Publications

Hexagonal transition metal diborides embody promising material systems for the purpose of protective thin films. Here, we focus on DC magnetron sputtered TiB2+z coating materials, comprehensively revisiting the impact of the stoichiometry on the structure-mechanical properties, from nearly stoichiometric TiB2.07 (B: 67 at. %) up to super-stoichiometric TiB4.42 (B: 82 at. %). The structural analysis confirmed the apparent correlation between the deposition pressure and the preferred {0001} orientation, which is essential to gain super-hardness (>40 GPa). In contrast, the hardness decreases for >10 GPa for 101¯1 and 1000 oriented thin films, underlining the pronounced anisotropy of TiB2+z. The broad stoichiometry variation revealed no predominant hardness effect based on a B-rich tissue phase. The excess B contributes to a decreasing column size correlating with a decreasing hardness of ≈ 7 GPa (B/Ti ratios >2.5) due to column boundary sliding events. Micro-cantilever bending experiments proved a declining fracture toughness from 3.02 ± 0.13 MPa√m for TiB2.43 to 2.51 ± 0.14 MPa√m for TiB4.42 to be column size dependent.

Authors

C. Fuger, R. Hahn, A. Hirle, P. Kutrowatz, M. Weiss, A. Limbeck, O. Hunold, P. Polcik, H. Riedl

Journal

Surface and Coatings Technology

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