Plasma-assisted Physical Vapour Deposition Research Articles

Perspective on pathways towards responsible surface engineering

In this perspective sustainability-relevant aspects of modern surface engineering technologies, which enable improved structural and functional surface properties, are critically evaluated. Although plasma-assisted physical vapour deposition (PVD) is increasingly employed to address global challenges, such as energy efficiency and reduction of CO2 emissions, their inherently resource-intensive nature is often not considered.Surface engineering research should thus embrace sustainability-relevant aspects from a processes and materials design point of view. While we are convinced that sustainability-relevant surface engineering has to be based on synchronised process and materials solutions, we will discuss processes and materials separately.In terms of processes, we are going to describe the challenges of state-of-the-art technology, including energy and mass balances as well as product cycles. With respect to materials, the coating and process purity as well as chemical and microstructural complexity are discussed.Such approaches are fully in line with the United Nations Sustainable Development Goal 12 Responsible Consumption and Production. We expect that the here discussed urgently needed pathways towards responsible surface engineering will become important for the surface engineering community and adopted within the near future. Responsible surface engineering includes the human behaviour and necessitates a change in mindset of materials scientists and process engineers. Hence, two main questions are critically evaluated in this perspective:1)What are sustainability-relevant aspects of PVD processes and materials?2)Which pathways are available to move towards responsible surface engineering?

Nanosized curing catalyst via nano-templated plasma PVD for attaining superior low-cure powder coating films

The addition of curing catalysts into powder coating is a key method to fabricate low-temperature curing powder coating for reducing energy consumption and expanding its applications to heat-sensitive substrates. However, the heterogeneous dispersion of the unmodified catalysts in powder coatings results in inconsistent catalysis of resin crosslinking, thus leading to compromised surface smoothness and gloss. Utilizing nanosized catalysts is an efficient solution to such problems. In this paper, we propose a nano-templated dielectric barrier discharge (DBD) plasma-assisted physical vapor deposition (PVD) strategy to fabricate the nanosized catalysts. The curing catalyst, 2-ethylimidazole (2-elm), is successfully vaporized and deposited on nano-carrier SiO2 (SiO2-NPs) in the DBD plasma reactor at atmospheric pressure, producing 2-elm@SiO2-NPs. The mechanical strength and chemical resistance of finishes of powder coating incorporated with the 2-elm@SiO2-NPs remained at low curing temperature (170 °C for 15 min) and fast curing condition (190 °C for 8 min). In addition, their surface qualities are comparable to that of the original powder coating, with up to 100 % gloss retention, successfully eliminating the issue of more than 25 % gloss attenuation of the powder coating with unmodified 2-elm. This study provides an effective, solvent-free strategy for fabricating nanosized curing catalysts and achieving high-quality film finishes.

Evaluation of titanium nitride/titanium aluminum nitride thin film coating, plasma nitriding on AISI 304 stainless steel using the plasma-assisted physical vapor deposition process, and thermal stress investigated through finite-element analysis

In the present paper, plasma-assisted physical vapor depositions (PAPVDs) have been used to extract the TiN and titanium aluminum nitride (TiAlN). Further, plasma nitriding (PN) has been used prior to thin-film deposition of TiN on AISI 304 stainless steel material using intentional biasing (in the coating). PAPVD is integrated to investigate the thermal resistant effect coating of AISI 304 stainless steel by TiN coating using finite-element analysis. The morphology of elements on the coating was studied by field emission scanning electron microscopy, X-ray diffraction (XRD), and energy-dispersive X-ray spectroscopy. From XRD analysis, it has been observed that at the coated zone Ti, TiN was found on the AISI 3O4 stainless steel. The results in microhardness through the Vickers microhardness tester have been measured up to 350 Hv for the base sample at a 10 g load. Moreover, TiN/(PN + TiN) coated samples were measured with an average microhardness of 2220, 963, and 720 Hv for the nitride sample. In addition to this, the microhardness of TiAlN was found up to 1890 and 2400 Hv for different samples. The thickness of the film is around 1.4279 µm (TiN) and 1.888 µm (TiAlN) in 1 h of deposition.

Investigation on Different TiCn Duplex Treatments Applied to Cold Work Tool Steel for Surface Properties Improvement

In this work, different plasma nitriding and coating thickness combinations were tested to improve surface proprieties of a cold work tool steel. A DIN X100CrMoV8-1-1 cold work tool steel was plasma nitrided, using a 5 vol-%. N2 + 95 vol-% H2 gas mixture, for 2.5- and 5.0-h nitriding times. Then, the non-nitrided and nitrided substrates were coated with titanium carbonitride (TiCN)-graded thin films produced by cathodic arc plasma-assisted physical vapor deposition. Different deposition parameters were used to produce coatings with thicknesses of 1.0 and 2.0 µm. The samples were characterized regarding the microstructure, surface hardness, coating adhesion, and friction coefficient, which were measured by ball-on-disc tests. In the plasma nitriding process, it was possible to generate a diffusion layer, without the formation of a compound layer, with depths of 58 µm and 68 µm for 2.5 and 5.0 h, respectively. Both plasma nitriding treatments avoided delamination of the TiCN coating when deposited on the cold work tool steel. The TiCN coatings significantly decreased the friction coefficient, regardless of substrate condition. The lowest friction values were found for the thinner coating. The deeper diffusion zone led to higher hardness value, and highest scratch crack propagation resistance of the coatings, meaning superior coating adhesion. The best surface properties were found when combining the deeper plasma nitriding diffusion layer with the thinner PVD coating.

A Quick and Accurate Method to Determine Submicron Size Coating Thickness Using Micro-Indentation along with a Mathematical Model

Hard and adherent wear-resistant thin surface coatings are synthesized on an aerospace alloy AA2219-T6 alloy using plasma-assisted physical vapor deposition. Submicron size TiN coatings with Ti interlayers are deposited and evaluated as a function of different deposition temperatures varying from 100 °C to 200 °C. Features of deposited surface layers are evaluated using different techniques; these include field emission scanning electron microscopy equipped with energy dispersive spectroscopy and X-ray diffraction. Mathematical models developed by Yu. A. Bykov and S. Hogmark are considered to estimate the coating thickness using the Composite Hardness measurements. The values predicted by Bykov’s model grossly underestimated the thickness values and thus a correction factor is proposed. The actual coating thickness is measured by sandwiching the thin coating between the substrate and electrolytically deposited nickel layer; the observations are made using field emission scanning electron microscope. The present study successfully used corrected Bykov’s Model along with micro-indentation proved to be an easy, quick and accurate method to estimate the coating thicknesses of thin hard coatings on the soft substrate over a wide range coating thicknesses.

Effect of surface characteristics and environmental aging on wetting of Cr-coated Zircaloy-4 accident tolerant fuel cladding material

With the goal of increasing the performance and safety of existing nuclear power plants, the research and development of Accident Tolerant Fuels (ATFs) are of high priority within the nuclear community. Two widely studied ATF concepts are the replacement of currently used zirconium alloy for other cladding materials that provide resistance to hydrogen production during accident conditions or the deposition of protective functional coatings on the Zircaloy cladding that mitigate the risk. While different protective coating options are being considered, Cr-coating is predominant. In this study, Cr-coating on Zircaloy-4 substrates were produced by Plasma Assisted Physical Vapor Deposition (PAVD), aiming at investigating their surface characteristics that may have an impact on the efficiency of heat transfer. The thickness, structure, and mechanical properties of the coatings were examined by scanning electron microscopy, focused ion beam, X-ray diffraction, and microindentation. Furthermore, surface topography, surface energy conditions, and surface chemistry were assessed using contact profilometry, atomic force microscopy, contact angle goniometry, and X-ray photoelectron spectroscopy. The static contact angle reduced from 75° for as-received substrates to almost 20° after coating. This significant increase in wettability observed after chromium deposition on Zircaloy changed with aging. For instance, over time, a hydrophobic recovery on the plasma-treated surfaces was detected. Correlations between surface chemistry and surface energy studies helped to explain the variation in contact angle with aging time. Results demonstrated that the formation of chromium oxides and hydroxides, and other carbonaceous species affected the surface coating affinity with water upon ambient exposure.

Wear and corrosion resistance of titanium carbo-nitride coated Al-7075 produced through PVD

Titanium carbo-nitride coatings were deposited using plasma-assisted physical vapour deposition technique on Al-7075 aluminium alloy plates. Studies were conducted to understand the bonding between the coating and substrate, and to examine the wear- and corrosion-resistant properties under heat treatments. The nature of bonding was characterized using scanning electron microscope. The pin-on-disc wear test, according to G99 ASTM standard, displayed the frictional force, coefficient of friction and wear for the samples. Simultaneously, the corrosion tests, according to G5-14 ASTM standard, performed for a period of 48 h, using electrochemical impedance and potentiodynamic polarization tests displayed the Nyquist and Tafel plots for analysis. The wear and corrosion rates of samples heat-treated at $$500^{\circ }\hbox {C}$$ for 1 h were found to be $$0.066\hbox {e-}6\,\hbox {g\,s}^{{-1}}$$ and $$2.962\hbox {e}2\,\hbox {g mm}^{-2}\,\hbox {s}^{{-1}}$$ , respectively. While that of samples heat-treated at $$500^{\circ }\hbox {C}$$ for 12 h were found to be $$0.366\hbox {e-}6\,\hbox {g s}^{{-1}}$$ and $$4.177\hbox {e}2\,\hbox {g mm}^{-2}\,\hbox {s}^{{-1}}$$ . Both the wear and the corrosion performance investigations were in good agreement with each other. Thus, the tribo-corrosive deterioration of titanium carbo-nitride coated Al-7075 had escalated with an increase in durations of the heat treatment.

Magnetic Sensing Properties of PVD Carbon Films Containing Vertically Aligned Crystallites.

The demands for magnetic sensors are uprising due to the rapid development of smart equipments and internet of things. Exploring magnetic sensitive materials which are easily obtainable and of low cost thereby become of great significance. Carbon film with crystallized features was recently reported with room-temperature ferro-magnetism and magnetoresistance, owing to its spin–orbital interactions at the graphene edges and temperature-depending carrier transport properties. Such phenomena indicate that the film can serve as a novel magnetic sensitive material. In this study, carbon films with vertically aligned nano-crystallites were obtained by a plasma-assisted physical vapor deposition (PVD) method. Basic test circuits were built on the films, and the sensing properties were investigated in external magnetic fields with different intensities and relative angles to the films surface. The results showed that the carbon-based sensing devices were capable to work in the temperature region of 250–400 K. The minimum field intensity and angle change to which the device can respond were 1 mT and 2°. By substrate-introduced enhancement, the maximum changing-rate of the film resistance could reach to 1100%/T. This research pointed out a practical and simple way to build magnetic sensors with PVD carbon films.

Effect of thickness on the dielectric properties and glass transition of plasma poly(ethylene oxide) thin films.

Plasma poly(ethylene oxide) thin films at different thicknesses of 20, 100, 250, 500 nm were deposited by plasma-assisted physical vapor deposition on glass substrates between aluminum electrodes in capacitor form at 5 W plasma discharge power. The structural analyses were performed by Fourier transform in7frared spectroscopy. The dielectric properties such as dielectric constant κ' and electric modulus M'' were defined by dielectric spectroscopy measurements. Dielectric spectroscopy measurements were performed in the angular frequency range of 10-1-106 rad/s and temperature range of 353-173 K range. The measurement results showed that α, β, and γ-relaxations, which are the expected relaxations in polymeric structures, are effective on total polarization in the investigated frequency and temperature range. Dielectric constant exhibits an increase till 500 nm, then reaches a saturation behavior. When resonance angular frequencies belonging to α-relaxation were fitted by Vogel-Fulcher-Tamman equation. It was observed that glass transition temperatures increase with decreasing thickness. These results support the influence of the dead layer to total polarization and the dynamics of the structure. Besides, it was shown that dielectric spectroscopy is a useful way to analyze the glass transition temperature in thin film form.

Study of APS and conventional sintering parameters for the manufacture of TiO2 targets for PAPVD

In surface science of functional oxides, titanium dioxide (TiO2) is one of the most investigated crystalline systems either in rutile or anatase phases. In this work commercial TiO2 powders are used to study the required process conditions to obtain TiO2 targets by Atmospheric Plasma Spray (APS) and conventional sintering, with suitable physical and chemical properties to be source material for Plasma Assisted Physical Vapor Deposition (PAPVD) for technological and medical applications. Two three factor Box Behnken experimental designs combined with surface modeling were employed to estimate the influence of spraying parameters (gun current, Ar/H2 ratio and standoff distance) and sintering parameters (heating rate, sintering temperature and holding time) within the targets microstructure (cracks and pores in cross section) and phases composition. The microstructure and composition of APS-deposited targets and sintered ones were characterized by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). The lowest defects percentages of the targets manufactured in this work were 0.41 ± 0.30 % for APS-deposited targets and 0.05 ± 0.04 % for the sintered ones using the optimal parameters suggested by the statistical model, which allowed confirming the advantages of sintering process and limitations of APS in terms of microstructural homogeneity, but also of the use of design of experiments in the modeling of systems of many variables when there is not diagnostic equipment of the processes available.

The effect of structure on tribological behavior of chromium-carbon coatings obtained by plasma-assisted physical vapor deposition

Two different kinds of chromium-carbon vacuum-deposited coatings have been investigated. The coatings were obtained by magnetron sputtering of chromium in a reactive argon-acetylene-nitrogen atmosphere and by non-reactive sputtering of a sintered chromium-nanodiamond target in argon. The structure of reactively sputtered coatings consisted of a diamond-like hydrogenatied carbon matrix with nanosized inclusions of pure chromium and chromium carbide and nitride phases and that of non-reactively sputtered was a mixture of nanosized chromium and Cr7C3 carbide. Carbon observed in the former case was in form of agglomerates few microns in size whose degree of graphitization varied from agglomerate to agglomerate. The existing coating structure–functional properties correlations are discussed.

Protective Properties of a Microstructure Composed of Barrier Nanostructured Organics and SiOx Layers Deposited on a Polymer Matrix.

The SiOx barrier nanocoatings have been prepared on selected polymer matrices to increase their resistance against permeation of toxic substances. The aim has been to find out whether the method of vacuum plasma deposition of SiOx barrier nanocoatings on a polyethylene terephthalate (PET) foil used by Aluminium Company of Canada (ALCAN) company (ALCAN Packaging Kreuzlingen AG (SA/Ltd., Kreuzlingen, Switzerland) within the production of CERAMIS® packaging materials with barrier properties can also be used to increase the resistance of foils from other polymers against the permeation of organic solvents and other toxic liquids. The scanning electron microscopy (SEM) microstructure of SiOx nanocoatings prepared by thermal deposition from SiO in vacuum by the Plasma Assisted Physical Vapour Deposition (PA-PVD) method or vacuum deposition of hexamethyldisiloxane (HMDSO) by the Plasma-enhanced chemical vapour deposition (PECVD) method have been studied. The microstructure and behavior of samples when exposed to a liquid test substance in relation to the barrier properties is described.

The thickness dependence of dielectric properties in the plasma polymer thin films

In this study, the results of dielectric spectroscopy of plasma polymerized poly(ethylene oxide) thin films are presented. The films were deposited by plasma-assisted physical vapour deposition at radio-frequency plasma discharge power of 5 W, and film thicknesses of 20, 100, and 250 nm. Dielectric measurements of the films were performed in the frequency range of 10−1–107 Hz and temperature was scanned between 173 and 353 K. The dielectric constant ([Formula: see text]) and dielectric loss ([Formula: see text]) of plasma polymerized poly(ethylene oxide) thin films were calculated by measuring capacitance (C) and dielectric loss factor (tanδ). It was observed that there were two relaxation mechanisms in the investigated frequency range. These were called α and β relaxations. These relaxations shift toward higher frequencies with increasing temperature. Moreover, α-relaxation starts to appear at different temperatures. This shows the difference between the polarizability abilities of samples at the same temperature and same frequencies. The reason for this behavior can be expressed by the dead layer concept, which is a result of good adhesion of the bottom layer of plasma polymer to the substrate. In light of these interpretations, with thinner samples it is possible to have structurally similar thin films like thin films deposited at high plasma power. A thinner film may support more transparency and these thinner films may be effective as coverage of optical devices, such as lenses, visors, etc.

Thickness Dependent Dielectric Loss of Plasma Poly (Ethylene Oxide) Films

Dielectric properties of plasma poly (ethylene oxide) (pPEO) thin film samples were investigated at room temperature. The thin film samples with different thicknesses were deposited by plasma assisted physical vapor deposition (PAPVD) technique at 5 W plasma discharge power. The thicknesses were 20, 100, 250, 500 nm. It was observed that dielectric constant increases with increasing thickness. The relaxation times determined by dielectric loss-frequency relation, shift toward higher frequencies with increasing thickness. In addition film thickness, heating processes were defined as another parameter. By this purpose, thin film samples were heated and cooled, respectively. It was observed that maxima and minima of dielectric loss at cooling process take place at lower frequencies in comparison with frequencies at which maxima and minima were detected at heating process. These results may show the effect of dead layer at thinner films. After heating process, it was observed from behavior of dielectric constant and dielectric loss that the crosslinking density increases by heating effect. This effect may cause additional reactions between free radicals which are production of PAPVD. Moreover, dynamic glass transition temperatures were calculated. These temperatures prove the effect of dead layer approximation.

Formation of polymer-based nanoparticles and nanocomposites by plasma-assisted deposition methods

During the last decades, metal-polymer nanocomposites have been subject to extensive research as their electrical, magnetic and optical properties are very sensitive to their specific compositions and morphological structures. Although there exist a variety of standardized and well-established production processes based on plasma-assisted physical vapor deposition methods, significant progress in the understanding of the self-organized formation process has only been achieved with the help of computer simulations. In particular, computational approaches based on kinetic Monte Carlo (KMC) and molecular dynamics (MD) simulations turned out to be successful in recent years because they offer the potential to simulate and predict the system behavior on sufficiently long time scales. In this paper, we review several formation processes of metal-polymer systems that have been investigated in joint experimental and theoretical KMC and MD studies. These comprise the growth of metallic nanocolumns in a polymer matrix and the growth of nanogranular structures on a polymer film.

Plasma discharge power dependent AC conductivity of plasma poly(ethylene oxide) thin films

Plasma polymerized poly(ethylene oxide) thin film samples with thickness of 500nm were deposited using plasma assisted physical vapour deposition at radio-frequency plasma discharge powers of 0, 2, 5 and 30W, respectively. For comparison, a conventional poly(ethylene oxide) precursor was also investigated. In order to investigate the effect of the plasma discharge power on the cross-linking density of the plasma poly(ethylene oxide) and poly(ethylene oxide) precursors, structural characterization using differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy was performed. Structural analysis showed that the density of cross-linking increased upon increasing the plasma discharge power. This increase was observed as an increase in the dynamic glass transition temperature during the DSC measurements. In addition to these characterizations, the dielectric response of the thin film plasma poly(ethylene oxide) samples and poly(ethylene oxide) precursors were measured. The dielectric spectroscopy results showed that changes in the cross-linking density changed the alternative current (AC) conductivity. The measured glass transition temperatures obtained using DSC are in accordance with the glass transition temperatures obtained from the temperature-dependent AC conductivity results. It was observed that the temperature-dependent AC conductivity exhibits Arrhenius behaviour. The activation energies obtained for the plasma polymer samples showed an increase from 0.38eV to 0.5eV upon increasing the plasma discharge power. The plasma discharge power dependent activation energy results also indicate the fragmentation of long polymer chains into more smaller oligomers and radicals occurred upon increasing the plasma power.

Micro-Abrasive Wear Testing of Surface Engineered Surgical Grade CoCrMo Alloy for Biotribological Applications

Abstract Wear of metal-on-metal hip joints is a concern due to the toxicity and biological reaction of wear debris. Retrieved CoCrMo hip implants have shown that abrasive wear is the predominant failure mechanism in such joints. There have been some efforts to improve the wear resistance of joint implants through the application of hard biocompatible ceramic coatings. However, the adhesion of the coatings has been a concern. The aim of the present work was to study the wear resistance of surface engineered CoCrMo alloy intended for biotribological applications by means of an abrasive wear test, based on the ball-crater technique. Different surface conditions were obtained on surgical grade wrought CoCrMo alloy: plasma nitrided, physical vapor deposition (PVD) coated (monolayer CrN and multilayer (TiN/CrN)×3) and modified using duplex surface engineering technology (a combination of the two previous approaches: plasma nitriding followed by plasma assisted PVD). The engineered surfaces were characterized by scanning electron microscopy, nanoindentation and, atomic force microscopy (AFM). Scratch test was used to determine the influence of the duplex technology on the adhesion of the coatings to substrate. The wear resistance of the different surface conditions was determined using a slurry abrasive micro-abrasion testing device. It was found that the duplex engineering technology enables a significant rise in the resistance of surfaces against concentrated loading modes, improving the adhesion of the coatings to the substrate; however, it has no significant influence improving the wear resistance of the samples during the abrasive wear tests.

Dielectric properties of plasma polymerized poly(ethylene oxide) thin films

Plasma polymerized poly(ethylene oxide) (pPEO) thin films were deposited by plasma assisted physical vapor deposition (PAPVD) with a constant thickness of 500nm. The crosslinking density of pPEO films was controlled through the discharge power. Differential scanning calorimetry (DSC) and broadband dielectric spectroscopy (BDS) were applied to analyze the structural peculiarities of these coatings. Both DSC and BDS detected an increase of the crosslink density with power, which correlated with the increasing dynamic glass transition temperature (Tg). It was shown that plasma power changes the structure of plasma polymer, and dielectric spectroscopy may be a suitable technique for structural analysis.

Anticorrosive property of Al coatings on sintered NdFeB substrates via plasma assisted physical vapor deposition method

An Al coating was achieved on NdFeB substrate via plasma assisted physical vapor deposition method. The coatings were treated with trivalent chromium passivation and were characterized by a scanning electron microscope equipped with an energy dispersive spectrometer. The adhesive strength between the coatings and NdFeB substrates was evaluated by tensile test. The coatings achieve much higher adhesive strength (25.7MPa) than that of Al coating without plasma assistance. The anticorrosive property of the coatings was studied by electrochemical impedance spectroscopy, neutral salt spray and potentiodynamic polarization curve tests. The corrosion current density of the passivated Al coated NdFeB specimens is 0.2205μA·cm−2, which is two orders of magnitude lower than that of bare NdFeB substrates. Also, the NSS and EIS tests confirm the excellent anticorrosive properties of the Al coated NdFeB specimens with plasma assisted physical vapor deposition method.

Tribological Properties of CrAlN and TiN Coatings Tested in Nano- and Micro-scale Laboratory Wear Tests

We investigated the tribological properties of CrAlN and TiN coatings produced by electron beam plasma-assisted physical vapor deposition by nano- and micro-scale wear tests. For comparison, we also conducted nano-indentation, nano-scanning wear tests, and pin-on-disk tribotests on uncoated M2 steel. The results indicate that, after nano-scale sliding tests against diamond indenter and pin-on-disk tests against ceramic alumina counterface pins, the CrAlN coating presents superior abrasive wear resistance compared to the TiN-coated and uncoated M2 steel samples. Against aluminum counterface, aluminum is more prone to attach on the CrAlN coating surface compared to TiN coating, but no apparent adhesive wear was observed, which has occurred on the TiN coating.