Melting of primary carbides in a cobalt-base superalloy

Abstract Melting of primary M 7 C 3 and MC eutectic carbides in a cobalt-base superalloy has been investigated. It is found that the melting phenomenon of primary M 7 C 3 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 M 7 C 3 eutectic carbide is that M 7 C 3 first transforms into M 23 C 6 and then M 23 C 6 melts rather than directly melts at or above 1280 °C, and the re-solidified structure is still M 23 C 6 eutectic carbide, but its lamellar spacing becomes finer with respect to primary M 7 C 3 eutectic carbide. Additionally, the higher the heat treatment temperature, the less the difference in the lamellar spacing of re-solidified M 23 C 6 . 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.