Effect of Microstructure on Hydrogen Embrittlement and Mechanical Properties of NiTi Biomaterials

Abstract

In this study, the effect of grain size on the mechanical properties and hydrogen embrittlement of a NiTi shape memory alloy (SMA) was investigated. Samples with different grain sizes were prepared through different annealing processes. For creating and evaluating hydrogen embrittlement, samples were immersed in an aqueous solution of 2% acidulated phosphate fluoride (APF) for 8, 16, and 72 h. Optical microscopy (OM), scanning electron microscopy (SEM), tensile test, and three-point bending test were conducted to characterize the samples. Results demonstrated samples with large grain sizes to be more susceptible to hydrogen embrittlement. Improvement in shape memory properties was achieved at smaller grain sizes. Besides, with increasing the immersion time, fracture stress reduced, while detwinning stress increased. Overall, the results of this study have demonstrated that grain refinement can bring about improved mechanical properties and abated hydrogen embrittlement in NiTi alloys, which can be of vital importance in biomedical applications.