Electrodeposition of nickel-BN composite coatings

Article abstract of DOI:10.1016/j.electacta.2008.06.034

Electrodeposition of nickel-boron nitride (Ni-BN) composites is carried out from a sulfamate bath containing up to 10 g/l of dispersed boron nitride particles with size 0.5 μm. Microhardness and wear resistance of the composites are investigated. Both the

Full text of DOI:10.1016/j.electacta.2008.06.034

Electrochimica Acta 54 (2009) 2571–2574
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Electrochimica Acta
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Electrodeposition of nickel–BN composite coatings
E. Pompeia, L. Magagnina,∗, N. Lecisb, P.L. Cavallottia
a Dip. Chimica, Materiali e Ing. Chimica G. Natta, Politecnico di Milano, Via Mancinelli 7, 20151 Milano, Italy
b Dip. di Meccanica, Politecnico di Milano, Milano, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Electrodeposition of nickel–boron nitride (Ni–BN) composites is carried out from a sulfamate bath contain-
ing up to 10 g/l of dispersed boron nitride particles with size 0.5 ␮m. Microhardness and wear resistance of
the composites are investigated. Both the properties are influenced by the amount of incorporated boron
nitride particles. Commercial surfactant containing alkyl-dimethyl-benzyl-ammonium saccharinate is
used to stabilize the electrolyte: the effects on mechanical properties and structure of the electrodeposits
are investigated. Morphology of the coatings and the effects of codeposited particles on metal matrix
structure are reported.
Received 31 January 2008
Received in revised form 19 May 2008
Accepted 12 June 2008
Available online 27 June 2008
Keywords:
Electrodeposition
Nickel
© 2008 Elsevier Ltd. All rights reserved.
Sulfamate
Boron nitride
Wear
1. Introduction
are investigated. Morphology of the coatings and the effects
of codeposited particles on metal matrix structure are also
Metal matrix composites (MMC) are materials in which the
properties of a metallic host material are modified by the addition
of a different type material (ceramic, polymer, etc.). Electrocode-
position is one of the most important techniques for producing
MMC. During this process, inert particles are suspended in a con-
ventional plating electrolyte and captured in the growing metal
layer in order to form a composite coating. Nickel, copper, gold
and silver are commonly used as the continuous metallic phase.
The dispersed phase can be hard oxide (Al2O3, TiO2 and SiO2),
carbides (WC, B4C and SiC), diamond or polymer (PTE and PTFE)
[1–6].
reported.
2. Experimental
A standard sulfamate based electrolyte was used for elec-
trodeposition. Bath composition and its operating condition are
given in Table 1. Demineralized water and chemicals of analyti-
cal grade were used for the preparation of baths. Brass (CZ121M)
foils were used as substrate for deposition and a nickel foil was
used as soluble anode. The average size of hexagonal boron nitride
particles, reported in Fig. 1, was 0.5 ␮m. Deposition was car-
ried out in a 250 ml Pyrex beaker with magnetic stirrer and
automatic temperature control unit. The solution was preheated
at process temperature and then boron nitride particles were
added to the bath. Before deposition, solution was sonicated for
30 min. Brass substrates were degreased with acetone and then
etched with H2SO4 10 vol.% for few minutes. After electrodepo-
sition for 50 min, deposits were cleaned with water and dried
with air at room temperature. Grain size and orientation of nickel
matrix were detected by X-ray diffraction with a Philips PW
1830. All samples were cut, mounted in epoxy resin and polished
using 1 ␮m Al2O3 abrasive paste. The cross-section morphology
of the deposits was examined with optical microscope and Zeiss
EVO50EP scanning electron microscope equipped with EDX ana-
lyzer. Vickers microhardness measurements were carried out with
Helmut Fischer indenter on cross-section with a load of 500 mN
Nickel–boron nitride (Ni–BN) composites are gaining impor-
tance for potential engineering applications due to their high
hardness and anti-wear properties [3,7,8].
In this work, the electrodeposition of nickel–BN compos-
ites from
a sulfamate bath is obtained. Microhardness and
wear resistance of the composites are investigated: both
properties are influenced by the amount of incorporated
boron nitride particles. Commercial surfactant containing alkyl-
dimethyl-benzyl-ammonium saccharinate is used; its effects on
mechanical properties and deposit structure and morphology
∗
Corresponding author. Tel.: +39 0223993124; fax: +39 0223993180.
E-mail address: luca.magagnin@polimi.it (L. Magagnin).
0013-4686/$ – see front matter © 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2008.06.034

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E. Pompei et al. / Electrochimica Acta 54 (2009) 2571–2574
Table 1
Bath composition and operating conditions
Nickel sulfamate, Ni(SO3NH2)2
Boric acid, H3BO3
BN powder concentration
Surfactant
390 g/l (1.55 M)
40 g/l (0.64 M)
10 g/l
0.5 g/l
Saccharine
3 g/l
pH
4
Temperature (◦C)
Current density (mA/cm2)
Deposition time (min)
Stirring (rpm)
50
50
50
300–800 (magnetic)
for 10 s. Unidirectional sliding ball-on-disc wear test were per-
formed at a normal load of 53.43 N with a sliding speed of
50 rpm.
3. Results and discussion
Fig. 2 shows XRD patterns for pure Ni, for Ni electrodeposited
from an electrolyte containing the surfactant only and surfactant
plus BN 10 g/l, respectively. Pure Ni deposit presents a strong prefer-
ential orientation along the (2 0 0) plane. Adding only the surfactant
to the plating solution, the XRD pattern shows a decrease in the
grain size and the loss of the deposit orientation (Fig. 2b). The incor-
poration of boron nitride particles in the nickel matrix favors the
loss of such orientation, as shown in Fig. 2c. BN particles do not
affect the grain size of the metal matrix. In all Ni–BN composite
XRD patterns, the main peaks of boron nitride are clearly visible.
In Fig. 3, SEM images of the cross-section of pure nickel, pure Ni
with surfactant and Ni–BN deposits obtained with particles con-
centrations of 1–5–10 g/l are reported. Pure Ni deposits obtained
adding only the surfactant to the plating solution, show the same
morphology of pure Ni coatings.
The presence of boron nitride particles embedded in the Ni
matrix is clearly visible in the Ni–BN 1 g/l deposit. Increasing the
amount of particles dispersed in the bath, the fraction of incor-
porated particles highly increases. For concentration of dispersed
particle in the solution from 1 to 10 g/l, the BN particles appear not
homogeneously distributed in the metal matrix. It is interesting to
note the presence of preferential incorporation paths due to the
formation of whirls in the plating solution. When whirls reach the
cathodic surface, they create a way of preferential incorporation.
Fig. 2. XRD patterns for Ni deposit from sulfamate electrolyte (a), sulfamate elec-
trolyte with 0.5 g/l surfactant (b) and sulfamate electrolyte with surfactant and BN
10 g/l (c).
The periodic nature of these whirls leads to the formation of areas
with high concentration of embedded particles disposed along flux
lines (Fig. 3d and e).
Some aggregation phenomena, probably due to the presence of
the surfactant, are present already in the Ni–BN 1 g/l deposit and
increase for higher concentration of dispersed particles. The maxi-
mum concentration of BN particles in the plating solution is limited
by the surfactant solubility.
Fig. 1. SEM image of agglomerated hexagonal boron nitride particles.

E. Pompei et al. / Electrochimica Acta 54 (2009) 2571–2574
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Fig. 3. SEM images of the cross-section for pure Ni deposit (a), pure Ni with surfactant (b) and Ni–BN deposits obtained with 1 g/l (c), 5 g/l (d) and 10 g/l (e) of dispersed
particles.
All deposits appear adherent to the substrate and compact.
Ni–BN composite coatings show a frosty appearance with a silky
brightness. Microhardness (Fig. 4) and weight loss are highly influ-
enced by the concentration of boron nitride particles in the plating
solution.
The presence of the surfactant in the plating solution leads to
an increase of the microhardness of the deposit, from 280 to about
400 HV, probably due to its influence on the grain size. The addition
of boron nitride particles in the plating solution causes a further
increase in the microhardness up to over 500 HV.
from 0.8 mg to about 1 mg adding 0.5 g/l of surfactant. Adding the
BN particles to the plating solution, the weight loss of composites
highly decreases with a minimum of 0.3 mg for a particles con-
centration of 10 g/l. Boron nitride particles concentration in the
solution has a slight influence on friction coefficient of compos-
ites, which decreases from 0.6 to 0.55 increasing BN concentration
from 0 to 10 g/l in solution.
The incorporation percentage of boron nitride particles in the
deposit increases when their concentration in the electrolyte was
increased; being such concentration limited by the solubility of
the surfactant. Details regarding preparation of Ni–BN compos-
ites are scarcely available in the literature. This article proposes
the electrodeposition method as a direct route for the production
In Fig. 5, weight loss and friction coefficient vs. particles con-
centration in the solution are reported. The weight loss of pure
nickel from surfactant containing electrolyte initially increases

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E. Pompei et al. / Electrochimica Acta 54 (2009) 2571–2574
of composite coatings, based on particles’ incorporation following
a Guglielmi mechanism from an electrolyte containing a suspen-
sion of particles. This method differs from the common two-steps
method, which implies a first electrophoretic step followed by a
second plating step.
4. Conclusions
Submicrometric boron nitride particles can be codeposited with
Ni from a sulfamate bath using a commercial surfactant to obtain a
composite coating. The concentration of the boron nitride particles
in the plating solution is limited by the solubility of the surfactant.
Its presence in the electrolyte decreases the grain size and increases
the weight loss of the deposits compared with a pure nickel deposit
obtained without additives. Morphology is not affected by the pres-
ence of the surfactant in the plating solution.
Compared to pure Ni coatings, Ni–BN composites show higher
microhardness and improved wear resistance. Both the properties
improve increasing the boron nitride particles concentration in the
electrolyte up to 10 g/l.
Fig. 4. Effects of concentration of dispersed BN particles on composite microhard-
ness.
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Fig. 5. Influence of dispersed particles concentration on wear behavior and friction
coefficient of the deposits.