Diffusion correlation in random alloys

The solid state diffusion process in random binary alloys has been simulated on a computer array of A and B atoms, coded in the relevant cubic symmetry. The process was a Monte Carlo sequence on which were superimposed the appropriate conditions of concentration and defect-atom exchange frequencies. Correlation factors for atoms and vacancies have been obtained for b.c.c. and f.c.c. random alloys. Their validity was verified for monatomic solids of the same symmetry, for which correlation factors are known to a high degree of accuracy from random walk analysis. The reproducibility of the simulation method varies between 4% and 1% contingent upon the degree of correlation. Semi-empirical polynomials of degree z−1 ( z is the coordination number for the particular lattice symmetry) for − t versus concentration describe the results obtained accurately ( t is defined by ƒ = (1+t)/(1−t)). Comparison with the calculations by Manning shows discrepancies which are only significant when there is considerable correlation. There are, however, substantial differences between the present results and those of Kikuchi and Sato over the entire concentration and frequency ranges.