A Study of Microstructural Evolution During Sintering Using Tessellation

Understanding the correlation between microstructure, properties, and processing conditions will aid in producing new or improved products. Microstructural characteristics typically used in materials science (grain size, pore size, etc.) may not identify the complete processing, microstructure, and property relationships because the relevant characteristics of the microstructure may be observed only at a higher length scale. A meso-scale characterization of microstructure was invaluable in identifying the effect of flocculation during slip casting on the evolution of the relationships during the sintering of alumina at 1350°C. Boundary tessellation of features segments a materialographic section into regions with dimensions larger than the scale of the feature. These regions contain the feature and its immediate environment allowing the definition of microstructural parameters on a meso-scale. To develop the methods and interpretation of meso-scale parameters, alumina powder cast under two dispersion conditions, dispersed and flocculated, sintered at 1350°C to minimize coarsening in the flocculated alumina during intermediate stage sintering, provides a materials system in which many of the variables associated with microstructure and processing are held constant for the two different 'materials' (dispersed and flocculated alumina) through a range of densities. The results of this work show that meso-scale characteristics of the microstructure obtained by boundary tessellation of pore sections were correlated with the observed higher densification rate for dispersed alumina at low densities (VV < ∼0.85) and the evolution to higher densities, while 'typical' microstructural parameters such as grain size, pore size, and surface area per unit volume did not correlate with the evolution of the densification rate. The presence of a rearrangement process at lower densities is proposed as the mechanism responsible for the differences in densification rate at relative densities below ∼0.90. Although the methodology developed for this study was specific to the sintering of alumina powder compacts formed by slip casting, the use of tessellation may be applied to other systems in which the spatial arrangement of 'particles' is of importance