A ternary boride self-lubricating friction-reducing composite coating and a preparation method thereof

Abstract

This invention discloses a ternary boride self-lubricating and friction-reducing composite coating and its preparation method, belonging to the field of laser surface modification technology. The preparation method involves mixing ternary boride, carbide, and self-lubricating and friction-reducing powder at a ratio of 80-90:1-9:2-12, ball milling, drying, and then cladding the mixture onto a metal substrate surface using a 1200-2500W laser to obtain the composite coating. The coating uses ternary boride as the hard matrix phase and carbide as the reinforcing phase, with the self-lubricating and friction-reducing phase uniformly distributed and metallurgically bonded to the substrate, free from pores and cracks. This invention breaks through the wear resistance limit of traditional self-lubricating coatings, solves the problem of easy cracking of the ternary boride composite self-lubricating phase, and the coating combines high hardness with a low coefficient of friction, making it suitable for high-load conditions.

Description

Technical Field

[0001] This invention relates to the field of composite coating technology, and in particular to a ternary boride self-lubricating and friction-reducing composite coating and its preparation method. Background Technology

[0002] In industries such as machinery manufacturing, aerospace, mining and metallurgy, and energy and power, high-value critical moving parts operate under high loads and frictional wear conditions for extended periods, making their surfaces prone to wear failure. This reduces equipment operating accuracy and production efficiency, and can even lead to equipment malfunctions and safety hazards. Surface modification technology, without altering the overall performance of the component substrate, can significantly improve surface wear resistance and friction reduction properties by preparing a high-performance reinforcing coating, thereby greatly extending the service life of the components. It is currently the core technical means to solve the problem of wear failure in metal parts.

[0003] Laser cladding technology, with its advantages of fast heating and cooling rates, minimal thermal damage to the substrate, high metallurgical bonding strength between the coating and the substrate, and dense and uniform structure, has been widely used for surface repair and strengthening of key components in aerospace, machinery manufacturing, and automotive fields. It can significantly improve the wear resistance and corrosion resistance of components, extend their service life, and reduce equipment maintenance costs.

[0004] Ternary borides combine the ductility and toughness of metallic materials with the high strength, high hardness, high wear resistance, and excellent high-temperature oxidation resistance of ceramic materials. Moreover, the raw material cost is low, and they do not rely on strategic materials such as tungsten and cobalt, making them wear-resistant coating materials with great application potential. For example, Chinese patent CN111235456B discloses a ternary boride and carbide-reinforced cermet powder for laser cladding additive manufacturing. The pre-alloyed powder is prepared by vacuum melting and gas atomization. After laser cladding, a wear-resistant coating with high hardness and good crack resistance can be obtained. Chinese patent CN115029601B discloses a high-entropy alloy / hard ceramic synergistic reinforcement composite coating, which improves the wear resistance of the high-entropy alloy coating by generating a ternary boride hard phase in situ.

[0005] The aforementioned existing technologies have all confirmed the excellent performance of ternary borides in the field of wear-resistant coatings. However, the ternary boride-based coatings prepared only have a single wear-resistant function, lack self-lubricating and friction-reducing properties, have a high coefficient of friction, and are prone to generating a large amount of frictional heat under friction and wear conditions, which leads to an increase in coating temperature and aggravated wear. They cannot meet the demanding service requirements of simultaneously requiring high wear resistance and low friction.

[0006] To address the friction reduction issue in coatings, existing technologies typically involve adding a self-lubricating phase to a plastic alloy matrix to prepare a self-lubricating composite coating. For example, Chinese patent CN110643992B discloses a boride-reinforced self-lubricating composite coating, using a nickel-based or cobalt-based alloy as the matrix, adding a zirconium diboride reinforcing phase and a nickel-coated molybdenum disulfide lubricating phase, achieving a combination of wear resistance and friction reduction. Chinese patent CN109183027B discloses a solid self-lubricating wear-resistant and corrosion-resistant composite coating, using a nickel-chromium-boron-silicon alloy as the matrix, adding a tungsten carbide hard phase and a molybdenum disulfide lubricating phase, suitable for surface strengthening of hot work die steels. Furthermore, Chinese patents CN112663047B and CN111575703B, among others, have also disclosed self-lubricating coating technologies using high-entropy alloys and titanium alloys as matrices, respectively.

[0007] It can be seen that existing self-lubricating coatings all use alloys with good plasticity, such as nickel-based, cobalt-based, and high-entropy alloys, as the substrate. However, the hardness and wear resistance of these substrates are much lower than those of ternary borides, resulting in an inherent upper limit to the wear resistance of the coating, making it difficult to adapt to extreme working conditions with high loads and strong wear.

[0008] However, because ternary borides have a high proportion of covalent bonds, poor room temperature plastic deformation ability, and fracture toughness far lower than nickel-based and cobalt-based alloys, they are prone to cracking due to huge residual thermal stress during the rapid solidification process of laser cladding. At the same time, commonly used self-lubricating phases such as molybdenum disulfide, tungsten disulfide, and hexagonal boron nitride have extremely poor physicochemical compatibility with ternary borides. This has led to the general consensus in the field that adding self-lubricating phases to the ternary boride matrix will further disrupt the continuity of the matrix, introduce weak interfaces and defects, significantly reduce the fracture toughness of the coating, and exacerbate the initiation and propagation of cracks, making it impossible to obtain a qualified and stable self-lubricating coating.

[0009] This has resulted in the absence of self-lubricating and friction-reducing composite coatings based on ternary borates on the market. Summary of the Invention

[0010] The main objective of this invention is to provide a ternary boride self-lubricating and friction-reducing composite coating and its preparation method, aiming to solve the technical problems that existing ternary boride-based coatings lack self-lubricating and friction-reducing properties, traditional self-lubricating coatings have limited wear resistance, and the addition of a self-lubricating phase to the ternary boride matrix easily leads to cracking, making it impossible to obtain a qualified coating.

[0011] To achieve the above objectives, this invention proposes a method for preparing a ternary boride self-lubricating and friction-reducing composite coating, comprising the following steps: S1. Weigh and mix ternary boride powder, carbide powder, and self-lubricating friction-reducing powder in a mass ratio of (80~90):(1~9):(2~12) to obtain a mixed powder; the ternary boride is one of diferromolybdenum diboride, tungsten cobalt boride, dinickel molybdenum diboride, and molybdenum cobalt boride; the self-lubricating friction-reducing powder is one or more of molybdenum disulfide, tungsten disulfide, hexagonal boron nitride, cubic boron nitride, nano copper, titanium silicon carbide, titanium aluminum carbide, calcium fluoride, and graphite. S2. Cleaning and pretreatment of the metal substrate surface; S3. After drying the mixed powder, it is clad onto the surface of a metal substrate using a laser cladding process under inert gas protection to obtain a ternary boride self-lubricating and friction-reducing composite coating; wherein the laser power is 1200~2500W and the scanning speed is 1~9mm / s.

[0012] In one possible implementation, the carbide powder is one or more of tungsten carbide, titanium carbide, niobium carbide, vanadium carbide, tantalum carbide, and silicon carbide.

[0013] In one possible implementation, in step S1, the mixing is performed by ball milling, with the mass ratio of the mixed powder to the milling balls being 1:(3~5), and the milling time being 1~3 hours.

[0014] In one possible implementation, in step S3, laser cladding is performed using a pre-placed powder spreading method or a synchronous powder feeding method.

[0015] In one possible implementation, when a pre-spreading powder method is used, the particle size of the mixed powder is 1~20μm and the powder spreading thickness is 0.2~3mm; when a synchronous powder feeding method is used, the particle size of the mixed powder is 40~120μm and the powder feeding rate is 5~30g / min.

[0016] In one possible implementation, when multiple overlaps are used, the overlap rate is 30% to 35%.

[0017] In one possible implementation, in the pre-powdering method, the mixed powder is adhered to the substrate surface by an adhesive; the adhesive is one of polyvinyl alcohol, stearic acid, polyacrylamide, and polyetherimide.

[0018] In one possible implementation, in step S3, the inert gas is one of argon, nitrogen, or helium, and the gas flow rate is 5~30 L / min.

[0019] In one possible implementation, the carbide is formed in the coating by direct addition.

[0020] A ternary boride self-lubricating and friction-reducing composite coating is prepared by the aforementioned method. The coating comprises a ternary boride hard phase, a carbide reinforcing phase, and a uniformly distributed self-lubricating and friction-reducing phase, and the coating is metallurgically bonded to the metal substrate.

[0021] Compared with the prior art, the beneficial effects of this application are as follows: By introducing a specific ratio of self-lubricating and friction-reducing phases such as molybdenum disulfide, tungsten disulfide, and hexagonal boron nitride into a ternary boride matrix, and combining this with carbide dispersion reinforcement, the coating retains the high hardness and high wear resistance of ternary boride while achieving stable self-lubricating and friction-reducing capabilities. The self-lubricating and friction-reducing phases enable the coating to continuously form a lubrication transfer film during friction and wear, significantly reducing the coating's coefficient of friction, reducing frictional heat generation and wear aggravation, and solving the problems of existing ternary boride coatings lacking self-lubricating function and having a high coefficient of friction. This allows the coating to simultaneously meet the dual requirements of wear resistance and low friction under high load conditions.

[0022] Meanwhile, by controlling the low addition ratio of the self-lubricating and friction-reducing phase, the continuity of the ternary boride matrix is ​​avoided; at the same time, the addition of carbides as a dispersion strengthening phase can refine the coating grains, passivate crack tips, and prevent crack propagation; combined with planetary ball milling for uniform mixing and optimized laser cladding parameters, the thermal stress and interface defects of cladding are reduced, and the final coating is dense, pore-free, and crack-free, and forms a strong metallurgical bond with the metal matrix, solving the problem of poor compatibility between the self-lubricating phase and the ternary boride, which easily leads to cracking.

[0023] Through experiments, this invention has verified that molybdenum diboride and cobalt tungsten boride are the most effective ternary boride matrix phases; tungsten carbide, tantalum carbide, and niobium carbide, as carbide reinforcing phases, can effectively refine grains and prevent crack propagation; and molybdenum disulfide, tungsten disulfide, and hexagonal boron nitride, as self-lubricating and friction-reducing phases, can form a stable lubrication transfer film on the friction surface. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0025] Figure 1 This is a microstructure diagram of the coating in Example 1 of the present invention; Figure 2 This is a microstructure diagram of the coating in Embodiment 2 of the present invention; Figure 3 This is a topographic image of the interface between the coating and the substrate in Embodiment 2 of the present invention. Figure 4 This is a coating wear morphology diagram of Embodiment 2 of the present invention; Figure 5 This is a microstructure diagram of the coating in Example 3 of the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0027] Example 1

[0028] S1. Powder preparation and mixing: Weigh molybdenum diboride powder, tungsten carbide powder, and molybdenum disulfide powder in a mass ratio of 87:7:6; wherein the particle size of molybdenum diboride powder is approximately 50 μm, the particle size of tungsten carbide powder is approximately 15~45 μm, and the molybdenum disulfide powder is of analytical grade.

[0029] Then, the prepared composite powder and stainless steel grinding balls were placed in a planetary ball mill at a mass ratio of 1:4. The main plate of the ball mill rotated at 150 r / min and the planetary disk rotated at 75 r / min. The ball mill was milled for 2 hours to obtain a uniformly mixed composite powder.

[0030] S2. Substrate preparation: Select 45 steel as the metal substrate, use anhydrous ethanol to ultrasonically clean the substrate surface to remove surface oil, impurities and rust, and let it air dry naturally.

[0031] S3. Drying and Laser Cladding: The mixed powder was placed in a vacuum drying oven and dried at 120℃ for 2 hours. A YLS-3000 laser was used for synchronous powder feeding laser cladding at a feed rate of 10 g / min. The laser cladding process parameters were: laser power 1500 W, scanning speed 3 mm / s, spot diameter 3.5 mm, overlap rate 30%, and 99.99% pure argon gas as the protective gas at a flow rate of 10 L / min. After cladding, the mixture was allowed to cool naturally to obtain a ternary boride self-lubricating and friction-reducing composite coating.

[0032] The microstructure of the coating prepared in this embodiment is as follows: Figure 1 As shown, the coating is dense and free of pores and cracks, and its microstructure consists of elongated and partially circular sulfide structures. The coating exhibits good metallurgical bonding with the 45 steel substrate.

[0033] X-ray diffraction analysis showed that the main hard phases of the coating were molybdenum diboride, tungsten carbide, and chromium tricarbide; the main friction-reducing phases were chromium sulfide, molybdenum disulfide, molybdenum trisulfide, and nickel trisulfide.

[0034] Friction and wear tests were conducted using a UMT-2 high-load scratch tester at room temperature (25℃). The coefficient of friction was 0.28, and the wear rate was... .

[0035] The experiment revealed that a sulfide self-lubricating transfer film was formed on the worn surface, protecting the coating from wear and improving the self-lubricating and friction-reducing properties of the composite coating.

[0036] Example 2

[0037] S1. Powder Preparation and Mixing: Weigh molybdenum diboride powder, tantalum carbide powder, and hexagonal boron nitride powder at a mass ratio of 83:5:12. The particle sizes of the molybdenum diboride powder, tantalum carbide powder, and hexagonal boron nitride powder are approximately 5 μm each. Place the prepared composite powder and grinding balls at a mass ratio of 1:5 in a planetary ball mill. Set the main mill speed to 120 r / min and the planetary disk rotation speed to 100 r / min, and mill for 3 hours.

[0038] S2. Substrate preparation: Select Q235 steel as the metal substrate, use anhydrous ethanol to ultrasonically clean the substrate surface to remove surface oil, impurities and rust, and let it air dry naturally.

[0039] S3. Drying and Laser Cladding: Place the mixed powder in a vacuum drying oven and dry at 150℃ for 3 hours. Laser cladding is performed using a pre-placed powder spreading method. First, mix the dried powder with 5% (by mass) polyvinyl alcohol and deionized water. Heat the deionized water to 90℃ to dissolve the polyvinyl alcohol. Under continuous stirring, add solid polyvinyl alcohol in small amounts several times, stirring for about 30 minutes until the solution is clear and free of particles.

[0040] The solution is then mixed into a paste and evenly coated onto the substrate surface with a pre-applied powder thickness of 1 mm. It is allowed to dry naturally for 24 hours, then dried at approximately 80°C in a drying oven for 4 hours, followed by a medium-temperature drying at 120°C for 2 hours, until the furnace cools to room temperature. A YLS-3000 laser is used for cladding, with the following parameters: laser power 2000W, scanning speed 4 mm / s, spot diameter 4 mm, overlap rate 30%, and 99.99% pure nitrogen as the protective gas at a flow rate of 10 L / min.

[0041] The microstructure of the coating prepared in this embodiment is as follows: Figure 2 As shown, the coating is dense and free of pores and cracks, and the microstructure is refined, exhibiting a fine and uniform dendritic-like structure.

[0042] Figure 3 The image shows the morphology of the interface between the coating and the substrate, indicating that the coating and the Q235 steel substrate have a good metallurgical bond.

[0043] X-ray diffraction analysis showed that the main hard phases of the coating were molybdenum diboride, tantalum carbide, and chromium tricarbide; the main friction-reducing phases were boron nitride, chromium nitride, and nickel triboride.

[0044] Friction and wear experiments showed a friction coefficient of 0.25 and a wear rate of [missing information]. . Figure 4 The coating wear morphology shows that a nitride lubricating film has formed on the worn surface. The surface is relatively smooth, and the wear mechanism is slight abrasive wear, resulting in a significant friction reduction effect.

[0045] Example 3

[0046] S1. Powder Preparation and Mixing: Weigh tungsten boride cobalt powder, niobium carbide powder, and tungsten disulfide powder at a mass ratio of 88:6:6. The particle sizes of the tungsten boride cobalt powder, niobium carbide powder, and tungsten disulfide powder are approximately 100 μm each. Place the prepared composite powder and grinding balls at a mass ratio of 1:5 in a planetary ball mill. Set the main mill speed to 150 r / min and the planetary disk rotation speed to 80 r / min, and mill for 1.5 hours.

[0047] S2. Substrate preparation: Select titanium alloy as the metal substrate, specifically Ti6Al4V titanium alloy. Use anhydrous ethanol to ultrasonically clean the substrate surface to remove surface oil and impurities, and then let it air dry naturally.

[0048] S3. Drying and Laser Cladding: The mixed powder is placed in a vacuum drying oven and dried at 130℃ for 2.5 hours. Simultaneous powder feeding laser cladding is used, with a powder feeding rate of 15 g / min. The laser cladding process parameters are: laser power 2250 W, scanning speed 2 mm / s, spot diameter 4 mm, overlap rate 35%, and 99.99% pure helium gas is used as the protective gas at a flow rate of 15 L / min.

[0049] The microstructure of the coating prepared in this embodiment is as follows: Figure 5 As shown, the coating is dense and free of pores and cracks, and its microstructure exhibits fine and uniform spherical and dendritic structures. The coating and the titanium alloy substrate have a good metallurgical bond.

[0050] X-ray diffraction analysis revealed that the main hard phases of the coating were cobalt tungsten boride, cobalt ditungsten diboride, and niobium carbide; the main friction-reducing phases were tungsten disulfide, chromium sulfide, and titanium sulfide. The average microhardness of the coating was [value missing]. .

[0051] The friction coefficient measured by the friction and wear test was 0.31, and the wear rate was... A sulfide lubricating film forms on the worn surface, reducing the tendency of hard phase concentration and achieving a balance between friction reduction and wear resistance.

[0052] Meanwhile, the following performance tests were performed on Examples 1-3: Hardness test: The microhardness of each coating and substrate was measured using an HX-500 microhardness tester. Five points were selected for microhardness measurement to obtain the average microhardness. The loading force was 500gf and the holding time was 10s.

[0053] Friction and wear test: Friction and wear test was conducted using a UMT-2 high-load scratch tester (friction and wear tester) to measure the friction coefficient and wear rate between the coating and the substrate.

[0054] The following data were obtained from the above experiments, as shown in Table 1:

[0055] Those skilled in the art will understand that, under the guidance of this invention, nickel molybdenum diboride and molybdenum cobalt boride can also be selected as ternary boride matrix phases, titanium carbide, vanadium carbide, and silicon carbide can be selected as carbide reinforcing phases, and cubic boron nitride, nano copper, titanium silicon carbide, titanium aluminum carbide, calcium fluoride, and graphite can be selected as self-lubricating and friction-reducing phases. All these alternative schemes fall within the protection scope of this invention.

[0056] The above are merely preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing a ternary boride self-lubricating and friction-reducing composite coating, characterized in that, Includes the following steps: S1. Weigh and mix ternary boride powder, carbide powder, and self-lubricating friction-reducing powder in a mass ratio of (80~90):(1~9):(2~12) to obtain a mixed powder; the ternary boride is one of diferromolybdenum diboride, tungsten cobalt boride, dinickel molybdenum diboride, and molybdenum cobalt boride; the self-lubricating friction-reducing powder is one or more of molybdenum disulfide, tungsten disulfide, hexagonal boron nitride, cubic boron nitride, nano copper, titanium silicon carbide, titanium aluminum carbide, calcium fluoride, and graphite. S2. Cleaning and pretreatment of the metal substrate surface; S3. After drying the mixed powder, it is clad onto the surface of a metal substrate using a laser cladding process under inert gas protection to obtain a ternary boride self-lubricating and friction-reducing composite coating; wherein the laser power is 1200~2500W and the scanning speed is 1~9mm / s.

2. The preparation method according to claim 1, characterized in that, The carbide powder is one or more of tungsten carbide, titanium carbide, niobium carbide, vanadium carbide, tantalum carbide, and silicon carbide.

3. The preparation method according to claim 1, characterized in that, In step S1, the mixing is performed by ball milling, with the mass ratio of the mixed powder to the milling balls being 1:(3~5), and the milling time being 1~3 hours.

4. The preparation method according to claim 1, characterized in that, In step S3, laser cladding is performed using either a pre-placed powder spreading method or a synchronous powder feeding method.

5. The preparation method according to claim 4, characterized in that, When using the pre-spreading method, the particle size of the mixed powder is 1~20μm and the powder spreading thickness is 0.2~3mm; when using the synchronous powder feeding method, the particle size of the mixed powder is 40~120μm and the powder feeding rate is 5~30g / min.

6. The preparation method according to claim 5, characterized in that, When multiple overlaps are used, the overlap rate is 30%~35%.

7. The preparation method according to claim 5, characterized in that, In the pre-placed powder method, the mixed powder is adhered to the substrate surface by an adhesive; the adhesive is one of polyvinyl alcohol, stearic acid, polyacrylamide, and polyetherimide.

8. The preparation method according to claim 1, characterized in that, In step S3, the inert gas is one of argon, nitrogen, or helium, and the gas flow rate is 5~30L / min.

9. The preparation method according to claim 2, characterized in that, The carbides are formed in the coating by direct addition.

10. A ternary boride self-lubricating and friction-reducing composite coating, characterized in that, The coating is prepared by any one of claims 1 to 9, wherein the coating comprises a ternary boride hard phase, a carbide reinforcing phase and a uniformly distributed self-lubricating and friction-reducing phase, and the coating is metallurgically bonded to the metal substrate.

Images