Oxidation accelerated dwell fatigue crack growth mechanisms of a coarse grained PM Ni-based superalloy at elevated temperatures

Fatigue crack growth (FCG) mechanisms of Ni-based superalloy FGH4098 at 650 degrees C-800 degrees C was investigated. The increased temperature and prolonged dwell time enhance the FCG rate by 2-3 orders of magnitude due to grain boundary (GB) oxidation. Characterization at the propagating crack tips with EBSD, TKD, TEM and EDX shows deformation (e.g. dislocations and stacking faults) mainly confines within gamma channel along with orientation change within grains due to the severe deformation. Pre-formed oxides at uncracked GB fracture under stress, facilitating FCG process. A mechanism map of interaction between deformation-assisted GB oxidation and FCG is proposed.