The effect of compaction pressure and sintering temperature on phase evolution and technological properties of alumina mullite zirconia ceramics

Alumina-mullite-zirconia ceramic composites were fabricated using a solid-state reaction involving nano silica, alumina, and zirconia powder mixes at varying sintering temperatures (1450-1600 °C) and compaction pressures (80-160 MPa). Magnesia was added in a consistent proportion to stabilize the tetragonal phase of zirconia at room temperature and as sintering aid. The densification parameters of sintered ceramic composites, namely bulk density, apparent porosity, and linear change, were measured. The phase composition and microstructure of sintered ceramics were determined using XRD and SEM. The results show that a specific quantity of nano silica (5 wt%) plays an important role in improving the sintering and densification parameters of sintered samples. Compaction pressures of up to 120 MPa enhanced the densification parameters in sintered samples due to increases in powder compact and sold state sintering processes. Stress-induced phase transformation from tetragonal to monoclinic in zirconia, which is accompanied by a 3-5% volume expansion, may improve the mechanical properties of sintered samples. This volume expansion forms a compressive stress zone around a crack tip, thereby preventing it from propagating.