Abstract The typical two-phase titanium alloy of Ti–5Al–2Sn–2Zr–4Mo–4Cr was subjected to severe plastic deformation (SPD) by using high energy shot peening (HESP) at room temperature. Here, we experimentally investigated the SPD-induced atomic diffusion and phase transformation in the HESP processed Ti–5Al–2Sn–2Zr–4Mo–4Cr. The experimental results revealed that the ellipsoid-shaped precipitates with about 30–50 nm in thickness occurred in the surface layer of the HESP processed Ti–5Al–2Sn–2Zr–4Mo–4Cr, which was characterized to be the ordered α2-Ti3Al phase with the D019 crystal structure. The underlying formation mechanism of these ordered α2-Ti3Al precipitates was attributed to the SPD-induced atomic diffusion behaviors at room temperature, i.e., SPD-induced diffusive phase transformation, significantly different from the conventional ordering transformation driven by thermodynamics at high temperature. During HESP, the extremely high stress and strain level provided the potential conditions for precipitation of α2-Ti3Al phase; meanwhile, the generation of high-density dislocations accelerated the atomic diffusion, thereby promoting the nucleation of α2-Ti3Al phase. Furthermore, the significant reduction of grain size to nanometer contributed to the stability of α2-Ti3Al phase at room temperature.

中文翻译：

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Ti-5Al-2Sn-2Zr-4Mo-4Cr中有序α-Ti3Al相的剧烈塑性变形诱发析出

摘要 对典型的 Ti-5Al-2Sn-2Zr-4Mo-4Cr 两相钛合金在室温下采用高能喷丸硬化 (HESP) 进行剧烈塑性变形 (SPD)。在这里，我们通过实验研究了 HESP 处理的 Ti-5Al-2Sn-2Zr-4Mo-4Cr 中 SPD 诱导的原子扩散和相变。实验结果表明，HESP 处理的 Ti-5Al-2Sn-2Zr-4Mo-4Cr 表面层出现了厚度约为 30-50 nm 的椭圆形析出物，其特征是有序的 α2-Ti3Al 相具有 D019 晶体结构。这些有序 α2-Ti3Al 析出物的潜在形成机制归因于室温下 SPD 诱导的原子扩散行为，即 SPD 诱导的扩散相变，与高温下由热力学驱动的常规有序转换显着不同。在HESP过程中，极高的应力应变水平为α2-Ti3Al相的析出提供了潜在条件；同时，高密度位错的产生加速了原子扩散，从而促进了α2-Ti3Al相的形核。此外，晶粒尺寸显着减小到纳米有助于 α2-Ti3Al 相在室温下的稳定性。