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采用恒应变速率和应变速率递增实验研究了变形态Ti-48Al-2.3Cr-0.2Mo(at%)合金的超塑性变形力学行为,并根据计算得到的变形激活能,结合超塑性变形的流变曲线形态,对TiAl基合金的超塑性变形机理进行了分析。超塑性拉伸试验分别在800~900℃区间和950~1100℃区间和应变速率ε=1×10-35×10-5 s-1的条件下进行。结果表明,变形态TiAl基合金超塑性变形的应变-应力曲线上几乎没有稳态塑性流变阶段。在950~1100℃区间,加工硬化现象显著。当T>1025℃或ε≤5×10-4 s-1时,应力-应变曲线呈典型的加工硬化形态,并且随着变形温度升高和应变速率降低,加工硬化阶段增长。原始组织中的高密度位错是引起加工硬化的原因。在800~900℃区间,应变速率敏感性因子m的最佳值在0.52~0.67之间,超塑性变形的表观激活能为Qapp=178 kJ/mol,晶界扩散是超塑性的速率控制机制。在950~1100℃区间,m的最佳值在0.63~0.77之间,超塑性变形的表观激活能值Qapp=290 kJ/mol,晶格扩散是超塑性变形的速率控制机制。
The superplastic deformation behavior of Ti-48Al-2.3Cr-0.2Mo (at%) alloy was studied by constant strain rate and strain rate increment. Based on the calculated deformation activation energy and the rheology of superplastic deformation Curve morphology, superplastic deformation mechanism of TiAl-based alloys were analyzed. The superplastic tensile tests were carried out in the temperature range of 800-900 ℃ and 950-1100 ℃ and the strain rate of ε = 1 × 10-35 × 10-5 s-1, respectively. The results show that there is almost no steady-state plastic rheological stage in the strain-stress curve of the superplastic deformation of the deformed TiAl-based alloy. In the 950 ~ 1100 ℃ range, work-hardening phenomenon is significant. When T> 1025 ℃ or ε≤5 × 10-4 s-1, the stress-strain curve is a typical work-hardening morphology, and the work-hardening phase increases as the deformation temperature increases and the strain rate decreases. The high density of dislocations in the original tissue is the cause of work hardening. The optimum value of strain rate sensitivity factor m is 0.52 ~ 0.67 at 800 ~ 900 ℃, and the apparent activation energy of superplastic deformation is Qapp = 178 kJ / mol. The grain boundary diffusion is the superplasticity rate control mechanism . In the range of 950 ~ 1100 ℃, the optimum value of m is between 0.63 and 0.77, and the apparent activation energy Qapp of superplastic deformation is 290 kJ / mol. Lattice diffusion is the rate control mechanism of superplastic deformation.