Tribological behavior of hydrogenated diamond-like carbon on polished alumina substrate with chromium interlayer for biomedical application

• Diamond-like carbon film on alumina substrate enhanced the mechanical properties.
• Adhesion between the coating and the substrate is important to reduce the wear.
• The a-C:H coated pin against a-C:H coated block showed low friction coefficient.
• Formation of transfer film is attributed to degree of graphitization as the applied load increased.

Diamond-like carbon (DLC) is a promising material for wear resistant films because of its high hardness and moderate elastic modulus. To enhance its performance in orthopedic implant applications, a better understanding of the tribological effect of DLC coating is essential. DLC with hydrogen, that is: hydrogenated amorphous carbon (a-C:H) was deposited on the polished alumina (Al2O3) substrate by magnetron sputtering. X-ray diffraction, energy dispersive spectroscopy and transmission electron microscopy were used to determine the phase compositions in the films. The a-C:H coated surface exhibits hydrophilic characteristic for protein absorption, with low water contact angles of 69.5°. It was found that the a-C:H, which has high hardness and moderate elastic modulus resulted in a relatively high H/E ratio of around 0.133. This result enables the film to conform well with the substrate and provide good wear resistance. The tribology test showed a significant reduction in the friction coefficient of the coated layer as compared to the uncoated surface rubbing on the Al2O3 counterface. The a-C:H coated pin against a-C:H coated block showed a stable and low friction coefficient under all loading conditions.