CC BY
3
UDK 66
Rakhmonov I. Ya.
Makhmudov N.A.
Israilov M.
Academy of the Armed Forces of the Republic of Uzbekistan
TRIBOTECHNICAL AND MECHANICAL PROPERTIES OF TI-AL-N NANOCOMPOSITE COATINGS OBTAINED BY PLASMA ION IMPLANTATION AND DEPOSITION
Annotation: The possibility of formation of nanocrystal Ti-Al-N coatings by plasma ion implantation and deposition is shown. Mechanical and tribotechnical characteristics of coatings compared to TiN coating are studied. Ti-Al-N nanocomposites have high hardness (H=35 GPa) and low wear capacity, higher wear resistance compared to TiN coating.
Keywords: nanocrystal coatings, metal plasma, HF voltage, mechanical and tribotechnical characteristics.
Introduction
Recently, much attention has been paid to research into the physical and mechanical properties of nanomaterials obtained in the form of coatings by various deposition methods.
The most common methods in industry are chemical (CVD), physical-chemical (PCVD) and physical deposition [1-3]. Nanocrystal coatings based on nitrides and carbides produced by these methods remove new physical and mechanical properties - increased mechanical strength, high hardness, high wear resistance compared to conventional monophasic paintings. Among the refractory compounds that show high functional characteristics, nanocrystal composites of systems (Me1x, Me21-x)N, obtained in the form of solid solutions of incorporation, take a special place. One element is titanium (Me1x), the second element is copper, aluminum, vanadium, molybdenum, niobium, silicon, etc. [4-8]. According to the referents, in order to provide high mechanical and tribotechnical characteristics of nanocrystal composites, it is necessary to create such a composition in which the surfaces of hard grains of feather metal nitride are coated with an amorphous-like damping interlayer. Volumetric support of such interlayer for different systems is determined by interatomic binding force and puts 7... 18% [9-11].
In order to test these conditions, we have chosen the most common Ti-Al-N-based compound, which has been widely used in the art to improve the cutting tools efficiency, the friction assemblies of machine parts, as well as a new method based on deposition of plasma ion implanted coatings during the application process.
The aim of this work is to study the possibilities of obtaining nanocomposite coatings (TiAl) N by ion implantation and deposition, to
determine the effect of physical and technological parameters on the structure, physical and mechanical properties and tribological characteristics of the obtained coatings.
Experiment and research methodology. For production of coatings (TiAl) N we used a new technological complex of synthesis of coatings on the basis of «Bulat» type installations equipped with HF (high frequency) generator (Fig.1) [12].
Standard HF generators designed for stationary machine can be used as pulse generators, but with one condition: HF power in pulse cannot be very different from the maximum permissible power in stationary mode. In other words, increasing pulse duty cycle results in significant reduction of maximum possible average HF power invested in discharge.
Fig. 1. Scheme of installation of synthesis of nanocrystal coatings on the basis of vacuum-arch series by ion implantation and deposition method: 1 - vacuum chamber; 2- a vaporizable material; 3 -a plasma flow; 4 shows the power supply of the evaporator; 5 - coaxial cable; 6 shows a variable capacitance capacitor; 7 - HF generator; 8 - products.
In order to expand the flexibility of the technological system, the simplest generator was created, which allows to obtain up to 100 kWH of power in a pulse at the average value of HF power not more than 20 kW. The pulse generator was based on the circuit of the core with the impact circuit [13]. Experimental results made it possible to develop a new technological scheme for obtaining coatings from streams of metal plasma with the use of a pulsed HF generator. Damping HF oscillations during one pulse create conditions for ion implantation into the surface of energy ions at the beginning of the pulse, and then for their deposition onto the surface at the corresponding value of decreasing voltage during the pulse. Thus, during one pulse, conditions appear both for ion implantation and for application of particles, regardless of the operating characteristics of the plant (partial pressure of the working gas, mode of operation of the plasma source, etc.). The selection of the maximum voltage amplitude at the beginning of the HF pulse
is determined by the amount of energy acquired by specific ions in this electric field (potential pit) [14]. Two main technological operations - implantation and deposition, which were not performed earlier in vacuum-arc deposition plants, are combined during each pulse. This makes it possible to select physical parameters of deposition, physical and mechanical properties of coatings depend significantly on them, as well as shortens the duration of the coating process and in general, increases the manufactures efficiency of operation of «Bulat» type plants.
The vaporizable material was titanium aluminum alloy (80 weight (wt) % Ti and 20 wt% Al) obtained by vacuum melting. Gas- making nitrogen was used as the reaction gas. Coatings 3... 4 ^m thick were deposited on polished samples of 38X2MTOA (8x8x30mm). Potential of shift moved on a substrate from HF of the generator which generated impulses of damped oscillations with a frequency <1 MHz, duration of each impulse of 60 of microsec, with a frequency of repetitions of 10 of kHz, average power in an impulse of 100 of kW. The magnitude of the negative auto displacement of the potential on the substrate, due to the HF diode effect, was 2... 3 kV at the beginning of the pulse (after actuation of the discharge device) and decreased to 100 V in the pulse (before actuation of the discharge device). The elemental composition of the coatings was determined by X-ray spectral microanalysis («Camebax»). Phase composition of coatings is determined by X-ray diffractometric method (DRONE-3). Hardness was measured by NANO INDENTER 11 (MTS Systems Inc., USA) a three-sided Berkovich indenter.
Tests for wear resistance carried out according to the scheme the plane cylinder by car of friction of MI1M at a speed of sliding of 1.3 m/s, load of 100 N, within one hour, by an to dip to AMG-10 brand oil, temperature ~ 600C. As cylinders X12M disks with a diameter of 40 mm of steel were used polished (Ra = 0.08 microns) (HRC 57-58). During these tests, the coefficient of friction, the volume wear of the coated shoe Wp and the weight wear of the roller Wk were measured. After the wear test, the surface relief of the coating in the direction perpendicular to the longitudinal axis of the friction track was recorded using a profilometer, and the volume wear was broken. The amount of countertel wear was determined by weighing before and after testing on analytical scales with an error of ± 0.1 mg. The samples were loaded to a given load in a step-by-step manner, and the test duration was 2 hours. Methods of VIMS, RFES were used to study the chemical composition of friction surfaces.
Discussion of results. Table 1 shows the results of studying structural state and mechanical properties of coatings (TiAl) N.
It has been found that in the process of deposition of plasma flows in the vacuum mind at nitrogen pressure PN = 0.003 Pa, when titanium alloy with aluminum is used as a spray cathode, a Ti-Al-N compound is formed with Al content of 16 at%, current {111}. According to the coating growth mechanism [15], the crystallographic orientation of grain growth is determined by the minimum total energy consisting of surface energy and deformation energy.
Coatings will grow towards {200} with low energy, when the determining factor is surface energy. In our case, {111} texture formation is because deformation dominates the growth process. This is possible under conditions of high mobility of atoms on the surface of the growing coating. As at the lowered sedimentation temperatures the mobility of atoms on a surface is insufficient to provide growth of grains in one crystallographic orientation and therefore in such conditions the texture is not formed.
Table 1.
Results of nanoindentation of structural state and sub structural characteristics of coating (TiAl) N obtained by ion implantation and deposition.
Material L, nm a, nm a, GPa E, GPa H, GPa Texture Viscosity- plasticity criterion
(TiAl)N 12...15 0,4273 -1,6 363,6 35,3 Strong {111} 0,09
The study of mechanical properties was carried out by nanoindenting at a load of 15 mN with a depth of the computerized layer of ~ 140 nm, which on the one hand preembroiders the surface layer enriched with impurity atoms, and on the other hand sets a value less than 0.1 of the film thickness when the influence of the substrate may not be taken into account. Figure 2 shows the comparative curves «load (unloading) - indenter change» for coating (TiAl) N.
According to the literature, the viscoplasticity criterion for all types of materials in a massive state does not exceed 0.04 [16]. The value we have obtained is 0.09, thus approaching the maximum possible value of 0.14 - for the amorphous state of the material [17]. However, unlike amorphous ale mothers, this ratio is achieved at a relatively low hardness (< 20 GPa) as far as the (TiAl) N system with an Al content of 16 at% is concerned, a high H/E ratio is obtained at a hardness close to 35 GPa, which corresponds to the super hardness threshold for the nanocrystal state of this system.
The results of the study of the tribotechnical characteristics of nanocomposite paintings (TiAl) N with Al 16 at% content compared to galvanic Cr and TiN coating obtained by vacuum-arc deposition are given in table 2.
Fig. 2. Curves «load (unloading) - indenter movement» when nanoindenting
the coating (TiAl) N.
As can be seen from Table 2, nanocrystal coatings (TiAl) N have a lower coefficient of friction and a higher critical impact load than galvanic Cr, which is often applied to the surface of friction parts to improve tribotechnical characteristics. These coatings also have a low wear capacity.
Table 2.
Tribotechnical characteristics of coverings.
Thickness, mKm, 7 3 3
frP 0,10 0,12 0,07
w: r 8,0 12,0 0,7
W -10-3, MM3 19,0 2,5 3,0
Load reduction, MPa, 800 1100 1310
The obtained results show that in the lubricating medium, as a result of physical-chemical reactions on the surface, conditions are created that contribute to a more equal-dimensional distribution of stresses and reduce the intensity of destruction of contacting materials. Figure 3 shows the results of the VIMS research of friction tracks. Mass spectra of secondary ions Al, Ti, AlTi, (TiAl) N were collected at certain intervals to determine the layer-by-layer distribution of the elements. Tuft plating was carried out before peaks characterizing the material
of the sub-spoon appeared in the spectrum, while the crater effect was taken to deepen into account.
j
io3
1Q
Ti Al
a uuuuu O 0 o o 0 o
A A ft ft ft ft ft o o o o o O 0
V V WW w v w O O O O O 0 o TiAl O O 0
o O O O 0 o o
liAIN
10'
10
20
30
a)
b)
c)
Fig. 3. Change of current intensities of secondary ions of coating (TiAl) N: a) initial; b) - after 30 min of friction; c) - after 1 hour of friction.
The change in the content of the above-mentioned substances by coating depth can be reported by the intensity of the corresponding ions at different spraying times. Mass spectra were collected after 30 minutes of friction (Fig. 3b) and 1 hour of friction (Fig. 3B). The results of the researching of the surface morphology of the friction tracks of the coating show that significant changes occur in the friction zone - diffusion of aluminum to the top (Figure 3b, c). Searches of friction tracks after 1 hour of friction by the RFES method show that a protective layer of Al2O3 is formed on the surface. Analysis of the surface of the process by RFES showed that the energy position of the X-ray electron Al2p lines on the surface varied from 72.4 eV (aluminum) to 75.0 eV (aluminum oxide). The existence of alumina is confirmed by the presence in the 01s spectrum of components with Ecv bond energy = 531.7 eV corresponding to this compound. In such way, in the course of friction on a surface the disperse strengthened structure of composite material (Al, Al -Al2O3) which has the low wearing-out ability is formed. The high resistance of the coatings to tar formation (Table 2) can be enhanced by their good adsorbing capacity with respect to surfactants
present in the lubricant, due to the developed surface pattern of the coating or porosity, as well as Al transfer, i.e. the implementation of the operation in the solvent transfer mode. Under such test conditions, they do not wear out. Conclusions
1. The method of ion implantation and deposition created nanocrystal coatings (TiAl) N, with crystallite size 12... 15 nm.
2. Mechanical characteristics of nanocrystal coatings are studied. The obtained wing (TiAl) N with Al 16 at% content have hardness H = 35 GPa, modulus of elasticity
E= 363.6 GPa, 0.09 viscoplasticity criterion.
3. At friction of the system of X12M-coating (TiAl) N steel in the oil medium of the AMr-10 there is a pe-distribution of aluminium in the coating - its diffusion to the surface with formation of the behind-the-shield layer of the Al2O3.
4. Based on analysis of obtained results it was found that nanocomposite coatings (TiAl) N with Al content of 16 at% have high tribotechnical characteristics. Wear capacity decreased 12 times compared to TiN, critical load increased ~ 20% compared to TiN.
PN - nitrogen pressure; L is crystallite size; A - grid period; N - hardness; E - module rest guests; a - tension; FRF - coefficient of friction; Wp - volume wear of coating; Wr - countertel wear.
We bring thank Pogrebnjak A.D for the help of data acquisition.
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