Abnormal growth behavior of carbides in nickel-based single-crystal superalloys by secondary misorientation

Three bicrystal nickel-based superalloys with different misorientations (7°, 13°, and 19°) have been prepared using the bicrystal seed crystal directional solidification technique. In the case of the 7° grain boundary, a higher quantity of carbides exhibit an elliptical shape with a smaller volume and discontinuous distribution. The 13° grain boundary is characterized by a reduced quantity of carbide with an increased size, switching from an elliptical shape to an “island-like” structure. When the misorientation angle is increased to 19°, the carbide size is further increased, the quantity decreases with a transformation to continuous elongated shapes that extend along the grain boundary direction. The mechanical behavior and damage evolution at the grain boundaries of nickel-based superalloys containing carbides have been examined on the basis of crystal plasticity theory combined with finite element simulation. Applying crystal plasticity theory and introducing the anisotropy differences generated by different angle grain boundaries, the stress-strain relationships, local stress distributions, and damage and fracture behavior in a three-dimensional typical volume element have been analyzed, employing ABAQUS finite element simulation software. The results indicate that an increase in grain boundary misorientation increases the likelihood of stress concentration around the carbides near the grain boundary, leading to more severe damage.