Hydrogen embrittlement behavior of Ni-Ti shape memory alloy with different microstructures in acidic fluoride solution

Abstract

Background: It is important to investigate the mechanism for the hydrogen embrittlement of Ni-Ti alloys in acidic fluoride solutions to improve the reliability and safety of these alloys as dental devices. Therefore, the hydrogen embrittlement behavior of Ni-Ti shape memory alloy immersed in acidic fluoride solution was investigated with a focus on the constituent phase in the microstructure of the alloy in this study. Methods: Three microstructures with different phases (parent single phase, mixture of parent and martensite phases, and martensite single phase) were prepared by tensile loading and unloading. The specimens were immersed separately in 50 mL of 0.2 % acidulated phosphate fluoride (APF) solution with pH 5.0 at room temperature (25°C) for various periods. Results: After immersion for 2 h, the tensile strengths of all the specimens were not significantly changed with respect to those of the non-immersed specimens. After immersion for 4 h, the tensile strengths of all the specimens immersed were decreased with respect to those of the non-immersed specimens, and the tensile strength of the martensite single phase specimen (C) was higher than that of parent single phase specimen (A) and the parent/martensite mixed phase specimen (B). After immersion for 6 h, the tensile strengths of all the specimens were decreased with respect to those of the specimens immersed for 4 h, and the tensile strength of specimen B was lower than that of specimens A and C. Conclusions: The susceptibility to hydrogen embrittlement of the Ni-Ti shape memory alloy with a microstructure including the parent phase tends to be high when the degree of corrosion is not significantly different for the alloy microstructure. Moreover, the effect of corrosion on the tensile strength of Ni-Ti shape memory alloy is significant when the microstructure includes the martensite phase. Hence, the significant degradation of tensile strength observed for specimen B was probably caused by a synergistic effect of hydrogen absorption and corrosion.

Influence of the Manufacturing Process on the Corrosion and Mechanical Behavior of Esophageal Stents

“…The significant change of mechanical properties of sample B2 could be caused by exerted corrosion activity associated with hydrogen embrittlement, when potential may change locally, but not sufficiently enough to reflect on a macroscopic scale. Hydrogen embrittlement may occur upon immersion in an acidic environment [41]. Stent failure due to hydrogen embrittlement is also described by Volenec et al [42].…”

B19-phase transition and related tensile properties of Ti50Ni30Cu20 shape memory alloy doped with hydrogen

“…For Ti-Ni-based alloys, the primary materials used for investigating the effect of hydrogen have been binary Ti-Ni superelastic alloys that exhibit a one-stage B2–B19′ martensitic transformation or multistage B2–R–B19′ transformation (Gamaoun et al, 2013; Ogawa et al, 2015; Yokoyama et al, 2015). Kuběnová et al (2013) found that the hydrogen-assisted heat treatments resulted in suppression or almost complete extinction of either B2–B19′ or R–B19′ phase transitions.…”