CREEP FRACTURE IN AL-SIC METAL-MATRIX COMPOSITES

Creep fracture behaviour of pure aluminium-matrix composites with 10-3 0 vol% SiC particulates at 623 K is reported. A comparison of tensile and compression creep data shows the existence of a ''transition stres s''. Above this transition stress no steady state creep is observed in tension. This transition stress is related to a transition from inter granular to transgranular fracture. The origin of transition stress is perhaps associated with the diffusional relaxation of stress concentr ation at the matrix/particle interface by lattice diffusion. The inter granular creep fracture of composites appears to be similar to that of unreinforced aluminium and it is power-law creep controlled. The tran sgranular creep fracture occurs by void nucleation and growth. The nuc leation strain for voids is quite small and hence the tertiary stage s tarts before the end of the primary stage. The ductile fracture models overestimate the strain to fracture and do not predict the observed s tress dependence of strain to fracture.