MODELING OF VOID DISTRIBUTION BY SIZE AT THE DIFFUSION ZONE

Abstract

At the interdiffusion and reaction diffusion which happens on the vacancy atomic diffusion  mechanism, the inequality of atoms  fluxes is caused by their differential mobility, give rise to a directional flux of vacancies.  This flux of vacancies cause an appearance of areas in a diffusion zone with supersaturation  and deficiency  in vacancies,  where  sinks / sources of non-equilibrium vacancies act.   The proposed model of void formation takes into account existence   two types of sinks / sources of non-equilibrium vacancies, depending on their location: in the phase volume and at the interfacial boundaries.  It is believed that the voids arise with a certain periodicity near the interfacial boundary, where there is a vacancy supersaturation  due to the different mobility of the components. The voids  move in volume of  growing phase,  their sizes change. The void radius increases as long as void is in the region  of the diffusion zone where there is a vacancy supersaturation. The void radius begins to decrease if the void  is in the area of the diffusion zone, where there is a  negative vacancy supersaturation  (the concentration of vacancies is less than the equilibrium) until it disappears. The simulation of void size distribution along the diffusion zone during the reaction diffusion process for a binary system is performed. The simulation results show that the work efficiency of vacancies sources/sinks affects not only the rate of void growth, but also the shape of the pore size distribution and their maximum size. In addition, each type of  vacancies sources/sinks has a different effect on the kinetics of void formation. Thus, the more work efficiency of vacancies sources/sinks in the phase volume, the wider the void formation area (the area where the voids exist) and the smaller the difference between pore sizes.