Sintering Crystalline Solids. I. Intermediate and Final State Diffusion Models

TLDR

Photomicrographs of pore and grain boundary structures in sintered powder compacts are presented to qualitatively describe the key phases of densification. The study selects appropriate grain and pore geometries for diffusion sintering models and emphasizes the need for simultaneous isothermal densification and grain growth data. The principal models assume bulk diffusion with grain boundaries acting as vacancy sinks, treating the pore phase as continuous at three‑grain edges or discontinuous at four‑grain corners. The models predict a constant density‑change rate when diffusion coefficient and grain size are fixed, and they also provide an explicit relationship between densification rate, pore spacing, and grain size during discontinuous grain growth.

Abstract

Photomicrographs of pore and grain boundary structures in sintered powder compacts are presented to provide the basis for qualitative description of the important phases of the course of densification. From this guide, appropriate grain shapes and pore shapes and locations are selected for the formulation of diffusion sintering models. The principle models presented are for bulk diffusion transport with the grain boundaries as vacancy sinks when the pore phase is continuous and coincident with three grain edges, and also when the pore phase is discontinuous and located at four-grain corners. These models predict that the rate of density change is constant when the diffusion coefficient and grain size are constant. The need for simultaneous isothermal densification and grain growth data is indicated. The explicit change in densification rate with discontinuous grain growth is predicted in terms of pore spacing and grain size.