Formation behavior of long needle-like M23C6 carbides in a nickel-based alloy without γ’ phase during long time aging

Abstract

This work aims to study the differences in the microstructure and mechanical properties of a new nickel-based alloy without γ′ phase during long-term aging at 675 °C. The test alloy C-HRA-2 for next-generation power plant applications was simulated for 5000 h at the service temperature. The formation of long needle-like M23C6 carbides inside the grains is a unique phenomenon compared to conventional nickel-based alloys. After aging for 500 h, the microstructure, strength and hardness tend to be stable, while the toughness shows a slow downward trend. Even so, the toughness still exceeds 110 J after aging for 5000 h. Compared with the alloy 617/617B containing the γ′ phase, the strength of the alloy without γ′ phase (C-HRA-2) reduced by about 5–10%, and the hardness lowered by 5–15%, but the elongation also increased by about 10–50%, and the toughness increased by about two times.