RU2786959C1 - Ultra-high temperature and oxidation-resistant coatings made of refractory metal diborides and silicon carbide on composite materials - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the process of producing ultra-high-temperature oxidation-resistant functional ceramic matrix materials for creating parts with a wide range of application, suitable for operation under extreme high-temperature and oxidating conditions. The process of producing refractory metal diborides modified with silicon carbide is implemented by the CVD method, by thermal gas-phase decomposition of the initial borohydrides of refractory metals (hafnium, zirconium, niobium, and tungsten borohydrides) and methylsilane on the surface of various materials heated to a temperature of 180 to 250 °C when applying refractory metal diborides and 600 to 650°C when modifying with silicon carbide. The process of applying refractory metal diborides (hafnium, zirconium, niobium, tantalum, tungsten) is implemented by passing highly volatile vapours of a solution of a refractory metal borohydride in an inert medium of argon or nitrogen under a residual pressure of the inert medium of 0.8 to 1.3 kPa for 2 hours at a temperature of 180 to 250 °C until a weight gain of the treated material of at least 12% wt. The process of modification with silicon carbide is implemented by passing methylsilane vapours in an inert medium of argon or nitrogen under a residual pressure of the inert medium of 10 to 25 Pa for 4 hours at a temperature of 600 to 650 °C until a weight gain of the treated material of at least 12% wt. and not less than 24% total wt. after applying refractory metal diborides and modifying with silicon carbide.

EFFECT: possibility of increasing the productivity of the technology for producing ultra-high temperature oxidation-resistant functional coatings from refractory metal diborides, increasing the fire and explosion safety of the process.

17 cl, 8 dwg

Description

FIELD OF TECHNOLOGY

The invention relates to a technology for producing ultrahigh-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten), modified with silicon carbide, by the CVD method, with gas-phase thermal decomposition of precursors. The developed functional coatings are used to create parts that have a wide range of applications and are operated under extreme high-temperature and oxidizing conditions.

PRIOR ART

A known method of obtaining diborides of refractory metals in the form of powders formed by heating the isolated complexes of metal borohydrides from their solutions, followed by decomposition in vacuum at 200°C. (Patent US No. 5,364,607 IPC C01B 6/15, 1994).

The disadvantage of this method is the use of reactive zirconium and hafnium borohydrides to obtain the corresponding intermediate complexes with their subsequent long-term isolation from hydrocarbon solutions.

A known method of obtaining diborides of refractory metals powder coatings by decomposition of borohydrides of refractory metals at a temperature of about 265°C. (Gary W. Rice and Richard L. Woodin, J. Am. Ceram. Soc, 71 [4] pp. 181-183 (1988).

The disadvantage of this method is the decomposition of vapors of borohydrides of refractory metals under the action of laser radiation to obtain powder diborides of the same composition. Use of reactive borohydrides of refractory metals.

A known method for producing refractory metal diborides by low-temperature chemical gas-phase decomposition of a complex (precursor) of refractory metal borohydrides with 1,2-dimethoxyethane (Kumar N., Yang Yu., Chem. Mater., 2007, 19, 3802-3807).

The disadvantage of this method is a small degree of deposition (less than 2%) of refractory metal diborides on the substrate.

The closest in terms of the ongoing technological process and the result obtained is known from patent RU 2675618, published on December 20, 2018, a method for obtaining functional coatings from refractory metal diborides by thermal gas-phase decomposition of refractory metal borohydrides on heated surfaces

The disadvantage of the presented method is the duration of the process, low yield of the final product in the form of a functional coating, its purity, safety and efficiency of the CVD method, a narrower range of applicable refractory metal diborides, which further affects the physicochemical characteristics of functional coatings. Lack of surface modification leading to rapid abrasion and lack of wear resistance of functional coatings. High application temperatures of refractory metal diborides, aggressive conditions for precursor precipitation. The inability to slow down and accelerate the deposition processes. Environmental friendliness of the process.

SUMMARY OF THE INVENTION

Accordingly, there is a need to eliminate at least some of the disadvantages mentioned above. In particular, there is a need to create an efficient, environmentally friendly, fire and explosion-proof method for obtaining ultra-high-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten), modified with silicon carbide, with a high yield of target products with high wear resistance. and increased resources.

The technical result of the invention is to increase the productivity of the technology for obtaining ultra-high-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten) by modifying the coating with silicon carbide, improving the qualitative and quantitative characteristics of the target products, as well as expanding their functional range.

Achieving the set goals is possible with the help of a method for obtaining ultrahigh-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten) modified with silicon carbide, carried out by the CVD method by thermal gas-phase decomposition of the initial precursors on the heated surfaces of the processed materials.

As precursors for obtaining functional coatings from diborides of refractory metals, volatile solutions of borohydrides of refractory metals in an organic solvent are used, for modification with silicon carbide, methylsilane is used.

The task of obtaining ultrahigh-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten) modified with silicon carbide is achieved by the CVD method. The process of applying diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten) is carried out by passing volatile vapors of a solution of refractory metal borohydride in an organic solvent (Hexane, Pentane) in an inert medium (Argon, Nitrogen) at a residual pressure of an inert medium of 0.8- 1.3 kPa, for 2 hours, at a temperature of 180-250°C until the weight of the product (processed material) is not less than 12% of the mass. The process of modifying with silicon carbide is carried out by passing methylsilane vapor in an inert medium (Argon, Nitrogen) at a residual pressure of an inert medium of 10-25 Pa, for 4 hours, at a temperature of 600-650°C until the weight gain of the product (material being processed) is not less than 12%. wt. and not less than 24% of the total mass. after deposition of refractory metal diborides and modification with silicon carbide.

Achieved technical result of the synthesis: increasing the productivity of the technology for obtaining ultra-high-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten) due to modification with silicon carbide, improving the qualitative and quantitative characteristics of the target products, as well as expanding their functional range. Increasing the fire and explosion safety of the process. Full control over the process from start to completion.

BRIEF DESCRIPTION OF THE DRAWINGS

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

Fig. 1 is a diagram of the process of obtaining ultrahigh-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten) and silicon carbide.

Fig. 2 - Scheme of the designed installation for obtaining ultra-high-temperature oxidation-resistant functional coatings from diborides of refractory metals (hafnium, zirconium, niobium, tantalum and tungsten) and silicon carbide.

Fig. 3a - results of AFM (atomic force microscopy) of the surface of materials before applying functional coatings of refractory metal diborides modified with silicon carbide.

Fig. 3b - results of AFM (atomic force microscopy) of the surface of materials after deposition of functional coatings of refractory metal diborides modified with silicon carbide.

Fig. 4a - results of SEM (scanning electron microscopy) of the surface of materials after deposition of functional coatings of refractory metal diborides modified with silicon carbide (diagram).

Fig. 4b - results of SEM (scanning electron microscopy) of the surface of materials after deposition of functional coatings of refractory metal diborides modified with silicon carbide (photograph of the surface).

Fig. 4c - results of SEM (scanning electron microscopy) of the surface of materials after deposition of functional coatings of refractory metal diborides modified with silicon carbide (contents of components presented in the table).

These drawings do not cover and, moreover, do not limit the entire scope of options for implementing this technical solution, but are only illustrative material of a particular case of its implementation.

DETAILED DESCRIPTION OF THE INVENTION

The synthesis is carried out by CVD by applying functional coatings from refractory metal diborides and modifying with silicon carbide, in accordance with the following equations reactions:

Hf (BH ₄ ) ₄ \u003d HfB ₂ + B ₂ H ₆ + H ₂ ,

Zr (BH ₄ ) ₄ \u003d ZrB ₂ + B ₂ H ₆ + H ₂ ,

2Ta (VN ₄ ) ₅ \u003d 2TaV ₂ + 3V ₂ H ₆ + 11H ₂ ,

2Nb (BH ₄ ) ₅ \u003d 2NbB ₂ + 3V ₂ H ₆ + 11H ₂ ,

W (BH ₄ ) ₄ \u003d WB ₂ + B ₂ H ₆ + H ₂ ,

CH ₃ SiH ₃ \u003d SiC + 3H ₂ .

Application of functional coatings (Fig. 1) is carried out on a specially designed high-performance installation (Fig. 2), maintaining a residual inert environment. The supply of precursors, solutions of refractory metal borohydrides 17 for applying functional coatings is carried out through evaporators 5, the temperature of the internal medium of which is controlled by a chiller-fan coil 29 in the presence of an inert carrier gas (Argon) 7. Precursors, solutions of refractory metal borohydrides 17 are preheated in the evaporator 5 to 60°C to improve the transition of precursor solutions into the volatile fraction. Temperature control is carried out by temperature sensors in place 14, temperature control by means of a chiller - fan coil unit 29 in evaporators 5, which makes it possible to locally influence the process of gas-phase decomposition of precursors, slowing down or accelerating the process of applying functional coatings.

In the reactor 1, a product (processed sample) 3 is installed and fixed on the Yolochka sample mounting system 2. Carbon-carbon composite materials, metals, ceramic materials, rubbers are used as a product (processed sample). However, the present invention is not limited to the embodiment and may have a variant in which materials are used as the product (processed sample), the properties of which are maintained up to 650°C. The reactor 1 is closed and sealed. On the control panel 28 start the process of applying functional coatings of diborides of refractory metals. A tube furnace 25 is included for preliminary purification of the inert carrier gas (Argon) from active chemical components, such as oxygen and OH groups, by heating it to 600 ° C and passing it through drying columns and systems with carbon filters and active cleaning copper chips. Reducing the concentration of impurities of active chemical components is carried out in the range of 0.00001-2%. When the temperature reaches 600°C in the tube furnace 25, a gas cylinder with an inert carrier gas (Argon) 23 is opened. 28 include a heating tape 4 to heat the reactor 1 to 180-250°C. Temperature control is carried out using a temperature sensor in place 15 and a temperature sensor on the controller 16 on the control panel 28. Using a vacuum membrane pump 30, the atmosphere in the reactor 1 is evacuated to an initial pressure of 0.13-0.4 kPa. The pressure is controlled using a pressure sensor in place 11 and a pressure sensor on the controller 18 on the control panel 28. In the process of heating the heating tape 4 of the reactor 1, and when the initial pressure is reached, the electric motor of the Herringbone sample mounting system 19 is turned on, which is made with the possibility of rotation of the workpiece (of the processed sample) around the longitudinal axis of the fastening system at a speed of 30 rpm, which makes it possible to evenly apply coatings to the sample. The speed is controlled and regulated on the control panel 28. On the gas distribution system 26, with the help of gas flow regulators 27, a line with an inert medium of carrier gas 9 is launched into the reactor 1 at a rate of 1-2 l/h. The feed rate of the carrier gas inert medium in the reactor 1 is controlled through the gas flow regulator 27 and the control panel 28. When the operating temperature is reached, a certain amount of the precursor, a solution of refractory metal borohydrides 17, is poured into the evaporators 5, pre-filled with the carrier gas inert medium 7. The refrigerant circulation is turned on in the evaporator jackets, with further heating of the refrigerant in the circulation line 21 and in the evaporator jackets 5, through the chiller - fan coil 29 to 60 ° C, to improve the transfer of solutions of refractory metal borohydrides into a highly volatile fraction. On the gas distribution system 26, the supply of an inert carrier gas medium is switched from line 9 to line 7 from the reactor 1 to the evaporators 5 at a rate of 10-15 l/h. Further, on the line from the evaporators 5 in the reactor 1, electrically adjustable valves 20 are opened in increments of 25% of the opening (25, 50, 75, 100%), for a smooth entry into the operating mode, in order to safely carry out the process, in order to avoid hydraulic shock of the vacuum membrane pump 30. When the process enters the operating mode, the residual pressure of the carrier gas inert medium reaches 0.8-1.3 kPa. Pumping out the residual inert medium of the carrier gas and by-products of decomposition during the application of functional coatings from diborides of refractory metals 10 is carried out through a vacuum membrane pump 30 to traps for condensate and gases 32, purified gases 33 enter the atmosphere of the exhaust system. The pressure is controlled using a pressure sensor in place 11 and a pressure sensor on the controller 18 on the control panel 28. The intensity of evaporation of precursors, solutions of borohydrides of refractory metals 17 is controlled by the rate of supply of an inert medium of carrier gas in line 7 to the evaporator 5, through flow controllers gas 27 on the gas distribution system 26, the temperature regime of the evaporators 5 (5-60 ° C), controlled by the chiller - fan coil 29 circulating refrigerant through the line 21 and in the jackets of the evaporators 5. The process of applying functional coatings from refractory metal diborides is carried out in the process of 2 hours, the time process depends on the initial concentration and volume of precursor solutions, the rate of supply of the inert medium of the carrier gas to the evaporators 5. Upon completion of the process of applying functional coatings from refractory metal diborides on the heated surfaces of materials, the pressure in the reactor 1 is restored to the initial 0.13-0.4 kPa . At the end of the process, the line from the evaporators 5 to the reactor 1 is blocked, using an electrically adjustable valve 20, the vacuum membrane pump 30 is turned off. On the control panel 28, the process of additional coating or modification with silicon carbide is started to impart resistance to oxidation by oxygen, since SiC forms a protective layer on material surface. On the gas distribution system 26, the supply of an inert carrier gas medium is switched from line 7 to line 9 from evaporators 5 to reactor 1 at a rate of 1-2 l/h. On the control panel 28 regulate the operation of the heating tape 4, heating the reactor 1 to 600-650°C. Temperature control is carried out using a temperature sensor in place 15 and a temperature sensor 16, the value transmitted to the controller of the control panel 28. When the operating temperature in the reactor 1 is reached and it is filled with an atmosphere of an inert carrier gas up to 101325 Pa, the vacuum rotary pump 31 is turned on. in the reactor 1 to obtain a pressure of 5-8 Pa. Next, the valve is opened on the gas cylinder with methylsilane 22, on the gas distribution system 26, the supply of methylsilane precursor to the reactor 1 is turned on at a rate of 10-15 l/h, due to the gas flow regulator 27. A line with methylsilane 6 and open the electrically adjustable valve 20 in increments of 25% opening (25, 50, 75, 100%), for a smooth exit to the operating mode, in order to safely carry out the process, in order to avoid hydraulic shock of the vacuum rotary pump 31. When entering the operating mode, the residual pressure inert medium in the reactor 1 10-15 Pa. The pressure is controlled by means of a pressure sensor in place 13 and a pressure sensor 18, the given value to the controller of the control panel 28. The process of applying silicon carbide is carried out in the process of 4 hours. The pumping of the residual inert medium of the carrier gas and by-products of decomposition during modification with silicon carbide 12 is carried out through a vacuum rotary pump 31 into the atmosphere of the exhaust system, due to the absence of dangerous, polluting harmful gases, traps and purification systems are not used. Upon completion, the valve on the gas cylinder with methylsilane 22 is closed, on the gas distribution system 26 the supply of methylsilane is turned off in line 6, through the gas flow regulator 27 to the reactor 1, the vacuum rotary pump 31 is turned off, the operation of the heating tape 4 is turned off. line 9, to the reactor 1 at a rate of 1-2 l/h, through the gas distribution system 26 and the gas flow regulator 27 is left to fill the reactor 1 with an atmosphere of an inert carrier gas atmosphere up to 101325 Pa. When the reactor 1 reaches a pressure of 101325 Pa and a temperature of 40°C, the electric motor of the Yolochka sample attachment system 19 is turned off, the tube furnace 25 is turned off, the valve on the cylinder with an inert medium 23 is turned off, the gas flow regulators 27 and the gas distribution system 26 are turned off. All mechanical taps and electrically adjustable taps 20 overlap. Reactor 1 is depressurized. Sample 3 is removed from reactor 1 and removed from the Yolochka 2 sample mounting system for further analysis (Fig. 3,4) on the content of end products, various physical and chemical tests, to check the quality of the applied functional coatings from diborides of refractory metals (diborides of hafnium, zirconium, tantalum, niobium and tungsten) modified with silicon carbide.

EXAMPLES OF IMPLEMENTATION OF THE PROPOSED METHOD

Example 1. Obtaining a coating of HfB ₂ modified with SiC.

CCCM (carbon-carbon composite material) is installed and fixed in the reactor, on the Yolochka sample attachment system. The reactor is closed and sealed. On the control panel, the process of applying functional coatings from refractory metal diborides is started. A tube furnace (600°C) is switched on, in which the carrier inert gas (Argon) is purified from active chemical components, such as oxygen and -OH groups. Reducing the concentration of impurities of active chemical components 0.00001%. Open the gas cylinder with an inert carrier gas (Argon). The line with an inert medium of carrier gas enters the gas distribution system, after passing through drying columns and a tube furnace. The control panel includes a heating tape, the reactor is heated to 200°C. Temperature control is carried out using a temperature sensor in place and a temperature sensor on the controller on the control panel. Using a vacuum membrane pump, the atmosphere in the reactor is evacuated to an initial pressure of 0.13 kPa. The pressure is controlled by a local pressure transducer and a pressure transducer to the controller on the control panel. In the process of heating the reactor and when the initial pressure is reached, the electric motor of the Yolochka sample attachment system is switched on at a speed of 30 rpm. On the gas distribution system, with the help of gas flow regulators, a line with an inert medium of carrier gas is launched into the reactor at a rate of 2 l/h. When the operating temperature is reached, 150 ml of Hf(BH ₄ ) ₄ are poured into the evaporators, pre-filled with an inert medium of the carrier gas. The refrigerant circulation is switched on in the evaporator jackets, with further heating of the refrigerant in the circulation line and in the evaporator jackets, through the chiller - fan coil unit to 60 ° C, to improve the transfer of solutions of refractory metal borohydrides into a volatile fraction. On the gas distribution system, the supply of the carrier gas inert medium from the reactor to the evaporators is switched at a rate of 15 l/h. Further, on the line from the evaporators to the reactor, electrically adjustable valves are opened with a step of 25% opening (25, 50, 75, 100%), the interval between each step is 5 minutes. When the process enters the operating mode, the residual pressure of the carrier gas inert medium reaches 0.8 kPa. The pumping of the residual inert medium of the carrier gas and by-products of decomposition during the application of functional coatings from diborides of refractory metals is carried out through a vacuum membrane pump to traps for condensate and gases (B ₂ H ₆ , H ₂ ), the purified gases enter the atmosphere of the exhaust system. The pressure is controlled by a local pressure transducer and a pressure transducer to the controller on the control panel. The functional coating process of the HfB ₂ coating is carried out in a 1 hour process. Upon completion of the coating process of HfB ₂ , the pressure in the reactor is restored to the initial 0.13 kPa. At the end of the process, the line from the evaporators to the reactor is closed, using an electrically adjustable valve, the vacuum membrane pump is turned off. On the control panel, the SiC modification process is started. On the gas distribution system, the supply of the carrier gas inert medium from the evaporators to the reactor is switched at a rate of 2 l/h. The operation of the heating tape is regulated on the control panel, and the reactor is heated up to 650°C. Temperature control is carried out using a temperature sensor in place and a temperature sensor on the controller on the control panel. When the operating temperature in the reactor is reached and it is filled with an atmosphere of an inert carrier gas up to 101325 Pa, a vacuum rotary pump is switched on. The reactor is evacuated to a pressure of 5 Pa. Next, the valve on the gas cylinder with methylsilane is opened, on the gas distribution system, the supply of methylsilane precursor to the reactor is switched on at a rate of 10 l/h, due to the gas flow regulator. A line with methylsilane goes to the reactor from the gas distribution system and an electrically adjustable valve is opened in increments of 25% opening (25, 50, 75, 100%), the interval between each step is 5 minutes. When entering the operating mode, the residual pressure of the inert medium in the reactor is 10 Pa. The pressure is controlled by a local pressure transducer and a pressure transducer to the controller on the control panel. The process of modifying SiC is carried out in the process of 4 hours. The pumping of the residual inert medium of the carrier gas and by-products of decomposition (H ₂ ) is carried out through a vacuum rotary pump into the atmosphere of the exhaust system; due to the absence of dangerous, polluting harmful gases, traps and purification systems are not used. Upon completion, the valve on the gas cylinder with methylsilane is closed, the supply of methylsilane is turned off on the gas distribution system, through the gas flow regulator to the reactor, the vacuum rotary pump is turned off, and the operation of the heating tape is turned off. The supply of carrier gas inert medium to the reactor at a rate of 2 l/h through the gas distribution system and the gas flow regulator is left to fill the reactor with an atmosphere of carrier gas inert medium up to 101325 Pa. When the pressure in the reactor reaches 101325 Pa, and the temperature reaches 40°C, the electric motor of the Yolochka sample attachment system is turned off, the tube furnace is turned off, the valve on the cylinder with an inert medium is closed, the gas flow regulators and the gas distribution system are turned off. All mechanical faucets and electrically controlled faucets are closed. Produce depressurization of the reactor. The sample is removed from the reactor and removed from the Yolochka sample mounting system for further analysis of the content of end products, various physical and chemical tests, to check the quality of the deposited coatings of HfB ₂ modified with SiC. The total gain of the processed material was 28% of the total mass. The gain upon completion of the application of HfB ₂ amounted to 16% of the total mass. Weight gain upon completion of the modification of SiC 12% total mass.

Claims (20)

1. A method for applying a functional coating of refractory metal diboride by thermochemical gas-phase decomposition of a refractory metal borohydride solution on the surface of a heated product placed in a reactor, characterized in that to deliver a solution of refractory metal borohydride to the surface of a heated product, an inert carrier gas is used, while a solution of refractory metal borohydride with a carrier gas is heated in an evaporator to transfer the refractory metal borohydride solution to a highly volatile fraction, a functional coating is obtained from a refractory metal diboride selected from the group including: zirconium, hafnium, niobium, tantalum, tungsten. 2. The method of claim 1 wherein the refractory metal diboride coating is further either coated or modified with silicon carbide. 3. The method according to claim 2, wherein the modification with silicon carbide is carried out for 4 hours. 4. The method according to p. 2, in which the modification with silicon carbide is carried out at a temperature of 600-650°C. 5. The method according to p. 2, in which the coating of silicon carbide determines the weight gain of the product is not less than 12% of the mass. 6. The method according to p. 1, in which the inert gas is preliminarily subjected to thermochemical treatment in order to clean it from impurity chemically active components. 7. The method according to p. 1, in which in the process of applying coatings on products produce their rotation. 8. The method according to claim 1, in which an inert gas, argon or nitrogen, is used as the carrier gas. 9. The method according to p. 1, in which materials are used as the product, the properties of which are maintained up to 650°C. 10. The method according to p. 1, in which the carrier gas is purified from chemically active components by passing it through drying columns, carbon filters and a copper oxygen absorber at temperatures up to 600 ° C. 11. The method according to p. 1, in which solutions of borohydrides of refractory metals with a carrier gas are preheated in an evaporator to 60°C. 12. The method according to p. 1, in which the deposition of a functional coating of refractory metal diboride is carried out at a residual pressure of an inert gas of 0.8-1.3 kPa. 13. The method of claim. 1, in which the deposition of a functional coating of refractory metal diboride is carried out within 2 hours. 14. The method according to p. 1, in which the deposition of a functional coating of refractory metal diboride is carried out at a product temperature of 180-250°C. 15. The method according to p. 1, in which the weight gain of the product is at least 12% of the mass. upon completion of deposition of the refractory metal diboride functional coating. 16. The method according to p. 2, in which the modification with silicon carbide is carried out at a residual carrier gas pressure of 10-25 Pa. 17. The method according to p. 2, in which the weight gain of the product is not less than 24% of the mass. after deposition of functional coatings of refractory metal diboride and silicon carbide.

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