Superhard Boride Ceramics Produced by Boro-Carbothermal Reduction

DOI: 10.62564/M4-WF1225

William G. Fahrenholtz

Missouri University of Science and Technology, United States


Boride ceramics have been proposed for use in extreme environments based on melting temperatures above 3000°C and other attractive properties such as high hardness. Inspired by the research of Professor Samsonov and others, our laboratory has investigated compositionally complex borides containing five different transition metals in an effort to identify new superhard ceramics. The most commonly studied compositionally complex boride has been (Hf,Nb,Ta,Ti,Zr)B2 with the metals present in nominally equimolar amounts. The initial search for harder materials involved substituting metals such as Cr, Mo, or W in place of Nb, which increased the hardness. Among the materials produced, (Cr,Hf,Ta,Ti,Zr)B2 had the highest hardness, which was about 48 GPa at a load of 0.49 N. Subsequently, new boride compositions were identified using a computational approach called the Disordered Enthalpy-Entropy Descriptor (DEED). Using DEED, (Cr,Mo,Ti,V,W)B2 was identified as a thermodynamically stable compound. The dense ceramic had a hardness of 48 GPa at a load of 0.49 N. Recently, machine learning predicted that (Hf,Mo,Ti,V,W)B2 should be superhard. This composition was synthesized by our group and found to have a hardness of 66 GPa at a load of 0.49 N. This presentation will provide a broad perspective on promising approaches for synthesis and densification of new borides that are identified through computational studies and produced by boro-carbothermal reduction.

Keywords
Boride ceramics

Acknowledgments
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References
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