Deformation mechanisms for AC8A/Al2O3(sf) composites over wide ranges of temperature and strain rate

The deformation mechanisms of the AC8A/Al2O3 short-fiber composite and AC8A alloy have been analyzed under the framework of dislocation creep and glide mechanisms over the wide temperature range 25–450°C and strain rate range of 10−5 to 103 s−1. Through careful considerations of various characteristic parameters involved in various constitutive equations, such as the stress exponent and activation energy, the controlling mechanisms have been assessed and discussed. The deformation of the complex AC8A composite and alloy seemed to be solely controlled by the dislocation glide+climb creep of the Al matrix at 350–450°C and 10−5 to 10−3 s−1, with n∼5 and Qt∼150 kJ mol−1 governed by lattice diffusion. At lower temperatures of 250–350°C and 10−5 to 10−3 s−1, dislocation glide+climb creep still dominated, with n∼5 and Qt∼83 kJ mol−1 governed by dislocation core diffusion. At elevated temperatures (250–450°C) and the highest strain rate (ε̇∼103 s−1), the data could not be explained by any creep-type process; thermally activated dislocation glide was the governing mechanism. As temperature decreased to less than 250°C, thermally activated dislocation glide was also dominant at all strain rates. In the latter case, the obstacles against traveling dislocations were basically immobile dislocations, which can be considered as intermediate-strength, and half-discrete and half-diffuse obstacles. In between these regions, mechanism transition occurred. Even at the highest strain rate of 103 s−1, the dislocation drag mechanism has not yet occurred for the current materials.