Damage and fracture mechanism of a nickel-based single crystal superalloy during creep at moderate temperature

By means of creep properties measurement, microstructure and fracture morphology observation, an investigation has been made into the damage and fracture mechanism of a nickel-based single crystal superalloy during creep at intermediate temperature. The results show that the deformation mechanism of the alloy is dislocations slipping in the γ matrix and shearing into γ′ phase, the dislocations shearing into γ′ phase may be decomposed to form the configuration of the partials plus stacking fault and the K–W locking. While in the latter stage of creep, the primary–secondary slipping systems are alternatively activated to shear and twist the cubical γ′/γ phases, which results in the initiation of the micro-crack occurring in the intersection regions of two slip systems. As creep goes on, the micro-cracks are propagated on the (001) plane along 〈110〉 directions. Because the multi-cracks are formed and propagated on the different cross-section of the sample during creep, which may result in the tearing edge or secondary cleavage plane generating at the tip of the cracks along the direction with bigger shearing stress. When the propagating primary cracks on (001) plane intersects with {111} secondary cleavage plane, the propagation of the primary cracks is terminated to form the square-like cleavage plane on the (001) plane. In further, the multi-cracks propagating on the different cross-section are joined by the tearing edge or secondary cleavage plane until the occurrence of creep fracture, this is thought to be the main reason of the creep fracture displaying the uneven and multi-level cleavage features.