Crack appearance of single-crystal nickel-base superalloys after thermomechanical fatigue failure

Thermomechanical fatigue (TMF) testing was conducted on single-crystal nickel-base superalloys. Distinct cracking behaviors were found to occur under different cycling conditions. A crack generally initiates from the specimen surface. For the TMF cycling without a compressive hold time, the crack initially grows perpendicular to the stress axis and then propagates along a twin plate. For the TMF cycling with a compressive hold time, the main crack propagates directly along a twin plate until final failure.