Identifying creep mechanisms in plastic flow

The mechanisms occurring in plastic flow at elevated temperatures may be divided into three distinct classes depending upon whether they are intragranular dislocation mechanisms, grain boundary sliding including superplasticity or diffusion creep occurring through vacancy flow. The characteristics of these various mechanisms are described and procedures are outlined for distinguishing between the different processes. Using this approach, it is shown that there is good experimental data supporting the occurrence of both Harper-Dorn creep and Nabarro-Herring diffusion creep as distinct creep processes. Recent results reported from computer simulations, combined with experimental observations, suggest the possible occurrence of grain boundary sliding at low temperatures in nanostructured and ultrafine-grained materials.