Layers In Multilayer Coatings Research Articles

Effect of Surface Pre-Treatment on Adhesive Strength of Multi-Component Vacuum-Arc Coatings

The results of investigations of multi-component nanostructured coatings of (TiAlSiY)N/CrN type are presented. The influence of different variants of substrate surface pretreatment on adhesive strength and hardness of coatings was studied. Pre-treatment of samples was carried out in plasma of two-stage gas discharge according to various technological schemes. Except for ion-plasma purification, some samples were pretreated with a sublayer of chromium within 5 minutes. The coatings were formed by a vacuum-arc deposition method at simultaneous spraying of two cathode targets. The first cathode is made of chromium, and the second cathode is made of multicomponent Ti - Al - Si - Y alloy obtained by vacuum-arc remelting of powder mixture of the mentioned elements. The coatings were deposited on polished stainless-steel substrates at negative 280 V bias potential. The geometry of the unit and its elements, as well as technological characteristics of the processes of evaporation-condensation were selected so that at a speed of rotation of samples 8 revolutions per minute the formation of the coating with a total thickness of about 9.0 microns occurred in approximately 60 minutes. The analysis of the composition of the coatings shows that the content of elements in the coating differs greatly from the content of elements in the sprayed cathodes. The X-ray diffractometry has shown that all deposition modes are characterized by the formation of phases with cubic (fcc) crystal lattice in both phase layers of multilayer coatings. In the layers formed at spraying of TiAlSiY alloy, a multi-element disordered solid solution (TiAlSiY)N with a crystal lattice of NaCl type and a lattice parameter of 0.4241 nm, as well as chromium mononitride CrN with a lattice parameter of 0.4161 nm, is determined. It has been established that preliminary formation of a chromium sublayer on the substrate leads to significant changes in adhesive strength of multi-component coatings compared to coatings without a sublayer.

Structure and mechanical properties of nanocrystalline Ni/Cu multilayer coatings produced by the electrocrystallization method

The paper presents the results of studies on the structure and mechanical properties of nanocrystalline multilayer Ni/Cu coatings. and for comparative purposes, also of nanocrystalline Ni and Cu coatings deposited by the electrocrystallization method. The structure of the produced coatings was characterized by the X-ray diffraction method and scanning electron microscopy. The tests of mechanical properties were carried out using the Depth Sensing Indentation (DSI) method. The curves of dependence of the loading force as a function of the penetration depth of the indenter of the tested coatings were determined. as well as the parameters characterizing the tested materials: indentation hardness (HIT), Martens hardness (HM), elastic modulus (EIT), elastic strain index (KH) and creep (CIT). The scratch test evaluated the adhesion of the material of coatings to the steel substrate as well as between the individual layers in multilayer coatings. Multilayer Ni/Cu coatings are characterized by, nanocrystalline structure, compact construction and uniform thickness over the entire covered surface. The materials of the tested coatings differ significantly in the course of plastic deformation and elastic deformation. The thickness of the layers in multilayer Ni/Cu coatings affects their mechanical properties.

Effect of number of layers on the toughness of TiN/TiC multilayer coatings

The structure and mechanical properties of titanium nitride/titanium carbide multilayer coatings on H13 hot work tool steel were investigated. All coatings were deposited by the pulsed–DC plasma–assisted chemical vapour deposition. Field emission scanning electron microscopy was used to study the crystalline structure of coatings. Indentation tests were carried out by atomic force microscopy and the Vickers hardness test. The objective of this paper is to determine mechanical properties such as the hardness, the elastic modulus and the toughness of different coatings. Increasing the number of layers in multilayer coatings increased the elastic modulus, the hardness and the toughness with respect to the single–layer coatings. Superior mechanical properties such as high hardness (26.7 GPa), high elastic modulus (327.6 GPa) and high toughness (17.7 MPa.m1/2) were related to multilayer coatings with 10 layers due to the compressive residual stress.

Study on the Hydrophobized Changes in Wettability of Sol-Gel Synthesized Nano Titanium Dioxide Films

The hydrophobized change in wettability of TiO2films has been investigated for glass coated with acidic TiO2nanosols containing varying concentrations of dispersed nanocrystalline titania, obtained by sol-gel method. The photo-induced change in wettability was evaluated by measuring the time dependent drop of water contact angle (WCA) after samples had been soaked in a decanoic acid (DA). TiO2films treated in this way exhibit superhydrophobic behaviour, with WCA greater than 1600. After radiation with UV (black light), the superhydrophobic properties are transformed into superhydrophilic properties, with WCA of almost 08. As TiO2content and layer thickness increase, high rates of photo-induced change are found. Use of a calcination temperature for the intermediate annealing of the single layers in multilayer coatings and a short final sintering step at a relatively high temperature (e.g. 500-700 °C for 10 min) allow the preparation of relatively thin TiO2 films on glass with a high photoactivity.

Characterization of TiCN and TiCN/ZrN coatings for cutting tool application

Coating a cutting tool improves wear resistance and prolongs tool life. Coating performance strongly depends on the mechanical and chemical properties of the coating material. In a machining process, the type of selected coating depends on the cutting condition because of the properties of the applied coating material. In addition, many factors, such as coating thickness, composition ratio, sequences of layers in multilayer coatings, and the deposition method influence the performance of a coating. In this study, the mechanical properties of TiCN and TiCN/ZrN were investigated using a ball on disk test. The substrate material made from a carbide-based cutting tool was also developed in-house. The analysis performed shows that the performances of TiCN and TiCN/ZrN coatings were found to be comparable to that of the commercial TiN-coated carbide-based cutting tool. Both the in-house and commercial coated inserts had significantly lower coefficient of friction than uncoated inserts, and the friction coefficient of TiCN coatings was constantly slightly lower than that of TiN coatings. Moreover, the coefficient of friction of the in-house developed TiCN was slightly lower than that of commercial TiN coating. However, the coefficient of friction of the in-house developed uncoated carbide inserts was slightly higher than that of commercial uncoated carbide inserts.

Investigation into the photo-induced change in wettability of hydrophobized TiO 2 films

The photo-induced change in wettability of hydrophobized TiO 2 films has been investigated for steel coated with acidic TiO 2 nanosols containing varying concentrations of dispersed nanocrystalline titania, such as Degussa P25. The photo-induced change in wettability was evaluated by measuring the time-dependent drop of water contact angle (WCA) after samples had been soaked in either n-octyltriethoxysilane (OTS) or decanoic acid (DA). TiO 2 films treated in this way exhibit superhydrophobic behaviour, with WCA greater than 160°. After radiation with UV (black light), the superhydrophobic properties are transformed into superhydrophilic properties, with WCA of almost 0°. As P25 content and layer thickness increase, high rates of photo-induced change are found, but a moderate calcination regime is required. On the other hand, hardness and E modulus pass through a maximum at 25 wt% P25, so that a P25 content between 25 and 50 wt% is the optimum for practical uses. With such stable coatings, wettability can be controlled over a wide range, and the switch between hydrophobic and hydrophilic states can be carried out repeatedly when DA is used as the hydrophobizing agent. Use of a low calcination temperature (450 °C) for the intermediate annealing of the single layers in multilayer coatings and a short final sintering step at a relatively high temperature (e.g. 630 °C for 10 min) allow the preparation of relatively thin TiO 2 films on steel with a high photoactivity.

Optical analysis of coatings by variable angle spectrophotometry

Variable angle spectrophotometry (VAS) involves measurement of transmittance and reflectance as a function of the angle of incidence, wavelength and polarisation. This provides a means for analysis that yields the thickness and optical constants of the individual layers in multi-layer coatings, as well as other parameters that can be related to optical material properties. In the past decade, VAS has evolved into an accurate tool for optical characterisation of coatings, with many advantages over ellipsometry. The paper describes the tools for measurement and analysis developed by the author for the UV/Vis/NIR and IR wavelength ranges. Examples are given for single- and multilayer stacks with materials like ZnO, Cr, ITO and SiO 2.

An automated directional reflectance/transmittance analyser for coating analysis

There is a growing need in the industry for motorized spectrophotometer accessories. Especially for measurements of directional reflectance and transmittance, which require many scans on the same sample at different angles of incidence, automation is beneficial. TNO TPD has developed a new motorised accessory for the measurement of directional reflectance and transmittance in the wavelength range between 250 and 2.500 nm. It is capable of making absolute measurements of the transmittance and reflectance of specular samples as well as performing BRDF measurements on diffuse samples. The accessory is a valuable tool in the optical characterisation of coatings and provides a means for analysis that yields the thickness and optical constants of the individual layers in multi-layer coatings, as well as other parameters that can be related to optical material properties.

Diamond-like carbon films in multilayered interference coatings for IR optical elements

In the majority of modern IR interference multilayer coatings (MLC), conventional film-forming materials (FFM) of fluoride and chalcogenide types are used. Such coatings are characterized by relatively low mechanical strength and stability against enhanced humidity and, therefore, require surface protection. Our present results support the view that mechanical strength of these MLCs can be improved by applying a diamond-like carbon (DLC) film as an external layer. Nanoindentation measurements show that the addition of a DLC film to ZnSe/BaF 2/Y 2O 3 IR antireflection MLC increases the combined hardness of the coatings from 0.5 to 3.6 GPa. The formation of an indent on the upper and subsequent layers of MLC has been studied by SEM and X-ray spectrum microanalysis. The resistance of DLC films applied onto MLC against light irradiation, organic solvents as well as against environmental factors was also studied. Atomic force microscopy (AFM) was used to study variations of the surface morphology of the initial MLC components before and after DLC film deposition.