CREEP-BEHAVIOR OF SIC PARTICULATE-REINFOR CED ALUMINUM-MATRIX COMPOSITE

Creep in aluminium reinforced by 30 vol.% silicon carbide particulates of 4.1 mum in size is investigated at temperatures 623, 673 and 723 K and in a broad region of applied stresses. The creep exhibits thresho ld behaviour, the true threshold stress decreases with increasing temp erature, but is not proportional to the shear modulus. The true applie d stress exponent of minimum creep strain rate n is approximately equa l to that for the matrix metal, i.e. to 5. The creep strain rate is co ntrolled by lattice diffusion in the matrix metal. The experimentally observed high values of the apparent stress exponent of minimum creep strain rate m, as well as high values of the apparent activation energ y of creep Q(c) are fully accounted for in terms of the threshold cree p behaviour. The creep is described by a constitutive equation that in cludes the threshold stress sigma(TH) besides the activation enthalpy of matrix lattice diffusion DELTAH(L) and the true stress exponent n. The creep strengthening effect of SiC particulate reinforcement in sho wn to be very significant.