Diffusion coefficients and atomic mobilities in fcc Ni–Cu–Mo alloys: Experiment and modeling

Abstract

Kinetic characteristics for Ni–Cu–Mo alloys are critically important for the establishment of the atomic mobility database in Ni-based superalloys. In the present work, the interdiffusion coefficients in fcc Ni–Cu–Mo alloys at 1273, 1373 and 1473 K have been determined from the concentration profiles across the solid–solid diffusion couples by means of EPMA (Electron Probe MicroAnalysis). The kinetic parameters for fcc Ni–Mo alloys are reassessed due to the discordance of self-diffusivity for Ni in fcc Ni–Mo and Ni–Cu phases. On the basis of the obtained interdiffusion coefficients in this work together with the thermodynamic description available in the literature, atomic mobilities of fcc Ni–Cu–Mo alloys were optimized as a function of the temperature and composition by means of CALTPP (CALculation of Thermo-Physical Properties) program. The three-dimensional surfaces for interdiffusivities, pre-exponential factor and activation energy for Cu and Mo were depicted for the purpose of understanding the variation of kinetic phenomenon. Good agreements between the calculated diffusivities, concentration profiles and diffusion paths and the experimental ones indicate that the presently obtained atomic mobilities of fcc Ni–Cu–Mo system are reliable.