Diffusion Coefficients of the Ni-Co-Fe Alloys Studied by Molecular Dynamics Simulation and CALPHAD Assessment

Diffusion is one of the key research interests in developing advanced materials and processes, but acquisition of diffusion coefficients is a bottleneck. Hereby we propose a hybrid scheme that couples the molecular dynamics (MD) simulation for calculating tracer diffusion coefficients, with the CALPHAD method providing experimental benchmarks for pure metals and assessing atomic mobilities. After verifying the scheme by studying the fcc Ni-Co-Fe ternary alloys (including its pure components and binary sub-systems) at 1600 K, for which sufficient amount of experimental data as well as the CALPHAD assessments are available, this scheme demonstrates the ability of establishing a mobility database efficiently with reduced experimental efforts. In order to reconcile the MD simulations with the experiments, a priority is to determine impurity and self-diffusion coefficients for pure metals by CALPHAD assessments of the experimental data from the literature as benchmarks and thus set up a set of elemental bases for pure metals. Then all the MD calculated tracer diffusion coefficients were normalized accordingly, followed by the CALPHAD assessments to develop an atomic mobility database, from which all types of diffusion coefficients can be readily calculated.