Accommodation mechanisms between type I {112}, type II '17¯2' and {130} compound twins in orthorhombic depleted uranium

In orthorhombic depleted uranium (DU), {130} compound twinning is the dominant deformation mechanism. Electron backscatter diffraction (EBSD) characterizations show that {130} twins form pairs with '17‾2' and {112} twins at grain boundaries (GBs), namely {130}−^′{17‾2}^′ and {130}−{112} twin pairs. Besides, {130} twins act as secondary twins in primary ′{17‾2}^′ and {112} twins, forming ′{17‾2}^′→{130} and {112}→{130} double twins. We systematically investigated these sequential twinning events in as-cast DU under quasi-static tension and compression. Through Schmid factor (μ), geometric compatibility factor (m^′) and twin shear displacement gradient tensor (e) analysis, it was found that when {130} twins meet GBs, {130} twins are preferred in adjacent grains at low-angle GBs. Comparatively, Type I {112} and Type II ′{17‾2}^′ twins are favored at high-angle GBs. The {112} twins are activated in the neighbor at GBs with the misorientation axes near [2‾33] and [23‾3], while ′{17‾2}^′ twins are preferably activated with the misorientation axes of GBs nearly around [010] and [01‾0]. The prediction agrees well with experimental results. For the two types of double twins, the operative secondary {130} twins are those that can most effectively relax the shear strain of the primary twins among the equivalent variants. The nucleation of secondary twins by dislocation dissociation is also discussed. The analysis offers insights into variant selection and plastic deformation simulation for DU application.