Small fatigue crack initiation and growth mechanisms of nickel-based superalloy GH4169 at 650 °C in air

•Small fatigue crack initiation and growth mechanisms of GH4169 at 650 °C were investigated.•The effect of δ phase on fatigue resistance and crack growth was discussed.•ΔK might be applicable to correlate the small crack and long crack growth rates.•Two three-stage models are proposed to describe the crack initiation and propagation process.

The aim of this paper is to identify the fatigue crack initiation and small crack growth mechanisms of GH4169 at 650 °C in air. Results show that fatigue cracks tend to initiate at oxidized inclusions. The crack incubation period takes up more than 90% of the fatigue lifetime. The δ phase can improve the crack initiation life and the total fatigue lifetime. The similarity between small crack and long crack growth data at relatively high ΔK can be attributed to the similarity of propagation mode. Two three-stage models are proposed to describe the cracks initiation and propagation processes.