Effect of Crystallographic Orientation on Subcritical Grain Boundary Cracking in a Conventionally Cast Polycrystalline Nickel-Based Superalloy

The role of grain orientation and grain boundary misorientation on the formation of subcritical grain boundary cracks in creep of a conventionally cast nickel-based superalloy has been studied. The crystallographic orientations of the grains adjacent to grain boundaries normal to the tensile axis were measured using electron backscattered diffraction. The difference in the Schmid factor for the {111} < 112 > slip system between the grains was compared to the occurrence of grain boundary cracking. In addition, the difference in the amount of potential primary creep was calculated. The cracked grain boundaries were found to have a larger difference in Schmid factor, as well as a larger difference in potential primary creep, compared with uncracked grain boundaries.