United States Patent (19) (11) Patent Number: 5,000,779 German Et Al

United States Patent (19) (11) Patent Number: 5,000,779 German et al. 45 Date of Patent: Mar. 19, 1991

54) PALLADIUM BASED POWDER-METAL ALLOYS AND METHOD FOR MAKING FOREIGN PATENT DOCUMENTS SAME 0058622 5/1979 Japan. 0.139663 9/1984 Japan. 75) Inventors: Randall M. German, Latham, N.Y.; OTHER PUBLICATIONS Laura L. Bourguignon, East Providence, R.I.; Dwarika P. Platinum Metals Review, p. 44, 1988, vol. 32. Agarwal, Attleboro, Mass.; Shaji Primary Examiner-Stephen J. Lechert, Jr. Faroog, Troy, N.Y. Assistant Examiner-N. Bhat Attorney, Agent, or Firm-George W. Dishong 73) Assignee: Leach & Garner, N. Attleboro, Mass. (57) ABSTRACT 21 Appl. No.: The subject of this invention is the development of new 195,721 alloys along with new processing approaches for the utilization of the alloys. A particular class of alloys (22 Filed: May 18, 1988 comprises at least one noble metal selected from the group comprising gold, palladium, silver and copper (51) Int. Cl...... a on a on a seed eveu as a e C22C 21/14 and an amount of between about 0.20 weight percent (52) U.S. C...... a do a was as so a 8 up a 4 w w 75/244; 75/247; and about 0.80 weight percent of at least one metalloid 419/12; 419/23; 420/.464; 420/497; 420/.502; selected from the group of metalloids consisting of bo 420/.505; 420/503 ron, phosphorous, silicon and lithium. Rapid solidifica 58) Field of Search ...... 419/12, 23; 75/244, tion technology in powder fabrication and the addition 75/247; 420/.502, 464, 503, 497, 505 of metalloids have been combined to produce a new class of palladium based alloys. The metalloid additions 56 References Cited greatly increase the hardness, enhance the fine grain U.S. PATENT DOCUMENTS structure and aid sintering densification. Net-shape 2,048,648 7/1936 Feussner et al...... 148/13 forming is a benefit derived from the characteristics of Powell ...... 120/09 the new alloys.

2,095,890 10/1937 2,138,599 11/1938 Gwyn ...... 200/166 4,149,883 4/1979 Harmsen et al...... 75/173 6 Claims, No Drawings 5,000,779 1 2 usual alloy formulation relies on mixtures of common PALLADIUM BASED POWDER-METAL ALLOYS high conductivity metals. One of the most successful AND METHOD FOR MAKING SAME alloy groups is located near the center of the palladium silver-copper ternary. These alloys have sufficient no BACKGROUND OF THE INVENTION 5 bility to protect against tarnish and corrosion in most 1. Field of the Invention industrial atmospheres. The mechanical properties of The present invention is concerned most generally the alloys can be altered over a considerable range with metals and alloys of metals having added thereto depending on the degree of ordering induced through metalloids which enhances the preparation of metal heat treatments. Thus, component fabrication is aided powders made from the modified metal or metal alloys 10 by the low strength and high ductility found in the and improves the properties of the metal powders when disordered state, and wear resistance in service is aided used in the forming of or net-shape forming of articles by the high strength found in the ordered state. from the metal or alloys by processes such as super There are factors associated with noble metal alloys solidus sintering. More particularly the present inven that prove to be a continual source of problems. First is tion is directed to palladium-silver-copper alloy compo 15 the cost of the raw material. The manufacturing se sitions of increased hardness containing metalloids quence to form a final product from ingot material which improve certain characteristics of the alloys. The requires time, and with expensive material there is a overall hardness of the basic alloy is increased, the desire for rapid inventory turnover. Since fabrication supersolidus temperature is reduced thereby aiding in involves waste and recycling, net-shape forming ap the supersolidus sintering process, the initial grain size 20 proaches, such as powder. metallurgy, have merit in in powder particles of the alloy is reduced and upon rapid product fabrication with minimal waste. Further atomization and rapid solidification the powder metal more, the palladium-silver-copper alloys exhibit high produced thereby has optimum particle and grain size work hardening rates. The traditional metalworking for use in supersolidus sintering for the net-shape form techniques involved in fabrication of contacts require a ing of articles made using the alloy powder. 25 large number of long anneals to eliminate the work 2. Description of the Prior Art hardening. Consequently, compromises in component One of the motivations for the development of the design, alloying, and product performance occur in invention herein disclosed was the need for high hard order to minimize manufacturing problems. ness, wear resistant and low resistivity electrical The following patents are representative of the devel contacts. Because of the problems and costs associated 30 with the current technology, new approaches were opments in recent years. Note that none of the patents considered and as a consequence of the research the discussed anticipate the alloy powder of the instant present invention was discovered. It is understood that invention nor do they have the particular characteris there are more applications for the products and the tics herein described. Clearly, Pd-Cu-Agalloys are well processes of the present invention than the making of 35 known and are said to be useful for electrical contacts. useful and superior electrical contacts; however, electri For example, see U.S. Pat. Nos. 2,187,378 and cal contacts and the problems associated with the pres 4,149,883. ent state of the art are used in discussing the prior art. The Japanese appear to be particularly active in this Alloys based on the noble metals are important in field. Note from the abstracts of the Japanese patents forming low-energy electrical contacts in modern elec that Pd-Cu-Ag alloys are known for various uses in trical systems. The noble metals resist oxidation and cluding use as an electrical contact material. However, corrosion, while exhibiting high electrical conductivi none of the abstracts disclose the particular alloy de ties. Because of this combination of properties, the fined and described herein. noble metals are used routinely in systems containing The abstract of Japanese Pat. No. 52-47516 discloses semiconducting components. Alloys with high contact 45 an electrical contact alloy containing 30-50% Pd; resistance, upon the closing of a contact would produce 10-50% Ag and 10-55% Cu. An alloy for use as an or result in voltage surges due to the high initial tran electrical contact containing 5-30% Ag, 5-30% Cu. and sient resistance which alloys having high contact resis 50-95% Pd is described in Japanese Pat. No. 53-48168. tance would possess. Such surges are fatal to semicon The abstract of Japanese Pat. Nos. 59-107048; ductors. Thus, there is a natural marriage of semicon 50 59-107049 and 59-107050 disclose slide contact material ducting materials and noble metals used for intercon containing 30-50% Pd; 20-40% Ag and 20-40% Cu. nections. For these reasons the noble metal alloys are An additional ingredient is added to each of the alloys used in potentiometer contacts, sliding contacts, com described in these three Japanese patents. In 59-i07048 mutators, circuit probes, slip rings, make-and-break the additional ingredient may be boron. Note however, contacts, and various relays or switches. 55 that there is no suggestion to add boron and phospho Over the years, the needed properties of noble metal rous to the composition or to select the more particular low-energy electrical contact alloys have been estab amount of Pd-Ag and Cu used in the instant invention. lished. Important requirements are a low contact resis Even more importantly, it should be noted that the use tance, resistance to oxidation, tarnish, and polymeriza of the metalloids such as boron and/or phosphorous in tion of organic vapors, high electrical and thermal con this prior art and others is as a deoxidizer and as such ductivity, high elastic modulus, high strength, and wear the amounts of the metalloids is almost an order of resistance. Most of these properties are easily attained magnitude less than the amount taught and claimed with noble metal alloys, but wear resistance requires a herein. In fact if too much metalloid is used in the pro high alloy hardness. Since the noble metals exhibitor cess where deoxidation is desired the process of making dering phases, it is common to rely on alloying additions 65 the alloy is hindered. What is being taught and claimed that promote a high hardness through precipitation or in the present specification is antithetical to the teaching ordering. Because of cost, and these other criteria re of the prior art. In the instant invention it is desireable to lated to the desireable properties of the material, the have the lower melting temperature as an aid in the 5,000,779 3 4. supersolidus sintering process. In addition, there is no improve the sinterability and the compaction of such teaching in these three patent abstracts to form the alloy powders when used to substantially net-shape form into a powder having the particular grain size and melt articles from such doped alloy powders. ing characteristics which make it particularly suitable to It is therefore a primary object of the present inven supersolidus sintering techniques. tion to provide a process for net-shape forming of arti U.S. Pat. No. 1,935,897 and British Pat. No. 354,216 cles of manufacture, out of doped noble metals using disclose a Pd-Cu-Agalloy which may contain a metal substantially spherical shaped particles, the particles loid deoxidizer such as boron. The inclusion of phos having small grain size, comprising the steps of doping phorous in addition to boron is not suggested. There is the metal with an amount of at least one metalloid se also no suggestion for selecting the particular range of 10 lected from the group of metalloids consisting of boron, ingredients nor of forming the alloy into a powder hav phosphorous, silicon and lithium to obtain said doped ing the characteristic grain size and melting properties metal; melting the doped metal; gas atomizing the found in the alloy powder of the present invention. melted doped metal; cooling rapidly the gas atomized The application of powder metallurgy to noble metal doped metal thereby producing the substantially spheri electrical contact alloys provides a possible solution to 15 cal powder particles having small grain size; compact several problems. First, the economic factors of rapid inventory turnover, minimized scrap, and easy material ing the powder particles into the configuration of the recycling are very favorable. Second, the reduced num article of manufacture; heating the compact for a time ber of manufacturing steps greatly aids productivity, and to a temperature depending upon the doped noble since direct shaping is possible. This decreases the time 20 metal the temperature between the solidus temperature that valuable material is in processing and decreases the and the liquidus temperature of the doped metal; and inventory control problems inherent with precious met cooling the heated compact thereby net-shape forming als. Third, the benefits of new compositional possibili the article of manufacture. ties cannot be overlooked. Since deformation is not It is another primary object of the present invention needed and work hardening is not a concern, new high 25 to provide a process for net-shape forming of articles of hardness compositions can be processed by powder manufacture, out of doped noble metal alloys using metallurgy. Previously, these compositions were un substantially spherical shaped particles, the particles available because of processing constraints. having small grain size, comprising the steps of: forming The development of new alloys with new processing a noble metal alloy; doping the alloy with an amount of approaches is the object of this invention. There has 30 at least one metalloid selected from the group of metal been combined, rapid solidification technology in pow loids consisting of boron, phosphorous, silicon and lith der fabrication with metalloid alloying to produce a ium to obtain said doped metal alloy; melting the doped new class of palladium-based low-energy electrical alloy; gas atomizing the melted doped alloy; cooling contact alloys. The metalloid additions greatly increase rapidly, typically water quenching, the gas atomized the hardness and aid sintering densification. Since net 35 doped alloy thereby producing the substantially spheri shape forming is an obvious component of this research, cal powder particles having small grain size; compact the modified alloys provide benefits and/or desireable ing the powder particles into the configuration of the characteristics. The instant invention opens up a wealth article of manufacture; heating the compact for a time of opportunities in forming complex shapes out of depending upon said doped noble metal alloy and to a coarse powder. The use of the coarse powder from the 40 temperature between the solidus temperature and the compositions of the present invention may indeed be liquidus temperature of the doped alloy; and cooling the ideal for full density processing by injection molding heated compact thereby net-shape forming the article of and supersolidus sintering (which is revolutionary be manufacture. cause to the present time it has been assumed that only Further primary objects of the present invention are fine powders of 10 micrometers or less were useful in 45 provide articles of manufacture produced by a pro injection molding. The fine powder is a major problem, cesses for net-shape forming of articles of manufacture, because of the long debinding time associated with the out of doped noble metals or doped metal alloys using fine particle size. Many are seeking a solution to this substantially spherical shaped particles, the particles problem.). The advantages of the present invention having small grain size, comprising substantially the include lower powder fabrication costs since traditional 50 atomization technologies will be suitable, easier han steps of the processes listed above. dling and molding with the coarse particle size, faster A still further primary object of the present invention processing because of rapid debinding and sintering, is to provide an alloy composition of matter comprising: and better properties because of the homogeneity of the at least one noble metal selected from the group com input powder. 55 prising gold, palladium, silver and copper; and an amount or between about 0.20 weight percent and SUMMARY OF THE INVENTION about 0.80 weight percent of at least one metalloid se The present invention provides for the use of metal lected from the group of metalloids consisting of boron, powders having particles comprising metalloids and at phosphorous, silicon and lithium. least one other metal, typically a noble metal, in a super Other objects of the present invention are to provide solidus sintering process which results in an article a noble metal alloy comprising: less than 60.0 weight which is substantially net-shape formed. The present percent palladium; less than 60.0 weight percent silver; invention is also directed to a metal or an alloy of metals less than 60.0 weight percent copper; less than 0.80 doped with typically two metalloids. Such metalloid weight percent boron; and less than 0.80 weight percent additions unexpectedly enhances the properties of the 65 phosphorous. doped alloy which properties allow for the making of Other objects of the present invention will be appar metal powders having small initial grain size, large par ent to those of ordinary skill in the art upon reading the ticle size and a lower solidus temperature all of which following detailed description of the invention. 5,000,779 5 6 The resultant properties are measured and compared DESCRIPTION OF THE PREFERRED with those of materials formed using traditional metal EMBODIMENTS lurgy techniques. There is no sacrifice in material prop The application of the invention to use in the making erties, as shown in Table 2. Table 1 lists the various of electrical contacts will be discussed in detail in order 5 alloy compositions that were tested along with some of to describe the various aspects of the present invention. the properties of the alloy compositions. It should be clearly noted that the potential for using Powder metallurgy is an attractive method of form rapid solidification technology in powder fabrication ing metals into useful engineering shapes. Specific at with metalloid additions along with the supersolidus tractions include excellent material utilization, low in sintering concept with binder assisted molding goes 10 ventory, rapid solidification rates, microstructural con beyond the narrow application to electrical contacts. trol, simple processing sequence, and net shape forming The process and the compositions are applicable to capabilities. The concept of net shape forming greatly injection molding and the properties are very interest reduces, or in some cases, eliminates machining ex ing and attractive and offer some significant and new penses. At the same time, material waste is alleviated or opportunities for advanced materials processing. The 15 at the least greatly reduced. This allows the fabrication opportunities are not restricted to the particular alloys of alloys which are difficult to form using traditional described herein; rather, there is a possible widespread metallurgy techniques due to undesirable material prop use for the technology and generic concepts disclosed erties, enabling cost-effective manufacturing of articles for forming several material systems. using these alloys. It also enables the development of 20 new alloys which are impossible to form using other The palladium-silver-copper system is used to dem methods for reasons such as segregation during casting, onstrate the advantages of supersolidus sintering tech solubility limits in melting, or extremely high melting niques applied to rapidly solidified powders. Metalloids temperatures. are added to enhance fine grain structure as well as aid This invention, in the preferred embodiment focuses sintering. The result is a material with impressive prop 25 on alloys based on the palladium-silver-copper system. erties for electrical contact applications and a process Two of the currently used alloys are described in which provides an economical fabrication route for ASTM specification numbers B540 and B563. The ex alloys which are difficult to form using conventional treme high hardness of these alloys which gives them metallurgy techniques. attractive properties for electrical contact applications The preferred embodiment of the present invention is 30 also makes them prohibitively expensive to manufac a palladium-based alloy which can be formed into arti ture. In some instances, multiple annealing cycles are cles made from powders of the alloy using powder required with annealing times as long as thirty hours. metallurgy (P/M) techniques. The palladium alloys are Powder metallurgy processing offers many advantages desirable for many applications where hardness, wear for this net-shape forming along with significant reduc resistance and low contact resistance/high conductivity 35 tions in refining costs. Furthermore, microstructural such as for electrical contact applications. Their ex manipulation enables the development of novel material tremely high hardness provides superior mechanical properties. Newly developed injection molding tech properties, but also makes machining very difficult and niques allow the formation of intricate shapes, so com costly. P/M offers an economical fabrication route ponent design no longer has restrictions relative to which would enable the production of components shape. The palladium-silver-copper alloy system is an which otherwise could be prohibitively expensive. This ideal candidate for powder metallurgy processing con invention involves the development of a palladium sidering the many benefits offered. based alloy which can be successfully used for the fabri The concept of powder metallurgy involves forming cation of articles, such as electrical contacts, using P/M metal into very fine particles with sizes on the order of techniques. 45 sub-micron to 100 microns. The particles are then com The alloy developed is based around 40 weight % pacted into a shape either by die compaction, isostatic palladium, 30 weight% silver and 30 weight % copper. pressing or injection molding. This stage often requires This composition has been determined by previous the use of a binder. The compact is subsequently sin researchers to have the highest hardness and, thus, opti tered, which is a heat treatment performed below the mum related properties. Metalloids are added to aid or SO liquidus temperature. The particles bond together, assist among other things sinterability. The sintering pores escape, and the compact densifies to near one technique chosen for this alloy is termed supersolidus hundred percent (100%) of the theoretical density. sintering. This method uses a sintering temperature The precious metal alloy systems have been exten greater than the solidus of the alloy, which promotes sively studied. Excellent property combinations are formation of a liquid at grain boundaries. Grains then 55 found in the simple ternaries like gold-silver-copper and slide and repack under capillary forces, resulting in a palladium-silver-copper. These systems are character fully dense material. The role of the metalloids is multi ized by ordering reactions that contribute considerable purpose: (1) Lower solidus temperature for supersolidus strengthening. Furthermore, they offer desirable prop sintering; (2) Decrease the initial grain size in powder erties for electrical contact applications including excel particles; (3) Increase overall hardness of the alloy. lent electrical conductivity, good corrosion and wear Optimum conditions for supersolidus sintering are resistance and low contact resistance. Due to cost con known to be large particle size with fine grain size. siderations the Pd-Ag-Cu system is preferred for gen Powders were gas atomized and immediately water eral applications such as low energy electrical contacts. quenched by a water spray system. The resultant parti Previous researchers reported a Vicker's hardness cles are substantially spherical (average diameter of 58 65 number of 450 for the composition 40 wt.% Pd; 30 wt. micrometers), with a very fine grain size (10 microme % Ag; and 30 wt.% Cu. through aging heat treatments. ters). These conditions make them ideal for the intended Therefore, early efforts related to the instant invention supersolidus sintering. focused upon such a composition. The system exhibits a 5,000,779 7 8 two phase microstructure. Although usually viewed as mechanical interlocking or cold bonding present to a problem due to casting segregation, the powder metal assist compaction. Pellets were hot compacted and sub lurgist utilizes a two phase system to enhance micro jected to debinding and presintering heat treatments. structural manipulation. Furthermore, alloying with the Debinding completely rids the sample of binder mate metalloids like boron, phosphorous, silicon and lithium rial which, if not removed, may be detrimental to suc provides an avenue to microstructural control for this cessful sintering; presintering provides sufficient alloy system. In addition, the metalloids lower the melt strength to handle the piece for subsequent sintering ing temperature, provide hardening and give a finer treatments. The optimized debinding cycle consisted of initial grain size. Initial experiments were performed on a heating rate of 1 K/min with holds at 140 C., 300 a twin roll quenching device. Metalloid additions were 10 C. and 450° C. for one hour, respectively. This was varied and the response of each composition was as followed by presintering at 600 C. for 60 minutes. Both sessed based on microstructure, hardness, fracture, an cycles were conducted in a hydrogen atmosphere. At nealing, melting, conductivity and grain growth mea completion of this cycle, the samples which are now in surements. A combination of boron and phosphorus the form of compacts were totally free of binder and was demonstrated to be the most favorable. 15 had sufficient strength for subsequent handling. It is understood that composition and sintering are The compacts were then sintered in a dry hydrogen interlinked in arriving at a useful final microstructure. atmosphere using a heating rate of 10 C./min up to 10 Emphasis is focused on a new sintering process termed C. below the final sintering temperature. To avoid over supersolidus sintering. During sintering, a thin liquid shooting the final temperature, the heating rate was film forms at grain boundaries allowing grains to slide 20 reduced to 3' C./min for the last 10 C. The compacts and repack under capillary forces. A combination was were held at temperature for 30 minutes. The final sin made of rapid solidification techniques with full density tering temperature for the alloy identified as Al was sintering. Rapid solidification would produce a fine 830 C. It should be noted that in general a lower sinter grain size with the potential for fast sintering densifica ing temperature is associated with higher doping levels. tion. Doping with metalloids gives a finer initial grain 25 The lower temperature reduces the loss of low density size, lowers the melting temperature and provides hard components which results in more uniform properties ening. Supersolidus sintering provides a basis for densi and microstructure. Lower temperatures also avoid fying fine grained prealloyed powders and is especially detrimental grain growth. appropriate for high performance systems. The process Following sintering, the compacts were dimensioned gives full density, without shape distortion, in short 30 and weighed for density measurements. No slumping sintering cycles. However, precise temperature control was detected. This is an important finding since often is necessary to prevent microstructural coarsening dur liquid phase sintering results in distortion. Generally, ing sintering. In this regard, the wide liquidus and soli the shrinkage was uniform except in the gravitational dus separation in the Pd-Ag-Cu system with the added direction there was more shrinkage. The sintered densi metalloids is an advantage. With the appropriate metal 35 ties for all of the alloys shown in Table 1 were over loid additions, the system is ideal for the intended super 92.5% of theoretical. In several instances, densities in solidus sintering. excess of 100% were detected or measured. Special care A two fluid atomization technique was used to pro was taken to ensure these were not errors in technique. duce rapidly solidified powders. The major parameters, A density greater than 100% of theoretical is explained gas pressure, superheat and nozzle diameter, are easily by two possible reasons: The assumption of ideal solu controlled. This powder was atomized with nitrogen tion of the alloy in the calculation may lead to deviation gas at 200 psi (1.4MPa). The nozzle diameter was 3 mm from the real density. Different crystal forms or the and the melt temperature was 1280 C. (1453 K.) with occurrence of interstitial atoms will make the actual a superheat of approximately 200 K. Immediately after density higher than the theoretical density. Addition sintering, the powders are subjected to a secondary 45 ally, the loss of low density components during thermal water quench system for rapid solidification. treatments may account for a higher actual density. The spherical nature of the particles are typical of gas This is possible with some of the ingredients in the alloy atomization. An examination of the internal microstruc system. High densities are most often associated with ture of the powder showed that there was a secondary higher content of Band P. The densities were measured dendrititic arm spacing of less than one micrometer. 50 on as-sintered samples/articles. That is there was no This indicates a cooling rate of 100,000 K./s, which is polishing or surface finishing performed. It was ob characteristic of gas atomization. The mean particle size served that removal of the surface layers resulted in for the resulting powders was 58 micrometers, which is slightly higher densities. This indicates the remaining considered to be relatively large. The characteristics of porosity is probably in the near surface regions. the resultant powders are ideal for the intended super 55 The hardness was measured on various samples sin solidus sintering. Large particles with fine grain struc tered between 830 C. and 860 C. The hardness ranged ture allows partial melting with an appropriately de from 49.7 to 50.1 HRC (Rockwell C scale) with a stan signed composition. These features provide optimum dard deviation of 0.3. Thus, there does not appear to be conditions for sintering to full density utilizing super a sintering temperature effect on the hardness. For com solidus sintering techniques. 60 parison, the palladium-silver-copper-gold-platinum al Experiments were conducted on fifteen (15) alloys. loys generally have a hardness below 40 HRC. The These represent various Pd-Ag-Cu compositions con higher hardness in the alloys of this invention is a result taining different concentrations of the metalloids, boron of the alloying or doping with metalloids. The hardness and phosphorus and are listed in Table 1. The evalua measurements of the 15 alloys studied and reported on tion is aimed primarily at isolating the optimum compo 65 in Table 1 are given in HRB units (Rockwell B scale). sition. It was desireable to add polyethylene wax as a Measurements of the tensile strength and % elonga binder to form compacts. Due to the spherical shape tion were also made on the A1 alloy. On a sample hav and high hardness of the powder, there is little or no ing a density of 99.3% theoretical (assuming a theoreti 5,000,779 9 10 cal density of 10.24 g/cm3 for the alloy) the transverse The present invention is not to be restricted in form rupture strength was 1215 MPa and the tensile strength nor limited in scope except by the claims appended was 515 MPa with 0.6% elongation on a specimen or hereto: sample with a 98.2% density. The low ductility and What we claim is: high strength are not surprising considering these are 5 1. An alloy composition of matter comprising: at least as-sintered materials with considerable alloying and one noble metal selected from the group consisting of hardening (ordering) additions. gold, palladium, silver and copper; and an amount of The measurements of the electrical resistivity demon- between about 0.20 weight percent and about 0.80 strated an obvious difference for the higher palladium weight percent of at least one metalloid selected from alloys, Al-A5. The increase in palladium, thus decrease 10 the group of metalloids consisting of boron, phospho in silver or copper contents, resulted in increased resis- rous, silicon and lithium. tivity. The high palladium alloys exhibited resistivities 2. A noble metal alloy comprising: an amount of of 33-34 micro ohm-cm, whereas the high silver and between about 5.0 weight percent and about 60.0 copper alloys had resistivities ranging from 17.4 to 23.5 weight percent palladium; an amount of between about micro ohm-cm. 15 5.0 weight percent and about 60.0 weight percent silver; TABLE ALLOY COMPOSITION ALLOY PROPERTIES Weight Density Resistvy Highest Hardness Alloy % Pd % Ag % Cu. 7% B % P % of Theory Micro Ohm-Cm In HRB Al 400 30.0 300 0.5 0.5 101.2 34.3 98.3 A2 400 300 300 0.25 0.25 99.0 30.7 98.9 A3 400 30.0 300 0.75 0.75 96.0 3.8 99.4 A4 40.0 30.0 300 0.25 0.75 97.3 32.6 94.1 A5 400 30.0 300 0.75 0.25 97.5 22.7 95.8 Bl 30.0 30.0 40.0. 0.5 0.5 99.5 21.4 90.5 B2 30.0 300 40.0 0.25 0.25 99.4 20.4 9.3 B3 30.0 300 40.0 0.75 0.75 100.3 21.3 88.6 B4 30.0 300 400 0.25 0.75 98.9 19.3 84.8 B5 30.0 300 400 0.75 0.25 100.0 19.6 90.5 Cl 300 400 300 0.5 0.5 100.6 21.9 93.9 C2 300 400 30.0, 0.25 0.25 97.0 23.5 8.5 C3 30.0 400 300 0.75 0.75 99.6 17.4 89.7 C4 300 40.0 300 0.25 0.75 92.5 22.8 79.8 C5 300 400 300 0.75 0.25 98.7 17.9 78.7 an amount of between about 5.0 weight percent and 35 about 60.0 weight percent copper; an amount of be tween about 0.05 weight percent and about 0.80 weight percent boron; and an amount of between about 0.05 Table 2 below compares the Al alloy of the invention weights percentt and aboutt 0.800. weight percent phospho with connercially available alloys, such as the tradi- 40 3. A noble metal alloycom rising: not less than 20.0 tional PdAgCul-AP alloys (known as the Paliney weight percent palladian E. less than 20.0 weight alloys), relative to the various properties of interest. percent silver; not less than 20.0 weight percent copper; Alloy Al containing 40 wt.% Pd, 30 wt.% Ag and 30 not less than 0.20 weight percent boron; and not less wt.% Cu with 0.5% B and 0.5% P by weight offers the than 0.20 weight percent phosphorous most favorable combination of properties for use in 45 4. A noble metal alloy comprising between about electrical contacts. The material is homogeneous with 300 and about 40.0 weight percent palladium, between respect to porosity and physical properties. Further- about 30.0 and about 40.0 weight percent silver be more, this composition offers high density and hardness tween about 30.0 and about 40.0 weight percent copper, combined with good resisitivity which makes it ideal between about 0.25 and about 0.50 weight percent bo. for electrical contact applications. The Table 2.8m 50 on and between about 0.25 and about d50 weight pares the mechanical and electrical properties of alloy percent phosphorous. 1. y ise E. alloys formed using tradi- 5. The noble metal alloy as recited in claim 1, 2, 3 or 1onal metailurgy techniques. 4 wherein said alloy is in the form of a substantially TABLE 2 spherical particle a plurality of said particles being a COMMERCIAL 55 metal powder. PROPERTY ALLOYS ALLOYA1 6. The noble metal alloy as recited in claim 5 wherein Resistivity, micro ohm-cm 25 to 35 27 to 33 said metal powder is produced by gas atomization and Ultimate Tensile Strength MPa. 380 to 1000 55 said particle size is less than about 100 micrometers Elongation, % to 20 0.6 wherein said particles are comprised of grains having a

arms-s-s- grain size less than aboutk sk 10k micrometers.