新型亚稳β钛合金Ti2448的温变形行为及本构模型Warm deformation behavior of new kind of metastable β titanium alloy Ti2448 and its constitute model

采用压缩实验研究应变速率和变形温度对新型亚稳β钛合金Ti2448温变形行为的影响。热模拟压缩实验在Gleeble−3800 热模拟机上进行，变形温度为473~673 K，应变速率为0.001~10 s −1 ，变形程度为45%。结果表明：在高、低应变速率下合金呈现不同的变形特性。低应变速率(0.001~0.1 s −1 )下，流动曲线呈现明显的应变硬化特性；在10 s −1 的高应变速率下，流动应力在达到饱和后，因温升效应而下降；在673 K 变形温度下流动应力因材料内部相变而具有显著的应变速率负敏感性。基于分段外推饱和模型和改进的Voce 模型分别构建Ti2448 合金在温变形高、低应变速率下的流动应力模型；该模型得到的预测曲线(应力—应变曲线)和实验曲线吻合较好，能够有效预测 Ti2448 合金在温变形过程中的流动应力，其中，改进的 Voce 模型能同时较好地描述饱和型和非饱和型应变硬化特性。

The effects of strain rate and deformation temperature on warm deformation behavior of a new kind of metastable β titanium alloy Ti2448 were investigated by using compression tests. The experiments were carried out on a Gleeble−3800 thermomechanical simulator at deformation temperatures of 473−673 K, strain rates of 0.001−10 s −1 , and height direction reduction of 45%. The results show that there are different deformation behaviors at high and low strain rates. At low strain rates (0.001−0.1 s −1 ), there are obvious work hardening behaviors in flow stress curves. At the high strain rate of 10 s −1 , the alloy presents obvious hardening firstly, then saturated state and further softening caused by temperature rise finally. At 673 K, the alloy significantly exhibits the stain rate negative sensitivity because of the phase change. Based on the model in which the whole stress—strain curve is divided into the strain hardening part and the saturated state part and the modified Voce model, constitutive models were developed to describe the flow behaviors of Ti2448 alloy at high and low strain rates, respectively. The stress—strain curves predicted by the developed model well fit with the experimental results, which confirms that the developed model can predict the flow stress of Ti2448 alloy validly and the modified Voce model can describe the strain hardening behavior of both the saturated state and the unsaturated state.

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