ICMCTF2010 Session B2: Arc and E-Beam Coatings and Technologies

The different PVD methods have found a wide-spread distribution in many industrial applications in the past. The electron beam (EB) evaporation with axial type guns is especially useable for depositions with a very high material throughput. Under such conditions EB-evaporation becomes economical and very attractive in comparison with other coating technologies.

We demonstrate the technical base for the large area and high productive electron beam evaporation. In special configurations it was realized to deposit a wide variety of alloys and compounds.

The plasma activation of the metal vapor and of the working gas gives further possibilities to control the layer growth and so the layer properties. We combined the EB evaporation with arc discharges so that the high arc discharge current density corresponds with the high rates of the EB-evaporation. We demonstrate the needed technical equipment for it and characterize a few plasma parameters. Whereas the first industrial applications were focused on the corrosion protection nowadays a couple of applications in modern technologies are under development. We present results of oxidic and carbon containing hard coatings and of electrical conducting layers for solar cells, which were deposited by using the plasma activated electron beam high-rate deposition.

The main reason of emergency and development of protective coatings was a purpose to increase details and components life. Production of optimal coatings provides for selection of necessary composition of coating, its structure, porosity and adhesion taking into account technological parameters of deposition process.

Hard coatings like TiAlN considerably enhance performance of tools or product, which are coated. It allows to increase working temperature and hardness of coatings. Moreover, using PVD-technology it is possible to develop multilayer composition coatings with nano thickness of each layer on the basis of refractory metal compounds. By varying of technological parameters of coating condensation it is possible to influence on their properties.

Multilayer combined deposits with alternate layers ensure optimal combination of wearability, strength and fracture strength.

Single- and multilayer systems were produced via vacuum-arc atomization of Ti-Al, Ti-Al-Y, Al-Ti cathodes in nitrogen atmosphere with further coatings condensation on steel substrates. Singlelayer coatings TiAlN with thickness 5-8 μm had microhardness Hμ=35-40 GPa. For creation of system with different layer thickness the time of one layer deposition varied from 10 to 30 sec. Total deposition time of coatings was the same and equal to 30-60 min. Thickness of sublayers was less than 100 nm. Microstructure, elemental and phase composition were studied by means of scanning microscopy, Auger-electron spectroscopy, X-ray microanalysis and X-ray structure analysis. Microhardness of vacuum-arc condensates was measured by means of systems PMT-3M and “Micron-Gamma”.

In this study influence of sublayers on structure properties of multilayer deposits TiAlN/TiAlYN (150-300 layers) with fixed total thickness 10-15 µm was examined.

Formed multilayer TiAlN/TiAlYN deposits had enhanced hardness and oxidation resistance in comparison with monolayer TiAlN owing to creation of protection amorphous Al₂O₃-Y₂O₃ layer, which prevented their further oxidation was established.

The Ti-Si-C-N quaternary system is a promising candidate for wear resistant coatings due to its good mechanical and thermal properties. MAX phase Ti₃SiC_2, due to its unique combination of mechanical, electrical and thermal properties, could potentially yield an attractive cathode material for reactive cathodic arc evaporation synthesis of Ti-Si-C-N coatings. The evolution of the surface microstructure and composition of sintered Ti₃SiC₂ cathodes during reactive cathodic arc evaporation in a pure N₂ atmosphere and non-reactive cathodic arc evaporation in an Ar atmosphere with the arc current of 50 A is presented here. The results show that the cathodic arcing induces a converted layer on the cathode surface, in a form of overlapping craters with a diameter of 3-100 μm. The craters are shallow bowl-shaped pits with a raised outer rim, regardless of an Ar or N₂ atmosphere. The microstructure and composition of the converted layer differs from the virgin Ti₃SiC₂ and it contains different features depending on the evaporation conditions. The virgin cathode consists of approximately 12 μm Ti₃SiC₂ grains mixed with a small amount of TiC grains of similar size. Under reactive N₂ atmosphere conditions, the converted layer is 3-10 μm thick and consists of 100-500 nm TiC and TiN grains surrounded by a matrix that is rich in Si. Minor amounts of nanosize Ti₃SiC₂ grains also exist in this layer. In the non-reactive case, the converted layer is 10-40 μm thick and contains comparable amounts of 200-700 nm large TiC and Ti₃SiC₂ grains in a Si rich matrix. The surface roughness Ra-value of the worn cathodes increases from 2.4 μm to 6.2 μm when N₂ is introduced in the deposition chamber.

It is advantageous to have a tool for a coating stoichiometry calculation to control coating deposition made from two different cathodes. Stoichiometry depends not only on arc currents ratio, but also on intensity and shape of magnetic field. This relation has been experimentally verified and is presented for TiAlN coating prepared by a new coating device Pi111. With the aid of this tool, it is possible to estimate coating parameters and to reach the desired Al/Ti ratio in a coating.

With increasing content of Al in a coating, cubic structure shifts to hexagonal structure. This change proves itself not only by hardness decrease, but also by a change of coating growth rate. For detailed description of this effect, method of calculation of coating stoichiometry described above was used.

Micro Arc Oxidation (MAO) is a novel technique used to improve surface properties of Ti6Al4V alloys. A number of studies have been carried out for producing a corrosion resistant coating on Ti6Al4V alloys by micro arc oxidation processes. However, there are very few studies on the optimization of the MAO process parameters for corrosion resistance of Ti6Al4V alloys. In this study, Taguchi experimental analysis method was used to systematically investigate the effects of four parameters (deposition time, frequency, current density, and concentration of electrolyte) with three levels on the corrosion resistance of coatings. Potentiodynamic polarization measurements were conducted to determine the corrosion resistance of the samples. The percentage contribution of each factor was determined by the ANOVA. The optimum coating parameters that affected the corrosion resistance were determined by using Taguchi method. The results showed that which parametre was the most significant factor affecting on the coatings’s corossion resistance.

Al₂O₃ films are deposited employing a monoenergetic Al⁺ beam generated by a flitered cathodic arc [1]. A critical Al⁺ ion energy of 40 eV for the formation of the α-Al₂O₃ phase at a substrate temperature of 720°C is determined. This energy is used as input for classical molecular dynamics and Monte-Carlo based simulations of the growth process, as well as ab initio calculations. The combination of theory and experiment indicates that in addition to surface diffusion the previously not considered diffusion in sub-surface regions appears to be an important atomistic mechanism for the phase formation of α-Al₂O₃.

[1] A. Atiser, S. Mraz, and J. M. Schneider, J. Phys. D: Appl. Phys. 42, 015202 (2009).

Deposition by high power impulse magnetron sputtering (HIPIMS) is emerging as the new paradigm for metal ion etching and self-ion-assisted deposition. While HIPIMS has indeed many advantages, some features are re-invented in light of the already forgotten accomplishments with arcs, and especially filtered arcs and pulsed arcs. Therefore, it seems appropriate to present a comparative study highlighting the common features and as well as the distinct differences, both in terms of plasma parameters and film properties.

This work was supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.

Highly transparent conductive Al-doped ZnO (AZO) thin film were deposited at 100℃ by laser induced high current pulsed arc (LIHCPA) from a Al-Zn alloy target. A pulsed current more than 1 kA was generated on the Al-Zn target in order to make highly ion energy and fully ionization plasma. The films properties were correlated with the growth conditions, including O₂ flow rate, pulsed arc current apply to the target and Al doping content. The microstructure properties of the films such as surface morphology, crystallinity and chemical composition were studies using scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The electrical and transmittance of the AZO films were investigated by the Hall measurement and UV/VIS spectrometer. The experimental XRD results show that the AZO films has preferred c-axis orientation along the (002) plane. The minimum resistivity is as low as 4.2×10^-4 Ω-cm with the carrier concentration of 7.3× 10²⁰ cm^-3 and Hall mobility of 20 cm²V^-1s^-1 and the average transmittance of films in the visible range (400-700 nm) is above 84 %. It was found that the O₂ flow rate affected not only the electrical properties of the films but also the band gap. The results clearly showed that when the O₂ flow rate increased from 30 sccm to 150 sccm, the resistivity increased from 4.2×10^-4 to 3.7 ×10^-3 Ω-cm, and also the band gap of the AZO films calculated by UV/VIS spectrometer measurement would decrease from 3.76 eV to 3.58 eV.