In this paper is presented morphological aspects and corrosion behaviour of composite coatings having nickel as metal matrix and silicon as dispersed phase obtained during electrodeposition process of nickel. Silicon mean diameter size of particles particles by 50 nm. The Ni-Si composite coatings were electrodeposited from a suspension silicon particles in aqueous nickel sulphate electrolyte by adding 10 g/L and 20 g/L of silicon particles in the electrolyte solution. The morphological aspects of the coatings and inclusion on particles were investigated using SEM and EDX. As test solution NH4OH 0.5 M (specific coke industry) was used in a three electrode open cell with nickel based nanostructured composite coatings as working electrode (WE), a platinum electrode as counter electrode (CE) and an Ag/AgCl electrode as reference electrode (RE)

Gina Genoveva ISTRATE

The Annals of “Dunarea de Jos” University of Galati Fascicle IX Metallurgy and Materials Science

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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 4 – 2013, ISSN 1453 – 083X 
 
 
 
 
ELECTRODEPOSITION AND CHARACTERIZATION  
OF Ni-Si NANOCOMPOSITE COATINGS  
 
Gina Genoveva ISTRATE 
“Dunarea de Jos” University of Galati, Faculty of Materials Science and Environment  
email: gistrate@ugal.ro 
 
ABSTRACT 
 
In this paper is presented morphological aspects and corrosion behaviour of 
composite coatings having nickel as metal matrix and silicon as dispersed phase 
obtained during electrodeposition process of nickel. Silicon mean diameter size of 
particles particles by 50 nm. The Ni-Si composite coatings were electrodeposited 
from a suspension silicon particles in aqueous nickel sulphate electrolyte by adding 
10g/L and 20g/L of silicon particles in the electrolyte solution. The morphological 
aspects of the coatings and inclusion on particles were investigated using SEM and 
EDX. As test solution NH4OH 0.5M (specific coke industry) was used in a three 
electrode open cell with nickel based nanostructured composite coatings as working 
electrode (WE), a platinum electrode as counter electrode (CE) and an Ag/AgCl 
electrode as reference electrode (RE). 
 
KEYWORDS: nanocomposite coatings, silicon, nickel, polarization resistance 
 
1. Introduction 
 
Composite materials have been designed to 
replace a growing proportion, ferrous and non-
traditional materials, which are characterized by some 
shortcomings on the performance, processes for 
obtaining and processing, dimensions, weights, 
geometric complexity, usage and costs. 
Applications of composite coating technology 
can now be found in general consumer products and 
more applications are on the horizon. 
Electrodeposition of ceramic, polymer and metal 
powders within metal, ceramic or polymer matrix 
produces composite coatings with attractive properties 
such as microhardness, polarization resistance, wear-
resistance [1]. The production of composite coatings 
can be achieved through electrochemical deposition of 
the matrix material from a solution containing 
suspended particles such as: oxides (TiO2 [2], Al2O3 
[3], CeO2 [4], ZrO2 [5]), carbides (SiC, WC), nitrides, 
metal powder (Si [6, 7], P [8], Co [9], W, B [6]). 
Nickel matrix composites containing particles 
like oxides, carbides, nitrides or diamond have been 
developed for their improved wear resistance and 
dispersion strengthening. 
Among the solid particles used for 
reinforcement, SiC is the most frequently studied and 
applied [9-11].  
Considerable researches have been mainly 
focused on the fundamental conditions of the 
electrolysis such as composition and pH of the 
electrolyte, the presence of additives, temperature 
agitation rate, density and type of the current, surface 
properties of particles, their size and concentration in 
the bath [12]. 
The present study aims to codeposit Si into 
nickel matrix. The effects of Si concentration in the 
suspension, current density, temperature and pH of 
the plating bath on silicon inclusion into the deposit 
were studied. Microhardness and corrosion behaviour 
of nickel–silicon (Ni–Si) composite in NH4OH 0.5 M 
solution have been studied. Microstructure of the 
composite has also been investigated and reported. 
The novelty of the work is the use of nanometer 
silicon as disperse phase. 
 
2. Experimental procedure 
 
The coating was plated on carbon steel plates 
(measuring 100x30x2 mm). The nickel matrix was 
prepared from sulphate electrolyte with the following 
composition NiSO4·7H2O 110g/L + Na2SO4 x 10H2O 
110 g/L + NH4Cl 25g/L+ H3BO3 15g/L, at cathodic 
current density 2 A/dm2 and 3 A/dm2 with electrolyte 
stirring. The stirring rate in the electrolyte was 500, 
750 and 1000 rpm. The electrodeposition was carried 
out for one hour. Silicon powder (dispersed phases) 
with a concentration 10 g/L and 20 g/L were 
introduced into the bath to obtain the composite 
coatings. The mean diameter size of particles of 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 4 – 2013, ISSN 1453 – 083X 
 
 
silicon powder was 50 nm. The pH of solution was in 
the range 5-6, the temperature was kept at 293K. 
The morphologic aspects of the coatings were 
investigated by scanning electron microscopy method. 
The experimental measurements of the Vickers 
microhardness of composite deposits are described in 
[13]. 
Also this paper present the electrochemical 
corrosion behavior of nanostructured composite 
coatings using potentiodynamic polarization method.  
As test solution NH4OH 0.5 M (specific coke 
industry) was used in a three electrode open cell with 
nickel based nanostructured composite coatings as 
working electrode (WE), a platinum electrode as 
counter electrode (CE) and an Ag/AgCl electrode as 
reference electrode (RE) (ERE = +200 mV/ENH). For 
potentiodynamic polarization measurements was used 
initial potential (I. P.) – 1000mV (Ag/AgCl), final 
potential (F. P.) + 600mV (Ag/AgCl) and a scan rate 
of 2 mV/s. The polarization potentiodynamic curves 
were recorded after 60 minutes of immersion. The 
corrosion current density (icorr) for the particular 
specimens was determined by extrapolating the anode 
and cathode Tafel curves. 
 
3. Results and discussion 
 
In Fig. 1 is presented the thicknesses of 
composite coatings obtained by electrodeposition at 
2A/dm2 and 3A/dm2 current density, 60 minutes 
deposition time and various stirring rate of the 
electrolyte.  
 
500
750
1000
2A/dm2 
3A/ dm2 
0
5
10
15
20
25
30
35
40
Th
ic
kn
es
s 
co
at
in
gs
, [
µm
]
Electrolyte stirring rate, [rpm]
C
ur
re
nt
 
de
ns
ity
, 
[A
/d
m
2]
 
Fig. 1. The thickness of Ni-Si composite coatings 
function current density and stirring rate 
 
From fig. 1 we can observed that deposited layer 
thickness increases with current density and decreases 
with increasing electrolyte stirring rate. The higher 
thickness of the composite coating was observed at 
these conditions of electrodeposition: current density 
3A/dm2 and 500 rpm electrolyte stirring rate. 
Fig. 2 show the minimum variation of the 
silicon content in the nanocomposite coatings 
according to the electrolyte stirring rate (current 
density 2A/dm2, 60 minutes deposition time). 
As it can be observed from figure 2 the content 
of Si nanoparticles is highest at a stirring rate of 500 
rpm and a dispersed phase containing 20 g/L (2.7% 
wt). It is also noted that at higher agitation rates (750, 
1000 rpm) the content of Si included is lower (except 
composite coating obtained at 750 rpm and a 
dispersed phase containing 10 g/L). 
 
500
750
1000
10g/L Si 50 nm
20g/L Si 50 nm
0
0,5
1
1,5
2
2,5
3
Co
nt
en
t S
i 5
0 
nm
, 
[w
t%
]
Electrolyte stirring rate, [rpm]
 
Fig. 2. Content of silicon wt% in the nickel 
matrix 
 
Figs. 3 – 4 compares morphological aspects of 
Ni-Si composite coatings by scanning electron 
microscopy method. 
 
 
Fig. 3. SEM surface morphology of Ni-Si 
composite coatings (20g/L Si, 2A/dm2, 500 rpm, 
60 min.) (x 10000) 
 
 
Fig. 4. SEM surface morphology of Ni-Si 
composite coatings (20g/L Si, 3A/dm2, 500 rpm, 
60 min.) (x 10000) 
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FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 4 – 2013, ISSN 1453 – 083X 
 
 
It has been found by SEM that with increasing 
current density, nodular structure is more pronounced, 
crystal size becomes larger. At a current density of 
2A/dm2 finer structure indicates a greater number of 
nucleation centers and thus a more homogeneous 
coating. The electrochemical investigation of each 
sample began with monitoring the open circuit 
potential (OCP). OCP changes immediately after the 
immersion into the testing solutions till reaching 
relatively stable stationary values.  
0 10 20 30 40 50 60 70
-600
-500
-400
-300
-200
-100
P
ot
en
tia
l, 
[m
V
]
T im e, [m in ]
 N i_S i nm _10 g /L , 2A /dm 2;
 N i_S i nm _10 g /L , 3A /dm 2;
 N i_S i nm _20 g /L , 2A /dm 2;
 N i_S i nm _20 g /L , 3A /dm 2.
 
Fig. 5. Open circuit potential Ni-Si composite 
coatings in NH4OH 0.5 M 
 
Fig. 5 show that potential value of composite 
coating Ni-Si obtained at 3 A/dm2 with 20 g/L silicon 
nano in electrolyte is more positive suggesting a more 
noble the deposit. This may be associated with an 
inhibition of the anodic reaction and therefore a 
higher resistance to corrosion 
The typical anodic potentiodynamic polarization 
curves of various nanocrystalline Ni-Si coatings 
measured in NH4OH 0.5 M solutions are shown in 
Fig. 6.  
-2 .5 -2 .0 -1 .5 -1 .0 -0 .5 0 .0 0 .5 1 .0 1 .5
-650
-600
-550
-500
-450
-400
-350
-300
-250
-200
P
ot
en
tia
l, 
[m
V
]
lo g  I, [µ A /c m 2]
 N i_ S i n m _ 1 0 g /L , 2 A /d m 2;
 N i_ S i n m _ 1 0 g /L , 3 A /d m 2;
 N i_ S i n m _ 2 0 g /L , 2 A /d m 2;
 N i_ S i n m _ 2 0 g /L , 3 A /d m 2.
 
Fig. 6. Polarization curves of Ni-Si composite 
coatings in NH4OH 0.5 M 
 
Corrosion rates of the coatings were derived 
from the Stern–Geary equation: 
⎟⎟
⎠
⎞
⎜⎜
⎝
⎛
+
⋅
=
ca
ca
p
corr R
i
ββ
ββ
303.2
1   (1) 
- icorr is the corrosion current density in 
Amps/cm2; 
- Rp is the corrosion resistance in ohms cm2; 
- βa is the anodic Tafel slope in Volts/decade or 
mV/decade of current density; 
- βc is the cathodic Tafel slope in Volts/decade 
or mV/decade of current density; 
- the quantity, )/()( caca ββββ +⋅ , is referred to as 
the Tafel constant. 
The polarization resistance, Rp, was determined 
from the slopes of the potential-current plots 
measured by the linear polarization curve (LSV) at a 
scanning rate of 2 mV/s. 
The corrosion potential (Ecorr), corrosion current 
density (icorr) and polarisation resistance (Rp), which 
were obtained from the potentiodynamic polarisation 
curves are summarized in Table 1. 
 
Table 1. Corrosion parameter values determined 
from polarization curves 
Composite 
coatings 
[500 rpm, 
60 min] 
Ecor, mV 
Ag/AgCl 
βa 
mV/dec 
βc 
mV/dec 
icor, 
µA/cm² 
Rp 
kΩ·cm2
Ni-Si, 
2A/dm2, 
10g/L Si nm
-384.0 139.8 123.4 0.8864 32.10 
Ni-Si, 
2A/dm2, 
20g/L Si nm
-406.0 145.0 67.8 1.5464 12.97 
Ni-Si, 
3A/dm2, 
10g/L Si nm
-383.3 154.5 73.5 0.9429 22.93 
Ni-Si, 
3A/dm2, 
20g/L Si nm
-414.8 194.1 75.0 2.0888 11.24 
 
From the data presented it can be seen that the 
corrosion potential tends to negative values for 
composite coating Ni-Si obtained with 20 g/L silicon 
nano in electrolyte solution. 
From potentiodynamic polarization curves the 
polarization resistance for composite coating Ni-Si 
obtained at 3 A/dm2 with 20 g/L silicon nano in 
electrolyte was 11.24 kΩ·cm2. For composite coating 
Ni-Si obtained at 2A/dm2 with 10 g/L silicon nano in 
electrolyte the polarization resistance was 32.10 
kΩ·cm2.  
 
10 g/L Si
20 g/L si
2A/dm2
3A/dm2
0
5
10
15
20
25
Co
rr
os
io
n 
ra
te
, 
[µ
m
/y
ea
r]
Disperse phase content [g/L]
 
Fig. 7. The variation of corrosion rate with the 
content of the disperse phase and current density 
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THE ANNALS OF “DUNAREA DE JOS” UNIVERSITY OF GALATI. 
FASCICLE IX. METALLURGY AND MATERIALS SCIENCE 
N0. 4 – 2013, ISSN 1453 – 083X 
 
 
The better corrosion resistance coating Ni-Si 
obtained at 2A/dm2 could be due to the fine surface 
structure of composite coating compared with coating 
Ni-Si obtained at 3A/dm2. Microhardness 
measurements were carried out using a Vickers 
microhardness tester, applying 20 g load for 10 s time 
[11]. 
380
400
420
440
460
480
500
520
500 750 1000
Electrolyte stirring rate [rpm]
M
ic
ro
ha
rd
ne
ss
 [H
V0
.0
2]
Current density 2A/dm2
Current density 3A/dm2
 
Fig. 8. Microhardness as a function of 
electrolyte stirring rate ( 10 g/L Si ) [13] 
 
The mean value of Vickers microhardness of 
pure nickel coatings has been found of about 300 
HV0.02 while composite coatings Ni-Si obtained at 
2A/dm2 with 10 g/L silicon nano in electrolyte is 
about 505 HV0.02. This result shows that the 
codeposition of Si nanoparticles ameliorates the 
mechanical properties by 70% microhardness 
increase. 
 
4. Conclusions 
 
Nano-sized Si particles were successfully co-
deposited in the nickel matrix by electrodeposition 
technique with a current density of 2 A/dm2and 3 
A/dm2. Deposited layer thickness increases with 
current density and decreases with increasing 
electrolyte stirring rate. It is also observed that the Ni–
Si nanocomposite sample deposited from electrolyte 
with a current density 2A/dm2 and with 20 g/L silicon 
nano in electrolyte solution has the highest corrosion 
resistance. This is due to the fact that it has the 
smallest crystallite.  
Highest microhardness value was obtained for 
composite coating Ni-Si at 2A/dm2 with 10 g/L 
silicon nano in electrolyte. 
 
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Electrodeposition and Characterization of Ni-Si Nanocomposite Coatings

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Electrodeposition and Characterization of Ni-Si Nanocomposite Coatings

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