The transition point between the Harrison type-A to type-B kinetics regimes as well as the emerging intermediate AB transition regime had been analyzed in detail by making use of lattice Monte Carlo simulations of tracer depth concentration profiles as a function of diffusion time and distance between grain boundaries e.g.. The principal model in this area was the grain boundary slab model. However, depending on the diffusion time and grain size a given tracer atom could be expected to cross a number of grain boundaries in its diffusion time. This had been taken into account in square and cubic grain models for determining the limit of the Harrison type-A regime. In the present study, the limits of the intermediate AB transition regime were determined, where the lattice Monte Carlo method was used to analyze the tails of tracer concentration depth profiles. The applicability of different solutions for the grain boundary diffusion analysis was numerically investigated for the 3D model. The solutions were those by Whipple-LeClaire and Suzuoka, Bokstein, Magidson and Svetlov, Levine and MacCallum for the type B kinetic regime and that by Divinski and Larikov for the intermediate Type-AB regime. A review was also presented of the progress that had been made concerning the limits of the various Harrison regimes, supplemented with the results of the present simulations. An empirical factor of 1.5 should be applied when Suzuoka or Whipple-LeClaire solutions were applied to the analysis of the tracer diffusion profile, tail section, in the polycrystalline material and an empirical factor of 2.0 should be applied when Bokshtein-Magidson-Svetlov solution was applied to the analysis of the tracer diffusion problem in the polycrystalline material.

Investigation of Harrison Type-A, B and Intermediate AB Kinetics Regimes in Grain Boundary Diffusion. I.V.Belova, G.E.Murch: Defect and Diffusion Forum, 2008, 283-286, 697-704