CN113443928B

CN113443928B - Preparation method of zirconium and/or tungsten-based multiphase ceramic coating

Info

Publication number: CN113443928B
Application number: CN202111000308.2A
Authority: CN
Inventors: 孙威; 邓南军; 熊翔; 张红波
Original assignee: Central South University
Current assignee: Central South University
Priority date: 2021-08-30
Filing date: 2021-08-30
Publication date: 2021-11-30
Anticipated expiration: 2041-08-30
Also published as: CN113443928A

Abstract

The invention provides a preparation method of a tungsten and/or zirconium-based complex phase ceramic coating, which comprises the following steps: adding the mixture of the carbon-carbon matrix and the chlorine salt metal powder into a graphite crucible, dissolving and flowing the mixture by utilizing molten salt under the high-temperature argon atmosphere, and preparing the ceramic coating on the surface of the carbon-carbon matrix by using a salt bath. The preparation method provided by the invention skillfully utilizes the carrier effect of the liquid phase of the molten salt at 1300-1700 ℃, and the ceramic complex phase coating with high density is deposited on the surface of the carbon-based material. The method provided by the invention has the advantages of short production period, simple process and cost saving.

Description

Preparation method of zirconium and/or tungsten-based multiphase ceramic coating

Technical Field

The invention belongs to the technical field of composite materials, and particularly relates to a preparation method of a zirconium and/or tungsten-based complex phase ceramic coating.

Background

The C/C composite material takes carbon fiber as a reinforcement, takes a carbon material as a matrix, and has a chemical composition of a high-temperature structural material with a single carbon element. The C/C composite material has the excellent performances of small density, high specific modulus, high specific strength, low thermal expansion coefficient, high specific strength, good thermal shock resistance and frictional wear resistance and the like, and is widely applied to the fields of aviation, aerospace, nuclear energy, electronics and the like. However, the service performance of the C/C composite material in a high-temperature oxygen-enriched environment is poor, and the C/C composite material is very easy to generate oxidation reaction with oxygen, so that the service cycle of the C/C composite material is seriously influenced.

The improvement of the oxidation resistance of the C/C composite material mainly comprises the following two methods: (1) modifying a C/C composite material matrix; (2) and modifying the C/C composite material coating. The modification of the coating is one of effective methods for improving the high-temperature oxidation of the carbon-based composite material, and the physical and chemical properties of the common ultrahigh-temperature ceramic coating are greatly different from those of the substrate, so that the compatibility of the two is poor. The anti-ablation coating prepared on the surface of the carbon-based material not only effectively blocks the diffusion of oxygen atoms to the matrix at high temperature, but also requires the matching of the physical and chemical properties of the matrix and better self-healing capability. The coating is required to have excellent performances of compact structure, strong self-healing capability, high bonding strength of a matrix interface and the like, and a single coating is difficult to meet the requirements, so that the current research on the anti-ablation coating is focused on the preparation of a complex phase coating.

The ultrahigh-temperature ceramic has excellent performances of high melting point, high hardness, low saturated steam pressure, good thermal shock resistance and the like, but the thermal expansion coefficient of the ultrahigh-temperature ceramic coating is greatly different from that of a C/C composite material, and even if gradient treatment is carried out, microcracks still exist on the surface of the ultrahigh-temperature ceramic coating. And the ceramic material has brittleness, the thermal stress caused by the anisotropic thermal expansion coefficient is up to 80-100 MPa under the thermal shock condition, and the service performance of the ultra-high temperature ceramic coating in a high-temperature oxygen-enriched environment is influenced by the factors.

The metal ceramic has the advantages of both ceramic materials and metal materials, and has good toughness, high temperature resistance, corrosion resistance and the like. The addition of the metal enables the ceramic material to show good toughness under thermal shock, reduces the thermal stress of the ceramic material and has wide application prospect. Tungsten is not only a noble metal with the highest melting point in known metal elements, but also has the melting point of 3400 ℃, higher strength and hardness under high-temperature conditions and high density (19.3 g/cm)³) The conductive and heat-conducting performance is excellent, the vapor pressure is low, and the electron work function is low (1.55 eV). At present, the methods for preparing tungsten-based metal coatings at home and abroad mainly comprise a solid-phase deposition method, a vapor deposition method, a liquid deposition method and the like.

ZrC (containing point 3540 ℃) has excellent high-temperature thermal stability, and is oxidized by itself to form liquid ZrO with self-healing effect in an aerobic environment above 2973K₂The ceramic coating can be sealed and filled with cracks and holes, so that the diffusion of oxygen atoms is prevented or inhibited. ZrO in molten state₂The viscosity is high, the high-speed scouring of air flow particles can be borne, and ZrC is an ideal thermal protection material.

Silicide has a lower melting point than the corresponding carbide, and SiO is generated during ablation₂The self-healing coating has excellent self-healing performance, and can effectively protect the coating from generating micro pores and cracks in high-speed airflow scouring at 1700 ℃ and inhibit oxygen atoms from diffusing into a matrix. Zirconium silicide has a higher melting point and produces ZrO during ablation as compared to other silicides₂Has strong self-healing effect.

At present, the preparation method of the ZrC coating mainly comprises a magnetron sputtering method, an ion beam assisted deposition method, a pulse laser deposition method, a fused salt pulse electrodeposition method, a Chemical Vapor Deposition (CVD) method and the like. Strong carbide elements (Cr, Ti, Zr and W) have good wettability with a C/C matrix, the strong carbide elements interact with the C/C matrix to form a metal carbide film on the surface of the matrix, transition group metal atoms nucleate and grow on the surface of the carbide film, the metal atoms continuously nucleate and grow on the outer surface of a coating at the high temperature of 1300-1700 ℃, and carbon atoms diffuse from the C/C matrix to the metal coating under the high temperature condition and form carbide with the transition group metal elements.

In the prior art, a metal coating obtained by a diamond salt bath plating method is thin; the bonding strength of the coating and the matrix obtained by other methods is low, the surface distribution of the coating is uneven, and the density is poor.

Disclosure of Invention

In view of the above, the invention aims to provide a preparation method of a zirconium and/or tungsten-based complex phase ceramic coating, and the coating prepared by the method provided by the invention is tightly combined with a substrate, and has a compact and uniform coating structure and higher thickness.

The invention provides a preparation method of a zirconium and/or tungsten-based complex phase ceramic coating, which comprises the following steps:

mixing chlorine salt and metal powder to obtain mixed powder; the metal powder comprises tungsten powder and/or zirconium powder;

removing oil stains and activating the carbon-carbon matrix to obtain an activated carbon-carbon matrix;

performing salt bath on the activated carbon-carbon matrix in mixed powder to obtain a zirconium and/or tungsten-based complex phase ceramic coating;

the carbon-carbon matrix is selected from graphite, carbon-carbon composite materials or modified carbon-carbon composite materials;

the temperature in the salt bath process is 1300-1700 ℃.

Preferably, the chlorine salt is selected from two or more of sodium chloride, potassium chloride and barium chloride.

Preferably, the particle size of the metal powder is 3-7 microns.

Preferably, the mass ratio of the chlorine salt to the metal powder is (1-5): 1.

preferably, the salt bath is carried out under a protective atmosphere.

Preferably, the pressure in the salt bath process is 0.01-0.03 MPa; the heat preservation time is 2-6 hours.

Preferably, the degreasing and activating treatment method comprises the following steps:

washing carbon-carbon matrix in ethanol and then in Na₂CO₃Soaking in the solution, washing with water, soaking in nitric acid solution, washing with water, and drying.

Preferably, the mass ratio of the mixed powder to the carbon-carbon matrix is (5-10): 1.

preferably, the salt bath further comprises, after completion:

and cooling the product subjected to salt bath, and then carrying out water bath, cleaning and drying to obtain the zirconium and/or tungsten-based complex phase ceramic coating.

The invention adopts the liquid phase generated by high-temperature molten salt and takes molten salt particles as carriers to realize that metal atoms such as tungsten, zirconium and the like are deposited on the carbon-based surface at a lower temperature to generate a corresponding metal ceramic compact coating. The tungsten-based ceramic coating is made of W₂C. A WC, W composite ceramic structure; the zirconium-based ceramic coating is a composite ceramic structure consisting of ZrC, Zr and ZrxSiy, and shows better ablation performance in the high-temperature ablation process.

The method skillfully utilizes the melting state of the molten salt at 1300-1700 ℃, and a part of metal tungsten and zirconium are dissolved in the liquid phase generated by the molten salt in the temperature range. When the temperature is lower, the liquid molten salt can partially ionize SiC on the surface of the matrix, effectively dissolve Zr and W metal particles, and is uniformly distributed on the surface of the carbon-based composite material under the action of a molten salt carrier; along with the reduction of the concentration of Si and C atoms on the surface, the Si and C atoms in the matrix begin to diffuse to the surface of the matrix, and the Si and C atoms reach the interface of the matrix/coating and form carbide with the metal active particles; the solubility of the molten salt to Zr, Si and C particles is limited, the dissolved particles begin to precipitate on the surface of the matrix, corresponding carbides and silicides are formed on the surface of the matrix, and the coating particles are smaller due to higher nucleation rate; as the temperature increases, the particles dissolved by the molten salt continue to precipitate, and part of the grains get enough energy to grow into large particles.

The molten salt in a molten state is beneficial to enhancing the wettability between the C/C matrix and the metal particles, and in the initial stage of the salt bath, the liquid phase of the molten salt enhances the physical adsorption and chemical adsorption of Zr and W particles, so that the reaction process of the metal particles and the C/C matrix is enhanced, and a carbide coating is rapidly formed on the surface of the C/C matrix; on the other hand, when the temperature is up to 1300-1700 ℃, molten salt ions move along with violent ions, and the activity of Zr and W is promoted by dissolution, so that the metal tungsten with the melting point up to 3400 ℃ nucleates and grows at 1300-1700 ℃, and a coating with uniform components is produced.

According to the invention, a carbide film is formed by using a strong carbide element and a C/C matrix under a high-temperature condition, the carbide coating provides an attachment point for the formation of a tungsten metal coating, molten salt moves violently within the temperature range of 1300-1700 ℃, the vibration frequency of tungsten atoms is increased, the nucleation energy of the metal element is reduced, and the metal atoms can nucleate and grow on the surface of the carbide layer. Under the condition of high temperature, tungsten atoms continuously nucleate and grow to generate hundred micron W on the surface of a carbon/carbon substrate₂C-W、Zr-ZrC-Zr_xSi_yComplex phase ceramic coating. The formation of carbides in the coating is related to the thermal diffusion behavior of carbon atoms, and the distance of carbon atoms diffusion inside the coating can be represented by the following formula:

the thickness of the carbide coating is related to the thermal diffusion of the activated carbon atoms in the coating

。

Compared with the prior art, the invention adopts the C/C composite material with larger size as the matrix, the ion movement of the fused salt is more violent in the temperature range of the invention, the formation of the coating is more favorable, and the W prepared by the process of the invention₂The C + W, Zr-ZrC-ZrxSiy complex phase coating is compact, and the thickness of the coating can reach 200 mu m. Due to the property limit of diamond, when the temperature exceeds 1000 ℃, the diamond has the tendency of graphitization, and the lower temperature causes the activation degree of tungsten atoms to be lower,the temperature adopted by the invention is 1300-1700 ℃, and is in the vicinity of the limit service temperature range of the chlorine salt. The movement of chloride ions is more violent in the temperature range, the heat movement of tungsten atoms is more positively promoted, and the thickness of the coating is more than 50 times of that of the tungsten-plating coating of the diamond salt bath. The method provided by the invention has the advantages of simple process flow, compact coating, ball milling and mixing of chlorine-based salt, zirconium powder and tungsten powder, uniform contact between metal particles and a matrix due to the liquid phase of high-temperature molten salt, and stable composition of the coating phase of the product.

Drawings

FIG. 1 shows C/C-W prepared in example 1₂A C-W composite material;

FIG. 2 shows C/C-W prepared in example 1₂An X-ray diffraction pattern of the C-W composite;

FIG. 3 is W prepared according to example 1 of the present invention₂SEM surface topography of the C-W composite coating;

FIG. 4 shows W prepared in example 1 of the present invention₂SEM sectional morphology of the C-W composite coating;

FIG. 5 is an X-ray diffraction pattern of the finished product prepared in example 2 of the present invention;

FIG. 6 is a SEM surface topography of a finished coating prepared according to example 2 of the invention;

FIG. 7 is an SEM cross-sectional view of a finished coating prepared in example 2 of the invention;

FIG. 8 is an X-ray diffraction pattern of a finished product prepared in example 3 of the present invention;

FIG. 9 is an SEM surface topography of a finished coating prepared according to example 3 of the invention;

FIG. 10 is an SEM cross-sectional view of a finished coating prepared according to example 3 of the invention;

FIG. 11 is an X-ray diffraction pattern of a finished product prepared in example 4 of the present invention;

FIG. 12 is an SEM surface topography of a finished coating prepared according to example 4 of the invention;

FIG. 13 is an SEM cross-sectional view of a finished coating prepared in example 4 of the invention;

FIG. 14 shows the XRD analysis of the coating after ablation of oxyacetylene prepared in example 3 of the present invention;

FIG. 15 shows the micro-topography of the coating surface after ablation of the finished oxyacetylene prepared in example 3 of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other examples, which may be modified or appreciated by those of ordinary skill in the art based on the examples given herein, are intended to be within the scope of the present invention. It should be understood that the embodiments of the present invention are only for illustrating the technical effects of the present invention, and are not intended to limit the scope of the present invention. In the examples, the methods used were all conventional methods unless otherwise specified.

The invention provides a preparation method of a zirconium and/or tungsten-based multiphase ceramic coating, which adopts a molten salt method to prepare the tungsten or zirconium ceramic coating and comprises the following steps:

and (3) performing salt bath on the activated carbon-carbon matrix in mixed powder to obtain the zirconium and/or tungsten-based complex phase ceramic coating.

In the present invention, the chlorine salt is preferably selected from two or more of sodium chloride, potassium chloride and barium chloride; the purity of the chlorine salt is preferably 99.4-99.6%, and more preferably 99.5%.

In the present invention, the metal powder is preferably tungsten powder or zirconium powder. In the invention, the purity of the tungsten powder is preferably 99.8-99.9%, and more preferably 99.9%; the purity of the zirconium powder is preferably 99.8-99.9%, and more preferably 99.9%. In the invention, the particle size of the metal powder is preferably 3-7 microns, more preferably 4-6 microns, and most preferably 5 microns.

In the invention, the mass ratio of the chlorine salt to the metal powder is preferably (1-5): 1, more preferably (2-4): 1, most preferably 3: 1.

in the present invention, the method of mixing is preferably ball-milling wet mixing; the solvent adopted by the ball milling wet mixing is preferably ethanol, more preferably absolute ethanol, the medium adopted by the ball milling wet mixing is preferably zirconium beads, and the time of the ball milling wet mixing is preferably 12-24 hours, more preferably 15-20 hours, and most preferably 16-18 hours.

In the present invention, it is preferable that the mixture further comprises:

and drying and sieving the mixed powder to obtain mixed powder.

In the invention, the drying is preferably vacuum drying, and the drying temperature is preferably 40-60 ℃, more preferably 45-55 ℃, and most preferably 50 ℃; the drying time is preferably 24 to 48 hours, more preferably 30 to 40 hours, and most preferably 35 hours.

In the invention, the screening mesh number is preferably 140-160 meshes, more preferably 145-155 meshes, and most preferably 150 meshes.

In the invention, the carbon-carbon matrix is graphite, a carbon-carbon composite material or a modified carbon-carbon composite material; the density of the graphite is preferably 1.6-1.8 g/cm²More preferably 1.7 g/cm²(ii) a The density of the modified carbon-carbon composite material is preferably 2.4-2.5 g/cm²More preferably 2.42 to 2.48 g/cm²Most preferably 2.44 to 2.46 g/cm²(ii) a The modified carbon-carbon composite material is preferably a C/C-SiC composite material.

The carbon-carbon matrix is not particularly limited in source, and can be prepared from carbon-carbon composite materials or modified carbon-carbon composite materials known to those skilled in the art, and the carbon-carbon matrix can be obtained from the market or prepared according to methods known to those skilled in the art. In the present invention, the method for preparing the C/C-SiC composite material preferably includes:

by adopting an evaporation technology, Si powder is laid at the bottom of the graphite tank, the C/C matrix is placed on a platform with a certain height away from the bottom of the graphite tank, and heat preservation is carried out under an inert atmosphere.

In the present invention, the graphite can preferably has a size of (160-200) × (180-220) mm, more preferably (170-190) × (190-210) mm, and most preferably 180 × 180 × 200 mm.

In the present invention, the C/C matrix is preferably a carbon-carbon composite material, which is commercially available; the C/C matrix is preferably cylindrical; the diameter of the C/C substrate is preferably 8-12 mm, more preferably 9-11 mm, and most preferably 10 mm; the height is preferably 8 to 12mm, more preferably 9 to 11mm, and most preferably 10 mm.

In the present invention, the certain height is preferably 25 to 35mm, more preferably 28 to 32mm, and most preferably 30 mm.

In the present invention, the inert atmosphere is preferably an argon atmosphere.

In the invention, the heat preservation temperature is preferably 1700-1900 ℃, more preferably 1750-1850 ℃ and most preferably 1800 ℃; the heat preservation time is preferably 1 to 3 hours, more preferably 1.5 to 2.5 hours, and most preferably 2 hours.

In the present invention, the method of degreasing and activating treatment preferably includes:

In the invention, the ethanol is preferably absolute ethanol, and the cleaning is preferably ultrasonic cleaning; the cleaning time is preferably 10-20 min, more preferably 12-18 min, and most preferably 14-16 min.

In the present invention, the Na is₂CO₃The solution is preferably Na₂CO₃An aqueous solution; the Na is₂CO₃The concentration of the solution is preferably 10-20 g/L, more preferably 12-18 g/L, and most preferably 14-16 g/L; the soaking time is preferably 15-25 min, more preferably 18-22 min, and most preferably 20 min; the soaking is preferably carried out under the condition of water bath; the soaking temperature is preferably 50-80 ℃, more preferably 55-75 ℃, more preferably 60-70 ℃ and most preferably 65 ℃.

In the present invention, the water is preferably deionized water; the cleaning is preferably ultrasonic cleaning; the cleaning time is preferably 10-20 min, more preferably 12-18 min, and most preferably 14-16 min.

In the present invention, the nitric acid solution is preferably an aqueous nitric acid solution; the mass concentration of the nitric acid solution is preferably 50-70%, more preferably 55-65%, and most preferably 60%.

In the invention, the soaking temperature in the nitric acid solution is preferably 50-80 ℃, more preferably 60-70 ℃, and most preferably 65 ℃; the soaking is preferably carried out by heating in a water bath.

In the invention, the mass ratio of the mixed powder to the carbon-carbon matrix is preferably (5-10): 1, more preferably (6-9): 1, most preferably (7-8): 1.

in the present invention, the salt bath is preferably carried out under a protective atmosphere, preferably argon; the pressure in the salt bath process is preferably 0.01-0.03 MPa, and more preferably 0.02 MPa; the temperature in the salt bath process is 1300-1700 ℃, more preferably 1400-1600 ℃, and most preferably 1500 ℃; the heat preservation time in the salt bath process is preferably 2-6 hours, more preferably 3-5 hours, and most preferably 4 hours.

In the present invention, the method for salt bath preferably comprises:

and (3) placing the activated carbon-carbon matrix at the bottom of the graphite crucible, adding the mixed powder into the graphite crucible, and performing in a medium-frequency graphitization furnace.

In the invention, the diameter of the graphite crucible is preferably 40-50 mm, more preferably 42-48 mm, and most preferably 44-46 mm; the height is preferably 55 to 65mm, more preferably 58 to 62mm, and most preferably 60 mm.

In the invention, the salt bath is dissolved and flows through the molten salt in the high-temperature argon atmosphere, so that the salt bath plating of the surface of the carbon-carbon matrix is realized.

In the present invention, the salt bath preferably further comprises, after completion of the salt bath:

In the present invention, the cooling method is preferably furnace cooling.

In the present invention, the water bath is used for desalting; the temperature of the water bath is preferably 80-100 ℃, more preferably 85-95 ℃, and most preferably 90 ℃; the time of the water bath is preferably 2-6 hours, more preferably 3-5 hours, and most preferably 4 hours.

In the invention, the cleaning method is preferably ultrasonic water washing to remove salt; the cleaning time is preferably 30-60 min, more preferably 35-55 min, more preferably 40-50 min, and most preferably 45 min.

In the invention, the phase composition of the prepared tungsten-based ceramic coating is preferably W₂C. W; the phase composition of the zirconium-based ceramic coating is preferably Zr, ZrC and Zr_xSi_y。

The method takes the C/C composite material, the graphite and the C/C-SiC as the matrix, and prepares the tungsten and zirconium ceramic coatings on the surface of the matrix, and the method provided by the invention has the advantages of simple process flow and higher deposition efficiency; the coating is tightly combined with the substrate, the coating structure is compact and uniform, and the coating thickness can reach 100-200 mu m or more.

Compared with the prior art, the invention adopts the C/C composite material with larger size as the matrix, the ion movement of the fused salt is more violent in the temperature range of the invention, the formation of the coating is more favorable, and the W prepared by the process of the invention₂The C + W, Zr-ZrC-ZrxSiy complex phase coating is compact, and the thickness of the coating can reach 200 mu m. Due to the limitation of the properties of the diamond, when the temperature exceeds 1000 ℃, the diamond has the tendency of graphitization, the lower temperature causes the activity degree of tungsten atoms to be lower, and the temperature adopted by the method is 1300-1700 ℃ and is near the limit use temperature range of chloride. The movement of chloride ions is more violent in the temperature range, the heat movement of tungsten atoms is more positively promoted, and the thickness of the coating is more than 50 times of that of the tungsten-plating coating of the diamond salt bath. The method provided by the invention has the advantages of simple process flow, compact coating, ball milling and mixing of chlorine-based salt, zirconium powder and tungsten powder, uniform contact between metal particles and a matrix due to the liquid phase of high-temperature molten salt, and stable composition of the coating phase of the product.

Example 1

Mixing sodium chloride, barium chloride and tungsten powder according to the mass ratio of 1: 1, adding the mixture into a ball milling tank, carrying out ball milling wet mixing for 24 hours by adopting absolute ethyl alcohol, drying the mixed powder subjected to ball milling in a vacuum drying box at 50 ℃, and sieving the mixed powder with a 150-mesh sieve for multiple times to fully mix the metal powder and the chloride.

The density of the carbon/carbon matrix (product of model M30 supplied by Togaku New materials Co., Ltd., Changsha) was 1.75g/cm³The surface of the base body is remained with partial oil stain in the processing process, and 10g/L Na is adopted₂CO₃Soaking the substrate in the solution at 80 deg.C water bath for 20min to remove oil stain, and ultrasonically cleaning with deionized water to remove residual Na on the surface₂CO₃Finally, the matrix is placed in a nitric acid solution with the mass concentration of 60% to be subjected to surface activation treatment in a water bath kettle at the temperature of 80 ℃, and the activated carbon matrix is dried after ultrasonic water washing.

Placing the C/C matrix subjected to decontamination and activation treatment at the bottom of a graphite crucible (phi 45 multiplied by 60 mm), adding mixed powder of chlorine-based salt and metal powder subjected to ball-milling drying, and performing salt bath tungsten plating, wherein the mass ratio of the mixed powder of the chlorine-based salt and the metal powder to the carbon/carbon matrix is 7: 1; performing salt bath tungsten plating in a medium-frequency graphitization furnace, and keeping the pressure in the furnace at 0.02 MPa; respectively preserving heat for 2h in an argon atmosphere at 1500 ℃ and 1700 ℃, and performing tungsten plating on the surface of the carbon/carbon matrix by salt bath through dissolution and flowing of molten salt; after the salt bath tungsten plating is finished, the sample is cooled along with the furnace, a large amount of chloride exists on the surface of the sample passing through the salt bath, the sample is placed in a water bath kettle at 80 ℃ for water bath for 4 hours, the sample subjected to water bath desalting is respectively subjected to ultrasonic water washing and alcohol washing for 10min, and finally the finished product can be obtained after drying.

In FIG. 1, (a) and (b) are C/C-W prepared under the process conditions of 1500 ℃ and 1700 ℃ in example 1 of the present invention, respectively₂As can be seen from FIG. 1, the surface of the finished product of the C-W composite material is grayish white and smooth.

FIG. 2 shows the X-ray diffraction patterns of the products prepared under the process conditions of 1500 ℃ and 1700 ℃ in example 1 of the present invention, wherein the phase compositions of the coating are W (01-1024) and W₂C(35-0776)。

In fig. 3, (a) and (b) are scanning electron microscope surface topography images of the coating of the product prepared under the process conditions of 1500 ℃ and 1700 ℃ in example 1 of the present invention, respectively, which shows that the coating has a dense surface and no microcracks; the crystal grains are irregularly granular, part of the crystals are convex, the surface is smooth as a whole and the connectivity between the crystal grains is good.

Fig. 4 (a) and (b) are sectional views of a scanning electron microscope of a coating of a product prepared under process conditions of 1500 ℃ and 1700 ℃ in example 1 of the present invention, respectively, and it can be seen that carbon atoms are continuously diffused toward a tungsten coating during molten salt plating, an interface between the coating and a substrate is concave-convex, and an average thickness of the coating is about 200 μm.

Example 2

Mixing sodium chloride, barium chloride and zirconium powder according to the mass ratio of 1: 1, adding the mixture into a ball milling tank, carrying out ball milling wet mixing for 24 hours by adopting absolute ethyl alcohol, drying the mixed powder subjected to ball milling in a vacuum drying box at 50 ℃, and sieving the mixed powder with a 150-mesh sieve for multiple times to fully mix the metal powder and the chloride.

The density of the modified C/C matrix (provided by Hunan Boyun New Material Co., Ltd.) is 2.55 g/cm³The surface of the base body is remained with partial greasy dirt in the processing process, and 15g/L Na is adopted₂CO₃Soaking the substrate in the solution at 80 deg.C water bath for 20min to remove oil stain, and ultrasonically cleaning with deionized water to remove residual Na on the surface₂CO₃Finally, the matrix is placed in a nitric acid solution with the mass concentration of 60% to be subjected to surface activation treatment in a water bath kettle at the temperature of 80 ℃, and the activated carbon matrix is subjected to ultrasonic water washing and drying.

Placing the modified C/C matrix subjected to decontamination and activation treatment at the bottom of a graphite crucible (phi 45 multiplied by 60 mm), adding ball-milled and dried mixed powder of chlorine-based salt and metal powder, and performing salt bath zirconium plating, wherein the mass ratio of the mixed powder of the chlorine-based salt and the metal powder to the modified carbon/carbon matrix is 7: 1; performing salt bath zirconium plating in a medium-frequency graphitization furnace, keeping the pressure in the furnace at 0.02MPa, preserving the heat for 2 hours in an argon atmosphere at 1500 ℃, and performing salt bath zirconium plating on the surface of the modified carbon/carbon matrix through dissolution and flowing of molten salt; and after the salt bath zirconium plating is finished, cooling the sample along with the furnace, placing the sample in a water bath kettle at 80 ℃ for 4 h when a large amount of chloride exists on the surface of the sample subjected to the salt bath, respectively carrying out ultrasonic water washing and alcohol washing on the sample subjected to water bath desalting for 10min, and finally drying to obtain a finished product.

FIG. 5 is an X-ray diffraction pattern of a finished product made in accordance with example 2 of the present invention showing coating phases comprising: ZrC (PDF number 73-0477) and Zr₂Si（PDF NO. 25-0757）、Zr₅Si₄（PDF NO. 42-1165）、SiC（PDF NO. 73-1664）。

FIG. 6 is a surface topography of a finished coating SEM prepared in example 2 of the present invention, and it can be seen from FIG. 6 that the zirconium-based metal coating formed on the surface of the modified C/C composite (CZ matrix) has fine grains, uniform grain size and high flatness; due to the existence of the carbon fibers on the surface of the CZ matrix, an effective nucleation substrate is provided for carbides and silicides, and dendritic crystals are formed in the direction vertical to the carbon fibers; under the high temperature condition, the violent movement of the molten salt particles promotes the breakage of dendritic crystals, so that the crystal grains formed on the surface of the CZ matrix are smaller.

Fig. 7 is a cross-sectional view of a finished coating SEM prepared in example 2 of the present invention, wherein a zirconium carbide phase is formed inside the modified C/C matrix, and the zirconium carbide phase is located between the carbon fiber and the carbonaceous phase, a portion of the zirconium carbide is deposited on the surface of the carbon fiber, and coats the carbon fiber tube, and after the zirconium particles dissolved in the molten salt fill the pores on the surface of the CZ matrix, a thin zirconium-based ceramic coating is formed on the surface of the CZ matrix.

Example 3

The preparation method of the C/C-SiC matrix comprises the steps of paving 180 g of Si powder (provided by Beijing Xinglong Yuan science and technology limited) at the bottom of a graphite tank (180 x 200 mm) by adopting an evaporation preparation technology, placing a C/C matrix (phi 10mm, h =10 mm and provided by Changshajun new material limited) on a platform which is 30mm away from the bottom of the graphite tank, preparing the C/C-SiC matrix by adopting an argon atmosphere and keeping the temperature at 1800 ℃ for 2h, and removing partial oil stains on the surface of the C/C-SiC matrix in the processing process by adopting 10g/L of Na₂CO₃Soaking the solution in 80 deg.C water bath for 20min to remove oil stain, and then soaking in waterDeionized water ultrasonic cleaning to remove residual Na on surface₂CO₃Finally, the matrix is placed in a nitric acid solution with the mass concentration of 60% to be subjected to surface activation treatment in a water bath kettle at the temperature of 80 ℃, and the activated carbon matrix is subjected to ultrasonic water washing and drying.

Placing the C/C-SiC matrix subjected to decontamination and activation treatment at the bottom of a graphite crucible (phi 45 multiplied by 60 mm), adding mixed powder of chlorine-based salt and metal powder which are dried by ball milling, and performing salt bath zirconium plating, wherein the mass ratio of the mixed powder of the chlorine-based salt and the metal powder to the C/C-SiC matrix is 7: 1; performing salt bath zirconium plating in a medium-frequency graphitization furnace, and keeping the pressure in the furnace at 0.02 MPa; preserving heat for 2 hours in an argon atmosphere at 1500 ℃, and performing salt bath zirconium plating on the surface of the carbon/carbon matrix through dissolution and flowing of molten salt; and after the salt bath zirconium plating is finished, cooling the sample along with the furnace, placing the sample in a water bath kettle at 80 ℃ for 4 h when a large amount of chloride exists on the surface of the sample subjected to the salt bath, respectively carrying out ultrasonic water washing and alcohol washing on the sample subjected to water bath desalting for 10min, and finally drying to obtain a finished product.

Compared with the embodiment 2, the SiC transition layer is introduced in the embodiment, so that the stress caused by the difference of the thermal expansion coefficients of the ceramic coating and the substrate is reduced.

FIG. 8 is an X-ray diffraction pattern of a finished product made in accordance with example 3 of the present invention, showing that the zirconium based ceramic coating phases consist essentially of: ZrC (PDF NO. 73-0477) and Zr₂Si（PDF NO.25-0757）、SiC（PDF NO.73-1664）。

Fig. 9 is an SEM surface topography of a finished coating prepared in example 3 of the present invention, as shown in fig. 9, the grains of the zirconium-based ceramic coating have non-uniform sizes, the large grains grow to be partially in contact, the small grains are mainly distributed among the large grains, and the large grains and the small grains are distributed alternately; the grains which grow preferentially show a spiral layered growth trend, the growth directions are different, the grains are mutually contacted, and the surface is tightly and effectively covered by the filling of small grains.

FIG. 10 is an SEM cross-sectional view of a finished coating prepared in example 3 of the present invention, wherein the thickness of the zirconium-based metal coating is about 35 μm, the small crystal grains are closely arranged, and the coating density is high; the cross section of the sample has three phases of white, gray and brown, and EDS analysis shows that the white phase is ZrC, the gray phase is SiC and the brown phase is C.

Example 4

The density of the modified C/C matrix (provided by Hunan Boyun New Material Co., Ltd.) is 2.52 g/cm³The surface of the base body is remained with partial greasy dirt in the processing process, and 15g/L Na is adopted₂CO₃Soaking the substrate in the solution at 80 deg.C water bath for 20min to remove oil stain, and ultrasonically cleaning with deionized water to remove residual Na on the surface₂CO₃Finally, the matrix is placed in a nitric acid solution with the mass concentration of 60% to be subjected to surface activation treatment in a water bath kettle at the temperature of 80 ℃, and the activated carbon matrix is subjected to ultrasonic water washing and drying.

Placing the modified C/C matrix subjected to decontamination and activation treatment at the bottom of a graphite crucible (phi 45 multiplied by 60 mm), adding mixed powder of chlorine-based salt and metal powder subjected to ball-milling drying, and performing salt bath zirconium plating, wherein the mass ratio of the mixed powder of the chlorine-based salt and the metal powder to the modified C/C matrix is 7: 1; performing salt bath zirconium plating in a medium-frequency graphitization furnace, and keeping the pressure in the furnace at 0.02 MPa; preserving heat for 4 hours in an argon atmosphere at 1500 ℃, and performing salt bath zirconium plating on the surface of the carbon/carbon matrix through dissolution and flowing of molten salt; after the salt bath zirconium plating is finished, cooling the sample along with the furnace; and (3) putting the sample in a water bath kettle with the temperature of 80 ℃ for 4 hours when a large amount of chloride exists on the surface of the sample subjected to the salt bath, respectively carrying out ultrasonic water washing and alcohol washing on the sample subjected to water bath desalting for 10min, and finally drying to obtain a finished product.

FIG. 11 is an X-ray diffraction pattern of the finished product prepared in example 4 of the present invention, showing that the coating phases consist essentially of: ZrC (PDF No. 73-0477), Zr₂Si（PDF No.25-0757）、Zr（ PDF No. 05-0665）。

FIG. 12 is an SEM surface morphology of the finished coating prepared in example 4 of the present invention, where the change of the coating composition is small under different holding times of salt bath plating, and no obvious SiC is detected on the surface of the sample after 4 hours of holding, which indicates that the coating gradually grows and is dense with the increase of the holding time, and diffusion of carbon atoms to the solid-liquid interface is hindered; compared with example 2, the sample prepared in example 4 has coarse grains on the surface, and large grains and small grains are distributed alternately.

FIG. 13 is an SEM cross-sectional profile of a finished coating made in accordance with example 4 of the present invention, the coating having a thickness of about 70 μm; the coating can be divided into two parts according to the density: compared with the micro-sectional morphology (figure 7) of the finished product in the example 2, the coating near the substrate interface of the sample finished product prepared in the example 4 forms a compact structure, and the surface loose area shows the trend of gradual densification.

Performance detection

The ablation performance of the finished product prepared in the above example was evaluated in a 3000 ℃ oxyacetylene environment (according to GJB323A-96 "ablation test method for ablative material", Standard), and the mass ablation rate and the line ablation rate of the finished product prepared in the example after ablation in oxyacetylene at 3000 ℃ are shown in Table 1:

table 1 ablative Properties of the products prepared in the examples

In example 1, the mass ablation rate and the line ablation rate of the tungsten-based complex phase ceramic coating tend to be close to zero with the increase of the preparation temperature, which indicates that the increase of the preparation temperature is beneficial to improving the ablation performance of the tungsten-based complex phase ceramic coating. In the examples 2 and 3, different substrates are adopted to prepare the zirconium-based complex phase ceramic coating, and the finished product (example 3) containing the SiC transition layer has better mass ablation rate and line ablation rate than the finished product of the modified C/C substrate in oxyacetylene ablation. In examples 2 and 4, the prolonged holding time has little influence on the ablation performance of the substrate in oxyacetylene. The oxyacetylene ablation mass ablation rate and the line ablation rate of the above examples are compared to illustrate the ablated microstructure of the finished product prepared in example 3, which is preferred in the examples.

The 60 sXRD analysis of the zirconium-based composite ceramic coating in example 3 by oxyacetylene ablation at 3000 ℃ is shown in FIG. 14; the phase of the coating being ZrO₂(PDF No. 83-0926), in the coating ZrxSiy, SiC under oxyacetylene ablation, Si is oxidized to form SiO₂Has the functions of sealing and anti-ablation below the temperature of 1973K, and SiO has the function of increasing along with the temperature₂The reaction mixture was evaporated, and thus no silicide phase was observed in the XRD analysis result.

The microstructure of the zirconium-based complex phase ceramic coating in example 3 ablated with oxyacetylene at 3000 ℃ for 60s is shown in FIG. 15. FIG. 15 (a) and (b) show the surface micro-topography of the ablated central region of the finished product of example 3, with a central region of up to 3000 ℃ and at this temperature, SiO is formed on the surface₂Essentially volatile, high-viscosity and molten ZrO₂Becomes a main phase component for suppressing diffusion of oxygen atoms into the matrix. End of ablation stage, ZrO₂The crystal grows rapidly, the crystal grains grow rapidly until the crystal boundaries are mutually contacted, and a compact structure is formed on the surface. EXAMPLE 3 ablation edge region of the finished product As shown in FIGS. 15 (d), (e), the edge region ZrO₂Microscopic pores exist among crystal grains, which is caused by the reason that the air flow scouring of the edge area is small and the viscosity of ZrO is high₂No uniform distribution on the surface and SiO inside₂Gas evolution at 3000 ℃ results in edge zone ZrO₂Micropores exist between the grains. Energy spectrum analysis of the central region and the edge region of the ablated sample As shown in FIGS. 15 (c) and (f), the sample surface coating was oxidized to form ZrO under the flame ablation of oxyacetylene₂。

As can be seen from the above examples, the invention adopts the C/C composite material with larger size as the matrix, the ion movement of the molten salt is more violent in the temperature range of the invention, the formation of the coating is more favorable, and the W prepared by the process of the invention₂The C + W, Zr-ZrC-ZrxSiy complex phase coating is compact, and the thickness of the coating can reach 200 mu m. Due to the limitation of the properties of the diamond, when the temperature exceeds 1000 ℃, the diamond has the tendency of graphitization, the lower temperature causes the activity degree of tungsten atoms to be lower, and the temperature adopted by the method is 1300-1700 ℃ and is near the limit use temperature range of chloride. The chloride ions move more violently within the temperature range of the invention and are directed to tungsten atomsThe thermal motion of the coating has more positive promoting effect, and the thickness of the coating is more than 50 times of that of the tungsten coating of the diamond salt bath. The method provided by the invention has the advantages of simple process flow, compact coating, ball milling and mixing of chlorine-based salt, zirconium powder and tungsten powder, uniform contact between metal particles and a matrix due to the liquid phase of high-temperature molten salt, and stable composition of the coating phase of the product.

While only the preferred embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

Claims

1. A method for preparing a zirconium and/or tungsten-based complex phase ceramic coating comprises the following steps:

the temperature in the salt bath process is 1500 ℃ or 1700 ℃;

the particle size of the metal powder is 3-7 microns;

the pressure in the salt bath process is 0.01-0.03 MPa; the heat preservation time is 2-6 hours;

the method for removing oil stain and activating treatment comprises the following steps:

washing carbon-carbon matrix in ethanol and then in Na₂CO₃Soaking in the solution, then washing with water, then soaking in a nitric acid solution, finally washing with water and drying;

the mass ratio of the mixed powder to the carbon-carbon matrix is (5-10): 1.

2. the method according to claim 1, wherein the chlorine salt is selected from two or more of sodium chloride, potassium chloride and barium chloride.

3. The method according to claim 1, wherein the mass ratio of the chlorine salt to the metal powder is (1-5): 1.

4. the method of claim 1, wherein the salt bath is conducted under a protective atmosphere.

5. The method of claim 1, further comprising, after completion of the salt bath: