Hard transparent dielectric coatings

Hard transparent corrosion-resistant dielectric coatings were investigated (a) for application to the direct protection of glass surfaces, (b) for application to the protection of thin film metallic window coatings used for reflection or transmission of solar radiation and (c) for use in codeposited metal-ceramic coatings. The dielectric coatings were Al₂O₃, SiO₂ and SiC in the thickness range 100–100 000 Å. The coatings were deposited under varying conditions of substrate temperature, gas composition, r.f. power and substrate preparation. The results of the following measurements on the dielectric coatings are presented: diamond pyramid hardness tests, optical reflectance and transmittance in the region 0.6–4.0 eV and corrosion resistance tests under cyclic conditions. The results showed a considerable improvement in the scratch resistance and hardness of glass by layering of hard dielectric coatings 2–5 μm thick.     

Hard implant coatings with antimicrobial properties

Infection of orthopaedic implants often leads to inflammation immediately after surgery and increases patient morbidity due to repetitive operations. Silver ions have been shown to combine good biocompatibility with a low risk of inducing bacterial resistance. In this study a physical vapour deposition system using both arc deposition and magnetron sputtering has been utilized to produce silver ion doped TiN coatings on Ti substrates. This biphasic system combines the advantages of silver induced bactericidity with the good mechanical properties of TiN. Crystallographic analysis by X-ray diffraction showed that silver was deposited as well in its elementary form as it was incorporated into the crystal lattice of TiN, which resulted in increasing hardness of the TiN-coatings. Elution experiments revealed a continuous release of Ag ions in phosphate buffered saline. The coatings showed significant inhibitory effects on the growth of Staphylococcus epidermidis and Staphylococcus aureus and practically no cell-toxicity in cytocompatibility tests.     

Studying barrier-discharge-stimulated plasmachemical reactions

Barrier-discharge stimulation of chemical reactions has been studied in the case of methane oxidation by atmospheric oxygen with the formation of carbon monoxide and hydrogen. Experiments in a plasmachemical reactor demonstrated the possibility of increasing the yield of synthesis gas (syngas) by means of plasma pretreatment of the initial mixture of air and methane in a 7: 1 ratio at atmospheric pressure. The output-gas composition was determined by gas chromatography. It is established that the plasma-discharge treatment of the initial gas mixture leads to a 15% increase in the amount of syngas at the reactor output and increases the reaction selectivity with respect to hydrogen and carbon monoxide by 3.2 and 6.5%, respectively.     

Hard UV-curable organo-mineral coatings for optical applications

Organically-modified silicate incorporating various amounts of zirconium precursor was synthesized via a sol-gel route. The material was deposited as thin films on PMMA substrates and densified by UV-curing. Mechanical properties were measured by nanoindentation and data were recorded continuously as a function of the penetration depth during the loading-unloading cycles. Values of hardness and Young modulus were found in the range 340-440 MPa and 4-6 GPa, respectively. It was shown that these values could be tailored by varying the relative amount of zirconium in the layer. The material exhibited a very elastic behaviour that was related to its high degree of cross-linking assessed by infrared spectroscopy. Results were compared with measurements published by various groups on related materials. The mechanical and optical properties of the samples made this class of materials promising as hard coatings for optical applications.     

Hard decorative TiN coatings by ion plating

Gold-coloured hard coatings of TiN have been obtained on carbon steel, stainless steel and stellite substrates by ion plating titanium in an atmosphere of nitrogen. Pure, stoichiometric and compact layers display a gold colour. The titanium evaporation source was heated by a 90°-deflected electron beam obtained from a cold-cathode discharge gun. Typically, deposition rates up to 500 Å min^?1 have been obtained. Particular attention was paid to the problem of adherence of the deposited layers to the substrate. Thin (approximately 0.2 μm) coatings deposited onto pulished substrates reproduce the original brilliance. Thicker coatings are dull and need some additional mechanical polishing. The colour of the coatings was identified by reflectance spectra and chromaticity coordinates. Abrasion tests performed on coated pieces showed excellent resistance to abraison.     

Hard pure carbon coatings from a voltage-assisted arc

A simple apparatus is described that produces hard carbon coatings by accelerating ions produced by a carbon arc operating in vacuum. Coatings up to 1.1 μm thick have been produced on a variety of metals and semiconductors.     

Hard coatings on light-metal components under mechanical surface loading

In this work the behaviour of hard coated light-metal components was investigated when they are mechanically loaded. Three lightmetal alloys, Ti-6Al-4V, AlSi7Mg and AlMgSi0.5 and 100Cr6 steel (as a reference material) were coated by two different physical vapour deposition processes: radio frequency magnetron sputtering and electron beam evaporation. The coating materials utilised were CrN and TiN. Standard test methods with different loading conditions were used to evaluate the substrate/coating-combinations: the hardness test (applying a static normal load), the scratch test (applying a combination of a static normal and a static tangential force) and the impact test (applying a dynamic normal load). It was observed that the load support of coated materials depends on the loading conditions. The coated aluminium alloys showed poor load support under all loading test conditions but produced a higher surface hardness than uncoated steel. Coated Ti-6Al-4V showed very good load support properties, similar to coated steel. All coated light-metal substrates demonstrated significant improvement in load support behaviour with an increase in coating thickness. The results of the scratch test, which is commonly used to asses adhesion properties of thin coatings, showed an immediate indenter-breakthrough on the aluminium alloy substrates, but causing no coating delamination. Due to this behaviour, the scratch test is not suitable to evaluate adhesion properties on coated soft light-metals. Yet the impact test allowed assessment of coating delamination on the aluminium alloys, proving its usefulness for adhesion measurement even on soft substrates. The study indicates that substitution of steel with coated lightmetal alloys is a viable proposition for certain applications.     

Hard coatings on aluminium alloy surfaces produced using microplasma oxidation

Abstract

The present paper reports on the production of oxide coatings on an aluminium alloy by microplasma oxidation and on their properties. The surface characteristics of the coatings were determined by surface and structural analytical techniques, i.e. SEM and X-ray diffraction. Thermo-analysis of the coatings was evaluated by means of differential scanning calorimetry and thermogravimetric analyses. It was ascertained that the coatings with a mixture of crystallised γ-Al₂O₃ and α-Al₂O₃ have significant microhardness, good electric resistance and good thermostability.     

Friction moment prediction of HVOF coatings and Electroplated Hard Chromium

Wear is one of the most critical problems in mechanics, oil, and gas industries among other industrial fields. Electrolytic Hard Chromium (EHC) and HVOF thermal spraying for applications of various materials have proved to be effective against wear. In this study, the results of wear tests for WC-12Co, Cr₃C₂-25NiCr, Tribaloy©-400, and EHC are predicted and compared using an artificial intelligence methodology. It has been shown that predicted wear analysis permits to determine friction moment for different loading conditions. The best candidate seems to be WC-12Co for which worn surface reveals prevailing adhesion mechanism responsible for the lowering of the friction moment.     

Pulse-periodic discharge in a plasmachemical ferroelectric packed-bed reactor

A plasmachemical method of cleaning the exhaust gases of Diesel engines from toxic components in a ferroelectric packed-bed reactor is described. Special features of the electric circuit of this plasmachemical system and the energy efficiency of the process of cleaning under the conditions of pulse-periodic input of energy to the discharge are considered.__________Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 78, No. 1, pp. 174–177, January–February, 2005.     

Hard amorphous Ti–Al–N coatings deposited by sputtering

Ti–Al–N coatings were deposited by direct current reactive magnetron sputtering using two titanium and two aluminum targets. Two series of films with Al/(Al + Ti) atomic ratios of ≈ 23.5 and ≈ 34.5% were studied. The amount of nitrogen in the films was varied from 0 to 44at.%. The incorporation of N atoms led to a change of the -Ti lattice preferential orientation from <100> to <001>, a decrease in the degree of crystallinity, and subsequently to the collapse of the crystalline structure. Annealing at 975K promotes the formation of the Ti₃Al compound. The hardness increases smoothly with the nitrogen content. The high hardness values (31 and 41GPa) measured for the films with the highest N contents may be explained by the deposition of a nanocomposite phase. For the Ti–Al–N film deposited with Al/(Al + Ti) atomic ratio of 34.5% the -Ti structure was completely transformed to TiO₂ upon oxidation. The high oxidation resistance of the film deposited with 44at.% N at 1075K is characteristic of Ti–Al–N films.     

Destruction of toxic organic compounds in a plasmachemical reactor

A method for the destruction of solid and liquid organic toxic waste in a three-jet plasma reactor with typical reaction temperatures 3000–5000 K has been developed. The high temperature of the process allows the destruction of the complex molecules of toxic substances. As a result simple substances and acids are produced. Acids are neutralized in the alkaline environment of a wet filter.     

Bolometric properties of silicon thin-film structures fabricated by plasmachemical vapor-phase deposition

A method of fabricating uncooled thermally sensitive sandwich structures based on amorphous hydrated silicon films is discussed and experimental results are reported. The structures have an area of 10⁻⁴ cm², a resistance of ≅10 kΩ, and a temperature coefficient of resistance ≃2%/K. At 30 Hz and a current of ≃1 μA, the excess noise exceeds the thermal resistance noise by a factor of 1.7. Pis’ma Zh. Tekh. Fiz. 23, 63–68 (June 26, 1997)     

Modeling the plasmachemical synthesis of nanopowdered materials using a combined plasmatron

Processes involved in the production of nanopowders using a combined plasmatron are analyzed. Results of numerical simulation of the plasmachemical synthesis are presented, including calculations of the motion and heating of a finely dispersed powder in the plasma jet at the output of the combined plasmatron. Based on analysis of the results of simulations, recommendations for the choice of optimum parameters of plasmatron operation are given.     

Hard damping coatings: an experimental procedure for extraction of damping characteristics and modulus of elasticity

Hard coatings can be used as damping treatments, when applied on the surface of a component (both internal and external surfaces). This can help to reduce the resonant vibration levels a component may undergo during operation. This paper discusses the experimental procedure developed for testing such materials at room and elevated temperatures. The procedure involves controlled tests for excitation level (frequency and amplitude) and temperature. The elevated temperature capability is achieved by a custom designed halogen-lamp furnace, which is attached to the test rig. The damping (internal friction) and the modulus of elasticity of the coating are extracted from response decays, where the amplitude-dependent behaviour is accounted for. The results shown here were obtained from a Nimonic C-263 beam specimen, coated with Rokide^® A (aluminium oxide). The data is presented as a function of the maximum (peak) strain that the coating undergoes at the interface with the substrate. The paper also discusses the underlying damping mechanism: friction between the coatings lamellae (“splats”), which is supported by evidence from scanning electron microscope images of the cross-section of a sample.     

Mid-frequency PECVD of a-SiCN:H films and their structural,mechanical and electrical properties

The mid-frequency pulsed plasma enhanced chemical vapour deposition (PECVD) of hydrogenated amorphous silicon carbonitride (a-SiCN:H) was investigated to prove the suitability of these films as a mechanical stiff insulator for the integration of piezoelectric fibres in microstructured aluminium plates. For the a-SiCN:H deposition trimethylsilane (SiH(CH₃)_3; 3MS) and nitrogen in mixture with argon were used. The films were characterised regarding their deposition rate, elastic modulus and hardness (nanoindentation), mechanical stress, elemental composition (ERDA) and electrical insulating properties.The breakdown field strength of μm-thick a-SiCN:H films is in the range of 2–4 MV/cm. At pressures of a few Pa the deposition rate reached values up to 6 μm/h. It is limited by the power absorption in the 100 kHz bipolar-pulsed discharge. Varying the pressure from 2 Pa to 15 Pa has only little influence on the film composition. With increasing pressure during deposition the elastic modulus of the films decreases from about 146 GPa to 100 GPa and the compressive film stress from 1.2 GPa to 0.55 GPa. By reducing the 3MS flow rate from 50 sccm to 10 sccm (at 8 Pa deposition pressure), the carbon and the hydrogen concentrations in the films were reduced by about 10 at. %. The Si-content is only slightly reduced but the N-content is more than tripled. In contrast, the changes in the mechanical film properties are comparatively small. The mechanical properties of a-SiCN:H films are not simply correlated to the stoichiometry but are rather controlled by the ion bombardment during growth.     

Mechanical and optical characteristics of superhard nanocomposite TiN/a-Si<Subscript>3</Subscript>N<Subscript>4</Subscript> and TiCN/a-SiCN coatings produced by PECVD

There is a continuous need for new hard and superhard (H > 40 GPa) materials for applications ranging from protective coatings for cutting tools and aerospace to automobile industries, MEMS and others. In this work nanocomposite hard coatings fabricated by plasma-enhanced chemical vapor deposition from TiCl₄/SiH₄/CH₄/N₂/H₂/Ar gas mixtures were found to possess unique properties such as superhardness, high toughness, and interesting optical properties and colors. The mechanical characteristics such as hardness and Young’s modulus were determined by depth-sensitive indentation. Film microstructure was studied by XRD, SEM, TEM, ERD-TOF, XPS, and AFM. Optical properties like color, refractive index and extinction coefficient were evaluated using combined spectrophotometry and spectroscopic ellipsometry. This multitechnique approach allowed us to determine the structure-property relationships. We have shown that nc-TiN/a-Si₃N₄ exhibits a hardness of 45 GPa, while the novel nc-TiCN/a-SiCN provides a hardness of 57 GPa in addition to a very high resistance to plastic deformation (1.8 GPa).     

Effect of substrate material on the structure of carbon films obtained by plasmachemical deposition

Carbon films were obtained on nickel and silicon substrates by plasmachemical deposition from a hydrogen-methane gas mixture activated by dc discharge. The deposits were characterized by Raman scattering and scanning electron microscopy. Nanographite films on nickel are formed at a significantly lower substrate temperature and methane concentration in the gas phase than on silicon.     

Effect of the active-medium temperature on the kinetics of plasmachemical processes in directly nuclear-pumped xenon laser

The influence of the temperature of an active medium on the output characteristics of a directly nuclear-pumped laser on atomic transitions in xenon has been studied. It is shown that the quenching of generation before reaching a maximum of the pumping neutron flux is caused primarily by the temperature dependence of the reaction rate constant for the dissociation of heteronuclear ArXe⁺ ions upon collisions with buffer gas atoms.