A phenomenological model was developed for the temperature dependence of the yield strength. An important feature of the model was that it assumed that hardening by thermal vacancies accounted for the yield-strength anomaly. Since the vacancy concentration varied as exp[-1/T], and the hardening due to vacancies varied as the square root of the vacancy concentration, the model predicted an exponential increase in strength, with increasing temperature, at intermediate temperatures. This increasing strength was cut off by the onset of dislocation creep. The model included strain-rate dependences that were consistent with experimental observations, and yielded an activation enthalpy for vacancy formation which was in excellent agreement with previously measured values.

A Model for the Yield Strength Anomaly of Fe-Al E.P.George, I.Baker: Philosophical Magazine A, 1998, 77[3], 737-50