TC4-DT钛合金线性摩擦焊接头组织特征及其形成机制

研究TC4-DT损伤容限型钛合金线性摩擦焊(linear friction welding,LFW)接头的组织特征及形成机制。利用光镜和扫描电镜对接头各区域微观组织进行表征,利用显微硬度计测试接头的显微硬度分布。结果表明:接头焊缝区(WZ)发生动态再结晶,焊接过程中WZ温度超过β转变点,焊后快冷的条件下发生了β→α′及β→α两种相变并析出了大量α′马氏体以及二次层片α;TC4-DT钛合金母材(BM)组织具有较高的变形抗力,使得接头形成的热力影响区(TMAZ)较窄。TMAZ内组织在强烈的热力耦合作用下拉长变形并破碎,焊后快冷的条件下析出少量α′马氏体及大量二次层片α;毗邻TMAZ的热影响区(HAZ)基本保留了BM不同位向的α集束的组织特征,但受热的影响α集束内α/β相界两侧元素相互扩散,层间β消耗,初生α长大;WZ组织的细晶强化和第二相强化,TMAZ组织的应变强化和第二相强化,以及HAZ内α相的长大使得接头上述区域显微硬度均高于BM。

Microstructure characteristics and formation mechanism of linear friction welded TC4-DT titanium alloy joint

The microstructure characteristics and formation mechanism of linear friction welded(LFW)TC4-DT damage-tolerant titanium alloy joint were investigated.The microstructure of each zone of the joint was analyzed in detail by using an optical microscopy and a scanning electron microscopy;the microhardness distribution of the joint was tested by means of a microhardness tester.The results show that dynamic recrystallization occurs in weld zone(WZ);the WZ temperature exceeds theβ-transus temperature during welding,and bothβ→α′andβ→αphase transformation occur in WZ under rapid cooling after welding,resulting in a large number ofα′martensite and secondary lamellarαare formed.Due to the high deformation resistance of TC4-DT titanium alloy,the thermo-mechanically affected zone(TMAZ)of this joint is relatively narrow.The structure of the TMAZ is elongated,deformed and broken seriously under the strong thermo-mechanically coupling effect.Moreover,a fewα′martensite and a large number of secondary lamellarαare formed in TMAZ under the condition of rapid cooling after welding.The microstructure characteristics ofαcolony with different orientation of the base metal(BM)is basically preserved in the heat affected zone(HAZ).However,due to the influence of heat,the mutual diffusion of elements occurs at theα/βphase boundary inαcolony,the interlayerβis consumed,and the primaryαgrows up.The refined crystalline strengthening and second phase strengthening of the WZ microstructure,the strain strengthening and second phase strengthening of the TMAZ microstructure,and the growth ofαphase in the HAZ make the microhardness of above zones higher than that of the BM.