Fabrication of Meta-Stable Monoclinic Zirconia Ceramics with a High Density Using a Piston-Cylinder Type High-Pressure Apparatus

Abstract

Single phase m-ZrO₂ ceramics (∼13mm^φ and 3-5mm^t) have been fabricated using a piston-cylinder type high-pressure apparatus under 1GPa at 1023-1173K, in which a newly developed high-pressure cell has been utilized to introduce pseudo-isostatic pressure. Starting material, meta-stable m-ZrO₂ powder prepared via a sol-gel method, was characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). Dense ceramics sintered at 1123K, free from macro-cracks, showed a high relative density of ∼ 99.5% and homogeneous microstructures consisting of fine grains (∼1μm). In-situ XRD analysis under high pressures and temperatures revealed that m- to t-ZrO₂ transition took place around 1123K under 1GPa. Mechanical properties of m-ZrO₂ ceramics have been evaluated ; the maximum values of bending strength (σ_b = 520MPa), Vickers hardness (H_v = 9.8GPa), and fracture toughness (K_IC = 3.9MPa·m^1/2) were achieved at the samples fabricated at 1123K.