Microstructural evolution and micromechanical modelling of the mechanical behavior of a ceramic particle-reinforced metal matrix composite

The objective of this study was to develop a thorough understanding of the precipitation characteristics and mechanical behavior of a 2124 Aluminum alloy reinforced with 13.2 volume% SiC whiskers. Microstructural development of the 2124 Al-SiC composite subject to controlled and systematic aging treatments was investigated using various techniques. The results indicate that the matrix of the composite material has a much greater dislocation density than the control alloy. The increased dislocation density facilitates the nucleation of the strengthening precipitates whereby the incubation time for precipitate nucleation and the time to reach peak hardness in the matrix of the composite are significantly reduced. Theoretical analysis of dislocation generation due to thermal contraction mismatch and of the punching of dislocations at whisker ends are examined in the context of microstructural development.; An experimental and theoretical investigation into the uniaxial stress-strain response of the 2124 Al-SiC whisker composite system was undertaken where the effects of accelerated aging of the matrix of the composite were incorporated into the modelling of deformation behavior. The 0.2% offset yield strength was found to be independent of aging state, whereas the strain to failure was found to decrease monotonically with an increase in aging time for the composite. A self-consistent approximation was formulated and was found to provide the most accurate predictions for the elastic response of the composite. A finite-element unit-cell model was used to predict the plastic response of the composite material.; The effects of SiC reinforcement and matrix aging treatment on crack growth under quasi-static and fatigue loading were also investigated. The composite exhibits a fatigue threshold value which is about twice that of the control alloy. However, the fatigue threshold is relatively insensitive to variations in both the aging treatment and the mean stress of the fatigue cycle in both the composite and control alloy. The resistance to quasi-static crack growth of the composite is reduced with increases in aging time with the overaged microstructure exhibiting perfectly brittle behavior.