Hydrogen resistance of Ni base alloys under stress corrosion and fatigue corrosion

One of the major problem for steam generator tubes in Pressurized Water Reactor (PWR) is the resistance of Ni base alloys to Stress Corrosion Cracking (SCC) and Corrosion Fatigue (CF). Previous studies of mechanisms involve the effect of hydrogen on the damage process together with segregation of impurities. It bas been shown that a galvanic cell may be established, in the power plant, upon contact due to the fact that the Ni base alloy is cathodic relative to the carbon steel support plate. Thus the aim of this research is to analyse the effect of hydrogen on the Ni base alloy fatigue behaviour, through CF tests in a 0.5 N H2SO4 solution at cathodic and free potentials in comparison to tests in air. These tests are performed on Ultra High Purity (UHP) Ni and Ni base alloys (corresponding to the FCC matrix of Inconel 600 and Inconel 690) to avoid the effect of impurities, such as sulphur, on localized corrosion and grain boundary (GB) embrittlement (S, 0, C, N < 10 ppm). Localized corrosion-deformation interactions are taken into account through the relation between cyclic plasticity, strain localization and hydrogen absorption. A particular attention is paid on the Persistent Slip Bands (PSB)-GB interactions in relation with hydrogen effects. (authors). 6 refs., 2 figs