Hydrogen Absorption and Thermal Desorption Behavior of Ni-Ti Superelastic Alloy Immersed in Neutral NaCl and NaF Solutions under Applied Potential

Abstract

The hydrogen absorption and thermal desorption behavior of Ni-Ti superelastic alloy immersed in neutral NaCl and NaF aqueous solutions at 25C under an applied cathodic potential for 2 h have been systematically investigated by hydrogen thermal desorption analysis. The critical potential for hydrogen absorption is independent of the type and concentration of solution. The amount of absorbed hydrogen increases with decreasing applied potential, although it is only slightly changed by the type of solution. The amount of hydrogen desorbed at low temperatures, for the alloy immersed in NaF solutions, is larger than those in NaCl solutions, suggesting that the type of solution affects the hydrogen states in the alloy. The present results indicate that for Ni-Ti superelastic alloy, compared with titanium and its alloys, the critical potential for hydrogen absorption is located in a more noble direction, and the amount of absorbed hydrogen is large in NaCl and NaF solutions. Thus, the hydrogen embrittlement of Ni-Ti superelastic alloy probably occurs more readily than those of titanium and its alloys in NaCl and NaF solutions.

Effects of the Hydrogen Absorption Conditions on the Hydrogen Embrittlement Behavior of Ni–Ti Superelastic Alloy

“…[10][11][12]34) The relationship between hydrogen absorption and corrosion processes should be investigated in the future. On the basis of the present and previous results, 6,[10][11][12][20][21][22][23][29][30][31] to greatly change the hydrogen embrittlement or hydrogen desorption behavior of Ni-Ti superelastic alloy, changing the type of solution seems to be more effective than changing the solution temperature, concentration, pH, charging current density or applied potential. Changing the type of solution possibly leads to a greater change in corrosion behavior.…”

“…6,[10][11][12][20][21][22][23]29,30) Moreover, a second peak was observed at a high temperature. Upon immersion in 1 M HCl solution at 60°C, 34) similar hydrogen desorption is often observed to that at a high temperature, although a second peak of hydrogen desorption is not observed.…”

“…6,[10][11][12][21][22][23]29,30) It appears that metallurgical factors of Ni-Ti superelastic alloy, such as the microstructure, chemical composition, phase stability and strength, often affect hydrogen embrittlement behavior. In fact, we have revealed that the hydrogen desorption behavior of the alloy is affected by the heat treatment before hydrogen charging.…”

“…In the case of immersion in ethanol solution containing hydrochloric acid, 12) the hydrogen desorption behavior is characterized by double peaks at approximately 150 and 350°C. Under cathodic charging in 0.9% NaCl aqueous solution, 6,[21][22][23] hydrogen desorption over a wide range of temperatures from room temperature to 400°C is observed. However, the tensile behavior of the alloy, particularly the stress plateau due to the stress-induced martensite transformation and the fractographic features, only slightly depends on these variations of the hydrogen desorption behavior, although the critical stress for the martensite transformation increases or decreases.…”

“…6,[10][11][12][21][22][23] Most previous studies on hydrogen embrittlement were conducted under similar conditions of hydrogen charging. It is desirable that hydrogen embrittlement is studied under the same hydrogen absorption conditions, because the obtained results can be compared among researchers.…”