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Вестник технологического университета. 2015. Т.18, №18 УДК 537.525.7:621.762
A. A. Khubatkhuzin, I. Sh. Abdullin, V. I. Khristoliubova, A. A. Rushintsev
ELECTROPHISICAL METHODS OF TREATMENT OF CARBON TOOL STEEL
Ключевые слова: ВЧплазма, пониженное давление, инструментальная сталь.
Получено покрытие на поверхности инструментальной стали магнетронным распылением, с помощью дугового разряда, реализованного на установке марки ННВ-6.6 и высокочастотной (ВЧ) плазмы пониженного давления. В результате формирования покрытия на поверхности достигнуто улучшение физико-механических свойств поверхностных слоев металлов и повышение их износостойкости.
Keywords: RFplasma, low pressure, tool steel.
Methods of hardening of metals are considered. The analysis and comparison of the considered methods is carried out. The covering on a surface of a tool steel by means of magnetron sputtering, NNV and RF plasma of lowered pressure is received. As a result of covering formation on a surface improvement of physical and mechanical properties of metals and hardness increase is received.
Trends in the development of industry in the world show that the increase of resources and metal and other material products allows to get the economic and environmental effects, which significantly reduces production costs. One effective way to extend the life of products of mechanical engineering is the modification of the properties of working surfaces exposed to abrasion during operation. The results of research of the processes of deterioration and destruction of various products during their operation have shown that the reliability of the product and the service life depends, and often completely determined by the state of the surface layer [1-3].
One of perspective methods to solve the problem of increasing the wear resistance of the surface is new, efficient and environmentally friendly method of coating, for example, by condensation from the gas phase, ion bombardment or ion-plasma method [4-6].
Coating was carried out by condensation of a vapor-plasma phase, which relates to the physical vapor deposition methods.
Coating was applied by the installation NNV-6.6, which is used for ion-plasma deposition method of protective, abrasion-resistant and decorative coating of various materials (Ti, Zr, Cr, Mn, Al, Mo, W, their oxides, nitrides, carbides, alloys) . Installation features allows to get high-quality single and multilayer coatings with different condensation temperatures.
The installation has three arc evaporators for creating and supplying to the chamber (the product) metal plasma stream. Vaporizers have water-cooled hermetic housing in the remote end of which insulated from the hull and the water-cooled cathode is placed. There is an arc initiation system at the cathode and the system to stabilize it in the form of a solenoid coil wound on top of the evaporator housing. Downstream plasma is focusing coil. The anode is the housing of arc evaporator.
Supply system and the gas flow control system is designed to maintain a certain pressure in the chamber during applying one or more reactive gases. The nitrogen concentration during the flowing of plasma chemical synthesis of nitride reaction depends on the flow of the reactant gas. Inlet valve are electro-mechanical devices which are connected with the system of measurement of
the vacuum. The gas is fed in portions with electromechanical valve, which duration of the opening is controlled by an automatic system, connected with the pressure vessel through the vacuum gauge.
The system of rotation of products consists of planetary mechanism with sockets or pendants. The rotator is disposed in the chamber, is electrically insulated from the vacuum chamber and has vacuum input rotation. Planetary rotation system contributes to a more uniform coating of products with protective coating.
Electric arc power sources, reference voltage, voltage clean are decorated as individual blocks which have special load characteristics and the total capacity of 20-50 kW. In addition, the plant has a source of ignition of the arc, stabilizing supply and focusing coils and other sources. Power supply of the arc has a constant load voltage 80-100 V, the operating voltage of 25-30 V at an operating current of 50-200 A. Source has steeply dipping load characteristic [7].
Reference voltage has a rigid load characteristic. It provides adjustable DC voltage from 0 to 300 V at 10 A. Equipped with an electronic device of short circuit protection, protection against microarc discharges on the product. The supply power of ionic cleaning provides a constant the regulated voltage from 100 to 2000 V at a current up to 20 A, has a rigid load characteristic, the system is equipped with protection against short circuits and interruptions of microarc discharges.
System for measuring of pressure in the chamber consists of a thermocouple converter for low vacuum and ionization converter high vacuum. Thermocouple of the vacuum gauge measures the vacuum up to 1.33 Pa and is not afraid to air inlet system. Low vacuum is usually measured at the entrance to the vacuum line. Ionization part of the vacuum gauge measures the vacuum from 1.33 to 0.000133 Pa [8]. High vacuum is measured in the chamber, the measuring system is connected to the inlet valve of the gas.
Cooling and heating system of chamber is designed to dissipate heat during operation in the condensing mode of coat and heating of chamber before opening to avoid condensation of moisture on the walls of the chamber. The system consists of pipes, solenoid valves, flow switch and water heating.
Temperature control system of products includes a viewing window with a curtain separating the vacuum chamber and the environment, as well as the radiation pyrometer. Infrared pyrometer registers integral temperature of product according to the intensity of emission within 5 ° C. For pyrometer "Smotrych" range of temperature measurement is from 300 to 700° C.
The automation system and locks are designed to avoid wrong actions of the personnel at work on the installation. Interlocks prevent emergencies, establish compliance with safety, produce shutdown systems in emergency situations. Locks do not allow the operator to open the high-vacuum valve in the presence of atmospheric pressure in chamber, or apply a high voltage to the product with the opened door of vacuum chamber.
Installation is equipped with instrumentation on the testimony of which mode of operation can be judged. The arc current, the current focus and stabilizing, the reference voltage are controlled.
During the coating from the plasma phase work pieces are placed in a vacuum chamber on rotator, on suspensions or on the surface of a metal drum. After the pre-evacuation of air from the vacuum chamber the working gas is supplied inside. The electrical arc is ignited on the cathode in the chamber. The cathode spots are appeared at on the face of the cathode during the arson of vacuum arc. The cathode material consisting of ionic, steam and microdroplet phase erodes from the cathode spots. Wherein the cathode evaporates and partially ionised in the electric field of the arc source. The flow of electrons flows toward the anode and the ions of vaporized material bombard the cathode. Due to the flow of electrons from the cathode, a metal plasma and residual gas phase conductivity is maintained and electric current flows in the anode-cathode gap. Metal plasma and a pair of cathode material due to gas-dynamic forces caused by the pressure difference in the arc evaporator and chamber expire in the workspace of the vacuum chamber. Plasma flow coming from the section of the evaporator in the free mode, extends a vacuum chamber, communicates with the condensation surface and forms a coating.
Table 1 - Parameters of the coating
1 2
Technological process Coating
Cathode material Ti, Hf
Current of arc on the 73+3
hafnium cathode, A
Current of arc on of the 2x62+3
titanium cathode, A
Plasmaforming gas N2
Pressure in chamber, mm hg (1-2)T0-3
Condensation time, min 60+5
Referense voltage, B 150
The rotational speed of 1,8
device, rev / min
Another considered method is magnetron sputtering and ion-plasma condensation, which relate to methods of
physical vapor deposition from vacuum. The method of magnetron sputtering is the process of sputtering of the cathode material as a result of ion bombardment of the working gas (typically argon) and the precipitation of spraying product which are basically neutral atoms on the treated surface. Under the sputtering cathode magnets are located. The magnetic field lines are closed in the form of arcs between the poles of magnets. When a DC voltage between the cathode and the anode nonlinear inhomogeneous electric field and an electric discharge excited. The electric field lines are perpendicular to the magnetic field lines and the cathode surface. Thus, the spraying takes place in the crossed electric and magnetic fields. Electrons emitted from the cathode surface by ion bombardment are "captured" by the magnetic field and perform complex cycloidal movement of closed trajectories in the vicinity of the cathode. As a result of the collision of electrons with atoms of the working gas they are ionized.
Positive ions generated in the discharge are accelerated towards the cathode, bombard the surface of the erosion zone, embossing particulate material therefrom. Leaving the surface of the target particles are deposited as a film on the substrate.
Appearance of magnetron sputtering installation is shown in Fig. 1.
Fig. 1 - Magnetron sputtering installation, general view
The method of ion-plasma condensation is based on the method of electric arc evaporation material. The mechanism of deposition is as follows, on the cathode in a vacuum arc is ignited. At the striking of a vacuum arc on the face surface of the cathode firstly rapidly moving cathode spots appear, which after a time of about 1 - 0.5 ms pass in slow moving cathode spots. The temperature of cathode spots of the arc discharge is reached about 104 K. The movable cathode spots are held at the end of the cathode with the electromagnetic field. The cathode is a replaceable part of the eroding material embedded in the electric evaporator. Of the slowly moving cathode spots the cathode material erodes consisting of ionic and vapor phases. Cathode simulates the electrons, while the metal cathode evaporates and partially ionized. The flow of electrons flows towards the anode (housing), and the ions of the evaporated material is deposited on the detail.
To investigate the effect of the interaction of low pressure RF plasma to the surface of the material the third experiment with the plasma of an inert gas, argon, the flow 0.06 g / sec and in a mixture of plasma-chemical gas, methane, the flow 0.004 g / s, and argon, the flow
0.06 g / s, was carried out. Chamber pressure was 24-26 Pa [9,10].
Table 2 - Parameters of the coating
1 2
Technological process Coating
Cathode material Ti, Hf
Current of arc on the 73+3
cathode, А
Plasmaforming gas N2, Ar
Pressure in chamber, mm hg (1-2)T0-3
Condensation time, min 120+5
The rotational speed of 1,8
device, rev / min
The result of ion implantation is the infiltration atoms of the plasma gas into the metal to a depth of 100 nm. The distinguishing feature of this technology is the use of "cold" plasma: the gas temperature in the plasma flow can be adjusted in the range from 40 to 600 0C.
It is based on the formation of ion flux with an energy of 10 - 100 eV, due to the formation of positive charge layer at the boundary between the body surface and a quasi-neutral plasma.
Ion energy is sufficient to heal the micropores and microcracks, elimination of fractured and relief layers, formation of compressive residual stress in the surface layer of the sample, and others.
The use of gas as the working fluid - can handle internal cavity of products.
Characteristics of plasma radio-frequency: power consumption 3,5 kW, output frequency 13,56 MHz. Samples were degreased and dehydrated before plasma processing for elimination of side effects. In all experiments was a negative potential on a product about -20 V for the purpose of increase of concentration of electric field near details. It is experimentally established that time of achievement of working temperature and receiving of a uniform distribution of temperature on all volume of a material is 15 - 20 minutes. Therefore all products were processed in plasma of pure argon within 25 minutes, then 20 minutes in mix of argon with propane-butane.
Results of the study were obtained using confocal microscope Olympus OLS LEXT 4100. This microscope has a high measurement accuracy at submicron distances along the axis XY (lateral resolution reaches 0.12 microns) due to a large aperture lens and the shorter wavelength. Also LEXT 0LS4100 with high accuracy is used to detect submicron height along the axis Z (resolution up to 10 nm) due to the confocal optical system and a small wavelength.
Microhardness and roughness measurement was applied to determination of physical mechanical properties. The relief and surface structure at a submicronic and nanometer scale was investigated by means of the scanning nanohardness gage «NanoScan-3D». On the «NanoScan» base the method of measurement of the hardness, based on measurement and the analysis of dependence of loading at indentation of indenter in a material surface from depth of introduction
of an indenter is realized. This method is a cornerstone of the standard of measurement of hardness ISO 14577. The indenter of Berkovich type is applied to mechanical tests. It represents a trihedral diamond pyramid with a corner at top near 142°. The method of a measuring dynamic indentation consists in the following: the indenter is pressed into a sample surface with a constant speed, at the achievement of the set loading the indenter is taken away in the opposite direction. In the course of such test record of values of loading and shift of an indenter corresponding to it is made. Feature: pezorezonanse cantilever tuning fork construction with high bending resistance (~2-104 N/m) [11, 12].
Studies have shown that the hardness of tool steel work pieces during the coating in the first case by installation NNV-6 was decreased from 12.08 GPa to 5.15 GPa, which indicates an increase in toughness and ductility, reduced internal stresses. The roughness of the tool steel work pieces increased from 113 nm to 1701.13 nm. This leads to the conclusion that this method is not efficient and require additional treatment in a plasma of induction discharge with the aim of material polishing and improvement of its physical and mechanical properties. During magnetron sputtering increasement of the hardness up to 18.9 GPa and roughness - 298.24 nm was registered. The test characteristics of the processing material in the plasma of capacitive discharge: Hardness -15.1 GPa, roughness - 224 nm.
Thus, it revealed that the physical and mechanical characteristics of the details treated with capacitive radio-frequency plasma discharge, have a high technological and operational characteristics in comparison with the above methods, magnetron sputtering and coating by plasma condensation of vapor-phase by plasma installation NNV-6. Gas saturation (carbonizing) of surface layers of metals and alloys at a depth of 1 micron during processing to 40 minutes was obtained, resulting in an increase of strength properties, durability and lifetime of the products. The advantage of ion implantation over other methods of introducing other impurities in solids is the versatility of the process which allows introducing any element of any material in strictly controlled quantity, as well as setting its depth distribution.
The complex approach to the study of surfaces with the use of methods to measure topography, roughness, hardness, wear resistance, modulus of elasticity, elastic recovery coefficient and the thickness of the modified layer in a single instrument was studied and mastered.
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© А. Khubatkhuzin - Ph.D., associate professor of Plasma Technology and Nanotechnology of High Molecular Weight Materials Department, KNRTU, [email protected]; 1 Abdullin - Ph.D., professor of Plasma Technology and Nanotechnology of High Molecular Weight Materials Department, KNRTU, [email protected]; V. Khristoliubova - Ph.D. student of Plasma Technology and Nanotechnology of High Molecular Weight Materials Department, KNRTU, [email protected]; A. Rushintsev - master of Garment and Footwear Design Department, KNRTU, [email protected]
© А. А. Хубатхузин - к. т. н., доц. каф. плазмохимических и нанотехнологий высокомолекулярных материалов, КНИТУ, [email protected]; И. Ш. Абдуллин - д.т.н., проф., зав. каф. плазмохимических и нанотехнологий высокомолекулярных материалов, КНИТУ, [email protected]; В. И. Христолюбова - аспирант той же кафедры, [email protected]; А. А. Рушинцев - магистр каф. конструирования одежды и обуви, КНИТУ, [email protected].
