Phase composition, microstructure, and mechanical properties of ZTA ceramics prepared by gelcasting using multi-gradation spherical powders

In this study, three micron-level spherical Al 2 O 3 powders (A: d 50 =98.7 μm; B: d 50 =48.7 μm; C: d 50 =5.9 μm), a submicron-level irregularly-shaped Al 2 O 3 powders (D: d 50 =0.8 μm), and a submicron-level irregularly-shaped yttria-stabilized zirconia powders (d 50 =0.5 μm) were used as raw materials to prepare 65 vol% zirconia-toughened alumina (ZTA) slurries with viscosity value of < 1.0 Pa·s near 100 s −1 by optimizing the pH value of slurries (pH=9–11) and particle gradation and powder ratio (A:B:C:D=0.63:5.67:2.7:1) using Dinger-Funk model. The ZTA ceramics prepared through gelcasting and pressureless sintering achieved a high densification of 97.94 % owing to high solid loading (65 vol%) and high sintering temperature (1700 ℃ for 2 h). Leveraging the synergistic effects of stress-induced t→m-ZrO 2 phase transformation toughening, micro-crack toughening, and dispersion strengthening, the ZTA ceramics exhibited good mechanical properties with a flexural strength of 577.2 MPa and a fracture toughness of 6.33 MPa·m 1/2 . Additionally, they exhibited apparent porosity, bulk density, and linear shrinkage of 0.42 %, 4.28 g/cm 3 , and 8.72 %, respectively. This study shows that the combination of gelcasting and pressureless sintering is a promising technical route to fabricate the high-strength and low-shrinkage ZTA ceramics using multi-gradation spherical Al 2 O 3 powders as raw materials.