Recrystallization behavior of pure molybdenum powder processed by high-pressure torsion

High-pressure torsion (HPT) was conducted on pure molybdenum (Mo) powder (99.95 wt%) under the applied pressure of 3 GPa with different revolutions at the temperature of 623 K followed by heating to 1673 K with a rate of 20 K per minute at the pure argon atmosphere. The microstrain and dislocation density for the HPT-processed Mo were calculated by X-ray diffraction (XRD). The microstructure after HPT and the followed heating process was characterized by metallurgical microscopy, electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the homogeneous ultrafine grains with non-equilibrium high angle grain boundaries (HAGBs) were formed in the Mo sample during HPT by continuous dynamic recrystallization (cDRX). The increasing HPT revolution results in the increase of dislocation density and the decrease of grain size, which tends to be stable beyond 5 turns due to the dynamic recovery accompanied by slight grain coarsing. Continuous static recrystallization (cSRX) occurred in the HPT-processed Mo sample with ultrafine grains during the followed heating process. The microstructure after heating is still with fine grains and homogeneous distribution even though the heating temperature up to 1673 K, which indicates the enhancement of the microstructure thermal stability.