Yttria-stabilized zirconia (YSZ) is well-known as a material with perfect mechanical, thermal, and electrical properties. It is used for manufacturing various high-temperature components for aerospace and energy generation, as well as wear- and corrosion-resistant devices in medicine. This work investigated the effect of a Y₂O₃ addition to ZrO₂ on the microstructure and mechanical properties of YSZ ceramics produced by one sintering schedule. ZrO₂ ceramics doped with 3, 4, 5, 6, 7, and 8 mol% Y₂O₃ (designated 3YSZ through to 8YSZ) were prepared by using conventional sintering at 1550 °C for 2 h in argon. The effect of yttria content was analyzed with respect to grain size, morphology of the microstructural features, phase composition, parameters of fracture surface, and flexural strength. The 7YSZ ceramics sintered at 1550 °C for 2 h showed the highest level of flexural strength due to the formation of the fine-grained microstructure containing mainly the monoclinic and tetragonal zirconia phases. The fracture micromechanism in the studied YSZ ceramics is discussed.

It is known that the yttria-stabilized zirconia (YSZ) material has superior thermal, mechanical, and electrical properties. This material is used for manufacturing products and components of air heaters, hydrogen reformers, cracking furnaces, fired heaters, etc. This work is aimed at searching for the optimal sintering mode of YSZ ceramics that provides a high crack growth resistance. Beam specimens of ZrO₂ ceramics doped with 6, 7, and 8 mol% Y₂O₃ (hereinafter: 6YSZ, 7YSZ, and 8YSZ) were prepared using a conventional sintering technique. Four sintering temperatures (1450 °C, 1500 °C, 1550 °C, and 1600 °C) were used for the 6YSZ series and two sintering temperatures (1550 °C and 1600 °C) were used for the 7YSZ and 8YSZ series. The series of sintered specimens were ground and polished to reach a good surface quality. Several mechanical tests of the materials were performed, namely, the microhardness test, fracture toughness test by the indentation method, and single-edge notch beam (SENB) test under three-point bending. Based on XRD analysis, the phase balance (percentages of tetragonal, cubic, and monoclinic ZrO₂ phases) of each composition was substantiated. The morphology of the fracture surfaces of specimens after both the fracture toughness tests was studied in relation to the mechanical behavior of the specimens and the microstructure of corresponding materials. SEM-EDX analysis was used for microstructural characterization. It was found that both the yttria percentage and sintering temperature affect the mechanical behavior of the ceramics. Optimal chemical composition and sintering temperature were determined for the studied series of ceramics. The maximum transformation toughening effect was revealed for ZrO₂-6 mol% Y₂O₃ ceramics during indentation. However, in the case of a SENB test, the maximum transformation toughening effect in the crack tip vicinity was found in ZrO₂-7 mol% Y₂O₃ ceramics. The conditions for obtaining YSZ ceramics with high fracture toughness are discussed.

Flexural strength, hardness, and fracture toughness are the basic mechanical properties of ceramic materials. Manufacturers widely use this set of properties to ensure the durability of ceramic products. However, many factors, such as chemical and phase compositions, sintering temperature, average grain size, density, and others, affect these properties, making it challenging to estimate corresponding reliability parameters correctly. Experimental examination of the impact of these factors on the mechanical properties of ceramics is a rather time-consuming and resource-consuming procedure. This work aims to predict the mechanical properties of zirconia ceramics using machine learning tools. The authors have created an experimental database for predicting the hardness, flexural strength, and fracture toughness of ZrO2-based ceramics based on chemical composition, phase composition, microstructural features, and sintering temperature on the mechanical properties of zirconia ceramics. The authors compare compared the effectiveness of using different machine learning algorithms and have found a high accuracy of the predicted values of each of the three mechanical properties using boosting ensemble methods. Also they developed a stacked ensemble of machine learning methods to improve the accuracy of determining the hardness property prediction task. We obtained the increase in accuracy of more than 10% (R2) using our approach.

The lifetime of products made of ceramic materials is related to their mechanical characteristics such as strength, hardness, wear resistance, and fracture toughness. The purpose of this work was to study the effect of sintering temperature on the phase-related peculiarities of the microstructures, causing changes in the flexural strength and fracture toughness of fine-grained ZrO₂–Y₂O₃–Al₂O₃–CoO–CeO₂–Fe₂O₃ ceramics. Flexural strength and fracture toughness tests were carried out using ceramics sintered in three modes (2 h at 1550 °C, 1580 °C, and 1620 °C in argon), and thorough phase, microstructure, and fractographic analyses were performed. For the ceramic sintered at 1550 °C, a mixed mechanism of intergranular fracture of the t-ZrO₂ phase particles and cleavage fracture of the Ce–Al–O phase particles was found, which is reflected in its comparatively low fracture toughness. For the ceramic sintered at 1580 °C, a fracture developed along the boundaries of the aggregates, made of completely recrystallized fine ZrO₂ grains with a high bond strength between adjacent t-ZrO₂ grains; this corresponds to the highest fracture toughness (5.61 ± 0.24 MPa·m^1/2) of this ceramic. For the ceramic sintered at 1620 °C, a transgranular fracture of the t-ZrO₂ phase and Ce–Al–O phase particles and crack propagation along the t-ZrO₂/Ce–Al–O interface were revealed; this caused a decrease in fracture toughness.

The purpose of this work is to study the effect of sintering modes, especially the sintering temperature, on the crystal lattice parameters and the morphology of the ZrO2–nY2O3 (n = 3–8 mol%) ceramic microstructure components in relation to corresponding fracture micromechanisms.The series of ZrO2–nY2O3 (n = 3–8 mol%) ceramics were sintered in an argon atmosphere at temperatures 1450C, 1500C, 1550C, and 1600C. The cross-sectional surfaces of samples were prepared for microstructure analysis using a grinding and polishing Struers Tegramin machine. Young’s ceramics modulus values were determined using an ultrasonic flaw detector Panametrics EPOCH III 2300. The samples’ density and porosity were determined by the Archimedes’ method. Scanning electron microscopes Hitachi SU3900 and Carl Zeiss EVO-40XVP were used to analyse the microstructure and fracture surface morphology of samples. For estimating chemical compositions in an energy-dispersive X-ray spectroscopy mode, an INCA ENERGY 350 spectrometer was utilized. Microhardness measurement was performed on a NOVOTEST TC-MKB1 microhardness tester. The fracture toughness of the material was estimated using a single-edge notch beam (SENB) test and the Vickers indentation test. Both the flexural strength and SENB tests were performed under three-point bending using a UIT STM 050 test machine. All mechanical tests were carried out in air at a temperature of 20C.Optimal sintering modes for a variety of YSZ ceramic compositions are found, taking into account the combined effect of the sintering temperature and a percentage of Y2O3, which resulted in a specified balance of cubic, tetragonal, and monoclinic zirconia phases, an optimal microstructure features, and the implementation of high-energy fracture micromechanisms responsible for high strength and fracture toughness of YSZ ceramics.To study the behaviour of YSZ ceramics in the operating atmosphere, their microhardness, flexural strength, and fracture toughness should be evaluated under the operating temperature and pressure conditions.Based on the research performed, it is possible to design the microstructure of YSZ ceramic with the necessary physical and mechanical properties to provide high reliability of ceramic products in various industry branches.The balance of cubic, tetragonal, and monoclinic zirconia phases, as well as the crystal lattice parameters change, was determined for YSZ ceramics stabilized with the various amounts of yttria, and it was linked to their mechanical behaviour; the Vickers indentation method and SENB method were used to estimate crack growth resistance of YSZ ceramics, and an appropriate fracture micromechanism was found.

Crack growth resistance of ZrO2-(3-8) mol% Y2O3 ceramics was investigated. Young's modulus by the ultrasonic flaw detection method were determined. Vickers hardness and parameters of cracks after Vickers indentation were obtained. Based on the Young's modulus values, Vickers hardness, and parameters of cracks, the fracture toughness of the investigated ceramics was calculated using 9 different equations of the Vickers indentation method. A comparative analysis of the calculated fracture toughness values with those obtained by the single-edge notch beam method was carried out. It was found that choosing the optimal equation for calculating fracture toughness by the Vickers indentation method is quite difficult and requires comparison with the results of standardized tests. It was shown that to determine crack resistance characteristics of the yttria-stabilized zirconia ceramics, the use of only the Vickers indentation method without comparison with other methods of fracture mechanics is incorrect.