Influence of diffusional stress relaxation on growth of stoichiometric precipitates in binary systems

Precipitation is usually connected with a significant misfit strain which may drastically influence the precipitation kinetics. Very recently it was demonstrated by Svoboda et al. [Svoboda J, Gamsjäger E, Fischer FD. Philos Mag Lett 2005;85:473] that the stress fields due to misfit strains can be effectively relaxed by the diffusive transport of vacancies in the matrix and their annihilation or generation at the precipitate/matrix interface. This idea has provided motivation to develop a new model for the simultaneous precipitate growth and misfit stress relaxation in binary systems. The actual state of the precipitate is described by its effective radius and by the thickness of the layer of the matrix atoms deposited at the precipitate/matrix interface. For these parameters the evolution equations are derived by application of the thermodynamic extremal principle. The model is applied to the Fe–C system by considering the growth of a cementite precipitate in the ferritic matrix. The influence of the stress relaxation on the precipitate growth kinetics is demonstrated.