Research progress in experimental and theoretical studies on mechanical behavior of superelastic nickel-titanium shape memory alloy in hydrogen-rich environments

Nickel-titanium shape memory alloy (NiTi-SMA) is a representative smart material with widespread applications in aerospace, rail transportation, civil engineering, biomedical engineering, solid-state refrigeration, and other fields. However, with expanding applications, NiTi-SMA devices are increasingly exposed to extreme service environments, particularly hydrogen-rich environments. Consequently, designing and assessing the reliability of NiTi-SMA devices operating in hydrogen-rich environments has become a pressing engineering challenge. Furthermore, the deformation behavior of superelastic NiTi-SMA in such environments is complex, involving multiple inelastic deformation mechanisms, significant nonlinearity, and diffusional-mechanically coupled effects, posing significant challenges for developing corresponding theoretical models. This represents a frontier issue in solid mechanics. Accordingly, this study reviews recent advances in understanding the mechanical behavior of superelastic NiTi-SMA in hydrogen-rich environments, covering both experimental and theoretical aspects. First, it summarizes experimental findings on deformation characteristics, including single-cycle and cyclic responses, tensile fracture, and fatigue failure, and discusses the microscopic mechanisms underlying hydrogen’s influence on NiTi-SMA’s mechanical behavior. Second, it reviews existing constitutive models, encompassing both macroscopic phenomenological approaches and micromechanical models based on crystal plasticity. Representative models and their predictive capabilities are briefly introduced. Finally, this study proposes directions for future research to further advance understanding and modeling in this field.