Stability of γ′ precipitates in a PWA1480 alloy

In the nickel-based superalloy PWA1480, 5–10-nm diameter γ precipitates form during heat treatment at 871 °C within the primary cuboidal γ′ precipitates that formed at high temperature (1079 °C). The stability of these γ precipitates during extended aging at 871 °C was investigated by atom probe tomography, computational thermodynamics, and diffusion-controlled growth kinetic modeling. The results show that these γ precipitates are not in thermodynamic equilibrium in the alloy and dissolve during extended aging. Thermodynamic and kinetic calculations indicate that the formation of these non-equilibrium precipitates is related to local concentration fluctuations in the primary γ′ phase that developed during diffusion-controlled growth of γ′ at high temperature.