Anisotropic plasticity in NiAl alloy under dynamical loading

We use molecular dynamics with a first principles-based interatomic potential to characterize the orientational dependence of shock-induced plasticity in NiAl B2 alloy. For all directions studied plasticity starts with the nucleation of superpartial loops encircling 1/2$<$111$>$ slip but the subsequent events exhibit marked anisotropy. For shocks in the [110] direction we find an intricate pattern of $<$111$>${\{}110{\}} and $<$100$>${\{}110{\}} slip with the plastic wave moving at the shock velocity. In the case of [111] shocks plastic deformation is dominated by $<$100$>${\{}110{\}} slip that forms when trailing superpartials nucleate inside the initial 1/2$<$111$>$ loops. For shocks in the [100] direction (the hard direction) much stronger shocks [(uniaxial stress almost twice larger than for [110] and [111]] are required before plastic deformation is observed; we find almost simultaneous, nucleation of multiple 1/2$<$111$>$ superpartials, leading to frequent intersections that severely limit their mobility and even lead to local amorphization. In the [100] and [111] shocks we find an elastic precursor separating the leading shock front and the plastic wave.