A method for preparing a reinforced and toughened composite coating

Abstract

The present invention provides a method for preparing a reinforced and toughened composite coating, comprising the following steps: S1, heating a reinforcing phase powder having a layered structure to obtain a first reinforcing phase powder; S2, vacuum filtering the first reinforcing phase powder to eliminate air in the interlayer gaps to obtain a second reinforcing phase powder; S3, dissolving a metal salt in a solvent, stirring until completely dissolved, and dropwise adding a coupling agent to obtain a metal-based precursor solution; S4, mixing the metal-based precursor solution with the second reinforcing phase powder under vacuum conditions to obtain a first mixed solution; S5, heating and drying the first mixed solution to obtain a first composite powder; S6, heat-treating the first composite powder at 250-350°C to obtain a second composite powder; S7, mixing the second composite powder with a metal-based nanopowder, and preparing a composite coating by plasma spraying. The preparation method of the present invention ensures that the reinforcing phase powder is well bonded to the metal interface and is evenly dispersed, thereby achieving the purpose of strengthening and toughening the composite coating.

Description

Technical Field

[0001] The present invention relates to the field of composite material manufacturing, and in particular to a method for preparing a reinforced and toughened composite coating. Background Art

[0002] Metal-based composite coating is a high-performance composite coating obtained by combining metal-based nanoparticles with metal or non-metallic reinforcing phase materials and then applying them to a substrate through methods such as laser cladding and high-temperature spraying. The composite coating can protect the substrate and improve the mechanical properties of the substrate. Currently, nano or quasi-nano materials with a layered structure are usually used as reinforcing phases. Such materials can refine grains, hinder dislocations, and transfer loads, thereby improving the strength and toughness of the composite coating. In existing preparation methods, the powdered reinforcing phase is first fully mixed with metal-based nanoparticles (metal, alloy, or metal oxide, etc.), for example, by ultrasonic dispersion, wet mechanical stirring mixing, ball milling, planetary high-energy ball milling, etc., and then the mixed composite powder is subjected to high-temperature spraying to finally obtain the desired composite coating on the target substrate. However, in existing preparation methods, there are usually problems such as poor mixing uniformity of metal-based nanoparticles and reinforcing phase materials, more pores in the composite coating, and less than ideal mechanical properties such as strength and toughness.

[0003] Porous carbon materials, with their lower density and higher specific surface area, are ideal materials for reinforcing phases. MXene and graphene have been the most studied of these materials. MXene is a type of transition metal carbide or nitride nanomaterial, produced by etching methods and exhibiting an accordion-like two-dimensional lamellar structure. However, direct solid-state mixing has proven ineffective in fully dispersing metal powders within MXene powders. Due to MXene's unique accordion-like structure, uniformly and controllably inserting large amounts of metal powder into the interlayers of the MXene is extremely difficult. Furthermore, van der Waals forces between the MXene layers easily lead to metal powder agglomeration. Furthermore, the lack of adhesion between the metal powder and the MXene reduces load transfer efficiency. This uneven dispersion of MXene and metal powders ultimately results in a high number of pores in the composite coating, reduced mechanical properties, and a shift in the fracture mechanism from ductile to brittle fracture. Consequently, the toughness and strength of MXene-based composite coatings prepared using existing methods are suboptimal.

[0004] Graphene is a two-dimensional honeycomb-like single-element material composed of sp2-hybridized carbon atoms. Similar to MXene, the primary issue currently hindering the research and development of graphene-metal matrix composites lies in the dispersion of graphene within the metal matrix. As the dispersion of graphene within the metal matrix increases, the contact area between graphene and matrix molecules increases, expanding the range of graphene's interaction with the matrix material and leading to an increase in the "adsorption and solidification" region within the matrix. When graphene is stacked (poorly dispersed), only the matrix molecules surrounding the graphene can undergo "adsorption and solidification," while matrix molecules further from the graphene surface are largely unaffected by the graphene. Consequently, due to the strong van der Waals forces between graphene sheets, graphene clusters tend to aggregate, making composites more prone to fracture than those with a uniform distribution. Uneven graphene distribution can significantly negatively impact material properties. A secondary issue lies in the interfacial bonding between graphene and the metal matrix. The interfacial bonding between the metal matrix and graphene is the primary factor determining the mechanical properties of the composite. During the preparation of graphene-reinforced metal-based composites, graphene may adhere to the surface of metal particles during the grinding process and react with the interface between the metal matrix during mechanical alloying and subsequent sintering to form carbides. Moreover, the graphene surface has wrinkles and defects, which can become reaction sites between graphene and metal, and also generate carbides. This is a brittle phase with hygroscopicity. Its presence in large quantities in the composite material may cause the composite material's strength to decrease. At the same time, in the traditional ball milling method for preparing mixed powders, the ball milling process consumes a lot of energy and takes a long time. Excessive grinding time may cause the graphene structure to be destroyed and also result in more pores in the composite material, resulting in reduced mechanical properties of the composite material and a transition from ductile fracture to brittle fracture. In addition, at this stage, the preparation of single-layer or few-layer graphene is relatively complex and expensive, making large-scale industrial applications difficult to bear.

[0005] In summary, the prior art still lacks a method for preparing a metal-based composite material coating that can obtain high strength and high toughness. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing a reinforced and toughened composite coating in response to the problems existing in the prior art.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is:

[0008] A method for preparing a reinforced and toughened composite coating, the method comprising the following steps:

[0009] S1. Heating a reinforcing phase powder having a layered structure to expand interlayer gaps of the reinforcing phase powder to obtain a first reinforcing phase powder;

[0010] S2. Vacuum-filtering the first reinforcing phase powder to eliminate air in the interlayer gaps to obtain a second reinforcing phase powder;

[0011] S3, dissolving the metal salt in a solvent, stirring until completely dissolved, and adding a coupling agent dropwise to obtain a metal-based precursor solution;

[0012] S4. Mixing the metal-based precursor solution and the second reinforcing phase powder under vacuum conditions to obtain a first mixed solution;

[0013] S5, heating and drying the first mixed solution to obtain a first composite powder;

[0014] S6, heat-treating the first composite powder at 250-350° C. to obtain a second composite powder;

[0015] S7. Mixing the second composite powder with metal-based nanopowder, and preparing the composite coating by plasma spraying.

[0016] In some embodiments, the reinforcing phase powder is MXene powder.

[0017] In some embodiments, the reinforcing phase powder is expanded graphite.

[0018] In some embodiments, in step S4: after the metal-based precursor solution and the second reinforcing phase powder are mixed, a butylamine solution is added dropwise to adjust the pH of the first mixed solution to 8.0-9.0.

[0019] In some embodiments, in step S1, the reinforcing phase powder is heated at a temperature of 700 to 900° C. for a heating time of 20 to 40 seconds; and in step S2, the first reinforcing phase powder is vacuum filtered for a time of 20 to 40 minutes.

[0020] In some embodiments, in step S3, the solvent is deionized water, and the coupling agent is silane coupling agent KH570; in step S5, the first mixed liquid is dried at 75-85° C. until the water is completely evaporated; and in step S6, the heat treatment time is 2.5-3.5 hours.

[0021] In some embodiments, the metal salt in step S3 is a zinc salt, and the metal-based nanopowder in step S7 is a zinc oxide nanopowder.

[0022] In some embodiments, the metal salt in step S3 is a nickel salt, and the metal-based nanopowder in step S7 is a nickel nanopowder.

[0023] In some embodiments, step S7 specifically includes the following steps:

[0024] S7-1, mixing the second composite powder and the metal-based nanopowder in a solvent at a mass ratio of 1:0.8 to 1.2 to obtain a third mixed solution, and adding a polyvinyl alcohol solution to the third mixed solution to obtain a preliminary slurry;

[0025] S7-2, atomizing the prepared slurry, and then heating and drying it to obtain a prepared powder;

[0026] S7-3, the prepared powder is formed into the composite coating by plasma spraying.

[0027] In some embodiments, in step S7-1: the second composite powder and the metal nanopowder are stirred and mixed in a solvent, the solvent is deionized water, the stirring speed is 3000-5000 r / min, and the stirring time is controlled at 3-5 hours; in terms of mass percentage, the concentration of the polyvinyl alcohol in the polyvinyl alcohol solution is 0.8%-1.2%.

[0028] In some embodiments, in step S7-2: the prepared slurry is introduced into a centrifugal atomizer through a peristaltic pump for atomization, and the atomized droplets enter a drying chamber, and the droplets are heated and dried during flight to obtain the prepared powder, and the prepared powder is collected in a collector at the lower end of the drying chamber under the action of gravity.

[0029] Due to the application of the above technical solutions, in the preparation method of the reinforced toughened composite coating provided by the present invention, the reinforcing phase powder is not directly physically mixed with the metal matrix in the solid phase, but a solution precursor method is adopted to insert metal ions on the surface of the reinforcing phase through a chemical reaction. The metal particles are firmly combined with the reinforcing phase, so that the composite material has good mechanical properties and improved tensile strength. Therefore, the interface between the reinforcing phase and the metal matrix in the composite material prepared by the chemical synthesis method is well bonded and evenly dispersed. The present invention makes full use of the layered structure of the reinforcing phase powder. First, in a liquid phase environment, metal ions of the target metal are inserted into the surface of the reinforcing phase powder and the interlayer gaps opened therein. After the metal ions are oxidized by heat treatment, a metal oxide with the same composition as the target metal-based nanopowder can be obtained. When the second composite powder is mixed with the metal-based nanopowder, the metal oxide combined in the interlayer constitutes the transition interface between the reinforcing phase and the metal-based nanopowder. In the transition interface, the energy and composition between the two phases change in a gradient, which not only enhances the direct bonding force between the two phases, but also enables the load to be uniformly and effectively conducted. In the composite coating prepared by the present invention, the reinforcing phase powder and the metal-based nanopowder can be well bonded and evenly dispersed at the interface, and the bonding surface between the two phases will generate great friction, which will prevent the further expansion and extension of the cracks, making it difficult for the cracks to penetrate, thereby achieving the purpose of strengthening and toughening the composite coating. DETAILED DESCRIPTION

[0030] The preferred embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art.

[0031] Example 1

[0032] This embodiment provides a method for preparing a MXene-based reinforced and toughened composite coating, wherein the MXene reinforcement phase has a two-dimensional layered nanostructure with accordion-shaped interlayer gaps. The preparation method is specifically implemented by the following steps:

[0033] S1. Heating the MXene powder to expand the interlayer gaps of the MXene powder to obtain a first MXene powder. In this embodiment, the MXene powder is heated in a muffle furnace at a temperature of 700 to 900° C. for 20 to 40 seconds. Specifically, the heating temperature is about 800° C. and the heating time is about 30 seconds.

[0034] S2. Vacuum filter the first MXene powder to eliminate air in the interlayer gaps of the first MXene powder, thereby obtaining a second MXene powder. The first MXene powder is vacuum filtered for 20 to 40 minutes. In this embodiment, a vacuum filtration apparatus is used to vacuum filter the first MXene powder for approximately 30 minutes, thereby maintaining open interlayer gaps in the second MXene powder while eliminating trapped air between the layers.

[0035] S3. Dissolve the metal salt in a solvent and stir until completely dissolved. During the stirring, a coupling agent is added dropwise to obtain a metal-based precursor solution, wherein the metal salt is a zinc salt. In this embodiment, the metal salt is specifically zinc acetate. The solvent is deionized water and stirring is performed using a magnetic stirrer.

[0036] S4. Under vacuum conditions, the metal-based precursor solution is mixed with the second MXene powder, ultrasonically homogenized, and butylamine solution is added dropwise during stirring to adjust the pH, and the pH of the first mixed solution is adjusted to a weak alkaline state of 8.0 to 9.0. In this embodiment, the pH of the first mixed solution is adjusted to about 8.5 to obtain a first mixed solution. Since the interlayer gaps of the second MXene powder opened above are maintained in a vacuum state, the metal-based precursor solution can be quickly and completely filled into the interlayer gaps without generating bubbles.

[0037] S5. Heat and dry the first mixed liquid to obtain a first composite powder. In this embodiment, the first mixed liquid is dried at about 80° C. until the water is completely evaporated. In this embodiment, the drying time is about 30 minutes.

[0038] S6. Heat-treating the first composite powder at 250-350°C to obtain a second composite powder for 2.5-3.5 hours. This process causes the metal ions in the above-mentioned metal salt solution to be oxidized by heat treatment and converted into metal oxides with the same composition as the target metal nanopowder, specifically zinc ions are oxidized to zinc oxide. This chemical change process constitutes a transition interface between the MXene and metal nanopowder phases. The energy and composition between the two phases change in a gradient at the transition interface, effectively increasing the compactness, mechanical properties and uniformity between the two phases. In this embodiment, the heat treatment is carried out in a muffle furnace at a treatment temperature of 280-320°C, specifically about 300°C, and the heating time is about 3 hours.

[0039] S7, mixing the second composite powder with the metal nanopowder, spraying and granulating, and preparing a composite coating by plasma spraying. In this embodiment, the metal nanopowder is specifically zinc oxide nanopowder. Step S7 specifically includes the following steps:

[0040] S7-1. Mix the second composite powder and the metal nanopowder in a solvent at a mass ratio of 1:0.8 to 1.2 to obtain a third mixed solution. Add the polyvinyl alcohol solution to the third mixed solution to obtain a preliminary slurry. In this embodiment, the second composite powder and the metal nanopowder are stirred in a solvent, specifically deionized water, at a stirring speed of 3000 to 5000 r / min for 3 to 5 hours. The concentration of the polyvinyl alcohol in the polyvinyl alcohol solution is 0.8% to 1.2% by mass. In this embodiment, the second composite powder and the metal nanopowder are mixed in deionized water at a mass ratio of approximately 1:1, at a stirring speed of approximately 4000 r / min, for approximately 4 hours.

[0041] S7-2. The prepared slurry is atomized and then heated and dried to obtain a prepared powder. In this embodiment, the slurry is introduced into a centrifugal atomizer via a peristaltic pump during atomization. The atomized droplets enter a drying chamber. During their flight, moisture in the droplets is rapidly evaporated by the high-temperature air. Due to gravity, the dried and agglomerated prepared powder is collected in a collector at the lower end of the drying chamber.

[0042] S7-3. The prepared powder is plasma sprayed to form a composite coating. In this embodiment, specifically, the dry prepared powder is carried into the plasma flame flow from the center axial direction or the inner radial direction by the powder feeding gas, quickly becoming a molten or semi-molten state. Under the dual action of the axial airflow and the tangential airflow, it is sprayed at high speed onto the substrate surface, causing plastic deformation and forming a composite coating.

[0043] This example discloses a method for preparing a composite coating using the two-dimensional nanomaterial MXene as a carbon source. The coating is primarily made by plasma spraying a layered MXene with metal nanopowders distributed between and on the outer surfaces of the MXene layers. MXene has a large surface area and low density. The large spacing between the layers, the large surface area, and the rich pore structure allow the metal nanopowders to fill and evenly disperse in the interlayer spaces. This not only increases the contact area between the MXene and the metal substrate, but also strengthens the interfacial bonding between the MXene and metal substrate, improving the mechanical properties of the material.

[0044] In this example, a favorable interfacial reaction transfers external forces exerted on the matrix of the composite material to the reinforcement phase, acting as a bridge between the matrix and reinforcement. Furthermore, the interface between the matrix and reinforcement prevents crack propagation and mitigates stress concentration. When stress is applied to the material, resulting in cracks, the interface between the tightly connected MXene layer and the metal layer within the material generates significant friction, making it difficult for the crack to penetrate, thereby strengthening and toughening the coating.

[0045] In this example, the accordion-like interlayer structure of MXene expands during heating. Under the action of an organic coupling agent, metal nanopowder is inserted into the interlayer spaces of the MXene through an in-situ synthesis method. This allows the metal and MXene layers to alternately mix and stack at the molecular level, ultimately forming a uniformly dispersed and orderly arranged metal-matrix composite coating with excellent mechanical properties such as high strength, high hardness, high wear resistance, and high ductility. The use of a coupling agent strengthens the bond between the matrix and the filler, effectively transferring the load and improving the mechanical properties of the coating.

[0046] Example 2

[0047] This embodiment provides a method for preparing an expanded graphite-based reinforced and toughened composite coating. Expanded graphite is a unique quasi-carbon nanomaterial with a three-dimensional layered porous structure. The preparation method is specifically implemented in the following steps:

[0048] S1. Heat the expandable graphite in a muffle furnace at a temperature of about 800° C. for about 30 seconds to expand the interlayer gap and obtain a first expandable graphite powder after expansion.

[0049] S2. Vacuum filtration is performed on the first expanded graphite powder for about 30 minutes to eliminate air in the interlayer gaps of the first expanded graphite powder to obtain a second expanded graphite powder.

[0050] S3. Dissolve nickel salt in deionized water, add silane coupling agent KH570, and mix evenly with a magnetic stirrer to form a nickel-based precursor solution. In this embodiment, the nickel salt is specifically nickel chloride hexahydrate.

[0051] S4. Under vacuum conditions, immerse the nickel-based precursor solution into the second expanded graphite powder and perform ultrasonic homogenization. Then, add the butylamine solution to the mixture and continuously stir to adjust the pH value to about 8.5 to obtain a first mixed solution.

[0052] S5. Dry the first mixed liquid at about 80° C. until the water is completely evaporated to obtain a first composite powder.

[0053] S6. Heat-treating the first composite powder at about 300° C. to obtain a second composite powder. The heat-treating time is 3.0 h.

[0054] S7, the second composite powder is mixed with the nickel nanopowder, spray granulated, and a composite coating is prepared by plasma spraying. The specific spray granulation and ion spraying methods are the same as those in Example 1 and are not described in detail here. In this embodiment, since the plasma arc energy is very concentrated, the powder can obtain greater kinetic energy and high temperature, thereby obtaining a coating with high density, low oxide mass fraction and porosity, and good substrate bonding performance.

[0055] This embodiment uses cheap expanded graphite as a carbon source. Expanded graphite is a unique quasi-carbon nanomaterial with a three-dimensional layered porous structure. Compared with traditional graphene, which is difficult to disperse and easily agglomerated, resulting in uneven load distribution, expanded graphite has a very large specific surface area, which can improve the mechanical locking of the metal matrix and graphene, thereby improving the stress transfer efficiency between the metal matrix and the graphite sheet. Moreover, there is more contact area between the expanded graphene and the metal matrix. It is precisely because of the increase in contact area that the bonding force between the expanded graphite and the metal matrix is also enhanced, which means that the material is destroyed and more energy is consumed. When stress is applied to the material, the expanded graphite can absorb the stress suffered by the main crack, and can effectively suppress the further growth and propagation of the crack at the crack tip, preventing the expansion of the crack and playing a toughening effect.

[0056] In this embodiment, a solution precursor method is used to prepare the composite material powder, and metal ions are generated on the surface of the reinforcement phase through chemical reaction. Therefore, the interface between the reinforcement phase and the matrix in the prepared composite material is well bonded and evenly dispersed.

[0057] Furthermore, in this embodiment, the interlayer space of the expanded graphite expands during heating. Under the action of an organic coupling agent, metal-based nanoparticles can be inserted into the interlayer space. In this way, the metal-based and reinforcement phase layers can alternately mix and stack at the molecular level, ultimately forming a composite coating with evenly dispersed and orderly arranged graphene layers. The use of a coupling agent strengthens the bond between the matrix and the filler, effectively transferring loads and improving mechanical properties.

[0058] The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a reinforced and toughened composite coating, characterized in that: The preparation method comprises the following steps: S1. Heating a reinforcing phase powder having a layered structure at 700-900° C. for 20-40 seconds to expand interlayer gaps of the reinforcing phase powder to obtain a first reinforcing phase powder, wherein the reinforcing phase powder is MXene powder or expanded graphite; S2. Vacuum filtration of the first reinforcement phase powder for 20 to 40 minutes to eliminate air in the interlayer gaps to obtain a second reinforcement phase powder; S3, dissolving the metal salt in a solvent, stirring until completely dissolved, and adding a coupling agent dropwise to obtain a metal-based precursor solution; S4. Under vacuum conditions, the metal-based precursor solution and the second reinforcing phase powder are mixed to obtain a first mixed solution, and then a butylamine solution is added dropwise to adjust the pH of the first mixed solution to 8.0-9.0, so that the metal-based precursor solution is filled into the interlayer gap; S5, heating and drying the first mixed solution to obtain a first composite powder; S6, heat-treating the first composite powder at 250-350° C. to obtain a second composite powder; S7. Mixing the second composite powder with metal-based nanopowder, and preparing the composite coating by plasma spraying.

2. The method for preparing a reinforced and toughened composite coating according to claim 1, characterized in that: In step S3: the solvent is deionized water, and the coupling agent is silane coupling agent KH570; In step S5: the first mixed liquid is dried at 75-85° C. until the water is completely evaporated; In step S6, the heat treatment time is 2.5 to 3.5 hours.

3. The method for preparing a reinforced and toughened composite coating according to claim 1, characterized in that: The metal salt in step S3 is zinc salt, and the metal-based nanopowder in step S7 is zinc oxide nanopowder; or The metal salt in step S3 is nickel salt, and the metal-based nanopowder in step S7 is nickel nanopowder.

4. The method for preparing a reinforced and toughened composite coating according to claim 1, wherein: The step S7 specifically includes the following steps: S7-1, mixing the second composite powder and the metal-based nanopowder in a solvent at a mass ratio of 1:0.8 to 1.2 to obtain a third mixed solution, and adding a polyvinyl alcohol solution to the third mixed solution to obtain a preliminary slurry; S7-2, atomizing the prepared slurry, and then heating and drying it to obtain a prepared powder; S7-3, the prepared powder is formed into the composite coating by plasma spraying.

5. The method for preparing a reinforced and toughened composite coating according to claim 4, characterized in that: In step S7-1, the second composite powder and the metal nanopowder are stirred and mixed in a solvent, wherein the solvent is deionized water, the stirring speed is 3000 to 5000 r / min, and the stirring time is controlled at 3 to 5 hours; in terms of mass percentage, the concentration of the polyvinyl alcohol in the polyvinyl alcohol solution is 0.8% to 1.2%.

6. The method for preparing a reinforced and toughened composite coating according to claim 4, characterized in that: In step S7-2, the prepared slurry is introduced into a centrifugal atomizer through a peristaltic pump for atomization, and the atomized droplets enter a drying chamber. The droplets are heated and dried during flight to obtain the prepared powder. The prepared powder is collected in a collector at the lower end of the drying chamber under the action of gravity.