Effect of pH values on the hydrogen damage behavior of TC4 Ti alloy

Purpose Ti, as a hydrogen-sensitive material, exhibits different degrees of hydrogen damage risk when used in the environment with different H + content. This paper aims to clarify the effect of pH values of NaCl solution on the hydrogen damage of Ti alloys. Design/methodology/approach The hydrogen damage behavior of TC4 alloy in 3.5 Wt.% NaCl solutions with different pH values were compared by cathodic hydrogen charging treatment. The morphologies were observed by Scanning Electron Microscope (SEM), and the distributions of H and O were detected by Glow Discharge Optical Emission Spectroscopy (GDOES). Findings The results show that in the acidic solution (pH = 1), the passive film on TC4 alloy is prone to dissolution, and the sample surface suffers severe corrosion instead of hydrogen-induced cracking in Ti substrate. In contrast, TC4 alloy is covered with dense surface films in neutral (pH = 7) or alkaline (pH = 12) solutions, while more hydrogen penetrates into the TC4 substrate to accelerate hydrogen-induced cracking. In a word, acidic solutions primarily accelerate the damage of passive film on TC4 alloy surface, whereas alkaline solutions mainly accelerate hydrogen-induced cracking in Ti substrate. Originality/value This investigation can provide a theoretical basis for the safe service of Ti alloys in seawater with varying pH values.