Dynamic plasticity-induced void collapse in a NiTi-based cylindrical shell during reverse phase transformation

This study is dedicated to investigating the dynamic damage performance of a NiTi cylindrical shell, with particular attention paid to the correlation between void collapse and shock-induced plasticity/phase transition. The results demonstrate that the void evolution in the 50 nm polycrystal and single crystal is clearly characterized by “nucleation → collapse → renucleation,” whereas grain-boundary-mediated deformation accommodation suppresses complete void collapse, and consequently no renucleation is observed in the 10 nm polycrystal. A high density of grain boundaries provides preferred nucleation sites for voids, resulting in an intergranular mode in the 10 nm sample, and contrarily, the 50 nm polycrystal shows a coexisting intergranular/transgranular manner. For the single crystal, we also find that voids are primarily distributed along the 〈110〉 direction before void collapse, which is attributed to the fact that the stress-induced B2 → B19 transformation along the 〈100〉 direction suppresses void nucleation. Interestingly, voids along the 〈100〉 direction are preferentially generated at the intersections of shear deformation bands during renucleation, and the resultant temperature rise degrades the spall strength. During shear localization, the reverse transformation causes dislocations to continuously migrate toward void surfaces, accelerating void collapse. These findings are expected to provide an atomistic insight into the dynamic failure mechanism of a metal-based cylindrical shell under implosion loading.