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OCCASION This publication has been made available to the public on the occasion of the 50th anniversary of the United Nations Industrial Development Organisation. DISCLAIMER This document has been produced without formal United Nations editing. The designations employed and the presentation of the material in this document do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations Industrial Development Organization (UNIDO) concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries, or its economic system or degree of development. Designations such as “developed”, “industrialized” and “developing” are intended for statistical convenience and do not necessarily express a judgment about the stage reached by a particular country or area in the development process. Mention of firm names or commercial products does not constitute an endorsement by UNIDO. FAIR USE POLICY Any part of this publication may be quoted and referenced for educational and research purposes without additional permission from UNIDO. However, those who make use of quoting and referencing this publication are requested to follow the Fair Use Policy of giving due credit to UNIDO. CONTACT Please contact [email protected] for further information concerning UNIDO publications. For more information about UNIDO, please visit us at www.unido.org UNITED NATIONS INDUSTRIAL DEVELOPMENT ORGANIZATION Vienna International Centre, P.O. Box 300, 1400 Vienna, Austria Tel: (+43-1) 26026-0 · www.unido.org · [email protected] • & •• I /1'-1-bb METAL-MATRIX COMPOSITES Pradeep Rohatgi* Samuel C. Weaver Professor. Materials Department and Director. Composites and Solidification laboratories The University of Wisconsin--Milwaukee Milwaukee. Wisconsi~ 53211. USA *Fon1erly Founder Director of Regional Research Laboratories at Trivandrum and Bhopal. Counfil of Scientific and Industrial Research. New Delhi - 110001, India. 479E/46i1E • • • • TABLE OF CONTENTS 1. INlRODUCTION .•.••.•• 1 2. STRENGT~ENING CONSIDERATIONS 5 3. POWDER METALLURGY-BASED METAL-MATRIX COMPOSITES. 11 3.1 In-Situ C0111Posites •• 14 3.2 Spray Casting ... 15 4. SOLIDIFICATION PROCESSING OF METAL-MATRIX COMPOSITES 16 4. 1 Casting Techniques. Microstructures. and Properties • 21 4.1.1 Sand Castings ..•. _ ......••••• 23 4.1.2 Die Castings ..... 24 4.1.3 Centrifugal Castings 24 4.1.4 Compocasting ..•• 24 4.1.5 Pressure-Die Casting •. 25 4.1.6 Squeeze Casting. • • • • • • • ••i. 25 4.1.7 Vacuum Infiltration Process. ... 27 4.1.8 Investment Casting ....•..... 28 4.1.9 Microstructures .••....•••• 28 4.1.10 Properties and Applic3tions ..... 29 . 5. THE CENTERS OF METAL-MATRIX COMPOSITE MATERIALS IN THE UNITED STATES ANO SOME OF THE DEVELOPING COUNTRIES .••....•.. 31 6. STATE OF THE ART IN METAL-MATRIX COMPOSITES AND RELEVANCE TO DEVELOPING COUNTRIES ...•.... 33 1. ELEMENTS OF EDUCATION AND TRAINING IN METAL-MATRIX COMPOSITES FOR DEVELOPING COUNTRIES . • . • . • . 39 7.1 Elements of Training Program in Metal-Matrix Composites . • . 41 8. SUMMARY ..... 43 9. INFORMATION RESOURCES ON METAL-MATRIX COMPOSITES . 44 APPENDIX I. SELECTED BOOKS ON METAL-MATRIX COMPOSITES 46 APPENDIX II. SELECTED PAPERS ON METAL-MATRIX COMPOSITES. 47 - 1 - • • • • 1 • lllTRODUCTION Metal-11atrix composites ("'C) are engineered cOllbinations of two or 11e>re 11aterials (one of which is a metal) where tailored properties are achieved by syste11atic cOlllbinations of different constituents. Conventional monolithic 11aterials have limitations in respect of achievable cOlllbinations of strength. stiffness and density. Engineered 11etal-11atrix COlllPOSites consisting of continuous lr discontinuous fibers. whiskers. or particles in a metal result in cOlllbinations of very high specific strength and specif·ic modulus to be achieved (Tables lA. 18; Fig. lA). Structurally, metal-matrix compo~ites consist of continuous or dis!~ntinuous fibers, whiskers. or particles in an alloy 111atrix which reinforce the lliltrix or provide it with requisite properties not achievable in 11e>nolithic alloys. Furthermore, systenaatic l design and synthesis procedures allow unique combinations of engineering properties like high elevated temperature strengths, fatigue strength, damping properties, electrical conductivity, thermal conductivity and expansion coefficient. In a·broader sense, cast COfllPOSites, where the volume and shape of phases is governed by phase diagrams. i.e., cast iron and aluminum-silicon alloys, hav~ been produced by foundries for a long time. The modern composites differ in the sense that any selected volume, shape and size of reinforcement can be introduced in the matrix. The modern composites are nonequilibrium mixtures of metals and ceramics where there are no thermodynamic restrictions on the relative volume percentages, shapes and sizes of ceramic phases. By carefully controlling the r~lative amounts and distri~ution of the ingredients constituting a composite, as welt as by tontrotling the proctssing conditions, MMCs can be imparted with a tailored set of useful engineering - 1 - ,. TABLE lA Mechanical Properties of Son1e Metal Matrix COftlPOSites Material Vo 1. Fr. Specific s,~r:if ic Fiber (S) Strength Modulus (N • II/kg) (N • II/kg) Al203 (FP)/Al-li o· 60 20000 1.59 x 107 go• 60 4986 - 6000 4.406 x 107 SiC/Ti-6 Al-4V o• 35 45337 1.11 x 107 go• 35 10622 C/Mg (Thomd) 38 28333 C/Al 30 28163 6.53 x 107 x l07 6061 Al 11481 ~ 2.53 2014 Al 17143 2.5g x 107 SiC(f) 100 78431 1.567 x 108 SiC(w) 100 6.67 x 105 2 .1g x 108- A1203(f) 100 50000 1.175 x 108 B(f) 100 1.538 x 105 1.62 x 108 C(f) 100 1.618 x 105 1.35 x 108 Be(f) 100 5g45g 1.68 x 108 W{f) 100 14g74 1. 79 x 107 B/Al o• 50 56604 1.g2 x 107 go• 50 5283 5.66 x 107 SiC/Al o• 50 8803 1 .og2 x 108 go• 50 J&g; - 2 - • • • • TABLE 18 Mechanical Properties of Cast Metal Matrix C011Posites Type of MMC Elastic Modules {GN/-2) Al Matrix 0 3.79 Continuous SiC Fiber 0.35 10.85 {Al-4.5 Cu Matrix) Continuous SiC Fiber 0.35 10.50 {Al-11.6 Si Matrix) Continuous Sic Fiber 0.35 10.25 (Al-4.8 Mg) Discontinuous SiC Fiber 0.44 11.6 (Al Matrix) i - 3 - . -. properties which can not be realized with conventional monolithic materials (Figs. lA. 18). Composite materials are attractive since they offer the possibility of attaining property combinations which are not obtained in monolithic materials and which can result in a nulllber of service benefits. These could include increased strength. decreased weight. higher service temperature. improved wear resistunce. higher elastic llOdulus. controlled coefficients of thermal expansion and improved fatigue properties. The quest for improved perfon1ance has resulted in a number of developments in the area of metal-matrix COlllposites. These include the preparation of the reinforcing phases and development of fabrication techniques. Reinforcement phases for metal-matrix composites fall into three important categories--continuous or discontinuous filament •• whiskers and particulat~. The greatest improvements in mechanical properties are obtained from filaments in the direction of filament alignment. with whiskers and particulate offering descending strength. but greater isotropy. in that order. A number of composite fabrication techniques have been developed that can be place~ into four broad categories: those involving liquid metallurgy; those involving powder metallurgical techniques; those involving diffusion bonding of foils; and those involving vapor phase infiltration. The liquid metallurgy techniques would include unidirectional solidification to produce directionally aligned metal-matrix composites. suspension of reinforcements in melts followed by solidification. compocasting and pressure infiltration. The liquid metallurgy techniques are least expensive and the multi step diffusion bonding techniques are most expensive. From a technological standpoint of property-performance relations~ip. the interface between the matrix and the reinforcing phase (fiber or particle) is - 4 - . of central importance. Processing of metal-matrix composite~ sometimes allows tailoring of the interface between the matrix and the fiber in order to suit specific property-perfonaanr.e requirements. The ccst of producing cast metal- 11atrix COlllPOSites has conie down rapidly. especially ;..1ith the use of low cost particulate reinforcements like gr~pnite and silicor. carbide. Low cost composites like metal-silicon carbide particle and metal-graphite particle arP. now connercially available. In recent years considerable activity has taken place in the area of metal-matrix composites. and Table 2 shows the different fibers and matrices combined to date. the fabrication techniques and the potential fields of application. Table 3 gives more recent data of the same type for cast composites. most of which are particulate. 2. STRENGTHENING CONSIDERATIONS l Composite materials technology offers unique opportunities to tailor the properties of metals and metal alloys. Under ideal conditions the composite exhibits mechanical and physical properties defined by the rule-of-mixture. That is: Pc = PmF m + P/ r ( 1) where: Pc • the properties of the composite material Pm• the properties of the matrix phase Pr= the properties of the reinforcement phase Fm• the volume fraction of the matrix phase Fr • 1-F m • the volume fraction of the reinforcement phase. By combining matrix and rP.inforcement phases exhibiting the appropriate properties, dramatic changes can be