Grain size effect on the small fatigue crack initiation and growth mechanisms of nickel-based superalloy GH4169

•Grain size effect on small crack initiation and growth mechanisms was investigated.•Crack initiation mechanism was different between fine and coarse grained material.•Crack driving force was discussed by using stress intensity factor and crack tip displacement.•The scattering of fatigue lives were dependent on the crack initiation mechanisms.

The aim of this paper was to identify the grain size effect on the small fatigue crack initiation and growth mechanisms of nickel-based superalloy GH4169. Results showed that there was a transition of fatigue crack initiation mechanism between fine-grained material and coarse-grained material. Small fatigue crack growth rates were almost constant across a wide range of crack lengths. Once the surface crack length reached the critical size of 200 μm, the crack would propagate fairly quickly. At a given experimental condition, the scattering of fatigue lives of the parallel specimens was dependent on the crack initiation mechanisms.