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

• Bulk W samples with refined microstructure were obtained by high-pressure torsion.
• Small crystallite and high dislocation density were achieved by high torsion strain.
• Microhardness of W was significantly improved upon the high torsion strain.
• Thermal stability of W was enhanced through high-pressure torsion.
• Recrystallization behavior of W with different equivalent strains was analyzed.

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 × 1014 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.