Grain-boundary sliding and its accommodation during creep and superplasticity

Abstract

The roles of grain-boundary sliding (GBS) and of other creep mechanisms in creep and fine-grain superplasticity are presented in relation to a model based on the division of grains into their central “cores“ and peripheral “mantles”; GBS and its accommodation is limited to the latter, which changes with the mode of accommodation,viz by fold formation, dislocation motion in the mantle or pure diffusion. This description is used to adapt from the literature or develop equations for creep rate based on dislocation or vacancy mechanisms, which are then combined to give plots of the various regimes of superplastic (or creep) behavior, all of which involve GBS in a quantitatively defined manner. The predictions of these equations are compared with a number of results in the literature and with those of a lead-thallium alloy of grain sizes intermediate between superplastic behavior and normal creep. Some preliminary comparisons of measured GBS are also made with the predictions of the model. Agreement is good.