Effect of anvil roughness on the flow patterns and hardness development in high-pressure torsion

Two sets of anvils having different surface roughness were used to systematically investigate the flow patterns developed on the top and bottom surfaces of stainless steel discs with an anvil misalignment of 100 µm during high-pressure torsion. It is shown that the flow patterns on the disc surfaces have different variation tendencies depending on whether the anvils have rough or smooth surfaces. Double-swirl flow patterns were observed on the top and bottom surfaces of discs after 1 and 5 turns when using an anvil with a smooth surface. In contrast, when using an anvil with a rough surface the double-swirl flow patterns appeared only on the top surface after 1 turn and a single swirl appeared on both surfaces after 5 turns. Hardness measurements on the top surfaces showed that discs processed using an anvil with a rough surface have greater hardness than discs processed using an anvil with a smooth surface. There was no obvious hardness difference on the bottom surfaces for discs processed using anvils with rough or smooth surfaces.