摘要
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, a 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 α and transformed β phase was obtained. Results show that when the cyclic times increase, more spheroidized α 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 α 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 α phase and growth of α 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.
引文
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