Application of thermohydrogen processing for formation of ultrafine equiaxed grains in near α Ti600 alloy

In this article, the grain refinement of the near α Ti600 alloy by thermohydrogen processing (THP) is investigated. The THP processing includes hydrogenation, high-temperature deformation, and vacuum dehydrogenation. The microstructural evolution in each stage of THP processing was carefully investigated by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM). The experimental results show that face-centered-cubic (fcc) hydride (δ phase) precipitates in the hydrogenated Ti600 alloy at the hydrogen contents of 0.31 wt pct and above. The critical role of hydrides in the processing of grain refinement is clearly demonstrated. The hydrides divided the α grains in hydrogenation treatment, promoted α-phase recrystallization, and facilitated the stabilization of finer α grain size in isothermal compression.