Assessment of the diffusion mobilites in the γ′ and B2 phases in the Ni–Al–Cr system

This work presents the assessment of the diffusion mobilities in both the γ′ (Ni3Al-L12) and B2 (NiAl) phases in the Ni–Al–Cr system utilizing the phenomenological model developed by Helander and Agren. Available experimental tracer diffusivity, interdiffusion coefficients and activation energies were evaluated and then used to optimize the composition- and temperature-dependent diffusion mobilities. For both the B2 and γ′ phases, the assessed diffusion mobility descriptions reproduce the Arrhenius temperature dependence for the Ni, Al and Cr tracer diffusivities and interdiffusion coefficients. The assessment reproduces the strong composition dependence of the diffusivities in the B2 phase observed experimentally. The measured composition dependences of the diffusivities in the γ′ phase are also replicated by the present mobility descriptions. The assessed mobility descriptions are validated by comparing calculated and measured composition profiles for a variety of Ni–Al and Ni–Al–Cr diffusion couples, including B2/B2, γ (fcc)/γ′ and γ/B2 couples.