Abstract
Outstanding mechanical performance (high strength, ductility) and very good corrosion resistance made nickel base alloy UNS N07718 one of the preferred materials in oil industry.1 However, the reported hydrogen embrittlement susceptibility could be a serious limit to the material application.2,3 Systematic studies of the solubility of hydrogen in the material, UNS N07718, were the subject of the current work, specifically in relation to differences in the microstructure. Specimens were aged at 720, 750, 800, and 870 °C respectively to generate differences in γ’, γ” and δ phase morphology and quantity. After cathodic charging in ammonium sulfate solution for 24 hours, specimens were melted, and the amount of the released hydrogen was analyzed via mass spectrometer. Specimens rich in δ phase precipitates revealed higher hydrogen contents in comparison to the specimens with high amount of γ’ and γ” precipitations and low amount of δ phase precipitations. Similar observations were made for the hydrogen diffusion coefficients, determined by means of Devanathan and Stachurski technique. The hydrogen diffusion coefficients of δ phase rich variants were about twice as high as of the variations with γ’ and γ” phases. The obtained experimental results provide an important contribution that clarifies the impact of microstructure on hydrogen embrittlement susceptibility of the material UNS N07718.
