The influence of equipment features on workpiece slippage under high pressure torsion

This paper presents the results of determining the effect of slippage under high pressure torsion (HPT) of commercially pure Cu samples using two versions of the equipment design. The first tool is the Ufa University of Science and Technology (UUST) equipment, which lacks a special system of alignment-stabilization of anvils and features a groove on the lower anvil, the upper anvil is flat. The second equipment comes from St. Petersburg State University (SPbU) and features the 0.4 mm deep grooves on the upper and lower anvils and is equipped with the system of alignment-stabilization of anvils. To assess slippage, the method of “joint torsion of the disk halves” was used. HPT was conducted using the “soft” Cu material at room temperature with different number of revolutions. After HPT n = 5 on the UUST equipment, with further torsion by the value of n = 0.25, slippage exceeded 50 %. After preliminary HPT n =10 on the UUST equipment, with further n = 0.25, slippage reached 90 %. After preliminary HPT n =10 on the SPbU equipment, with further torsion by the value of n = 0.25, slippage ≈17 %, after preliminary HPT n = 25 slippage ≈30 %. The thickness h of samples during HPT on the SPbU equipment exhibited a less pronounced decrease with increasing the n than during HPT on the UUST equipment. This explains less slippage occurs at increasing n during HPT on the SPbU.