Research progress of hydrogen effect in NiTi shape memory alloys

NiTi shape memory alloys are commonly subjected to mechanical stress and chemical corrosion challenges when used in orthodontic arch wires, cardiovascular stents, and fluid valve actuators. This exposure leads to hydrogen embrittlement to a certain degree, consequently affecting the reliability and safety of NiTi components.Focusing on the hydrogen effect in NiTi alloys, the location of hydrogen atoms, various states and diffusion behavior were reviewed in this paper. Methods to characterize hydrogen content, states, distributions and diffusivity were also summarized. The effects of hydrogen on the martensitic transformation and damping behavior of NiTi shape memory alloys were also introduced. Furthermore, hydrogen embrittlement behavior, influencing factors and mechanisms in NiTi alloys were discussed in this paper. Strategies to prevent or delay the hydrogen effect on NiTi shape memory alloys were also summarized. Finally, research directions, including diffusion behavior in each phase of NiTi alloys, visual characterization methods of hydrogen distribution, and hydrogen-martensitic transformation interaction were proposed in this paper, aiming to provide valuable insights and reference points for researchers studying NiTi shape memory alloys.