Orientation-dependent shock compression behavior of non-porous/porous NiTi shape memory alloy: An atomic scale study

Abstract

Crystal orientation has a strong influence on the mechanical behavior of a material, especially at high-strain-rate impact loading. In this study, the effects of different crystallographic orientations on the non-porous/porous NiTi shape memory alloy (SMA) under high-strain-rate impact loading are studied by using molecular dynamic methods. The structural phase transformation process, energy propagation trajectory, defect dislocation evolution, and shock wavefront changes of the NiTi SMA under shock compression are comparatively analyzed. The simulation results show that for three typical crystal orientations, [100], [110], and [111], the phase transformation structures extend in the form of disordered dots, "X"-shaped meshes, and line segments, respectively. Both phase transformation and phase transformation-induced plasticity are more likely to occur in the [110] NiTi SMA; thus, more energy is dissipated, and the propagation speed of the shock wave is the lowest. In addition, the magnitude of the shock wave propagation velocity in the three crystal orientations is of the following order: [111] crystal orientation > [100] crystal orientation > [110] crystal orientation. Finally, the presence of voids affects the propagation patterns of the wavefront, and the crystal orientation directly affects the shape of the shock wavefront and the steepness of the shock wavefront for porous samples. In terms of the crystal orientation and voids, the [110] crystal orientation and voids uniformly arranged along a straight line can improve the buffer performance of the single-crystal NiTi SMA under high-strain-rate impact loading.