Effect of Heat Treatment of the Starting Powders on the Consolidation of Zirconia-Toughened Alumina Composites

Abstract

The influence of heat treatment temperature of the starting powders, ranging from 400 to 1450°C, on the consolidation of zirconia-toughened alumina (ZTA) composites was studied. In these composites, particles of a ZrO₂ (Y₂O₃, CeO₂) solid solution with high fracture toughness are dispersed in an Al₂O₃ matrix. The powders for developing the ZTA composites (wt.%)—90 Al₂O₃–10 (ZrO₂ (Y₂O₃,CeO₂) (90 AZK) and 70 Al₂O₃–30 (ZrO₂ (Y₂O₃,CeO₂) (70 AZK)—were produced using a combination of hydrothermal synthesis and mechanical mixing. Cold uniaxial pressing and sintering in air at 1600°C for 1.5 h were employed for the consolidation. The sintered materials were examined by X-ray diffraction and scanning electron microscopy. The compaction of the composites was associated with the brittle fracture of hard sintered agglomerates (for 90 AZK) and with the plastic deformation effect (for 70 AZK). The sintering of the 90 AZK and 70 AZK composites was accompanied with ZrO₂ phase transformations, abnormal growth of the Al₂O₃ grains, and zonal segregation effect. The Zener pinning effect in the 70 AZK composites inhibited the abnormal growth of Al₂O₃ grains. The increased porosity of the 90 AZK composites was due to the bimodal distribution of the starting powder agglomerates in accordance with the shape factor. The Vickers hardness of the 90 AZK samples varied from 6.4 to 4.4 GPa and that of the 70 AZK samples from 10.3 to 7.2 GPa. The decreased hardness of the 90 AZK composites was attributed to the formation of a two-scale porous microstructure. The topological memory of the ceramics was demonstrated to determine the conditions for microstructural design of advanced ZTA composites for tool, structural, and functional purposes with the required properties.