Diffusion and γ′ Phase Coarsening Kinetics in Ruthenium Containing Nickel Based Alloys

The present paper reports the interdiffusion of Re, W, Ru and Co in the binary and pseudo-binary Ni based alloys at 1523 K and the γ′ phase coarsening kinetics of model superalloys at 1324 K. Both Re and W concentration gradients caused Ru uphill diffusion in the respective pseudo-binary diffusion couple, whereas Ru concentration gradient promoted uphill diffusion for W but not for Re. Interestingly, Re uphill diffusion occurred under the influence of Co concentration gradient but the reverse effect was not observed. The cross interdiffusion coefficients qualitatively determined from the uphill diffusion profiles were in reasonable agreement with those reported previously. Comparison of the interdiffusion coefficients in the binary and the pseudo-binary diffusion couples showed that Ru and W decreased the diffusivity of each other whereas Co appeared to be more powerful barrier atoms than Ru to decrease the Re diffusivity. Furthermore, it was evident that the coarsening kinetics of the γ′ phase in both Ru-free and Ru-containing model superalloys were controlled by diffusion and Ru was found to have no effect on the rate constant of the γ′ phase coarsening. Materials Trasnsactions Vol. 49 No. 4 2008 p: 792-799