Development of an ω-Phase in Grade 2 Titanium Processed by HPT at High Hydrostatic Pressure

High-pressure torsion was used to process grade 2 titanium to 10 turns using different pressures up to a maximum of 8 GPa. X ray diffraction showed that the as-received material and the material processed at pressures of 2 GPa and 4 GPa were single phase but the material processed at 8 GPa contained both the h.c.p. and the simple hexagonal ω-phase. Nanoindentation was used to determine the mechanical behavior and the results show a pronounced increase in hardness due both to the severe plastic deformation processing and to the phase transformation at the highest pressure. A maximum hardness of ~4.7 GPa was attained.

采用高压扭转（High-pressure torsion）工艺，以最高8 GPa的不同压力对2级工业纯钛进行10转的加工处理。X射线衍射（X-ray diffraction）分析结果表明，供货态材料以及经2 GPa、4 GPa压力加工的试样均为单相组织，而经8 GPa压力加工的试样同时存在密排六方（hexagonal close-packed，h.c.p.）结构与简单六方ω相。采用纳米压痕（nanoindentation）测试表征其力学行为，结果显示，剧烈塑性变形工艺与最高压力下发生的相变共同导致材料硬度显著提升，最终测得的最高硬度约为4.7 GPa。