Hardening of pure metals by high pressure torsion: a physically-based model employing volume averaged defect evolutions

A physically based model to predict the increment of hardness and grain refinement of pure metals due to severe plastic deformation by high-pressure torsion (HPT) is proposed. The model incorporates volume-averaged thermally activated dislocation annihilation and grain boundary formation. Strengthening is caused by dislocations in the grain and by grain boundaries. The model is tested against a database containing all available reliable data on HPT-processed pure metals. It is shown that the model accurately predicts hardening and grain size of the pure metals, irrespective of crystal structure (face-centred cubic, body-centred cubic and hexagonal close packed). Measured dislocation densities also show good correlation with predictions. The influence of stacking fault energy on hardening is very weak (of the order of ?0.03 GPa per 100 J mol?1)