PVD coatings as an environmentally clean alternative to electroplating andelectroless processes

Today the development of clean technologies in all spheres of industrial ma nufacturing is an essential task, not only for material and metal finishing but also for plasma surface engineering. Among the most critical group of technologies which needs to be replaced by alternative technologies are pro cesses used to produce functional galvanic and decorative coatings. The ele ctroplating of finishes, such as hard chromium, cadmium and nickel in metal finishing is today recognized as a major source of environmental pollution in every country. Therefore wet bath technologies have started to lose fav our compared with high performance dry coating methods such as physical vap our deposition (PVD), plasma-assisted chemical vapour deposition, chemical vapour deposition and thermal spraying. Among these techniques, the results obtained with PVD coatings in metal cutting and forming in the last 15 yea rs show the most promising solution of the complicated situation in which g alvanic coatings seemed to be technologically and economically irreplaceabl e. In this paper the general situation in this field is shown. Already today i t is possible to replace efficiently some of the galvanic processes in spec ific cases (e.g. Cr, Ni, Cd, Zn, Au). It is important to point out that PVD is considered to be a technique which can provide not only metallic, but a lso alloyed and ceramic coatings with a virtually unlimited range of chemic al composition and therefore controlled protective, mechanical and wear-res istant properties. Entering into competition with galvanic coatings the man ufacturers of PVD coaters were confronted with new requirements: a huge qua ntity of substrates of the same size, to be chemically and plasma cleaned a nd then coated at the highest possible deposition rate. For industrial mass production one can therefore use only large PVD batch systems or in-line c oaters. The alternative for today's low price galvanic coatings is therefor e dry and clean PVD technologies, fully supported by legislation on environ mental protection. The economics depend directly on the substrate type and the quantity. The first positive results on the replacement of electrodeposited nickel on aluminium substrates and hard chrome on soft iron are also reported here. A soldering lest was made on a sputtered nickel layer. Wear and corrosion t ests were performed with iron cores, coated with PVD CrN coating. All tests were made in the Slovenian automotive industry. Results show that for a la rge number of substrates PVD clean technology is already economically compe titive with galvanic coatings. (C) 1999 Elsevier Science S.A. All rights re served.