Composition and temperature dependence of kinetic behavior of γ′ precipitation in Ni–Al–Cr–Mo quaternary model superalloys: A phase field study

The characteristic of the γ′ strengthening phase plays a crucial role in the development of high performance nickel-based superalloys, which is strongly dependent on the kinetic behavior of γ′ precipitation. Herein, the precipitation kinetics of the nanoscale γ′ phase in Ni–10 Al–8.5 Cr–x Mo at% (x = 2, 3, and 4) quaternary alloys aged at 1073 K are investigated using CALPHAD-assisted phase field simulations. Our calculations show that the higher Mo content and lower aging temperatures delay the growth and coarsening kinetics of the γ′ phase, which can be attributed to the decrease of Al chemical mobility. Moreover, although Mo is a γ–stabilized element, previous experiments, thermodynamic calculations, and our simulations all indicate that the γ′ volume fraction increases abnormally with increasing Mo concentration in Ni–Al–Cr–Mo quaternary alloys, which is attributed to Mo occupying the Al sites of γ′-Ni₃Al and the elemental partitioning behaviors between the γ matrix and the γ′ phase. In addition, Mo is a potential element to reduce the content of Re and W elements in nickel-based superalloys because of its lower density and stronger solid solution strengthening effect in the γ matrix. Our work can guide the design and development of lightweight nickel-based superalloys with superior microstructural stability and mechanical properties for engineering applications.