Nanocomposite layers of ceramic oxides and metals prepared by reactive gas-flow sputtering

Thin nanocomposite layers of ceramic oxides in conjunction with a second metallic phase were prepared by reactive gas-flow sputtering. The two nanogranular phases were dispersed into each other by co-deposition from two separate targets. TiO2 and Al2O3 were chosen as ceramic phase, respectively, which was obtained by sputtering one of the metals and reacting with oxygen. In order to investigate the influence of a hard and a ductile metal, either tungsten or copper was chosen as the second metallic phase. Highly compact thin films could be prepared as was revealed by SEM. A low hydrogen content of 1–2 at.% was measured by SIMS indicating a low sample porosity and an effective residual gas displacement from the surface of the growing film. X-Ray diffraction revealed the TiO2-derived films to contain rutile-phase grains of average grain size of less than 10 nm. Mechanical and tribological properties of the 3- to 4-μm thick coatings were determined by a micro-indenter operating with a Vickers-type diamond and by a pin-on-disk tester. The plastic microhardness HUpl amounted up to 24.1 GPa in case of TiO2-derived nanocomposite films and up to 14.8 GPa in case of Al2O3-based films. Also, with respect to tribological properties TiO2:Cu and TiO2:W coatings were superior over Al2O3-derived ones. A wear coefficient of 0.35×10−6 mm3/Nm was obtained for optimised TiO2 films against an alumina sphere under unlubricated sliding conditions. In lubricated pin-on-disk tests wear coefficients on the order of 0.1×10−6 mm3/Nm were obtained for both metal-doped TiO2 and Al2O3 films.