An evaluation of the shearing patterns introduced by different anvil alignments in high-pressure torsion

Abstract

A two-phase duplex stainless steel was used to investigate the influence of different amounts of anvil misalignment on the shearing patterns produced during high-pressure torsion (HPT) and subsequently on the hardness distributions across the disc upper surfaces. The results show that for a perfect alignment of the anvils, to within < 25 mu m, the discs exhibit regular flow patterns as anticipated from conventional analysis whereas for anvil misalignments of 100 or 200 mu m the discs develop double-swirl patterns on the upper surfaces. These double swirls increase in size with increasing anvil misalignments and decrease in size with increasing numbers of torsional turns. The origin of these double swirls is investigated by examining a model based on a buckling theory for loaded beams and the development of instabilities within the discs during HPT processing. It is demonstrated that this model provides a satisfactory explanation for the reports of swirls and vortices in samples processed by HPT.