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

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.