Susceptibility to Hydrogen Absorption and Hydrogen Thermal Desorption of Titanium Alloys Immersed in Neutral Fluoride Solution under Applied Potential

Abstract

The susceptibility to hydrogen absorption and hydrogen thermal desorption of titanium alloys has been investigated in a neutral 2.0% NaF solution at 37C under various applied cathodic potentials. Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys absorb hydrogen under less noble potentials than À1:5 V, À1:9 V and À1:4 V versus a saturated calomel electrode, respectively. The amounts of absorbed hydrogen of Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys under an applied potential of À2:0 V for 24 h are approximately 1200, 100 and 1100 mass ppm, respectively. Upon immersion in the 2.0% NaF solution under an applied potential, the hydrogen thermal desorption behavior of Ti-0.2Pd alloy differs from those immersed in acid fluoride solutions, whereas the hydrogen thermal desorption behaviors of Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys are similar to those immersed in acid fluoride solutions. The present results indicate that in a neutral fluoride solution, the effects of an applied potential on the hydrogen absorption and desorption behaviors of Ti-6Al-4V alloy are considerably smaller than those of commercial pure titanium reported previously, Ti-0.2Pd and Ti-11.3Mo-6.6Zr-4.3Sn alloys.

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

“…28) With immersion in the neutral 0.2% and 2.0% NaF solutions at 37 C for 24 h, the critical potential for the hydrogen absorption of commercial pure titanium was À1:2 V. 28) Similarly, the critical potentials for the hydrogen absorption of Ti-0.2Pd, Ti-6Al-4V and Ti-11.3Mo-6.6Zr-4.3Sn alloys were À1:5 V, À1:9 V and À1:4 V in the 2.0% NaF solution at 37 C for 24 h, respectively. 22) Thus, the susceptibility of applied potential to the hydrogen absorption of Ni-Ti superelastic alloy is probably higher than those of titanium and its alloys. Furthermore, for the same applied potential or same applied current density, the amount of absorbed hydrogen of Ni-Ti superelastic alloy is much larger than those of titanium and its alloys reported previously.…”

“…Furthermore, for the same applied potential or same applied current density, the amount of absorbed hydrogen of Ni-Ti superelastic alloy is much larger than those of titanium and its alloys reported previously. 22,28) For example, the amount of absorbed hydrogen of commercial pure titanium immersed in 2.0% NaF solution at 37 C under an applied potential of À1:2 V (current density of approximately 10-20 A/m 2 ) for 24 h is approximately 60-70 mass ppm. 28) Hence, when the same amount of hydrogen evolves on the surface of the specimen, the amount of hydrogen absorbed into Ni-Ti superelastic alloy is presumably larger than those absorbed into titanium and its alloys.…”

“…In this case, the hydrogen absorption behavior appears to depend on the surface conditions, including the nature of surface oxide films on titanium alloys. 22) The oxide film on Ni-Ti superelastic alloy is mainly TiO 2 , similar to those on titanium and its alloys. Unless the hydrogen absorption behavior of Ni-Ti superelastic alloy is examined practically in each environment, the truth will be unknown.…”

“…For titanium alloys, such as Ti6Al-4V alloy, however, the hydrogen absorption behavior is not necessarily consistent with the electrochemical behavior. 21,22) In addition, the hydrogen absorption behavior of Ti-6Al-4V alloy strongly depends on the type of solution. In this case, the hydrogen absorption behavior appears to depend on the surface conditions, including the nature of surface oxide films on titanium alloys.…”

Relationship between Hydrogen Absorption and Corrosion Behavior of Ti-6Al-4V Alloy Immersed in Acidic Fluoride Solutions

“…15) In contrast, for Ti-6Al-4V alloy immersed in neutral NaF solution, the hydrogen absorption behavior may be related to the surface conditions rather than an electrochemical factor. 16) Therefore, it is necessary to confirm experimentally the extent to which the hydrogen absorption behavior of Ti-6Al-4V alloy is related to its electrochemical behavior in APF solution.…”