A model for solute diffusion in metals based on elasticity concepts

Abstract

On the basis of elasticity theory, a model for solute diffusion in metals is presented. Postulating a vacancy mechanism, the basic problem is considered to be the calculation of the enthalpy of movement of a solute ion from a normal lattice site into the saddle-point position adjacent to the vacant site. In this model the solute ion is considered to behave as an elastic sphere and thus part of the enthalpy of jumping is assumed to result from the two-dimensional hydrostatic compression of the solute ion and part from the dilation of the constriction which represents the saddle point. An equation is derived on the basis of this model which permits calculation of the activation energy for solute diffusion in terms of the Goldschmidt radius of the solute and the compressibilities of the solute and solvent. The theory is compared with solute diffusion activation energies measured experimentally in nickel and silver as solvents, and good agreement between theory and experiment is observed.