~ 20

o.._~~~~-1-~~~~--~~~~...... ~~~~---1 25 30 35 40 45 valve head diameter [mm]

Figure 14: Masses of inlet valves [20]

0,40 -----~-----~----~

>. g 0,30 +----l---h"":__+---f------1---~ Cl) ·13 ~ 0,25 +----~----+---__,______,___~

0,20 .,--~----.-----r------

! Source: £. Campo and V. LuPffic 0, 15 ~-~----+---~--~-~----J 800 900 1000 1100 1200 1300 1400 Turbine inlet temperature [0 C]

Figure 15: Increase in thermal efficiency with increasing gas temperature at turbine inlet [24] Shower" hHd Fiim cooling _/ Pin rin cooling c-ling

\ Pin fin cooling

Figure 16: FMW 701F first stage airfoils geometry: a) nozzle guide vane and b) blade [24]

Figure 17: Application potential for intermetallic structural materials in gasturbines [24] o~---~___...._...__~------+-~~~~ 150 250 350 450 Yield strength [N/mm2]

Figure 18: Weight reduction as a function of yield strength. Comparison between auto body structures (BH-steels) and crash elements (micro alloyed resp. P-alloyed steels) [32]

• bake-hardening steels • pot galvaniz.ed high strength steels--+--+­ 400 Ell phosphorus alloyd steels • micro alloyed steels 300

100

0 1984 85 86 87 88 89 90 91 92 93 year

Figure 19: Increase in use of high strength steel strips in automotive industry [30] ~~ ~ dynamic tension tests with flat samples ,,/

0.20 QS!E500TM -v ~ ------~-:::::.----•"' ~ IF (HS) +------.,.---- ';' FeP04 ------·· A 0 15 E · ZSIEl80BH ~ ~ -o-- ...... - ... o 0.10 ~ Al 5182 ------0------

0.05 ...... _ ...... _ _._...... ____._ ...... ____.___._...... ____.__._ ... 100.____._~1000~ 0.001 O.ot 0.1 1 IO strain rate [l/s]

Figure 20: Dissipated specific energy of high strength steels during dynamic room temperature tests as a function of the strain rate [31]

700 600 ZStE 300 BH ] 500 z .5 400 "' ~"' "'~ 300 0 ti:

200 0,02 0,04 0,06 0,08 0,1 0,2

logarithmic strain 4>

Figure 21: Flow stress of bake-hardening steels compared to steel St14 [30] ZStE180 BH ZStE220 BH 80-----. 70 60 ~ 50 2 40 0 30 I co 20 10 O"------' 80 ..------. 70 60 c 50 ~ 40 • 30 N I 20 co 10

~40 160 180 140 180 180 Temperotur, ·c

Figure 22: Influence of temperature and time on the bake hardening effect BHO (without pre-deformation) and BH2 (2% pre-deformation) [29]

/ Umm ~\ /Pct,._--ga-lvan_iz_ed_/~. ~// / \ j/ lowotr..,~ // /// ,./ l,Omm ~--~--~ ~\ ./c:id rolled / /,- /?../,.______,, '\ ) / high !tr

sheet thickness. quality, desi81J I laser welding :

source: Thyssen

Figure 23: Schematic description of the production of tailored blanks [32] 2,0mm 0,8mm

0,7mm I,5mm 0,7mm

bottom sheet inner door sheet

source: Thyssen

Figure 24: Examples of the design of tailored blanks [32]

New Process: EB Casting Electron beam gun

Solid metal

Figure 25: New casting processes: Current Induction Skull Crucible [23] Conventional New Process: Process: Liquid Metal Cooling (LMC) Radiation Cooling

W•ler COO ..d Conduction ooollng ohm pl••• 0 0 Llqyld Wlthdr•w•I metel b•th direction

Figure 26: Comparison of conventional cooling and liquid metal cooling during directional and single crystal solidification [23]

1~.--~~~~~~~~~~~ C0treot9d to IN7'8 d•rw.tty 140 MPa. 101 h

120 .. .Qac""• ..... P."'.' .... e: 0 OS ,._ill ti. cc Full 9¥"'1boll. z 2 generatkw'I .. 100 KC~"•···•••···· !; ~ '8 !

o...... _._ ...... __..__.._ ...... _._...._."4el ...... -...-' 4 e a 10 12 14 1e 1a 20 Chromium Content (wt%)

Figure 27: Maximum operation temperature of Ni-base alloys as a function of Cr-content. The temperatures are defined by creep resistance. The values are related to the creep strangth of Ni-base alloy 738 [23/33] 80 • IN738LC • Ti2A1Nb ,_..., N ,..... • IMI834 • TiAl ---E 60 (\1 . CJ supera2

...... ~ rn rn c:0 40 ..c 00 =0 -0 3 20 -ro(.) t!::

0

Figure 28: Room temperature fracture toughness K1c ofTiAl-alloys compared to Ni-base alloy IN738LC and Ti-alloy IMI834 [24]

Q ;al 15 s: I ~ 101-..._,.....>.....::...~ v ..: 0 5 • 711 • 100 ~ Nl-8Ased Alloys "'

o....___._~~~..__.__._~~~ 0 200 400 600 800 1000 1200 TEMPERATURE ["CJ

Figure 29: 0.2% yield strength ofTixAl as a function of temperature compared to conventional Ti- and Ni-base alloys [Kumpfert J. et al.] Figure 30: Oxidation behavior of titanium alloys [37]

'J§ 1000 I ~ 38.5 wt.•1.cr .!: 800°~ 0 ~ 600 17wt.%(r ~ .!::: ---.. 0 :'. 400 ------g 75wt%(r "~""''\o ", \ 5. ~ 0 200 a~ '\_o ::.e0 e,"­ N e,t:::~...... c:i o~.~-.--~"T-~~~.,._~.,...... :::::::&.._, 0 200 400 600 800 1000 1200 temperature in °(

Figure 31: 0.2% proof stress ofNiAICr as a function of temperature and Cr-content (36]

a) b)

so~~~~~~~~~

0~ /•HIPtd & ·= 100" 40 ..,,,.,.,.,....· hot utruOtd :::. i HIPtd & "'.... 'e I • :.... ·-· ~ 30 i hot utrudtd ....0 10J . b - /HIPtd ·= j 2 j )IC.':t 20 HIPtd c: I .--· ·;:; /" 1.0 I . 10 :....--=--~- ~ Ill 0.1 o~~~~~~~~---< 400 600 800 1000 1200 0 200 400 600 800 temperature in °( temperature in °(

Figure 32: Temperature dependence of elongation and fracture toughness of NiAl-38,5Cr processed by HIP or HIP and extruding (36] ~

l i £ ::E u: J LOO • 'N'ES<

M AISi I :ICuM,i

00 00 100 200 :;oo 400 soo 100 200 JOO TrCJ TrCJ

Figure 33: Youngs modulus and 0.2%-yield strength ofMg-Mg2Si as a function of temperature [44]

thermal expansion coefficient [10-6/K] 28

28

24

20 o ...... D·"""·C'··"· .. :·~·~~~=~~~~:~~~~---~---+·-· 0------0------0-·--- - 8C-(Mg28U30Al70 18 .. a.. 8C-(Mg281l40Al80 ·+· 8C-(Mg28UCIOAICIO 18 - 8C·Al8112CuMgNI

14L-~--'~~-'-~~-'-~~-'-~--' 0 100 200 300 400 tlOO temperature [0 C]

Figure 34: Coefficient of thermal expansion of different Mg-Mg2Si alloys as a function of temperature, compared to standard piston alloy [18] 500 .. • .. -- · Al7475-T61 ,....., .. - ODS-Al-3% Al203 cu 400 ll. '" :;...... v.i 300 v.i 0 ts v.i (+..o 200 0 £ 100 ' ~ ...... - Q. 0 100 200 300 400 500 Temperature [° C]

Figure 35: Proof stress of ODS-Al as a function of temperature, compared to Al7475 [Raufoss Inc., Norway]

IM281a-rel Proof ten'1>·: T•27S C 1.00

45MPa

~ 0.75 -c: ·a;.... Ci5 a. 0.50 IolJS.Al + n Aknina I eCD u 180 MPa

145MPa 100MPa

0 50 100 10000 Time {h)

Figure 36: Creep behavior of ODS-Al (Al+ 3% alumina) [Raufoss Inc., Norway] • AlC:t • A1Sil2 C:t • A1Si20 C:t 0 A1Si12 Fe5C:t

• II content of dispersoid [vol%]

* AJC:t • AJSi12 C:t i:: • AJSi20 0 C:t ·~ 0 AJSi12 u0 Pe5Cx

• 10 content of dispersoid [vol%]

Figure 37: Ultimate tensile strength and elongation of different dispersion strengthend Al­ alloys as a function of dispersoid content (50] 'iii' ~ MA1Si12 ..c: CuMgNi !ii 5 ~ X DISPAL 4> M 2o1 ~c + DISPAL ...4> H 1o2 4>

·.:::~ :; ·j ... IOO iliO IOO • temperature [°C]•

,...... j Jf Al Si 1 2 ~ CuHgNi c 0 ·.::: .It DISPAL cOil"' M 2o1 0 ~ a) + DISPAL M 1o2 ~ Ill temperature (0 C]

Figure 38: Ultimate tensile strength and elongation of different dispersion strengthend A1- a1loys as a function of temperature [50] Figure 39: Creep behavior of ODS-Ni-base alloy MA6000 as afunction of temperature, compared to standard Ni-base alloys

,...._ j - PM 2000 Fe-ODS [ "' --+------

Temperature ° C

Figure 40: Creep behavior of ODS-Fe alloy PM2000 as a function of temperature, compared to standard high temperature alloys [54] lncttased stability during long-tenn ISs:l Oeavage exposutt below f::·.:::::4 Grain boundary aging tempentutt e:::iJ Ductile tnnsgnnular

Intrinsic I toughness "' of Al-Li alloys ..c ~ ~"

Na+K, 4-ll 4-11 4-11 <1 <1 <0.0S ppm H, ppm 0.5-1.S 0.5-1.S 0.5-1.S 0.5-1.S <0.2 <0.01 Large brittle particles Commercial alloys State of the art, 1994 Potential state of the 2001 (3%Si, ... ) Vaclite alloys art,

Figure 41 : Increase of toughness as a function of the decrease of impurities for AlLi alloys

Metric Tons (000"•) 25

20 -

93

Figure 42: North American magnesium die-cast alloy consumption 200°c Ht ., ...... Jtt " It

JI

It •

RT ... u 211 II ,.. • lit ' ... ' ... 2

....,... AIC:.SJHC. lllAJ'Zd JllsZMDl llfl',....al • • Tt Tt T4 n •• ILmla.u Da. ... I

Figure 43: Properties of selected aluminium and magnesium alloys ,994

AZ AUo'V'"" Ju;.••...-••

------,998

A""°' All<>V• 404'0....-_ ~ AS Alloys..,.,....

Figure 44: Magnesium alloy utilization trend 1994 - 1998 • ,!:©·,. ! • .:: ... ~ •,. -:

mixing Al+SiC

D ball milling

d c::::) eo cold isostatic v compaction -----=------' incapsulation D

degassing

hot isostatic compaction

turning capsule extrusion 1 forging

Figure 45: Powder-metallurgical production of particulate reinforced aluminium 100~-- .... E 80 ~ ~ 60 .<;; -5- 110 ~ 20 .;..

hltf u -___ u,l "' 0 CZ2I =-' Q 0% 10% 15% Volumen S1C

Figure 46: Typical properties of melt metallurgical produced particulate reinforced aluminium

PM-2124MMC OSP-2014 MMC 2024 ---- Dur2014MMC

o,._~...._~_._~__._~~'--~-'-~_._~_._~--.J'--~-'-~~ 0 0, 1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9 1,0

Dehnung (%]

Figure 47: Comparison of the stress-strain behaviour of prticulate reinforced aluminium alloys produced by different technologies. The 2024 alloy is not reinforced. PM means Powder Metallurgical, OSP means Spray Deposition (Osprey), Dur means Duralcan process (melt metallurgical) 6.0

0 2024 • Alz01 2.0 5.0 • 2014 .., 0 E E- 4.0 l.5 E (/) (/) ~ :::> 0 _J _J 3.0 0 ..... 1.0 > ::c D'X. ,16p.m Cl a: [Li 2.0 < ~ "'~ 20% ,16fi-m 0.5 1.0 20% ,63fi-m 20% ,142 .m 0 0 0 500 1000 1500 2000 SLIDING DISTANCE ,m

Figure 48: Weight loss vs. sliding distance for different particulate reinforced aluminium alloys

...----or-----,...--..--.,.....,~.,....,..."T""---..---.....--....---r Gr/Epo~, (Li--

CF-AMC (T)

\ ~Discontinuous AMC a: ~ w , ______- ,,,llllllllr11##_; ___ _ Glass/Epoxy, (L) \ o~ Steel Al-alloys Ti-alloys

Glass/Epoxy, (T) Gr/Epoxy, (T) (L) : Longitudinal (T) : Transverse 10- 100 1000 Specific Strength, a /p, (MPa/Mg/m3)

Figure 49: Specific modulus vs. specific strength for selected materials Manufacturing Use

...... ,. ;·· .o J •• ..-~_...... : ,·_. Incineration

;\ ..

,..

Landfill Disposal

. Landfill

Figure 50: Lifecycle of materials beginning with raw materials

Figure 51: Cross-section of a SiC long-fibre reinforced titanium matrix composite Abriviations

CTE Coefficient of thermal expansion DBTT Ductile Brittle Transition Temperature HIP Hot isostatic pressing CIP Cold isostatic pressing RT Room temperature VPS Vacuum Plasma Spraying SHS Self propagating high temperature synthesis TMT Thermomechanical treatment SRP Smelting reduction process MA Micro alloyed PA Phosphorus alloyed YS Yield strength UTS Ultimate tensile strength CISC Current Induction Skull Crucible DS Direction Solidification scs Single Crystal Solidification DP Dual Phase (Steel)