Dislocation structure, phase stability, and yield stress behavior of L12 intermetallics: Ir3X (X = Ti, Zr, Hf, V, Nb, Ta)

Abstract

The structure and mobility of superdislocations in Ir3X (X = Ti, Zr, Hf, V, Nb, Ta) with L12 structure were investigated in the framework of the modified Peierls-Nabarro (PN) model with first-principles generalized stacking fault energetics calculated using the all-electron full-potential linearized augmented plane wave method (FLAPW). Superlattice intrinsic stacking fault (SISF)-bound superdislocations (Kear splitting scheme) are strongly preferred energetically in Ir3V, Ir3Nb, and Ir3Ta, whereas antiphase boundary (APB)-bound superdislocations (Shockley splitting scheme) are predicted in Ir3Ti, Ir3Zr, and Ir3Hf. Because APB-bound superdislocations are considered responsible for the yield stress anomaly, our results predict that positive yield stress temperature dependence could only be expected in Ir3Ti, Ir3Zr, and Ir3Hf, and a negative one in Ir3V, Ir3Nb, and Ir3Ta. The connection of the mechanical behavior of the Ir3X alloys with the L12 → D019 structural instability is established and the electronic origins of this instability are analyzed.