Formation Mechanism of Lamellar M 23 C 6 Carbide in a Cobalt-Base Superalloy During Thermal Exposure at 1000 °C

The precipitation of the lamellar-shaped M 23 C 6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 °C has been investigated. Such a precipitation is not commonly observed in cobalt-base superalloys. It is found that M 23 C 6 particles nucleate preferentially at stacking faults (SFs) in the dendritic matrix and grow along the SFs to develop a lamellar character. Additionally, a Cr depletion zone is observed in the vicinity of the lamellar M 23 C 6 carbide, which strongly supports the presence of Suzuki segregation.