A micro-nano multi-scale modified tungsten carbide wear-resistant coating with hard outside and soft inside and a preparation method thereof

Abstract

A hard-external, tough-internal, micro / nano-scale modified tungsten carbide wear-resistant coating and its preparation method are disclosed, relating to the field of wear-resistant coatings. The preparation method includes the following steps: S1: Premixing carbon black and cobalt powder, then mixing with rare earth powder, chromium powder, chromium carbide powder, and tungsten carbide powder, adding a polymer molding agent and deionized water to obtain a mixed slurry; granulating the mixed slurry, semi-alloying, and vacuum sintering to obtain nano-spraying powder, submicron spraying powder, micron spraying powder, and micro / nano composite spraying powder; S2: Sandblasting the surface of the substrate to be sprayed; S3: Sequentially spraying the micro / nano composite spraying powder, micron spraying powder, submicron spraying powder, and nano spraying powder onto the substrate surface using a supersonic flame spraying method, thus obtaining the hard-external, tough-internal, micro / nano-scale modified tungsten carbide wear-resistant coating. This hard-external, tough-internal, micro / nano-scale modified tungsten carbide wear-resistant coating is a gradient coating, which can reduce residual stress during spraying and extend the service life of the coating.

Description

Technical Field

[0001] This invention relates to the field of wear-resistant coatings, specifically to a hard-outer-hard-inner-tough micro / nano multi-scale modified tungsten carbide wear-resistant coating and its preparation method. Background Technology

[0002] As a crucial safety component of an aircraft, the landing gear is a vital support system for takeoff, landing, taxiing, and parking. It is a primary load-bearing structure that absorbs and dissipates the impact energy generated during landing and taxiing, ensuring the aircraft's safety during ground operations. New high-performance surface protection technologies are essential for ensuring the landing gear of modern large aircraft has the same lifespan as the airframe.

[0003] The main load-bearing components of modern aircraft landing gear, such as the landing gear outer cylinder, piston rod, and axles, are mostly made of 300M steel. After heat treatment and strengthening, 300M steel has a tensile strength of 1960–2100 MPa and a hardness of HR C52–56. Applying a coating to the surface of the 300M steel landing gear allows the coating and the steel substrate to complement each other. The surface possesses the high hardness and high wear resistance of the coating, while the core retains the original hardness, strength, and toughness of the selected steel substrate.

[0004] To reduce residual stress and cracking during coating preparation, existing technologies disclose methods for creating gradient coatings. For example, Chinese invention patent application number 202011092484.9 discloses a high-density, corrosion-resistant gradient metal-ceramic composite coating and its spraying method. In this composite coating, the first layer is obtained by spraying with a first spraying agent, and the second layer is obtained by spraying with a second spraying agent. The powder feed rates of the first and second spraying agents show opposite trends. This composite coating exhibits a gradient distribution of components, leading to the disappearance of obvious interfaces, a reduction in the gradient of thermophysical property differences, and a decrease in internal stress, thereby improving the coating's performance and service life.

[0005] Therefore, it can be seen that the current methods for preparing gradient coatings generally emphasize the gradient change of the powder feeding gas flow rate, and there are few reports on schemes for modifying tungsten carbide wear-resistant coatings through micro-nano multi-scale modification. Summary of the Invention

[0006] The present invention aims to provide an externally hard and internally tough micro-nano multi-scale modified tungsten carbide wear-resistant coating and its preparation method, so as to reduce residual stress during coating preparation and extend the service life of the coating.

[0007] To solve the above technical problems, the specific solution adopted by the present invention is as follows: a method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating, comprising the following steps:

[0008] S1: Carbon black and cobalt powder are premixed, then mixed with rare earth powder, chromium powder, chromium carbide powder and tungsten carbide powder, and a polymer molding agent and deionized water are added to obtain a mixed slurry. The mixed slurry is granulated, semi-alloyed and vacuum sintered to obtain a spraying powder. When the particle size of tungsten carbide powder is 80-100nm, the obtained spraying powder is a nano spraying powder.

[0009] When the particle size of tungsten carbide powder is 0.3-0.8 μm, the resulting spray powder is a submicron spray powder;

[0010] When the particle size of tungsten carbide powder is 3-5 μm, the resulting spray powder is micron-sized spray powder.

[0011] When the tungsten carbide powder is a mixture of powders with particle sizes of 0.3-0.8 μm, 3-5 μm and 80-100 nm, the resulting spray powder is a micro-nano composite spray powder.

[0012] S2: Sandblasting treatment of the substrate surface to be sprayed;

[0013] S3: A micro-nano composite powder, micron powder, submicron powder and nano powder are sequentially sprayed onto the substrate surface using a supersonic flame spraying method to obtain a micro-nano multi-scale modified tungsten carbide wear-resistant coating that is hard on the outside and tough on the inside.

[0014] As a further optimization of the above technical solution, in the preparation process of micro-nano composite spraying powder, tungsten carbide powder with a particle size of 0.3-0.8 μm accounts for 50-80% of the total mass of tungsten carbide powder, tungsten carbide powder with a particle size of 3-5 μm accounts for 10-20% of the total mass of tungsten carbide powder, and the remainder is tungsten carbide powder with a particle size of 80-100 nm.

[0015] As a further optimization of the above technical solution, in the preparation process of the spray powder, tungsten carbide powder, cobalt powder, and chromium powder are taken according to the following mass percentages: tungsten carbide powder 80-90%, cobalt powder 8-15%, and chromium powder 0.1-6%; rare earth powder is 0.01-0.2% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder; carbon black is 0.01-6.2% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder; and chromium carbide powder is 0.01-0.1% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder.

[0016] As a further optimization of the above technical solution, the rare earth powder is one or more of Y powder, Ce powder, CeO2 powder and Y2O3 powder.

[0017] As a further optimization of the above technical solution, the particle size of carbon black, chromium powder and cobalt powder is 0.8-1.2μm, the particle size of rare earth powder is 0.01-0.3μm, and the particle size of chromium carbide powder is 0.01-0.3μm.

[0018] As a further optimization of the above technical solution, the mixed slurry is conveyed to the spray drying tower for granulation. The spray disc rotation speed in the spray drying tower is 15000-18000 r / min, and the temperature in the spray drying tower is 220±10℃.

[0019] As a further optimization of the above technical solution, the temperature for semi-alloying vacuum sintering is 1100±20℃.

[0020] As a further optimization of the above technical solution, the process conditions for supersonic flame spraying are as follows: kerosene flow rate 6.0 GPH, oxygen flow rate 1850 SCHF, powder feed rate 60 g / min, spraying distance 380 nm, spray gun moving speed 500 mm / s, and step distance 5 mm.

[0021] A wear-resistant coating of tungsten carbide with external hardness and internal toughness, prepared by the above method, comprises a micro-nano composite layer sprayed on a substrate, wherein a micron layer, a submicron layer and a nano layer are sequentially attached from the inside to the outside of the micro-nano composite layer; the total thickness of the wear-resistant coating is 200-300 micrometers, the thickness of the micro-nano composite layer is 1 / 2 of the total thickness of the wear-resistant coating, the nano layer is 1 / 3 of the total thickness of the wear-resistant coating, and the sum of the thicknesses of the submicron layer and the micron layer is 1 / 6 of the total thickness of the wear-resistant coating.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The externally hard and internally tough micro-nano multi-scale modified tungsten carbide wear-resistant coating of the present invention is a gradient coating. The outer layer of the gradient coating has higher hardness and stronger impact resistance and wear resistance. The toughness of the coating gradually increases from the outside to the inside. The micro-nano composite layer has high toughness and low porosity, and has good adhesion to the substrate to be coated. This reduces the residual stress during coating preparation, and the coating is tightly bonded to the substrate, reducing the risk of the coating peeling off from the substrate surface and extending the service life of the coating.

[0024] This invention modifies tungsten carbide wear-resistant coatings through the combined action of rare earth elements and carbon, improving the hardness and toughness of the coatings and thus extending their service life. The rare earth elements and carbon added in this invention can inhibit the decarburization of WC particles during the supersonic flame spraying process, preventing the formation of the W2C hard and brittle phase, purifying the interface, and refining the microstructure, resulting in a coating with high hardness and excellent corrosion resistance. Attached Figure Description

[0025] Figure 1 The elastic modulus diagram is shown for the coating prepared in Example 1;

[0026] Figure 2 To verify the elastic modulus diagram of the micron-sized coating in the experiment;

[0027] Figure 3 To verify the elastic modulus diagram of the submicron coating in the experiment;

[0028] Figure 4 To verify the elastic modulus diagram of the nano-coating in the experiment;

[0029] Figure 5 To verify the microstructure of the coatings prepared in the experiment after nanoindentation, a) micron coating, b) submicron coating, c) nano coating, and d) micro-nano composite coating;

[0030] Figure 6 This is a schematic diagram of a nanoindentation experimental scheme;

[0031] Figure 7 To verify the experimental submicron coating and compare the XRD patterns of the coatings prepared in experiments 1-3;

[0032] Figure 8 To verify the submicron coating and compare the WC retention in the coatings prepared in experiments 1-3;

[0033] Figure 9 To verify the EBSD morphology of the experimental submicron coating;

[0034] Figure 10 To verify the phase structure of the experimental submicron coating;

[0035] Figure 11 To verify the size distribution of WC in the submicron coating tested;

[0036] Figure 12 To verify the size distribution of W2C in the experimental submicron coating. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. Parts not described or disclosed in detail in the following embodiments of the present invention should be understood as prior art known or should be known by those skilled in the art.

[0038] This invention discloses a method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating, comprising the following steps:

[0039] S1: Carbon black and cobalt powder are premixed, then mixed with rare earth powder, chromium powder, chromium carbide powder, and tungsten carbide powder. A polymer molding agent and deionized water are added to obtain a slurry. This slurry is then fed into a spray drying tower for granulation. The spray disc rotation speed in the tower is 15000-18000 r / min, and the tower temperature is 220±10℃. The granulated particles are then subjected to semi-alloying vacuum sintering to obtain a coating powder. Semi-alloying vacuum sintering is performed at a temperature of 1100±20℃ under vacuum. Sintering at this temperature and under vacuum results in spherical particles with a loose internal structure and a dense outer layer, with a particle size distribution of 5-15 μm and a bulk ratio of 4.8-5.03 g / cm³. 3 ;

[0040] In the preparation of the spray powder, tungsten carbide powder, cobalt powder, and chromium powder are taken according to the following mass percentages: tungsten carbide powder 80-90%, cobalt powder 8-15%, and chromium powder 0.1-6%; rare earth powder is 0.01-0.2% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder; carbon black is 0.01-6.2% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder; and chromium carbide powder is 0.01-0.1% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder.

[0041] In the preparation of the spray powder, the rare earth powder added is one or more of Y powder, Ce powder, CeO2 powder and Y2O3 powder. The particle size of carbon black, chromium powder and cobalt powder is 0.8-1.2μm, the particle size of rare earth powder is 0.01-0.3μm, and the particle size of chromium carbide powder is 0.01-0.3μm.

[0042] The prepared spraying powders specifically include nano spraying powder, submicron spraying powder, micron spraying powder and Wiener composite powder. The main difference between the different powders lies in the particle size of the tungsten carbide powder.

[0043] When the particle size of tungsten carbide powder is 80-100nm, the resulting spray powder is a nano-spray powder.

[0044] When the particle size of tungsten carbide powder is 0.3-0.8 μm, the resulting spray powder is a submicron spray powder;

[0045] When the particle size of tungsten carbide powder is 3-5 μm, the resulting spray powder is micron-sized spray powder.

[0046] When the tungsten carbide powder is a mixture of powders with particle sizes of 0.3-0.8 μm, 3-5 μm, and 80-100 nm, the resulting spray powder is a micro-nano composite spray powder. In the mixed powder, tungsten carbide powder with a particle size of 0.3-0.8 μm accounts for 50-80% of the total mass of tungsten carbide powder, tungsten carbide powder with a particle size of 3-5 μm accounts for 10-20% of the total mass of tungsten carbide powder, and the remainder is tungsten carbide powder with a particle size of 80-100 nm.

[0047] S2: Sandblast the substrate surface to be coated, blow the substrate surface clean after sandblasting, and preheat the substrate surface.

[0048] S3: A multi-scale modified tungsten carbide wear-resistant coating, consisting of micro-nano composite powder, micron-sized powder, submicron-sized powder, and nano-sized powder, is sequentially sprayed onto the substrate surface using a supersonic flame spraying method. This process yields a hard outer and tough inner micro-nano multi-scale modified tungsten carbide coating. Specifically, a JP 8000 spraying equipment is used for supersonic flame spraying, with kerosene as the fuel and oxygen as the combustion aid. The specific spraying parameters are: kerosene flow rate 6.0 GPH, oxygen flow rate 1850 SCHF, and powder feed rate 60 g / min. -1 Spraying distance: 380nm; spray gun moving speed: 500mm.s -1 Step distance 5mm.

[0049] The present invention also discloses an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating. The wear-resistant coating is prepared by the above-mentioned preparation method. The coating includes a micro / nano composite layer sprayed on a substrate. The micro / nano composite layer is attached with a micron layer, a submicron layer and a nano layer from the inside to the outside. The total thickness of the wear-resistant coating is 200-300 micrometers. The thickness of the micro / nano composite layer is 1 / 2 of the total thickness of the wear-resistant coating, the nano layer is 1 / 3 of the total thickness of the wear-resistant coating, and the submicron and micron layers are 1 / 6 of the total thickness of the wear-resistant coating.

[0050] Example 1

[0051] A method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating:

[0052] S1: Prepare nano-spraying powder, submicron spraying powder, micron spraying powder and micro-nano composite spraying powder respectively;

[0053] The preparation process of the nano-coating powder is as follows: First, tungsten carbide powder, cobalt powder, and chromium powder are weighed in a mass ratio of 86:10:4, and this is recorded as the first component. Then, rare earth powder, carbon black, and chromium carbide powder are weighed, and this is recorded as the second component. In the second component, the mass of carbon black is 5% of the mass of the first component, the mass of chromium carbide powder is 0.01% of the mass of the first component, and the rare earth powder is CeO2 powder, with the rare earth powder mass being 0.01% of the mass of the first component. Finally, a polymer molding agent is weighed, with the polymer molding agent mass being 5.98% of the mass of the first component. The polymer molding agent is a mixture of PVP and CMC, with an addition ratio of 1:1. The particle size of the tungsten carbide powder is 90 nm. The particle sizes of the carbon black, chromium powder, and cobalt powder are all 1.0 μm, the particle size of the rare earth powder is 0.2 μm, and the particle size of the chromium carbide powder is 0.2 μm.

[0054] The polymer molding agent is dissolved in deionized water to prepare a polymer molding agent mixture. The concentration of the polymer molding agent mixture is not required, as long as PVP and CMC can be fully dissolved.

[0055] Then, cobalt powder and carbon black are premixed, and then mixed with tungsten carbide powder, rare earth, chromium powder and chromium carbide powder. Then, a polymer molding agent mixture and deionized water are added. The amount of deionized water added is controlled so that the solid-liquid ratio of the mixture is 70%. The mixture is stirred evenly to obtain a mixed slurry.

[0056] Finally, the mixed slurry is fed into a spray drying tower for granulation. Specifically, centrifugal spray drying is performed using filtered dry air as the medium. The temperature inside the spray drying tower is 220℃, and the rotation speed of the spray disc inside the spray drying tower is 16000 r / min. After granulation, particulate matter is obtained. The particulate matter is then sintered in a vacuum environment at a temperature of 1100℃ to obtain spherical particles with a loose interior and a dense outer layer, which is the nano-spray powder.

[0057] The preparation process of submicron spray powder is generally the same as that of nano spray powder, except that the particle size of tungsten carbide powder is 0.8 μm in the preparation process of submicron spray powder.

[0058] The preparation process of micron-sized spray powder is generally the same as that of nano-sized spray powder, except that the particle size of tungsten carbide powder is 3 μm in the preparation process of micron-sized spray powder.

[0059] The overall preparation process of micro-nano composite spray powder is the same as that of nano spray powder. The difference is that in the preparation process of micro-nano composite spray powder, tungsten carbide powder is a mixture of 0.8 μm, 3 μm and 90 nm particle sizes. Tungsten carbide powder with a particle size of 0.3 μm accounts for 50% of the total mass of tungsten carbide powder, tungsten carbide powder with a particle size of 3 μm accounts for 20% of the total mass of tungsten carbide powder, and tungsten carbide powder with a particle size of 80 nm accounts for 30% of the total mass of tungsten carbide powder.

[0060] S2: Sandblast the substrate surface to be coated, blow the substrate surface clean after sandblasting, and preheat the substrate surface.

[0061] S3: A multi-scale modified tungsten carbide wear-resistant coating, consisting of micro-nano composite powder, micron-sized powder, submicron-sized powder, and nano-sized powder, is sequentially sprayed onto the substrate surface using a supersonic flame spraying method. This process yields a hard outer and tough inner micro-nano multi-scale modified tungsten carbide coating. Specifically, a JP 8000 spraying equipment is used for supersonic flame spraying, with kerosene as the fuel and oxygen as the combustion aid. The specific spraying parameters are: kerosene flow rate 6.0 GPH, oxygen flow rate 1850 SCHF, and powder feed rate 60 g / min. -1 Spraying distance: 380nm; spray gun moving speed: 500mm.s-1 Step distance 5mm.

[0062] The wear-resistant coating of modified tungsten carbide with external hardness and internal toughness at multiple scales, prepared in this embodiment, has a thickness of 300 micrometers, of which the thickness of the micro-nano composite layer is 150 micrometers, the thickness of the nano layer is 100 micrometers, and the thickness of the submicrometer and micrometer wear-resistant coatings is 50 micrometers each.

[0063] It should be noted that the method for controlling the coating thickness during supersonic flame spraying is existing technology and will not be elaborated here.

[0064] Example 2

[0065] A method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating:

[0066] S1: Prepare nano-spraying powder, submicron spraying powder, micron spraying powder and micro-nano composite spraying powder respectively;

[0067] The preparation process of the nano-coating powder is as follows: First, tungsten carbide powder, cobalt powder, and chromium powder are weighed in a mass ratio of 86:10:4, and this is recorded as the first component. Then, rare earth powder, carbon black, and chromium carbide powder are weighed, and this is recorded as the second component. In the second component, the mass of carbon black is 0.01% of the mass of the first component, the mass of chromium carbide powder is 0.5% of the mass of the first component, and the rare earth powder is Y2O3 powder, with the mass of rare earth powder being 0.2% of the mass of the first component. Finally, a polymer molding agent is weighed, with the mass of the polymer molding agent being 5.98% of the mass of the first component. The polymer molding agent is a mixture of PVP and CMC, with an addition ratio of 1:1. The particle size of the tungsten carbide powder is 80 nm. The particle sizes of the carbon black, chromium powder, and cobalt powder are all 0.8 μm, the particle size of the rare earth powder is 0.01 μm, and the particle size of the chromium carbide powder is 0.01 μm.

[0068] The polymer molding agent is dissolved in deionized water to prepare a polymer molding agent mixture. The concentration of the polymer molding agent mixture is not required, as long as PVP and CMC can be fully dissolved.

[0069] Then, cobalt powder and carbon black are premixed, and then mixed with tungsten carbide powder, rare earth, chromium powder and chromium carbide powder. Then, a polymer molding agent mixture and deionized water are added. The amount of deionized water added is controlled so that the solid-liquid ratio of the mixture is 70%. The mixture is stirred evenly to obtain a mixed slurry.

[0070] Finally, the mixed slurry is fed into a spray drying tower for granulation. Specifically, centrifugal spray drying is performed using filtered dry air as the medium. The temperature inside the spray drying tower is 230°C, and the rotation speed of the spray disc inside the spray drying tower is 18000 r / min. After granulation, particulate matter is obtained. The particulate matter is then sintered in a vacuum environment at a temperature of 1100°C to obtain spherical particles with a loose interior and a dense outer layer, which is the nano-spray powder.

[0071] The preparation process of submicron spray powder is generally the same as that of nano spray powder, except that the particle size of tungsten carbide powder is 0.3 μm in the preparation process of submicron spray powder.

[0072] The preparation process of micron-sized spray powder is generally the same as that of nano-sized spray powder, except that the particle size of tungsten carbide powder is 5 μm in the preparation process of micron-sized spray powder.

[0073] The overall steps of the preparation process of micro-nano composite spray powder are the same as those of nano spray powder. The difference is that in the preparation process of micro-nano composite spray powder, tungsten carbide powder is a mixture of 0.8 μm, 5 μm and 100 nm particle sizes. Tungsten carbide powder with a particle size of 0.8 μm accounts for 80% of the total mass of tungsten carbide powder, tungsten carbide powder with a particle size of 5 μm accounts for 15% of the total mass of tungsten carbide powder, and tungsten carbide powder with a particle size of 100 nm accounts for 5% of the total mass of tungsten carbide powder.

[0074] S2: Sandblast the substrate surface to be coated, blow the substrate surface clean after sandblasting, and preheat the substrate surface.

[0075] S3: A multi-scale modified tungsten carbide wear-resistant coating, consisting of micro-nano composite powder, micron-sized powder, submicron-sized powder, and nano-sized powder, is sequentially sprayed onto the substrate surface using a supersonic flame spraying method. This process yields a hard outer and tough inner micro-nano multi-scale modified tungsten carbide coating. Specifically, a JP 8000 spraying equipment is used for supersonic flame spraying, with kerosene as the fuel and oxygen as the combustion aid. The specific spraying parameters are: kerosene flow rate 6.0 GPH, oxygen flow rate 1850 SCHF, and powder feed rate 60 g / min. -1 Spraying distance: 380nm; spray gun moving speed: 500mm.s -1 Step distance 5mm.

[0076] The wear-resistant coating obtained in this embodiment has a thickness of 240 micrometers, of which the thickness of the micro-nano composite layer is 120 micrometers, the thickness of the nano layer is 80 micrometers, and the thickness of the submicrometer and micrometer wear-resistant coatings is 20 micrometers each.

[0077] It should be noted that the method for controlling the coating thickness during supersonic flame spraying is existing technology and will not be elaborated here.

[0078] Example 3

[0079] A method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating:

[0080] S1: Prepare nano-spraying powder, submicron spraying powder, micron spraying powder and micro-nano composite spraying powder respectively;

[0081] The preparation process of the nano-coating powder is as follows: First, tungsten carbide powder, cobalt powder, and chromium powder are weighed in a mass ratio of 86:10:4, and this is recorded as the first component. Then, rare earth powder, carbon black, and chromium carbide powder are weighed, and this is recorded as the second component. In the second component, the mass of carbon black is 6.2% of the mass of the first component, the mass of chromium carbide powder is 0.01% of the mass of the first component, and the rare earth powder is Ce powder, with the rare earth powder accounting for 0.3% of the mass of the first component. Finally, a polymer molding agent is weighed, with the polymer molding agent accounting for 5.98% of the mass of the first component. The polymer molding agent is a mixture of PVP and CMC, with an addition ratio of 1:1. The particle size of the tungsten carbide powder is 90 nm. The particle sizes of the carbon black, chromium powder, and cobalt powder are all 0.8 μm, the particle size of the rare earth powder is 0.01 μm, and the particle size of the chromium carbide powder is 0.01 μm.

[0082] The polymer molding agent is dissolved in deionized water to prepare a polymer molding agent mixture. The concentration of the polymer molding agent mixture is not required, as long as PVP and CMC can be fully dissolved.

[0083] Then, cobalt powder and carbon black are premixed, and then mixed with tungsten carbide powder, rare earth, chromium powder and chromium carbide powder. Then, a polymer molding agent mixture and deionized water are added. The amount of deionized water added is controlled so that the solid-liquid ratio of the mixture is 70%. The mixture is stirred evenly to obtain a mixed slurry.

[0084] Finally, the mixed slurry is fed into a spray drying tower for granulation. Specifically, centrifugal spray drying is performed using filtered dry air as the medium. The temperature inside the spray drying tower is 220°C, and the rotation speed of the spray disc inside the spray drying tower is 15000 r / min. After granulation, particulate matter is obtained. The particulate matter is then sintered in a vacuum environment at a temperature of 1120°C to obtain spherical particles with a loose interior and a dense outer layer, which is the nano-spray powder.

[0085] The overall steps of the preparation process of submicron spray powder are the same as those of nano spray powder, except that the particle size of tungsten carbide powder is 0.5 μm in the preparation process of submicron spray powder.

[0086] The preparation process of micron-sized spray powder is generally the same as that of nano-sized spray powder, except that the particle size of tungsten carbide powder is 4 μm in the preparation process of micron-sized spray powder.

[0087] The overall preparation process of micro-nano composite spray powder is the same as that of nano spray powder. The difference is that in the preparation process of micro-nano composite spray powder, tungsten carbide powder is a mixture of 0.5 μm, 4 μm and 90 nm particle sizes. Tungsten carbide powder with a particle size of 0.5 μm accounts for 60% of the total mass of tungsten carbide powder, tungsten carbide powder with a particle size of 4 μm accounts for 20% of the total mass of tungsten carbide powder, and tungsten carbide powder with a particle size of 90 nm accounts for 20% of the total mass of tungsten carbide powder.

[0088] S2: Sandblast the substrate surface to be coated, blow the substrate surface clean after sandblasting, and preheat the substrate surface.

[0089] S3: A multi-scale modified tungsten carbide wear-resistant coating, consisting of micro-nano composite powder, micron-sized powder, submicron-sized powder, and nano-sized powder, is sequentially sprayed onto the substrate surface using a supersonic flame spraying method. This process yields a hard outer and tough inner micro-nano multi-scale modified tungsten carbide coating. Specifically, a JP 8000 spraying equipment is used for supersonic flame spraying, with kerosene as the fuel and oxygen as the combustion aid. The specific spraying parameters are: kerosene flow rate 6.0 GPH, oxygen flow rate 1850 SCHF, and powder feed rate 60 g / min. -1 Spraying distance: 380nm; spray gun moving speed: 500mm.s -1 Step distance 5mm.

[0090] To verify the performance of the wear-resistant coating prepared in this invention, the following verification tests were conducted: the micron spraying powder, submicron spraying powder, nano spraying powder and micro-nano composite spraying powder prepared in Example 1 were used to spray the coatings, and the specific spraying methods were the same as in Example 1. The resulting coatings were micron coatings, submicron coatings, nano coatings and micro-nano composite coatings.

[0091] The properties of the obtained coatings were tested, and the porosity and mechanical properties of WC-CoCr coatings with different WC sizes are shown in Table 1 below:

[0092] Table 1. Porosity and mechanical properties of WC-CoCr coatings with different WC sizes

[0093] As can be seen from Table 1, the crack toughness of the nano-coating, submicron coating, micron coating, and micro-nano composite coating gradually increases. The hardness of the nano-coating is greater than that of the submicron coating and the micron coating, indicating that the wear-resistant coating prepared by the present invention is a gradient coating with hardness on the outside and toughness on the inside.

[0094] The coatings obtained in Example 1 and the verification test were subjected to hardness tests, and the test method used was the existing nanoindentation test method.

[0095] Figure 5Microscopic morphology images of the micron coating, submicron coating, nano coating and micro-nano composite coating obtained in the indentation test are shown.

[0096] Figure 1 This is a graph showing the elastic modulus of the gradient coating prepared in Example 1. Figure 2-4 The figures show the elastic modulus of the micron-sized coating, submicron-sized coating, and nano-sized coating obtained in the verification experiment.

[0097] Depend on Figure 1-4 It can be seen that the maximum indentation depth of the micron coating is 1190 nm, the maximum indentation depth of the submicron coating is 1200 nm, the maximum indentation depth of the nano coating is 1800 nm, and the maximum indentation depth of the gradient coating obtained in Example 1 is 1070 nm.

[0098] The minimum indentation depth of the micron coating is 1100 nm, the minimum indentation depth of the submicron coating is 1020 nm, the minimum indentation depth of the nano coating is 1300 nm, and the minimum indentation depth of the gradient coating obtained in Example 1 is 1020 nm.

[0099] This demonstrates that the gradient coating prepared in this embodiment of the invention has a small elastic modulus and a minimal fluctuation range. The presence of residual stress in the coating can cause it to peel off and fracture. This phenomenon is mainly due to the release of elastic energy stored in the coating caused by mismatch strain. Therefore, the generation of residual stress is caused by elastic strain. The gradient coating prepared in this invention has a small elastic modulus and a small fluctuation range, indicating that it can not only absorb a large amount of energy under impact conditions but also reduce the presence of residual stress in the coating, thereby avoiding failure caused by coating peeling and extending the service life of the coating.

[0100] The gradient coating prepared by this invention is used to spray aircraft landing gear to form a protective layer. Therefore, its wear resistance and corrosion resistance are particularly important. Generally, WC-CoCr coatings also suffer from high-temperature decarburization during the formation process, which affects the hardness and corrosion resistance of the coating. In the process of preparing the wear-resistant coating, this invention modifies the coating by adding rare earth elements and carbon, thereby improving the coating's overall performance, such as toughness, corrosion resistance, and wear resistance.

[0101] Using the submicron coating obtained in the verification experiment as a reference, the following comparative experiments were conducted:

[0102] Comparative Experiment 1

[0103] The preparation process of the submicron coating in this comparative experiment and the verification experiment is generally the same. The difference is that in this embodiment, no rare earth and carbon are added when preparing the spray powder. Therefore, the coating obtained has not been modified by rare earth and carbon.

[0104] Comparative Experiment 2

[0105] The preparation process of the submicron coating in this comparative experiment and the verification experiment are generally the same. The difference is that in this embodiment, only CeO2 powder is added and no carbon is added when preparing the spraying powder.

[0106] Comparative Test 3

[0107] The preparation process of the submicron coating in this comparative experiment and the verification experiment are generally the same. The difference is that in this embodiment, only carbon black is added when preparing the spray powder, and no rare earth is added.

[0108] The performance of the coatings obtained from comparative and verification tests was compared:

[0109] The table below shows the performance of the submicron coating in the verification experiment and the coatings prepared in comparative experiments 1-3:

[0110] As can be seen from the table above, the hardness of the submicron coating prepared by adding rare earth and carbon in the verification test is 1282HV, which is greater than that of the comparative test 1-3. This shows that the addition of rare earth and carbon increases the hardness of the coating, thereby enhancing its wear resistance.

[0111] The submicron coating prepared by adding rare earth elements and carbon in the verification test had a porosity of 0.2%, which was lower than that of the comparative tests 1-3. This indicates that the coating obtained by adding rare earth elements and carbon has better compactness, thereby enhancing its corrosion resistance.

[0112] The self-corrosion current density in the submicron coating during the verification test was 3.538 μA / cm. 2 The value is lower than that of the comparative test 1-3, indicating that it has higher corrosion resistance, with corrosion resistance performance improved by more than 20%.

[0113] <X-ray diffraction patterns and WC retention in the submicron coating obtained in verification experiments, and in the coatings obtained in comparative experiments 1-3>

[0114] Figure 7 To verify the submicron coating in the experiment and compare the XRD diffraction patterns of the coatings prepared in experiments 1-3, Figure 8 To verify the retention of WC in the submicron coatings used in the experiment and to compare the wear-resistant and corrosion-resistant coatings prepared in experiments 1-3, the retention of WC in the four coatings was determined by the RIR method based on the XRD patterns of the coatings (73.2-83.6%).

[0115] from Figure 7 , 8As can be seen from the results, the amount of WC retained in the coatings obtained in both the verification and comparative experiments is less than the amount of raw materials added. This is partly because during the supersonic flame spraying process, a small amount of WC particles in the WC-CoCr composite spraying powder dissolves and decarburizes upon heating, and then oxidizes and decarburizes upon contact with the surrounding air, producing W2C, which reduces the amount of WC retained. On the other hand, a small amount of WC particles dissolves during the spraying process, and the C elements dissolved into the binder phase come into contact with the air to generate CO2 or CO, forming local carbon-depleted areas in the binder phase. As a result, W2C precipitates from the binder phase during the coating formation process.

[0116] However, the retention of WC in the submicron coating of the verification test was 83.8%, which is greater than that of comparative examples 1-3. This indicates that the combined effect of rare earth elements and carbon in this invention inhibits the decarburization of WC during supersonic flame spraying, reduces the formation of the W2C brittle phase, and thus improves the wear resistance of the prepared coating.

[0117] EBSD images of submicron coatings used in validation experiments

[0118] like Figure 9 As shown, the size of WC particles in the coating is smaller than that in the thermal spray powder. This is because the total WC particles undergo dissolution and reaction during the thermal spraying process. The WC particles oxidize and decarburize during spraying to form W2C, and the reaction process is shown in Equation 1. Besides the oxidative decarburization of dissolved WC, WC particles also undergo direct decarburization during heating, as shown in Equation 2.

[0119]

[0120] Verification experiment on the phase distribution of the submicron coating

[0121] Figure 10 The diagram illustrates several phase structures of the submicron coating used in the verification experiment. Red represents the WC phase, green represents the W2C phase, yellow represents a small amount of elemental Co phase, and the unidentified white areas represent the amorphous binder phase. From... Figure 10 It can be observed that most W2C exists in the binder phase and mainly appears in association with Co, while a small amount of W2C appears around the WC particles.

[0122] Figure 11 and Figure 12 The size distributions of the WC and W2C phases were shown separately. It was observed that the WC particles in the coating were distributed between 0.1 and 1 μm, mainly between 0.1 and 0.5 μm, which is significantly smaller than the size in the powder raw material. The W2C particles were mainly smaller than 0.1 μm.

[0123] This invention, by adding carbon (C), not only inhibits the formation of the brittle W2C phase due to WC oxidation during the thermal spraying process of WC-CoCr composite spray powder, but also improves the uneven hardness distribution and low hardness caused by the small amount of WC particles dissolving in the binder phase during spraying, forming localized carbon-depleted zones. The addition of rare earth elements not only inhibits the precipitation and growth of tungsten carbide grains and improves coating hardness, but also has a good deoxidizing effect, purifying the interface. In particular, the reactive nature of rare earth elements not only promotes the segregation of C at the WC interface, but also reacts with C elements in WC, causing them to aggregate on the WC surface, further suppressing the formation of W2C due to WC oxidation and decarburization during the thermal spraying process of WC-CoCr composite spray powder.

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating, characterized in that, Includes the following steps: S1: Carbon black and cobalt powder are premixed, then mixed with rare earth powder, chromium powder, chromium carbide powder and tungsten carbide powder, and a polymer molding agent and deionized water are added to obtain a mixed slurry. The mixed slurry is granulated, semi-alloyed and vacuum sintered to obtain a spraying powder. When the particle size of tungsten carbide powder is 80-100nm, the obtained spraying powder is a nano spraying powder. When the particle size of tungsten carbide powder is 0.3-0.8 μm, the resulting spray powder is a submicron spray powder; When the particle size of tungsten carbide powder is 3-5 μm, the resulting spray powder is micron-sized spray powder. When the tungsten carbide powder is a mixture of powders with particle sizes of 0.3-0.8 μm, 3-5 μm and 80-100 nm, the resulting spray powder is a micro-nano composite spray powder. S2: Sandblasting treatment of the substrate surface to be sprayed; S3: The substrate surface is coated with micro-nano composite powder, micron powder, submicron powder and nano powder in sequence by supersonic flame spraying to obtain a micro-nano multi-scale modified tungsten carbide wear-resistant coating with hard exterior and tough interior. The polymer molding agent is composed of a mixture of PVP and CMC, with a PVP to CMC addition ratio of 1:

1.

2. The method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 1, characterized in that, In the preparation process of micro-nano composite spray powder, tungsten carbide powder with a particle size of 0.3-0.8 μm accounts for 50-80% of the total mass of tungsten carbide powder, tungsten carbide powder with a particle size of 3-5 μm accounts for 10-20% of the total mass of tungsten carbide powder, and the remainder is tungsten carbide powder with a particle size of 80-100 nm.

3. The method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 1, characterized in that, In the preparation of the spray powder, tungsten carbide powder, cobalt powder, and chromium powder are taken according to the following mass percentages: tungsten carbide powder 80-90%, cobalt powder 8-15%, and chromium powder 0.1-6%; rare earth powder is 0.01-0.2% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder; carbon black is 0.01-6.2% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder; and chromium carbide powder is 0.01-0.1% of the total mass of tungsten carbide powder, cobalt powder, and chromium powder.

4. The method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 1, characterized in that, Rare earth powder is one or more of Y powder, Ce powder, CeO2 powder and Y2O3 powder.

5. The method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 1, characterized in that, The particle size of carbon black, chromium powder, and cobalt powder is 0.8-1.2 μm, the particle size of rare earth powder is 0.01-0.3 μm, and the particle size of chromium carbide powder is 0.01-0.3 μm.

6. The method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 1, characterized in that, The mixed slurry is fed into a spray drying tower for granulation. The spray disc rotation speed in the spray drying tower is 15000-18000 r / min, and the temperature in the spray drying tower is 220±10℃.

7. The method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 1, characterized in that, The temperature for semi-alloying vacuum sintering is 1100±20℃.

8. The method for preparing an externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 1, characterized in that, The process conditions for supersonic flame spraying are: kerosene flow rate 6.0 GPH, oxygen flow rate 1850 SCHF, and powder feed rate 60 g / min. -1 Spraying distance: 380 nm; spray gun moving speed: 500 mm / s -1 Step size 5 mm.

9. A wear-resistant coating of tungsten carbide with external hardness and internal toughness at micro-nano multi-scale obtained by any of the preparation methods in claims 1-8.

10. The externally hard and internally tough micro / nano multi-scale modified tungsten carbide wear-resistant coating according to claim 9, characterized in that, The wear-resistant coating includes a micro-nano composite layer sprayed onto a substrate, on which a micron layer, a submicron layer, and a nano layer are sequentially attached from the inside out. The total thickness of the wear-resistant coating is 200-300 micrometers, the thickness of the micro-nano composite layer is 1 / 2 of the total thickness of the wear-resistant coating, the nano layer is 1 / 3 of the total thickness of the wear-resistant coating, and the sum of the thicknesses of the submicron layer and the micron layer is 1 / 6 of the total thickness of the wear-resistant coating.

Images