Hydrogen diffusion and interpretation of the 200 K anelastic relaxation in NiTi alloys

The internal friction, the Young’s modulus, and the heat flow have been measured as a function of temperature (20–360 K) at kilohertz frequencies in a H-free and H-doped Ni50.8Ti49.2 alloy, solubilized under vacuum and rapidly furnace cooled. The chemical H-diffusion coefficient DC has been deduced from absorption experiments (323–1063 K) and has been compared with the Einstein diffusion coefficient DE derived from a Snoek (or Zener)-type relaxation PH. The comparison has allowed the interpretation of the so-called 200 K relaxation as a Snoek (or Zener)-type relaxation due to hydrogen.