Dependence of surface oxidation on hydrogen absorption and desorption behaviors of Ti-6A1-4V alloy

The hydrogen absorption and desorption behaviors of surface oxidized and degassed Ti-6Al-4V alloys under a condition of hydrogen pressure near to the pressure during glow discharge conditioning in reactor were evaluated by thermal desorption spectroscopy (TDS). The equilibrium hydrogen concentration, C-eq, of degassed Ti-6Al-4V alloy decreased with increase of temperature. The C-eq was about half of that of pure Ti in the temperature region of 673-873 K. The desorption peak of degassed Ti-6Al-4V ahoy appeared at the temperature of 790 K. The peak temperature was almost the same even when the absorption amount changed. The absorption amount, C-ab, Of surface oxidized ahoy largely decreased with the increase of atomic ratio (O/Ti) on the top surface and the thickness of the oxide layer when adsorption time was 1 h. In addition, the desorption peak shifted to a higher temperature region with the increase of O/Ti ratio. In the surface oxidized Ti-6Al-4V alloy with an oxide layer of about 10 nm, the C-ab was two orders of magnitude smaller than that of the degassed sample when the absorption temperature and time were kept at lower than 650 K and 1 h, respectively. However, the C-ab of surface oxidized alloy became comparable with that of degassed sample when the absorption temperature was higher than 800 K because the oxide layer disappeared in the higher temperature region. (C) 1999 Elsevier Science B.V. All rights reserved.