Effect of the deformation temperature on the structural refinement of BCC metals with a high stacking fault energy during high pressure torsion

Abstract

The structural evolution in bcc metals (molybdenum, niobium) with a high stacking fault energy (300 and 200 mJ/m^–2, respectively) is studied during high pressure torsion in Bridgman anvils at temperatures of 290 and 80 K. It is established that cryogenic deformation of these metals does not result in twinning; however, banded structures are formed at the initial stage of deformation. Misoriented kink bands, which inhibit the formation of a homogeneous submicrocrystalline structure similarly to twins, form in molybdenum. The banded structures in niobium are characterized by low-angle misorientations; they do not suppress the formation of a submicrocrystalline structure and the refinement of microcrystallites to nanosizes.