(1. 燕山大学 机械工程学院，秦皇岛 066004；
2. 中国第二重型机械集团 德阳万航模锻有限责任公司，德阳 618000)
摘 要: 在TA15钛合金模锻件应以模糊晶为主的低倍组织中发现了局部粗大的清晰晶。利用金相拼接和逐点统计方法，结合微拉伸、SEM等手段，分析对比了粗大清晰晶区、模糊晶区的显微组织与力学性能，着重探讨了局部粗晶的形成机制。结果表明：各晶区内显微组织均呈典型双态组织，显示了两相区变形的基本特征。与模糊晶区相比，粗大清晰晶区内初生等轴α相(αp)含量略低，且存在粗大片层组织；存有大量的粗大原始β晶粒(连续的晶界α相包围的晶粒)，平均尺寸可达124 μm，是模糊晶区平均尺寸(32 μm)的近4倍。这些异常粗大的β晶粒是导致低倍粗晶的最主要因素，同时也是导致合金的强度和塑性均下降的主要原因之一。热物理模拟结果表明，双相区变形后出现的粗大清晰晶对应变速率敏感。慢速率变形会增大形成低倍粗晶的倾向，这主要与变形过程中动态αp→β相变有关。对于模锻件而言，局部粗大清晰晶区火次应变小使其较模糊晶区应变速率慢，再经多火次小应变(慢速率)累积导致了β晶粒明显粗化。
关键字: 钛合金；低倍组织；清晰晶；模糊晶；原始β晶粒
（1. School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China;
2. Deyang Wanhang Die Forging Co., Ltd., China National Erzhong Group, Deyang 618000, China）
Abstract:A local coarse-grained macrostructure which was identified as the clear structure, was found in the TA15 titanium alloy die forging. Usually, the macrostructure of TA15 titanium alloy forging was required to display a fuzzy structure with fine microstructures. The microstructure and mechanical properties in the coarse-grained areas were investigated by means of optical microscope (OM), scanning electron microscope (SEM) as well as micro-tension tests. The formation mechanism for the local coarse-grained macrostructure was discussed. The results show that the microstructures in various areas of forging display a duplex microstructure of titanium alloy which typically shows the microstructural characteristics of titanium alloy during hot deformation in the (α+β) region. Compared with the fuzzy structure area, the fraction of primary equiaxed α (αP) in the clear structure area is slightly lower, and a coarse lamellar microstructure is found. Especially, a large number of coarse original β grains which are surrounded by α phase on grain boundaries are found in the clear structure area, and their average grain size reaches 124 μm, which is nearly 4 times of that (32 μm) in the fuzzy structure area. The abnormal coarse β grains are considered to be a critical factor for the formation of local coarse-grained macrostructure, and meanwhile, they can cause a decrease in strength and plasticity. Furthermore, the results of thermal-mechanical tests show that the coarse-grained macrostructure is sensitive to the strain rate. Lower strain rate causes an increase in the probability of such coarse-grained macrostructure. This is mainly related to the occurrence of αp→β dynamic transformation during deformation. For the forging with the clear structure, the lower strain rate in each forging step, which is caused by the small strain within the same deformation time as compared to the fuzzy structure area, as well as the further cumulative effect of small strain in subsequent forging steps results in a significant coarsen of original β grains.
Key words: titanium alloy; macrostructure; clear structure area; fuzzy structure area; original β grain
