Microstructure and Microhardness Evolution in Pure Molybdenum Processed by High‐Pressure Torsion

Abstract

Molybdenum, a refractory metal with a body‐centered cubic lattice, is processed by high‐pressure torsion (HPT) at room temperature under an applied pressure of 6.0 GPa and torsional straining from one‐half to ten turns. The microstructures are characterized by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM), and measurements are 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 five turns and a saturation microhardness of ≈660 Hv. The grain size after ten turns shows a slight decrease at the center, and the microhardness is slightly lower than after five turns due to the occurrence of limited dynamic recovery.