Abstract Scope |
Crack growth resistance at high temperatures under dwell-fatigue loading conditions is a high priority property for modern nickel based superalloys for disc applications. Due to a combined influence of cyclic- and time-dependent failure mechanisms, crack growth rates can be largely variable. An unusual crack retardation behaviour, contrasting to fast and continuous crack acceleration, can be obtained under the low to intermediate mechanical driving forces, represented by stress intensity factor range K. This talk provides detailed characterisation undertaken to interpret the underlying mechanisms of such crack growth behaviour in nickel disc alloys. These include a special experimental procedure of sequential block loading between baseline fatigue cycles and dwell-fatigue cycles to obtain crack growth resistance curves, metallographic and fractographic analysis, and FIB-TEM analysis. The role of microstructure, dwell time, on-test overageing, and load history will be discussed. |