The effect of temperature on the fatigue performance of notched specimens of nickel-based single crystal alloys

Nickel-based single crystal superalloys are extensively used in aircraft engine turbine blades due to their superior high-temperature properties. However, geometric discontinuities in these components lead to local stress concentrations, often assessed using notched specimens. This study performed uniaxial tensile and notched fatigue tests at 760 and 980 °C under varying loading conditions, revealing comparable fatigue lives despite the temperature difference. At 760 °C, the alloy showed higher yield strength but lower ductility, with fatigue life primarily governed by rapid crack propagation and quasi-cleavage fracture. At 980 °C, reduced yield strength and enhanced ductility were observed, with crack growth dominated by creep effects and influenced by microstructural evolution and plastic deformation. Numerical simulations using a coupled damage-crystal plasticity model closely matched the experiments. The results suggest that faster crack growth at 760 °C is offset by greater local plastic energy dissipation, while at 980 °C, slower crack growth is counterbalanced by continuous creep and plastic deformation—leading to a dynamic compensation between mechanisms and ultimately similar fatigue lives.