Mapping the X-B-C Systems: Search for the Elusive X2BC Phase
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| Year of publication | 2022 |
| Type | Conference abstract |
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| Description | Binary borides and binary carbides have been known for many decades. Their outstanding mechanical‚ electrical and thermal properties made them indispensable in the industry‚ either in bulk or as thin films. The idea of combining these systems into a ternary X-B-C system naturally evolved. Such systems in the form of bulk have been investigated since the 1950s. The X has been from all of the s‚ p d and f blocks of the periodic table of the elements. Different structures were found. The orthorhombic Mo2BC phase‚ being the first with the X2BC stoichiometry‚ was described by Jeitschko in 1963 [1]. This structure attracted interest for its superconducting properties. Sixty years later‚ this is still the only synthesised X2BC phase. An interest in the X-B-C thin films can be traced to the mid-1980s‚ with experimental work accelerating in the 1990s. The focus was on the Ti-B-C system in the form of multilayers or in the form of a crystalline-crystalline nanocomposite. Superior mechanical properties of this system were described. A renaissance of the X2BC phases‚ this time in the form of the thin films‚ has begun in 2009 when the Mo2BC phase was prepared by direct current magnetron sputtering [2]. This phase was no longer studied for its superconducting properties‚ in which other materials superseded it‚ but for its highly unusual combination of high hardness and moderate ductility. Theoretical studies describing other crystalline ternary X2BC phases predicting the thermodynamic possibility of their preparation together with even better mechanical properties followed [3]. Since then‚ several different systems from these predictions have been studied‚ including W-B-C‚ Nb-B-C and Ta-B-C. No definitive proof of the existence of any X2BC phase apart from the original Mo2BC phase was found. This contribution will cruise through the ups and downs of this research in the last decade. It will be shown that thin films from these systems can have interesting mechanical and thermal properties even without the formation of the desired and elusive X2BC phase. It will be discussed why these phases won’t form even under energetically very harsh conditions such as HiPIMS. We will also sketch the possibilities for the future directions of the studies of the X2BCs. |
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