(1. 燕山大學(xué) 機(jī)械工程學(xué)院，秦皇島 066004；
2. 中國(guó)第二重型機(jī)械集團(tuán) 德陽(yáng)萬(wàn)航模鍛有限責(zé)任公司，德陽(yáng) 618000)
摘 要: 在TA15鈦合金模鍛件應(yīng)以模糊晶為主的低倍組織中發(fā)現(xiàn)了局部粗大的清晰晶。利用金相拼接和逐點(diǎn)統(tǒng)計(jì)方法，結(jié)合微拉伸、SEM等手段，分析對(duì)比了粗大清晰晶區(qū)、模糊晶區(qū)的顯微組織與力學(xué)性能，著重探討了局部粗晶的形成機(jī)制。結(jié)果表明：各晶區(qū)內(nèi)顯微組織均呈典型雙態(tài)組織，顯示了兩相區(qū)變形的基本特征。與模糊晶區(qū)相比，粗大清晰晶區(qū)內(nèi)初生等軸α相(αp)含量略低，且存在粗大片層組織；存有大量的粗大原始β晶粒(連續(xù)的晶界α相包圍的晶粒)，平均尺寸可達(dá)124 μm，是模糊晶區(qū)平均尺寸(32 μm)的近4倍。這些異常粗大的β晶粒是導(dǎo)致低倍粗晶的最主要因素，同時(shí)也是導(dǎo)致合金的強(qiáng)度和塑性均下降的主要原因之一。熱物理模擬結(jié)果表明，雙相區(qū)變形后出現(xiàn)的粗大清晰晶對(duì)應(yīng)變速率敏感。慢速率變形會(huì)增大形成低倍粗晶的傾向，這主要與變形過(guò)程中動(dòng)態(tài)αp→β相變有關(guān)。對(duì)于模鍛件而言，局部粗大清晰晶區(qū)火次應(yīng)變小使其較模糊晶區(qū)應(yīng)變速率慢，再經(jīng)多火次小應(yīng)變(慢速率)累積導(dǎo)致了β晶粒明顯粗化。
關(guān)鍵字: 鈦合金；低倍組織；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
