Ni-P Matrix Research Articles

Development and electrochemical characterization of Ni‐P coated tungsten incorporated electroless nickel coatings

Ni‐P-W alloy and composite coatings were prepared by incorporation of sodium tungstate/tungsten and Ni‐P coated tungsten into electroless nickel bath respectively. Good inter-particle interactions among the depositing elements i.e. Ni and P with the incorporating tungsten particles were achieved by means of pre-coated tungsten particle by electroless nickel covering prior to its addition into the electroless bath. The pre-coated tungsten particles got incorporated uniformly into the Ni-P matrix of the coating. The particles and the coatings were characterized at different stages by different techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). The electroless Ni-P coating incorporated with pre-coated tungsten exhibited considerably high hardness, thickness and deposition rate. The performance and corrosion resistance characteristics of the composite coating incorporated with the nickel coated tungsten were found to be superior over other conventional Ni-P-W ternary alloy coatings currently reported.

Electroless Nickel-Phosphorus Composite Coatings

Electroless nickel composite coatings possess excellent mechanical and tribological properties such as, hardness, wear and corrosion resistance. Composite coatings can easily be coated not only on electrically conductive materials but also on non-conductive materials like as fabrics, plastics, rubber, etc. This review emphasizes on the development of electroless nickel composite coatings by incorporating different types of hard/soft particles (micro/nano size) in the electroless Ni-P matrix to improve the mechanical and tribological properties of the coatings. The preparation of electroless bath for nickel-phosphorus composite coating, methods to incorporate hard and/or soft particles in the bath, factors affecting the particle incorporation in the coating and its effect on coating structure, hardness, wear resistance, friction behavior, corrosion resistance, and mechanical properties are discussed thoroughly.

Influence of SiC Content and Heat Treatment on the Corrosion Resis-Tance and Oxidation Resistance of Ni-P-SiC Composite Coating

Ni-P alloy and SiC micron particles were codeposited on Q235 steel by electroless plating. The composition, microstructure, micro-hardness, corrosion resistance and oxidation resistance of the composite coating were studied. The results revealed that the deposited composite coating shows dispersed SiC particles and continuous Ni-P matrix. When the content of SiC was 8g/L and the heat treatment temperature was 300°C, the corrosion potential and corrosion current of Ni-P-SiC coating were-0.292V, and 8.2×10-7 A/cm2, respectively, while those of Ni-P composite coating were-0.501V, and 4.2×10-5 A/cm2, respectively. Ni-P-SiC composite coating with high content of SiC exhibits better oxidation resistance than Ni-P coating.

Electrodeposition Process of Composite Ni-P+Ni(OH)<sub>2</sub>+PTFE Coatings

Co-deposition process of amorphous nickel and PTFE particles in the presence of Ni (OH)2carrier suspended in the bath by magnetic stirring, was investigated. Composite Ni-P+Ni (OH)2+PTFE coatings and comparative Ni-P deposits, were electrodeposited on low carbon steel substrate under galvanostatic conditions at room temperature. The physical and chemical characterization of the coatings was carried out using X-Ray diffraction analysis and microanalysis, stereometric quantitative microscopy and atomic absorption spectroscopy. The optimum production conditions of the composite coatings based on the Ni-P matrix into which PTFE and Ni (OH)2components can be embedded uniformly, were found.

Tailoring Structural and Electrochemical Properties of Composite Ni-Based Electrocoatings

Oxygen electroevolution reaction (OER) was studied in alkaline medium on the Ni-P+TiO2composite electrocoatings obtained from the Watts type bath containing the suspension of TiO2particles. The comparable Ni-P coatings were electrodeposited from the supporting electrolyte without titanium dioxide. The galvanostatic electrodeposition of all coatings was conducted on a polycrystalline copper substrate at the deposition current density of 240 mA cm-2for 30 min. The electrolysis process was carried out at temperatures of 293-333 K. It was found that the mass increment and the content of TiO2in the obtained coatings is a decreasing function of the electrodeposition temperature. It was also acertained that the built-in TiO2as the composite component into the Ni-P matrix has no effect on the improvement of the electrocatalytic properties of the Ni-P+TiO2composite electrodes towards OER probably due to limitation of the size of the electrochemically active surface area of the electrode material obtained under proposed conditions.

Comparison of Electrocatalytic Activity of the Composite Ni-P+NiO and Ni-P+Ni(OH)<sub>2</sub> Coatings for Hydrogen Evolution

The object of this work were composite electrocoatings with an amorphous Ni-P matrix containing crystalline NiO or Ni (OH)2component. The Ni-P+NiO, Ni-P+Ni (OH)2and Ni-P electrocoatings were deposited on a Cu substrate under galvanostatic conditions at room temperature. The electrocatalysts were characterized in the process of hydrogen evolution in 5 M NaOH solution in dependence on their deposition conditions, phase composition and chemical constitution. Based on the potentiodynamic polarization curves, the parameters of the Tafel equation and exchange current densities, were determined as a criterion for estimation of catalytic properties of these electrode materials towards hydrogen evolution reaction in an alkaline medium.

Production and Structure of Nickel-Phosphorus Electrolytic Coatings Modified with Metallic Tungsten or Nickel Oxide

Electrodeposited Ni-P, Ni-W-P, Ni-P+W and Ni-P+NiO+W coatings were obtained in the galvanostatic conditions at the current density jdep = -200 mA cm-2. A stereoscopic microscope was used for surface characterization of the coatings. The phase composition of the coatings was determined using X-ray diffraction (XRD) method. The chemical composition of the deposits was determined using atomic absorption spectroscopy (AAS). It was found out that the introduction of the tungsten powder in one case, and the nickel oxide and tungsten powder in the other into the electrolytic Ni-P matrix results in obtaining the coatings with a very rough surface. The coatings obtained in this way may be useful while applying them as electrode materials in electrochemistry.

Influence of CNTs Concentration on the Microstructure and Electrochemical Properties of Ni-P-MWNTs Composite Coating

Ni-P-multi-walled carbon nanotubes (Ni-P-MWNTs) composite coating was successfully co-deposited on 45 steel substrate by electroless plating. The microscopic morphology of Ni-P-MWNTs composite coating was observed by SEM. The influences of CNTs concentration in plating bath on the microstructure and corrosion resistance of the composite coating were investigated. The results indicated that the deposited composite coating shows dispersed CNTs and continuous Ni-P matrix, and there are no pores and cracks and other defects at the interface between the substrate and composite coating, and the thickness of the composite coating is about 50 μm. The Ni-P-MWNTs composite coating with 0.3g/L CNTs in bath displayed the best corrosion resistance, the corrosion potential of the composite coating is-0.372V.

Electroless Ni-P-PTFE-Al2O3 Dispersion Nanocomposite Coating for Corrosion and Wear Resistance

With the aim to produce a coating having good corrosion and wear resistance alongside hardness but lesser friction coefficient, Ni-P-PTFE-Al2O3 (NiPPA) dispersion coating was developed. This was achieved by introducing nanosized polytetrafluoroethylene (PTFE) and alumina (Al2O3) in the Ni-P matrix deposited on mild steel substrate. The coating was characterized using scanning electron microscopy, energy dispersive analysis of x-ray, and x-ray diffractrometry. Microhardness and wear resistance of the coating was measured using Vicker’s hardness tester and Pin-on-Disc method, respectively. The corrosion behavior was measured using electrochemical polarization and immersion tests with and without exposure in 3.5% NaCl solution. It is observed that codeposition of Al2O3 and PTFE particles with Ni-P coating results in comparatively smooth surface with nodular grains. The NiPPA coating was observed to have moderate hardness between electroless Ni-P-PTFE and Ni-P-Al2O3 coating and good wear resistance with lubricating effect. Addition of both PTFE and Al2O3 is observed to enhance corrosion resistance of the Ni-P coating. However, improvement in corrosion resistance is more due to addition of Al2O3 than PTFE. Continuous exposure for 10-20 days in corrosive solution is found to deteriorate corrosion protection properties of the coating.

Research on the Microstructure and Tribological Properties of the Electroless Ni-P-PTFE Composite Repairing Coating on Gears

The abrasion of axle parts would shorten their useful life, which could be significantly ameliorated to improve the wear resistance of gears through surface repairing and lower production cost. In this work, preparation technology of electroless Ni-P-PTFE composite repairing coatings on 45# carbon steel was investigated by the method of cerium induced codeposition. Coatings with PTFE ranging of 0-10g/L and Ce2+ of 0-1.0g/L were obtained. SEM and XRD were employed to study the worn surface topography, wear mechanism and microstructure of the coatings, respectively. The results indicate that the PTFE particles uniformly distributed throughout the Ni-P matrix, on the edge position of Ni-P crystal cells, and small amounts of which were wrapped in the crystal cells. The wear mechanism manifested as adhesion and slight grain-abrasion, along with associated ploughed grooves. It was also demonstrated that the wear rate of deposits is 2×10-6mm3.N-1.m-1 in condition of dry sliding, which is smaller than it by 3 orders of magnitude. Obviously, electroless Ni-P-PTFE coating improves the wear resistance of gears significantly and can be used as repairing coating.

Incorporation of Ceramic Particles into Nickel and Cobalt Electroless Deposits

Abstract- The aim of this work was to elucidate factors affecting electroless codeposition of metals with ceramic particles. Codeposition of SiC, SiO 2 and Al 2 O 3 particles with Ni-P and Co-P matrixes in citrate-malonate alkaline solutions was compared. The positive surface charge of SiC particles corresponded to increased adsorption of hypophosphite anions, while negatively charged SiO 2 and Al 2 O 3 particles showed high adsorption of metal ions. It resulted in high incorporation of the carbide into the metal layers and low percentages of oxides in the coatings. Adsorption of nickel ions on SiC particles was promoted by the presence of maleic acid in the bath, however it did not improve incorporation of the particles into the Ni-P matrix. Equilibrium distribution of the species in the plating baths was also calculated. Keywords- Electroless Deposition; Nickel; Cobalt; Composite; Surface Charge; Adsorption I. INTRODUCTION Composite coatings are produced usually by incorporation of solid particles into a metallic matrix in electrolytic or electroless processes

Wear, Hardness and Corrosion Resistance Characteristics of Tungsten Sulfide Incorporated Electroless Ni-P Coatings

A novel composite coating containing WS2 in Ni-P matrix was obtained by electroless deposition route. The incorporation of tungsten sulfide particles enhanced the hardness and corrosion resistance of the Ni-P coatings. It was established that the electroless Ni-P-WS2 coatings were able to sustain the low coefficients of friction under severe sliding condition in comparison with the Ni-P coatings. It is evident that the Ni-P-WS2 coatings have the option of being used as solid lubricants to the sliding parts of machineries in aerospace industries. The incorporation of WS2 and the existence of Ni3P in the matrix have been ascertained by XRD, SEM and AFM.

Electroless Ni-P-CNT composite coating on aluminum powder

Ni-P-CNT composite coatings were deposited on micro-sized aluminum particles using electroless plating technique and the effect of different process parameters on the microstructural characteristics of the produced composite coatings were investigated. The results showed that a uniform Ni-P-CNT composite coating could be successfully deposited on the aluminum particles provided the electroless processing parameters were adjusted carefully. The most favorable coating quality was achieved at bath temperature of 80 °C, bath pH of 5.5 and CNT concentration of 1.25 g/lit. While a higher CNT concentration resulted in increased CNT agglomeration and poor CNT distribution in the Ni-P matrix, a lower CNT concentration resulted in fewer incorporated CNTs. Higher bath temperatures intensified the hydrogen gas evolution during the process and resulted in poor uniformity and presence of porosity in the coating. Low bath pH resulted in poor CNT incorporation and distribution in the Ni-P matrix and clustering of a large part of CNTs out of the coating.

Electroless ternary NiCeP coatings: Preparation and characterisation

Electroless ternary NiCeP deposits were prepared from alkaline citrate bath containing nickel sulphate, cerium chloride and sodium hypophosphite. Concentration of rare earth cerium was varied from 1 to 2g/L to obtain ternary deposits containing variable Ce and P contents. The influence of cerium on the deposit properties was analysed. The deposit exhibited a maximum cerium content of 6.2±0.1wt.% when the cerium chloride concentration was 2g/L. The result of the Pd stability test showed that the stability of the bath was reduced due to Ce salt addition. The microhardness measurements made on both as-plated and heat treated samples exhibited a peak hardness of 1006±11VHN for cerium concentration of 1.5g/L. The concept of kinetic strength analysis was proved to be applicable only for binary and not for ternary alloys due to multistep deposition mechanism with different kinetic energies. X-ray diffraction (XRD) patterns of as-plated and heat treated samples revealed peaks corresponding to Ni (111) and nickel phosphide (Ni3P). Higher amount of Ce incorporation in NiP matrix increased the crystallisation temperature of the deposit which could be due to the suppression of nickel crystallisation prior to Ni3P compound formation and thus increasing the activation energy for the formation of stable phases. Surface compositional analysis using X-ray photoelectron spectroscopy (XPS) carried out on as-plated NiCeP-2 deposit showed a prominent peak of P existing in +1 oxidation state as higher alkalinity favoured hypophosphite deposition in the ternary alloy coating. It was observed that the co-deposition of Ce in NiP matrix improved the continuous salt spray exposure for 168h.

Deposition and corrosion resistance of electroless Ni-PCTFE-P nanocomposite coatings

The present work deals with the process of electroless deposition and electrochemical corrosion behavior of nickel-polychlorotrifluoroethylene-phosphorous (Ni-PCTFE-P) nanocomposite coatings. The process of autocatalytic-catalytic reduction of Ni in nickel sulfate and sodium hypophosphate solution with PCTFE suspended particles has been employed for the formation of the electroless Ni-PCTFE-P composite coatings. Surface morphology and composition of the composite coatings are characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) measurements and X-ray diffraction (XRD) analysis. Corrosion behavior of coatings is evaluated using open-circuit potential (EOCP) measurements, electrochemical impedance spectroscopy (EIS) and polarization techniques in 3.5wt.% NaCl solution. The study reveals significant shift in corrosion potential towards the noble direction, decrease in corrosion current density, increase in charge transfer resistance and decrease in double‐layer capacitance values with the incorporation of PCTFE particles in the Ni-P matrix. The significant improvement in corrosion resistance observed for Ni-PCTFE-P nanocomposite coatings (25.3kΩ cm2) compared to Ni-P (16kΩ cm2) could have resulted from the microstructural differences of pure Ni-P with Ni-PCTFE-P nanocomposite coatings.

Phase transformation behavior of nanocrystalline Ni–W–P alloys containing various W and P contents

In the present investigation, electroless (EL) ternary Ni–W–P coatings were prepared using hypophosphite based alkaline bath by varying sodium tungstate as tungsten source (5–80g/L). Maximum amount of W incorporation (8.2±1wt.%) was obtained when the bath contained about 20g/L of tungsten source. At very high concentrations of W source in the bath the deposit contained about 4wt.% W and 2wt.% P. All the as-deposited ternary coatings exhibited nodular surface morphology. X-ray diffractograms (XRD) obtained for as-deposited EL NiWP alloys indicated that crystallinity of the coatings increased with decrease in phosphorus content. Calculated grain size for the deposits varied from 1.2 to 12.7nm when the tungsten source varied from 5 to 80g/L in the bath. Higher crystallization temperatures were obtained due to W codeposition in NiP matrix. Presence of metastable phases such as Ni5P2 and NiP apart from stable Ni and Ni3P was identified for the heat treated deposits (400°C/1h) containing lower amount of W and higher amount of P. Whereas other ternary deposits after the heat treatment predominantly revealed face centered cubic (f.c.c.) Ni (111) peak. Activation energy for the crystallization of all the alloys has been carried out by modified Kissinger method. Microhardness measurements were carried out on all the deposits isothermally heat treated at 600°C for 1h.

High-Temperature Oxidation Resistance of Electroless Ni-P-ZrO<sub>2</sub> Composite Coatings

Electroless Ni-P coating containing ZrO2 particles was successfully co-deposited on low carbon steel substrate. The surface and cross-sectional micrographs of the composite coatings were observed with scanning electron microscopy (SEM). And the chemical composition of the coating was analyzed with energy dispersive spectroscopy (EDS). The oxidation resistance was evaluated by weight gains during high temperature oxidation test. The results showed that the embedded ZrO2 particles with irregular shape uniformly distributed in the entire Ni-P matrix, and the coating showed a good adhesion to the substrate. The weight gain curves of Ni-P-ZrO2 composite coatings and Ni-P coating at 923K oxidation experiments were in accordance with . The ZrO2 particles in Ni-P matrix could significantly enhance the high temperature oxidation resistance of the carbon steel substrate as compared to pure Ni-P coating.

Effect of reinforcing submicron SiC particles on the wear process of electrolytic NiP coatings

The effect of submicron silicon carbide frictional strengthening admixtures and heat treatment on the wear process of nickel phosphide coatings obtained by electrolytic deposition is studied. Despite the heat treatment and admixtures of silicon carbides, the wear of the coatings is of abrasion-oxidizing nature; in the case of NiP-SiC composite coatings, the oxide films formed during the friction process do not exhibit the shield effect; these films show a considerable effect on the wear of silicon-free NiP coatings. The silicon carbide admixtures increase the hardness of the electrolytic coatings but prevent the oxide films formed in the frictional process from attaching to the contact surface. Annealing of the coating reduces the wear rate. In the process of heat treatment, the crystalline phase Ni3P is formed in the NiP matrix, increasing the coating hardness. At the same time, in the process of annealing of NiP-SiC composite coatings, the NiP matrix cracks around the silicon carbides. As a result, silicon carbides are extracted in the frictional process and the wear rate of the NiP-SiC composite coating grows.

Ni-P-SiC composite coatings electroplated on carbon steel assisted by mechanical attrition

In this work, Ni-P-SiC composite coatings were electroplated on carbon steel substrate assisted by mechanical attrition (MA). The MA action was conducted by dispersing glass balls on the cathodic surface, vibrating in the horizontal direction. The experimental results show that, under the assistant of MA action, the adhesion of Ni-P-SiC coating on the steel substrate can be improved efiectively, and the Ni-P-SiC coatings exhibit a crystallized structure and Ni-P matrix can combine tightly with SiC particles, and the hardness and corrosion resistance of these coatings increase markedly. During heat treatment, the defects produced in conventional Ni-P-SiC composite coatings can be avoided assisted by MA action. Both of the wear resistance and corrosion resistance of these coatings can be improved further.

Heat Treated NiP–SiC Composite Coatings: Elaboration and Tribocorrosion Behaviour in NaCl Solution

Tribocorrosion behaviour of heat-treated NiP and NiP–SiC composite coatings was investigated in a 0.6 M NaCl solution. The tribocorrosion tests were performed in a linear sliding tribometer with an electrochemical cell interface. It was analyzed the influence of SiC particles dispersion in the NiP matrix on current density developed, on coefficient of friction and on wear volume loss. The results showed that NiP–SiC composite coatings had a lower wear volume loss compared to NiP coatings. However, the incorporation of SiC particles into the metallic matrix affects the current density developed by the system during the tribocorrosion test. It was verified that not only the volume of co-deposited particles (SiC vol.%) but also the number of SiC particles per coating area unit (and consequently the SiC particles size) have made influence on the tribocorrosion behaviour of NiP–SiC composite coatings.