Synergistic effects of Al and Mo on coarsening kinetics of Ni-based superalloys at 1200°C

The interaction effects of γ-strengthening and γ'-former elements have long troubled the alloying design of superalloys, especially improving γ'-thermostability by Al addition against higher temperatures. Here we establish a thermodynamics-based phase-field model to reveal the γ'-coarsening kinetics at 1200°C for well-designed ternary Ni-based superalloys containing γ'-former element Al and γ-strengthening element Mo. The inhibition effect of Al on coarsening is interestingly enhanced by Mo addition to signify their synergistic effects. The contributions of lattice misfit, diffusion coefficients and elemental partitioning are analysed by decoupling coarsening theories. And an estimation method of the coarsening rate controlled by slow-diffusing element is also established.