Linear evolution of the γ′-(Ni, Cu)3Al phase composition in Cu-based high-temperature alloys.

The ordered γ′-(Ni, Cu)3Al is a crucial strengthening phase that improves the high-temperature resistance of Cu-based alloys, so it is important to predict the kinetic evolution of the composition and microstructure of the phase for high-temperature applications. Herein, this paper discusses the temporal evolution of the composition and coarsening of the γ′ phase in a model ternary Cu50Ni37.5Al12.5 (at%) alloy during isothermal aging at 600, 700, 800, and 900 °C for 1–36 h. It is found that the γ′ phase composition evolves linearly toward a binary γ′ phase as the aging time increases during the process of aging at 800 and 900 °C, which cannot be predicted by the ternary phase diagrams alone. Meanwhile, through the utilization of the aforementioned linear law, the γ phase composition can be predicted at a given temperature within the alloy by determining the volume fraction of the γ′ phase. Additionally, the activation energy for coarsening decreases, and the coarsening rate of the γ′ phase increases owing to the higher diffusion rate of Cu at high temperatures. The addition of microalloying elements with strong enthalpic interactions is beneficial for reinforcing the structural stability of the γ′ phase. This work provides a simple method for the compositional analysis and performance prediction of Cu–Ni–Al alloys at elevated temperatures and sheds light on the subsequent compositional design and optimization of Cu-based high-temperature alloys. [ABSTRACT FROM AUTHOR]