Microstructure and microhardness evolution in pure molybdenum processed by high-pressure torsion.

Abstract

Molybdenum, a refractory metal with a body-centred cubic lattice, was processed by high-pressure torsion (HPT) at room temperature under an applied pressure of 6.0 GPa and torsional straining from 1/2 to 10 turns. The microstructures were characterized by electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM) and measurements were taken of the Vickers microhardness. The results show a gradual evolution of homogeneity in grain size and microhardness with increasing numbers of HPT turns with an average grain size of ~690 nm at the sample edge after 5 turns and a saturation microhardness of ~660 Hv. The grain size after 10 turns showed a slight decrease at the centre and the microhardness was slightly lower than after 5 turns due to the occurrence of limited dynamic recovery.