Closed Field Unbalanced Magnetron Sputtering Research Articles

Investigation of Cu-doped amorphous carbon film in improving corrosion resistance and interfacial conductivity of proton exchange membrane fuel cell

This study investigated Cu-doped a-C films prepared under a substrate bias gradually reducing from 120 to 60 V and different Cu target currents of 0, 0.15, 0.2, 0.3, 0.5 A, respectively, using closed field unbalanced magnetron sputtering physical vapour deposition technique. While the Cu-doped a-C film at the lowest Cu target current of 0.15 A (A0.15) remained an amorphous microstructure, Cu nanoprecipitates occurred at Cu target currents of 0.2–0.5 A. All the Cu-doped a-C films prepared exhibited good combination of corrosion resistance to a corrosive chemical mixture of 0.5 M H2SO4 + 5 ppm HF (as suggested by the corrosion current densities) and interfacial electric conductivity (as demonstrated by the interfacial contact resistance, ICR). Among all coatings, A0.15 showed the best corrosion resistance and interfacial electric conductivity, which is attributable to the precipitate-free Cu-doped amorphous microstructure. The measured current density of A0.15 was 1.95 × 10−7 A/cm2 at 0.6 V (vs. SCE) during potentiodynamic polarization, which was lower than that of the Cu-free a-C film at 7.34 × 10−7 A/cm2. The ICR value of A0.15 was 4.40 mΩcm2 at an assembly pressure of 1.4 MPa, which is about one third of the Cu-free a-C film. This study demonstrates a new deposition strategy combining Cu-doping and the control of substrate bias to improve the corrosion resistance and interfacial electric conductivity of a-C films for PEMFC.

Comparative Performance Evaluation of Magnetron Sputtered TiN, AlCrN, and TiAlCrN Coatings

This study presents a comparative performance evaluation of magnetron-sputtered TiN, AlCrN, and TiAlCrN coatings on tool steel substrates. Coatings play a pivotal role in enhancing the durability of engineering components exposed to harsh conditions. TiN is known for outstanding hardness and durability, AlCrN for superior wear resistance, and TiAlCrN for exceptional thermal stability and oxidation resistance. The substrate (EN 1.2363) underwent PVD coating using a closed-field unbalanced magnetron sputter ion plating (CFUBMSIP) process in a water-cooled stainless-steel vacuum chamber with four magnetron ports, operating for 3 hours per batch followed by 12 hours of natural convection cooling, utilizing TiN, AlCrN, and TiAlCrN films deposited for 180 minutes in an Ar and nitrogen atmosphere. X-ray diffraction (XRD) revealed distinctive crystal structures, with all coatings exhibiting a common preferred orientation of the (111) plane and TiAlCrN showing a ternary nitride phase. Scanning electron microscopy (SEM) images displayed the compact nature of TiAlCrN with finer grains, while TiN exhibited a densely compacted with no evidence of delamination and AlCrN showed denseness with smaller grains. Nano-indentation test was conducted to assess the coatings' hardness and elastic modulus. TiAlCrN exhibited the highest hardness (3091±243 HV), highest elastic modulus (369.86±54.19 GPa), and the best wear rate (0.1887 x 10-4 mm3/Nm-1) suggesting potential suitability for applications demanding superior rigidity and wear resistance. The study provides valuable insights for materials scientists and engineers in optimizing coating selection for specific applications.

Application of honeycomb pattern to Ti2AlN MAX phase films by plasma etching

The honeycomb pattern possesses a distinctive hexagonal structure capable of seamless repetition on a flat surface, leaving no gaps. Moreover, all arm thicknesses and angles are equal to one another. This remarkable configuration is deemed biomimetic, with numerous examples found in nature. Notably, it exhibits remarkably low density and exceptional mechanical strength. MAX phase films have gathered significant attention due to their exceptional capacity to amalgamate the essential properties of both metals and ceramics. Additionally, they possess the unique ability to effectively mend surface cracks that may arise as a result of friction-wear, restoring the material to a certain degree of integrity. In this study, Ti2AlN MAX phase thin films were deposited on M2 steel substrates by a closed field unbalanced magnetron sputtering system (CFUBMS). 750 °C heat treatment was applied to obtain the produced films in crystalline form. In addition, plasma etching parameters suitable for the phase structure of the deposited film were determined. With the inductive coupling plasma etching (ICP) process, the honeycomb pattern was given to the Ti2AlN MAX phase films with a continuous and smooth geometry at a depth of 2 μm. This study gives ideas for the development of multi-coating systems in which patterns of different geometries are included in a single layer.

Corrosion behavior of metallic coatings on titanium bipolar plates of proton exchange membrane water electrolysis

The corrosion resistance, conductivity, and cost of the metallic bipolar plates are the main limitations for the Proton Exchange Membrane Water Electrolysis (PEMWE) commercialization. In the present study, Ta, Nb, and Ti non-precious metallic coatings were deposited by closed-field unbalanced magnetron sputtering to increase the corrosion resistance and conductivity of titanium bipolar plates in PEMWE, respectively. The coating samples suffer from corrosion in a simulated extreme anode operating environment of PEMWE (0.5 M H2SO4 + 5 ppm HF, 80 °C, O2). The surface of the Ti coating forms the micropores due to the high dissolution rate in initial formation stage of the passivation film, resulting in a higher current density (1.41 × 10−6 A cm−2). The hydrolysis reaction of Ta coating causes the adsorption of sulfide ions, thereby affecting the density of the passivation film. Despite the Ta coating exhibiting a favorable current density (4.82 × 10−7 A cm−2), ICR (463.11 mΩ cm2) is lamentably poor. The surface of Nb coating has been completely covered by Nb2O5 and NbO2 in the simulated PEMWE environment. The reoxidation process of NbO2 promotes the rate of passivation film formation and provides excellent conductivity. Therefore, Nb coating exhibits the lowest current density and interfacial contact resistance of 2.23 × 10−8 A cm−2 and 119.78 mΩ cm2, respectively, which is very low compared to the bare titanium bipolar plates.

Deposition of alternative plasmonic ZrHfN thin films via closed-field dual-cathode DC unbalanced magnetron sputtering for enhanced SEF substrate applications

We present the preparation of zirconium hafnium nitride thin films as an alternative plasmonic sensing material. The ZrHfN thin films were deposited by closed-field dual-cathode DC unbalanced magnetron sputtering without an external substrate heating/biasing. A comprehensive investigation into the effect of zirconium sputtering current on the physical structural, and chemical compositions was systematically characterized by grazing-incidence X-ray diffraction, transmission electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, and X-ray absorption spectroscopy. Our results indicate that the optimal ZrHfN thin films deposited at 500 mA-IZr exhibit good crystallinity and high surface roughness, which presents excellent surface-enhanced fluorescent substrate performance for detecting rhodamine 6G at a limit of detection of 5.99 × 10−8 M, an enhancement factor of 15.62 ± 0.79-fold and displaying reusability through 25 cycles. These findings suggest promising prospects for developing ZrHfN-based SEF sensor chips for diverse applications in the future.

Scratch hardness of diamond-like carbon (DLC) coatings deposited by closed-field unbalanced magnetron sputtering

Thin coatings are subject to scratch and wear damage in tribological applications. Scratch hardness numbers are used to evaluate scratch and abrasive wear resistance. Few studies have measured the scratch hardness of thin films, and a proper scratch hardness measurement method for thin coatings is still lacking. In this study, the scratch hardness of these DLC coatings was measured at both micro-scale and nano-scale, respectively. The micro-scratch test using a 200 µm tip is an inapplicable method because the substrate effect has dominated the scratch hardness measurement. On the other hand, a nano-scratch hardness test using a sharper tip is an effective method to measure the scratch hardness of thin coatings. Although the scratch hardness introduces a lateral force compared with the indentation hardness, it well correlates with the nano-indentation hardness. The ratio of the scratch hardness to the indentation hardness is close to 1 for DLC coatings due to the amorphous structure. It proves that the tangential force induced by scratching does not influence the hardness property. In addition, a simple approach is proposed to obtain the scratch hardness of DLC coatings qualitatively without width measurement.

Pulsed-dc bias magnetron sputtered TiB2 ceramic coating

Titanium diboride, TiB2, is well known as a ceramic material with a hexagonal structure which presents various attractive properties, such as high hardness and excellent corrosion, thermal oxidation, and wear resistance. However, one drawback of TiB2 coatings is their poor adhesion to substrate materials due to high compressive residual stress after deposition. The present study aimed to assess whether a PVD-TiB2 coating with both high hardness and sufficiently good adhesion to the substrate and good wear properties can be developed by a closed-field unbalanced magnetron sputtering system using pulsed-dc biasing. The TiB2 coating deposited on AISI M2 steel substrates was characterized in terms of the structural, mechanical and tribological property. From the experimental results, it can be concluded that a closed-field unbalanced magnetron sputtering system using pulsed-dc biasing can be used to produce a TiB2 coating with sufficiently good adhesion (82 N), and high hardness (2300 HK0.01), and low friction (0.34) under given deposition conditions. The deposition conditions, particularly substrate biasing and rotation, which inhibited the formation of (001) orientation, played a role in the coating's lack of superhardness.

Investigation of properties of novel multilayer Cr/CrN/CrTiN/CrTiAlN hard coating with four bilayers

A novel multilayer Cr/CrN/CrTiN/CrTiAlN hard coating with four bilayers was developed by reactive closed field unbalanced magnetron sputtering (CFUBMS). The substrate temperature was kept in the range of 170 °C to 200 °C. The reactive gas flow was controlled by Optical Emission Monitoring. A thickness of 1.8 μm was determined using a calotester. The morphology and chemical composition were studied by electron microscopy (SEM and EDS). Nanohardness of 34.1 GPa and a modulus of elasticity of 386 GPa were determined using the nanoindentation technique. The scratch test against a diamond Rockwell indenter did not show features indicating poor adhesion. The reciprocating wear test revealed strong resistance to wear, and a coefficient of friction of 0.19 was determined. The developed multilayered hard coating showed optimal mechanical properties for industrial applications on instruments of low-temperature materials.

The effect of different annealing temperatures on the mechanical and tribological properties of the Ti2AlN MAX phase films

Ti2AlN MAX phase films produced at different N2 flow rates and different annealing temperatures were deposited on 52100 steel substrates using the closed-field unbalanced magnetron sputtering technique. N2 flow rates were changed to 2, 3.5, and 5 sccm. Due to the increasing N2 flow rate, film thickness decreased from 2 to 1.3 µm. Then the produced films were subjected to annealing at temperatures of 700, 750, and 800°C. After the film produced at a flow rate of 2 sccm was annealed at 750°C, the presence of the Ti2AlN MAX phase was determined. The binding energies of Ti 2p, Al 2p, and N 1s determined in the XPS analysis confirmed the existence of the Ti2AlN film. The friction coefficient measured for Ti2AlN MAX phase films was calculated as 0.53, the hardness value as 22.8 GPa, the elastic modulus as 291.4 GPa, and the wear rate as 2.96 × 10−4 mm3/(N·m).

Effect of Nb and V doped elements on the mechanical and tribological properties of CrYN coatings

One of the most promising approaches to enhancing the tribological properties of engineering coatings is to add transition elements to the structure. In this study, Nb-doped CrYN and V-doped CrYN thin films were deposited by pulsed DC reactive sputtering in a closed-field unbalanced magnetron sputtering (CFUBMS) system. The deposition parameters examined were target current (1, 1.5 and 2 A), deposition pressure (0.15, 0.25 and 0.35 Pa), pulse frequency (100, 200 and 350 kHz) and duty cycle (85 %, 70 % and 50 %). A Taguchi L9 orthogonal design was used to define the deposition process parameters for each doped film. The Nb and V-doped CrYN thin films were characterized in terms of their microstructure, thickness, composition, hardness and tribological properties by X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy dispersive spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), nanohardness and pin-on-disc testing, respectively. The bond strength between the substrate and the films (adhesion) was analyzed by scratch testing. For the Nb-doped thin films, a maximum hardness value of 21.4 GPa and the lowest friction coefficient of 0.36 were obtained. On the other hand, in the V-doped thin films, the maximum hardness value was 16.1 GPa, while the lowest friction coefficient obtained was 0.11. In addition, Nb-doped and V-doped CrYN thin films exhibited extraordinary adhesion properties. The effect of the selected deposition parameters (target current, pulse frequency, and duty cycle) in relation to the film thickness, hardness, and coefficient of friction properties of the Nb and V-doped CrYN thin films were investigated using the Taguchi approach and optimum operating conditions were identified and confirmed.

Influence of Nb and Ta on the corrosion and mechanical properties of CrYN coatings

Barrier coatings are applied to many machine components that are exposed to aggressive/harsh service conditions to prevent corrosion, oxidation, and wear at high temperatures. These coatings are widely used to protect structural components of gas/steam turbines in the energy and aerospace industries against aggressive operating conditions. In this study, Nb and Ta-doped CrYN films were deposited onto 316L stainless steel (SS) using the CFUBMS (Closed Field Unbalanced Magnetron Sputtering) technique. Then, the corrosion resistance, and structural and mechanical properties of the CrYN:Nb/Ta thin films were investigated. SEM, XPS, EDS, nanoindentation and potentiostat tester were used to determine the structural, mechanical and corrosion properties of the thin films, respectively. The highest hardness was found to be 21.4 GPa for CrYN:Nb films and 18.2 GPa for CrYN:Ta films. The results show that the coated specimens (lowest Icorr value 4 nA obtained in all tests) have higher corrosion resistance than the uncoated specimens (substrate Icorr value 1826 nA). In addition, it has been observed that the corrosion resistance of Ta-doped CrYN thin films is somewhat better than the niobium-doped thin films.

Abrasion-resistant, transparent, conductive In2O3@SiO2 films

External smart wearable films requires that films have good transparency, electrical conductivity, wear resistance and corrosion resistance, but the research on some issues have not been discussed anywhere. The composite In2O3@SiO2 functional films intended for smart wearable devices were synthesised via closed-field unbalanced magnetron sputtering from a powder target. This study investigated the impact of the Si:In atomic ratio in the target on the films' transparency, conductivity, resistance to sweat corrosion, and wear resistance, while elucidating the underpinning mechanisms. Results revealed that the film roughness declined from 4.41 to 1.5 nm with increasing Si:In ratio, and the preferred orientations observed in the pure In2O3 film were lost upon the incorporation of SiO2 particles. The films maintained a visible-region transmittance of 82–85%. However, the band gaps and sheet resistances increased from 3.78 to 4.3 eV and 52–2740 Ω·sq−1, respectively. The In2O3@SiO2 film with 10 at. % SiO2 demonstrated relative structural integrity, and minimal changes in optical and electric properties after acid treatment. Films with 15 at. % SiO2, both with and without exposure exhibited pitting and peeling, with changes in transmittance and sheet resistance of 14.44% and 13.08%, respectively. The alkali-treated films displayed minimal changes. The pure In2O3 film failed after 30 h of vibration. After 48 h of vibratory wear, the In2O3@SiO2 films' transmittance decreased to approximately 72%, and sheet resistances increased to 2.5 KΩ for 10 at. % SiO2 and 23 KΩ for 15 at. % SiO2. The evenly dispersed SiO2 nanodots of the In2O3@SiO2 film with 10 at. % SiO2 showed superior overall properties, including transparency, conductivity, sweat corrosion resistance, and wear resistance, attributed to the ‘maze effect’ obstructing corrosion pathways and the ‘mosaic pattern’ enhancing the abrasive properties.

Effect of cermet interlayer on the electrochemical behavior of Cr3C2-NiCr/DLC duplex coating

Duplex coating consisting of a Cr3C2-NiCr interlayer and a top DLC film was prepared using the high-velocity oxyfuel (HVOF) spraying and a closed field unbalanced magnetron sputtering (CFUBMS). The electrochemical behaviors of the Cr3C2-NiCr/DLC duplex coatings in 3.5 wt% NaCl solution was investigated by comparing it with a single DLC film and a single Cr3C2-NiCr coating. Then the role of cermet interlayer on the anticorrosion mechanism of the duplex coatings was explored. Results showed that introducing the cermet interlayer increased the surface roughness of DLC films without changing its microstructure. In the dynamic potential polarization test, duplex coatings maintained high surface integrity even after corrosion, and corrosion only occurs in localized areas. The inclusion of an interlayer avoided substrate corrosion caused by penetrating cracks and therefore provided excellent corrosion resistance.

Tribological behavior of a novel Si- and WC- co-reinforced a-C multilayer coating at 25– 500 °C

To improve the applicability of a-C coatings in a wide temperature range, a novel Si- and WC- co-reinforced amorphous carbon coating (SiC-nWCC), consisting of Si-doped a-C nanolayers and WC/a-C nano-multilayers, is proposed in this paper. A series of SiC-nWCC coatings with different modulation ratios (0.49–1.98) were fabricated by a closed field unbalanced magnetron sputtering system. The influences of modulation ratio on the microstructure, mechanical properties together with thermal stability of SiC-nWCC coatings were explored. The tribological behaviors of SiC-nWCC coatings against M50 steel balls were investigated at room temperature to 500 °C in ambient air. The results show that the SiC-nWCC coating with the modulation ratio of 1.98 achieved superior wide-temperature applicability, featuring the average friction coefficient lower than 0.17 and the wear rate less than 9.84 × 10−6 mm3/N·m in the whole temperature range of 25–500 °C. The excellent wide-temperature tribological performance of the SiC-nWCC coating are mainly attributed to the good thermal stability and the formation of temperature adaptive tribological layers. At 25 °C, sp2-rich carbon is the main lubrication phase of tribological layers, and at 200– 400 °C, the lubrication performance of coating relies on both sp2-rich carbon and Si-rich oxides, and at 500 °C, the self-lubrication phases of Si-rich oxides and WO3 are account for the outstanding lubricating performance of coating. This work provides a profound insight for developing the wide-temperature applicable a-C based coatings.

A comprehensive performance study of NiCrCN coated 316L stainless steel as bipolar plates for proton exchange membrane fuel cell

NiCrCN coatings are deposited on the surfaces of 316 L stainless steel (SS316L) substrates via closed field unbalanced magnetron sputtering ion plating (CFUMSIP) to improve the corrosion resistance and electrical conductivity of proton exchange membrane fuel cell (PEMFC) bipolar plates. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results show that CrN, Cr2N, Ni, and Cr7C3 phases exist in NiCrCN coatings. As the Cr target current grows from 2 A to 6 A, the Cr7C3 content in the carbon compounds increases from 3.39% to 11.46%, and the interfacial contact resistance (ICR) value is reduced from 18.0 mΩ cm2 to 11.2 mΩ cm2. When the Cr target current reaches 4 A, the NiCrCN coating shows the most intensive cross-sectional growth pattern by cold-field scanning electron microscopy (CFSEM) results, and the current density after prolonged polarization (0.11 μA cm−2) is much lower than that of SS316L (1.86 μA cm−2).

NANOHARDNESS AND MODULE OF ELASTICITY OF CR-BASED NITRIDE COATINGS DEPOSITED AT TEMPERATURES BELOW 200°C

Sets of Cr-based hard coatings were prepared via reactive closed field unbalanced magnetron sputtering (CFUBMS). Substrate temperature was kept in range of 150 to 200ºC during deposition. Nanohardness (H) andeffective modulus of elasticity (E*) of the CrN, CrAlN, CrTiN and CrTiAlN coatings were examined using depth-sensing indentationmethod. The results from the combined examination of the research ratios showed that the triple and quaternary hard coatings have superior mechanical properties and they strongly depend on the deposition conditions

High-Temperature Oxidation Behaviour of CrSi Coatings on 316 Austenitic Stainless Steel.

In this study, a closed-field unbalanced magnetron sputtering system, which is environmentally friendly and has high deposition efficiency, was used to deposit CrSi coatings on 316 austenitic stainless steel. This system utilised separate Cr and Si targets, and the appropriate content of Cr and Si of the coatings was adjusted by changing the currents applied to the targets. A series of CrSi coatings with different Si/Cr ratios were produced, and their oxidation behaviour at elevated temperatures was investigated. By analysing the weight gain, surface morphology and microstructure, composition and phase constituents, the oxidation behaviour at 600 °C, 700 °C and 800 °C was investigated and the optimized coating to protect the stainless steel has been identified. The outcome of the research indicated that a small amount of Si (between 4-7 at.%) in Cr coatings is effective in protecting the austenitic stainless steel against oxidation at high temperatures, while a high Si content (around 10 at.% or more) makes the coating more brittle and prone to cracking or delamination during oxidation at 800 °C.

Annealing Effect on Microstructure of Novel Ti Doped DLC Multilayer Films

Diamond-like films (DLC) are an exceptional engineering material with excellent performance such as high hardness, low friction coefficient, superior wear resistance and chemical inertness. However, two major problems of high internal stress and poor thermal stability have seriously limited its industrial applications. In particular, the microstructures and properties of pure DLC films are highly sensitive to high temperature. Therefore, the purpose of this study is to investigate the effect of annealing temperature on the microstructures of the as-prepared films. Ti-doped DLC multilayer films were synthesized by closed field unbalanced magnetron sputtering. The as-deposited films were annealed in the range of 200 to 800 °C. The surface morphology, phase structure and bonding structure of the films were characterized by SEM, AFM, GIXRD and Raman spectroscopy. The resulting films remained a smooth surface after annealing and maintained the nature of amorphous carbon up to 600 °C. The formed phases of graphite carbon and TiC nanocrystallines occur above 600 °C. In addition, the D- and G-bands showed a significant blue shift and the FWHMG shows a declining trend up to 600 °C. This result revealed that the films had high graphitization temperature and good thermal stability due to the formation of TiC nanocrystallines and its novel structure design containing elemental doping, multilayer structuring and functionally graded layering.

Investigation of corrosion protection with conductive chromium-aluminum carbonitride coating on metallic bipolar plates

To further enhance the performance of metal bipolar plates, the CrAlCN coating with high corrosion resistance and conductivity was deposited on the SS316L substrate by using Closed Field Unbalanced Magnetron Sputter Ion Plating (CFUMSIP) technique. Meanwhile, the inexpensive acetylene gas (C2H2) was utilized as a carbon source. XRD and XPS results indicate that the proportion of carbides in the coating increase with increasing carbon contents. Electrochemical measurements show that the C-doped coating significantly improves the corrosion resistance of the SS316L bipolar plates. The C doping enhances the conductivity of the CrAlN coating, and the C-doped sample obtains the lowest ICR value (2.94 mΩ cm2, before corrosion), which is well below the DOE target (≤10 mΩ cm2). The excellent conductivity and hydrophobicity of C-doped coating increase the power density of a single cell. This study demonstrates that the CrAlCN coatings have great application prospects in the bipolar plates field.

Silicon wafer as a feasible candidate for tribological characterization of thin coatings under high contact stress?

Silicon (Si) wafer is generally used as the substrate for structural analysis and residual stress measurement of thin coatings. A few studies can be found for mechanical and tribological characterization wherein Hertzian contact stress never exceeded 1 GPa. Si, being single crystal, pure, and having low surface roughness (Ra) is an ideal potential candidate for thin coating analysis. However, Si wafer breaks immediately under higher contact stress. The current study aims to push the contact stress limit to test thin coatings on Si wafer especially for friction and wear testing. To serve the purpose, different bias DLC coatings (−120 V, −80 V, −40 V, Zero V, +40 V, +80 V, +120 V) were deposited on Si wafer employing closed field unbalanced magnetron sputtering (CFUMS) system. Using conveniently available experimental approach, Hertzian contact stress in tribological tests has been pushed up to 2.6 GPa successfully on DLC coated Si wafer. Thus, it is feasible to test thin coatings on Si wafer at high contact stress which will provide useful and consistent friction and wear data such that further test using the steel substrate will be reduced by a significant margin. A thorough mechanical, tribological and structural (Raman) analysis is presented. It was found that −120 V possessed the highest hardness (H: 17.6 GPa), modulus (E: 184 GPa) and residual stress (4.5 GPa). The same coating produced the lowest sp2/sp3 ratio, wear rate using contact stress (0.092 × 10−13 mm4/N) and wear/friction energy (0.071 × 10−13 mm3/J2) in comparison to other coatings used in the study. Counter body analysis for −120 V shows the minimum scratch area depicting friction between transfer film and DLC hence the lowest coefficient of friction (0.061) was obtained. Moreover, surface topography is explained with the aid of atomic force microscope (AFM) images and surface roughness (Ra) data. AFM revealed craters and bumpy like surfaces for positive and negative biased samples respectively.