Tribology of ultra high molecular weight polyethylene film on Si substrate with chromium nitride, titanium nitride and diamond like carbon as intermediate layers

This paper presents tribological studies on composite films consisting of different intermediate hard layers (chromium nitride (CrN), titanium nitride (TiN) and diamond like carbon (DLC)) on Si substrate followed by soft ultra high molecular weight polyethylene (4–5 μm thick) as the top layer. The tribological properties of the composite films were evaluated on a ball-on-disc tribometer (composite film sliding against a 4 mm diameter Si3N4 ball) at a normal load of 40 mN and a linear speed of 0.052 m/s. The wear durability of the composite films increases with increasing hardness of the intermediate layers. The composite film with harder intermediate layers (TiN with 24 GPa and DLC layers with 57 GPa and 70 GPa of hardness) provides the best tribological performance with more than 300,000 cycles of sliding when the experiments were stopped. The critical loads of scratching correlate with the wear performances of the composite films. Application of only a few nanometer overcoat of perfluoropolyether on the most wear resistant composite films can further increase the wear lives (more than one million cycles) even at a higher normal load of 70 mN.