Hard Amorphous Carbon PVD Coatings
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HARD AMORPHOUS CARBON PVD COATINGS
0. KNOTEK, F. LUFFLER AND J. BRAND Institut fUr Werkstoffkunde B, Aachen Templergraben 55, W-5100 Aachen, F.R.G.
University
of
Technology,
ABSTRACT Amorphous diamond-like carbon (ADLC) coatings are deposited on cemented carbides, high speed steels (HSS) and other steels, using arc-ion plating. The paper describes both the problems and the potential of this process with its many influencing parameters. It also details a number of properties of hydrogen-free a-C films deposited at coating temperatures of 200 °C; as an example, a tribological application is described. INTRODUCTION Diamond and diamond-like coatings are steadily gaining importance in industry due to their extraordinary material properties [1]. The deposition of thin diamond coatings is preferably done with CVD processes. The problem of those deposition techniques is, however, the rather high coating temperature of about 800-1000 °C, which limits the number of substrate materials. The amorphous diamond-like carbon coatings offer an alternative. These ADLC films may be deposited at moderate temperatures of about 200 OC with different technologies [2,3]. These coatings don't reach quite the high hardness values of diamond, but show similar properties due to a high level of tetrahedral bindings (sp'). Additionally there are also graphite (spa) and other (sp') bond systems [4,5]. An advantage of the amorphous structure is the low roughness. Due to the low friction coefficient and the high resistance to wear and chemical attack, these coatings highly qualify for tribological applications. Arc-ion plating (ALP) offers a rather new way of depositing ADLC coatings even on large-sized substrates of varying materials. DEPOSITION OF AMORPHOUS PLATING PROCESS
DIAMOND-LIKE
CARBON
COATINGS
USING
THE ARC-ION
The necessary carbon for thin film growth in CVD and plasma-CVD processes results from decomposition of hydrocarbon gases. The set free hydrogen is built in the coatings (a-C:H-films) and is used for saturating free bonds and for reducing internal stresses. Since ADLC coatings tend to show peel off effects due to high residual stresses, the incorporation of hydrogen is usually evaluated to be of advantage. A high content of hydrogen (up to 50 %) may, however, lead to the formation of soft polymeric parts in these CVD coatings [6]. Within the AIP-process, the available carbon results from evaporation of a carbon target through a high energetic arc beam. Hydrogen containing reactive gases may be added to the process in order to support a-C:H coatings, but also hydrogen-free coatings with good adhesion properties may be produced. Advantages of this technique are the high level of ionisation of the target material and the easy control of film growth. Figure 1 shows the Mat. Res. Soc. Symp. Proc. Vol. 270. 01992 Materials Research Society
470
number of parameters that influence the coating process. be assigned to the following three categories.
cathodej kind of production share of soot geometry surface topography princip
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