A model for the yield strength anomaly of Fe-Al

A phenomenological model is introduced for the temperature dependence of the yield strength of Fe-Al. The key feature of the model is that it incorporates hardening by thermal vacancies to account for the yield strength anomaly. Since the vacancy concentration C-V varies as exp(-1/T) and the hardening due to vacancies varies as C-V(1/2), the model predicts at intermediate temperatures an exponential increase in strength with increasing temperature. This increasing strength is terminated by the onset of dislocation creep. The model includes strain rate dependences that are consistent with experimental observations and yields an activation enthalpy for vacancy formation which is in excellent agreement with a previously measured value.