Effect of microstructure on fatigue resistance of Inconel 740H and Haynes 282 nickel-based alloys at high temperature

Fatigue crack growth behavior of Inconel 740H and Haynes 282 nickel-based alloys at 20 C-?, 700 C-? and 750 C-? was studied. Results showed increased fatigue crack growth rate for both the two alloys, while increased fatigue threshold in Inconel 740H at high temperatures. The size and distribution of MC carbides, serrated grain boundaries and twins deflected crack growth path. The strengthening ?' phase was interacted with dislocations by Orowan bypass and shear mechanisms at room temperature, while ?' was sheared in Haynes 282 and Orowan bypassed in Inconel 740H alloy at elevated temperatures. The cross slip, dislocation climbing and entanglement reduced the resistance of dislocation movement and accelerated the accumulation of damage. The higher content of Cr in Haynes 282 alloy promoted formation of M(23)C(6 )carbide while the lower content in Inconel 740H alloy promoted thicker oxide layer. The Cr content needed careful tuning as it was superior to microstructural factors for higher fatigue threshold at elevated temperatures.