Microstructure and recrystallization behavior of pure W powder processed by high-pressure torsion

摘要

High-pressure torsion (HPT) was conducted on pure W powder (99.9 wt.%) at the temperature of 713 K and the Vickers microhardness along the disk radius was measured. The microstructure and thermal stability after HPT were characterized by X-ray diffraction (XRD) and differential scanning calorimetry (DSC), respectively. The results show that the increasing equivalent strain resulted in grain refinement, microhardness improvement and thermal stability enhancement. The nanostructured W samples with crystallite size of 32.5 nm, dislocation density of 9.19 x 10(14) m(-2) and average microhardness of 1020 Hv were obtained through 4 GPa and 10 revolutions of HPT. For HPT samples at 2 GPa and 5 turns, uniformly distributed nucleation sites around grain boundaries led to the recrystallization temperature increasing. A complex recrystallization mechanism occurred in the sample after 4 GPa and 10 turns, including continuous dynamic recrystallization (cDRX) during HPT and continuous static recrystallization (cSRX) during DSC heating. (C) 2015 Elsevier Ltd. All rights reserved.