ICMCTF2008 Session B2: Arc and E-Beam Coatings and Technologies

The radially expanding plasma jet generated in a Hot Refractory Anode Vacuum Arc (HRAVA) was used to deposit thin chromium and titanium films on glass substrates. The arc was sustained between a water-cooled cylindrical cathode and a non-consumed cylindrical tungsten anode seprated by a 10 mm gap, for time periods up to 120 s, operating with a current (I) of 200 - 300 A. The chromium cathode had a 30 mm diameter and 20 mm height, and was used with 32 mm diameter, 30 mm high anode. The titanium cathode was 60 mm diameter and was used with a 60 mm diameter anode.

Thin films were deposited on glass substrates exposed to the anodic plasma. A mechanical shutter controlled the deposition onset and exposure duration time. The distance from the arc axis to the substrate (L) was varied between 80 and 110 mm. The film thickness was measured by a profilometer, and macroparticle (MP) presence on the coating surface was examined by optical microscopy. It was found that the deposition rate of Cr films increased with arc current and reached ~ 1.4µm/min at I=300A, L=80mm. The total MP flux was less then 1mm^-2min^-1 for I=300A, L=110mm. The deposition rate of Ti films reached 1µm/min at I=200A, L=80mm.

Plasma-assisted Electron Beam Physical Vapour Deposition (EBPVD) processing may in some be cases more attractive than sputtering for commercial applications, as it offers the potential for lower running costs and higher maximum deposition rates. In this paper, we deposit Cr-Cu based coatings using EBPVD. Due to the low miscibility of Cr and Cu (the former with or without an interstitial solid solution of N), predominantly metallic nanocomposite coatings with high resilience and toughness and a hardness close to that of ceramic coatings (>15GPa) can be produced by magnetron sputtering, at thicknesses of around 3-5µm.

One of the main advantages of a metallic coating (in contrast with a typical ceramic coating) is less coating internal stress, which can result in improved resilience under load and better adhesion to the substrate. Nanocomposite coatings that are predominantly metallic are therefore excellent candidates to be deposited with much higher thicknesses (>10µm) and (by EBPVD) at high deposition rates. Such thick coatings could have numerous advantages over standard, thin, vapour deposited coatings in applications where wear, corrosion and oxidation resistance are required which, at the moment, can be satisfied only by other processing techniques such as electroplating and thermal spraying, where desirable combinations of materials, composition and structure are relatively limited and hardness, adhesion and toughness are relatively low.

Several techniques are employed for coating characterisation, such as X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Hardness and wear performance have been evaluated for the deposited films by means of nanoindentation, reciprocating sliding and ball-on-plate impact tests, respectively. The corrosion resistance is investigated by potentiodynamic testing, whilst the high temperature oxidation resistance is examined by means of thermo-gravimetric analysis, X-ray diffraction and scanning electron microscopy.

Vacuum arc deposition technology for film deposition is established for industrial deposition of hard coatings as TiN, ZrN, TiAlN. A disadvantage of this deposition method is that great particles and droplets are emitted and will be incorporated in the deposited layers. By means of pulsing the arc discharge the particle emission can be reduced. But, there smoothness is not comparable with films are deposited by sputtering. For deposition of thin, smooth films by arc, magnetic filter equipment has been applied successfully separate these particles from arc plasma. The industrial using of such a technique for the deposition of thicker films is unproductive due the high loss of deposition rate. Alternative a mechanical gladding of arc deposited thick films often has been preferred. We present a new developed simple filter arrangement for pulsed arc deposition (Laser-Arc). Only a simply additional absorber electrode connected to an electrical potential positive with respect to the plasma is used instead of a different number of magnet coils as usual in the applied classical filters. The electrode is placed in front of the arc cathode (roll) at an obliquely inclined angle which takes account of the divergence of the plasma flow. On this way the charged plasma particle will be separated from macro- and micro-particles and will be deflected for deposition on the substrates. The advantages of this kind of filter are unlimited linear extension of deposition area, simple construction and high efficiency. The transparency of the filter has been measured to be more than 60% in the case of super hard carbon (ta-C) film deposition. A changing of the surface roughness of standard polished silicon wafers could not be observed up to a film thickness of more than 2 microns.

Besides the demonstration of the principle of this new filter technique, first results of thick ta-C film deposition and its potential of the up scaling for industrial using will be discussed.