Interaction between the TiC(TiCN)-Ni-Mo hardmetals and chromium vapours

The interaction between TiC or TiCN-based hardmetals with a Ni-Mo binder, or cermets, and chromium vapour in a vacuum was investigated over a wide temperature range acceptable for depositing wear-resistant coatings without the formation of a liquid phase in the cermets. Computer modelling in the Ti-C-Cr system showed that a direct interaction of TiC with chromium, leading to the formation of chromium carbides, is not possible because of the high thermodynamic stability of titanium carbide. It was established experimentally that as a result of the interaction between the cermets and chromium vapours, a coating characterized by a two-layer structure was deposited on the cermet surface. The coating consists of an inner layer adjacent to the substrate, which is composed of the chromium and carbon solid solution in nickel, and an outer layer composed of a mixture of (Cr, Ni)₇C₃ and (Cr, Ni)₂₃C₆. The activation energy of the deposition process is 387 kJ mol^–1 which is close to the value of the chromium heat of evaporation. The coating deposition process is supposed to be limited by the rate of the external supply of chromium from the vapour phase. The results of the investigation of the structure, composition and morphology of the coating are presented. A mechanism responsible for the interaction of the cermets with chromium vapour leading to the formation of the two-layer coating, is proposed.     

Investigation of the wear resistance of vacuum-deposited chromium under dry friction and sand blasting conditions

The wear resistance of 20–6000--thick vacuum-deposited chromium coatings under dry friction and sand blasting conditions can be varied by varying the deposition conditions, especially the substrate temperature and deposition rate. The wear resistance of coatings deposited on substrates at t_s < 300° C approaches that of electrodeposited coatings. It was shown that wear-resistant properties of the coatings studied are related to their structure, microhardness and other physicomechanical properties.     

Reactively sputtered oxide optical coatings for inertial confinement fusion laser components

Results to date are presented for a study of reactively sputtered oxide optical coatings which are candidate materials for use in the NOVA Terawatt neodymium glass laser under development at Lawrence Livermore Laboratory, Livermore, California. Experimental details are described for the deposition of TiO₂ on fused silica substrates by r.f. diode sputtering of titanium in a reactive Ar-O₂ atmosphere. Specific deposition procedures are presented for variation of the phase composition and grain size of the coatings over wide ranges. High laser damage thresholds are reported for TiO₂, and glassy coatings appear to be more damage resistant than polycrystalline coatings. Phase composition appears to be less important to damage resistance than grain size. Application of the reactive sputtering process to preparation of damage-resistant oxides of In-Sn and tantalum is also described and damage thresholds obtained to date are reported.     

Deposition of functional coatings on polyethylene terephthalate films by magnetron-plasma-enhanced chemical vapour deposition

Magnetron-plasma enhanced chemical vapour deposition (PECVD) is a process tool which allows the deposition of plasma polymer coatings at process pressures below 1 Pa. The striking features of this technology are the relatively easy realisation of large area deposition as well as the possibility of the combination with sputtering processes for multilayer coating designs. SiO_xC_y coatings were deposited on polymer film in a roll-to-roll deposition machine. Dynamic deposition rates as high as 120 nm?m/min were achieved. The process was set up with both the monomer hexamethyldisiloxane and the monomer tetraethylorthosilicate (TEOS) and with mixtures thereof. The coatings were analysed by Fourier transform infrared spectroscopy. This method identifies the existence of different types of Si-O bonding in the layer. The results show how the layer properties are linked to the plasma parameters of the deposition process. The properties were compared to sputtered SiO₂ and to layers obtained by other PECVD processes. Elastic recoil detection analysis (ERDA) was used in order to determine the composition of the samples. Both IR spectroscopy and ERDA revealed that the usage of TEOS provided more SiO₂-like layers. The process was applied to the deposition of optical multilayer coating in a roll-to-roll coating system.     

Abscheidung leitender und nichtleitender Hartstoffschichten auf metallischen und keramischen Werkstoffen mittels Hochfrequenz-Plasma-CVD

Deposition of conductive and nonconductive hard coatings on metallic and ceramic materials by RF-PA-CVD Conductive titanium nitride and nonconductive aluminium oxide layers were deposited on conductive and nonconductive substrates by a RF-PA-CVD process. The influence of substrate material, pressure, plasma power and the components of the gas mixture on the layer properties was investigated. TiN coatings with a homogeneous structure could be deposited by using TiCl₄ as precursor. The properties of the layer are strongly influenced by the substrate material. An increasing pressure causes a faster deposition rate and a higher chlorine content. A lower chlorine content and at the same time a faster deposition rate can be achieved by increasing the r.f. power. Aluminium and aluminium oxide layers could be deposited on steel and Si₃N₄ substrates by using AlCl₃ as precursor in dependence on the CO₂ content in gas mixture. Higher CO₂ content facilitates the deposition of aluminium oxide.     

Optimising deposition parameters of W-DLC coatings for tool materials of high speed steel and cemented carbide

The paper presents the results of investigations on the selection of optimal deposition parameters for W-DLC coatings produced by pulsed reactive magnetron sputtering in order to obtain the coatings with high adhesion to the high speed steel (HSS) and cemented carbide (HM) substrates. To optimise the deposition parameters for W-DLC coatings Taguchi's method was used. An acetylene flow rate, the substrate bias voltage, the thickness of W-DLC coatings and the thickness of chromium sublayer were selected as deposition parameters and for each of them three levels of values were determined. Adhesion, wear resistance and hardness of coatings were chosen as the criteria for selecting the optimum deposition parameters. The test results showed that all the selected parameters have a significant effect on the adhesion of coatings. The thickness of W-DLC coatings has a very significant effect on the adhesion to HSS substrates and in a case of HM substrates the same effect has the thickness of a chromium sublayer. The wear resistance of coatings increases with an increasing acetylene flow rate and decreases with the increasing substrate bias voltage. High correlation was found between the H/E ratio of coatings and their wear resistance as well as toughness. The W-DLC coating showing the best properties (L_C3 ≈ 90 N, k_V = 3.8 × 10⁻⁷ mm³/Nm) was marked by the nanocomposite structure containing about 40% of nanocrystalline tungsten carbide phase and 60% of amorphous carbon matrix.     

Microstructure control for sputter-deposited ZrO2, ZrO2·CaO and ZrO2·Y2O3

The microstructure of pure and oxide-stabilized cubic ZrO₂ has been determined as a function of the principal deposition conditions for coatings prepared by r.f. diode reactive sputtering. Broad control of crystal structure, phase composition, grain size and crystallographic orientation is obtained by appropriate selection of the target composition, substrate bias and substrate temperature. The crystal structure and phase composition obtained for coatings are compared with predictions based on the equilibrium phase diagrams. The microstructural control demonstrated in this work should make possible rapid, efficient and systematic optimization of ZrO₂ coatings for future engineering applications.     

Fabrication of titania coatings on stainless steel via laser-induced deposition of colloidal titanium oxide from sol–gel suspension

A novel processing route that exploits the application of laser energy to induce deposition of colloidal titania (TiO₂) from sol–gel suspension was developed to produce titania coatings onto stainless steel (AISI316) substrate. Various laser parameters were investigated in order to establish the feasibility and to work out the key factors and optimal conditions for effectively fabricating these coatings on the substrate. The SEM, EDS, ATR-FTIR, XRD, and contact angle measurement were employed to analyse surface morphology, phase composition, crystalline structure, and the surface properties of the deposited titania coatings. Results show that the laser energy density plays a key role in controlling the deposition process and the deposited coating's properties, whilst traverse speed is also an effective factor. Higher laser energy density delivered to the specific area leads to thicker coatings and higher crystalline phases in the deposited coatings. At lowest energy density of 4.4 J mm⁻² tested in this work, the deposited coating is mainly amorphous, although a small amount of anatase phase is detectable. More crystalline phases are formed including anatase, rutile, substoichiometric titanium oxides, ilmenite and hematite when the laser energy density is increased to 8.7–17.4 J mm⁻². Further increases in laser energy density to 21.7 J mm⁻² results in an increase in the amount of rutile phase and the disappearance of substoichiometric titanium oxide phase. The coated surfaces show an elemental composition very close to the theoretical atomic ratio of TiO₂ which is significantly different from that of the as-dried coating from the same sol. Laser irradiation over a control solution, which has the same composition as the titania sol, but without the titania precursor, was also carried out and the result showed that no change on the solution composition was detected under all laser conditions, but slight oxidation of the substrate was observed at the higher laser energy density.     

Recent progress in VO2 smart coatings: Strategies to improve the thermochromic properties

Vanadium dioxide (VO₂) has attracted a great interest for smart coating applications because of its promising thermochromic properties. Thermochromic performance of VO₂ is closely related to the phase composition and the microstructure, which are largely dependent on the synthesis method and growth control. This review summarizes the recent progress in fabrication of VO₂ by gas deposition. Representative deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), sol–gel and chemical solution methods and their relative merits are discussed. To be practically applicable, high-performance thermochromic VO₂ films are desired, often featured with a suitable phase transition temperature (T_c), high luminous transmittance (T_lum) and good modulation capability of solar energy (ΔT_sol). Focused on the strategies used to improve thermochromic properties, this review also covers topics such as multilayer construction, elemental doping, substrate selection, and structure modification. Some theoretical progresses in understanding thermochromic coatings, including phase transition mechanism and energy modeling are also provided. Although significant progress has been made in improving the thermochromic performance of VO₂ films, challenges are still present, particularly in commercial applications. Discussions on future trend and perspectives, as well as some important issues, of VO₂ films used as smart coatings will be given finally.     

Electrochemical investigation and characterization of thin-film porosity

In thin-film applications it is necessary to control film properties such as homogeneity and porosity to obtain high-quality coatings. Electrochemistry can be a very helpful tool since it can provide information about processes taking place at the interface between substrate and coating. Different thin carbon-based coatings were deposited via physical vapour deposition methods and vapour phase polymerization on pure iron substrates: fullerene films, which were modified by an ion bombardment and thin films of poly(p-xylylene), which is a very good insulating polymer. The film porosity and stability of the film/substrate system against aqueous corrosion were investigated and compared using cyclic voltammetry. The dependence of porosity and film stability on various deposition process parameters such as film thickness and plasma conditions was measured via the dissolution current density and the open circuit potential shift of the substrate material. It could be shown that the two measurements, current density I_crit. and open circuit potential E_ocp. can provide useful complementary information about film porosity that can lead to a better understanding of the coatings properties and the deposition process as well.     

热喷涂制备二氧化钛涂层中锐钛矿相调控的研究进展

二氧化钛(TiO_2)涂层在许多领域具有重要的应用价值,如光催化降解和光电池,近年来引起了相关研究者的广泛关注。在众多涂层制备技术中,热喷涂技术可以快速、高效、大面积、大批量地制备TiO_2涂层,且得到的涂层力学性能良好,喷涂成本较为低廉,因而使热喷涂TiO_2涂层的应用更具前景。TiO_2涂层的晶相组成是影响涂层最终性能的一个重要因素,而控制涂层中晶相组成的关键是调控亚稳态的锐钛矿相含量。综述了近些年来国内外制备TiO_2涂层常用的热喷涂技术,如传统粉末热喷涂、液料热喷涂以及冷喷涂等,分别阐述了不同热喷涂技术中通过调节一些重要参数达到调控涂层中锐钛矿相的方法,并讨论了材料掺杂对TiO_2涂层中锐钛矿相的影响,指出了目前调控涂层中锐钛矿相存在的问题和后续的研究方向。     

Characterization of anodic spark-converted titanium surfaces for biomedical applications

The aim of the present study was to characterize the surface morphology, microstructure and the chemical composition of anodic spark-converted titanium surfaces. The coatings were prepared in an electrochemical cell by the anodic spark deposition technique in an aqueous solution of CaH₂PO₄)₂. The coatings were characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The properties of the coatings are described in terms of morphology.     

Pack codeposition of Al and Cr to form diffusion coatings resistant to high temperature oxidation and corrosion for γ-TiAl

Abstract

Thermochemical analyses were carried out for a series of pack powder mixtures formulated for codepositing Al with Cr to form diffusion coatings on γ-TiAl resistant to high temperature oxidation by the pack cementation process. Based on the results obtained, experimental studies were undertaken to identify optimum pack powder mixtures for codepositing Al with Cr to form diffusion coatings with an adherent and coherent coating structure. The results of the thermochemical calculations performed indicated that codeposition of Al and Cr is possible with CrCl₃.6H₂O and AlCl₃ activated pack powders containing elemental Al and Cr as depositing sources. However, experimental results obtained at 1100°C revealed that CrCl₃.6H₂O is not suitable for use as an activator for codepositing Al with Cr on γ-TiAl. It caused a significant degree of degradation indicated by weight losses instead of coating deposition to the substrate. However, adherent coatings with excellent structural integrity consisting of an outer Cr doped TiAl₃ layer containing Al₆₇Cr₈Ti₂₅ phase and an inner layer containing TiAl₃ and TiAl₂ phases were successfully codeposited at 1100°C using pack powder mixtures activated by AlCl₃. It is suggested that such coatings were formed via a sequential deposition mechanism through inward diffusion of aluminium and chromium. Conditions that affect the pack codeposition process, and hence need to be carefully controlled, are discussed in relation to the mechanism of the formation of diffusion coatings with an integral structure free from microcracking on γ-TiAl.     

Nanoindentation and atomic force microscopy measurements on reactively sputtered TiN coatings

Titanium nitride (TiN) coatings were deposited by d.c. reactive magnetron sputtering process. The films were deposited on silicon (111) substrates at various process conditions, e.g. substrate bias voltage (V_B) and nitrogen partial pressure. Mechanical properties of the coatings were investigated by a nanoindentation technique. Force vs displacement curves generated during loading and unloading of a Berkovich diamond indenter were used to determine the hardness (H) and Young’s modulus (Y) of the films. Detailed investigations on the role of substrate bias and nitrogen partial pressure on the mechanical properties of the coatings are presented in this paper. Considerable improvement in the hardness was observed when negative bias voltage was increased from 100–250 V. Films deposited at |V _B| = 250 V exhibited hardness as high as 3300 kg/mm². This increase in hardness has been attributed to ion bombardment during the deposition. The ion bombardment considerably affects the microstructure of the coatings. Atomic force microscopy (AFM) of the coatings revealed fine-grained morphology for the films prepared at higher substrate bias voltage. The hardness of the coatings was found to increase with a decrease in nitrogen partial pressure.     

Chemical constitution and microstructure of TiC x coatings chemically vapour deposited on Fe-C substrates; effects of iron and chromium

TiC _x coatings were chemically vapour deposited in an industrial reactor on Fe-C substrates with carbon contents between 0.06 and 1.20 wt % C. Electron probe microanalyses showed that significant amounts of chromium and iron were present in the coatings and that chromium was also present in the substrate region adjacent to the coatings. By comparing calculated and measured lattice parameters (corrected for the internal stresses present) it became evident that the chromium was in solid solution in TiC _x , whereas the iron was not. This was confirmed by micro Auger electron spectroscopy and X-ray diffraction phase analyses. The carbon to metal ratio,x, of the TiC _x coatings decreased with increasing distance to the coating/substrate interface. The effect of iron on the X-ray diffraction line broadening and hardness of the coatings was large (in contrast with the effect of chromium) and increased with increasing distance to the coating/substrate interface because of a decreasing iron particle size. The TiC _x crystallite size was small and constant throughout the thickness of the coatings. The chromium present in the substrate region adjacent to the TiC _x coatings influenced the microstructure of the substrate by formation of iron, chromium-carbides and reduced the growth rate of the coatings.     

The deposition and optical properties of Ge1−xCx thin film and infrared multilayer antireflection coatings

The effects of deposition parameters on the deposition rate, microstructure, and composition of Ge_1−xC_x thin films prepared by plasma enhanced chemical vapor deposition were studied and the films' infrared optical properties were investigated. The results show that the carbon content of these films increases as the precursor gas flow ratio of CH₄:GeH₄ increases, while the infrared refractive index of these films decreases from 4 to 2. The deposition rate increases with the radio-frequency power and reaches a constant value when the power goes above 60 W. Ge_1−xC_x/diamond-like carbon infrared antireflection coatings were prepared, and the transmittance of the coatings in the band of 8 to 14 μm was 88%, which is superior to that of Zinc Sulfide substrate by 14%.     

Thermal stability of nitride coatings formed by ion-plasma deposition

Titanium nitride and chromium nitride coatings were formed on a gray cast iron by condensation from a plasma phase in vacuum with the ion bombardment of the sample surface by titanium or chromium plasma flows in a residual nitrogen atmosphere. The element and phase composition of coatings were studied before and after annealing for 1-43 h in air at temperature 700 °C using Auger electron spectroscopy (AES) and X-ray diffraction (XRD). It is established that titanium nitride coatings are single-phase TiN system with a (1 1 1) preferred growth orientation, and chromium nitride coatings—a two-phase system: CrN and Cr₂N phases. The annealing of coatings at the atmospheric pressure and the temperature of 700 °C in the range of 1-43 h results in the deceleration of the oxidation process of the material substrate for chromium nitride with respect to titanium nitride coatings.     

Nanostructured Pt-γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CeO<Subscript>2</Subscript> catalytic materials and coatings

A new process is described for the suspension synthesis of polycrystalline Pt-γ-Al₂O₃-CeO₂ catalytic materials and coatings, with maltose, C₁₂H₂₂O₁₁, as a reductant and structure former. The process parameters have been optimized in terms of the dispersion medium composition and the way in which Pt is introduced. The coatings are highly uniform in chemical and phase composition, as evidenced by quantitative analysis, optical microscopy, and x-ray microanalysis results. Characteristically, the coatings have a highly porous structure and good adhesive properties. Catalysts prepared by the proposed process show high activity for the oxygen oxidation of CO. The process can be used to fabricate Pt-Pd-Rh catalysts on block supports for the purification of vehicle exhaust gases and industrial off-gases. It has the advantage that high-porosity multicomponent catalytic coatings can be produced on cordierite block supports in a single step.     

Synthesis and characterization of plasma assisted chemically vapor deposited tantalum

This study focuses on the synthesis of tantalum (Ta) coatings on high strength steel by plasma assisted chemical vapor deposition using tantalum pentachloride (TaCl₅) as a preferred precursor and hydrogen (H₂) as a reducing agent. The interrelationships governing the growth kinetics, compositions, and coating properties are discussed as a function of deposition temperature, total pressure, and gas composition. The synthesized tantalum coatings are shown to be essentially pure with trace amounts of oxygen, carbon, and chlorine. The coatings are found to be dense and to exhibit conformal coverage. Preferential formation of the α-Ta phase is noted to occur when coatings are grown sequentially and in-situ on a TaN_x seed layer.     

Towards large area deposition of Cr2AlC on steel

Cr₂AlC belongs to the MAX phases, which are promising materials for protective coatings on steel due to their unique combination of properties like corrosion and oxidation resistance, good electrical conductivity, low friction coefficient, damage tolerance, and high temperature stability. Here the deposition of Cr₂AlC thin films has been carried out by magnetron sputtering of a Cr₂AlC compound target. The effect of the substrate temperature on the constitution was investigated. It was found that the MAX phase structure is stable in a substrate temperature range between 1123 K and 723 K. At lower substrate temperatures, the structure of the film is X-ray amorphous. A temperature of approximately 870 K was determined for the transition from amorphous to crystalline Cr₂AlC using differential scanning calorimetry. A phase purity of more than 90% MAX phase in the films was reached and the equilibrium volume is in excellent agreement with our ab initio calculations. The here presented deposition method provides a pathway towards large area deposition of MAX phase Cr₂AlC coatings on steel.