Hydrogen thermal desorption behavior of Ni–Ti superelastic alloy subjected to tensile deformation after hydrogen charging

Abstract

The hydrogen thermal desorption behavior of Ni–Ti superelastic alloy subjected to tensile deformation after hydrogen charging has been investigated. Cathodic hydrogen charging is performed with a current density of 10 A/m 2 in a 0.9% NaCl aqueous solution for 2 h at room temperature (25 °C). In this case, hydrogen desorption is observed from room temperature to 400 °C. For the specimen immediately after hydrogen charging, upon tensile loading covering the stress plateau region caused by stress-induced martensite transformation followed by unloading, hydrogen that desorbs at low temperatures (approximately 150 °C) is observed markedly. In contrast, for the specimen aged for 240 h at room temperature in air after hydrogen charging, most hydrogen that desorbs at low temperatures shifts to a higher-temperature region and diffuses toward the center of the specimen, although the charged hydrogen does not diffuse out. Variation in hydrogen desorption behavior is rarely observed, even upon tensile loading in the plastic deformation region of the martensite phase followed by unloading. The present results suggest that dynamic processes such as stress-induced martensite and reverse transformations affect hydrogen desorption behavior at low temperatures of hydrogen-charged Ni–Ti superelastic alloy.