Composite Interfaces. Vol. 4. No. 5, pp. 287-298(1997) @vSP1997 Interfaces in metal matrix composites K. K. CHAWLA Department of Materials and Metallurgical Engineering, New Mexico institute of Mining and Technology, Socorro, New Mexico 87801, USA Received 23 June 1996: accepted 3 November 1996 Abstract-The interface region in a given composite has a great deal of importance in determining the ultimate properties of the composite. An interface is, by definition, a bidimensional region through which there occurs a discontinuity in one or more material parameters. In practice, there is always some volume associated with the interface region over which a gradual transition in material parameter(s)occurs. The importance of the interface region in composites stems from two main reasons: (i) the interface occupies a very large area in composites, and(ii) in general, the reinforcement and the metal matrix will form a system that is not in thermodynamic equilibrium. One can discuss the interface in a composite at various levels. An opti should be neither so simple that it covers only a few special cases nor so complex that it is not useful in designing composites from processing and applications points of view. In this paper. my objective is to give examples of interface microstructure in different metal matrix composite systems and suggest some ways of controlling the interface characteristics in order to control the properties of the composite. I shall give examples of the interface microstructure in different manx composites (particle and fiber reinforced as well as laminates)and discuss some of the ant implications various aspects of metal matrix composites, from the processing stage to ultimate perform Keywords: Metal matrix composite; interface: particle; fiber; reinforcement. 1 INTRODUCTION Metal matrix composites consist of a metal or an alloy as the continuous matrix and a reinforcement that can be particle, short fiber or whisker, ntinuous fib Table I provides examples of some important reinforcements used in metal matrix composites as well as their aspect(length/diameter) ratios and diameters. MMCs are really not new. Any heat treated steel or a two-phase metallic alloy is really a metal matrix composite. Hypereutectic Al-Si alloys represent a particulate metal matrix composite inasmuch as their microstructure consists of Si particles in an Al matrix. Metallurgists have controlled the shape and size of Si particles by means of alloy chemistry and solidification techniques. The new emphasis on MMCs involves mixing of reinforcement fiber or particles with a suitable metal matrix, generally larger volume fractions than ones found in steels and other alloys. In particular, itInterfaces in metal matrix composites K. K. CHAWLA Department of Materials and Metallurgical Engineering, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA Received 23 June 1996; accepted 3 November 1996 Abstract_The interface region in a given composite has a great deal of importance in determining the ultimate properties of the composite. An interface is, by definition, a bidimensional region through which there occurs a discontinuity in one or more material parameters. In practice, there is always some volume associated with the interface region over which a gradual transition in material parameter(s) occurs. The importance of the interface region in composites stems from two main reasons: (i) the interface occupies a very large area in composites, and (ii) in general, the reinforcement and the metal matrix will form a system that is not in thermodynamic equilibrium. One can discuss the interface in a composite at various levels. An optimum one should be neither so simple that it covers only a few special cases nor so complex that it is not useful in designing composites from processing and applications points of view. In this paper, my objective is to give examples of interface microstructure in different metal matrix composite systems and suggest some ways of controlling the interface characteristics in order to control the properties of the composite. I shall give examples of the interface microstructure in different metal matrix composites (particle and fiber reinforced as well as laminates) and discuss some of the important implications on various aspects of metal matrix composites, from the processing stage to ultimate performance of the composite. Keywords: Metal matrix composite; interface; particle; fiber; reinforcement. 1. INTRODUCTION Metal matrix composites consist of a metal or an alloy as the continuous matrix and a reinforcement that can be particle, short fiber or whisker, or continuous fiber. Table 1 provides examples of some important reinforcements used in metal matrix composites as well as their aspect (length/diameter) ratios and diameters. MMCs are really not new. Any heat treated steel or a two-phase metallic alloy is really a metal matrix composite. Hypereutectic Al-Si alloys represent a particulate metal matrix composite inasmuch as their microstructure consists of Si particles in an Al matrix. Metallurgists have controlled the shape and size of Si particles by means of alloy chemistry and solidification techniques. The new emphasis on MMCs involves mixing of reinforcement fiber or particles with a suitable metal matrix, generally in larger volume fractions than ones found in steels and other alloys. In particular, it