Dislocation core structures and yield stress anomalies in molybdenum disilicide

Stacking fault energies in MoSi2 due to shear along < 331 > have been calcu lated by modified embedded atom method (MEAM) calculations. Preliminary cal culations have also been made of dislocation core structures and their resp onse to applied stress. The results are used to investigate the configurati on and mobility of 1/2 < 331 > dislocations. Shear of 1/6 < 331 > in the {1 03} plane of MoSi2 produces an anti-phase boundary (APB) whose geometry, ca lled 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 u nstable. MEAM calculations show that there is a stable fault close to APB(2 ) with a displacement of similar to1/8 < 331 > in the same direction. The { 103} planes have an unusual five laver stacking sequence with successive pl anes 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 ha ve asymmetrical arrangements which will respond differently to the directio n of the applied stress, explaining the yield stress asymmetry in MoSi2. Al l 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 ph enomena. Published by Elsevier Science Ltd.