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

• Published in: International journal of refractory metals & hard materials 2018-04, Vol.72, p.367-372
• Main Authors: Li, Ping, Lin, Quan, Wang, Xue, Tian, Ye, Xue, Ke-Min
• Format: Article
• Language: English
• Subjects: Crystallization; Dislocation density; Dynamic recrystallization; Electron backscatter diffraction; Grain boundaries; Heating; High-pressure torsion (HPT); Metallurgy; Microstrain; Microstructure; Molybdenum; Molybdenum powder; Recrystallization; Recrystallization behavior; Thermal stability; Torsion; Transmission electron microscopy; X-ray diffraction
• ISSN: 0263-4368; 2213-3917
• DOI: 10.1016/j.ijrmhm.2018.01.002

High-pressure torsion (HPT) was conducted on pure molybdenum (Mo) powder (99.95wt%) under the applied pressure of 3GPa with different revolutions at the temperature of 623K followed by heating to 1673K with a rate of 20K 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 1673K, which indicates the enhancement of the microstructure thermal stability. •Ultrafine-grained Mo with non-equilibrium high angle boundaries was obtained by high-pressure torsion with 5 to 15 turns.•Grain refinement mechanism of continuous dynamic recrystallization occurred during 5 turns of high-pressure torsion.•Dynamic recovery accompanied by ongoing formation of new cell structure occurred in 10 and 15 turns of high-pressure torsion.•Heated microstructure with fine grains and homogeneous distribution are of nobler thermal stability.