INTERFACIAL BEHAVIOR OF 6061 AL2O3 METAL-MATRIX COMPOSITES/

Ultramicroindentation and electron probe microanalysis (EPMA) techniqu es were used to evaluate the behaviour of the interfaces between the p articles and matrix in two aluminium based metal matrix composites. Th ree distinct regions were observed from ultramicroindentation correspo nding to the particle, interface, and matrix. It was noted that althou gh the hardness of the interface was consistently higher than that of the matrix, both regions exhibited age hardening behaviour. Elastic mo duli values, estimated from the ultramicroindentation data, also showe d that both the matrix and interfacial region exhibited age hardening behaviour, again with the interfacial region exhibiting higher stiffne ss than the matrix. Data from EPMA indicated that magnesium enrichment occurred in the interfacial region between the particle and the matri x and the extent of this enrichment increased with aging time. It is s uggested that the high dislocation density in the matrix regions adjac ent to particles, associated with differential coefficients of thermal expansion between the two phases, leads to enhanced precipitation in these regions.