Electroless Ni-B Coatings Research Articles

A Systematic Investigation of Lead-Free Electroless Ni-B-W Coating Properties Using Taguchi’s Methodology

Electroless Ni-B (ENB) coatings have industrial importance due to their excellent mechanical properties. The inclusion of W (ENB-W) to the coatings further enhances their mechanical properties and thermal stability. Nevertheless, the ENB or ENB-W coatings are deposited from a heavy metal-stabilized bath, and the very commonly used stabilizer is lead nitrate. The present work is an attempt to obtain an ENB-W coating with enhanced mechanical properties and elimination of the stabilizer from the bath. To achieve this, the coating bath temperature, the heat treatment temperature and the heat treatment duration were varied systematically following a strategy adopted from Taguchi’s experimental design. The mechanical properties targeted include surface microhardness and scratch hardness. Multi-objective optimization was performed using gray relational methodology. The predicted bath temperature was 85 °C, while the predicted heat treatment temperature was 450 °C and there was 3 h of heat treatment time. The optimized lead-free ENB-W coatings had a microhardness of 1096.2 HV100 and scratch hardness of 13.86 GPa. In fact, single-objective optimization for surface microhardness and scratch hardness by Taguchi’s methodology also predicted the same optimal parametric condition for both scratch hardness and surface microhardness. This was comparable to that of a lead-stabilized ENB-W coating and higher than the as-plated stabilizer free ENB-W coatings. The coating failure of the optimized ENB-W alloy was tested using a progressive scratch test, which showed that there was no chevron or transverse cracks within the load range considered. Analysis of corrosion resistance revealed that the corrosion potential of the optimized coatings was −407 mV, and this was comparable to that of a lead-based ENB-W coating.

Deposition and process parameter optimization of electroless Ni-B coating from a stabilizer free bath to achieve enhanced microhardness, scratch-hardness and adhesion using taguchi’s methodology

Electroless nickel boron coatings have wide industrial usage. However, they are generally obtained from a lead-stabilized bath. The present work investigates and optimizes the scratch-hardness and microhardness obtained from stabilizer-free electroless nickel boron bath in a quest to eliminate lead nitrate/heavy metals, which are potentially toxic. The bath temperature, heat treatment temperature, and duration were varied at three levels. Enhanced scratch-hardness (12.581 GPa) was obtained at 85 °C bath temperature and heat treatment at 350 °C for 1 h. At the same time, the highest microhardness (886.17 HV100) was obtained at a parametric combination of 95 °C bath temperature and heat treatment at 450 °C for 1 h. Multi-objective optimization was carried out using grey relational analysis. The parametric combination predicted in multi-objective optimization was 85 °C bath temperature and heat treatment at 350 °C for 1 h where the microhardness was 846.34 HV100. Furthermore, an analysis of variance was also carried out to investigate the importance of the factors in controlling scratch-hardness and microhardness. The highest contribution was observed from heat treatment duration. Further investigation of the optimized coating was done by the progressive scratch test, which recorded that the first critical load of failure improved compared to non-heat treated electroless Ni-B coatings. The coatings were also characterized using field emission scanning electron microscope, energy dispersive x-ray spectroscopy, and x-ray diffraction. The coatings in optimized condition showed no transverse or chevron cracks within 5–24 N.

Effects of propylamine and ethylenediamine intercalation of α-ZrP on the corrosion resistance and tribological properties of electroless Ni-B coatings

In this study, propylamine and ethylenediamine intercalated α-ZrP nanocomposites (denoted by P-α-ZrP and E-α-ZrP, respectively) were synthesized. The effects of propylamine and ethylenediamine intercalated α-ZrP nanocomposites and their reinforcements on the corrosion resistance and mechanical properties of Ni-B coatings were investigated and compared. The morphology and structure of the three composites were characterized using transmission electron microscopy, atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, infrared spectroscopy, thermogravimetric analysis, and particle size analysis. Both propylamine and ethylenediamine intercalation increase the layer spacing of α-ZrP, but do not change the lamellar structure of α-ZrP. The EIS test results show that both Ni-B/P-α-ZrP and Ni-B/E-α-ZrP composite coatings have significantly lower corrosion rates than Ni-B and Ni-B/α-ZrP composite coatings. Compared to Ni-B/α-ZrP, the corrosion rates are reduced by 32 % and 76 % respectively. The Rct values for Ni-B/P-α-ZrP and Ni-B/E-α-ZrP composite coatings are also distinctly higher than Ni-B/α-ZrP, with Ni-B/E-α-ZrP having the highest values. In addition, Ni-B/P-α-ZrP and Ni-B/E-α-ZrP composite coatings are both harder than Ni-B/α-ZrP and have lower average coefficients of friction and wear rates than Ni-B/α-aZrP. Among them, the Ni-B/E-α-ZrP composite coating has the highest microhardness (1163.64 ± 21.20 HV) and the best wear resistance. The wear rate is reduced by 87 % and 65 % compared to Ni-B and Ni-B/α-ZrP composite coatings respectively. In conclusion, both P-α-ZrP and E-α-ZrP are better than α-ZrP in terms of enhancement, with E-α-ZrP being the best.

Investigation of the Supercapacitive Behavior of Electroless Ni-B Coatings

Amorphous electroless Ni-B coatings were deposited on steel substrates with different surface morphologies and B contents (6.5–8.64 wt.%) that could be changed by altering the temperature and the composition of the baths. The supercapacitive behavior of the coatings was evaluated by cyclic voltammetry and galvanostatic charge–discharge measurements, and it was found that Ni-B coatings had higher capacitance than pure electroless Ni or the bulk Ni plate. A close relationship was identified between the microstructure, the B content, and the capacitive behavior of the coatings. The presence of the B alloying element had the most significant effect in determining the capacitance, while the surface area and particle size also contributed to its increase. A surface-specific capacity of 31 mF/cm2 was achieved by the coating containing the highest B content and largest AFM surface area. Furthermore, it was revealed that the particle size of the deposits was determined by the combined effect of the bath temperature and the B content under the applied experimental conditions. The obtained results indicate that Ni-B coatings are promising candidates for supercapacitive applications.

Scratch and corrosion behaviour study of electroless Ni-B reinforced with ultrasonicated nano TiO2

The present investigation is a study into the scratch and corrosion response of as-coated Ni-B-TiO2 as compared to the as-deposited Ni-B coatings. Ultrasonicated nano TiO2 particles were used to reinforce electroless Ni-B coatings. The presence of hard nano TiO2 particles improved the scratch hardness of the Nickel-Boron-TiO2 coatings. During the scratch test for an applied load of 20 N, the Nickel-Boron-TiO2 coating showed a decrease of 42 % in scratch width as compared to the Ni-B coatings. Corrosion behavior also showed remarkable improvement with the addition of nanoparticles. As compared to the Nickel-Boron coatings, the corrosion potential Ecorr improved by 5 % while the corrosion current density Icorr showed a 1.5-fold decrease for Ni-B- TiO2 coatings. The double-layer capacitance Cdl which is a qualitative indicator of the porosities present in the coatings was nearly halved with the addition of TiO2 nanoparticles. The specimen underwent SEM analysis for the morphological study and scratch testing to determine the scratch hardness and corrosion behaviour to identify the electrochemical response to a corrosive environment.

Tribological Electroless Ternary Ni-B-W Coatings: A Suitable Alternative to Hard Chromium Coatings

Abstract Concerns raised about the environmental ramifications of electrodeposited hard chromium (EHC) plating are perhaps the paramount challenge posed to the finishing industries to find a suitable alternative. Electroless Ni-B coatings have attracted much attention due to their superior mechanical and tribological properties; those are enhanced further in electroless Ni-B-W coatings. Electroless Ni-B-W can be a suitable alternative for the replacement of EHC in a variety of engineering applications. In the present study, the changes in morphological features, deposition rates with respect to time, and deposition mechanisms of electroless Ni-B-W coatings are studied thoroughly. After heat treatment, all deposited coatings are characterized thoroughly for the evaluation of their mechanical and tribological characteristics. This is helpful in the comparison of characteristics with properties of industrial EHC coatings. To analyze the coating-substrate adhesion in the electroless depositions, scratch tests with progressive load and repetitions are carried out. Frictional behavior and failure mechanisms at the scratch tracks of all fabricated coatings are also studied through repetitive scratch tests. Heat treatment of electroless Ni-B-W coatings induced significant improvements in mechanical, tribological properties and adhesion behavior. The present study establishes beyond doubt that owing to a specific set of properties, electroless Ni-B-W coatings show tremendous potential to be recommended as a replacement for chrome coatings.

A Hybrid Approximation to Wear Analysis in Electroless Ni-B Coatings: Conformity of Experimental and Finite Element Methods

A Hybrid Approximation to Wear Analysis in Electroless Ni-B Coatings: Conformity of Experimental and Finite Element Methods

A comparative study on morphological, mechanical and tribological properties of electroless NiP, NiB and NiBP coatings

The aim of this paper is to fabricate the NiBP polyalloys coatings by electroless coating technique on the aluminum substrate. A comparative investigation of morphological and hardness properties between NiP, NiB and NiBP coatings is employed. Also, the effect of heat treatment process on the nanoindentation behaviors of the electroless nickel-based alloys is studied. The highest hardness of 8.76 GPa and Young's modulus of 180.36 GPa were obtained electroless NiBP coatings in the case of as-plated conditions. After heat treatment process at 400°C in an inert atmosphere, electroless NiB coatings showed the highest hardness value of 10.02 GPa and Young's modulus of 207.48 GPa when compared with NiP and NiBP coatings. Although electroless NiB coatings exhibited the highest Young's modulus and harness value, electroless NiBP coatings showed the best protection against wear in all loads of 1, 2 and 3N and all sliding velocities of 100, 200 and 400 mm/s due to showing H/E ratio of NiBP coatings comparing with NiB and NiP coatings.

Optimization of Ni-B coating bath and effect of DMAB concentration on hardness and wear

In this study, reducing agent amount, stabilizer amount, coating bath temperature and stirring speed parameters were examined for optimization of electroless Ni-B coatings, and the effect of reducing agent amount on hardness and wear of the coating was investigated. The pH of the electroless Ni-B coatings made for 1 h was set to 6, nickel chloride (NiCl2.6H2O) as the nickel source, sodium acetate (C2H3NaO2) as the complexing agent, thiourea as the stabilizer (CH4N2S) and DMAB ((CH3)2NBH2) as the reducing agent was used in the coatings. The bath parameters were varied as; the amount of reducing agent (2 g/L, 3 g/L and 4 g/L), coating bath temperature (65°C, 70°C and 75°C), stabilizer amount (0.5 mg/L, 1 mg/L, and 2 mg/L) and stirring speed (250, 300 and 350 rpm). After determining the optimum conditions, the effects of the amount of reducing agent on the coating were examined. Scanning Electron Microscopy (SEM), X-ray diffractometer (XRD), Vickers nano-hardness test and tribometer were used for characterization of coatings. In the optimization studies, it was observed that the coating morphology was in the form of cauliflower and columnar structures were formed in the cross-section images. According to optimization results on the morphologies, the samples which compact and free-crack have been investigated phase structure, hardness and tribology properties. In XRD analysis, coatings produced with different amounts of reducing (DMAB) are amorphous as-deposited, after annealed at 400°C for 2 h, nickel borides (Ni2B and Ni3B) phases are formed and increased the preferential orientation (111) of the nickel crystal plane. The effect of DMAB concentration on coating was examined in as-deposited condition and post annealing. The formation of nickel borides after annealing increases the hardness. The effect of DMAB concentration on the coating after annealed was examined and it was observed that the wear resistance of the dense and homogeneously dispersed sample in the coating matrix was more perfect than other samples. Consequently, hardness (850 HV), coefficient of friction (0.37) and wear rate (2.92 × 10−7 mm3/Nm) of B2 sample which free-crack and compact was obtained. These results indicate a high strengthen B2 sample produced with 3 g/L DMAB concentration and 70°C bath temperature could utilize in a harsh medium.

Improvement of the NiBrAl Casting Alloy Surface Properties by Electroless Ni-B Plating for Dynamic Marine Applications

The use of NiBrAl casting alloy for the construction of marine propellers is expanding due to the resistance to fatigue, corrosion and wear under the effect of particles suspended in fluid. In this study, the nanostructure of the Ni-B coating is created by the electroless plating method on the NiBrAl alloy surface. After plating, the specimens are heat-treated, and the temperature and optimum time of the heat treatment are found to be 410°C and 70 min. The microstructural study by scanning electron microscopy and X-ray diffraction shows that, by conducting the heat treatment after plating, the amorphous structure of the coating becomes crystalline. After heat treatment cauliflower colonies experience 17% growth due to their constituent crystallites. After plating and heat treatment, the hardness of the surface increased from 410 to 788 and 1365 Vickers, respectively. According to the pin-on-disk wear test results, the wear resistance improves due to plating and heat treatment. The microscopic study of the worn surfaces shows that the heat treatment turns the wear mechanism from adhesive to slightly abrasive. The corrosion resistance evaluation by the polarization test shows that heat treatment leads to the reduction of corrosion resistance. According to the results, the electroless Ni-B coatings can be considered as one of the best options to improve the properties and performance of NiBrAl alloys, under service conditions.

Replacement of Lead stabilizer in electroless Nickel-Boron baths: Synthesis and characterization of coatings from bismuth stabilized bath

Only a few compounds have been completely characterized as stabilizers in alkaline electroless nickel‑boron plating and most of them have serious impact on health or the environment. In this paper, the effects of bismuth salts on the bath stability and characteristics of electroless NiB deposits obtained from an alkaline electroless nickel bath reduced by borohydride are presented. The objective of this paper is to propose a healthy and environmental friendly electroless NiB coating. The process of production was maintained the same as traditional NiB to facilitate the industrial adaptation. Bismuth accelerates the rate of deposition up to 10−5 mol/L and inhibits plating from a concentration of 0.01 mol/L. The bismuth ions in the NiB bath act as stabilizer but some bismuth also co-deposits with the nickel‑boron coating, leading to a coating with 3 wt% bismuth. The coating presents a homogeneous surface morphology with a 15.11 μm/h plating rate in agitated and non-replenished bath. The X-ray diffraction patterns of electroless NiB coatings stabilized by Bi3+ exhibit a single broad peak, indicating a strong tendency to form amorphous structure. The coatings present the typical high hardness of NiB coatings (830 hv50), with a relatively smooth surface. The wear behavior was characterized by ball-on-disc tests and a friction coefficient of 0.45 is obtained after 100 m of test with 5 N charge and an alumina ball. Scratch test results show the first damage after 16 N. NiB-Bi coatings have impressive properties and can replace lead stabilized electroless NiB in different fields.

Effect of Heat Treatment on Tribological Properties of Ni-B Coatings on Low Carbon Steel: Wear Maps and Wear Mechanisms

Among the alternatives for using low-carbon steel in parts with heavy wear, as gears and bearing surfaces, Ni-B electroless coatings deposited on these steels are considered due to their wear resistance. Wear maps, elaborated from friction or wear results found for different evaluated conditions, are a very useful tool for the selection of materials based on tribological properties. However, wear maps for electroless Ni-B coatings are very scarce. In this work, dry sliding wear tests with different loads and sliding velocities were performed on Ni-B electroless coatings applied on AISI/SAE 1018 steel, with and without heat treatment at 450 °C for 1 h, with the aim of determining the effect of the heat treatment on the friction coefficients and wear rates. Contour and profile maps, and finally friction and wear maps, were constructed for each of the coatings evaluated. The coating properties before and after the heat treatment were studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), scratch tests, nanoindentation, and differential scanning calorimetry (DSC). Sliding wear tracks were studied using SEM, energy-dispersive spectroscopy (EDS), and micro-Raman spectroscopy. Good agreement between experimental and predicted values was found in friction and wear maps. Wear mechanisms change from flattening in less severe conditions to abrasion in more severe conditions, besides spalling and adhesive wear in untreated coatings. Moreover, abrasive wear is lower in heat-treated coating than in untreated coating.

Characterisation and corrosion study of electroless Nickel-Boron coating reinforced with alumina nanoparticles

Abstract This investigation deals with the study of 1 g/l alumina reinforced electroless Ni-B coatings on a low carbon steel substrate. Reinforced coatings were prepared from the as-received nano powders. The alumina nano particles were ultra-sonicated before being introduced into the coating bath. The reinforced coatings exhibited an improvement in hardness, and corrosion resistance. A significant increase of nearly 10%, was observed in case of the hardness of the reinforced coatings. Corrosion potential increased by about 6% with the addition of alumina nano particles. The agglomerated nano particles seem to embed in the nodular boundaries of the cauliflower like Ni-B morphology and in inter nodular porosities. This, in turn, improved the corrosion resistance by forming an intimate sacrificial layer on the vulnerable substrate material.

Characterization of Thermal Stability and High-Temperature Tribological Behavior of Electroless Ni-B Coating

A preliminary study has been conducted using sequences of isothermal heat treatments and unidirectional high-temperature wear test following ball-on-flat geometry against an alumina counterface, to assess thermal stability and high-temperature tribological properties of the crystalline electroless Ni-B coating, a potential candidate for high-temperature solid lubricant coating. Isothermal heat treatment of 450 °C/15 h causes a significant amount of B diffusion into the Fe substrate without altering the coating’s through-thickness hardness and nanostructure. At room temperature, a very low wear rate is observed, which increases up to two orders of magnitude above a testing temperature of 100 °C. Room-temperature wear behavior is mostly governed by oxidative wear, where friction-induced heating produces a thick oxide scale on the wear track, which subsequently decreases the wear rate by preventing direct contact between the coating and counterface. In the case of wear tests above 100 °C, removal of the same oxide layer occurs through local plastic deformation, essentially plastic ratcheting at the contacting region by flow softening of the contacting surface layer due to a local rise in temperature. Worn track morphology shows similarity with the severe wear seen in steel–steel contacts. Experimental observations have been explained and validated using the concept of contact point flash temperature. A quantitative assessment of contact point flash temperature has been carried out adopting the methodology, proposed by Ashby et al. The effects of applied normal load, test geometry, choice of counterface material, and testing temperatures on the transition of wear mechanism are critically discussed.

Friction and Wear Performance of Electroless Ni-B Coatings at Different Operating Temperatures

Electroless Ni-B coatings are deposited on AISI 1040 steel specimens and heat treated at 350 ∘C for 1 h to improve their properties. Coating characterization is done using energy dispersive X-ray analysis, scanning electron microscope and X-ray diffraction techniques. The as-deposited coatings are amorphous and become crystalline on heat treatment. Microhardness of the coatings improves significantly on heat treatment due to the precipitation of boride phases. The tribological behavior of the heat treated coatings is observed on a pin-on-disk tribological test setup by varying the applied normal load, speed of the counterface material and the test temperature. The wear and coefficient of friction of the coatings are significantly affected by the load, speed and test temperature which in turn control the in-situ oxide formation and microstructural changes during the wear process. This is further confirmed by examining the worn specimens using scanning electron microscope and energy dispersive X-ray analysis.

Production and properties of composite electroless Ni-B-SiC coatings

The study of electroless Ni-B coatings is pursued in order to obtain deposits on metal substrates with advanced properties such as high microhardness for particularly demanding engineering uses. In the present study, composite Ni-B coatings enhanced with SiC microparticles on a steel substrate were prepared using the method of electroless plating. Structure characterization was performed by means of X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM) in order to draw conclusions concerning the dispersion and incorporation of SiC particles in the Ni-B matrix and how they affect surface roughness measured by a profilometer. Vickers microhardness tests were performed in order to demonstrate the notable increase in microhardness compared to the bare substrate. Furthermore, Tafel electrochemical tests in 3.5% NaCl(aq) were carried out in order to evaluate how the ceramic microparticles affect the behaviour of coatings in the corrosive medium. The results indicate, that improved deposits are obtained capable to withstand very demanding applications where high microhardness along with resistance to corrosion is a prerequisite.

Evaluation of Friction Behavior of Electroless Ni-B Coating and its Optimization under Engine Oil Lubricated Condition

The present study deals with the deposition of electroless Ni-B coating on mild steel substrate. The friction behavior under lubricated condition is analyzed on a pin – on – disc type tribo – tester. The applied normal load, sliding speed and sliding time are varied at three different levels. Their effect on coefficient of friction (COF) of the deposits is analyzed. Experiments are carried out following the combinations in Taguchi’s L27 orthogonal array. Finally, an attempt is made to optimize the tribo – testing parameters for minimum COF of the deposits.

Optimization of Wear Performance of Electroless Ni-B Coating under Lubrication

This paper presents an experimental study on tribological behavior of electroless Ni-B coating under lubricated condition based on Taguchi’s method. Mild steel specimens are used as the substrate material for the deposition of Ni-B coating and the thickness of the deposits is found to be around 35 μm. Based on Taguchi’s L27 orthogonal array of experiments, the wear tests are done on a pin-on-disc type tribotester This experiment is carried out by utilizing the combination of process parameters of the tribotester like normal load, sliding speed and duration of sliding. The analysis of the experimental data is carried out with the help of MINITAB® software package. It is seen that the normal load is the most significant factor followed by sliding time at 99% confidence level. The surface morphology, composition and compound analysis of the coatings are done by means of scanning electron microscope, energy dispersed X-ray micro-analyzer and X-ray diffraction analyzer respectively. Finally, a confirmation test is carried out to validate the analysis.

Optimization of Wear Performance of Electroless Ni-B Coating under Lubrication

This paper presents an experimental study on tribological behavior of electroless Ni-B coating under lubricated condition based on Taguchi’s method. Mild steel specimens are used as the substrate material for the deposition of Ni-B coating and the thickness of the deposits is found to be around 35 μm. Based on Taguchi’s L27 orthogonal array of experiments, the wear tests are done on a pin-on-disc type tribotester This experiment is carried out by utilizing the combination of process parameters of the tribotester like normal load, sliding speed and duration of sliding. The analysis of the experimental data is carried out with the help of MINITAB® software package. It is seen that the normal load is the most significant factor followed by sliding time at 99% confidence level. The surface morphology, composition and compound analysis of the coatings are done by means of scanning electron microscope, energy dispersed X-ray micro-analyzer and X-ray diffraction analyzer respectively. Finally, a confirmation test is carried out to validate the analysis.

Study on Influence of Zwitterionic Surfactant on the Surface Finish and Surface Morphology of Electroless Ni-B Coatings on Al 7075-T6 Alloy

The influence of Zwitterionic - propanesulfonate surfactant on the surface properties such as surface roughness, surface morphology and microhardness of Ni-B coatings using electroless alkaline bath was reported in this paper. Ni-B deposits obtained from nickel chloride as the source of nickel and borohydride as the reducing agent at a pH of 11 and 12 and temperature 85 ± 2 OC. This study reveals that the Ni – B coatings were clearly influenced by the addition of surfactant propanesulfonate on surface roughness and surface morphology. Electroless nickel (EN) - B coatings with addition of surfactant has changed the surface morphology from non-smooth nodular appearance to a smooth surface with average roughness value 1.4μm, which is less than the Ra value of without surfactant 1.98μm. The hardness of the deposit increased with lesser concentration of the surfactant when compared to without surfactant addition. Surface morphology and composition of the Ni–B coatings was analyzed by scanning electron microscope (SEM) and X-ray diffraction (XRD).