Method for preparing self-lubricating composite coating by prefabricating solid lubricating powder

Abstract

The method of preparing a self-lubricating composite coating by prefabricating solid lubricating powder of the present invention relates to the technical field of laser surface modification, and in particular to a method of pre-placing solid lubricating powder on the surface of a workpiece, and then performing ultra-high-speed laser cladding to prepare a self-lubricating composite coating. The method of the present invention comprises the following steps: 1) performing surface pretreatment on the workpiece; 2) prefabricating solid lubricating powder on the surface of the workpiece; 3) preparing cladding powder; 4) preheating the workpiece; 5) ultra-high-speed laser cladding. The technical solution of the present invention solves the problems in the prior art that 1) the hardness of the coating increases, resulting in an increase in the friction factor and severe wear of the coating; 2) the solid lubricating powder and hard phase powder in the cladding layer are discrete or piled up, and the distribution is uneven; 3) the solid lubricating powder gathers in large quantities on the surface of the coating, the lubricating phase cannot be completely immersed in the coating, and is easily scraped off.

Description

Technical Field

[0001] The invention discloses a method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder, and relates to the technical field of laser surface modification, in particular to a method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder on a workpiece surface and then performing ultra-high speed laser cladding. Background Art

[0002] Surface wear of workpieces is one of the important factors affecting the work efficiency and service life of workpieces. Ultra-high-speed laser cladding technology uses a high-energy-density laser beam to fuse the cladding material with the substrate surface, so that the cladding layer and the substrate form a good metallurgical bond, thereby improving the mechanical properties and wear resistance of the substrate. Compared with other traditional surface modification technologies, it has the advantages of high processing efficiency, low coating dilution rate, and green environmental protection. It can effectively improve the hardness, wear resistance and corrosion resistance of the surface, and shows unique process advantages and application prospects in the preparation of high-quality cladding layers.

[0003] The main methods of using ultra-high-speed laser cladding to improve the wear resistance of the workpiece surface are to increase the surface hardness and reduce the surface friction factor. For example, the patent applied for by the Institute of New Materials of Guangdong Academy of Sciences (a tungsten carbide reinforced high entropy alloy composite powder for ultra-high-speed laser cladding and its coating and preparation method and application, publication number: CN114147215A) and the patent applied for by Shanghai Jiaotong University (a preparation method of gear surface strengthening coating and gear, publication number CN113981441A) respectively use high entropy alloy powder and iron-based powder for ultra-high-speed cladding to improve the wear resistance by increasing the hardness of the coating. However, high hardness often causes a high friction factor, increases the wear of the coating, and reduces the service life of the coating. To solve this problem, scholars began to use laser cladding technology to prepare self-lubricating coatings with anti-friction properties, so that the surface has very good friction and wear resistance.

[0004] Conventional methods for preparing self-lubricating coatings by laser cladding are mostly to add solid lubricating powder to the cladding powder, such as the patent applied for by the Beijing Institute of Aeronautical Materials of China Aero Engine Corporation (a high-temperature wear-resistant self-lubricating coating material, its preparation method, coating and its preparation method, publication number: CN114908312A), by adding a certain amount of Cu and Mo as lubricants, providing lubrication performance at low temperatures, generating composite oxides at high temperatures to further play a lubricating effect, and cooperating with the enamel oxide generated by the hard phase and the bonding phase to reduce the wear rate of the coating. However, during the cladding process, solid lubricating powder is easy to decompose at high temperatures, react with air, and lose lubrication performance. Another example is the patent applied for by Shanghai University of Engineering Science (a nickel-based self-lubricating coating on titanium alloy surface by laser cladding and its preparation method, publication number: CN108411300A), by adding nickel-coated molybdenum disulfide as solid lubricating powder to the cladding powder, and then performing laser cladding, so that titanium alloy parts can meet the use requirements under harsh working conditions. However, the lubricating powder and hard phase powder in the cladding layer may be unevenly distributed such as discrete or piled up due to the difference in mass density, affecting the quality and mechanical properties of the coating; and under the convection of the molten pool generated by the cladding, the mass density of the solid lubricating powder in the cladding powder is lower than that of the hard phase powder, resulting in a large amount of solid lubricating powder gathering on the surface of the coating, so that the lubricating phase cannot be completely immersed in the coating and is easily scraped off.

[0005] In view of the problems existing in the above-mentioned prior art, it is very necessary to study and design a new method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder, so as to overcome the problems existing in the prior art. Summary of the invention

[0006] According to the above-mentioned prior art, 1. The increase in coating hardness leads to an increase in the friction coefficient, which increases the amount of coating wear and reduces the service life of the coating; 2. The conventional laser cladding method for preparing self-lubricating coatings will cause the solid lubricating powder and the hard phase powder in the cladding layer to be dispersed or piled up due to the difference in mass density, which affects the quality and mechanical properties of the coating; 3. Under the convection of the molten pool generated by laser cladding, due to the low mass density of the solid lubricating powder in the cladding powder, the solid lubricating powder is gathered in large quantities on the surface of the coating, and the lubricating phase cannot be completely immersed in the coating, which is easy to be scraped off and other technical problems, and a method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder is provided. The present invention mainly pre-places the solid lubricating powder on the surface of the workpiece, and then uses ultra-high-speed cladding to clad the cladding powder formed by mixing the matrix powder and the hard phase powder to the position of the pre-placed solid powder on the workpiece to prepare a self-lubricating composite coating with good friction reduction and wear resistance.

[0007] The technical means adopted by the present invention are as follows:

[0008] A method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder comprises the following steps:

[0009] 1) Pre-treat the workpiece surface: Use a grinder to roughly grind the workpiece surface, rinse it with water, and then ultrasonically clean it in anhydrous ethanol. After cleaning, dry it for later use;

[0010] 2) Prefabricate solid lubricating powder on the surface of the workpiece: Prefabricate solid lubricating powder on the surface of the workpiece;

[0011] 3) Preparation of cladding powder: mixing the matrix powder with the hard phase powder to prepare cladding powder, and drying the powder;

[0012] 4) Preheat the workpiece: Preheat the workpiece before ultra-high-speed cladding;

[0013] 5) Ultra-high-speed laser cladding: Under the protective gas state, a laser is used to perform ultra-high-speed cladding of the cladding powder prepared in step 3) at the position where the solid lubricating powder is preset.

[0014] Furthermore, the workpiece is a rotating part with requirements on dimensional accuracy and surface quality.

[0015] Furthermore, the requirement for rough grinding the workpiece with a grinder and polisher in step 1) is to remove the oxide film on the surface of the workpiece and to eliminate any coarse scratches on the surface of the workpiece.

[0016] Furthermore, the solid lubricating powder in step 2) can be divided into: soft metals, metal compounds, inorganic substances and organic substances according to the basic raw materials;

[0017] Furthermore, soft metals are metals with a relatively soft texture, including: Pb, Sn, hl, Ag, Zn;

[0018] Further, metal compounds include: MoS2, Pb02, Fe304, CaF2, BF3;

[0019] Further, inorganic substances include: graphite, graphite fluoride, and BN having a layered crystal structure;

[0020] Furthermore, organic substances include: thermoplastic resins, polytetrafluoroethylene, polyethylene, and nylon.

[0021] Furthermore, the method is characterized in that:

[0022] The method of prefabricating the solid lubricating powder on the surface of the workpiece in step 2) includes: bonding method and spraying method;

[0023] Furthermore, the bonding method refers to mixing alloy powders together with various adhesives at room temperature, and applying them on the metal surface to be treated in a paste or paste form by mechanical or manual brushing. It is simple and flexible and does not require any equipment. However, the adhesive of the coating is decomposed by heat during the cladding process, which will produce a certain amount of gas. During the rapid solidification and crystallization of the cladding layer, it is easy to be retained inside the cladding layer to form pores.

[0024] Furthermore, the spraying method is to heat the coating material to a molten or semi-molten state, accelerate it under the atomizing gas and obtain a certain kinetic energy, and spray it onto the surface of the part. It has less contamination on the substrate surface and the coating, but requires additional equipment and is difficult to process.

[0025] Further, the adhesives used in the bonding method include: varnish, silicate glue, water glass, oxygenated cellulose ether, cellulose acetate, alcohol rosin solution, hydrocarbon solution, fatty oil, B2 glue;

[0026] Furthermore, the adhesive will decompose when heated and produce gas, which can easily affect the organizational structure of the cladding layer. Therefore, it is necessary to preheat the workpiece before cladding to decompose the adhesive.

[0027] Furthermore, the spraying method includes: flame spraying, plasma arc spraying, and arc spraying.

[0028] Furthermore, the matrix powder in step 3) is a self-fluxing alloy powder, including iron-based (Fe), nickel-based (Ni), and cobalt-based (Co) alloy powders; it can improve the wettability of the melt to the matrix metal, improve the process forming performance of the cladding layer, and has good adaptability to various substrates such as carbon steel, stainless steel, alloy steel, and cast steel;

[0029] Furthermore, the hard phase powder in step 3) can enhance the comprehensive mechanical properties of the coating, such as microhardness and wear resistance, and includes: tungsten carbide powder, titanium carbide powder, and nano-diamond powder;

[0030] Furthermore, the matrix powder and the hard phase powder in step 3) are mixed by manual mixing and uniform mixing; mechanical mixing, using mechanical equipment to mix the powders, including a grinder, a ball mill, a two-dimensional or three-dimensional mixer;

[0031] Furthermore, the cladding powder in step 3) is required to meet the required use requirements, including: high temperature resistance, corrosion resistance, and oxidation resistance; good solid fluidity; thermal expansion coefficient and thermal conductivity close to the workpiece material; good wettability; and good cladding processability.

[0032] Furthermore, in step 4), the workpiece is preheated to 200-400°C to enable the binder used to function and prevent contamination of the cladding layer; at the same time, it prevents cracks in the workpiece due to excessive temperature gradients during ultra-high-speed cladding. The appropriate preheating temperature can be selected according to different binders and substrates.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The method for preparing a self-lubricating composite coating by using prefabricated solid lubricating powder provided by the present invention adds a lubricating phase to the cladding layer, thereby ensuring the hardness of the coating and reducing the friction coefficient, thereby preparing a self-lubricating coating with anti-friction properties;

[0035] 2. The method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder provided by the present invention pre-places the solid lubricating powder on the surface of the substrate, and utilizes the molten pool convection effect generated by laser cladding to make the lubricating powder enter the cladding layer, thereby ensuring the self-lubricating effect of the cladding layer during the friction process, and avoiding the phenomenon that the lubricating phase agglomerates on the coating surface in large quantities due to the large difference in mass density between the solid lubricating powder and the hard phase powder, and cannot be completely distributed in the coating, and is easily scraped off;

[0036] 3. The method for preparing a self-lubricating composite coating by prefabricated solid lubricating powder provided by the present invention pre-places the solid lubricating powder on the surface of a substrate and then performs ultra-high-speed cladding, thereby reducing the contact between the solid lubricating powder and the air, allowing the lubricating powder decomposed at high temperature to be regenerated in a closed space as the temperature decreases, avoiding reaction with other substances, retaining more lubricating phases, and making the cladding layer have very good friction and wear resistance.

[0037] 4. The cladding layer prepared by the method for preparing a self-lubricating composite coating with prefabricated solid lubricating powder provided by the present invention can achieve the following: bonding strength with the substrate ≥400MPa; coating surface hardness ≥700HV; wear resistance is more than 2.5 times higher than that of H13 steel; and the friction and wear performance of the surface lubricating coating is more than 30% higher than that of the traditional coating.

[0038] In summary, the technical solution of the present invention solves the problems in the prior art that: 1. The increase in the hardness of the coating leads to an increase in the friction coefficient, which increases the wear of the coating and reduces the service life of the coating; 2. The conventional laser cladding method for preparing self-lubricating coatings will cause the solid lubricating powder and the hard phase powder in the cladding layer to be dispersed or piled up due to the difference in mass density, which affects the quality and mechanical properties of the coating; 3. Under the convection of the molten pool generated by laser cladding, due to the low mass density of the solid lubricating powder in the cladding powder, the solid lubricating powder is accumulated in large quantities on the surface of the coating, the lubricating phase cannot be completely immersed in the coating, and is easily scraped off. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0040] Figure 1 This is a schematic diagram of the operation of pre-setting solid lubricating powder in the present invention;

[0041] Figure 2 It is a schematic diagram of the ultra-high speed cladding operation of the present invention;

[0042] Figure 3 It is a schematic diagram of the cross section of the coating obtained after ultra-high speed cladding of the present invention.

[0043] In the figure: 1, clamping part 2, workpiece 3, solid lubricating powder 4, laser beam 5, coating powder flow 6, self-lubricating composite coating 7, WC particles 8, MoS2. DETAILED DESCRIPTION

[0044] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0045] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0046] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit exemplary embodiments according to the present invention. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, it indicates the presence of features, steps, operations, devices, components and / or combinations thereof.

[0047] Unless otherwise specifically stated, the relative arrangement, numerical expressions and numerical values ​​of the parts and steps described in these embodiments do not limit the scope of the present invention. At the same time, it should be clear that, for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The technology, methods and equipment known to ordinary technicians in the relevant field may not be discussed in detail, but in appropriate cases, the technology, methods and equipment should be regarded as a part of the authorization specification. In all examples shown and discussed here, any specific value should be interpreted as being merely exemplary, rather than as a limitation. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once a certain item is defined in an accompanying drawing, it does not need to be further discussed in subsequent drawings.

[0048] In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the device or element referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention: the directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0049] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below their position devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0050] In addition, it should be noted that the use of terms such as "first" and "second" to limit components is only for the convenience of distinguishing the corresponding components. If not otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present invention.

[0051] The present invention provides a method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder, comprising the following steps:

[0052] 1) Perform surface pretreatment on the workpiece 2: Use a grinder to roughly grind the surface of the workpiece 2, rinse it with water, and then perform ultrasonic cleaning in anhydrous ethanol. After cleaning, dry it for later use;

[0053] 2) Prefabricate solid lubricating powder on the surface of the workpiece: Prefabricate solid lubricating powder on the surface of the workpiece 2 by bonding or spraying;

[0054] 3) Preparation of cladding powder: mixing the matrix powder with the hard phase powder to prepare cladding powder, and drying the powder;

[0055] 4) Preheating the workpiece 2: Preheat the workpiece 2 before ultra-high-speed cladding;

[0056] 5) Ultra-high-speed laser cladding: Under the protective gas state, a laser is used to perform ultra-high-speed cladding of the cladding powder prepared in step 3) at the position where the solid lubricating powder is preset.

[0057] Workpiece 2 is a rotating part with requirements for dimensional accuracy and surface quality.

[0058] The requirement for rough grinding the workpiece 2 using a grinder and polisher in step 1) is to remove the oxide film on the surface of the workpiece 2 and to eliminate any coarse scratches on the surface of the workpiece 2.

[0059] The solid lubricating powder in step 2) can be divided into: soft metal, metal compound, inorganic substance and organic substance according to the basic raw materials;

[0060] Soft metals are metals with soft texture, including: Pb, Sn, hl, Ag, zn;

[0061] Metal compounds, including: MoS2, Pb02, Fe304, CaF2, BF3;

[0062] Inorganic substances, including: graphite, graphite fluoride, and BN with layered crystal structures;

[0063] Organic substances, including: thermoplastic resins, polytetrafluoroethylene, polyethylene, nylon.

[0064] The prefabrication method of prefabricating the solid lubricating powder on the surface of the workpiece 2 in step 2) includes: bonding method spraying method;

[0065] The bonding method refers to mixing alloy powders together with various adhesives at room temperature, and applying them to the metal surface to be treated in a paste or paste form by mechanical or manual brushing. It is simple and flexible and does not require any equipment. However, the binder of the coating will decompose when heated during the cladding process, and a certain amount of gas will be generated. During the rapid solidification and crystallization of the cladding layer, it is easy to be retained inside the cladding layer to form pores; the adhesives used in the bonding method include: varnish, silicate glue, water glass, oxygen-containing cellulose ether, cellulose acetate, alcohol rosin solution, hydrocarbon solution, fatty oil, B2 glue; the adhesive will decompose after heating and produce gas, which is easy to affect the organizational structure of the cladding layer, so it is necessary to preheat the workpiece before cladding to decompose the adhesive.

[0066] The spraying method is to heat the coating material to a molten or semi-molten state, accelerate it under the atomizing gas and obtain a certain kinetic energy, and then spray it onto the surface of the part. It has little contamination on the substrate surface and the coating, but requires additional equipment and is difficult to process.

[0067] The spraying method includes: flame spraying, plasma arc spraying, and arc spraying.

[0068] The matrix powder in step 3) is a self-fluxing alloy powder, including: iron-based (Fe), nickel-based (Ni), and cobalt-based (Co) alloy powders; it can improve the wettability of the melt to the matrix metal, improve the process forming performance of the cladding layer, and has good adaptability to various substrates such as carbon steel, stainless steel, alloy steel, and cast steel; the hard phase powder can enhance the microhardness of the coating, the wear resistance and other comprehensive mechanical properties, including: tungsten carbide powder, titanium carbide powder, and nano diamond powder; the mixing method of the matrix powder and the hard phase powder includes a manual method, manual mixing evenly; a mechanical mixing method, using mechanical equipment to mix the powder, including a grinder, a ball mill, and a two-dimensional and three-dimensional mixer; the cladding powder is required to meet the required use requirements, including: high temperature resistance, corrosion resistance, and oxidation resistance; good solid-state fluidity; thermal expansion coefficient and thermal conductivity are close to those of the workpiece material; good wettability; and good cladding processability.

[0069] In step 4), the workpiece is preheated to 200-400°C to enable the binder to function and prevent contamination of the cladding layer; at the same time, it prevents cracks in the workpiece due to excessive temperature gradients during ultra-high-speed cladding. The appropriate preheating temperature can be selected according to different binders and substrates.

[0070] Example 1

[0071] As shown in the figure, the present invention provides a method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder, wherein H13 hot working die steel is selected as workpiece 2, MoS2 is selected as solid lubricating powder 3, M2 iron-based powder is selected as matrix powder, and WC ceramic particles are selected as hard phase powder, and ultra-high-speed laser cladding is performed to prepare the composite coating. The solid lubricating powder MoS2 and the organic binder water glass are mixed and stirred into a paste by bonding, and are manually and evenly coated on the predetermined position of the hot working die steel workpiece. The matrix powder M2 and the hard phase powder WC ceramic particles are weighed according to the atomic ratio of WC:M2=1:5. After weighing, the powder is placed in a ball mill, and the ball mill tank is filled with inert gas Ar gas as a protective gas. The speed is 300r / min, and the time is 120min, to make WC / M2 ceramic particles reinforced metal-based mixed powder. The mixed powder is placed in a heating furnace for drying, and the heating temperature is 180°C and the heating time is 45min;

[0072] Workpiece 2 was preheated at 250°C for 60 minutes to decompose the coated binder. Under the condition of introducing protective gas Ar gas, gas flow rate of 5L / min, protective gas pressure of 1.10MPa, CO2 laser was used, laser power of 2KW, scanning speed of 500mm / min, spot diameter of 2mm, and the cladding powder prepared in step 3) was ultra-high-speed cladding on the surface of H13 hot working die steel, where the solid lubricating powder MoS2 was coated, to obtain a 1mm thick coating.

[0073] Example 2

[0074] On the basis of Example 1, the present invention also provides a method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder. The workpiece, solid lubricating powder, matrix powder, and hard phase powder used are all consistent with those in Example 1, except that silicate glue is selected as a binder, mixed with solid lubricating powder MoS2 into a paste, and manually applied to a predetermined position of the workpiece. The preheating temperature, cladding powder, and cladding parameters used are consistent with those in Example 1, and ultra-high-speed cladding is performed to obtain a 1 mm thick coating.

[0075] Example 3

[0076] On the basis of Example 1, the present invention also provides a method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder. The workpiece, solid lubricating powder, matrix powder, and hard phase powder used are all consistent with those in Example 1. The difference is that MoS2 is sprayed on the surface of the matrix by arc spraying. In order to control the variables, the workpiece is still preheated at 250°C for 60 minutes. The cladding powder and cladding parameters used are consistent with those in Example 1, and then ultra-high-speed cladding is performed to obtain a 1 mm thick coating.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a self-lubricating composite coating by prefabricating solid lubricating powder, characterized in that: The method for preparing a self-lubricating composite coating using prefabricated solid lubricating powder comprises the following steps: 1) Surface pretreatment of the workpiece (2): Use a grinder to roughly grind the surface of the workpiece (2), rinse it with water, and then ultrasonically clean it in anhydrous ethanol. After cleaning, dry it for later use; 2) Prefabricate solid lubricating powder on the workpiece surface: Prefabricating solid lubricating powder on the surface of the workpiece (2); 3) Preparation of cladding powder: The matrix powder is mixed with the hard phase powder to prepare the cladding powder, and then the cladding powder is dried; 4) Preheating the workpiece (2): Before performing ultra-high speed cladding, preheating the workpiece (2); 5) Ultra-high-speed laser cladding: Under the protective gas state, a laser is used to perform ultra-high-speed cladding of the cladding powder prepared in step 3) at the position where the solid lubricating powder is prefabricated.

2. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 1, characterized in that: The workpiece (2) is a rotating part with requirements for dimensional accuracy and surface quality.

3. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 1, characterized in that: The requirement for using a grinder to roughly grind the workpiece (2) in step 1) is to remove the oxide film on the surface of the workpiece (2) and to leave no coarse scratches on the surface of the workpiece (2).

4. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 1, characterized in that: The solid lubricating powder in step 2) can be divided into soft metals, metal compounds, inorganic substances and organic substances according to the raw materials; The soft metal is a metal with a relatively soft texture, including: Pb, Sn, Ag, Zn; The metal compound includes: MoS2, PbO2, Fe3O4, CaF2, BF3; The inorganic substances include: graphite, graphite fluoride, and BN with layered crystal structures; The organic matter includes: polytetrafluoroethylene, polyethylene, and nylon.

5. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 4, characterized in that: The method of prefabricating the solid lubricating powder on the surface of the workpiece (2) in step 2) includes: bonding method and spraying method; The bonding method is to mix the alloy powders together with various adhesives at room temperature, and apply the paste or paste to the metal surface to be treated by mechanical or manual brushing; The spraying method is to heat the coating material to a molten or semi-molten state, accelerate it under atomizing gas, obtain kinetic energy, and spray it onto the surface of the part.

6. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 5, characterized in that: The adhesives used in the bonding method include: varnish, silicate glue, water glass, oxygenated cellulose ether, cellulose acetate, alcohol rosin solution, hydrocarbon solution, fatty oil, B2 glue; The adhesive will decompose when heated to generate gas, which can easily affect the organizational structure of the cladding layer. Therefore, it is necessary to preheat the workpiece before cladding to decompose the adhesive.

7. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 5, characterized in that: The spraying method includes: flame spraying, plasma arc spraying, and arc spraying.

8. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 1, characterized in that: The matrix powder in step 3) is a self-fluxing alloy powder, including iron-based (Fe), nickel-based (Ni), and cobalt-based (Co) alloy powders; it can improve the wettability of the melt to the matrix metal, improve the process forming performance of the cladding layer, and has good adaptability to carbon steel, stainless steel, alloy steel, and cast steel substrates; The hard phase powder in step 3) can enhance the comprehensive mechanical properties of the microhardness and wear resistance of the coating, including: tungsten carbide powder, titanium carbide powder, nano diamond powder; The mixing methods of the matrix powder and the hard phase powder in step 3) include manual mixing and uniform mixing; mechanical mixing, using mechanical equipment to mix the powders, including grinders, ball mills, and two-dimensional and three-dimensional mixers; The cladding powder in step 3) is required to meet the required use requirements, including: high temperature resistance, corrosion resistance, and oxidation resistance; good solid fluidity; thermal expansion coefficient and thermal conductivity close to those of the workpiece material; good wettability; and good cladding processability.

9. The method for preparing a self-lubricating composite coating from a prefabricated solid lubricating powder according to claim 1, characterized in that: In the step 4), the workpiece is preheated to 200-400°C.

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