Niobium enrichment and environmental enhancement of creep crack growth in nickel-base superalloys

摘要: Abstract These initial results strongly suggest that the enrichment and segregation of niobium at grain boundary surfaces played an important role in environmental enhancement creep crack growth Inconel 718. The precise mechanism, however, still needs to be established. Available evidence suggests mechanism involves formation fracture a brittle oxide film on which reduces alloy's resistance. Oxidation decomposition NbC particles tip boundaries appear principal source niobium. segregated (in form Ni3Nb precipitates) is expected also contribute embrittlement. oxygen would external (pseudo-equilibrium) surface oxide. consistent with observed independence pressure from 2.67 100 kPa. rate controlling process identified reactions carbides (266 versus 287 kJ/mol) or lower activation energy for moist argon air (about 190 understood. It may reflect additional embrittlement contribution hydrogen, transfer process. Further studies are underway critically examine this other hypotheses developing more complete understanding. nickel-base superalloys demonstrated by correlation between sensitivity concentration series commercial alloys. detailed aspects interactions under investigation will reported later.