RU2791259C1 - METHOD FOR GAS-THERMAL SPRAYING OF WEAR-RESISTANT COATINGS BASED ON Ti/TiB2 SYSTEM - Google Patents

Abstract

FIELD: metallurgy.

SUBSTANCE: invention relates to the field of metallurgy, in particular to gas-thermal application of wear-resistant coatings of composite powder of Ti/TiB₂ system, saving their efficiency under impact of negative temperatures. A method for gas-thermal spraying of wear-resistant coatings based on Ti/TiB₂ system includes purification of a substrate surface with blasting processing and alcohol, obtainment of a dispersed powder mixture of titanium with titanium diboride, introduction into a plasma jet of powder material, and its spraying, while a homogenized powder mixture is synthesized from fine-dispersed titanium diboride powder of a fraction of 0.5-4 mcm and titanium powder of a fraction from 10 to 40 mcm, with a titanium diboride content from 10 wt.% to 30 wt.%, which is subjected to mechanochemical synthesis in a high-energy abrasive installation for 3-6 minutes, at rotational speeds of 1000-1200 rpm.

EFFECT: invention allows for formation of coating with integrated hardness up to 997 HV, low porosity, high wear resistance and corrosion resistance, including an area of negative temperatures up to -60°C.

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Description

The invention relates to the field of metallurgy, in particular to the gas-thermal deposition of wear-resistant coatings from a composite powder of the Ti/TiB ₂ system, which retain their effectiveness when exposed to negative temperatures.

At present, the widespread use of titanium in various branches of mechanical engineering is due to the fact that it has such properties as corrosion resistance, resistance to fatigue failure, high specific strength, low modulus of elasticity, low density, cold resistance, and others [1,2].

The disadvantages of titanium, which limit its use, include low hardness and wear resistance. An effective way to improve these properties can be the creation of a metal-matrix composite based on titanium and the formation of functional coatings from it on the surfaces of products of various geometries.

When developing composite powders for sputtering, oxygen-free refractory compounds, in particular, transition metal borides, are widely used as a reinforcing phase [3]. Among them, titanium diboride stands out as the most promising due to its high hardness (hardness of the order of 25-35 GPa), thermal conductivity, wear resistance and oxidation resistance. In open sources, there is no information about the methods of forming functional coatings from titanium diboride with a thickness of more than 20 microns, implemented using basic technologies. The most promising of the gas-thermal methods for the formation of composite coatings is plasma spraying. The essence of this method is the introduction of powder into a plasma jet, due to which there is a partial penetration and transfer of powder particles to the substrate with the formation of a coating.

A known method for producing a composite material Ti/TiB (patent RU 2711699, C22C 29/14, B22F 3/14, B22F 3/18, B22F 3/087) [4]. The method includes mixing titanium powder with an average particle size of 25 ± 10 μm and titanium diboride powder, the average particle size of which is 4 ± 1.5 μm, in a vibratory disk mill at a rotor speed of 700 rpm for 60 minutes in an ethanol medium with cooling, and subsequent synthesis of the composite material by spark plasma sintering at a temperature of 1000°C, a pressure of 40 MPa, for 15 min.

Titanium and titanium diboride powders are used as initial components. Their homogenization is carried out in a vibrating disk mill in an ethanol medium, for a time range of 30 to 120 minutes, the synthesis is carried out by spark plasma sintering (SPS). After the SPS process, the workpieces are subjected to deformation-heat treatment by hot sheet rolling on a two-roll rolling mill. As a result, the samples produced have a microhardness value of up to 680 HV.

The disadvantage of this method is the production of a composite material having an insufficient level of microhardness, wear resistance and corrosion resistance for use in modern engineering objects. Also, the disadvantage is the limitation of the dimensions and shape of the manufactured product when using the SPS method, the inability to form functional coatings from a composite material.

Known composite alloy based on Co-TiB ₂ -BN (patent RU 2539553, C22C 19/07) [5]. The alloy based on cobalt contains, wt. %: chromium - 17.4-21.1; silicon - 2.6-4.9; rhenium - 3.0-5.0; zirconium - 4.0-6.0; cerium - 0.2-0.6; lanthanum - 0.1-0.5; yttrium - 0.3-0.7; aluminum - 2.0-4.0; titanium boride - 10.0-12.5; boron nitride - 10.0-12.5; Co - the rest. EFFECT: invention makes it possible to increase microhardness, adhesive strength and corrosion resistance of coatings. The invention relates to precision alloys intended for the implementation of micrometallurgical processes, specifically to alloys based on cobalt for deposition of functional coatings with high physical and mechanical properties by heterophase transfer.

To create a powder, it is necessary to melt a precision alloy in an induction melting plant, with the sequence of introducing components: (Co+Cr+Si)→Zr→Al→Re→(Ce-La-Y)→(TiB ₂ +BN). After receiving the ingot, it is crushed using a jaw crusher to a fraction of 5-7 mm and crushed in a dezentering plant to 50-80 microns. A coating is sprayed from the prepared powder by microplasma and supersonic cold gas-dynamic methods. The microhardness of the coating with microplasma spraying is 4.2 GPa, with supersonic cold gas-dynamic spraying - 4.6 GPa. All coatings have corrosion resistance class 2-3.

The disadvantage of this method is the low corrosion resistance, low wear resistance and high porosity of composite coatings (up to 12%). A long chain of operations for the production of powder suitable for spraying and high labor intensity lead to a significant increase in the cost of the process.

A known method of applying wear-resistant coatings based on titanium diboride, titanium and aluminum on die steel (patent RU 2659561, C23C 4/04, C23C 4/12, C23C 14/32) [6]. The method includes an electric explosion of a composite electrically exploding conductor (EVN), consisting of a two-layer flat aluminum shell weighing 60-530 mg and a core in the form of a mixture of titanium diboride powders weighing 0.5-2.0 mass of the shell, and titanium weighing 0 .5-2.0 mass of the shell, formation of a pulsed multiphase plasma jet from the explosion products, melting the surface of die steel with it at an absorbed power density of 4.6-4.8 GW / m ² , deposition on the surface of the explosion products with the formation of a composite coating on it system TiB ₂ -Ti-Al and subsequent repetitively pulsed electron-beam treatment of the surface of the coating at an absorbed energy density of 40-60 J/cm ² , pulse duration 150-200 μs and the number of pulses 10-30. The invention is aimed at forming a wear-resistant coating with high adhesion to the substrate at the level of cohesion on the surface of the die steel.

The disadvantage of the known method is the limitation of overall dimensions and surface area, which can be coated with EWH, low wear resistance, high coefficient of friction (0.5-0.6) and low deposition performance. The impossibility of sputtering on large-sized products of complex shape complicates the process of industrial implementation of the development.

The closest in technical essence to the claimed invention is a method of applying a wear-resistant coating (patent RU 2578872, C23C 4/10, C23C 14/06, C23C 4/06) [7], selected as a prototype. A well-known patent provides a method for obtaining a wear-resistant coating by a plasma method using a powder containing titanium diboride.

A method for applying a wear-resistant coating to a steel surface includes cleaning the surface, obtaining a dispersed powder mixture of a self-fluxing alloy and titanium diboride, introducing the mixture into a plasma jet and spraying it, followed by melting the coating surface. The surface is cleaned by polishing, and as a self-fluxing alloy, a cobalt alloy is used, previously mechanically alloyed with aluminum powder with a particle size of less than 1 μm, while the initial components of the mixture must be introduced in the following ratio, wt. %: cobalt alloy 34.0-59.5; aluminum 6.0-10.5; titanium diboride 30.0-60.0. As a result, the microhardness and wear resistance of the coating increase, as well as the quality of the coating by reducing the porosity of the base layer.

The prototype indicates that the mechanoalloying operation is applied using a laboratory mixer system. An analysis of scientific sources indicates the impossibility of forming a single mechanical system of matrix and reinforcing powders using this method [8], and in the process of spraying a mixture of this kind, it is impossible to control the distribution of the reinforcing component in the coating, resulting in the formation of zones depleted in titanium diboride, which significantly reduces the integral hardness of the composite coating.

The disadvantage of this method is the high porosity (up to 11%) of the developed composite coating, low corrosion resistance and microhardness, the maximum value of which is 473 HV. Non-informative modes for studying wear resistance, given in the patent, do not correspond to the modern level of requirements for products operating in extreme conditions, which indirectly indicates low wear resistance of coatings.

The technical result of the present invention is the creation of a method for thermal spraying of wear-resistant coatings based on the Ti/TiB ₂ system, in which the synthesized composite powder of the Ti/TiB ₂ system is a single mechanical system of matrix and reinforcing components, for spraying wear-resistant and corrosion-resistant coatings that are effective at exposure to negative temperatures. The content of the reinforcing component in the composite powder is from 10% to 30% (mass), which makes it possible to form a coating with an integral hardness of up to 997 HV, low porosity, high wear resistance and corrosion resistance, including the area of negative temperatures up to -60°C.

The technical result is achieved by the method of thermal spraying of wear-resistant coatings based on the Ti / TiB ₂ system, including cleaning the surface of the substrate by shot blasting and alcohol, obtaining a dispersed powder mixture of titanium with titanium diboride, introducing a powder material into the plasma jet and spraying it, characterized in that titanium diboride is introduced in the form of a fine powder fraction of 0.5-4 microns in mass. ratio from 10% to 30% to titanium powder with a fraction from 10 to 40 microns. Mechanochemical synthesis from a homogenized powder mixture of titanium and titanium diboride is carried out in a high-energy abrasive installation for 3-6 minutes and at rotation speeds of 1000-1200 rpm. The formation of a composite coating with a controlled change in the stoichiometry of the reinforcing component from TiB ₂ to TiB is carried out using a thermal spraying installation at a voltage of 32 to 36 V, a current of 25 to 32 A and a carrier gas flow rate of 1 to 2 l/min.

To effectively achieve the technical result, the reinforcing powder of titanium diboride is introduced in an amount of 10% to 30% (wt.) To the matrix titanium powder, mechanical alloying is carried out in a high-energy abrasive installation for 3-6 minutes at rotation speeds of 1000-1200 rpm. The particle size of titanium diboride should be in the range from 0.5 to 4 microns, and pure titanium - from 10 to 40 microns. When using the stated synthesis modes and powder sizes, dense volume-reinforced granules of close to spherical shape are formed, consisting of firmly bound matrix and finely dispersed filler evenly distributed in it. When using titanium and titanium diboride of a different fractional composition, it is not possible to obtain the developed composite powder with the necessary properties for coating. When using larger powder materials, Ti>40 µm, TiB ₂ >4 µm, it is impossible to reach a sufficiently energy-efficient operating mode of the abrasive plant, and therefore it is impossible to obtain dense pore-free cores, which are the basis of the reinforced powder material. The use of finer powder materials (Ti<10 μm, TiB ₂ <1 μm) does not allow obtaining the required structure of the composite powder, since the lack of matrix base material in the powder mixture excludes the possibility of forming strong interstitial bonds with the reinforcing fine filler, which, in turn, Due to the high surface energy, it agglomerates into clusters and is unevenly distributed in the powder mixture.

Finely dispersed reinforcing material is added in an amount of 10% -30% (wt.). When adding material less than 10%, an effective increase in the hardness of the sprayed coating is not achieved, when adding more than 30%, a strong mechanical bond between the particles of the matrix and reinforcing component is not provided, which leads to embrittlement of the sprayed coating, zones of titanium diboride not bonded to the matrix are formed, which increases porosity .

In the process of high-energy abrasive processing at processing speeds of less than 1000 rpm, sufficient mechanical energy is not transferred to the material to introduce solid components into matrix particles and there is no formation of dense volume-reinforced particles. At processing speeds of more than 1200 rpm, significant heating and subsequent strong oxidation of the matrix material occurs, as a result of which the plasticity of the matrix material decreases, which leads to the impossibility of uniform distribution of the reinforcing component and the formation of a composite powder, the particles of which represent a single mechanical system with a type of bulk reinforcement. For the formation of reinforced powder material from the entire volume of the source material loaded into the grinder, 3-6 minutes of processing is sufficient. With a shorter processing time, the required amount of energy is not transferred to the material being processed to form granules of a single mechanical system, which reduces the quality of the composite material, and longer processing noticeably increases the cost of the resulting material due to a noticeable increase in the energy intensity of the process.

Modes of microplasma spraying vary in voltage, current strength and consumption of the carrier gas. The voltage values should be in the range from 32 to 36 V, the current strength - from 25 to 32 A. When spraying with lower voltage and current values, due to the short-term temperature effect, an insufficient amount of thermal energy is transferred to the particles of the composite powder, as a result of which they they do not have time to be melted by the plasma jet, which reduces the ability of adhesion to the substrate and makes it impossible to spray a high-quality coating. Also, due to a smaller amount of thermal energy in the coating, titanium dioxide is formed in an amount of less than 5% (wt.), Which reduces the hardness of the coating. When the power of the recommended modes is exceeded, the composite powder burns out and oxidizes in the plasma jet, the combustion products and powder stick in the plasma torch through-holes, which makes it impossible to spray a high-quality coating. The carrier gas flow rate is in the range of 1 to 2 l/min. As the gas flow rates decrease, the coating deposition rate is greatly reduced. At high flow rates of the carrier gas, the composite powder stays in the plasma jet for too short a time and does not have time to melt to form adhesion with the substrate material at a sufficient level.

The practical implementation of the proposed technical solution was carried out according to the following developed scheme:

- mechanical mixing of the powder components of the matrix and reinforcing materials, with a mass content of titanium diboride from 10% to 30%), for half an hour to homogenize the powder mixture;

- high-energy abrasive processing of the powder for 3 minutes at a speed of rotation of the cups in the range of 1000-1200 rpm;

- deposition of functional coatings based on the resulting composite volume-reinforced powder material by microplasma spraying.

The essence of the invention is illustrated by drawings, which shows:

in fig. 1 - SEM image of a transverse microsection of a particle of a composite powder obtained by the proposed method;

in fig. 2 - SEM image of a transverse microsection of the characteristic microstructure of a coating from a composite powder obtained by the proposed method;

in fig. 3 is a characteristic diffraction pattern of a coating from a composite powder formed by the proposed method.

In FIG. 1 revealed the microstructure of the synthesized composite powder with bulk reinforcement. The particles of the reinforcing component are characterized by a darker contrast, size and shape of the particles.

In FIG. 2 reveals the microstructure of the coating deposited from the composite powder of the ILPVg system. Distinctive features of the reinforcing component, such as darker contrast and characteristic size, presented in the coating are correlated with those identifiable in the microsection of the powder.

In FIG. 3 shows the diffraction pattern of the composite coating. The presence of titanium phases, titanium monoboride, and titanium dioxide can be distinguished from the reflexes of the diffraction pattern. Titanium dioxide is formed as a result of the synthesis of a composite powder and its spraying by the gas-thermal method. As a result of deposition using the microplasma method, due to the temperature effect, TiB ₂ changes its stoichiometry and passes into the TiB phase. Physical and mechanical properties do not undergo significant changes, since the hardness index for titanium diboride powder reaches about 35 GPa, and for titanium boride 32 GPa.

Homogenization of mixtures of initial powders was carried out in a Mixer-0.5 mixer, which makes it possible to achieve a uniform distribution of the matrix and reinforcing components in the powder mixture.

The mechanosynthesis of the mixtures was carried out in a vibratory bowl grinder "IVCh-3".

The deposition of the developed powders was carried out by the microplasma method on the UGNP-7/2250 installation.

The microstructure of transverse sections of composite powders and coatings was studied using a scanning electron microscope (SEM), TESCAN VEGA3.

The phase composition of the coating was determined on a Bruker D8 Advance X-ray diffractometer.

The microhardness of the coatings was studied on a PMT-3 microhardness tester.

The porosity of the coatings was determined using a Leica DM-2500 optical microscope in automatic mode from a micrograph of a transverse section.

Corrosion resistance tests were carried out in an Espec SU-261 environmental chamber over a temperature range of -60°C to +40°C.

The study of wear resistance was carried out on a machine for testing materials for friction 2168 UMT, using a pair of samples, pure steel from steel grade 45X and samples with a composite coating of the Ti/TiB ₂ system sprayed onto the contact surface. The samples were mated according to the ring-ring kinematic scheme, with a loading mode of 0.5 MPa, a rotation speed of 100 rpm, for 5 hours.

Examples of specific implementation of the method:

Example 1. Titanium diboride powder with a fraction of 0.5 to 4 µm was added to titanium powder with a fraction of up to 40 μm in an amount of 10% (mass.). The powder mixture was homogenized for half an hour, followed by a high-energy abrasion treatment for 6 minutes, at a rotation speed of the cups of 1000 rpm.

The deposition of coatings from the developed powder composite was carried out under the deposition modes: voltage - 36 V; current strength - 25 A; conveying gas consumption - 2 l/min.

A plate made of steel grade 20Kh23N18 was used as a substrate. Before sputtering, the substrate was shot-blasted and degreased with alcohol.

As a result, a coating with a thickness of more than 60 microns, a hardness of 680 HV, a porosity of 6.4% was applied, the corrosion resistance can be assigned to the "Perfectly resistant" resistance group, since the corrosion rate was less than 0.001 mm/year, the wear values were 0.008397 g/km, wear rate - 0.003797 g/h.

Example 2. Titanium diboride powder with a fraction of 0.5 to 4 µm was added to titanium powder with a fraction of up to 40 μm in an amount of 30% (mass.). The powder mixture was homogenized for half an hour, followed by a high-energy abrasion treatment for 3 minutes, at a cup rotation speed of 1200 rpm.

The deposition of coatings from the developed powder composite was carried out under the deposition modes: voltage - 32 V; current strength - 32 A; conveying gas consumption - 1 l/min.

A plate made of steel grade 20Kh23N18 was used as a substrate. Before sputtering, the substrate was shot-blasted and degreased with alcohol.

As a result, a coating with a thickness of more than 60 microns, a hardness of 997 HV, a porosity of 3.7% was applied, the corrosion resistance can be attributed to the "Perfectly resistant" resistance group, since the corrosion rate was less than 0.001 mm/year, the wear values were 0.003176 g/km, wear rate - 0.001436 g/h.

Information sources

1. Medko V.S.; Radkevich M.M.; Tretyakov V.P. Technology of construction materials. - St. Petersburg: POLYTECH-PRESS (Peter the Great St. Petersburg Polytechnic University), 2019. - 218 p.

2. Popovich A.A. Fundamentals of materials science. Part 1 // Textbook. - Publishing house of the Polytechnic University. - Saint Petersburg. - 2018. - 220 p.

3. Pribytkov G.A., Korzhova V.V., Krinitsyn M.G., Firsina I.A., Korosteleva E.N. Hardness and abrasive wear resistance of electron beam coatings deposited with composite powders "titanium monoboride - titanium bond" // International conference "Chemistry of oil and gas. Promising materials with a hierarchical structure for new technologies and reliable designs”, 2018. - P. 360-361.

4. RF patent No. 2711699 description of the invention to the patent "Method of obtaining a composite material Ti / TiB" / Ozerov M.S., Sokolovsky B.C., Klimova M.V., Stepanov N.D., Zherebtsov S.V.; Appl. 08/21/2019; Published 01/21/2020; Bull. No. 3, 9 p.

5. RF patent No. 2539553 description of the invention to the patent "Composite alloy based on Co-TiB ₂ -BN" / Vasiliev A.F., Farmakovskiy B.V., Kuznetsov P.A., Yurkov M.A., Farmakovskaya A. Ya., Nizkaya A.V., Kovaleva A.A., Deev A.A., Chernysh A.A., Eliseev A.A., Bobkova T.I.; Appl. 11/12/2013; Published 01/20/2015; Bull. No. 2, 5 p.

6. RF patent No. 2659561 description of the invention to the patent "Method of applying wear-resistant coatings based on titanium, titanium and aluminum diboride on die steels" / Romanov D.A., Martusevich E.V., Gromov V.E.; Appl. 07/11/2017; Published 07/02/2018; Bull. No. 19, 7 p.

7. RF patent No. 2578872 description of the invention to the patent "Method of applying a wear-resistant coating" / Shveikin G.P., Rudenskaya N.A., Frolov V.Ya., Rudenskaya M.V., Kuzmin V.I.; Appl. 11/24/2014; Published 03/27/2016; Bull. No. 9, 5 p.

8. Patent of the Russian Federation No. 164445 utility model to the patent "Mixer" / Krivelev D.M.; Appl. 01/31/2016; Published 08/27/2016, 12 p.

Claims (2)

1. The method of thermal spraying of wear-resistant coatings based on the Ti / TiB ₂ system, including cleaning the surface of the substrate by shot blasting and alcohol, obtaining a dispersed powder mixture of titanium with titanium diboride, introducing a powder material into the plasma jet and spraying it, characterized in that a homogenized powder material is synthesized a mixture of fine powder of titanium diboride fraction of 0.5-4 microns and titanium powder of fraction from 10 to 40 microns at a mass ratio of titanium diboride powder to titanium powder from 10% to 30%, which is subjected to mechanochemical synthesis in a high-energy abrasive installation for 3- 6 minutes at rotation speeds of 1000-1200 rpm. 2. The method according to claim 1, characterized in that the spraying is carried out using a thermal spray installation at a voltage of 32 to 36 V, a current of 25 to 32 A and a carrier gas flow rate of 1 to 2 l/min.

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