Functionally Graded Al2O3-CTZ Ceramics Fabricated by Spark Plasma Sintering

Zirconia-Toughened Alumina (ZTA) Nanoceramics with a Gradient Microstructure: A Comparative Study of ZTA Ceramics with Fibrous and Granular Morphology

ZrO2-toughened Al2O3 (ZTA) ceramic composites with a porosity gradient and with improved mechanical properties have a wide range of possible applications. We fabricated nanofibrous and nanogranular Y-ZTA and Ce-ZTA composites with a gradient microstructure by creating a temperature gradient during SPS sintering, with the use of asymmetric graphite tool arrangement (ASY). In this study, we examined the morphology effect of the starting materials on the sintering process and on the final microstructure, as well as the mechanical properties of the composites. A large temperature difference was established for both the granular and fibrous samples fabricated in the ASY configuration, which resulted in gradient porosity along the ceramics bodies: the upper part of the ceramics showed a highly porous fine microstructure, while the opposite side was highly densified. The final microstructure of the composites can be tailored by varying the morphology of the starting ceramics or the graphite configuration. A highly porous skeleton-like structure was formed by sintering fibres in the ASY configuration, whereas the granular precursors resulted in a much less porous composite. The microstructure affected the mechanical properties of the composite. Improved hardness and more than 50% higher compression strength were obtained for the granular Ce-ZTA samples as compared to the fibrous sample. Gradient porosity with fibrous or granular morphology promotes the penetration of bioactive nanosized hydroxyapatite (HAp) into the pore structure. Fibrous ZTA absorbs HAp more effectively due to its higher porosity as well as its bimodal pore structure.

Preparation and Characterization of Fibrous Alumina and Zirconia Toughened Alumina Ceramics with Gradient Porosity

This paper investigated a synthesis process for highly porous Al₂O₃, Y-ZTA, and Ce-ZTA ceramic nanocomposites with gradient microstructure and improved mechanical properties. Ceramic nanofibres were synthesized as the starting material. The gradient microstructure was developed during spark plasma sintering using an asymmetric graphite arrangement that generated significant temperature differences (80-100 °C) between the opposite sides of the samples. Structural and mechanical properties of the fibrous ceramic composites were investigated. The effect of the temperature gradient on properties was also discussed. While the asymmetric configuration resulted in a gradient porosity, reference samples fabricated in standard graphite configuration were uniformly porous. The gradient structure and the ZrO₂ addition led to improved hardness and compression strength of the sintered samples. However, the opposite sides of the samples exhibited considerable variations in both microstructure and in terms of properties. The upper part of the Ce-ZTA ceramic showed a highly porous structure with 18.2 GPa hardness, while the opposite side was highly densified with 23.0 GPa hardness. Compressive strength was 46.1 MPa and 52.1 MPa for Y-ZTA and Ce-ZTA sintered at 1300 °C, respectively, despite their high porosity. The research provided a promising approach to prepare highly porous ZTA composites with high strength for a wide range of applications.