基于M-K理论的NbTiAl合金高温成形极限曲线预测

Prediction of High Temperature Forming Limit Curve of NbTiAl Alloy Based on M-K Theory

目的NbTiAl合金在常温下的塑性较差,针对300℃时NbTiAl合金的成形性能进行研究,探究其在高温环境下的力学性能和成形极限,分析理论预测成形极限的可行性,为进一步研究铌合金性能和扩展其工程应用提供理论参考。方法采用高温单拉和高温成形极限试验,获得了NbTiAl板材在300℃的应力应变曲线及成形极限曲线,使用Swift硬化模型针对塑性变形段进行拟合,并采用M-K失稳理论,结合相应的材料本构模型,对NbTiAl合金在高温环境下的成形极限进行了理论预测,并与实验数据进行了对比。结果NbTiAl合金在300℃时的塑性应变阶段仍然具有加工硬化效应,在初始厚度不均度f_(0)为0.998时,得到的理论曲线与试验点在左侧拉-压区符合得较好,但对右侧拉-拉区的理论预测与试验结果相差较大。结论NbTiAl合金在300℃时具有较好的成形性,采用合适的不均匀度系数,利用M-K理论可以较好地预测NbTiAl合金高温成形极限曲线左侧拉-压区的极限应变,但对右侧拉-拉区域极限应变的预测结果误差较大。

The work aims to study the formability of NbTiA alloy at 300℃aiming at the poor plasticity of NbTiAl alloy at room temperature,so as to explore its mechanical properties and forming limit at high temperature,analyze the feasibility of theoretical prediction of forming limit,and provide theoretical reference for further research on the properties of niobium alloy and expansion of its engineering application.The stress-strain curve and forming limit curve of NbTiAl sheet at 300℃were obtained by high temperature single tension test and high temperature forming limit test.The plastic deformation section was fitted by Swift hardening model.The forming limit of NbTiAl alloy at high temperature was theoretically predicted by M-K instability theory and corresponding material constitutive model,and was compared with the test data.NbTiAl alloy still had work hardening effect in the plastic strain stage at 300℃.The theoretical curve obtained at the initial thickness non-uniformity f_(0)=0.998 was in good agreement with the test point in the left tension-compression zone,but the theoretical prediction results of the tension-tension zone were quite different from the test results.The NbTiAl alloy has good formability at 300℃,and the appropriate non-uniformity coefficient combined with M-K theory can predict the limit strain of NbTiAl alloy in the left tension-compression zone of the high temperature forming limit curve,but the prediction error of the limit strain in the right tension-tension zone is large.