Twinning and kinking behaviors of α-uranium under high strain rate compression

Uranium (U) and its alloys are frequently subjected to dynamic deformation during their applications in nuclear industry. Owning to the low-symmetry crystal structure of α-U (the allotropic form of uranium stable up to 940 K), twinning and kinking play critical roles in its dynamic plastic deformation. However, the twinning and kinking behaviors of α-U under dynamic deformation have not yet been fully understood. In this work, we employed a split Hopkinson pressure bar (SHPB) to dynamically compress coarse-grained α-U to strains of 5%, 15%, 25%, and 27%. The resulting twin and kink bands were characterized using electron back-scatter diffraction (EBSD). Our results reveal that both the width and density of twins increase with increasing impact strain. Four types of twins were identified: {130}, $ʹ\left\{1\bar{7}2\right\}ʹ$, {112}, and $ʹ\left\{1\bar{7}6\right\}ʹ$. Kink bands emerged after 15% impact strain, with their boundaries perpendicular to the [100] direction of matrix and their [100] directions oriented at a 45° angle relative to that of matrix. The {130}, $ʹ\left\{1\bar{7}2\right\}ʹ$, and {112} twins were observed within the kink bands, and the {112} twins inside the kink bands were found to initiate secondary {130} twin. Fine and randomly oriented grains were observed inside the adiabatic shear bands of α-U. Based on these findings, we propose a twin-induced rotational dynamic recrystallization to describe the formation of adiabatic shear band in uranium. This study provides new insights into the plastic deformation mechanisms of uranium under dynamic loading.