1-s2.0-0257897295024867-main

E L S E V I E R Surface and Coatings Technology 81 (1996) 225-232

JW'R/A [ COATIN6S

il#OLO T

Electrodeposited composite coatings of copper with inert, semiconductive and conductive particles

V.D. Stankovic a, M. Gojo b

a Technical Faculty of Bor, University of Belgrade, JNA 12, 19210 Bor, Yugoslavia b Faculty of Printing, University ofZagreb, Getaldiceva 2, 41000 Zagreb, Croatia

Received 16 November 1994; accepted in final form 16 May 1995

Abstract

Data for the codeposition of some types of inert, semiconductive and conductive particles with copper in the electroplating are presented. It is shown that current density and particle concentration in the plating bath strongly affect the particle content in the composites produced. The nature of the particles also has a great influence on the amount of particles entrapped in composites. The presence of particles in composites changes their characteristics, making them better or worse with respect to tensile strength, hardness or surface texture. The particle distribution in electrodeposited composites is uniform across and over the coating.

Keywords: Composite coatings; Electroplating; Codeposition; Particles; Surfaces

1. Introduction

The production of composite coatings by electrolytic codeposition of fine inert [1 -5 ] , semiconductive [-6,7] and conductive [8,9] particles with metal from plating baths has occupied the attention of numerous investigators from western and eastern countries. The interest shown in these inclusion deposits was due to their various intrinsic engineering applications. Despite the potential interest in such deposits and many years of work in this field, only a few large-scale commercial baths have been developed so far for industrial production of such composites. Some of these are composite Ni-SiC and Co-SiC coatings for some engine parts [-3,10]. Some decorative coatings are also produced in such a way (mainly with an Ni matrix) [-1,8,11], having a significant commercial effect. Composite coatings were also used in solving some antifriction problems [8,11], for improving corrosion protection [ 11], for lubrication [12,13], in sliding electrical contacts [5,8] etc. It could be pointed out that, in general, isolated, highly specialized and quite small baths for production of such composites are in use at present [ 1,8,11,14]. A new series of composite coatings that appeared recently were investigated with the aim of application in electrochemistry and electronics. Examples are Ni-RuO2 composite prepared as a cathode for hydrogen production [7,15], polyaniline-Pt particles, polypyrrole-TiO2 [ 16,17], Au- polymer particles, Cu-polystyrene [ 18].

0257-8972/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved SSDI 0257-8972(95)02486-7

In the early days of research on composite coatings, attention was directed primarily towards determination of optimum conditions for their production, i.e. current density, temperature, particle concentration and bath composition, as well as towards explaining the role of some monovalent ions such as T1,Cs,Rb as well as some kinds of organic additives in the codeposition process. The effect of various anions and pH values on the particles' adsorption process at the cathode was also examined El]. A hypothesis was offered that codeposition of particles into the metal matrix is a result of an adsorption of metal ions at the particle surface, giving a positive charge to the latter and making them attracted to the cathode [ 19]. Kinetics and mechanism of particle codeposition with a metal matrix have been investigated by Cellis et al. [4,20], using the codeposition of alumina particles with copper and gold as a model system. A most comprehensive mathematical model describing the codeposition process was recently given by the same group of researchers [20]. The influence of the particles' presence in the electrolyte on the mass transfer enhance- ment was extensively investigated by Sonnenwald et al. [21]. The effect of hydrodynamic conditions on the particle content in codeposits was also investigated [5,22]. A comprehensive overview of plating bath composition together with other relevant data for composite coating production and a review of some characteristics and properties, elaborating on metal deposits containing

226 V.D. Stankovic, M. Gojo/Surface and Coatings Technology 81 (1996) 225-232

uniformly dispersed inert particles, was recently given by Saifullin [23]. Other Russian investigators [23-25] , have also widely studied the properties of various types of composites produced electrochemically, using different combinations of baths. However, there are still insuffi- cient published data available on the influence of incorporated particles and their amount in coatings on the quality of composites, i.e. on their mechanical, electrical, thermal and corrosion performances.

The aim of this work is to provide more information about the codeposition of inert, semiconductive and conductive particles in copper coatings on a metal substrate. The characterization of deposited coatings will be presented in order to obtain some data about surface quality as well as to determine some mechanical properties of these composites.

2. Experimental

2.1. Cell and Electrode Arrangement

Experiments were performed in a simple beaker cell with either magnetic or mechanical stirring in order to keep particles in suspension. Stirring intensity was kept at a constant value of 600 rev min - 1 in all experiments.

Two kinds of electrode arrangements were used in experiments.

(i) In the cylindrical arrangement electrodes were placed coaxially and a copper anode was situated in the middle of the cell while the cathode, made from stainless steel sheet, was placed at the cell wall. Only the side towards the anode was used for deposition of a composite. The outer side was insulated.

(ii) Flat electrodes made of the same materials as the cylindrical electrodes and placed side by side in the beaker were used in preparing composite coating samples for microhardness testing as well as for surface texture investigations.

Table 1 Size of particles

Kind of particle Mean diameter (gm)

et-A120 3 0.3 SiC 2.3 MoS 2 6.1 Graphite 5.4

was issued and the particle content was gravimetrically determined.

2.3. Experimental procedure

After degreasing and washing of the electrodes, they were placed in the cell containing an electrolyte suspension prepared previously. The codepositions were conducted under galvanostatic conditions at different current densities. The coating thickness was obtained within the range 15-150 gm. This depended on the characterization procedures envisaged for the composites samples. To reach a desired thickness, the process time was estimated on the basis of the applied current and Faraday's law, assuming 100% current efficiency. The coatings were peeled off the cylindrical cathode and samples were prepared for chemical, mechanical and metallographic analysis. The coatings obtained using the flat cathode served for analysing the surface topography and to determine microhardness. After switching off the cell, the cathode is removed from the cell, thoroughly rinsed with distilled water to remove the electrolyte and particles from the surface and then dried by air. After that a characterization of the coating was made.

3. Results

3.1. Content of particles embedded in coatings

2.2. Electrolyte

The electrolyte used in this study was an acid copper sulphate system, containing 0~-A1203, SiC, M o S 2 , and graphite particles. The copper ion concentration in the bath used was 50 g Cu 2+ dm -3 with 50 g HzSO 4 dm -a (0.5 M).

Chemicals (analytical grade) were dissolved in distilled water. For pre-plating a similar bath was utilized. The particle concentration in the electrolyte varied in the range 10-125 g d m -3. The mean diameters of the particles used in composite deposits are specified in Table 1. The fractional analysis of the particles was derived by a Malvern Laser Particle Sizer. The concentration of particles in the bath was periodically checked and on request adjusted. This means that a suspension sample

The concentration of particles included in the metal matrix was determined by the wet method [5,26] or by counting [27], depending on the particle type.

The effect of current density on the amount of codeposition of AIzO3 particles is shown in Fig. 1 in which the particle (weight per cent) content in the composite Cu-A1203 is plotted against current density and for different alumina particle concentrations in the electrolyte. Obviously, both parameters strongly influence the inclusion of particles in the coatings. The complex nature of this behaviour is also evident, namely for the coatings containing A1203 particles, the curves of amount of particles embedded vs. current density exhibit a maximum as is shown in Fig. 1.

These maximal values are obtained at current densities between 1 and 2 A dm-2. Outside this range, the content

V.D. Stankovic, IlL Gojo/Surface and Coatings Technology 81 (1996) 225 232 227

0 ~ 4

.,z

x - 125g/din 3

o - 60g/drn 3

/ x / ' ~ " ~ x • - lOg /d in 3

10 30

CURRENT DENSITY, Aldm 2

Fig. 1. Change in amount (weight per cent) of embedded alumina particles in composite coatings vs. current density, for different concentrations of particles suspended in electrolyte.

of incorporated particles decreases significantly. A similar effect has already been observed by Buelens et al. [5] and Wragg et al. [27]. The shape of this dependence is explained by a change in the mechanism by which particles are caught. It was shown that the increase in the particle content in coatings with increasing current density appears in the region where the reduction of metal ions occurs under charge transfer control and where the reduction of adsorbed cations onto the alumina particles is the rate-determining step. Once the reduction of metal ions occurs under diffusion control (for current densities higher than 2 A dm 2 [-5,203, for given hydrodynamic conditions the codeposition of alumina particles decreases gradually with further increase in current density.

The codeposition process also depends on the particle concentration in the bath. This dependence is clearly evident from Fig. 1. Increased concentration of alumina particles in the electrolyte corresponds to an increased particle content in the composite. The particle concentration in the electrolyte as well as the particle content in the composite, also influences the rate of codeposition as described by Kariapper and Foster [2].

In Fig. 2 the change in the amount (weight per cent) of SiC particles in the composite coating vs. current density is presented at various particle concentrations in the bath. As shown in Fig. 2 the particle content in the deposit increases with the increase in particle concentration in suspension in a similar manner to that observed for the bath with alumina and described by

x - 125 9/d in 3

o - 609/drn 3

• - 2 0 9 / d i n 3 x /

/

X o

I I I f I

0 ~,0 t,0 3,0

CURRENT DENSITY,A ldm 2

Fig. 2. Amount (weight per cent) of embedded SiC particles in composite coatings vs. current density for different concentrations of particles suspended in electrolyte.

other investigaters [-2,27]. The influence of current density on the amount of incorporated particles is more complex than that observed for the baths containing alumina particles. As shown in Fig. 2, with increasing current density the mass fraction of embedded particles increases up to a current density of about 1 A dm -z. When this value is exceeded, the particle content in the coatings decreases, indicating that a change in the mechanism of particle entrapment occurs at lower current densities. After reaching a minimum value, in the current density range from 2 to 2.5 A dm -2, the amount of particles in the codeposit starts to increase slowly. This second increase in particle content in the composite can be attributed to a change in particle attachment to the cathode. A similar effect is observed for the system Au-AI203 [5], but no analysis of this phenomenon has been done.

3.2. Surface quality of composite coatings

Surface quality was analysed by optical microscopy and scanning electron microscopy (SEM). The roughness of the surface was measured with a Pertometer CSD instrument, while the particle distribution across the composite was investigated by metallographic analysis, and it was shown that the particles have a uniform distribution in the coating as illustrated by Fig. 3.

Metallographic analysis of obtained composites has also shown that an increased particle content was

228 V.D. Stankovic, M. Gojo/Surface and Coatings Technology 81 (1996) 225 232

Fig. 4. SEM image of Cu~1203 composite coating: current density, 6 A dm 2; particle concentration, 60 g dm -3

Fig. 3. Metallographic photograph of Cu AI203 composite coating: current density, 1 A dm 2; particle concentration, 60 g dm -3.

obtained on those sites where some nodular irregularities on the surface had grown [9,19].

3.2.1. Surface topography The surface topography of the composite coatings

obtained depends on many parameters such as applied current density, particle concentration in the suspension, particle type and hydrodynamic conditions (stirring rate in this case). It was observed visually that certain irregularities such as nodules and whiskers appear growing at the surface. These excrescences grow in the direction of the electrolyte flow, reflecting hydrodynamic occur- rences in the vicinity of the working electrode [ 19]. The appearance of such irregularities was only observed for the Cu-SiC system and was expressed more for composites obtained from concentrated suspensions. These whiskers adhere poorly to the surface and can easily be removed. For other types of composites investigated here, the appearance of whiskers is not observed, only nodules. The SEM photograph presented in Fig. 4 shows alumina particles captured by copper grains. In case of the composites containing A1203 particles a smooth surface was obtained even at higher current densities.

Looking at the surface using SEM, it is possible clearly to recognize SiC particles with their crushed shape as illustrated by SEM image given in Fig. 5.

The coatings containing MoS 2 particles appear dark in colour. For them, this coloration depends on the particle content in the coating. In other words, a darker colour is found in those composites obtained from concentrated suspensions or at that current density to which a higher particle content corresponds, while a lower particle content corresponds to the lighter colour. At higher current densities, smaller and bigger cauli- flower-like structures appear on the surface, containing

Fig. 5. SEM image of Cu SiC composite coating: current density, 6 A dm-2; particle concentration, 60 g dm -3.

an increased amount of particles in them. In Fig. 6, the SEM image of the Cu-MoS2 system is shown in which the particles entrapped in the coating are apparently visible. It is also observed that a quite smooth surface of the composite Cu-MoS2 is obtained at lower current densities, in spite of reasonably coarse particle

Fig. 6. SEM image of Cu MoS2 composite coating: current density, 6 A dm z; particle concentration, 60 gdm 3.

V.D. Stankovic, h/Z Gojo/Surface and Coatings Technology 81 (1996) 225-232 229

utilization. Higher currents correspond to the rough and developed surface.

Composites observed after codeposition of graphite particles with copper appear brown to dark in colour, depending on the experimental conditions. These coatings are very rough sponge-like and powdered deposits as shown in SEM photograph presented in Fig. 7.

Being conductive, graphite particles in suspension together with the cathode act as a suspension electrode [28]. This means that graphite particles in contact with the current feeder (cathode) are polarized and deposition of copper occurs onto particles as well as onto the cathode. Such a mechanism of codeposition results in an unsuitable deposit structure and in coppering of graphite particles which was also observed.

3.2.2. Surface roughness

The roughness of the composite coatings was determined by means of a Pertometer CSD instrument. Analysing the obtained profilograms, one may remark that the type of particle entrapped in a coating strongly influences the surface quality. Applied current density also affects the surface roughness, where this effect is more significant for composites containing semiconductive and conductive particles. Although that can be attributed to the particle size, since A120 3 particles are smaller by one order of magnitude than the larger particles, it also results from the difference in mechanism of codeposition of inert and conductive particles.

The composites of Cu with alumina particles have exhibited the greatest smoothness. Measured values of the arithmetic mean deviation R a were in the range from 0.55 jam for the coating obtained at 1 A dm -e to 0.63 jam at 6 A dm 2. This means that the change in the current density does not affect the surface smoothness significantly. Two other measured characteristics of the surface, the maximum height Rma x of irregularities and ten-points Rz height of irregularities were 4.24 ~tm and

3.69 lain respectively. These values were measured using a sample of Cu-A1203 obtained at 6 A dm -2, which was a little rougher than that produced at the lowest current density.

Composite coatings of Cu with SiC particles have also displayed substantial smoothness for these kinds of coatings even if the particles incorporated in the matrix are almost eightfold larger. Ra was in the range from 0.44 jam measured on the coating obtained at 1 A dm -2 to 0.98 jam for 6 A dm 2. In Fig. 8, the profilograms of Cu-SiC composites are presented, to illustrate the influence of current density on surface roughness.

Composite coatings of Cu with MoS2 particles have significantly higher roughness than the Cu-AI20 3 and Cu-SiC coatings. The values of Ra are in the range between 1.43 jam which corresponds to the current density of 1 A dm 2 and 4.4 jam for 6 A din-3. Even greater surface roughness parameters are obtained by measuring coatings containing graphite particles, even if they are a little smaller than M o S 2 particles, namely, the values of Ra are from 6.5 jam to 15.5 jam measured on samples obtained at the lowest and highest current density respectively. In Fig. 9, the profilograms of four different composite coatings are presented, obtained under iden- tical experimental conditions (current density, particle concentration etc.). Data for surface parameters are also given.

It can be pointed out that the kinds of particles and current density have a greater influence on the surface roughness than the particles' sizes themselves. It should also be noted, on the basis of SEM images as well as data presented in Fig. 9, that the composites of Cu with M o S 2 and graphite particles have a more developed surface; in comparison with the Cu-AI20 3 and Cu-SiC composites they were smoother and more compact. This fact can be utilized for production of composites with very high specific surface area, those particles with some catalytic properties being entrapped in the coatings, and

I 2.,5 .,~rn

R a -- 0,60 t4 rn Rz = z',72un £rnax = 6,52j~rn (a)

I 2,5 jura

(b)

Fig. 7. SEM image of Cu-C composite coating: current density, 6 A dm z; particle concentration, 60 g dm 3.

Fig. 8. Profilograms of Cu-SiC composite coatings showing effect of applied current density (particle concentration, 60 g dm-3): (a) current density, 1 A dm-2; (b) current density, 6 A dm z.


Ro = 0,G3pm R z = z,,z.2~lm Rmax=5,38Nm

2,5 )am

R o = 0,08t4m Rz= 7,27Hm Rmex= 8,57,u m

2,5 Hm

10 ]~m

(a)

(b)

R e 4,L/~m R z = 26.,6Nm Rmox = 28,6~m (c)

~/~ I 25 ~m

R o = 15,S jura Rz= 72,Tj~m Rma x = 85,0 j~m (d)

Fig. 9. Profilograms of composite coatings obtained from different baths at a constant current density of 6 A din-2 (particle concentration, 60 g dm-3): (a) Cu-AlzO3; (b) Cu-SiC; (c) Cu-MoS2; (d) Cu C.

such coatings can serve afterward as catalysers in some chemical or electrochemical processes [-7,15].

3.3. Mechanical characteristics

Only tensile strengths and microhardnesses of the composites are investigated at this stage.

3.3.1. Tensile strength To determine a tensile strength, the obtained compos-

ite coating was stripped from the substrate as described earlier and samples of defined dimensions were cut for the measurement. Dimensions of test foils were 12.5 mm in width and 140 mm in total length. The initial measure-

ment length was 50 mm and the whole length 87.5 mm. These dimensions are defined by JUS C.A4.002. (Standards for Mechanical Testing of Metals), issued in 1985, which originates from ISO 6892 published in 1984. The tensile speed was 5 N ram-2 s-1 for each test.

In Fig. 10 the dependence of tensile strength of the Cu-AI20 3 composites on mass fraction of alumina particles in coatings is presented. Tensile strength increases with increasing alumina particles content in the composite up to about 2% by weight. Further increases in the particle content in the composite do not affect the tensile strength significantly. The change in the tensile strength of the Cu-SiC composite with particle content in the coatings is shown in Fig. 11. The presence of SiC particles in a small amount (less than 2% by weight) causes an increase in the tensile strength, similarly to the composite coatings containing alumina particles. When this value is exceeded, the tensile strength decreases gradually, reaching a minimum value at a concentration of SiC particles in the metal matrix of about 4 5% by weight.

It should be remarked that the investigated composite coatings behave differently to the pure electrolytically obtained copper during the measurement process, namely, the breaking of samples occurs suddenly, similarly to the behaviour of less ductile materials. In other words, the elongation which appears before breaking was almost negligible in comparison with that observed for a pure copper sample.

3.3.2. Microhardness The microhardness of the investigated composites was

measured with a Mikroharte Carl Zeiss D32 instrument.

300

: E

20o z

#

N 03 2 u J I--

10C

/

I I 1 I I

0 I 2 3 4 5 % wt, ~-- A[203

Fig. I0. Tensile strength vs. amount (weight per cent) of AlzO 3 particles in composite coatings.

300

} i

~oo

uJ i --

100

i / i i i

0 1 2 3 4 5

V.D. Stankovic, M. Gojo/Surface and Coatings Technology 81 (1996) 225-232 231

% wt, SiC

Fig. 11. Tensile strength vs. amount (weight per cent) of SiC particles in composite coatings.

Table 2 Microhardness of composite coatings

Type of coating Microhardness Relative (HV) microhardness

Cu~1203 157 1.267 Cu-SiC 166.5 1.344 CB-B4C 170.2 1.374 Cu-MoS2 78.9 0.637 Cu-C 49 0.387 C ~ B a S O 4 117.9 0.95

The results obtained, presented in Table 2, show that the presence of particles in composite coatings exhibits two opposite effects. Hard particles (abrasives) involve a certain increase in microhardness while soft particles such as MoS2, BaSO4 or C incorporated into metal matrix have an opposite effect as one can see in Table 2.

Relative microhardness is here defined as the ratio of composite microhardness to the microhardness of pure electrolytic copper. The increase in composite coating microhardness has already been discussed by Buelens et al. [5], although they have not published a quantitative contribution of the particles' presence in the coating, but have just noted an increase in microhardness. In Table 2 some additional microhardnesses of composites which are not discussed earlier but were also investigated are given, such as Cu-boron carbide as well as Cu-BaSO4.

4. Conclusion

The amount of particles incorporated in coatings during the electroplating process depends on the par-

ticles' type, their concentration in a bath, and applied current density.

Distribution of inert particles over and across the coating is uniform and an acceptable surface quality is obtained. In case of semi- and especially conductive particles entrapment a sponge-like structure of the surface appears, producing irregular coatings, the rough- nesses of which are markedly high, becoming rougher with the increase in current density.

Microhardness is higher in composites containing hard particles while soft particles give "softer" coatings.

Particle content in the composite strongly influences the tensile strength, increasing it at lower values of particle content (less than 2% by weight). Higher particle content in coatings exhibits a different effect on tensile strength.

References

[1] T.W. Tomaszewski, Trans. Inst. Met. Finish., 54 (1976) 45. [2] A.MJ. Kariapper and J. Foster, Trans. Inst. Met. Finish., 52

(1974) 87. [3] J.R. Roos, J.P. Celis and J.A. Helsen, Trans. Inst. Met. Finish.,

55 (1977) 113. [4] J.P. Celis and J.R. Roos, J. Electrochem Soc., 124 (1977) 1508. [5] C. Buelens, J.P. Celis and J.R. Roos, J. Appl. Electrochem., 13

(1983) 541. [6] LI. Antropov, M.I. Bikova and V.I. Shklanaja, Zasch. met., 17

(4) (1981) 420. [7] C. Iwakura, N. Furukowa, M. Tanaka and S. Nakamatsu, ISE

Meet., Montreux, August 1991, Abstract No. 3-05. [8] M.A. Belenkij and A.F. Ivanov, Elektroosazdenie Metallitcheskih

Pokritij, Metallurgiya, Moscow, 1985. [9] V.D. Stankovic and M. Gojo, ISE Meet., Montreux, August

1991, Abstract No. 3 24. [ 10] L. Ausmann and I. Rankic, Jug. Simp. o Korozifi, Antikorozifi i

Kiselootpornoj Zastiti, Zbornik radova, Skoplje, October 1988. [ 11] I.G. Habibullin and R.S. Sajfulin, Anticorrosion Coatings, Meet.

on Thermostable Coatings, Proc., Nauka, Leningrad, 1983, p. 84. [12] C. Kollia, Z. Loizos and M. Spirellis, Surf. Coat. Technol., 45

(1991) 155. [13] T. Visvikas, S. Psarrou, F. Kotzia, C. Kollia and N. Spirellis,

Electrochemistry of Alloys and Composite Materials, Int. Semin., Budva, September 25-28, 1994, p. 55.

[14] V. Stankovic, Electrochemistry of Alloys and Composite Materials, Int. Semin. Budva, September 25-28, 1994, p. 47.

[15] C. Iwakura, N. Furukawa and M. Tanaka, Electrochim. Acta, 37 (1992) 757.

[16] F. Beck, M. Dahlhaus and N. Zahedy, Electrochim. Acta, 37 (1992) 1265.

[17] F. Beck, M. Dahlhaus and N. Zahedi, ISE Meet., Montreux, August 1991, Abstract No. 3 48.

[18] Y. Eng, J.T. Beard and H.Y. Cheh, ISE Meet., Montreux, August 1991, Abstract No. 1L 3-1.

[19] M.M. Davliev, A.N. Abdulin and A.V. Golovin, Zasch. Met., 25 (1990) 698.

[20] J.P. Celis, J.R. Roos and C. Buelens, J. Electrochem. Soc., 134 (1987) 1402.

[21] P.J. Sonnenwald, W. Visscher and E. Barendreht, J. Appl. Electroehem., 20 (1990) 563.

[22] A. Lavanant and G. Maurin, ISE Meet., Montreux, August 1991, Abstract No. 3 30.


[-23] R.S. Saifulin, Neorganicheskie Kompozitsionnie Materiali, Himija, Moscow, 1983.

[24] B.G. Burov and B.M. Krekuman, Anticorrosion Coatings, Meet. on Thermostable Coatings, Proc., Nauka, Leningrad, 1983, p. 218.

[25] I.V. Guseva, T.S. Mascenko and A.I. Borisenko, Anticorrosion Coatings, Meet. on Thermostable Coatings, Proc., Nauka, Leningrad, 1983, p. 207.

[-26] V.D. Stankovic, B. Stanojevic and D. Markovic, 1SE Meet., Maastricht, September 1987, Extended Abstr., Vol. II, p. 893.

1-27] A.A. Wragg, C. George and R.M. Hooper, 41st, ISE Meet., Prague, August 1990, Proceedings Vol. II, Abstract No. Th MS 10-1.

[28] H. Kametani, Meet. on Cell Design in Electrowinning and Electrorefining, Southampton University, Southampton, July 1974.

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