In this work, the hot deformation characteristics of a near-$\alpha$ Ti-Al-2SnZr-2Mo alloy (Ti6242 alloy) with a Fine-Grained (FG) microstructure ($d_{\alpha }$ = 2.86 $\mathsf{\mu }$m) were investigated at two levels of temperature, T = 730 ${}^{\circ }$C and T = 840 ${}^{\circ }$C. The initial microstructure consists of equiaxed nodules of the $\alpha$ phase as well as some $\alpha$ lamellae sparsely distributed and separated by thin layers of the BCC $\beta$ phase. For both temperatures, three strain rates (${10}^{-4},{10}^{-3},{10}^{-2}{s}^1$) were analysed during loading. Moreover, the microstructural evolution ($\alpha$ size and morphology) was also evaluated by conducting interrupted tensile tests. The different tensile testing conditions greatly influence the stress-strain response of the material as well as the microstructure evolution. Indeed, various phenomena can take place such as elongation of the grain structure, globularization, dynamic recrystallization and grain growth of the equiaxed areas depending on the temperature, the strain rate and the strain level. The FG Ti6242 alloy exhibits interesting superplastic ductility at T = 840 ${}^{\circ }$C. At this temperature either a very gradual flow softening (at higher strain rate) or flow hardening (at lower strain rate) can be observed and are related respectively to one or more of the following mechanisms: lamellae globularization, DRX and grain growth. At the intermediate strain rate, both mechanisms, strain hardening and softening, coexist. At T = 730 ${}^{\circ }$C, the onset of the $\alpha$ lamellae globularization was only promoted at low strain rate. A mechanical behavior model was developed in the temperature range of 730–840 ${}^{\circ }$C, which was able to take into account all the observed phenomena: viscosity, softened behavior and strain hardening. Constitutive equations were calibrated from the stress-strain responses and microstructural observations, and the computed results were in good agreement with the experiments.

中文翻译：

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Ti-6242S合金在热和超塑性条件下变形机制的实验分析和行为建模

在这项工作中，$\alpha$ 具有细晶粒（FG）微结构的Ti-Al-2SnZr-2Mo合金（Ti6242合金）（$d_{\alpha }$ = 2.86 $\mathsf{\mu }$m）在两个温度水平（T = 730 ）下进行了研究${}^{\circ }$C和T = 840${}^{\circ }$C.初始微观结构由 $\alpha$ 阶段以及一些 $\alpha$ 薄层稀疏分布并被薄薄的BCC隔开 $\beta$相。对于两种温度，三个应变率（${10}^{-4}，{10}^{-3}，{10}^{-2}{s}^{\mathrm{1个}}$）在加载过程中进行了分析。此外，微观结构的演变（$\alpha$尺寸和形态）也通过进行不连续的拉伸试验进行了评估。不同的拉伸测试条件极大地影响了材料的应力应变响应以及微观结构的演变。实际上，取决于温度，应变速率和应变水平，会发生各种现象，例如晶粒结构的伸长，球化，动态再结晶以及等轴区域的晶粒生长。FG Ti6242合金在T = 840时表现出有趣的超塑性延展性${}^{\circ }$在此温度下，可以观察到非常缓慢的流动软化（在较高的应变速率下）或流动硬化（在较低的应变速率下），并且分别与以下一种或多种机理相关：片状球化，DRX和晶粒长大。在中等应变速率下，应变硬化和软化这两种机制共存。在T = 730时${}^{\circ }$C，发病 $\alpha$片状球状化仅在低应变速率下被促进。在730–840温度范围内开发了机械行为模型${}^{\circ }$C，它能够考虑到所有观察到的现象：粘度，软化行为和应变硬化。根据应力-应变响应和微观结构观测值对本构方程进行了校正，计算结果与实验结果吻合良好。