考虑不连续屈服的钛合金高温变形本构模型

以发生不连续屈服的钛合金高温变形流动曲线特性为基础,讨论各阶段的变形机制。利用位错增殖动态理论和统一粘塑性理论,构建反映变形温度和应变速率影响且能描述不连续屈服、下屈服点后存在轻微应变硬化、动态再结晶等变形特性的高温粘塑性本构模型。将所建模型应用于新型亚稳β钛合金Ti2448发生明显不连续屈服的高温变形,并用改进的遗传算法确定模型中的相关材料参数。预测值与实验值误差在5%以内,表明这种基于内变量构建的本构模型不仅物理意义清晰,能够有效描述发生不连续屈服的钛合金高温变形,而且具有较强的外推能力,能为其它钛合金的本构模型构建提供参考。

Constitutive Model of Titanium Alloy during Hot Deformation Considering Discontinuous Yielding Behavior

The deformation mechanism of titanium alloy at every stage during hot deformation was discussed, based on the characteristics of flow stress curves with discontinuous yielding. A viscoplastic constitutive model was built on the premise that the discontinuous yielding phenomenon was associated with the rapid dislocation multiplication at an early stage of yielding and the unified viscoplastic theory. In this model, the effect of deformation temperature and strain rate was considered. This model can describe the discontinuous yielding phenomenon, the slight degree of strain hardening after the low yield point and the mechanism of dynamic recrystallization when the strain achieved to the critical value where the dynamic recrystallization takes place. Applying the constitutive model to the isothermal compression of one new kind of metastable beta Ti2448 titanium alloy, the material constants in the model were identified by the GA-based global optimization method which was adopted in this paper. The relative difference between the predicted and experimental values is less than 5%, which implies that this constitutive model with high prediction based on the internal state variables can not only offer clear physical insight, but also can describe the flow behaviors of Ti2448 titanium alloy during hot deformation with discontinuous yielding. The generality of this model makes it possible to extend the theory to other titanium alloys that have discontinuous yielding phenomenon