Nanostructured hard coatings deposited by cathodic arc deposition: From concepts to applications
Surface and Coatings Technology
The vacuum cathodic arc deposition (CAD) process is now widely used on an industrial scale to prepare protective hard coatings on cutting tools, metal molds, etc.... It has been recognized that high ionization levels of cathodic arc discharges and high ion energy can provide advantages such as enhanced adhesion required for mechanical applications involving high loads. CAD allows deposition of a wide range of hard compounds as nitrides or carbonitrides. However, CAD is also often associated macrodroplet generation that degrades the surface roughness of coatings. The recent trend is to develop advanced nanostructured hard coatings in order to enhance properties as hardness, toughness, and oxidation resistance. This paper recalls the basic aspects of both CAD technology and nanostructured thin films synthesis. Deposition and characterization of both nanocomposite and nanolayered hard coatings are described. Mechanical behaviors of nitrides can be significantly enhanced by nanolayering. The first example deals with the development of hard nanolayered nitrides coatings for cutting tools protection. It is clearly shown in this example that TiN/AlTiN coatings perform better than CrN/AlTiN and TiN/CrN for the same periods and the best performance is reached for the thinnest periods. It is also shown, in a second example, how silicon addition in CrN can lead to enhancement of oxidation resistance associated with the nanocomposite structure. Thus, relationships are established between deposition conditions, nanostructure and mechanical behaviors or oxidation resistance of the coatings. This short review recalls that CAD remains a powerful and industrial technology for nanostructured hard coatings deposition.