Evolution of γ′ Particles in Ni-Based Superalloy Weld Joint and Its Effect on Impact Toughness During Long-Term Thermal Exposure

Effects of long-term thermal exposure on γ′ particles evolution and impact toughness in the weld joint of Nimonic 263 (N263) superalloy were deeply studied at 750 °C. Results showed that the precipitates in the weld metal were mainly composed of fine γ′ particles, bulky MC carbides, and small M₂₃C₆ carbides. With the thermal exposure time increasing from 0 to 3000 h, γ′ particles in the weld metal grew up from 19.7 nm to 90.1 nm at an extremely slow rate. After being exposed for 1000 h, γ′ particles coarsened and some of them transformed into acicular η phase. At the same time, MC carbides decomposed to form η phase and γ′ particles. This dynamic transition ensured the slight reduction in impact toughness of the weld metal after the thermal exposure, which indicated the stable serving performance of N263 weld joint.