Electroless Nickel Phosphorus Research Articles

Wear Resistance Behavior of Low-, Mid-, and High-Phosphorus Electroless Ni-P Coatings Heat-Treated in the Air Environment

The high-temperature heat treatment of electroless nickel–phosphorus (Ni-P) coatings in an air environment, and its consequences have scarcely been investigated. This work investigated tribological characteristics of the high-temperature, heat-treated, electroless Ni-P coatings on steel substrates with low-, mid-, and high-phosphorus content for which the average phosphorus content was 2.4 wt.%, 7.1 wt.%, and 10.3 wt.%, respectively. X-ray fluorescence and energy dispersive spectroscopy were implemented to determine the phosphorus content of the coatings. The oxidation of Ni and the formation of the NiO layer on the coating surface was confirmed by the X-ray diffraction technique. A reciprocating sliding method on a ball-on-flat system was utilized to evaluate the coating’s friction and wear behavior. Among the coatings with varying phosphorus content, a high hardness of 1086 HV was found for high-phosphorus coating when heat-treated at 400 °C in an air environment, and that was decreased to 691 HV when heat-treated at 650 °C. The oxidation of nickel in the electroless Ni-P coating occurred when heat-treated at 400 °C in an air environment, and this phenomenon was increased more when the temperature was increased to 650 °C. The characteristics of the NiO layer that formed on the surface of the heat-treated electroless Ni-P coating were influenced by the concentration of phosphorus, which caused different colors of NiO to be seen on the Ni-P coating surface. A greenish black NiO layer on the low-phosphorus and black NiO layer on the mid- and high-phosphorus Ni-P coating was developed during heat treatment at 650 °C in an air atmosphere. The adhesion and tribological characteristics of the Ni-P coatings were affected by the NiO layer developed on the heat-treated Ni-P coating surfaces. The Ni-P coatings with mid- and high-phosphorus content showed enhanced wear-resistance characteristics when they underwent heat treatment in an air atmosphere at the high temperature of 650 °C. The wear volume obtained for as-plated mid-phosphorus and high-phosphorus Ni-P coatings was 0.111 mm3 and 0.128 mm3, respectively, and that was reduced to 0.031 mm3 and 0.051 mm3, respectively, after the high-temperature heat treatment.

Zincate Replacement, an Economical a Sustainable Alternative for the Metal-Coating of Aluminum

Aluminum parts are of great value for many industries as they are cost-effective, very lightweight combined with a good mechanical strength. However, when parts are exposed to corrosive and abrasive conditions it is preferred to protect them with anodizing, powder coating, or for technical critical applications with nickel-phosphorus (NiP) coatings. Most preferred for functional parts such as scroll compressors, connectors,... is electroless NiP (EN) as it is has a low thickness variation in the final deposit and does not need the application of current like galvanic NiP coatings.Depositing an adherent layer of electroless NiP onto aluminum needs an alloy-specific pre-treatment. The largest challenge in pre-treatment lies in the very fast formation of Al2O3 oxide under neutral pH conditions of 4 - 9. For decades a very effective way to inhibit the re-oxidation of aluminum is the use of alkaline zinc as interim coatings that dissolve in the electroless NiP electrolyte before NiP deposition starts. Commercial solutions are optimized to produce an as thin and homogenous as possible zinc deposit to minimize the drag-in of zinc into the NiP electrolyte. At levels of 80 - 200 mg/l zinc starts to lower the adhesion and plating rate of deposited EN coatings. As results the nickel process needs to be discarded before nickel deposition capacity of electrolyte is fully reached (~ 40 g/l plated Ni). The impact of Zn contamination is most critical as lower the thickness of the EN layer is. At very thin thicknesses below 4 µm the increase of zinc is very large, and electrolytes need to be discarded at 6-12 g/l plated nickel creating higher chemical waste, maintenance effort, and cost. Due to technical changes in many applications, different and more parts will be composed of aluminum. In contrast to established applications NiP that exhibit EN layers > 5 µm new applications arise with the upcoming EV and Battery market that request thinner NiP layers. The most extreme case is reel-to-reel plating of thin (< 50 µm) foils with NiP deposits below 4 µm.In the present work, the application of a new chemical concept of aluminum pre-treatment for low-thickness EN coatings will be presented that reduces the number of needed process steps compared to double zincate by at least 2 steps (excl. rinses) without the need for special equipment such as pulse plating and others. Differences in the initiation of electroless NiP deposition and the correlated adhesion will be evaluated. As a model case, the application of thin NiP layers (< 4 µm) on pure Aluminum foils will be shown and discussed. Figure 1

Hardness and tribological behaviour of annealed electroless nickel phosphorus composite layers with incorporated boron particles

In this study, a possible alternative to hard chromium coatings is investigated. Amorphous boron particles have been incorporated in electroless nickel‑phosphorus (NiP) deposits, yielding a dispersion coating. The distribution of the particles is homogenous and the maximum mass fraction of particles embedded in the coating is 6.2 ± 0.2 wt%. Measurements of the zeta potential and particle size of amorphous boron particles in a diluted electrolyte showed that the particles withstood agglomeration until 120 days. Primary and secondary hardness maxima are observed after thermal annealing at 400 °C and 860 °C due to the formation of nickel phosphide, nickel boride and nickel boride phosphide phases. X-ray diffractometry shows an increase in nickel and nickel phosphide crystal size at 400 °C before levelling off at 600 °C. The annealing duration should be kept between 30 and 60 min for optimal hardness. The wear resistance increases when the coating is annealed at 400 °C. DSC measurements on nickel phosphorus incorporated with boron particles, Ni-P-B, bulk material with P-content (9.6 ± 0,6 wt%) and B-content (4.5 ± 0.8 wt%) showed that the solidus line lies at 926 °C, which is why a maximum annealing temperature of 860 °C was chosen to avoid melting of the material. The relative texture and phase coefficients, RTC and RPC, showed that the nickel phase is preferred in the NiP system at 400 °C and 600 °C while the Ni3P phase is preferred in the Ni-P-B system at the same annealing temperature. REM and EDX area analyses are used to show the areal distribution of nickel, phosphorus, and boron before and after the annealing process along the thickness of the coating. A diffusion layer between substrate and coating that contains iron nickel boride and iron nickel phosphide lamellar structure is observed.

Influences of La3+ Concentrations on Properties of Electroless Nickel–Phosphorus–Boron Coatings

Influences of La3+ Concentrations on Properties of Electroless Nickel–Phosphorus–Boron Coatings

Enhanced electroless Ni-P plating quality on binderless tungsten carbide by atmospheric pressure plasma pretreatment

Precision glass molding (PGM) has been widely utilized in optical components production, during which binderless tungsten carbide (WC) is a popular mold material. Researchers have proposed the application of electroless nickel‑phosphorus (NiP) plating on WC molds, offering good surface finish, non-stick properties, and enhanced corrosion resistance, while typical NiP plating pretreatment is complex, time-consuming, carrying risks of surface damage and pollution. In this study, Atmospheric-pressure (AP) plasma surface processing has been proposed as an alternative pretreatment technique to enhance electroless NiP plating quality on binderless WC, contributing to the reduction of plating steps, time, smoothing of the plated NiP layer, and improvement in adhesion quality. The interaction mechanism between AP plasma and WC has been analyzed. The influence of AP plasma surface pretreatment on the surface quality of NiP plating has been investigated in detail. Surface characterization and adhesion test have been conducted to evaluate the effectiveness of AP plasma pretreatment method. Despite the fact the replication of substrate roughness exists in typical NiP plating process, the surface roughening and enhanced surface energy induced by AP plasma pretreatment can have a smoothing effect for the following electroless NiP plating process. The effectiveness of ICP AP plasma as an alternative pretreatment technique for high-quality electroless NiP plating on binderless WC has been validated.

Molecular dynamics simulation of the nano-cutting mechanism of a high-phosphorus NiP coating

Electroless nickel-phosphorus workpieces undergo a variety of surface/subsurface deformations and internal organizational changes throughout the nano-cutting process that have a major impact on the machining quality of microstructured functional surfaces. In this paper, molecular dynamics simulations were performed for nano-cutting of electroless nickel-phosphorus (Ni–P) workpieces obtained at different cooling rates (1e11 K/s, 1e12 K/s, 1e13 K/s). To research the mechanisms of material removal and surface formation during nano-cutting, the impacts of various cutting depths on atomic ordering, cutting force, cutting temperature, shear strain, material pile-up, and surface shape were examined. The simulations showed that material removal of NiP coatings was mainly based on nanoscale extrusion rather than macroscale shear. The radial distribution function of NiP coatings was dominated by the Ni–P pair, the cutting force of the nano-cutting process was more stable, the thrust force was smaller, and the machined surface roughness Ra was smaller when the cooling rate was higher. However, the number of atoms on the upper surface of the workpiece increased more, and the actual machined surface contour line deviated from the ideal surface contour when the cooling rate was faster. To increase the forming accuracy of the machined surface on NiP without destroying the machined surface roughness, the cooling rate must be slowed appropriately for the NiP alloy to form a tiny amount of crystalline organization or to minimize the nano-cutting depth.

Effect of Surface Activation on the Corrosion Resistance of a MAO/Ni-P Composite Coating on LZ91 Magnesium Alloy

BackgroundLZ91 Magnesium alloy with a dual-phase structure has improved mechanical properties and a low density of about 1.48 g/cm3 but their limited resistance to corrosion limits their application. Therefore, it is a great challenge to increase the stability of LZ91 alloys under corrosive factors and environments. MethodsThis study uses micro-arc oxidation (MAO) and an electroless nickel-phosphorus (Ni-P) plated composite film to increase the corrosion resistance of LZ91 magnesium alloy. Before electroless Ni-P plating, the MAO layers are activated by palladium catalysts at different pH values to produce composite coatings. SEM, EDS and Image J are used to determine the surface properties and elemental composition of the samples. The corrosion resistance is measured using a potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution. FindingsThe results show that the MAO coating is activated by an acid catalyst and the surface is obviously corroded. The electroless Ni-P plating grows into the MAO coating and the substrate corrodes. Therefore, corrosive medium (chloride ion) easily enter to the substrate and pitting corrosion occurred. On the contrary, activation by a neutral catalyst (pH=7) maintains the original structure of the MAO coating and provides a good bonding interface for the Ni-P coating. Form the potentiodynamic analysis can be finds that the corrosion potential for the neutral catalyst treated sample is -0.35V and the corrosion current density value is 1.77×10−6 A/cm2, so the corrosion characteristic become better than the acid catalyst treated samples. In terms of the long-term resistance after 48 h, EIS analysis shows that the resistance value remains at about 7.6×104 Ω•cm2. A composite coating that is compact and with excellent resistance to corrosion resistance is produced, which provides better protection for LZ91 magnesium alloys.

Thermomechanical performance enhancement of nickel-phosphorus mold by Ti-DLC coating

Glass molding technology is an ideal method for the mass production of the glass components, and electroless nickel-phosphorus (Ni-P) plating is widely used in the glass molding process as the mold material. However, the service life of the Ni-P mold reduces due to the diffusion of Ni atoms at high temperatures. To prolong its service life and protect the mold surface, a titanium-diamond-like carbon (Ti-DLC) coating is deposited on the Ni-P mold. This research studies the crystallization and diffusion of Ni atoms in both the Ni-P mold and the Ti-DLC coated Ni-P mold under a thermomechanical field. Additionally, the influence of Ti-DLC coating on the crystallization and diffusion behavior of single crystal Ni was investigated. The results show that the Ti-DLC coating protects the mold surface by suppressing the diffusion of Ni atoms rather than preventing the crystallization of Ni-P. The number of microbumps is used to describe the extent to which Ti-DLC coating improves the thermomechanical performance of Ni-P molds. The date shows the Ti-DLC coated Ni-P mold exhibit superior stability in 80 cycles of molding for no microbumps appearing on the surface. While the microbumps appear on the Ni-P mold surface after one-time molding, thus the thermomechanical performance of the Ni-P mold is further enhanced by Ti-DLC coating.

A novel preparation and characterization of electroless NiP/MWCNT composite coated UHMWPE fabric in terms of wettability, electrical conductivity, thermal stability and breaking load resistance

Poor wettability results in fragile bonding between the ultra-high molecular weight polyethylene (UHMWPE) fabric and matrix of the composites. To overcome this issue, the present study proposes a novel approach for the deposition of electroless nickel-phosphorus (NiP) and nickel-phosphorus/multi walled carbon nanotube (NiP/MWCNT) coating on the surface of UHMWPE. The influence of coatings on the morphology, phase structure, crystal size, functional groups, surface roughness, wettability, water absorption property, electrical conductivity, thermal stability, peeling load and breaking load of UHMWPE fabric are detailed. After MWCNT was reinforced, the cauliflower structure reported for NiP coated UHMWPE (NiP-UHMWPE) was altered for NiP/MWCNT-coated UHMWPE (NiP/MWCNT-UHMWPE). The crystal size of NiP has slightly increased to 1.307 nm for NiP/MWCNT-UHMWPE from 1.22 nm of NiP-UHMWP. The contact angle of NiP-UHMWPE (84.36°) was relatively lower than the NiP/MWCNT-UHMWPE (92.46°) and UHMWPE (102°), due to the formation of more nickel globules in the surface of NiP-UHMWPE. Though the wettability was high for the NiP and NiP/MWCNT coating, the water absorption percentage has not increased for NiP-UHMWPE and NiP/MWCNT-UHMWPE. The electrical conductivity was improved for NiP/MWCNT-UHMWPE after the reinforcement of MWCNT. The breaking load of the NiP and NiP/MWCNT coated UHMWPE fabric improved by 6.24% and 12.11% respectively. The more detailed study in terms of functional group, crystal structure, compounds, electrical conductivity, thermal stability, peeling load, and tensile failure analysis of coated UHMWPE fabric are reported in this article.

Mechanical and tribological characterization of deep eutectic solvent assisted electroless Ni–P-hBN coating

Compositions and processing methods govern various characteristic features of electroless coatings. Electroless nickel–phosphorus (Ni–P) composite coatings containing varying amounts of hBN, deposited using a deep eutectic solvent (DES), achieved better tribological properties as compared to the coating of the same composition deposited in the conventional method. This study also attempted to determine the specific concentration of hBN particles in the electroless bath that deposits Ni–P-hBN coating with a superior combination of mechanical and tribological characteristics. Stronger bond formations of hBN particles in the Ni–P alloy matrix ensured by hBN's metallic behavior potentially influence its tribological properties.

WET TREATMENT AND THE BEHAVIOR OF ELECTROLESS NI-P DEPOSITION AT 40 °C ON POLISHED ALUMINA

The morphology and adhesion strength of the autocatalytic electroless nickel phosphorus (Ni-P) film, deposited at 40 ºC on polished alumina (Al2O3 99.6%) substrate, pretreated by sulfur/nitric solution, sensitizing with acid stannous chloride and activated using palladium chloride solutions, was studied using contact angle (CA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), mechanical profilometer (DekTak), and direct laser writer (“maskless lithography”). The results showed that after treatment of the polished Al2O3 substrate, it presented a high performance in the electroless deposition of Ni-P thin-film at low temperature (40 ºC). It was obtained a more compact and continuous film, with small grain size and strong adherence.

Analysis of Tool Wear and Counter Surface Roughness in the Flexible Abrasive Tool Finishing

This work uses the solvent casting method to fabricate an elastomeric tool with polyurethane as the base material and silicon carbide (SiC) as embedded abrasive particles. The distribution of abrasive particles and the pore structure in the fabricated tools are analyzed. The fabricated tools are porous in nature and have self-replenishing as well as self-lubrication properties. Aluminum 6061 alloy and electroless nickel-phosphorus plating having different initial roughness are selected as workpieces to study the wear mechanisms and loading of the flexible abrasive tool. The rotational speed of the tool, tool compression, and feed rate are fixed input process parameters. Total finishing time, sliding distance, and roughness are varied to obtain output responses. The workpiece material is also taken into account as a variable parameter in this study. These materials are classified as different counter surfaces as their surface roughness and mechanical properties vary. The finishing time and sliding distance for these counter surfaces differ in order to relate their effects on tool wear and loading. The nickel-plated surface shows a higher percentage reduction in surface roughness of 92% as compared to the aluminum surface, with a 62% reduction in surface roughness. The coefficient of friction, wear, and tool condition are analyzed to understand the mechanism of tool wear and tool loading. In this process, both two-body and three-body abrasions occur simultaneously and continuously.

Wear-reducing nickel-phosphorus and graphene oxide-based composite coatings: Microstructure and corrosion behavior in high temperature geothermal environment

Polymer coating modified with graphene oxide (GO) and duplex electroless Nickel-Phosphorus (Ni-P) with polytetrafluoroethylene (PTFE) coating were investigated for their corrosion behavior in simulated high-temperature geothermal environments with/without H2S and CO2 gases for geothermal applications. The polymer coating with added GO nanosheets demonstrated low wetting ability and suppressed corrosion effects of the substrate at 120 °C. The Ni-P/PTFE duplex coating with the lowest P content was suitable in an H2O liquid environment at 120 °C while high P was more promising in the two-phase CO2/H2S environment. Nevertheless, all the coatings were unprotective and allowed substrate corrosion at 250 °C in the H2S/CO2 environment.

Corrosion Properties of Ni-P-B Dispersion Coating for Industrial Knives and Blades

Industrial blades, particularly the one used in food processing, requires not only a high hardness and a good wear protection but also an adequate corrosion protection. Currently, there is a wide variety of materials being used for this purpose that satisfy the above requirements. However, they come at a cost. Typically, steel with a high number of alloyed elements is chosen because the alloyed elements improved the steel quality. For example, incorporation of nickel, chromium, phosphorus and molybdenum in the steel improves amongst others the corrosion protection. However, the thermal processing of such steel, that is quenching, repeated tempering and followed by nitriding or boriding, is lengthy and complicated which drive the cost to produce knives using such steel up.Besides steel cutting tools, there is also cutting tools made from ceramic and carbide. Compared to steel knives, carbide knives have a longer lifespan and provide a higher temperature tolerance, which results in the application of the carbide cutting tools at higher speed and for longer periods without experiencing tool failure. Admittedly, due to carbides high hardness and thus the increase in difficulty to machine carbide, the production cost of carbide cutting tools is much higher compared to their steel counterparts. For ceramics, while the material is corrosion free and can maintain hardness and wear properties at a very high temperature, it is also more brittle than steel and carbide cutting tools. This results in premature chipping of the cutting edge and a shorter lifespan of the blade.To further reducing the production cost of industrial knives, the alternative of using a low alloyed steel which is coated with a hard coating and adjacently thermally treated for 1 h is investigated. This method is chosen because the tempering process of the low alloyed steel is not as lengthy as for high alloyed steel. The homogenously incorporated boron particles in the nickel phosphorus coating reduce the subsequent thermal treatment duration due to a shorter diffusion path compared to the conventional boriding. Previous study by the author [1] shows this approach to produce a high hardness at approx. 900 HV. Electroless nickel phosphorus coating is applied due to its good anti-corrosive properties. The presence of boron as particles in the coating or as boride after thermal treatment could change the corrosion behaviour of the coating. To date, no studies have yet been done to determine its corrosion properties and benchmarking this Ni-P-B dispersion coating with the other coating systems.In this study, the corrosion behaviour of the dispersion layer as coated and after thermal treatments at different temperatures is investigated. The corrosion resistance in NaCl 3.5 % is characterized though potentiodynamic polarisation and electrochemical impedance spectrometry. The results will be evaluated and compared to the other established coating systems.[1] The previous study will be presented at 241st ECS Meeting in Vancouver, Canada and has not yet been published at the time this abstract is submitted for the 242nd ECS Meeting in Atlanta.

Electroless Nickel Phosphorus Coatings to Mitigate the Corrosion of Construction Steel

Reinforced concrete is widely used in structures and construction, but its durability is limited due to corrosion of the embedded steel rebars. Thus, mitigation of corrosion of construction steel rebars is an important area of research. The present work reports the ability of electroless nickel phosphorus coating for corrosion protection of Fe-600-grade steel rebars used for construction purposes in chloride and sulphate environment. The coating deposited on Fe-600 rebar was Ni-P and was subjected to electrochemical tests in 3.5% NaCl and 0.5M H2SO4. Severe corrosion pitting and cracking were observed for the uncoated rebar while Ni-P coating showed nobler corrosion potential and low corrosion current density in the corrosive environments.

A two-dimensional thermodynamic model based on Helmholtz free energy for wettability regulation of textured metal surfaces

To provide theoretical support for the wettability regulation of textured metal surfaces, a two-dimensional (2-D) thermodynamic model based on Helmholtz free energy is proposed to reveal the nature of the infiltration phenomenon. The relationship between the apparent contact angle and the free energy of the infiltration system is established. Micropyramid arrays (MPAs) with different pitches are textured on a high-phosphorus electroless nickel-phosphorus (Ni-P) alloy plating by ultraprecision machining for the verification of the theoretical model. The results show that the minimum free energy corresponds to the apparent contact angle of the water droplet when it is stable on the textured surface. MPA-textured surfaces with smaller pitches have a wider variation range of apparent contact angle and are expected to achieve better hydrophobicity. Periodic energy barriers created by the MPAs promote the free energy consumption. By employing ultrasonic assistance, secondary microstructures are generated on the inclined sidewalls of the micropyramids, thus enhancing the energy barrier effect. A maximum apparent contact angle of 124.4° is obtained for the MPA-textured surface machined with ultrasonic vibration when the pitch is 20 μm. The experimental apparent contact angle values are all within the theoretical range, indicating the feasibility of the theoretical model.

Impact of Die Coatings on Forming Conditions in Electromagnetic Embossing of Thin Sheet Metal

In electromagnetic embossing, the interaction of the magnetic field and the induced current density results in body forces that enable the replication of optical microstructures into thin sheet metals. However, as the sheet metal is completely penetrated by the magnetic field, electromagnetic properties of the dies need to be considered in process design, as they influence the forming conditions by changing the field distribution, force vectors and eddy current densities. With die coatings like electroless nickel–phosphorus (NiP), the electromagnetic properties of the die change. Therefore, the effect of both - die substrate and coating material - was studied to find advantageous conditions for electromagnetic embossing. Within two-dimensional electromagnetic field simulation, the electromagnetic properties of coating and substrate material were varied in addition to the coating thickness. To validate the results, electromagnetic embossing experiments were carried out. Here, different dies were fabricated from aluminum (uncoated) and cold work steel with 200 µm and 400 µm thick electroless nickel–phosphorus coatings that were subsequently micro-structured in optical surface quality. It was demonstrated by numerical and experimental results that the coating and the substrate influence the electromagnetic embossing significantly in correspondence to their shielding behavior and field interaction due to electromagnetic properties and coating thickness.

The effect of fluoride on the formation of an electroless Ni–P plating film on MAO-coated AZ31B magnesium alloy

This study adds fluoride to the electroless nickel-phosphorus (Ni–P) plating solution to prevent the deterioration of MAO-coated AZ31B Magnesium alloy after contact with an electroless plating bath. During the electroless Ni–P plating process, fluoride reacts with Ni2+ ions and the MAO coating to form interphases (NaMgF3), which exhibit good bonding and corrosion resistance. NaMgF3 buffers H+ ions formed from the initiation of Ni–P deposition, preventing the interface of materials from damaging the MAO coating with H+ ions. As immersion time increases, nickel is scattered over the coating.The fundamental data for MAO/Ni–P coated AZ31B Mg alloy determines whether there is fluoride in the electroless Ni–P plating solution. The results show that the coating for a fluoride-containing solution is more resistant to corrosion than those in fluoride-free solution. The compositions, structure and morphology of the MAO/Ni–P coatings that formed for different working parameters are determined using energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The corrosion resistance of the MAO/Ni–P coatings is calculated in a 3.5 wt.% NaCl solution using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) and a salt spray test (SST).

Study on adhesion failure of electrically conducting electroless Ni-P coating on polyethylene terephthalate substrate

Demand for lightweight, flexible and low-cost electrically conductive materials are rapidly increasing in fields like medical, automobile, aerospace, textile and electronics. Plastics may accomplish these requirements, due to their lightweight, flexibility and low cost. However, plastics are electrically non-conductive in nature. This limitation may be addressed by deposition of a conductive coating on plastic substrates. However, the main challenge is to ensure good adhesion between such metallic coating and non-metallic substrate. In this work, electrically conducting nickel-phosphorus (Ni-P) coating was deposited on polyethene terephthalate (PET) substrate through electroless route at different coating durations i.e. 1, 3 and 5 min. Constituents of electroless bath were kept constant for all deposition runs. Bath temperature and pH were also fixed at 80 °C and 8 respectively. The surface morphology of Ni-P coated film was characterised by scanning electron microscope (SEM). The adhesion of Ni-P coating at different coating times i.e. 1, 3 and 5 min were assessed through optical imaging, bend test and scotch-tape test. Swelling and delamination of the films from the substrates were observed as deposition duration was increased beyond 2 min.

Particle-Size-Dependent Anticorrosion Performance of the Si3N4-Nanoparticle-Incorporated Electroless Ni-P Coating

Electroless Nickel–Phosphorus (Ni-P) coating is recognized mostly for its outstanding corrosion and wear-resistant behavior. The intrinsic corrosion and wear-resistant properties of Ni-P-based coating could be further upgraded by incorporating appropriate second-phase additive particles into the coating matrix. However, such properties of the Ni-P-based coating greatly rely on the surface and microstructural evolution arising with the co-deposition of the additive particles. In this study, submicron Si3N4 (average size ~200 nm) and nano Si3N4 (average size ~20 nm) particles were incorporated while depositing a Ni-P alloy in a low-carbon steel substrate to develop the Ni-P-Si3N4 composites through the electroless coating method. The 20 nm Si3N4-incorporated composite coating constituted fewer defects such as cavities and micropores on the surface, but such defects significantly appeared on the surface of the composite after the incorporation of 200 nm Si3N4 nanoparticles. Subsequently, the composite Ni-P-Si3N4, developed with the co-deposition of 20 nm nanoparticles, is enriched with enhanced anticorrosion characteristics compared with the composite developed with 200 nm nanoparticles. The enhancement of anticorrosion behavior was attributed mainly to the Si3N4 nanoparticles that covered the substantial volume of the coating and led to inhibit the formation of corrosion active sites such as defects and metallic Ni phase.