Dislocation core structures and yield stress anomalies in molybdenum disilicide

Stacking fault energies in MoSi2 due to shear along <331> have been calculated by modified embedded atom method (MEAM) calculations. Preliminary calculations have also been made of dislocation core structures and their response to applied stress. The results are used to investigate the configuration and mobility of 1/2<331> dislocations. Shear of 1/6<331> in the {103} plane of MoSi2 produces an anti-phase boundary (APB) whose geometry, called APB(1), is different from that produced by 1/6<331> in the opposite direction, APB(2). Calculations show that APB(1) is stable and APB(2) is unstable. MEAM calculations show that there is a stable fault close to APB(2) with a displacement of ∼1/8<331> in the same direction. The {103} planes have an unusual five layer stacking sequence with successive planes offset by 1/5<301>. Shear of 1/10<351> in the correct direction gives a low energy intrinsic fault. This vector is close to the 1/8<331> shear that produces a stable fault. Various dissociated configurations of 1/2<331> dislocations are considered based on these partials. All can have asymmetrical arrangements which will respond differently to the direction of the applied stress, explaining the yield stress asymmetry in MoSi2. All of the slip systems (<100>{0kl} and <111>{110} as well as <331>{103}) exhibit yield stress anomalies at different temperatures. Different core configurations at high and low temperatures are used to explain the phenomena.