Combined vacuum-arc hardening of frictional unit components
For increasing the service life of steel components that form a friction pair and are operated under conditions of dynamic loads, elevated temperatures and corrosive media, the process of working contact surface modification has been developed with the use of the vacuum-arc technique. The process...
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| Cite this: | Combined vacuum-arc hardening of frictional unit components / V.A. Belous, I.G. Yermolenko, Yu.A. Zadneprovsky, N.S. Lomino // Вопросы атомной науки и техники. — 2016. — № 4. — С. 93-99. — Бібліогр.: 8 назв. — англ. |
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Belous, V.A. Yermolenko, I.G. Zadneprovsky, Yu.A. Lomino, N.S. 2017-04-04T06:48:28Z 2017-04-04T06:48:28Z 2016 Combined vacuum-arc hardening of frictional unit components / V.A. Belous, I.G. Yermolenko, Yu.A. Zadneprovsky, N.S. Lomino // Вопросы атомной науки и техники. — 2016. — № 4. — С. 93-99. — Бібліогр.: 8 назв. — англ. 1562-6016 https://nasplib.isofts.kiev.ua/handle/123456789/115410 621.793.74:669.094.54 For increasing the service life of steel components that form a friction pair and are operated under conditions of dynamic loads, elevated temperatures and corrosive media, the process of working contact surface modification has been developed with the use of the vacuum-arc technique. The process has been realized in a two-stage technological cycle, including hardening of the base material by ion-plasma nitriding that replaces effectively the “furnace” nitriding, and a subsequent deposition of protective coatings Mo-N (molybdenum nitride) and Ti-N (titanium nitride). Various physical properties of the modified samples (microhardness depth profiles, as well as structure peculiarities of nitrided layers and nitride coatings) have been investigated as functions of the parameters of the process under development. Comparative laboratory tests of service characteristics (abrasion/corrosion resistances) of the components have been made, and an essential improvement of these characteristics has been demonstrated for the modified surfaces. В целях увеличения эксплуатационного ресурса стальных деталей, представляющих собой пару трения и работающих в условиях динамической нагрузки, повышенной температуры и коррозионной среды, разработан процесс модифицирования контактирующих рабочих поверхностей с использованием вакуумно- дугового метода. Этот процесс реализован в двухстадийном технологическом цикле: упрочнение основы методом ионно-плазменного азотирования, эффективно заменяющим «печное» азотирование, и последующее осаждение защитных покрытий Mo-N и Ti-N. Исследована зависимость ряда физических свойств модифицированных образцов (профили микротвeрдости по глубине от поверхности, а также структурные особенности азотированных слоeв и нитридных покрытий) от параметров разрабатываемого процесса. Выполнены сравнительные лабораторные испытания служебных характеристик (абразивной и коррозионной стойкостей) деталей и продемонстрировано существенное улучшение этих характеристик для модифицированных поверхностей. В цілях збільшення експлуатаційного ресурсу сталевих деталей, що є парою тертя і працюючих в умовах динамічного навантаження, підвищеної температури і корозійного середовища, розроблено процес модифікування контактуючих поверхонь з використанням вакуумно-дугового методу. Цей процес реалізовано в двохстадійному технологічному циклі: зміцнення основи методом іонно-плазмового азотування, ефективно замінюючим «пічне» азотування, і подальше осадження захисних покриттів Mo-N і Ti-N. Досліджено залежність ряду фізичних властивостей модифікованих зразків (профілі мікротвердості по глибині від поверхні, а також структурні особливості азотованих шарів і нітридних покриттів) від параметрів процесу, що розробляється. Виконано порівняльні лабораторні випробування службових характеристик (абразивної і корозійної стійкості) деталей і продемонстровано істотне поліпшення цих характеристик для модифікованих поверхонь. en Національний науковий центр «Харківський фізико-технічний інститут» НАН України Вопросы атомной науки и техники Физика радиационных и ионно-плазменных технологий Combined vacuum-arc hardening of frictional unit components Комбинированноe упрочнениe деталей узлов трения вакуумно-дуговым методом Комбіноване зміцнення деталей вузлів тертя вакуумно-дуговим методом Article published earlier |
| institution |
Digital Library of Periodicals of National Academy of Sciences of Ukraine |
| collection |
DSpace DC |
| title |
Combined vacuum-arc hardening of frictional unit components |
| spellingShingle |
Combined vacuum-arc hardening of frictional unit components Belous, V.A. Yermolenko, I.G. Zadneprovsky, Yu.A. Lomino, N.S. Физика радиационных и ионно-плазменных технологий |
| title_short |
Combined vacuum-arc hardening of frictional unit components |
| title_full |
Combined vacuum-arc hardening of frictional unit components |
| title_fullStr |
Combined vacuum-arc hardening of frictional unit components |
| title_full_unstemmed |
Combined vacuum-arc hardening of frictional unit components |
| title_sort |
combined vacuum-arc hardening of frictional unit components |
| author |
Belous, V.A. Yermolenko, I.G. Zadneprovsky, Yu.A. Lomino, N.S. |
| author_facet |
Belous, V.A. Yermolenko, I.G. Zadneprovsky, Yu.A. Lomino, N.S. |
| topic |
Физика радиационных и ионно-плазменных технологий |
| topic_facet |
Физика радиационных и ионно-плазменных технологий |
| publishDate |
2016 |
| language |
English |
| container_title |
Вопросы атомной науки и техники |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| format |
Article |
| title_alt |
Комбинированноe упрочнениe деталей узлов трения вакуумно-дуговым методом Комбіноване зміцнення деталей вузлів тертя вакуумно-дуговим методом |
| description |
For increasing the service life of steel components that form a friction pair and are operated under conditions of
dynamic loads, elevated temperatures and corrosive media, the process of working contact surface modification has
been developed with the use of the vacuum-arc technique. The process has been realized in a two-stage
technological cycle, including hardening of the base material by ion-plasma nitriding that replaces effectively the
“furnace” nitriding, and a subsequent deposition of protective coatings Mo-N (molybdenum nitride) and Ti-N
(titanium nitride). Various physical properties of the modified samples (microhardness depth profiles, as well as
structure peculiarities of nitrided layers and nitride coatings) have been investigated as functions of the parameters
of the process under development. Comparative laboratory tests of service characteristics (abrasion/corrosion
resistances) of the components have been made, and an essential improvement of these characteristics has been
demonstrated for the modified surfaces.
В целях увеличения эксплуатационного ресурса стальных деталей, представляющих собой пару трения и
работающих в условиях динамической нагрузки, повышенной температуры и коррозионной среды,
разработан процесс модифицирования контактирующих рабочих поверхностей с использованием вакуумно-
дугового метода. Этот процесс реализован в двухстадийном технологическом цикле: упрочнение основы
методом ионно-плазменного азотирования, эффективно заменяющим «печное» азотирование, и
последующее осаждение защитных покрытий Mo-N и Ti-N. Исследована зависимость ряда физических
свойств модифицированных образцов (профили микротвeрдости по глубине от поверхности, а также
структурные особенности азотированных слоeв и нитридных покрытий) от параметров разрабатываемого
процесса. Выполнены сравнительные лабораторные испытания служебных характеристик (абразивной и
коррозионной стойкостей) деталей и продемонстрировано существенное улучшение этих характеристик для
модифицированных поверхностей.
В цілях збільшення експлуатаційного ресурсу сталевих деталей, що є парою тертя і працюючих в умовах
динамічного навантаження, підвищеної температури і корозійного середовища, розроблено процес
модифікування контактуючих поверхонь з використанням вакуумно-дугового методу. Цей процес
реалізовано в двохстадійному технологічному циклі: зміцнення основи методом іонно-плазмового
азотування, ефективно замінюючим «пічне» азотування, і подальше осадження захисних покриттів Mo-N і
Ti-N. Досліджено залежність ряду фізичних властивостей модифікованих зразків (профілі мікротвердості
по глибині від поверхні, а також структурні особливості азотованих шарів і нітридних покриттів) від
параметрів процесу, що розробляється. Виконано порівняльні лабораторні випробування службових
характеристик (абразивної і корозійної стійкості) деталей і продемонстровано істотне поліпшення цих
характеристик для модифікованих поверхонь.
|
| issn |
1562-6016 |
| url |
https://nasplib.isofts.kiev.ua/handle/123456789/115410 |
| citation_txt |
Combined vacuum-arc hardening of frictional unit components / V.A. Belous, I.G. Yermolenko, Yu.A. Zadneprovsky, N.S. Lomino // Вопросы атомной науки и техники. — 2016. — № 4. — С. 93-99. — Бібліогр.: 8 назв. — англ. |
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| fulltext |
ISSN 1562-6016. ВАНТ. 2016. №4(104) 93
UDC 621.793.74:669.094.54
COMBINED VACUUM-ARC HARDENING
OF FRICTIONAL UNIT COMPONENTS
V.A. Belous, I.G. Yermolenko, Yu.A. Zadneprovsky, N.S. Lomino
National Science Center “Kharkov Institute of Physics and Technology”
Kharkov, Ukraine
E-mail: yaz@kipt.kharkov.ua
For increasing the service life of steel components that form a friction pair and are operated under conditions of
dynamic loads, elevated temperatures and corrosive media, the process of working contact surface modification has
been developed with the use of the vacuum-arc technique. The process has been realized in a two-stage
technological cycle, including hardening of the base material by ion-plasma nitriding that replaces effectively the
“furnace” nitriding, and a subsequent deposition of protective coatings Mo-N (molybdenum nitride) and Ti-N
(titanium nitride). Various physical properties of the modified samples (microhardness depth profiles, as well as
structure peculiarities of nitrided layers and nitride coatings) have been investigated as functions of the parameters
of the process under development. Comparative laboratory tests of service characteristics (abrasion/corrosion
resistances) of the components have been made, and an essential improvement of these characteristics has been
demonstrated for the modified surfaces.
The development of turbine engineering makes
necessary the improvement in the reliability of turbine
control systems, in particular, the components of the
steam distribution unit. The structure of this unit in the
turbine K-325 comprises the elements that form the
friction pair, operate under dynamic loads, and are
subject to abrasion/corrosion wears, too. Fig. 1
illustrates some of those elements.
Fig. 1. Friction pair elements: “Support” (1) and
“Joint” (2). (The arrows show the contacting areas)
At plant conditions, for hardening of the mentioned
unit elements it was customary to use “furnace”
nitriding [1]. In accordance with the technical
requirements of PJSC “Turboatom” to increase the wear
resistance of the friction surfaces of the rotating
“Support” and “Joint”. That protective coatings have
proposed that thin (up to 10 μm) layers of very hard
nitride-based coatings, well-proven earlier in all kinds
of service applications [2], should be used. However,
since the “furnace” nitriding had appeared incompatible
with a subsequent vacuum-arc deposition of coatings
because of their poor adherence, then, as an alternative,
the method of ion nitriding in the plasma created by the
two-step vacuum-arc discharge (TSVAD) was used
[34].
During deposition of wear-resistant coatings on the
bumpy surface of the «Joint», the molybdenum nitride
film was formed, while on the concave surface of the
“Support” the titanium nitride coating was formed. (In
this particular case, the deposition of coatings having
different compositions was caused by the necessity to
overcome the setting-up effect typical for materials of
the same composition). The two successive stages
(nitriding + protective coating deposition) were realized
in a single technological process with one-time loading
of the elements into the vacuum chamber.
STAGES OF ST.25CrMoVa MODIFICATION
Fig. 2 shows the characteristic temperature-time
curve for the element at different stages of its surface
modification. The limiting heating temperature in the
TSVAD plasma and during metal ion bombardment was
determined (at a fixed heat removal to the element
holder) by the applied potential value and the duration
time of each of the process stages. The stage duration
was also dependent on the mass of the elements to be
hardened.
Fig. 2. Different stages of sample surface modification
process in the temperature-time coordinates
In the “Cleaning” stage, the sample was exposed to
argon plasma created by means of the TSVAD. The use
of this stage, being the result of low-energy action of the
discharge plasma on the processed surface, has allowed
us to avoid local discharge positioning that may lead to
faulty production. The next stage, conditionally called
“Heating”, took place as the unit element was
bombarded by metal (titanium/molybdenum) ions at a
mailto:yaz@kipt.kharkov.ua
94 ISSN 1562-6016. ВАНТ. 2016. №4(104)
higher accelerating potential, and it terminated upon
attaining the working temperature of nitriding. In the
“Ion nitriding” stage, nitrogen was let in the chamber
volume, and the two-step vacuum-arc discharge was
initiated. As the run of the curve in Fig. 2 shows, by the
end of the stage a certain temperature drop (within 10%)
of the processed surfaces occurred. The current density
of gaseous ions, accelerated by the -500 V potential
applied to the unit element, was found to be
~ 1 mA/cm
2
. The duration of the nitriding stage was no
more than one hour.
The “Sublayer deposition” stage followed
immediately after the nitriding of the base material
(st.25CrMoVa) was completed. A thin (≤ 2 μm)
titanium or molybdenum layer was deposited by the
vacuum-arc method on the surface of the “Support” or
the “Joint”, respectively. This provided a high degree of
adherence to thicker (up to 10 μm) nitride layers of the
metals deposited at the next stage of surface
modification.
The process of integrated hardening of the unit
element was completed by the deposition of the coating
based on titanium/molybdenum nitrides. At this stage, a
gradual temperature decrease took place, since the
energy contribution from the deposited ions at a lower
potential applied to the element, did not compensate the
heat removal losses.
The modification of the “Support” steel surface
through deposition of the Ti-N coating was realized by
using a similar pre-nitriding procedure as that applied
for the “Joint” with the Mo-N coating.
OPTIMIZATION OF COATING
DEPOSITION MODES
When forming coatings of different compositions
(MoN and TiN), the gaseous pressure value was chosen
out of the necessity to provide approximately equal
microhardness values Hμ for these coatings. This
requirement was dictated by the peculiarities interaction
of hardened element performance in the friction pair
under symmetrical contact loads.
The coating deposition process was also optimized
when choosing the substrate bias potential. This
parameter of the deposition process had an effect on the
characteristics of the both coatings. Thus, the maximum
hardness values for the Mo-N coatings were obtained at
minimum bias potentials; that corresponded to “colder”
deposition conditions. The increase of the potential, and
hence, of temperature in the condensation region led to
more equilibrium conditions of deposition; and in this
case the microhardness of the deposited coatings was
reduced (Table 1).
Table 1
Coating microhardness at different bias potentials
(PN2 = (1.5…2)∙10
-3
Torr)
U, V
Нµ, GPа
Mo-N Ti-N
50 33.9 27.2
60 29 26.2
100 23.5 24.5
It should be noted that some modes of Mo-N coating
deposition are typified by the appearance of
microcracks. The titanium nitride coatings exhibited no
cracking in the whole range of deposition parameters
under study. That may testify to a lower level of internal
stresses in these coatings.
The absence of cracks on the coating surfaces is the
necessary, but insufficient criterion of fitness for service
applications. Though having rather high internal stress
levels, very hard coatings of Mo-N composition may
also exhibit cracking at their relaxation with time and
(or) under loads, which has a detrimental effect on their
performance characteristics. Therefore, the final choice
of the mode of coating deposition, and hence, of the
optimum Hμ value, was made on the basis of the
performance test results.
DEPTH DISTRIBUTION OF NITROGEN
CONCENTRATIONS IN STEEL
For measuring the hardened layer thickness,
metallographic sections of the processed samples were
prepared. In the measurements, the indentation
technique aided by the Nanoindenter G200 was used.
The initial microhardness on the non-nitrided surface of
st.25CrMoVa samples was determined to be no more
than 3.5 GPa.
Fig. 3 shows the depth distributions of the nitrogen
content and the microhardness for two samples (one –
nitrided only, the other – subjected to nitriding + a
subsequent Mo-N coating deposition. (The nitrogen
concentration profiles were measured with a 10 μm step
on the electron microscope, using the X-ray
fluorescence analysis).
Fig. 3. Depth profiles of nitrogen concentration and
microhardness for the processes of ionic nitriding and
nitriding plus Mo-N coating deposition. (The hatching
defines the region related to the coating)
The increased (up to 45 at.%) nitrogen content of the
deposited coating (shaded region in Fig. 3) is attributed
to the synthesis of the corresponding molybdenum
nitride phases, i. e., to the stable-state presence of
nitrogen in the steel. It is just the presence of these
phases that explains the higher hardness of the deposited
nitride layer. Under the Mo-N coating, there was a thin
intermediate Mo layer deposited for improving the
adhesive properties under higher vacuum conditions
(P ~ 10
-5
Torr); and the points on the curve in Fig. 3 just
refer to this layer having the minimum nitrogen
m
ISSN 1562-6016. ВАНТ. 2016. №4(104) 95
concentration. As is seen from the figure, the spatial
extent (~ 10 μm) of the dip, related to the mentioned
minimum, substantially exceeds the thickness of the
deposited Mo layer. This is possibly due to the
processes of steel surface denitriding that occur during
surface heating under ion bombardment, which is used
before deposition of the molybdenum interlayer.
It also follows from Fig. 3 that the nitrogen
concentration and the depth of its penetration into the
substrate material for the samples subjected to different
ion-plasma treatments are essentially different. The
coating-bearing nitrided samples exhibit higher
concentrations of nitrogen and its greater penetration
depths than the samples that were subjected to nitriding
only. As a result of the process of ion-plasma nitriding,
the nitrogen is concentrated in the near-surface layer of
the steel substrate to a depth up to 20 μm, whereas at
depths up to ~ 80 to 100 μm the nitrogen concentration
is reduced to a level of ~ 2.5 at.%.
Considering that the process of nitride coating
deposition was carried out in the nitrogen atmosphere,
and with substrate heating (see Fig. 2), it was necessary
to verify whether the process of substrate nitriding has
ceased or still continued at the stage of coating
deposition. For this purpose, we have investigated the
nitrogen depth profile through the use of the
metallographic section of the steel sample that
underwent coating deposition but without the stage of
prenitriding. Fig. 4 shows the data of microprobe X-ray
fluorescence analysis related to the behavior of the main
substrate component, Fe, and to the plasma flow
components (Mo and N) participating in the process of
coating deposition.
Fig. 4. Distributions of Мо, N and Fe components in the
metallographic section of the sample
with Mo (2 μm) and Мо-N (4.5 μm) layers
We call your attention to the component distribution
in the intermediate layer adjacent partially to the ~ 2 μm
thick substrate surface and partially to the Mo layer
deposited on the substrate surface (~ 1.5 μm in
thickness). The interlayer exhibits the concentration
distribution of the Fe atoms as being the main
components of the substrate, and the deposited Mo
atoms. The existence of this layer can be explained in
terms of the processes of ion mixing, which take place
as the steel surface is exposed to molybdenum ions. The
ion mixing results from partial sputtering of the
substrate atoms, their ionization in the near-surface
layer and subsequent return to the surface under the
action of the applied negative potential. As regards the
nitrogen atoms in the Mo sublayer, they were not
observed there, i.e., there was no penetration of nitrogen
into the steel substrate at the stage of vacuum-arc
coating deposition. In turn, the Mo layer is a barrier for
the escape of nitrogen already absorbed by the substrate
surface both at the stage of Mo deposition and the stage
of application of the Mo-N coating. As the deposition
processes are carried out, the samples continue to heat,
and the concentration of nitrogen atoms in the steel
substrate of the sample, formed in the stage of nitriding,
gets redistributed deep into the metal.
In this way, the two-stage process of ion-plasma
treatment has resulted in the formation of the layer of
improved hardness (H ~ 5 GPa) on the steel sample
surface to a depth of 100 μm, and the nitride coating
with H ~ 30 GPa.
STRUCTURAL CHARACTERISTICS
OF THE MODIFIED LAYERS
Fig. 5 gives the comparative transverse-fracture
photographs taken from different samples: initial (1),
hardened by ion nitriding (2), and with Mo-N and Ti-N
coatings deposited onto the nitrided surface (3).
Fig. 5. Transverse fracture pictures:
1 – initial steel st.25CrMoVa; 2 – nitrided steel;
3 – nitrided steel with Ti-N and Mo-N coatings
The pictures were taken using the scanning electron
microscope. The structure of the initial steel sample
shows the presence of specific grained formations with
predominance of large-size grains (~ 100 μm). After ion
nitriding (see Fig. 5 (2)) some structure ordering with
grain refining to a layer depth of ~ 70 μm takes place.
The essential steel structure rearrangement with grain
refinement down to 1…3 μm (immediately under the
coating) and with a tendency of grain coarsening up to
~ 10 μm is observed at a depth of down to ~ 100 μm
(see Fig. 5 (3)). This behavior of steel structure
characteristics reflects the mode of spatial distribution
m
96 ISSN 1562-6016. ВАНТ. 2016. №4(104)
of nitrogen deep in the metal, and is responsible for the
formation of the hardness H(t) profile (see Fig. 3).
CRYSTALLOGRAPHIC STUDIES
OF THE COATED SAMPLES
The analysis of X-ray spectra taken from the coated
samples (Fig. 6) gives the following estimates for the
crystal orientations in the obtained coatings. The
titanium nitride-based coatings exhibit predominantly a
strong reflection (111), which corresponds to the NaCl –
type crystalline structure with the parameter
a = 0.426 nm and the coherent-scattering region of size
L ≈ 41 nm. The X-ray spectrum for the molybdenum
nitride-based coatings is more complicated. It shows
three γ-Mо2N lines with the lattice parameter а = 0.420
and the size L ≈ 11 nm. Note that the amplitudes of each
of the reflections under discussion differ insignificantly
from each other.
Fig. 6. X-ray patterns of protective coatings based on
Ti-N (above) and Mo-N (below)
The differences between the X-ray spectra of Ti-N
and Mo-N coatings are also confirmed by structural
electrooptical images of fractured samples having
coatings of different compositions (Fig. 7).
Fig. 7. Electrooptical images of Тi-N and MoN-coatings
fractures
In fact, while the photograph of the Ti-N-coating
clearly shows the columnar structure of the preferred
orientation, the crystallites seen in the fracture of the
Mo-N-base coating are smaller-sized, and their
preferred orientation is absent.
INTERNAL STRESSES IN THE COATINGS
The analysis of X-ray spectra taken from the
samples with coatings of different compositions has
enabled us to estimate the macrodeformational
compression stresses in the chosen (optimal) modes of
deposition; the obtained results are given in Table 2.
Table 2
Macrodeformational compression stresses
and microhardness of the coatings
Coating
Potential
displacement,
В
Hμ,
GPа
Compressive
deformation
ε, %
Mo-N -85 27.8 -1.84
Ti-N -90 25.8 -0.77
As it follows from the table, the level of the stresses
in the Mo-N-base coatings is substantially higher than in
the Ti-N-coatings, even though their microhardness
values differ insignificantly.
ADHESIVE CHARACTERISTICS
OF THE COATINGS
In principle, the vacuum-arc deposition techniques
provide a satisfactory adherence of coatings to the
substrate. This is achieved by applying ion-beam
cleaning of the base surface done immediately before
application of coatings. This cleaning technique not
only provides the removal of possible impurities off the
surface, but also initiates the process of ion mixing of
the sputtered base atoms with the deposited coating
atoms.
The ion-plasma nitriding followed by application of
protective coatings also provides high adhesion
characteristics of the obtained coating-base formation.
The good adhesion is additionally contributed by thin (1
to 2 μm) intermediate layers of titanium or molybdenum
deposited onto the nitrided surface of the base with the
use of the same cathodes as the ones used for
subsequent Ti or Mo nitride layers.
Fig. 8. Transverse fractures of steel samples with
deposited layers of metals and their nitrides
Fig. 8 gives the photographs of brittle fractures of
the samples having coatings of different compositions.
ISSN 1562-6016. ВАНТ. 2016. №4(104) 97
The attention is drawn to a high degree of consistency
the substrate-metal and metal-its nitride interface
profiles, this bearing witness to a reasonable level of
adhesion.
Fig. 9 presents the photos of the track produced as
the diamond indenter passed under increasing load
conditions over the surface of the Mo-N-coating, which
was deposited onto the steel samples being in the initial
and nitrided states. (The total run length of the indenter
in the figure is ~ 400 μm). We call your attention to a
substantial delay in the onset of cracking (and peeling)
of the coating deposited on the nitrided base in
comparison with the coating deposited on the initial-
state steel.
Fig. 9. Мо-N-coated surfaces with track marking
of diamond indenter run:
а – coating on the initial-state steel base;
b – coating on the nitrided steel
So, the application of the given technique has
confirmed the fact of improvement in the adhesive
properties of coatings as they are deposited on the
nitrided steel base.
PHYSICAL AND MECHANICAL
CHARACTERISTICS OF THE COATINGS
Tables 3 and 4 give the research data on the physical
and mechanical characteristics of the obtained Ti-N and
Mo-N-coatings, depending on whether the coatings
were deposited on the initial surface of steel or on its
surface after nitriding.
Table 3
Physical-and-mechanical properties
(“Micron-Gamma” measurements)
Table 4
Physical-and-mechanical properties
(G200 and PМТ-3 measurements)
Modified surface Н, GPа E, GPа H/E
Ti-N 34 436 0.08
Nitriding + Ti-N 36.5 425 0.09
Mo-N 32 308 0.1
Nitriding + Mo-N 38 381 0.1
The investigations were performed using different
methods and devices, in particular, the facility “Micron-
Gamma” [7] when working with the Vickers indenter
(see Table 3), and the devices G200 and PMT-3 at
nano- and microindentation (see Table 4). Despite the
fact that the two methods give somewhat different
results, these differences are insignificant. As it follows
from Fig. 3, the process of nitriding has led to an
appreciable increase in the hardness of the steel base
from 2.7 up to 9 GPa. However, on subsequent
deposition of the protective coatings Ti-N and Mo-N, all
the Hμ values measured with one method (see Table 3),
and also, the Hμ and H values measured with the other
method (see Table 4), are practically no different from
the corresponding values for the coatings deposited on
the initial steel surface. This implies that the parameters
describing the physical-mechanical characteristics of the
coatings (see Tables 3 and 4) are independent of the
properties of the base, onto which the coatings were
deposited. Surely, this conclusion is valid for relatively
thick coatings, when their thickness considerably
exceeds the depths of indentation.
The parameter H/E is one of the important
characteristics of the material [5]. It characterizes the
ability of the material to resist changes in shape and
dimensions under deformation. It can be also used for
estimating the frictional wear of the material. There are
empirical relationships [6], which enable one to define
the type of the structural state by using the mentioned
parameter. As it is evident from Table 5, the range of
H/E values for our Mo-N and Ti-N-coatings varies
between 0.06 and 0.08, and that corresponds to fine-
crystalline structural condition. In this case, the
physical-mechanical properties of the modified layers of
different compositions, but appearing to be the
contacting pair in the frictional unit, differ
insignificantly.
WEAR RESISTANCE OF THE COATINGS
The wear rates of different coating materials were
compared by measuring the parameter Il, which is the
ratio of the indentation depth to the path length covered
by the diamond indenter over the surfaces of the given
materials. As it follows from the data given in Table 5,
the resistance of the nitride coatings Ti-N and Mo-N to
the given wear mode is essentially dependent on what
substrate the coatings were deposited. And in the case of
the nitrided steel, the linear wear index is lower than
that of the coatings deposited on the initial material.
Modified
surface
Micro-
hardness,
GPа
Nano
hard-
ness,
GPа
Elastic
modu-
lus,
GPа
H/E
Ti-N 29.7 28.6 451 0.06
Nitriding +
Ti-N
28.9 29.2 447 0.065
Mo-N 29.8 30.3 377 0.08
Nitriding +
Mo-N
28.5 32.1 439 0.07
98 ISSN 1562-6016. ВАНТ. 2016. №4(104)
Table 5
Linear wear of different materials
Coating St.25CrMoVa Linear wear Іl, 10
-7
Ti-N
0.95
nitriding 0.52
Mo-N
0.75
nitriding 0.61
TRIBOLOGICAL CHARACTERISTICS
OF THE COATINGS
The comparison of friction coefficients of different
materials (Table 6) was carried out using the “Micron-
Gamma” facility. The diamond indenter was used as a
counterbody; therefore, the friction coefficient values
given in Table 6 are relative and can be used only for
the purposes of comparison with different materials.
Table 6
Coefficients of diamond indenter friction over different
materials at different loads
Coating St.25CrMoVa
Coefficient of friction, ffr
Load, g
225 375 525
Ti-N
0.09 0.09 0.09
nitriding 0.05 0.06 0.06
Mo-N
0.09 0.09 0.09
nitriding 0.065 0.066 0.07
Note the load independence of the ffr values listed in
the table. In this case, the friction coefficients for the
coatings deposited on the nitrided base are substantially
lower than those found for the coatings deposited onto
the steel base not subjected to nitriding.
PERFORMANCE CHARACTERISTICS
OF THE MODIFIED SAMPLES
To investigate corrosion resistance in the 3% NaCl
medium, the potentiometer testing technique was used.
Fig. 10 shows the current density j curves as functions
of the potential φ for the following samples: initial steel,
discharge-nitrided steel, and the nitrided steel having the
protective Mo-N and Ti-N-coatings.
Fig. 10. Current-voltage characteristics of different
samples in aggressive medium at corrosion testing:
1 – steel in the initial state; 2 – steel after “furnace”
nitriding; 3 – steel after ion-plasma nitriding;
4 – Mo-N-coated nitrided steel;
5 Ti-N–coated nitrided steel
For comparison, the same figure gives the corrosion
test data for the steel subjected to “furnace” nitriding.
From the behavior of the j(φ) curve for the initial
st.25CrMoVa it follows that this material has a low
corrosion resistance. The performance of “furnace” or
ion-plasma nitriding processes results in improving the
anticorrosion properties of steel. Notably that the second
of the two mentioned processes has a distinct advantage.
However, the highest protective properties against
corrosion medium are exhibited by the samples
subjected to a combined modification, when the Mo-N
or Ti-N-coatings were deposited onto the steel surface
that underwent nitriding in the gas-discharge plasma.
Fig. 11 shows the comparative data on the resistance
of different samples under abrasive action. The abrasive
wear of the coatings was performed with the setup
described in ref. [8]; it was estimated by the weight loss
of the sample surface exposed to abrasion cycling.
Fig. 11. Abrasive wear of different sample
As can be seen from Fig. 11, the application of the
above-discussed processes for modifying the initial steel
surface leads to a substantial improvement of its
abrasion resistance. Thus, ionic nitriding increases the
abrasion resistance by more than an order of magnitude,
while the Ti-N-coating deposited on the nitrided steel
base increases the resistance of the initial steel by a
factor of more than 20, and the Mo-N-coating – by a
factor of up to 500.
CONCLUSIONS
1. To replace the “furnace” nitriding, the method of
ion-plasma nitriding of the steel has been offered, which
is compatible with a subsequent coating deposition.
2. The pilot process of vacuum ion-plasma nitriding
of the surface has been developed for full-scale
components forming the friction pair. As a result, layers
of improved hardness have been formed on the sample
surface to a depth up to 100 μm.
3. Processes of depositing protective Mo-N- and
Ti-N-coatings on the nitrided sample surfaces have been
investigated. In the selected optimized modes of
deposition, coatings with close values of microhardness
(at a level of 29 GPa) have been obtained.
4. The process of combined vacuum-arc hardening
in a single technological cycle (nitriding + coating) has
been developed for full-scale components.
5. Diversified studies on physical characteristics
have been made for modified layers applied for
protecting working surfaces of the components. The
ISSN 1562-6016. ВАНТ. 2016. №4(104) 99
steel base nitriding results in size reduction of the
structure formations, viz., the grain size decreases by an
order of magnitude.
6. The use of protective coatings on the nitrided steel
surface has provided a substantial improvement in the
service characteristics of the hardened samples. Their
corrosion resistance has become nearly fivefold higher,
while the abrasion resistance has increased by one to
two orders of magnitude.
REFERENCES
1. Yu.M. Lakhtin, Ya.D. Kogan, G.I. Shpis, et al.
Theory and technology of nitriding. M.: “Metallurgiya”,
1991, 320 p.
2. I.I. Aksyonov, A.A. Andreyev, V.A. Belous, et al.
Vacuum arc. Plasma sources, coating deposition,
surface modification. Kiev: “Naukova Dumka”, 2012,
728 p.
3. L.P. Sablev, N.S. Lomino, R.I. Stupak,
A.A. Andreyev, A.M. Chikryzhov. Two-step vacuum-
arc discharge: characteristics and initiation techniques.
// Reports on the 6
th
International Conference
“Equipment and heat treatment technologies for metals
and alloys”. Kharkov: NSC KIPT, 2005, v. 2, p.159-
169.
4. A.A. Andreyev, V.M. Shulayev, L.P. Sablev.
Steel nitriding in a low-pressure gaseous arc discharge //
PSE. 2006, v. 4, N 3-4, p. 191-1975.
5. Yu.V. Mil’man. New techniques of
micromechanical testing of materials by the local rigid-
indenter loading method // Current materials science of
the XXI century. Kiev: “Naukova Dumka”, 1998,
p. 637-656.
6. S.A. Firstov, V.F. Gorban’, Eh.P. Pechkovsky.
New methodology of processing and analysis of the
results of automatic indentation of materials. Kiev:
“Logos”, 2009, p. 23.
7. S.R. Ignatovich, I.M. Zakiyev. Universal micro-
nanoindentometer “Micron-Gamma” // Zavodskaya
Laboratoriya. Diagnostika Materialov. 2011, N 1, v. 77,
p. 61-67 (in Russian).
8. I.I. Aksyonov, V.A. Belous, Yu.A. Zadneprovsky,
V.I. Kovalenko, N.S. Lomino. The effect of small
silicon additives on the service characteristics of nitride-
titanium coatings // Voprosy Atomnoj Nauki i Tekhniki.
Seriya “Fizika radiatsionnykh povrezhdenij i
radiatsionnoe materialovedenie”. 2011, N 4, p. 145-149
(in Russian).
Статья поступила в редакцию 21.03.2016 г.
КОМБИНИРОВАННОE УПРОЧНЕНИE ДЕТАЛЕЙ УЗЛОВ ТРЕНИЯ
ВАКУУМНО-ДУГОВЫМ МЕТОДОМ
В.A. Белоус, И.Г. Ермоленко, Ю.А. Заднепровский, Н.С. Ломино
В целях увеличения эксплуатационного ресурса стальных деталей, представляющих собой пару трения и
работающих в условиях динамической нагрузки, повышенной температуры и коррозионной среды,
разработан процесс модифицирования контактирующих рабочих поверхностей с использованием вакуумно-
дугового метода. Этот процесс реализован в двухстадийном технологическом цикле: упрочнение основы
методом ионно-плазменного азотирования, эффективно заменяющим «печное» азотирование, и
последующее осаждение защитных покрытий Mo-N и Ti-N. Исследована зависимость ряда физических
свойств модифицированных образцов (профили микротвeрдости по глубине от поверхности, а также
структурные особенности азотированных слоeв и нитридных покрытий) от параметров разрабатываемого
процесса. Выполнены сравнительные лабораторные испытания служебных характеристик (абразивной и
коррозионной стойкостей) деталей и продемонстрировано существенное улучшение этих характеристик для
модифицированных поверхностей.
КОМБІНОВАНЕ ЗМІЦНЕННЯ ДЕТАЛЕЙ ВУЗЛІВ ТЕРТЯ
ВАКУУМНО-ДУГОВИМ МЕТОДОМ
В.A. Білоус, І.Г. Єрмоленко, Ю.А. Заднепровський, М.С. Ломіно
В цілях збільшення експлуатаційного ресурсу сталевих деталей, що є парою тертя і працюючих в умовах
динамічного навантаження, підвищеної температури і корозійного середовища, розроблено процес
модифікування контактуючих поверхонь з використанням вакуумно-дугового методу. Цей процес
реалізовано в двохстадійному технологічному циклі: зміцнення основи методом іонно-плазмового
азотування, ефективно замінюючим «пічне» азотування, і подальше осадження захисних покриттів Mo-N і
Ti-N. Досліджено залежність ряду фізичних властивостей модифікованих зразків (профілі мікротвердості
по глибині від поверхні, а також структурні особливості азотованих шарів і нітридних покриттів) від
параметрів процесу, що розробляється. Виконано порівняльні лабораторні випробування службових
характеристик (абразивної і корозійної стійкості) деталей і продемонстровано істотне поліпшення цих
характеристик для модифікованих поверхонь.
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