置氢钛合金搅拌摩擦焊片层组织的超塑性行为及氢的作用机制

超塑成形（SPF）与搅拌摩擦焊（FSW）技术组合用于生产钛合金整体构件具有广阔应用前景，然而在钛合金FSW过程中易发生工具磨损，且焊核很难得到与母材相近的超塑变形能力，制约了接头整体成型。置氢可减轻工具磨损，大范围调节钛合金超塑变形能力，是实现钛合金FSW接头均匀成型的理想选择。本项目拟采用FSW对置氢（不同含量）TC4合金进行焊接，得到片层组织焊核。采用TEM和EBSD获得不同FSW参数下片层组织中氢化物含量及分布和马氏体界面关系信息；通过拉伸实验获得焊核超塑性性能；对超塑变形样品进行微观组织分析，获得氢含量、马氏体界面关系、氢化物含量及分布、相变与超塑性性能及片层组织球化的关系。通过这些研究，揭示置氢钛合金片层组织超塑性变形机制及氢诱导片层组织球化的微观机制及影响因素，建立从置氢钛合金片层组织获得良好超塑性的途径，实现FSW片层组织的可控制备，为钛合金整体构件的FSW/SPF提供参考。

The combination of superplastic forming (SPF) and friction stir welding (FSW) has great application prospects in producing integrated components of titanium alloys. However, tool wear easily takes place during FSW of Ti alloys, which limits the developing of FSW of Ti alloys. Besides, it is difficult to obtain the similar superplastic deformation ability of the nugget with the base material (BM), which hinders the uniform SPF of the entire FSW joints. Hydrogen is the temporary element in Ti alloys, which can adjust the superplastic deformation ability of the nugget to obtain the similar superplastic deformation ability with the BM. Therefore, the SPF of FSW joints of hydrogenated Ti alloys is a sound method of producing integrated components of titanium alloys. However, there is no report on superplastic behavior of the lamellar microstructure of FSW titanium alloy joints. In this study, Ti-6Al-4V (TC4) will be hydrogenated with different contents of hydrogen, and then be welded by FSW, obtaining a lamellar microstructure in the weld nugget. The detailed information of hydride contents, distributions and martensite boundaries at different FSW parameters will be obtained by TEM and EBSD techniques. The superplastic behavior of the weld nugget will be studied by the tensile test. By microstructural analysis on the deformed specimens, the relationship between hydrogen contents, hydride contents, misorientation, martensite boundaries, phase transformation, and spheroidization will be built. Through these detailed studies, the mechanism and influential factors of superplastic deformation and spheroidization of the lamellar microstructure with hydrogenation will be clarified. Further, a more effective way to control the lamellar microstructure with hydrogenation by controlling FSW parameters and improve their superplasticity will be proposed. All these investigations will provide guidance for the FSW/SPF process in producing integrated components of titanium alloys.