Influence of hydrogen on microstructure and mechanical properties of TC4ELI titanium alloy welded joints

TC4ELI titanium alloy has a great application prospect in hydrogen fuel engine, but there is a risk of hydrogen damage in the welded structure of hydrogen-related components. The tensile, fatigue and nanoindentation test pieces of welded TC4ELI with 0.2% hydrogen were obtained by electron beam welding and high temperature gas charging of hydrogen. Combined with X-ray diffraction, secondary ion mass spectrometry and other microscopic characterization methods, mechanical tests such as nanoindentation and low-cycle fatigue tests were carried out to deeply investigate the influence of hydrogen on the microstructure and mechanical properties of TC4ELI welded joints. The results show that hydrogen charging can promote the transformation of α phase into β phase and precipitate δ hydride in each zone of TC4ELI welded joints. More hydride precipitated in the weld metal, and the corresponding elastic modulus and hardness decreased the most, resulting in uniform microstructure and properties of welded joints. The elastic modulus and fracture strain of TC4ELI welded joints decreased significantly after hydrogen charging, and the fracture mode changed from transgranular dimple fracture to intergranular brittle fracture due to the influence of hydride. The low-cycle fatigue life of hydrogen-charged TC4ELI is significantly reduced due to stress-induced hydride cracking at low stress level; however, at high stress level, due to hydrogen-induced local plasticity, it exhibits better fatigue resistance.