Microstructure of Carbides at Grain Boundaries in Nickel Based Superalloys

It is well known that carbides at grain boundaries play an important role in affecting mechanical properties of nickel based superalloys. In order to deeply understand the relationship between grain boundary structures and properties, in this work, we have investigated the microstructure of grain boundaries with different misorientation angles in bicrystals of nickel based superalloys. It is found that the bicrystals with smaller misorientation angles contain denser M23C6 but sparse MC particles at grain boundaries, and this kind of bicrystals presents longer stress rupture lives. It was observed that MC carbides were decorated by M23C6 and M6C particles at grain boundaries. The formation of these carbide particles, therefore, is likely due to the local fluctuation of chemical composition around MC carbides. In addition, the orientation relationships between MC carbides and γ/γ′ matrix were also determined.