ELECTROCHEMISTRY AND OTHER
PROCESSES OF CHEMICAL TECHNOLOGY
Russian Journal of Applied Chemistry, 2013, Vol. 86, No. 8, pp. 1235−1242.
Pleiades Publishing, Ltd., 2013.
Original Russian Text © K.V. Murzenko, Yu.D. Kudryavtsev, V.I. Balakai, 2013, published in Zhurnal Prikladnoi Khimii, 2013, Vol. 86, No. 8, pp. 1261−1268.
Properties of Composite Nickel–Cobalt–Aluminum Oxide
Coating Deposited from Chloride Electrolyte
K. V. Murzenko, Yu. D. Kudryavtsev, and V. I. Balakai
South-Russian State Technical University, Novocherkassk, Rostov-on-Don oblast, Russia
Received December 21, 2012
Abstract—Effect of the cathodic current density, pH value, electrolyte temperature, and concentration of aluminum
oxide introduced into the electrolyte on the wear, microhardness, and internal stresses in nickel–cobalt–aluminum
oxide composite electrolytic coatings was studied. It is shown that the coatings under consideration can be used
instead of chromium coatings.
Use of composite electrochemical coatings (CEC)
makes it possible to improve the reliability and durability
of new and restored machine components. In addition,
with composite electrochemical coatings used, it is
frequently possible to replace deﬁ cient alloyed steels
and cast irons with less expensive grades of metals.
Composite electrochemical coatings containing hard
oxides, carbides, and nitrides of metals as a second
phase are used to impart to machine component surfaces
necessary mechanical properties: hardness, wear
resistance, corrosion resistance, and high-temperature
strength. CECs based on nickel and iron have been
primarily developed for replacing wear-resistant
chromium coatings and some of these have found
application in automobile industry.
The conventional chromium-plating process
can yield hard chromium coatings possessing good
physicomechanical properties, such as the corrosion
resistance, wear resistance, hardness, and low friction
coefﬁ cient. However, chromium-plating electrolytes
based on hexavalent chromium salts have serious
disadvantages. To these belong the low throwing
power (TP), high toxicity of chromium-plating
electrolytes, extremely low current efﬁ ciency (CE) in
electrodeposition of chromium coatings, and decrease
in hardness at elevated temperatures. In addition,
the standard chromium-plating electrolytes based on
chromic acid are among the most noxious electrolytes
in modern industries.
Their replacement with electrolytes based on
trivalent chromium salts is not a solution because these
electrolytes are also toxic. Moreover, coatings deposited
from the so far developed electrolytes cannot replace
those produced from the standard chromium-plating
electrolytes primarily in those ﬁ elds of technology
where the functional properties of chromium coatings
and their high wear resistance are required.
A study of the dry-friction wear of coatings has
shown that CECs with aluminum oxide are markedly
advantageous over other kinds of coatings. For example,
the wear rates of pure electrolytic iron, iron–boron
carbide deposits, and iron–aluminum oxide deposits at a
contact pressure of 8.1 MPa were, respectively, 91, 9.4,
and 5 mg h
The seizure and wear of iron–titanium carbide
coatings were observed already in the ﬁ rst minutes
of their service under a pressure of 4.0 MPa. First
indications of seizure (consisting in ﬂ uctuations of the
friction momentum) were observed for hard electrolytic
iron (microhardness 5.8 GPa) at a pressure of 5.5 MPa.
However, the thin layer of oxides, present on the coating
surface, precluded intense seizures and scufﬁ ng of