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Electrochimica Acta 113 (2013) 797– 802

Contents lists available at ScienceDirect

Electrochimica Acta

jo u r n al hom ep age: www.elsev ier .com/ locate /e lec tac ta

pitaxial growth of zinc on ferritic steel under high current densitylectroplating conditions

homas Greula,b, Christian Comendaa, Karl Preisa, Johann Gerdenitscha,affaela Sagla, Achim Walter Hasselb,∗

voestalpine Stahl GmbH, Steel Division, Voestalpine-Straße 3, 4020 Linz, AustriaInstitute for Chemical Technology of Inorganic Materials, Johannes Kepler University Linz, Altenberger Str. 69, 4040 Linz, Austria

r t i c l e i n f o

rticle history:eceived 18 January 2013eceived in revised form 6 July 2013ccepted 13 July 2013

a b s t r a c t

The dependence of the crystal orientation of electrodeposited zinc of the grain orientation on ferritic steelsubstrate at high current density deposition (400 mA cm−2) during a pulse-plating process was investi-gated by means of EBSD (electron backscatter diffraction) measurements. EBSD-mappings of surface andcross-sections were performed on samples with different surface preparations. Furthermore an industrial

vailable online 22 July 2013

eywords:pitaxyinclectrodepositionBSD

sample was investigated to compare lab-coated samples with the industrial process. The epitaxial growthof zinc is mainly dependent on the condition of the steel grains. Deformation of steel grains leads to ran-dom orientation while zinc grows epitaxially on non-deformed steel grains even on industrial surfaces.

© 2013 Elsevier Ltd. All rights reserved.

. Introduction

Various aspects like the influence of pH, temperature, currentensity or an external magnetic field on the electrodeposition ofinc from acidic sulphate electrolytes have been studied so far1–4]. Furthermore the effects of inorganic impurities such as Ge5], Pb2+ [6], Cu, Pb, Ni, Sn, Sb [7] or Fe [8] and organic additivesike sodium dodecylsulphate, dodecyltrimethylammonium bro-

ide, octylphenolpoly(ethyleneglycolether)n, n = 10 [9] PEG 2000010], sodium lauryl sulphate, Arabic gum [11] and tartaric acid [12],n current efficiency or the structure of the zinc layer were inves-igated thoroughly.

Another important aspect is the preparation of the surface andherefore the microstructure of the surface to be coated which plays

role in the electrodeposition of zinc [13]. Studies have shownhat there is a relationship between the texture of the steel sub-trate and the deposited zinc layer shown by XRD pole figures [14].hese studies have been carried out at current densities of up to00 mA cm−2 and it was shown that electrodeposited zinc followsurger’s orientation relation [15]. It is also shown that the texture

f electrodeposited zinc is dependent on pH, current density andemperature [16].

∗ Corresponding author. Tel.: +43 732 2468 8700; fax: +43 732 2468 8905.E-mail addresses: hassel@elchem.de, achimwalter.hassel@jku.at (A.W. Hassel).

013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.ttp://dx.doi.org/10.1016/j.electacta.2013.07.077

Heteroepitaxial growth is also known from other systems andcan be for instance used to produce isoorientated Re, W, Monanowires for different applications [17,18]. It is also known thatthe phase transition from bcc to hcp systems in Nb-Zr [19] orin Ti alloys [20] show orientation relations between parent bccand resulting hcp grains. For these studies electron backscat-ter diffraction was used to determine the orientation relationand to calculate the misorientation angle between single grains[21].

Considering the industrial process known as gravitel process[22] for the electroplating of steel strips there are two main dif-ferences to most literature found.

• Current densities used in the plating process usually start at300 mA cm−2 and can reach 900 mA cm−2, a regime that has notbeen studied well.

• Electroplating in the gravitel process is a pulse plating process.That means there are times where dissolution of zinc and there-fore new crystallisation centres, due to cementation of impuritiesfrom the electrolyte, can occur.

To improve this process it is important to get a deeper insightinto the crystallisation and crystal growth under these condi-

tions. Therefore EBSD is used to study crystal growth and therelation between parent steel grains and corresponding zincgrains. Furthermore the influence of surface condition is investi-gated.

7 mica Acta 113 (2013) 797– 802

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surements with different grain size. In both cases the grains on theelectropolished steel samples are well defined. Measurements onthe zinc surface show worse results with approximately half of thesurface showing a signal in the EBSD measurement.

98 T. Greul et al. / Electrochi

. Experimental

.1. Chemicals

The zinc electrolyte in use was an analytical grade sulphatelectrolyte with 90 g L−1 Zn2+ (analytical grade ZnSO4·7H2O/Carloth GmbH + Co. KG) and 20 g L−1 Na (analytical grade Na2SO4, J.T.aker®) with pH 1.55 at 55 ◦C (H2SO4 98% analytical grade, Merck).or electropolishing Struers A2 electrolyte was used (Struers,ALLERUP DK). Ethanol for rinsing the samples was of analyticalrade (Merck).

The steel sheet used as substrate for the measurements was aow carbon steel sheet produced by voestalpine Stahl GmbH.

.2. Electroplating

Before electroplating all samples were rinsed with deionisedater and etched for 3 s in 100 g L−1 H2SO4 at room temperature.

Electroplating was done in a flow cell at an electrolyte velocityf 4 m s−1 and a current density of 400 mA cm−2 whit a EA-PS9036-40 Galvanostat (Elektro-Automatik GmbH & Co. KG, VIERSEN,ermany). To simulate the gravitel process [22] with high currentensities and 12 cells as used in the plating process for the indus-rial sample, the current was alternating with 24 pulses (duty cycle:.6–1.7 s on, 1 s off). The temperature was kept at 55 ◦C with a LaudaROLine RP855 Thermostat. A 119 mm × 75 mm big DSA (dimen-ionally stable anode) made from Ti coated with IrO2 from De Noraas used as an anode. The sample size of the annealed and of the

kin pass rolled sample was 119 mm × 84 mm with an area for zinceposition of 119 mm × 75 mm. To ensure constant flow conditionshe spot, where the EBSD measurement is done, was chosen in the

iddle of the sample.The electropolished samples were prepared on mechanically

olished 34 mm × 24 mm sized steel plates. Electropolishing wasone using a Struers LECTROPOL 5 with the Struers A2 electrolyte at0 V. After electropolishing the samples where rinsed with analyt-

cal grade ethanol and mounted into a 119 mm × 84 mm (standardample size for the flow cell in use) steel matrix for electrodeposi-ion. To ensure that the grain structure does not change, the heatnput at the measurement spot was kept to a minimum. The finalhickness of the zinc layer was about 2.5 �m, for the samples usedor the surface measurements. For the cross section samples thehickness of the zinc layer was about 7.5 �m.

.3. Analytics

Surface light optical micrographs (LOM) where taken with anlympus BX 61 Microscope using the extended focal imaging mode.

EBSD measurements were performed with a Zeiss Supra 35 FEG-EM and an Oxford Channel 5 System. For surface analysis thelectropolished samples were measured before and after electro-lating on the same spot to calculate the misorientation anglesetween zinc and the parent steel grain.

The cross sections were measured just after electroplating tonsure a contamination free surface.

.4. Calculations

Misorientations between steel grains and corresponding zincrains were calculated from the Euler angles sets. First the rotationatrix g was calculated from:

⎛

= ⎜⎝

cos ϕ1 cos ϕ2 − sin ϕ1 sin ϕ2 cos ̊ sin ϕ1 cos ϕ2 + cos ϕ1 sin ϕ2

− cos ϕ1 sin ϕ2 − sin ϕ1 cos ϕ2 cos ̊ − sin ϕ1 sin ϕ2 + cos ϕ1 cos ϕ

sin ϕ1 sin ̊ − cos ϕ1 sin ̊

Fig. 1. Current transient and potential transient of the 1st and the 13th pulse inelectrodeposition of a 2.5 �m thick zinc layer.

ϕ1, ̊ and ϕ2 are the Euler angles from Bunge notation. After calcu-lating the rotation matrix g the misorientation of the [0 0 0 2] planeof zinc to the [1 0 0] plane of the corresponding steel grain wascalculated using:

�g = gbcc · g−1hcp

�gij = Sigbcc · (Sjghcp)−1 = Si · �g · Sj

(2)

cos � = (g11 + g22 + g33 − 1)2

(3)

where gbcc is the rotation matrix of the steel grain, ghcp is the rota-tion matrix of a corresponding zinc grain, Si is one of 24 symmetricmatrix operators for a cubic system and Sj is one of the 12 symmet-ric matrix operators for the hexagonal system. � is the resultingmisorientation angle and defined as the minimum of all 288 sym-metrically equivalent combinations.

3. Results and discussion

3.1. Transients

Fig. 1 shows the current and the potential transient of the 1st andthe 13th pulse during electrodeposition of a 2.5 �m thick zinc layerfor a surface EBSD measurement. The current transients show nosignificant difference between the two pulses. Looking at the poten-tial transients of the measured cell potentials there is no differencein shape but a difference of 25 mV in cell potential. This might bedue to hydrogen evolution on the steel surface and therefore higherresistance due to a smaller surface available for the deposition.Such an effect has been confirmed by high speed electroreflectancespectroscopy [23].

3.2. Surface EBSD measurements

Electropolished ferritic steel surfaces were measured before andafter electrodeposition of zinc. Fig. 2 shows two sets of these mea-

cos ̊ sin ϕ1 sin ˚

2 cos ̊ cos ϕ2 sin ˚

cos ˚

⎟⎠ (1)

T. Greul et al. / Electrochimica Acta 113 (2013) 797– 802 799

F samp(

bmcfogsteo

tgdpot

ig. 2. Inverse pole figure-map of the EBSD measurements of electropolished steeltop and bottom).

Looking at the LOM-image of such a surface (Fig. 4) it cane clearly seen that there is a difference between the measure-ent spot and the surrounding area. This might be due to carbon

ontamination from cracking of residual organic carbon on the sur-ace by the electron beam during the measurement. It can be alsobserved, that there are distinct zinc grains corresponding to steelrains where no EBSD pattern can be measured. These grains showpot-like defects. It is assumed that these defects appear due to con-amination from the measurement and lead to roughening of thelectrodeposited zinc layer. This leads to a reduction of the qualityf the measurement.

Nevertheless calculation of the misorientation angles betweenhe zinc [0 0 0 2] plane and the iron [1 0 0] plane of correspondingrains was performed. The results (Fig. 5) show a strong depen-

ence of the orientation of the zinc grains on the orientation of thearent steel grains. The misorientation between the [0 0 1] plainf the ferritic steel grains and the [0 0 0 2] plane of the zinc crys-als was 43.4◦ with a standard deviation of 1.66◦. This is within the

Fig. 3. Standard IPF-triangle for

les (right) and corresponding zinc layer (left) of 2 samples with different grain size

range of Burger’s orientation relation that states a relation betweenthe [1 1 0] plane of a bcc structure to the [0 0 0 2] plane of a corre-sponding hcp system.

Comparing the single measurements with the grain sizeindependently, similar misorientation angles around 43◦ areobserved. A higher standard deviation was found for smaller grainsize.

3.3. EBSD measurements on cross sections

As mentioned in Section 3.2 the measurements of the surfacelead to a degradation of the measurement quality on zinc. Fur-thermore the carbon contamination from the first measurementof the steel substrate might have an influence on the electroplat-

ing process and furthermore on the properties of deposited zinclayer. Therefore zinc was deposited on the uncontaminated sub-strate and the EBSD measurements were performed on a crosssection of the sample with a 7.5 �m thick zinc layer. The main

iron (left) and zinc (right).

800 T. Greul et al. / Electrochimica Acta 113 (2013) 797– 802

Fig. 4. Light optical micrograph of a 2.0 �m thick zinc layer on the EBSD measure-ment spot (left side) and the surrounding area (right third).

30 35 40 45 50 55 600

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miso rientati on angle / °

The other 4 steel grains are from an elevated part of the steel

ig. 5. Probability of the misorientation angle of zinc electrodeposited on ferriticteel from surface measurements, resolution is 1◦ , N = 55.

dvantage of this preparation is, that even samples from indus-rially electroplated steel strip can be measured with high quality

appings (Figs. 6, 8, 9 and 11).The zinc layer deposited on the electropolished substrate shows

he same behaviour than the one investigated in Section 3.2. Onost of the steel grains just one zinc grain is growing, but there are

lso steel grains with more than one zinc grain. These grains showo uniform colouring in the inverse pole figure (IPF) image, whichorresponds to a change in crystal orientation in the grain due toeformation.

Calculation of the misorientation angles leads to a mean mis-

rientation of 42.16◦ with a standard deviation of 4.12◦. It can belso seen, that the zinc grains growing on steel grains witch showo uniform colouring in the IPF-map show random orientations

Fig. 6. Inverse pole figure map of the crosssection of

Fig. 7. Probability of the misorientation angle of zinc electrodeposited on elec-tropolished ferritic steel from EBSD measurement of a crossection, resolution 1◦ ,N = 30.

compared to the rest. There are also spots where the zinc layershows a decrease in thickness of about 30%. The zinc grains on thesespots show a colour gradient in the IPF-map. This might be due todeformations after electroplating, like scratches or an artefact fromthe preparation of the cross section. Excluding such grains from thecalculations of the mean misorientation angle leads to a misorien-tation of 43.54◦ ± 1.81◦. The probability of the misorientation angleis shown in Fig. 7.

These results show that on electropolished substrate, sur-face EBSD measurements and crosssection EBSD measurementsshow the same results and zinc follows Burger’s orientationrelation.

Fig. 8 shows a map of a zinc layer on an annealed steel stripbefore skin-pass rolling. Beside big grains without deformation,small deformed grains are found. On the big grains zinc follows,as on the electropolished surface Burger’s orientation relation witha misorientation angle between steel grain and corresponding zincgrain of 42.54◦ ± 1.48◦. On the smaller grains a random orientationof the zinc grains is found.

Fig. 9 shows a cross section of a zinc layer on a deformedsteel surface produced by skin pass rolling. Due to the strongdeformation of the steel surface multiple zinc grains are foundon each steel grain. The zinc grains on the single steel grainsshow no orientation relation to the parent grain and are ran-domly oriented. The mean misorientation angle is 26.31◦ ± 12.97◦

where the large standard deviation is an expression of the randomorientation.

To compare the results from the lab to an industrial sample,an electroplated steel strip from an industrial electrogalvanisingline was used for an EBSD measurement. This sample shows mul-tiple zinc grains per steel grain (Fig. 11). On the left side of Fig. 11a highly deformed area can be seen (first steel grain on the left).

strip, where no deformation occurs during skin-pass rolling. Theleft most grain shows no epitaxial growth and a misorientationangle of 39.8◦ ± 5.02◦. The grains to the right also show multiple

a zinc layer on an electropolished steel surface.

T. Greul et al. / Electrochimica Acta 113 (2013) 797– 802 801

Fig. 8. Inverse pole figure map of the crosssection of a zinc layer on an annealed steel surface.

Fig. 9. Inverse pole figure map of the crosssection of a zinc layer on a skin pass roled steel surface.

0 10 20 30 40 50 60 70 80 900

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25

30

35

40mean misorientation26.3 ° ± 13.0 °

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Fig. 10. Probability of the misorientation angle of zinc electrodeposited on col

◦ ◦

rains but have a uniform misorientation angle of 42.3 ± 1.63 .his data proves the comparability of samples produced in the labith those from the industrial process and thus the relevance of

eported results. It was also shown for several samples, that zinc

Fig. 11. Inverse pole figure map of the crosssec

d ferritic steel, from EBSD measurement of a crossection, resolution 5◦ , N = 25.

grows epitaxially following Burger’s orientation relation on lowstress steel grains. Deformation of the steel grains and thereforea distortion in their crystal lattice leads to random growth of zinc(Figs. 3 and 10).

tion of an industrially coated steel sheet.

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. Conclusion

On electropolished ferritic steel surfaces Zn grows epitaxially fol-lowing Burger’s orientation relation.Surface deformation before electroplating leads to multiple zincgrains with random orientation on each steel grain.Zinc can grow epitaxially on industrial surfaces provided there islittle deformation on the surface.Multiple zinc grains on one steel grain can show identical orien-tation relations.

eferences

[1] I. Zouari, F. Lapicque, An electrochemical study of zinc deposition in a sulfatemedium, Electrochimica Acta 37 (1992) 439.

[2] P. Guillaume, N. Leclerc, C. Boulanger, J. Lecuire, F. Lapicque, Investigation ofoptimal conditions for zinc electrowinning from aqueous sulfuric acid elec-trolytes, Journal of Applied Electrochemistry 37 (2007) 1237.

[3] R.C. Salles, G.C. de Oliveira, S.L. Díaz, O.E. Barcia, O.R. Mattos, Electrodepositionof Zn in acid sulphate solutions: pH effects, Electrochimica Acta 56 (2011) 7931.

[4] J.A. Koza, I. Mogi, K. Tschulik, M. Uhlemann, C. Mickel, A. Gebert, L. Schultz,Electrocrystallisation of metallic films under the influence of an external homo-geneous magnetic field – early stages of the layer growth, Electrochimica Acta55 (2010) 6533.

[5] D. Mackinnon, P. Fenn, The effect of germanium on zinc electrowinning fromindustrial acid sulphate electrolyte, Journal of Applied Electrochemistry 14(1984) 467.

[6] R. Ichino, C. Cachet, R. Wiart, Mechanism of zinc electrodeposition in acidicsulfate electrolytes containing Pb2+ ions, Electrochimica Acta 41 (1996) 1031.

[7] Y. Shindo, Impurity element effect on electrogalvanized zinc coation, in: 6thInternational Conference on Zinc and Zinc Alloy Coated Steel Sheet, Chicago,USA, 04–07 April 2004, Association for Iron & Steel Technology, Warrendale,PA, 2004, p. 1165.

[8] H. Nakano, S. Oue, S. Hisano, S. Kobayashi, H. Fukushima, Codeposition behavior

of impurities during electrogalvanization in sulfate baths in the presence of Feions, ISIJ International 47 (2007) 1029.

[9] A. Gomes, M. da Solva Pereira, Zn electrodeposition in the presence of surfac-tants. Part I. Voltammetric and structural studies, Electrochimica Acta 52 (2006)863.

[

cta 113 (2013) 797– 802

10] J. Ballesteros, P. Díaz-Arista, Y. Meas, R. Ortega, G. Trejo, Zinc electrodepositionin the presence of polyethylene glycol 20000, Electrochimica Acta 52 (2007)3686.

11] A. Recéndiz, I. González, J. Nava, Current efficiency studies of the zinc elec-trowinning process on aluminum rotating cylinder electrode (RCE) in sulfuricacid medium: influence of different additives, Electrochimica Acta 52 (2007)6880.

12] O. Aaboubi, J. Douglade, X. Abenaqui, R. Boumedmed, J. VonHoff, Influence oftartaric acid on zinc electrodeposition from sulphate bath, Electrochimica Acta56 (2011) 7885.

13] K. Raeissi, A. Saatchi, M. Golozar, J. Szpunar, Effect of surface preparation onzinc electrodeposited texture, Surface and Coatings Technology 197 (2005)229.

14] K. Raeissi, M. Bateni, A. Saatchi, M. Golozar, J. Szpunar, The effect of [gamma]-fiber texture intensity of carbon steel substrate on zinc hetero-epitaxial growth,Surface and Coatings Technology 201 (2006) 3116.

15] H. Nakano, Effects of plating factors on morphology and appearance of electro-galvanized steel sheets, Transactions of Nonferrous Metals Society of China 19(2009) 835.

16] K. Raeissi, A. Saatchi, M. Golozar, Effect of nucleation mode on the morphologyand texture of electrodeposited zinc, Journal of Applied Electrochemistry 33(2003) 635.

17] A.W. Hassel, B. Bello-Rodriguez, A. Smith, Y. Chen, S. Milenkovic, Preparationand specific properties of single crystalline metallic nanowires, Physica StatusSolidi B 247 (2010) 2380.

18] S. Milenkovic, A. Smith, A.W. Hassel, Single crystalline molybdenum nanowires,nanowire arrays and nanopore arrays in nickel–aluminium, Journal ofNanoscience and Nanotechnology 9 (2009) 3411.

19] D. Srivastava, S. Banerjee, S. Ranganathan, The crystallography of the bcc tohcp (orthohexagonal) martensitic transformation in dilute Zr-Nb alloys, Trans-actions of the Indian Institute of Metals 57 (2004) 205.

20] C. Cayron, B. Artaud, L. Briottet, Reconstruction of parent grains from EBSD data,Materials Characterization 57 (2006) 386.

21] A. Heinz, P. Neumann, Representation of orientation and disorientation data forcubic, hexagonal, tetragonal and orthorhombic crystals, Acta CrystallographicaA 47 (1991) 780.

22] K. Kösters, M. Mascheck, Die elektrolytische Breitbandverzinkungsanlage

der VOESTALPINESTAHL LINZ GesmbH nach dem Gravitel-System unddie Eigenschaften der Gravigal®-Produktpalette, Galvanotechnik 80 (1989)3790.

23] A.W. Hassel, M.M. Lohrengel, Initial stages of cathodic breakdown of thin anodicaluminium oxide films, Electrochimica Acta 40 (1995) 433.