Influence of type and morphology of carbides on stress-rupture behavior of a cast cobalt-base superalloy

摘要

AbstractThe relationships between the type and morphology of carbides and stress-rupture property have been studied in a cast cobalt-base superalloy. Different types and morphologies of carbides are achieved by varying the heat treatment conditions. After heat treatment at 1240?°C/4?h, the primary M7C3decomposes into M23C6, and the formed M23C6and primary MC partially dissolve into the matrix. After heat treatment at 1280?°C/4?h, the primary M7C3melts, resulting in the formation of a highly developed lamellar structure of M23C6, and the primary MC mostly dissolves into the matrix. The heat treatment at 1100?°C/300?h gives rise to the carbide transformation of M7C3→ M23C6and a profusion of secondary M23C6carbide around M23C6and MC. The samples in stress-rupture test at 980?°C for 83?MPa manifest the following rupture life: 1280?°C sample > 1240?°C sample?>?as-cast sample > 1100?°C sample. The longer rupture life of the samples of 1240?°C and 1280?°C is derived from the stable microstructure, dispersed MC carbide morphology and the supersaturated matrix. The shortest rupture life of the 1100?°C sample is mainly attributed to the overaging. Additionally, the carbide transformations of M7C3→ M23C6, MC → M23C6, M23C6→ M6C take place in the as-cast sample during creep exposure.Graphical abstractDisplay OmittedHighlights?The rupture life is following: 1280?°C sample > 1240?°C sample?>?as-cast sample > 1100?°C sample.?The stable microstructure, dispersed MC carbide morphology and the supersaturated matrix are beneficial to rupture life.?The carbide transformations of M7C3→ M23C6, MC → M23C6, M23C6→ M6C occur in as-cast alloy during stress-rupture.