A corrosion and abrasion resistant composite coating and a method for preparing the same

Abstract

This invention belongs to the field of surface strengthening technology, specifically relating to a composite coating resistant to cavitation and abrasion and its preparation method. The preparation method of the composite coating resistant to cavitation and abrasion provided by this invention includes the following steps: (1) preparing a high-elasticity alloy coating on the substrate surface using laser cladding technology; (2) preparing a hard alloy coating on the surface of the high-elasticity alloy coating using flame spraying; and (3) preparing a sealing protective layer on the surface of the hard alloy coating. This method uses laser cladding technology to achieve metallurgical bonding between the high-elasticity alloy coating and the substrate, improving the bonding force between the coating and the substrate, and also has high processing precision, maintaining high quality even for thinner coatings; the hard alloy coating formed by flame spraying has high hardness and good wear resistance, further improving the cavitation and abrasion resistance of the composite coating.

Description

Technical Field

[0001] This invention belongs to the field of surface strengthening technology, specifically relating to a composite coating resistant to cavitation and abrasion and its preparation method. Background Technology

[0002] Cavitation and erosion can severely damage power flow components such as turbines, ship propellers, and water pumps, reducing operating efficiency and even causing damage to flow components, affecting the operation of the machine and creating major safety hazards. They can also shorten the service life of flow components, and the high annual maintenance and repair costs indirectly cause significant economic losses, seriously restricting the development of industries such as shipbuilding, water conservancy and hydropower.

[0003] Modifying the surface of components and applying anti-cavitation and anti-erosion coatings to reduce or offset damage is an economical, easy-to-apply, and widely used protective method. Anti-cavitation and anti-erosion coatings include metallic coatings (including cermet coatings) and organic coatings. Metallic coatings have excellent mechanical and heat resistance properties and are widely used in many fields. However, the high hardness of traditional metallic coatings (including cermet coatings) often leads to high porosity and easy cracking, affecting service life and preventing them from fully realizing their performance advantages. High elastic modulus metals such as shape memory alloys, multi-component reinforced alloys, and amorphous alloys can combine high strength and high toughness, and have good cavitation resistance, but their wear resistance is generally average. Organic coatings are easily affected by internal and external factors such as temperature, water, oxygen, and pollutants, resulting in aging phenomena such as powdering, peeling, and reduced adhesion.

[0004] Therefore, it is essential to develop multifunctional coating materials that resist cavitation and abrasion in the harsh working conditions of industries such as shipbuilding, water conservancy and hydropower. Summary of the Invention

[0005] This invention is based on the inventor's discoveries and understanding of the following facts and problems:

[0006] CN201811109146.4 discloses a plasma-clad copper-based shape memory alloy anti-cavitation coating and its preparation method. This plasma-clad copper-based shape memory alloy anti-cavitation layer has a smooth surface, free from defects such as cracks and pores, and exhibits good anti-cavitation and wear resistance. However, this coating is prepared using gas-shielded welding, plasma spraying, or micro-beam plasma welding of alloy materials, resulting in a physical bond between the functional layer and the substrate, leading to poor adhesion. Furthermore, the copper-based alloy has low hardness; under real-world continuous operation, when the sealing layer is damaged, the wear resistance is poor, the coating is prone to failure, and its durability is low.

[0007] CN201710288314.X discloses a method for preparing a ceramic-based composite coating resistant to seawater cavitation. The method involves sequentially spraying a metal transition layer and an Al2O3-based or ZrO2-based ceramic coating onto a metal substrate using atmospheric plasma spraying equipment. An epoxy resin and triethylenetetramine are mixed uniformly and then applied to the surface of the ceramic coating, followed by impregnation and curing. The coating obtained by this method has high hardness and good abrasion resistance, but it is prone to cracking and has poor cavitation resistance. Furthermore, the organic sealing agent used is not resistant to instantaneous high temperatures and is prone to failure under continuous impact from air bubbles. The coating prepared using atmospheric plasma spraying is only physically bonded to the substrate, resulting in poor adhesion and easy detachment.

[0008] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention propose a method for preparing a composite coating resistant to cavitation and abrasion. This method employs laser cladding technology to achieve metallurgical bonding between the highly elastic alloy coating and the substrate, improving the adhesion between the coating and the substrate. Furthermore, it offers high processing precision, maintaining high quality even for thinner coatings. The hard alloy coating formed using flame spraying improves the shear strength and bonding strength of the coating, giving it both strength and toughness, thereby further enhancing the composite coating's resistance to cavitation and abrasion.

[0009] The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to an embodiment of the present invention includes the following steps:

[0010] (1) A high-elasticity alloy coating is prepared on the substrate surface using laser cladding technology;

[0011] (2) A hard alloy coating is prepared on the surface of the high elasticity alloy coating obtained in step (1) by flame spraying.

[0012] (3) Prepare a sealing protective layer on the surface of the hard alloy coating obtained in step (2).

[0013] The advantages and technical effects of the preparation method of the cavitation and abrasion resistant composite coating in this invention are as follows: 1. The method of this invention uses laser cladding to prepare a high-elasticity alloy coating on the substrate surface, which can form a good metallurgical bond between the high-elasticity alloy coating and the substrate, resulting in high bonding strength and extending service life; 2. The high-elasticity alloy coating prepared by the laser cladding technology in this invention has high surface quality, few defects, and is not easily damaged; the method has high processing precision, and even with a small coating thickness, it can still maintain high quality, possessing excellent resistance to cavitation and abrasion, and is suitable for surface repair of complex irregular structural parts. 3. In the method of this embodiment, the hard alloy coating is prepared by flame spraying. Flame spraying has concentrated energy, uniform heating, good melting, and high kinetic energy of powder particles. The powder flies in the air for a very short time, and the temperature of the spray gun system itself is not high and it is not easily oxidized. The resulting coating has high shear strength and bonding strength. The residual internal stress in the coating is almost all compressive stress, so even a thicker coating is not prone to cracking and peeling. 4. The sealing protective layer prepared by the method of this embodiment can not only prevent air bubbles from entering the gaps and causing damage, but also reduce the residual tensile stress of the coating and transform it into compressive stress, further improving the hardness and wear resistance of the coating.

[0014] In some embodiments, in step (1), the high-elasticity alloy coating includes at least one of Fe-based high-elasticity alloy, Co-based high-elasticity alloy, and Ni-based high-elasticity alloy; and / or, the thickness of the high-elasticity alloy coating is 200 μm to 2 mm.

[0015] In some embodiments, in step (1), the laser cladding coating includes: feeding high-elasticity alloy powder into a laser and cladding under inert gas protection; wherein: the laser power is 0.5 to 10 KW, the spot size is Φ1 to 25 mm, the scanning rate is 0.5 m / min to 50 m / min, the overlap rate is 30 to 80%, and the powder feeding speed is 1 to 150 g / min.

[0016] In some embodiments, step (1) further includes performing heat treatment, grinding treatment and sandblasting treatment on the high elasticity alloy coating in sequence.

[0017] In some embodiments, in step (2), the cemented carbide coating includes at least one of tungsten carbide, chromium carbide, and niobium carbide; and / or, the thickness of the cemented carbide coating is 200 μm to 1000 μm.

[0018] In some embodiments, in step (2), the flame spraying method is a fuel-based flame spraying method or a gas-based flame spraying method; preferably, in the fuel-based flame spraying method: the fuel flow rate is 5-10 GPH, the oxygen flow rate is 1500-3000 SCFH, the powder feed rate is 30-90 g / min, and the spray distance is 100-450 mm; in the gas-based flame spraying method: propane is used as the fuel, the oxygen to propane flow ratio is 3.0-6.0, the powder feed rate is 30-90 g / min, and the spray distance is 100-300 mm.

[0019] In some embodiments, in step (3), the sealing protective layer includes at least one of polyurethane elastomer, aluminum phosphate containing nano-Al2O3, and aluminum phosphate containing MgO; and / or, the thickness of the sealing protective layer is 300-1200 μm.

[0020] In some embodiments, in step (3), when the material of the sealing protective layer is polyurethane elastomer, the sealing protective layer is prepared by spraying; when the material of the sealing protective layer is aluminum phosphate containing nano-Al2O3 or aluminum phosphate containing MgO, the sealing protective layer is prepared by vacuum impregnation.

[0021] This invention also provides a composite coating resistant to cavitation and abrasion, which is prepared using the method described above.

[0022] The advantages and technical effects of the cavitation and abrasion resistant composite coating of the present invention are as follows: 1. In the embodiments of the present invention, the sealing protective layer can not only prevent air bubbles from entering the pores and causing damage, but also reduce the residual tensile stress of the coating and transform it into compressive stress, thereby further improving the hardness and wear resistance of the coating; 2. In the embodiments of the present invention, the composite coating has both strength and toughness, thus possessing good cavitation and abrasion resistant properties and being able to adapt to complex working conditions.

[0023] In some embodiments, the thickness of the composite coating is 700 μm to 4200 μm. Attached Figure Description

[0024] Figure 1 This is a flowchart of the preparation of the cavitation-resistant and abrasion-resistant composite coating in Example 1. Detailed Implementation

[0025] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0026] The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to an embodiment of the present invention includes the following steps:

[0027] (1) A high-elasticity alloy coating is prepared on the substrate surface using laser cladding technology;

[0028] (2) A hard alloy coating is prepared on the surface of the high elasticity alloy coating obtained in step (1) by flame spraying.

[0029] (3) Prepare a sealing protective layer on the surface of the hard alloy coating obtained in step (2).

[0030] The method for preparing the cavitation and abrasion resistant composite coating of this invention employs laser cladding to prepare a high-elasticity alloy coating on the substrate surface. This allows the high-elasticity alloy coating to form a good metallurgical bond with the substrate, exhibiting high adhesion and extending service life. The high-elasticity alloy coating prepared by laser cladding technology has high surface quality, few defects, and is not easily damaged. This method has high processing precision, maintaining high quality even with a small coating thickness, and possesses excellent resistance to cavitation and abrasion. It is also suitable for surface repair and strengthening of complex irregular structural parts. The hard alloy coating is prepared by flame spraying. Flame spraying has concentrated energy, uniform heating, good melting, and high powder particle kinetic energy. The powder has a very short flight time in the air, and the spray gun system itself has a low temperature, making it less prone to oxidation. The resulting coating has high shear strength and bonding strength, and the residual internal stress within the coating is almost entirely compressive stress, making even thicker coatings less prone to cracking and peeling. The prepared sealing protective layer not only prevents air bubbles from entering the pores and causing damage but also reduces the residual tensile stress of the coating and transforms it into compressive stress, further improving the coating's hardness and wear resistance.

[0031] In some embodiments, preferably, in step (1), the high-elasticity alloy coating includes at least one of Fe-based high-elasticity alloy, Co-based high-elasticity alloy, and Ni-based high-elasticity alloy; and / or, the thickness of the high-elasticity alloy coating is 200 μm to 2 mm. More preferably, the Fe-based high-elasticity alloy includes at least one of Fe-Cr-(Mo)-PC, Fe-Cr-Ni, and Fe-Cr-B; the Co-based high-elasticity alloy includes Co-Cr-Mo; and the Ni-based high-elasticity alloy includes at least one of Ni-Cr and Ni-Cu.

[0032] In this embodiment of the invention, the constituent materials of the high-elasticity alloy coating are preferred. This type of alloy has a high elastic limit, high strength, high hardness, and low hysteresis effect, and selectively possesses properties such as corrosion resistance, temperature resistance, and fatigue resistance. The high-elasticity alloy coating made from this material serves as an energy buffer layer, which can buffer the force generated when the substrate surface is impacted, preventing the impact force from directly reaching the component surface, thereby achieving a protective effect. The high-elasticity alloy coating has a high elastic modulus and is not easily deformed. The stress generated between the coating and the substrate is small, so the bonding surface is less prone to defects and cracks, which is beneficial to protecting the bonding strength of the coating and thus protecting the mechanical properties of the substrate. This can further improve the cavitation and abrasion resistance of the composite coating.

[0033] In some embodiments, preferably, in step (1), the laser cladding coating includes: feeding high-elasticity alloy powder into a laser and cladding under inert gas protection; wherein: the particle size of the high-elasticity alloy powder is in the range of 15μm to 180μm, the laser power is 0.5 to 10KW, the spot size is Φ1 to 25mm, the scanning rate is 0.5m / min to 50m / min, the overlap rate is 30% to 80%, and the powder feeding speed is 1 to 150g / min. More preferably, the laser is selected from any one of a CO2 laser, a YAG laser, or a fiber laser. Even more preferably, step (1) further includes sequentially performing heat treatment, grinding treatment, and sandblasting treatment on the high-elasticity alloy coating.

[0034] In this embodiment of the invention, the process parameters of laser cladding technology are preferred, which can improve the consistency of the high-elasticity alloy coating and further improve the bonding force between the coating and the substrate. Heat treatment of the high-elasticity alloy coating can eliminate residual stress, and surface grinding can remove protrusions. Sandblasting can then be used to roughen the surface, which can prepare for the preparation of the hard alloy coating, thereby improving the bonding force between the high-elasticity alloy coating and the hard alloy coating and extending the service life of the coating.

[0035] In some embodiments, preferably, in step (1), the substrate is pretreated before applying the high-elasticity alloy coating. More preferably, the pretreatment includes sequential surface cleaning and surface roughening treatment. The surface cleaning includes at least one of solvent cleaning, flame heating, acid immersion treatment, mechanical grinding, and sandblasting. The surface roughening treatment uses sandblasting, and the abrasive used includes at least one of quartz sand, alumina sand, and chilled iron sand.

[0036] In this embodiment of the invention, cleaning the surface can remove oil, rust, paint, etc. from the substrate surface, making the component surface clean; further roughening the substrate surface can enhance the adhesion between the coating and the substrate and eliminate stress effects.

[0037] In some embodiments, preferably, in step (2), the cemented carbide coating includes at least one of tungsten carbide, chromium carbide, and niobium carbide; and / or, the thickness of the cemented carbide coating is 200 μm to 1000 μm.

[0038] In this embodiment of the invention, the material of the cemented carbide coating is preferred, so that the resulting cemented carbide coating has high hardness and can provide high strength, and can withstand greater impact and cutting forces.

[0039] In some embodiments, preferably, in step (2), the flame spraying method is a fuel-based flame spraying method or a gas-based flame spraying method; preferably, in the fuel-based flame spraying method: the fuel flow rate is 5-10 GPH, the oxygen flow rate is 1500-3000 SCFH, the powder feed rate is 30-90 g / min, and the spray distance is 100-450 mm; in the gas-based flame spraying method: propane is used as the fuel gas, the oxygen to propane flow ratio is 3.0-6.0, the powder feed rate is 30-90 g / min, and the spray distance is 100-300 mm. More preferably, hard alloy powder is prepared for spraying to prepare a hard alloy coating, the particle size of the hard alloy powder is 5-150 μm, and before spraying, the hard alloy powder is heated to 120°C in a drying oven and kept at that temperature for half an hour. Even more preferably, the high-elasticity alloy coating is preheated by the flame of the spray gun before spraying.

[0040] In this embodiment of the invention, the process parameters of the flame spraying method are preferred, which can improve the consistency of the cemented carbide coating, reduce the formation of defects, and further improve the cavitation and abrasion resistance of the composite coating. The alloy powder is heated and dried before spraying to prevent it from getting damp and clumping, thus improving the processing efficiency. The preheating treatment can eliminate the moisture on the surface of the workpiece and further improve the bonding strength between the coatings.

[0041] In some embodiments, preferably, in step (3), the sealing protective layer comprises at least one of a polyurethane elastomer coating, aluminum phosphate containing nano-Al2O3, and aluminum phosphate containing MgO; and / or, the thickness of the sealing protective layer is 300–1200 μm. More preferably, the aluminum phosphate containing nano-Al2O3 has an Al2O3 content of 1–10 wt.% and an Al2O3 particle size of 100–800 nm; and the aluminum phosphate containing MgO has an MgO content of 1–10 wt.%.

[0042] In this embodiment of the invention, the preferred composition material of the sealing protective layer is a material that is harmless to the human body and will not cause water pollution when used in hydraulic machinery. This material also gives the sealing protective layer high wettability, adhesion and chemical stability, as well as strong corrosion resistance and impact resistance.

[0043] In some embodiments, preferably, in step (3), when the material of the sealing protective layer is polyurethane elastomer, the sealing protective layer is prepared by spraying; when the material of the sealing protective layer is aluminum phosphate containing nano-Al2O3 or aluminum phosphate containing MgO, the sealing protective layer is prepared by vacuum impregnation.

[0044] More preferably, the spraying method includes: mixing polyurethane elastomer with solvent, spraying it onto the surface of hard alloy coating using a spray gun, using multiple spraying passes, drying each layer after spraying before applying the next layer, until the thickness reaches 300-1200 μm; the spraying temperature should be controlled between 5℃ and 35℃, and the relative humidity should be less than 80%.

[0045] The impregnation method includes: immersing the coated substrate in a sealing agent, impregnating it in a vacuum device for 10-30 minutes, curing it at room temperature and pressure for 8-30 hours, and then placing it in a heating and insulation device to cure it at 400-800°C for 1-6 hours, repeating the above operation 2-5 times. In some embodiments, preferably, step (3) further includes surface treatment of the sealing protective layer.

[0046] In this embodiment of the invention, surface treatment of the sealing protective layer can remove uneven and non-uniform components and process the substrate to a suitable surface roughness and shape for operation.

[0047] This invention also provides a composite coating resistant to cavitation and abrasion, which is prepared using the method described above.

[0048] The cavitation and abrasion resistant composite coating of this invention has a sealing and protective layer that not only prevents air bubbles from entering the pores and causing damage, but also reduces the residual tensile stress of the coating and transforms it into compressive stress, further improving the hardness and wear resistance of the coating. This composite coating has both strength and toughness, thus possessing good cavitation and abrasion resistance and being able to adapt to complex working conditions.

[0049] In some embodiments, preferably, the thickness of the composite coating is 700 μm to 4200 μm.

[0050] In this embodiment of the invention, the coating of this thickness can effectively buffer the impact force on the surface of the component and provide a certain strength, forming a protective mechanism for the substrate. However, for some workpieces with more complex shapes, the coating thickness should not be too thick, so as not to damage the structure of the component and increase the weight too much, thereby affecting the normal and stable operation of the component.

[0051] The technical solution of the present invention will now be described in detail with reference to specific embodiments and accompanying drawings.

[0052] Example 1

[0053] The flowchart for preparing the cavitation- and abrasion-resistant composite coating in this embodiment is as follows: Figure 1 As shown.

[0054] (1) Substrate pretreatment: 304 stainless steel is selected as the substrate. Oil stains, rust and other impurities on the surface are cleaned and debris and dust are removed. Quartz sand is used to sandblast the surface to roughen it to Ra 4μm.

[0055] (2) Applying a high-elasticity alloy coating: Selecting spherical AlSi with a particle size of 15–45 μm. 10 Mg alloy powder with a sphericity >95% should be dried before use to prevent moisture and clumping. The alloy powder is fed into a CO2 laser and clad under inert gas protection. The laser power is set to 6-10KW, the spot size is Φ3.3mm, the scanning rate is 8.5m / min, the overlap rate is 55%, and the powder feeding speed is 70g / min.

[0056] A high-elasticity alloy coating with a thickness of 350μm was obtained by cladding, and then heat treatment was performed to eliminate residual stress. The surface was then polished to remove protrusions, and then sandblasted to roughen the surface, in preparation for the preparation of the second coating layer.

[0057] (3) Preparation of hard alloy coating: Select Cr3C2-WC powder with a particle size range of 10-30μm, place the powder in a drying oven and heat it to 120℃, keep it at that temperature for half an hour; select Praxair JP5000 spraying equipment, set the fuel flow rate to 6.5GPH, the oxygen flow rate to 1800SCFH, the powder feed rate to 90g / min, and the spray distance to 330mm;

[0058] Before spraying, the surface of the sample is preheated by the flame of the spray gun, and a hard alloy coating with a thickness of 1000μm is obtained by spraying.

[0059] (4) Preparation of sealing protective layer: Polyurethane elastomer coating is selected as the sealing layer material. The surface of the material is simply sanded until it is flat, epoxy primer is brushed on, and after drying, polyurethane elastomer coating is sprayed with a hand-held spray gun. Each coat is 100μm thick until the coating thickness is 1mm. After each coat is sprayed, it is dried once. The construction temperature should be controlled between 5℃ and 35℃, and the relative humidity should be less than 80%. Finally, the uneven parts of the surface are removed to complete the preparation of the sealing protective layer.

[0060] Example 2

[0061] (1) Substrate pretreatment: Low carbon steel is selected as the substrate. Oil stains, rust and other impurities on the surface are cleaned and debris and dust are removed. Quartz sand is used to sandblast the surface to roughen it to Ra 2.5μm.

[0062] (2) Applying a high-elasticity alloy coating: Selecting spherical NiCr with a particle size of 15–45 μm. 20 Alloy powder with a sphericity >95% should be dried before use to prevent moisture and clumping. The alloy powder is fed into a CO2 laser and clad under inert gas protection. The laser power is set to 10-12KW, the spot size is Φ6mm, the scanning rate is 15m / min, the overlap rate is 80%, and the powder feeding speed is 90g / min.

[0063] A 200μm thick high-elasticity alloy coating is obtained by cladding, followed by heat treatment to eliminate residual stress, surface grinding to remove protrusions, and then sandblasting to roughen the surface in preparation for the preparation of the second coating layer.

[0064] (3) Preparation of cemented carbide coating: Select WC-10Co-4Cr powder with a particle size range of 8-35μm, place the powder in a drying oven and heat it to 120℃, and keep it at that temperature for half an hour; select a gas-fired spraying equipment, set the propane flow rate to 33L / min, the oxygen flow rate to 100L / min, the powder feed rate to 45g / min, and the spray distance to 200mm;

[0065] Before spraying, the surface of the sample is preheated by the flame of the spray gun, and a hard alloy coating with a thickness of 700μm is obtained by spraying.

[0066] (4) Preparation of sealing protective layer: Aluminum phosphate containing ZnO is selected as sealing material. Aluminum phosphate is prepared by diluting a solution of aluminum hydroxide (Al(OH)3) and orthophosphoric acid (85% H3PO4) with deionized water. The molar ratio of Al(OH)3:H3PO4 P / Al is about 3.5. The solution is mixed and heated slightly on a magnetic stirrer. 4.5wt.% ZnO particles are added to the solution and stirred to obtain a well dispersed sealing agent.

[0067] The workpiece is immersed in aluminum phosphate sealing agent, immersed in vacuum equipment for 30 minutes, cured at room temperature and pressure for 8 hours, and then placed in an oven to heat and cure at 450℃ for 3 hours. The above immersion and heat treatment operation is repeated 3 times to complete the sealing treatment. Finally, the surface is polished.

[0068] Example 3

[0069] (1) Substrate pretreatment: ZG06Cr13Ni4Mo was selected as the substrate. Oil stains, rust and other impurities on the surface were cleaned and debris and dust were removed. Quartz sand was used to sandblast the surface to roughen it to Ra 4.5μm.

[0070] (2) Coating with a high-elasticity alloy coating: Select spherical NiCoCrFe alloy powder with a particle size of 45-105μm. Dry it before use to prevent moisture and clumping. Put the alloy powder into a CO2 laser and perform cladding under inert gas protection. Set the laser power to 5-8KW, the spot size to Φ5mm, the scanning rate to 5m / min, the overlap rate to 60%, and the powder feeding speed to 75g / min.

[0071] A high-elasticity alloy coating with a thickness of 400μm was obtained by cladding, and then heat treatment was performed to eliminate residual stress. The surface was then polished to remove protrusions, and then sandblasted to roughen the surface, in preparation for the preparation of the second coating layer.

[0072] (3) Preparation of hard alloy coating: Select WC-10Co-4Cr powder with a particle size range of 15-30μm, place the powder in a drying oven and heat it to 120℃, keep it at that temperature for half an hour, select Praxair JP8000 spraying equipment, set the fuel flow rate to 6.5GPH, the oxygen flow rate to 1950SCFH, the powder feed rate to 75g / min, and the spray distance to 380mm;

[0073] Before spraying, the surface of the sample is preheated by the flame of the spray gun, and a hard alloy coating with a thickness of 800μm is obtained by spraying.

[0074] (4) Preparation of sealing protective layer: Aluminum phosphate containing nano-Al2O3 is selected as sealing agent. Aluminum phosphate is prepared by diluting a solution of aluminum hydroxide (Al(OH)3) and orthophosphoric acid (85% H3PO4) with deionized water. The molar ratio of Al(OH)3:H3PO4 P / Al is about 3.2. The solution is mixed and heated slightly on a magnetic stirrer. 5 wt.% of alumina nanoparticles are added to the solution and stirred to obtain a well dispersed sealing agent.

[0075] The workpiece is immersed in aluminum phosphate sealing agent and impregnated in a vacuum device for 30 minutes. After curing at room temperature and pressure for 12 hours, it is then placed in an oven and cured at 400℃ for 2 hours. The above impregnation and heat treatment operations are repeated 3 times to complete the sealing process. Finally, the surface is polished.

[0076] Comparative Example 1

[0077] (1) Clean the 3mm thick stainless steel substrate and pre-treat the surface with 60-mesh brown corundum sand to make its roughness meet the requirements of spraying.

[0078] (2) A NiCrAlY alloy coating with a thickness of 30 μm was prepared on the substrate surface by supersonic flame spraying. The parameters used were: the pressures of oxygen, propane and compressed air were 1.8 MPa, 0.4 MPa and 0.6 MPa, respectively, and the flow rates were 550 slpm, 60 slpm and 400 slpm, respectively. The powder feeding gas pressure was 0.6 MPa, the flow rate was 10-20 slpm, the powder feeding rate was 60 g / min, and the spraying distance was 200 mm.

[0079] (3) A ceramic coating with a thickness of 80 μm was prepared on the surface of the alloy transition layer by plasma spraying. The material of the ceramic coating was ZrO2. The parameters used were: the pressure of argon and hydrogen was 0.4 MPa and 0.2 MPa, respectively, and the flow rates were 40 slpm and 3 slpm, respectively; the powder feeding gas pressure was 0.08 MPa, the flow rate was 3 slpm, and the powder feeding rate was 30 g / min; the current during the spraying process was 600 A, the voltage was 60 V, and the spraying distance was 110 mm.

[0080] (4) Add 1.2wt% Al to Na2SiO3 inorganic sealing agent, apply the coating by brushing, and finally dry it at room temperature.

[0081] Comparative Example 2

[0082] In this comparative example, ZG06Cr13Ni4Mo was selected as the substrate, and no coating was prepared on its surface.

[0083] Comparative Example 3

[0084] The preparation method of this comparative example is the same as that of Example 1, except that step (2) is omitted.

[0085] Comparative Example 4

[0086] The preparation method of this comparative example is the same as that of Example 1, except that step (3) is omitted.

[0087] Comparative Example 5

[0088] The preparation method of this comparative example is the same as that of Example 1, except that: in step (2), a high-elasticity alloy coating is prepared by supersonic flame spraying. The specific process parameters are: a propane gas fuel spraying equipment is selected, the oxygen flow rate is set to 800 / L*min, the powder feed rate is 80g / min, and the spray distance is 350mm; the thickness of the prepared coating is 360μm.

[0089] The coatings prepared in Examples 1-3, Comparative Examples 1, 3-5, and Comparative Example 2 were tested for their resistance to cavitation and erosion. The results are shown in Table 1. The test conditions were as follows:

[0090] The cavitation resistance performance was tested according to the national standard GBT6383 using a vibration cavitation tester. The vibration head was 1 mm away from the sample, the vibration frequency was 20 kHz, the temperature was 20 ℃, and the test time was 12 hours. The average weight loss rate within 12 hours was calculated.

[0091] The abrasion resistance was tested using a mud abrasion tester. The slurry was sand, the rotation speed was 650 m / min, and the test time was 48 h. The erosion rate was calculated as: Erosion rate = Erosion weight loss ÷ Specimen weight * 100%.

[0092] Table 1

[0093]

[0094]

[0095] As can be seen from the data in the table above, after preparing a high-elasticity alloy coating on the substrate surface using laser cladding technology and a hard alloy coating using flame spraying, the composite coating has very good resistance to cavitation and abrasion. Even under very harsh conditions, the average weight loss rate in the 12-hour cavitation test is less than 6.8 mg / h, and the erosion rate in the 48-hour abrasion test is less than 2.5%.

[0096] Comparative Example 1 uses supersonic spraying to prepare NiCrAlY alloy coating and plasma spraying to prepare ceramic coating. Since the functional coating prepared by this method is physically bonded to the substrate, the bonding force is poor, the coating is prone to cracking, and the cavitation erosion resistance is poor. The average weight loss rate in the 12-hour cavitation erosion test reached 10.65 mg / h.

[0097] Comparative Example 2 uses ZG06Cr13Ni4Mo as the substrate and does not prepare a coating on its surface. The test results show that the substrate without coating treatment has poor resistance to cavitation erosion and abrasion erosion, which cannot meet the application requirements of related fields.

[0098] Compared with Example 1, Comparative Example 3 did not coat the substrate surface with a high-elasticity alloy coating, but only prepared a hard alloy coating. The hard alloy coating still had relatively good wear and corrosion resistance. However, since there was no high-elasticity alloy coating as an energy buffer layer, it could not buffer the force when the coating was impacted, resulting in poor cavitation erosion resistance. The average weight loss rate of the cavitation erosion test reached 8.22 mg / h in 12h.

[0099] Compared with Example 1, Comparative Example 4 only coated the substrate surface with a high-elasticity alloy coating and did not prepare a hard alloy coating. The high-elasticity alloy coating can buffer the impact force on the coating and has relatively good cavitation resistance. However, the high-elasticity alloy coating has low hardness and poor abrasion resistance. The erosion rate reached 3.7% in the 48-hour abrasion test.

[0100] Compared with Example 1, Comparative Example 5 used supersonic flame spraying to prepare a high-elasticity alloy coating. Since the high-elasticity alloy coating only formed a physical bond with the substrate, the bonding force was poor, resulting in the composite coating's resistance to cavitation erosion and abrasion erosion being inferior to that of Example 1.

[0101] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0102] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A method for preparing a composite coating resistant to cavitation and abrasion, characterized in that, Includes the following steps: (1) A high-elasticity alloy coating is prepared on the substrate surface using laser cladding technology; the high-elasticity alloy coating is AlSi 10 The Mg alloy has a high-elasticity alloy coating with a thickness of 200~350μm; the laser cladding coating technology includes: feeding alloy powder into a CO2 laser, cladding under inert gas protection, setting the laser power to 6~10 KW, the spot size to Φ3.3 mm, the scanning rate to 8.5 m / min, the overlap rate to 55%, and the powder feeding speed to 70 g / min; (2) A hard alloy coating is prepared on the surface of the high elasticity alloy coating obtained in step (1) by flame spraying. (3) Prepare a sealing protective layer on the surface of the hard alloy coating obtained in step (2).

2. The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to claim 1, characterized in that, The step (1) also includes heat treatment, grinding and sandblasting of the high elasticity alloy coating in sequence.

3. The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to claim 1, characterized in that, In step (2), the cemented carbide coating includes at least one of tungsten carbide, chromium carbide, and niobium carbide; and / or, the thickness of the cemented carbide coating is 200 μm to 1000 μm.

4. The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to claim 1 or 3, characterized in that, In step (2), the flame spraying method is either a fuel-based flame spraying method or a gas-based flame spraying method.

5. The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to claim 4, characterized in that, In the fuel-based flame spraying method: the fuel flow rate is 5~10 GPH, the oxygen flow rate is 1500~3000 SCFH, the powder feed rate is 30~90 g / min, and the spray distance is 100~450 mm; in the gas-fired flame spraying method: propane is used as the fuel gas, the oxygen to propane flow ratio is 3.0~6.0, the powder feed rate is 30~90 g / min, and the spray distance is 100~300 mm.

6. The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to claim 1, characterized in that, In step (3), the sealing protective layer includes at least one of polyurethane elastomer, aluminum phosphate containing nano-Al2O3, and aluminum phosphate containing MgO; and / or, the thickness of the sealing protective layer is 300~1200μm.

7. The method for preparing the cavitation-resistant and abrasion-resistant composite coating according to claim 6, characterized in that, In step (3), when the material of the sealing protective layer is polyurethane elastomer, the sealing protective layer is prepared by spraying; when the material of the sealing protective layer is aluminum phosphate containing nano-Al2O3 or aluminum phosphate containing MgO, the sealing protective layer is prepared by vacuum impregnation.

8. A composite coating resistant to cavitation and abrasion, characterized in that, It is prepared by the method described in any one of claims 1 to 7.

9. The cavitation-resistant and abrasion-resistant composite coating according to claim 8, characterized in that, The thickness of the composite coating is 700μm~4200μm.

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