Preparation and application of graphene nanosheet modified Co50 surface cladding coating

Abstract

The invention discloses preparation and application of a graphene nanosheet modified Co50 surface cladding coating, and belongs to the technical field of composite coatings. Comprising the following steps that the surface of a 40Cr steel base material is pretreated; graphene and cobalt powder are mixed, and composite powder is obtained; the composite powder is subjected to ball milling, and composite cladding powder is obtained; and the composite cladding powder is deposited on the surface of a pretreated 40Cr steel base material through a laser cladding technology, and the graphene nanosheet modified Co50 surface cladding coating is obtained. The prepared cobalt-based alloy doped graphene composite powder is directly deposited on the surface of 40Cr steel through laser cladding, and the hardness and wear resistance of the 40Cr steel can be remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of composite coatings, and particularly relates to the preparation and application of a graphene nanosheet modified Co50 surface cladding coating. Background Art

[0002] With the rapid development of high-end equipment manufacturing, mechanical key components (such as aero-engine blades, oil drilling tools, die punches, etc.) face severe wear and corrosion problems under extreme working conditions such as high temperature, high load, and strong corrosion. Cobalt-based alloy coatings are widely used as surface strengthening materials in the above fields due to their excellent high-temperature strength, corrosion resistance, and anti-wear performance. Traditional cobalt-based coatings are mainly prepared by technologies such as laser cladding and plasma spraying. However, limited by the material system design, their microhardness is mostly lower than 450 HV, the dry friction coefficient is generally higher than 0.6 (ASTM G99 standard), and pitting corrosion is likely to occur in a high-chloride ion environment (corrosion current density > 1×10 -5 A / cm 2 , ASTM G59 standard), which is difficult to meet the requirements of modern industry for long life and high reliability of components.

[0003] In recent years, the nano-reinforcement phase modification technology has become an important direction for improving the performance of metal-based coatings. Research shows that the addition of hard particles such as tungsten carbide (WC) and titanium nitride (TiN) can improve the coating hardness, but it will exacerbate the abrasive wear between friction pairs, resulting in an increase rather than a decrease in the friction coefficient; while solid lubricants such as molybdenum disulfide (MoS2) and hexagonal boron nitride (h-BN) can improve lubricity, but due to poor thermal stability (decomposition temperature < 400 °C) and lack of conductivity, they cannot form effective electrochemical protection in corrosive media. Graphene (Gr), as a representative of two-dimensional nanomaterials, has characteristics such as a theoretical strength of 130 GPa, in-plane thermal conductivity of 5300 W / (m·K), and interlayer shear strength of 0.1 MPa. In theory, it can simultaneously achieve the multi-functional synergy of "reinforcement-lubrication-corrosion protection". However, there are three major bottlenecks in the compounding of Gr and metal matrix in the existing technology: 1) The specific surface area of Gr nanosheets is large, and the van der Waals force causes serious agglomeration during the powder mixing process. Conventional mechanical stirring (such as a V-type mixer) can only achieve micron-scale dispersion; 2) The wettability between Gr and cobalt is poor (contact angle > 120°), and element segregation is likely to occur during laser cladding, forming defects such as interface pores; 3) Gr will undergo a carbon dissolution reaction in a high-temperature molten pool (> 1500 °C), resulting in the destruction of the sp 2 hybrid structure and loss of intrinsic properties.

[0004] In the existing patented technologies, CN113046703 uses graphene quantum dots to modify cobalt-based coatings. Although the corrosion resistance is improved, the increase in hardness is less than 15%. US20210071112A1 pre-deposits a graphene film layer on the substrate surface through chemical vapor deposition, but the process is complex and the coating bonding strength is lower than 250 MPa. Therefore, developing a preparation technology for cobalt-based composite coatings that can achieve efficient dispersion of graphene, strong interfacial bonding, and integration of structure and function has become a key problem that urgently needs to be solved in this field. Summary of the Invention

[0005] In view of the above technical problems, the present invention proposes a preparation and application of a graphene nanosheet modified Co50 surface cladding coating.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] One of the objects of the present invention is to provide a preparation method of a graphene nanosheet modified Co50 surface cladding coating, including the following steps:

[0008] Pre-treat the surface of the 40Cr steel substrate;

[0009] Mix graphene with cobalt powder to obtain a composite powder;

[0010] Ball-mill the composite powder to obtain a composite cladding powder;

[0011] Use laser cladding technology to deposit the composite cladding powder on the surface of the pre-treated 40Cr steel substrate to obtain a graphene nanosheet modified Co50 surface cladding coating.

[0012] The present invention uniformly composites nano-graphene (Gr) and cobalt-based powder (Co50) through high-energy ball milling, and uses laser cladding technology to prepare a composite coating on the surface of a 40Cr steel substrate. Through the dispersion and interfacial strengthening effects of the nano-sheet layer of Gr, the grain structure of the coating is refined, the microhardness is increased, and the friction coefficient is reduced, which is suitable for surface strengthening of high-condition mechanical components.

[0013] Further, the specific operation steps of the pre-treatment include: using 80-600 mesh sandpaper to polish the surface of the 40Cr steel substrate to Ra 0.4-0.8 μm, and then cleaning it step by step with acetone and absolute ethanol, and drying it in vacuum.

[0014] Further, the mixing method of the graphene and the cobalt powder is the wet mixing method, and the specific steps include: adding the graphene and the cobalt powder into absolute ethanol and stirring until all the absolute ethanol evaporates.

[0015] Further, the mass ratio of the graphene to the cobalt powder is (0.1-0.3):(9.7-9.9); and / or,

[0016] The cobalt powder is Co50 with a particle size of 45 - 75 μm; and / or,

[0017] The graphene is monolayer graphene with a thickness of 0.8 - 1.2 nm.

[0018] Furthermore, the specific operation steps of the ball milling include: setting the ball - to - powder ratio as 10∶1, under argon atmosphere, setting the revolution speed at 400 rpm and the rotation speed at 800 rpm for 3 - hour dry ball milling, pausing for 10 minutes every 30 minutes to prevent overheating, and finally obtaining the mixed powder through 200 - mesh vibrating screening.

[0019] Furthermore, the parameters of the laser cladding technology are: laser power 1400 - 1500 w, spot diameter 3.2 mm, and scanning rate 8 mm / s.

[0020] Furthermore, the parameters during the deposition process are: powder feeding speed 0.5 - 0.75 g / s, carrier gas flow rate 8 L / min.

[0021] The second object of the present invention is to provide a graphene nanoplate - modified Co50 surface cladding coating prepared by the above - mentioned preparation method, with a thickness of 0.8 - 1.2 mm.

[0022] The third object of the present invention is to provide an application of the above - mentioned graphene nanoplate - modified Co50 surface cladding coating in the field of mechanical components.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] In the present invention, a cobalt - based composite coating wrapped with graphene is deposited on a 40Cr steel substrate by laser cladding, and a good metallurgical bond is formed between the graphene - wrapped cobalt - based powder and the substrate. And compared with the pure cobalt - based alloy powder coating, the composite coating with added graphene prepared in the present invention significantly improves the hardness of 40Cr steel. Moreover, the unique two - dimensional structure of graphene in the present invention can form a friction layer with low shear strength on the contact surface, improving the wear resistance of the composite coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments and descriptions thereof of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0026] Figure 1 It is the scanning electron microscope image of the pure cobalt - based powder (left) in Comparative Example 1 and the composite cladding powder (right) in Example 1 of the present invention;

[0027] Figure 2Microstructure morphology diagrams of the pure cobalt-based alloy powder coating (left) in Comparative Example 1 and the graphene nanosheet-modified Co50 surface cladding coating (right) in Example 1 of the present invention;

[0028] Figure 3 Microhardness diagrams of the pure cobalt-based alloy powder coating in Comparative Example 1 and the graphene nanosheet-modified Co50 surface cladding coating in Example 1 of the present invention;

[0029] Figure 4 Scanning electron microscope diagrams of the friction coefficient of the pure cobalt-based alloy powder coating (left) in Comparative Example 1 and the graphene nanosheet-modified Co50 surface cladding coating (right) in Example 1 of the present invention. Detailed implementation manners

[0030] Now, various exemplary implementation manners of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0031] It should be understood that the terms used in the present invention are only for describing specific implementation manners and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded from the range.

[0032] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which the present invention pertains. Although the present invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to the documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0033] Without departing from the scope or spirit of the present invention, various improvements and changes can be made to the specific implementation manners of the specification of the present invention, which are obvious to those skilled in the art. Other implementation manners obtained from the specification of the present invention are obvious to those skilled in the art. The specification and examples of the present invention are only exemplary.

[0034] Regarding the terms "comprising", "including", "having", "containing", etc. used herein, they are all open-ended terms, meaning including but not limited to.

[0035] An embodiment of the present invention provides a method for preparing a graphene nanosheet modified Co50 surface cladding coating, comprising the following steps:

[0036] 1) Before conducting the laser cladding experiment, pretreat the surface of the 40Cr steel substrate;

[0037] 2) Mix graphene with cobalt powder to obtain a composite powder;

[0038] 3) Ball-mill the composite powder to obtain a composite cladding powder;

[0039] 3) Use laser cladding technology to deposit the composite cladding powder on the surface of the pretreated 40Cr steel substrate to obtain a graphene nanosheet modified Co50 surface cladding coating.

[0040] In some embodiments of the present invention, the specific operation steps of the pretreatment in step 1) include: grinding the surface of the 40Cr steel substrate with 80-600 mesh sandpaper to Ra 0.4-0.8 μm to remove the oxide layer and impurities, and then cleaning step by step with acetone and absolute ethanol, and drying in vacuum.

[0041] In some embodiments of the present invention, the mixing method of graphene and cobalt powder in step 2) is the wet mixing method, and the specific steps include: adding graphene and cobalt powder into absolute ethanol and stirring until all the absolute ethanol evaporates.

[0042] In some embodiments of the present invention, the mass ratio of graphene to cobalt powder in step 2) is (0.1-0.3)∶(9.7-9.9); and / or,

[0043] In some embodiments of the present invention, the cobalt powder in step 2) is Co50, and the particle size is 45-75 μm; and / or,

[0044] In some embodiments of the present invention, the graphene in step 2) is monolayer graphene, and the thickness is 0.8-1.2 nm.

[0045] In some embodiments of the present invention, the specific operation steps of the ball milling in step 3) include: setting the ball-to-material ratio to 10∶1, under the argon atmosphere, setting the revolution speed to 400 rpm and the rotation speed to 800 rpm for dry ball milling for 3 hours, pausing for 10 minutes every 30 minutes to prevent overheating, and finally obtaining the mixed powder through 200-mesh vibrating screening.

[0046] In some embodiments of the present invention, the parameters in the process of using laser cladding technology in step 4) are: laser power 1400-1500 w (preferably 1500 w), spot diameter 3.2 mm, and scanning rate 8 mm / s.

[0047] In some embodiments of the present invention, the parameters during the deposition process in step 4) are as follows: the powder feeding speed is 0.5 - 0.75 g / s (preferably 0.75 g / s), and the carrier gas flow rate is 8 L / min.

[0048] The graphene nanosheet modified Co50 surface cladding coating prepared by the above preparation method has a thickness of 0.8 - 1.2 mm.

[0049] The graphene nanosheet modified Co50 surface cladding coating can be applied in the field of mechanical components.

[0050] To better describe the content of the present invention, the following is a specific embodiment of this application:

[0051] 1) Select a 40Cr steel substrate, remove the surface oxide layer and processing marks by multi-directional grinding with coarse and fine sandpapers, and then clean it step by step with acetone and absolute ethanol. After drying, a clean substrate is obtained, meeting the surface finish requirements for laser cladding.

[0052] 2) Place graphene and Co50 alloy powder into an ethanol solution and mix them. Then, gradually increase the temperature in a vacuum drying oven to remove the solvent, obtaining a non-agglomerated composite powder, achieving complete coating of graphene on metal particles.

[0053] 3) Place the composite powder in a planetary ball milling tank, and through the mechanical alloying effect of alternating variable speeds, achieve the interfacial bonding between graphene and Co50 particles. The whole ball milling process is carried out under the protection of an inert atmosphere, and finally, a composite cladding powder with uniform dispersion and no compositional segregation is obtained.

[0054] 4) Precisely transport the composite cladding powder to the surface of the substrate through a coaxial powder feeding device, and use an XL-F2000W fiber laser system to perform layer-by-layer cladding, dynamically adjusting the spot trajectory and energy density to form a composite coating with dense metallurgical bonding and uniform thickness.

[0055] The following is a detailed explanation of the specific embodiment:

[0056] In step 1), before obtaining the 40Cr steel substrate and performing laser cladding, surface treatment is required. After removing the floating rust with an industrial scouring pad along the rolling direction, it is successively cross-ground with 80-mesh, 240-mesh, and 600-mesh sandpapers to Ra 0.4 - 0.8 μm (such as Ra = 0.58 μm), and then vacuum dried after cleaning with acetone and ethanol.

[0057] In step 2), the uniform composite of graphene and Co50 alloy powder is realized by the alcohol solvent dispersion method. After the ethanol is evaporated by gradient heating, it is transferred to a vacuum drying oven to complete the solidification of the powder. Specifically, when implementing, single-layer graphene (thickness 0.8 - 1.2 nm) and Co50 powder (particle size 45 - 75 μm) are weighed according to a mass ratio of 0.2∶9.8, and anhydrous ethanol is injected until the liquid-solid ratio is 3∶1. It is placed in a planetary mixer (rotation speed 200 rpm) and continuously mixed for 30 minutes. Finally, it is solidified in a vacuum drying oven (vacuum degree 50 Pa) for 6 hours to obtain loose composite powder.

[0058] In step 3), the nano-level uniform dispersion of the graphene / Co50 composite powder is realized by the planetary ball milling process. The powder agglomeration is broken and the interfacial combination is promoted through the action of high-energy mechanical force under the protection of inert gas. Specifically, during the operation, the composite powder and cemented carbide grinding balls are loaded into a zirconia ball milling tank replaced with argon according to a ball-to-material ratio of 10∶1. The revolution speed is set at 400 rpm and the rotation speed is 800 rpm for dry ball milling for 4 hours. It is paused for 10 minutes every 30 minutes to prevent overheating. Finally, the composite cladding powder is obtained through 200-mesh vibrating screening.

[0059] In step 4), a graphene / Co50 composite coating is prepared based on the coaxial powder feeding laser cladding technology. The XL-F2000W fiber laser system is used in combination with coaxial powder feeding for multi-pass overlapping cladding under argon protection. The laser power is set at 1500 W, the spot diameter is 3.2 mm, and the scanning speed is 8 mm / s. The molten pool temperature is controlled in the range of 1650 - 1800 °C (such as 1723 ± 45 °C), and the interlayer cooling time ≤ 30 s. Finally, a directionally solidified coating with a thickness of 0.8 - 1.2 mm is obtained.

[0060] All raw materials used in the present invention are obtained by purchasing on the market.

[0061] The technical solution of the present invention is further described below through examples.

[0062] Example 1

[0063] A preparation method for a graphene nanosheet modified Co50 surface cladding coating, comprising the following steps:

[0064] 1) Select a 40Cr steel plate with dimensions of 100 mm × 50 mm × 8 mm. First, use 3M TMThe 7447 type scouring pad is used to mechanically remove the surface scale; install 80-mesh alumina sandpaper on a pneumatic grinder, and grind coarsely along a 45° cross track at a speed of 3000 rpm and a pressure of 0.2 MPa for 3 passes. Replace it with 240-mesh silicon carbide sandpaper for circumferential grinding until there are no macroscopic scratches on the surface. Finally, use 600-mesh diamond sandpaper to polish parallel to the laser path until Ra = 0.6 ± 0.1 μm; place the substrate in a 40 kHz ultrasonic bath, clean it with ethanol at 35 °C for 15 minutes, then blow the residual droplets with dry compressed air at 0.3 MPa, and transfer it to a 60 °C vacuum box for desorption for 30 minutes;

[0065] 2) Weigh 2.0 g of graphene and 18.0 g of Co50 powder (D50 = 58 μm) and place them in a polytetrafluoroethylene beaker, and add 60 mL of absolute ethanol to form a mixed system; transfer the semi-dry powder to a vacuum drying oven (Shanghai Yiheng DZF-6050), evacuate to 50 Pa at 60 °C and dry for 6 hours to finally obtain a composite powder with a flowability index (Hausner Ratio) of 1.18. SEM observation shows that graphene uniformly coats the surface of Co50 particles in a wrinkled structure;

[0066] 3) Take 20 g of the composite powder prepared in step 2) and load it into a 500 mL zirconia ball mill jar (Retsch PM400, Germany), add WC-Co grinding balls with a total weight of 200 g and sizes of Φ5 mm / Φ8 mm / Φ10 mm, and displace with argon 3 times until the oxygen content < 50 ppm; set the planetary ball mill to rotate at 400 rpm for revolution and 800 rpm for rotation, and operate in a clockwise / counterclockwise alternating rotation mode. The temperature of the cylinder is controlled at 25 ± 3 °C through a circulating water cooling system; after ball milling for 3 hours, the powder is sieved through a 200-mesh nylon sieve by vibration (amplitude 2 mm, frequency 50 Hz). SEM-EDS analysis shows that graphene is embedded in the gaps between Co50 particles in a stacked form of 3-5 layers;

[0067] 4) Load the composite cladding powder prepared in step 3) into a TS-04 type coaxial powder feeder (carrier gas flow rate 8 L / min, argon purity 99.999%), and fix the 40Cr steel substrate on a five-axis numerical control platform; start the XL-F2000W laser (beam quality M 2 ≤1.1), set the defocus amount to +2 mm to form a 3.2 mm diameter light spot, and perform 12 passes of cladding using a serpentine scanning path (lap rate 35%); laser power 1500 w, light spot diameter 3.2 mm, scanning rate 8 mm / s, powder feeding speed 0.75 g / s, and the deposition efficiency reaches 78 g / min. After the obtained coating is sampled by wire cutting, metallographic observation shows that the interlayer bonding is dense and there are no pores. SEM shows that graphene is distributed in a network in the Co matrix (spacing 2-5 μm), and the average value of microhardness test (load 500 g) is 586 HV0.5 (see Figure 3 ), which is 47% higher than the substrate.

[0068] Comparative Example 1

[0069] Same as Example 1, except that graphene is not added, and a pure cobalt-based alloy powder coating is prepared.

[0070] Figure 1 SEM images of the pure cobalt-based powder (left) in Comparative Example 1 and the composite cladding powder (right) in Example 1 of the present invention; it can be seen from the figure that the powders are uniformly mixed and Gr is wrapped on the surface of the cobalt-based powder.

[0071] Figure 2 Microstructure morphology diagrams of the pure cobalt-based alloy powder coating (left) in Comparative Example 1 and the graphene nanosheet-modified Co50 surface cladding coating (right) in Example 1 of the present invention; from Figure 2 it can be seen that the microcrystals of the graphene nanosheet-modified Co50 surface cladding coating are refined, indicating that the hardness and wear resistance of the composite coating doped with graphene will be affected.

[0072] Figure 3 Microhardness diagrams of the pure cobalt-based alloy powder coating in Comparative Example 1 and the graphene nanosheet-modified Co50 surface cladding coating in Example 1 of the present invention.

[0073] Figure 4 SEM images of the friction coefficients of the pure cobalt-based alloy powder coating (left) in Comparative Example 1 and the graphene nanosheet-modified Co50 surface cladding coating (right) in Example 1 of the present invention. It can be seen from the figure that the friction marks of the composite coating doped with graphene become narrower after friction, indicating that the friction effect of the graphene nanosheet-modified Co50 surface cladding coating has been improved.

[0074] The above is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A preparation method of a graphene nanosheet modified Co50 surface cladding coating, characterized in that, It includes the following steps: Pre-treat the surface of the 40Cr steel substrate; Mix graphene with cobalt powder to obtain composite powder; Ball mill the composite powder to obtain composite cladding powder; Deposit the composite cladding powder on the surface of the pre-treated 40Cr steel substrate by laser cladding technology to obtain a graphene nanosheet-modified Co50 surface cladding coating.

2. The preparation method of the graphene nanosheet modified Co50 surface cladding coating according to claim 1, wherein, The specific operation steps of the pre-treatment include: grinding the surface of the 40Cr steel substrate with 80-600 mesh sandpaper to Ra 0.4-0.8μm, then cleaning it step by step with acetone and absolute ethanol, and drying it in vacuum.

3. The preparation method of the graphene nanosheet modified Co50 surface cladding coating according to claim 1, characterized in that, The mixing method of the graphene and cobalt powder is the wet mixing method, and the specific steps include: adding graphene and cobalt powder into absolute ethanol and stirring until all the absolute ethanol evaporates.

4. The preparation method of the graphene nanosheet modified Co50 surface cladding coating according to claim 1, characterized in that, The mass ratio of the graphene to the cobalt powder is (0.1-0.3):(9.7-9.9).

5. The preparation method of the graphene nanosheet-modified Co50 surface cladding coating according to claim 4, characterized in that the cobalt powder is Co50 with a particle size of 45-75μm; and / or the graphene is single-layer graphene with a thickness of 0.8-1.2nm.

6. The preparation method of the graphene nanosheet modified Co50 surface cladding coating according to claim 1, characterized in that, The specific operation steps of the ball milling include: setting the ball-to-material ratio to 10:1, under argon atmosphere, setting the revolution speed to 400rpm and the rotation speed to 800rpm for 3 hours of dry ball milling, pausing for 10 minutes every 30 minutes, and finally obtaining the mixed powder through 200-mesh vibrating screening.

7. The preparation method of the graphene nanoplatelet modified Co50 surface cladding coating according to claim 1, wherein, The parameters of the laser cladding technology are: laser power 1400-1500w, spot diameter 3.2mm, scanning speed 8mm / s.

8. The preparation method of the graphene nanosheet modified Co50 surface cladding coating according to claim 1, characterized in that, The parameters during the deposition process are: powder feeding speed 0.5-0.75g / s, carrier gas flow rate 8L / min.

9. A graphene nanosheet modified Co50 surface cladding coating prepared by the preparation method according to any one of claims 1-8, characterized in that, The thickness of the coating is 0.8-1.2mm.

10. An application of the graphene nanosheet-modified Co50 surface cladding coating according to claim 9 in the field of mechanical components.

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