The effect of M₂₃C₆ carbides on the formation of grain boundary serrations in a wrought Ni-based superalloy

The effect of M₂₃C₆ carbides on the formation of grain boundary serrations (GBSs) has been systematically investigated in a solid solution strengthened Haynes 230 alloy. It is found that GBS occur in this alloy during the slow cooling process and are accompanied by the precipitation of intergranular planar M₂₃C₆ carbides. The amplitude and proportion of GBS increase with the rise of the solution temperature and time. If the specimens are cooled directly without any solution treatments, the grain boundaries remain planar and granular M₂₃C₆ carbides precipitate at them. The sequential evolutions of GBS and M₂₃C₆ carbides are investigated by scanning electron microscopy (SEM) examination. High-resolution transmission electron microscope (HRTEM) investigations reveal the coherent interfacial plane of M₂₃C₆ carbides formed at grain boundaries to be (1 1 1̄). These facts indicate that the nucleation and oriented growth of M₂₃C₆ carbides at grain boundaries play an important role in the formation of GBS. Based on the interfacial energy calculations and the tensions balance relation, a semi-quantitative model about the GBS formation is proposed.