Microstructure and properties of AlB2-type WB2 thin films deposited by direct-current magnetron sputtering

In this study, AlB2-type WB2 films are deposited on YG8 (WC–Co) substrates by DC magnetron sputtering at different substrate bias voltages and temperatures. Their effects on the film microstructure, elemental composition, mechanical and tribological properties are investigated systematically by various analysis methods, including X-ray diffraction (XRD), electron probe X-ray microanalyzer (EPMA), field emission scanning electron microscopy (FESEM), high resolution transmission electron microscopy (HRTEM), atomic force microscopy (AFM), nano-indentation, ball-on-disk tribometer and micro scratch tester. The as-deposited films show an under-stoichiometric composition with rich tungsten concentration and have an obvious columnar structure. With the substrate bias voltage increasing (from 0 V to − 150 V), the orientation of the films changes from (0 0 1) to (1 0 1). And films obtained at − 50 V show superior mechanical and tribological properties. By increasing the substrate temperature to 500 °C, the maximum hardness about 40.5 GPa and the best adhesive strength of 60 N are detected. The films with the fine-grain amorphous structure, produced at 300 °C and − 50 V, exhibit the minimum friction coefficient of 0.28. And the minimum wear rate of 2.3 × 10− 7 mm3/mN is obtained for the films deposited at − 50 V and 400 °C. The properties described above are attributed to the variations of microstructure and morphologies in the films. Furthermore, the wear track and debris are also discussed by virtue of FESEM/EDS to explore the self-lubricating behavior of the AlB2-type WB2 film.