Dislocation slip or deformation twinning: confining pressure makes a difference

While b.c.c. metals deform plastically by dislocation motion or deformation twinning, the atomistic mechanisms governing the choice of deformation modes are not well established. Molecular dynamics simulations using the Finnis–Sinclair potential were carried out to explore the pressure dependence of the deformation response of b.c.c. molybdenum. The crystal was sheared in (1 1 2)[1̄ 1̄ 1] under various confining pressures. The homogeneous nucleation stress of deformation twinning was found to increase with increasing confining pressure. Under sufficient pressure (0 1 1)[1̄ 1̄ 1] dislocations were nucleated instead of twins. Details of the dislocation and twin nucleations were analyzed with the help of the multi-layer generalized stacking fault energies. A two-fault (n=2) metastable twin state was found, in contrast to previous results using pair potentials.