Threshold creep behaviour of aluminium dispersion strengthened by fine alumina particles

Results of an investigation of creep in aluminium strengthened by 2.6 vol.% fine alumina particles-ODS-2.6Al alloy-are presented with an emphasis on threshold creep behaviour. At temperatures ranging from 623 to 723 K the measured minimum creep strain rates covered six orders of magnitude. The true threshold stress sigma(TH) decreases with increasing temperature approximately linearly and the same holds for sigma(TH)/G ratio, where G is the shear modulus of the matrix metal-aluminium. The threshold stress is suggested to originate from attractive dislocation/particle interaction although the detachment stress sigma(d) scales the temperature dependence of the shear modulus. The minimum creep strain rate (epsilon)over dot(m) is controlled by matrix lattice diffusion and the true stress exponent n of the minimum creep strain rate is close to 5. The results for ODS-2.6Al are compared with similar ones for ODS-Al-30SiC(p) composite. From the comparison it follows that the load transfer effect is absent in this latter composite with heavily dispersion strengthened matrix and that the threshold stress effect plays the dominant role, similar to that in ODS-2.6Al alloy. (C) 1998 Elsevier Science S.A. All rights reserved.