EFFECTS OF MICROSTRUCTURE ON OPTIMUM HEAT-TREATMENT CONDITIONS IN METAL MATRIX COMPOSITES

It is well known that the microstructure of metal-matrix composite materials is significantly different from that of the unreinforced matrix. Heat treatments which optimized strength values in the matrix therefore, no longer do so in the composite. It is thus beneficial to find these variations in the heat treatment process, and to pinpoint the microstructural mechanisms responsible. It is known that, in addition to a higher dislocation density, the composite also has a very fine grain size and many whisker interfacial nucleation sites. This study has found that the time required for solutionizing appears to be much shorter in the composite primarily due to the very small grain size. It was also observed that artificial ageing was not very effective in the composite since the precipitates nucleated and grew on the whisker interfaces, therefore, only natural ageing was necessary to achieve peak tensile and yield strengths.