Three-layer Coatings Research Articles

Stability of layered coatings under biaxial thermomechanical loading

The three-dimensional problem of stability of layered coatings at normal and high temperatures and small precritical strains is formulated and solved and the characteristic equations are derived. The temperature dependence of the physical and mechanical parameters of specific layered coatings is established experimentally. Three-layer coatings on a homogeneous substrate at different temperatures are considered as an example. Recommendations for establishing the optimal service conditions for layered structural members with coatings are formulated.

Three-Layer Coating for Stents with Nanostructured Surface

A three-layer coating for stents with a nanostructured surface of calcium phosphate (CaP) is pre-sented. The coating stack consists of (a) a TiNbN layer deposited by physical vapour deposition and acting as diffusion barrier against allergenic ions, (b) a SiO2 xerogel layer providing good adhesion properties and designing the nanoporosity of the outer CaP layer (c) precipitated electrochemically. The verification of the SiO2-layer (and therewith its influence onto adhesion and structure of the outer CaP layer) succeeded only by use of XPS because of the very small amount of the xerogel. SEM results verified a homogeneous nanoscale nanoporous structure of the CaP coating. It is char-acterised by high adhesion strength. If applied for stent covering the nanoscale CaP coating has promising properties to initiate rapid endothelium formation and reduced risk of restenosis.

Electrophoretic analysis of proteins and enantiomers using capillaries modified by a successive multiple ionic-polymer layer (SMIL) coating technique

The applicability of three-layer coatings consisting of three different polymers (A(+)-B(-)-C(+) coating) prepared by a successive multiple ionic-polymer layer (SMIL) coating technique to the immobilization of polypeptides and/or proteins onto the inner surface of the capillaries was investigated to provide a high-performance separation medium for proteins and enantiomers in capillary electrophoresis (CE). To obtain a stable protein-coated capillary, high molecular mass poly(ethyleneimine) (PEI) was employed as the first layer in the A(+)-B(-)-C(+) coating, and then a cationic protein was immobilized as the third layer. Comparisons of analytical performances between the A(+)-B(-)-C(+) coating and the conventional SMIL-coated (A(+)-B(-)-A(+) coating) capillary were conducted. The CE separation of cationic proteins was successfully achieved with the prepared capillaries. In addition, the polypeptide- and protein-coated capillaries were applied to the chiral separation of a binaphthyl compound. It should be noted that the chiral separation efficiency was strongly dependent on the second anionic polymer layer of the coating. Effects of the interaction between oppositely charged ionic polymer layers on the separation efficiency are discussed.

Numerical simulation of composite surface coating as a functionally graded material

Ceramic coatings established on a valve and piston of an internal combustion engine were studied. Numerical investigations have been performed with the use of a FEM-based software. For the needs of investigations in a microscale, the micromechanical model has been developed. The coating in this model is considered as a functionally graded material with properties changing smoothly accordingly to a linear function. There have been also studied two kinds of three-layered ceramic coatings: first one was based on Al 2O 3 (valve) and second one on ZrO 2 (piston).

Nickel–alumina graded coatings obtained by dipping and EPD on nickel substrates

Nickel substrates have been coated by Ni/Al 2O 3 composite films by a dipping process using aqueous suspensions that contain a temporary binder. Two-layer and three-layer graded coatings have been produced, consisting of pure Ni powder and Ni/Al 2O 3 composites with Al 2O 3 contents of 15 and 30 vol.% as intermediate layers to release sintering and thermal stresses. The laminates were further coated with a ceramic layer of Al 2O 3/ZrO 2 that was deposited by electrophoretic deposition using a non-aqueous suspension. A continuous, thin Al 2O 3 layer surrounding Ni grains developed at the intermediate composite layer of Ni/Al 2O 3 allows the ceramic coating to maintain strongly adhered to the nickel substrate by means of a porous substrate/coating interface.

Optimization of solar absorbing three-layer coatings

Abstract The optimization of spectrally selective solar-absorbing three-layer coatings was studied from both theoretical and experimental points of view. The base layer consists of a cermet (ceramic–metal composite) material, where small metal clusters are embedded in the dielectric surrounding. The results show considerable enhancement of the solar absorption due to the metal nanoparticles. Theoretical treatment of the optical properties of the cermet was carried out using effective medium theory. The experimentally determined optical constants of calibration samples were used to calculate the film reflectance of single or multiple layers. Theoretically optimized three-layer coatings show solar absorptance value as high as 0.97 and moderate reflectance at 2.5 μm giving low thermal emittance. Experimental optimization was carried out through control of the coatings layer by layer. The metal content and the film thickness are two important parameters for cermet films. Only thickness is sensitive to the middle and top layer. The optical properties are matched in such a way that the base layer functions as main absorber, the top layer reduces the reflectance from the front surface, and the middle layer links the base and the top layers. An experimentally optimized solar absorptance of 0.97 with a thermal emittance of 0.05 was obtained, which shows that the optimization procedure is reliable.

Ti-N vacuum-plasma coatings for turbine compressor blades

Ti-N three-layer vacuum-plasma coatings 50–60-μm thick deposited on VT3- and OT4-alloy turbine compressor blades by a high-energy technology were studied. The gas-abrasive wear resistance of the coatings on VT3 alloy was superior to those on OT4 alloy at 20°C, but inferior at 250°C. The coatings were not susceptible to climatic corrosion. Their cycle-temperature stability were higher on OT4 alloy.

The structure and properties of metal and metal-ceramic coatings produced by physical vapour deposition

The present work summarises the structure and properties of heat-resistant coatings produced by the vacuum electron-beam evaporation and condensation of heat-resistant CoCrAlY alloys and ceramics onto a base of partially stabilized zirconia ZrO 28%Y 2O 3. Two-layer CoCrAlY/ZrO 2 and three-layer coatings in which the metal coating consists of two functionally linked layers are considered: the inner layer, plastic, is designed for relaxation of thermal stresses, wilst the outer layer is to provide protection from high-temperature oxidation.

Thermal cyclic response of EB PVD yttria-stabilized [formula omitted] coatings

Thermal cyclic tests were conducted with plane corset-type specimens from five superalloys with EB PVD ZrO 2 + 8wt.%Y 2O 3 CoCrAlY two and three with (plastic layer) layers coatings. Testing of specimens made of differently deformed and cast alloys with three-layer coatings has shown the efficiency of the plastic layer. The characteristic feature of the ceramic layer obtained with appropriate regard for the procedure of its application is safe adhesion between the ceramic and metallic layers, as was revealed during testing. Spallation of the ceramic layer was not observed before the destruction of specimens, when there was no cracks formation in the layers and when there appeared single and multiple cracks. Variants of damage formation and damage growth in multilayer coatings were considered.

Preparing vitreous coatings on metals by the sol-gel method

Protective vitreous coatings on steel obtained by the sol-gel technology are described, which consist of SiO2 with additions of up to 15 wt.% B2O3 and ZnO. Methods for preparing the initial solutions, depositing one-, two-, and three-layer coatings, and the temperature and time regimes of treatment are described. The physicochemical properties of film-forming solutions, gels, and coatings are investigated.

Two- and three-layer coatings produced by deposition in vacuum for gas turbine blade protection

This paper deals with the microstructure and properties of oxidation-resistant metal/ceramic coatings produced by the electron beam evaporation of M-Cr-Al-Y alloys and zirconia partially stabilized by yttria. The effect of thermophysical conditions of deposition on the properties of the condensed zirconia and protective coatings is shown. The results of furnace tests in air and gas turbine fuel ash showed that the double-layer metal/ceramic coatings increase the oxidation and corrosion resistance of nickel alloys at 750–1000 °C. Burner tests of specimens and blade models with Co-Cr-Al-Y/ZrO 2 coatings in a gas stream showed that the metallic coatings possess higher thermal fatigue resistance due to the deposition of the ceramic layer of 50–120 μm thickness. The relationship between the thermal cyclic life and multicycle fatigue resistance of alloys with vacuum-deposited metal/ceramic coatings is expressed by a curve with a maximum corresponding to ZrO 2-Y 2O 3 90–120 μm thick. Potential improvement of M-Cr-Al-Y/ZrO 2 coatings is increased in service when a ductile interlayer is inserted between the oxidation-resistant layer and base metal. Data are given about the dependence of the mechanical properties of heat-resistant nickel alloys on ZrO 2-Y 2O 3 coatings of 60–150 μm thickness.

Design of three-layer antireflection coatings: some comments

With Kard's method it is possible to select the thicknesses of the layers and obtain reasonably accurate refractive index values. Two examples are given:

Design of three-layer antireflection coatings: a generalized approach

A generalized theoretical formulation for multilayer antireflection coatings (ARCs) has been established, which has scope for considering both zero and nonzero reflectance at one or more than one wavelength. Starting with this, a new design method for three-layer ARCs making use of input reflectance parameters at two wavelengths (R(1) and R(2) at lambda(1) and lambda(2)) has been developed. It allows for determination of all the unknown design parameters explicitly without any a priori conditions on them. The scope of the method has been extended by incorporating optimization of the resultant solutions through an optimizing parameter, integrated reflection loss R* to obtain efficient designs with respect to spectral bandwidth, residual reflection loss, etc. The resulting hybrid methodology is found to be generalized in that it can be used to design a wide range of ARC systems, broad band to V-type, irrespective of the nature of the substrate (absorbing or nonabsorbing) and spectral region of use, with adaptability to simpler/complex ARC systems and other thin film systems such as dichroics/beam splitters and achromatic reflectors.

Technical note: Design and performance of a movable post-cathode magnetron sputtering system for making PBFA II accelerator ion sources

A post-cathode magnetron sputter deposition system is described for depositing one-, two- or three-layer coatings with uniform thickness and film properties on the inside of a cylindrical substrate. The system uses a unique movable post-cathode which allows the substrate to remain stationary during the deposition process. Film stress is controlled by cycling the sputtering pressure during the sputter deposition process.

Factory-applied anticorrosive insulation for large-diameter pipes

Pipes protected with epoxy and layered polyethylene coatings are described. Analysis of the condition of the epoxy insulation on sections of gas lines laid under different soil and climatic conditions--including salty, periodically flooded soils with a high corrosion activity--showed that this type of coating, in combination with cathodic polarization, ensures effective protection of the metal from corrosion. The quality of pipes with a polyethylene coating is improved by chromating the pipes. Two-layer and three-layer polyethylene coatings were evaluated. Problems in the production technology of the pipes and their coating materials were assessed.

A new combination of coatings on carbide cutting tools

A new combination of two- and three-layer coatings on carbide-cutting instruments can be obtained by forming a boride-containing underlayer (CoWB) by a diffusion process, and by chemical vapour deposition (CVD) of TiC-TiCN or TiC-Al 2O 3 on the CoWB. The effect is shown of the thickened cobalt net structure on the increase in WC grains and on the decrease in contact surface between the grains of (Ti, Ta, W)C after repeated heating and chemical treatment of the carbide alloy. Comparative tests of cutting on steel and cast iron were carried out using various types of coated cutting plates. Combined coatings are found to prolong the lifetime of carbide instruments by more than 200% in comparison with the coating obtained by CVD alone.

Three-layer antireflection coatings: a new method for design and optimization

A new algorithm for the design of multilayer antireflection coatings (ARC) is developed. This makes use of a closed-loop nonlinear approximation technique to arrive at the exact thickness of each layer. The method offers a simpler and faster optimization procedure. It has been successfully used in the design of broadband ARCs on substrates with a wide range of refractive indices. Detailed analysis of the effect of errors in the refractive index and thickness of each layer, individually and collectively on the ultimate performance of the system, is discussed in detail. To minimize the effects of these errors, in situ correction (dynamic correction) procedure at each stage of development of the system is suggested.

Experimental examination of the damping properties of the VT3-1 and VT8 alloys with layered metal coatings

1. The VT3-1 and VT8 alloys have exceptionally low damping properties (the oscillation decrement varies in the range 0.02–0.09%) which may result in a severe vibrational stress state of members of the structures made of these materials. 2. The deposition of coatings containing electrolytically precipitated copper, nickel, chromium and also enamel with a total thickness of 90–130μm, on the specimens of the VT3-1 and VT8 alloys increased the damping characteristic (the decrement of bending oscillations) by 16–60 times at room temperature and by 22–83 times at a temperature of ≈250°C. 3. Of the coatings tested, preference should be given (with other condition being equal) to the four-layer coatings whose total thickness is smaller than that of the three-layer coatings.

Optical interference coatings prepared from solution

Recently E. M. Laboratories introduced colloidal silica and titania solutions from which one can produce optical thin films. Single quarterwave V-coats and three-layer AR coatings for the visible as well as four-and five-layer AR coatings at 1.06 microm were prepared using these solutions. Reflection spectra and ellipso-metric measurements showed that these films are essentially optically equivalent to those prepared by e-beam evaporation. However, the former films lacked the rub durability of the latter films. This deficiency was traced by frustrated multiple internal reflectance (FMIR) spectroscopy and by Auger electron spectroscopy (AES) to organic solvents trapped within the titania matrix. X-ray diffraction (XRD) showed the silica films to be amorphous whereas the titania films were slightly crystalline with the anatase structure.

Low Absorption T1I/KC1/T1I Antireflection Coatings For KC1 Surfaces

Efficient T1I/KC1/T1I antireflection (AR) coatings (< 0.1% reflectance per surface), which are highly resistant to laser radiation damage (< 0.04 % absorption per AR coating at A = 10.6 um) have been fabricated. The three-layer AR coatings were designed by replacing one of the layers of a two-layer AR coating with a Herpin equivalent structure. Thickness of the layers of the resultant three-layer AR coatings can be varied continuously over ranges defined by the indices of the coating materials and the substrate. The ability to vary the thickness of the layers enables the optimization of the coating design with respect to one or more requirements, for example, low absorption, environmental durability or ease of fabrication. The TlI films deposit with an orthorhombic structure, the orientation of which is dependent on the KC1 substrate orientation. Therefore, the refractive index of the TlI films depends on the substrate orientation. The influence of the substrate orientation on the TlI refractive index can be eliminated by coating the KC1 substrate with a thin layer (~200 A) of SrF2 prior to depositing the TlI film.