Negative yield stress temperature anomaly and structural instability ofPt3Al

Abstract

First-principles electronic structure and total energy calculations of the phase stability and dislocation prop­ erties of Pt3Al are employed to reveal the origins of its yield stress low temperature anomaly (LTA). An analysis of the dislocation structure and mobility, based on generalized stacking fault calculations, demon­ strates that the LTA is connected with the L12^ D 0 'c structural transformation rather than, as traditionally believed, with features of the dislocation structure in the L12 phase. We also explain why the yield stress and slip geometry have a strong orientation dependence and why small deviations from stoichiometry lead to dramatic changes in its mechanical behavior.