A comparative study on thermomechanical and low cycle fatigue failures of a single crystal nickel-based superalloy

The cyclic deformation and lifetime behaviors of a single crystal nickel-based superalloy CMSX-4 have been investigated under out-of-phase thermomechanical fatigue (OP TMF) and isothermal low cycle fatigue (LCF) conditions. OP TMF life exhibited less than a half of LCF life although smaller inelastic strain range and lower mean stress level during OP TMF were observed compared to those during LCF. During OP TMF cycling, the maximum tensile strain at the minimum temperature was found to accelerate the surface crack initiation and propagation. Additionally, the multiple groups of parallel twin plates near crack provided a preferential path for crack propagation.

► There was a significant decrease in OP TMF lives compared to LCF lives.
► OP TMF condition was found to accelerate surface crack initiation and propagation.
► The localized twins provided a preferential crack path during OP TMF cycling.
► LCF deformation appears to be more largely dependent on the diffusion.
► OP TMF deformation appears to be dominated by {1 1 1}〈1 1 2〉 partial dislocation movement.