| AVS 63rd International Symposium & Exhibition | |
| Thin Film | Monday Sessions |
| Session TF+PS+SE-MoA |
| Session: | Plasma-based Deposition Techniques and Film Characterization |
| Presenter: | Paulius Malinovskis, Uppsala University, Sweden |
| Authors: | P.M. Malinovskis, Uppsala University, Sweden J.P. Palisaitis, Linkoping University, Sweden P.O.A. Persson, Linköping University, Sweden E.L. Lewin, Uppsala University, Sweden U.J. Jansson, Uppsala University, Sweden |
| Correspondent: | Click to Email |
Transition metal diborides (MeB2) with the AlB2-type structure have many unique properties such as high hardness, high conductivity and oxidation resistance One of the most studied diboride compounds is TiB2 but also other transition metals like Cr, Nb and Mo can form the simple AlB2 type structure.
Non-reactive magnetron sputtering is an excellent technique to deposit thin films of different MeB2 phases. It is well-known that phases with rather simple crystal structures are preferably formed in magnetron sputtering where the quenching rates of the incoming atoms are high. Such metastable MeB2 films may be chemically more reactive in a tribocontact and form a lubricating tribofilm of metal oxides and layered BOx. Some metal oxides such as MoO3 and boric acid (forming in humid atmosphere from BOx) have been predicted to exhibit low friction coefficients. Consequently, it is possible that metastable MeB2 films with the AlB2-structure may exhibit excellent low friction properties. Another way to tailor metal diboride properties is to alloy it with third element, e.g. carbon.
In this study we have investigated the microstructure, mechanical and tribological properties of DC magnetron sputtered MoB2-x and Mo-B-C thin films from Mo/B and graphite carbon target. The films were characterized with XRD, XPS, TEM, nanoindentation and tribological ball-on-disk method. All films exhibited the AlB2-type structure with substoichiometric MeB2-x grains surrounded by a tissue phase of a-B and a-BCx. The MoB2-x films were substoichiometric with respect to boron and exhibited a much higher hardness compared to bulk samples, which could be attributed to a hardening effect of the tissue phase. Friction measurements confirmed the hypothesis that a significant tribofilm formation is present on the metastable MoB2-x films. However, a reduced friction coefficient could not be observed. Addition of carbon resulted in a change in the composition of the tissue phase. This caused a reduction in hardness and a reduction of the friction coefficient. General trends in the phase formation and properties of Mo-B-C films will be explained in detail and compared with other Me-B-C systems (Me= Ti, Cr, Nb).