A grade 2 pure titanium with an initial grain size of ≈50 μm is processed by high‐pressure torsion (HPT) at room temperature under an imposed pressure of 6.0 GPa. The microhardness variations are examined and the results show that the disks are reasonably homogeneous after 10 turns of torsional straining. The microstructural evolution is systematically characterized by optical microscopy, X‐ray diffraction, and transmission electron microscopy to provide information on the effect of shear strain on grain size and microstructure. The results demonstrate that the initial coarse structure is gradually refined from the edge to the center of the disk under the shear stress during HPT processing and an ultrafine‐grained pure Ti is achieved with an average grain size of ≈96 nm after 10 turns. A model is developed by considering the formation of subgrain boundaries, twins, and high‐angle grain boundaries for the grain refinement of pure Ti processed by HPT.

中文翻译：

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高压扭转作用下纯钛的显微组织演变和显微硬度变化

初始晶粒尺寸约为50μm的2级纯钛在室温下于6.0 GPa的施加压力下通过高压扭曲（HPT）进行处理。检查了显微硬度的变化，结果表明，经过10次扭转应变后，圆盘相当均匀。通过光学显微镜，X射线衍射和透射电子显微镜系统地表征了显微组织的演变，以提供有关剪切应变对晶粒尺寸和显微组织的影响的信息。结果表明，在HPT加工过程中，在剪切应力作用下，初始的粗组织逐渐从圆盘的边缘到中心逐渐细化，经过10圈旋转后，获得了平均晶粒尺寸约为96 nm的超细晶粒纯Ti。