THE EFFECT OF MICROSTRUCTURE ON THE FRACTURE-TOUGHNESS OF A METAL-MATRIX COMPOSITE

The fracture behaviour and plane strain fracture toughness, K(IC), of four 8090-based metal-matrix composites containing 20 weight % SiC particles, 3, 6 and 23 mum in diameter, has been evaluated as a function of matrix ageing condition. Toughness values are found to be almost independent of reinforcement size. Ageing at 170-degrees-C results in a monotonic decrease in toughness with increasing strength up to the peak condition, with no subsequent recovery in toughness on overageing. However, unlike reinforced 8090, the composites are not found to be susceptible to intergranular embrittlement on overageing. The observed trends are found to be independent of reinforcement size. These findings are explained in terms of the strength, work hardening behaviour and nature and distribution of void-nucleating particles in the matrix.