Reactivity of Cr(CO)6 in atmospheric pressure CVD processes for the growth of various metallurgical coatings (original) (raw)
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Manufacturing Technology
This article presents the study of the influence of the bias voltage and CH4/N2 gas ratio on the structure and chemical composition of Cr(C,N) coatings. The coatings were deposited by cathodic arc evaporation of pure Cr (99.99 %) cathode under an atmosphere of a mixture of CH4 and N2 gasses at the low deposition temperature of 300 ˚C. The ratio of reactive gasses was changed from 0 to 100 %. Energy-dispersive spectroscopy showed a linear dependence of resulting C/N ratio on the process gas ratio. The roughness of layers prepared from a mixture of process gasses is higher compared to pure gasses.
Surface & Coatings Technology, 2008
Phase stability Cr-O-N coatings were produced by reactive cathodic arc deposition at different N 2 /O 2 flow ratios onto cemented carbide substrates. The structure, and mechanical properties of the coatings depend strongly on their oxygen content. The increase of the oxygen content leads to a decrease of the mean crystallite size of the nanocrystalline cubic (B1 structure) Cr-O-N phase and to an enhancement of the (002) preferred orientation. At O/(O + N) ratios N 0.7 the coatings crystallize in the rhombohedral Cr 2 O 3 structure. The morphology of the samples, as studied by scanning electron microscopy (SEM), is columnar. The hardness of the coatings increases up to a maximal value of 28 GPa with increasing the oxygen content. Higher oxygen contents lower the hardness of the coatings. X-ray powder diffraction (XRD) studies were performed in situ at high temperatures, in vacuum and in air. The crystallite growth at elevated temperatures, both in vacuum and in air, is hindered significantly by the presence of oxygen in the coatings. The Cr-O-N coatings with the B1 structure, annealed in vacuum and in air, provide an improved thermal stability, with no evidence of oxidation or formation of the Cr 2 N phase up to 900°C.
Thermal treatment effect on structural and mechanical properties of Cr–C coatings
Transactions of the IMF
In the present study, the effect of thermal treatment on the mechanical and structural properties of chromium carbide coatings with different thicknesses is evaluated. The coatings were deposited by cathodic magnetron sputtering on XC100 steel substrates. Samples were annealed in vacuum, at different temperatures ranging from 700 to 1000°C for 1 h, resulting in the formation of chromium carbides. X-ray diffraction (XRD), microanalysis X/energy-dispersive X-ray spectrometer (EDS), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy analysis were used to characterise the samples. Mechanical properties were evaluated by nano-indentation tests and the residual stress was calculated with the Stoney formula. The XRD analysis suggests the formation of the Cr 7 C 3 , Cr 23 C 6 carbides at 900°C. For thin films, they transformed totally to ternary (Cr, Fe) 7 C 3 carbides and their partial transformation has been observed in the case of thick films at 1000°C, without the formation of Cr 3 C 2. The EDS and XPS showed the diffusion mechanism between the chromium film and the steel substrate for the Cr, Fe, C, O elements during the annealing treatment. The increase of chromium film thickness from 0.5 to 2.64 µm, contributed to the significant enhancement of mechanical properties such as hardness (H) (from 12 to 26.3 GPa) and Young's Modulus (E) (from 250 to 330 GPa), respectively.
Phase Composition and Physical Properties of Co-Cr Base Coating
Coating structure was mainly composed of α-fcp- and β-fcc-cobalt. Selected temperature interval for coating formation, according to XRD analysis, allowed us to form inter-metalloid compounds of CoxCry-type cobalt with chromium. Subsequent melting of a surface layer by a plasma jet resulted to doping of the coating surface by Mo atoms (compounds) from doping electrodes. It was demonstrated that essential improvement of servicing characteristics was due phase transformations induced by high-temperature plasma jet, Mo doping, redistribution of elements in the coating, and appearance of micro- and nano-grained structure, as well as decreasing porosity due to repeated melting.
Materials Letters, 2007
We report here the synthesis and characterisation of Cr coatings by an environmental friendly Plasma Assisted Metal-Organic Chemical Vapour Deposition (PAMOCVD) process. The Cr coatings were developed using Cr(acac) 3 as the chemical vapour source at a substrate temperature and a power density of 550°C and 70 mW/cm 2 , respectively. The films were characterized using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy and Vicker's microhardness measurements. The investigations revealed that the Cr films are nanocrystalline, free from pores and cracks and have hardness of 1200 HV. The energy dispersive analysis of X-rays and XPS confirmed the presence of Cr in the films.
Materiali in tehnologije, 2024
With the goals of protecting boiler tubes from hostile surroundings, increasing thermal efficiency, and minimizing time losses from damage, thermal-spray coating methods for high-temperature operations were created. Ceramic-metal composite materials (e.g., Cr3C2-NiCr) are well known for protecting components from erosion decay in a high-temperature environment. In this investigation, the high-velocity oxy-fuel (HVOF) thermal-spray technique was employed to successfully deposit several variations of feedstocks containing Cr3C2-NiCr and NiCr powders onto a medium-carbon steel substrate, with and without filtering through a 400-mesh screen. Utilizing X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD), the microstructure features of the deposited coatings were assessed. The experiment results demonstrate that the crystallite and grain sizes of the deposited coatings can be increased by reducing the powder size through a sifting process using a 400-mesh sieve. This procedure also resulted in a coating with a higher density and lower porosity. Furthermore, new compounds including Cr2O3 and MnCr2O4 were formed in the coating layers as indicated by the XRD spectra. These phenomena are in good agreement with the EDS mapping of Cr and O, which reveals highly similar distributions. Manganese was originally a part of the substrate composition. Manganese could diffuse rapidly across the Cr2O3 layer and form the MnCr2O4 compound, indicating the manganese diffusion from the substrate into the Cr3C2-NiCr coating. The formation of MnCr2O4 can be attributed to the prior emergence of the Cr2O3 compound.
High-temperature corrosion of Cr2O3-forming alloys in CO-CO2-N2 atmospheres
Oxidation of Metals, 1994
The corrosion of Fe-28Cr, Ni-28 Cr, Co-28Cr, and pure chromium in a number of gas atmospheres made up of C0-C02(-N2) was studied at 900~ In addition, chromium was reacted with H2-H20-N2, and Fe-28Cr was reacted with pure oxygen at 1 atm, Exposure of pure chromium to H2-H20-N2 produced a single-phase of Cr203. In a CO-C02 mixture, a sublayer consisting of Cr203 and Cr7C3 was formed underneath an external Cr203 layer. Adding nitrogen to the C0-C02 mixture resulted in the formation of an additional single-phase layer of Cr2N next to the metal substrate. Oxidizing the binary alloys in CO-C02-N2 resulted in a single Cr203 scale on Fe-28Cr and Ni-28Cr, while oxide precipitation occurred below the outer-oxide scale on Co-28Cr, which is ascribed to the slow alloy interdiffusion and possibily high oxygen solubility of Co-Cr alloys. Oxide growth followed the parabolic law, and the rate constant was virtually independent of oxygen partial pressure for Fe-28Cr, but varied between the different materials, decreasing in the order chromium >Fe-28Cr > Ni(Co)-28Cr: The formation of an inner corrosion zone on chromium caused a reduction in external-oxide growth rate. Permeation of carbon and nitrogen through Cr203 is thought to be due to molecular diffusion, and it is concluded that the nature of the atmosphere affects the permeability of the oxide.
Surface and Coatings Technology, 2007
Chromium carbide and chromium oxide coatings deposited by physical vapor deposition methods have been successfully applied in molding industries for their excellent tribological performances. In addition, nanocomposite coatings have recently attracted interest because of their high hardness, wear resistance, and good thermal and chemical stability. In this study, Cr-C-O/a-C nanocomposite coatings were synthesized by cathodic-arc evaporation with plasma enhanced duct equipment. A pure CO 2 reactive gas was introduced to react with chromium to form Cr-C-O/a-C nanocomposite coatings during the deposition process. The atomic content ratio of O/(C + O) increased with increasing CO 2 deposition pressure. A nanocomposite structure of coexisting Cr 2 O 3 and Cr 7 C 3 crystallites and amorphous carbon phases was found in the Cr-C-O/a-C coatings. The nanoindentation test revealed the nanocomposite Cr-C-O/a-C coatings with the highest atomic content ratio of O/(C + O) possessed the highest hardness of 23 GPa.
Multi-technique study of corrosion resistant CrN/Cr/CrN and CrN : C coatings
Surface & Coatings Technology, 2006
The three-layer CrN/Cr/CrN coatings were deposited on three types of steel substrates by means of PVD. The second series of these coatings was implanted with nanoclusters of carbon by using a pulsed microplasma cluster source. The physical and chemical properties of the coatings were investigated by using a multi-technique approach. The chemical composition of the samples was studied by XPS combined with cyclic Ar ion sputtering. Multi-point AES measurements and Auger chemical imaging were used to characterize the oblique cross-section of the coatings. Surface investigations revealed that CrN layers were characterized by the ratio of Cr : N = 1 with a low concentration of oxynitride compounds and that the nanoclusters of carbon were localized in the topmost sublayer of the coatings. XRD measurements were performed to study the residual stresses present in the CrN multiple-layers and in the coatings doped with carbon nanoclusters. It was found that the compressive residual stresses are present in the external layer of all multiple-layer coatings, independently from the type of substrate. The corrosion tests have been carried out by the techniques of open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS) in electrochemical cell with NaCl solution. Obtained experimental results demonstrated that the corrosion process begins at the surface defects of the coatings and propagates towards the substrate.
Journal of Nuclear Materials, 2015
Under various conditions, chromium carbides appear to be relatively stable in the presence of molten fluoride salts and this suggests that their use in corrosion resistant coatings for fluoride salt environments could be beneficial. One method for producing these coatings is the carburization of sprayed Cr coatings using methane-containing gaseous precursors. This process has been investigated for the synthesis of binder-free chromium carbide coatings on nickel-based alloy substrates for molten fluoride salt corrosion resistance. The effects of the carburization process on coating microstructure have been characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM) in conjunction with energy dispersive spectroscopy (EDS). Both plasma-sprayed and cold-sprayed Cr coatings have been successfully converted to Cr 3 C 2 , with the mechanism of conversion being strongly influenced by the initial porosity in the as-deposited coatings.