Fig. 1 a Initial torsion model. b Crystallographic relationship showing the torsion axes along $\left[11\overline{2 }0\right]$ and $\left[10\overline{1 }0\right]$. The Z-direction is always along $\left[0001\right]$, and the Y-direction is the torsion axis. When Y is along $\left[10\overline{1 }0\right]$, X is along $\left[11\overline{2 }0\right]$; when Y is along $\left[11\overline{2 }0\right]$, X is along $\left[ {10\overline{1}0} \right]$

Fig. 2 a Evolution of torque with respect to torsion angle around $\left[ {11\overline{2}0} \right]$ and $\left[ {10\overline{1}0} \right]$. b Gradient shear stress distribution on the cross-section of the torsion sample. Other stress components are negligible during torsion

Fig. 3 Torsion behavior around the $\left[11\overline{2 }0\right]$ axis, illustrating the dislocation behavior at various torsion angles. The basal dislocation can be identified by the green atoms, which represent the basal staking faults created by the basal partial dislocations. The prismatic dislocations are the ones in white

Fig. 4 a–d Torsion behavior around the $\left[11\overline{2 }0\right]$ axis, illustrating the dislocation slip at various torsion angles. e–h Distribution of von Misses stress

Fig. 5 Torsion behavior around $\left[ {10\overline{1}0} \right]$ axis. a–d Evolution of dislocations with increasing torsion angle. Basal and prismatic dislocations as well as $\left\{ {11\overline{2}1} \right\}$ twin are activated to accommodate the torsion deformation. e, f Distribution of von Misses stress indicating the local deformation is accommodated by dislocations, formation of grain boundary and twin. The boxed regions will be further analyzed to reveal the cross slip and twinning mechanisms

Fig. 6 a–c A basal trailing partial nucleates and catches up with the leading partial, erasing the basal stacking fault in between. d Cross slip from basal plane to prismatic plane. e–g Screw prismatic dislocation glides along the Burgers vector direction, i.e., $\langle 11\overline{2 }0\rangle$, causing the dislocation line to shift downward by a distance of six atomic layers (indicated by the black arrow). h Sketch showing the cross slip from basal plane to prismatic plane. The horizontal and vertical planes are basal and prismatic slip planes, respectively

Fig. 7 a A prismatic dislocation connected to a basal dislocation is observed. b Length of prismatic plane is decreasing while the basal dislocation length is increasing, indicating the cross slip from prismatic plane to basal plane. c, d Basal dislocation shortens, while the prismatic dislocation elongates and shifts upward (indicated by the black arrow), meaning that cross slip from basal to prismatic is taking place. e Sketch showing the double cross slip from prismatic plane to basal plane, then back to prismatic plane

Fig. 8 Interaction between basal and prismatic dislocations. The dislocation line of full dislocation with Burgers vector of $\frac{1}{3}\langle 11\overline{2 }0\rangle$ is shown in green, and the dislocation line for basal partial dislocation with Burgers vector of $\frac{1}{3}\langle 10\overline{1 }0\rangle$ is shown in orange. a A screw prismatic dislocation is connected to a dissociated basal dislocation. b, c Prismatic dislocation interacts with the basal dislocation. d Bottom prismatic dislocation can move to basal plane and further dissociate into basal partials

Fig. 9 a–d Cross-section view along the $\left[10\overline{1 }0\right]$ axis showing the nucleation and detwinning of the $\left\{ {10\overline{1}1} \right\}$ twin. The atoms in the perfect lattice are hidden, and only lattice defects are shown. e–h Evolution of $\left\{ {10\overline{1}1} \right\}$ twin from nucleation, growth to detwinning

Fig. 10 Snapshots showing nucleation and growth of $\left\{ {11\overline{2}1} \right\}$ twin during torsion