-
ukeyrkey
maplre
outly pnie cugenhepacity. Detailed tribological tests and
characterization showed that DC- and PC-
ly usedation, lhas berrent (ell asine ma
into the electroplatedss/strength, toughness,[30,31]. Under
identi-idiamond composite
Surface & Coatings Technology 258 (2014) 12021211
Contents lists available at ScienceDirect
Surface & Coatin
l seposition of nanocomposite coatings has mainly been focused
on deter-mining the optimum conditions for production: electrolysis
conditions(composition of the electrolytic bath, presence of
additives, pH value)
(611 Hv) is reported to be higher than that of a DC-plated
composite(540 Hv) [32]. The PC-plated NiPSiC composite was also
reported topossess better tribological behavior than the DC-plated
deposit [33].rangeof engineeringapplicationsdue to their
enhancedproperties [812].Oxides, carbides, diamond particles,
nitrides, oxometallates and oil-containing microcapsules have all
been incorporated into a nickel matrixto improve the tribological
properties [1323]. Research on the electrode-
polymers in an electrolytic bath are incorporatedcoating to
improve its properties, such as hardnewear/friction resistance, and
corrosion resistancecal conditions, the microhardness of a
PC-plated Nfor industrial applications dating back to 1970
[1].Composite coatings with incorporating different types of
particles ex-
hibit distinctly improved properties, such as higher hardness,
wear resis-tance and corrosion resistance compared to pure metal or
alloy coatings[27]. Particle-reinforced metal matrix composites
(MMCs) have a wide
period [15]. As a result, PC plating is a promising procedure.
It can controlthe microstructure, composition and properties of
electrodeposits byvarying the electrical parameters [28,29] and
thus, can be used to depositMMC coatings through co-deposition. In
the co-deposition process, ne(micro- and nanoscale) particles of
metal, non-metallic compounds orand current conditions (type of
imposed currendensity) [2227].
Corresponding author. Tel.: +90 380 73140 05; fax:E-mail
address: [email protected] (H. Gl).
http://dx.doi.org/10.1016/j.surfcoat.2014.07.0020257-8972/ 2014
Elsevier B.V. All rights reserved.terials. Electrodepositionase
particles dispersedjective of investigations
than large grains, as in bubble coalescence. Additionally,
metals deposit-ed by the PC technique have less absorbed hydrogen
than those pro-duced using a continuous current due to desorption
during the offof composite coatings containing second phthroughout
the metal matrix has been the ob1. Introduction
Electrolytic co-deposition is widecomposites due to its ease of
preparOver the past decade and a half, thereconcentrated on
conventional direct cuplating and electroless plating, as
wdeposition processing for nanocrystallto obtain metal
matrixow-cost and versatility.en an extensive researchDC)
electroplating, pulseon production-scale co-
Pulse current (PC) plating is an established method of
electrodepos-iting metals and alloys that signicantly affects the
mechanism ofmetal crystallization. The pulse parameters (such as
peak current densi-ty, duty cycle and frequency) can control the
adsorption or desorption ofa species in the electrolyte and the
surface diffusion in more ways thanDC plating. During the off
period, small grains re-crystallize becausetheir high surface
energy makes them less thermodynamically stablet and values of the
current The purpose onanoscale Al2O3sults with our prwere deposited
bPC method was
+90 380 731 31 24. 2014 Elsevier B.V. All rights reserved.Wear
mechanisms coated nanocomposite layers yielded different wear
mechanisms depending on the sliding velocity.Friction
coefcientSurface damage its increased load bearing caEffect of PC
electrodeposition on the structof NiAl2O3 nanocomposite
coatings
H. Gl a,, M. Uysal b, H. Akbulut b, A. Alp b
a Duzce University, Gumusova Vocational School, Department of
Metallurgy, 81850 Duzce, Turb Sakarya University, Department of
Metallurgical & Materials Engineering, 54187 Sakarya, Tu
a b s t r a c ta r t i c l e i n f o
Article history:Received 6 November 2013Accepted in revised form
1 July 2014Available online 9 July 2014
Keywords:Nano-compositePC and DC electro co-depositionWear
resistance
In this study, NiAl2O3metaltrolyte by pulse current (PC)tests
were performed with aThe wear tests were carriedcomparedwith our
previoustrodepositionmethod can sigposite coatings. For the
samparticle content, more homoproved friction coefcients. T
j ourna l homepage: www.ere and tribological behavior
trix composite (MMC) coatingswere prepared from amodiedWatt's
type elec-ating under current densities varying between 1 and 9
A/dm2. The tribologicalciprocating ball-on-disk apparatus sliding
against a M50 steel ball ( 10 mm).at sliding velocities of 50, 100
and 150 mm/s under a constant load. The resultsublishedwork of DC
electrodeposited coatings. The results showed that the elec-cantly
affect themicrostructure and tribological behavior of NiAl2O3
nanocom-rrent density, PC electrodeposition creates coatings with
higher co-depositedous particle distribution, higher wear
resistance at high sliding distance and im-superior dispersion of
Al2O3 nanoparticles in PC-coatedmaterials contributed to
gs Technology
v ie r .com/ locate /sur fcoatf this study is to co-deposit a
layer of soft Ni and hardceramic particles by PC plating and to
compare the re-eviously published work in which [27], the coatingsy
DC method with same current densities. Since thesuggested to
increase deposited particle content and
Administrator
Administrator
Administrator
Administrator
Administrator
Administrator
Administrator
Administrator
-
to provide better distribution, it was assumed to determine the
opti-mum experimental conditions to obtain best wear resistance,
frictioncoefcient, hardness, etc. Although there are several
studies on thewear of NiAl2O3 nanocomposite coatings and numerous
reports onDC and PC electrodeposition of metals and alloys, to the
best of ourknowledge, there is no a comprehensive work to
investigate the effectof current density between DC and PC plating
techniques on the tribo-logical behaviors of NiAl2O3 nanocomposite
coatings at differentsliding velocities. In the present work, Ni
matrix composite coatingscontaining nanoscale Al2O3 particles were
prepared using a pulseplating procedure to study their
microstructure and tribological perfor-mance. The effect of current
density, and thus the co-deposited percent-age and distribution of
Al2O3 nanoparticles, on the microstructure andthe subsequent wear
performance of both DC- and PC-coated materials
domly chosen areas and then average particle volume percent was
cal-culated. A Rigaku D/MAX/2200/PC model device was used for
X-ray
1203H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211analysis at a speed of 1/min over a range of 20100. The
coating hard-ness was measured with a Vickers microhardness
indenter (Leica
Table 1Bath and electrodeposition conditions for nano-Al2O3
reinforced MMC production.
Nickel sulfate (Ni2SO46H2O) (g/l) 300Nickel chloride (NiCl26H2O)
(g/l) 50Boric acid (H3BO3) (g/l) 40Sodium dodecyl sulfate (g/l)
0.1Hexadecylpyridinium bromide (HPB) (mg/l) 200Alumina (Al2O3)
(g/l) 20pH 4Temperature (C) 45Current density (A/dm2) 1, 3, 6 and
9Current typeDuty cyclePulse frequency
PC50%50 Hz
Plating time (h) 2were compared using reciprocating ball-on-disk
tests under differentsliding speeds.
2. Experimental procedure
The plating electrolyte used for electrodeposition of the
nanoparticle-reinforcedMMCswas aWatt's-type bath. The bath
composition and elec-trodeposition conditions are shown in Table 1.
These experimental pa-rameters were obtained by carrying out
several studies to optimize(surfactant content, current density,
Al2O3 content in the electrolyte andstirring speed, etc.) the
values before attempting to compare the micro-structure and wear
characteristics of DC- and PC-electroplated coatings.The average
particle size of the -Al2O3 used for the reinforcing phasewas 80
nm. Several experiments were conducted to determine the suf-cient
amount of surfactant to create a colloidal electrolyte. For this
pur-pose, prior to deposition, 5 different measurements were
carried out fordetermining the zeta potentials of the
nanoparticle-suspended solutionswith a Malvern Zetasizer Nano
Series Nano-ZS.
In the electrodeposition experiments, four different current
densi-ties, 1, 3, 6 and 9 A/dm2, were studied to determine the
optimum condi-tions for obtaining a homogeneousmicrostructure,
thusmaximizing theimprovement of wear resistance by pulse
electrodeposition method.The experimental results obtained from our
previous DC coated coat-ings were used for comparison with PC
method. Plating time was keptconstant at 2 h for each
electroplating run. Before deposition, substrateswere polished with
600 mesh emery paper. Al2O3 nanoparticles weredispersed into the
plating bath electrolyte by stirring magnetically for20 h and then
treated in a high frequency homogenizator for 0.5 h.
Mi-crostructural investigations were performed with a JEOL-JSM
6060LVinstrument. The particle volume percent were calculated
directly fromthe 6060LV SEM image analysis program, which was based
on phaseareamethod. Themeasurementswere carried out from10different
ran-VMHT) and a load of 50 g for 15 s. At least 5 measurements were
con-ducted on each sample and the results were averaged.
Wear and friction testswere performedwith a reciprocating
ball-on-disk CSM tribometer in accordance with DIN 50324 and
ASTMG99-95astandards at room temperature and at 5565% relative
humidity underdry sliding conditions. The counterpart was a M50
steel ball ( 10 mm)with a hardness of 62 Rc. The system measures
the friction coefcientand time-dependent depth proles using
sensitive transducers. Thedepth transducer was located vertically
on top of the sample. The testswere performed at a constant applied
load of 1.0 N at sliding speeds of50, 100 and 150 mm/s. After each
test, the amount of wear on the com-posite was calculated by
measuring the wear width and depth using a3D surface proler (KLA
Tencor P6) and low magnication optical mi-crographs. These
measurements were also compared with the verticaltransducer depth
proles, and thus, the wear rate of the compositeand the steel ball
was determined. Lattice distortion and grain size ofthe Ni matrix
were determined by calculating the lattice constantsusing basic
reections from the crystal planes.
3. Results and discussions
3.1. Effect of current density on deposition
Figs. 1 and 2 show the effect of current density on the volume
per-centage of Al2O3 in the deposited layers. The microstructures
in Fig. 1show cross-sections of DC and PC co-deposited
nanocompositeswhere-as, Fig. 2 presents the relationship between
current type and currentdensity on the co-deposited Al2O3 content.
The microstructures pro-duced by PC electrodeposition, shown in
Fig. 1, exhibit more homoge-neous particle distribution than those
produced by the DC method.Similar results were reported by
different researchers and explainedby less agglomerated
nano-ceramic particles in the case of PC currentapplication [34].
During the Ton time the applied pulse current resultedin a high
driving force to tend the ceramic particles to adsorb on thecathode
surface. However, during the Toff time the loosely
adsorbednano-Al2O3 particles de-attached from the agglomerated
state andmoved into the electrolyte. The volume percentage of Al2O3
in the DC-plated coatings increased signicantly with current
densities up to3.0 A/dm2 (approximately 9 vol.%). Above 3.0 A/dm2,
there was nomeasureable particle content increase in the deposited
layer (shownin Figs. 1 and 2a). This maximum in the current density
versus Al2O3volume percentage curve can be attributed to the
transition fromactivation-controlled metal deposition to
diffusion-controlled particletransfer [27]. As shown in Fig. 2a,
for PC electrodeposition, however,the co-deposited particle content
increased linearly with current densi-ty. It has been reported that
PC coating is a more efcient depositionprocess for nanocrystalline
NiAl2O3 composite coatings than that ofDC deposition and that it
produces less agglomeration of the aluminananoparticles embedded in
nanocrystalline Ni matrix [28].
The application of PC technique results in the production of
compos-ite coatings with higher percentages of incorporation, and a
more uni-form distribution of ceramic particles in the Ni matrix
than thoseattained under DC regime [35]. The reason can be
explained in termsof electro recrystallization. Electro
crystallization occurs via two com-peting processes (i.e. the
buildup of existing crystals and the formationof new ones) which
are inuenced by different factors. The major rate-determining steps
have been revealed to be charge transfer at the elec-trode surface
and surface diffusion of adions on the crystal surface. Graingrowth
is favored at low current density and high surface diffusionrates,
while high current density (overpotential) and low surface
diffu-sion rates promote the formation of new nuclei. If the
average currentdensity is similar, PC plating can satisfy the
latter two requirementssince it permits considerably higher
overpotentials than the limitingDC current density [36]. However,
in the current work the peak currentdensities in the PC technique
were chosen as equal with the current
densities in the DC technique. Since the duty cycle in the PC
technique
Administrator
Administrator
-
DC
PC
part
1204 H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211was 50%, this causes to apply lower current densities
during theelectroplating compared with DC technique. Because of
this reason,surface diffusion rate in the presence of PC is
decreasing and causes toobtain coarser Ni grains. Therefore, the
nucleation and growth mecha-nisms become surface diffusion dominant
deposition [34]. On theother hand, in the PC technique, during the
T the applied similar cur-
a) 1 A/dm2 DC b) 3 A/dm2
e) 3 A/dm2 d) 1 A/dm2 PC
Fig. 1.Cross sectional SEMmicrographsofMMCco-depositions
showingdistribution of Al2O3PC, e) 3 A/dm2 PC and f) 9 A/dm2
PC.on
rent density PC provides more powerful effect to transfer the
Al2O3 par-ticle through cathode. Therefore, at the Ton peak density
applicationtime, PC permits higher overpotentials and increased
entrapment ofthe Al2O3 particles [37]. The decrease in the
concentration gradient intheDCmethodprevents to insert into cathode
from the electrolyte cath-ode interface, which is a type of Nernst
boundary layer. As it is known,Nernst boundary layer is formed
because of the concentration differ-ence at very close section of
the cathode electrode [38]. In the case ofPC technique, the
negative effect of the Nernst boundary layer againstnano-particle
entrapment on the cathode can easily be overcome.Therefore, similar
results reported by many researchers about advan-tages of using PC
technique. Karathanasis et al. [39] reported thatthere is a strong
dependence of the percentage of the embedded parti-cles on the type
of the applied current for composite coatings and theyfound PC is
more dominant than DC technique. In our present study,specically
the imposition of the PC regime leads to higher incorpora-tion
percentage of particles compared to DC condition. Therefore,
itseems that there is a proper combination of Ton and Toff at a
givenduty cycle of 50%, which permits a sufcient replenishment of
thecatholyte enriched in particles during Toff and adequate
depositiontime Ton that allows the total engulfment of particles in
the matrix. Ad-ditionally, Sheu et al. [37] also showed that pulse
plating leads to higherco-deposition percentage of particles
compared to DC, regardless of thecurrent density. This could be
associatedwith prolonged relaxation timeToff that permits a
satisfactory replenishment of Al2O3 particles in thecatholyte and
therefore, leads to the increase in the particle incorpora-tion in
the matrix.
Fig. 2b compares the XRD patterns of selected nanocomposites
cre-ated by both current types at 9 A/dm2. These XRD results agree
withthe SEM microstructures and quantitative analysis; the
nano-Al2O3content is increased with PC electrodeposition.
Co-deposition of Al2O3also affected the relative intensity of
certain crystal planes in the XRDpatterns. An unreinforcedNi
coating, deposited for comparison, exhibit-ed preferential growth
along the (111) crystal plane. The growth orien-tations of
co-depositedNiAl2O3 composite coatingswere not randomlyoriented for
both DC and PC coated materials. For DC-deposited nano-
c) 9 A/dm2 DC
f) 9 A/dm2 PC
icles coatedwith currentdensities; a) 1A/dm2DC, b) 3A/dm2DC, c)
9A/dm2DC, d) 1A/dm2composite coatings, the (220) peak was faint,
and the (311) peak be-came stronger with increasing Al2O3 content.
The dominant planes are(111) and (200) for Ni in the DC coated
materials and it seems thatthe DC deposit exhibits a mixed [211] +
[100] orientation, with amore profound [211] orientation. zkan et
al. [40] and Sohrabi et al.[41] reported the same results that,
introducing the nano-ceramicparticles into the Ni coatings promoted
to obtain high intensity (111)diffraction lines and thus,
dispersion at the [211] direction. We havepreviously reported that
the XRD patterns of nickel nanocompositecoatings reect textural
changes dependent on the particle content ofthe deposited layer
[27]. The crystallographic orientation of the PC-deposited coatings
was somewhat different from that of the DC-coated samples. The
PC-deposited nanocomposites exhibited obviouspreference for the
(200) and (111) planes. This comprise the PC depositexhibits a
mixed [100] + [211] orientation with a more profound[100]
orientation. PC deposition is seen to produce a preferred
orienta-tion more easily than DC deposition. This provides evidence
that PCcoating provided preferential texture and the nano-Ni grains
in the PCtechnique grown through the (200). Since the PC technique
providedhigher preferential nucleation and growth along the (200)
comparedwith DC technique, PC technique yielded coarser Ni
grains.
High frequency effect can be an alternative reason to obtain
coarsegrains in the PC coatedmaterials. According to the
experimental resultsfrom the work of Lajevardi and Shahrabi [42],
the [100] orientation be-comes dominantwhen the frequency is
decreased. They can only obtainthat at the frequency level of 100
Hz, the (200) line produced very lowintensity. Since the applied
frequency in this study is 50 Hz, we have at-tributed that the high
orientation at [100] direction for PC coated mate-rials can be
another reason. On the other side, Kollia and Spyrellis [43]have
investigated the effect of pulse parameters on the textural and
-
particles' surface charge by absorbed molecules or ions, thereby
pro-moting electrophoretic migration of the suspended
particles.
3.2. Microhardness of composite coatings
Fig. 3 compares the microhardness of unreinforced Ni and
NiAl2O3composite coatings produced by both DC and PC methods. The
micro-hardness generally increased with nanoparticle content. This
increaseis related to the dispersion hardening effect; the presence
of Al2O3nanoparticles obstructs the movement of dislocations in the
nickel ma-trix [44]. From Fig. 3, it can be seen that the
microhardness of NiAl2O3nanocomposite coatings created with both DC
and PC methods was
1205H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211% V
ol. A
l2O
3 in
coat
ings
0
3
6
9
12
15
18PCDCa)
20 g/l Al2O3200 mg/l HPBmicrostructural modications of the
nickel electrodeposits. Based ontheir results, they deduced that at
high duty cycles [211] is the preferredorientation and decreasing
the duty cycle resulted in [100] orientation.
To ease the comparison of microstructural and tribological
analytics,the same electrolyte was used for both the PC and
DCmethods. As seenin Fig. 2c, the zeta potential of the electrolyte
is very close to 0mVwhen100 mg/l HPB is added to the electrolyte.
Any additional surfactant be-yond the baseline 100 mg/l would
increase the zeta potential. It isknown that a high positive or
negative zeta potential is critical forsuspending nanoparticles and
preventing agglomeration during elec-trodeposition.Other authors
studying electrodeposition indifferent sys-tems reported similar
results. For example, Chen et al. [6] demonstratedthat enhanced
deposition results are associatedwithmodication of the
higher than that of the pure Ni coating and increased with
increasingnano-Al2O3 content. There are three reasons behind this
increase [14,18,24,27]: particle strengthening, dispersion
strengthening and grainrening. Particle strengthening is related to
the incorporation of hardparticles at a volume percent above 20%.
Dispersion strengthening is as-
Current Density (A/dm2)1 3 6 9
b)
Concentration of surfactant (HPB) (mg/l)0 100 200 300 400
Zeta
Pot
entia
l (m
V)
-30
-20
-10
0
10
20
30
c)
Fig. 2. a) The volume percentage of co-deposited Al2O3 particles
in various current densi-ties for each current type, b) XRD
patterns of composite coatings producedwith DC and PCcurrent types
at a constant current density (9 A/dm2), and c) the relationship
betweenamount of surfactant and zeta potential.sociated with the
incorporation of ne particles (b1 m) at a volumefraction less than
15%; thematrix carries the load while the small parti-cles hinder
dislocationmotion. The thirdmechanism involves thenucle-ation of
small grains on the surface of incorporated particles, resulting
ina general structural renement. The presence of these smaller
grainsimpedes dislocation motion and increases microhardness. The
resultsobserved in this study can be explained by the second and
third mech-anisms. The ne particles incorporatedwithin the Nimatrix
restrain thegrowth of Ni crystals and impede the motion of
dislocations by way ofgrain rening and dispersive-strengthening
effects.
In general, the hardness of coatings produced by DC deposition
im-proved less than that produced by PC deposition. As discussed
before,PC-deposited coatings containmore reinforcing nanoparticles;
thus, im-proved hardness seems to be due to the increased
concentration of thereinforcing hard particles in the coatings. The
increase in hardness ob-served in PC-deposited coatings, however,
is not as high as the increasednanoparticle content in such
coatings would lead us to expect. This re-sult can be attributed to
the smaller Ni matrix grain size and randomcrystallographic
orientation in DC-deposited coatings.
3.3. Grain size and lattice distortion of composite coatings
The matrix grain sizes of nanocomposites deposited via both
DC(studied previously) and PC methods were calculated from the
XRDdata using Scherer's formula [27]. Fig. 4 shows the effect of
current den-sity on thematrix grain size for the DC and PCmethods.
Fig. 4 clearly in-dicates that the Ni grains were smaller in DC-
than in PC-depositedcoatings. Although the electro co-deposited
particle content was higherin the PC-coatedmaterials and matrix
grains are expected to be renedby such an increase in particle
content, the DC method yielded ner
Current Density (A/dm2)
Mic
roha
rdne
ss (H
v)
200
300
400
500
600
700DCPC
Ni 1 3 6 9
Fig. 3. Effect of current density on microhardness produced with
direct and pulse current
composite coatings.
-
by lattice parameter mismatch at the coating and substrate
interface,(2) thermal stresses arising from differing thermal
expansion coef-cients at the substrate and coating interface, and
(3) residual or intrinsicstress from particular plating conditions
and bath composition.
3.4. Wear and friction properties
3.4.1. Effect of current density on wear and friction
propertiesThe relationships between wear rate and current density
in DC and
PC-plated nanocomposites are illustrated in Fig. 6. Fig. 6a
clearly showsthat increasing current density, resulted in a
signicant decrease in thewear rate for DC-plated nanocomposites.
Increasing sliding speed caused
Fig. 5. Effect of current density on lattice distortion of the
nickel matrix produced with di-rect (a) and pulse current (b)
composite coatings.
1206 H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211matrix grains. This is because the surface diffusion is
dominant in nucle-ation and growth in the PC coating compared with
DC technique [34].Increasing the current density results in
increasing the ner grains.Lajevardi and Shahrabi [42] found that in
the (200) planewhen the cur-rent density increased from 2 A/dm2 to
8 A/dm2 the grain size of Ni wasreduced from 34 nm to 31 nm. The
reason for this decrease in the parti-cle size is due to the
changing of the preferred crystalline orientationand/or embedded
particles content in the coating [42]. Same results re-ported
bymany authors. Beltowska-Lehman et al. [45] reported that
theaddition of larger Al2O3 particles results in a slight decrease
of the aver-age matrix grain size with increasing current density.
The presence ofnano-particles provides more nucleation sites by
increasing the surfacearea of cathode in accordance with perturbing
matrix growth andconsequently results in ner grain size [46]. In
this study, increasingthe current density for both PC and DC caused
to increase the co-deposited particle content and therefore, the
grain size of matrix be-comes to be ner.
The colloidal particles in aqueous solution are in charged
state.Consequently, a charged particle suspended in an electrolyte
solutiontends to be surrounded by an ionic cloud. It was reported
that thenano-ceramic particles could adsorb Ni2+ ions. There are
two types ofspecies that include Ni2+ cations and Ni2+/ceramic
particle clouds inelectrolyte. At high current densities, nickel
ions and Ni2+/Al2O3 are ac-celerated to deposit on the cathode
surface. Thismechanism is valid untilhigh amount of hydrogen
evolution causes a reduction in the current ef-ciency as well as
hindering the adsorption of nanoparticles to themetalsurface
[35].
Lattice distortion of the Ni matrix for both the DC and PC
techniques
Current Density (A/dm2)
Gra
in S
ize
(nm
)
45
50
55
60
65
70
75
80PCDC
1 3 6 9
Fig. 4. Effect of current density on grain size of the nickel
matrix for each current type (di-rect and pulse current).was
calculated using basic reections from the crystal planes as
denedbyMisbah-Ul et al. [47]. The calculated lattice distortions
demonstratedthat the composite matrix lattice constants depend on
current densityand current type, as shown in Fig. 5. Increasing
current density causednegative lattice distortions in the Ni matrix
for both the DC and PCmethods (Fig. 5a and b). In general, these
lattice distortionswere higherin DC- than in PC-deposited coatings.
As previously discussed in theXRD analysis, PC electro
co-deposition does not have a profound effecton the texture and,
therefore, crystallographic orientation. Despite thedecreased (200)
plane intensity, no signicant orientation change wasobserved in
coatings deposited by PC nanoparticle co-deposition. Incontrast, DC
electro co-deposition decreased the intensity of the maincrystal
plane, (200), and increased the intensity of the (111)
plane.Moreover, the intensity of other subsidiary crystal planes
also increasedin the DC method. Therefore, it was inferred that the
DC method exhib-ited smaller matrix grains. The origins of negative
lattice distortion innanoparticle-reinforced MMCs can be summarized
by three types ofstresses, as reported by El-Sherik and co-workers
[48]; these threestresses are (1) lattice mist stresses resulting
from distortion causedsharp increments in the wear rate for the
coatings deposited with DCmethod. As evident from Fig. 6b,
PC-deposited NiAl2O3 composite coat-ings withstood wear better than
DC-deposited coatings, this can be at-tributed to the increased
alumina particle content and homogenousparticle distribution. The
higher Ni matrix grain size is another advanta-geous factor for
increasing wear resistance in the PC coatedmaterials. Asdiscussed
before, increasing the intensity of (002) plane results in
higherductility in the Ni based coatings and this caused to
increase plastic de-formation energy absorbability which prevents
microcrack formationand subsequent delamination. As stated by zkan
et al. [40] increasingthe intensity of the (002) plane deposition
of Ni resulted in the growthin the [100] direction. The combined
high ductility and higher amountof Al2O3 particle content resulted
in better tribological properties provid-ing both resistance to
deformation hardening and load carrying capacity.However,
increasing particle content in the deposited layer with
currentdensity no signicant change observed in the wear rate of
PC-platednanocomposites (Fig. 6b). This was attributed to the
increasing the par-ticle content in the deposited coatings and this
may result in decreasingplastic deformation capability, which
causes to reveal fatigue wear
Administrator
-
causes wear debris formation in the form of delamination
failures,which reveals ne wear debris.
Fig. 7a and b shows the friction coefcient variation in DC- and
PC-plated nanocomposites depending on sliding speed and current
density.In general, it can be concluded that increasing sliding
speed decreasedthe friction coefcient for both DC- and PC-plated
nanocomposite coat-ings. DC and PC-plated nanocomposites have very
similar friction coef-cients for all current densities at sliding
speeds of 100 mm/s and150 mm/s, except in theDC-plated coatings,
small increments in the fric-tion coefcient values have been
observed with increasing current den-sity. The increment in the
friction coefcient in the DC plated coatingscan be explained in
terms of poor interfacial bonding between Ni andAl2O3 when compared
with PC coated materials. The friction coefcientat 50 mm/s,
however, exhibited signicantly different characteristicswith
increasing current density. The friction coefcient for
DC-platedcoatings were extremely high (approximately 0.7) at the 1
A/dm2 and3 A/dm2 current densities. A further increase in the
current density re-sulted in a sharp decrease in the friction
coefcient. In contrast, coef-cients for the PC-plated nanocomposite
coatings remained around0.430.52, and no signicant variation have
been observed by changingthe current density. As stated in the
experimental section, the depositionprocess was carried out with a
constant 200 mg/l surfactant and 20 g/lparticle concentration in
the electrolyte. The interfacial bond betweenAl2O3 nanoparticles
and the Ni matrix is thought to be one of the mostinuential factors
in sliding wear resistance. It is known that PC deposi-tion
provides not only a higher concentration of second phase
nanopar-ticles in the electrodeposited layer but also better
interface propertiesbetween the matrix and ceramic particles [51].
It is also evident from
1207H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211occurred because of microcrack formation. On the other
hand, the effectof sliding speed on thewear rate of PC-produced
composites is more in-teresting and impressive. Increasing sliding
speed in the PC-plated nano-composites resulted in a remarkable
decrease in thewear rate.When thewear rates of DC- and PC-coated
nanocomposites are compared in thecase of 1 A/dm2 current density
deposition condition, remarkably highwear resistance is observed
for the PC-plated nanocomposites. For exam-ple, for the sliding
speed of 150 mm/s, the wear rate was recorded as 17 104 mm3/Nm in
the DC-plated material whereas the wear rate wasmeasured as 2 104
mm3/Nm in the PC-produced nanocomposite.Therefore, thewear rate of
PC-deposited coatingwas found to be approx-imately 8 times lower
than that of DC-plated material for 1 A/dm2 cur-rent density
deposition condition. In the sliding wear, the decrease inthe wear
rate by increasing sliding wear have been observed by
severalauthors, studied in the dry wear conditions [49, 50].
Therefore, the de-crease in the wear rate by increasing the sliding
distance is an expectedfeature in the electrodeposited Ni coatings.
The unusual result here isthe increase in the wear rate with
sliding distance in the DC coated ma-terials. This increase can be
attributed to the insufcient interfacial inter-face bonding and
inhomogeneous distribution of nano-Al2O3 nano-particles in the DC
coated materials that could result in decreasing loadbearing
capacity. As explained and discussed in the microstructure ofthe PC
and DC deposited materials, the entrapment of the
nano-Al2O3particles on the cathode is more effective in the PC
technique sincepulse effect result in overcoming theNernst boundary
layer and providesmore homogenous particle distribution. In the DC
coated layers, the par-ticle de-attachment from the surface during
sliding occurs because of theAl2O3 particle agglomeration.
Increasing sliding speed result in increas-ing the stress
concentration around the agglomerated particles and
our SEM micrographs that PC deposition promotes more
homogenousdistribution and segregation free particle distribution.
Thus, increasingsliding speed caused the wear rate of DC-coated
materials to increase,
Fig. 6. Effect of sliding speed on the wear rate of NiAl2O3
composite coatings preparedwith different current types and
densities, a) DC and b) PC.Fig. 7. Effect of sliding speed on
friction coefcient of NiAl2O3 composite coatings pre-
pared with different current types and densities, a) DC and b)
PC.
-
but PC-coated materials exhibited the opposite; increasing
sliding speeddecreased thewear rate. This result implies that
optimizing the load car-rying capacity depends on tribo-oxide
formation, which governs thewear phenomena and, thus, decreases the
wear rate.
Fig. 8 illustrates theworn surfaces of DC and PC-produced
nanocom-posite samples tested at a sliding speed of 50 mm/s. Fig.
8ac shows themorphology of the worn surfaces of nanocomposite
coatings depositedat different DC current densities. The worn
surface of the 1 A/dm2 DCcoated Ni/Al2O3 nanocomposite sliding
against M50 steel ball is rela-tively smooth but displays a few
debris (Fig. 8a), indicating that thecoating experienced
predominantly adhesive wear character associatedwith fatigue crack.
Increasing current density from 1 A/dm2 to 9 A/dm2
resulted in decrease in the plastic deformation of the coatings
due to theincreased quantity of co-deposited nanoparticles.
Increasing currentdensity also increased the ne debris areas that
are evidence for the de-lamination wear, which occurred because of
microcrack formation. Thenano-particle agglomeration in the DC
coated materials activated tostart micro crack formation and
subsequent delamination with nedebris.
The worn surfaces of the PC-deposited nanocomposites tested at
thesliding speed of 50 mm/s, shown in Fig. 8df. It is evident from
thewornmicrographs, delamination cracks and smeared wear debris
were ob-served, conrming that the wear process of NiAl2O3
composites isgoverned by a combination of abrasion and adhesion
mechanisms.Since the PC coatedmaterials showed coarseNimatrix
grains and prefer-ential growth at (200) plane, there are much more
plastic deformationevidences compared with DC coated materials. At
low current density,theworn surface (Fig. 8d) exhibited
predominantly adhesive wear char-
corresponds to the higher amount of particle co-deposition in
the PCmethod. At high current densities, the discrepancy in
deformation ofthe nanoscale reinforcement phase and the matrix
leads to stress con-centrations at the edges of the reinforcement
phase, fueling the forma-tion of small debris. Thus, increasing the
particle content leads to anincrease in debris (Fig. 8e and f).
In Fig. 9, the surfaces of DC- and PC-produced nanocomposites
wornat the sliding speed of 150 mm/s are presented. The worn
surfaces ofboth DC and PC coatedmaterials showmixed type of
wearmechanismsof adhesive and abrasive. The wear of DC-coated
materials starts withpredominantly abrasive mechanisms and
continues with plastic defor-mation of wear debris leading surface
hardening of smeared ductile Nimatrix; thereafter, followed by
fatigue, which produces very smallwear debris associated with some
particle agglomeration, most likelyby delamination (Fig. 9ac).
Increasing the current density resulted indecreased formation of ne
debris because increased co-deposited par-ticle content increases
the load bearing ability. As seen in Fig. 9df, theworn surfaces of
PC-produced coatings are different from those of DC-coated samples.
Taking into account all the current density conditions,the surfaces
of PC-coated materials were smoother than those of DC-coated
samples. Moreover, signicantly larger quantities of very
smalldebris were detected on PC-coated materials than on DC
samples. ForPC-coated materials, increased current density resulted
in decreasedne debris formation and increased surface smoothness.
As shown inFig. 9df, the worn surfaces of the PC coated Ni/Al2O3
nanocompositessliding against steel ball is not only smooth and
show the signs of slightfatigue and adhesion wear, which indicates
that the coating is slightlydamaged by the counterpart steel
compared with DC coated materials.
ris
t cu
1208 H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211acteristics caused by detachment of the smeared matrix
after plastic de-formation and, later, deformation hardening
(showed with the arrow).The extensive deformation and wear of
samples tested at sliding speedsof 50mm/s is attributed to the low
quantity of co-deposited particles. Ascan be seen from Fig. 8e and
f, increasing the current density leads to de-crease the soft phase
smearing on the worn surfaces and therefore, theamount of plastic
deformation decrease. The width of the abrasivewear scar of the PC
deposited Ni/Al2O3 nanocomposite coating is muchmore higher than
that of the DC deposited Ni/Al2O3 coatings, which
a) 1A/dm2 DC
Abrasive groove
Debris
Deb
Deattachment
b) 3A/dm2 DC
e) 3 A/dm2 PCd) 1 A/dm2 PC
Fig. 8. SEMmorphology of the wear tracks of composite coatings
preparedwith differen2 2 2 2DC, c) 9 A/dm DC d) 1 A/dm PC, e) 3
A/dm PC and f) 9 A/dm PC.As shown in Fig. 9d, some ne plows and
scratches are observed onthe worn surface for the coating deposited
at 1 A/dm2 current density,indicating the abrasive wear also
occurred besides the adhesion and fa-tiguewear. Themixedmode of
wearmechanism in the PC coatedmate-rials is attributed to the
ductile structure of the Nimatrix because of thecoarser grain size
and higher particle co-deposition compared with DCcoated materials.
Homogeneous distribution of the particles resultedin
decreasingmicrocrack formation contrary to the DC
coatedmaterials.Therefore, the worn surfaces of the PC coated
nanocomposites featured
Abrasive groove
MicrocrackMicrocrack c) 9A/dm2 DC
f) 9 A/dm2 PC
rrent types and current densities for 50mm/s sliding speed; a) 1
A/dm2 DC, b) 3 A/dm2
-
fere
1209H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211with less scufng, small plowing and some extend of
abrasion. This re-sult indicates that some polishing took place,
most likely by pull out ofalumina particles or material transfer
during the sliding process. This
2
Abrasive groove
Debrisa) 1A/dm2 DC b) 3A/dm2 DC
e) 3 A/dm2 PCd) 1 A/dm2 PC
Fig. 9. SEM morphology of the wear tracks of composite coatings
prepared with difb) 3 A/dm2 DC, c) 9 A/dm2 DC d) 1 A/dm2 PC, e) 3
A/dm2 PC and f) 9 A/dm2 PC.phenomenonwas also observed byHoua and
Chen [28] in pulse electro-deposited NiW/Al2O3 composite coatings
and was considered whenassessing the increased load bearing
capacity. Because comparativelylower friction coefcients were
obtained for PC-coated samples com-pared with DC-coated
nanocomposite materials by increasing the cur-rent density, another
reason for the surface smoothness could beoxidation, which produces
tribo-oxide layers.
The surfaces of nanocomposites worn out at the sliding speeds
of50 mm/s and 150 mm/s were also analyzed by EDS facility.
Increasingsliding speed in DC-coated materials showed increased
amount of Aland other components transferred from the steel ball.
After the50 mm/s wear test, EDS analysis performed from several
regions alongthe wear scar of DC- and PC-coated materials and
conrmed the ab-sence of signicant oxygen content. This result shows
that the slidingspeed was insufcient to generate heat at the
interface between thesteel ball and nanocomposite surface. The
PC-coated worn surfacesafter the 150 mm/s test exhibited a thick
oxide transfer layer over themajority of the wear scar with the
metallic coating exposed in large lo-calized regions within the
scar. Similar results were also reported byLekka et al. [52]; at
high sliding speeds, Ni-based composite coatingsunderwent
tribo-oxidative wear, and localized EDS analysis revealedthe wear
tracks to be partially covered by a nickel oxide layer (lightgray
zone). The scars along the sliding direction were attributed
tothird body abrasion causedmainly by detachment of nickel oxide
akesthat interpose themselves between the deposit and the counter
materi-al. Since the particle distribution is not homogenous in the
DC coatedmaterials compared with PC produced coatings, the oxidized
regionscan easily undergo delamination crack and the ne wear debris
oc-curred. The delamination in the form of ne debris in the DC
coatedma-terials prevented to form an effective tribo-oxidation
layer.
Fig. 10ac depicts the original diagram of friction coefcient
andsteel ball penetration (wear depth) changes versus sliding
distance inDC- and PC-produced composites tested at different
sliding speeds.For ease of comparison, only the diagrams for
nanocomposites deposit-ed at 3 A/dm2 are presented. As seen from
the diagrams for DC-
Abrasive groove
c) 9A/dm2 DC
f) 9 A/dm2 PC
nt current types and current densities for 150 mm/s sliding
speed; a) 1 A/dm2 DC,produced nanocomposites, increasing sliding
speed decreased the fric-tion coefcient and increased the amount of
wear. Fig. 10b clearlyshows that the steel ball penetration sharply
increased with increasingsliding distance, where the friction
coefcient remained nearly stable byincreasing the sliding distance.
In fact, the continuous increase in wear(ball penetration) with
sliding distance is because of the wear charac-teristics of the
nanocomposite. As stated previously, the predominantwear mechanism
of the DC-coated materials for the 50 mm/s slidingspeed was
delamination caused by rstly, adhesive plastic deformationand
continuing surface hardening and then fatigue that produce
verysmall wear debris. Since poor homogeneous distribution of
nano-Al2O3 particles were produced in the DC method composite
coatings ahigh wear rate obtained compared with PC method coated
nanocom-posites tested under similar conditions. The PC deposited
nanocompos-ite tested at 50 mm/s sliding speed, exhibit the high
friction coefcientsince the smeared wear debris and a combining
effect of abrasion andadhesion mechanisms. Increasing the sliding
speed, the surfaces of thePC coated materials revealed smooth
nature because of oxidation ofthe matrix phase leading signicant
decrease in the friction coefcient.Therefore, this decrease at the
high sling speeds was attributed to thetribo-oxides formation on
the worn surfaces and surface smoothnesscombined with good load
bearing capacity in the PC produced nano-coatings.
To reveal and make a better comparison between the wear
mecha-nisms of the DC and PC coatedmaterials some selected worn
nanocom-posite surfaces were scanned with 3D prolometry. The
results arepresented in Fig. 11. For brevity, only the
nanocomposites tested at50 mm/s are chosen. It can be seen from
Fig. 10a which represents theworn surface of the DC plated
composite produced at 1.0 A/dm2 thatthere is a very rough surface
and that a severe surface damage occurred,revealing a large, deep
valley. The rough surface is evidence that signif-icant amounts of
wear products were smeared on the surface, including
-
a) 3A/dm2 DC/50mm/s b) 3A/dm2 DC/150 mm/s
in d
1210 H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211c) 3A/dm2 PC/50 mm/s
Fig. 10. Variation of friction coefcient and wear track depth
for NiAl2O3 nanocomposites150 mm/s.agglomerated Al2O3
nano-particles (Fig. 11a). In the case of PC coatedworn surface a
very smooth surface was obtained (Fig. 11b). Increasingcurrent
density resulted in decreasing, smearing and scufng on thewear
surface. It is probably because of increasing particle content
inthe deposited layer made possible by the increasing current
density inDC method (Fig. 11c). Applying PC deposited samples with
a currentdensity of 9.0 A/dm2 yielded a smoother surface and fewer
protrudedareas than the sample produced by DC plating. These
results also
Fig. 11. 3D prolometry results of composite coatings
preparedwith different current types andDC d) 9 A/dm2 PC.d) 3A/dm2
PC/150 mm/s
ifferent sliding speeds: (a) DC, 50 mm/s; (b) DC, 150 mm/s; (c)
PC, 50 mm/s; and (d) PC,prove that PC plating produces better
interfaces between nanocompos-ite constituents and results in
better tribological behavior (Fig. 11d).
4. Conclusions
Several electrodepositedNiAl2O3 nanocomposite coatingswere
pre-pared by DC and PC electrodeposition methods with the same
currentdensity and similar experimental parameters. A detailed
comparison
current densities andwear tested at 150 mm/s; a) 1 A/dm2 DC, b)
1 A/dm2 PC, c) 9 A/dm2
-
revealed the effect of electrodeposition method and current
density onthe co-deposited nanoparticle content, particle
distribution, matrix mi-crostructure, hardness, wear rate and
friction coefcient. The followingconclusions can be drawn from this
study:
1. Nanocomposites produced with PC electrodeposition contain
higherquantities of Al2O3 nanoparticles and more homogeneous
particledistribution than those produced with DC deposition. At a
currentdensity of 9.0 A/dm2, the volume percent of Al2O3 was found
to be8.81% and 12.7% for DC and PC deposition, respectively.
2. The microhardness of the coatings increased with dispersed
nano-particle content. The nano-Al2O3 reinforced electrodeposited
coat-ings yielded hardness values as high as 641 Hv with the DC
methodand 656 Hv with the PC plating method.
3. Increasing current density decreased the wear rate in
DC-platednanocomposites. However, increasing current density did
not showsignicant change in the wear rate of PC-plated
nanocomposites.
4. Increasing sliding speed in DC-plated nanocomposite materials
in-creased their wear rate. Contrary to the DC-plated
nanocomposites,increasing sliding speed resulted in a remarkable
decrease in thewear rate of PC-plated materials and decreased the
friction coef-cient for both DC- and PC-plated materials.
Acknowledgments
[12] M. Surender, B. Basu, R. Balasubramaniam, Trib. Int. 37
(2004) 743749.[13] B. Szczygie, M. Koodziej, Electrochim. Acta 50
(2005) 41884195.[14] T. Lampke, B.Wielage, D. Dietrich, A. Leopold,
Appl. Surf. Sci. 253 (2006) 23992408.[15] M.D. Ger, Mater. Chem.
Phys. 87 (2004) 6774.[16] F. Hu, K.C. Chan, Mater. Chem. Phys. 99
(2006) 424430.[17] A. Abdel Aal, Z.I. Zaki, Z. Abdel Hamid, Mater.
Sci. Eng. A 447 (2007) 8794.[18] Q. Feng, T. Li, H. Yue, K. Qi, F.
Bai, J. Jin, Appl. Surf. Sci. 254 (2008) 22622268.[19] M.
Stroumbouli, P. Gyftou, E.A. Pavlatou, N. Spyrellis, Surf. &
Coat. Tech. 195 (2005)
325332.[20] C.B. Wang, D.L. Wang, W.X. Chenc, Y.Y. Wang, Wear
253 (2002) 563571.[21] W. Wang, F.Y. Hou, H.i. Wang, H.T. Guo, Scr.
Mater. 53 (2005) 613618.[22] T. Tsubotaa, S. Taniib, T. Ishidab, M.
Nagata, Y. Matsumoto, Diam. Relat. Mater. 14
(2005) 608612.[23] S.A. Lajevardi, T. Shahrabi, J.A. Szpunar,
Appl. Surf. Sci. 279 (2013) 180188.[24] H. Gl, F. Kl, M. Uysal, S.
Aslan, A. Alp, H. Akbulut, Appl. Surf. Sci. 258 (2012)
42604267.[25] E.A. Pavlatou, M. Raptakis, N. Spyrellis, Surf.
& Coat. Tech. 201 (2007) 45714577.[26] P. Gyftou, E.A.
Pavlatou, N. Spyrellis, Appl. Surf. Sci. 254 (2008) 59105916.[27]
H. Gl, F. Kl, S. Aslan, A. Alp, H. Akbulut, Wear 267 (2009)
976990.[28] H. Kung-Hsu, C. Yann-Cheng, Applied Surf. Sci. 257
(2011) 63406346.[29] D. Landolt, A. Marlot, Surf. Coat. Technol. 8
(2003) 169170.[30] C.T.J. Low, R.G.A. Wills, F.C. Walsh, Surf.
Coat. Technol. 201 (2006) 371383.[31] B. Tushar, S.P. Harimkar,
Surf. Coat. Technol. 205 (2011) 41244134.[32] H.W. Lee, S.-C. Tang,
K.-C. Chung, Surf. Coat. Technol. 120121 (1999) 607.[33] K.H. Hou,
W.H. Hwu, S.T. Ke, M.D. Ger, Mater. Chem. Phys. 100 (2006)
5459.[34] S.R. Allahkaram, S. Golroh,M.Mohammadalipour,Mater. Des.
32 (2011) 44784484.[35] V. Zarghami, M. Ghorbani, J. Alloys Compd.
598 (2014) 236242.[36] A.F. Zimmermann, D.G. Clark, K.T. Aust, U.
Erb, Mater. Lett. 52 (2002) 8590.[37] H.H. Sheu, P.C. Huang, L.C.
Tsai, K.H. Hou, Surf. Coat. Technol. 235 (2013).[38] J.H. Choi,
J.S. Park, S.H. Moon, J. Coll. Inter. Sci. 251 (2002) 311317.[39]
A.Z. Karathanasis, E.A. Pavlatou, N. Spyrellis, Electrochim. Acta
54 (2009) 25632570
(529535).[40] S. zkan, G. Hap, G. Orhan, K. Kazmanl, Surf. Coat.
Technol. 232 (2013) 734741.[41] A. Sohrabi, A. Dolati, M. Ghorbani,
A. Monfared, P. Stroeve, Mater. Chem. Phys. 121
1211H. Gl et al. / Surface & Coatings Technology 258 (2014)
12021211This work is supported by the Scientic and Technical
ResearchCouncil of Turkey (TUBITAK) under contract number 106M253.
The au-thors thank the TUBITAK MAG workers for their nancial
support.
References
[1] Y.S. Dong, P.H. Lin, H.X. Wang, Surf. Coat. Technol. 200
(2006) 36333636.[2] M.R. Vaezi, S.K. Sadrnezhaad, L. Nikzad,
Colloids Surf. A Physicochem. Eng. Asp. 315
(2008) 176182.[3] S.T. Aruna, V.K. William Grips, K.S. Rajam, J.
Alloys Compd. 468 (2009) 546552.[4] K.H. Hou, M.D. Ger, L.M. Wang,
S.T. Ke, Wear 253 (2002) 9941003.[5] S.C. Wang, W.C.J. Wei, Mater.
Chem. Phys. 78 (2003) 574580.[6] L. Chen, L. Wang, Z. Zeng, J.
Zhang, Mater. Sci. Eng. A 434 (2006) 319325.[7] S.A. Lajevardi, T.
Shahrabi, J.A. Szpunar, A. Sabour Rouhaghdam, S. Sanjabi, Surf.
Coat.
Technol. 232 (2013) 851859.[8] L. Wang, Y. Gao, H. Liu, Q. Xue,
T. Xu, Surf. & Coat. Tech. 191 (2005) 16.[9] L. Chen, L. Wang,
Z. Zeng, T. Xu, Surf. & Coat. Tech. 201 (2006) 599605.
[10] N.K. Shrestha, T. Takebe, T. Saji, Diam. Relat. Mater. 15
(2006) 15701575.[11] D.J. Riley, Curr. Opin. Colloid Interface Sci.
7 (2002) 186192.(2010) 497505.[42] S.A. Lajevardi, T. Shahrabi,
Appl. Surf. Sci. 256 (2010) 67756781.[43] C. Kollia, N. Spyrellis,
J. Appl. Electrochem. 20 (1990) 10251032.[44] G. Wu, N. Li, D.
Zhou, K. Mitsuo, Surf. Coat. Technol. 176 (2004) 157164.[45] E.
Beltowska-Lehman, P. Indyka, A. Bigos, M. Kot, L. Tarkowski, Surf.
Coat. Technol.
211 (2012) 6266.[46] I. Gurrappa, L. Binder, Sci. Technol. Adv.
Mater. 9 (2008) 4354.[47] I. Misbah-Ul, K.A. Hashmi, M.U. Rana, T.
Abbas, Solid State Commun. 121 (2002)
5154.[48] A.M. El-Sherik, J. Shirokoff, U. Erb, J. Alloys Compd.
389 (2005) 140143.[49] R.A. Al-Samarai, K. Rafezi Ahmad, Y.
Al-Douri, Int. J. Sci. Res. Publ. 2 (2012).[50] A.M. AI-Qutub, I.M.
Allam, M.A. Abdul Samad, J. Mater. Sci. 43 (2008) 57975803.[51]
A.Z. Karathanasis, E.A. Pavlatou, N. Spyrellis, J. Alloys and Comp
494 (2010)
396403.[52] M. Lekka, A. Lanzutti, A. Casagrande, C. Leitenburg,
P.L. Bonora, L. Fedrizzi, Surf. Coat.
Technol. 206 (2012) 36583665.
Effect of PC electrodeposition on the structure and tribological
behavior of NiAl2O3 nanocomposite coatings1. Introduction2.
Experimental procedure3. Results and discussions3.1. Effect of
current density on deposition3.2. Microhardness of composite
coatings3.3. Grain size and lattice distortion of composite
coatings3.4. Wear and friction properties3.4.1. Effect of current
density on wear and friction properties
4. ConclusionsAcknowledgmentsReferences