Coupled Diffusion-Mechanical Model of NiTi Alloys Accounting for Hydrogen Diffusion and Ageing

Abstract

Certain shape memory alloys (SMAs) are considered to be good absorbents of hydrogen atoms (e.g., NiTi). However, upon the absorption of hydrogen atoms, SMAs exhibit deteriorated effects of superelasticity and shape memory mechanisms. In this paper, we have developed a coupled model, based on experimental results, that demonstrates the effects of hydrogen diffusion on NiTi SMAs. The proposed model has been derived thermodynamically while appending the chemical potential of hydrogen to the energy balance law. The effects of hydrogen distribution on the mechanical behavior have been taken into consideration to simulate the ageing effects. Moreover, the model considers the saturation of transformation stress, the preservation of the transformation strain of the hydrogen-induced residual martensite and the recovery of superelasticity after hydrogen desorption. The model has been simulated by means of UMAT and UMATHT subroutines and ABAQUS finite-element software. The numerical results indicate a strong agreement with the experimental ones.