Coating Growth Rate Research Articles

Influence of Ar/C2H2 ratio on the structure of hydrogenated carbon films

Abstract The amorphous hydrogenated carbon films (a-C:H) were obtained on Si (1 1 1) wafers by plasma jet chemical vapor deposition (PJCVD). a-C:H coatings have been prepared at 1000 Pa in argon/acetylene mixture. The Ar/C2H2 gas volume ratio varied from 1:1 to 8:1. It was demonstrated that by varying the Ar/C2H2 ratio the composition, growth rate of the coatings, and consequently the structure of the film, can be controlled. The growth rate and surface porosity of coatings deposited at Ar/C2H2 = 8:1 ratio decrease slightly with an increase in the distance between the plasma torch nozzle and substrate from 0.04 to 0.095 m. The transmittance of the coatings in the IR region of 2.5–25 μm slightly increases, while the absorption peaks at 2850–2960 cm−1 related with sp3 CH2–3 modes remain unchanged with an increase in the distance. The Raman spectroscopy indicated that the a-C:H coating formed at the Ar/C2H2 = 8:1 and 0.06 m has the highest sp3 C–C fraction. The proposed PJCVD technique allows to achieve the growth rates up to 300 nm/s.

The Influence of Process Parameters on Chemistry, Roughness and Morphology of Siloxane Films Deposited by an Atmospheric Plasma Jet System

AbstractSiloxane coatings were deposited onto Vycor™ glass and silicon substrates from a tetraethyl orthosilicate (TEOS) precursor using the PlasmaStream™ atmospheric plasma jet system. The TEOS precursor was nebulized into He/O2 plasma and the coating growth rate was controlled by the number of passes of the jet over the ceramic substrates. The system process parameters were systematically varied to study their influence on the coating properties. The chemical properties, surface roughness, and morphology of the 1–200 nm thick coatings were studied as a function of both applied plasma power and TEOS flow rate. The deposited coatings were examined using ellipsometry, contact angle measurement, optical profilometry, Fourier transform infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM).

Dimensional Stability, Microstructure, and Cohesion Strength of Composite Solid Lubricant Coatings after Heat Treatment

PS304 is a plasma spray deposited coating composed of Ni-Cr, Cr 2 O 3 , Ag, and BaF 2 -CaF 2 that has been developed for reduction of friction and wear at high temperatures. Physical properties of the coating after varying heat treatments and using varying weight percentages of chromium in the Ni-Cr constituent have been investigated. Dimensional stability was reduced with increasing heat treatment temperature and the coating growth rate decreased with time. The dimensional stability was also reduced as the Cr content in the Ni-Cr constituent increased from 10 to 30 wt%. Coating growth was due to oxidation of the Ni-Cr constituent. The optimum cohesion strength for PS304 was essentially the same after heat treatment at 650 or 725°C for 100 h. Further investigation indicated that heat treatment at 725°C for 100 h increases the dimensional stability in a high temperature service environment.

Deposition of silicon-enriched nickel aluminide coatings on internally cooled airfoils

Abstract Aluminum diffusion coatings enriched with silicon were prepared by chemical vapor deposition on various nickel-based materials such as almost pure nickel and Rene 80. Aluminum and silicon chloride served as precursors. They were generated in-situ by feeding gaseous hydrogen chloride (HCl) into a heated reaction chamber (1100 °C) which contained aluminum and silicon donating material. An excess of hydrogen gas flow was found to improve the coating growth rate. Due to the high reactivity of aluminum, high ratios of silicon to aluminum donator had to be maintained (at least 10: 1). The coating thickness was determined from glow discharge spectroscopy and metallographic cross sections. Co-deposition and two-step deposition (first aluminizing and then siliconizing) were performed. Silicon contents of up to 50 at.% could be achieved. In contrast, a two-step process including first aluminizing and then siliconizing leads to an undesired replacement of aluminide by silicide. Al–Si diffusion coatings could be realized on internal cooling channels of turbine airfoils by single-step co-deposition.

Deposition of silicon enriched nickel aluminide coatings on internally cooled airfoils

Aluminum diffusion coatings enriched with silicon were prepared by chemical vapor deposition on various nickel-based materials such as almost pure nickel and Rene 80. Aluminum and silicon chloride served as precursors. They were generated in-situ by feeding gaseous hydrogen chloride (HCl) into a heated reaction chamber (1100 °C) which contained aluminum and silicon donating material. An excess of hydrogen gas flow was found to improve the coating growth rate. Due to the high reactivity of aluminum, high ratios of silicon to aluminum donator had to be maintained (at least 10: 1). The coating thickness was determined from glow discharge spectroscopy and metallographic cross sections. Co-deposition and two-step deposition (first aluminizing and then siliconizing) were performed. Silicon contents of up to 50 at.% could be achieved. In contrast, a two-step process including first aluminizing and then siliconizing leads to an undesired replacement of aluminide by silicide. Al–Si diffusion coatings could be realized on internal cooling channels of turbine airfoils by single-step co-deposition.

Modelling heat and mass transfer in batch , top-spray fluidised bed coating processes

The objective of this study was the development of a new process model for the different heat and mass transfer phenomena during fluidised bed coating processes. The model is based on the discretisation of the bed into horizontal control volumes, in which the heat and mass balances for air, water vapour, droplets, particles and coating material were established. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions which were measured in a fluidised bed pilot reactor using a scanning probe. A sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidisation air and atomisation air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on this sensitivity study, it was concluded that nozzle parameters are as important as the fluidisation air properties for coating growth rate uniformity and process yield.

Preparation and microstructural characterization of TiC and Ti0.6W0.4∕TiC0.6 composite thin films obtained by activated reactive evaporation

Titanium carbide-based coatings were deposited on W substrates at a high coating growth rate by activated reactive evaporation at 500 and 600°C in a L560 Leybold system using propene as reactive atmosphere. The crystal structure, lattice parameter, preferred orientation, and grain size of the coatings were determined by x-ray diffraction technique using CuKα. The analysis of the coating morphology was performed by scanning electron microscopy (SEM), and the composition of the films was analyzed by Auger electron spectroscopy and electron-probe microanalysis. Experimental results suggested that temperature was one of the most important parameters in the fabrication of stoichiometric TiC coatings. Thus, TiC coatings were obtained at 600°C, whereas TiC0.6 nonstoichiometric coatings codeposited with a free Ti phase were obtained at 500°C, giving rise to the formation of a composite thin film. After annealing at 1000°C, the stoichiometric films remained stable, but a crack pattern was formed over the entire coating surface. In addition, Ti0.6W0.4∕TiC0.6 composite thin coatings were obtained for the films synthesized at 500°C. The formation of a Ti0.6W0.4 ductile phase in the presence of a TiC0.6 phase was responsible to avoid the coating cracking.

Physical and mathematical simulation of plasma-chemical heterogeneous synthesis from plasma fluxes

A physicomathematical model of obtaining variable-composition compounds by the ion-plasma method is developed. Specifically, the model is applied to synthesis of titanium nitride coatings. The mathematical part of the model takes into account the basic stages of the process, such as adsorption, desorption, dissociation, chemisorption, accommodation, sputtering, and surface migration. It makes it possible to find the coating growth rate, coating stoichiometry, and packing density of the adlayer as functions of the basic physical parameters of the process.

Conversion coating growth on 2024-T3 Al alloy. The effect of pre-treatments

The cleaning pre-treatments, generally based on alkaline etching and acid pickling, provide a surface standard condition before the application of conversion coatings. In this work, the effect of cleaning pre-treatments on the surface morphology and activity of 2024-T3 Al alloy and on chromium-free Ce-based conversion coatings formation has been studied. Variations in the open circuit potential of the alloy of ~ 1.5 V were registered during the cleaning pre-treatment, accounting for the complex electrochemical phenomena involved. Even though, the presence and concentration of additives such as H 2O 2 was found to be essential to a fast kinetics coating formation, effective cleaning pre-treatments are demonstrated to be associated to the production of grained well structured coatings, allowing necessary redox reactions for conversion coating formation. The effect of copper-rich areas and its effect on the conversion coating growth rate and morphology were also studied using benzotriazole additions at different stages in the cleaning pre-treatments.

Combined Effect of Spin Speed and Ionic Strength on Polyelectrolyte Spin Assembly

Polyelectrolyte spin assembly (PSA) of multilayers is a sequential process featuring adsorption of oppositely charged polyelectrolytes from dilute solutions undergoing spin-coating flow. Here, we report on the dependence of PSA multilayer buildup of poly(sodium 4-styrenesulfonate) and poly(allylamine hydrochloride) on solution ionic strength and spin speed. We observed that at a given spin speed, the PSA coating growth rate (thickness/bilayer) and polymer surface coverage shows a nonmonotonic dependence on salt concentration, first increasing and then decreasing with increasing solution ionic strength. This is argued to be a manifestation of two competing mechanisms responsible for the layer formation. At low salt concentrations, the electrostatic interactions control the multilayer assembly process, while at high salt concentrations it is dominated by shear flow. We explain this nonmonotonic behavior in the framework of a Flory-like theory of multilayer formation from polyelectrolyte solution under shear flow. Additionally, the PSA process led to multilayer coatings with a radial dependence on thickness at lower spin speed in the shear-dominated regime. On increasing spin speed, such radial dependence subsided, eventually leading to uniform coatings by planarization. The surface topography of the multilayered coatings adsorbed at salt concentration less than 0.1 M was flat and featureless for all studied spin speeds. Unique morphological features in the films were formed at salt concentration higher than 0.1 M, the size of which depended on the spin speed and solution ionic strength.

Numerical Spray Model of the Fluidized Bed Coating Process

In this study, a new model for the batch top-spray fluidized bed coating process is presented. The model is based on the one-dimensional (axial) discretization of the bed volume into different control volumes, in which the dynamic heat and mass balances for air, water vapor, droplets, core particles, and coating material were established. The coupling of the droplet phase's mass and heat transfer terms with the gas and solid phases was established by means of a droplet submodel in which droplet trajectories were individually simulated. The model calculation method combines a Monte Carlo technique for the simulation of the particle exchange with the first-order Euler's method for solving the heat and mass balances, enabling the prediction of both the dynamic coating mass distribution and the one-dimensional (axial) thermodynamic behavior of the fluidized bed during batch operation. The simulation results were validated using experimental two-dimensional spatial air temperature and air humidity distributions, which were measured in a fluidized bed pilot reactor using a scanning probe. Sensitivity analysis was carried out to study the effect of controllable process variables, such as fluidization air and atomization air properties, as well as the properties of the spraying liquid upon the simulated dynamic temperature and humidity distributions. Also, the effects of relevant process variables on growth rate uniformity and process yield were studied. Based on these sensitivity studies it was concluded that nozzle parameters, such as air pressure and positioning with respect to the bed, are as important as the fluidization air properties (humidity, temperature, and flow rate) for the coating growth rate uniformity and process yield.

Incoloy 909 합금의 최적 알루미나이징 확산 코팅

An Fe-Ni-Co based superalloy Incoloy 909 (Incoloy 909) has been used for gas turbine engine component material. This alloy is susceptible to high temperature oxidation and corrosion because of the absence of corrosion resistant Cr. For the improvement of durability of the component of Incoloy 909 aluminizing-chromate coating by pack cementation process has been investigated at relatively low temperature of about to protect the surface microstructure and properties of Incoloy 909 substrate. As a previous study to aluminizing-chromate coating by pack cementation of Incoloy 909, the optimal aluminizing process has been investigated. The size effects of source Al powder and inert filler powder and activator selection have been studied. And the dependence of coating growth rate on aluminizing temperature and time has also been studied. The optimal aluminizing process for the coating growth rate is that the mixing ratio of source Al powder, activator and filler are 80%, 1% and 19% respectively at aluminizing temperature and time 20 hours.

Gas phase aluminizing of nickel alloys with hydrogen chloride

Aluminizing of novel nickel alloy Haynes 282 and alloy 201 was performed by chemical vapor deposition. Aluminum chloride served as precursor and was generated in-situ by feeding gaseous hydrogen chloride (HCl) into the retort reacting with a solid high-melting aluminum alloy at about 1350 K. In comparison to over-pack aluminizing this process offers the advantage to control the coating growth by simply adjusting the HCl gas flow. Either continuous HCl flow or discontinuous addition was applied. Hydrogen (H 2) to HCl gas flow ratios from 0:1 up to 9:1 (total flow of 50 l/h in every case) were tested at atmospheric pressure. Coating thickness was determined from glow discharge spectroscopy and metallographic cross sections. It is shown that formation of the desired β-NiAl phase is relatively insensitive to the gas flow ratio, yet forms best at hydrogen excess with a H 2 to HCl flow ratio of approx. 4:1 (40:10 l/h). Discontinuous addition of HCl does not lower coating growth rate significantly in either case because the chloride introduced into the chamber is not consumed in the aluminum deposition process. The results are explained by thermo-chemical calculations showing that an excess of hydrogen chloride reduces formation of NiAl on the part to be coated. Isothermal oxidation tests revealed an improved oxidation resistance of the aluminized surfaces.

Nanocrystalline Structure Produced by Complex Surface Treatments: Plasma Electrolytic Nitrocarburizing, Boronitriding, Borocarburizing, and Borocarbonitriding

In present study, the feasibility of improving tribological performance of low carbon chromium steel by applying complex surface treatments which combines the method of Plasma electrolytic saturation (PES) is investigated. The different regimes of diffusion treatments on the surface affect the mechanical and tribological characteristics of the steel substrates by production of nanocrystalline interlayers. The major advantage of the PES technique was shown to be the extremely high nanocrystalline coating growth rate by the aggressive ionized particles. The combination of characteristics far exceeds the capabilities of the diffusion procedure by means of PES technique. It was found that the different compositions of interlayers produced by means of complex diffusion treatments eliminate the sharp slope of the microhardness profile. The gradual decrease of microhardness with distance from the surface, provides a good tribological performance. The boride layer reveals the highest value of microhardness among the produced interlayers. In the case of tribological performance, the boronitrided sample shows the best characteristics which are related to the formation of nanocrystalline nitride layer beneath the top boride layer.

Effects of reactive gaseous mixture and time on the growth rate and composition of aluminium diffusion coatings by CVD-FBR on 12Cr-ferritic steel

Aluminium deposition on ferritic steel HCM12 A (P-122) by chemical vapour deposition in a fluidized bed reactor (CVD-FBR) has been studied. A thermodynamic study of the partial pressures of the gaseous species present in the system during the CVD, was performed using the Thermocalc software. The coating obtained was studied by XRD, SEM and EDX. The influence of the HCl input ratio on the H 2/HCl reactive gas mixture was investigated. It was found that with an increase of HCl input thicker coatings consisting of the Fe–Al intermetallic phase were formed. By increasing the deposition time the thickness of the Al-layer also increases and the Fe 2Al 5 and FeAl 3 intermetallic phases are formed.

Kinetics of ultrafine coating of SiO 2 nanoparticles, suspended in non-thermal CH 4/C 2H 6 plasma

Capacitively coupled RF discharges in methane and ethane (1000–3000 Pa, 5–15 W/cm 3) were used for the in-flight coating of SiO 2 nanopowders (NP) with an a-C:H layer [A. Kouprine, F. Gitzhofer, M. Boulos, A. Fridman, Polymer-like C:H thin film coating of nanopowders in capacitively coupled RF discharge, Plasma Chemistry and Plasma Processing 24 (2) (2004) 189–215]. In this present work a model of the chemical kinetics of this plasma processing has been developed, based on the GRI-Mech 3.0 mechanism [G.P. Smith, D.M. Golden, M. Frenklach, Gas Research Institute, Detailed chemical reaction mechanism. Available from: <http://www.me.berkeley.edu/gri_mech/>], and calculations are performed, using the Chemkin-II code. The model includes the formation of two solid phases: an amorphous C:H coating, deposited on the suspended NP, and soot, incepted in the gas phase. Non-equilibrium plasma effects are taken into account by the rates of radical species’ production, using the reference data on the “ G-value”. The CH 3 and H species appear to have key roles in surface activation and the nanofilm growth. The results demonstrate the competitive character of the formation of the two solid phases: the C:H coating is dominant under T gas < 1400–1600 K, depending on the conditions, and soot commencing to dominate at higher temperatures. This division corresponds to the passage from non-thermal plasma conditions, with the dominance of single-valent radicals and solid phase growth on the substrate only, to the plasma thermalisation with the formation of two-valent radicals and v. inception of the solid phase. The results are validated experimentally by the observation of soot formation as a function of the gas temperature, by the mass spectrograph data on the gas composition after plasma reforming, and by the reference data on coating growth rates and induction times for soot formation.

Model concepts on the mechanism of microarc oxidation of metal materials and the control over this process

Based on a critical analysis of literature data, new model concepts on the mechanism of microarc oxidation (MAO) are developed. The correctness of these model concepts is confirmed by experimental results on the average growth rate of oxide-ceramic coatings for different duration of the MAO process on AД31, MA2-1, and MЛ-5 alloys, the morphology of the surface structure of coatings of different thickness, the comparative electrical strength of dielectric coatings, which is assessed during self-quenching of the MAO process and in air. Equivalent electric circuits developed describe this process and are experimentally shown to be the “tool” which allows controlling MAO of aluminum and magnesium alloys.

Low temperature, fast deposition of metallic titanium nitride films using plasma activated reactive evaporation

Titanium and titanium nitride thin films were deposited on silica glass and W substrates at a high coating growth rate by plasma-activated reactive evaporation (ARE). The crystal structure, preferred orientation and grain size of the coatings were determined by x-ray diffraction (XRD) technique using Cu-Kα x rays. The analysis of the coating morphology was performed by field-emission scanning electron microscopy (FE-SEM). The composition of the films was analyzed by Auger electron spectroscopy (AES) and electron-probe microanalysis (EPMA). The titanium and titanium nitride condensates were collected on a carbon-coated collodion film then characterized by transmission electron microscopy (TEM) in order to study the structures of the deposits at very short deposition times. The resistivity of the films was measured by using the four-point-probe method. The titanium coatings were found to consist of very fine particles (40nm in grain size) and to exhibit a strong (002) texture. The titanium nitride coatings were substoichiometric (TiNx,x&amp;lt;1), with an oxygen content ranging from 7 to 15 at. % depending on the deposition conditions. The deposits were found to exhibit a (111) preferred orientation. This behavior became stronger with coating thickness. In spite of the presence of oxygen, all the TiNx coatings obtained at low temperature and a high growth rate in this work exhibited a rather high electrical conductivity.

Effects of Processing Parameters on Alumina Coatings Deposited on Nickel Substrates by Reacting Aluminum Chloride and Hydrogen/Carbon Dioxide Gas Mixtures

Pure nickel coupons were used as substrates in the deposition of alumina (Al{sub 2}O{sub 3}) from the reaction of aluminum chloride (AlCl{sub 3}) with hydrogen/carbon dioxide gas mixtures in the temperature range of 954--1,100 C and system pressures of 2.7--13.3 kPa. The apparent activation energy estimated from the coating growth rate averaged 320 kJ/mol at 13.3 kPa. At temperatures <1,000 C, transition {theta}, {kappa}, and {delta} modifications were codeposited with {alpha}-Al{sub 2}O{sub 3}, whereas single-phase {alpha}-Al{sub 2}O{sub 3} was deposited at higher temperatures. At high AlCl{sub 3} partial pressures, nickel aluminide phases were sometimes codeposited with Al{sub 2}O{sub 3}, which was attributed to the reaction of AlCl{sub 3} with the nickel substrate in the presence of hydrogen gas.

Effect of Deposition Parameters on the Microstructure and Growth Rate of CVD Mullite Environmental Barrier Coatings

ABSTRACTSi-based ceramics such as SiC require environmental barrier coatings to protect against hot-corrosion and recession in gas turbine applications. Dense, crystalline mullite coatings of uniform thickness have been deposited by hot-wall chemical vapor deposition (CVD) on SiC substrates, using the AlCl3-SiCl4-CO2-H2 system. The effects of the CVD deposition parameters such as temperature, total reactor pressure, and metal-chloride partial pressure on the coating microstructure and growth kinetics have been investigated, and are discussed in this paper.