Diffusion of vacancies and impurities in metals was important in many processes occurring in structural materials. This diffusion often takes place in the presence of spatially rapidly varying stresses. Diffusion under stress was frequently modelled by local approximations to the vacancy formation and diffusion activation enthalpies which were linear in the stress, in order to account for its dependence on the local stress state and its gradient. Here, more accurate local approximations to the vacancy formation and diffusion activation enthalpies, and the simulation methods needed to implement them, were introduced. The accuracy of both these approximations and the linear approximations were assessed via comparison to full atomistic studies for the problem of vacancies around a Lomer dislocation in Al. Results show that the local and linear approximations for the vacancy formation enthalpy and diffusion activation enthalpy were accurate to within 0.05 eV outside a radius of about 13Å (local) and 17Å (linear) from the centre of the dislocation core or, more generally, for a strain gradient of roughly up to 6 x 106 m-1 and 3 × 106 m-1, respectively. These results provide a basis for the development of multiscale models of diffusion under highly non-uniform stress.

Modelling Diffusion in Crystals under High Internal Stress Gradients. D.L.Olmsted, R.Phillips, W.A.Curtin: Modelling and Simulation in Materials Science and Engineering, 2004, 12[5], 781-97