CREEP-BEHAVIOR OF SIC PARTICULATE-REINFORCED 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 threshold behaviour, the true threshold stress decreases with increasing temperature, but is not proportional to the shear modulus. The true applied stress exponent of minimum creep strain rate n is approximately equal to that for the matrix metal, i.e. to 5. The creep strain rate is controlled 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 energy of creep Q(c) are fully accounted for in terms of the threshold creep behaviour. The creep is described by a constitutive equation that includes 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 shown to be very significant.