Lutsenko G. The influence of external fluxes and fluctuations on the ripening at high initial supersaturation

The thesis is devoted to the investigation of the precipitation and ripening processes both in the closed and open systems with high volume fraction of new phase. The process of ripening was considered with taking into account the noise from different sources. At that the idea of diffusion screening was supplemented with taking into consideration for noise of the composition. A noise of concentration appears in the deviation of parent phase concentration in the vicinity of particle from the mean-field value. First the dependence of noise level on the volume fraction of new phase was obtained. Also the correlation effects were investigated by using the simulations. Both factors lead to the widening of the particle size distribution and to the distribution parameters more close to the experimentally observed ones. Also the ripening of scallop phase Cu6Sn5 in open system Cu/molten solder was analyzed. In our model the deviations from mean-field approximation caused by noise of chemical potentials were taken into account. The obtained value of standard deviation s=0.42 is in close agreement with experimental results. The ripening in non-dilute binary solutions was theoretically analyzed with taking into account the influence of non-equilibrium vacancies, generated by non-equal intrinsic fluxes of the components. It was shown analytically and by computer simulations, that in case of coherent precipitates the ripening kinetics demonstrates 3 stages, with second stage characterized by time-exponent more close to 1/2 instead of well-known 1/3 law. The ripening of the stoichiometric ternary phase in weak solid solution was considered. The growth of non-stoichiometric particles of intermediate ternary phase during the decomposition of supersaturated weak solution was considered. In contrast to the binary systems a non-parabolic growth of precipitates can be caused by purely diffusive reasons (without taking into account a interface kinetics). The ripening of 3D-islands in thin films was analyzed for two cases - without external flux and in the presence of external flux which varies in time.