Microstructure and properties of ZrO₂-ZrSiO₄ ceramic composites obtained by reactive sintering

Abstract

ZrO₂-ZrSiO₄ composites obtained from mixtures of 3Y-TZP and SiO₂ powders were investigated. Commercial 3Y-TZP powder and mixtures containing 5 or 10 wt% of SiO₂ were prepared. Specimens (n=10/group) were uniaxially compacted and sintered at 1500 °C-2 h (5 °C/min). Sintered samples were characterized by their relative density, X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, and Vickers nanoindentation. The monolithic-ZrO₂ sample presented full densification while increasing of SiO₂ content progressively reduced the relative density. The crystalline phases presented in composites were tetragonal-ZrO₂, cubic-ZrO₂, ZrSiO₄, monoclinic-ZrO₂, and residual cristobalite (SiO₂). Microstructural analysis indicated a distribution of zirconia grains, with heterogeneous regions rich in SiO₂ surrounded by ZrSiO₄ grains. Vickers hardness of 1590±19 HV for monolithic ZrO₂, 1475±27 HV for ZrO₂-5 wt% SiO₂, and 1336±32 HV for ZrO₂-10 wt% SiO₂ were obtained indicating reduction in hardness with increasing SiO₂ fraction. Furthermore, a reduction in fracture toughness was observed (7.2±0.8, 6.7±0.5, and 5.4±1.0 MPa.m^1/2, respectively) and Young’s moduli measured were 174.1, 169.7, and 225.9 GPa, respectively. These experiments demonstrated, preliminarily, that the ZrO₂-ZrSiO₄ composite, based on 3Y-TZP-SiO₂ powder mixtures, can achieve good levels of densification and present reasonab le mechanical properties, requiring improvements in microstructural homogenization. However, the presence of SiO₂ and ZrSiO₄ can improve the adhesion of zirconia to resin cement, requiring future studies focused on adhesion to confirm its viability.

Keywords:
ceramic composites; ZrO₂-SiO₂ system; reactive sintering; phase transformations; mechanical properties