Stability of Ceramics Based on ZrO 2 Doped with Y 2 O 3 Under Hydrothermal Action
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Vol. 61, No. 4, November, 2020
STABILITY OF CERAMICS BASED ON ZrO2 DOPED WITH Y2O3 UNDER HYDROTHERMAL ACTION Yu. I. Komolikov,1,4 I. D. Kashcheev,2 V. R. Khrustov,3 and V. I. Pudov1 Translated from Novye Ogneupory, No. 8, pp. 14 – 17, August, 2020.
Original article submitted July 6, 2020. The influence of hydrothermal action on the physical and mechanical properties of ZrO2–Y2O3 (3 mol%) ceramics was investigated. The properties of specimens sintered at 1350°C in air and at 1850°C in vacuum followed by oxidative annealing at 1200°C in air were compared. The characteristics of specimens sintered at 1850°C were shown to be practically unchanged after hydrothermal treatment while specimens sintered at 1350°C showed a significant drop in strength and hardness of about 40 – 50%. Keywords: ceramic based on ZrO2 doped with Y2O3, hydrothermal action.
properties and eventually destroy the product [3, 4]. The present article reports results from research on the physical and mechanical properties of ceramics based on ZrO2–Y2O3 (3 mol%) under hydrothermal action.
INTRODUCTION Ceramics based on ZrO2 are widely used in modern technology because of their unique combination of properties (high mechanical strength, hardness, wear resistance, refractoriness, thermal conductivity, chemical inertness), which is responsible for stringent requirements on their reliability, longevity, and stability. Completely stabilized ZrO2 with a concentration of stabilizing additive that ensures preservation of the cubic phase of ZrO2 (C-ZrO2) has the most stable properties among ZrO2 systems [1]. Ceramics stabilized by Y2O3 (8 – 10 mol%) have reduced mechanical strength, hardness, wear resistance, and heat resistance. Tetragonal ZrO2 (T-ZrO2) has better strength parameters. Modern technologies can produce ceramics based on T-ZrO2 doped with 1.5 – 3.5 mass% Y2O3 that have bending strength values up to 2,000 MPa [2]. Degradation of the mechanical properties (aging) during exposure to moist and biologically aggressive media is one of the main limitations preventing broad application of T-ZrO2 ceramics. Aging includes the occurrence of a spontaneous tetragonal-monoclinic transition (T-ZrO2–M-ZrO2) that is associated with a volume increase and generation of surface microcracks that, in turn, degrade the mechanical 1 2 3 4
EXPERIMENTAL Test specimens were prepared using ZrO2–Y2O3 (3 mol%) solid solution powder obtained via coprecipitation of the components [5]. Starting specimens were molded as cylinders of diameter 12 mm and length 30 mm using slip-casting technology as described before [5]. Next, the blanks were dried, fired preliminarily at 900°C, and processed. The relative density of the blanks was about 35%. Specimens of length 25 mm and cross section 5 ´ 5 mm were cut from the blanks for mechanical tests and dilatometric studies. The obtained specimens were finally sintered under various conditions, e.g., one part was fired in air in an SNOL muffle furnace at 1350°C for 2 h; another, in a vacuum furnace at 1850°C for 1 h followed by oxidative
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