Effect of aging at room temperature on hydrogen embrittlement behavior of Ni-Ti superelastic alloy immersed in acidic fluoride solution

Abstract

Background: It is important to investigate the mechanism for the hydrogen embrittlement of Ni-Ti superelastic alloy in acidic fluoride solutions so that the reliability and safety of the alloy as a dental device can be improved. The purpose of the present study is to investigate the effect of aging at room temperature on the hydrogen embrittlement behavior of Ni-Ti superelastic alloy immersed in acidic fluoride solution. Methods: Specimens were immersed separately in 50 mL of 0.2 % acidulated phosphate fluoride (APF) solution with pH 5.0 at room temperature for 16 h. The hydrogen-charged specimens were aged for various periods at room temperature in air to adjust the hydrogen distribution. Results: The specimen that was tested immediately after immersion in 0.2 % APF solution fractured near the critical stress for martensitic transformation without martensitic transformation. The tensile strength of the immersed specimen was partially recovered by aging at room temperature for 24 h. In addition, the tensile strength of the specimen immersed in 0.2 % APF solution was completely recovered by aging at room temperature for 240 h. Conclusions: After aging at room temperature for 24 h, the tensile strength of the immersed specimen was partially recovered. In addition, the tensile strength of the specimen immersed in 0.2 % APF solution was completely recovered by aging at room temperature for 240 h. These results indicate that the mechanism for the hydrogen embrittlement of Ni-Ti superelastic alloys aged at room temperature after immersion in 0.2 % APF solution is dependent on the aging time.

Hydrogen-Assisted Aging Applied to Storage and Sealing Materials: A Comprehensive Review

“…Yamabe et al [34], Fujiwara et al [35], and Simmons et al [36] tested elastomeric sealing material NBR at room temperature, 30 • C, and 110 • C, and found that there is no hydrogenation or structural activity below 30 • C, but at 110 • C, compression set is increased by 40%, which indicates that with increasing temperature, the elastomeric sealing materials show a thermal aging tendency. Menon et al [37], Castagnet et al [38], and Klopffer et al [39] tested different types of thermoplastic polymeric sealing materials at room temperature and 20-80 • C, respectively, and observed some random behavior. The degree of crystallinity can be increased with increasing temperature, but mechanical properties do not change.…”

“…This reaction causes permanent changes in structure, composition, and morphology. In this method, materials remain in contact with different chemicals, mostly immersed in the solution and charged with hydrogen [36,37,40,41]. This type of aging is frequently seen by both storage and sealing materials due to their continuous interaction with chemicals.…”

“…Chemical aging is one of the most common forms of aging found in hydrogen storage and sealing materials. In hydrogen-storing metallic materials, the hydrogen's distribution and state influence the hydrogen embrittlement and the tensile properties of the metal and lead to complete aging [37,42]. In hydrogen-sealing materials, cracks are formed by the decomposition of the backbone and the hydrolysis of crosslinks, which leads to aging [40].…”

“…Ogawa et al [37] used martensitic Ni-Ti alloy specimens and acidulated phosphate fluoride (APF) solutions for the aging test. Cathodic electrolysis was used for charging the samples with hydrogen, and the charged specimens were aged for 16 h in the air at room temperature.…”

Revisiting the effects of low-concentration hydrogen in NiTi self-expandable stents

“…However, during the production stages, hydrogen absorption occurs frequently during acid washing and electropolishing processes [7]. This fact may be critical since it has been often reported that the contamination of hydrogen can lead to several detrimental effects such as: (1) suppression of martensitic phase transformation [8][9][10][11][12], (2) noticeable increase of the transformation stress threshold [7,8,10,11,13,14] and (3) embrittlement [7,10,13,[15][16][17][18]. Recently, Duerig et al [19] have pointed out several aspects of hydrogen in Ni-Ti and highlighted both localized and highly dynamic effects.…”