Particle reinforced metal matrix composites are now being produced commerically, and in this paper the current status of these materials is reviewed. The different types of reinforcement being used, together with the alternative processing methods, are discussed. Depending on the initial processing method, different factors have to be taken into consideration to produce a high quality billet. With powder metallurgy processing, the composition of the matrix and the type of reinforcement are independent of one another. However, in molten metal processing they are intimately linked in terms of the different reactivities which occur between reinforcement and matrix in the molten state. The factors controlling the distribution of reinforcement are also dependent on the initial processing method. Secondary fabrication methods, such as extrusion and rolling, are essential in processing composites produced by powder metallurgy, since they are required to consolidate the composite fully. Other methods, suc...

Particle reinforced aluminium and magnesium matrix composites

Deformation and failure of metal-matrix composites, by the nucleation and growth of voids within the ductile matrix, are studied numerically and experimentally. The matrix material is modelled as an elastic-viscoplastic ductile porous solid to characterize the evolution of damage from void formation. The material systems chosen for parametric analyses and for quantitative comparisons between numerical analyses and experiments are aluminum alloys discontinuously reinforced with SiC. The brittle reinforcement phase, in the form of spheres, particulates with sharp corners, or cylindrical whiskers, is modelled as elastic or rigid, with the interfaces between the ductile matrix and the brittle reinforcement assumed to be perfectly bonded. The overall constitutive response of the composite and the evolution of matrix failure are analyzed using finite element models within the context of axisymmetric and plane strain formulations. Detailed parametric analyses of the effects of (i) reinforcement shape, (ii) reinforcement volume fraction, (iii) mechanical properties of the matrix, (iv) nucleation strain and volume fraction of void-nucleating particles, and (v) reinforcement distribution on the overall deformation and ductility of the composite are discussed. The numerical predictions of yield strength, strain hardening exponent and ductility for the composites with different volume fractions of SiC particulates are also compared with experimental measurements.

An analysis of the effects of matrix void growth on deformation and ductility in metal-ceramic composites

Particle-reinforced metal matrix nanocomposites fabricated by selective laser melting : a state of the art review

The effect of SiC volume fraction and particle size on the fatigue behavior of 2080 Al was investigated. Matrix microstructure in the composite and the unreinforced alloy was held relatively constant by the introduction of a deformation stage prior to aging. It was found that increasing volume fraction and decreasing particle size resulted in an increase in fatigue resistance. Mechanisms responsible for this behavior are described in terms of load transfer from the matrix to the high stiffness reinforcement, increasing obstacles for dislocation motion in the form of S’ precipitates, and the decrease in strain localization with decreasing reinforcement interparticle spacing as a result of reduced particle size. Microplasticity was also observed in the composite, in the form of stress-strain hysteresis loops, and is related to stress concentrations at the poles of the reinforcement. Finally, intermetallic inclusions in the matrix acted as fatigue crack initiation sites. The effect of inclusion size and location on fatigue life of the composites is discussed.

Effect of SiC volume fraction and particle size on the fatigue resistance of a 2080 Al/SiCp composite

Fatigue of particle-and whisker-reinforced metal-matrix composites

The fatigue behavior of a naturally aged powder metallurgy 2xxx series aluminum alloy (Alcoa MB85) and a composite made of this alloy with 15 vol pct SiCp, has been investigated. Fatigue lives were determined using load-controlled axial testing of unnotched cylindrical samples. The influence of mean stress was determined at stress ratios of −1, 0.1, and 0.7. Mean stress had a significant influence on fatigue life, and this influence was consistent with that normally observed in metals. At each stress ratio, the incorporation of SiC reinforcement led to an increase in fatigue life at low and intermediate stresses. When considered on a strain-life basis, however, the composite materials had a somewhat inferior resistance to fatigue. Fatigue cracks initiated from several different microstructural features or defect types, but fatigue life did not vary significantly with the specific initiation site. As the fatigue crack advanced away from the fatigue crack initiation site, increasing numbers of SiC particles were fractured, in agreement with crack-tip process zone models.

Fatigue behavior of a 2xxx series aluminum alloy reinforced with 15 vol pct sicp

PARTICULATE-reinforced aluminum composites are considered strong candidates for many structural applications by virtue of their ability to be processed by conventional and relatively inexpensive means and because they possess an attractive combination of mechanical properties coupled with low density. SiC particlereinforced aluminum (SiCp/A1) composites are typical of this class of materials in which significant increases in modulus of elasticity, yield strength, and ultimate tensile strength have been achieved over unreinforced alloys while maintaining usable levels of ductility and fracture toughness, tt,2,31 Many applications for which these materials can be considered involve cyclic loading, and therefore, fatigue properties are of critical interest. Despite this fact, the exact role of the reinforcement phase in fatigue crack initiation and growth processes is not well understood. Although it has been shown that the presence of reinforcement can increase fatigue lives, ~4-sl this effect is reportedly dependent on the strengths of the matrix and the reinforcement/matrix interface. In some cases, fatigue life has even been reduced by the incorporation of reinforcement phases.tS.6~ Improvements in the fatigue behavior of aluminumbased metal-matrix composites, in some cases, may result from an increase in the number of cycles to initiate a fatigue crack. Williams [9a~ studied a cast SiCw/2124-T6 A1 composite in which cracks initiated at approximately 70 to 80 pct of the total lifetime, whereas in unreinforced material, cracks were observed after only 5 pct of the total lifetime. Crack initiation in this composite was observed at reinforcement/matrix interfaces, indicating poor

http://rd.springer.com/content/pdf/10.1007%2FBF02661094.pdf

J. J. Bonnen

Papers

Fatigue behavior of a 2xxx series aluminum alloy reinforced with 15 vol pct sicp

Fatigue Behavior of a Alloy Reinforced with 2xxx Series Aluminum 15 Vol Pct SiCp