Orientation-dependent multi-spall performance of monocrystalline NiTi alloys under shock compression

Abstract

The primary objective of this work was committed to large-scale non-equilibrium molecular dynamics modeling for the investigation on multiple spall performance, microstructural evolutions, and melting state of NiTi alloys along three typical crystal orientations. We discovered that there was a single-wave structure present in the [100] orientation, whereas elastic-plastic two-wave structures were found in [110] and [111], exhibiting a significant anisotropy in elastic-plastic wave velocity. Compared to [110] and [111] orientations, multi-spallation was more likely to be generated in the [100] direction. During accumulative dynamic damage, there was also a strong sensitivity of void evolution to orientation. For [100], voids tended to be densely distributed in the material and exhibited a strip-shaped manner. In contrast, a more scattered void distribution was observed for the other two orientations, showing a flaky pattern. Interestingly, dislocations in the spall region were almost annihilated before approaching void nucleation. According to void statistics, the peak number of voids, void nucleation rate, and spall region size were identified to be in a good uniformity along [110], [100], and [111]. For all the cases, the samples experienced partial melting in the released state and were followed by a recovery of structural order degree. However, there was an insignificant anisotropy in the melting state for each crystal orientation during multi-spallation.