Structure and hardness of molybdenum upon deformation under pressure at room and cryogenic temperatures

This article considers the effect of the stacking fault energy and deformation temperature on the structure formation of a molybdenum single crystal with an initial orientation (110). The deformation is performed via high-pressure torsion at room and cryogenic temperatures, 290 and 80 K, respectively. The structural analysis and hardness behavior of the studied material indicate that lowering the temperature does not change the deformation mechanism from dislocation slip to twinning. We observe the localization of the deformation, band structure formation, and the formation of misoriented microcrystallites. The initial single crystal converts into a polycrystal immediately after the early stages of deformation (e > 2). Misoriented submicron-scale elements are formed at 290 K at a smaller true strain than those formed at 80 K. This deformation results in the structural refinement at both temperatures but does not allow for the formation of a homogeneous misoriented structure with high-angle boundaries. A decrease in the deformation temperature leads to a fall in the plasticity of molybdenum, that is, the application of high pressure fails to prevent its brittle fracture.