Three-dimensional twinning dominated shock spallation in single crystal tungsten containing He bubble under three directions

Molecular dynamics simulations were performed to investigate the spallation behavior of Hebubble-containing body centered cubic (BCC) tungsten under shock loading along the [100], [101], and [111] directions. The anisotropy of the local spallation related stress in the bubblecontaining region is associated with the different plastic deformation modes preceding spallation. In particular, the lower stresses under [101] and [111] loading arise from a mixed twinning-dislocation deformation mode. Nevertheless, spallation around the He bubble is primarily triggered by twin nucleation and growth for all shock directions, with clear anisotropy in both the number of activated twinning systems and the corresponding atomistic growth paths. Under [100] shock tension, four twinning systems are activated and twin growth proceeds through the coupled layer-by-layer path and face centered cubic (FCC) related transformation path. Under [101] and [111] shock compression, two and three twinning systems are activated, respectively, and the same growth mode is observed. In contrast, under [101] and [111] shock tension, although two and three twinning systems are still activated, respectively, twin growth changes to the two-layer-by-two-layer path together with the hexagonal close packed (HCP) related transformation path. Schmid-factor analysis shows that the activated systems agree well with those having the largest absolute resolved shear stresses. Crystallographic analysis further establishes an intrinsic correspondence between the two groups of twinning paths: the FCC related path is associated with the layer-by-layer mode, whereas the HCP related path corresponds to the two-layer-by-two-layer mode.