Low‐Vacuum Low‐Cost Deposition of Tribological Coatings

TiN coatings of some microns in thickness were deposited by different reactive plasma deposition technologies such as Magnetron Sputtering Magnetically Assisted, Arc Source Ion Plating and Sputter Ion Plating Plasma Assisted on various unheated metal parts. The source to substrate distances was between 8 and 25cm. Deposition were performed in specially designed plants in the pressure range between 10^‐3–10^‐1 mbar and under variable vacuum and plasma conditions. The experiments were carried out with the intention of obtaining isotropic coatings on substrates of complex geometry. Thickness distribution, morphology, hardness and tribological properties of these coatings were investigated and correlated with the gas pressures and the measured plasma parameters during deposition. The aim of this work was to find effective processes and conditions for the reliable low cost deposition of hard coatings at relatively high gas pressures. The investigations were supported by the European Union in the TIPCOAT‐Project: Brite EuRam BE‐3815/Contract BRPR‐CT97‐0397     

SiOx plasma thin film deposition using a low-temperature cascade arc torch

Plasma thin films were deposited from gas mixtures of hexamethyldisiloxane (HMDSO) and oxygen (O₂) using a low-temperature cascade arc torch (LTCAT). Various properties of the deposited HMDSO plasma coatings, including refractive index (RI), surface contact angle, and hardness were evaluated. The characterization results using X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ellipsometry, and water contact angle measurements indicated that, with increased O₂ addition, the deposited HMDSO plasma thin films were of inorganic SiO_x nature. It was also found that, in the LTCAT plasma system, O₂ addition significantly improves the hardness of the resulting HMDSO plasma coatings. The film hardness of the deposited HMDSO plasma coatings measured by a standard pencil test (ASTM D3363-05) reached 6H with increased O₂ addition in the HMDSO/O₂ gas mixture. Such hard plasma coatings could be potentially used for many important industrial applications, such as anti-scratch coatings on plastic glasses and various plastic lens materials.     

Overview on the Development of Nanostructured Thermal Barrier Coatings

Thermal barrier coatings （TBCs） have successfully been used in gas turbine engines for increasing operation temperature and improving engine efficiency. Over the past thirty years, a variety of TBC materials and TBC deposition techniques have been developed. Recently, nanostructured TBCs emerge with the potential of commercial applications in various industries. In this paper, TBC materials and TBC deposition techniques such as air plasma spray （APS）, electron beam physical vapor deposition （EB-PVD）, laser assisted chemical vapor deposition （LACVD） are briefly reviewed. Nanostructured 7-8 wt pct yttria stabilized zirconia （7-8YSZ）TBC by air plasma spraying of powder and new TBC with novel structure deposited by solution precursor plasma spray （SPPS） are compared. Plasma spray conditions, coating forming mechanisms, microstructures,phase compositions, thermal conductivities, and thermal cycling lives of the APS nanostructured TBC and the SPPS nanostructured TBC are discussed. Research opportunities and challenges of nanostructured TBCs deposited by air plasma spray are prospected.     

Entwicklung hochverschleißbeständiger wolframschmelzkarbidbasierter Schichten auf Aluminiumbauteilen durch Plasma‐Pulver‐Auftragschweißen

Development of high wear‐resistant FTC‐based coatings on aluminium components using plasma transferred arc welding Nowadays, functional surfaces of components can be effectively protected from extreme wear with the help of fused tungsten carbide (FTC) coatings. The wear protection of steel components using FTC has been well known for many years. This paper presents the feasible study of improving the wear resistance of aluminium components with FTC particles using plasma powder arc welding. The FTC coatings are developed with two methods: one is the dispersion of carbide particles in aluminium and the other one is the combination of dispersing and alloying of FTC‐based composite powders. In this research, coatings within a thickness range of a few millimeters are developed with varying process parameters and compositions of the filler materials. The developed coating systems are tested with regard to their specific properties and their wear resistance. Finally, their application potential is presented.     

Korrosionsinhibierende Plasmapolymerschichten auf Stahluntergründen

Plasma polymeric coatings with inhibitory effect on steel surfaces The plasma based surface technique facilitates scientifically and technically, economically and ecologically interesting alternatives to traditional treatment procedures. From that the evolution of a new procedure for the improvement of the corrosion resistance of low‐alloy steel surfaces through ultrathin plasma polymeric coatings was a main topic at the iLF in the last years. After plasma based super cleaning process under oxidized conditions should be produced plasma polymeric coatings with a corrosion inhibiting / passivation effect. For this purpose corrosion inhibitor molecules are implanted into the normally electrochemically inactive coating during the process of the plasma based polymerization of silicon‐organic monomers. Through that it has been proved that the long‐term corrosion protection improves. Besides the surface of the produced plasma polymer shift can be modified by plasma‐technical procedures so that it shows also optimal adhesion promoter characteristics.     

Abscheidung,Charakterisierung und Anwendung von Plasma‐Polymerschichten auf HMDSO‐Basis

Deposition, Characterisation and Application of HMDSO‐based Plasma Polymer Films High quality organosilicone coatings can be produced via plasma enhanced chemical vapor deposition of hexamethyldisiloxane (HMDSO). In this article aspects of deposition, analysis and application of HMDSO/O₂ processes are presented. The coatings’ organic/inorganic character can be adjusted by an appropriate combination of plasma power and gas mixture which is shown by XPS. Particularly multi layer and gradient layer systems can be deposited within the same process. Quantitative chemical depth profiling of such layer systems can be performed by secondary neutral mass spectrometry (SNMS). AFM investigations exhibit that the surface roughness of the coatings is determined by the appearance of hemispherical agglomerates, which is more pronounced, the more glass‐like the coatings are. As an example of use it is shown, that an appropriate HMDSO plasma treatment can distinctly improve the tribological behavior of elastomer devices. The presented work is done within a project of the German Federal Ministry of Education and Research (BMBF) entitled: “nano functionalization of interfaces for data‐, textile‐, building‐, medicine‐, bio‐, and aerospace‐ technology”.     

Kunststoffoptiken mit Antireflex‐ und Antibeschlageigenschaften durch Plasmaätzen und Beschichtung

Plastic optics exhibiting anti‐reflection and anti‐fogging properties produced by plasma etching and coating Plasma treatments are capable to generate antireflective surface structures on various polymers. On PMMA a self organized surface with nep‐like bumps exhibits excellent optical properties. Many other materials like polycarbonate, zeonex and lacquers can be etched after depositing a very thin initial layer to form a more holey structure. These surfaces attain high transmission values too and can be better stabilized by coatings than the nep‐ structure on PMMA. Interesting for practical applications are hydrophilic top‐layers to provide anti‐fogging properties in combination with improved transmission.     

Nanocomposite‐Beschichtungen auf CBN‐Werkzeugen

Nanocomposite coatings on CBN‐tools CBN (cubic boron nitride) cutting materials are often used to improve the properties of cutting tools. This allows new applications and processes, which are not possible with common cutting materials (e.g. hard metals). Today CBN cutting materials are mostly coated to estimate the wear by an optical evaluation. Coatings on CBN cutting materials for enhancement of the tribological properties are normally not used. For improvement of the properties of used CBN tools during the cutting process a coating technology was developed. This technology combines the advantages of CBN cutting materials with the excellent properties (e.g. hardness, temperature stability) of nanostructured materials. Investigations with different coating systems and pre‐treatment processes were done to test the CBN cutting tools. These investigations have been shown, that nanocomposite coatings can be used to enhance the tool life of CBN cutting tools. Important for an increase in the tool life is a very good coating adhesion, which can be reached by special adhesion layers and an optimized coating structure.     

Schichtentwicklung für die schmiermittelfreie Umformung von hochfesten Aluminiumwerkstoffen

Development and evaluation of coatings for lubricant free forming of high strength aluminium Many applications in light weight construction require massive formed high strength aluminium parts. For economical and ecological reasons the use of lubricants for massive forming has to be avoided. Both, lubricant free forming and processing of high strength materials are big challenges that can be realized by using coated tools with functional surfaces that show high wear resistance, low friction and low adhesion to aluminium [1–7]. For goal‐oriented surface engineering different coating technologies, such as Physical Vapour Deposition (PVD) and Chemical Vapour Deposition (CVD) have been used for the preparation of specimens. The coating properties are evaluated by mechanical tests and numeric simulation to investigate the massive forming processes and the coating‐substrate‐behaviour. On the base of TiCN‐, TiC‐TiN‐ and DLC‐coatings on steel it is shown how relevant coating properties like Young’s Modulus, crack behaviour and hardness can be analyzed with regard to small coating thicknesses. In order to scale up the results to industrial conditions, finally the simulation is correlated to real deforming.     

Investigation of wear resistance and microstructure of a newly developed chromium and vanadium containing iron‐based hardfacing alloy

Plasma transferred arc (PTA) welded Ni and Co‐based alloys have gained high acceptance in many industrial applications for the wear protection of components. Recently, the cost of nickel and cobalt is rising drastically. This paper presents the development of a cost‐effective high chromium and vanadium containing iron‐based hardfacing alloy with high hardness and wear resistance. The welding processing of the alloy is carried out by PTA welding of atomized powders. Investigations on powder production as well as on weldability are presented. The coatings are metallographically studied by optical microscopy, SEM, EDX and micro‐hardness measurements. The wear resistance properties of the coatings are examined using pin on disk, dry sand rubber wheel and Miller testing, the corrosion properties are determined by immersion corrosion tests. The newly developed iron‐based alloy has nearly the same wear resistance as Ni‐based alloys with fused tungsten carbides at a higher level of corrosion resistance and much lower cost.     

A New Reactive Atom Plasma Technology (RAPT) for Precision Machining: the Etching of ULE® Surfaces

Results on reactive atom plasma etching performed on ULE® (Corning Ultra Low Expansion) glass samples at atmospheric pressure are presented for the first time. A reactive atomic plasma technology (RAPT®), has been developed by RAPT Industries and employed for the finishing of optical surfaces. An atmospheric pressure argon inductively coupled plasma (ICP) excites a reactive gas injected through its centre. The plume of hot neutral excited species reacts at the substrate yielding controlled and repeatable trenches. In the case of ULE a material removal (up to 0.55 mm³/s) is obtained without pre‐heating the samples. Among the factors influencing the results, an increase in gas concentration at the same power does not change the sample temperature, indicating that thermo‐chemical effects do not influence the removal rates. Due to the plasma constructive constrains, increasing the gas concentration is more practical and of wider effect than increasing the power. The benefits of the process are illustrated and the extension of the technology to large optical surfaces discussed.     

Effect of Zr on microstructure of metallic glass coatings prepared by gas tunnel type plasma spraying

Metallic glass is one of the most attractive advanced materials, and many researchers have conducted various developmental research works. Metallic glass is expected to be used as a functional material because of its excellent physical and chemical functions such as high strength and high corrosion resistance. However, the application for small size parts has been carried out only in some industrial fields. In order to widen the industrial application fields, a composite material is preferred for the cost performance. In the coating processes of metallic glass with the conventional deposition techniques, there is a difficulty to form thick coatings due to their low deposition rate. Thermal spraying method is one of the potential candidates to produce metallic glass composites. Metallic glass coatings can be applied to the longer parts and therefore the application field can be widened. The gas tunnel plasma spraying is one of the most important technologies for high quality ceramic coating and synthesizing functional materials. As the gas tunnel type plasma jet is superior to the properties of other conventional type plasma jets, this plasma has great possibilities for various applications in thermal processing. In this study, the gas tunnel type plasma spraying was used to form the metallic glass coatings on the stainless-steel substrate. The microstructure and surface morphology of the metallic glass coatings were examined using Fe-based metallic glass powder and Zr-based metallic glass powder as coating material. For the mechanical properties the Vickers hardness was measured on the cross section of both the coatings and the difference between the powders was compared.     

Plasma‐induzierte Polymerisation von Acrylaten

Plasma‐induced polymerisation of acrylates Plasma processes are suitable for the generation of complex polymers from simple monomeric compounds. For example, during the process of plasma polymerisation thin polymeric films are deposited onto a solid substrate from the vapour phase by plasma excitation. This process is characterized by the activation, ionization and fragmentation of gaseous precursors which subsequently combine to oligomers and polymers. Another possibility is the plasma‐induced polymerization of monomers within a liquid coating. Thereby, the polymerisation is initiated by reactive plasma species similar to other radiation induced polymerisation techniques such as UV or electron beam curing. However, one advantage of the plasma process is the spacious distribution of the plasma which enables curing of liquid coatings on complex shaped substrates. Herein results of the plasma‐induced polymerisation of acrylates are presented with respect to double bond conversion, surface energy and the generation of microstructures.     

Plasmamessungen und Schichteigenschaften

Plasma Analysis and Thin Film Properties of Sputter‐ and Ionplating PVD‐Processes For a large number of thin film applications just few thin film coating processes are used in industrial scale production. For example, Magnetron Sputtering (MS), Ionplating (IP), Arc Source Ablation (AS) and technical variations of them. Recent developments allow beside traditional dc modes also the use of pulsed dc modes, as for instance in magnetron sputtering and arc source deposition. In this work the Reactive Low Voltage Ionplating (RLVIP) with pulsed substrate bias (Ionplating Plasma Assisted IPPA), DC and DC‐pulse Magnetron Sputtering and Arc source deposition in DC‐ and DC‐pulse mode is of interest concerning their plasma. Pulsing the substrate‐bias of the RLVIP (IPPA) influences film stress and optical absorption but is not easy to handle in industrial production. Pulsing the sputter processes leads to massive changes in the coating plasma and the coatings itself. And finally pulsing the arc‐current of the Arc Source Ablation processes implements advantages for lower cathode temperatures, for use of less conducting cathode materials, less droplet formation and improved chemical reactivity with oxygen.     

Plasmaelektrolytische Oxidation thermisch gespritzter Aluminiumschichten

Plasma electrolytic oxidation of arc sprayed aluminium coatings Up to now different post treatment methods are developed to improve the properties of thermally sprayed coatings. In this work, arc sprayed aluminium coatings on aluminium substrates are post‐treated by plasma electrolytic oxidation. To estimate the wear resistance of resulting oxide coatings, two abrasive wear tests (ASTM G65 and ASTM C1624) are carried out. Worn surfaces are examined by scanning electron microscopy in order to establish the wear mechanisms. These results of the abrasive wear tests are correlated with the parameters of the PEO process and the resulting micro structures of the coatings.     

Mechanical properties of carbon-modified silicon oxide barrier films deposited by plasma enhanced chemical vapor deposition on polymer substrates

Cohesive and adhesive properties of silicon oxide barrier coatings deposited from an oxygen/hexamethyldisiloxane gas mixture by plasma enhanced chemical vapor deposition, with controlled incorporation of carbon on 12 μm thick polyethylene terephtalate films were investigated. The reactor was equipped with a 2.45 GHz slot antenna plasma source and a 13.56 MHz-biased substrate holder. The two plasma sources were operated separately or in a dual mode. It was found that no or negligible internal stresses were introduced in the silicon oxide coatings as long as the increase of energy experienced by the film was compensated by the densification of the oxide. For a range of process parameters and carbon content on the changes of the crack onset strain, adhesion, and cohesion were found to be similar. Generally a high crack onset strain or good adhesion and cohesion were measured for films with an increased carbon content, although this was obtained at the expense of the gas barrier performance. Promising approaches towards high-barrier thin films with good mechanical integrity are proposed, based on coatings with a gradient in the carbon content and in the mechanical properties, on nano-composite laminates, and on organo-silane treatments.     

Mikrowellen‐PECVD für kontinuierliche Großflächenbeschichtung bei Atmosphärendruck

Microwave PECVD for continuous wide area coating at atmospheric pressure Plasma processes are applied for a variety of surface modifications. Examples are coatings to achieve an improved corrosion and scratch protection, or surface cleaning. Normally, these processes are vacuum based and therefore suitable to only a limited extend for large area industrial applications. By use of atmospheric pressure plasma technology integration in continuously working manufacturing lines is advantageously combined with lower costs and higher throughput. Microwave plasma sources present powerful modules for plasma enhanced chemical vapour deposition at atmospheric pressure. At Fraunhofer IWS processes and equipment as well as application specific materials are developed. The coatings are suitable for scratch resistant surfaces, barrier and corrosion protective layers or anti‐reflex layers on solar cells. The film properties achieved are comparable with those produced by low pressure processes.     

Entwicklung von Oxid – Keramik zur Anwendung als Wärmedämmschichten

Development of Oxide Ceramics for an Application as TBC The standard thermal barrier coating material yttria stabilised zirconia (YSZ) is limited in long term operation to a maximum temperature of about 1200°C. As a result further increase of the gas inlet temperature and hence the efficiency of gas turbines are hardly to achieve with YSZ coatings. In a screening procedure especially perowskite (ABO₃, A = Sr,Ba, B = Zr) and pyrochlore (A₂B₂O₇, e.g. A = La and other rare earth elements, B = e.g. Zr) materials have been identified as possible candidates for thermal barrier coatings. Basic physical properties (e.g. thermal expansion coefficient, thermal diffusivity and conductivity) of several candidates have been determined using sintered, dense samples. The possibility of optimization of the properties by using specific compositions will be discussed. From promising materials powders which are suitable for plasma‐spraying have been produced by spray‐drying. New TBC systems consisting of new materials (BaZrO₃, La₂Zr₂O₇) deposited by atmospheric plasma spraying and vacuum plasma sprayed MCrAlY bondcoats were tested in a gas burner facility. Especially La₂Zr₂O₇ coatings gave promising results. A further improvements could be achieved by the use of layered or graded coatings with a YSZ coating at the bondcoat interface and on top a layer of the new TBC material. First results of thermal cycling tests with 1250 and 1350°C surface temperature will be presented.     

Numerical modeling of SiH4 discharge for Si thin film deposition for thin film transistor and solar cells

Amorphous and microcrystalline silicon thin films are used in solar cells as a multi-junction photovoltaic device. Plasma enhanced chemical vapor deposition is used and high deposition rate of a few nm/s is required while keeping film quality. SiH₄ is used as a precursor diluted with H₂. Electron impact processes give complex interdependent plasma chemical reactions. Many researchers suggest keeping high H/SiH_x ratio is important. Numerical modeling of this process for capacitively coupled plasma and inductively coupled plasma is done to investigate which process parameters are playing key roles in determining it. A full set of 67 volume reactions and reduced set are used. Under most of conditions, CCP shows 100 times higher H/SiH₃ ratio over ICP case due to its spatially localized two electron temperature distribution. Multi hollow cathode type CCP is also modeled as a 2 × 2 hole array. For Ar, the discharge is well localized at the neck of the hole at a few Torr of gas pressure. H₂ and SiH₄ + H₂ needed higher gas pressure and power density to get a multi hole localized density profile. H/SiH₃ was calculated to be about 1/10.     

Formation of high heat resistant coatings by using gas tunnel type plasma spraying

Zirconia sprayed coatings are widely used as thermal barrier coatings (TBC) for high temperature protection of metallic structures. However, their use in diesel engine combustion chamber components has the long run durability problems, such as the spallation at the interface between the coating and substrate due to the interface oxidation. Although zirconia coatings have been used in many applications, the interface spallation problem is still waiting to be solved under the critical conditions such as high temperature and high corrosion environment. The gas tunnel type plasma spraying developed by the author can make high quality ceramic coatings such as Al2O3 and ZrO2 coating compared to other plasma spraying method. A high hardness ceramic coating such as Al2O3 coating by the gas tunnel type plasma spraying, were investigated in the previous study. The Vickers hardness of the zirconia (ZrO2) coating increased with decreasing spraying distance, and a higher Vickers hardness of about Hv = 1200 could be obtained at a shorter spraying distance of L = 30 mm. ZrO2 coating formed has a high hardness layer at the surface side, which shows the graded functionality of hardness. In this study, ZrO2 composite coatings (TBCs) with Al2O3 were deposited on SS304 substrates by gas tunnel type plasma spraying. The performance such as the mechanical properties, thermal behavior and high temperature oxidation resistance of the functionally graded TBCs was investigated and discussed. The resultant coating samples with different spraying powders and thickness are compared in their corrosion resistance with coating thickness as variables. Corrosion potential was measured and analyzed corresponding to the microstructure of the coatings. Keywords: High Heat Resistant Coatings, Gas Tunnel Type Plasma Spraying, Hardness,