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PTFE nanocomposite coatings on mild steel surface
Accepted Manuscript Title: Pulse electrodeposition of self-lubricating Ni-W/PTFE nanocomposite coatings on mild steel surface Author: S. Sangeetha G. Paruthimal Kalaignan J. Tennis Anthuvan PII: DOI: Reference:
S0169-4332(15)02546-5 http://dx.doi.org/doi:10.1016/j.apsusc.2015.10.127 APSUSC 31608
To appear in:
APSUSC
Received date: Revised date: Accepted date:
8-7-2015 16-10-2015 17-10-2015
Please cite this article as: S. Sangeetha, G.P. Kalaignan, J.T. Anthuvan, Pulse electrodeposition of self-lubricating Ni-W/PTFE nanocomposite coatings on mild steel surface, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.10.127 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights PTFE polymer inclusion on Ni-W alloy matrix was electrodeposited by pulse current method.
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Tribological properties and electrochemical characterizations of the nanocomposite coatings were analyzed.
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The Hydrophobic behaviour of Ni-W/PTFE nanocomposite coating was measured.
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Ni-W/PTFE nanocomposite coatings have showed superior tribological properties and corrosion resistance relative to that of the Ni-W alloy matrix.
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Pulse electrodeposition of self-lubricating Ni-W/PTFE nanocomposite coatings on mild steel surface S. Sangeetha1 and G. Paruthimal Kalaignan1*, J. Tennis Anthuvan2
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1. Advanced Nanocomposite Coatings Laboratory, Department of Industrial Chemistry, Alagappa University, Karaikudi 630 003, India
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2. M. Kumarasamy College of Engineering, Karur, Tamilnadu, India.
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Corresponding Author phone No: +91-9443135307, Fax: +914565 225202. Email id: [email protected]
Abstract
Ni-W/PTFE
nanocomposite
coatings
with
various
contents
of
PTFE
(polytetafluoroethylene) particles were prepared by pulse current (PC) electrodeposition from the Ni-W plating bath containing self lubricant PTFE particles to be co-deposited. Co-deposited PTFE particulates were uniformly distributed in the Ni–W alloy matrix. The coatings were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX), X-ray Diffractometry (XRD) and Vicker’s micro hardness tester. Tafel Polarization and electrochemical Impedance methods were used to evaluate the corrosion resistance behaviour of 1 Page 1 of 35
the nanocomposite coatings in 3.5% NaCl solution. It was found that, the Ni-W/PTFE nanocomposite coating has better corrosion resistance than the Ni-W alloy coating. Surface roughness and friction coefficient of the coated samples were assessed by Mitutoyo Surftest SJ-
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310 (ISO1997) and Scratch tester TR-101-M4 respectively. The contact angle (CA) of a water droplet on the surface of nanocomposite coating was measured by Optical Contact Goniometry
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(OCA 35). These results indicated that, the addition of PTFE in the Ni-W alloy matrix has
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resulted moderate microhardness, smooth surface, less friction coefficient, excellent water
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repellency and enhanced corrosion resistance of the nanocomposite coatings. Keywords: Ni-W/PTFE nanocomposite coatings, coefficient of friction, Microhardness,
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Electrochemical characterization, contact angle.
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Introduction
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Electrodeposition of nanocomposite coatings has been developed for enhanced tribological and corrosion resistance of alloying matrix [1-3]. Composite electrodeposition is a
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method of co-deposition of inert particles such as ceramic, metallic, or polymers with a metal matrix. The electrodeposited Ni-W alloy matrixes have been of great interest for its admirable microhardness, corrosion and wear resistance [4]. Introduction of Tungsten to the alloy matrix has unique properties such as higher tensile strength, thermal stability, higher hardness and corrosion resistance [5]. Generally, pulse current deposition (PC) offers a finer grained deposit with more particles embedded, as the current density employed in PC can be significantly higher than that of direct current. Lajevardi et.al has investigated the influence of pulse plating parameters and properties of Ni- TiO2 nanocomposite coatings [6]. Pulse deposition has caused a high nucleation rate and significant changes in the coating morphology. Because, during pulse
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ON time (TON) the current or potential is applied and the pulse OFF time (TOFF) zero current is applied. Thus the current is periodically turned off to cause this layer to discharge to an extent. This process permits the ions to pass through the surface of the cathode more easily. Moreover,
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pulse deposition has less adsorbed hydrogen and can easily control the microstructure of the deposits than the coatings achieved from other techniques [7]. Particles agglomeration is an
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undesirable problem during electrodeposition of a nanocomposite coating, which would decline
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the tribological properties of the deposition. The addition of cationic surfactant in an electrolytic bath has improved the distribution of co- deposited particles. Surfactant generally plays an
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essential role in the deposition process and has offered various improved properties of the deposits, such as the smoothness, brightness and homogeneity. The cationic surfactant CTAB
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(Cetyltrimethyl ammonium bromide) is preferred for its strong adsorbed capability [8]. The
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important benefits for the inclusion of hard particles like Al2O3, TiO2, and SiO2 into the metal
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deposits are to achieve the higher microhardness and wear resistance of the nanocomposite coatings [9-11]. Improved lubricity has been attained by incorporating PTFE, h-BN and MoS2
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particles into the nanocomposite coatings [12-14]. Among them, PTFE is chemically inert and its coefficient of friction is lower than that of almost any other polymers. Since of its very low surface energy, PTFE has outstanding non-stick properties. Nanocomposite coatings containing PTFE particles are mainly considered in recent time because of their extremely useful properties such as self-lubrication, coefficient of friction, wear resistance etc. Based on such properties, the span of application of PTFE as a solid lubricant has received significant research attention in recent years. A study on the wear and friction behaviour of PTFE filled with alumina particles were investigated by Zhijiang et.al [15]. Wear and corrosion properties of EN-PTFE-MoS2 had been reported [12]. Effects of Cu content in electroless Ni–Cu–P–PTFE composite coatings and
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their anti-corrosion properties were given by Zhao et.al [16 & 17]. A proper heat treatment effect of EN-PTFE-SiC composite coating was systematically studied by Huang et.al [18]. This work was aimed to prepare pulse electrodeposition of Ni-W/PTFE nano composite coatings to attain
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high corrosion resistance, low friction coefficient and lower surface roughness values. A comparative study of the properties of pulse electrodeposition of Ni-W alloy matrix and Ni-
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nanocomposite coatings and its properties are also discussed.
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W/PTFE nanocomposite coatings were determined. The importance of PTFE inclusion into the
2. Experimental process
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Ni-W/PTFE nano-composite coatings were deposited on mild steel substrates from the
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nickel sulphate bath solution containing PTFE particles. The bath constituents and their
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compositions are given in Table 1. The mild steel plates of size 3 × 2.5 × 0.05 cm were dipped in 5% H2SO4 for 10 min and then cleaned with distilled water followed by drying. Then the specimens were degreased with trichloroethylene to remove the oily impurities adhered on the surface. Thus pretreated mild steel specimens were used as cathode. Pure nickel bar (99.9%) of size 5×5×0.5 cm was used as the anode. All the solutions were prepared by using triple distilled water. Prior to electrodeposition, PTFE particles were ultra sonicated for 60 s. Cetyl trimethyl ammonium bromide (CTAB) surfactant was employed for particle dispersion to prevent agglomeration of PTFE particles in the solution. The cationic surfactant can adsorb on the particle surface has developed a net positive charge on its surface, so increasing their affinity towards the cathode and hence increases the stability of particle suspension and prevents 4 Page 4 of 35
agglomeration. Like this, it is understood that, cationic surfactant enhances the incorporation of particles in the metal matrix. Besides, zeta potential of the nanoparticles would be increased by the addition of cationic surfactant CTAB. The positive Zeta potential has given an extra adhesion
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force between the inert particles and the cathode. Additionally, mechanical stirring (600 rpm) was used for thorough mixing of all the components and maintained the plating temperature at
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65°C. The inert particles were in contact with the bath solution for 24 hours and then stirred well.
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Certainly, the stirring has offered a uniform mass transfer and good particle adherence to the cathode. By the use of magnetic stirrer the suspended particles were thoroughly mixed in order to
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attain the uniform distribution of nanoparticles in bath solution. It is well known that, the tungsten content of the alloy deposition mostly depends upon the type of the complexing agent
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used in the electrolytic bath. Citrate bath has been used to include higher tungsten content into
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the composite coatings. PTFE concentration in the electrolytic bath was varied between 5 and 20
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g/L. Both Ni-W alloy and Ni-W/PTFE nanocomposite coatings were deposited on mild steel substrates by using pulse current technique. The Pulse electrodeposition was carried out by
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employing a Myriad bipolar pulsed power supply. The micro hardness of the electrodeposits was measured by using MHG Everyone Hardness tester (Hong Kong) on the Vicker’s scale. It had a diamond pyramid of a square base with an angle of 136° at the vertex between two opposite faces. The micro hardness of the deposits in kg/mm2 was determined in each case by using the formula
Where, L is the load applied in (50 gm) and d the diagonal of the indention (µm). The reported microhardness value of incorporating boron nitride particles into the Ni-W alloy matrix
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is an average value of the three measurements. Scanning electron microscope (SEM) was used to characterize the surface morphology of the composite coatings of size 1cm ×1cm. The deposited surface was subjected to EDAX (Energy Dispersive X-ray analysis) for the determination of
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chemical composition of the composites deposited on the surface. The crystalline structure of the plated substrate was identified by X-ray diffraction using Brooker D8 advance X-ray
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diffractometer operated with Cu Ka radiation (nickel filtered) at a rating of 40 KV, 20 mA. The
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scan rate was 0.05 per step with the measuring time of 15 per step. The crystallite size of the
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deposits was calculated by using the Scherrer’s equation [19].
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)
Where, D is the crystalline size, λ is the incident radiation (1.5418 Å), β is the corrected
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peak width at half-maximum intensity and θ the angular position. Electrochemical measurements
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were carried out by using an electrochemical analyzer (EG&G – Auto Lab Analyzer Model:
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6310) containing three electrode cell assembly. Corrosion experiments were carried out in 3⋅5
wt% NaCl solution kept at 30° C. The exposed 1 cm2 area of mild steel substrate was acted as working electrode. A rectangular Pt foil and a saturated calomel electrode (SCE) were used as auxiliary and reference electrodes respectively. The potentiodynamic polarization studies were
carried out for the potential range from -0⋅75 to –1⋅25 V with respect to the OCP at a scan rate of
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2 mV/s. The potential E (V vs. SCE) was plotted against log I (A cm–2) to obtain polarization curve. From this polarization curve, the corrosion potential (Ecorr) and corrosion current (Icorr)
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parameters were obtained. Impedance measurements were performed after the immersion of
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specimen for 2 minutes in 3⋅5 wt% NaCl solution for attaining the steady state potential. The
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same three electrode cell setup was used for performing this experiment. The impedance spectra were found to be in the frequency range of 10 K cs-1 – 100 m cs-1. Surface Roughness of the
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coatings was assessed by using Roughness Measuring Station (Make: Mitutoyo, Model: Surftest SJ-310). This instrument was used to analyze the average roughness value (Ra) with Probe
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movement and travelling distances 0.5 mm/s and 5 mm respectively. Moreover, Scratch tester TR-101-M4 (Make-DUCOM) was used to determine the coefficient of friction for the coatings.
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All the samples were run against at 5N normal loads at 0.2 ms-1 speed. Thickness of the coatings was measured by the cross-sectional FE-SEM images. The measurement of water repellency of the Ni-W/PTFE nanocomposite coating was evaluated by determining the static contact angle for water drops with the help of Optical Contact Goniometry (OCA 35).
3. Results and discussion 3.1 Effect of PTFE particle concentration in the bath
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The variation of PTFE particle concentrations in the plating bath and deposits are shown in Fig. 1. The PTFE particle concentration in the bath was increased from 5 to 20 g/L at a current density of 1.2 Adm-2 at 65 °C and the amount of particles co-deposited also increased. The
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higher amount of in the co-deposited PTFE particles on the cathode surface can be explained by Guglielmi’s two step adsorption model [20]. According to this model, co-deposition of particles
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depends on the two step adsorption model. The first step is the physical adsorption (loose),
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which mainly consists of particle concentration in the electrolytic bath. The strong adsorption of the second step is dominated by high over potential, it considers as a rate determining step.
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During this step, the rate of adsorption of co-deposited particles is high. The maximum amount of PTFE particle inclusion was noticed at 20 g/L. Increasing the PTFE particle content in the
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plating bath may enhance the flux of PTFE particles adjacent to the electrode surface, and then
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enhances the PTFE particle content in the composite films. Beyond 20g/L of PTFE particle
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concentration in the electrolytic bath may result in the agglomeration of PTFE particles in the bath, which may slow down the particles co-deposition in the bath. Hence, 20 g/L of PTFE
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particle concentration was taken as an optimum concentration for this study. Cationic surfactant (CTAB) is useful in dispersing the PTFE particles in the bath. However, for any stable surfactant content, the PTFE particles were found to agglomerate and settle down during the electrodeposition process, once the PTFE content in the electrolytic bath goes beyond certain value. When compared with DC technique, Pulse deposition leads to higher co-deposition of PTFE particles on the cathode surface. This is due to the extended relaxation time TOFF, that permits an adequate replenishment of PTFE particles in the electrolyte, and therefore leads to increase the particle inclusion in the Ni-W alloy matrix. 3.2 XRD measurement 8 Page 8 of 35
Fig. 2 shows the XRD patterns of the Ni-W alloy and Ni-W/PTFE nano composite coatings. The XRD measurement was carried out to characterize the Ni-W alloy and Ni-W/PTFE nanocomposite coatings. The diffractograms were scanned in a 2θ range of 10 - 70° at a rate of
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2 min-1. The XRD patterns have shown the main peaks corresponding to (111), (200) and (220) crystallographic planes of Nickel at 2θ = 44.16°, 51.42° and 76.37° which assigned to the face-
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centered cubic (fcc) according to the report of JCPDS (65- 2865). The peaks for W appeared at
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2θ = 38.37°, 44.60° and 64.91° with very weak intensity in all the XRD patterns. Because, it is due to low content of the W and completely soluble in the Nickel solution to form Ni-W alloy
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matrix. The intensity of the diffraction peaks of Ni-W/PTFE nanocomposite coating is lower than that of the Ni-W alloy coating. This is attributed to reduce the grain size of the Ni-W/PTFE
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nanocomposite coating by the addition of PTFE nanoparticles into the plating bath. PTFE nano
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particles have provided more nucleation sites and hence retard the crystal growth. Figs 2b & 2c
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indicate the inclusion of PTFE in the Ni-W alloy matrix at lower and higher concentrations (5 g/L & 20 g/L) respectively. The peak at 2θ = 17.5 ° correspond to the PTFE particles and this
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pattern was confirmed by JCPDS data (47-2217) [21]. Increase of PTFE particle concentration has increased the corresponding peak intensity of PTFE. It is because of more particles incorporated in higher concentration (20 g/L) of PTFE. The average grain sizes of crystalline deposits were calculated by using the Debye–Scherrer’s equation (2). The grain sizes of Ni-W alloy and Ni-W/PTFE nanocomposite coating at lower and higher concentrations were found to be 46 nm 34 nm and 26 nm respectively. Addition of second phase PTFE particles in the coating has enhanced the nucleation sites and inhibited the growth of the Nickel crystal resulting small sized grains. When PTFE polymer concentration increases (20 g/L), the sharp crystalline nature changed to semi crystalline and the peak intensity was also reduced.
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3.3 SEM with EDAX The surface morphology of Ni-W alloy and Ni-W/PTFE nanocomposite coating at
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different concentrations of PTFE particles are shown in Fig. 3 (a-c). The grain structure of the Ni-W alloy matrix has long needle shaped particles (Fig 3a). The Surface morphology of Ni-
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W/PTFE nanocomposite coating at different concentrations of PTFE particles such as 5 g/L and 20 g/L are shown in Figs 3b & fig 3c respectively. After the inclusion of PTFE particles into the
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Ni-W alloy matrix, the surface morphology was modified to flower like structure. At a minimum
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concentration (5 g/L) of PTFE particle inclusion in the Ni-W/PTFE nanocomposite coating, some micro cracks with dissimilar grain were obtained. However, when the concentration of
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PTFE particles increases (20 g/L), the grain size was decreased and obtained the crack free compact structure besides the smooth and more regular surface morphology. The decrease in
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grain size of nanoparticles has provided more nucleation sites and retarded the crystal growth.
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The decrease in grain size was due to more uniform distribution of PTFE particles in the Ni-W
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alloy matrix (Fig. 4). Pulse current electrodeposition was another important reason for the decrease in grain size and more compact structure. Because, during direct current deposition there is one diffusion layer, but for Pulse deposition two diffusion layers (pulsating diffusion layer and stationary diffusion layer) are formed due to the pulse current [22, 23]. In addition, longer TOFF promotes the transfer of more particles near the cathode and consequently a higher number of particles are incorporated. During the TON (40 ms pulse), nucleation and growth of the metal nanoparticles have taken place. But the TOFF (60 ms pulse) has allowed to compensate the depletion of metal ions around the electrode and prevented the overlapping of diffusion zones. Hence, smaller grain size and compact structure were achieved in pulse current method. EDAX analysis was used to find the % of elements present in the Ni–W/PTFE nanocomposite coatings. 10 Page 10 of 35
This analysis has confirmed the successful electrodeposition of PTFE on the Ni-W alloy matrix. The elements Ni, W, C, and F can be precisely detected as shown in Fig. 3 (a-c). During Ni-W alloy deposition NiWO4 was formed, which react with citrate to form [(WO4) (Cit) (H) x]
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electrochemical reduction of WO42− ion occurs as W + 4H2O
(3)
3.4 Effect of PTFE concentration on coating thickness
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WO42- + 8H+ + 6e-
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complex. After that, metallic tungsten was deposited from tungstate complex [24]. The
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The effect of PTFE particle concentrations on the Ni-W/PTFE nanocomposite coating
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thickness was illustrated in Fig. 5. It was found that, the coating thickness was increased with increasing the concentration of PTFE polymer upto 20 g/L. At 20 g/L PTFE concentration,
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mechanical stirring, effect of surfactant, electrostatic adsorption and deposition rate have attained
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a relative balance, so that the coating thickness achieved the maximum. In addition, codeposition of second phase PTFE particles were uniformly distributed over the Ni-W matrix by
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pulse deposition and enhance the nucleation of fine grains result in an increase in coating thickness. In order to create a better understanding of Ni-W/PTFE nanocomposite coatings thickness of the coating was determined by cross sectional FE-SEM image (Fig. 6). However, when the PTFE concentration exceeds 20 g/L, thickness of the coating began to decrease gradually. This may be due to the fact that, the polymer increases beyond 20 g/L resulted in particles got agglomerated. Hence, only a smaller number of particles were incorporated in the coating. During agglomeration a nonuniform distribution of particles was also observed. 3.5 Effect of Microhardness
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The Vickers microhardness values of the Ni-W/PTFE nanocomposite coatings as a function of self lubricating PTFE particle concentration in the electrolytic bath are shown in Table 2. The final value mentioned for the microhardness test of a coating was the average of 5
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measurements on various locations of the coating. It can be seen that, the microhardness of a coating was improved and varied considerably with the concentration of PTFE particles. The
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microhardness value of the Ni-W alloy matrix was 420 HV. After the inclusion of PTFE particles
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(5 g/L), the microhardness value was reduced to 370 HV. But further increasing the concentration of PTFE particles (upto 20 g/L) the microhardness value was slightly increased
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from 375 to 496. The improvement of microhardness can be due to the more second-phase particle dispersion tends to have superior mechanical properties of the nanocomposite coatings.
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Another important reason for an increase in the microhardness was due to grain refining and
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dispersion strengthening of the particles [25]. Moreover, the microhardness and other mechanical
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properties were not only depends on the amount of dispersed particles, but also the metal matrix particles. The crystallite size was affected the microhardness value. The higher microhardness
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value was obtained from the smaller crystalline size. In addition, pulse deposition has significantly increased the microhardness values due to the fine grain size and compact nature of the coatings. As shown in XRD data at 5 g/l of PTFE, particle inclusion in Ni-W/PTFE nanocomposite coating was 34 nm. At higher PTFE concentration (20 g/l), the particle size of the nanocomposite coating was 26 nm. Hence, the smaller crystalline size has enhanced the microhardness values. Also, the enhancement of PTFE concentration has shown only slight improvement of microhardness. It was due to the soft and lubricating nature of the PTFE particles. 3.6 Effect of Surface roughness 12 Page 12 of 35
Surface roughness measurements on the electrodeposited coatings are repeated three times at various locations and recorded the average values. The average surface roughness (Ra) values of Ni-W alloy matrix were 0.78 µm. After the inclusion of PTFE (optimized
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concentration 20 g/L) particles in the Ni-W/PTFE nanocomposite coating, the average surface roughness (Ra) value was reduced to 0.38 µm. Thus, the solid lubricant polymer has played a
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vital role to reduce the surface roughness. The decrease in roughness is probably due to the dense
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coating and self lubricating property of the PTFE particles. PC deposition has offered uniform and dense surface than DC deposition. Pulse deposited coatings were achieved with greater
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cathodic current densities of the coatings. It is well known that, lesser over potential coating generates deposition with larger surface irregularities on the surface of the cathode; while higher
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over potential deposits generate coatings with smooth surfaces. So, the average surface
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3.7 Effect of Coefficient of friction
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roughness value of pulse current deposition of Ni-W/PTFE nanocomposite coating is reduced.
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Fig.7. shows the friction coefficient of Ni-W alloy and various concentrations of PTFE particle inclusion of Ni-W/PTFE nanocomposite coatings. It was noticed that, Ni-W/PTFE nanocomposite coatings have much lower friction coefficient than the Ni-W alloy coating. The friction coefficient value of Ni-W alloy coating was ~0.58, whereas for the case of nickel coating is ~0.78. After the inclusion of PTFE particles in the Ni-W alloy matrix, the value of friction coefficient was decreased significantly. When compared to Ni-W alloy coating the self lubricating polymer incorporation of Ni-W/PTFE nanocomposite coating has better tribological properties. As far as Ni-W alloy coating is concerned, some micro holes and cracks also seen on the surface of the coating which reduced the tribological properties and led to increase the friction coefficient values. As PTFE incorporated into the Ni-W alloy matrix, the porosity of the 13 Page 13 of 35
surface was filled with polymer material. Thus, cracks and micro holes were filled by the self lubricant PTFE polymer and formed as a solid lubricant film on the surface of the Ni-W/PTFE nanocomposite coating. Inclusion of solid lubricant was promising effect of decreasing the
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nanocomposite coatings had much lower than that of Ni-W alloy coating.
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friction coefficient values [26]. As a result, the friction coefficient values of Ni-W/PTFE
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3.8 Potentiodynamic polarization study
The potentiodynamic polarization behaviour of Ni-W alloy matrix and Ni-W/PTFE
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nanocomposite coating deposited with different concentrations of PTFE particles is depicted in Fig. 8. The calculated corrosion current (Icorr) and corrosion potential (Ecorr) values from the
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Tafel polarization curves are summarized in Table 3. It may be observed that, the corrosion resistance of the coatings increases with increasing the concentration of PTFE particles. The
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corrosion potential shifts in the noble direction and the corrosion current is decreased, showing
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that the PTFE polymer inclusion protects the Ni-W alloy matrix from corrosion. Both Ni-W
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alloy and Ni-W/PTFE nanocomposite coatings have displayed some active-passive conversions. Additionally, Ni-W/PTFE nanocomposite coatings have shown a more positive shift in corrosion potential (Ecorr = −0. 316 V) than that of Ni-W alloy (Ecorr = −0. 564 V). The existence of the wider passive region with a positive shift of corrosion potential for the Ni-W/PTFE nanocomposite coatings may be related to the refined grain size and inclusion of PTFE particles which probably acted as an internal physical barrier, thus improving the anticorrosion property of the Ni-W/PTFE nanocomposite coating. As we discussed earlier, the addition of polymer material has covered the cracks and holes of the Ni-W alloy matrix and hence the self lubricating PTFE polymer layer has enhanced the anticorrosion property of the nanocomposite coatings. The corrosion current densities of Ni-W alloy and Ni-W/PTFE deposition were found to be 13.6 and 14 Page 14 of 35
3.53 µA/cm2 respectively. The concentration of PTFE particles was increased upto 20 g/L the corrosion resistance also increased. This increased corrosion resistance can be attributed to the compact, dense and fine grained nature of the pulse deposition of Ni-W/PTFE nanocomposite
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coating. This compact structure was confirmed from SEM and EDAX results. These values have indicated that, Ni-W/PTFE nanocomposite coating has much lower corrosion current density
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3.9 Electrochemical Impedance Spectrum (EIS) Measurements
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signifying better corrosion resistant than that of the Ni-W alloy coating.
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Fig 9 shows the Nyquist plots of the Ni–W alloy matrix and Ni–W/PTFE nano composite coatings containing different concentrations of PTFE particles in 3.5% of NaCl solution. The
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Nyquist plots of all depositions have shown a single semicircular arc in the investigated frequency region. The increased radius of semicircular arc was indicative for the better
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anticorrosion property of the coatings [27]. The equivalent circuit of Ni-W/PTFE nanocomposite
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coating was shown in Fig.10. Meanwhile, the parameters derived from EIS were summarized in
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Table 4. The results of the EIS also indicated a similar trend in the corrosion resistance that was observed in potentiodynamic polarization studies. The higher Rct value was obtained for the 20 g/L of PTFE particles in Ni-W-/PTFE nanocomposite coating. This coating has offered more protection capability against corrosion. The double layer capacitance (Cdl) is small representative smooth surface nature of the deposits. The addition of PTFE particles in the nanocomposite coating has reduced the capacitance of the double layer values. The usage of pulse current and incorporation of PTFE polymer nanoparticles in the Ni-W alloy matrix has resulted in an enhancement of the corrosion resistance for the nanocomposite coatings. Pulse current deposition has contributed to higher particle inclusion and more uniformity of particle distribution in Ni-W alloy matrix. Furthermore, the coverage of the PTFE polymer into Ni-W alloy matrix was 15 Page 15 of 35
effectively completed in pulse electrodeposition and contributed the more protective nature of the Ni-W/PTFE nanocomposite coating.
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3.10 Contact angle measurements To understand the water-repellency of Ni-W alloy matrix and Ni-W/PTFE
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nanocomposite coatings, the contact angle measurement was made. Contact angle measurement
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is a simple quantitative method to analyze the wettability/hydrophobic nature of the solid surface. Surfaces with contact angle value larger than 90° are said to be hydrophobic. The
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volume of water droplet was 8 µL for both Ni-W alloy matrix and Ni-W/PTFE nanocomposite coatings were shown in Fig. 11. The contact angle for the Ni-W alloy matrix (A) was about
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98.2°, while that for the PTFE polymer inclusion of Ni-W/PTFE nanocomposite coating (B) 109.9°, which shown a better water repellency/hydrophobic nature. This means that,
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incorporation of the self lubricating PTFE polymer has improved the water repellency of Ni-
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W/PTFE nanocomposite coating. It has confirmed that, improvement of water repellency was
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mainly depends on the self lubricating property of PTFE polymer, which improved the corrosion resistance behaviour of the nanocomposite coatings [28]. 4. Conclusions
The self lubricating Ni-W/PTFE nanocomposite coatings were successfully prepared by pulse electrodeposition on the mild steel substrate. Inspection of XRD, SEM and EDAX analysis indicated that, PTFE particles have fully covered onto the Ni-W alloy matrix. Chemically inert and solid lubricant nature of the Ni-W/PTFE nanocomposite coatings has significantly decreased the coefficient of friction, surface roughness and moderate microhardness than the Ni-W alloy matrix. Higher PTFE concentration increases the thickness of the coating and hydrophobic 16 Page 16 of 35
nature of the coating. A contact angle measurement of Ni-W/PTFE nanocomposite coating has shown a hydrophobic behaviour (109.9°). These properties have enhanced the corrosion resistance behaviour of pulse electrodeposition of Ni-W/PTFE nanocomposite coatings. The
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addition of PTFE in the Ni-W alloy matrix has resulted moderate microhardness, smooth surface, less friction coefficient, excellent water repellency and enhanced corrosion resistance of the
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nanocomposite coatings
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Acknowledgement
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The authors thank to the Head of the physics department, Alagappa University, Karaikudi for
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providing the XRD analysis to carry out this research work.
References [1] A. Abdel Aal, M. Bahgat, M. Radwan, Nanostructured Ni–AlN composite coatings, Surf. Coat. Technol. 201 (2006) 2910-2918.
17 Page 17 of 35
[2] S. Lei, S. Chufeng, G. Ping, Z. Feng, L. Weimin, Mechanical properties and wear and corrosion resistance of electrodeposited Ni–Co/SiC nanocomposite coating, Appl. Surf. Sci. 252 (2006) 3591-3599.
(h) nanocomposite coatings, Appl. Surf. Sci. 276 (2013) 174-181.
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[3] Z.Shahri, S.R.Allahkaram, A. Zarebidaki, Electrodeposition and characterization of Co–BN
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[4] A.S.M.A. Haseeb, U. Albers, K. Bade, Friction and wear characteristics of electrodeposited
us
nanocrystalline nickel–tungsten alloy films, Wear. 264 (2008) 106-112.
[5] S. Ranganatha, T.V. Venkatesha, K. Vathsala, Electroless Ni–W–P Coating and Its Nano-
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WS2 Composite: Preparation and Properties, Ind. Eng. Chem. Res. 51 (2012) 7932−7940. [6] S.A. Lajevardi, T. Shahrabi, Effects of pulse electrodeposition parameters on the properties
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of Ni–TiO2 nanocomposite coatings, Appl. Surf. Sci. 256 (2010) 6775–6781.
d
[7] M.S. Chandrasekar, M. Pushpavanam, Pulse and pulse reverse plating- Conceptual,
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advantages and applications, Electrochim Acta. 53 (2008) 3313-3322. [8] F. Kilic, H. Gul, S. Aslan, H. Akbulut, Effect of CTAB concentration in the electrolyte on
Ac ce p
the tribological properties of nanoparticles SiC reinforced Ni metal matrix composite (MMC) coatings produced by electrodeposition, Colloids surf A: Physiochemical eng asp. 419 (2013) 53-60.
[9] S. Bogden, K. Malgorzata, Composite Ni/Al2O3 coatings and their corrosion resistance, Electrochim Acta. 50 (2005) 4188-4195. [10] K.L. Cheng, Comparative Corrosion Resistance of Electroless Ni-P/nanoTiO2 and NiP/nano CNT Composite Coatings on 5083 Aluminum Alloy, Int. J. Electrochem. Sci. 7 (2012) 12941 –12954.
18 Page 18 of 35
[11] S. Sina, A. Abdollah, Corrosion resistance enhancement of Ni-P-nano SiO2 composite coatings on aluminum, Appl. Surf. Sci. 303 (2014) 125-130. [12] M. Mohammadi, M. Ghorbani, Wear and corrosion properties of electroless nickel
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composite coatings with PTFE and/or MoS2 particles, J. Coat. Technol. Res. 8 (2011) 527– 533.
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composite coatings, Electrochim. Acta. 54 (2009) 2571-2574.
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[13] E. Pompei, L. Magagnin, N. Lecis, P.L Cavallotti, Electrodeposition of nickel–BN
[14] C. Baimin, B. Qiniling, Y. Jun, X. Yanqiu, H. Jingcheng, Tribological properties of solid
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lubricants (graphite, h-BN) for Cu-based P/M friction composites, Tribol Int. 41 (2008) 1145–1152.
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[15] W. Zhijiang, W. Lina, Q. Yulin, C. Wei, J. Zhaohua, Self-lubricating Al2O3/PTFE
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3315-3318.
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composite coating formation on surface of aluminum alloy, Surf. Coat. Technol. 204 (2010)
[16] Q. Zhao, Y. Liu, E.W. Abel, Effect of Cu content in electroless Ni–Cu–P–PTFE composite
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coatings on their anti-corrosion properties, Mater. Chem. Phys. 87 (2004) 332–335. [17] Q. Zhao, Y. Liu, Electroless Ni–Cu–P–PTFE composite coatings and their anticorrosion properties, Surf. Coat. Technol. 200 (2005) 2510-2514. [18] Y.S. Huang, X.T. Zeng, X.F. Hu, F.M. Liu, Heat treatment effects on EN-PTFE-SiC composite coating, surf. Coat. Technol. 198 (2005) 173-177. [19] B.D. Cullity, S.R. Stock, S. Stock, Elements of X-ray Diffraction, Addison-Wesely, London, 2001. [20] N. Gugliemi, Kinetics of the Deposition of Inert Particles from Electrolytic Baths, J. Electrochem Soc. 119 (1972) 1009-1011.
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[21] H.Y. Yi, D.G. Chang, L.W. Xiu, P.T. Jiang, Electrochemical Preparation and Characterization of Ni–PTFE Composite Coatings from a Non-Aqueous Solution without Additives, Int. J. Electrochem. Sci. 7 (2012) 12440-12455. Frequency-regulated Pulsed
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[22] T Yiming, W. Peng, H Jung, A. Rose, N. Yun Hau,
Electrodeposition of CuInS2 on ZnO Nanorod Arrays as Visible Light Photoanodes, J.
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Mater. Chem. A, 3 (2015) 15876-15881.
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[23] L. Bing, F. Chunhua, C. Yan, L. Jingwei, Y. Lingguang, Pulse current electrodeposition of Al from an AlCl3-EMIC ionic liquid, Electrochim Acta. 56 (2011) 5478-5482.
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[24] K.A. Kumar, G.P. Kalaignan, V.S. Muralidharan, Pulse electrodeposition and characterization of nano Ni-W alloy deposits, App. Surf. Sci. 259 (2012) 231-237.
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[25] L.T. See, W. Xiaojin, C. Weiwei, Y. Caizhen, G. Wei, Microstructures and Properties of
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Electrodeposited Cu-Bi Composite Coatings, Int. J. Electrochem. Sci. 9 (2014) 2266 –2277.
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[26] M. Zouari, M. Kharrat, M. Dammaka and M. Barletta, A comparative investigation of the tribological behavior and scratch response of polyester powder coatings filled with different
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solid lubricants, Prog Org Coat. 77 (2014) 1408–1417. [27] S. Sangeetha, G.P Kalaignan, Tribological and electrochemical corrosion behavior of Ni-W/BN (hexagonal) nano-composite coatings, Ceram Int. 41 (2015) 10415-10424. [28] S. Sangeetha, G.P Kalaignan, Studies on electrodeposition and characterization of PTFE polymer inclusion in Ni-W-BN nanocomposite coatings for industrial Applications, RSC Adv. 5 (2015) 74115-74125.
Table captions 20 Page 20 of 35
Table 1: Composition of the electrolytic bath and its operating conditions. Table 2: microhardness values of Ni-W and Ni-W/PTFE coatings. Table 3: Derived results of the potentiodynamic polarization measurements.
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Table 4: Electrochemical impedance analysis data.
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Figure captions
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Fig.1. Effect of amount of PTFE in the bath (grams per litre) on the weight percentage of PTFE in the nanocomposite coatings. Fig.2. XRD Patterns of (a) Ni–W alloy (b) Ni–W/PTFE (5 g/L) and (c) Ni–W/PTFE (15 g/L) coatings.
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Fig.3. SEM with EDAX spectrum of (a) Ni–W alloy (b) Ni–W/PTFE (5 g/L) and (c) Ni– W/PTFE (15 g/L) coatings.
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Fig.4. Image of PTFE distribution in the Ni-W alloy coatings.
Fig.5. Plot of coating thickness versus concentration of PTFE on the electrodeposition bath. Fig.6. Cross-sectional FE-SEM images of (a) Ni-W alloy (b) Ni-W/PTFE
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Fig.7. Plot of Friction Coefficient versus concentration of PTFE on the electrodeposition bath.
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Fig.8. Potentiodynamic polarization curves recorded for Ni–W alloy matrix and the Ni–W/PTFE coatings.
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Fig.9. Nyquist plot of Ni–W-alloy matrix and the Ni–W/PTFE coatings. Fig.10. Equivalent electrical circuit used to simulate experimental data of impedance spectrum. Fig.11. Contact angle measurements of a water droplet (8 µL) on the (a) Ni-W (b) Ni-W/PTFE
Pulse Plating bath
Table 1 Composition
Plating conditions
Nickel Sulphate
0.17M
Pulse peak c.d 1.2 A/cm2
Sodium tungstate
0.15M
pH 8 Time 60 min
Tri Ammonium Citrate (TAC) Ammonium Chloride
0.30 M
Temperature 65°C
0.20 M
Constant Stirring
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Cetyltrimethyl ammonium Bromide (CTAB)
0.50 g/L
PTFE(AlfaAesar-A12613)
5-20 g/L
Pulse duty Cycle On time- 40 ms Off time- 60 ms
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0.06 M
Table 2 Microhardness (HV)
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M
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420 375 448 470 496
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PTFE concentration (g/L) 0 5 10 15 20
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Dimethyl Sulphoxide
Table 3 PTFE concentration (g/L) 0 5 10 15
Ecorr Vs SCE (mV) -564 -473 -435 -395
Icorr (µA cm-2) 13.18 11.29 07.65 05.44
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20
-316
03.53
Cdl (µFcm-2) 52.70 46.15 43.04 38.37 34.28
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Rct (Ω cm2) 600 690 740 830 900
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te
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PTFE concentration (g/L) 0 5 10 15 20
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Table 4
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S0169-4332(15)02546-5 http://dx.doi.org/doi:10.1016/j.apsusc.2015.10.127 APSUSC 31608
To appear in:
APSUSC
Received date: Revised date: Accepted date:
8-7-2015 16-10-2015 17-10-2015
Please cite this article as: S. Sangeetha, G.P. Kalaignan, J.T. Anthuvan, Pulse electrodeposition of self-lubricating Ni-W/PTFE nanocomposite coatings on mild steel surface, Applied Surface Science (2015), http://dx.doi.org/10.1016/j.apsusc.2015.10.127 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Highlights PTFE polymer inclusion on Ni-W alloy matrix was electrodeposited by pulse current method.
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Tribological properties and electrochemical characterizations of the nanocomposite coatings were analyzed.
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The Hydrophobic behaviour of Ni-W/PTFE nanocomposite coating was measured.
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Ni-W/PTFE nanocomposite coatings have showed superior tribological properties and corrosion resistance relative to that of the Ni-W alloy matrix.
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Pulse electrodeposition of self-lubricating Ni-W/PTFE nanocomposite coatings on mild steel surface S. Sangeetha1 and G. Paruthimal Kalaignan1*, J. Tennis Anthuvan2
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1. Advanced Nanocomposite Coatings Laboratory, Department of Industrial Chemistry, Alagappa University, Karaikudi 630 003, India
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2. M. Kumarasamy College of Engineering, Karur, Tamilnadu, India.
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Corresponding Author phone No: +91-9443135307, Fax: +914565 225202. Email id: [email protected]
Abstract
Ni-W/PTFE
nanocomposite
coatings
with
various
contents
of
PTFE
(polytetafluoroethylene) particles were prepared by pulse current (PC) electrodeposition from the Ni-W plating bath containing self lubricant PTFE particles to be co-deposited. Co-deposited PTFE particulates were uniformly distributed in the Ni–W alloy matrix. The coatings were characterized by Scanning Electron Microscopy (SEM), Energy Dispersive X-Ray Analysis (EDAX), X-ray Diffractometry (XRD) and Vicker’s micro hardness tester. Tafel Polarization and electrochemical Impedance methods were used to evaluate the corrosion resistance behaviour of 1 Page 1 of 35
the nanocomposite coatings in 3.5% NaCl solution. It was found that, the Ni-W/PTFE nanocomposite coating has better corrosion resistance than the Ni-W alloy coating. Surface roughness and friction coefficient of the coated samples were assessed by Mitutoyo Surftest SJ-
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310 (ISO1997) and Scratch tester TR-101-M4 respectively. The contact angle (CA) of a water droplet on the surface of nanocomposite coating was measured by Optical Contact Goniometry
cr
(OCA 35). These results indicated that, the addition of PTFE in the Ni-W alloy matrix has
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resulted moderate microhardness, smooth surface, less friction coefficient, excellent water
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repellency and enhanced corrosion resistance of the nanocomposite coatings. Keywords: Ni-W/PTFE nanocomposite coatings, coefficient of friction, Microhardness,
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Electrochemical characterization, contact angle.
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Introduction
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Electrodeposition of nanocomposite coatings has been developed for enhanced tribological and corrosion resistance of alloying matrix [1-3]. Composite electrodeposition is a
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method of co-deposition of inert particles such as ceramic, metallic, or polymers with a metal matrix. The electrodeposited Ni-W alloy matrixes have been of great interest for its admirable microhardness, corrosion and wear resistance [4]. Introduction of Tungsten to the alloy matrix has unique properties such as higher tensile strength, thermal stability, higher hardness and corrosion resistance [5]. Generally, pulse current deposition (PC) offers a finer grained deposit with more particles embedded, as the current density employed in PC can be significantly higher than that of direct current. Lajevardi et.al has investigated the influence of pulse plating parameters and properties of Ni- TiO2 nanocomposite coatings [6]. Pulse deposition has caused a high nucleation rate and significant changes in the coating morphology. Because, during pulse
2 Page 2 of 35
ON time (TON) the current or potential is applied and the pulse OFF time (TOFF) zero current is applied. Thus the current is periodically turned off to cause this layer to discharge to an extent. This process permits the ions to pass through the surface of the cathode more easily. Moreover,
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pulse deposition has less adsorbed hydrogen and can easily control the microstructure of the deposits than the coatings achieved from other techniques [7]. Particles agglomeration is an
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undesirable problem during electrodeposition of a nanocomposite coating, which would decline
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the tribological properties of the deposition. The addition of cationic surfactant in an electrolytic bath has improved the distribution of co- deposited particles. Surfactant generally plays an
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essential role in the deposition process and has offered various improved properties of the deposits, such as the smoothness, brightness and homogeneity. The cationic surfactant CTAB
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(Cetyltrimethyl ammonium bromide) is preferred for its strong adsorbed capability [8]. The
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important benefits for the inclusion of hard particles like Al2O3, TiO2, and SiO2 into the metal
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deposits are to achieve the higher microhardness and wear resistance of the nanocomposite coatings [9-11]. Improved lubricity has been attained by incorporating PTFE, h-BN and MoS2
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particles into the nanocomposite coatings [12-14]. Among them, PTFE is chemically inert and its coefficient of friction is lower than that of almost any other polymers. Since of its very low surface energy, PTFE has outstanding non-stick properties. Nanocomposite coatings containing PTFE particles are mainly considered in recent time because of their extremely useful properties such as self-lubrication, coefficient of friction, wear resistance etc. Based on such properties, the span of application of PTFE as a solid lubricant has received significant research attention in recent years. A study on the wear and friction behaviour of PTFE filled with alumina particles were investigated by Zhijiang et.al [15]. Wear and corrosion properties of EN-PTFE-MoS2 had been reported [12]. Effects of Cu content in electroless Ni–Cu–P–PTFE composite coatings and
3 Page 3 of 35
their anti-corrosion properties were given by Zhao et.al [16 & 17]. A proper heat treatment effect of EN-PTFE-SiC composite coating was systematically studied by Huang et.al [18]. This work was aimed to prepare pulse electrodeposition of Ni-W/PTFE nano composite coatings to attain
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high corrosion resistance, low friction coefficient and lower surface roughness values. A comparative study of the properties of pulse electrodeposition of Ni-W alloy matrix and Ni-
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nanocomposite coatings and its properties are also discussed.
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W/PTFE nanocomposite coatings were determined. The importance of PTFE inclusion into the
2. Experimental process
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Ni-W/PTFE nano-composite coatings were deposited on mild steel substrates from the
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nickel sulphate bath solution containing PTFE particles. The bath constituents and their
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compositions are given in Table 1. The mild steel plates of size 3 × 2.5 × 0.05 cm were dipped in 5% H2SO4 for 10 min and then cleaned with distilled water followed by drying. Then the specimens were degreased with trichloroethylene to remove the oily impurities adhered on the surface. Thus pretreated mild steel specimens were used as cathode. Pure nickel bar (99.9%) of size 5×5×0.5 cm was used as the anode. All the solutions were prepared by using triple distilled water. Prior to electrodeposition, PTFE particles were ultra sonicated for 60 s. Cetyl trimethyl ammonium bromide (CTAB) surfactant was employed for particle dispersion to prevent agglomeration of PTFE particles in the solution. The cationic surfactant can adsorb on the particle surface has developed a net positive charge on its surface, so increasing their affinity towards the cathode and hence increases the stability of particle suspension and prevents 4 Page 4 of 35
agglomeration. Like this, it is understood that, cationic surfactant enhances the incorporation of particles in the metal matrix. Besides, zeta potential of the nanoparticles would be increased by the addition of cationic surfactant CTAB. The positive Zeta potential has given an extra adhesion
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force between the inert particles and the cathode. Additionally, mechanical stirring (600 rpm) was used for thorough mixing of all the components and maintained the plating temperature at
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65°C. The inert particles were in contact with the bath solution for 24 hours and then stirred well.
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Certainly, the stirring has offered a uniform mass transfer and good particle adherence to the cathode. By the use of magnetic stirrer the suspended particles were thoroughly mixed in order to
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attain the uniform distribution of nanoparticles in bath solution. It is well known that, the tungsten content of the alloy deposition mostly depends upon the type of the complexing agent
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used in the electrolytic bath. Citrate bath has been used to include higher tungsten content into
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the composite coatings. PTFE concentration in the electrolytic bath was varied between 5 and 20
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g/L. Both Ni-W alloy and Ni-W/PTFE nanocomposite coatings were deposited on mild steel substrates by using pulse current technique. The Pulse electrodeposition was carried out by
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employing a Myriad bipolar pulsed power supply. The micro hardness of the electrodeposits was measured by using MHG Everyone Hardness tester (Hong Kong) on the Vicker’s scale. It had a diamond pyramid of a square base with an angle of 136° at the vertex between two opposite faces. The micro hardness of the deposits in kg/mm2 was determined in each case by using the formula
Where, L is the load applied in (50 gm) and d the diagonal of the indention (µm). The reported microhardness value of incorporating boron nitride particles into the Ni-W alloy matrix
5 Page 5 of 35
is an average value of the three measurements. Scanning electron microscope (SEM) was used to characterize the surface morphology of the composite coatings of size 1cm ×1cm. The deposited surface was subjected to EDAX (Energy Dispersive X-ray analysis) for the determination of
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chemical composition of the composites deposited on the surface. The crystalline structure of the plated substrate was identified by X-ray diffraction using Brooker D8 advance X-ray
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diffractometer operated with Cu Ka radiation (nickel filtered) at a rating of 40 KV, 20 mA. The
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scan rate was 0.05 per step with the measuring time of 15 per step. The crystallite size of the
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deposits was calculated by using the Scherrer’s equation [19].
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)
Where, D is the crystalline size, λ is the incident radiation (1.5418 Å), β is the corrected
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peak width at half-maximum intensity and θ the angular position. Electrochemical measurements
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were carried out by using an electrochemical analyzer (EG&G – Auto Lab Analyzer Model:
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6310) containing three electrode cell assembly. Corrosion experiments were carried out in 3⋅5
wt% NaCl solution kept at 30° C. The exposed 1 cm2 area of mild steel substrate was acted as working electrode. A rectangular Pt foil and a saturated calomel electrode (SCE) were used as auxiliary and reference electrodes respectively. The potentiodynamic polarization studies were
carried out for the potential range from -0⋅75 to –1⋅25 V with respect to the OCP at a scan rate of
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2 mV/s. The potential E (V vs. SCE) was plotted against log I (A cm–2) to obtain polarization curve. From this polarization curve, the corrosion potential (Ecorr) and corrosion current (Icorr)
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parameters were obtained. Impedance measurements were performed after the immersion of
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specimen for 2 minutes in 3⋅5 wt% NaCl solution for attaining the steady state potential. The
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same three electrode cell setup was used for performing this experiment. The impedance spectra were found to be in the frequency range of 10 K cs-1 – 100 m cs-1. Surface Roughness of the
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coatings was assessed by using Roughness Measuring Station (Make: Mitutoyo, Model: Surftest SJ-310). This instrument was used to analyze the average roughness value (Ra) with Probe
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movement and travelling distances 0.5 mm/s and 5 mm respectively. Moreover, Scratch tester TR-101-M4 (Make-DUCOM) was used to determine the coefficient of friction for the coatings.
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All the samples were run against at 5N normal loads at 0.2 ms-1 speed. Thickness of the coatings was measured by the cross-sectional FE-SEM images. The measurement of water repellency of the Ni-W/PTFE nanocomposite coating was evaluated by determining the static contact angle for water drops with the help of Optical Contact Goniometry (OCA 35).
3. Results and discussion 3.1 Effect of PTFE particle concentration in the bath
7 Page 7 of 35
The variation of PTFE particle concentrations in the plating bath and deposits are shown in Fig. 1. The PTFE particle concentration in the bath was increased from 5 to 20 g/L at a current density of 1.2 Adm-2 at 65 °C and the amount of particles co-deposited also increased. The
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higher amount of in the co-deposited PTFE particles on the cathode surface can be explained by Guglielmi’s two step adsorption model [20]. According to this model, co-deposition of particles
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depends on the two step adsorption model. The first step is the physical adsorption (loose),
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which mainly consists of particle concentration in the electrolytic bath. The strong adsorption of the second step is dominated by high over potential, it considers as a rate determining step.
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During this step, the rate of adsorption of co-deposited particles is high. The maximum amount of PTFE particle inclusion was noticed at 20 g/L. Increasing the PTFE particle content in the
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plating bath may enhance the flux of PTFE particles adjacent to the electrode surface, and then
d
enhances the PTFE particle content in the composite films. Beyond 20g/L of PTFE particle
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concentration in the electrolytic bath may result in the agglomeration of PTFE particles in the bath, which may slow down the particles co-deposition in the bath. Hence, 20 g/L of PTFE
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particle concentration was taken as an optimum concentration for this study. Cationic surfactant (CTAB) is useful in dispersing the PTFE particles in the bath. However, for any stable surfactant content, the PTFE particles were found to agglomerate and settle down during the electrodeposition process, once the PTFE content in the electrolytic bath goes beyond certain value. When compared with DC technique, Pulse deposition leads to higher co-deposition of PTFE particles on the cathode surface. This is due to the extended relaxation time TOFF, that permits an adequate replenishment of PTFE particles in the electrolyte, and therefore leads to increase the particle inclusion in the Ni-W alloy matrix. 3.2 XRD measurement 8 Page 8 of 35
Fig. 2 shows the XRD patterns of the Ni-W alloy and Ni-W/PTFE nano composite coatings. The XRD measurement was carried out to characterize the Ni-W alloy and Ni-W/PTFE nanocomposite coatings. The diffractograms were scanned in a 2θ range of 10 - 70° at a rate of
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2 min-1. The XRD patterns have shown the main peaks corresponding to (111), (200) and (220) crystallographic planes of Nickel at 2θ = 44.16°, 51.42° and 76.37° which assigned to the face-
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centered cubic (fcc) according to the report of JCPDS (65- 2865). The peaks for W appeared at
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2θ = 38.37°, 44.60° and 64.91° with very weak intensity in all the XRD patterns. Because, it is due to low content of the W and completely soluble in the Nickel solution to form Ni-W alloy
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matrix. The intensity of the diffraction peaks of Ni-W/PTFE nanocomposite coating is lower than that of the Ni-W alloy coating. This is attributed to reduce the grain size of the Ni-W/PTFE
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nanocomposite coating by the addition of PTFE nanoparticles into the plating bath. PTFE nano
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particles have provided more nucleation sites and hence retard the crystal growth. Figs 2b & 2c
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indicate the inclusion of PTFE in the Ni-W alloy matrix at lower and higher concentrations (5 g/L & 20 g/L) respectively. The peak at 2θ = 17.5 ° correspond to the PTFE particles and this
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pattern was confirmed by JCPDS data (47-2217) [21]. Increase of PTFE particle concentration has increased the corresponding peak intensity of PTFE. It is because of more particles incorporated in higher concentration (20 g/L) of PTFE. The average grain sizes of crystalline deposits were calculated by using the Debye–Scherrer’s equation (2). The grain sizes of Ni-W alloy and Ni-W/PTFE nanocomposite coating at lower and higher concentrations were found to be 46 nm 34 nm and 26 nm respectively. Addition of second phase PTFE particles in the coating has enhanced the nucleation sites and inhibited the growth of the Nickel crystal resulting small sized grains. When PTFE polymer concentration increases (20 g/L), the sharp crystalline nature changed to semi crystalline and the peak intensity was also reduced.
9 Page 9 of 35
3.3 SEM with EDAX The surface morphology of Ni-W alloy and Ni-W/PTFE nanocomposite coating at
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different concentrations of PTFE particles are shown in Fig. 3 (a-c). The grain structure of the Ni-W alloy matrix has long needle shaped particles (Fig 3a). The Surface morphology of Ni-
cr
W/PTFE nanocomposite coating at different concentrations of PTFE particles such as 5 g/L and 20 g/L are shown in Figs 3b & fig 3c respectively. After the inclusion of PTFE particles into the
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Ni-W alloy matrix, the surface morphology was modified to flower like structure. At a minimum
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concentration (5 g/L) of PTFE particle inclusion in the Ni-W/PTFE nanocomposite coating, some micro cracks with dissimilar grain were obtained. However, when the concentration of
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PTFE particles increases (20 g/L), the grain size was decreased and obtained the crack free compact structure besides the smooth and more regular surface morphology. The decrease in
d
grain size of nanoparticles has provided more nucleation sites and retarded the crystal growth.
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The decrease in grain size was due to more uniform distribution of PTFE particles in the Ni-W
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alloy matrix (Fig. 4). Pulse current electrodeposition was another important reason for the decrease in grain size and more compact structure. Because, during direct current deposition there is one diffusion layer, but for Pulse deposition two diffusion layers (pulsating diffusion layer and stationary diffusion layer) are formed due to the pulse current [22, 23]. In addition, longer TOFF promotes the transfer of more particles near the cathode and consequently a higher number of particles are incorporated. During the TON (40 ms pulse), nucleation and growth of the metal nanoparticles have taken place. But the TOFF (60 ms pulse) has allowed to compensate the depletion of metal ions around the electrode and prevented the overlapping of diffusion zones. Hence, smaller grain size and compact structure were achieved in pulse current method. EDAX analysis was used to find the % of elements present in the Ni–W/PTFE nanocomposite coatings. 10 Page 10 of 35
This analysis has confirmed the successful electrodeposition of PTFE on the Ni-W alloy matrix. The elements Ni, W, C, and F can be precisely detected as shown in Fig. 3 (a-c). During Ni-W alloy deposition NiWO4 was formed, which react with citrate to form [(WO4) (Cit) (H) x]
x-5
electrochemical reduction of WO42− ion occurs as W + 4H2O
(3)
3.4 Effect of PTFE concentration on coating thickness
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WO42- + 8H+ + 6e-
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complex. After that, metallic tungsten was deposited from tungstate complex [24]. The
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The effect of PTFE particle concentrations on the Ni-W/PTFE nanocomposite coating
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thickness was illustrated in Fig. 5. It was found that, the coating thickness was increased with increasing the concentration of PTFE polymer upto 20 g/L. At 20 g/L PTFE concentration,
d
mechanical stirring, effect of surfactant, electrostatic adsorption and deposition rate have attained
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a relative balance, so that the coating thickness achieved the maximum. In addition, codeposition of second phase PTFE particles were uniformly distributed over the Ni-W matrix by
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pulse deposition and enhance the nucleation of fine grains result in an increase in coating thickness. In order to create a better understanding of Ni-W/PTFE nanocomposite coatings thickness of the coating was determined by cross sectional FE-SEM image (Fig. 6). However, when the PTFE concentration exceeds 20 g/L, thickness of the coating began to decrease gradually. This may be due to the fact that, the polymer increases beyond 20 g/L resulted in particles got agglomerated. Hence, only a smaller number of particles were incorporated in the coating. During agglomeration a nonuniform distribution of particles was also observed. 3.5 Effect of Microhardness
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The Vickers microhardness values of the Ni-W/PTFE nanocomposite coatings as a function of self lubricating PTFE particle concentration in the electrolytic bath are shown in Table 2. The final value mentioned for the microhardness test of a coating was the average of 5
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measurements on various locations of the coating. It can be seen that, the microhardness of a coating was improved and varied considerably with the concentration of PTFE particles. The
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microhardness value of the Ni-W alloy matrix was 420 HV. After the inclusion of PTFE particles
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(5 g/L), the microhardness value was reduced to 370 HV. But further increasing the concentration of PTFE particles (upto 20 g/L) the microhardness value was slightly increased
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from 375 to 496. The improvement of microhardness can be due to the more second-phase particle dispersion tends to have superior mechanical properties of the nanocomposite coatings.
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Another important reason for an increase in the microhardness was due to grain refining and
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dispersion strengthening of the particles [25]. Moreover, the microhardness and other mechanical
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properties were not only depends on the amount of dispersed particles, but also the metal matrix particles. The crystallite size was affected the microhardness value. The higher microhardness
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value was obtained from the smaller crystalline size. In addition, pulse deposition has significantly increased the microhardness values due to the fine grain size and compact nature of the coatings. As shown in XRD data at 5 g/l of PTFE, particle inclusion in Ni-W/PTFE nanocomposite coating was 34 nm. At higher PTFE concentration (20 g/l), the particle size of the nanocomposite coating was 26 nm. Hence, the smaller crystalline size has enhanced the microhardness values. Also, the enhancement of PTFE concentration has shown only slight improvement of microhardness. It was due to the soft and lubricating nature of the PTFE particles. 3.6 Effect of Surface roughness 12 Page 12 of 35
Surface roughness measurements on the electrodeposited coatings are repeated three times at various locations and recorded the average values. The average surface roughness (Ra) values of Ni-W alloy matrix were 0.78 µm. After the inclusion of PTFE (optimized
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concentration 20 g/L) particles in the Ni-W/PTFE nanocomposite coating, the average surface roughness (Ra) value was reduced to 0.38 µm. Thus, the solid lubricant polymer has played a
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vital role to reduce the surface roughness. The decrease in roughness is probably due to the dense
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coating and self lubricating property of the PTFE particles. PC deposition has offered uniform and dense surface than DC deposition. Pulse deposited coatings were achieved with greater
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cathodic current densities of the coatings. It is well known that, lesser over potential coating generates deposition with larger surface irregularities on the surface of the cathode; while higher
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over potential deposits generate coatings with smooth surfaces. So, the average surface
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3.7 Effect of Coefficient of friction
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roughness value of pulse current deposition of Ni-W/PTFE nanocomposite coating is reduced.
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Fig.7. shows the friction coefficient of Ni-W alloy and various concentrations of PTFE particle inclusion of Ni-W/PTFE nanocomposite coatings. It was noticed that, Ni-W/PTFE nanocomposite coatings have much lower friction coefficient than the Ni-W alloy coating. The friction coefficient value of Ni-W alloy coating was ~0.58, whereas for the case of nickel coating is ~0.78. After the inclusion of PTFE particles in the Ni-W alloy matrix, the value of friction coefficient was decreased significantly. When compared to Ni-W alloy coating the self lubricating polymer incorporation of Ni-W/PTFE nanocomposite coating has better tribological properties. As far as Ni-W alloy coating is concerned, some micro holes and cracks also seen on the surface of the coating which reduced the tribological properties and led to increase the friction coefficient values. As PTFE incorporated into the Ni-W alloy matrix, the porosity of the 13 Page 13 of 35
surface was filled with polymer material. Thus, cracks and micro holes were filled by the self lubricant PTFE polymer and formed as a solid lubricant film on the surface of the Ni-W/PTFE nanocomposite coating. Inclusion of solid lubricant was promising effect of decreasing the
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nanocomposite coatings had much lower than that of Ni-W alloy coating.
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friction coefficient values [26]. As a result, the friction coefficient values of Ni-W/PTFE
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3.8 Potentiodynamic polarization study
The potentiodynamic polarization behaviour of Ni-W alloy matrix and Ni-W/PTFE
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nanocomposite coating deposited with different concentrations of PTFE particles is depicted in Fig. 8. The calculated corrosion current (Icorr) and corrosion potential (Ecorr) values from the
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Tafel polarization curves are summarized in Table 3. It may be observed that, the corrosion resistance of the coatings increases with increasing the concentration of PTFE particles. The
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corrosion potential shifts in the noble direction and the corrosion current is decreased, showing
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that the PTFE polymer inclusion protects the Ni-W alloy matrix from corrosion. Both Ni-W
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alloy and Ni-W/PTFE nanocomposite coatings have displayed some active-passive conversions. Additionally, Ni-W/PTFE nanocomposite coatings have shown a more positive shift in corrosion potential (Ecorr = −0. 316 V) than that of Ni-W alloy (Ecorr = −0. 564 V). The existence of the wider passive region with a positive shift of corrosion potential for the Ni-W/PTFE nanocomposite coatings may be related to the refined grain size and inclusion of PTFE particles which probably acted as an internal physical barrier, thus improving the anticorrosion property of the Ni-W/PTFE nanocomposite coating. As we discussed earlier, the addition of polymer material has covered the cracks and holes of the Ni-W alloy matrix and hence the self lubricating PTFE polymer layer has enhanced the anticorrosion property of the nanocomposite coatings. The corrosion current densities of Ni-W alloy and Ni-W/PTFE deposition were found to be 13.6 and 14 Page 14 of 35
3.53 µA/cm2 respectively. The concentration of PTFE particles was increased upto 20 g/L the corrosion resistance also increased. This increased corrosion resistance can be attributed to the compact, dense and fine grained nature of the pulse deposition of Ni-W/PTFE nanocomposite
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coating. This compact structure was confirmed from SEM and EDAX results. These values have indicated that, Ni-W/PTFE nanocomposite coating has much lower corrosion current density
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3.9 Electrochemical Impedance Spectrum (EIS) Measurements
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signifying better corrosion resistant than that of the Ni-W alloy coating.
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Fig 9 shows the Nyquist plots of the Ni–W alloy matrix and Ni–W/PTFE nano composite coatings containing different concentrations of PTFE particles in 3.5% of NaCl solution. The
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Nyquist plots of all depositions have shown a single semicircular arc in the investigated frequency region. The increased radius of semicircular arc was indicative for the better
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anticorrosion property of the coatings [27]. The equivalent circuit of Ni-W/PTFE nanocomposite
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coating was shown in Fig.10. Meanwhile, the parameters derived from EIS were summarized in
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Table 4. The results of the EIS also indicated a similar trend in the corrosion resistance that was observed in potentiodynamic polarization studies. The higher Rct value was obtained for the 20 g/L of PTFE particles in Ni-W-/PTFE nanocomposite coating. This coating has offered more protection capability against corrosion. The double layer capacitance (Cdl) is small representative smooth surface nature of the deposits. The addition of PTFE particles in the nanocomposite coating has reduced the capacitance of the double layer values. The usage of pulse current and incorporation of PTFE polymer nanoparticles in the Ni-W alloy matrix has resulted in an enhancement of the corrosion resistance for the nanocomposite coatings. Pulse current deposition has contributed to higher particle inclusion and more uniformity of particle distribution in Ni-W alloy matrix. Furthermore, the coverage of the PTFE polymer into Ni-W alloy matrix was 15 Page 15 of 35
effectively completed in pulse electrodeposition and contributed the more protective nature of the Ni-W/PTFE nanocomposite coating.
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3.10 Contact angle measurements To understand the water-repellency of Ni-W alloy matrix and Ni-W/PTFE
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nanocomposite coatings, the contact angle measurement was made. Contact angle measurement
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is a simple quantitative method to analyze the wettability/hydrophobic nature of the solid surface. Surfaces with contact angle value larger than 90° are said to be hydrophobic. The
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volume of water droplet was 8 µL for both Ni-W alloy matrix and Ni-W/PTFE nanocomposite coatings were shown in Fig. 11. The contact angle for the Ni-W alloy matrix (A) was about
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98.2°, while that for the PTFE polymer inclusion of Ni-W/PTFE nanocomposite coating (B) 109.9°, which shown a better water repellency/hydrophobic nature. This means that,
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incorporation of the self lubricating PTFE polymer has improved the water repellency of Ni-
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W/PTFE nanocomposite coating. It has confirmed that, improvement of water repellency was
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mainly depends on the self lubricating property of PTFE polymer, which improved the corrosion resistance behaviour of the nanocomposite coatings [28]. 4. Conclusions
The self lubricating Ni-W/PTFE nanocomposite coatings were successfully prepared by pulse electrodeposition on the mild steel substrate. Inspection of XRD, SEM and EDAX analysis indicated that, PTFE particles have fully covered onto the Ni-W alloy matrix. Chemically inert and solid lubricant nature of the Ni-W/PTFE nanocomposite coatings has significantly decreased the coefficient of friction, surface roughness and moderate microhardness than the Ni-W alloy matrix. Higher PTFE concentration increases the thickness of the coating and hydrophobic 16 Page 16 of 35
nature of the coating. A contact angle measurement of Ni-W/PTFE nanocomposite coating has shown a hydrophobic behaviour (109.9°). These properties have enhanced the corrosion resistance behaviour of pulse electrodeposition of Ni-W/PTFE nanocomposite coatings. The
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addition of PTFE in the Ni-W alloy matrix has resulted moderate microhardness, smooth surface, less friction coefficient, excellent water repellency and enhanced corrosion resistance of the
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nanocomposite coatings
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Acknowledgement
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The authors thank to the Head of the physics department, Alagappa University, Karaikudi for
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providing the XRD analysis to carry out this research work.
References [1] A. Abdel Aal, M. Bahgat, M. Radwan, Nanostructured Ni–AlN composite coatings, Surf. Coat. Technol. 201 (2006) 2910-2918.
17 Page 17 of 35
[2] S. Lei, S. Chufeng, G. Ping, Z. Feng, L. Weimin, Mechanical properties and wear and corrosion resistance of electrodeposited Ni–Co/SiC nanocomposite coating, Appl. Surf. Sci. 252 (2006) 3591-3599.
(h) nanocomposite coatings, Appl. Surf. Sci. 276 (2013) 174-181.
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[3] Z.Shahri, S.R.Allahkaram, A. Zarebidaki, Electrodeposition and characterization of Co–BN
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[4] A.S.M.A. Haseeb, U. Albers, K. Bade, Friction and wear characteristics of electrodeposited
us
nanocrystalline nickel–tungsten alloy films, Wear. 264 (2008) 106-112.
[5] S. Ranganatha, T.V. Venkatesha, K. Vathsala, Electroless Ni–W–P Coating and Its Nano-
an
WS2 Composite: Preparation and Properties, Ind. Eng. Chem. Res. 51 (2012) 7932−7940. [6] S.A. Lajevardi, T. Shahrabi, Effects of pulse electrodeposition parameters on the properties
M
of Ni–TiO2 nanocomposite coatings, Appl. Surf. Sci. 256 (2010) 6775–6781.
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[7] M.S. Chandrasekar, M. Pushpavanam, Pulse and pulse reverse plating- Conceptual,
te
advantages and applications, Electrochim Acta. 53 (2008) 3313-3322. [8] F. Kilic, H. Gul, S. Aslan, H. Akbulut, Effect of CTAB concentration in the electrolyte on
Ac ce p
the tribological properties of nanoparticles SiC reinforced Ni metal matrix composite (MMC) coatings produced by electrodeposition, Colloids surf A: Physiochemical eng asp. 419 (2013) 53-60.
[9] S. Bogden, K. Malgorzata, Composite Ni/Al2O3 coatings and their corrosion resistance, Electrochim Acta. 50 (2005) 4188-4195. [10] K.L. Cheng, Comparative Corrosion Resistance of Electroless Ni-P/nanoTiO2 and NiP/nano CNT Composite Coatings on 5083 Aluminum Alloy, Int. J. Electrochem. Sci. 7 (2012) 12941 –12954.
18 Page 18 of 35
[11] S. Sina, A. Abdollah, Corrosion resistance enhancement of Ni-P-nano SiO2 composite coatings on aluminum, Appl. Surf. Sci. 303 (2014) 125-130. [12] M. Mohammadi, M. Ghorbani, Wear and corrosion properties of electroless nickel
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composite coatings with PTFE and/or MoS2 particles, J. Coat. Technol. Res. 8 (2011) 527– 533.
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composite coatings, Electrochim. Acta. 54 (2009) 2571-2574.
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[13] E. Pompei, L. Magagnin, N. Lecis, P.L Cavallotti, Electrodeposition of nickel–BN
[14] C. Baimin, B. Qiniling, Y. Jun, X. Yanqiu, H. Jingcheng, Tribological properties of solid
an
lubricants (graphite, h-BN) for Cu-based P/M friction composites, Tribol Int. 41 (2008) 1145–1152.
M
[15] W. Zhijiang, W. Lina, Q. Yulin, C. Wei, J. Zhaohua, Self-lubricating Al2O3/PTFE
te
3315-3318.
d
composite coating formation on surface of aluminum alloy, Surf. Coat. Technol. 204 (2010)
[16] Q. Zhao, Y. Liu, E.W. Abel, Effect of Cu content in electroless Ni–Cu–P–PTFE composite
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coatings on their anti-corrosion properties, Mater. Chem. Phys. 87 (2004) 332–335. [17] Q. Zhao, Y. Liu, Electroless Ni–Cu–P–PTFE composite coatings and their anticorrosion properties, Surf. Coat. Technol. 200 (2005) 2510-2514. [18] Y.S. Huang, X.T. Zeng, X.F. Hu, F.M. Liu, Heat treatment effects on EN-PTFE-SiC composite coating, surf. Coat. Technol. 198 (2005) 173-177. [19] B.D. Cullity, S.R. Stock, S. Stock, Elements of X-ray Diffraction, Addison-Wesely, London, 2001. [20] N. Gugliemi, Kinetics of the Deposition of Inert Particles from Electrolytic Baths, J. Electrochem Soc. 119 (1972) 1009-1011.
19 Page 19 of 35
[21] H.Y. Yi, D.G. Chang, L.W. Xiu, P.T. Jiang, Electrochemical Preparation and Characterization of Ni–PTFE Composite Coatings from a Non-Aqueous Solution without Additives, Int. J. Electrochem. Sci. 7 (2012) 12440-12455. Frequency-regulated Pulsed
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[22] T Yiming, W. Peng, H Jung, A. Rose, N. Yun Hau,
Electrodeposition of CuInS2 on ZnO Nanorod Arrays as Visible Light Photoanodes, J.
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Mater. Chem. A, 3 (2015) 15876-15881.
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[23] L. Bing, F. Chunhua, C. Yan, L. Jingwei, Y. Lingguang, Pulse current electrodeposition of Al from an AlCl3-EMIC ionic liquid, Electrochim Acta. 56 (2011) 5478-5482.
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[24] K.A. Kumar, G.P. Kalaignan, V.S. Muralidharan, Pulse electrodeposition and characterization of nano Ni-W alloy deposits, App. Surf. Sci. 259 (2012) 231-237.
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[25] L.T. See, W. Xiaojin, C. Weiwei, Y. Caizhen, G. Wei, Microstructures and Properties of
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Electrodeposited Cu-Bi Composite Coatings, Int. J. Electrochem. Sci. 9 (2014) 2266 –2277.
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[26] M. Zouari, M. Kharrat, M. Dammaka and M. Barletta, A comparative investigation of the tribological behavior and scratch response of polyester powder coatings filled with different
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solid lubricants, Prog Org Coat. 77 (2014) 1408–1417. [27] S. Sangeetha, G.P Kalaignan, Tribological and electrochemical corrosion behavior of Ni-W/BN (hexagonal) nano-composite coatings, Ceram Int. 41 (2015) 10415-10424. [28] S. Sangeetha, G.P Kalaignan, Studies on electrodeposition and characterization of PTFE polymer inclusion in Ni-W-BN nanocomposite coatings for industrial Applications, RSC Adv. 5 (2015) 74115-74125.
Table captions 20 Page 20 of 35
Table 1: Composition of the electrolytic bath and its operating conditions. Table 2: microhardness values of Ni-W and Ni-W/PTFE coatings. Table 3: Derived results of the potentiodynamic polarization measurements.
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Table 4: Electrochemical impedance analysis data.
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Figure captions
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Fig.1. Effect of amount of PTFE in the bath (grams per litre) on the weight percentage of PTFE in the nanocomposite coatings. Fig.2. XRD Patterns of (a) Ni–W alloy (b) Ni–W/PTFE (5 g/L) and (c) Ni–W/PTFE (15 g/L) coatings.
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Fig.3. SEM with EDAX spectrum of (a) Ni–W alloy (b) Ni–W/PTFE (5 g/L) and (c) Ni– W/PTFE (15 g/L) coatings.
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Fig.4. Image of PTFE distribution in the Ni-W alloy coatings.
Fig.5. Plot of coating thickness versus concentration of PTFE on the electrodeposition bath. Fig.6. Cross-sectional FE-SEM images of (a) Ni-W alloy (b) Ni-W/PTFE
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Fig.7. Plot of Friction Coefficient versus concentration of PTFE on the electrodeposition bath.
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Fig.8. Potentiodynamic polarization curves recorded for Ni–W alloy matrix and the Ni–W/PTFE coatings.
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Fig.9. Nyquist plot of Ni–W-alloy matrix and the Ni–W/PTFE coatings. Fig.10. Equivalent electrical circuit used to simulate experimental data of impedance spectrum. Fig.11. Contact angle measurements of a water droplet (8 µL) on the (a) Ni-W (b) Ni-W/PTFE
Pulse Plating bath
Table 1 Composition
Plating conditions
Nickel Sulphate
0.17M
Pulse peak c.d 1.2 A/cm2
Sodium tungstate
0.15M
pH 8 Time 60 min
Tri Ammonium Citrate (TAC) Ammonium Chloride
0.30 M
Temperature 65°C
0.20 M
Constant Stirring
21 Page 21 of 35
Cetyltrimethyl ammonium Bromide (CTAB)
0.50 g/L
PTFE(AlfaAesar-A12613)
5-20 g/L
Pulse duty Cycle On time- 40 ms Off time- 60 ms
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0.06 M
Table 2 Microhardness (HV)
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420 375 448 470 496
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PTFE concentration (g/L) 0 5 10 15 20
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Dimethyl Sulphoxide
Table 3 PTFE concentration (g/L) 0 5 10 15
Ecorr Vs SCE (mV) -564 -473 -435 -395
Icorr (µA cm-2) 13.18 11.29 07.65 05.44
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20
-316
03.53
Cdl (µFcm-2) 52.70 46.15 43.04 38.37 34.28
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Rct (Ω cm2) 600 690 740 830 900
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PTFE concentration (g/L) 0 5 10 15 20
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Table 4
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