Effect of Re content on precipitation behaviour of secondary phases in a single-crystal Ni-based superalloy during high-temperature thermal exposure

Abstract

The precipitation of secondary phases in single-crystal Ni-based superalloys with different contents of Re are investigated using TEM and SEM. The results show that after full heat treatment, the size of secondary γ′ phase decreases gradually with increasing Re content. During long-term thermal exposure at 1093 °C, some needle-like and rod-like secondary phases precipitate from the γ matrix. With increasing Re content and prolonging of the thermal exposure, the amounts of precipitated phases clearly increase. In the alloy with 2·5 wt-% Re, the needle-like phases are identified as M6C carbides. In the alloy with 3 wt-% Re, both M6C carbides and μ phase are found. In the alloy with 3·5 wt% Re, the needle-like and rod-like precipitated phases are identified as μ and P phases. Stacking fault was found in the P phase and that part was identified as μ phase by SAD; that is, there is intergrowth of P and μ phases.