Crystallographic-orientation-dependence plasticity of niobium under shock compressions

P Li and YF Huang and K Wang and SF Xiao and L Wang and SL Yao and WJ Zhu and WY Hu, INTERNATIONAL JOURNAL OF PLASTICITY, 150, 103195 (2022).

DOI: 10.1016/j.ijplas.2021.103195

Plastic deformation mechanism of metals under shock compressions is one of longstanding interests in compression science and materials related field. In this work, shock responses of Nb under the shock compressions along 001, 110 and 111 directions are investigated using large- scale nonequilibrium molecular dynamics (NEMD) simulations. A new reliable embedded atom method (EAM) potential is specially developed for purposes of studying the deformation twinning under high pressures. Our results indicate that the shock wave front exhibits split two wave structures in all three shock direction. In contrast to traditional understandings, the overdriven pressure of 110 is smaller than that of 001, which is attributed to their different twinning threshold and growth speed. The deformation twins are considerably more pronounced for the shock along 001 and 110 directions than that along 111 direction, which take place along 112111 systems. Twins nucleate at the shock front and rapidly grow accompanied by dislocation nucleation and multiplication between the twins. Different twinning mechanisms for the shock along 001 and 110 directions are identified. For the shock along 001, the deformation twin is formed through successive movements of atoms on the alternative (112) plane along the 110 and 113 direction. For the shock along 110, the atoms on each (112) plane directly move along the 111 direction layer by layer. Using a lattice model combined with the transition state theory, we find that uniaxial compressions along specific directions play the key role for the twinning mechanism.

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