Electroless Ni-P Coatings Research Articles

Influence of load and temperature on tribological behaviour of electroless Ni-P deposits

Electroless Ni-P coatings have shown tremendous potential as tribology material at room temperature. However, the performance of the same in high temperature field needs to be evaluated as investigation reveals the softening of most of the coating materials. In the current study, both as-deposited as well as heat treated samples are developed for the performance evaluation. Coatings are tested under different loads with a constant speed and at temperatures ranging from room temperature (R.T.) to 500°C. Tribological tests are carried out on a pin-on- disc tribotester by selecting a wear track diameter of 60 mm for 5 minutes. Wear is reported in the form of wear rate by following Archard's equation. The microstructure characterization of the coating is performed using SEM (Scanning Electron Microscopy), EDX (Energy Dispersive X-Ray Analysis) and XRD (X-Ray Diffraction Analysis). Coating is developed with phosphorous weight percentages around 9% on cylindrical mild steel samples and the deposition thickness is observed to be around 50 μm. The as-deposited coating is found to be amorphous in nature and hardness of the as-deposited coating is found to be around 585HV01. Friction coefficient increases initially with the increase in temperature from room temperature up to 100°C but thereafter gradually decrease with the increase in temperature. Initial increase in temperature (up to 100°C) provides higher rate of wear compared to room temperature but with further increase it drops in most of the cases. Wear rate increases with the increase in temperature but as it crosses or nears the phase transformation temperature (around 340°C), the scenario gets reversed. From X-ray diffraction analysis, it is found that coating is amorphous in as-deposited condition but transforms into a crystalline structure with heat treatment.

Tribological Behaviour of Electroless NiP Coatings with an Extreme Pressure Additive: Synergistic or Antagonistic?

Electroless nickel–phosphorus (ENiP) coatings are widely used in many applications because of their excellent corrosion and wear resistance properties. However, their behaviour under lubricated conditions is less explored. This study examines the friction and wear properties using an Schwing–Reib–Verschleiss tribometer and the film-forming properties using scanning electron microscopy with energy-dispersive X-ray spectroscopy, atomic force microscopy and X-ray photoelectron spectroscopy of an extreme pressure (EP) additive for ENiP/steel and steel/steel contacts. The results show that the ENiP coating forms EP additive-derived tribofilms and these tribofilms consist of pad-like structures. These pad-like films have superior wear resistance properties compared to those formed on steel surfaces. The EP additive interacts synergistically with the ENiP coating and forms a tribofilm of about 130 nm thickness. The EP additive-derived tribofilms formed on the ENiP coating have a layered-structure, comprised of phosphates in the outermost layer followed, in order, by sulphides and phosphides. The results indicate that the ENiP coating could be a potential candidate for applications operating under elevated contact conditions lubricated with, for example, gear oils.

Study on the Mechanical Properties of Heat-Treated Electroless NiP Coatings Reinforced with Al2O3 Nano Particles

This work reports the effects of electroless co-deposition of Al2O3 nanoparticles and NiP to obtain a NiP-Al2O3 coating on the structure and mechanical properties of the composite coatings. The effects of annealing heat treatments at 373 K, 473 K, 573 K, and 673 K (100 °C, 200 °C, 300 °C, and 400 °C) on the structure and properties of the coatings were evaluated. The as-deposited coatings are a mixture of crystalline and amorphous phases that tend to crystallize during heat treatment. Heat treatment at higher temperatures causes the precipitation of the Ni3P phase. The mechanical properties of as-deposited and heat-treated NiP-Al2O3 coatings were evaluated using depth-sensing indentation tests performed at loads of 200 mN. The incorporation of Al2O3 nanoparticles induces strengthening of the NiP coating by dispersion. Heat treatment of the NiP-Al2O3 coatings induced crystallization of the amorphous phase with the formation of nanosized grains and the precipitation of Ni3P. Consequently, there is an increase in the hardness and Young’s modulus of the coatings to 15.4 ± 0.5 and 227 ± 2.8 GPa, respectively, in a combined hardening effect induced by dispersion of the Al2O3 nanoparticles and crystallization and precipitation during heat treatment.

Wear Analysis of Electroless Ni-P Coating Under Lubricated Condition Using Fuzzy Logic

Wear Analysis of Electroless Ni-P Coating Under Lubricated Condition Using Fuzzy Logic

A highly anticorrosive chromium-free conversion coating prepared on electroless Ni–P coating

Abstract Two kinds of chromium-free conversion coatings, including manganate conversion coating (MCC) and manganate/silicate composite conversion coating (MSCC), were prepared on electroless Ni–P coatings (ENPC) to improve the anticorrosive property of ENPC instead of chromate conversion coating (CCC). The EDX and XPS analyses illustrated the chemical compositions of MCC and MSCC mainly contained Ni(OH)2, NiO and MnO2, which acted as a physical barrier to inhibit the transfer of the charges and the movement of the ions in corrosion process. Compared with the MCC, an additional layer of polymeric silicate was formed on the surface of MSCC, which leaded to better corrosion resistance. In potentiodynamic polarization test, the MSCC showed the lowest corrosion current density (icorr) with value of 0.050 μA/cm2, which decreased by around two orders of magnitude compared with untreated ENPC. Moreover, the polarization resistance (Rp) of MSCC was about 7 times higher than that of CCC. The fitting parameters of EIS explained the reason why the MSCC exhibited better anticorrosive performance than the MCC. The result of neutral salt spray test (NSS) intuitively proved that the MSCC can replace the CCC to improve the anticorrosive property of ENPC.

Wear Performance Optimization for Electroless Ni-P Coating

Optimization of the wear performance of electroless Ni-P coating is carried out with the help of Taguchi orthogonal array design. Tribological testing parameters (applied load, sliding speed and duration of testing) are optimized with the help of L27 array in order to get the best wear performance from the coating. Load and time were found to be the most significant factors. Interaction between load and time is also found to hold some amount of significance towards the system response (wear). The characterization of the coating is carried out through scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction analysis. The coating morphology is found to resemble a nodular structure and the coating is mainly amorphous in as deposited state. However, post heat treatment at 400ºC for one hour the coating transforms into crystalline structure. The wear mechanism is also studied and found to be a mixture of abrasive and adhesive wear phenomena.

Influence of Nano Al2O3 Particles on the Adhesion, Hardness and Wear Resistance of Electroless NiP Coatings

Influence of Nano Al2O3 Particles on the Adhesion, Hardness and Wear Resistance of Electroless NiP Coatings

Effect of rare element cerium on the morphology and corrosion resistance of electro-less Ni-P coatings

This paper reports an experimental study on the microstructure and corrosion resistance of electro-less Ni-P coatings with increasing content of the rare element cerium (Ce). Surface morphology and the composition of the electro-less Ni-P coatings were studied by scanning electron microscope (SEM), X-ray energy dispersed analysis (EDS) and X-ray diffraction analysis (XRD). Hardness and Adhesive force are researched by a HX-200 Vickers diamond indenter micro-hardness tester. Furthermore, we study the adhesive force by using the Revetest scratch tester. We get the possession of Ce amorphous Ni-P coatings which has excellent properties in anti-corrosion. The effect of the rare element cerium concentration on corrosion resistance of the coatings was evaluated in the groundwater immersion test and porosity test, respectively. The results indicated that added little the rare element cerium into the plating bath increased the phosphorus content of the coatings, decreased the corrosion rates, it also decreases the porosity of the amorphous Ni-P coatings. The lowest corrosion rates of the amorphous Ni-P coatings in groundwater immersion test is 4.1 um · h-1, at the rare element cerium concentration of 0.12g · L-1.

The effect of nonmetallic element P in electroless Ni-P coating on the passivation process during chemical conversion treatment

Pure Ni and electroless Ni-P coating (ENPC) were passivated by a chemical conversion treatment. The passive films formed on pure Ni and ENPCs (with content of P 2.9, 7.2 and 11.7 at.% respectively) were analyzed by X-ray photoelectron spectroscopy (XPS). High-resolution XPS was also used to analyze the chemical states of the elements detected in the passive films. The results indicated that the detected Ni and P were in elemental states, and no compound with Ni and P element was detected in passive film, meaning that Ni and P did not participate in the formation of the passive film. The content of film-forming reaction product in passive film increases with the content of element P in Ni-P coating, suggesting that the nonmetallic P in Ni-P coating played an important role in the formation of the passive film. The XPS results were used to analyze the formation mechanism of the passive film. Copyright © 2014 John Wiley & Sons, Ltd.

The Effect of pH Value of Plating Bath on the Properties of Electroless Ni-P Coating on Phenolic Plastic Substrate

Electroless Ni–P coatings with different phosphorus contents have been developed to deposit on phenolic plastic in plating bath with different pH values. The effects of pH value on the phosphorus content and the microstructure were investigated by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD). The hardness of the coating was measured using Vicker’s indenter and the wear resistance was evaluated by a block-on-ring wear tester under dry condition. The results showed that with the increase of the pH value ranging from 4.4 to 5.4, the phosphorus content exhibited a decreasing trend from 11.01 wt.% to 7.76 wt.% . The structure of the electroless Ni–P coating transformed from amorphous phase, to a mixture of amorphous phases and nanocrystalline, and finally to nanocrystalline phase with the decrease of phosphorus content. The wear resistance of phenolic plastic was obviously enhanced by plating Ni–P coating. The hardness increased with the decrease of phosphorus content. However, the wear resistance did not always follow the hardness, indicating that not only the hardness but also other factors, such as internal stress and surface morphology, had an effect on the wear resistance of Ni–P coating.

Effect of novel ternary ligand system on acidic electroless Ni-P plating on AZ91D magnesium alloy

The electroless Ni-P coatings on AZ91D magnesium alloy substrate were prepared using the acidic hypophosphite-reduced electroless nickel bath containing the novel ternary ligand system. The results indicate that the deposition rate varies with the ternary ligand concentration in plating solution. The structural and morphological characteristics of the coatings were analyzed by XRD and SEM. The anticorrosion properties of the Ni-P coatings were evaluated in 3.5% NaCl solution by electrochemical impedance and potentiodynamic polarization methods. The amount of ternary ligands in electroless plating bath has an significant effect on the surface morphology and structure of Ni-P coatings. The decrease of crystallization temperature and increase of crystallization heat of all the deposits with an increase in ternary ligand concentration are found by DSC measurements. The coating obtained with 0.035 mol/L ternary ligand additive in plating bath can offer a better surface homogeneity and improve corrosion resistance.

Optimization of Tribological Properties of Electroless Ni-P Coatings under Lubrication Using WPCA

This work presents an experimental study of tribological performance of electroless Ni-P coating under lubricated condition. Mild steel specimens are used as the substrate material for the deposition of Ni-P coating. Tribological tests are carried out based on L27 orthogonal array (OA) varying three test parameters viz. normal load, sliding speed and sliding time in a multi-tribotester using block-on-roller configuration in lubricated condition. The experimental results for friction coefficient and wear are analysed using weighted principal components analysis (WPCA). An optimal test parameter combination is found out for minimum wear and friction coefficient. It is seen that the optimum combination of parameters are found at higher level of normal load, sliding speed and sliding time at 99% confidence level. Finally, a confirmation test is carried out to validate the analysis.

Post-treatment Processes for Corrosion Resistance on Electroless Ni-P Coating

Electroless Ni- P coatings on steel substrate were post- treated with γ- aminopropyltriethoxy silane(3-APTS), stearic acid and compound of the both respectively, and then for the posttreated coatings, the contact angle with pure water was measured and the corrosion performance was evaluated by means of nitric acid spot test and test with filter paper containing K3[Fe(CN)6] solution, immersion test in salt water and electrochemical measurements. The results showed that the post-treatments with the three agents all can enhance the corrosion resistance of the Ni-P coatings;while the appearance of the post- treated coatings was not changed; however among the three agents the compound of 3-APTS/stearic acid is superior to the other two individuals. Besides, the relevant mechanism concerning the inhibition effect of the agents was also discussed.

A comparative corrosion study of electroless Ni-P coatings treated by microwave and conventional furnace annealing

AbstractThis work aims at studying the corrosion behavior of electroless Ni-P coating on mild steel substrate heat-treated by microwave and conventional furnace (muffle) annealing. The corrosion behavior of the deposits has been evaluated by potentiodynamic polarization studies in 3.5 wt% sodium chloride solution. The heat treatment temperatures of both the microwave and the conventional furnace annealing were kept at regular intervals to study the corrosion performance of the coatings. Microwave heat treatment significantly improved the corrosion performance of the coatings. Further, corrosion mechanisms of as-coated, various microwave- and conventional heat-treated coatings were discussed for the consideration of phase constituents, grain sizes and microstrain.

Effect of Heat Treatment on Erosion-Corrosion Behavior of Electroless Ni-P Coatings in Saline Water

To prevent premature failure of heat exchanger tubes enduring rapid seawater flow, amorphous electroless Ni-P coatings were prepared on copper-nickel alloy (CuNi 90/10) substrates. The influence of post-deposition vacuum heat treatment at different annealing temperatures (190, 300, 400, 500, and 600°C) on the erosion-corrosion resistance of the annealed coatings was examined by X-ray diffraction, scanning electron microscopy, potentiodynamic polarization, and electrochemical impedance spectroscopy. It was found that precipitation of a crystalline phase took place in the coating matrix at 400°C. The highest microhardness was achieved for coatings undergoing heat treatment at 400°C due to the formation of the stable Ni3P phase. Electrochemical results indicated that all the Ni-P coatings present passivity and better corrosion resistance than the uncoated CuNi 90/10 substrate. The Ni-P coating treated at 500°C demonstrated the best erosion-corrosion resistance, which represented the optimization of the balance between erosion and corrosion resistance.

Corrosion Resistance of Sintered NdFeB Magnets with Various Surface Coatings

Pure Ni coating and multi-layered Ni-P coatings were deposited on sintered NdFeB magnets by ion beam sputtering and electroless plating to improve the corrosion resistance of magnets, respectively. The structure and preferred growth orientation, surface morphology, the adhesive strength between coatings and magnets, and corrosion properties of samples were investigated by XRD, SEM, high-low temperature shock test and potentiodynamic polarization curves, respectively. It was found that electroless Ni-P coatings are amorphous with nodules distributed, Ni coating deposited by ion beam sputtering is crystalline and spherical Ni grains are densely packed. Ni coating deposited by ion beam sputtering can provide better protection for sintered NdFeB than that of electroless Ni-P coating.

Wear Behavior of Electroless Ni-P Coatings in Brine Solution and Optimization of Coating Parameters

Abstract The present paper studies the wear behavior of electroless Ni-P coating in brine medium and optimization of the coating process parameters for minimum wear using Taguchi method based on L27 orthogonal array. The study is carried out using different combinations of four coating process parameters, namely, concentration of nickel source (A), concentration reducing agent (B), bath temperature (C) and annealing temperature (D). The wear tests are conducted with a pin-on-disk Wear & Friction Monitor. The optimum combination of process parameters for minimum depth of wear is obtained. ANOVA is performed to find out the significance of the coating parameters and their interactions. The surface morphology and composition of coatings are studied with the help of scanning electron microscopy (SEM), energy dispersed X-ray (EDX) analysis and X-ray diffraction (XRD) analysis. It is found that Ni-P coating is amorphous in as-deposited condition but gradually turns crystalline with heat treatment. The worn surface morphology reveals abrasive as well as corrosive wear mechanism.

Friction performance of electroless Ni-P coatings in alkaline medium and optimization of coating parameters

The present paper studies the friction performance of electroless Ni-P coating in alkaline medium (10% NaOH solution) and optimization of the coating process parameters is performed for minimum friction using Taguchi method based on L27 orthogonal array. The study is carried out using different combinations of four coating process parameters, namely, concentration of nickel source (A), concentration reducing agent (B), bath temperature (C) and annealing temperature (D). The friction tests are conducted with a pin-on-disk tribometer. The optimum combination of process parameters for minimum friction is obtained. Also, analysis of variance (ANOVA) is performed to find out the significant contribution of each coating process parameters and their interactions. ANOVA reveals that bath temperature has the maximum contribution in controlling the friction behaviour of Ni–P coating. The surface morphology and composition of coatings are studied with the help of scanning electron microscopy (SEM), energy dispersed X-ray (EDX) analysis and X-ray diffraction (XRD) analysis. It is found that the Ni-P coating is amorphous in as-deposited condition but gradually turns crystalline with heat treatment.

Tribo-corrosion Behavior of Electroless Ni-P Coatings in Alkaline Corrosive Environment

The present article considers an experimental study of tribo-corrosion behavior of electroless Ni–P coatings in alkaline environment sliding against alumina. The study of wear and friction behaviour is carried out using different load and sliding speed with the help of a pin-on-disk tribometer. The wear rate increases with decrease in sliding speed and increase in the applied load. The friction coefficient initially decreases with increase in the applied load and then remains at nearly steady level at higher applied load. Also, it is found that the friction coefficient is lower at higher sliding speed. The friction coefficient does not change with the sliding duration after the initial transient running-in time. The coating is characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) analysis. The wear mechanism is also studied and has been found to be mostly abrasive in nature.

Erosion-Corrosion Behavior of Electroless Ni-P Coating on Copper-Nickel Alloy in 3.5 wt.% Sodium Chloride Solution

The present investigation concerns electroless Ni-P coatings prepared onto the copper-nickel alloy (CuNi 90/10) to enhance the erosion-corrosion resistance. X-ray diffraction technique (XRD), scanning electron microscopy, and electrochemical methods were utilized to study the heat treatment effects on the erosion-corrosion resistance and the physical properties of the coatings. The results indicated that both the as-plated and coating with post-heat treatment (PHT) showed much higher self-passivation ability and much lower current densities than that of the copper-nickel alloy (CuNi 90/10). XRD results showed that both the as-plated and coating with PHT had amorphous structure and the effect of PHT at 190 °C on the structure of Ni-P coating was not significant. Compared with coating with PHT, the as-plated exhibited lower erosion-corrosion resistance due to some small pits and cracks. The coating with PHT demonstrated significant improvement of erosion-corrosion resistance in 3.5 wt.% NaCl solution, which was attributed to better protective film, lower porosity of coatings, and high micro-hardness compared with Ni-P coating without PHT.