Factors affecting the corrosion fatigue life in nickel based superalloys for disc applications

Abstract

Abstract. The nickel based superalloy 720Li is employed in the gas turbine due to its mechanical performance at elevated temperature. A comprehensive assessment of the materials behaviour under representative service conditions is reported to address the drive for ever increasing temperatures and more arduous environmental exposure. Fatigue experiments have been performed in an air and air/SO x environment at 700• C containing a mixed salt as a contaminant. There is an intimate relationship between local salt level (flux), stress level and stress state, i.e. static or cyclic. The interaction with these variables with the work hardened layer present on the surface of all tested specimens as a result of the shot peening process directly affects the crack initiation process. If specific conditions of environment and stress are achieved, a significant reduction in fatigue life is observed.

Corrosion fatigue and damage tolerance in the nickel‐based superalloy RR1000 subjected to SO2 environments

“…5 This is extremely challenging in the laboratory setting; however, previous papers have reported the design of in situ environment test cells for the assessment of structural metals under hot sulphur-bearing environments. 6 From the perspective of mechanical behavior and fatigue in particular, hot corrosion may be especially problematic should the corrosive attack lead to the development of localized surface pits. Recent studies have evaluated the fatigue strength of alternative nickel superalloys subjected to pre-existing pitting damage, 7,8 and this supports the ranking of alloys based on environmental resistance.…”

“…Future superalloy developments, required to resist such Type II damage, must incorporate an accurate assessment of fatigue behavior under representative operating conditions 5 . This is extremely challenging in the laboratory setting; however, previous papers have reported the design of in situ environment test cells for the assessment of structural metals under hot sulphur‐bearing environments 6 …”