Atomistic study of diffusional mass transport in metals

Rigorous theoretical or phenomenological treatments of microstructure evolution in processes such as ageing or irradiation are based on particular mechanisms of mass transport, i.e. diffusion mechanisms. The information about such mechanisms is usually taken from simple theoretical models derived from experimental data. This works well in simple cases, but is limited in complicated situations like anisotropic diffusion, diffusion in alloys, etc., where the diffusion mechanism is not obvious. In the light of this, the atomic-scale molecular dynamics (MD) technique is a useful tool for identifying and studying actual mechanisms. In this paper we present the results of state-of-the-art MD studies applied to diffusional processes in bulk pure metals. We give a general formulation of the treatment of MD simulations of diffusion and discuss and compare methods to extract information about particular diffusion mechanisms. Examples of calculation of self-diffusion and defect diffusion coefficients and correlation factors, and treatment of diffusion mechanisms, are given for vacancy and self-interstitial atom diffusion in fcc, bcc and hcp metals. The cases of mass transport via small defect clusters (both vacancy and interstitial) are also discussed and examples are presented.