High temperature creep behaviour of an Al-8.5Fe-1.3V-1.7Si alloy reinforced with silicon carbide particulates

The creep behaviour of an Al-8.5Fe-1.3V-1.7Si (the 8009Al type, all numbers indicate wt.%) alloy reinforced with 15 vol.% silicon carbide particulates — the Al-8.5Fe-1.3V-1.7Si-15SiCp composite — is investigated at three temperatures ranging from 623 to 723 K. The measured minimum creep strain rates cover seven orders of magnitude. The creep behaviour is observed to be associated with the true threshold stress that decreases more strongly with increasing temperature than the shear modulus of aluminium. The minimum creep strain rate is controlled by the lattice diffusion in the composite matrix, and the true stress exponent is close to 5. The results are compared with those obtained investigating the creep behaviour of an unreinforced Al-8.5Fe-1.3V-1.7Si alloy in the same temperature range. The creep strength of the composite as characterised by the minimum creep strain rate is found to be up to six orders of magnitude higher in the composite than in the alloy. This creep strengthening is attributed to a much higher true threshold stress in the composite than in the alloy, which is primarily due to finely dispersed alumina particles appearing in the composite matrix as a result of composite fabrication. The creep behaviour is interpreted in terms of athermal detachment of dislocations from interacting particles admitting a temperature dependence of the relaxation factor that characterises the strength of dislocation/particle interaction.