TC21细晶钛合金TIG焊接接头组织及力学性能研究

开展了不同晶粒尺寸的细晶粒TC21钛合金的TIG焊接实验，研究了母材及接头组织和力学性能。结果表明：细晶粒TC21钛合金TIG焊接接头抗拉强度达到母材的95％左右，焊接性较好；但是焊接接头脆化严重，伸长率和断面收缩率均较低。焊缝中心和热影响区组织相似，为α’马氏体组织。相同焊接规范下，21μm的细晶TC21合金焊缝及热影响区为片状或长粒状α’组织；而7μm的细晶TC21合金接头中α’丛的尺寸较小且相互交错，形成针状或短粒状α’组织。硬度测试表明：靠近母材的热影响区细晶区存在一个软化区，该区域硬度最低，而焊缝中心与热影响区粗晶区分界处（细晶过渡区（FTZ））也存在硬度的下降，不过此区域下降幅度不大。常温拉伸断口呈准解理断裂特征，随着母材晶粒度的增大，焊接接头解理特征越明显。

Study on Microstructure and Mechanical Properties of Fine Grain TC21 Alloy in TIG

Fine grain TC21 alloy with various grain sizes were welded by conventional TIG welding. The mechanical properties of welded joint were investigated. The results showed that the tensile strength of welded joint of fine grain TC21 with various grain sizes was about 95% one of the base metal, the weldability of TC21 alloy was good by and large. But welded joint was seriously brittle, the specific elongation and reduction of cross section area of welded joint were more lower than that of the base metal. The microstructure of fusion zone (FZ)and heat-affected zone(HAZ) were similar ,which were called α′ martensites. With the same parameters, the microstructure of FZ and (HAZ) of 2μm TC21 alloy were lamellar or long granular α′ structures, whereas the microstructure of welded joint of 7μm TC21 alloy was needle or small granular α′ structure, which α′ clusters was small and crossed. Hardness measurements showed there was a softened zone in fine grain heat-affected zone(FHAZ) near the base metal, the hardness of softened zone was the lowest. However, the boundaries between FZ and coarse grain heat-affected zone(CHAZ) of welded joint was another softened zone, but hardness decreased slightly in this zone. Tensile fractures of welded joint presented character of quasi-cleavage crack. Cleavage features of fractography of weld joint were more obvious with increasing grain size of the base metal.