CN114457301B

CN114457301B - High-speed steel self-lubricating coating and preparation method thereof

Info

Publication number: CN114457301B
Application number: CN202110722872.9A
Authority: CN
Inventors: 陆晓刚; 林正华; 潘鹏; 陈蕴博; 左玲立; 郎兆林; 黄福生; 陈晶; 林健
Original assignee: Fujian Hengda New Materials Co ltd; Beijing National Innovation Institute of Lightweight Ltd
Current assignee: Fujian Hengda New Materials Co ltd; Beijing National Innovation Institute of Lightweight Ltd
Priority date: 2021-06-28
Filing date: 2021-06-28
Publication date: 2022-12-30
Anticipated expiration: 2041-06-28
Also published as: CN114457301A

Abstract

The invention relates to a high-speed steel self-lubricating coating and a preparation method thereof, belongs to the technical field of self-lubricating wear-resistant coatings, and solves the problems of large friction coefficient, weak tensile strength, easy peeling of the coating and the like caused by poor self-lubricating property of a WC-10Co-4Cr coating in the prior art. The invention provides a high-speed steel self-lubricating coating and a preparation method thereof, wherein the high-speed steel self-lubricating coating comprises the following components in percentage by mass: co:9% -10%, cr:3.5% -4.2%, C (n): 0.1-0.7 percent of WC, and the balance of WC, wherein the coating is prepared by mixing WC-10Co-4Cr powder, KH570 coupling agent and graphene suspension, drying and sieving to obtain mixed powder; is obtained by using supersonic flame thermal spraying. The novel self-lubricating coating obtained by the invention has excellent functions of wear resistance and drag reduction, effectively reduces the friction coefficient and the abrasion loss of the coating, and enhances the fracture toughness and the corrosion resistance of the coating; the preparation process is simple and easy for industrial application.

Description

High-speed steel self-lubricating coating and preparation method thereof

Technical Field

The invention relates to the technical field of self-lubricating wear-resistant coatings, in particular to a high-speed steel self-lubricating coating and a preparation method thereof.

Background

The WC-based ceramic coating prepared by the supersonic flame thermal spraying has high microhardness and coating bonding strength, and has outstanding wear resistance, corrosion resistance and impact resistance, and is widely applied to a plurality of industrial application fields such as aviation, ships, metallurgy and the like to improve the service life and performance of components.

WC-10Co-4Cr is one of the most representative materials in the WC-based ceramic coating. The elements of the WC-10Co-4Cr coating form a system which is mutually coordinated and mutually strengthened. The density of the coating can be improved by taking the metal Co phase as an ideal binder, the corrosion resistance of the coating is effectively improved by adding the Cr element, and the high hardness of the coating is endowed by using the WC as the hard alloy.

However, the high hardness of WC makes the coating have poor self-lubricating properties, resulting in a large friction coefficient of the coating (the friction coefficient can reach 0.5 to 1.0), and the tensile strength of the coating is weak, and the tensile force during the friction process is liable to cause microcracks. In addition, due to the low toughness of the coating, cracks are easily propagated to cause the peeling of WC hard particles, which leads to the increase of the friction coefficient and the reduction of the corrosion resistance, and finally influences the service life of the protective coating.

Disclosure of Invention

In view of the above analysis, the embodiment of the invention aims to provide a high-speed steel self-lubricating coating and a preparation method thereof, so as to solve the problems of large friction coefficient, weak tensile strength, easy peeling of the coating and the like caused by poor self-lubricating performance of the existing WC-10Co-4Cr coating.

The embodiment of the invention provides a high-speed steel self-lubricating coating and a preparation method thereof.

On one hand, the invention provides a high-speed steel self-lubricating coating which comprises the following components in percentage by mass: co:9% -10%, cr:3.5% -4.2%, C (n): 0.1 to 0.7 percent and the balance of WC.

Furthermore, the raw materials for preparing the high-speed steel self-lubricating coating comprise graphene and WC-10Co-4Cr powder, and the high-speed steel self-lubricating coating is obtained by adopting a supersonic flame thermal spraying method.

Further, the mass ratio of the graphene to the WC-10Co-4Cr powder is 1:1000 to 140.

On the other hand, the invention provides a preparation method of a high-speed steel self-lubricating coating, which comprises the following steps:

step 1, placing expanded graphite in absolute ethyl alcohol for ultrasonic stripping, and assisting mechanical stirring to obtain a graphene turbid liquid;

step 2, mixing WC-10Co-4Cr powder, KH570 coupling agent and the graphene suspension obtained in the step 1; drying and sieving to obtain mixed powder;

and 3, thermally spraying the mixed powder obtained in the step 2 by using a supersonic flame to obtain a coating.

Further, in the step 1, the expanded graphite is obtained by heating flaky expandable graphite by microwave;

the microwave heating time is 30-40 seconds, and the microwave heating power is 700-1000 watts;

the granularity of the powder of the expandable graphite is 80 to 100 meshes, and the purity is 99.9 percent.

Further, in the step 1, the power of ultrasonic stripping is 80-120W, and the ultrasonic time is 30-50 minutes; the rotation speed of the mechanical stirring is 800-1000 r/min.

Further, in the step 2, the WC-10Co-4Cr powder comprises the following components in percentage by mass: 9% -10%, cr:3.5 to 4.2 percent of the total weight of the alloy, and the balance of WC, and the grain diameter is 15 to 45 mu m.

Further, the mass ratio of the expanded graphite to the WC-10Co-4Cr powder is 1:1000 to 140.

Furthermore, the surface blasting roughening treatment is carried out on the high-speed steel before the step 3, brown corundum with the particle size of 0.3-0.9 mm is adopted in the blasting roughening treatment, the treatment mode is vertical blasting, the blasting air pressure is 0.3-0.6 MPa, the blasting distance is 50-100 mm, and the blasting treatment is carried out until the surface roughness reaches Ra 3-5.

Further, in the step 3, the technological parameters of the supersonic flame thermal spraying are as follows: the nitrogen flow is 20-25L/min, the oxygen flow is 800-900L/min, the kerosene flow is 0.4-0.5L/min, the powder feeding amount is 35 x 2-55 x 2g/min, and the spray distance is 200-450 mm.

Compared with the prior art, the invention can realize at least one of the following beneficial effects:

1. the components of the high-speed steel self-lubricating coating comprise 0.1-0.7% of C (n), and the high-speed steel self-lubricating coating has excellent performances of abrasion resistance, drag reduction, toughness and corrosion resistance, and the embodiment shows that compared with the original WC-10Co-4Cr coating, the average friction coefficient of the self-lubricating coating is stabilized to be about 0.31, and the friction coefficient is reduced by 38%; the abrasion loss is only 0.61-0.75 mg, which is reduced by 25% -39%; the fracture toughness value is 8.38 +/-0.083-8.72 +/-0.078 MPa.m ^1/2 The improvement is increased by 19.4 to 24.2 percent; the corrosion current density is reduced to 3.21-2.89 multiplied by 10 ^-6 A·cm ^-2 The corrosion rate is reduced to 0.27-0.33V/mm.a by 20-28 percent ^-1 And the reduction is 20 to 58 percent.

2. The preparation method comprises the steps of adopting expandable graphite as a precursor, obtaining the expandable graphite after microwave heating, placing the expandable graphite in an absolute ethyl alcohol solution for ultrasonic stripping and assisting mechanical stirring to obtain a graphene turbid liquid; adding WC-10Co-4Cr powder and a KH570 coupling agent into the graphene suspension, and uniformly mixing; drying and screening to obtain graphene modified WC-10Co-4Cr mixed powder; based on the supersonic flame thermal spraying technology, the graphene modified WC-10Co-4Cr coating is sprayed on the surface of high-speed steel metal (such as M42 high-speed steel), and the examples show that the coating abrasion loss can be as low as 0.61mg, and the friction coefficient can be as low as 0.31 (for example, the coating abrasion loss after the modification by adding 0.3wt.% of graphene is only 0.61mg, and the friction coefficient is stabilized at 0.31), and compared with the unmodified coating, the friction coefficient can be reduced by 38%. The novel self-lubricating coating obtained by the invention has excellent functions of wear resistance and drag reduction, and effectively reduces the friction coefficient and the abrasion loss of the coating.

3. The embodiment of the invention adopts a wet ball milling process to realize that the graphene is dispersed and uniformly distributed in the WC-10Co-4Cr powder, and the high-quality graphene modified WC-10Co-4Cr coating is deposited on the surface of the M42 high-speed steel based on the supersonic flame thermal spraying technology, so that the process is simple and reliable, and the economy is good.

4. The continuous transfer film with self-lubricating property and high bonding property formed by the graphene modified WC-10Co-4Cr coating reduces the friction coefficient of a substrate, the graphene self-lubricating transfer film is formed on the surface of the coating in the friction and wear process, and C (n) plays a role of a lubricant.

The wear resistance of the existing coating mainly depends on WC hard alloy particles with high hardness, and the WC particles are easy to peel off in the later stage of wear; according to the invention, the graphene is added, so that the WC particles are wrapped and bridged, and the peeling phenomenon of the WC particles can be effectively reduced. The high-speed steel self-lubricating coating plays a role in reducing the friction coefficient and the abrasion loss of the coating, can replace the conventional electroplated hard chromium, and is applied to easily-abraded components.

5. In order to reduce the friction coefficient of the WC-10Co-4Cr coating and exert the antifriction and self-lubricating characteristics of graphene, the finished graphene is modified into WC-Co powder in a stirring and vacuum freezing mode in the prior art, but the finished graphene is expensive, compared with the prior art, the graphene is prepared from the expanded graphite which is low in price, the WC-10Co-4Cr powder is modified by the graphene material prepared at low cost, and the novel self-lubricating wear-resistant coating is prepared on the surface of M42 high-speed steel through supersonic flame thermal spraying, so that the method has very important significance for promoting the industrial application of the WC-10Co-4Cr coating.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.

FIG. 1 is a graph comparing friction coefficient curves of M42 high speed steel, WC-10Co-4Cr coatings prepared in comparative example 1, and graphene-modified WC-10Co-4Cr self-lubricating coatings prepared in examples 1 to 3;

FIG. 2 is a graph comparing the wear amounts of M42 high speed steel, WC-10Co-4Cr coating prepared in comparative example 1, and the graphene-modified WC-10Co-4Cr self-lubricating coatings prepared in examples 1 to 3;

FIG. 3 is a line graph showing the fracture toughness test results of the WC-10Co-4Cr coating prepared in comparative example 1 and the graphene-modified WC-10Co-4Cr self-lubricating coatings prepared in examples 1 to 3;

FIG. 4 is a microscopic morphology of the frictional wear surface of the WC-10Co-4Cr coating prepared in comparative example 1;

FIG. 5 shows the micro-morphology of the frictional wear surface of the graphene-modified WC-10Co-4Cr self-lubricating coating prepared in example 2.

Detailed Description

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.

The invention discloses a high-speed steel self-lubricating coating which is a graphene modified WC-10Co-4Cr self-lubricating coating and comprises the following components: co:9% -10%, cr:3.5% -4.2%, C (n): 0.1 to 0.7 percent of WC, and the balance of WC.

The raw materials of the high-speed steel self-lubricating coating comprise graphene and WC-10Co-4Cr powder, and the high-speed steel self-lubricating coating is obtained by a supersonic flame thermal spraying method. Wherein the mass ratio of the graphene to the WC-10Co-4Cr powder is 1.

Graphene, a two-dimensional (2D) nanomaterial formed by the periodic arrangement of carbon atoms in hexagons, is the basic unit for building the most commonly used solid lubricant, graphite. The unique nano-layered structure of the graphene endows the coating with a lower friction coefficient, so that the coating obtained by modifying WC-10Co-4Cr through the graphene has self-lubricating property and high bonding property, the friction coefficient of a matrix is reduced, and good antifriction and self-lubricating effects are achieved.

On the other hand, the preparation method of the high-speed steel self-lubricating coating is disclosed, and comprises the following steps:

step 1: placing the expanded graphite in absolute ethyl alcohol for ultrasonic stripping, and assisting in mechanical stirring to obtain a graphene turbid liquid;

and 2, step: mixing WC-10Co-4Cr powder, KH570 coupling agent and the graphene suspension obtained in the step (1); drying and sieving to obtain mixed powder;

and 3, step 3: and (3) thermally spraying the mixed powder obtained in the step (2) by using a supersonic flame to obtain a coating.

Specifically, the expanded graphite is obtained by heating flaky expandable graphite by microwave, wherein the microwave heating time is 30-40 seconds, and the microwave heating power is 700-1000 watts.

Specifically, the expandable graphite has a powder particle size of 80 mesh and a purity of 99.9%, and the volume thereof can be expanded by 200 to 400 times in the C-axis direction after heating.

It should be noted that expandable graphite is a crystalline compound in which non-carbonaceous reactants are physically or chemically inserted between graphite layers and bonded to the hexagonal network planes of carbon while maintaining the layered structure of graphite. It not only maintains the excellent physical and chemical properties of graphite, but also shows new performance which the original graphite and intercalation material do not have due to the interaction of the intercalation material and graphite layer. When the graphite with the intercalated interlaminar compound is subjected to high temperature, the interlaminar compound is decomposed to generate thrust along the direction of a C axis between graphite layers, the thrust is far greater than the interlaminar bonding force of graphite particles, and the graphite layers are pushed away under the action of the thrust, so that the graphite particles expand by a high factor of 200-400 times along the direction of the C axis, and vermicular expanded graphite is formed.

The expandable graphite is usually prepared by using crystalline flake graphite as a raw material and using concentrated sulfuric acid, fuming nitric acid or alkali metal with unstable chemical properties as an intercalating agent, and performing intercalation oxidation reaction on the intercalating agent and graphite. The expanded graphite props up the distance between graphite layers, the molecular acting force between the sheet layers is weakened, and then the nano-scale graphene is obtained by stripping through high temperature, ultrasonic wave or chemical treatment.

Specifically, in the step 1, the power of ultrasonic stripping is 80-120W, and the ultrasonic time is 30-50 minutes; the rotation speed of the mechanical stirring is 800-1000 r/min.

The graphene is prepared in an organic solvent, a surfactant, an aqueous solution or an ionic liquid by an ultrasonic action, preferably in absolute ethyl alcohol, and the graphene is produced by the expansion graphite through exfoliation under the ultrasonic action. The method has the advantages of cheap and easily-obtained raw materials, simple and easy operation, no pollution, good repeatability and relatively high graphene yield, and can be used for large-scale production.

Utilize mechanical high-speed stirring, can make the graphite alkene turbid liquid disperse more.

Specifically, in the step 2, the WC-10Co-4Cr powder comprises the following components in percentage by mass: 9% -10%, cr:3.5 to 4.2 percent of the total weight of the alloy, and the balance of WC, and the grain diameter is 15 to 45 mu m.

Specifically, in the step 2, the graphene and the WC-10Co-4Cr powder are mixed by planetary ball milling, the ball-material ratio is 3-5, the ball milling speed is set to 400-600 r/min, and the ball milling time is 5-8 hours.

The working principle of the planetary ball mill is that the grinding material and the test material roll at high speed in a grinding tank to generate strong shearing, impact and rolling on the material so as to achieve the purposes of crushing, grinding, dispersing and emulsifying the material. The planetary ball mill is provided with four ball milling tanks on the same turntable, and when the turntable rotates, the ball milling tanks revolve around the turntable shaft and simultaneously rotate around the self shaft center to perform planetary motion. The grinding balls in the jar collide with each other in high speed motion, grinding and mixing the sample. The planetary ball mill can grind and mix products with different particle sizes and different materials by a dry method and a wet method, and the minimum particle size of the ground product can be 0.1 micron. The planetary ball mill can well meet the requirements of various material process parameters, preferably, the ball milling rotating speed is set to be 400-600 r/min, the ball milling time is 5-8 hours, graphene and WC-10Co-4Cr powder can be well ground, and the planetary ball mill has the advantages of small batch, low power consumption and low price.

The ball-material ratio is the mass ratio of materials in the ball mill to a grinding body, and is an important parameter influencing the ball milling process, the number of balls is too small, the times of impact and grinding are few, and the efficiency is low; if too much, the impact between the balls is affected, and the crushing effect cannot be fully exerted. Preferably, the ball-to-feed ratio is 3-5.

In order to ensure the uniform dispersion of graphene and good bonding property with WC-10Co-4Cr powder, KH570 silane coupling agent is added during ball milling and mixing. The mass ratio of the added mass of the silane coupling agent to the expanded graphite is 2. The graphene surface contains a large number of active functional groups, the graphene reacts with a silane coupling agent, the compatibility of the graphene and a WC-10Co-4Cr polymer is promoted by the existence of Y groups in the structure of the silane coupling agent, and the compatibility of the KH570 and a WC-10Co-4Cr interface is improved due to the existence of carbon-carbon double bonds, so that the graphene and WC-10Co-4Cr powder are better combined.

When the amount of graphene added exceeds 1% by mass of the WC-10Co-4Cr powder, it is agglomerated in a mixed solution with WC-10Co-4 Cr. Since the silane coupling agent KH570 is grafted to the graphene surface functional group, the graphene has better dispersibility in the mixed solution, so that the compatibility of the graphene and the mixed solution is improved. Therefore, in the prepared graphene modified coating material, the addition amount of the graphene is not more than 1% of the mass of the WC-10Co-4Cr powder. Because, the expanded graphite carries out the supersound and peels off and becomes graphite alkene, and mass loss can be ignored almost, and weigh graphite alkene quality and compare the difficulty, consequently weigh expanded graphite quality can. Through repeated tests and comparisons, in the step 2, the mass ratio of the raw material expanded graphite to the WC-10Co-4Cr powder is preferably 1: 1000-140, namely the addition amount of the graphene is about 0.1% -0.7%.

Specifically, in the step 2, after ball milling, the mixed solution of graphene and WC-10Co-4Cr is dried at 90-120 ℃ for 30-48 hours, and the particle size of the dried and sieved mixed powder is 15-30 μm.

In order to improve the dispersibility of the graphene in the mixed material and further improve the comprehensive performance of the mixed material, a vacuum drying oven (such as a new DZF-6050 type) is adopted for drying, the temperature is set to be 90-120 ℃, the drying time is 30-48 hours, the graphene is dried by using the parameters, the sample is extremely fluffy and is not easy to agglomerate, and the chemical property of the material is not influenced.

And drying and sieving the mixed solution of the graphene and the WC-10Co-4Cr to ensure that the mixed powder reaches the optimal spraying particle size of 15-30 mu m. Generally, the smaller the particle size of the powder, the better the leveling property of the coating during self-curing, and the smoother and smoother the appearance of the coating film, but the electrification of the powder is proportional to the square of the particle size, the electrification of the powder is reduced when the powder is too fine, the coating efficiency is reduced, and the ultra-fine powder (particle size < 10 μm) is substantially uncharged. The powder coating rate and the charging performance of the powder coating have an important relationship. The electrification amount of the coating particles is improved, and the powdering rate is improved. The charge amount of the particles is proportional to the square of the particle diameter of the particles. The particle size is increased, the charge of the coating particles is increased, and the powdering rate is improved. However, the particle size of the particles cannot be too large, and the gravity action of the coating particles exceeds the aerodynamic force and the electrostatic force, but the powdering rate is reduced. Therefore, the optimum spray particle size is selected to be 15 to 30 μm.

Before the coating is prepared on the surface of the high-speed steel by using the supersonic flame thermal spraying method, the method also comprises the following steps:

step A: before spraying, acetone is used for removing oil and dirt on the surface of the high-speed steel;

and B: and carrying out surface sand blasting roughening treatment on the high-speed steel.

Specifically, in the step a, acetone is used to degrease and decontaminate the surface of the high-speed steel, and specifically, acetone is used to wipe the surface of the high-speed steel for at least 3 times until the surface of the high-speed steel is clean, free of oil stains and has a distinct metallic luster, so that the surface of the high-speed steel is clean and changed from hydrophobic property or local hydrophobic property to hydrophilic property, that is, the high-speed steel is in an activated state.

Specifically, in the step B, the high-speed steel is subjected to surface blasting roughening treatment, in which the surface of the cleaned and preprocessed substrate is formed into a uniform rough surface with unevenness, so as to increase the contact area between the coating and the surface of the substrate, and the roughness of the coating is controlled, so that deformed flat particles in the coating are interlaced with each other, thereby forming an interlocked lamination. The surface roughness is increased, the residual stress of the coating is improved, the compressive stress is generated by the coating, the macroscopic residual stress of the coating is reduced, the coating and the substrate are bonded more strongly, the surface can be further purified, and the surface activating effect is realized.

More specifically, in order to achieve the purpose of good mechanical bonding between the roughened surface and the coating, in the step B, the sand blasting roughening treatment adopts brown corundum vertical sand blasting with the particle size of 0.3-0.9 mm, the sand blasting air pressure is 0.3-0.6 MPa, the spraying distance is 50-100 mm, and the sand blasting treatment is carried out until the surface roughness reaches Ra 3-5, so that the coating and the high-speed steel surface achieve the best bonding effect.

Specifically, the specific process parameters for preparing the coating by using the supersonic flame are as follows: the nitrogen flow is 20-25L/min, the oxygen flow is 800-900L/min, the kerosene flow is 0.4-0.5L/min, the powder feeding amount is 35 x 2-55 x 2g/min, and the spray distance is 200-450 mm.

It should be noted that the supersonic flame spraying technology is one of thermal spraying technologies, and a coating prepared by the supersonic flame spraying technology has the advantages of compact coating, low porosity, high bonding strength, high hardness, low residual stress and low oxygen content, and has become a standard technology for spraying a carbide coating. More specifically, the supersonic flame spraying equipment selects Praxair TAFA JP-5000, the fuel is aviation kerosene, and the flow rate of the kerosene is 0.4-0.5L/min; the gas is oxygen and nitrogen, the flow rate of the nitrogen is 20-25L/min, and the flow rate of the oxygen is 800-900L/min. Generally, the higher the kerosene flow, the more the power of the spray gun is, the more the powder is melted during the spraying process, the higher the particle speed is, the higher the kinetic energy is, the more dense the coating is, and the higher the hardness is. However, the kerosene flow cannot be too large, the selection of parameters of the spraying equipment judges according to the performance detection result of the coating and the color of the flame flow, the kerosene and the oxygen are ensured to be in proportion, the improper proportion will affect the performance of the coating, if the color of the flame flow is yellow, the kerosene amount is too high, and if the color of the flame flow is blue, the oxygen is too high.

The supersonic flame spraying technology ensures that the coating is in a high-temperature environment for a long time, carbide strengthening phases are separated out from the tissues, hard phases are increased, the local volume shrinkage is caused by the separation of crystalline phases, the large pores are reduced, and the coating becomes compact.

In the process of supersonic flame spraying, if the spraying parameters are not properly selected, the formed coating structure has more pores and overproof porosity and cannot meet the use requirement of a wear-resistant coating, and the obtained coating structure has uniform structure, no layering and no cracks, the powder is fully melted and no unmelted particles by adjusting the parameters, preferably, the powder feeding amount is 35 multiplied by 2 to 55 multiplied by 2g/min and the spraying distance is 200 to 450mm.

After spraying, a reciprocating type friction and wear testing machine, model UMT3, is adopted to respectively test the tribological properties of the graphene modified WC-10Co-4Cr coating and the original WC-10Co-4Cr coating prepared by the invention, and the friction coefficient is measured.

The abrasion loss is measured by an analytical balance, and the model is as follows: and MT-XSR, respectively measuring the mass of the sample before and after the friction and wear test, and obtaining the wear loss.

Adopting an indentation method to measure the fracture toughness of the coating, and equipment comprises the following steps: the average value of the HV-5 type Vickers hardness tester, load 5kg, dwell time 15s,10 measurements was taken as the fracture toughness value of the coating.

The coatings were tested for corrosion resistance using a PAR4000 electrochemical integrated test system, selecting a 3.5% NaCl solution at a test temperature of 27 + -1 deg.C.

Compared with the prior art, the method adopts expandable graphite as a precursor to prepare the graphene, the preparation raw materials are cheap and easy to obtain, and the preparation method is simple. The high-speed steel self-lubricating coating prepared by the invention, namely the graphene modified WC-10Co-4Cr coating, has excellent tribological properties. In the sliding friction process, a graphene self-lubricating transfer film is formed on the surface of the coating, so that the effect of reducing the friction coefficient and the abrasion loss of the coating is achieved, the coating can replace the existing electroplated hard chromium, and the coating can be applied to parts easy to abrade.

The invention adopts the supersonic flame spraying technology to spray the high-speed steel self-lubricating coating, namely the graphene modified WC-10Co-4Cr coating, and has the effects of uniform coating, no layered cracks and high bonding strength.

Compared with the prior art, the high-speed steel self-lubricating coating has excellent performances of abrasion resistance, drag reduction, toughness and corrosion resistance.

Example 1

The embodiment provides a high-speed steel self-lubricating coating, a preparation method and a spraying method thereof, wherein the M42 high-speed steel graphene modified WC-10Co-4Cr coating is prepared by the method and sprayed, and the specific details are as follows:

s1: heating expandable graphite (80 mesh, 99.9% purity) in a domestic microwave oven at 800W for 30 s to obtain expanded graphite;

s2: respectively weighing the expanded graphite obtained in the step S1 and WC-10Co-4Cr powder according to a mass ratio of 1; the WC-10Co-4Cr powder comprises the following components: 9.2%, cr:3.68 percent of WC, and the particle size of 15-45 mu m;

s3: placing the expanded graphite weighed in the step S2 in an absolute ethyl alcohol solution for ultrasonic stripping for 40 minutes, wherein the ultrasonic power is 100W, and simultaneously, mechanically stirring at the rotating speed of 800r/min to finally obtain a graphene suspension;

s4: and (4) mixing WC-10Co-4Cr powder with the graphene suspension obtained in the step (S3) by adopting a planetary ball mill, and adding a KH570 silane coupling agent to improve the bonding strength. The planetary ball milling speed is 500r/min, the ball material ratio is 5;

s5: drying the product after ball milling in the step S4 for 48 hours at the drying temperature of 90 ℃, and screening to obtain mixed powder with the powder granularity of 15-30 microns;

s6: removing oil and dirt on the surface of the M42 high-speed steel by using acetone, then vertically blasting sand by using brown corundum with the particle size of 0.3-0.9 mm, wherein the sand blasting air pressure is 0.5MPa, the blasting distance is 60mm, and the sand blasting is stopped after the sand blasting treatment is carried out until the surface roughness is Ra3.2;

s7: and (4) spraying the mixed powder obtained in the step S5 to the surface of the M42 high-speed steel treated in the step S6 by using supersonic flame thermal spraying equipment to obtain the graphene modified WC-10Co-4Cr coating. The spraying process parameters are as follows: the nitrogen flow is 23L/min, the oxygen flow is 860L/min, the kerosene flow is 0.43L/min, the powder feeding amount is 50 multiplied by 2g/min, and the spraying distance is 230mm.

The high-speed steel self-lubricating coating component obtained in the example 1 comprises Co:9.2%, cr:3.68%, C (n): 0.1% and the balance WC.

A reciprocating type friction and wear testing machine is used for testing the tribological performance, in this example 1, 0.1wt.% of graphene is added to prepare the graphene modified WC-10Co-4Cr self-lubricating coating, the average friction coefficient is 0.31, and the wear loss is 0.75mg.

The fracture toughness value measured by a Vickers hardness tester is 8.38 +/-0.083 MPa.m ^1/2 。

The current density measured by electrochemical comprehensive test corrosion is 3.21 multiplied by 10 ^-6 A·cm ^-2 The corrosion rate is 0.33V/mm.a ^-1 。

Example 2

s1: heating expandable graphite (90 mesh, 99.9% purity) in a domestic microwave oven at 800W for 30 s to obtain expanded graphite;

s2: weighing the expanded graphite obtained in the step S1 and WC-10Co-4Cr powder according to a mass ratio of 1; the WC-10Co-4Cr powder comprises the following components: 9.8%, cr:3.92 percent of WC, and the particle size is 15-45 mu m;

s3: placing the expanded graphite weighed in the step S2 in an absolute ethyl alcohol solution for ultrasonic stripping for 40 minutes, wherein the ultrasonic power is 100 watts, and simultaneously, mechanically stirring at the rotating speed of 800r/min to finally obtain a graphene suspension;

s4: and (4) mixing WC-10Co-4Cr powder with the graphene suspension obtained in the step (S3) by adopting a planetary ball mill, and adding a KH570 silane coupling agent to improve the bonding strength. The planetary ball milling speed is 600r/min, the ball-material ratio is 4;

s6: removing oil and dirt on the surface of the M42 high-speed steel by using acetone, then vertically blasting sand by using brown corundum with the particle size of 0.3-0.9 mm, wherein the sand blasting air pressure is 0.5MPa, the spray distance is 60mm, and stopping after the sand blasting treatment is carried out until the surface roughness is Ra4.5;

s7: and (4) spraying the mixed powder obtained in the step S5 on the surface of the M42 high-speed steel treated in the step S6 by using supersonic flame thermal spraying equipment to obtain the graphene modified WC-10Co-4Cr coating. The spraying process parameters are as follows: the nitrogen flow is 23L/min, the oxygen flow is 860L/min, the kerosene flow is 0.43L/min, the powder feeding amount is 50 multiplied by 2g/min, and the spraying distance is 230mm.

The high-speed steel self-lubricating coating obtained in the example 2 comprises Co:9.8%, cr:3.92%, C (n): 0.3% and the balance of WC.

A reciprocating friction and wear tester is used for tribological performance testing, in this example 2, 0.3wt.% of graphene is added to prepare the graphene modified WC-10Co-4Cr self-lubricating coating, the average friction coefficient is 0.31, and the wear amount weighed by an analytical balance is 0.61mg.

The fracture toughness value measured by a Vickers hardness tester is 8.65 +/-0.09 MPa.m ^1/2 。

The current density measured by electrochemical comprehensive test corrosion is 3.05 multiplied by 10 ^-6 A·cm ^-2 The corrosion rate is 0.29V/mm.a ^-1 。

Example 3

s1: expandable graphite (100 mesh, 99.9% purity) is heated by microwave for 30 seconds in a household microwave oven with 800 watts of power to obtain the expanded graphite;

s2: respectively weighing the expanded graphite obtained in the step S1 and WC-10Co-4Cr powder according to a mass ratio of 1; the WC-10Co-4Cr powder comprises the following components: 10%, cr:4 percent of WC with the grain diameter of 15-45 mu m;

s4: and (4) mixing WC-10Co-4Cr powder with the graphene suspension obtained in the step (S3) by adopting a planetary ball mill, and adding a KH570 silane coupling agent to improve the bonding strength. The planetary ball milling speed is 600r/min, the ball-material ratio is 3;

s6: removing oil and dirt on the surface of the M42 high-speed steel by using acetone, then vertically blasting sand by using brown corundum with the particle size of 0.3-0.9 mm, wherein the sand blasting air pressure is 0.5MPa, the spray distance is 60mm, and stopping after the sand blasting treatment is carried out until the surface roughness Ra3.9;

The high-speed steel self-lubricating coating obtained in example 3 comprises the following components in percentage by mass: 10%, cr:4%, C (n): 0.5% and the balance of WC.

A reciprocating type friction and wear testing machine is used for testing the tribological performance, in this example 3, 0.5wt.% of graphene is added to prepare the graphene modified WC-10Co-4Cr self-lubricating coating, the average friction coefficient is 0.31, and the wear loss is 0.67mg.

The fracture toughness value measured by a Vickers hardness tester is 8.72 +/-0.078 MPa.m ^1/2 。

The corrosion current density measured by electrochemical comprehensive test is 2.89 multiplied by 10 ^-6 A·cm ^-2 The corrosion rate is 0.27V/mm.a ^-1 。

Comparative example 1

The comparative example provides an original WC-10Co-4Cr coating and a spraying method in the prior art, and specifically comprises the following steps:

s1: removing oil and dirt on the surface of the M42 high-speed steel by using acetone, then vertically blasting sand by using brown corundum with the particle size of 0.3-0.9 mm, wherein the sand blasting air pressure is 0.5MPa, the blasting distance is 60mm, and the sand blasting is stopped after the sand blasting treatment is carried out until the surface roughness is Ra3.5;

s2: and (3) spraying WC-10Co-4Cr powder onto the surface of the M42 high-speed steel treated in the step S1 by using a supersonic flame thermal spraying device to obtain a WC-10Co-4Cr wear-resistant coating. The spraying process parameters are as follows: the nitrogen flow is 23L/min, the oxygen flow is 860L/min, the kerosene flow is 0.43L/min, the powder feeding amount is 50 multiplied by 2g/min, and the spray distance is 230mm.

The graphene-modified WC-10Co-4Cr coatings prepared in examples 1 to 3 and the WC-10Co-4Cr coating prepared in comparative example 1 were respectively subjected to a tribology performance test and a vickers hardness tester fracture toughness test by using a reciprocating friction wear tester, and the measured friction coefficient, wear loss, and fracture toughness coefficient are shown in fig. 1, fig. 2, and fig. 3.

The results in FIG. 1 show that the coefficient of friction of M42 high speed steel stabilizes at 0.82; the friction coefficient of the supersonic flame thermal spraying WC-10Co-4Cr coating is 0.5; the friction coefficient of the WC-10Co-4Cr coating is stabilized to about 0.31 after the graphene is modified, and compared with the unmodified coating, the friction coefficient is reduced by 38%.

After the friction and wear test is carried out for 60 minutes, the abrasion loss of the M42 high-speed steel is weighed by an analytical balance to be 2.2mg; the abrasion loss of the WC-10Co-4Cr coating is 1mg; and the abrasion loss of the coating after the addition of 0.3wt.% graphene modification is minimum, and is only 0.61mg. Compared with a WC-10Co-4Cr coating, the wear loss is reduced by 25 to 39 percent.

As shown in fig. 3, the coatings with 0.1wt.%, 0.3wt.% and 0.5wt.% graphene content were tested for fracture toughness and the fracture toughness values were 8.38 ± 0.083MPa · m ^1/2 ，8.65±0.09MPa·m ^1/2 And 8.72 +/-0.078 MPa.m ^1/2 Compared with the fracture toughness (7.02 +/-0.07 MPa.m) of the original WC-10Co-4Cr coating ^1/2 ) Respectively increased by 19.4%, 23.2% and 24.2%.

The frictional wear appearances of the WC-10Co-4Cr coating and the graphene modified coating are respectively shown in fig. 4 and 5, and it can be seen that a graphene self-lubricating film is formed on the surface of the graphene modified coating in the frictional wear process; compared with the original coating, the peeling area of the coating after graphene modification is obviously reduced.

Table 1 shows the polarization values of the WC-10Co-4Cr coatings and the graphene-modified WC-10Co-4Cr self-lubricating coatings prepared in examples 1 to 3 in a 3.5% NaCl solution. As can be seen from the table, the corrosion tendency of the coating after graphene modification is greatly reduced. Wherein the corrosion current density is 4.02 × 10 ^-6 A·cm ^-2 Reduced to 3.21-2.89X 10 ^-6 A·cm ^-2 The reduction is 20 to 28 percent; the corrosion rate is also reduced by 20-58%. The corrosion resistance of the graphene modified WC-10Co-4Cr self-lubricating coating is greatly improved.

TABLE 1 polarization of WC-10Co-4Cr coatings and graphene-modified WC-10Co-4Cr self-lubricating coatings prepared in examples 1 to 3% in NaCl solution 3.5%

The above results show that: the friction coefficient of the graphene modified WC-10Co-4Cr self-lubricating coating is lower than that of the WC-10Co-4Cr coating and is further lower than that of the surface of M42 high-speed steel. The graphene modified WC-10Co-4Cr self-lubricating coating prepared by the invention has better self-lubricating property for the WC-10Co-4Cr coating. In addition, the abrasion loss of the graphene modified WC-10Co-4Cr self-lubricating coating is smaller than that of the original WC-10Co-4Cr coating, which shows that the graphene modified WC-10Co-4Cr self-lubricating coating prepared by the invention has an antifriction effect on the WC-10Co-4Cr coating.

The high-speed steel self-lubricating coating, namely the graphene modified WC-10Co-4Cr self-lubricating coating, has excellent functions of wear resistance, drag reduction, toughness and corrosion resistance, and can greatly reduce the friction coefficient and the wear loss of the coating.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims

1. A high-speed steel self-lubricating coating is characterized by comprising the following components in percentage by mass: co:9% -10%, cr:3.5% -4.2%, C (n): 0.1-0.7% of WC;

the raw materials of the coating comprise graphene and WC-10Co-4Cr powder, and the coating is obtained by adopting a supersonic flame thermal spraying method;

the preparation method of the coating comprises the following steps:

step 2, mixing WC-10Co-4Cr powder, a KH570 coupling agent and the graphene suspension obtained in the step 1, wherein the mass ratio of the added KH57 coupling agent to the expanded graphite is 2; drying and sieving to obtain mixed powder;

step 3, performing hot spraying on the mixed powder obtained in the step 2 by using supersonic flame to obtain a coating;

in the step 3, the technological parameters of the supersonic flame thermal spraying are as follows: the nitrogen flow is 20-25L/min, the oxygen flow is 800-900L/min, the kerosene flow is 0.4-0.5L/min, the powder feeding amount is 35 x 2-55 x 2g/min, and the spray distance is 200-450 mm.

2. The high speed steel self-lubricating coating of claim 1, wherein the mass ratio of graphene to WC-10Co-4Cr powder is 1:1000 to 140.

3. A preparation method of a high-speed steel self-lubricating coating is characterized by comprising the following steps:

step 2, mixing WC-10Co-4Cr powder, KH570 coupling agent and the graphene suspension obtained in the step 1, wherein the mass ratio of the expanded graphite to the WC-10Co-4Cr powder is 1: 1000-140, wherein the mass ratio of the added KH57 coupling agent to the expanded graphite is 2; drying and sieving to obtain mixed powder;

step 3, performing thermal spraying on the mixed powder obtained in the step 2 by using supersonic flame to obtain a coating;

in the step 2, the WC-10Co-4Cr powder comprises the following components in percentage by mass: 9% -10%, cr:3.5 to 4.2 percent of WC, and the balance of WC, wherein the grain diameter is 15 to 45 mu m;

4. The method according to claim 3, wherein in the step 1, the expanded graphite is obtained by microwave heating of expandable graphite in a flake form;

the particle size of the expandable graphite powder is 80-100 meshes, and the purity is 99.9%.

5. The preparation method according to claim 3, wherein in the step 1, the power of the ultrasonic stripping is 80-120W, and the ultrasonic time is 30-50 minutes; the rotating speed of the mechanical stirring is 800-1000 r/min.

6. The preparation method according to claim 3, characterized in that the step 3 is preceded by a step of performing surface blasting coarsening treatment on the high-speed steel, wherein brown corundum with a particle size of 0.3-0.9 mm is adopted in the blasting coarsening treatment, the treatment mode is vertical blasting, the blasting air pressure is 0.3-0.6 MPa, the blasting distance is 50-100 mm, and the blasting treatment is performed until the surface roughness reaches Ra 3-5.