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.