Creep deformation behavior during densification of ZrB 2 -SiBCN ceramics with ZrO 2 additive
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ISSN 2226-4108 CN 10-1154/TQ
Research Article
Creep deformation behavior during densification of ZrB2–SiBCN ceramics with ZrO2 additive Bo FENG, Zhenhang WANG, Yunhao FAN, Jinghua GU, Yue ZHANG* Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191, China Received: March 8, 2020; Revised: May 14, 2020; Accepted: May 29, 2020 © The Author(s) 2020.
Abstract: ZrB2–SiBCN ceramics with ZrO2 additive are hot-pressed under a constant applied pressure. The densification behavior of the composites is studied in a view of creep deformation by means of the Bernard-Granger and Guizard model. With determination of the stress exponent (n) and the apparent activation energy (Qd), the specific deformation mechanisms controlling densification are supposed. Within lower temperature ranges of 1300–1400 ℃, the operative mechanism is considered to be grain boundary sliding accommodated by atom diffusion of the polymer-derived SiBCN (n = 1, Qd = 123±5 kJ/mol) and by viscous flow of the amorphous SiBCN (n = 2, Qd = 249±5 kJ/mol). At higher temperatures, the controlling mechanism transforms to lattice or intra-granular diffusion creep (n = 3–5) due to gradual consumption of the amorphous phase. It is suggested that diffusion of oxygen ions inside ZrO2 into the amorphous SiBCN decreases the viscosity, modifies the fluidity, and contributes to the grain boundary mobility. Keywords: zirconium boride; polymer-derived SiBCN; creep deformation; densification mechanism; viscosity
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Introduction
Zirconium boride (ZrB2) is characterized by extremely high melting point, high strength and hardness, chemical inertness against molten metals or slags, high electrical and thermal conductivities, and good oxidation resistance [1–3]. These outstanding properties make it an appropriate candidate for diverse applications, such as molten metal crucibles, electronic substrates, and thermal protective materials in the future hypersonic aviation system [4–6]. However, fully-dense ZrB2 ceramic is difficult to fabricate due to its strong * Corresponding author. E-mail: [email protected]
covalent bonding and low self-diffusion coefficient [3]. The densification of this material has attracted extensive attention over these years. Silicon or carbon containing materials such as SiC, Si3N4, C, B4C, and SiBCN, are generally introduced into ZrB2 ceramic to significantly improve its sinterability, mechanical property, oxidation and ablation resistance [1,2,7–10]. SiC is recognized to be the preferred addition since it can effectively restrain the coarsening of ZrB2 grains and enhance the comprehensive performance of the material [1,2]. Si3N4 is able to react with B2O3 originated from the surface of ZrB2 powder, decrease vapor phase transport of boron oxide during sintering process, and help promote densification [7]. The introduction of carbon or carbides can also remove the surface oxide (ZrO2 and B2O3) by carbothermal
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