Size-dependent deformation mechanism transition in titanium nanowires under high strain rate tension

Abstract

Tensile deformation of single crystal titanium nanowires (NWs) with size ranging from 3nm to 20nm along [0001] orientation is investigated by molecular dynamics (MD) simulations. For all NWs, the initial yielding at different strain rates is induced by the nucleation of 101¯2 twinning. Following the saturation of twin volume fraction, the size dependent transition of deformation mechanisms in twinned regions is observed. At the strain rate from 108s−1 to 109s−1, following the deformation twinning, the phase transformation from HCP to FCC dominates the plastic deformation of Ti NWs. By increasing sample size to 20nm, phase transformation can be replaced by prismatic dislocation slip. At the strain rate from 109s−1 to 1010s−1, the critical size for the transition from phase transformation to full dislocation slip decreases with the applied strain rate. With further increasing sample size, after the saturation of 101¯2 twins, the initial single crystal NW transforms to nanocrystalline NW. Subsequent plastic deformation mechanism in the nanocrystalline Ti NW with large size is transferred from grain boundary dominate deformation to the cooperation of grain boundary deformation and dislocation activity. Furthermore, deformation mechanism map is proposed to provide a deep understanding of the plastic deformation of Ti NWs.