The functional devices made by NiTi shape memory alloys (SMAs) are often serviced in hydrogen (H)-rich environment. Recently experimental results showed that the martensite transformation (MT) of NiTi SMA changed strongly after charging H, which originates from the H diffusion in the material and an additional transformation resistance caused by the absorbed H atoms. In this work, a multi-scale diffusional-mechanically coupled constitutive model is constructed to describe the super-elastic deformation of NiTi SMA wires in H-rich environment. In the grain scale, a crystal plasticity-based constitutive model is developed within the framework of irreversible thermodynamics. Four deformation mechanisms, i.e., elasticity, MT, transformation-induced plasticity (TRIP) and H expansion are taken into account. Since the H atoms can be trapped by the lattice defects, the total H concentration is further decomposed into two parts, i.e., the lattice hydrogen concentration and the trapped one. The generalized thermodynamic forces of MT and TRIP are derived from the Gibbs free energy and Clausius-Duhem inequality. The evolution of H concentration field is derived by combining the chemical potential, diffusion balance equation and the Fick's law. In the polycrystalline aggregate scale, in order to measure the interaction among the grains and obtain the overall response of the polycrystalline aggregate, a diffusional-mechanically coupled self-consistent homogenization method is developed. Meanwhile, the finite volume method is employed to calculate the H concentration in each grain. An assumption of uniform stress field in the macroscopic scale is adopted to achieve the scale transition from the polycrystalline aggregate to the whole wire. To validate the prediction capability of the proposed model, the predictions are compared with the experiments. Moreover, the influences of loading rate on the deformation of the wires in the process of in-situ charging H are predicted and discussed.

由 NiTi 形状记忆合金 (SMA) 制成的功能设备通常在富含氢 (H) 的环境中使用。最近的实验结果表明，充氢后 NiTi SMA 的马氏体相变 (MT) 发生强烈变化，这源于材料中的氢扩散和吸收的氢原子引起的额外相变阻力。在这项工作中，构建了一个多尺度扩散-机械耦合本构模型来描述 NiTi SMA 线在富氢环境中的超弹性变形。在晶粒尺度上，在不可逆热力学的框架内开发了基于晶体塑性的本构模型。考虑了四种变形机制，即弹性、MT、相变诱导塑性（TRIP）和 H 膨胀。由于H原子可以被晶格缺陷捕获，因此总H浓度进一步分解为两部分，即晶格氢浓度和被捕获的氢浓度。MT 和 TRIP 的广义热力学力源自吉布斯自由能和克劳修斯-迪昂不等式。H浓度场的演化是结合化学势、扩散平衡方程和菲克定律得出的。在多晶聚集体尺度上，为了测量晶粒之间的相互作用并获得多晶聚集体的整体响应，开发了一种扩散-机械耦合自洽均匀化方法。同时，采用有限体积法计算每个晶粒中的H浓度。采用宏观尺度均匀应力场假设，实现从多晶聚集体到整线的尺度转变。为了验证所提出模型的预测能力，将预测与实验进行了比较。此外，加载速率对钢丝在加工过程中变形的影响预测和讨论了原位充电 H。