The Influence of Silicon Dioxide on the Stability of the Phase Composition and Mechanical Properties of Alumina-Toughene
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ICAL SCIENCE OF MATERIALS
The Influence of Silicon Dioxide on the Stability of the Phase Composition and Mechanical Properties of Alumina-Toughened Zirconia-Based Ceramics A. A. Dmitrievskiia,*, A. O. Zhigacheva, D. G. Zhigachevaa, and V. V. Rodaeva a
Derzhavin State University, Tambov, 392000 Russia *e-mail: [email protected]
Received March 13, 2020; revised April 15, 2020; accepted April 24, 2020
Abstract—The influence of SiO2 impurity (with a concentration varying from 0 to 10 mol %) on the stability of tetragonal ZrO2 (t-ZrO2) and on a set of micro- and macromechanical properties of calcia-stabilized (CCaO = 6.5 mol %) alumina-toughened (C Al2O3 = 5.8 mol %) zirconia-based ceramics (ATZ ceramics) has been studied. It has been found that the introduction of SiO2 (CSiO2 = 5 mol %) raises fracture toughness Kc by nearly twofold (from 7.05 to 12.43 MPa m1/2), slightly decreases hardness H (from 12.75 to 10.9 GPa), and improves ultimate compression strength σS (from 2.44 to 2.73 GPa) and ductility (compression strain ε grows from 5.3 to 7.3%) of ATZ ceramics. It has been shown that the above improvements were achieved by means of a reduction in t-ZrO2 stability. DOI: 10.1134/S1063784220120075
INTRODUCTION Before 1975, zirconia-based ceramics (hereinafter, “ZrO2 ceramics”) was applied only as a refractory (fireproof) material. Wide application of pure ZrO2 as engineering or structural ceramics was limited by the spontaneous tetragonal ZrO2 (t-ZeO2)-to-monoclinic ZrO2 (m-ZrO2) phase transition under cooling (950°C), which is accompanied by an increase in volume by about 4% and shear strain (~16%). As a result, the material breaks down [1]. A sharp expansion of the applicability domain of ZrO2 ceramics occurred after the discovery of transformation hardening [2]. The essence of this is that the tetragonal phase of ZrO2 ceramics persists at room temperature if stabilizers considerably improving the mechanical performance of t-ZrO2 (Y2O3, CeO2, MgO, CaO, etc.) are introduced into it. The currently available stabilized ZrO2 ceramics offers a unique set of mechanical properties: record high (for oxide ceramics) fracture toughness KC, high wear resistance and bending strength, and low friction coefficient. Additionally, this material has a low thermal conductivity and a high melting point and is chemically inert and radiation-resistant. All of these things open a wide scope of application from mechanical engineering to medicine [3, 4]. The most efficient way to further improve the performance of ZrO2 ceramics (including improvement of a hardness/cracking resistance relationship) is to
make ZrO2-based composites. The greatest success was achieved using a combination of zirconia and alumina [3–5]. In ZrO2 + Al2O3 composites, the advantages of zirconia ceramics coincide with those of alumina ceramics (high hardness H, Young’s modulus E, and compression strength σs). Depending on the ZrO2-to-Al2O3 concentration ratio in the composite, one distinguishes zirconia-toughened alumina (ZTA) and alumina-toughened zirconia (ATZ) [6
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