Preparation and property of sol-enhanced Ni-B-TiO2 nano-composite coatings

Article abstract of DOI:10.1016/j.jallcom.2014.08.060

Ni-B-TiO₂ nano-composite coatings were fabricated on mild steel by using a novel sol-enhanced method. It was found that highly dispersed Ni-B-TiO₂ nano-composite coatings can be directly in-situ electrodeposited by adding a small quantity of TiO₂ sol solution and (DMAB) into the basic watts solution. The mechanical property of sol-enhanced Ni-B-TiO₂ coatings was significantly improved compared with that of Ni and Ni-B coatings. The microhardness of the sol-enhanced Ni-B-12.5 mL/L TiO₂ coating was ～1061 HV₂₀₀ compared to ～677 HV₂₀₀ of Ni-B coating and ～350 HV₂₀₀ of Ni coating. Meanwhile, the wear resistance has also been improved remarkably. The corrosion resistance of sol-enhanced Ni-B-12.5 mL/L TiO₂ coating was decreased compared with that of pure Ni coating but significantly better than that of Ni-B coating.

Full text of DOI:10.1016/j.jallcom.2014.08.060

Accepted Manuscript
Preparation and property of sol-enhanced Ni-B-TiO nano-composite coatings
2
Yuxin Wang, Shu-jen Wang, Xin Shu, Wei Gao, Wei Lu, Biao Yan
PII:
S0925-8388(14)01915-X
DOI:
http://dx.doi.org/10.1016/j.jallcom.2014.08.060
JALCOM 31913
Reference:
To appear in:
Journal of Alloys and Compounds
Received Date:
Revised Date:
Accepted Date:
15 June 2014
1 August 2014
5 August 2014
Please cite this article as: Y. Wang, S-j. Wang, X. Shu, W. Gao, W. Lu, B. Yan, Preparation and property of sol-
enhanced Ni-B-TiO nano-composite coatings, Journal of Alloys and Compounds (2014), doi: http://dx.doi.org/
2
1
0.1016/j.jallcom.2014.08.060
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Preparation and property of sol-enhanced Ni-B-TiO nano-composite
2
coatings
1
Yuxin Wang , Shu-jen Wang , Xin Shu , Wei Gao
1
1
1,∗
2
Wei Lu , Biao Yan
2
1
Department of Chemical & Materials Engineering, the University of Auckland, PB
2019, Auckland 1142, New Zealand
9
2
School of Materials Science and Engineering, Tongji University, Shanghai 200092,
China
Abstract
Ni-B-TiO
2
nano-composite coatings were fabricated on mild steel by using a novel
nano-composite
coatings can be directly in-situ electrodeposited by adding a small quantity of TiO sol
solution and (DMAB) into the basic watts solution. The mechanical property of
sol-enhanced Ni-B-TiO coatings was significantly improved compared with that of
Ni and Ni-B coatings. The microhardness of the sol-enhanced Ni-B-12.5 mL/L TiO
sol-enhanced method. It was found that highly dispersed Ni-B-TiO
2
2
2
2
coating was ~1061 HV200 compared to ~677 HV200 of Ni-B coating and ~350 HV200
of Ni coating. Meanwhile, the wear resistance has also been improved remarkably.
2
The corrosion resistance of sol-enhanced Ni-B-12.5 mL/L TiO coating was decreased
compared with that of pure Ni coating but significantly better than that of Ni-B
coating.
∗
Corresponding author. Department of Chemical & Materials Engineering, the University of Auckland, PB 92019,
Auckland 1142, New Zealand. Tel.: +64 9 3737599 Ext. 88175, Fax: +64 9 3737463.
E-mail addresses: w.gao@auckland.ac.nz (Wei Gao), ywan943@aucklanduni.ac.nz (Yuxin Wang).

Keywords: Sol-enhanced method, Ni-B, Nano-composite coatings, Mechanical
property, Corrosion resistance
1
. Introduction
In recent years, Ni-B coatings have attracted much attention due to their excellent
properties such as thickness uniformity, superior wear resistance, fine solderability,
good conductivity, and cost effectiveness. Ni-B has been considered as potential
candidate to replace hard Chromium coating for their relatively high hardness and
good wear resistance [1-6]. Ni-B coatings can be fabricated either by electroplating or
electroless plating. Electroless Ni-B coatings can be deposited using dimethylamine
borane [7, 8] or sodium borohydride [9-13] as reducing agents. The major advantages
of electroless Ni-B coatings are their high hardness and superior wear resistance.
However, the major limitation which hinders its application is the high operating
temperature (70-90°C) and strictly controlled PH during the plating process [14]. In
contrast with the electroless plating, electroplating process shows broader application
prospect as it is easy to operate and the deposition rate can be controlled by adjusting
the voltage or current [15, 16]. However, comparing to the studies on electroless Ni-B
coatings [1-13], few reports can be found on the electroplating Ni-B coatings in the
last few years [14, 17-19].
To further improve the performance of Ni-B coatings, many different methods
including composite intensifying [14, 17, 19-21] and heat treatment [7, 10, 13, 22, 23]
were attempted in the last decades. Ni-B composite coatings have also been explored
by suspension of solid ceramic particles in the plating solutions. However, limited
achievements were obtained due to the agglomeration of nano- or micro-particles. The
second strengthening phases with high surface energy tend to agglomerate during the

plating process. We have recently developed a novel technology, sol-enhanced
technology, which combines sol-gel method and electroplating process together to
fabricate nanocomposite coatings. This technology fabricates alloy coatings with
highly dispersive oxide nanoparticles, resulting in significantly improved mechanical
properties [24-26]. This paper reports our work on the Ti containing sol enhanced
Ni-B nano-composite coatings.
2
. Experimental
2.1 Sample preparation
Both Ni-B coatings and Ni-B-TiO
2
nano-composite coatings were electroplated onto
3
the mild steel substrate (20×30×1 mm ). The steel substrates were mechanically
polished using SiC paper to a grit of #1200, then degreased ultrasonically in ethanol.
Before electroplating, the specimens were pre-treated in 1 mol/L HCl solution for 2
min at room temperature.
2
TiO sol was prepared as reported in the previous research [24-26]. The electroplating
system consists of a mild steel sample as the cathode and a Ni plate as the anode.
Watts solution was used as the base plating solution. In order to get the Ni-B coating,
proper amount of dimethylamine borane (DMAB) were added into the basic watts
solution as the reducing agent and source of boron. After the TiO
the bath slowly, the electroplating was conducted immediately. The bath composition
and plating parameters are given in Table 1. The concentrations of TiO sol used in
2
sol was added into
2
this study are 0, 5, 10, 12.5, 15, 20 and 50 mL/L. For comparison, Ni coating was also
prepared in watts solution with the identical plating parameters. The bath composition
and plating parameters are given in Table 1.

2.2 Sample Characterization
The phase structure of the coatings was characterized by X-ray diffraction (XRD)
with Cu Kα radiation (V = 30 kV, I = 10 mA). Diffraction patterns were recorded in
the 2θ range from 20 to 90° at a scanning step of 0.02° using Bruker D2 Phaser
diffractometer. Both the surface morphology and cross-section microstructure of
2
Ni-B-TiO nano-composite coatings were analyzed using a FEI Quanta 200 field
emission environmental scanning electron microscope.
Vickers microhardness of coating surface was measured using a load of 200 g with a
holding time of 15 s. The results for the hardness were the average of 5
measurements. The wear tests of coatings were carried out in a micro-tribometer
(
Nanovea, USA) in air at 25°C and relative humidity of ~50% under non-lubricated
conditions. All wear tests were performed under a load of 7 N. A ceramic ball was
used and the sample was tested linearly at a disk speed of 100 rpm. The amplitude
was set to be 10 mm and the test time was set to be 30 min (60 meters). The width of
the wear track was measured using optical microscope images. The volume removed
was then calculated from the wear track width.
The electrochemical tests were conducted in an electrochemical workstation
(
CHI604D) using a classical three-electrode system. Potentiodynamic polarization
−1
was measured at a scan rate of 1 mVs at room temperature in 3.5 wt. % NaCl
solution. Salt spray test was carried out following the ASTM B117 standard to
examine the corrosion resistance of the produced coatings. The samples were placed
in the SALTRON salt spray cabinet and the exposing area of samples was adjusted to
2
cm . The other areas were sealed by cello tape and silicon rubber. A 5 wt. % salt
1
o
solution (NaCl) was used for the test. The testing temperature is 35 C and the testing

pressure was set to 1 bar absolute.
3
. Results and discussion
3.1 Phase structure of coatings
The phase composition and structure of pure Ni-B and sol-enhanced Ni-B-TiO
2
nano-composite coatings with different sol concentrations were investigated using
XRD presented in Fig. 1. As can be seen from Fig. 1, all the coatings have similar
face-centered cubic (fcc) lattice structure with preferential (111) growth orientation.
2
Beside the plane (111), Ni (200) and (220) planes can be seen. No TiO peaks could
be detected from the composite coatings, probably due to the low quantity of TiO
particles and high intensity of other diffraction peaks.
2
3.2 Surface morphology and cross-section of coatings
Fig. 2 presents the surface morphology of Ni-B and sol-enhanced Ni-B-TiO
2
nano-composite coatings. All coatings show a typical morphology of a spherical ball
type. Unlike the earlier study made by Krishnaveni et al. [17-19], no cracks can be
observed on the coating surface due to the addition of stress relieving agents. A small
amount of stress relieving agents was added into the watts solution before
electroplating; and it can decrease the high stress which caused by the hydrogen
evolution during electrolysis [18].
Ni-B coating has a relatively large grain size with an average diameter of 9.6 µm as
shown in Fig. 2(a). After adding the TiO
enhanced nano-composite coatings present more uniform structure. No clear TiO
nanoparticles can be seen on the surface of the sol-enhanced Ni-B-TiO coating. This
is due to their extremely small size and high dispersion in the coatings. However, by
2
sol into the solution, the morphology of sol
2
2

2
virtue of EDS probe, the existence of TiO nanoparticles can be confirmed in the grain
boundaries. The content of Ti in the grain boundary areas increases gradually
following with the sol concentration. Meanwhile, the grain size of coatings decreased
gradually as shown in Fig. 2(b) and Fig. 2(c). The mean grain size of sol-enhanced
Ni-B-12.5 mL/L TiO
respectively. The refinement of grain size is probably due to the highly dispersed TiO
nanoparticles. When gradually raising the TiO sol addition, the increasing amount of
TiO nanoparticles can provide more nucleation sites and will distribute in the grain
2 2
and Ni-B-50 mL/L TiO was decreased to 7.4 and 4.7 µm,
2
2
2
boundary areas to hinder the grain growth.
Thickness and apparent microstructure of the coatings were investigated by SEM
2
analysis as shown in Fig. 3. Both Ni-B and sol-enhanced Ni-B-TiO coating present a
uniform and continuous coating with a thickness of 15-18 µm. No defects or cracks
were observed at the interfaces of the two coatings, evidence of a good adhesion
between the mild steel substrate and coating.
3
.3 Mechanical property of coatings
.3.1 Microhardness
3
2
Fig. 4 presents the value of microhardness as a function of TiO sol concentration.
The mechanism of Ni-B coating prepared by electroplating method using DMAB is
not yet fully understood. Krishnaveni et al [18] presumed that during the
electroplating process, DMAB were adsorbed on the already formed nickel surface
and subsequently decomposed to get boron, accommodating boron within the unit cell
of fcc nickel. The microhardness of Ni-B coating is ~677 HV200, a normal value of
electroplating Ni-B but much higher than ~350 HV200 of Ni coating.

At low sol concentration, microhardness increases significantly with increasing TiO
content. 12.5 mL/L TiO sol enhanced nano-composite coating possesses the highest
microhardness of ~1061 HV200. However, further increasing the amount of TiO
2
2
2
concentration to 50 mL/L led to a decrease of micro-hardness to ~587 HV200, which is
even worse than that of Ni-B coating.
The strengthening mechanism of composite coatings can be mainly attributed to two
factors. One is the amount of second phase or hard particles incorporated into the
coatings matrix, which provides the dispersion strengthening effect. The other is the
microstructure change of coating matrix which caused by the embedded second phase
or hard particles.
For sol-enhanced Ni-B-TiO
into the electrolyte, large quantity of Ni ions in the solution will lead to the
polymerization reaction of sol. Well dispersed TiO nanoparticles were in situ formed
2 2
nano-composite coatings, after the TiO sol was added
2
under the effect of ethanol and DEA [27]. Then these nanoparticles were absorbed
onto the deposited surface and embedded into the Ni-B coating matrix. Uniform
distributed TiO
strengthening.
2
nanoparticles lead to a good effect of second phase dispersion
The strengthening mechanism resulting from particles dispersion hardening is known
as Orowan mechanism, and can be expressed as follows [25]:
σ = 2Gb/λ
(Eq. 1)
where G and b are the shear modulus of the matrix and Burger’s vector of the
dislocation, and λ is the distance of dispersed particles. The Orowan mechanism
indicates that the yield stress σ is determined by the stress required for a dislocation

line to pass by the two adjacent particles. The shorter distance of dispersed particles,
the better strengthening effect will be. Parameters including the particle spacing, the
particle size and the particle volume fraction dominate the effect of dispersion
strengthening. The increasing TiO
2
sol addition in the bath leads to an increase of
TiO nanoparticles in the deposit and decrease of the particle distance. When the
2
matrix carries the load, the highly dispersed nanoparticles impede the mobility of the
dislocations, improving the hardness of the coatings.
The relationship between yield stress and grain size can be described mathematically
by the Hall-Petch equation as below [25]:
HV = 3σ
y
(Eq. 2)
(Eq. 3)
-
1/2
σ
y
0
= σ +kd
where σ
y
0
is the yield stress, σ is a materials constant for the starting stress of
dislocation movement or the resistance of the lattice to dislocation motion, k is the
strengthening coefficient which is a constant value for different material and d is the
average grain diameter. Equations (1) and (2) suggest that the strength of materials
increases when their grain size is refined. During the electroplating process, the
embedded nanoparticles increased the number of nucleation sites and also distributed
in the grain boundaries acted as the obstacles which inhibit the grain growth.
Therefore, the grain size was decreased as evidenced by Fig. 2, and led to a grain
refinement strengthening effect.
Higher TiO
and grain refinement, resulting in a significant increase of mechanical property for the
coating. However, TiO nanoparticles start to agglomerate when excessive TiO sol
were added into the electrolytes, and tend to cause porous structure in the grain
2
sol concentration in the solution leads to better dispersion strengthening
2
2

boundaries. It will reduce the effect of dispersion and grain refinement strengthening,
ultimately lead to a deterioration of the mechanical property.
3
.3.2 Tribological properties
Tribological and wear property of Ni-B-TiO
average friction coefficient of Ni-B and sol-enhanced Ni-B-TiO
coatings. The friction coefficient of Ni-B coating is ~0.4. Comparing with the above
.6 which measured by Krishnaveni et al [18, 19]. The friction coefficient of Ni-B
2
coatings were studied. Fig. 5 shows the
nano-composite
2
0
decreases mainly due to its low surface roughness. The addition of stress relieving
agents made the coating surface more uniform and free of cracks. After adding the sol
concentration to 12.5 mL/L, the average friction of coating decreases to ~0.315. The
decrease in friction coefficient is due to the higher hardness, the smoother surface and
2 2
the incorporation of TiO nanoparticles in the Ni-B matrix. The hard TiO
nanoparticles embedded in the coatings can reduce the direct contact between Ni-B
matrix and abrasive surface. It may also act as a solid lubricant during the wear
process. However, excessive sol addition caused a friction coefficient increase. The
average friction coefficient of Ni-B-50mL/L TiO
be mainly attributed to the hardness decrease and the microstructure change. Too
much TiO start to agglomerate in the grain boundary areas and induce porosity.
Nevertheless, due to the large amount of nanoparticles embedded into the coating
2
coating increases to ~0.355. It can
2
matrix and lubrication effect, the average friction coefficient of Ni-B-50 mL/L TiO
coating is still lower than Ni-B.
2
2
The improved wear resistance of sol-enhanced Ni-B-TiO coating can be further
demonstrated by the worn surface images and wear volume loss shown in Fig. 6 and
Fig. 7. For the Ni-B coating, the mainly wear mechanism is adhesive wear, the most

common wear behavior of electroplating Ni-P and Ni-B coatings [17-19]. Clearly
worn place and plough lines can be seen on the surface. The corresponding wear track
-13
3
width and wear volume loss is ~350 µm and 2.46×10 m . After adding the sol
concentration to 12.5 mL/L, the worn area decreases and the plough lines become
more uniform. The corresponding wear track width and wear volume loss decreased
-13
3
to ~283 µm and 1.05×10 m due to the higher microhardness and lower friction
coefficient.
The improvement of wear resistance with hardness increase and friction coefficient
decrease could be interpreted by using Archard’s law [28, 29], which can be expressed
as:
Q = KW/H = KLN/H
(Eq. 4)
Where Q represents the wear rate, W is the total normal load which equals to the
product of applied load (N) and total sliding distance (L), K is the wear coefficient,
and H is the hardness of the wear surface. Under the same wear test conditions, the
wear rate is inversely proportional to the coating surface hardness and proportional to
the friction coefficient.
Although the microhardness of the sol-enhanced Ni-B-50 mL/L TiO
2
coating is lower
-13
3
than the Ni-B coating, it presents better wear resistance (~333 µm and 1.94×10 m )
-13
3
than Ni-B coating(~350 µm and 2.46×10 m ), which is probably due to the lower
friction coefficient compared to Ni-B coating. Comparing with the sol-enhanced
Ni-B-12.5 mL/L TiO
2
coating, it shows larger worn place area, which is probably due
to the porous structure caused by nanoparticles agglomeration.

3.4 Corrosion resistance of coatings
The potentiodynamic polarization curves for Ni, Ni-B and sol-enhanced Ni-B-TiO
2
composite coatings are shown in Fig. 8. It can be clearly noticed that Ni possesses the
best corrosion properties as its Ecorr value (~-0.282 V) is less negative and its Icorr
2
value (~3.53 µA/cm ) is lower than other coatings. Ecorr value of Ni-B coating is more
negative (~-0.388V) compared with the other coatings. The Icorr of Ni-B coating is
2
~
13.55 µA/cm , much higher than that of Ni coating. After adding a proper amount of
2 2
TiO sol, the Ecorr value and Icorr value of sol-enhanced Ni-B-12.5 mL/L TiO coating
2
were increased to -0.362 V and decreased to ~5.53µA/cm , respectively, showing a
good improvement of corrosion resistance, although it is still worse than the
traditional Ni coating. However, the corrosion resistance of the composite coating
decreased when excessive TiO
2
sol (50 mL/L) was added, evidenced by the Ecorr of
2
~
-0.373 V and increased Icorr of ~18.5 µA/cm .
Fig. 9 shows the surface morphologies of Ni-B and sol-enhanced Ni-B-TiO
2
composite coatings after salt spray test for 120 h. The traditional Ni-B coating
presented a seriously corroded surface and rust area can be clearly noticed in Fig. 9a.
2
The sol-enhanced Ni-B-12.5 mL/L TiO coating displays a much improved corrosion
resistance as only two small corrosion pits can be seen by the white arrows in Fig. 9b,
which is consistent with the potentiodynamic polarization results.
The improvement of corrosion resistance can be mainly attributed to the following
reasons. During the electroplating process, the in-situ formed nanoparticles well
distributed in the grain boundary areas can decrease the number of defects in the
coating layer, making the coating more compact and less penetrable. Additionally, the

TiO
between the corrosive solution and the coating matrix to some extent [14, 17].
However, when excessive TiO sol (50 mL/L) was added, the coating surface
2
nanoparticles distributed in the coating surface can reduce the contact area
2
exhibited a heavily corroded surface which is even worse than the Ni-B coating. A
large area of coating surface was covered by rusts as shown in Fig. 9c. This can be
mainly ascribed to the nanoparticles agglomeration, which increases the quantity of
defects and lead to a porous structure in the coating, resulting in significant
deterioration of corrosion resistance. Considering the above corrosion results, further
research will be conducted on the duplex coating system in order to further improve
the corrosion and wear resistance [30, 31].
4
. Conclusions
A novel Ni-B-TiO
amount of dimethylamine borane and TiO
2
nano-composite coating was developed by adding a proper
sol into the basic watts electroplating
2
solution. The microhardness has been significantly improved from ~350 HV200 of Ni
coating and ~677 HV200 of Ni-B coating to ~1061 HV200. The corresponding wear
resistance has also been greatly enhanced. The proper amount of TiO
effectively avoid the particle agglomeration, hence, no clear TiO nanoparticles can be
found in sol-enhanced Ni-B-TiO coatings. The highly dispersed TiO nanoparticles
2
sol addition can
2
2
2
can make the coating matrix more compact and decrease the grain size, resulting in a
combination of good particle dispersion strengthening and grain refinement
strengthening. The novel coating presented much better corrosion property than the
Ni-B coating but slightly weaker than pure Ni coating. This new process is based on
the traditional watts solution, and therefore is easy to be used in coating industry. The
improved coatings may find a broader application in aerospace, petrochemical,
seawater desalination and other industries.

Acknowledgments
This paper was sponsored by NPRP Grant NPRP-4-662-2-249 from the Qatar
National Research Fund (a member of Qatar Foundation). The related research was
also supported by a New Zealand Marsden Grant and an Auckland UniServices
project. The authors would like to thank the technical stuff in the Department of
Chemical and Materials Engineering and the Research Centre of Surface and
Materials Science for various assistances. We also want to express our gratitude to
Glen Slater, Chris Goode and technical stuff in Rigg Electroplating Ltd, New Zealand.
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Figure and Table Captions:
Table 1 Bath composition and electroplating parameters
Fig. 1 XRD spectra of sol-enhanced Ni-B-TiO
Fig. 2 Surface morphology and composition analysis: (a) Ni-B and sol-enhanced
nano-composite coating (b) Ni-B-12.5mL/L TiO ,(c) Ni-B-50mL/L TiO
2
nano-composite coatings
2
2
Fig. 3 Cross-section image: (a) Ni-B and (b) sol-enhanced Ni-B-12.5 mL/L TiO
nano-composite coating
2
Fig. 4 Microhardness of sol-enhanced Ni-B-TiO
Fig. 5 Average friction coefficient: (a) Ni-B, and sol-enhanced nano-composite
coating (b) Ni-B-12.5 mL/L TiO , (c) Ni-B-50 mL/L TiO
Fig. 6 Wear track images: (a) Ni-B and sol-enhanced nano-composite coating (b)
Ni-B-12.5mL/L TiO , (c) Ni-B-50mL/L TiO
Fig. 7 Wear volume loss: (a) Ni-B and sol-enhanced nano-composite coating (b)
Ni-B-12.5 mL/L TiO , (c) Ni-B-50 mL/L TiO
Fig. 8 Potentiodynamic polarization curves: (a) Ni, (b) Ni-B, (c) Ni-B-12.5 mL/L
TiO and (d) Ni-B-50 mL/L TiO composite coatings in 3.5% NaCl aqueous solution
2
nano-composite coating
2
2
2
2
2
2
2
2
Fig. 9 Surface morphologies of coatings after salt spray test in 5 wt. % NaCl solution
for 120 h without removing the corrosion products: (a) Ni-B, (b) Ni-B-12.5 mL/L
2 2
TiO coating, and (c) Ni-B-50 mL/L TiO coating.

Table 1 Bath composition and electroplating parameters
Composition and conditions
NiSO
NiCl
BO
DMAB
Stress relieving Additives
TiO Sol concentration
4
-6H
2
O
250 g/L
40 g/L
2
-6H
2
O
H
3
3
35 g/L
3 g/L
Little amount
0-50 mL/L
3.5±0.2
2
PH value
o
45±1 C
Temperature
Agitation speed
Plating time
Current density
400 rpm
30 min
2
50 mA/cm

2
Fig. 1 XRD spectra of sol-enhanced Ni-B-TiO nano-composite coatings

Fig. 2 Surface morphology and composition analysis: (a) Ni-B and sol-enhanced
nano-composite coating (b) Ni-B-12.5mL/L TiO ,(c) Ni-B-50mL/L TiO
2
2

Fig. 3 Cross-section image: (a) Ni-B and (b) sol-enhanced Ni-B-12.5 mL/L TiO
nano-composite coating
2

2
Fig. 4 Microhardness of sol-enhanced Ni-B-TiO nano-composite coating

Fig. 5 Average friction coefficient: (a) Ni-B, and sol-enhanced nano-composite
coating (b) Ni-B-12.5 mL/L TiO , (c) Ni-B-50 mL/L TiO
2
2

Fig. 6 Wear track images: (a) Ni-B and sol-enhanced nano-composite coating (b)
Ni-B-12.5mL/L TiO , (c) Ni-B-50mL/L TiO
2
2

Fig. 7 Wear volume loss: (a) Ni-B and sol-enhanced nano-composite coating (b)
Ni-B-12.5 mL/L TiO , (c) Ni-B-50 mL/L TiO
2
2

Fig. 8 Potentiodynamic polarization curves: (a) Ni, (b) Ni-B, (c) Ni-B-12.5 mL/L
TiO and (d) Ni-B-50 mL/L TiO composite coatings in 3.5% NaCl aqueous solution
2
2

Fig. 9 Surface morphologies of coatings after salt spray test in 5 wt. % NaCl
solution for 120 h without removing the corrosion products: (a) Ni-B, (b)
2 2
Ni-B-12.5 mL/L TiO coating, and (c) Ni-B-50 mL/L TiO coating.

Highlights
A novel Ni-B-TiO
2
nano-composite coating was developed based on the watts
solution.
2
Highly dispersed Ni-B-TiO nano-composite coating was in-situ electrodeposited.
The mechanical property of this novel coating has been significantly improved.
This new process is easy to be used in coating industry.