SUBSTITUTIONAL DIFFUSION IN AN ORDERED SYSTEM

A general treatment of the atomic diffusion in alloys is given using the path probability method with an approximation taking a pair of lattice points as the basic cluster. Diffusion coefficients for ternary alloys for any degree of order by vacancy mechanism are given. The equations are then simplified by regarding the third atomic species as the isotope of the second atomic species. The theory then gives the isotope diffusion coefficient in binary alloys as functions of the degree of order and of the composition; this diffusion coefficient corresponds directly to the experimental results, and they are compared. The specific importance of the correlation effect in the multicomponent system is emphasized. The calculation of the required physical quantities, the degree of long-range order, short-range order, the distribution of the vacancies, etc., in the equilibrium state in ternary alloys with vacancies are also given in the Appendices.