Procedure Qualification of TC4ELI Titanium Alloy with Horizontal Electron Beam Welding for Submersible Hull

The horizontal electron beam welding (EBW) was used on TC4ELI alloy with 60 mm thickness, and the welding procedures and the properties of the joints involved in the manufacturing of the submersible hull were investigated. The weld had α′ martensite microstructure, which was uniform along the welding penetration, and the microhardness of the weld was 322–356 HV0.2. The tensile strength of the joint was 915 MPa, equivalent to that of the base metals, and the percentage elongation after fracture was more than 12%. The impact absorption energies of both the weld and heat-affected zone specimens were above 30 J, and the bending angle of the joint reached 180°. The effects of the microstructure and macromorphology on the mechanical properties of the joints are discussed. The properties proved the reliability of EBW for the manned submersible hull, which would contribute to developing the manned submersibles. 1. Introduction The manned submersible is a deep-sea detector, and the hull of the manned submersible is one of the significant parts that needed the excellent performance to protect the engineers and apparatus. Welding is essential for manufacturing the manned submersible hull. The GTA welding procedure of 10Ni–8Co steel was studied for the manned submersible hulls, and the effects of the procedure on the joints properties were investigated (Takeda et al. 1981). The welding procedure, electron beam welding (EBW), was also applied on 10Ni–8Co steel and Ti6Al4V ELI alloy for the hull of the submersible SHINKAI 2000 in Japan, which can operate up to a depth of 2000 m (Endo et al. 1981a, 1981b, 1985). The collapse behavior of the hull was studied by using three models (Yokota et al. 1985). The fabrication procedures using EBW were studied on the material tested for the hull of SHINKAI 6500 (Takagawa et al. 1990). EBW was suitable to manufacture the hulls of the manned submersibles with several inches thick titanium alloys or high-strength steels, owing to many advantages (Zhao & Liu 2014; Tsai & Wang 2014; Huang et al. 2012; Sabol et al. 2014; Yang et al. 2014; Kaur et al. 2015; Brown et al. 2011; Fu, et al. 2014a, 2014b). But in these studies, the procedures of EBW were not explicitly investigated, and the microstructure and the properties of the joints along the welding penetration were also not discussed. The TC4ELI alloy (Ti6Al4V ELI) was also used to make the hulls of the manned submersible in China. Herein, the procedure and properties of EBW using horizontal gun were studied, and the feasibility of manufacturing the hull by EBW was evaluated.