Influence of the Duration of High-Temperature Exposure to Hydrogen on the Composition of Surface Layer of Heat-Resistant Nickel Alloy

The effect of the duration of the exposure of alloy ZhS6U to hydrogen at 1473 K for 0, 15, 30, and 60 min on the chemical composition of the surface and internal layers is studied. It is shown that the surface layer of the alloy is oxidized by trace amounts of oxygen present in the hydrogen, while the inner layers do not undergo oxidation. At the same time, the Al content in the surface layer increases abnormally from 17 to 34% after 15 min, and the Cr and Ni contents decrease from 20 to 5% and from 62 to 20%, respectively, at a slight change in the Mo and Co contents. The abnormally high content of O₂ and Al in the surface layer is apparently a result of the high rate of oxidation of Al and of the diffusion of low-melting Al from the lower layers of the alloy to the upper thin porous Al₂O₃ film. The low Ni content in the surface layer indicates intense oxidation of nickel despite the previously formed gas-permeable Al₂O₃ film.