Nickel-chromium Coatings Research Articles

Characterisation of nicr flame and plasma sprayed coatings for use in high temperature regions of boilers

Nickel–chromium coatings have been plasma sprayed onto a stainless steel surface in order to protect it from the high temperature and erosive conditions encountered in power plant boilers. Microstructure, porosity, and microhardness of the coatings have been studied. High temperature oxidation behaviour was studied in an atmosphere similar to service conditions used in power plant, and thermal fatigue tests were performed in an experimental combustion chamber. Finally, adhesion between the steel substrate and NiCr coating was evaluated by means of tensile tests. The results obtained are discussed with particular reference to the evolution of microstructure owing to thermal effects and coating deposition method.

Laser Processing of High-Chromium Nickel-Chromium Coatings Deposited by Various Thermal Spraying Methods

Abstract High-chromium (Cr) nickel (Ni)-Cr coatings were deposited by thermal spraying in air and in an argon (Ar) gas atmosphere. Coatings sprayed in Ar gas were free of pores and defects and of t...

Diffusion processes during plasma spraying of nickel-chromium coatings on powder steels

Diffusion processes during plasma spraying of nickel-chromium coatings on powder steels

Friction and wear of chromium and nickel coatings

Conventional chromium plating has a considerably higher wear resistance than electroless nickel, heat-treated electroless nickel, electroplated nickel, heat-treated chromium and crack-free chromium coatings in all tests, even though it does not have the highest hardness. The ranking order of the other coatings depends upon the dominant material removal mechanism and can change from test to test. Transitions between severe and mild wear occur in electroless nickel and chromium owing to changes in phase, brittleness and scratch indentation size effects. Heat treatment effects the transition by crystallizing the amorphous electroless nickel, variation of the electroplating conditions alters the crystal structure of chromium and reduction of the scratch size changes the dominant material removal mechanism from fracture to plastic deformation. The relative merits of each coating and the role of laboratory data in coatings selection and design are discussed.

Microstructural study of plasma-sprayed alumina and nickel chromium coatings

The microstructure of arc-plasma-sprayed alumina and nickel chromium is analysed by use of different methods. X-ray analysis provides the phase composition of the coatings. A quantitative metallurgical analysis carried out with the aid of an automatized image analyser is used to determine porosity and pore distributions as well as the content of non-melted grains within the sprayed alumina coatings. This method permits the estimation of the influence of the kind of powder used for spraying and the distance between the plasma torch and the substrate on the coating microstructure. Some details of metallurgical analysis are also discussed and the coating characteristics are complemented by density measurements.

The Corrosion Resistance of Nickel-Chromium and Copper- Nickel-Chromium Coatings on Mild Steel Substrates

SummaryAtmospheric corrosion tests have been carried out in Birmingham over a period of up to four years on mild steel panels electroplated with various nickel-chromium and copper-nickel-chromium coating systems. The performance of the following systems was investigated: (1) single layer bright nickel with microcracked and microporous chromium topcoats both with and without copper undercoats; (2) double layer nickel with microcracked and microporous chromium topcoats both with and without copper undercoats; (3) double layer nickel with conventional chromium both with and without copper undercoats. Panels with various thicknesses of single layer bright nickel and double layer nickel were included in the trials and two thicknesses of copper undercoat were investigated. The results show that the substitution of a copper undercoat for part of the nickel coating thickness does not have a beneficial effect upon the corrosion resistance of the coating system and may, particularly under thinner nickel coatings, h...

鋼素地上の銅-ニッケル-クロムメッキと二重ニッケル-クロムメッキの腐食試験結果

Superior corrosion resistivity of nickel-chromium coating can be presumed to some extent from the electrochemical investigation previously reported.A series of corrosion tests, including outdoor exposure at seaside, was carried out to study the performance of copper-nickel-chromium and double nickel-chromium plated steel test pannels.As a result, the following conclusions were obtained:(1) In the salt spray and sulfur dioxide test, any superiority of the double nickel-chromium coatings to the copper-nickel-chromium coating was not observed.(2) In the Korrodkote and CASS test, the performance of the former was excellent, regardless of the thickness. On the other hand, the latter was rapidly deteriorated.(3) In the outdoor exposure at seaside, the former with total thickness of 30μ was excellent, but the former with total thickness of 20μ was often inferior to the latter with total thickness of 40μ.(4) As the proportion of semibright nickel in a double nickel coating is increased, its durability in the outdoor exposure increases. Contrary to this, quite reversed phenomenon was observed in the Korrodkote and CASS tests.

銅-ニッケル-クロムおよび二重ニッケル-クロムメッキの局部電池作用について (その1)

銅-ニッケル-クロムおよび二重ニッケル-クロムメッキの局部電池作用について (その1)

鉄素地上のNi-CrメッキとCu-Ni-Crメッキの耐食性の比較

Relative durability of decorative copper-nickel-chromium versus nickel-chromium coatings was investigated by means of accelerated corrosion tests.In this series of experiments bright plating baths, widely used in the present Japan, were adopted to prepare corrosion test panels.5% neutral salt spray test and acetic acid salt spray test were used to determine the relative durability of coatings of different thickness and composition, from the standpoint of both pinhole-rusting and pitting corrosion.As a result, it is concluded that the copper-nickel-chromium is more corrosion resistant than the nickel-chromium of the same total thickness.Other details of discussion will follow in this paper.

The Nickel and Chromium Plating of Tinplate

SynopsisTinplate, as a base for chromium plated sheet required for fabrication, offers the advantage over steel of being easily polished, but difficulties have arisen, especially with coke grades of tinplate, in obtaining nickel deposits sufficiently adherent to withstand chromium plating and fabrication without flaking.These difficulties are attributed to two effects:—(1) the mechanical effect during straining of variations in thickness of the tin coating, (2) the effects of hydrogen produced during plating, particularly the disruptive effect produced by the conversion of atomic hydrogen (diffusing through the nickel) into gas at the site of discontinuities (foreign particles, fissures, etc.) at the interface—nickel/tin.The diffusion of hydrogen to the tin surface can be prevented by depositing a film of copper before nickel plating. Tinplate which has been coated with a composite deposit of copper, nickel and chromium can be fabricated without flaking of the deposit. If the deposit is brittle, however, it is liable to crack on deformation, giving an unsightly appearance. Certain nickel deposits may be seriously embrittled by chromium plating.The porosity of composite deposits of copper, nickel and chromium on tinplate is considerably lower than on steel of average quality, but their protective value may be destroyed at bends formed during fabrication especially with coke grades of tinplate. Tinplate of charcoal quality offers the advantages of superior finish, better adhesion of the deposit and a lower tendency for the protective value of the coating to be destroyed on deformation.Tinplate may also be satisfactorily plated with chromium alone. The plated sheet can be pressed without flaking of the coating, the protective value of which is less readily reduced by deformation than that of the composite nickel-chromium coatings, but it is more difficult to obtain a good finish in the absence of a nickel undercoating.