Transition from athermal to thermally activated detachment of dislocations from small incoherent particles in creep of an Al–8.5Fe–1.3V–1.7Si alloy reinforced with silicon carbide particulates

A recent investigation of creep behaviour in an Al–8.5Fe–1.3V–1.7Si–15SiCp composite (the subscript p stands for particulates) at temperatures from 623 to 723 K is extended to temperatures ranging from 773 to 823 K to find out whether the true threshold creep behaviour, typical for temperatures between 623 and 723 K disappears at these higher temperatures or not. It is found that at temperatures ranging from 773 to 823 K the apparent stress exponent of minimum creep strain rate, mc, increases with increasing applied stress σ which strongly suggests an absence of the true threshold stress. Accepting the creep model of Rösler and Arzt (Acta Metall. Mater. 38 (1990) 671) the creep behaviour of the composite at the temperatures 773 to 823 K is interpreted in terms of the thermally activated detachment of dislocations from small, predominantly Al12(Fe, V)3Si phase particles incoherent with the composite matrix. The disappearance of the true threshold creep behaviour at these temperatures is then due to a transition from athermal detachment occurring at temperatures from 623 to 723 K to thermally activated detachment of dislocations from small particles at the higher temperatures mentioned above.