钛合金焊缝组织循环热处理及球化过程分析

Cyclic Heat Treatment and Spheroidizing Mechanism of Titanium Alloy Welding Microstructure

针对钛合金焊缝组织不均匀、脆性大、塑性差等问题,提出一种针对焊接接头的新型热处理工艺:α+β与α两相区循环热处理,讨论了不同热处理工艺对组织形貌的影响,得到由具有一定比例的等轴α相、条状α相及β转变相组织,提高循环次数球化的α相增多,长径比明显减小,有明显的球状的α相,其长径比普遍小于3,除此之外在球化的α相周围分布着取向各有不同的细小条状α相。经过4次循环热处理的焊接接头拉伸得到强塑积达到14441.17MPa·%,焊接接头的塑性有所提高。结合EBSD、TEM等测试结果的分析,解释了该现象产生的原因,解释针状α相的断裂及条状α相的长大,在热处理过程中位错、孪晶的移动形成的亚晶界及β相的分解促进了热蚀坑的形成过程。该方法可以有效地将焊接组织均匀化,缓解焊接组织的应力集中,在未来航空航天领域有很重要的应用价值。

Considering the issues of coarse microstructure and awful mirco-orientation distribution of TC4 titanium alloy welded-joint with high friability and low plasticity,α post welding cyclic heat treatment between α+β and β-transus temperature were designed,and the effect of different heat treatment processes on the tissue morphology was discussed.The tri-modal microstructure of equiaxial α phase, lamellar a and transformed β phase was obtained.Results show that when the cyclic times increase,more spheroidized a phases appear, and the length to diameter ratio decreases significantly,which is generally less than 3.In addition,there are different kinds of small bars of α phase around spheroidized a phase.After four times cyclic heat treatment,the product of strength and elongation of the welded joint achieves 14441.17 MPa·%and the plasticity of the joint increases.The phenomenon is explained by analyses of EBSD and TEM.Besides, the fracture of needle-like a phase and growth of a phase in bar are also explained.In the process of heat treatment,the sub-boundary caused by the movement of dislocation and twins and decomposition of β phase promote the formation of thermal etching pits.In conclusion,the designed heat treatment can homogenize the welding microstructure and relieve the stress concentration,which is of great practical value in aerospace field.