The finding of anisotropic compatibility of grain boundaries in a directionally solidified superalloy

Abstract The anisotropic compatibility of grain boundaries (GBs) is found in a directionally solidified superalloy, when loading is aligned with (L sample) or transverse (T sample) to the grain growth direction. The greater compatibility of GBs is shown in the L sample by calculating the parameter m′ of the GBs using two developed models. The first model considers the theoretical scenario that grains grow along the perfect [001] orientation, and the compatibility between the neighbouring grains with all kinds of orientation difference is calculated. The second model, termed as Schmid-factor-tolerance model, considers the effects of asymmetrical slip systems caused by the deviation of grain growth direction from the [001] orientation in a real microstructure. Validation of the model is achieved through fatigue tests, demonstrating its capability to interpret and predict the crack initiation behaviours at grain boundaries. Combined with the fatigue tests to illustrate the anisotropic fracture behaviours of the L and T specimens, it shows that the intergranular cracks are more likely to occur in the T specimen with poor compatibility, which proves the capability of predicting the intergranular cracks for the Schmid-factor-tolerance model.