Limitations on the sintering of graded particle systems

Improvement of compact density is commonly achieved by blending coarse and fine particles, but these compacts will not densify without the presence of a significant amount of liquid phase. It was proposed that two step sintering (TSS) could be applied to sinter the fine particle matrix, potentially accommodating the presence of inclusions of large particles. This hypothesis was false. Compacts were prepared with similar green density but with different ratios of coarse, medium, and fine particles and then subjected to TSS. The results indicated that constrained sintering limits densification on both ends of the particle packing spectrum: A fine particle matrix containing large particles fails to densify because the matrix cannot shrink around the inclusion; the densification of fine particle pockets in a skeletal network composed of large particles does not allow sufficient shrinkage in the pockets of small particles.