Investigation of friction at µN and mN force range on hard coatings

In recent years 'low load' tribology has received more attention due to the emergence of special devices like MEMS, and new materials such as bioimplants, polymers and textured surfaces. The tribological characterization of MEMS materials is challenging, because the devices operate at nominal contact pressures of only a few MPa and low wear rates of nm/hr. In this work, the friction and wear behavior of the commonly used industrial coatings titanium nitride (TiN) and diamond-like carbon (DLC) are investigated with normal forces in between Newton (conventional tribology) and nanoNewton (nanotribology). As the applied normal force reduces from mN's to µN's, the effect of surface roughness becomes strikingly apparent in the recorded tangential force. The friction of TiN coating appears to be less sensitive to surface roughness variations and chemical changes of the countermaterial, than DLC. The behavior of DLC at low contact pressures is different from the well-known low friction behavior of DLC coatings at high contact pressures.status: publishe