Enhancement of the corrosion resistance of titanium alloys of the Ti-Al-Mo-V system by carbonitriding

We study the regularities of formation of coatings on titanium alloys of the Ti-Al-Mo-V system in the process of saturation in carbon-and-nitrogen-containing media (with an oxygen content of at most 0.01–0.0005 vol.%) and their corrosion-electrochemical behavior in an 80% aqueous solution of sulfuric acid. The difference between the phase compositions of the coatings formed in different temperature ranges of saturation is revealed. Thus, nitride coatings are formed on the surface at temperatures below 1100°C and carbonitride coatings are formed above 1100°C. It is shown that the physicochemical characteristics of nitride coatings formed in carbon-and-nitrogen-containing media are better than the corresponding characteristics of nitride coatings obtained by nitriding for the same temperature, time, and gas-dynamic parameters of saturation. As the content of cubic δ-nitride in the coating increases, the corrosion characteristics of the surface after saturation in carbon-and-nitrogen-containing media increase. Despite a significant surface roughness of carbonitride coatings, their corrosion resistance is high. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 4, pp. 78–83, July–August, 2006.     

Effects of duty ratio at high frequency on growth mechanism of micro-plasma oxidation ceramic coatings on Ti alloy

The aim of this work is to study the effects of duty ratio on the growth mechanism of the ceramic coatings on Ti–6Al–4V alloy prepared by pulsed single-polar MPO at 2,000 Hz in NaAlO₂ solution. The phase composition of the coatings was studied by X-ray diffraction, and the morphology and the element distribution in the coating were examined through scanning electron microscopy and energy dispersive spectroscopy. The thickness of the coatings was measured by eddy current coating thickness gauge. The corrosion resistance of the coated samples was examined by linear sweep voltammetry technique in 3.5% NaCl solution. Duty ratio influenced the composition and structure of the coatings. Many residual discharging channels on the coating surface showed that the spark discharge at 2,000 Hz was mainly attributable to the breakdown of the oxide film, which was suitable for the elements both from the electrolyte and from the substrate to join MPO process, and therefore, the coating was mainly composed of Al₂TiO₅. Because of the increase of the congregation and the adsorption of Al from the electrolyte with increasing duty ratio, the redundant Al on the electrode surface led to the formation of γ-Al₂O₃. And Al and Ti in the coating existed in the form of the reverse gradient distribution. Meantime, ceramic coatings improved the corrosion resistance of Ti alloy, and the coating surface morphology and thickness determined the coated samples prepared at D = 20% had the best corrosion resistance among the coated samples.     

Influence of coating on short steel fiber reinforcements on corrosion behavior of aluminium base short steel fiber reinforced composites

Steel fiber reinforced aluminium composites are attractive materials of high specific strength but exhibit poor resistance against electrochemical corrosion. The study discusses the electrochemical corrosion behavior of uncoated, copper and nickel coated short steel fiber reinforced aluminium and Al–2Mg matrix composites in 1 (N) NaCl solution. Galvanic corrosion between the steel fiber and aluminium governs the corrosion behavior of these composites. It has been observed that open circuit potential (OCP) is shifted to more negative side with copper coating on the fibers and to the more positive side on coating the fibers with nickel. Compared to the uncoated fiber higher corrosion current density indicates corrosion rate was observed for the copper coated fiber reinforced composites where as a lower current density was noted for the nickel coated fiber reinforced composites was observed. Addition of 2 wt% magnesium to aluminium alloy matrix increased the corrosion current density. The corrosion mechanism in these composites is dominated by galvanic cell formation that is evident from the dissolution of Al matrix near the peripheral region of steel fibers.     

Structure, mechanical properties and corrosion resistance of nanocomposite coatings deposited by PVD technology onto the X6CrNiMoTi17-12-2 and X40CrMoV5-1 steel substrates

This article presents the research results on the structure and mechanical properties of nanocomposite coatings deposited by PVD methods on the X6CrNiMoTi17-12-2 austenitic steel and X40CrMoV5-1 hot work tool steel substrates. The tests were carried out on TiAlSiN, CrAlSiN and AlTiCrN coatings. It was found that the structure of the PVD coatings consisted of fine crystallites, while their average size fitted within the range 11–25 nm, depending on the coating type. The coatings demonstrated columnar structure and dense cross-sectional morphology as well as good adhesion to the substrate, the latter not only being the effect of adhesion but also by the transition zone between the coating and the substrate, developed as a result of diffusion and high-energy ion action that caused mixing of the elements in the interface zone. The critical load L _C2 lies within the range 27–54 N, depending on the coating and substrate type. The coatings demonstrate a high hardness (~40 GPa) and corrosion resistance.     

Tribotechnical properties of coatings on titanium alloys

We compare the antifriction properties of different types of coatings on titanium alloys under conditions of boundary friction as applied to parts of the hydraulic cylinders of an aircraft. We show that gasthermal titanium carbide coatings cladded with nickel and with both copper and nickel have better antifriction characteristics than ones obtained by chrome electroplating, nickel chemoplating, thermooxidation, anodization, etc. Kiev International University of Civil Aviation; J.S.S.T.C. “Antonov,” Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 55–62, March–April, 1998.     

Formation of high-strength metallic coatings by pulse plating

We present the results of experimental investigation of high-strength multilayer metallic coatings deposited by pulse currents. It is shown that both monometallic (nickel, zinc, and copper) and composite (tinnickel, tin-copper, and copper-nickel) multilayer electroplated coatings exhibit better characteristics of strength than their components. We discuss possible causes of this phenomenon. Dnepropetrovsk State Technical University of Railroad Transport, Dnepropetrovsk. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 33, No. 2, pp. 89–100, March–April, 1997.     

Corrosion and electrochemical properties of binary cobalt and nickel alloys

The influence of pH of electrolyte on the tungsten content and current efficiency of a Co–W coating is determined. We determine the corrosion rates of Co–W and Ni–Pd alloys by the polarization resistance method and show that the coatings are classified as belonging to highly corrosion-resistant coatings. The catalytic reactivity of coatings in a model reaction of hydrogen release is assessed. Dependences of the corrosion resistance and catalytic reactivity of Co–W and Ni–Pd alloys on the contents of the components are obtained, and their character is justified. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 6, pp. 89–92, November–December, 2008.     

Structural features of the Fe−Mo−Cr−B powder materials for gas-thermal coatings

We study distinctive features of the structure of Fe−Mo−Cr−B powder materials used for the formation of amorphous gas-thermal coatings. It is shown that the introduction of vanadium and rare-earth metals in the structure of these powder materials affects the phase composition of borides, increases the range of sizes of their particles, and makes their distribution more homogeneous, which promotes the transition to the amorphous state in the process of application of coatings. We emphasize that the use of powders for the application of hardening and regenerating coating to metallic products proves to be quite promising. “L'vivs'ka Politeknika” State University, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 5, pp. 63–66, September–October, 1996.     

Effect of mineral fillers on the properties of silicone coatings

We study the influence of mineral fillers on the properties of silicone composite coatings and show that oxides and natural silicates of metals promote the formation of the structure of coatings but does not affect their corrosion resistance. We also determine the physicomechanical and thermal characteristics of filled materials. Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 32, No. 5, pp. 67–70, September–October, 1996.     

Protective coating for magnesium alloy

A phosphate–permanganate conversion coating was applied as the pretreatment process for AZ91D magnesium alloy substrate. Zn–Ni alloys were electrodeposited onto the treated AZ91D magnesium alloy from sulfate bath. The morphology and phase composition of the coatings were determined with X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The results reveal that the conversion rate depends on pH of solution and treatment time. Salt spray and the electrochemical polarization testing were applied to evaluate the corrosion performance of phosphate–permanganate and Zn–Ni coated alloys. It was found that Ni content in deposit is a function of current density and bath composition. Zn–13 wt.% Ni coating provides very good corrosion protective function to inner AZ91D magnesium alloy. Phosphate–permanganate treatment enhances the corrosion resistance of Zn–Ni coatings.     

Corrosion-mechanical behavior of the protective coatings of check valves of the oil-and-gas field equipment

We study the corrosion and corrosion-mechanical behavior of nickel–chromium coatings deposited on 30KhMA steel by the plasma-powder surfacing. It is shown that these coatings exhibit high corrosion resistance both in the vapor-gas and liquid phases of the NACE medium even in the presence of abrasive materials (1%) and under the conditions of stirring. It is demonstrated that the zone of fusion of the base metal with the material of the coating is not damaged and has no exfoliations after 200 h of testing for hydrogen-induced cracking in NACE media. All specimens passed through the tests for hydrogensulfide stress-corrosion cracking under a load of 0.8σ_0.2 [for the base metal (30KhMA)] and did not fail as a result of testing for 720 h. The material of the coating exhibits good corrosion-mechanical properties. Thus, it can be successfully used for manufacturing the elements of Christmas trees and check valves operating under the action of hydrogen sulfide.     

Electrochemical characteristics of electric-arc aluminum coatings on AZ31 magnesium alloy

The possibilities of improvement of the corrosion resistance of AZ31 magnesium alloy by spraying AlSi5 electric-arc coatings with their subsequent melting by an Nd : YAG laser of quasicontinuous action are analyzed. The electrochemical characteristics of the surface layers in aqueous media are studied. It is shown that the AlSi5 electric-arc coatings significantly increase the corrosion resistance of the magnesium alloy. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 112–114, September–October, 2008.     

Influence of the structure on the regularities of cavitation wear of eutectic coatings

We analyze the influence of the structure and the main physicomechanical characteristics of eutectic coatings obtained using concentrated sources of energy on the mechanism and kinetics of their cavitation wear. We establish a correlation between the rate of cavitation wear, the size of the structural components, and the mechanical characteristics of the coating. Ukrainian National Technical University “Kiev Polytechnic Institute,” Kiev. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 34, No. 2, pp. 69–74, March–April, 1998.     

Nickel-based wear-resistant coatings by vacuum melting

In various coating processes nickel-based hard alloy powders are applied in either an atomized or a mechanically pulverized form. The coatings show good corrosion resistance, a high abrasion resistance and a relatively low melting point. Since boron is sparingly soluble in nickel, the boride Ni₃B forms a low melting eutectic at about 1000 °C with the nickel solid solution. Boron and silicon act simultaneously as deoxidizers and improve both the properties of the coating and the bonding to the substrate. Diffusion into the substrate occurs during the coating procedures.In this paper we discuss the behaviour of heterogeneous powder compounds with nickel hard alloys. For many applications mixtures with various carbides are used. During coating, reactions take place between the Ni-Cr matrix and the added carbides. These heterogeneous or quasi-alloys, which are used because of their abrasion resistance, are metastable.The abrasion resistance depends primarily on the phases as well as on their grain size, the grain size distribution and alterations to the matrix. When carbidic quasi-alloys are exposed to abrasion and corrosion at high temperatures, reactions of the existing phases during use cannot be completely excluded. Heat treatment causes changes in the structure and abrasion resistance of carbide-containing quasi-alloys.It is difficult to follow reactions which take place during coating either in the fused mass of quasi-alloys or in heterogeneous compounds. Because of their relatively low melting points nickel-based hard alloys can be coated by furnace melting. Hence carbide compounds with Ni-Cr-B-Si powder alloys are most suitable for research also. In these mechanical alloys segregation, of relevance to practical applications, can be studied as well as the formation of various phases during the coating or heat treatment processes.The behaviour of mixtures of Ni-Cr-B-Si powder alloy with different amounts of a number of carbides is reported. The structures of the resulting phases were studied and we tried to correlate these with the results of our abrasion tests.For tungsten carbide-nickel hard alloy mixtures the formation of the ? phase is influenced by the coating parameters and the matrix as well as by the diffusion of iron from the substrate into the coating.We also investigated mixtures of an Ni-Cr-B-Si matrix with TiC (Ti, W)C and NbC. The wear resistance against steel and SiC was measured. Various wear mechanisms and the properties of the carbide-matrix interface the wear results.     

Mixed manganese spinel oxides: optical properties in the infrared range

Spinel oxides in manganite family are studied in terms of optical properties in the infrared range (3–12 μm). The reflectivity is measured on sintered pellets. The complex refractive index is estimated by fitting hemispherical directional reflectance in both polarizations, perpendicular and parallel. The influence of different metallic cations (Ni, Co, Fe, Cu) is compared. In particular, in the case of manganese nickel copper oxides, the impact of variations in copper and nickel contents is evaluated. Cationic distribution is determined and correlated to the optical characteristics. These materials, usually used for NTC thermistor applications, are investigated for IR charges in coating.     

Structure and mechanical properties of gradient coatings deposited by PVD technology onto the X40CrMoV5-1 steel substrate

This paper presents the research results on the structure and mechanical properties of gradient coatings deposited by PVD methods on the X40CrMoV5-1 steel substrate. The tests were carried out on TiAlN, TiCN and AlSiCrN coatings. It was found that the structure of the PVD coatings consisted of fine crystallites, while their average size fitted within the range of 15–50 nm, depending on the coating type. The coatings demonstrated columnar structure as well as good adherence to the substrate, the latter not only being the effect of adhesion but also by the transition zone between the coating and the substrate, developed as a result of diffusion and high-energy ion action that caused mixing of the elements in the interface zone. The critical load L _C2 lies within the range of 46–59 N, depending on the coating type. The TiAlN coatings demonstrate the highest hardness and abrasive wear resistance. The good properties of the PVD gradient coatings make them suitable in various engineering and industrial applications.     

Analysis of the stressed state of bodies with multilayer thin coatings

We develop a procedure for the analysis of the stress-strain state of structural elements with thin multilayer coatings based on the simulation of these coatings by shells with the corresponding geometric and mechanical characteristics. In this approach, the influence of coatings on the mechanical state of the entire body-coating system is described by special generalized boundary conditions. The efficiency of the proposed approach is demonstrated by comparing the results obtained by using the developed approximate procedure with the exact solution of a Lamé test problem of loading of a solid cylinder with n-layer coating. Pidstrygach Institute of Applied Problem in Mechanics and Mathematics, National Academy of Sciences of Ukraine, Lvov, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 136–150, January–February 2000.     

Corrosion protection of ENIG surface finishing using electrochemical methods

Four types of thin film coating were carried out on copper for electronic materials by the electroless plating method at a pH range from 3 to 9. The coating performance was evaluated by electrochemical impedance spectroscopy and potentiodynamic polarization testing in a 3.5 wt.% NaCl solution. In addition, atomic force microscopy and X-ray diffraction were also used to analyze the coating surfaces. The electrochemical behavior of the coatings was improved using the electroless nickel plating solution of pH 5. The electroless nickel/immersion gold on the copper substrate exhibited high protective efficiency, charge transfer resistance and very low porosity, indicating an increase in corrosion resistance. Atomic force microscopy and X-ray diffraction analyses confirmed the surface uniformity and the formation of the crystalline-refined NiP {1 2 2} phase at pH 5.     

Production of conversion oxide-ceramic coatings on zirconium and titanium alloys

We consider the possibilities of surface hardening of zirconium and titanium alloys with conversion oxide-ceramic coatings. These coatings have been produced by the method of plasma-electrolytic treatment in alkaline solutions. We have established that the plasma temperature in discharge spark channels reaches (6–9) · 10³ K. The thickness of the coatings is 100 to 120 and 30 to 40 μm, and their microhardness is ∼ 800 and ∼ 1000 MPa for zirconium and titanium alloys, respectively. The functional properties of the coatings depend on the synthesis conditions, including the electrolyte composition, the cathode and anode current densities, and also the treatment time. We have evaluated the thickness, microhardness, and wear resistance of the coatings under conditions of dry friction and cavitation as well as their fatigue strength and corrosion resistance. We have established that this treatment provides a high wear and corrosion resistance of the alloys under study with insignificant decrease in their fatigue strength. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 42, No. 2, pp. 117–124, March–April, 2006.     

Influence of the inhibitor NEFGAN-1 on the corrosive and biological activity of soils

We established that the vital activity of sulfur-cycle bacteria (Thiobacillus) is the cause of intensive fracture of bituminous coatings at the Horodok-Yavoriv section of the main gas pipeline. The inhibitor NEFGAN-1 decreases the number of Thiobacillus thiooxidans, ferrooxidans, and thioparus bacteria by 60–70%, protects 20 steel against corrosion in aqueous extracts of soils by 90%, and increases the corrosion and biocidal resistance of the bituminous coating. This inhibitor as a component of the bituminous coating was experimentally and industrially tested at “L'vivtransgaz.” Karpenko Physicomechanical Institute, Ukrainian Academy of Sciences, L'viv; Ivano-Frankivs'k Technical University of Oil and Gas, Ivano-Frankivs'k. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 35. No. 6, pp. 85–87, November–December, 1999.