Synergistic effect in nickel-Teflon composite electrolytic coatings

Article abstract of DOI:10.1134/S1070427208120252

The possible synergistic effect in the manifestation of the wear resistance and antifriction properties of nickel-Teflon composite electrolytic coatings was analyzed. The results of calculations of the diagnostic properties of the coatings in terms of the

Full text of DOI:10.1134/S1070427208120252

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2008, Vol. 81, No. 12, pp. 2169–2171. © Pleiades Publishing, Ltd., 2008.
Original Russian Text © V.V. Ivanov, V.I. Balakai, N.Yu. Kurnakova, A.V. Arzumanova, I.V. Balakai, 2008, published in Zhurnal Prikladnoi Khimii, 2008,
Vol. 81, No. 12, pp. 2059–2061.
BRIEF
COMMUNICATIONS
Synergistic Effect in Nickel–Teflon Composite
Electrolytic Coatings
V. V. Ivanov, V. I. Balakai, N. Yu. Kurnakova, A. V. Arzumanova, and I. V. Balakai
South-Russian State Technical University (Novocherkassk Polytechnic Institute), Novocherkassk,
Rostov oblast, Russia
Received March 25, 2008
Abstract—The possible synergistic effect in the manifestation of the wear resistance and antifriction properties
of nickel–Teflon composite electrolytic coatings was analyzed. The results of calculations of the diagnostic
properties of the coatings in terms of the “concentration-wave” model are discussed in comparison with the
corresponding experimental data.
DOI: 10.1134/S1070427208120252
It is well known [1] that nickel–boron–Teflon
composite electrolytic coatings (CECs) exhibit a syner-
gistic effect: Their wear resistance and antifriction
properties are better than those calculated in terms of
the additive model. The synergism of the solid and
lubricating components consists in that the lubricating
Teflon phase is concentrated on the friction surface,
thus enhancing the antifriction characteristics and wear
resistance of the solid phases of the coatings, and that
the coatings contain nanoparticles of certain solid phases
(probably borides Ni3B and Ni2B). These nanoparticles
have a spherical or cylindrical shape with a cross section
diameter of 1.2–2.5 nm; they apparently exhibit the prop-
erties of solid lubricants [1].
f 0 = α<f 0solid> + (1 – α)<f 0
>
lub
– δ(<f 0solid> – <f 0lub>),
(2)
where α = αsolid and (1 – α) = αlub are the volume frac-
tions of the solid and lubricating components of CEC,
respectively; δ = 4(1 – α)α2[1 – k(1 – kn)], relative syn-
ergistic effect; k, size parameter characterizing the dis-
persity of the solid component of CEC: the ratio be-
tween the mean size of microparticles rsolid of solid phases
in the surface later and the thickness of this layer Δx,
i.e., k = rsolid (rsolid + Δx)–1 (at rsolid → Δx k → 0.5); kn,
nanostructure parameter of the solid component of
CEC: the volume fraction of solid phase nanoparticles
of spherical or cylindrical shape in the surface layer Δx
(0 ≤ kn < 1); <I0lin, solid>, <f 0solid>, <I0lin, lub>, and <f 0lub
are the mean values of the corresponding individual
characteristics in the solid and lubricating components
of CEC [2].
>
To verify the assumption that nanoparticles of
only low-boron nickel phases contribute to the overall
synergistic effect observed with nickel–boron–Teflon
CECs, we examined boron-free nickel–Teflon CECs.
In this case, the possible synergism would be exclu-
sively due to the first factor, concentration of Teflon
microparticles on the friction surface.
The calculated data for the linear wear I0lin and fric-
tion coefficient f 0 of nickel–Teflon CECs in the CEC/
CEC friction couple were obtained within the two-
component approximation of the “concentration-wave”
model [2] by the formulas:
In accordance with the data of Kryachko et al. [3],
the influence of the characteristics of counterbody
(CB) material (St45 steel in our case) on the CEC
properties was taken into account as follows:
Ilin = I0 + (Δα – Δδ)(I0solid – I0lub) + (α + δ)(ΙCB – I0solid ), (3)
f = f 0 + (Δα – Δδ)( f 0solid – f 0lub) + (α + δ)( fCB – f 0solid ), (4)
I0lin = α<I0lin, solid> + (1 – α)<I0lin, lub
+ δ(<I0lin, solid> – <I0lin, lub>),
>
where Δδ ≅ 2α(3α – 2)Δα is the change in the rela-
tive synergistic effect [3]; Δα = α* ≅ (αI0solid + ICB)×
(1)
2169

2170
IVANOV et al.
Table 1. Phase composition and concentration of components of composite coatings
Weight fraction
Volume fraction
Coating
CEC component
Solid
Lubricating
Solid
Lubricating
Solid
Phase composition
α
%
Ni
Ni–Teflon
Ni
–
Ni
Teflon
Ni
100
0
99.1
0.9
98.3
1.7
100
0
95.4
4.6
91.6
8.4
1.00
0.954
0.916
0.856
Lubricating
Solid
Lubricating
Teflon
Ni
Teflon
96.9
3.1
85.6
14.4
(I0solid + ICB)–1 – α = (1 – α)ICB(I0solid + ICB)–1 is the change
in the volume concentration of solid phases in going
from CEC to wear products of the CEC/CB couple (for
the CEC/CEC friction couple, Δα is formally equal to
zero) [3]; (α + δ) = α[1 + 2α(1 – α)(1 + kn)]; I0lin and f 0
are the linear wear rate and CEC friction coefficient in
the CEC/CEC friction couple, determined by formulas
(1) and (2).
the case of friction over St45 steel, (Ilin)min = 0.520 μmh–1
for kn = 0 is attained at α = 0.80, and with an increase
in kn to 0.20, this value decreases to 0.356 at α = 0.75.
Apparently, the observed quantitative changes in Ilin(α)
dependences are due to a rise in the contribution of nickel
nanoparticles to the synergistic effect of the CECs.
An analysis of the f (α) dependences revealed a regu-
lar decrease in the friction coefficient with an increase
in the volume fraction of Teflon and decrease in fCB
in the entire range of α. However, the maximal syn-
ergistic effect, i.e., the maximal deviation of the de-
pendences f (α) from the values calculated in terms of
the corresponding additive model, is attained at α =
0.72 0.02.
Composite electrolytic coatings with Teflon volume
fractions of 4.6, 8.4, and 14.4% were prepared from an
electrolyte of the following composition (g l–1): nickel
chloride hexahydrate 200–250, nickel sulfate heptahy-
drate 2.5–5.0, boric acid 25–40, Chloramine B 0.5–2.5,
and F-4D-E (Teflon) emulsion 10–20. Electrolysis
conditions: pH 1.0–5.5, temperature 18–30°C, cathode
current density 0.5–9 A dm–2.
It should be noted that the calculated data can be
used for determining the compositions of Ni–Teflon
CECs with prescribed wear resistance and antifriction
properties. From the same data, we can determine the
optimal composition of a wear-resistant antifriction
coating, i.e., a formulation with the minimal value of
(Ilin f )|kn. For example, at kn = 0, the minimal value of
this parameter is attained for CECs (friction over St45
steel) at the Teflon volume fraction of about 0.25.
From the data on the phase composition and con-
centration of CEC components (Table 1), using the
calculation procedures described in [2, 3], we obtained
the concentration dependences Ilin(α) and f (α) at fixed
values of the parameter kn = 0, 0.05, 0.1, 0.15, and 0.2
for the CEC/CEC and CEC/St45 friction couples.
Note that the individual characteristics of the solid
and lubricating CEC components that we used in the
calculations, namely, for nickel, Ilin, solid = 1.1 μm h–1,
fsolid = 0.25; for Teflon, Ilin, lub = 7.5 μmh–1, flub = 0.03;
and for St45 steel, Ilin, St45 = 1.2 μm h–1, fSt45 = 0.24,
corresponded to the stationary step of the mode of dry
friction of two identical materials at a specific load of
3 MPa and a friction velocity V = 0.048 m s–1.
Experimental data on the wear resistance of CECs
in friction couples with St45 steel are in reasonable
agreement with the calculated data at k = 0.5 and kn =
0.07 (Table 2). The nanostructure parameter equal to
0.07 was used for obtaining predictable data on the other
tribological characteristics of the CECs (Table 2).
Thus, the concentration-wave model with the pa-
rameters k = 0.5 and kn = 0.07 allows satisfactory inter-
pretation of the experimental data on the linear wear
rate of Ni–Teflon CECs in friction over St45 steel and
prediction of the corresponding friction coefficients.
Within the framework of the model we used, the quan-
tity kn > 0 means not only a high dispersity of micro-
Analysis of the Ilin(α) dependences for CEP in the
case of friction over the identical material showed that
the minimum of the linear wear rate, 0.673 μm h–1, at
kn = 0 is attained at α = 0.86. As the nanostructure pa-
rameter increases to 0.20, the minimum of the linear
wear rate decreases to 0.401 μm h–1 at α = 0.83. In
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 12 2008

SYNERGISTIC EFFECT IN NICKEL–TEFLON COMPOSITE ELECTROLYTIC COATINGS
2171
Table 2. Wear and antifriction properties of nickel and composite coatings in a friction couple with St45 steel
Linear wear rate Ilin-, μmh–1
Friction coefficient f
Coating
α
calculation experiment
calculation
experiment
Ni
1.000
0.954
1.20
0.782
1.20
0.79
0.24
0.217
0.24
–
Ni–Teflon
0.916
0.856
1.000
0.954
0.898
0.835
0.608
0.455
1.100
0.767
0.630
0.434
0.59
0.46
1.10
0.74
0.56
0.42
0.192
0.156
0.25
0.218
0.185
0.155
–
–
0.25
0.21
0.17
0.15
Ni–В
Ni–В–Teflon
particles of Ni and γ-Fe phases, but also the presence
among them of spherical or cylindrical nanofragments
enhancing the effect of the CEC lubricating component.
their wear resistance and antifriction properties, com-
pared to the additive values.
(2) The synergism of the solid and lubricating
components of the composite electrolytic coatings un-
der consideration consists in concentration of Teflon
on the wear surface, enhancing the antifriction proper-
ties and wear resistance of nickel, and in the presence
of spherical or cylindrical nickel nanoparticles acting
as solid lubricants.
It should be noted that the experimental data on
the linear wear rate and friction coefficient for the
nickel–boron–Teflon CEC, reported in [1] (Table 2),
were satisfactorily described by the concentration wave
model with a higher nanostructure parameter kn = 0.17.
In so doing, it was assumed [1] that, along with Teflon
concentration on the surface of the CEC/St45 friction
couple, nanoparticles of the specific shape were
formed only from boron-containing phases.
REFERENCES
1. Ivanov, V.V., Balakai, V.I., Ivanov, A.V., and Arzu-
manova, A.V., Zh. Prikl. Khim., 2006, vol. 79, no. 4,
pp. 619–621.
The data we obtained suggest that, in nickel–
boron–Teflon CECs, not only Ni3B and Ni2B, but also
Ni and γ-Fe phases act in friction as lubricating com-
ponents along with Teflon. On the whole, the role of
boron-containing phases consists in that the wear resis-
tance of the coatings is enhanced owing to their indi-
vidual charactetistics I0lin and the friction coefficient of
the surface decreases owing to the formation of the
corresponding nanoparticles.
2. Ivanov, V.V., Shcherbakov, I.N., Ivanov, A.V., and
Bashkirov, O.M., Izv. Vyssh. Uchebn. Zaved., Sev.-
Kavk. Region, Tekh. Nauki, 2005, no. 5, pp. 42–46.
3. Ivanov, V.V. and Shcherbakov, I.N., in Problemy
sinergetiki v tribologii, triboelektrokhimii, materia-
lovedenii i mekhatronike: Materialy IV Mezhdunarod-
noi nauchno-prakticheskoi konferentsii (Problems of
Synergism in Tribology, Triboelectrochemistry, Ma-
terials Science, and Mechatronics: Proc. IV Int. Sci-
entific and Practical Conf.), Novocherkassk: Yuzh-
no-Ross. Gos. Tekh. Univ. (NPI), November 4, 2005,
pp. 25–26.
CONCLUSIONS
(1) Ni–Teflon composite electrolytic coatings
show a synergistic effect consisting in enhancement of
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 81 No. 12 2008