Американский Научный Журнал PROPERTIES OF HIGH-ENTROPIC FECOCRNITATIMO COATINGS (40-49)

The FeCoCrNiTaTiMo alloy and coatings based on it have been synthesized by mechanical alloying. - The optical microstructure of high-entropy coatings exhibits irregularity, which is clearly visible on the maps of energy-dispersive spectroscopy. XPS spectra indicate the formation of high-entropy coatings. Analysis of the elemental composition shows the complexity of the high-entropy alloy FeCoCrNiTaTiMo. The structure consists of solid solutions with a chaotic arrangement of atoms of elements. The microhardness of our coating (345 HV) is not inferior to stainless steels, and the wear resistance of the coating is 3•10-4 g/min. High-entropy FeCoCrNiTaTiMo coatings turn out to be antifrictional, which obviously leads to energy savings. The thickness of the surface layer d(I) is determined by one fundamental parameter - the molar (atomic) volume of the element and is equal to 12.3 nm. it is shown that the formation of a cellular nanostructure in a coating can ocMor according to several models. Скачать в формате PDF
40 American Scientific Journal № ( 41 ) / 2020
PROPERTIES OF HIGH -ENTROPIC FECOCRNITATIMO COATINGS
1Yurov V. М.,
2Salkeeva A. К.,
2Kusenova A.S. 1Karaganda University named after E.A. Buketov 2Karaganda Technical University
Kazakhstan, Karaganda

Abstract . The Fe CoCrNiTaTiMo alloy and coatings based on it have been synthesized by mechanical
alloying. - The optical microstructure of high -entropy coatings exhibits ir regularity, which is clearly visible on the
maps of energy -dispersive spectroscopy. XPS spectra indic ate the formation of high -entropy coatings. Analysis of
the elemental composition shows the complexity of the high -entropy alloy FeCoCrNiTaTiMo. The struct ure
consists of solid solutions with a chaotic arrangement of atoms of elements. The microhardness of our coating
(345 HV) is not inferior to stainless steels, and the wear resistance of the coating is 3•10 -4 g/min. High -entropy
FeCoCrNiTaTiMo coatings tur n out to be antifrictional, which obviously leads to energy savings. The thickness
of the surface lay er d(I) is determined by one fundamental parameter - the molar (atomic) volume of the element
and is equal to 12.3 nm. it is shown that the formation of a cellular nanostructure in a coating can ocMor according
to several models.
Key words: high -entropy al loy, plasma coating, surface layer, microhardness, friction, wear resistance, wear
resistance of the coating.

Introduction
According to the authors of [1], a distinctive
feature of high -entropy alloys (HEAs) from traditional
ones is that these alloys ha ve a high entropy of mixing,
which affects the formation of structures based on solid
solutions. A little over 1 5 years have passed since the
discovery of high -entropy alloys (2004). The first
review was made as a complete material science cycle
"productio n - structure - properties" for a new class of
vacuum -plasma coatings - nitrides of multielement
metal high -entr opy alloys in [2]. An analysis was made
of the current state of obtaining such coatings, their
morphology, elemental and phase compositions,
structure, substructure, stress state, and functional
properties depending on the main formation
parameters: substr ate temperature during deposition,
the magnitude of the bias potential applied to the
substrate, and the composition of the gas atmosphere.
Then there were many works devoted to the synthesis
and study of various HEAs [3 -9]. The last review on
HEAs was mad e in [10]. The analysis of more than 200
obtained high -entropy alloys (HEAs) made it possible
to establish the relationship between the electron
concentration, phase composition, lattice parameter
and properties of solid solutions based on bcc and fcc
latt ices. The main conditions for the appearance of
high -entropy chemical compounds - the Laves phase,
σ- and μ-phases, are revealed. For the formation of a
100% high -entropy σ-phase, a necessary condition is
that all elements that make up the HES must form a σ-
phase in two -component alloys in various
combinations, and the electron concentration of the
allo y must be in the range of 6.7 -7.3 el./at. For the
formation of a 100% hig h-entropy Laves phase, it is
necessary to have: the total negative enthalpy of mixing
of the alloy at the level of -7 kJ/mol and below; pairs
with a difference in atomic sizes of more than 12 %; the
presence in the alloy of two elements with an enthalpy
of mixing less than -30 kJ/mol, the average electron
concentration should be in the range of 6 -7 el./at. It is
shown that the ratio of the lattice parameters of solid -
solution HES, dete rmined in the experiment, to the
lattice parameter of the most refractory metal in the
HES determines the value of the elastic modulus.
In this work, the physicomechanical properties of
the high -entropy FeCoCrNiTaTiMo coating
synthesized by us are investig ated.
Methods for the synthesis of the
FeCoCrNiTaTiMo alloy and coatings.
To prepare the tablets, micropowders of the
corresponding metals were taken (Fig. 1a) and mixed
in equiatomic proportions. Then the prepared mixture
of powders was placed in a grind ing bowl of a planetary
ball mill (Fig.1b) made of tungsten carbide, and
grinding bodies (balls 5 -10 mm in diameter) also made
of tungsten carbide were added, the mass of which was
equal to 10 masses of the powder mixture. After that,
the glass was filled with Galosha gasoline, the lid was
tightly closed, and the planetary ball mill was turned on
(rotation speed was 500 rpm, operating time 5 hours).
The homogenized compositions obtained in this way
were then dried in a vacuum and, using a mold
(pressure of 20 tons), were pressed into flat disks 12
mm in diameter and 3 mm thick ( Fig.1c).

American Scientific Journal № ( 41 ) / 2020 41

a) metal microstrips
b) ball mill


c) flat discs
Figure 1 - Synthesis of the FeCoCrNiTaTiMo alloy: metal micropowders (a), planetary ball mill (b),
synthesized flat disks (c)

Experimental technique. In the study of the
microstructure of the coatings of the samples, we used
an Epiquant metallographic microscope (Fig. 2 a). This
device operates on the principle of a linear analyzer and
is intended for structural and analytical studies of solid,
heteroge neous substances, in which physical and
technological properties depend on the geometric
microstructure and the structural components of which
have different reflection coefficients (Fig. 2 b).

а) b)
Figure 2 - Microscope "Epiquant" (a), pictures of the coating (x1000) (b)

Electron microscopic examination was carried out
on a JEOL JSM -5910 scanning electron microscope
(Fig. 3 a). The studies were carried out at an
accelerating voltage of 20 kV. For each sample, 4
images were taken from 4 points of the surface at
magnifications: 245, 1060, 4500 and 14600 times (Fig.
3 b).

а) b)
Figure 3 - Microscope JEOL JSM -5910 (a) and SEM images of coatings (b)
X-ray fluorescence electron spectroscopy (XPS)
was carried out using a TESCAN MIRA 3 electron
microscope. The elemental composition (Fig. 4 a) and
the unevenness of the eleme ntal composition (Fig. 4 b)
were determined.

42 American Scientific Journal № ( 41 ) / 2020
а)
б)
Figure 4 - Elemental composition (a) and uneven elemental composition (b).

On an XRD -6000 X -ray diffractometer (Fig. 5 a),
the phase composition and structure parameters of the
deposited ion -plasm a coating were studied (Fig. 5 b).

а) b)
Figure 5 - XRD -6000 diffractometer (a) and a section of the diffractogram (b)

Система Quanta 200 3 D совмещает в себе
сканирующий электронный микроскоп с
термоэмиссионным катодом (рис. 6 а),
сфокусированный ионный пучок, позволяющий
прецизионно наносить и удалять материалы,
определяя толщину покрытия (рис. 6 б ).

а) b)
Figure 6 - Quanta 200 3D system (a) and coating thickness (b)

Investigation of the morphology (Fig. 7 b) of the
surface of the films obtained by thermal evaporation in
a vacuum was carried out on a JSPM -5400 atomic force
microscope (AFM) manufactured by JEOL (Fig. 7 a).

American Scientific Journal № ( 41 ) / 2020 43

а)

b)
Figure 7 - AFM JSPM -5400 (a) and 3D - coating surface (b)

The experimental setup for determining the
friction coefficients was built by us on the principle of
modularity. The general scheme of the installation for
determining the friction coefficients is shown in Fig. 8
a, and the appearance of the graphical presentation of
research results using the syst em is shown in Fig. 8 b.

1 - known clamping weight, 2 - sample, 3
- sliding surface, 4 - measuring table, 5 -
force transducer, 6 - electronics uni t and
drive
а)

b)
Figure 8 - General scheme of the installation (a) and the type of graphical representation research results (b)

We used the method of testing for microabrasive
wear by the action of a rotating steel ball on a flat sample
with the addition of an emulsion containing abrasive
particles (Fig. 9 b). A spherical crater, called a calotte, is
formed at the point of contact; therefore, the device for this
type of testing was called a caloteter (Fig. 9 a).

а) b)
Figure 9 - Calotester device (a) and wear test (b)

The control of coatings for hardness was carried
out on an HVC -1000A electronic microhardness meter
(Fig. 10 a). The results are shown in Fig. 10 b.

44 American Scientific Journal № ( 41 ) / 2020
а) b)
Figure 10 - Microhardness meter HVC -1000A (a) and the result (b)
Structure of FeCoCrNiTaTiMo coatings. In fig.
11 shows the optical microstructure of high -entropy
(HES) FeCoCrNiTaTiMo coatings at two points. The
unevenness of the coating is observed, w hich is clearly
visible on the maps of energy dispersive spectroscopy
(emf) of this coating (Fig. 12).


Figure 11 - Optical microstructure of FeCoCrNiTaTiMo coatings




Figure 12 - Energy dispersive spectroscopy FeCoCrNiTaTiMo

The distribution maps of elements (Fig. 12) show the nonequilibrium of the che mical elements Fe, Co, Mo in
comparison with the elements Ta, Cr, Ni. The concentration of other elements is negligible. The XPS spectra
shown in Fig. 13 and in t able. 1 indicate the formation of high -entropy coatings.

American Scientific Journal № ( 41 ) / 2020 45

Table 1
Chemical composition in% FeCoCrNiTaTiMo
Fe Co Cr Ni Ta Ti Mo
17 18 16 16 18 16 9

Figure 13 - XPS spectra FeCoCrNiTaTiMo

The content in the spectra in Fig. 12 and 13
elements of tungsten are quite noticeable. It was not
added in our metal micropowders, but appeared in t he
process of grinding the powders with tungsten carbide
balls. In fig. 14 shows PEM FeCoCrNiTaTiMo .

Figu re 14 - PEM coating FeCoCrNiTaTiMo

Studies have shown that the alloy of the
FeCoCrNiTaTiMo system consists of large elongated
grains with an aver age width of 100 -150 μm and an
average length of 200 -300 μm. It should be noted that
black precipitates about 5 -7 microns in size are
observed in the alloys. According to the literature data,
these precipitates are oxides (Me 2O3). In the course of
the study, more complex struc tural components were
discovered. The inner part of the grains of the alloys is
similar to the eutectoid structure. The grains are
separated by thick layers of the second phase.
In fig. 15 shows the diffraction pattern of the
FeCoCrNiTaTiMo coating. Phases are present: Fe, Ti,
TaFe 2, possibly the presence of phases TaCo 2, Mo, Ti,
Ni2Ti, TaCrNi, TiCr, TiNi, Fe 5Ta 3.
Special tantalum alloys are used in industry for
high temperature applications, for making cutters with
high cutting speeds and for making acid -resistant
hardware. The presence of cobalt in high -speed steels
does not increase their har dness, but shifts the
temperature of the onset of hardness loss to 600 °C,
while in ordinary steel it decreases from 200 °C. Cobalt
is also widely used to obtain magn etic materials with
high magnetic permeability and alloys for permanent
magnets (alloys of cobalt with iron, platinum; alloys
based on cobalt, alloyed with aluminum, nickel,
copper, titanium, samarium, lanthanum, cerium).

46 American Scientific Journal № ( 41 ) / 2020
Figure 15 - Diffraction patte rn of FeCoCrNiTaTiMo coating

The introduction of cobalt additives into the alloys
in the amount of 0.5 -4.0% helps to reduce the grain
size, due to which the coercive force (demagnetization
resistance) and residual magnetization increase.
Industrial alloy s for "alnico" magnets contain
aluminum, nickel, cobalt, the rest of iron. Certain alloys
also include copper and titanium.
An analysis of the elemental composition (Fig. 13 -
15) shows the complexity of the high -entropy
FeCoCrNiTaTiMo alloy. The structure o f seven -atomic
high -entropy alloys consists of solid solutions with a
chaotic arrangement o f element atoms. It is assumed
that lattice distortions due to doping with atoms of
different sorts is one of the reasons for the stability of
the structures of soli d solutions at higher temperatures
than intermetallic compounds.
Microhardness of coatings. The results of
measurements of the microhardness of the
FeCoCrNiTaTiMo coatings are given in Table 2.
Table 2
Microhardness of the FeCoCrNiTaTiMo coating in argon
Microhardness 1 2 3 4 5 6 7 8 The
average
HV 342 292 299 292 370 298 265 331 307

Comparative data on the values of microhardness
(HV) of high -entropy equiatomic and traditional alloys
(for example, typical high -strength stainless steels and
alloys of n ickel, cobalt or titanium) are given in table.
3. The microhardness of our FeCoCrNiTa TiMo coating
(Table 2) is not inferior to stainless steels.
Table 3
Microhardness of stainless steels
Alloy Microhardness, HV Alloy Microhardness, HV
Х18Н9Т 186 20ХН 260
316 Stainless steel 189 Hastelloy C 236
ШХ15 200 17-4 PH Stainless steel 362
Х12М 225 Stellite 6 413

Wear resistance of coatings. The results of studies
of the wear resistance of FeCoCrNiTaTiMo coatings
are shown in Table 4.
Tabl e 4
Wear resistance of FeCoCrNiTaTiMo coatings
Sample wear (weight in grams) for 30 min
Before 15,14852 15,14857 15,14859 15,14856 The average 15,148566
After 15,14745 15,14763 15,14759 15,14759 Difference 0,000986

Table 4 shows the wear resistance o f the
FeCoCrNiTaTiMo coating ~ 3x10 -4 g/min.
Tribological features of FeCoCrNiTaTiMo
coatings . The deposition of FeCoCrNiTaTiMo was
carried out on a stationary sample for an hour with a
reference voltage of 150 and 250 volts in a constant
power mode of 1.5 kW.

American Scientific Journal № ( 41 ) / 2020 47

Table 5
Coefficients of friction for copper and aluminum
coatings on copper for aluminum
coefficient of friction error coefficient of friction error
FeCoCrNiTaTiMo 0,256 0,006 0,278 0,002

High -entropy coatings FeCoCrNiTaTiMo turn out
to be a ntifriction, which obviously leads to energy
savings. The surface layer of high -entropy coatings
FeCoCrNiTaTiMo. In fig. 16 shows the thickness of the
deposited coating over 40 minutes. From the figure, a
columnar structure is observed; it has a size of ab out
1.5 microns.

Figure 16 - Thickness of FeCoCrNiTaTiMo coating in argon gas atmosphere

In [11 -13], we showed that the thickness of the
surface layer d(I) is determined by one fundamental
parameter - the molar (atomic) volume of an elem ent ( υ
= M/ ρ, M i s the molar mass (g/mol), ρ is the density
(g/cm 3)), which periodically changes in accordance
with the table of D.I. Mendeleev:
()= 0.17 ⋅10−9
For seven -atom high -entropy FeCoCrNiTaTiMo
alloys, the thickness of the surface layer will have the
value s given in Table 6.
Table 6
Thickness of the surface layer d FeCoCrNiTaTiMo
Alloy ρ, g/sm 3 М, mol -1 d(I), nm d(II), nm
FeCoCrNiTaTiMo 7,15 519 14,9 149

Atomic force microscopy. In fig. 17 shows 3D
images of the surface of FeCoCrNiTaTiMo coatings on
AI SI-201 steel samples at three different points, and
below their fractal structures. The cellular structure of
the high -entropy coating is observed. In [14], we gave
the following explanation of this structure. Plasma
deposition of coatings is a thermodynam ically
nonequilibrium process in an open system. The
formation of a cellular nanostructure in a coating can
occur according to several models:
- a cellular s ubstructure is often formed during
solidification as a result of concentration hypothermia;
- Benar d cells are an example of self -organization.
The control parameter of self -organization is the
temperature gradient leading to a cellular substructure;
- a c ellular dislocation structure is a process of
self -organization of dislocations under conditions of
multiple slip.

48 American Scientific Journal № ( 41 ) / 2020



Figure 17 - 3D images of the surface of the FeCoCrNiTaTiMo coatings at three different points,
and below their fractal structures.
Conclusion.
In conclusion, the following main conclusions can
be drawn:
- the FeCoCrNiTaTiMo alloy and coatings based
on it have been synthesized by mechanical alloying;
- the optical microstructure of high -entropy
coatings reveals unevenness, which is clearly visible on
the maps of energy -dispersive spectroscopy;
- XPS spectra indicate the forma tion of high -
entropy coatings;
- analysis of the elemental composition shows the
complexity of the high -entropy alloy
FeCoCrNiTaTiMo. The structure consists of solid
solutions with a chaotic arrangement of atoms of
elements;
- the microhardness of our coat ing (307 HV) is not
inferior to stainless steels, and the wear resistance of the
coating is 3•10 -4 g/min;
- high -entropy coatings FeCoCrNiTaTiMo turn
out to be antifriction, which obviously leads to energy
savings;
- the thickness of the surface layer d(I) is
determined by one fundamental parameter - the molar
(atomic) volume of the element and is equal to 12.3 nm;
- it has been shown that the formation of a cellular
nanostructure in a coating can occur according to
several models.
The work was carried out under the program
of the Ministry of Education and Science of the
Republic of Kazakhstan. Grants № 0118RK000063
and № F.0781.

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