Adhesion and hardness of ZrN films sputtered on WC substrates

Zirconium nitride (ZrN) is a transition metal nitride widely studied to be used in different technological fields, like protective coatings and optoelectronics. High hardness, strong wear resistance, chemical stability and high corrosion resistance make transition metal nitride films suitable for tribological applications. For this kind of applications it is essential to evaluate and to control the film adhesion to the coated tool and its hardness properties. In this work ZrN films were RF-sputtered on WC–wt.10 % Co substrates using different assistance bias voltages (up to 20 V) applied during the film growth. The structural properties of the obtained coatings were analysed using x-ray diffraction (XRD) measurements. It was found that the substrate bias strongly influenced the incorporation of residual oxygen impurities in the films. A structural switch from the (200) to the (111) preferential crystal structure was detected with the increasing bias voltage. In addition, transmission electron microscopy (TEM) analyses showed some twinning features inside the deposited films. The film properties were correlated to the film adhesion, studied by scratch test, and to their wear resistance, carried out by ball-on-disc tribometry. The maximum obtained critical load was about 70 N and the wear rate was about 2.23*10^-6 mm3/Nm. Nanoindentation measurements is in progress in order to correlate them with the structural features and wear resistance properties of the grown films.