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High-Entropy Metal Diborides: A New Class of High-Entropy Materials and a New Type of Ultrahigh Temperature Ceramics.
- Source :
- Scientific Reports; 12/2/2016, p37946, 1p
- Publication Year :
- 2016
-
Abstract
- Seven equimolar, five-component, metal diborides were fabricated via high-energy ball milling and spark plasma sintering. Six of them, including (Hf<subscript>0.2</subscript>Zr<subscript>0.2</subscript>Ta<subscript>0.2</subscript>Nb<subscript>0.2</subscript>Ti<subscript>0.2</subscript>)B<subscript>2</subscript>, (Hf<subscript>0.2</subscript>Zr<subscript>0.2</subscript>Ta<subscript>0.2</subscript>Mo<subscript>0.2</subscript>Ti<subscript>0.2</subscript>)B<subscript>2</subscript>, (Hf<subscript>0.2</subscript>Zr<subscript>0.2</subscript>Mo<subscript>0.2</subscript>Nb<subscript>0.2</subscript>Ti<subscript>0.2</subscript>)B<subscript>2</subscript>, (Hf<subscript>0.2</subscript>Mo<subscript>0.2</subscript>Ta<subscript>0.2</subscript>Nb<subscript>0.2</subscript>Ti<subscript>0.2</subscript>)B<subscript>2</subscript>, (Mo<subscript>0.2</subscript>Zr<subscript>0.2</subscript>Ta<subscript>0.2</subscript>Nb<subscript>0.2</subscript>Ti<subscript>0.2</subscript>)B<subscript>2</subscript>, and (Hf<subscript>0.2</subscript>Zr<subscript>0.2</subscript>Ta<subscript>0.2</subscript>Cr<subscript>0.2</subscript>Ti<subscript>0.2</subscript>)B<subscript>2</subscript>, possess virtually one solid-solution boride phase of the hexagonal AlB<subscript>2</subscript> structure. Revised Hume-Rothery size-difference factors are used to rationalize the formation of high-entropy solid solutions in these metal diborides. Greater than 92% of the theoretical densities have been generally achieved with largely uniform compositions from nanoscale to microscale. Aberration-corrected scanning transmission electron microscopy (AC STEM), with high-angle annular dark-field and annular bright-field (HAADF and ABF) imaging and nanoscale compositional mapping, has been conducted to confirm the formation of 2-D high-entropy metal layers, separated by rigid 2-D boron nets, without any detectable layered segregation along the c-axis. These materials represent a new type of ultra-high temperature ceramics (UHTCs) as well as a new class of high-entropy materials, which not only exemplify the first high-entropy non-oxide ceramics (borides) fabricated but also possess a unique non-cubic (hexagonal) and layered (quasi-2D) high-entropy crystal structure that markedly differs from all those reported in prior studies. Initial property assessments show that both the hardness and the oxidation resistance of these high-entropy metal diborides are generally higher/better than the average performances of five individual metal diborides made by identical fabrication processing. [ABSTRACT FROM AUTHOR]
Details
- Language :
- English
- ISSN :
- 20452322
- Database :
- Complementary Index
- Journal :
- Scientific Reports
- Publication Type :
- Academic Journal
- Accession number :
- 119940171
- Full Text :
- https://doi.org/10.1038/srep37946