阅读说明：本技术 在石墨表面制备硬质金属碳化物涂层的方法 (Method for preparing hard metal carbide coating on graphite surface ) 是由 吴振宇 陈益钢 卿铧文 于 2021-06-16 设计创作，主要内容包括：本发明公开了一种在石墨材料表面制备硬质金属碳化物涂层的方法,将石墨材料埋入以硼砂为基盐的混合盐浴中,并加热至熔融状态,进行涂层的制备反应。反应一段时间后,取出石墨样品,淬火至室温,洗净样品表面残盐后干燥,即可在石墨表面获得一层致密耐磨的金属碳化物涂层。本发明方法用于多种含碳材料表面致密化改性,制备工艺简单、设备要求低、成本低廉。所制备的金属碳化物涂层具有极高的硬度和极佳的耐磨性能,和优良的耐腐蚀性能；本发明方法广泛应用于各种复杂恶劣环境下及相关特种应用条件,包括航空航天工程和恶劣海洋环境。(The invention discloses a method for preparing a hard metal carbide coating on the surface of a graphite material. After reacting for a period of time, taking out the graphite sample, quenching to room temperature, cleaning residual salt on the surface of the sample, and drying to obtain a layer of compact and wear-resistant metal carbide coating on the surface of the graphite. The method is used for surface densification modification of various carbon-containing materials, and has the advantages of simple preparation process, low equipment requirement and low cost. The prepared metal carbide coating has extremely high hardness, excellent wear resistance and excellent corrosion resistance; the method is widely applied to various complex severe environments and relevant special application conditions, including aerospace engineering and severe marine environments.)

1. A method for preparing a hard metal carbide coating on the surface of a graphite material is characterized by comprising the following steps:

a. pretreatment of the surface of a graphite material:

cutting an original graphite material which is not processed into a target size, and then grinding and polishing the surface of the graphite material by using sand paper and a polishing pad;

b. preparing materials:

taking base salt, metal carbide, a reducing agent and a fluxing agent as mixed salt components, fully stirring and uniformly mixing to obtain mixed powder; then placing the mixed powder in a crucible to be used as salt bath powder for later use;

c. pretreatment:

horizontally placing the graphite material subjected to pretreatment in the step a and embedding the graphite material into the mixed powder in the crucible prepared in the step b, and compacting the graphite material; placing the crucible in a muffle furnace, raising the furnace temperature to 150-250 ℃, and preserving the temperature for at least 2 hours;

d. salt bath treatment and post-treatment:

heating the muffle furnace to 800-1050 ℃ at a heating rate of not less than 5 ℃/min, and preserving heat for 2-8 hours to carry out salt bath treatment on the graphite material; quenching the treated material at room temperature, and then ultrasonically cleaning the material for at least 30 minutes by using boiling water or dilute nitric acid with the concentration of 5-10 vol.%; and then the cleaned material is placed in a blast drying oven and dried at the temperature of 120-130 ℃ for at least 30min, so that the hard metal carbide coating is prepared on the surface of the graphite material.

2. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in the step a, graphite materials include, but are not limited to, bulk graphite, flake graphite, earthy graphite, and artificially treated graphite substrates; wherein, the carbon content of the graphite processed by manpower is more than or equal to 0.3 wt.%, and at least one of high-purity graphite, isostatic pressing graphite, expandable graphite, graphite fluoride, colloidal graphite and graphene is adopted.

3. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in the step a, after the original untreated graphite material is roughly ground on the surface by using 280-mesh and 600-mesh abrasive paper, 1000-mesh and 2000-mesh abrasive paper and a polishing pad not less than 10000-mesh are selected for fine grinding and polishing; and then ultrasonically cleaning the polished graphite material by absolute ethyl alcohol, placing the polished graphite material in a blast drying oven, and fully drying the graphite material at the temperature of 120-130 ℃ to finish the surface pretreatment of the graphite material.

4. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in the step b, Na is adopted as the base salt₂B₄O₇And B₂O₃，Na₂B₄O₇And B₂O₃The mass ratio of (1-3) to (1).

5. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in the step b, the metal carbide forming element is one element oxide or a combination of any several element oxides of titanium (Ti), zirconium (Zr), vanadium (V), tantalum (Ta), niobium (Nb), tungsten (W), molybdenum (Mo), chromium (Cr), manganese (Mn) and iron (Fe).

6. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in the step B, the reducing agent adopts B₄C. Any one or combination of more of magnesium (Mg), lanthanum (La), calcium (Ca), aluminum (Al), zirconium (Zr), titanium (Ti) and silicon (Si).

7. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: the fluxing agent adopts NaF, NaCl, KCl and BaCl₂、AlF₃At least one of (1).

8. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in the step b, the particle size of the salt bath powder is 0.5-5 microns.

9. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in the step b, the mixed salt is weighed according to the mass fraction ratio shown in the following table, and comprises base salt, metal carbide forming elements, reducing agent and fluxing agent:

wherein, in the table, Na₂B₄O₇And B₂O₃As base salt, Nb₂O₅And Cr₂O₃As metal carbide-forming element, NaF as flux, B₄C is taken as a reducing agent.

10. The method of preparing a hard metal carbide coating on a graphite surface according to claim 1, wherein: in said step d, the carbon content of the substrate of the hard metal carbide coating prepared on the graphite surface is not less than 0.3 wt.%.

Technical Field

The invention belongs to the technical field of material surface modification and thin film material preparation, and particularly relates to a method for preparing a hard metal carbide coating on the surface of a graphite material.

Background

The graphite material has the advantages of good electrical and thermal conductivity, low thermal expansion coefficient, excellent thermal shock resistance, corrosion resistance, low density, good chemical stability and the like, and is widely applied to various national defense and civil fields such as electronics, machinery, metallurgy, petrochemical industry, semiconductors, nuclear industry, aerospace and the like. Compared with metal materials, the graphite material has soft texture, low hardness and easy processing, and the excellent physical and chemical properties make the graphite play a significant role in the production life and future development of human beings. However, graphite materials tend to produce powder and debris during use due to their low lubricity and strength, which adversely affects their own mechanical strength and stability. Particularly when graphite is used in relatively harsh environments, such as molds, corrosion-resistant protective layers, etc., this has greatly limited its deep application in the fields of machinery, mechanics and corrosion science. The general modification methods of graphite materials are mainly divided into two main categories: matrix modification and surface coating.

The matrix modification method is to add additives into the matrix, such as adding some oxides or filling ceramic substances into the matrix of the material, so that the high-temperature oxidation resistance of the material is improved or enhanced. However, these additives generally degrade some of the desirable properties of the graphite material itself. For example, most of these widely used additives are excellent insulators, and when added to a matrix, lead to a decrease in the conductive properties of graphite.

Coating methods are currently the most widely used graphite surface modification methods. The method is to prepare a coating different from a matrix material on the surface of a matrix so as to realize the functions of protection, isolation, enhancement, modification and the like, and the basic principle is shown in figure 1.

The surface improvement technology of the current coating method mainly comprises the following steps: slurry coating, solution dipping, powder embedding, Chemical Vapor Deposition (CVD), and the like. The slurry brushing method is simple in process, convenient to operate and free of special equipment. However, the coating produced is liable to crack due to poor uniformity of coverage when it is applied. The method mainly stays at the manual coating stage at present, most of the methods stay at the state of meeting a few specific requirements, and large-scale industrial application cannot be realized. The solution impregnation method is mainly used for the oxidation resistance of the graphite material at the low temperature range of 500-1200 ℃. Due to the limitation of the principle, the method cannot realize the preparation of the hard coating on the graphite surface. The embedding method is a method widely used in the densification modification treatment of the graphite surface at present, but the coating prepared by the method has poor interface binding force and is easy to crack and fall off; the coating generated at high temperature in the preparation process can cause large thermal stress of the substrate and influence the service life of the coating. Meanwhile, the embedding method has certain requirements on high temperature conditions, a vacuum system and a gas protection system. These defects also greatly limit the applicability of the embedding method. The coating prepared by chemical vapor deposition has the difficult-to-solve principle problems of poor binding force with a graphite matrix and easy falling, and meanwhile, the method has high requirements on equipment and the problems of certain toxicity and environmental hazard of raw materials. These disadvantages further limit their use in practical production.

Disclosure of Invention

In order to solve the problems of the prior art, the invention aims to overcome the defects of the prior art and provide a method for preparing a hard metal carbide coating on the surface of graphite, wherein the graphite material has the characteristic of lubrication due to soft texture and may cause some problems in the using process. Such as graphite rotors in an electric vacuum pump, can cause the rotor to chip due to powder debris that occurs during operation. The traditional graphite surface modification technology can destroy many excellent performances of graphite, such as electrical conductivity, thermal conductivity, corrosion resistance and the like. Therefore, the invention aims to improve the mechanical property of the graphite material while maintaining the excellent characteristics of the graphite material.

In order to achieve the purpose, the invention adopts the following inventive concept:

the basic principle of the method is as follows: the metal oxide and the reducing agent are subjected to oxidation-reduction reaction in the molten salt at high temperature to form a metal simple substance, and the metal simple substance reacts with the graphite material immersed in the molten salt to generate a metal carbide coating on the surface of the metal simple substance.

The preparation method of the graphite material surface hard carbide coating of the invention is applicable to the following basic conditions: the carbon content of the matrix calculated according to the mass fraction is not lower than 0.3 wt.%. The method provided by the invention can greatly improve the performances such as graphite surface hardness and the like while maintaining the excellent electric and thermal conductivity of the graphite material, improves the mechanical strength of the graphite material, and has excellent compatibility with a graphite base material. In addition, in the practical operation aspect, the method has the advantages of low cost, simplicity and convenience in operation, low requirement on equipment and capability of realizing large-scale mass production.

According to the inventive concept, the invention adopts the following technical scheme:

a method for preparing a hard metal carbide coating on the surface of a graphite material comprises the following steps:

a. pretreatment of the surface of a graphite material:

cutting an original graphite material which is not processed into a target size, and then grinding and polishing the surface of the graphite material by using sand paper and a polishing pad;

b. preparing materials:

taking base salt, metal carbide, a reducing agent and a fluxing agent as mixed salt components, fully stirring and uniformly mixing to obtain mixed powder; then placing the mixed powder in a crucible to be used as salt bath powder for later use;

c. pretreatment:

horizontally placing the graphite material subjected to pretreatment in the step a and embedding the graphite material into the mixed powder in the crucible prepared in the step b, and compacting the graphite material; placing the crucible in a muffle furnace, raising the furnace temperature to 150-250 ℃, and preserving the temperature for at least 2 hours;

d. salt bath treatment and post-treatment:

heating the muffle furnace to 800-1050 ℃ at a heating rate of not less than 5 ℃/min, and preserving heat for 2-8 hours to carry out salt bath treatment on the graphite material; quenching the treated material at room temperature, and then ultrasonically cleaning the material for at least 30 minutes by using boiling water or dilute nitric acid with the concentration of 5-10 vol.%; and then the cleaned material is placed in a blast drying oven and dried at the temperature of 120-130 ℃ for at least 30min, so that the hard metal carbide coating is prepared on the surface of the graphite material.

Preferably, in the step a, the graphite material includes, but is not limited to, bulk graphite, flake graphite, soil graphite, and artificially processed graphite matrix. The earthy graphite is aphanitic graphite.

Further preferably, the carbon content of the graphite subjected to manual treatment is more than or equal to 0.3 wt.%, and at least one of high-purity graphite, isostatic pressure graphite, expandable graphite, graphite fluoride, colloidal graphite and graphene is adopted.

Preferably, in the step a, after the original untreated graphite material is roughly ground on the surface by using 280-mesh and 600-mesh sand paper, 1000-mesh and 2000-mesh sand paper and a polishing pad not lower than 10000-mesh are selected for fine grinding and polishing; and then ultrasonically cleaning the polished graphite material by absolute ethyl alcohol, placing the polished graphite material in a blast drying oven, and fully drying the graphite material at the temperature of 120-130 ℃ to finish the surface pretreatment of the graphite material. Preferably, the purity of the absolute ethyl alcohol is more than or equal to 99.7 Vol.%.

Preferably, in said step b, Na is used as the base salt₂B₄O₇And B₂O₃，Na₂B₄O₇And B₂O₃The mass ratio of (1-3) to (1).

Preferably, in the step b, the metal carbide is one element oxide or a combination of any several element oxides of titanium (Ti), zirconium (Zr), vanadium (V), tantalum (Ta), niobium (Nb), tungsten (W), molybdenum (Mo), chromium (Cr), manganese (Mn), and iron (Fe).

Preferably, in the step B, the reducing agent is B₄C. Any one or combination of more of magnesium (Mg), lanthanum (La), calcium (Ca), aluminum (Al), zirconium (Zr), titanium (Ti) and silicon (Si).

Preferably, the fluxing agent adopts NaF, NaCl, KCl and BaCl₂、AlF₃At least one of (1).

Preferably, in the step b, the particle size of the salt bath powder is 0.5-5 microns.

Preferably, in the step b, the mixed salt is weighed according to the mass fraction ratio shown in the following table, including the base salt, the metal carbide forming element, the reducing agent and the fluxing agent:

wherein, in the table, Na₂B₄O₇And B₂O₃As base salt, Nb₂O₅And Cr₂O₃As metal carbide, NaF as promoterFlux, B₄C is taken as a reducing agent.

Preferably, in said step d, the carbon content of the matrix of the hard metal carbide coating prepared on the graphite surface is not less than 0.3 wt.%.

Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:

1. the invention realizes the preparation of the metal carbide film with high hardness performance on the surface of the graphite material, and the preparation method is simple and convenient and is easy for large-scale production;

2. the invention can realize the regulation and control of the surface appearance, structure, thickness and hardness of the coating under different requirements by controlling the types, treatment temperature and processing duration of the metal carbide forming elements;

3. the coating prepared by the invention has extremely high hardness performance. Meanwhile, the coating has excellent wear resistance, excellent conductivity and corrosion resistance;

4. the method of the invention does not need special gas protection, has low equipment cost and simple and convenient process flow. The prepared coating has controllable appearance, adjustable size and wide application scene. Can be applied to the fields of new energy automobile industry, marine industry of ships and aerospace on a large scale.

Drawings

FIG. 1 shows the principle of surface modification by coating method.

FIG. 2 is a comparison of samples before and after treatment. The left side is the pre-treated original graphite sample and the right side is the treated coated graphite sample.

FIG. 3 is a field emission Scanning Electron Micrograph (SEM) of the Nb-Cr composite carbide coating prepared in example 2.

FIG. 4 is a field emission Scanning Electron Micrograph (SEM) of the Nb-Cr composite carbide coating prepared in example 3.

FIG. 5 is a field emission Scanning Electron Micrograph (SEM) of the Nb-Cr composite carbide coating prepared in example 4.

FIG. 6 is an energy dispersive X-ray spectroscopy (EDS) photograph of the Nb-Cr composite carbide coating prepared in example 4.

FIG. 7 is an SEM and EDS image of the Nb-Cr composite carbide coating prepared in example 5: (a) is SEM picture; (b) to correspond to the EDS diagram in (a), elements C, Nb, Cr are labeled with yellow, pink and green, respectively.

FIG. 8 is the microhardness (HV0.1) of Nb-Cr composite carbide coatings under different processing conditions.

Detailed Description

The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:

example 1

In this example, referring to fig. 1, a method for preparing a hard metal carbide coating on the surface of a graphite material comprises the following steps:

selecting a graphite block with the size of 50 multiplied by 10mm, and grinding, polishing and cleaning the graphite block; after the surface of an original untreated graphite block is roughly ground by 280-mesh and 600-mesh abrasive paper, 1000-mesh and 2000-mesh abrasive paper and a 10000-mesh polishing pad are selected for fine grinding and polishing; then, ultrasonically cleaning the polished graphite material by absolute ethyl alcohol, placing the polished graphite material in a forced air drying oven, and fully drying the graphite material at 120 ℃ to finish the surface pretreatment of the graphite block;

then embedding the mixture into 200g of mixed salt powder prepared according to the mass fraction ratio shown in the table, and uniformly stirring;

the base salt is Na₂B₄O₇And B₂O₃The mass ratio of (A) to (B) is 3: 1;

and (3) placing the crucible filled with the mixed powder and the graphite sample at 250 ℃ for heat preservation for 5 hours, and dewatering and drying. Then the muffle furnace was heated to 950 ℃ at a temperature rise rate of 5 ℃/min and the temperature was maintained for 7 hours. The treated sample was quenched in an oil bath at room temperature and then ultrasonically cleaned with boiling water for 60 minutes. The washed sample was dried in a forced air drying oven at 130 ℃ for 1 hour.

A comparison of the prepared Nb-Cr composite carbide coating coated sample with the original graphite sample is shown in fig. 2.

Example 2

This embodiment is substantially the same as embodiment 1, and is characterized in that:

a method for preparing a hard metal carbide coating on the surface of a graphite material comprises the following steps:

selecting a graphite block with the size of 50 multiplied by 10mm, and grinding, polishing and cleaning the graphite block; after the surface of an original untreated graphite block is roughly ground by 280-mesh and 600-mesh abrasive paper, 1000-mesh and 2000-mesh abrasive paper and a 10000-mesh polishing pad are selected for fine grinding and polishing; then, ultrasonically cleaning the polished graphite material by absolute ethyl alcohol, placing the polished graphite material in a forced air drying oven, and fully drying the graphite material at 120 ℃ to finish the surface pretreatment of the graphite block;

then, embedding the graphite blocks into 200g of mixed salt powder prepared according to the mass fraction ratio shown in the table, and uniformly stirring;

the base salt is Na₂B₄O₇And B₂O₃The mass ratio of (A) to (B) is 2: 1;

and (3) placing the crucible filled with the mixed powder and the graphite sample at 250 ℃ for heat preservation for 5 hours, and dewatering and drying. Then the muffle furnace was heated to 950 ℃ at a temperature rise rate of 5 ℃/min and the temperature was maintained for 7 hours. The treated sample is quenched with clear water at room temperature and then ultrasonically cleaned with a dilute nitric acid solution (5-10 vol.%) for 30 minutes. The washed sample was dried in a forced air drying oven at 130 ℃ for 1 hour.

The SEM photograph of the resulting Nb — Cr composite carbide coating is shown in fig. 3.

Example 3

This embodiment is substantially the same as the previous embodiment, and is characterized in that:

a method for preparing a hard metal carbide coating on the surface of a graphite material comprises the following steps:

selecting a graphite block with the size of 50 multiplied by 10mm, and grinding, polishing and cleaning the graphite block; after the surface of an original untreated graphite block is roughly ground by 280-mesh and 600-mesh abrasive paper, 1000-mesh and 2000-mesh abrasive paper and a 10000-mesh polishing pad are selected for fine grinding and polishing; then, ultrasonically cleaning the polished graphite material by absolute ethyl alcohol, placing the polished graphite material in a forced air drying oven, and fully drying the graphite material at 120 ℃ to finish the surface pretreatment of the graphite block;

then, embedding the graphite blocks into 200g of mixed salt powder prepared according to the mass fraction ratio shown in the table, and uniformly stirring;

the base salt is Na₂B₄O₇And B₂O₃In a mass ratio of 2:1

And (3) placing the crucible filled with the mixed powder and the graphite sample at 250 ℃ for heat preservation for 5 hours, and dewatering and drying. The muffle furnace was then heated to 1000 ℃ at a ramp rate of 5 ℃/min and held for 7 hours. The treated sample is quenched with clear water at room temperature and then ultrasonically cleaned with a dilute nitric acid solution (5-10 vol.%) for 30 minutes. The washed sample was dried in a forced air drying oven at 130 ℃ for 1 hour.

The SEM photograph of the resulting Nb — Cr composite carbide coating is shown in fig. 4.

Example 4

This embodiment is substantially the same as the previous embodiment, and is characterized in that:

a method for preparing a hard metal carbide coating on the surface of a graphite material comprises the following steps:

selecting a graphite block with the size of 50 multiplied by 10mm, and grinding, polishing and cleaning the graphite block; after the surface of an original untreated graphite block is roughly ground by 280-mesh and 600-mesh abrasive paper, 1000-mesh and 2000-mesh abrasive paper and a 10000-mesh polishing pad are selected for fine grinding and polishing; then, ultrasonically cleaning the polished graphite material by absolute ethyl alcohol, placing the polished graphite material in a forced air drying oven, and fully drying the graphite material at 120 ℃ to finish the surface pretreatment of the graphite block;

then, embedding the graphite blocks into 200g of mixed salt powder prepared according to the mass fraction ratio shown in the table, and uniformly stirring;

the base salt is Na₂B₄O₇And B₂O₃The mass ratio of (A) to (B) is 2: 1;

and (3) placing the crucible filled with the mixed powder and the graphite sample at 250 ℃ for heat preservation for 5 hours, and dewatering and drying. The muffle furnace was then heated to 1050 ℃ at a ramp rate of 5 ℃/min and held for 7 hours. The treated sample is quenched with clear water at room temperature and then ultrasonically cleaned with a dilute nitric acid solution (5-10 vol.%) for 30 minutes. The washed sample was dried in a forced air drying oven at 130 ℃ for 1 hour.

The SEM photograph of the resulting Nb — Cr composite carbide coating is shown in fig. 5.

The EDS spectrum of the obtained Nb-Cr composite carbide coating is shown in fig. 6.

Example 5

This embodiment is substantially the same as the previous embodiment, and is characterized in that:

a method for preparing a hard metal carbide coating on the surface of a graphite material comprises the following steps:

selecting a graphite block with the size of 50 multiplied by 10mm, and grinding, polishing and cleaning the graphite block; after the surface of an original untreated graphite block is roughly ground by 280-mesh and 600-mesh abrasive paper, 1000-mesh and 2000-mesh abrasive paper and a 10000-mesh polishing pad are selected for fine grinding and polishing; then, ultrasonically cleaning the polished graphite material by absolute ethyl alcohol, placing the polished graphite material in a forced air drying oven, and fully drying the graphite material at 120 ℃ to finish the surface pretreatment of the graphite block;

then, embedding the graphite blocks into 200g of mixed salt powder prepared according to the mass fraction ratio shown in the table, and uniformly stirring;

the base salt is Na₂B₄O₇And B₂O₃The mass ratio of (A) to (B) is 2: 1;

and (3) placing the crucible filled with the mixed powder and the graphite sample at 250 ℃ for heat preservation for 5 hours, and dewatering and drying. The muffle furnace was then heated to 1050 ℃ at a ramp rate of 5 ℃/min and held for 7 hours. The treated sample is quenched with clear water at room temperature and then ultrasonically cleaned with a dilute nitric acid solution (5-10 vol.%) for 30 minutes. The washed sample was dried in a forced air drying oven at 130 ℃ for 1 hour.

The SEM photograph of the obtained Nb — Cr composite carbide coating is shown in (a) of fig. 7.

The EDS spectrum corresponding to the Nb-Cr composite carbide coating is shown in fig. 7 (b).

FIG. 8 is a plot of the microhardness (HV0.1) change of Nb-Cr composite carbide coatings under different processing conditions. The hardness-applied loads used in this example were: 100 g. Each test data point is obtained by testing 3 times respectively and taking the average value. It can be analyzed from fig. 8 that the prepared coating is compact and uniform, the coating is well combined with the graphite matrix, the surface hardness of the coating is as high as 3000HV, and the coating shows extremely high hardness performance.

It can be seen from the relevant performance tests and data analysis of the above embodiments that the corrosion resistance of the prepared coating is greatly improved even without weakening the conductivity and corrosion resistance of the coating, so that excellent surface hardness is obtained, the mechanical properties of the coating are improved, and the application scenarios of the graphite material are greatly expanded.

Example 6

This embodiment is substantially the same as the previous embodiment, and is characterized in that:

in this embodiment, the metal carbide forming element is an oxide of one or a combination of oxides of several elements selected from titanium (Ti), zirconium (Zr), vanadium (V), tantalum (Ta), niobium (Nb), tungsten (W), molybdenum (Mo), chromium (Cr), manganese (Mn), and iron (Fe).

In this implementationIn the examples, the reducing agent is B₄C. Any one or combination of more of magnesium (Mg), lanthanum (La), calcium (Ca), aluminum (Al), zirconium (Zr), titanium (Ti) and silicon (Si).

In this example, NaF, NaCl, KCl, BaCl were used as flux₂、AlF₃At least one of (1).

In the embodiment, the particle size of the salt bath powder is 0.5-5 microns.

In this example, the carbon content of the substrate of the hard metal carbide coating prepared on the graphite surface was not less than 0.3 wt.%.

In the method for preparing the hard metal carbide coating on the surface of the graphite material in the above embodiment, the graphite material is buried in the mixed salt bath with borax as a base salt, and is heated to a molten state to perform the preparation reaction of the coating. After reacting for a period of time, taking out the graphite sample, quenching to room temperature, cleaning residual salt on the surface of the sample, and drying to obtain a layer of compact and wear-resistant metal carbide coating on the surface of the graphite. The embodiment is used for surface densification modification of various carbon-containing materials, and has the advantages of simple preparation process, low equipment requirement and low cost. The prepared metal carbide coating has extremely high hardness, excellent wear resistance and excellent corrosion resistance. The method can be widely applied to various complex severe environments and relevant special application conditions, including aerospace engineering and severe marine environments.

The embodiments of the present invention have been described above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention should be replaced with equivalents as long as the object of the present invention is met, and the technical principle and the inventive concept of the present invention are not departed from the scope of the present invention.