The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia

Volodymyr Kulyk; Zoia Duriagina; Bogdan Vasyliv; Valentyna Vavrukh; Taras Kovbasiuk; Pavlo Lyutyy; Volodymyr Vira

doi:10.3390/ma15082707

The Effect of Sintering Temperature on the Phase Composition, Microstructure, and Mechanical Properties of Yttria-Stabilized Zirconia

Materials (Basel). 2022 Apr 7;15(8):2707. doi: 10.3390/ma15082707.

Authors

Volodymyr Kulyk¹, Zoia Duriagina^{1

2}, Bogdan Vasyliv³, Valentyna Vavrukh¹, Taras Kovbasiuk¹, Pavlo Lyutyy¹, Volodymyr Vira⁴

Affiliations

¹ Department of Materials Science and Engineering, Lviv Polytechnic National University, 12 S. Bandera Str., 79013 Lviv, Ukraine.
² Department of Materials Engineering, The John Paul II Catholic University of Lublin, 14 Racławickie Al., 20-950 Lublin, Poland.
³ Department of Hydrogen Technologies and Alternative Energy Materials, Karpenko Physico-Mechanical Institute, 5 Naukova Str., 79060 Lviv, Ukraine.
⁴ Department of Strength of Materials and Structural Mechanics, Lviv Polytechnic National University, 12 S. Bandera Str., 79013 Lviv, Ukraine.

Abstract

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.

Keywords: YSZ ceramics; fracture micromechanism; fracture toughness; microhardness; microstructure.