Effect of the degree of high power impulse magnetron sputtering utilisation on the structure and properties of TiN films

TiN films were deposited using high power impulse magnetron sputtering (HIPIMS) enabled four cathode industrial size coating system equipped with HIPIMS power supplies. The standard version of this system allows control over the ion bombardment during coating growth by varying the strength of the electromagnetic field of the unbalancing coils and bias voltage applied to the substrate. The coatings were produced in different coating growth conditions achieved in combined HIPIMS — direct current (dc) unbalanced magnetron sputtering (HIPIMS/UBM) processes where HIPIMS was used as an additional tool to manipulate the ionisation degree in the plasma. Four cathode combinations were explored with increasing contribution of HIPIMS namely 4UBM (pure UBM), 1HIPIMS + 3UBM, 2HIPIMS + 2UBM and 2HIPIMS (pure HIPIMS) to deposit TiN coatings. Optical emission spectroscopy (OES) measurements were carried out to examine the plasma generated by the various combinations of HIPIMS and UBM cathodes. The micro-structural study was done by scanning electron microscopy (SEM). X-ray diffraction (XRD) technique was used to calculate the residual stress and texture parameter. It has been revealed that the residual stress can be controlled in a wide range from − 0.22 GPa to − 11.67 GPa by intelligent selection of the degree of HIPIMS utilisation, strength of the electromagnetic field of the unbalancing coils and the bias voltage applied to the substrate while maintaining the stoichiometry of the coatings. The effect of the degree of HIPIMS utilisation on the microstructure, texture and residual stress is discussed. Combining HIPIMS with dc-UBM sputtering is also seen as an effective tool for improving the productivity of the deposition process

CrN/NbN coatings deposited by HIPIMS: A preliminary study of erosion-corrosion performance

Nanoscale CrN/NbN multilayer PVD coatings have exhibited resistance to erosion-corrosion. However growth defects (under dense structures and droplets) in the coating produced by some deposition technologies reduce the ability to offer combined erosion-corrosion resistance. In this work a novel High Power Impulse Magnetron Sputtering (HIPIMS) technique has been utilised to pretreat substrates and deposit dense nanoscale CrN/NbN PVD coatings (HIPIMS-HIPIMS technique). This new technique, rich with metal ion plasma, deposits very dense structures and offers virtually defect free coatings (free of droplets as observed in cathodic arc technique and under-dense structures observed in standard dc sputtering). Plasma diagnostic studies revealed a high metal ion-to-gas ion ratio (Cr:Ar) of 3:1 for HIPIMS pretreatment conditions with the detection of 14% Cr2+ and 1% Cr3+ ions and J(s) of 155 mAcm(-2). For deposition conditions the metal ion-to-gas ratio was approximately 1:4 which is significantly higher compared to DC at 1:30. Characterisation results revealed a high adhesion of L-C 80 N, high hardness of 34 GPa and Young's modulus of 381 GPa. Low friction coefficient (0.46) and dry sliding wear coefficient, K-C (1.22 x 10(-15) m(3)Nm(-1)) were recorded. The effect of deposition technique (droplet defect and intergranular void free coatings) on erosion-corrosion resistance of CrN/NbN coatings has been evaluated by subjecting the coatings to a slurry impingement (Na2CO3 + NaHCO3 buffer solution with Al2O3 particles of size 500-700 mu m) at 90 degrees impact angle with a velocity of 4 ms(-1). Experiments have been carried at -1000 mV, + 300 mV and + 700 mV representing 3 different corrosion conditions. (c) 2009 Elsevier B.V. All rights reserved

Defect growth in multilayer chromium nitride/niobium nitride coatings produced by combined high power impulse magnetron sputtering and unbalance magnetron sputtering technique

In recent years, high power impulse magnetron sputtering (HIPIMS) has caught the attention of users due to its ability to produce dense coatings. However, microscopic studies have shown that HIPIMS deposited coatings can suffer from some surface imperfections even though the overall number of defects can be significantly lower compared to, for example, arc deposited coatings of similar thicknesses. Defects can degrade the coating performance thus any kind of defect is undesirable. To better understand the nature of these imperfections and the science of their formation, a series of Chromium Nitride/Niobium Nitride (CrN/NbN) coatings were deposited using HIPIMS technique combined with unbalanced magnetron sputtering (UBM) by varying deposition times (t = 15 to 120 minutes). All other deposition parameters were kept constant in order to deposit these coatings with a consistent deposition rate and stoichiometry. In addition, coatings were deposited using pure UBM technique to compare the defects generated by these two different physical vapour deposition approaches. High-resolution scanning electron microscopy images revealed that HIPIMS/UBM and pure UBM CrN/NbN coatings have similar types of defects which could be categorised as: nodular, open void, cone-like and pinhole. Interestingly, there was no evidence of droplet formation in HIPIMS/UBM deposited coatings. The defect density calculation indicated that the defect density of HIPIMS/UBM coatings increased (from 0.48 to 3.18%) with the coating thickness. A coating produced in a relatively clean chamber had a lower defect density. Potentiodynamic polarisation experiments showed that the fluctuation in corrosion currents in HIPIMS/UBM coatings reduced with the coating thickness. This indicated that though visible on the surface, most of these defects did not penetrate thorough the whole thickness of the coating

Amorphous Boron containing silicon carbo-nitrides created by ion sputtering

Silicon carbo-nitride films with Boron were deposited onto Silicon, glass and SS304 Stainless Steel substrates using the ion beam assisted deposition (IBAD) method. The coating composition, rate of ion-assistance and substrate temperature were varied. Films were examined by X-Ray Diffraction, Scanning Electron microscopy, Energy Dispersive X-Ray analysis, Cathodoluminescence, Atomic Force Microscopy and Nano-indentation. The composition and chemical bonding variation was found to be dependent on deposition conditions. All coatings were amorphous, fully dense and showed high hardness up to 33 GPa. It is suggested that the low friction coefficient of about 0.3, measured against Al2O3 using the pin-on-disc method, may be the result of the presence of C nanoclusters which are formed under the low energy deposition conditions. Films deposited on Stainless Steel had an onset of rapid thermal oxidation at 1150 °C in air as determined by thermogravimetric analysis. The films have a Tauc bandgap between 2.2 and 2.8 eV and were also exceptionally high electrical resistive which may indicate the presence of localised state

Inactivation of bacteria under visible light and in the dark by Cu films. Advantages of Cu-HIPIMS-sputtered films

Introduction: The Cu polyester thin-sputtered layers on textile fabrics show an acceptable bacterial inactivation kinetics using sputtering methods. Materials and methods: Direct current magnetron sputtering (DCMS) for 40s of Cu on cotton inactivated Escherichia coli within 30min under visible light and within 120min in the dark. For a longer DCMS time of 180s, the Cu content was 0.294% w/w, but the bacterial inactivation kinetics under light was observed within 30min, as was the case for the 40-s sputtered sample. Results and discussion: This observation suggests that Cu ionic species play a key role in the E. coli inactivation and these species were further identified by X-ray photoelectron spectroscopy (XPS). The 40-s sputtered samples present the highest amount of Cu sites held in exposed positions interacting on the cotton with E. coli. Cu DC magnetron sputtering leads to thin metallic semi-transparent gray-brown Cu coating composed by Cu nanoparticulate in the nanometer range as found by electron microscopy (EM). Cu cotton fabrics were also functionalized by bipolar asymmetric DCMSP. Conclusion: Sputtering by DCMS and DCMSP for longer times lead to darker and more compact Cu films as detected by diffuse reflectance spectroscopy and EM. Cu is deposited on the polyester in the form of Cu2O and CuO as quantified by XPS. The redox interfacial reactions during bacterial inactivation involve changes in the Cu oxidation states and in the oxidation intermediates and were followed by XPS. High-power impulse magnetron sputtering (HIPIMS)-sputtered films show a low rugosity indicating that the texture of the Cu nanoparticulate films were smooth. The values of R q and R a were similar before and after the E. coli inactivation providing evidence for the stability of the HIPIMS-deposited Cu films. The Cu loading percentage required in the Cu films sputtered by HIPIMS to inactivate E. coli was about three times lower compared to DCMS films. This indicates a substantial Cu metal savings within the preparation of antibacterial film

Target poisoning during CrN deposition by mixed high power impulse magnetron sputtering and unbalanced magnetron sputtering technique

Target poisoning phenomenon in reactive sputtering is well-known and has been studied in depth over the years. There is a clear agreement that this effect has a strong link on the quality, composition, properties and pronouncedly on the deposition rate of PVD coatings. With the introduction of IPVD techniques such as the relatively novel High Power Impulse Magnetron Sputtering (HIPIMS), which have highly ionized plasmas of the depositing species (metal and gas ions), target poisoning phenomenon is highly contested and thus has been left wide open for discussion. Particularly there have been contradicting reports on the presence of prominent hysteresis curves for reactive sputtering by HIPIMS. More work is needed to understand it which in turn will enable reader to simplify the coating deposition utilizing HIPIMS. This work focuses on the study of Chromium (Cr) targets when operated reactively in argon + nitrogen atmosphere and in different ionizing conditions, namely (a) pure HIPIMS (b) HIPIMS combined with UBM (Unbalanced Magnetron Sputtering) and (c) pure UBM. Nitrogen flow rate was varied (5 sccm to 300 sccm) whereas the average power on target was maintained around 8kW. Target resistance vs N2 flow rate curves for these conditions have been plotted in order to analyze the poisoning effect. When only one UBM target was operating target poisoning effect was prominent between the flow rates of 80 and 170 sccm. However it appeared reduced and in nearly same flow rate ranges (90 and 186 sccm) when only one HIPIMS target was operating. When 4 UBM targets were operated, target poisoning effect was evident however expectedly moved to higher flow rates (175 sccm and above) whereas appeared diminished when 2 UBM and 2 HIPIMS were running simultaneously. Further, to analyze the effect of actual target conditions (poisoning) on deposition rate and on the properties of the films deposited, commercially widely used Chromium nitride (CrN) coatings were deposited in mixed HIPIMS and UBM plasma and at 5 different flow rates of nitrogen. Detail characterization results of these coatings have been presented in the paper which will assist the reader in deposition parameter selection. Keywords : HIPIMS, UBM, CrN, Nitrogen flow rate, target poisoning, PVD coating

Lubricated sliding wear mechanism of chromium-doped graphite-like carbon coating

The current research aims to discuss the tribological behaviour of Chromium-doped graphite-like carbon coatings and suggest a wear mechanism under both dry (in air) and boundary lubricated sliding condition based on phase composition of the wear product generated in wear track during pin-on-disc experiments. As expected, the friction coefficient reduces from 0.22 to 0.12 due to addition of lubricant. Raman analysis indicates that wear mechanism is oxidative in dry sliding condition whereas it is chemically reactive in the presence of lubricant. It is speculated that the key-factor of reduced friction and wear coefficient in lubricated condition is the formation of CrCl3 due to tribochemical reaction between coating and oil. CrCl3 has graphite-like layered structure; therefore it acts like solid lubricant

Isothermal and dynamic oxidation behaviour of Mo−W doped carbon-based coating

The oxidation behaviour of Mo−W doped carbon-based coating (Mo−W−C) is investigated in elevated temperature (400°C−1000°C). Strong metallurgical bond between Mo−W−C coating and substrate prevents any sort of delamination during heat-treatment. Isothermal oxidation tests show initial growth of metal oxides at 500°C, however graphitic nature of the as-deposited coating is preserved. The oxidation progresses with further rise in temperature and the substrate is eventually exposed at 700°C. The performance of Mo−W−C coating is compared with a state-of-the-art coating, which shows preliminary oxidation at 400°C and local delamination of the coating at 500°C leading to substrate exposure. The graphitisation starts at 400°C and the diamond-like structure is completely converted into the graphite-like structure at 500°C. Dynamic oxidation behaviour of both the coatings is investigated using Thermo-gravimetric analysis carried out with a slow heating rate of 1°C/min from ambient temperature to 1000°C. Mo−W−C coating resists oxidation up to ~800°C whereas delamination of coating is observed beyond ~380°C. In summary, Mo−W−C coating provides improved oxidation resistance at elevated temperature compared to coating

Structure and wear mechanisms of nano-structured TiAlCN/VCN multilayer coatings

Dry sliding wear of transition metal nitride coatings usually results in a dense and strongly adhered tribofilm on the worn surface. This paper presents detailed electron microscopy and Raman spectroscopy characterizations of the microstructure, a newly developed multilayer coating TiAlCN/VCN and its worn surface after pin-on-disc sliding wear against an alumina ball. The friction coefficient in a range of 0.38–0.6 was determined to be related to the environmental humidity, which resulted in a wear coefficient of the coating varying between 1017 and 1016 m3 N1 m1. TEM observation of worn surfaces showed that, when carbon was incorporated in the nitride coating, the formation of dense tribofilm was inhibited

Study of the Effect of RF-power and process pressure on the morphology of copper and titanium sputtered by ICIS

Inductively Coupled Impulse Sputtering is a promising new technique for highly ionised sputter deposition of materials. It combines pulsed RF-power ICP technology to generate plasma with pulsed high voltage DC bias on the cathode to eliminate the need for a magnetron. To understand the effect of power and pressure on the coating morphology, Copper and Titanium films have been deposited in a power-pressure matrix. The RF-power was increased from 2000 - 4000 W. The pressure was set to 6 Pa and 13 Pa respectively. For Copper, the morphology changes from columnar to fully dense with increasing power and the deposition rate drops from 360 nmh-1 to 210 nmh-1 with higher process pressure. Titanium morphology does not change with power or pressure. The deposition rate is lower than predicted by the differences in sputtering yields at 68 nmh-1 for a pressure of 6 Pa