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Microstructure and mechanical properties of high-entropy borides derived from boro/carbothermal reduction
Affiliation:1. School of Electromechanical Engineering, Guangdong University of Technology, Guangzhou, Guangdong 510090, China;2. Immobilisation Science Laboratory, Department of Materials Science and Engineering, University of Sheffield, Sheffield S1 3JD, United Kingdom;3. Department of Process Engineering and Applied Science, Dalhousie University, Halifax B3J 1Z1, Canada;1. Department of Physics and Astronomy, University of California, Irvine, CA, 92697, USA;2. Department of NanoEngineering, Program of Materials Science and Engineering, University of California, San Diego, La Jolla, CA, 92093, USA;3. Department of Materials Science and Engineering, University of California, Irvine, CA, 92697, USA;4. Department of Mechanical and Aerospace Engineering, University of California, Irvine, CA, 92697, USA;5. Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY, 11973, USA;1. National Research Council of Italy, Institute of Science and Technology for Ceramics, Faenza, 48018 RA, Italy;2. Elettra - Sincrotrone Trieste S.C.p.A., Strada Statale 14 - Km 163, 5 in AREA Science Park, 34149, Basovizza, Trieste, Italy
Abstract:Starting from metal oxides, B4C and graphite, a suite of high-entropy boride ceramics, formulated (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)B2, (Hf0.2Zr0.2Mo0.2Nb0.2Ti0.2)B2 and (Hf0.2Mo0.2Ta0.2Nb0.2Ti0.2)B2 derived from boro/carbothermal reduction at 1600 °C were fabricated by spark plasma sintering at 2000 °C. It was found that the synthetic high-entropy boride crystalized in hexagonal structure and the yield of the targeting phase was calculated to be over 93.0 wt% in the sintered ceramics. Benefitting from the nearly full densification (96.3% ? 98.5% in relative density) and the refined microstructure, the products exhibited the relatively high Vickers hardness. The indentation fracture toughness was determined to be comparable with the single transition metal-diboride ceramics. It should be noted that the formation of high-entropy boride ceramics were featured with the relatively high hardness at no expense of the fracture toughness.
Keywords:High-entropy boride ceramic  Boro/carbothermal reduction  Spark plasma sintering  Microstructure  Mechanical properties
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