Efficiency of Two-Stage Ion-Plasma Process for Depositing Alloyed Diffusion Aluminide Coatings on High-Temperature Nickel Alloys

Diffusion ion-plasma coatings deposited by two-stage process in a MAP-1 installation with the use of three nickel alloys of the Ni – Cr – Al – Y system with additives of tantalum, tungsten, and rhenium, and two aluminum alloys with additives of nickel, yttrium, and silicon are considered. The structure and the chemical and phase compositions of coatings on high-temperature nickel alloys ZhS6U, ZhS26, and ZhS32 are studied depending on the thickness of the layers of the initial alloys. It is shown that the two-stage process of deposition of coatings considerably improves their service characteristics.     

Influence of Nickel Sulfate Additives to Electrolytes Subjected to Microarc Oxidation on the Structure,Composition, and Properties of Coatings Formed on Titanium

The influence of nickel sulfate additives to acid and basic electrolytes for microarc oxidation on the structure, composition, and properties of coatings formed on VT1-0 titanium were studied to produce poorly soluble titanium anodes. We established the possibility of incorporating nickel (nickel oxide) into the composition of coatings. X-ray diffraction analysis showed that the coatings contained nickel oxide β-NiO with a cubic lattice, TiO₂ in the form of rutile, and SiO₂ in the form of high-temperature β-cristobalite. The maximum thickness and nickel content in the surface layer and the minimum values of both the anodic dissolution currents and the electrical strength were obtained for the coatings formed in silicate-alkali (3 g/L KOH + 4.5 g/L Na₂SiO₃) electrolyte with the addition of 1 g/L of nickel sulfate NiSO₄.     

Diffusion saturation of nickel alloys with aluminum and chromium from the gas phase by the circulation method

Protective coatings on parts made of high-temperature nickel alloys increase substantially their service life and resistance to oxidation and corrosion in a high-temperature gas medium. A promising direction in this respect is the use of a gas circulation method for depositing protective coatings that envisages separated positioning of the saturated alloy and the saturating powder containing chromium, aluminum, cobalt, and other elements. Transfer of these elements to the surface of the saturated alloy occurs by means of forced circulation of the gas phase in the closed volume of the installation at a specified temperature. The present work is devoted to the problem of diffusion saturation of the surface of nickel alloys of the ZhS type with Cr and Al by the gas circulation method. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 21–25, October, 1998.     

Heat resistance of aluminide coatings on nickel obtained by mechanochemical heat treatment

Mechanochemical heat treatment (MCHT) is a new direction in the creation of protective coatings with a controlled micro- and macrostructure. The use of MCHT provides diffusion coatings with an anomalously large thickness and a structure that is most favorable for the operating conditions. Results of a study of high-temperature aluminide coatings on nickel deposited by an MCHT method are presented. Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 10, pp. 13–15, October, 1998.     

Orientation relations in aluminide coatings on single crystals of nickel superalloys

The crystallographic orientation of NiAl refractory coatings on the surface of single crystals of high-temperature nickel alloy ZhS32 is studied. The orientation relation between single-crystal substrates based on an fcc γ-phase and coatings based on a bcc β-phase is studied.     

Effect of ion-plasma coatings on characteristics of long-term strength of alloy ZhS6U

Results of a study of long-term strength of alloy ZhS6U after deposition of strengthening coatings from seven nickel alloys of the Ni-Co-W-Mo-Cr-Al (Ta, Re, Nb, Ti) system, chromium or titanium carbides, and of an additional external refractory SDP-2 coating of the Ni-Cr-Al-Y system common for all the compositions are presented. The structure and the element composition of the coatings in the initial state and after testing for high-temperature strength are studied. __________ Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 6, pp. 37–41, June, 2007.     

Boron and phosphorus saturation of nickel coatings on titanium alloys

The use of titanium alloys for parts that operate under contact friction conditions is possible if the alloy's tribological characteristics are substantially improved. This paper concerns the investigation of technological, high-temperature, diffusion saturation with boron and phosphorus coatings on titanium alloy surfaces by the chemical precipitation of nickel.Translated from Metallovedenie i Termicheskaya Obrabotka Metallov, No. 2, pp. 13 – 15, February, 1995.     

Dry sliding wear behaviour of nickel aluminides coatings produced by self-propagating high-temperature synthesis

Nickel aluminides coatings have been produced by self-propagating high-temperature synthesis using concentrated solar energy, with nickel composition of coatings ranging from 45 to 75 at.%. The dry sliding wear behaviour of coatings has been performed in a pin-on-disk tribometer. NiAl coatings (50 at.% Ni) have been tested against Al₂O₃ and WC–Co balls, while other coatings have been tested against Al₂O₃ balls. In all the coatings a three-body abrasion is produced by the particles detached from the coating surface and then oxidized, which remain between the ball and the coating. NiAl coatings exhibit the lowest wear coefficient while coatings with the highest Ni content have the highest wear coefficients. Wear coefficients show that NiAl coatings or coatings composed mainly of NiAl have a high wear resistance.     

High-temperature corrosion behaviors of typical nickel alloy coatings in a simulated boiler coal ash/gas environment in the Zhundong region

The high-temperature corrosion behaviors of five nickel alloy coatings used in coal-fired boilers in the Zhundong region (Xinjiang province) were investigated in simulated coal ash and coal-combusted flue gas environment at 650°C for 250 and 500 hr. The samples were analyzed by weight gain experiment, X-ray diffraction test, and scanning electron microscopy technique with energy-dispersive spectroscopy. The results indicated that the corrosion level is in the order of NiCrMo13 ≈ Hastelloy C-276 (276) > NiCrBSi > Inconel 718 (718) > 45CT. The compositions of the corrosion scale in five nickel alloy coatings mainly consist of NiO, Ni₃S₂, and Cr₂O₃. The enrichment of Cr in the corrosion scale in 45CT, 718, and NiCrBSi coatings inhibits the formation of oxide and sulfide on the coating surface. The presence of W and Mo in nickel alloy coatings accelerates the formation of corrosion products, thus weakening the corrosion resistance of NiCrMo13 and 276 in simulated coal ash and coal-combusted flue gas environment.     

Mathematical Simulation of Phase Formation and Growth in Nickel Aluminizing

A mathematical model is developed for simulating the formation and growth of phases in the diffusion of aluminum through the nickel matrix of high-temperature alloys. The kinetic laws of diffusion processes in multiphase coatings deposited from a gaseous phase by the method of circulation are determined. The suggested mathematical model is tested experimentally.     

Influence of Superficial Y2O3 Coatings on High-Tempera- ture Oxidation of Ni

在Ni基体上制备了Y2O3涂层, 并对其如何影响Ni在900 ℃的氧化性能进行了研究。作为对比,采用相同的工艺在Ni基体上制备了CeO2涂层。900 ℃下恒温氧化表明： Y2O3或CeO2对Ni的氧化机理没有影响;但与CeO2相比,Y2O3在降低Ni的氧化速度上有更强的作用。此外Y2O3和CeO2涂层的厚度也对Ni的氧化影响不明显。对Y2O3或CeO2如何影响Ni的氧化性能进行了分析     

含纳米Ni粉高温陶瓷涂层/GH202合金界面反应的研究

涂层失效一般是由涂层与基底界面的显微组织演变引起的,对高温下含纳米Ni粉的陶瓷涂层与合金组织的演变进行了研究,结果表明:陶瓷涂层/合金试样在900℃下进行真空扩散退火后,合金基底内在靠近界面的附近依次出现了Al2O3的晶间氧化物和针状TiN氮化物析出层;在长时间扩散过程中,纳米镍粉逐渐聚集长大,与合金基底在界面处融为一体,形成涂层与基体的咬合,使涂层与基体的结合趋向于冶金结合,具有抑制涂层失效的作用。     

Investigation of high-performance acid zinc nickel electrolyte

Zinc nickel alloy coatings are increasingly demanded by the automotive industry due to their highly improved corrosion protection over pure zinc and other zinc alloy coatings. To produce zinc nickel coatings with a nickel incorporation of 12 to 16%, mainly alkaline zinc nickel electrolytes are used in the plating industry. Continuous improvements in the field of acidic zinc nickel alloy electrolytes now meet the needs of the automotive industry while being advantageous in specific fields of application.In this paper, zinc nickel coatings deposited from alkaline as well as from ammonium-free acid zinc nickel electrolytes are investigated. The morphology is evaluated by scanning electron microscopy; the texture is investigated by focused ion beam, and X-ray diffraction patterns identify the structure of the coating. The corrosion protection of the zinc nickel coatings and the adhesion of the zinc nickel coatings have been bench-marked. For applications on fasteners, the coefficients of friction have been measured and compared.     

High-Temperature Oxidation of Nickel-Based Cermet Coatings Containing WC and Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanosized Particles

This paper investigates the high-temperature oxidation of cermet coatings composed of two types of nanosized particles (WC and a mixture of WC and Al₂O₃) incorporated in nickel and produced by co-electrodeposition. For this purpose, high-temperature oxidation tests were conducted at three temperatures (500, 600, and 700 °C) in dry air with 6 time intervals up to 96 h and mass changes at each specific time interval was measured. Statistical techniques were used to calculate the oxidation rate constants (k) and growth-rate time constants (a) for all coatings. The confidence intervals associated with tests were also calculated. The results showed linear to sub-parabolic oxidation rates for coatings composed of only WC particles and sub-liner to liner oxidation rates for coating with both WC and Al₂O₃ particles. The reduction in oxidation rates for coatings with both WC and Al₂O₃ particles were correlated to the addition of Al₂O₃ particles in the matrix.     

Effect of α-Al2O3 coatings on the interface of Ni/SiC composites prepared by electrodeposition

This paper describes an investigation on the effect of α-Al₂O₃ coating on the interface between nickel and SiC particle. Uniform, dense and well-adhered α-Al₂O₃ coatings were obtained on the surface of SiC particles by sol–gel technology. The nickel-based composites reinforced with α-Al₂O₃-coated SiC particles (CS_p) or uncoated SiC particles (UCS_p) prepared by composite electrodeposition were heated at 600 °C to study the reactivity and the resulting interfaces. The results showed that the Ni/CS_p composites presented excellent thermal stability without interfacial reaction, while nickel silicide formed in the Ni/UCS_p composites. It indicated that high-temperature interfacial reaction between SiC particles and nickel matrix was efficiently inhibited by the α-Al₂O₃ coatings. Moreover, great differences of the local mechanical properties of interfaces were observed by the nanoindentation characterization.     

Molten carbonate-induced hot corrosion of nickel

The accelerated oxidation of pure nickel in the presence of a molten carbonate mixture has been studied in O₂ and CO₂-containing atmospheres. The oxidation rate of nickel with carbonate coatings was at least four orders of magnitude faster than that without salt coatings. The extent of oxidation, in terms of unit area weight gain, depended on both the amount of carbonate mixture coatings and the gas atmosphere. The unit area weight gain due to oxidation increased with increasing amounts of salt coatings up to a certain value. These observations suggest that the termination of nickel oxidation results from the exhaustion of either the salt coatings or metallic nickel. Porous and particulate oxide products were observed from scanning electron microscopic (SEM) examinations. The energy-dispersive analysis of x-rays (EDAX) shows that no salt remains on the specimen surface after the oxidation experiment.     

Prevention of nickel release from electroplated articles in the context of allergic contact dermatitis: further outcomes

‘Nickel Allergy’ sometimes occurs when nickel-containing articles are in direct and prolonged contact with the skin, leading to corrosion of elemental nickel by sweat, liberating sufficient nickel ions to be absorbed through the skin and initiate an allergenic effect. EU ‘Nickel Restrictions’ impose limits on the amount of nickel released from articles intended for use in this application but permits a non-nickel surface coating that can ensure the rate of nickel release does not exceed 0.5?μg?cm^?2?week^?1 after 2 years of normal use. The official tests for coated items are simulated wear and corrosion under EN 12472 followed by determination of nickel release under EN 1811, and articles shall not be placed on the market unless they pass these tests. A paper published in Transactions during 2015 reported bright nickel coatings with top coats that would prevent nickel release and pass these tests. Regular chromium deposited from a hexavalent electrolyte was the benchmark, with microporous chromium and supplementary organic coatings evaluated for improved performance. All prevented nickel release, but the best low-cost commercial coating was regular (conventional) chromium deposited from a hexavalent electrolyte. Further tests reported here were conducted to evaluate bright nickel deposits with top coats of tin–cobalt alloy, and of hexavalent chromium with supplementary coatings of coloured physical vapour deposition and electrophoretic coatings. Tests with trivalent chromium top coats deposited from proprietary chloride and sulphate electrolytes showed that regular (conventional) chromium over bright nickel failed the nickel release test. But microporous trivalent chromium deposits passed the tests satisfactorily.     

Electrodeposition and Corrosion Resistance of Ni-Graphene Composite Coatings

The research on the graphene application for the electrodeposition of nickel composite coatings was conducted. The study assessed an important role of graphene in an increased corrosion resistance of these coatings. Watts-type nickel plating bath with low concentration of nickel ions, organic addition agents, and graphene as dispersed particles were used for deposition of the composite coatings nickel-graphene. The results of investigations of composite coatings nickel-graphene deposited from the bath containing 0.33, 0.5, and 1 g/dm³ graphene and one surface-active substance were shown. The contents of particles in coatings, the surface morphology, the cross-sectional structures of the coated samples, and their thickness and the internal stresses were studied. Voltammetric method was used for examination of the corrosion resistance of samples of composite coatings in 0.5 M NaCl. The obtained results suggest that the content of incorporated graphene particles increases with an increasing amount of graphene in plating bath. The application of organic compounds was advantageous because it caused compressive stresses in the deposited coatings. All of the nickel-graphene composite layers had better corrosion resistance than the nickel coating.     

Oxidation Mechanisms of Copper and Nickel Coated Carbon Fibers

Differential-Thermal Analysis (DTA) and X-ray diffraction analysis were applied to determine the mechanisms of high-temperature oxidation of copper- and nickel-coated carbon fibers. Both kinds of coatings were deposited by electroless plating onto the fiber surface. The as-deposited copper film was crystalline, whereas the nickel coating consisted of an amorphous Ni–P alloy. Coated fibers were heated from room temperature to 900 °C in air at 10 °C min^?1. For the copper coating, the main oxidation product formed at low temperatures was Cu₂O, while at higher temperatures was CuO. The crystallization of Ni–P took place at 280–360 °C with the formation of Ni and Ni₃P. The final compounds were NiO, Ni₂P and Ni₃(PO₄)₂. After complete oxidation of the carbon fibers, copper and nickel-oxidized microtubes were obtained. Besides, while copper reduced the temperature of the fiber oxidation, nickel coatings increased the minimum temperature needed for this reaction.     

Microbially influenced corrosion and inhibition of nickel–zinc and nickel–copper coatings by Pseudomonas aeruginosa

The present study describes the effect of Pseudomonas aeruginosa on the corrosion rate of nickel–zinc and nickel–copper alloy coatings. The presence of bacteria was associated with decreases in R_ct values, suggesting that P. aeruginosa promoted the corrosion of nickel–copper alloy coatings. However, R_ct values of nickel–zinc coatings increased in response to bacterial inoculation, corresponding to a decrease in corrosion rate for nickel–zinc alloy coatings. Our results suggest that the activity of P. aeruginosa facilitated the corrosion of nickel–copper alloy, while serving a protective function for the nickel–zinc alloy.