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Contents lists available at SciVerse ScienceDirect

Applied Surface Science

j ourna l ho me page: www.elsev ier .com/ locate /apsusc

lectrochemical and structural properties of electroless Ni-P-SiCanocomposite coatings

mir Farzaneha,b, Maysam Mohammadic,∗, Maryam Ehteshamzadeha,c,arzad Mohammadid

Department of Materials Science and Engineering, Faculty of Engineering, Shahid Bahonar University of Kerman, IranDepartment of Materials Science and Engineering, Faculty of Mechanical Engineering, University of Tabriz, IranHigh Technology and Environmental Sciences, International Center for Science, Materials Research Institute, Kerman, IranDepartment of Materials Engineering, The University of British Columbia, Vancouver, BC, Canada

a r t i c l e i n f o

rticle history:eceived 17 January 2013eceived in revised form 24 March 2013ccepted 26 March 2013vailable online xxx

eywords:

a b s t r a c t

Silicon carbide (SiC) nanoparticles were co-deposited with nickel-phosphorous (Ni-P) coatings throughelectroless deposition process. The effects of annealing temperature and SiC contents on properties of thecoatings were investigated. Corrosion performance of the coatings was examined using potentiodynamicpolarization and electrochemical impedance spectroscopy (EIS). X-ray diffraction and Scanning ElectronMicroscopy (SEM) were employed for structural and morphological studies, respectively. It was shownthat the structure of the as-deposited Ni-P-SiC nanocomposite coating was amorphous, and changed to

lectroless coatingano-compositeorrosioneat treatment

the nickel crystal, nickel phosphide (Ni3P) and silicide compounds (NixSiy) with heat treatment. Additionof the SiC concentration in the coating bath affected both composition and morphology of the coating.Presence of SiC nanoparticles in the Ni-P coating enhanced the corrosion resistance of the coating. HigherSiC contents, however, negatively affected the corrosion behavior of the coatings. Heat treatment alsoimproved the corrosion resistance of the Ni-P-SiC coating. Annealing at 400 ◦C decreased the corrosioncurrent density of the coating by approximately 60%.

. Introduction

Electroless nickel coatings (Ni-P) are widely used in variousndustries since they have interesting properties such as high wearnd corrosion resistance, good weldability, electrical conductivitynd uniform coating thickness [1,2]. Co-deposition of solid parti-les into the Ni-P coating can improve tribological properties ofhe coating [3]. These solid particles can be either hard or lubricantarticles. Hard particles, such as Al2O3 [4], TiO2 [5], CeO2, Si3N4 [6]nd diamond [7], enhance wear resistance of Ni-P coating as theyncrease the coating hardness. Lubricant particles including PTFE,

oS2 [8,9], graphite [10] and carbon nanotubes [11], on the otherand, have been used to decrease the friction coefficient of the Ni-Poating.

Among the hard particles, silicon carbide (SiC) is the most com-

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ercially used particle. Co-deposition of SiC particles can result inppropriate tribological properties for electroless nickel coating. Its noteworthy that electroless Ni-P-SiC coating has been considered

∗ Corresponding author. Present address: The University of British Columbia,epartment of Materials Engineering, 309-6350 Stores Road, V6T1Z4 Vancouver,anada. Tel.: +1 604 822 6964.

E-mail address: maysam.mohammadi84@gmail.com (M. Mohammadi).

169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.apsusc.2013.03.156

© 2013 Elsevier B.V. All rights reserved.

as an alternative for “hard chromium” coating in the automotiveand aerospace industries [12,13].

Many studies have been done on the Ni-P-SiC coating usingmicron-size particles [13–18]. However, interesting propertiesof nanomaterials necessitate the investigation of fabrication andcharacterization of Ni-P-SiC composite coatings using nano-sizedparticles.

Mechanical and tribological properties of the Ni-P-SiCnanocomposite coatings have been subjects of many studies[19–22]. Corrosion resistance of these coatings, as one of theimportant properties, may also be affected by co-deposition of theSiC nanoparticles. Comprehensive study on the influences of SiCnanoparticles on corrosion performance of Ni-P coating has notyet been performed.

This work deals with the influences of the SiC nanoparticles andheat treatment on the properties of the electroless Ni-P-SiC coating.Morphology, structure, microhardness and corrosion resistance ofthe coatings were investigated in this study.

tructural properties of electroless Ni-P-SiC nanocomposite coatings,

2. Experimental procedure

Electroless Ni-P and Ni-P-SiC coatings were deposited on mildsteel specimens (30 × 50 × 6 mm). Prior to the electroless plating,

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Table 1Electroless bath composition and operating conditions.

Bath composition Operating conditions

Nickel sulphate (g/L) 21 pH 4.5 ± 0.2Sodium hypophosphite (g/L) 24 Deposition temp. (◦C) 90 ± 1Lactic acid (g/L) 23 Bath vol. (mL) 250Picric acid (g/L) 2.2 SiC content (g/L) 2–8

tbfd

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Ssncam

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3

3

wibNgNoti

Fig. 1. XRD patterns of as-deposited and heat treated Ni-P-SiC coatings at different

ature was from 400 to 700 C. The full width of the peaks at

he substrates were polished to 1000-grid emery paper followedy cleaning in acetone, acid pickling in sulfuric acid (H2SO4, 8% Vol.or 1 min) and immersion in ethanol. The substrates were rinsed inoubly distilled water after each of the pretreatment steps.

The chemical composition of the electroless plating bath and theoating operating conditions are listed in Table 1. These depositiononditions resulted in a nickel coating matrix containing 10 wt.%hosphorous. �-SiC nanoparticles with average size of 50 nm weresed as the SiC source. Cetyltrimethyl ammonium bromide (CTAB)as also added to the plating bath as a surfactant to achieve parti-

les dispersion and surface charge adjustment.Electroless nickel bath containing the SiC particles and the sur-

actant was stirred magnetically for 24 h followed by 20 min ofltrasonic dispersion before plating. Magnetic stirring was used toeep particles suspended during the deposition process. The depo-ition processes were carried out for 60 min to achieve the coatinghickness of 14–16 �m. Heat treatment of the coatings was per-ormed at two temperatures of 400 and 700 ◦C for 60 min in argontmosphere.

X-ray diffraction analysis (Philips X‘pert, Cu K� radiation) andcanning Electron Microscopy (SEM, VEGA/TESCAN) were used fortructural and morphological investigations, respectively. Hard-ess measurements were carried out on the cross section of theoatings, using Vickers diamond indentation under 25 gf loads. Theverage value of five different points was reported for each speci-en.Electrochemical studies were conducted at room temperature

sing 263A EG&G Princeton Applied Research (PAR) potentio-tat/galvanostat and a standard three electrodes cell in an aqueousolution of 3.5 wt.% NaCl. Platinum wire and saturated calomellectrode (SCE) were used as the counter electrode and ref-rence electrode, respectively. Defined samples area of 1 cm2

as exposed to the electrolyte. The potentiodynamic polarizationurves were recorded at potential scan rate of 1 mV s−1. Elec-rochemical impedance spectroscopy (EIS) measurements wereerformed with an amplitude of 5 mV at Open Circuit PotentialOCP) in the frequency range of 105–10−2 Hz. The samples wereept in the electrolyte to reach near steady-state conditions asonitored by OCP before running electrochemical experiments.

. Results and discussion

.1. Effects of heat treatment

The Ni-P-SiC coatings (deposited in the presence of 2 g/L SiC)ere used to investigate the effects of heat treatment on the coat-

ng properties. Heat treatment temperature of 400 ◦C was selectedased on its optimum effect on mechanical properties of electrolessi-P coating [23]. Dong et al. [24] and Jiaqiang et al. [25] investi-ated annealing temperatures of up to 600 ◦C for the electrolessi-P-SiC coating. However, little attention has been paid to effectsf higher annealing temperatures. Therefore, the influences of heat

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reatment at 700 ◦C on properties of Ni-P-SiC coating were alsonvestigated in this study.

temperatures.

3.1.1. Microstructure and microhardnessThe XRD patterns of the as-deposited and heat treated electro-

less Ni-P-SiC coatings are presented in Fig. 1. XRD pattern of theas-deposited coating shows a broad peak at 44.5◦, which representsthe nickel matrix. This pattern indicates that the as-deposited Ni-Pcoating matrix was amorphous, which could be due to the latticedisorder that caused by phosphorous atoms in the nickel coatingstructure [1,26,27]. There is only one more peak in the XRD patternof the as-deposited coating (2� = 36.12◦), which corresponds to theSiC particles.

As Fig. 1(a) shows, the broad peak of the nickel is eliminatedafter heat treatment. This reveals that the Ni-P coating matrix wascrystallized through the heat treatments. XRD results also show theNi3P phase in the heat treated coatings. Annealing at high temper-ature causes phosphorous segregation in the grain boundaries ofthe matrix and formation of phosphorous rich zones. Nickel atomsfrom the matrix react with phosphorous atoms once the phospho-rous content in the area exceeds a certain amount, contributing toprecipitation of Ni3P with body centered tetragonal (BCT) crystalstructure [28,29].

Formation of NixSiy phases (Ni3Si, Ni2Si, Ni5Si2, etc.) in the Ni-P-SiC coating, which are marked in the XRD patterns (Fig. 1(a)), wasthe other effect of heat treatment. Nickel atoms can diffuse into theSiC lattice at high temperature. As a consequence, the Si C bondsare broken and the Si atoms react with the Ni atoms, contributingto formation of nickel silicides (NixSiy) [25].

Fig. 1(b) compares the effects of annealing temperature on thestructure of the Ni-P-SiC coating. As apparent, the Ni3P and NixSiydiffraction peaks were heightened when heat treatment temper-

◦

tructural properties of electroless Ni-P-SiC nanocomposite coatings,

their half maximum (FWHM) also decreased with temperature.These changes reveal that heat treatment at higher temperatures

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Fig. 2. Microhardness evaluation of Ni-P-SiC coatings as a function of heat treatmentt

ep

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Table 2Corrosion parameters of the as-deposited and heat treated Ni-P-SiC coatings deter-mined from the polarization curves.

Annealing Temperature icorr (�A cm−2) Ecorr (mV) RP (� cm2)

tance than the as-deposited coating. Comparing between thecorrosion current densities of the heat treated samples it was foundthat annealing temperature play an important role on electro-chemical behavior of the Ni-P-SiC coating. The coating that was

emperature.

ncouraged both the formation and growth of the Ni3P and NixSiyhases [30].

Fig. 2 shows the effect of annealing temperature on the micro-ardness of the Ni-P-SiC coating. The coating microhardness

ncreased from 600 to 1300 HV after heat treatment at 400 ◦C,hich can be attributed to the phase transition from amorphousi-P to crystalline Ni3P and Ni [24,31,32]. Fig. 2 also indicates that

urther increase in the heat treatment temperature declined theoating microhardness. It has been reported that semi-coherenti3P phases created at 400 ◦C can be transformed to non-coherentrecipitates at higher temperatures, contributing to lower coatingicrohardness. Grain growth of the crystalline Ni and Ni3P phases

t 700 ◦C can also reduces the coating microhardness [24,27].

.1.2. Electrochemical performanceFig. 3 shows the potentiodynamic polarization curves of the as-

eposited and heat treated Ni-P-SiC coatings. This figure revealshat the heat treatment, regardless of the annealing temperature,hifted the polarization curve of the Ni-P-SiC coating to more posi-ive potentials and lower current densities. This means that the heatreatment affected the electrochemical behavior of the compos-te coating. Corrosion current density of the samples was obtained

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sing Tafel extrapolation. The values of the polarization resistance

ig. 3. Potentiodynamic Polarization curves of the as-deposited and heat treatedi-P-SiC coatings.

As-deposited 1.65 −606 13,940400 ◦C 0.56 −512 41,070700 ◦C 0.79 −560 29,114

of the samples (Rp) can be calculated by considering their corrosioncurrent densities and using Eqs. (1) and (2).

icorr = B

RP(1)

B =[

2.3(1

ˇox+ 1

ˇred)]−1

(2)

where ˇox and ˇred are the values of anodic and cathodic Tafelslopes, respectively. Generally, the value of ˇox varies between 60and 120 mV/dec, while ˇred ranges between 60 mV to infinity. It hasbeen shown that approximation of B = 26 mV provides a good esti-mate of Rp from corrosion current density [33]. The values of the Rp

of the samples were calculated using Eq. (1) and the mentioned esti-mation (B = 26 mV). The corrosion factors of the samples includingcorrosion current densities, corrosion potentials and polarizationresistances are reported in Table 2.

According to Table 2, the heat treated Ni-P-SiC coating showedlower corrosion current densities and higher polarization resis-

tructural properties of electroless Ni-P-SiC nanocomposite coatings,

Fig. 4. Bode and Bode phase diagrams (a) and Nyquist plots (b) of the as-depositedand heat treated Ni-P-SiC coatings.

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Ft

ac

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rdiciT

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wFtl

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dwdrcc

TCc

Fig. 6. Experimental and modeled Nyquest spectrum of the as-deposited and heat

ig. 5. Schematic of equivalent circuit used for modeling the impedance spectra ofhe coatings.

nnealed at 400 ◦C showed better corrosion resistance than theoating annealed at 700 ◦C.

The Bode, Bode phase and Nyquist plots of the as-depositednd heat treated Ni-P-SiC coating are shown in Fig. 4. Bode plotsFig. 4(a)) demonstrate that the impedance values did not varyn the frequency range of 105–104, which shows the solutionesistance. The impedance magnitude increased as the frequencyecreased to 0.1. According to Bode phase diagrams, the values ofhe phase were the maximum at frequency range 100–20 Hz forll the coatings. This indicates that the samples showed capacitiveehavior in this frequency range [34].

Different corrosion behavior of the as-deposited and heatreated coatings is obvious from their Nyquest diagrams (Fig. 4(b)).he electroless deposition method has been characterized byormation a uniform and nonporous coating [1,2]. Therefore, elec-rolyte can not simply diffuse into the layer. Moreover, the Nyquestnd Bode phase results showed one time constant in the investi-ated frequency domain. Thus, a simple equivalent circuit shown inig. 5 (Randles equivalent circuit) was used to model the EIS resultsnd determine the corrosion parameters of the coating.

In this circuit, RS is the solution resistance, and RC and CPE rep-esent the charge transfer resistance and constant phase element ofouble layer, respectively. Constant phase element (CPE) has been

ntroduced to imitate electrochemical behavior of an imperfectapacitor. CPE is mainly used to explain the system heterogene-ty and distribution of physical properties of the system [35–37].he impedance of CPE is defined as:

CPE = 1Q (iω)n (3)

here Q is the general admittance function (with the unit ofcm−2sn−1), ω is the angular frequency and n represents the devia-ion of real capacitance from ideal capacitance. The average doubleayer capacitance (Cdl) can be calculated using Eq. (4) [38].

= Cndl(R

−1S + R−1

C )1−n

(4)

The experimental and calculated impedance results of the as-eposited and heat treated Ni-P-SiC coatings are presented in Fig. 6,hich shows a good match between experimental and simulated

−4

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ata. The value for � square was less than 10 in all cases rep-esenting an acceptable fit. The calculated value of the electricalircuit components for the as-deposited and heat treated Ni-P-SiCoatings are reported in Table 3.

able 3alculated impedance parameters of as-deposited and heat treated Ni-P-SiCoatings.

Annealing temperature RS (� cm2) RC (� cm2) Cdl (�F cm−2) n

As-deposited 7.98 13,212 16.87 0.815400 ◦C 8.58 59,784 6.36 0.933700 ◦C 8.23 28,123 14.75 0.858

treated Ni-P-SiC coatings.

Comparing the results in Tables 2 and 3 demonstrates that theRP values calculated from polarization curves are different from RCvalues obtained from EIS results. The difference is less than factorof two, which is the expected error when using B = 26 mV as anapproximation in Eq. (1) [33].

The EIS results indicate that the heat treatment increasedthe charge transfer resistance (RC) of the Ni-P-SiC coating anddecreased the double layer capacitance (Cdl). These reveals that,like what was observed from the polarization curves, heat treatedsamples had better corrosion resistance than the as-deposited one.It is also apparent that the heat treatment at 400 ◦C provided bettercorrosion behavior for the Ni-P-SiC coating than at 700 ◦C.

Negative effect of heat treatment on the corrosion resistance ofelectroless Ni-P coating has been reported previously [39]. Crys-tallization of nickel coating and formation of Ni3P phase, andconsequently larger surface proportion of the grain boundaries,have been reported as the reasons for such phenomenon. Thus, theimprovement in the corrosion resistance of the Ni-P-SiC coatingwith heat treatment can be attributed to the SiC particles and theinteraction between these particles and the Ni-P coating matrix.

As previously mentioned here, nickel atoms can diffuse into theSiC lattice at high temperature and provide more coherent bound-aries between the SiC particles and nickel matrix [29]. Moreover,reaction of Ni and SiC particles during the heat treatment maycause shrinkage in the coating, contributing to a coating with lowerporosity and higher compactness [25]. As a result, heat treatmentcan improve the barrier property and consequently corrosion resis-tance of the Ni-P-SiC coating.

Electrochemical measurements also showed that increasing theheat treatment temperature from 400 to 700 ◦C improved the cor-rosion resistance of the coating. Conversion of the semi-coherentNi3P phase to non-coherent phase could contribute to the lowercorrosion resistance of the Ni-P-SiC heat treated at 700 ◦C [24,30].Furthermore, larger amount of nickel silicides formed at 700 ◦C may

tructural properties of electroless Ni-P-SiC nanocomposite coatings,

increase the inhomogeneity of the coating and cause more numberof corrosion microcells, and consequently higher corrosion rate.

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F n conf

3

3

c(ccspucbpce

c

ig. 7. EDX spectra of the Ni-P (a) and the Ni-P-SiC coating deposited from a solutiounction of SiC concentration in the bath (e).

.2. Effects of SiC content

.2.1. Morphology and compositionEffect of SiC particles concentration on the coatings composition

oating was studied using Energy-dispersive X-ray spectroscopyEDX). Fig. 7(a–c) show the EDX spectra of the Ni-P and the Ni-P-SiCoatings deposited in the presence of 0, 2 and 8 g/L SiC nanoparti-les, respectively. Weight percentages of nickel, phosphorous andilicon were roughly estimated through this analysis. Since the SiCarticles were the only source of Si in the coating, the Si wt.% wassed to estimate the SiC content. Dependence of SiC content of theomposite coating on SiC particles concentration in the depositionath is shown in Fig. 7(d). This figure reveals that the amount of SiCarticles co-deposited into the Ni-P coating increased as the SiC

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oncentration in the deposition bath was increased. However, thisffect was more significant in lower concentrations of SiC particles.

Surface morphologies of the electroless Ni-P-SiC coatings fabri-ated in the presence of 0, 2, 4 and 8 g/L SiC nanoparticles are shown

taining 2(b) and 8 g/L SiC (c), and variation of SiC content of the coating (wt.%) as a

in Fig. 8. The SEM images indicate that the coating morphology wasaffected by co-deposition of the SiC particles. As apparent, higherSiC concentration resulted in smaller spherical nodules size of thecoating. This may interpreted as the SiC nanoparticles may eitherprovide more nucleation sites for the Ni-P deposition or limit thelateral growth of the Ni-P layer.

Comparison between Fig. 8(c) and (d) reveals that an increasein the SiC particles concentration from 4 g/L to 8 g/L has little influ-ence on the coating morphology, however, caused presence of tinycracks in the coating (shown by white arrows in Fig. 8(d)). Forma-tion of the cracks could be due to higher stress levels in the coatinginduced by more SiC particles co-deposited into the coating.

3.2.2. Electrochemical performance

tructural properties of electroless Ni-P-SiC nanocomposite coatings,

As shown in the previous section, heat treatment at 400 ◦Cimproved corrosion resistance of the Ni-P-SiC coating. Therefore,all the coatings were heat treated at 400 ◦C before electrochemicalinvestigations.

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uced

tccaadtc

TC

Fig. 8. SEM micrographs of the Ni-P-SiC coatings prod

Fig. 9 illustrates the potentiodynamic polarization behavior ofhe Ni-P and the Ni-P-SiC coatings deposited in different SiC con-entration. Co-deposition of SiC nanoparticles, depending on theirontent, shifted the polarization curves to less negative potentialsnd lower current densities. However, these changes did not follow

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linear trend with SiC contents. The value of corrosion currentensities, corrosion potentials and the calculated polarization resis-ances of the coatings are summarized in Table 4. Comparing theorrosion current densities of the coatings with that of bare mild

able 4orrosion parameters of Ni-P-SiC coatings determined from the polarization curves.

Sample icorr (�A cm−2) Ecorr (mV) RP (� cm2)

Ni-P (0 g/L SiC) 2.51 −662 9123Ni-P-SiC (2 g/L) 0.56 −512 41,070Ni-P-SiC (4 g/L) 0.93 −537 24,730Ni-P-SiC (8 g/L) 1.27 −618 18,110

in SiC concentration of 0 (a), 2 (b), 4 (c) and 8 g/L (d).

steel, which was reported in the authors’ previous publication [30]reveals that all of the investigated electroless nickel coatings can beused for corrosion protection of mild steel in saline environments.These results also reveal that the composite coatings showed bet-ter corrosion resistance than the Ni-P coating. The lowest corrosion

tructural properties of electroless Ni-P-SiC nanocomposite coatings,

current density was shown by the Ni-P-SiC coating deposited in thepresence of 2 g/L SiC nanoparticle.

The Bode, Bode phase and the Nyquist plots of the Ni-P-SiC coatings are shown in Fig. 10. Variation of the impedance

Table 5Calculated impedance parameters of the Ni-P, Ni-P-SiC coatings.

Samples RS (� cm2) RC (� cm2) Cdl (�F cm−2) n

Ni-P 7.35 29,455 29.99 0.77Ni-P-2 g/L SiC 8.58 59,784 6.36 0.93Ni-P-4 g/L SiC 7.49 49,141 12.75 0.85Ni-P-8 g/L SiC 7.65 32,533 22.67 0.88

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mw

mgarlo

nomtc

FN

Fig. 9. Polarization curves of Ni-P and Ni-P-SiC coatings.

agnitude and phase with frequency (Fig. 10(a)) were similar tohat was explained in previous section.

The Nyquest diagrams of the Ni-P-SiC coating (Fig. 10(b)) wereodeled using the equivalent circuit that was shown in Fig. 5. A

ood match between the experimental and calculated data waschieved as the values of � square were less than 10−4. The fittingesults of EIS measurements for the Ni-P and Ni-P-SiC coatings areisted in Table 5. The variation of the RC value with the SiC contentf the coating was similar to that of the RP (Table 4).

Electrochemical studies revealed that incorporation of SiCanoparticles into the Ni-P coating improved corrosion resistancef the coating. This effect may be attributed to the lower effective

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etallic surface area of the Ni-P-SiC coatings compared to that ofhe Ni-P coating [40]. Volume fraction of the SiC particles in theoatings can be calculated using densities of the SiC particles and

ig. 10. Bode and Bode phase diagrams (a) and Nyquist plots (b) of the Ni-P andi-P-SiC coatings.

PRESS Science xxx (2013) xxx– xxx 7

Ni-%P matrix as well as SiC wt.% of the coating (Fig. 7(d)). It can beassumed that the area covered by SiC particles on the surface of thecoatings is the same as their vol.%. Thus, the ratio of metallic surfacearea of the Ni-P-SiC coatings to that of the Ni-P coating would be inthe range of 0.72–0.86 (±0.2). The variation of the corrosion currentdensity of the coating with SiC co-deposition, however, was moresignificant than the variation of the metallic surface area. There-fore, different metallic surface area of the coatings could not be theonly reason for their different electrochemical performance.

The incorporation of the SiC nanoparticles into the Ni-P coatingmay enhance the coating compactness and limit diffusion of thecorrosive species into the coating, contributing to the better cor-rosion resistance. Comparing the obtained electrochemical resultswith those reported by Huang et al. [41] it can be concluded that thenano-scale SiC particles have more positive effects on the corrosionbehavior of the Ni-P coatings compared to micro-scale particles.

As was shown, increasing the SiC concentration from 2 g/L to 4and 8 g/L lowered the charge transfer resistance (RC), and increasedthe double layer capacitance (Cdl) and corrosion current density(icorr) of the coatings. These variations reveal that further increase inthe SiC concentration in the deposition bath resulted in the coatingswith lower corrosion resistance. This can be attributed to largernumber of SiC particles codeposited into the coating, which, inturn, can decrease the coating homogeneity. The Ni-P-SiC coatingdeposited in the presence of 8 g/L SiC particles showed the lowestcorrosion resistance among the composite coatings. This behaviorcan be due to the presence of cracks and defects in this coating(see Fig. 8(d)). These cracks allow the corrosive species to perme-ate through the coating and attack larger surface area of the coatingor the substrate.

According to the electrochemical studies, Ni-P-SiC compositecoating that was deposited in the presence of 2 g/L SiC nanoparti-cle provided the optimum corrosion performance among the otherinvestigated coatings, which improved the corrosion resistance ofthe Ni-P coating by approximately 70%.

4. Conclusion

The structure, morphology and corrosion behavior of theelectroless Ni-P matrix composite coatings co-deposited withnano-sized SiC particles were investigated. The main conclusionsare as follows:

Co-deposition of the SiC nanoparticles into the Ni-P coatingaffected the morphology of the deposited coating and decreasedthe nodules size. Corrosion performance of the Ni-P coating wasimproved by co-deposition of the SiC nanoparticles. However, SiCconcentration higher than 2 g/L negatively affected the corrosionresistance of the coating. The as-deposited Ni-P-SiC coating hadan amorphous structure, while the heat treated composite coat-ing contained a combination of crystalline nickel, Ni3P and silicidecompounds (NixSiy). Heat treatment also enhanced the corrosionresistance of the Ni-P-SiC coating. The Ni-P-SiC coating heat treatedat 400 ◦C had the best performance in term of corrosion resistancecompared to the as-deposited coating and the heat treated coatingat 700 ◦C.

This study showed that the Ni-P-SiC nanocomposite coatings,like Ni-P coating, can be used in the saline corrosive environmentsto improve corrosion resistance of mild steel, in addition to itsmechanical properties. However, investigation of the long termcorrosion performance of the Ni-P-SiC nanocomposite coatings ishighly recommended.

tructural properties of electroless Ni-P-SiC nanocomposite coatings,

Acknowledgment

Funding support for this work was provided by Vice ChancellorResearch of International center for Science & High Technology and

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