V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
523–530
VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED
ON COPPER AND CARBON
KOMPOZITI NA OSNOVI BAKRA IN OGLJIKA, KONDENZIRANI
IZ PLINSKE FAZE
Viktor Bukhanovsky1, Mykola Rudnytsky1, Mykola Grechanyuk2,
Rimma Minakova3, Chengyu Zhang4
1National Academy of Science of Ukraine, Pisarenko Institute for Problems of Strength,
2 Tymiryazevska str., 01014 Kyiv, Ukraine
2Eltechmash (Gekont) Science & Technology Company, Vinnitsa, Ukraine, Vatutina str. 25, 21011 Vinnitsa, Ukraine
3National Academy of Science of Ukraine, Frantsevich Institute for Problems of Materials Science,
3 Krzhizhanovskogo str., 03680, Kyiv, Ukraine
4Northwestern Politechnical University, Xi’an, China, 710072 Xi’an, China
victan@ipp.kiev.ua
Prejem rokopisa – received: 2015-03-10; sprejem za objavo – accepted for publication: 2015-07-28
doi:10.17222/mit.2015.057
The production technology, structure, electrical conductivity, coefficient of friction, hardness, strength, and plasticity over a
temperature range of 290–870 K of copper-carbonic composites with laminated structures and carbon contents from 1.2 to 7.5 %
of volume fractions for sliding electrical contacts of current-collecting devices obtained by electron-beam evaporation and vapor
condensation are studied. Thermodynamic activation analysis of the hardness and strength of the composites was carried out.
Correlations between the hardness and strength of the composites were established.
Keywords: condensed composites, electron-beam technology, electrical, tribotechnical and mechanical characteristics,
correlation
[tudirana je tehnologija izdelave, struktura, elektri~na prevodnost, koeficient trenja, trdota, trdnost in plasti~nost v tempera-
turnem obmo~ju 290–870 K kompozita baker-ogljik s plastovito strukturo in vsebnostjo ogljika od 1,2 do 7,5 % volumenskega
dele`a, za drsne elektri~ne kontakte za prenos tokov, dobljene z izparevanjem v elektronskem curku in s kondenzacijo par.
Izvedena je bila analiza termodinami~ne aktivacije trdote in trdnosti kompozitov.
Klju~ne besede: kondenzirani kompoziti, tehnologija elektronskega curka, elektri~ne, tribotehni~ne in mehanske zna~ilnosti,
korelacija
1 INTRODUCTION
Nowadays composite materials (CMs) based on
copper and carbon are widely used as electrocontact
materials for current-collecting devices.1–6 In addition to
the conventional powder metallurgy processes for pro-
ducing these materials, they are also obtained by high
rate electron beam evaporation of copper and carbon
from individual water cooled crucibles, with layer by
layer condensation of the mixed vapour flow on a rotat-
ing steel disk.7–13 The technology of high rate electron
beam evaporation-condensation is the alternative to
powder metallurgy: the thermal dispersion of the liquid
melt and consolidation of dispersed particles flow (wit-
hout special molding to obtain a high-density material
state) with a limited amount of admixtures within a
closed space. The apparent advantages of the electron-
beam technology, which makes the development of a
new generation of composite materials for electrical
contacts possible, are as follows:
• the possibility of mixing the vapor flows of sub-
stances that do not dissolve well within each other at
the atomic and molecular levels, to create composite
materials and coatings (facing layers) with the
desired structure, chemical composition and perfor-
mance characteristics, which cannot be obtained by
other methods;
• simplicity and efficiency compared to powder me-
tallurgy, as the material is formed in one technolo-
gical cycle;
• the possibility to create gradient structures by varying
the deposition rate of the components being evapo-
rated in the course of the process;
• the possibility to obtain laminated composite ma-
terials, which is practically impossible to achieve
using traditional methods;
• ecological purity, as this technology eliminates all
atmospheric emissions.
Electron beam evaporation and condensation techno-
logy is used to produce electrical contact Cu-C CMs
with specific laminated structures and chemistries within
one production cycle. The composition determines its
unique physical-mechanical and operational properties.
Condensed copper-carbon composite materials with
carbon contents from 1.2 to 7.5 % of volume fractions in
the form of sheets of 3 to 5 mm in thickness were
produced by the Gekont (Eltekhmash) Science &
Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530 523
UDK 669.018.25:669.3:661.666:536.7 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 50(4)523(2016)
Technology Company and, at present, these materials are
in series production in Ukraine. These sheet materials
are used in current-collecting devices as the operating
floors of copper contact clips which are attached to them
by brazing.
The present paper covers data on the production
technology and experimental investigations of the struc-
ture, electrical and tribotechnical characteristics, strength,
hardness, and plasticity of condensed laminated compo-
site materials of the Cu-C system for current-collecting
devices with carbon contents from 1.2 to 7.5 % of vol-
ume fractions over a temperature range of 290–870 K.
2 MATERIALS AND EXPERIMENTS
One of the advantages of copper-carbon CMs is the
potential to vary their electroconductive and tribotech-
nical properties over a wide range by changing the
copper and carbon contents in the composite. High-speed
electron beam evaporation and condensation is regarded
here as the most common and easily implemented manu-
facturing method.
However, there are almost insurmountable difficulties
with obtaining Cu-C CMs using the aforementioned
production process, i.e. a lack of physicochemical inte-
raction between copper and carbon, a very high melting
temperature of carbon, and the difficulty of its transfor-
mation into a vapor state. Taking these issues into
consideration, the original electron-beam technology of
carbon evaporation through a molten tungsten mediator
was designed by the Eltechmash (Gekont) Science &
Technology Company, and experimental industrial
specimens of Cu-C CMs with the carbon contents within
a particular range were obtained.
The principle of the method of evaporation through a
molten tungsten mediator is as follows. Tungsten carbide
is formed upon contact between molten tungsten and
carbon, which is thermodynamically unstable under the
given temperature conditions, decomposing into atomic
tungsten and carbon on the surface of the molten tung-
sten mediator. As the elasticity of the carbon vapour is
two orders of magnitude lower than the elasticity of the
tungsten vapour, it is mainly carbon which evaporates
from the surface. This process ensures the atomic trans-
fer of carbon to the rotating steel substrate and makes it
possible to obtain the condensed Cu-C CMs with the
specified laminated structure.
The materials for study were condensed composites
of the Cu-C system, which were created using elec-
tron-beam technology with carbon contents of (1.2, 3.5,
5.0 and 7.5) % of volume fractions.
The Cu-C composites condensed from the vapor
phase were obtained using the L5 electron-beam facility
designed at the Eltechmash (Gekont) Science & Techno-
logy Company. The physical configuration and a
schematic diagram of the equipment are given in Figures
1 and 2, respectively. The equipment comprises work
chamber 1 (Figure 2), which on its side wall has gun
chamber 2 connected to it, which contains electron-beam
heaters 3, 4, 5 and 6. The vacuum system, comprised of
two fore pumps, two booster pumps and two high-
vacuum units, serves to provide a dynamic vacuum in the
evaporation and condensation chambers.
On the upper flange of the work chamber 1 there is
mechanism 15 (Figure 2) that rotates the 800 mm dia-
meter steel substrate 14. The mechanism design allows it
V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
524 Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530
Figure 2: Scheme of the L5 electron-beam facility. Designations: 1 –
work chamber; 2 – gun chamber; 3, 4, 5 and 6 – electron-beam
heaters; 7 – substrate rotation rod; 8 – crucible for evaporation of
copper; 9 – crucible for evaporation of carbon; 10, 11 – ingots of
copper and carbon, respectively; 12, 13 – mechanisms for introducing
ingots into the vapor flow zone; 14 – steel substrate for condensation
of copper and carbon vapor flows; 15 – substrate rotation mechanism
Slika 2: Shema L5 naprave z elektronskim curkom. Oznake: 1 – de-
lovna komora; 2 – komora s pu{ko; 3, 4, 5 in 6 – grelci elektronskega
curka; 7 – palica za vrtenje podlage; 8 – lon~ek za izparevanje bakra;
9 – lon~ek za izparevanje ogljika; 10, 11 – ingota bakra in ogljika; 12,
13 – mehanizma za podajanje ingotov v podro~je toka par; 14 –
podlaga iz jekla za kondenzacijo par bakra in ogljika; 15 – mehanizem
za rotacijo podlage
Figure 1: Physical configuration of the L5 electron-beam facility
designed at the Eltechmash (Gekont) Science&Technology Company
Slika 1: Konfiguracija naprave z L5 elektronskim curkom, postavljena
v Eltechmash (Gekont) Science&Technology podjetju
to be operated for a long time at a temperature of 870 ±
50 K without destroying the vacuum. The substrate,
fixed to the rotating rod 7 was heated to the required
temperature by 40 kW electron-beam heaters 5 and 6.
The original material was heated to evaporation by 100
kW electron-beam heaters 3 and 4. All heaters have inde-
pendent cathode-glow and electron-beam controls.
The evaporation unit has crucibles 8 and 9 with
diameters of 100 and 70 mm for evaporation of copper
and carbon, ingots 10 and 11 for evaporation, and me-
chanisms 12 and 13 that allow the ingots to be put in the
evaporation zone.
In the present study, the copper-carbon condensates
are obtained by means of copper and carbon evaporation
from separate crucibles followed by their precipitation
on a rotating steel substrate coated with a layer of cal-
cium fluoride. The steel substrate was heated to a tem-
perature of 935–965 K. The original materials were M0
grade copper ingots, 100 mm in diameter, after electron-
beam remelting, and GMZ grade carbon ingots with a
diameter of 70 mm.
The process of carbon evaporation involves the
following stages. A batch of VA grade tungsten of 400 g
weight was placed on the surface of the carbon ingot.
When a vacuum level in the region of 1.3–4.0×10–3 Pa is
reached in the work chamber, electron-beam heating of
the substrate to a temperature of 950±15 K is performed.
Simultaneously, the surfaces of both ingots are electron
beam heated to the melting temperature of the base metal
– copper, and intermediate for the carbon – tungsten with
a current of 1.15–1.3 A. The melt pools became
homogeneous after 15–20 min of heating. A layer from
the copper evaporation crucible was the first to be
precipitated on the substrate. At the production stage,
evaporation from both crucibles was performed
simultaneously at a beam current of 2.2–2.4 A for copper
and 2.6–3.8 A for carbon under an acceleration voltage
of 20 kV. By varying the beam current one can readily
regulate the evaporation rate of carbon and its con-
centration in the composite over wide ranges.
By maintaining the substrate temperature in the range
935 K to 965 K, the re-evaporation of copper from the
surface of the condensed material is prevented. The conden-
sation rate of the tempered vapour flow was 20 μm/min.
The resulting condensed materials were 2–3 mm thick
disks of 800 mm in diameter.
At the end of the technological process, the con-
densed composite material was separated from the
substrate. The condensed material obtained was annealed
in a vacuum furnace at 1170 K for three hours to relieve
internal stresses, stabilise the structure, and enhance its
ductility.
In this study, the authors used the characterisation
techniques that include macro-and microstructure analy-
sis using optical and scanning electron microscopy,
electrical resistance methods, tribotechnical tests,
mechanical tensile tests at room and high temperatures,
and hot hardness measurements. The carbon and copper
contents were determined using the mortar method
(volumetric analysis).
The structure of the composite materials was inve-
stigated by light and scanning electron microscopy using
a Neophot-2 light microscope and a Jeol Superprobe 733
raster electron microscope. Specimens for metallogra-
phic analysis were prepared using chemical etching in a
40 % hydrochloric acid solution and ion etching in a
glow discharge. The authors studied the specimen surfa-
ces and cross sections perpendicular to the substrate.
The electrical conductivity of the Cu-C CMs was
determined by indirect bridge method measurements
according to GOST 7229-76.14
The coefficient of friction of Cu-C CMs with copper
was determined by the measurement of moment of
friction and the determination of adhesion bond strength
at the contact of copper specimen rotating under load
with a composite counter-specimen according to GOST
27640-88.15
The mechanical characteristics were determined at
ambient (outdoor) and elevated temperatures up to 870 K
(in vacuum not below 0.7 mPa) from the results of me-
chanical tensile tests on standard flat fivefold
proportional specimens with a gauge length of 15 mm, 3
mm width and ~2 mm thickness, using a 1246-R unit 16
according to ISO 689217 and ISO 78318, respectively. The
specimens were cut from ~2 mm thick composite
material after vacuum annealing at 1170 K for 3 h. The
carbon content in the composites varied from 1.2 to 7.5
% of volume fractions. Three to five specimens were
tested at each temperature. The deformation rate was 2
mm/min, which corresponded to a relative strain rate of
~2.2×10–3 s–1. During the tests deformation diagrams
were recorded to determine the proof strength Rp0,2, the
ultimate strength Rm, the percentage elongation after
fracture A, and the percentage non-proportional
elongation at the maximum force Ag. In addition, the
percentage reduction of cross-sectional area Z was
evaluated.
The Cu-C composite hardness was estimated in the
temperature range from 290 K to 870 K by Vickers
indentation in the plane parallel to the surface of
condensation. The pyramidal indenter was made of a
synthetic corundum single crystal. Indentation loads
were 10 N. The tests were carried out at a pressure no
more than 0.7 mPa on a UVT-2 unit19,20 according to
DSTU 2434-94.21
3 RESULTS AND DISCUSSION
The electron-beam process provides a particular
laminated composite structure with alternating copper
layers, containing dispersed carbon particles, of 150 μm
to 300 μm in thickness with carbon layers of 6 to 8 μm
thickness (Figure 3). The copper grain size is 0.1–0.3
μm. The mean size of the dispersed carbon particles in
the copper matrix does not exceed 20 nm.
V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530 525
The electrical conductivity of the CMs with carbon
contents from 7.5 to 1.2 % of volume fractions varies in
the range from 3.49×107 to 4.07·107 S/m, which is 60 to
70 % of that of copper. Generally the electrical conduc-
tivity of the condensed CMs is almost one and a half
times that of the many known Cu-C powder compo-
sitions.1–6 The maximum magnitude of the transferred
current (up to 3000 A) for the condensed Cu-C CMs is
two times higher than that of silver.
The results of the investigation of the tribotechnical
characteristics of the condensed Cu-C CMs together with
a copper contact wire show that the friction coefficient
for the composites with 4.0 – 7.0 % of volume fractions
of C decreases by 3 – 4 times as compared with the
tough-pitch copper.
In operation, current-collecting device materials are
subjected not only to intensive wear and electrical ero-
sion, but also to mechanical loads at elevated tempera-
tures. Therefore, studies on their mechanical properties
over the operating temperature ranges are of clear scien-
tific and practical interest.
Hardness, strength and plasticity characteristics of
the copper-carbon composites over the temperature range
290 – 870 K are presented in Table 1. From Table 1, the
hardness and strength losses due to heating are conti-
nuous. With increasing temperature, the hardness de-
creases monotonically from maximum values of
805–951 MPa at room temperature to minimum values
of 74–138 MPa at 870 K. The tensile strength and proof
V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
526 Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530
Figure 3: Microstructure of the Cu-5.0 % of volume fractions of C
composite (scanning electron micrograph): a) composite surface
microstructure (without etching), b) micro-layer structure of the
composite, observed after ion etching (wide dark layers – copper,
narrow light layers and spots – carbon), c) polygonal structure of the
layers, observed after ion etching
Slika 3: SEM posnetek mikrostrukture kompozita Cu-5,0 % volumen-
skega dele`a C; a) mikrostruktura povr{ine kompozita (brez jedkanja),
b) struktura kompozita z mikro plastmi, opa`ena po ionskem jedkanju
({irok temni pas je baker, ozke svetlej{e plasti in to~ke so ogljik), c)
poligonalna struktura plasti, opa`ena po ionskem jedkanju
Table 1: Strength and plasticity characteristics of the Cu-C compo-
sites in the 290–870 Ê temperature range
Tabela 1: Zna~ilnosti trdnosti in plasti~nosti kompozita Cu-C, v tem-
peraturnem podro~ju 290–870 K
T, K HV(MPa)
Rm
(MPa)
Rp 0,2
(MPa) A (%) Ag (%) Z (%)
Composite Cu = 1.2 % of volume fractions of C
290 951 260 235 27.8 20.2 70.5
370 783 233 196 21.0 15.2 59.0
470 579 194 153 16.7 11.3 40.0
570 389 165 136 14.9 9.0 34.4
670 290 127 107 20.7 12.0 35.0
770 186 93 86 29.3 4.8 36.5
870 138 60 53 40.4 20.2 40.2
Composite Cu = 3.5 % of volume fractions of C
290 926 257 225 24.7 20.3 42.3
370 724 216 186 20.0 16.4 35.4
470 571 185 145 16.5 12.1 34.5
570 381 145 128 14.5 10.0 33.0
670 263 107 100 11.3 7.8 30.5
770 177 83 75 10.5 3.2 27.0
870 127 50 47 9.2 2.0 23.2
Composite Cu = 5.0 % of volume fractions of C
290 828 253 186 8.5 5.5 28.2
370 666 213 173 6.7 4.3 24.6
470 552 167 140 4.6 4.1 22.0
570 373 127 117 4.5 4.2 20.2
670 252 104 96 6.0 3.2 18.3
770 174 65 59 6.6 2.0 17.4
870 122 37 34 8.2 2.5 17.0
Composite Cu = 7.5 % of volume fractions of C
290 805 250 180 7.5 4.5 25.0
370 618 210 167 5.7 4.0 22.5
470 526 155 133 4.1 3.7 20.0
570 359 107 100 4.0 3.6 19.2
670 211 95 90 4.5 3.0 17.3
770 126 55 49 5.5 2.5 16.4
870 74 30 32 7.0 2.0 16.0
strength of the material decrease from 250–260 MPa and
180–235 MPa at room temperature to 30–60 MPa and
32–53 MPa at 870 K, respectively. Moreover, the
hardness and the strength of Cu-C condensed CMs
decrease with increasing carbon content in the composite
over the entire temperature range.
The temperature dependences of CMs plastic proper-
ties are of a more complicated nature, with peaks caused
by hot brittleness typical of copper and its alloys. In
particular, a sharp decrease in plasticity values is ob-
served at 570 K. An increase of the carbon content in
composites facilitates the decrease of their plastic cha-
racteristics at all investigated temperatures.
Owing to their particular structure the condensed
CMs surpass the tough-pitch cast copper and most of
known Cu-C powder composites of similar composition
in mechanical characteristics (including strength, plasti-
city and hardness).1–6
Thermodynamic activation analysis of the composites
was used to estimate its strength and hardness variations
with temperature by a procedure presented earlier.20,22 To
establish basic strength variation patterns over the tem-
perature range under study, the exponential equations
describing temperature dependences of strength and
hardness were used:
R A
U
kT
=
⎛
⎝
⎜ ⎞
⎠
⎟’ exp
3
(1)
H cA
U
kT
=
⎛
⎝
⎜ ⎞
⎠
⎟’ exp
3
(2)
where R is strength characteristic, MPa; HV is Vickers
hardness, MP; T is the temperature, K; U is the activa-
tion energy (enthalpy) of plastic strain, eV; k is the
Boltzmann constant; A’ is a constant function of the
material parameters and strain rates, and ñ is the pro-
portionality constant, c = H/R.
In Figure 4 the data obtained are presented as a
function of ln Rp0.2, ln Rm, ln HV-1/T coordinates. As is
seen, the temperature dependences of strength and hard-
ness of Cu-C CMs consist of several regions, corres-
ponding to the temperature intervals 290–460 K,
460–710 K, and 710–900 K, which are (0,20–0,35),
(0,35–0,52), and (0,52–0,65) Tmelt
Cu . Within these intervals
they parameters vary linearly, obeying Equations (1) and
(2). Moreover, within each of the intervals the tempera-
ture dependences of strength and hardness are parallel to
each other for all the composites studied.
Each of these regions corresponds to a certain plastic
strain mechanism. Equations (1) and (2) were used to
determine the activation energies of plastic strains from
experimental strength and hardness data for different
temperature intervals in the range from 0.20 to 0.65 Tmelt
Cu .
They correspond to average strain rates of 10–3 s–1 under
applied stresses, exceeding a 10–4 shear modulus. As is
clear from Table 2, the values of activation energy
obtained for all the investigated Cu-C CMs within each
assigned temperature interval virtually coincide, and are
in a range from 1.5 to 3 times lower than those of tough-
pitch copper. The latter is evidence for the fact that the
intensity of thermal softening of Cu-C system compo-
sites decreases significantly in comparison with that of
tough-pitch copper, in particular at temperatures higher
than 0,52 Tmelt
Cu .
Table 2: Activation energies of plastic strains of a Cu-C composites
and commercially pure copper
Tabela 2: Aktivacijske energije plasti~ne deformacije kompozita
Cu-C in komercialno ~istega bakra
Material
Strength
charac-
teristic
U, eV in the temperature interval (K)
290...460 460...710 710...900
Cu-1.2 % of
volume
fractions of C
HV 0,03 0,12 0,30
Rm 0,02 0,07 0,31
Rp0,2 0,02 0,07 0,30
Cu-3.5 % of
volume
fractions of C
HV 0,03 0,12 0,30
Rm 0,02 0,07 0,33
Rp0,2 0,02 0,06 0,32
Cu-5.0 % of
volume
fractions of C
HV 0.03 0.11 0.30
Rm 0.02 0.07 0.33
Rp0,2 0.02 0.06 0.32
Cu-7.5 % of
volume
fractions of C
HV 0.03 0.11 0.34
Rm 0.02 0.07 0.34
Rp0,2 0.02 0.06 0.33
Cu 14, 17
HV 0.05 0.22 0.91
Rm 0.03 0.14 0.93
Rp0,2 0.03 0.13 0.90
In this respect, the plots of the strength and hardness
temperature dependences are diagrams of the Ashby
V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530 527
Figure 4: Temperature dependences of the hardness HV, the tensile
strength Rm, and the proof strength Rp0,2 of copper-carbon composites
over the temperature range 290–900 K
Slika 4: Temperaturna odvisnost trdote HV, natezne trdnosti Rm in
meje plasti~nosti Rp0,2 kompozita baker-ogljik v obmo~ju 290–900 K
deformation mechanisms23. According to Ashby, for bcc
metals of group IB under the conditions investigated, the
mechanisms of dislocation sliding are acting at tempe-
ratures below 0.5 Tmelt and the mechanisms of dislocation
creep at higher temperatures. At present, the concept of
thermally activated dislocation motion across the local
barriers is commonly accepted as a mechanism which
controls the rate of the plastic flow process for many
types of crystalline solid bodies. During deformation of
commercially pure copper in the temperature range from
0.2 to 0.3 Tmelt, the process of blocking dislocations by
impurities takes place. In the temperature range from
0.35 to 0.55 Tmelt, the strength of copper is governed by
the processes of release of Cottrell and Suzuki atmo-
spheres.24
The analysis and comparison of activation energies of
plastic strains in copper and copper-based composites
(Table 2) as well as earlier theoretical and experimental
work on deformation, internal friction, creep, and self-
diffusion of copper21,22 allow a conclusion about plastic
flow development accompanied by significant activation
energy variations in passing from one temperature
interval to another. This result points to a progressive
change of active (controlling), thermally activated plastic
strain mechanisms. Possible dominant mechanisms for
metals are presented in22–24. The patterns of strength-tem-
perature and hardness-temperature curves are similar,
obeying general relationships in their variations with
temperature.
The analysis of experimental and calculated data
demonstrated that the above strength characteristics were
controlled by the same plastic strain mechanisms and
their temperature intervals were coincident. Therefore,
correlations between strength characteristics should be
established within the temperature intervals where
strength is controlled by the same mechanisms or at least
the latter do not change (for Cu-C composites these
intervals are 290–460 K, 460–710 K, and 710–900 K).
The correlation analysis is aimed at establishing the
functional relation between the hardness HV, the tensile
strength Rm, and the proof strength Rp0,2 of Cu-C com-
posites. Empirical distributions of Rm and Rp0,2 (Figure
5) are the aggregate of points on the plane whose coordi-
nates correspond to the values of the above characteri-
stics at different fixed temperatures.
As is seen, correlation fields possess several regions
that are adequately described by the linear regression
function. This function is common for all the investi-
gated Cu-C CMs within each region. Such a form of the
function is in full agreement with theoretical calculations
of the linear hardness-strength relation. Temperature
intervals for these regions, as expected, are coincident
with the intervals of dominant plastic strain mechanisms.
The results of calculations of the correlation and
regression coefficients of the linear function y = ax + b
or Rm (Rp0,2) = aHV + b describing the empirical distri-
bution areas, are summarized in Table 3.
Table 3: Empirical regression coefficients a and b for strength-hard-
ness correlation of a Cu-C composites
Tabela 3: Empiri~na regresijska koeficienta a in b za korelacijo
trdnost-trdota kompozita Cu-C
Correlation T ()K a b Correlationcoefficient
Rm  HV
290...460 0.14 125 1.0
460…710 0.22 63 0.99
710…900 0.51 −10 1.0
Rp0.2  HV
290...460 0.16 71 1.0
460…710 0.15 63 0.99
710…900 0.42 −6 1.0
V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
528 Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530
Figure 6: Production specimen of sliding contact for current-
collecting device in electric transport made with Cu-C condensed CMs
Slika 6: Izdelan vzorec drsnega kontakta za napravo za zbiranje toka v
elektri~nem transportu, narejen na osnovi kondenziranih Cu-C kom-
pozitov
Figure 5: Correlation field and strength-hardness regression lines for
Cu-C composites at different temperatures: 1 – Rm  HV; 2 – Rp0,2 
HV
Slika 5: Korelacijsko polje regresijskih linij trdnost-trdota za kompo-
zit Cu-C pri razli~nih temperaturah: 1 – Rm  HV; 2 – Rp0,2  HV
Due to excellent tribotechnical, electrotechnical,
mechanical and operating characteristics, the condensed
Cu-C CMs produced by the Eltechmash (Gekont) Scien-
ce & Technology Company are used for the manufacture
of sliding contacts for current-collecting devices in
electric transport (Figure 6). These materials exhibit
excellent operating characteristics and are successfully
used in Ukraine.
4 CONCLUSIONS
1) An original technology for obtaining condensed
laminated composite materials of the Cu-C system by
means of high-speed electron-beam evaporation-conden-
sation was developed. Condensed Cu-C composites with
a thickness of 2–3 mm and carbon content from 1.2 to
7.5 % of volume fractions were obtained using electron-
beam technology for the first time.
2) The electrical conductivity of Cu-C CMs varies
with the carbon content in the range from 3.49×107 S/m
for Cu-7.5 % of volume fractions of C to 4.07×107 SC/m
for Cu-1.2 % of volume fractions, which is from 60 % to
70 % of that of copper. Generally the electrical conduc-
tivity of the CMs is almost one and a half times that of
the many known Cu-C powder compositions.
3) The friction coefficient of Cu-C composites with
4.0 – 7.0 % of volume fractions of C with a copper
contact wire decreases by 3 – 4 times compared with
tough-pitch copper.
4) Owing to their particular structure the CMs
surpass tough-pitch cast copper and many known Cu-C
powder composites of similar composition in mechanical
characteristics (including strength, plasticity and hard-
ness).
5) Static strength and hardness variation behaviour
and correlations between these properties were experi-
mentally established over a wide temperature range .
6) Thermodynamic activation analysis of hardness
and strength characteristics were carried out. The vari-
ation of the tensile strength, proof strength, and hardness
of composites upon heating is controlled by the same
mechanisms, with their temperature intervals being
coincident.
7) The coefficients of regression equations relating
hardness to other strength characteristics of Cu-C com-
posites were determined for each temperature interval.
8) The CMs developed are very promising materials
for sliding contacts in current-collecting devices for
electric transport.
List of notation:
A – percentage elongation after fracture, %
Ag – percentage non-proportional elongation at maxi-
mum force, %
H – hardness, MPa
HV – Vickers hardness, MPa
R – strength characteristics, MPa
Rm – the tensile strength, MPa
Rp0.2 – the proof strength, MPa
T – thermodynamic temperature, K
Tmelt – melting temperature, K
Tmelt
Cu – melting temperature of copper, K
U – activation energy (enthalpy) of plastic strain, eV
Z – percentage reduction of area, %
A’ – constant being the function of material parameters
and strain rates
a, b – regression coefficients
c – proportionality constant
k – Boltzmann constant
5 REFERENCES
1 G. G. Gnesin (Ed.), Sintered materials for electrical and electronic
applications, Handbook, Metallurgy, Moscow 1981, 343
2 V. I. Rakhovsky, G. V. Levchenko, O. K. Teodorovich, Interrupting
contacts of electric appliances, Energy, Moscow-Leningrad 1966,
293
3 T. Shubert, T. Weisgarber, B. Kieback, Fabrication and Properties of
Copper/Carbon Composites for Thermal Management Applications,
Advanced Materials Research, 59 (2008), 169–172, doi:10.4028/
www. scientific.net/AMR.59.169
4 Q. Hong, M. W. Li, J. Z. Wie et al., New Carbon-Copper Composite
Materials Applied in Rail-Type Launching System, JEEE Tran-
sactions on Magnetics, 43 (2007), 137–140, doi:10.1109/TMAG.
2006.887534
5 T. S. Koltsova, L. I. Nasibulina, I. V. Anoshkin et al., Direct Syn-
thesis of Carbon Nanofibers on the Surface of Copper Powder,
Journal of Materials Science and Engineering B, 2 (2012) 4,
240–246
6 E. P. Shalunov, V. Y. Berent, Uniform Current-Collecting Elements
of Dispersion-Hardened Copper with Graphitic Lubrication for
Current Collectors of Heavy-Duty and High-Speed Electric Trains,
Electrical Contacts and Electrodes, Frantsevich Institute of Materials
Science Problems, National Academy of Sciences of Ukraine, Kiev,
2004, 202–210
7 B. A. Movchan, I. S. Malashenko, Vacuum-Deposited Heat-Resistant
Coatings, Naukova Dumka, Kiev 1983
8 N. Grechanyuk, I. Mamuzi}, P. Shpak, Modern electron-beam tech-
nologies of melting and evaporation of materials in vacuum, used by
Gekont Company, Ukraine, Metalurgija, 41 (2002) 2, 125–128
9 N. I. Grechanyuk, I. Mamuzi}, V. V. Bukhanovsky, Production tech-
nology and physical, mechanical, and performance characteristics of
Cu-Zr-Y-Mo finely-dispersed microlayer composite materials,
Metalurgija, 46 (2007) 2, 93–96
10 N. I. Grechanyuk, V. A. Osokin, I. N. Grechanyuk, R. V. Minakova,
Vapour-Phase Condensed Materials Based on Copper and Tungsten
for Electrical Contacts, Structure, Properties, Technology, Current
Situation and Prospects for Using Electron Beam Physical Vapour
Deposition Technique to Obtain Materials for Electrical Contacts,
First Announcement, Modern Electrometallurgy, (2005) 2, 28–35
11 N. I. Grechanyuk, V. A. Osokin, I. N. Grechanyuk, R. V. Minakova,
Basics of Electron Beam Physical Vapour Deposition Technique
Used to Obtain Materials for Electrical Contacts, Structure and
Properties of Electrical Contacts, Second Announcement, Modern
Electrometallurgy, (2006) 2, 9–19
12 V. V. Bukhanovsky, N. P. Rudnitsky, I. Mamuzich, The Effect of
Temperature on Mechanical Characteristics of Copper-Chromium
Composite, Materials Science and Technology, 25 (2009) 8,
1057–1061, doi:10.1179/174328408 X365829
V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530 529
13 V. V. Bukhanovsky, N. I. Grechanyuk, R. V. Minakova et al., Produc-
tion Technology, Structure and Properties of Cu-W Layered Compo-
site Condensed Materials for Electrical Contacts, International
Journal of Refractory Metals and Hard Materials, 29 (2011) 5,
573–581, doi:10.1016/j.ijrmhm.2011.03.007
14 Cables, Wires and Cords, Method of Measurement of Electrical
Resistance of Conductors, GOST 7229-76
15 Engineering materials and lubricants, Experimental evaluation of
coefficient of friction, GOST 27640-88
16 V. V. Klyuev, Test Equipment, Handbook, vol. 2., Mashinostroenie,
Moscow 1982
17 ISO 6892:1998(E), Metallic Materials – Tensile Testing at Ambient
Temperature, 1998
18 ISO 783:1999(E), Metallic Materials – Tensile Testing at Elevated
Temperature, 1999
19 M. M. Aleksyuk, V. A. Borisenko, V. P. Krashchenko, Mechanical
Tests at High Temperatures, Naukova Dumka, Kiev 1980
20 V. A. Borisenko, Hardness and Strength of Refractory Materials at
High Temperatures, Naukova Dumka, Kiev 1984
21 Method of Determining High-Temperature Hardness by Pyramidal
and Bicylindrical Indentation, DSTU 2434-94, 1995
22 V. A. Borisenko, V. P. Krashchenko, Temperature dependences of
hardness of group IB Metals, Acta Met., 25 (1977) 3, 251–256,
doi:10.1016/0001-6160(77)90143-2
23 V. P. Krashchenko, V. E. Statsenko, Temperature and deformation
rate effects on basic processes controlling copper strength, Probl.
Prochn., (1981) 4, 78–83
24 E. P. Pechkovskii, Physical substantiation of the true strain-tem-
perature diagram for polycrystalline bcc metals, Strength Mater., 32
(2000) 4, 381–390, doi:10.1023/A:1026617020771
V. BUKHANOVSKY et al.: VAPOUR-PHASE CONDENSED COMPOSITE MATERIALS BASED ON COPPER AND CARBON
530 Materiali in tehnologije / Materials and technology 50 (2016) 4, 523–530