Surface treatment in a cathodic arc plasma : Key step for interface engineering.

The effect of substrate surface treatment (substrate sputter cleaning) in a cathodic arc plasma prior to unbalanced magnetron deposition of transition metal nitride coatings on the performance of the coated components has been investigated. In particular the influence of parameters such as ion species, ion energy and exposure time on the changes in substrate surface topography, microstructure and micro-chemistry were studied employing transmission electron microscopy, energy dispersive X-ray analysis, electron energy loss spectroscopy, X-ray diffraction, atomic force microscopy and optical microscopy. The consequences for both the microstructure of subsequently grown transition metal nitride coatings and their adhesion were elucidated. The relevance for practical applications was demonstrated using the example of dry high-speed milling tests, which showed that an appropriate choice of substrate surface pre-treatment parameters can double the life time of the coated tools. This was found to be due to an improved adhesion as a result of a combina-tion of reduced oxygen incorporation at the interface between coating and substrate and local epitaxial growth of the coating. The latter is promoted by certain sub-strate surface pre-treatment procedures, which provide clean surfaces with preserved crystallographic order

Hybrid HIPIMS and DC magnetron sputtering deposition of TiN coatings: Deposition rate, structure and tribological properties

High power impulse magnetron sputtering (HIPIMS) has the advantage of ultra-dense plasma deposition environment although the resultant deposition rate is significantly low. By using a closed field unbalanced magnetron sputtering system, a hybrid process consisting of one HIPIMS powered magnetron and three DC magnetrons has been introduced in the reactive sputtering deposition of a TiN hard coating on a hardened steel substrate, to investigate the effect of HIPIMS incorporation on the deposition rate and on the microstructure and mechanical and tribological properties of the deposited coating. Various characterizations and tests have been applied in the study, including XRD, FEG-SEM, cross-sectional TEM, Knoop hardness, adhesion tests and unlubricated ball-on-disk tribo-tests. The results revealed that, both the DC magnetron and hybrid-sputtered TiN coatings exhibited dense columnar morphology, a single NaCl-type cubic crystalline phase with strong (220) texture, and good adhesion property. The two coatings showed similar dry sliding friction coefficient of 0.8 – 0.9 and comparable wear coefficient in the range of 1 – 2× 10-15 m3N-1m-1. The overall deposition rate of the hybrid sputtering, being 0.047 μm/min as measured in this study, was governed predominantly by the three DC magnetrons whereas the HIPIMS only made a marginal contribution. However, the incorporated HIPIMS has been found to lead to remarkable reduction of the compressive residual stress from -6.0 to -3.5 GPa and a slight increase in the coating hardness from 34.8 to 38.0 GPa

Characterization of arc discharge plasmas in the combined steered arc/unbalanced magnetron deposition process

Cathodic arc discharges have been used successfully as sources of highly ionized flux of particles in substrate etching and implantation providing an improved adhesion of PVD coatings deposited by the combined steered arc/unbalanced magnetron method. Substrates biased at -1,200 V in arc plasmas are subjected to ion bombardment which cleans the surface and creates implantation defects thus modifying the interface with subsequently sputter deposited coatings. The etching rate depends on the magnitude of the ion flux while the implantation profiles are dominated by the energy of the bombarding species. In the present work, diagnostic studies of Cr cathodic arc discharges with a current of 100 A show a strong dependence of ion fluxes on the pressure and type of residual gas. The increase of the Ar gas pressure increases the ion saturation current density measured by Langmuir probes. Optical emission spectroscopy measurements of the emission from different charge states of Cr ions revealed an increased fraction of neutral metal atoms after a critical pressure of 10-2 Pa. These results indicate that at higher pressures a significant fraction of the ion flux is comprised of Ar+ and that the mean charge state decreases. The etching rate of substrates biased at -1,200 V in the Cr arc plasma increases from 4 nm.min-1 to 8 nm.min -1. The obtained results suggest a two-stage etching procedure starting with arc operation at high Ar pressure (PAr = 0.09 Pa) to achieve faster metal removal by Ar and Cr ion bombardment. In the second stage pure Cr ion bombardment at residual gas pressure (PAr &le 6 10-4 Pa) allowed an enhanced ion implantation up to 20 nm and Cr accumulation of approximately 37 at % at the interface substrate/coating. TixAl(1-x)N films deposited after the two stage etching method have lower stress gradients at the interface and improved critical load values up to 85 5 N

Industrial scale manufactured superlattice hard PVD coatings

Superlattice hard PVD coatings exhibit high hardness values up to 60 GPa, wear resistance, and excellent protection against corrosion depending oil the choice of the material partners involved. TiAlN/CrN, TiAlN/VN, TiAlYN/VN, TiAlN/ZrN, and CrN/NbN superlattice coatings with typical periods lambda of 3-4 nm have been produced economically under production conditions in industrial sized coating equipment. Some of the coatings are characterised by high compressive stresses up to 10 GPa. In such cases the utilisation of the combined cathodic arc/unbalanced magnetron deposition method (arc bond sputtering technology) in combination with the introduction of a lower stressed monolithically grown base layer provides a sufficiently high bonding strength at the interface. The major deposition steps are: (1) pump down and preheating; (2) bombardment of the substance surface with multi-ionised metal ions generated in a steered cathodic arc discharge (3) deposition of a base layer (0.1-0.2 mum) using the unbalanced magnetron; (4) deposition of the superlattice coating with simultaneously operated unbalanced magnetrons or a combination of simultaneously operated unbalanced magnetrons and steered cathodic arc sources

Optimization of in situ substrate surface treatment in a cathodic arc plasma: A study by TEM and plasma diagnostics

Cr ions generated by a steered cathodic arc discharge are utilized to control and enhance the adhesion properties of 3.5 mum thick TixAl(1-x)N based coatings deposited on high speed steel substrates, A two-step etching procedure (negative substrate bias, U-S=1200 V) is suggested, operating the arc discharge initially in an Ar atmosphere (p(Ar)=0.09 Pa.. 6.75x10(-4) Torr) to achieve predominantly metal removing effects (etching rate: 9 nm min(-1)) with a mixture of Ar and Cr ions. In the second stage at residual gas pressure level (p(Ar) less than or equal to 0.006 Pa, 4.5x10(-5) Torr, etching rate: 4 nm min(-1)) pure Cr ion irradiation leads to a Cr penetration as deep as 20 nm with a Cr accumulation of approximately 37 at % at the interface substrate/coating. This procedure promotes localized epitaxial growth of TixAl(1-x)N and enhances critical load values up to 85 +/-5 N. (C) 2001 American Vacuum Society

Industrial use of HiPIMS and the hiP‐V hiPlus technology

It has been demonstrated by several groups that HiPIMS is a state of the art tool for applying demanding coatings with superior film properties. The real industrial breakthrough for the HiPIMS‐technology, has not yet happened. On the other hand, the up till now available HiPIMS‐PS were mainly been up‐scaled “prototypes”, far away from industrial work horses. With the hiP‐V HiPIMS power system, a direct derivative of a robust power supply technology already in commercial use for public transportation systems, another milestone is set to make the HiPIMS technology go mainstream. HiPIMS is not a revolution that will make all other technologies obsolete, yet it is a very powerful complement. With a reliable, multi‐functional power supply and with a rapid arc‐handling, it could possibly be a start of a new era in thin film production. Just consider the possibility of etching and implantation to increase cleanliness and adhesion of the samples. Until now, most of the R&D work done in HiPIMS, has been dedicated to hard coatings and tool coatings. Here, HiPIMS is surely useful but not the expected technological breakthrough. For the future, the implementation of the new positive reverse pulse, the hiP‐V hiPlus HiPIMS technology, is opening a whole new field of possible applications for i.e. nonconductive substrates where no bias can be applied. Glass and plastics can be processed with remarkable results in hardness, enhanced film properties and additionally, it is achieved at lower substrate temperatures. It has been a slow start for HiPIMS, but the future looks bright.Peer reviewe