Slippage during High-Pressure Torsion: Accumulative High-Pressure Torsion—Overview of the Latest Results

Abstract

This overview examines the results of a study of the effect of slippage in high-pressure torsion (HPT). A number of papers in this area and the works of the authors of this overview are considered. The authors used the method of the “joint HPT of the disk halves”. This method is the simplest and most illustrative method for evaluating slippage during HPT. The authors used 10 and 20 mm diameter anvils, with a groove on the lower anvil and a calculated pressure of 6 GPa. In the case of the HPT of solid bulk metal glass (BMG), slippage starts at the early stages of HPT and is total. Slippage may also be significant at the early stages of the HPT of such metallic materials as Ti, Ni, Fe-0.1%C, and Zr-2.5%Nb. Slippage increases with the number of revolutions, n. There is no slippage at the initial stages of the HPT of copper. However, after HPT Cu n = 10, slippage can be total. Nevertheless, studies show that the structure of samples using HPT, obtained by the authors, is similar to the nanostructure observed by other authors after using HPT with similar materials. Thus, notwithstanding slippage during HPT, deformation during HPT still occurs, and nanostructure formation occurs. Therefore, the formation of a nanostructure in samples during HPT is not proof of the absence of slippage. The authors provide a possible explanation for this. The authors propose a new method—“accumulative high-pressure torsion”—to achieve a high strain in various materials. In this procedure, several cycles are repeated, according to the following scheme: “HPT for n = 1 or 2 turns of the anvil → cutting the specimen into pieces → unstacking the stacked pieces on the anvil and subsequent HPT for n = 1 or 2”. Studies performed on a number of materials demonstrate that novel method transforms the structure more efficiently than regular HPT.