Interdiffusion in Ni-rich, Ni-Cr-Al alloys at 1100 and 1200 °C: Part II. Diffusion coefficients and predicted concentration profiles

Abstract

Ternary interdiffusion coefficients were measured in the Ni solid solution γ (fcc) phase of the Ni-Cr-Al system at 1100 and 1200 °C. Extensive use was made of both γ/γ and γ/γ + β (β-NiAl structure) diffusion couples. Two analysis techniques were employed to calculate the interdiffusion coefficients. When the Matano planes for Al and Cr were not coincident, numerous integral calculations were made to determine an average diffusion coefficient and to assess the effect of the noncoincidence of the Matano planes. The results of the diffusivity measurements showed that$\tilde D_{AlAl}^{N1}$ is approximately four times greater than$\tilde D_{AlCr}^{N1}$, while$\tilde D_{CrAl}^{N1}$ and$\tilde D_{CrCr}^{N1}$ are of the same magnitude. For all concentrations,$\tilde D_{AlAl}^{N1}$ is two to three times greater than$\tilde D_{CrCr}^{N1}$. Both$\tilde D_{AlAl}^{N1}$ and$\tilde D_{AlCr}^{N1}$ increase with increasing Al concentration, whereas$\tilde D_{CrAl}^{N1}$ and$\tilde D_{CrCr}^{N1}$ show little concentration dependence on Cr alone. A ternary, finite-difference interdiffusion model was employed to predict concentration profiles for the γ/γ couples utilizing the concentration dependence of the measured diffusivities. Good agreement was observed between the predicted and measured concentration profiles for both 1100 and 1200 °C.