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H. Riedl, V. Moraes, C. Fuger, H. Euchner, R Hahn, T. Wojcik, M. Arndt, P. Polcik, P.H. Mayrhofer:
"Is WB2-z a proper Base System for designing Ternary Diboride based Thin Films?";
Talk: 46th International Conference on Metallurgical Coatings and Thin Films, San Diego; 2019-05-19 - 2019-05-24.

Future tasks in many different fields of academia and industry are directed towards environmental sustainability, and hence the application of ultra-stable materials featuring novel properties. A rather new and highly promising class of thin film materials are borides. Especially, transition metal borides (TMBs) exhibit a tremendous potential to be applied in various applications ranging from wear and corrosion resistant coatings, to superconductive thin films, or as superhard and extremely stable protective layers in diverse fields of engineering. In contrast to classic diborides - such TiB2, ZrB2, WB2, or ReB2, which has been theoretically predicted to be the most incompressible material exceeding the properties of diamond - are ternary or even multinary diborides (e.g. W1-xMxB2) relatively unexplored. Based on atomistic modelling studies [1,2] (Density Functional Theory calculations) is the stabilization of ternary diborides dominated by two hexagonal competing structure types - α AlB2-prototype (SG-191) vs. ω-W2B5-x-prototype (SG-194) - as well as structural defects (especially vacancies). These facts emphasize distinct difficulties for PVD based synthesis of ternary diboride thin films.
Within this study, we want to address the challenges in depositing ternary diborides in a prototype based on α-W1-xMxB2 solid solutions, applying non-reactive sputtering processes, whereas M represents different transition metals such as Ta or Ti [2]. Due to the strong tendency of WB2 to be stabilized through structural defects in the AlB2 structure type - exhibiting distinct advantages concerning the relatively low ductility of TMBs in general - it can be an excellent base system for studying various alloying concepts utilizing physical vapour deposition (PVD) techniques. To gain an in-depth insight on the specific effects of selected transition metals on α structured W1-xMxB2 coatings, we correlated the synthesis parameter with structure property relationships applying a set of high-resolution characterization techniques as well as micro-mechanical testing methods - also after exposing to diverse aggressive¬ environments in terms of oxidation and thermal treatments.

Project Head Helmut Riedl:
CDL-SEC