Diffusion behavior in Nickel-Aluminium and Aluminium-Uranium diluted alloys

TL;DR

This study uses a low-cost classical molecular statics technique to accurately model impurity diffusion in Nickel-Aluminium and Aluminium-Uranium alloys, aligning well with experimental data and revealing vacancy-mediated migration mechanisms.

Contribution

It demonstrates the effectiveness of CMST in calculating microscopic parameters and macroscopic diffusion properties in alloy systems, including vacancy mechanisms and potential vacancy drag at lower temperatures.

Findings

Calculated diffusion coefficients agree with experimental data.

Diffusion occurs via vacancy exchange in the studied alloys.

Possible vacancy drag mechanism below 550K in Al-U alloy.

Abstract

Impurity diffusion coefficients are entirely obtained from a low cost classical molecular statics technique (CMST). In particular, we show how CMST is appropriate in order to describe the impurity diffusion behavior mediated by a vacancy mechanism. In the context of the five-frequency model, CMST allows to calculate all the microscopic parameters, namely: the free energy of vacancy formation, the vacancy-solute binding energy and the involved jump frequencies, from them, we obtain the macroscopic transport magnitudes such as: correlation factor, solvent-enhancement factor, Onsager and diffusion coefficients. Specifically, we perform our calculations in f.c.c. diluted Ni-Al and Al-U alloys. Results for the tracer diffusion coefficients of solvent and solute species are in agreement with available experimental data for both systems. We conclude that in Ni-Al and Al-U systems solute atoms migrate by direct interchange with vacancies in all the temperature range where there are available experimental data. In the Al-U case, a vacancy drag mechanism could occur at temperatures below 550K.