A method for preparing a graphene-reinforced powder metallurgy nickel-based superalloy composite powder

Abstract

The application discloses a preparation method of graphene reinforced powder metallurgy nickel-based high-temperature alloy composite powder, and comprises the following steps: (1) modifying graphene nanosheets by using a bridging agent to obtain modified graphene nanosheets; (2) compounding powder metallurgy nickel-based high-temperature alloy powder and the modified graphene nanosheets to obtain a composite powder precursor; and (3) performing thermal cracking on the composite powder to obtain the graphene reinforced powder metallurgy nickel-based high-temperature alloy composite powder. The preparation method can improve the bonding degree of the graphene and the powder metallurgy nickel-based high-temperature alloy powder, and simultaneously solves the problem of poor mechanical properties caused by interface bonding defects.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of powder metallurgy. Specifically, it is a method for preparing graphene reinforced powder metallurgy nickel-based superalloy composite powder. BACKGROUND

[0002] As a key material that cannot be replaced in the modernization of national defense strategy construction and social and economic development, powder metallurgy nickel-based superalloy is widely used in the field of modern aerospace due to its excellent tensile strength, oxidation corrosion resistance, fatigue creep resistance and good organizational stability. At present, in the aero-engine, the use of powder metallurgy nickel-based superalloy is more than 40%, among which the key components such as turbine disc, blade, combustion chamber and other components with high working temperature, high working load and severe oxidation corrosion environment are almost made of powder metallurgy nickel-based superalloy.

[0003] With the continuous development of the field of aerospace, the demand for high thrust-to-weight ratio and high bypass ratio of aero-engine increases, and single alloy material cannot meet the demand of balancing strength while still maintaining the demand for materials such as material stability, high thermal conductivity, corrosion resistance and wear resistance.

[0004] The continuous development of carbon materials has opened up new research directions in the fields of science and engineering. Carbon is one of the elements that exist universally in nature, and new synthetic materials based on carbon have created a colorful world for mankind. Since the discovery of carbon nanotubes in the last century, graphene has been the focus of scientific research and engineering in recent years. In 2004, two scientists from the University of Manchester, Novoselov and Geim, prepared single-layer nanosheet structure graphene material by exfoliating graphite, which triggered a research boom worldwide. Through the study of graphene, it was found that this material has excellent performance that is difficult for ordinary materials to achieve, such as: ultra-high strength (about 130 GPa), high thermal conductivity (5000 J / (m·K·s)) and high specific surface area (2630 m 2 / g), especially the mechanical properties of graphene such as Young's modulus and fracture strength reach 1100 GPa and 125 GPa, which is one of the strongest materials known.

[0005] Therefore, by combining the high strength and high Young's modulus of graphene with the high strength and high creep resistance of powder metallurgy nickel-based superalloy, a graphene reinforced powder metallurgy nickel-based superalloy with excellent performance can be prepared. However, due to the surface van der Waals force, graphene is prone to agglomeration, and it is difficult to disperse uniformly in the powder metallurgy nickel-based superalloy; and the wettability of graphene and powder metallurgy nickel-based superalloy powder is poor, it is difficult to combine them through traditional smelting metallurgy method, which ultimately restricts the development and application of graphene reinforced powder metallurgy nickel-based superalloy.

[0006] To solve the above problems, through domestic and foreign relevant literature patent retrieval, Jiang et al. of Lanzhou University of Technology and Fernandes et al. of Paraiba University studied graphene reinforced pure Ni alloy. The organic compound of carbon is used as the carbon source to generate graphene in situ, and the uniformly dispersed graphene reinforced pure Ni alloy is successfully synthesized by the powder metallurgy method. Compared with other non-in situ addition of graphene synthesis method, the Ni element matrix acts as the catalyst and support carrier of graphene in this method, which improves the integrity of graphene and ensures the good contact interface between graphene and Ni alloy, providing effective load transfer guarantee for pure Ni alloy, and thus the mechanical properties of the alloy can be improved. Chinese patent (CN1112008087A) discloses a method for improving the comprehensive performance of nano-carbon material reinforced nickel-based high-temperature alloy, which proposes to coat a dense Ni layer on the surface of carbon nanomaterial to solve the problems of poor mechanical properties and high-temperature oxidation resistance caused by easy agglomeration of carbon nanomaterial and poor interfacial bonding with the matrix; through a specific ball milling process, a mixed powder with uniformly dispersed carbon nanomaterial is obtained to realize further uniform dispersion of carbon nanomaterial; and through a powder forming method, a carbon nanomaterial nickel-based composite material with excellent mechanical properties is obtained. However, the above method cannot well solve the technical problem of poor wettability between graphene and powder metallurgy nickel-based high-temperature alloy powder; and there are still some defects in effectively dispersing graphene in the metal matrix. As known, if graphene is added to the powder metallurgy nickel-based high-temperature alloy and the graphene cannot be effectively dispersed, it will have an impact on the subsequent series of thermal processes, leading to irreversible reaction between graphene and nickel-based high-temperature alloy matrix elements, and finally affecting the mechanical properties. SUMMARY

[0007] Therefore, the technical problem to be solved by the present application is to provide a preparation method of graphene reinforced powder metallurgy nickel-based high-temperature alloy composite powder, which improves the bonding degree of graphene and powder metallurgy nickel-based high-temperature alloy powder and solves the problem of poor mechanical properties caused by interfacial bonding defects.

[0008] To solve the above technical problems, the present application provides the following technical solutions:

[0009] A preparation method of graphene reinforced powder metallurgy nickel-based high-temperature alloy composite powder, comprising the following steps:

[0010] (1) modifying graphene nanosheets by using a bridging agent to obtain modified graphene nanosheets;

[0011] (2) compounding the powder metallurgy nickel-based high-temperature alloy powder with the modified graphene nanosheets to obtain a composite powder precursor;

[0012] (3) pyrolyzing the composite powder precursor to obtain a graphene reinforced powder metallurgy nickel-based superalloy composite powder.

[0013] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder described above, in step (1): the graphene nanosheet is a sheet structure with a thickness of 1-5 layers; the graphene nanosheet is obtained by reduction of graphene oxide, and the graphene oxide is prepared by Hummers method.

[0014] Graphene is a two-dimensional sheet material, so 1 layer thickness is the thickness of one layer of carbon atoms; according to the International Organization for Standardization (ISO), when the number of layers is less than or equal to ten, it can be called graphene, otherwise it should be called graphite. The more the number of layers, the stronger the van der Waals force between the layers, and the stronger the π-π stacking effect, which is more likely to form agglomeration and defects.

[0015] Hummers method is chosen because Hummers method is the most common and most economical method for preparing multi-layer (less than 10 layers) graphene, but it is difficult to prepare single-layer graphene. Considering the performance and economic benefits of the prepared material, hummers method is adopted. In addition to hummers method, there are also methods such as mechanical exfoliation and CVD, but considering the cost and other factors, it is difficult to mass-produce.

[0016] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder described above, in step (2): the particle size of the powder metallurgy nickel-based superalloy powder is ≤53 μm, the average particle size is 25-40 μm, the purity is 99.99%, and the powder shape is spherical; the powder metallurgy nickel-based superalloy powder is screened by a screening machine for 3 times or more.

[0017] The particle size of the powder metallurgy nickel-based superalloy powder is controlled to be within 53 μm. When the particle size is greater than 53 μm, the subsequent nickel-based superalloy will have coarse grains, which will affect the mechanical properties. And the grain boundary of the small grain original particle cannot be effectively eliminated. Therefore, based on a large amount of engineering data, the particle size of the powder nickel-based superalloy is-270 mesh, i.e. the particle size is ≤53 μm.

[0018] Other types of vibrating screening machines can be used, but ultrasonic vibrating screening machines have higher efficiency. The purpose of multiple screening is to maximize the concentration of powder particle size within the above range and to minimize the error of the instrument.

[0019] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder, in step (2): the composition of the powder metallurgy nickel-based superalloy powder in mass percentage is as follows: Cr 15.5%, Co 12.5%, Mo 3.8%, W 3.8%, Al 2.0%, Ti 3.5%, Nb 0.6%, B 0.006%, Zr 0.025%, C 0.02%, and Ni is the balance.

[0020] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder, in step (1): the bridging agent, graphene nanosheet and water are mixed and then mechanically stirred under ultrasonic conditions to modify the graphene nanosheet.

[0021] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder, characterized in that, in step (1): the mass ratio of the bridging agent, graphene nanosheet and water is 1:100:1000; the bridging agent is dissolved in water at room temperature, then the graphene nanosheet is added, and then ultrasonic stirring is performed until the graphene nanosheet is completely dispersed in the bridging agent solution, and finally the temperature is raised to 60-80°C, and the ultrasonic stirring is continued for greater than or equal to 6 hours. The graphene nanosheet is dispersed by ultrasonic stirring before being heated, which allows the graphene nanosheet to gradually disperse, and then the temperature is slowly raised, so that the modification of the bridging agent to the graphene nanosheet is more sufficient.

[0022] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder, in step (2): the powder metallurgy nickel-based superalloy powder is added to the mixture obtained in step (1), and mechanical stirring is performed under ultrasonic conditions to uniformly composite the powder metallurgy nickel-based superalloy powder and the modified graphene nanosheet; after the compounding is completed, filtration is performed, and the filter residue is dried to obtain the composite powder precursor.

[0023] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder, in step (2): the mechanical stirring temperature is greater than or equal to 85°C, and the mechanical stirring time is greater than or equal to 12 hours; the drying temperature is greater than or equal to 90°C, and the drying time is greater than or equal to 24 hours.

[0024] If the stirring temperature is lower than 85°C, the solvent cannot be effectively dried and removed. Adding a certain temperature to assist stirring during the stirring process is to gradually evaporate the solvent during the stirring process. Similarly, if the drying temperature is less than 90°C, the residual solvent cannot be effectively removed.

[0025] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder, in step (3): the pyrolysis temperature is greater than or equal to 500°C, the vacuum degree is less than 5x10 -3Pa, the thermal cracking time is greater than or equal to 16 hours.

[0026] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder, the bridging agent is polyvinyl alcohol, the molecular weight is 89000-98000, and the powder metallurgy nickel-based superalloy powder is prepared by the following method: vacuum induction furnace melting and pouring into a master alloy ingot, and then argon atomization method is used to powder the master alloy ingot.

[0027] In the application, the bridging agent is selected as polyvinyl alcohol. It is found in the experiment that similar substances to polyvinyl alcohol have similar effects, but under the conditions of the preparation method of the application, polyvinyl alcohol with a specific degree of polymerization is the most suitable as the bridging agent of graphene nanosheets and powder metallurgy nickel-based superalloy powder, and only contains C, H and O three elements. In the later thermal cracking process, the thermal cracking temperature is low (less than 500 DEG C), and the thermal cracking product is carbon dioxide and water, which is easy to remove and will not have other effects on the original substrate material. Therefore, polyvinyl alcohol is the most suitable. Therefore, polyvinyl alcohol is selected as the bridging agent.

[0028] The molecular weight of polyvinyl alcohol is controlled in the range of 89000-98000, because the molecular weight is too small to play an effective bridging role, and the molecular weight is too large, which is difficult to dissolve.

[0029] The technical scheme of the application achieves the following beneficial technical effects:

[0030] 1. In the application, the bridging agent is used to modify the graphene nanosheet in water, and then the powder metallurgy nickel-based superalloy powder and the modified graphene nanosheet are compounded in water, so that the bridging agent plays a "bridging" role between the graphene nanosheet and the powder metallurgy nickel-based superalloy powder, and the combination degree of the graphene and the powder metallurgy nickel-based superalloy powder is improved (the improvement of the combination degree can effectively improve the mechanical properties of the prepared composite material: the atomic combination of the graphene nanosheet reinforcing phase and the nickel-based matrix phase is realized through subsequent process, the grain refinement effect of the composite material is realized, the combination defect of the graphene material and the matrix interface is completely solved, and the mechanical properties of the material are improved), the problem that the graphene and the powder metallurgy nickel-based superalloy powder are difficult to mix uniformly due to large density difference is solved, and the problem of poor mechanical properties caused by interface combination defect is also solved, the strengthening effect of the graphene nanosheet in the metal matrix is fully played, so that the mechanical properties of the material are effectively improved; and then through the hot forming process (hot isostatic pressing, isothermal extrusion or isothermal forging, or 3D printing and other powder forming methods), the graphene nanosheet reinforced powder metallurgy nickel-based superalloy composite material with excellent comprehensive performance is prepared, and the problem of the graphene reinforced powder metallurgy nickel-based superalloy in use is solved.

[0031] 2. Graphene nanosheets have a large specific surface area. Their layered structure contains certain atomic defects, and the edges of the layers have numerous surface atoms and suspended oxygen-containing groups (-COOH, -CHO, -OH, etc.). This results in high surface activity of graphene, causing the nanosheets to tend to overlap, fold, and aggregate to reduce surface energy. Aggregation still occurs during the composite, thermoforming, and hot deformation processes of graphene nanosheets and metal powders. Compared to existing methods of modifying metal powders, the method in this invention enables the graphene nanosheets and metal powder particles to be bridged together and effectively solves the problem of aggregation during composite, thermoforming, and hot deformation processes.

[0032] 3. The operation method of this invention is simple, the process is highly controllable, and the manufacturing cost is low, making it suitable for the preparation of graphene nanosheet powder metallurgy nickel-based high-temperature alloy composite powder. Attached Figure Description

[0033] Figure 1 Flowchart of the preparation process of graphene-reinforced powder metallurgy nickel-based high-temperature alloy composite powder in this invention;

[0034] Figure 2 The overall process route for graphene-reinforced powder metallurgy nickel-based high-temperature alloy composite materials in this invention;

[0035] Figure 3 A comparison of the bonding states of graphene-reinforced powder metallurgy nickel-based superalloy powders prepared by the mixing method in the prior art and by the method of the present invention;

[0036] Figure 4 Schematic diagram of FGH96 powder particles coated with graphene nanosheets. Detailed Implementation

[0037] Example 1

[0038] The preparation method of graphene-reinforced powder metallurgy nickel-based superalloy composite powder in this embodiment includes the following steps:

[0039] (1) A ZG25 vacuum induction melting furnace is used to melt and prepare a powder metallurgy nickel-based superalloy master alloy ingot. Then argon gas atomization (AA) method is used to prepare a powder metallurgy nickel-based superalloy powder (the composition of the powder metallurgy nickel-based superalloy powder is as follows in mass percentage: Cr 15.5%, Co 12.5%, Mo 3.8%, W 3.8%, Al 2.0%, Ti 3.5%, Nb 0.6%, B 0.006%, Zr 0.025%, C 0.02%, graphene 0.005%-4%, and Ni the balance), and the powder is screened more than three times by an ultrasonic vibration screening machine to obtain a powder metallurgy nickel-based superalloy powder with a particle size of -270 mesh (FGH96, the particle size of the powder metallurgy nickel-based superalloy powder is ≤53 μm, the average particle size is 25-40 μm, the purity is 99.99%, and the powder shape is spherical).

[0040] (2) Polyvinyl alcohol is dissolved in water (the weight ratio of polyvinyl alcohol to water is 1:1000, w / w), the dissolution temperature is room temperature, and the dissolution time is more than 6 hours. Graphene nanosheets are mixed with the polyvinyl alcohol aqueous solution according to a weight ratio (1:100, w / w), and the mixture is continuously stirred under ultrasonic dispersion at room temperature for 6 hours until all the graphene nanosheets are dispersed in the polyvinyl alcohol solution. Then the mixture is heated to 60°C and continuously stirred for 6 hours. After the stirring stops, a golden yellow surface-bridging agent modified graphene nanosheet dispersion is obtained. The graphene nanosheets used are 1-5 layers thick and have a sheet structure; the graphene nanosheets are obtained by reduction of graphene oxide, and the graphene oxide is prepared by the Hummers method.

[0041] (3) The powder metallurgy nickel-based superalloy powder prepared by the AA method is mixed with the modified graphene nanosheet dispersion prepared in the previous step, wherein the weight of the powder metallurgy nickel-based superalloy powder is 1 kg, and the content of the graphene nanosheets is 1 g. The mixture is stirred at 85°C for 12 hours until the mixture reaches a semi-dry state.

[0042] The semi-dry mixture is transferred to a vacuum oven for sufficient drying, the drying temperature is 90°C, and the drying time is 24 hours. A graphene reinforced powder metallurgy nickel-based superalloy composite powder precursor is obtained, and the morphology thereof is shown in FIG. 1. Figure 3

[0043] (4) The graphene reinforced powder metallurgy nickel-based superalloy composite powder precursor obtained after drying is vibrated and filled into a 304 stainless steel can with a diameter of 60 mm and a height of 100 mm. Then the can is vacuumed, first pre-vacuumed at room temperature for 2 hours, and then gradually heated to 500°C and vacuumed to 5×10 -3 ​After holding for 20 h at Pa, the canning was sealed, and the preparation of graphene reinforced powder metallurgy nickel-based superalloy composite powder was completed.

[0044] Example 2

[0045] The preparation method of the graphene reinforced powder metallurgy nickel-based superalloy composite powder in this example includes the following steps:

[0046] (1) A 500 kg vacuum induction furnace was used to melt the powder metallurgy nickel-based superalloy to prepare a powder metallurgy nickel-based superalloy master alloy ingot. Then argon gas atomization method (AA method) was used to prepare a powder metallurgy nickel-based superalloy powder (the composition of the powder metallurgy nickel-based superalloy powder in mass percentage is as follows: Cr 15.5%, Co 12.5%, Mo 3.8%, W 3.8%, Al 2.0%, Ti 3.5%, Nb 0.6%, B 0.006%, Zr 0.025%, C 0.02%, graphene 0.005%-4%, and Ni balance), and screening was performed to obtain a powder metallurgy nickel-based superalloy powder with a particle size of -270 mesh (FGH96, the particle size of the powder metallurgy nickel-based superalloy powder is ≤53 μm, the average particle size is 25-40 μm, the purity is 99.99%, and the powder shape is spherical).

[0047] (2) Polyvinyl alcohol was dissolved with water in a weight ratio of 1:1000 at room temperature for more than 6 hours. 50 g of graphene nanosheets were mixed with the polyvinyl alcohol aqueous solution in a weight ratio of 1:100 (w / w) under ultrasonic dispersion at room temperature. The mixture was continuously stirred for 10 h until all the graphene nanosheets were dispersed in the polyvinyl alcohol solution. Then the solution system was heated to 65°C and continuously stirred for 12 h. After the stirring stopped, the golden yellow surfactant modified graphene nanosheets were obtained.

[0048] (3) 10 kg of the powder metallurgy nickel-based superalloy powder was mixed with the modified graphene nanosheet dispersion prepared in the previous step. The mixture was stirred at a temperature of 85°C for 12 h until the mixture reached a semi-dry state, and a graphene reinforced powder metallurgy nickel-based superalloy composite powder precursor was obtained. At this time, the composite powder with the maximum theoretical content of graphene was obtained, and the content of graphene was 0.5 wt.%, close to the maximum theoretical content.

[0049] The calculation method of the maximum theoretical content is as follows:

[0050] For the design requirements of the composite material, there is a certain relationship between the content of the reinforcing phase in the material and the performance. With the increase of the content of the reinforcing phase graphene in the composite material, the performance of the material will be improved. However, too much content of graphene will cause agglomeration due to its own nano effect, which will affect the macroscopic performance of the composite material.

[0051] Therefore, there is a limit to the amount of graphene added in the FGH96 composite material. A calculation model of a sphere coated is used, as shown in Figure 4 The black circle represents the FGH96 powder particle, and the golden yellow hexagon represents the graphene coated on the outer layer of the FGH96 powder particle. It is assumed that the FGH96 powder is all uniform powder particles, that each FGH96 powder particle is uniformly coated with a layer of graphene nanosheet at the initial stage of powder mixing, and that there is no aggregation and folding phenomenon between the graphene. When each FGH96 powder particle is uniformly coated with a layer of graphene, it is considered that the maximum amount is reached. When the content of graphene continues to increase, the graphene on the surface of the FGH96 powder will cover multiple layers of stacked graphene, thereby forming a stacked aggregation.

[0052] At this time, the maximum mass fraction (ω) of GNSs coated on the outer surface of the FGH96 powder is:

[0053]

[0054] wherein r is the FGH96 powder particle of 270 mesh, about 53 μm; n is the number of sheet layers of GNSs; d is the sheet layer thickness of a single layer of graphene, about 0.334 nm; ρ FGH96 and ρ GNSs are the densities of FGH96 and GNSs, respectively, and are 8.5 g / cm 3 and 2.3 g / cm 3 , respectively.

[0055] From the above relationship, the theoretical maximum amount of GNSs in the FGH96 alloy composite material is calculated to be 0.5 wt.%.

[0056] (4) The dried graphene powder metallurgical nickel-based high-temperature alloy composite powder precursor is vibrated and filled into a 304 stainless steel jacket with a diameter of 600 mm and a height of 1500 mm. Then the jacket is vacuumed, first pre-vacuumed at room temperature for 4 h, then gradually heated to 500°C and vacuumed to 3x10-3Pa, and then sealed and welded after holding for 24 h, to complete the preparation of the graphene reinforced powder metallurgical nickel-based high-temperature alloy composite powder.

[0057] Microhardness test is performed on the material

[0058] The FGH96 alloy without adding graphene, the composite material prepared by the conventional mechanical stirring method, the published literature (Gao of Beijing University of Aeronautics and Astronautics) and the mixing method of the present patent are respectively subjected to microhardness test, and the results are shown in the following table.

[0059] The existing mechanical stirring method is a mechanical stirring method without adding a bridging agent. The specific steps are as follows:

[0060] (1) The graphene nanosheet and water are mixed in a certain proportion by weight (1:10, w / w), and stirred for 6 h under ultrasonic dispersion at room temperature until all the graphene nanosheets are dissolved in water. Then, the solution is heated to 60°C and stirred for 6 h. After the stirring stops, the graphene nanosheet aqueous solution is obtained.

[0061] (2) The FGH96 powder is mixed with the graphene nanosheet aqueous solution prepared in the above step, and stirred at a temperature of 85°C for 12 h until the mixture reaches a semi-dry state, and then transferred to a vacuum oven for sufficient drying.

[0062] (3) The FGH96 and graphene composite powder are pyrolyzed at 450°C in a vacuum environment (1×10 -3 Pa) for 10 h, and then the prepared mixture is loaded into a 304 stainless steel tank. Thus, the graphene nickel-based superalloy powder mixed by the conventional method is obtained.

[0063]

[0064] From Figure 3 It can be seen that: by using the conventional method, the graphene cannot be well coated on the metallurgical nickel-based superalloy composite powder particles; and by using the preparation method of the present application, the graphene is well coated on the metallurgical nickel-based superalloy composite powder particles, and the surface texture of the particles changes significantly.

[0065] The method in the literature: the surface of FGH96 is modified first, and polyvinyl alcohol cannot effectively bridge between FGH96 powder and graphene. In addition, graphene may agglomerate during the mixing process, which makes the combination of graphene and FGH96 powder insufficient, and thus the mechanical properties (i.e. hardness) are not as good as described in the patent.

[0066] Compared with the method in the literature, the method of the present patent directly modifies the graphene with PVA and then composites with FGH96 powder. In this way, the polyvinyl alcohol with a specific molecular weight can play a bridging role between the graphene nanosheet and the FGH96 powder. In addition, the graphene nanosheet is difficult to agglomerate before being composited with the FGH96 powder, which is more conducive to being loaded on the surface of the FGH96 powder, thereby improving the hardness of the composite material.

[0067] Because the PVA is used to modify, the bridging effect of PVA makes the graphene loaded on the surface of FGH96 more uniform, and the aggregation and folding of graphene itself is greatly reduced. The uniformly loaded and non-aggregated graphene can play a better strengthening role in the material, and thus the macro hardness of the material is improved.

[0068] When the modified graphene nanosheet prepared in the present application is added, the microhardness increases by 5.29% compared with no graphene added, and compared with the conventional mixing method and the method in the literature, the microhardness is improved to different degrees, especially when the modified graphene nanosheet is added at the maximum amount, the microhardness increases more, and the mechanical properties of the material are obviously improved.

[0069] Note: The published literature is An Approach to the Uniform Dispersion of Graphene Nanosheets in Powder Metallurgy Nickel-Based Superalloy; Materials 2019, 12, 974.

[0070] Obviously, the above examples are only examples for the sake of clarity, and are not limitations on the embodiments. Based on the above description, other different forms of changes or variations can also be made by those of ordinary skill in the art. All embodiments do not need to be exhausted here, and obvious changes or variations derived therefrom are still within the protection scope of the claims of the present patent application.

Claims

1. A method of producing a graphene-reinforced powder metallurgy nickel-based superalloy composite powder, characterized by, It comprises the following steps: (1) modifying the graphene nanosheet by using a bridging agent to obtain a modified graphene nanosheet; the graphene nanosheet is a sheet structure with a thickness of 1-5 layers; the mass ratio of the bridging agent, the graphene nanosheet and water is 1:100:1000; first, the bridging agent is dissolved in water at room temperature, then the graphene nanosheet is added, and then ultrasonic stirring is performed until the graphene nanosheet is completely dispersed in the bridging agent solution, and finally the temperature is raised to 60-80℃, and the ultrasonic stirring is continued for more than or equal to 6 hours; the bridging agent is polyvinyl alcohol with a molecular weight of 89000-98000; (2) compounding the powder metallurgy nickel-based superalloy powder with the modified graphene nanosheet to obtain a composite powder precursor; the particle size of the powder metallurgy nickel-based superalloy powder is ≤53μm, the average particle size is 25-40μm, the purity is 99.99%, and the powder shape is spherical; the powder metallurgy nickel-based superalloy powder is sieved for 3 times or more than 3 times by using a sieving machine; (3) pyrolyzing the composite powder precursor to obtain a graphene reinforced powder metallurgy nickel-based superalloy composite powder.

2. The method of claim 1, wherein the graphene-reinforced powder-metallurgy nickel-based superalloy composite powder is prepared by the steps of: preparing a graphene dispersion solution by dispersing graphene in a solvent; preparing a nickel-based superalloy powder by a powder-metallurgy method; and mixing the graphene dispersion solution and the nickel-based superalloy powder. In step (1), the graphene nanosheet is obtained by reducing graphene oxide, and the graphene oxide is prepared by using the Hummers method.

3. The method of claim 1, wherein the graphene reinforced powder metallurgy nickel-based superalloy composite powder is prepared by the steps of: preparing a graphene solution by dispersing graphene in a solvent; preparing a nickel-based superalloy precursor powder; and mixing the graphene solution and the nickel-based superalloy precursor powder to obtain the graphene reinforced powder metallurgy nickel-based superalloy composite powder. In step (2), the powder metallurgy nickel-based superalloy powder comprises the following components in mass percentage: Cr 15.5%, Co 12.5%, Mo 3.8%, W 3.8%, Al 2.0%, Ti 3.5%, Nb 0.6%, B 0.006%, Zr 0.025%, C 0.02%, and Ni the balance.

4. The method of claim 1, wherein the graphene-reinforced powder-metallurgy nickel-based superalloy composite powder is prepared by the steps of: preparing a graphene dispersion solution by dispersing graphene in a solvent; preparing a nickel-based superalloy powder by a powder-metallurgy method; and mixing the graphene dispersion solution and the nickel-based superalloy powder. In step (1), the bridging agent, the graphene nanosheet and water are mixed and then mechanically stirred under ultrasonic conditions to modify the graphene nanosheet.

5. The method of claim 4, wherein the graphene reinforced powder metallurgy nickel-based superalloy composite powder is prepared by the steps of: mixing a nickel-based superalloy powder with graphene oxide; and reducing the graphene oxide to graphene by a chemical reduction method. In step (2), the powder metallurgy nickel-based superalloy powder is added to the mixture obtained in step (1) and mechanically stirred under ultrasonic conditions to uniformly compound the powder metallurgy nickel-based superalloy powder and the modified graphene nanosheet; after the compounding is completed, the filter residue is dried to obtain the composite powder precursor.

6. The method of claim 5, wherein the graphene reinforced powder metallurgy nickel-based superalloy composite powder is prepared by the steps of: mixing a nickel-based superalloy powder with graphene oxide; and reducing the graphene oxide to graphene by a chemical reduction method. In step (2), the maximum addition amount of the modified graphene nanosheet is 0.5wt.% of the addition amount of the powder metallurgy nickel-based superalloy powder; the mechanical stirring temperature is greater than or equal to 85℃, the mechanical stirring time is greater than or equal to 12 hours; the drying temperature is greater than or equal to 90℃, and the drying time is greater than or equal to 24 hours.

7. The method of claim 1-6, wherein the method is characterized by, In step (3): thermal cracking temperature greater than or equal to 500°C, vacuum degree less than 5 x 10 -3 Pa, thermal cracking time greater than or equal to 16 hours.

8. The method of claim 1-6, wherein the method is characterized by, The powder metallurgy nickel-based superalloy powder is prepared by using a vacuum induction furnace to melt and cast a master alloy ingot, and then performing argon gas atomization to powderize the master alloy ingot.

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