PHASE COMPOSITION STABILITY OF NANOSTRUCTURED COMPOSITE CERAMICS BASED ON CaO–ZrO2 UNDER HYDROTHERMAL IMPACT

Abstract

Structure, phase composition, and mechanical properties (microhardness within indenter penetration depths of 1200 nm ≤ h ≤ 6000 nm and fracture toughness) are studied on nanostructured zirconia ceramics (CaO stabilized) hardened with corundum and SiO₂ during accelerated aging under hydrothermal conditions (T_ag = 134°C, P = 3 atm, H = 100%, 0 ≤ t_ag ≤ 25 h). The use of CaO as a stabilizer of the zirconia tetragonal phase (instead of “conventional” Y₂O₃) promotes increasing resistance to hydrothermal effects of composite ZrO₂ + Al₂O₃ and ZrO₂ + Al₂O₃ + SiO₂ ceramics. The reached fracture toughness (more than in 40%) via introduction of silica (\({{C}_{{{\text{Si}}{{{\text{O}}}_{2}}}}}\) = 5 mol %) increase provides a satisfactory hardness/fracture toughness (H = 12.3 GPa, K_C = 6.66 MPa m^1/2) ratio of the Ca–ZrO₂ + Al₂O₃ + SiO₂ composite ceramics even after its accelerated 25-h aging.