M A T E R I A L S C H A R A C T E R I Z A T I O N 6 2 ( 2 0 1 1 ) 1 6 4 – 1 7 3

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Characterization of electrodeposited nickel coatings fromsulphamate electrolyte without additive

A. Godona, J. Creusa, X. Feaugasa, E. Confortob, L. Pichonc, C. Armandd, C. Savalla,⁎aLaboratoire d'Etudes des Matériaux en Milieux Agressifs, EA3167, Université de La Rochelle, Av. Michel Crépeau, F-17042 La Rochelle,FrancebFédération de Recherche en Environnement pour le Développement Durable (FR-EDD), FR CNRS 3097, Centre Commun Analyses,Université de La Rochelle, 5 Allée de l'Océan, F-17042 La Rochelle Cedex 9, FrancecInstitut Pprime, UPR 3346 CNRS, Université de Poitiers, SP2MI, Boulevard Marie et Pierre Curie, BP 30179, 86962 Chasseneuil,Futuroscope Cedex, FrancedINSA Toulouse, Département de Physique, 135 avenue de Rangueil, 31077 Toulouse Cedex 4, France

A R T I C L E D A T A

⁎ Corresponding author. Tel.: +33 5 46 45 72 9E-mail address: csavall@univ-lr.fr (C. Sava

1044-5803/$ – see front matter © 2010 Elsevidoi:10.1016/j.matchar.2010.11.011

A B S T R A C T

Article history:Received 28 June 2010Received in revised form25 October 2010Accepted 18 November 2010

In this paper, the influence of deposition current density on microstructure and purity ofnickel coatings was studied. Complementary characterization methods (SEM, TEM, XRD,EBSD, GDOES and SIMS) were used to investigate different scales of the microstructure andto understand the metallurgical states of the coatings. As deposition current densitydecreases, grain refinement and texture modifications are observed which are linked withthe grain boundary character (disorientation angle and Coincidence Site Lattice). Moreover,in sulphamate bath without additive, the contamination by light elements and metallicimpurities strongly depends on deposition parameters and must be taken into account todiscuss the microstructure changes.

© 2010 Elsevier Inc. All rights reserved.

Keywords:Electrodeposited nickelGrain refinementGrain boundariesEBSDChemical composition

1. Introduction

Nanocrystalline materials have been the subject of intensiveresearch because of their unique properties [1–3]. For example,concerning the corrosion resistance of pure metals, severalworks report that the susceptibility to localized corrosion islower in nanocrystalline materials [4–6], but the mechanismsresponsible for this superior corrosion resistance are notclearly established [5,7]. As corrosion resistance can beaffected by several metallurgical parameters (defects, grainsize, grain boundary, purity, crystallographic texture, rough-ness, etc.), a careful control of microstructure is necessary.

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Nanocrystalline nickel with a grain size below 100 nm wasobtained by electrodeposition but deposition parameterslargely vary from one study to another. For example, inadditive-free Watts bath [8] ultra-fine-grained nickel electro-deposits (grain size down to 100 nm) were obtained by pulseplating at very high pulse-current. By using organic additives(especially saccharin in the case of nickel), several studiesshow that it was possible to produce nanocrystalline nickelcoatings in different baths with grain sizes in the range of 6–100 nm [6,8,9]. It was shown that the use of organic additivesleads to an increase of the contamination of coatings [10,11],which can affect both mechanical properties and corrosion

.

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resistance. Few studies have tried to explain the influence ofdeposition parameters by a careful analysis of the microstruc-ture [8,12]. In most cases, only one parameter is studied,mainly grain size which is evaluated by analyzing thebroadening of the diffraction peaks [3,9,13] or by scanningelectron microscopy [14,15]. However, it was shown that forthe same electrodeposited nickel sample, the size of structuralelements can largely vary depending on the observation tool,and thus themicrostructure needs to be evaluated at differentscales [11].

Among the different baths, sulphamate based bath is ofparticular interest as it leads to ductile deposits with lowinternal stress [17,18], even without sulphur (S) containingadditive [16].

In this paper, an additive-free sulphamate bath is used inorder to limit the incorporation of impurities and especially Sbecause of its dramatic effect on corrosion resistance. Theinfluence of current density on the microstructure and oncontamination of nickel coatings is studied by using differentcharacterization methods. The correlation between structuralobservations at different scales and chemical analysis allowsunderstanding the metallurgical states of the coatings.

2. Material and Methods

Nickel coatings were prepared by direct-current galvanostaticdeposition in a three-electrode cell by using a VSP potentiostatfrom Biologic. A conventional sulphamate bath (V=400 mL)without additive was used, and composed of 300 g/L Ni(NH2

SO3)2.4H2O, 15 g/L NiCl2.6H2O, and 30 g/L H3BO3. Solutionswere prepared by dissolving pure salts in ultrapure water(18.2 MΩ cm) and pH was then adjusted to 4.2 by adding nickelcarbonate. Special attention was devoted to avoid contami-nation of the bath. A thermostated glass reactor was used tofix the temperature at 50 °C and the solution was mechani-cally stirred during the deposition. The anode was of purenickel (99.99%) and embedded in a polypropylene anode bag.Nickel substrates (S=2 cm2) were polished with silicon carbide(particle size 5 μm), sonicated for 2 min, rinsed with ultrapurewater and dried before electrodeposition. Deposition currentdensitywas varied between 1 and 50 mA/cm2. In the following,the nomenclature of samples (Table 1) refers to this depositionparameter (for example CD 1 refers to a deposition currentdensity of 1 mA/cm2). Cathodic efficiency was estimated byweighting the samples before and after deposition. Depositiontime was adjusted to obtain thicknesses of 50 μm.

Table 1 –Mean sizes deduced from SEM, EBSD and TEMfor coatings elaborated at different current densities.

Name jmA/cm2

Φ (SEM)μm

d (EBSD)μm

d (TEM)μm

CD1 1 0.37 0.25 0.120CD5 5 0.74 0.35 0.180CD10 10 1.4 – –CD20 20 3.9 – –CD50 50 4.3 1.02 –

The surfacemorphologywas observedby scanning electronmicroscopy (SEM)with a FEI Quanta 200 ESEM-FEGoperating at20 kV as acceleration voltage. Electron backscatter diffraction(EBSD) was used to obtain grain size and to characterizemicrotexture and grain boundaries. For top-view EBSD analy-ses, samples of 75 μm thickness were electrodeposited andthen electropolished in a H2SO4/CH3OHmixture [19] in order toremove 25 μm. After electropolishing, samples were very flat,with a roughness below 2 nm (estimated by Atomic ForceMicroscopy experiments). For cross-section EBSD analyses,samples were cut with a wire saw and cross-sections weremechanically polished. A final polishing was performed withOPSpreparation fromStruers. EBSDmapswere acquired athalfof the coating thickness using an acceleration voltage of 25 kVon SEMand the TSLOIMData collection 5 Software, with a stepsize of 30 nmor 70 nm, depending on the grain size. A clean-upwas performed onmaps in order to remove points which werenot indexed or to index according to the first neighbours thosewhich were originally incorrectly indexed. Grain size andorientation pictures were then calculated using TSL OIMAnalysis 5 software.

Complementary transmission electronic microscopy (TEM)observations were carried out with a JEOL JEM 2011 electronmicroscope operating at 200 kV. Foils for TEM were thinned indouble twin-jet electro-polisher using an electrolyte of 25%nitric acid and 75% methanol at a temperature of 30 °C and acurrent of 150 mA. To understand themicrostructure observedat high current density, TEM observations were also per-formed on the cross-sections of sample CD50. For thisspecimen, stereographic analyses (stereographic projection)were established for each observed grain in order to evaluatethe orientation of each grain. Special care was taken in themarking of TEM specimens. So, the direction of the normal ofthe electrodeposited surface was identified on the stereo-graphic map of each studied grain.

X-ray diffraction analyses in θ–2θmode were performed ona Brucker apparatus (AXS D8-Advanced) with the Cu-Kαradiation (λ=0.15405 nm). Spectra were acquired between 40°and 100°, with a step width of 0.02° and the Kα2 peak andbackground were removed. Composition analyses wereobtained by Glow Discharge Optical Emission Spectrometry(GD Profiler from Horiba Jobin Yvon). Secondary Ion MassSpectrometry (IMS 4FE6 from CAMECA) was also used withtwo ionic sources Cs+ (at 14.5 keV) and O2

+ (at 5.5 keV) to obtainthe best sensitivity. Concentration profiles were acquired aftera pulverization of 5 to 10 μm in order to avoid surfacecontamination effects. All atomic elements were analyzedexcept nitrogen. For both methods, the detection limit for thiselement was too high. Calibration with bulk nickel samples ofknown composition was performed for quantitative analysis.Several profiles were obtained for each sample, leading toreliable results. However, due to the small volumes which areanalyzed by these techniques, concentration values cannot begiven with a high accuracy.

3. Results

Theaimof thiswork is touse complementary analyses to obtainan overview of the metallurgical state of electrodeposited

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coatings. Section 3.1 describes surface morphologies in relationwith SEM observations. Section 3.2 outlines the interest to useX-ray diffraction analyses to study themacroscopic texture andto extract dimensional data. The following Sections 3.3 and 3.4deal with the opportunity to obtain spatial information usingEBSD maps and TEM analyses. Finally, chemical compositionwas analyzed in connection with structural results.

3.1. Scanning Electron Microscopy

SEM views presented in Fig. 1 show the surface morphology ofcoatings prepared at different current densities. At highcurrent densities, large crystallites with a truncated pyramidalshape are observed leading to bright deposits in goodagreement with previous results in sulphamate bath [12,15].A strong hydrogen evolution leads to the formation of bubblesand edge effects at current densities above 50 mA/cm2. As thecurrent density decreases, this pyramidal morphology isreplaced by a nodular morphology. The mean size of thenodules deduced from SEM was estimated by statisticalanalyses of images obtained at different magnifications(Table 1). The values suggest a refinement at low currentdensity. However, the morphological features observed by

Fig. 1 – SEM top views showing the surfacemorphology of the coatib: CD5 (5mA/cm2), c: CD10 (10mA/cm2), and d: CD50 (50 mA/cm2))

SEM cannot be directly assigned to grains and other charac-terization tools will be used below to clarify this point.

3.2. X-ray Diffraction Analysis

The diffraction patterns for different deposition currentdensities are plotted on Fig. 2. At high current density (above30 mA/cm2), a strong crystallographic texture along the <100>direction is observed, which is replaced by a <110> preferredorientation at current densities below 20mA/cm2. At 1 mA/cm2,no preferred orientation is observed but the (220) line isslightly high and the (200) one is slightly low respectively to anon texture nickel sample (JCPDS data no. 00-004-0850).Complementary texture analysis by using inverse pole figuresobtained by EBSD will be presented in Section 3.3, confirmingthe above results. For coating CD1, a broadening of thediffraction peaks can be noticed, suggesting a grain refinementeffect. Assuming a Cauchy-shaped profile, the full width athalf maximum (FWHM) was evaluated for each diffractionpeak, after correction by the experimental broadening esti-mated by using the LaB6 standard sample. The Scherrerequation obviously led to a strong underestimation ofthe grain sizes of these coatings. So, an approach based on

ngs deposited at different current densities. (a: CD1 (1 mA/cm2),.

Fig. 2 – θ–2θ scans of coatings elaborated at different currentdensities.

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Williamson–Hall diagrams was used in order to estimatecrystallite sizes and internal stresses. The approach developedby Reimann [20] and used by Thiele [11] in electrodepositednickel was followed, which takes into account the elasticanisotropy of nickel.

The Williamson–Hall plots obtained for coatings depositedat 1 mA/cm2 (CD1) led to a mean internal stress (<σ2>1/2)of 300 MPa. This value is in the range of those previouslyreported in electrodeposited nickel [11] which showed anincrease of mean internal stress as the grain size decreases.The mean size of coherent scattering regions for sample CD1deduced from this analysis is around 130 nm. For coatingsdeposited at higher current densities, the broadening of thediffraction peaks is smaller. Moreover, for these coatings, thepresence of a crystallographic texture does not allow thisapproach.

3.3. Electron Backscatter Diffraction

Top-view orientationmaps for coatings elaborated at differentcurrent densities are presented on Fig. 3. Inverse pole figureswere calculated from these orientation maps, showing theorientation densities for the different crystallographic direc-tions parallel to the sample normal direction. The preferredorientation along the <100> direction suggested by θ–2θ XRDscans for coatings prepared at 50 mA/cm2 (CD50) is confirmed.Comparison with SEM views shows that the large truncatedpyramidal structures aremainly orientedwith their <100> axisperpendicular to the substrate surface. Between these pyra-midal grains, much smaller grains are found, with differentcrystallographic orientations. Even if a preferred orientationalong the <110> direction is found for the coating prepared at5 mA/cm2 (CD5), the texture is less marked (as the proportionof pixels which <110> crystal direction is disoriented versus thesample normal direction is higher). For the coating depositedat the lowest current density (CD1), the crystallographictexture along the <110> direction is very weak, in accordancewith θ–2θ XRD scans. Grain boundary position is super-imposed as grey lines to the orientation maps of Fig. 3.Neighbouring pixels in the map with disorientation smallerthan 5° are associated with the same grain. According to this

disorientation angle, the grain size distribution can bemeasured and a mean grain size (dEBSD) can be evaluated.For each sample, the analyzed area was large enough to takeinto account more than 5000 grains. The results are given inTable 1, and in accordance with SEM observations, the grainsize decreases and the grain distribution becomes narrowerwhen the deposition current density is reduced.

EBSD orientation maps obtained on cross-sections ofdifferent deposits are given on Fig. 4. The growth directionwhich is perpendicular to the surface of the substrate is alsoshown on this figure. For the CD50 sample, fibers (whose axisis perpendicular to the substrate surface) characterized by adominant colour are observed. These fibers are formed bygrains slightly disoriented with regard to the neighbouringgrains, but with the (100) direction mainly parallel to thegrowth direction. Between these fibers, some less orientedregions are found. The thickness of these fibers (around 5 μm)is quite similar to the size of large crystallites with a truncatedpyramidal shape, which are observed on the surface (4.3 μm,Table 1). As the deposition current density decreases, thesefibers are no longer observed and the mean size of the grainsdecreases. It can be noticed that the grains do not show anyelongation along the growth direction whatever the deposi-tion current density.

Two parameters are mainly used to describe the nature ofgrain boundaries: the disorientation angle and the Σ factor,which denotes the fraction of atoms in the grain boundaryplane which are coincident to both lattices. These parameterswere evaluated by using EBSD [21] and are given in Table 2and Fig. 5. An increase of the fraction of high angle grainboundaries (HAGB) is observed as the grain size decreases andas the marked texture along the <100> direction is replaced byaweak texture along the <110> direction (Table 2). The amountof coincidence site lattice (CSL) is also strongly modified,showing a decrease of the abundance of Σ1 boundaries and anincrease of the number of Σ3 and Σ9 boundaries when thegrain size decreases (Fig. 5).

3.4. Transmission Electronic Microscopy

Grain size was evaluated using TEM observation on apopulation around 150 grains and the mean values are givenfor CD1 and CD5 in Table 1. These values are lower than theones obtained by EBSD, but for the CD1 sample, the value is inagreement with XRD analysis (130 nm). As a strong heteroge-neity of grain sizes was observed for CD50, the mean value isnot relevant for this sample. TEM observations were alsoperformed on cross sections for this sample to evaluate thecrystallographic orientation of different grains. These analy-ses are time consuming, thus only a semi-statistical studyon 56 grains at different locations inside the sample wasperformed. However, 56 grains seemed to be sufficient toreflect the heterogeneity of the sample, as the results were notsignificantly modified when this number was increased.Different populations of grains were identified, characterizedby three angles ψ(100), ψ(111) and ψ(110) (Fig. 6). ψ(hkl) relatesthe angle between (hkl) plane and the normal to the coatingsurface. The first one (V1) corresponds to the largest grains(>700 nm) and exhibits an angle ψ(100) near 0. Thismeans thatthis crystallographic population mainly contributes to the

Fig. 3 – Left: Top view orientation maps obtained by EBSD for coatings elaborated at different current densities: CD1 (a), CD5 (b),and CD50 (c). Right: Inverse pole figures of the normal direction for the three coatings.

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macroscopic texture observed by XRD. In a “random” zone (cf.EBSD analyses), three other kinds of crystallographic popula-tions were identified (Fig. 6), which do not correspond tomacroscopic texture obtained by XRD. The size of these grainsis generally lower (130 to 250 nm) than the grain with V1variant. The correlations of these observations with SEM andEBSD results show that two kinds of regions can be distin-guished in the CD50 coating: the first one corresponds to large

grains with a <100> preferred orientation and the second oneis associated with “random” regions, with a much lower grainsize and weaker texture.

3.5. Composition Analysis

Table 3 lists the different elements detected in the coatingsand their contents in weight ppm obtained by SIMS and

Fig. 4 – Cross-section orientation maps obtained by EBSD for coatings elaborated at different current densities: CD1 (a), CD5 (b),and CD50 (c). The substrate surface normal is given by an arrow.

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GDOES. For the coating CD50, impurity amounts are very low,leading to a purity around 99.99%. However, for the coatingsprepared at lower current density the contamination drasti-cally increases especially for light elements (H, O, C, etc.) andfor Cl and Cu. For these coatings, some impurity contents aregiven with a large inaccuracy, and the purity of the coatingcould not be evaluated. In these cases and especially forchloride for which the concentration in ppm was not given,the quantification was not reliable as the reference samplescontained much lower amounts of these elements. Concen-tration profiles and cartographies were obtained for eachatomic element, showing that the impurities were homoge-

neously distributed laterally and through the thickness of thecoatings.

4. Discussion

Electrodeposited layers often exhibit a fiber texture, i.e.preferred crystallographic orientation of their crystallitesalong the growth direction, which is the case for depositsCD5 and CD50. Our results are in good agreement withpublished results for sulphamate bath which report a strongcrystallographic texture along the <100> axis associated

Table 2 – Classification of the grain boundaries characterfor coatings deposited at different current densities. Low-angle grain boundaries (LAGB) are characterized by adisorientation angle below 15° and high-angle grainboundaries are characterized by a disorientation angleabove 15°.

CD1 CD5 CD50

LAGB/HAGB(%)

7 93 9 91 42 58

LCSL/HCSL(%)

42 58 57 43 57 43

CSL denotes coincidence site lattice (CSL) with low sigma (LCSL,Σ<29) or high sigma (HCSL, Σ>29).

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with large grains for deposition currents between 30 and200 mA/cm2 [12,13]. Based on cross-section observations byoptical microscopy or SEM after chemical etching, the <100>texture has been associated with the formation of longcolumnar grains, some of them extending across the wholethickness of the coatings (10 to 50 μm) [15,18]. Cross-sectionobservations of the CD50 coating by optical microscopy afteracidic etching show kinds of columns, parallel to the growthdirection, with a width of few micrometers (Fig. 7a). EBSDand TEM observations on cross sections allow to distinguishunambiguously the grains and to evaluate their orientations.The results obtained by EBSD clearly show that these “columns”are formed by grains weakly disoriented with regard to theirneighbouring, with the <100> direction perpendicular to thesubstrate surface. This microstructure, associated with a quitehigh amount of low angle grain boundaries and particularly ofΣ1 boundaries explains the large disagreement between thestructure size elements deduced by EBSD and SEMobservationsin these coating (Table 1). Results obtained by TEM confirm thatthe largest grains (and the more numerous) are oriented withone direction <100> parallel to the growth direction. However, asignificant amount of grains, much smaller (<250 nm), isdifferently oriented.

As the current densities decrease, grain refinement isobserved associated with the evolution of the <100> texturetowards a less marked <110> texture, in good agreement withpublished results in similar bath [18,23]. In the literature, such

Fig. 5 – Amounts of LCSL plotted versus Σ value for coatingsdeposited at different current densities.

texture changes are associated with a grain size decrease,obtained by using pulse plating [2,22] or organic additives[23,24]. For coatings deposited at low current densities, verythin fibers parallel to the growth direction are observed oncross-sections after chemical etching (Fig. 7b). However, EBSDobservations clearly show that the grains are not elongatedalong the growth direction. In agreement with the resultsobtained for the coating CD50, EBSD is a powerful tool toobserve themicrostructure of electrodeposited coatings and toavoid artefacts linked with chemical etching necessary todisplay grains with more conventional observation techni-ques. EBSD analyses presented here show that these evolu-tions of texture and grain size are associated with an increaseof the amount of high angle grain boundaries. Particularly, adecrease of the fraction of Σ1 boundaries and an increase ofthe fraction of Σ3 boundaries are observed as the grain sizedecreases. Similar trends were reported in copper proceededby equal Channel Angular Extrusion [25]. Several studies sug-gest that the presence of low-Σ coincidence site lattice (CSL)boundaries could be associated with a better corrosionresistance [7,26] and with better mechanical properties [27].However, this can be moderated by the fact that the presenceof low-Σ coincidence site lattice boundaries seems to becorrelated with high impurity contents.

At low current densities, equiaxed nickel with very lowgrain sizes can be deposited in direct current mode withoutadditive. For these deposits, good correlations between grainsizes deduced from EBSD and nodule sizes deduced from SEMare found. At low deposition current densities, the randomorientation of grains is linked with high disorientationsbetween grains, which appear as distinct entities in top-viewSEM observations of the coatings. A mean grain size valuearound 250 nm is found by EBSD (with a disorientation of 5°)for the coating prepared at the lowest current density. Amuchsmaller value is deduced from analyzing the broadening of thediffraction pattern in accordancewith the grain sizemeasuredby TEM. Thus, the choice of the disorientation angle valueused to define grain size by EBSD needs to be validated by acorrelation with XRD or TEM analyses.

Our results show that the grain refinement and thechanges of crystallographic orientation are linked withan increase of the amounts of several impurities. As thenickel anode was of high purity, Co and Cu contaminationprobably originates from the chemicals of the bath. Copper,which is nobler than nickel, is preferentially deposed atlow current density (and thus at low overpotential).Because of their position in the Mendeleïv table, thesemetallic impurities can easily replace nickel in the coatingand should act as substitution impurities. The changes ofthe microstructure are probably linked with the incorpora-tion of light atomic elements. Inhibition phenomena[28,29], are known to strongly influence electrocrystallisa-tion processes. In the case of nickel electrodepositionfrom Watts bath, Amblard et al. [30] show that interfacialinhibitors (Hads, Ni(OH)2, etc.) led to several growth modesand textures, depending on deposition parameters, butdifferent species including C, O, N, H or Cl atoms wereproposed [29,31]. A significant drop of the deposition efficiencywas observed as the deposition current density decreases from98% (for coatings deposited at 50mA/cm2) to around 84% (for

Fig. 6 – TEM observations (CD50) and stereographic projections showing the orientation of different grains in a “randomoriented” region. The table gives the grain population in terms of angle between the coating normal surface and the (hkl) plane.

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coatings deposited at 1 mA/cm2). Voltammograms obtained inthe plating bath with the same stirring conditions allowed usto estimate the dioxygen reduction current density around

Table 3 – Impurity content in weight ppm for coatingsdeposited at different current densities. For the values initalics, the quantification was not possible as thereference samples contained a much lower amount ofthese impurities.

H C O S Cl Fe Co Cu Mo

CD50 1 5 25 <1 <1 4 32 25 <40CD5 ≈70 ≈100 ≈400 6 ×230 15 100 150 <40CD1 ≈130 ≈400 ≈1000 25 ×1000 7 155 ≈600 <40

0.1 mA/cm2 and thus the contribution of this reaction couldexplain the decrease of deposition efficiency. At low currentdensities, and thus low deposition rates, this reaction couldhinder the growth of crystallites, contributing to the refinementeffect.Moregenerally, theadsorptionofdifferent foreignspecies(including O, H, C, and Cl) at the cathode surface probablyprevents grain growth by avoiding surface diffusion of adatomsand significant amounts of these species are incorporated intothe coatings. EBSD analyses show that, in coatings deposited atlowcurrentdensity, grainboundariesaremoredefective (higherdisorientation angle and Σ factor) with probably an increasedconcentration of vacancies. Thus, the results are consistentwith a decrease of grain size when current density decreases,associated with the incorporation of impurities at grainboundaries.

Fig. 7 – a) Cross-section view of the coating CD50 obtained byopticalmicroscopy after chemical etching, and b) cross-sectionview of the coating CD5 obtained by SEM after chemicaletching.

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5. Conclusion

Although extensive experimental works have been pub-lished concerning characterization of nickel electrodepos-ited coatings, a study combining composition analyses andmulti-scale microstructural characterization is missing. Insulphamate bath without additive, microstructure modifica-tions are linked with the incorporation of impurities andparticularly light atomic elements whose content largelydepends on electrodeposition conditions. Deposits obtainedat current densities above 20 mA/cm2 show a strong <100>texture along the growth direction but are characterized bydifferent structural heterogeneities which can be evidencedby using complementary observation tools. TEM and EBSDobservations offer the opportunity to distinguish the differ-ent microstructural scales and to better understand themicrostructure of coatings. As the current density decreases,grain refinement and texture modifications are observedwhich are associated with more defective grain boundaries

and higher contamination. Both light elements and substi-tution impurities are incorporated when grain sizedecreases, which can affect mechanical properties andcorrosion resistance. So, chemical contamination of electro-deposited coatings must be carefully evaluated beforediscussing the influence of their microstructure onproperties.

Acknowledgement

Thanks are due to the Agence Nationale de la Recherche (GIPANR Program no. ANR-06JCJC-0023-01) for the financialsupport.

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