Mechanical and wear characteristics of a-C:H/Cr/AlN/Ti multilayer films deposited by PVD/PACVD

The effects of the AlN/Ti interlayer on the properties of this system of coatings were investigated by several means. X-Ray photoelectron spectroscopy was used in order to assess the type of chemical bonds present in the coatings. The surface and section morphologies were observed by scanning electron microscopy, while the mechanical characteristics (hardness, adherence to the substrate and wear behavior) were analyzed by nanoindentation, scratch tests and ball-on-disc friction tests. The results showed that the presence of AlN/Ti interlayers is reducing the carbon sp3 content and is increasing the bonded oxygen at the surface of the coatings, which, in turn, leads to an increased chemical activity, giving rise to abrasive wear and a higher friction coefficient. The adhesion to the steel substrate of these multilayer coatings, compared to an a:C-H/Cr coating, used as reference, was greatly improved. However, the hardness was gradually degraded, compared to the same a:C-H/Cr film. This indicates that the AlN/Ti interlayers might decrease the mechanical strength of the top DLC films, but can bring benefits in terms of adhesion to the steel substrate. The mechanical and wear characteristics of the a:C-H/Cr/AlN/Ti/steel system are dependent on, and can be varied due to the deposition process parameters.