ICMCTF2013 Session B1-1: PVD Coatings and Technologies

An overview will be given about the development of both technologies during the last 20 years from basic processes in the laboratory scale to the industrial applicable deposition source. Just as well the combination of both technologies in form of the laser assisted pulsed arc deposition process (Laser-Arc) will be presented. The advantages of this combination are presented with resprect of introduction for high volume coating of parts and tools.

Mainly advantages of the Laser-Arc technology are to have a very controlled pulsed arc deposition technology with a high deposition rate (2 µm/h twofold rotating axes of a planetary). By the laser controlling of pulsed arc evaporation a longtime using of the applied rotating graphite cathodes is guaranteed and ta-C films with a thickness up to 10 microns can be deposited. By integration of a filter unit for separation of particles from the carbon plasma, an improved ta-C film quality can be obtained, regarding their roughness, hardness and Young´s modulus with an acceptable loss of the deposition rate.

The nature of the Laser-Arc-Module system is, that this carbon ion source can be integrated in commercial available coating machines, independently of producer.

Sputtering carbon containing coatings with high power impulse magnetron sputtering (HIPIMS) is discussed to suffer from the low ionization probability of carbon to significantly modify the resulting coating properties compared to state of the art technology. But B.M. De Koeven et al. reported in 2003 on an increased density for HIPIMS deposited carbon films of 2.7 g/cm³, mainly attributed to the Ar ion bombardment connected with a very low hardness of only ~ 7 GPa. Coating hardness up to 25 GPa were published by R. Chistyakov et al. using modulated pulse power sputtering (MPP).

In this paper a reactive C-DLC deposition using HIPIMS technology will be reported. Within this study optical emission spectroscopy was carried out and ionized carbon was detected. When adding C₂H₂ to the HIPIMS sputtering of the graphite target the CII emission line increased even more. The deposited layers were investigated in dependence off of the acetylene content in the process and the applied bias voltage especially regarding their hardness. By modification of the deposition parameters DLC films with a plastic hardness of 65 GPa (indentation hardness of 41 GPa) were realized, while the deposition rate was well above 1 µm/h.

Several micrometer thick super-hard tetrahedral amorphous carbon (ta-C) films have been prepared by pulsed laser deposition on polished High-Speed-Steel (HSS)- substrates and HSS- driller. The first aim was to investigate if and how various process parameters influence the tribological properties and the wear parameters of these ta-C layers on polished steel substrates.

Furthermore the influences of an intermediate layer and of internal stress in these ta-C layers on the drill process were analyzed . It will be shown, that an intermediate layer of tungsten carbide optimizes the adhesion of the ta-C layers at the HSS- drillers. Built up edge and wear of the drillers is reduced by improving the mechanical properties of the ta-C layers by adjusting the ablation process and stress reduction process.

Drill- tests with these ta-C coated HSS- drillers in an aluminium cast alloy (G-AlSi12(Cu)) with minimal quantity lubrication shows a high reduction of the demand for energy as well as a strong increase of the durability of these drillers up to 400 times and more. Hence it is possible to elevate the cost effectiveness in case of ta-C coated drillers.

The coating of cutting edges is a technical challenge because of a possible edge rounding. Often the strictly convex zones are exposed to an extensive ion bombardment during the coating process. Consequently a local overheating and re- sputtering can occur. On the other hand, the deposition of a thicker film causes an edge rounding because of geometrical reasons.

To solve this problem a process has been developed to sharpen the cutting edges during the deposition of the protective coating. The solution is a combination of a certain adjustment of the ion energies of the coating plasma and the materials composition of the film. Thus it is possible to stop and to reverse the rounding of the edges.

For example, with an 8 micron-thick Si-doped AlCrN/TiN film the cutting edge radius can be reduced from 3 micron at the tool blank to 300 nanometers at the surface of the coating.

Due to this process new perspectives of tool coating technologies can be opened.

The present study explored the deposition of Fe/SiC multilayers on Si (100) substrate at 400ºC using pulsed laser deposition (PLD). These samples were annealed isochronally at temperatures of 800ºC and 1000ºC for 2 h under an inert environment. XRD pattern revealed the amorphous nature of SiC films deposited at 400ºC and crystalline nature in the samples annealed at 800 ºC. On further increasing the annealing temperature to 1000ºC, a number of secondary phases like Fe₃C, SiO₂ and FeSiO₃ starts forming in the XRD pattern, causes reaction of SiC, Fe and oxygen at their interface and the interdiffusion of either matrix at higher annealing temperatures. A weak reflection from Fe (100) detected in all samples. X-ray photoelectron spectroscopy (XPS) study shows the binding energy of iron incorporated with iron carbide, iron silicon carbide and binding energy of Si and C incorporated with SiC. FESEM analysis revealed the formation of pyramidal like morphology in SiC films annealed at 800 and 1000ºC. Room temperature ferromagnetism with significant increment in the remnant magnetization and decrease in coercively was observed in Fe/SiC multilayers. The enhanced structural and magnetic properties of Fe/SiC multilayers could be a better approach towards spintronics applications at microscale.