SOLUTE SEGREGATION IN VACANCY GRADIENTS GENERATED BY SINTERING AND TEMPERATURE CHANGES

The heating, cooling, sintering or irradiation of a material can generate vacancy flows which produce solute gradients around vacancy sources and sinks such as free surfaces, grain boundaries and internal pores. The magnitude and spatial extent of such solute gradients are calculated in terms of the solute diffusivity, the solvent diffusivity, the binding energy of a solute-vacancy pair, the magnitude and spatial extent of the vacancy gradient and the total vacancy flow. For substitutional solutions, it is shown that solute enrichment of vacancy sinks occurs when the solute-vacancy binding energy is much larger than, the thermal energy, provided that solute-vacancy pairs are relatively mobile. In contrast when the solute-vacancy binding energy is the order of the thermal energy or less, solute depletion will occur around vacancy sinks in substitutional solutions if the solute diffusivity exceeds the solvent diffusivity. © 1969.