Electroless Coatings Research Articles

Study of corrosion and friction reduction of electroless Ni–P coating with molybdenum disulfide nanoparticles

One composite coating of Ni–P alloys containing MoS2 nanoparticles was prepared by electroless technique based on the better friction reduction ability of MoS2 and better anticorrosion property of electroless Ni–P alloys on carbon steel surfaces. Electrochemical method—that is, using Tafel polarization curves—was carried out in order to study the corrosion performance of the coating. The results indicate that the anticorrosion ability of the composite coating was decreased because of the addition of nano-MoS2 particles. The corrosional surfaces were studied and analyzed through scanning electron microscopy (SEM). The corrosion mechanism of the composite coatings was mainly ascribed to the formation of microcells around the nanosized MoS2 particles, and the active ion-like Cl− destroyed the surface film and induced the corrosion on the inside part of the coating. The friction coefficient of electroless composite coatings was measured by end-facing tribometer. It was found that the friction coefficient of the Ni–P–(nano-MoS2) composite coating decreased greatly compared with those of Ni–P electroless coatings.

Influence of electroless coatings of Cu, Ni–P and Co–P on MmNi 3.25Al 0.35Mn 0.25Co 0.66 alloy used as anodes in Ni–MH batteries

Electroless coatings of Ni–P, Co–P and Cu were applied on the surface of non-stoichiometric MmNi 3.25Al 0.35Mn 0.25Co 0.66 (Mm: misch metal) metal hydride alloy. Elemental analysis was made with Energy Dispersive X-ray Analysis (EDAX). The structural analysis of bare and coated alloys was done by X-ray diffraction (XRD) whereas surface morphology was examined with scanning electron microscope (SEM) and transmission electron microscope (TEM). The electrode characteristics inclusive of electrochemical capacity and cycle life were studied at C/5 rate. Superior performance is obtained with copper coated alloy. Microstructure observations indicate that the observed excellent performance could be attributed to uniform and efficient surface coverage with copper. Also, lanthanum surface enrichment in samples during Cu coating leads to improvement in performance. It is inferred from electro analytical investigations that copper coatings act as microcurrent collectors with alterations in hydrogen transport mechanism and facilitate charge transfer reaction on the alloy surface without altering battery properties. Moreover, supportive first time TEM evidence of existence of such copper nano current collectors (about 8 nm in diameter and length about 20 nm) is reported.

Wear and Friction Testing of Hard and Soft Lubricious Coatings in Dry Sliding for Use in Small Arms Action Components

Abstract Use of liquid lubricants in dry and dusty environments can lead to malfunction or jamming of small arms weapon actions. To eliminate the need for liquid lubricants, dry or “lubricious” coatings are desired for various key interfaces of such components. The tribological performance of a variety of coatings was assessed under unlubricated sliding conditions to simulate a pin-in-slot component geometry. Coating screening tests were run using a cylinder-on-flat geometry and self-mated coated couples. Tests were run in both reciprocating and unidirectional modes, with sliding velocities up to 3.6 m/s, at room temperature and 150°C. Progressive wear of the coating was monitored using a replicating technique and the measured width of the wear scar on the cylindrical pin, from which the wear coefficient was determined. Failure of the coating was determined not by visual wear-through of the coating, which can be misleading, but by an increase in the coefficient of friction (COF) and/or the occurrence of galling. In the high speed unidirectional tests, friction could be measured directly. However, in the reciprocating tests, test rig design limited the speed at which the COF could be determined. An improved rig design resulted from this work. The screening tests ranked the tribological performance of the coatings using the coefficient of friction, the wear coefficient, and number of cycles to coating failure. The coating types assessed covered a broad range of hardness, composition, and deposition methods. Coating types investigated included hard vapor-deposited TiCN coatings, relatively soft organic PTFE-filled resin-bonded coatings, modified anodized coatings (for aluminum), electroless nickel alloy coatings, PTFE-filled electroless nickel coatings, phosphate pre-treatment combined with dry-film burnished MoS2, and a ferritic nitro-carburizing treatment. Substrates included medium carbon steel, D2 tool steel, and 6061-T6 aluminum.

Effect of surfactants on the surface roughness, hardness and microstructure of electroless (Ni-P) coatings

The effect of surfactants on the surface roughness, hardness and microstructure of electroless nickel-phosphorus (ENi-P) coating obtained from an alkaline bath is presented in this paper. In this study the influence of surfactants such as Sodium Dodecyl Sulfate (SDS) and Cetyl Trimethyl Ammonium Bromide (CTAB) on the electroless Ni-P coated samples has been investigated. The variation on surface morphology was examined using Scanning Electron Microscope (HRSEM), surface roughness were measured using a stylus instrument and surface hardness were measured using a hardness tester. It was observed that the surface roughness, surface hardness and surface morphology of ENi-P coating were clearly influenced by the surfactants.

The corrosion resistance of electroless deposited nano-crystalline Ni–P alloys

Coatings of Ni–P alloys are increasingly used for their shiny appearance, the high degree of hardness and very good corrosion resistance. Electroless coatings are preferred in industry compared to the electroplated ones because they adhere well to different materials and form a homogeneous coating even on complicated geometries. Electroless Ni–P alloys produced as a coating on technical iron in a commercial autocatalytic hypophosphite-type plating bath were studied, with regard to their corrosion behaviour upon immersion in near neutral sulphate and chloride electrolytes. The anodic polarization curves of the alloys showed a current plateau at potentials E < +0.2 V SCE confirming their high corrosion resistance. The dynamic cathodic polarization curves in deaerated solutions showed a Tafel behaviour with a slope of ca. −0.4 V, indicating inhibition of oxygen reduction on “as received” and on mechanically polished surfaces. Corrosion rates of ca. 0.5–0.7 μA/cm 2 were found during prolonged immersion in near neutral solutions open to air. Potentiostatic polarization at selected potentials in the range of the current plateau (−0.1 V SCE, +0.1 V SCE) showed a steady decrease of the current density following a power law with exponent −0.5, thus a diffusion controlled process. These results show that the suppression of the anodic dissolution and the low corrosion rates of Ni–P alloys cannot be associated with the oxide-film passivity. Despite this fact, black spots identified as localized corrosion appeared on mechanically polished and “as plated” electroless Ni–P deposits after prolonged potentiostatic polarization at potentials in the range of dissolution suppression.

Wear behavior of Ni–P and Ni–P–Al 2O 3 electroless coatings

In this research, hardness and wear resistance of two types of electroless coating have been investigated including Ni–P and Ni–P–Al 2O 3 coatings. These coatings were applied on AISI 1045 steel discs by electroless deposition process and then they were heat treated at 200, 400 and 600 °C for 1 h. Wear resistance of deposits was measured by the pin on disc method and wear surfaces and debris were studied by scanning electron microscopy (SEM). Also, microstructural changes were evaluated by X-ray diffraction (XRD) analysis. The results showed that the existence of alumina particles in Ni–P coating matrix led to an increase in the hardness and wear resistance of the deposits. It was also found that heat treated coatings at about 400 °C have the maximum hardness and wear resistance.

Effect of multi-walled carbon nanotubes as reinforced fibres on tribological behaviour of Ni–P electroless coatings

After multi-walled carbon nanotubes (MWNTs) were modified and dispersed uniformly in electrolyte, the MWNTs composite coatings were prepared by electroless deposition. Hardness tests were carried out using a Vickers Hardness indenter. The friction and wear behavior of the Ni–P–MWNTs composite coatings in carbon-steel rings were investigated by using a ring-on-plate wear tester at pure liquid paraffin. Moreover, the friction and wear behavior of nine kinds of wear combinations, which were composed of plates and rings of different composite coatings, were studied. The experimental results indicated that addition of MWNTs would result in an increase in microhardness and an improvement of tribological properties of the Ni–P composite coating significantly. The Ni–P–MWNTs composite coatings revealed lower wear rate and friction coefficient compared with Si–C composite coatings. Moreover, the wear combination, which composed of the Ni–P–MWNTs composite coatings, showed a more excellent ability of friction-reduction and wear resistance than other combinations, and their friction coefficient and wear rate were 0.1087 and 1.49 × 10 − 6 kg/m, respectively.

Studies on Electroless Coatings

Since the introduction of Electroless (EL) coating in 1946 by Brenner and Riddle, the process has been the subject of steady growth. It is one of the most elegant methods available for the production of protective coatings on surface. The technique involves the autocatalytic reduction, at the substrate/solution interface, of cations released from suitable chemical reducing agents with in the EL bath. EL coating technique is simple one, as can be manifested just by controlling pH and temperature of the coating bath. Such coatings are reported to provide excellent physical and mechanical properties. The nickel, silver and copper based alloy and composite EL coatings are being studied at Indian Institute of Technology Roorkee since 1985 and this paper deals with the gist of the same. The structural behavior of Ni-P coatings for different phosphorus contents has been extensively studied. Transmission electron microscopy (TEM) and magnetic movement studies have been used as tools for structural and kinetic studies, respectively. Submicron size coating islands and their transformations have been deduced. The metallography studies using hot stage within TEM to follow the phase transformations occurring at various temperatures have been studied for Ni-B, EL coatings. As a forward step towards composite coatings, Ni-P-C, Ni-P-Al2O3, Ni-P-ZrO2 etc. have been developed by co-deposition techniques. Ag-graphite composite coatings produced by EL technique exhibits ~5 times higher wear resistance and ~ 2 times better corrosion resistance apart from being a good electrical conductor. The tribological behavior of EL Ni-P-X and Ni-P coatings on steel and aluminium substrates in different conditions i.e., as-coated, heat treated at various temperatures at different extents of time with different normal loads, have been studied in terms of dry sliding friction and wear against counter face of case hardened steel. In Ni-P-X nanocoatings (X= ZrO2-Al2O3-Al3Zr), X has been produced in-situ and are composed of nano-sized particles. Such coating could be produced uniformly on carbon fibre of 7µ diameter. Ni-P and Cu are also coated successfully on graphite/ oxide powders of ~ 120µ sizes. Micro-thickness coatings are paving ways to nanocoatings. These are the coatings in which either the thickness of the coating is in nano level or the second phase, that dispersed in the coating matrix is of nano-size. Ni-P-Ferrite nano coatings with thickness less than ~0.1mm thick, is found to exhibit about 20db of absorption of microwave in the rage of 12-18 GHz which can be exploited for radar applications. Here the nano-sized ferrite particles are co-deposited along with the Ni-P EL coatings.

Electroless Nickel Plating of Atomised and Sponge Iron Compacts

Electroless coatings are obtained by means of an autocatalytic chemical reduction process for depositing different metals. Electroless nickel plating is an engineering coating, normally used for its excellent corrosion and wear resistance. Little information exists about the application of this type of coating on powder metallurgy products, compared with the large amount of data available on coatings on wrought metal products by means of the same technique. The present paper discusses the effect of the different grades (20, 15, 10, 7 and 5%) and types (irregular and regular) of porosity of iron powder metallurgy compacts, on the properties of the electroless nickel coating: thickness, composition, deposition rate, microhardness, porosity, adhesion and corrosion resistance. Sponge and atomised iron compacts with different porosities were obtained by pressing at different densities (5.5 - 7.0 g cm-3) and sintering at 1120 ° C in an N2 - H2 atmosphere. The sintered parts were successfully coated by electroless nickel deposition using a hypophosphite bath with the same composition and conditions for all the compacts, and the coating was subsequently characterised. The ferroxyl test was used to evaluate the grade of superficial porosity, and the salt spray test helped to obtain the corrosion resistance of the nickel - phosphorus deposits on the PM compacts. Electron and optic microscopy techniques were used to analyse the coating thickness quantitatively. Also, measurements were performed to determine the microhardness achieved in the coatings. Results show that, for both types of powder, levels of porosity > 12% cause coatings with deficient properties: low corrosion resistance, high levels of porosity, dispersion in microhardness and low thickness. However, the coatings obtained in the pieces made with the atomised powder have better characteristics than those elaborated with iron sponge powder.

Electroless preparation and tribological properties of Ni-P-Carbon nanotube composite coatings under lubricated condition

Ni-P-Carbon nanotube (CNT) composite coatings as well as Ni-P-SiC and Ni-P-graphite coatings were prepared by electroless plating. The tribological properties of these composite coatings were investigated using a ring-on-block test rig under lubricated condition. The Ni-P-CNT composite coatings exhibited not only high wear resistance but also low friction coefficient compared with the Ni-P-SiC and Ni-P-graphite composite coatings. The favorable effects of CNTs on the tribological properties of the electroless coatings are attributed to improved mechanical properties and unique topological structure of the hollow nanotubes. In addition to preventing the rough contact between the two mating metal surfaces, the shorter CNTs can easily slide or roll within the surfaces of friction pairs. Therefore, the wear rate and friction coefficient of Ni-P-CNT composite coatings can be substantially reduced.

Characterization of carbon fabric coated with Ni-P and Ni-P-ZrO2-Al2O3 by electroless technique

Ni-P and Ni-P-ZrO2-Al2O3 (Ni-P-X) composite coatings on carbon fiber woven fabric have been attempted by electroless (EL) coating technique. For producing Ni-P EL coating, a sodium hypophosphite is used as reducing agent in alkaline bath whereas for producing composite coating, in the same bath, the co-precipitation of Al2O3 along with ZrO2 by a chemical reaction has been used. The bath used was maintained at pH value of 9 ± 0.25 and a temperature of 90 ± 2°C for all the coatings under investigation. The morphology of coatings has been studied under SEM and the phases have been identified by XRD and TEM. The phases like microcrystalline nickel, amorphous nickel, Ni5P4 and Ni12P5 have been identified to be present. The grain size of these phases has been seen to be in the range of 5–10 nm. The tensile strength of as-coated and heat treated samples of both the types of coatings have been compared with that of uncoated fabric. The UTS values of uncoated carbon fabric used has been found to 3.7 N/mm2 whereas that for heat treated after coating the fabric samples with Ni-P and Ni-P-ZrO2-Al2O3 EL coatings have been observed to be 11.1 and 12.4 N/mm2 respectively.

Optimization of the Preplating Processes in the Fabrication of Electrolessly Tin-Coated Copper Tube

Despite the recent extensive examination of electroless coatings, the effect of the preplating processes on the formation of electroless coatings has remained unresolved. The ability of different preplating processes, degreasing and pickling, to clean the contaminated copper surface before deposition was studied by contact angle determinations, residual oil measurements, and potentiostatic polarization cycles. The influence of preplating processes on the buildup of electroless tin coatings and subsequent deposit structure was studied by scanning electron microscopy. Alkaline degreasers were found to effectively eliminate the organic soil from the surface, thus facilitating uniform coating nucleation and good adhesion properties. Pickling gave rise to a regular coating appearance throughout the structure. In addition, the applicability of contact angle measurements for studying the efficiency of cleaning treatments was demonstrated.

The Scraping Test and Adhesion Measurements of Diamond and Nickel Electroless Coatings

The scraping method, and a tester using the scraping method, have been introduced and applied to evaluate the effects of deposition processes and surface treatments on the adhesion of nickel electroless coatings and diamond coatings. An energy description for the adhesion based upon the scraping test and an elastic-plastic crack propagation mode for the separation of the coating/substrate have also been introduced to illustrate the energy characteristic of the adhesion and the elastic-plastic fracture mechanics foundation of the scraping test. We have also discussed the influence of coating thickness on adhesion for NiP coatings deposited on carbon tool steel substrates, and suggested the scraping energy as the description for the adhesion strength obtained from the scraping test. It was found that the adhesion of the NiP/steel substrate reduced with the increase of the thickness of the NiP coatings until the adhesion limit reached the critical coating thickness. It was also found that the adhesion of diamond coatings was greatly affected by the temperature of the hot filament, the treatments of the substrate surface, and the composition of the etching solutions.

Corrosion and hydrogen penetration properties of electro- and electroless depositions

Abstract Experiments were carried out to produce electroplated and electroless depositions of various metals and alloy coatings. These coatings were then tested for corrosion protection performance by weight loss measurements after immersion in acid and salt solutions representing accelerated corrosion conditions. Hydrogen penetration resistance was studied by electrolytically introducing hydrogen into the samples and measuring the quantity of the penetrated gas. The results are compared with those for steel substrates to evaluate the coating performance. Performance after heat treatment was also investigated. Chemical analysis and microstructural characterisation were carried out using the scanning electron microscope and electron microprobe. Among different electroplating coatings investigated, zinc–nickel was found to give the best all round corrosion protection. Electroless coatings, however, offer much better resistance against hydrogen penetration.

Electrolytic and electroless coatings of Ni–PTFE composites

Abstract This work consists of the realization and characterization of composite coatings of Ni–PTFE carried out by electroless deposition on the one hand and electrolytic deposition on the other hand, obtained by pulsed current (CPS) and d.c. current (DC). The evolution of some properties of these coatings generated by various procedures, properties such as morphology, hardness, ductility and wear resistance, are highlighted.

The Spreading Kinetics of Ag–28Cu(L) on Nickel(S): Part II. Area of Spread on Surfaces Plated with Electrolytic Ni

Furnace brazing is commonly used in the electronic industry to attach I/O pins, lid-seal rings, and heat spreaders to cofired multilayer ceramic packages. Despite the widespread industry usage of electrolytic and electroless Ni coatings to render base metal surfaces wettable by braze fillers, there is no fundamental treatment of “brazeability” in the published literature that can be used by the materials technologist to design coatings for a given application. In this study, dynamic hot stage microscopy is used to establish the parameters that control the spreading of eutectic Ag–Cu braze on surfaces plated with electrolytic Ni. The effects of plating thickness, substrate type, plating annealing, and the braze thermal cycle are considered. A braze spreading mechanism developed for polycrystalline Ni foil in Part I of this study is linked to Ni-plated surfaces through consideration of differences in microstructure. Eventual extension of this improved understanding to surfaces plated with electroless Ni–B and Ni–P deposits will result in shortened product design time and improved manufacturing process control.

Magnetic moment studies on nickel coated titanium powders

Titanium aluminide intermetallics are gaining greater importance due to their low density, high melting temperature, good high temperature properties and oxidation resistance. Their brittle behaviour at low temperatures has resulted in several investigations aimed at improving their ductility. This can be improved either by suitably alloying or by microstructure control [1–5] and in some cases by both. In general, microstructural refinements developed through processing lead to improvements in both strength and ductility [6]. Thus, processing techniques that increase the range of attainable microstructures are fundamental to the development of new engineered materials. These alloys cannot be produced by the traditional metallurgical processes, because of the restricted range of the atomic percentage of the alloying elements. Conventional powder metallurgical (P=M) techniques can be used for preparing these alloys, with an additional step involving coating on the elemental powders. There are several coating methods available like vapour phase deposition techniques, spray deposition, electroplating, and electroless coating. Each of these has its advantages and disadvantages. Vapour phase deposition methods can be used for coating towbased fibres such as carbon fibres [7]. Electroplating methods can also be used for carbon fibres, for which the substrate should be a conducting material. Coating a powder with a particular element is easier by the electroless coating method because it gives a uniform coating on the substrate. The electroless plating process is an intermediate step in the fabrication of ceramic–metal and metal– metal composites, because it gives a uniform adherent metal coating on substrates. Electroless nickel can be applied to metallic surfaces as well as non-metallic materials to provide a coating of uniform thickness with excellent chemical and physical properties [8]. The production of the titanium aluminide intermetallic alloy from mixtures of the elemental powders may not produce a chemically homogeneous product under normal P=M processes. With pre-alloyed powders, the problem of heterogeneity can be largely eliminated, but it is not cost-effective. Electroless coatings on metal powders enable the coated powder to exhibit a high level of homogeneity during P=M preparation. The aim of this work was to investigate the feasibility of obtaining a satisfactory electroless nickel coating on Ti elemental powders and to analyse this coating with the help of magnetic properties. Measurement of magnetic moment is a novel idea to confirm the presence of nickel on the titanium elemental powders. The presence of nickel coating on titanium powders was further confirmed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) studies. Elemental powders of commercially pure titanium (,75 im) were used for the coating of nickel. The composition of the chemical deposition bath used for the coating of nickel on titanium powder is given in Table I. The proportion of elemental powders added to the coating bath was 70 g to 1 l. A pH of 8–9 was maintained by adding ammonia solution to the bath. With slow stirring, using a magnetic stirrer, all of the particles were allowed to come into contact with the solution. A temperature of 88 8C was maintained throughout the experiment. The coating time was varied (20, 30 and 40 min.) to increase the amount of nickel coated on the elemental powders. The coated powders were rinsed in distilled water, filtered out and dried under infrared (IR) light. Chemical analysis for the presence of nickel was done using dimethyl glyoxime dissolved in methanol. A purple precipitate confirmed the presence of nickel. The presence of coating was analysed with the help of SEM. The presence of nickel as a coating on the elemental powders was confirmed by EDS analysis. Figs 1 and 2 show the SEM micrographs of the uncoated and coated titanium powders. Fig. 3 shows the EDS analysis of nickel-coated titanium powders. Figs 2 and 3 establish the presence of nickel as a coating on the substrate. The magnetic moment test was conducted on the coated particles to confirm the increase in the coating thickness with time. The coating material and the substrate are ferromagnetic and paramagnetic, respectively. From the theory of magnetism, the magnetic moment increases directly with the increase in susceptibility of the material. This concept is used here to determine the increase in coating thickness. Fig. 4 shows magnetic moment plotted against magnetic field for different coating durations. The magnetic moment slowly increases

Factors affecting the adhesion of electroless coatings

In this paper, we study the factors affecting the first stage of autocatalytic (electroless) growth: the nucleation processes. The initiation of the process was achieved with the nickel electroless method on iron and copper substrates. Both acidic and alkaline baths were used for generalization of the layers.

Laser-induced prenucleation of alumina for electroless plating

This paper deals with the deposition of palladium from decomposition of a thin palladium acetate layer on rough and porous alumina ceramic surfaces by irradiating it with a UV excimer laser. The palladium acetate layer was formed from a combination of propyl glycol methyl ether acetate solvent and photoresist, and the undecomposed material was removed with the photoresist remover. The discontinuous palladium cluster film formed by the technique was used as seed for electroless coatings. Different patterns were obtained using point focus as well as projection pattering method and subsequently plated with adhesive layers of electroless Ni-B coatings.

Engineering Properties of Chromium Plating and Electroless and Electroplated Nickel

The wear of chromium plating and electroless and electroplated nickel under dry sliding conditions is not directly related to hardness. The maximum wear resistance of electroless nickel does not occur at its peak hardness and chromium plating has the highest wear resistance even though it is not the hardest coating. As-deposited electroless nickel is susceptible to serious adhesive wear against plain carbon steel but this can be eliminated by a controlled heat treatment. The wear of electroplated and electroless coatings is strongly influenced by the nature of the counterface material. In particular, extremely high wear rates are encountered with stainless steel but the work shows that this can be avoided by chromium plating its electrocounterface. The results in general indicate that the wear of electroplated and electroless coatings is crucially dependent upon the wear mechanism: heat treatment of electroless nickel improves the adhesive wear resistance for metal/metal sliding but impairs the ductility for flexing, gouging, and heavy abrasive wear. The relative positions of electroplated, electro less, and composite coatings in the range of engineering coatings available are considered and the importance of wear diagnosis in materials selection and design is discussed.