Ti-22Al-24Nb合金热成形工艺参数优化研究

Optimization of Hot Forming Parameters for Ti-22Al-24Nb Alloy

采用Gleeble-3500热模拟试验机研究Ti-22Al-24Nb合金在温度900～1110℃和应变速率0.01～10 s^(-1)条件下的热变形行为。分析了该合金的高温流变应力曲线特性和不同相区的热变形激活能及变形机制,并根据基于Prasad和Murty失稳判据下的加工图及相应的组织特征优化了该合金的热成形工艺参数。结果表明,Ti-22Al-24Nb合金的流变应力对热成形工艺参数敏感;其在(α_2+B2)两相区的主要变形机制为晶界滑移,对应的变形激活能为603.56 kJ/mol,而B2单相区的变形激活能为406.25kJ/mol,其变形主要以动态回复和动态再结晶的变形机制为主。根据这两种加工图的比较和组织观察可知,Ti-22Al-24Nb合金选择基于Prasad失稳判据下的加工图更为合理;其对应的主要失稳区为900～990℃、0.2～10 s^(-1)和1035～1095℃、1～10 s^(-1),且失稳区所预测的组织中主要存在绝热剪切带和局部流变失稳现象;而动态再结晶及胞状亚结构的组织易出现在η峰区,表明该合金较优的热力参数区间是990～1035℃、0.01～0.03 s^(-1),1040～1090℃、0.02～1 s^(-1)和1090～1110℃、0.01～0.18 s^(-1)。

Hot deformation behavior of Ti-22Al-24Nb alloy was investigated in the temperature range of 900～1110 ℃ and strain rate range of 0.01～10 s^-1 by Gleeble-3500 thermo-mechanical simulator.Characteristics of flow stress curve at elevated temperature,hot deformation activation energy in different phase regions and deformation mechanisms were analyzed,and hot forming parameters of the alloy were optimized by processing maps under instability criterion of Prasad and Murty and corresponding structural characteristics.The results show that the flow stress of the alloy is sensitive to the hot forming parameters.The main deformation mechanism in the（α2＋B2） two-phase region is grain boundary sliding,the corresponding activation energy is 603.56 kJ/mol,and the deformation activation energy of the B2 single-phase region is 406.25 kJ/mol,whose main deformation mechanism is dynamic recovery and dynamic recrystallization.According to the comparison of two kinds of processing maps and the microstructure observation,the processing map of the alloy based on the Prasad instability criterion is more reasonable.The corresponding main instability zones are 900～990 ℃,0.2～10 s^-1 and 1035～1095 ℃,1～10 s^-1,and the adiabatic shear bands and the local plastic instability in the microstructure are predicted by the instability zones.However,the dynamic recrystallization and the microstructure of the cellular substructure are easy to appear in the η peak regions,indicating that the better thermodynamic parameter ranges are 990～1035 ℃ together with 0.01～0.03 s^-1,1040～1090 ℃ together with 0.02～1 s^-1 and 1090～1110 ℃ together with 0.01～0.18 s^-1.