ICMCTF2004 Session B2-1: Arc and E-Beam Coatings and Technologies

Filtered cathodic arc (FAD) provides a unique opportunity to obtain metal or carbon ion beams with a good control of their energy and flux density. The technique is industrially scalable and the FAD source can be combined at the same deposition chamber with other plasma sources. Such combination is essential for the preparation of advanced nanocomposite coatings. For example, supertough nanocrystalline/amorphous coatings and adaptive chameleon tribological coatings are best produced using hybrid deposition methods, e.g. combining magnetron sputtering and pulsed laser ablation [1-3]. In hybrid processes, it is possible to grow composite materials which individual phases require drastically different deposition conditions. This paper provides examples of hybrids of FAD with magnetron sputtering, pulsed laser deposition, and atomic gas sources. These processes were explored for the production of nanocomposite materials, where metal, carbon, and dichalcogenide phases were combined into the coatings with advanced wear protective and low friction properties. Discussion of the hybrid processes highlights their main advantages for the nanocomposite coating growth.

[1] A. A. Voevodin, S. V. Prasad, J. S. Zabinski, Nanocrystalline carbide / amorphous carbon composites, J.Appl.Phys. 82 (1997) 855-858.

[2] A. A. Voevodin, J. S. Zabinski, Supertough wear resistant coatings with 'chameleon' surface adaptation, Thin Solid Films 370 (2000) 223-231.

[3] A. A. Voevodin, J. J. Hu, T. A. Fitz, J. S. Zabinski, Nanocomposite tribological coatings with "chameleon" friction surface adaptation, J.Vac.Sci.Technol.A 20 (2002) 1434-1444.

It is well known that incorporation of Al atoms to TiN and CrN films shows phase transitions from the cubic to hexagonal structure at certain Al amount. In our previous work, the micro-hardness of Ti_1-xAl_xN changed from 20 GPa to 32 GPa with keeping NaCl structure. Further, the Cr_1-xAl_xN films showed maximum hardness of 27 GPa with X=0.6, which was similar transition behavior to the case of Ti_1-XAl_xN films.

The purpose of this study is to obtain maximum solubility of three kinds of metals, Ti, Cr and Al keeping the c-phase. In this study, effects of Cr addition into Ti_1-xAl_xN films were investigated by measuring changes in lattice parameter.

Ti_0.1Cr_0.2Al_0.7N films were synthesized by the arc ion plating method (AIP) between 400 and 650°C. The micro-hardness of films showed maximum value of 30 GPa at 520°C. The crystal structures changed from the cubic to the mixture phase with cubic and hexagonal structure with increasing deposition temperature. The grain size of Ti_0.1Cr_0.2Al_0.7N at 520°C was approximately 100 nm and indicated by dots in the photographs.

In vacuum arc deposition systems, the depositing plasma is generated at the surface of the cathode, and is often passed through an aperture in the anode on its way to the substrate. In this work, the influence of the aperture diameter on the plasma transport was measured. The plasma source consisted of a conical Cu cathode of 17 mm diam, and an annular Cu anode of D=10, 17, 30, 40 and 50 mm i.d. and 20 mm thick, through which the plasma beam entered into the 160 mm diameter and 500 mm length cylindrical duct. Magnetic coils positioned co-axially with the duct axis produced an approximately axial magnetic field guiding the plasma in the duct. The arc current, I_arc, was in the range of 30-100 A. A 130 mm diam. negatively biased planar disk probe, positioned normal to the duct axis at a distance of 150 mm from the anode exit, was used to measure the ion saturation current, I_p. The ion saturation current to the duct wall, I_d, the arc voltage, V_arc, and the probe and duct floating potentials with respect to the anode, were measured as functions of D, I_arc, and the axial magnetic field B.

Generally, I_p and I_d increased almost linearly with D. I_p as function of I_arc increased almost linearly for D=40 mm, increased and became saturated for D=17 mm, whereas for D=10 mm, I_p first increased up to a maximum value at I_arc=80 A and decreased for larger values of I_arc. V_arc increased with D, and for all D, V_arc decreased with increasing I_arc. Both probe and chamber floating potentials were negative relative to the anode, and became increasingly negative with increasing D and B. It was shown that the system efficiency I_p/I_arc increased with increasing D, from ~0.8% at D=10 mm to 10% for large D. However, at large D (≥ 50 mm), the probability of the arc extinguishing increased.

The Hot Refractory Anode Vacuum Arc (HRAVA) is a metallic coating plasma source using a conventional water-cooled metal cathode, and an anode made from a non-consumable refractory material. The metallic plasma plume is generated by re-evaporation of cathode material from the anode, which is heated by the arc, vastly reducing the macroparticle contamination from that obtained with conventional cathodic vacuum arc sources. In the present work, an asymmetric anode geometry, intended to control the plasma plume direction, is investigated.

Arcs were sustained between a cylindrical copper cathode and a thermally isolated, 32 mm diameter cylindrical graphite anode whose distal end was cut off at various angles, so that its minimal and maximal lengths L1 and L2 could differ. Anodes with three cut-off angles were investigated: (1) symmetrical anode, L1=L2=30mm (2) L1=25mm, L2=30mm; (3) L1=20mm, L2=30mm. The time dependent anode temperature was measured using high-temperature thermocouples at two points a few mm below the distal surface near the minimal and maximal length points and at one point near the rear surface. Arc currents of 120-225 A were sustained for periods up to 150 s with distances of 9-18 mm between the electrodes.

The measured anode temperature increased with arc time and approached a steady-state value. The anode temperature increased linearly with arc current. The steady state temperature of the asymmetric anodes was approximately 100C greater, and rose at a faster rate, than that of the symmetric anodes. The temperature measured near L1 reached approximately 1200, 1300 and 1400K for anodes (1), (2) and (3), respectively, 30s after arc ignition for Iarc=175 A and electrode distance 18 mm. The maximal anode temperature near L2 in the asymmetric anodes decreased by about 100-150o when the electrode separation was increase from 9 to 18mm (175 A), while the temperature at near L1 and the rear surface varied only weakly.