Optimal preparation of high-entropy boride-silicon carbide ceramics
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ISSN 2226-4108 CN 10-1154/TQ
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Optimal preparation of high-entropy boride-silicon carbide ceramics Yan ZHANGa,†, Shi-Kuan SUNb,†, Wei-Ming GUOa,*, Liang XUa, Wei ZHANGa, Hua-Tay LINa,* a
School of Electron-mechanical Engineering, Guangdong University of Technology, Guangzhou 510006, China b Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, UK Received: June 2, 2020; Revised: August 27, 2020; Accepted: August 31, 2020 © The Author(s) 2020.
Abstract: High-entropy boride-silicon carbide (HEB-SiC) ceramics were fabricated using boridebased powders prepared from borothermal and boro/carbothermal reduction methods. The effects of processing routes (borothermal reduction and boro/carbothermal reduction) on the HEB powders were examined. HEB-SiC ceramics with > 98% theoretical density were prepared by spark plasma sintering at 2000 ℃. It was demonstrated that the addition of SiC led to slight coarsening of the microstructure. The HEB-SiC ceramics prepared from boro/carbothermal reduction powders showed a fine-grained microstructure and higher Vickers’ hardness but lower fracture toughness value as compared with the same composition prepared from borothermal reduction powders. These results indicated that the selection of the powder processing method and the addition of SiC phase could contribute to the optimal preparation of high-entropy boride-based ceramics. Keywords: high-entropy boride-silicon ceramics; borothermal reduction; boro/carbothermal reduction; microstructure; mechanical properties
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Introduction
In recent years, high-entropy ultra-high temperature boride (HEB) ceramics have been extensively studied by combining the concepts of ultra-high temperature boride ceramic (UHTC) and high-entropy materials [1–3]. HEB ceramics were found to exhibit high hardness and superior oxidation resistance [4–6]. Accordingly, HEB ceramics are considered to possess potential for the broad application [4]. However, HEB ceramics suffered from the difficulty in densification mainly due to the strong covalent bonds and low † Yan Zhang and Shi-Kuan Sun contributed equally to this work. * Corresponding authors. E-mail: W.-M. Guo, [email protected]; H.-T. Lin, [email protected]
diffusion rate during the sintering process, as previously observed in traditional UHTC boride systems (e.g., ZrB2 and HfB2) [4,5,7,8]. Gild et al. [4] fabricated high-entropy boride ceramics by the combination of high-energy ball milling of the precursors and subsequent spark plasma sintering (SPS) at 2000 ℃. The as-sintered materials exhibited relatively higher hardness (21.0–22.5 GPa) and better oxidation resistance as compared to traditional boride ceramics. However, the relative density reported was only 92.4% due to the contamination of the powder during the milling procedure. The particle size and purity of powders were effectively improved by borothermal reduction and boro/carbothermal reduction, promoting sintering densification [3,9]. Our recent works reported that HEB ceramics could r
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