A high content tungsten carbide uniformly distributed nickel-based composite coating and a preparation method thereof

Abstract

The present application relates to a kind of high content tungsten carbide uniform distribution nickel-based composite coating and its preparation method, its preparation raw material uses nickel-chromium powder and tungsten carbide powder as main powder, and join multiple alloy powder and pure element powder.Nickel-based composite coating preparation process mainly includes powder mixing, substrate pretreatment and coating preparation, using the strong reaction of B4C and metal component in mixed powder, and high efficiency, heat input controllable plasma surfacing means, realize the preparation of nickel-based composite coating at low temperature.The prepared nickel-based composite coating is crack-free, porosity is only 0.09~0.85%, WC particle retention is high, uniformly distributed in coating;The hardness of coating reaches 65.7~68.0HRC;If the wear resistance of 42CrMo steel is defined as 1, the relative wear resistance of the coating of the present application is 8.46~10.53, with high hardness, high wear resistance.

Description

Technical Field

[0001] This invention belongs to the field of composite coatings, and relates to a nickel-based composite coating with high WC particle retention and uniform distribution, high hardness and high wear resistance, and its preparation method. Technical Background

[0002] Nickel-based tungsten carbide composites possess high wear resistance, excellent corrosion resistance, and impact resistance, exhibiting superior comprehensive performance and are widely used in high-wear environments. Laser cladding, supersonic flame spraying, and flame welding are commonly used techniques in the coating preparation process. However, these techniques typically operate at high temperatures. Firstly, the difference in thermophysical properties between the substrate and coating materials can lead to severe substrate deformation, high coating dilution, or stress cracking between the coating and substrate, complicating the process. Secondly, since tungsten carbide particles react with the nickel-based melt, it is necessary to minimize the coating preparation temperature to increase tungsten carbide retention and reduce its solubility. Furthermore, the density of tungsten carbide particles is much higher than that of the nickel-based melt, thus tending to settle at the bottom of the coating. Therefore, it is necessary to consider how to prepare the coating at a lower temperature to retain the highest possible content of tungsten carbide particles with low solubility, while achieving low porosity, crack-free coating, low coating dilution, and good interfacial bonding.

[0003] B4C powder exhibits a strong reactivity with transition metals, generating a cryogenic effect that lowers the melting point of the mixed powder. Utilizing the melting point-lowering effect of B4C powder, along with the low coating dilution rate, high coating bonding strength, and high coating quality characteristics of plasma cladding, it is possible to minimize the coating preparation temperature. This allows for the preparation of nickel-based composite coatings with high tungsten carbide retention, low porosity, crack-free properties, good bonding strength, high hardness, and high wear resistance at low temperatures. Summary of the Invention

[0004] This invention aims to provide a nickel-based composite coating with a high content of uniformly distributed tungsten carbide and its preparation method. The invention utilizes the low-temperature reaction of B4C with Ni-20% Cr and Fe-72% Si powders, along with the high wear resistance of WC particles, to form a WC mass ratio of 55-65%. The low temperature during coating preparation ensures the integrity of the WC particles, and the WC particles form a uniformly distributed mixture with the binder phase. This results in a nickel-based composite coating with high wear resistance, high hardness, high density, few structural defects, and no cracks. Furthermore, the process is simple and easy to control.

[0005] The raw material ratio of the nickel-based composite coating, calculated by total mass, is as follows: Ni-20% Cr: 28.46%–36.59%, particle size range 48–74 μm; B4C: 1.80%–2.31%, particle size range 10–25 μm; Fe-72% Si: 1.94%–2.50%, particle size range 45–58 μm; Mo: 1.40%–1.80%, particle size range 48–58 μm; Cu: 1.40%–1.80%, particle size range 48–58 μm. The B4C in these raw material powders can undergo a low-temperature reaction with Fe-72% Si, Ni, Cr, and other metallic elements, with a melting point of 939.5–955.1 °C. The hard phase is WC, with a mass percentage of 55% to 65%, and is prepared by carbothermal reduction-crushing method, with a particle size range of 25 to 150 μm.

[0006] WC particles undergo rapid decomposition and melting at temperatures above 1250℃. Therefore, using ordinary Ni-based pre-alloyed powder often results in a low WC particle retention rate in the coating. After decomposition and melting, WC particles alloy with the binder phase, forming a eutectic structure, making it difficult to reflect the high hardness and high wear resistance characteristics of the original WC particles.

[0007] After weighing the selected powder, the binder phase powder is first mixed, with 1.0% to 1.5% of polyacrylic acid copolymer binder added during mixing. After the binder phase is mixed evenly, it is then mixed with WC. This process utilizes the effect of the polyacrylic acid copolymer binder to prevent WC particles from segregating in the mixed powder; it also increases the flowability of the mixed powder and improves the stability of powder supply during plasma cladding, thereby obtaining a high-quality coating.

[0008] After powder mixing, a nickel-based composite coating was prepared under low heat input conditions using a heat-controlled plasma cladding process. The prepared coating exhibited high density, few structural defects, and no cracks; its hardness ranged from 65.7 to 68.0 HRC; if the wear resistance of 42CrMo steel is defined as 1, the relative wear resistance of the nickel-based composite coating ranged from 8.46 to 10.53; it possessed the characteristics of high hardness, high wear resistance, and low preparation temperature.

[0009] The preparation method of a nickel-based composite coating with a high content of uniformly distributed tungsten carbide and possessing the above properties includes the following steps:

[0010] Step (1): Powder mixing:

[0011] Taking the preparation of 1 kg of nickel-based tungsten carbide mixed powder as an example:

[0012] Binder phase powder mixing: Take 284.6g~365.9g Ni-20% Cr powder, 18.0g~23.1g B4C powder, 19.4g~25.0g Fe-72% Si powder, 14.0g~18.0g Mo powder, and 14.0g~18.0g Cu powder; the total amount of the binder phase powder formed by the above powders is 350~450g; put these together into a container and perform preliminary stirring and grinding for 10min; add the preliminary mixed powder and 4.50~5.25g of polyacrylic acid copolymer binder into a roller or V-shaped barrel for powder mixing; set the powder mixing speed to 18~22r / min and the mixing time to 9~14h; obtain a nickel-based binder phase mixed powder with certain fluidity and uniform mixing; Nickel-based tungsten carbide powder preparation: Add 550g~650g of nickel-based binder phase mixed powder to the obtained nickel-based binder phase mixed powder. WC powder is placed into a ball mill jar; the particle size range of WC powder is 25-150 μm; without adding milling balls, it is mixed at a speed of 200-300 r / min for 8-12 h; the operation mode is to alternate between clockwise and counterclockwise, and change the rotation direction every 30 min, with the tilt angle set at 30-40°; a dry, uniformly mixed nickel-based tungsten carbide mixed powder with good flowability is obtained.

[0013] Step (2): Pretreatment of the matrix material:

[0014] The substrate surface is cleaned by sandblasting or grinding with a grinding wheel to remove the oxide film and achieve a certain degree of surface roughening. After treatment, the substrate material is cleaned with ethanol or propanol and dried. The substrate is preheated to 200-300℃ and held at that temperature for 4-7 hours. The substrate types used include carbon steel and alloy steel. The substrate preheating equipment includes box furnace, muffle furnace, tube furnace, and salt bath furnace.

[0015] Step (3): Coating preparation:

[0016] The uniformly mixed powder is loaded into the powder feeding device of the coating preparation equipment, and the substrate material is transferred to the working area; the coating is prepared by plasma welding.

[0017] The spray gun height for plasma cladding is 9–11 mm, the gun swing amplitude is 12–15 mm, the swing speed is 2000–2100 mm / min, and the gun movement speed is 10–13 mm / min. The powder feeding device has a powder feeding speed of 90–110 rpm, a powder feeding gas flow rate of 5–7 L / min, an ion gas flow rate of 2.5–3 L / min, and a shielding gas flow rate of 11–13 L / min. The shielding gases include argon and nitrogen. The cladding current is 80–90 A.

[0018] After the coating is prepared, it is cooled directly to room temperature in the air, or slowly cooled by wrapping it with asbestos, or kept at 200-240℃ for 2-4 hours using heat treatment equipment; the heat treatment equipment includes box furnace, muffle furnace, and salt bath furnace; thus obtaining a nickel-based composite coating.

[0019] In the above coating preparation process, a low welding current was used to achieve good metallurgical bonding, and the coating had few defects. The high-density nickel-based composite coating with a porosity of only 0.09-0.85% has the following advantages compared with existing nickel-based tungsten carbide coatings:

[0020] (1) The B4C component in the mixed powder can effectively reduce the preparation temperature required for the coating. When combined with plasma transfer arc welding, it enables the preparation of the coating at a lower operating temperature.

[0021] (2) In this nickel-based composite coating, the retention of WC particles is relatively high and they are uniformly distributed in the coating area. At the same time, there are also hard phase particles M7(B,C)3 and M with a high volume fraction. 23 (B,C)6, which improves the hardness and wear resistance of the coating.

[0022] (3) The nickel-based composite coating has no defects such as cracking, has a porosity of only 0.09 to 0.85%, has a dense structure, and can achieve good metallurgical bonding between the coating and the substrate.

[0023] (4) The hardness of the nickel-based composite coating reaches a relatively high level of 65.7 to 68.0 HRC. If the wear resistance of 42CrMo steel is defined as 1, the relative wear resistance of the nickel-based composite coating prepared by the present invention reaches 8.46 to 10.53, which has the characteristics of high hardness and high wear resistance.

[0024] (5) The nickel-based composite coating produced by the present invention has the advantages of simple preparation process, simple equipment, strong operability, low energy consumption and low cost. Attached Figure Description

[0025] Figure 1 Example 1: XRD diffraction pattern of nickel-based composite coating

[0026] Figure 2 Example 1: Scanning electron microscope image of the cross-section of the nickel-based composite coating.

[0027] Figure 3 Scanning electron microscope (SEM) images of the nickel-based composite coating area prepared in Comparative Example 1. Detailed Implementation

[0028] Example 1

[0029] 1. Powder Mixing: Weigh 30.90% Ni-20% Cr powder, 1.95% B4C powder, 2.11% Fe-72% Si powder, 1.52% Mo powder, and 1.52% Cu powder according to the mass ratio, and place them together in a container for preliminary stirring and grinding for 10 minutes. Then, add the preliminary mixed powder, along with 1.05% of the total weight of polyacrylic acid copolymer binder, into a V-shaped barrel, and mix at a speed of 20 r / min for 10 hours. This yields a binder phase powder with certain fluidity and uniform mixing; its melting point is 951.6℃.

[0030] Add 62.00% WC powder to the obtained nickel-based binder phase mixed powder and place it in a ball mill jar. The particle size range of the WC powder is 25-150 μm, and the average particle size is 34 μm. Do not add milling balls and mix at a speed of 220 r / min for 12 h. The operation mode is to alternate between clockwise and counterclockwise, change the rotation direction every 30 min, and set the tilt angle to 40°. A uniformly mixed nickel-based tungsten carbide mixed powder with good flowability is obtained.

[0031] 2. Pretreatment of the substrate: The Q255 substrate is treated with a sandblasting machine to remove the oxide film on the surface; it is cleaned with ethanol and then dried; the Q255 substrate is placed in a box furnace, heated to 200℃, and kept at that temperature for 7 hours.

[0032] 3. Coating Preparation: The dried mixed powder is loaded into the powder feeding device, and the preheated Q255 substrate material is transferred to the working area; the coating is prepared by plasma cladding; the spray gun height is 10mm, the welding gun swing amplitude is 15mm, the swing speed is 2100mm / min, the powder feeding speed of the powder feeding device is 95rpm, the powder feeding gas flow rate is 6L / min, the ion gas flow rate is 2.5L / min, and the shielding gas flow rate is 11L / min; the shielding gas is argon; the cladding current is 87A; the welding gun moving speed is 12mm / min; after the coating preparation is completed, it is transferred to a box furnace, held at 200℃ for 3h, and then cooled with the furnace; a nickel-based composite coating is obtained.

[0033] The nickel-based composite coating prepared by the above method consists of the following phases: γ-Ni, WC, M7(B,C)3, and M... 23 (B,C)6. Figure 1 The XRD diffraction pattern of the coating shows that the nickel-based composite coating is composed of these phases. Figure 2 The cross-sectional scanning electron microscope image of the coating shows that the WC particles in the nickel-based composite coating are of high retention and relatively uniform distribution, with intact morphology, indicating low solubility; the hard phases M7(B,C)3 and M 23The (B,C)6 volume fraction is relatively high and is distributed relatively evenly in the coating. The porosity of this nickel-based composite coating is 0.53%, there are no cracks in the coating area, and the hardness is 67.1 HRC. According to the volume wear rate calculation, if the wear resistance of 42CrMo steel is defined as 1, the relative wear resistance of this nickel-based composite coating reaches 9.45, which has the characteristics of high hardness and high wear resistance.

[0034] Comparative Example 1: Pre-alloyed powder was used as the binder phase powder, and its composition was the same as that of the binder phase alloyed in Example 1 of the present invention. After being mixed with WC particles, plasma welding was performed with the same process parameters. The specific preparation steps are as follows:

[0035] 1. Powder Mixing: Weigh 38.00% nickel-based self-fluxing alloy powder and 62.00% WC powder according to the mass ratio, and place them together in a container for preliminary stirring and grinding for 10 minutes. The nickel-based self-fluxing powder is a pre-alloyed powder with the following composition: 66.2% Ni, 16% Cr, 3.5% B, 3.5% Si, 3% Mo, 3% Cu, 4% Fe, and 0.8% C. The WC powder has a particle size range of 25–150 μm and an average particle size of 34 μm. Then, place the pre-mixed powder into a ball mill jar. Without adding milling balls, mix at a speed of 220 r / min for 12 hours. The mill operates by alternating clockwise and counterclockwise rotation, changing the rotation direction every 30 minutes, with the tilt angle set to 40°. A uniformly mixed nickel-based tungsten carbide powder with good flowability is obtained.

[0036] 2. Pretreatment of the substrate: The Q255 substrate is treated with a sandblasting machine to remove the oxide film on the surface; it is cleaned with ethanol and then dried.

[0037] 3. Coating Preparation: The dried mixed powder is loaded into the powder feeding device, and the preheated Q255 substrate material is transferred to the working area; the coating is prepared by plasma cladding; the spray gun height is 10mm, the welding gun swing amplitude is 15mm, the swing speed is 2100mm / min, the powder feeding speed of the powder feeding device is 95rpm, the powder feeding gas flow rate is 6L / min, the ion gas flow rate is 2.5L / min, and the shielding gas flow rate is 11L / min; the shielding gas is argon; the cladding current is 87A; the welding gun moving speed is 12mm / min; after the coating preparation is completed, it is directly air-cooled to room temperature to obtain a nickel-based composite coating.

[0038] The nickel-based composite coating prepared by the above method consists of the following phases: γ-Ni, WC, M7(B,C)3, and M... 23 (B,C)6. Figure 3The scanning electron microscope (SEM) image of the coated area shows that the WC particle retention in this nickel-based composite coating is low, much lower than in Example 1, and the morphology of the WC particles has changed significantly, indicating that they have undergone a large degree of dissolution during the preparation process. The hardness is 63.1 HRC. Based on the volumetric wear rate calculation, if the wear resistance of 42CrMo steel is defined as 1, then the relative wear resistance of this nickel-based composite coating is 6.48. However, both the hardness and wear resistance are lower than those of the composite coating prepared according to the mixed powder used in Example 1 of this invention.

[0039] Example 2

[0040] 1. Powder Mixing: Weigh 28.46% Ni-20% Cr powder, 1.80% B4C powder, 1.94% Fe-72% Si powder, 1.40% Mo powder, and 1.40% Cu powder according to the mass ratio, and place them together in a container for preliminary stirring and grinding for 10 minutes; then add the preliminary mixed powder, along with 1.00% of the total weight of polyacrylic acid copolymer binder, into a V-shaped barrel, and mix at a speed of 22 r / min for 9 hours; a binder phase powder with certain fluidity and uniform mixing is obtained; its melting point is 955.1℃;

[0041] Add 65.00% WC powder to the obtained nickel-based binder phase mixed powder and place it in a ball mill jar. The particle size range of the WC powder is 48-80 μm, and the average particle size is 67 μm. Do not add milling balls and mix at a speed of 240 r / min for 11 h. The operation mode is to alternate between clockwise and counterclockwise rotation, change the rotation direction every 30 min, and set the tilt angle to 32°. A uniformly mixed nickel-based tungsten carbide mixed powder with good flowability is obtained.

[0042] 2. Pretreatment of the substrate: GCr15 substrate was polished with a grinding wheel to remove the oxide film on the surface; it was cleaned with propanol and then dried; the substrate was heated to 240℃ in a muffle furnace and held at that temperature for 6 hours.

[0043] 3. Coating Preparation: The dried mixed powder was loaded into the powder feeding device, and the preheated GCr15 substrate material was transferred to the working area. The coating was prepared using plasma welding. The welding torch height was 9 mm, the torch swing amplitude was 13 mm, the swing speed was 2000 mm / min, the powder feeding speed of the powder feeding device was 100 rpm, the powder feeding gas flow rate was 6 L / min, the ion gas flow rate was 2.6 L / min, and the shielding gas flow rate was 12 L / min. The shielding gas was nitrogen. The welding current was 90 A, and the torch moving speed was 12 mm / min. After the coating was prepared, it was transferred to a muffle furnace and held at 240℃ for 4 h, then cooled with the furnace to obtain a nickel-based composite coating.

[0044] The nickel-based composite coating prepared by the above method consists of the following phases: γ-Ni, WC, M7(B,C)3, and M... 23 (B,C)6. In this nickel-based composite coating, the retention of WC particles is relatively low, but the distribution is still relatively uniform. The hard phases M7(B,C)3 and M 23 The (B,C)6 volume fraction is very high and relatively uniformly distributed in the coating. This nickel-based composite coating is crack-free, has a porosity of 0.09%, a hardness of 68.0 HRC, and a metallurgical bond is formed between the substrate and the coating. Based on volumetric wear rate calculations, if the wear resistance of 42CrMo steel is defined as 1, then the relative wear resistance of this nickel-based composite coating reaches 10.42, exhibiting high hardness and high wear resistance.

[0045] Example 3

[0046] 1. Powder Mixing: Weigh 32.53% Ni-20% Cr powder, 2.05% B4C powder, 2.22% Fe-72% Si powder, 1.60% Mo powder, and 1.60% Cu powder according to the mass ratio, and place them together in a container. Perform preliminary stirring and grinding for 10 minutes. Then, add the pre-mixed powder, along with 1.25% of the total weight of polyacrylic acid copolymer binder, into a roller drum. The mixing speed is 20 r / min, and the mixing time is 10 h. A binder phase powder with certain fluidity and uniform mixing is obtained. Its melting point is 946.3℃.

[0047] Add 60.00% WC powder to the obtained nickel-based binder phase mixed powder and place it in a ball mill jar. The particle size range of the WC powder is 96-150 μm, and the average particle size is 136 μm. Do not add milling balls and mix at a speed of 200 r / min for 10 h. The operation mode is to alternate between clockwise and counterclockwise, change the rotation direction every 30 min, and set the tilt angle to 35°. A uniformly mixed nickel-based tungsten carbide mixed powder with good flowability is obtained.

[0048] 2. Pretreatment of the substrate: The 42CrMo substrate was treated with a sandblasting machine to remove the oxide film on the surface; it was cleaned with propanol and then dried; the 42CrMo substrate was preheated to 300℃ in a box furnace and held at that temperature for 4 hours.

[0049] 3. Coating Preparation: The dried mixed powder is loaded into the powder feeding device, and the preheated 42CrMo substrate material is transferred to the working area; the coating is prepared by plasma welding; the spray gun height is 10mm, the welding gun swing amplitude is 12mm, the swing speed is 2050mm / min, the powder feeding speed of the powder feeding device is 110rpm, the powder feeding gas flow rate is 7L / min, the ion gas flow rate is 2.8L / min, and the shielding gas flow rate is 11L / min; the shielding gas is argon; the welding current is 85A; the welding gun moving speed is 13mm / min; after the coating preparation is completed, the workpiece is wrapped with asbestos and slowly cooled to room temperature; a nickel-based composite coating is obtained.

[0050] The nickel-based composite coating prepared by the above method consists of the following phases: γ-Ni, WC, M7(B,C)3, and M... 23 (B,C)6. In this nickel-based composite coating, the WC particles are retained in a high amount and are uniformly distributed with intact morphology. The hard phases M7(B,C)3 and M 23 (B,C)6 has a high volume fraction and is relatively uniformly distributed in the coating, with elongated M... 23 The (B,C)6 volume fraction is relatively high. This nickel-based composite coating is crack-free, has a porosity of 0.46%, and a hardness of 67.6 HRC, demonstrating a metallurgical bond between the substrate and the coating. Based on volumetric wear rate calculations, if the wear resistance of 42CrMo steel is defined as 1, then the relative wear resistance of this nickel-based composite coating reaches 10.53, exhibiting high hardness and high wear resistance.

[0051] Example 4

[0052] 1. Powder Mixing: Weigh 36.59% Ni-20% Cr powder, 2.31% B4C powder, 2.50% Fe-72% Si powder, 1.80% Mo powder, and 1.80% Cu powder according to the mass ratio, and place them together in a container for preliminary stirring and grinding for 10 minutes; then add the preliminary mixed powder, along with 1.50% of the total weight of polyacrylic acid copolymer binder, into a V-shaped barrel, and mix at a speed of 19 r / min for 12 hours; a binder phase powder with certain fluidity and uniform mixing is obtained; its melting point is 939.5℃;

[0053] Add 55.00% WC powder to the obtained nickel-based binder phase mixed powder and place it in a ball mill jar; the particle size range of WC powder is 48-80 μm, and the average particle size is 61 μm; without adding milling balls, mix at a speed of 300 r / min for 8 h; the operation mode is to alternate between clockwise and counterclockwise, change the rotation direction every 30 min, and set the tilt angle to 30°; a uniformly mixed nickel-based tungsten carbide mixed powder with good flowability is obtained.

[0054] 2. Pretreatment of the substrate: The Q235 substrate is treated with a sandblasting machine to remove the oxide film on the surface; it is cleaned with propanol and then dried; the substrate is placed in a tube furnace and kept at 220℃ for 6 hours.

[0055] 3. Coating Preparation: The dried mixed powder is loaded into the powder feeding device, and the preheated Q235 substrate material is transferred to the working area; the coating is prepared by plasma cladding; the spray gun height is 11mm, the welding gun swing amplitude is 15mm, the swing speed is 2040mm / min, the powder feeding speed of the powder feeding device is 95rpm, the powder feeding gas flow rate is 5L / min, the ion gas flow rate is 2.7L / min, and the shielding gas flow rate is 12L / min; the shielding gas is argon; the cladding current is 82A; the welding gun moving speed is 10mm / min; after the coating preparation is completed, it is directly air-cooled to room temperature to obtain a nickel-based composite coating.

[0056] The nickel-based composite coating prepared by the above method consists of the following phases: γ-Ni, WC, M7(B,C)3, and M... 23 (B,C)6. In this nickel-based composite coating, the WC particles are retained in a high amount and are uniformly distributed with intact morphology. The hard phases M7(B,C)3 and M 23 The (B,C)6 volume fraction is relatively high and evenly distributed throughout the coating. This nickel-based composite coating region is crack-free, exhibits relatively high porosity (0.87%), and a hardness of 65.7 HRC, demonstrating a metallurgical bond between the substrate and the coating. Based on volumetric wear rate calculations, if the wear resistance of 42CrMo steel is defined as 1, the relative wear resistance of this nickel-based composite coating reaches 8.46, exhibiting high hardness and high wear resistance.

[0057] Example 5

[0058] 1. Powder Mixing: Weigh 34.15% Ni-20% Cr powder, 2.16% B4C powder, 2.33% Fe-72% Si powder, 1.68% Mo powder, and 1.68% Cu powder according to the mass ratio, and place them together in a container. Perform preliminary stirring and grinding for 10 minutes. Then, add the pre-mixed powder, along with 1.40% of the total weight of polyacrylic acid copolymer binder, into a roller drum. The mixing speed is 18 r / min, and the mixing time is 14 h. A binder phase powder with certain fluidity and uniform mixing is obtained. Its melting point is 941.1℃.

[0059] Add 58.00% WC powder to the obtained nickel-based binder phase mixed powder and place it in a ball mill jar. The particle size range of the WC powder is 25-45 μm, and the average particle size is 31 μm. Do not add milling balls and mix at a speed of 270 r / min for 9 h. The operation mode is to alternate between clockwise and counterclockwise, change the rotation direction every 30 min, and set the tilt angle to 34°. A uniformly mixed nickel-based tungsten carbide mixed powder with good flowability is obtained.

[0060] 2. Pretreatment of the substrate: The 42Mn2 substrate was treated with a grinding wheel to remove the oxide film on the surface; it was cleaned with ethanol and then dried; the 42Mn2 substrate was preheated to 280℃ in a salt bath furnace and kept at that temperature for 5 hours.

[0061] 3. Coating Preparation: The dried mixed powder is loaded into the powder feeding device, and the preheated 42Mn2 substrate material is transferred to the working area; the coating is prepared by plasma cladding; the spray gun height is 9mm, the welding gun swing amplitude is 12mm, the swing speed is 2070mm / min, the powder feeding speed of the powder feeding device is 90rpm, the powder feeding gas flow rate is 5L / min, the ion gas flow rate is 3.0L / min, and the shielding gas flow rate is 13L / min; the shielding gas is nitrogen; the cladding current is 80A; the welding gun moving speed is 11mm / min; after the coating preparation is completed, it is transferred to a salt bath furnace and heated to 230°C to obtain a nickel-based composite coating.

[0062] The nickel-based composite coating prepared by the above method consists of the following phases: γ-Ni, WC, M7(B,C)3, and M... 23 (B,C)6. In this nickel-based composite coating, the WC particles are well-preserved and have intact morphology, but the WC distribution on the top of the coating is relatively low, and the hard phases M7(B,C)3 and M 23 The (B,C)6 content is relatively high and evenly distributed throughout the coating. This nickel-based composite coating is crack-free, has a porosity of 0.67%, a hardness of 65.9 HRC, and exhibits a metallurgical bond between the substrate and the coating. Based on volumetric wear rate calculations, if the wear resistance of 42CrMo steel is defined as 1, the relative wear resistance of this nickel-based composite coating reaches 9.01, demonstrating high hardness and high wear resistance.

Claims

1. A method for preparing a nickel-based composite coating with uniformly distributed tungsten carbide, characterized in that: Includes the following steps: Step (1): Powder mixing: Taking the preparation of 1 kg of nickel-based tungsten carbide mixed powder as an example: Binder phase powder mixing: Take 284.6g~365.9g Ni-20%Cr powder, 18.0g~23.1g B4C powder, 19.4g~25.0g Fe-72%Si powder, 14.0g~18.0g Mo powder, and 14.0g~18.0g Cu powder; the total amount of binder phase powder formed by the above powders is 350~450g; put these together into a container and perform preliminary stirring and grinding for 10min; add the preliminary mixed powder and 4.50~5.25g of polyacrylic acid copolymer binder into a roller or V-shaped barrel for powder mixing; set the powder mixing speed to 18~22r / min and the mixing time to 9~14h; obtain a nickel-based binder phase mixed powder with certain fluidity and uniform mixing. Preparation of nickel-based tungsten carbide powder: 550 g to 650 g of WC powder was added to the obtained nickel-based binder phase mixed powder and placed in a ball mill jar; the particle size range of the WC powder was 25 to 150 μm; without adding milling balls, the mixture was stirred at a speed of 200 to 300 r / min for 8 to 12 hours; the operation mode was clockwise and counterclockwise alternating, changing the rotation direction every 30 minutes, and the tilt angle was set at 30 to 40°; a dry, uniformly mixed nickel-based tungsten carbide mixed powder with good flowability was obtained. Step (2): Pretreatment of the matrix material: The substrate surface is cleaned by sandblasting or grinding with a grinding wheel to remove the oxide film and achieve a certain degree of surface roughening; after treatment, the substrate material is cleaned with ethanol or propanol and dried; the substrate is preheated to 200-300℃ and held at that temperature for 4-7 hours; the substrate types used include carbon steel and alloy steel; the substrate preheating equipment includes box furnace, muffle furnace, tube furnace, and salt bath furnace; Step (3): Coating preparation: The uniformly mixed powder is loaded into the powder feeding device of the coating preparation equipment, and the substrate material is transferred to the working area; the coating is prepared by plasma welding. The spray gun height for plasma cladding is 9–11 mm, the gun swing amplitude is 12–15 mm, the swing speed is 2000–2100 mm / min, and the gun movement speed is 10–13 mm / min. The powder feeding device has a powder feeding speed of 90–110 rpm, a powder feeding gas flow rate of 5–7 L / min, an ion gas flow rate of 2.5–3 L / min, and a shielding gas flow rate of 11–13 L / min. The shielding gases include argon and nitrogen. The cladding current is 80–90 A. After the coating is prepared, it is cooled directly to room temperature in air, or slowly cooled by wrapping it with asbestos, or kept at 200-240℃ for 2-4 hours using heat treatment equipment; the heat treatment equipment includes box furnace, muffle furnace, and salt bath furnace; thus obtaining a nickel-based composite coating; In the above coating preparation process, a relatively low welding current of 80-90A was used to achieve good metallurgical bonding and few coating defects. The B4C in the mixed powder can effectively reduce the preparation temperature required for the coating, and when combined with plasma transfer arc welding, the coating can be prepared. In this nickel-based composite coating, WC particles are uniformly distributed in the coating area, and hard phase particles M7(B,C)3 and M are also present. 23 (B,C)6 plays a role in improving the hardness and wear resistance of the coating; the nickel-based composite coating did not show cracking defects, the porosity was only 0.09-0.85%, the structure was dense, and it could achieve good metallurgical bonding between the coating and the substrate; the hardness of the nickel-based composite coating reached 65.7-68.0 HRC, and the wear resistance of 42CrMo steel was defined as 1. The relative wear resistance of the prepared nickel-based composite coating reached 8.46-10.53, which has the characteristics of high hardness and high wear resistance.

2. A nickel-based composite coating with uniformly distributed tungsten carbide, characterized in that, The nickel-based composite coating is prepared by the preparation method described in claim 1.

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