Melting of primary carbides in a cobalt-base superalloy

Melting of primary M7C3 and MC eutectic carbides in a cobalt-base superalloy has been investigated. It is found that the melting phenomenon of primary M7C3 and MC eutectic carbides occurs at approximately 1280 and 1320 °C, respectively, in particular the melting of MC eutectic carbide is firstly found. The melting process of primary M7C3 eutectic carbide is that M7C3 first transforms into M23C6 and then M23C6 melts rather than directly melts at or above 1280 °C, and the re-solidified structure is still M23C6 eutectic carbide, but its lamellar spacing becomes finer with respect to primary M7C3 eutectic carbide. Additionally, the higher the heat treatment temperature, the less the difference in the lamellar spacing of re-solidified M23C6. On the other hand, after primary MC eutectic carbide melts, the finer Chinese script MC eutectic carbide associated with compositional change is produced upon re-solidification in comparison to the original as-cast structure.