Effect of silicon on microstructure and stress rupture properties of a corrosion resistant Ni-based superalloy during long term thermal exposure

The influence of silicon on microstructure and stress rupture properties of GH3535 nickel-based superalloy during long term thermal exposure at 700 °C was investigated. After long term thermal exposure, the secondary carbides precipitated along grain boundaries. Si addition induced the formation of M12C carbides, while only M6C carbides were observed in Si free alloy. The secondary M12C carbides exhibited particular orientation relationship with matrix for the alloy with Si, but the secondary M6C carbides are incoherent with matrix for the Si free alloy. It is believed that the difference in the types of the secondary carbides was originated from Si. The stress rupture life decreased after 1000 h thermal exposure for the Si free alloy, but no noticeable changes could be detected for the alloy with Si. The interface between the secondary M6C carbides and matrix became the main site for crack initiation after 1000 h thermal exposure for the Si free alloy. But no cracks was detected at the interface between the secondary M12C carbides and matrix even after 10,000 h thermal exposure, which may be related to the strong interfacial cohesive force between secondary carbides and matrix.