CN112281106A

CN112281106A - Preparation method of graphene-doped nanosheet nano-alumina coating

Info

Publication number: CN112281106A
Application number: CN202011189302.XA
Authority: CN
Inventors: 赵晓兵; 姚李帆
Original assignee: Changzhou University
Current assignee: Changzhou University
Priority date: 2020-10-30
Filing date: 2020-10-30
Publication date: 2021-01-29

Abstract

The invention belongs to the technical field of wear resistance and corrosion resistance of metal surfaces, and particularly relates to a preparation method of a graphene-doped nanosheet nano-alumina coating. Firstly, composite powder which is uniformly mixed and suitable for the plasma spraying process is prepared, and then the preparation of the high-wear-resistant anticorrosive coating is realized by utilizing the plasma spraying technology. The graphene-doped nanosheet alumina coating prepared by the method has the advantages of low porosity, high bonding strength and the like, greatly improves the wear-resisting and corrosion-resisting properties of a metal matrix, and can greatly prolong the service life of the surface coating under severe working conditions.

Description

Preparation method of graphene-doped nanosheet nano-alumina coating

Technical Field

The invention belongs to the technical field of wear resistance and corrosion resistance of metal surfaces, and particularly relates to a preparation method of a graphene-doped nanosheet nano-alumina coating.

Background

The nano-alumina is a ceramic material with a structural unit between 1nm and 100nm, and has the characteristics of high melting point, high hardness, high wear resistance, oxidation resistance and the like of the ceramic material and the special effect of large specific surface area of the nano-material. The coating prepared by the aluminum oxide material is the most widely applied material for improving the performances of corrosion resistance, abrasion resistance, thermal barrier resistance and the like of the material, but the coating still has the problems of surface abrasion and corrosion of mechanical parts under the environments of strong alkali, strong acid and corrosive salt ions, and has the defect of poor toughness, so the bonding strength with a metal matrix needs to be improved.

The plasma spraying is a processing technology which utilizes plasma jet as a heat source to heat refractory powder materials such as ceramics, metals or alloys to a molten or semi-molten state, and sprays the refractory powder materials to the surface of a base material which is subjected to surface treatment in advance at a high speed to form a coating by deposition, and has the characteristics of high equivalent, high heat flow and high quenching speed. The plasma spraying technology has wide material selection, and ceramics, metals and even some high molecular polymers are used for depositing as coatings, so the coating has wide application and is convenient for large-area construction. Plasma spraying can deposit a coating on the surface of a substrate to greatly improve the wear-resisting and corrosion-resisting properties of the coating or repair key parts of the substrate on the premise of not damaging the substrate, and in short, the plasma spraying is the most widely applied one in the surface engineering technology. Of course, the porosity and cracks of the coating prepared by the plasma thermal spraying technology are difficult to eliminate, the roughness of the prepared coating is high, and the coating and the substrate are mechanically combined, so the combination strength still needs to be improved.

Disclosure of Invention

In order to solve the problems of surface abrasion and corrosion of mechanical parts under severe working conditions and improve the bonding strength of a coating and a metal matrix, the invention adopts nano-alumina doped graphene nanosheet to form mixed powder, and deposits the coating on the metal surface through a plasma spraying technology, thereby improving the wear-resisting and corrosion-resisting properties of the material, ensuring that the surface of the mechanical part is more wear-resisting in a corrosive solution, improving the durability of the mechanical part, simultaneously improving the porosity and the bonding strength to a certain extent, and being better applied to surface strengthening of the mechanical part under severe working conditions.

The invention is realized by the following technical scheme through three steps:

(1) preparing graphene-doped nanosheet alumina composite powder for plasma spraying;

the composite powder comprises the following components in percentage by mass: 0.1-1 wt.% graphene nanoplatelets, 99-99.9 wt.% nano alumina; preferably 0.5 wt.% graphene nanoplatelets, 99.5 wt.% nano alumina.

The preparation method of the composite powder comprises the following steps: the preparation method comprises the steps of mixing 6-8 graphene nanosheets (Changzhou sixth-element material science and technology limited company, the graphene nanosheets are composed of a plurality of stacked graphene layers, the total thickness of the graphene nanosheets is 2-2.5 nm, and the size of the graphene nanosheets is 3-5 microns) and aluminum oxide powder (Shanghai New-field material technology limited company, the particle size of the graphene nanosheets is 50nm) fully, ball-milling the mixture for 4 hours by using a planetary ball mill, promoting the mixture to be uniform, drying the ball-milled composite powder in a drying box at 60 ℃, pouring the composite powder into a clean mortar, grinding the composite powder by using a grinding rod, sieving, adding a PVA solution into the powder of 80-200 meshes for granulation, wherein the mass ratio of the powder to the PVA solution is 4:1, and enabling the aluminum oxide powder to wrap the surfaces of the graphene nanosheets, so that the composite powder with good flowability is obtained finally.

The ball grinding beads are of three specifications, namely 10mm of large balls, 4mm of medium balls and 2mm of small balls. The mass ratio of the ball milling beads to the powder is 1.5:1, and the mass ratio of the ball milling beads to the powder is 1:2: 4. The revolution of the ball mill is 380 r/min; in order to ensure the quality of the composite powder, the ball milling time is strictly controlled to be 4 h.

And (3) granulating the sieved powder by using PVA (5 wt.% PVA solution), specifically, taking powder of 80-200 meshes, pouring 20g of the powder into a mortar each time, adding 5g of the PVA solution, mixing the PVA solution and the composite powder together by using a grinding rod, and fully contacting the composite powder and the PVA solution to fully improve the flowability of the powder, so that the grinding and stirring time can be properly increased to ensure that the PVA and the powder are fully contacted and mixed.

(2) Before spraying, carrying out oil and stain removal treatment on the matrix, drying and then carrying out surface sand blasting pretreatment;

substrates include, but are not limited to, stainless steel, titanium alloys, carbon steel, copper alloys, and the like.

The oil and stain removal is carried out by soaking in acetone solution, ultrasonic cleaning with absolute ethyl alcohol and sand blasting treatment on the base material before plasma spraying, so as to remove an oxide layer on the surface, improve the surface roughness of the base material and increase the bonding strength of the coating and the base body to ensure that the coating is not easy to fall off. The material used for sand blasting is brown corundum (24-80 #), a base material is assembled on a special plate and placed into a sand blasting tank, compressed air (the pressure is 0.4-0.6 MPa) is used for enabling sand grains to obtain a pressure, a valve is opened to enable the compressed air and the sand grains to be mixed, the mixture is sprayed out through a rubber hose, an angle between 30-90 degrees is formed between a sand blasting nozzle and the base material in the sand blasting process, and uniform sand blasting is carried out on each part slowly and at a constant speed in the moving process of the sand blasting nozzle.

(3) And (3) preparing a coating, namely melting the powder prepared in the step (1) through plasma thermal spraying by using a 9MB plasma spray gun, and depositing the melted powder on the substrate which is processed in the step (2) and is arranged on a rotary worktable in batches to obtain the coating doped with the graphene nanosheet alumina coating.

H₂The flow rate is 8slpm, the Ar flow rate is 40slpm, the spraying power is 30-45 Kw, the spraying distance is 60-120 mm, the powder feeding rate is 30g/min, and H₂As the torch combustion gas, Ar is used as the plasma gas and the shielding gas.

The diameter of the rotary table is 50-300 mm, and the rotation speed is 80-300 rpm.

The thickness of the obtained composite coating is 200-300 μm.

Step (3) of the present invention may cause some powder not to melt and remain on the surface of the substrate during the experiment, and in order to prevent this factor from causing errors in the subsequent characterization process, the surface must be cleaned. And (4) putting the sprayed coating into a beaker, putting the beaker into an ultrasonic cleaning machine, cleaning the beaker with absolute ethyl alcohol, and naturally drying the beaker.

Step (3) in the experimental process, the surface roughness of the coating of the sample prepared in the experimental process in the step (3) is measured by using a three-dimensional scanning electron microscope; testing the wear resistance of the surface wear-resistant coating by a friction wear tester; measuring the corrosion resistance of the coating by using an electrochemical workstation; the microstructure of the composite powder and the coating is characterized by an X-ray diffractometer (XRD) and a Field Emission Scanning Electron Microscope (FESEM), and the microhardness of the coating is tested by a Vickers hardness tester.

The coating preparation method disclosed by the invention is simple to operate, easy to control, wide in adaptability and high in economic benefit.

The invention has the advantages that:

(1) in the process of preparing the composite powder, the nano alumina powder is wrapped on the surface of the graphene nanosheet by adjusting the ball milling parameters and the using amount of the binder, so that the gasification loss of the graphene nanosheet in the spraying process is avoided while the powder flowability is improved.

(2) According to the invention, the graphene nanosheet and the nano-alumina are compounded, and under the spraying parameters, the bonding strength between the alumina ceramic coating and the substrate is increased.

(3) A small amount of graphene nano sheets are compounded, so that the wear-resisting and corrosion-resisting properties of the nano aluminum oxide ceramic coating are greatly enhanced.

(4) The content of the composite graphene nanosheet is low, and the plasma spraying technology can be used for preparing a coating in a large area, so that the method has better economy.

The invention is further described in detail below with reference to the figures and the detailed description.

Drawings

FIG. 1 is a Raman spectrum of the nano alumina abrasion resistant layer in example 1;

FIG. 2 is an XRD pattern of the coatings of examples 1-4 and comparative example 1;

FIG. 3 is a graph of the amount of abrasion of the coatings of examples 1 to 4 and comparative example 1;

FIG. 4 is a graph of the bond strength of the coatings of examples 1-4 and comparative example 1;

FIG. 5 is a graph of roughness of the coatings of examples 1-4 and comparative example 1;

FIG. 6 shows the coating of example 1 at 0.5mol/L H₂SO₄Polarization curve graph under environment;

FIG. 7 is a plot of the polarization of the coating of example 1 in a 1mol/L NaOH environment;

FIG. 8 is a plot of the polarization of the coating of example 1 in a 3.5 wt.% NaCl environment;

FIG. 9 is a surface SEM image of the coating of example 1.

Detailed Description

Example 1

The first step is as follows: preparing graphene-doped nanosheet alumina powder required for plasma spraying;

199g of nano-alumina powder and 1g of graphene nanosheet are weighed by a balance and placed into a clean nylon ball milling tank, and 49.75g of nano-alumina powder and 0.25g of graphene nanosheet are placed into each tank, so that 50g of powder is obtained. Selecting zirconium dioxide ball milling beads, wherein the mass ratio of the ball materials is 1.5: 1. The ball milling beads are added according to the specification of large (10mm), medium (4mm) and small (2mm) in a mass ratio of 1:2:4, namely 10.7g of large balls, 21.4g of medium balls and 42.9g of small balls. The mass ratio of the absolute ethyl alcohol to the powder is 1:1, after weighing is finished, the powder and the absolute ethyl alcohol are added into a ball milling tank for 3 times, the total volume of the absolute ethyl alcohol, the powder and ball milling beads is not more than 2/3-4/5 of the ball milling tank, after preparation is finished, the ball milling tank is placed on a planetary ball mill, the setting time is 4 hours, and the revolution is 380 r/min. The ball milling for 4 hours is to enable the nano alumina powder and the graphene nanosheets to be mixed more uniformly and enable the nano alumina to better wrap the graphene nanosheets, so that the loss of the graphene nanosheets can be reduced in the spraying process of the powder, and the mixing is not uniform due to too long or too short time.

After ball milling of the powder for 4 hours, the ball milling beads and the composite powder were separated with a stainless steel standard sieve while rinsing with alcohol. Spreading preservative film on the tray, pouring the separated powder, naturally volatilizing alcohol for a certain time, and placing in an oven at 60 deg.C for 8 hr. And continuously grinding the dried composite powder, and then sieving the powder by a standard sieve of 80 meshes and 200 meshes to obtain the powder between the powder and the composite powder.

In order to enhance the flowability of the powder and prevent clogging of the spray gun during plasma spraying, the composite powder needs to be reprocessed and a PVA solution is added to enhance the powder flowability. 20g of the powder is taken out each time and poured into a mortar, then 5g of PVA solution is added by a rubber head dropper, and then a grinding rod is used for stirring, so that the powder and the PVA solution are fully mixed. This process is recommended to grind for a longer time to ensure thorough mixing, prevent clogging of the muzzle during the experiment, and use a new ball mill jar, which is advantageous for mixing the composite powder with the PVA solution because of its rough surface. Too little PVA solution is added to cause the size of the powder to be too small, and too much PVA solution is added to cause the fluidity of the powder to be reduced, so that the mass ratio of the 5% PVA solution to the powder is controlled to be about 1: 4. And after the mixing is finished, putting the mixture into an oven for drying, wherein the set temperature is 80 ℃, and the time is 8 hours. Then taking out, continuously grinding and sieving, and taking powder of 80-200 meshes, namely the final plasma spraying powder for spraying.

The second step is that: the matrix is pretreated before spraying, including ultrasonic cleaning, drying and surface sand blasting;

the substrate used in this spray coating is #45 steel (the substrate of the present invention includes, but is not limited to, #45 steel, stainless steel, titanium alloys, copper alloys, and the like). Three kinds of #45 steel substrates of 20 mm. times.20 mm. times.0.5 mm, 10 mm. times.10 mm. times.0.5 mm, and 2 mm. times.2 mm. times.12 mm were prepared. Before spraying, the base body is pretreated, firstly, the base body is degreased and decontaminated, the base body is cleaned by ultrasonic waves, a cleaning medium is absolute ethyl alcohol, and then, the base body is dried. And carrying out sand blasting treatment on the sprayed surface so as to remove an oxide layer on the surface and improve the roughness of the surface of the substrate so as to enhance the bonding strength of the coating and the substrate. The sand blasting is carried out by using 60-mesh brown jade sand, arranging a base material on a special plate, and placing the plate into a working area for sand blasting. The nozzle and the base material form an angle of 45 degrees (within a range of 30-90 degrees) in the sand blasting process, and the nozzle and the base material move slowly to ensure that each part is uniformly blasted with sand, and the sand blasting pressure can be within a range of 0.4-0.6 MPA. And after the sand blasting is finished, the base material is assembled on a clamp used for spraying to prepare for spraying.

The third step: preparing a coating;

plasma spray H₂The flow is 8slpm, the Ar flow is 40slpm, the spraying power is 35Kw, the spraying distance is 80mm, the powder feeding rate is 30g/min, the moving speed of a spraying gun nozzle relative to a rotary spraying surface is 5-120 mm/s, and the spraying is carried out for 25 times.

After the spraying, some powder may remain on the surface of the substrate without melting or be oxidized at high temperature to form impurities to be attached to the surface of the substrate, which cause errors in the subsequent characterization process, so that the surface needs to be cleaned again. And (3) putting the sprayed coating into a beaker, putting the beaker into an ultrasonic cleaning machine for cleaning, wherein the cleaning medium is still absolute ethyl alcohol, cleaning with deionized water for the last time, and naturally drying. The coatings were characterized after obtaining clean coated pieces.

The results of various characterization tests of the coating are as follows: the abrasion loss was 2.93mg, the porosity was 9.67%, the bonding strength was 52.95MPa, the microhardness was 880HV, and the coating thickness was 330 μm.

Example 2

The first, second and third steps are the same as in example 1, and the ratio of the powder in the first step is only adjusted to 0.3 wt.% graphene nanosheet/99.7 wt.% nano-alumina.

The results of various characterization tests of the coating are as follows: the abrasion loss was 4.20mg, the porosity was 11.16%, the bonding strength was 51.03MPa, the microhardness was 750HV, and the coating thickness was 230 μm.

Example 3

The first, second and third steps are the same as in example 1, and the ratio of the powder in the first step is adjusted to 1 wt.% graphene nanosheet/99 wt.% nano alumina.

The results of various characterization tests of the coating are as follows: the abrasion loss was 4.00mg, the porosity was 11.25%, the bonding strength was 47.07MPa, the microhardness was 650HV, and the coating thickness was 390. mu.m.

Example 4

The first, second and third steps are the same as in example 1, and the ratio of the powder in the first step is adjusted to 0.1 wt.% graphene nanosheet/99.9 wt.% nano-alumina.

The results of various characterization tests of the coating are as follows: the abrasion loss was 6.09mg, the porosity was 12.23%, the bonding strength was 49.79MPa, the microhardness was 750HV, and the coating thickness was 240 μm.

Example 5

The first, second and third steps are the same as the embodiment 1, and only the spraying distance in the third step needs to be adjusted to 60 mm.

The results of various characterization tests of the coating are as follows: the abrasion loss was 6.75mg, the porosity 18.77%, the bond strength 22.76MPa, the microhardness 480HV and the coating thickness 230 μm.

Example 6

The first, second and third steps are the same as the embodiment 1, and only the spraying distance in the third step needs to be adjusted to 120 mm.

The results of various characterization tests of the coating are as follows: the abrasion loss was 7.86mg, the porosity was 19.65%, the bonding strength was 25.35MPa, the microhardness was 380HV, and the coating thickness was 200 μm.

Example 7

The difference from the embodiment 1 is that: only the spraying power of the third step needs to be adjusted to 30 KW.

The results of various characterization tests of the coating are as follows: the abrasion loss was 6.50mg, the porosity was 13.57%, the bonding strength was 44.09MPa, the microhardness was 550HV, and the coating thickness was 380. mu.m.

Example 8

The difference from the embodiment 1 is that: and adjusting the spraying power of the third step to 45 KW.

The results of various characterization tests of the coating are as follows: the abrasion loss was 7.5mg, the porosity was 14.36%, the bond strength was 45.36MPa, the microhardness was 580HV, and the coating thickness was 320 μm.

Comparative example 1

The difference from the embodiment 1 is that: the powder ratio of step one is only adjusted to 100 wt.% nano alumina.

The results of various characterization tests of the coating are as follows: the abrasion loss was 7.10mg, the porosity was 13.55%, the bonding strength was 35.07MPa, the microhardness was 600HV, and the coating thickness was 200 μm.

Comparative example 2

The difference from the embodiment 1 is that: only the nano alumina powder in the first adjusting step is micron alumina.

The results of various characterization tests of the coating are as follows: the abrasion loss was 10.50mg, the porosity was 14.66%, the bonding strength was 31.43MPa, the microhardness was 450HV, and the coating thickness was 130 μm.

Comparative example 3

The powder prepared according to the proportion in the example 1 is directly and uniformly mixed to be used as spraying powder, and the spraying powder is not mixed with PVA solution through a ball mill, so that a plasma spray gun is blocked in the preparation process of the coating in the step three, and the coating cannot be prepared.

Comparative example 4

The difference from the embodiment 1 is that: the composition of the powder of step one need only be adjusted to 20 wt.% nano-titania/80 wt.% nano-alumina.

The results of various characterization tests of the coating are as follows: the abrasion loss was 7.5mg, the porosity was 12.22%, the bonding strength was 30.32MPa, the microhardness was 790HV, and the coating thickness was 240 μm.

Comparative example 5

The difference from the embodiment 1 is that: only the composition of the powder of step one needs to be adjusted to 0.5 wt.% nano titanium oxide/99.5 wt.% nano aluminum oxide.

The results of various characterization tests of the coating are as follows: the abrasion loss was 7.45mg, the porosity was 13.97%, the bond strength was 32.76MPa, the microhardness was 580HV, and the coating thickness was 200 μm.

Characterization of various properties of the coating

The coatings prepared in each of the examples and comparative examples were measured for surface roughness (fig. 5) using a hyper-focal depth scanning microscope (VHX-6000), the roughness corresponding to the normal range of the coating prepared by plasma thermal spraying; testing the wear resistance of the coating by a friction and wear tester; measuring the corrosion resistance of the coating by using an electrochemical workstation; the microstructure of the coating was characterized by X-ray diffractometry (XRD), Field Emission Scanning Electron Microscopy (FESEM) (fig. 9).

Upon raman spectroscopy testing of the example 1 coating (fig. 1), comparing the graphene nanoplatelets, it can be seen that there is an D, G, G' peak of graphene in the coating that corresponds exactly to the graphene nanoplatelets, and that the peaks of alumina between 100 and 500 of example 1 also correspond exactly to the original powder.

The results of X-ray diffraction measurements of the coating of example 1, i.e., the pure nano-alumina coating and the nano-alumina powder, are shown in FIG. 2, which shows that after atmospheric plasma spraying, the α -Al concentration is between 60 and 70 °₂O₃Is converted into gamma-Al₂O₃It is supposed that the phase change occurs under the high temperature rapid cooling of the plasma spraying.

The X-ray diffraction measurements of the coatings prepared in the examples and comparative examples are shown in FIG. 2, in which a portion of the α -Al is observed after the atmospheric plasma spraying₂O₃Is converted into gamma-Al₂O₃It is supposed that the phase change occurs under the high temperature rapid cooling of the plasma spraying.

The coatings prepared in the examples and the comparative examples are subjected to a friction wear test, the test piece is pretreated before measurement, the surface roughness of the coating is reduced to 4 mu M by the target, and then the coating is cleaned, dried and weighed, and the recorded data is M₁The same weighing record data after the friction and wear test is M₂And then the mass loss before and after the abrasion is calculated. The pair grinding pair of the friction and wear test is silicon nitride (Si)₃N₄) The number of revolutions of the counter-grinding pair was 300r/min, the friction radius was 5mm, the friction time was 30min, and the wear loss data are shown in FIG. 3. It is visually apparent from the figure that the abrasion amounts of examples 1 to 4 and comparative example 1 are lower than that of the matrix, and particularly, example 1 exhibits superior abrasion resistance.

The coatings prepared in examples and comparative examples were tested for bonding strength using a universal tester. Before testing, the test piece is adhered to a standard drawing test piece by using E7 glue, and then the bonding strength is tested, wherein the tensile increasing speed of a universal testing machine is set to be 0.2N/s. The results are shown in FIG. 4. The bonding strength of the example 1 is the maximum and reaches 52.95MPa, the bonding strength of the example 3 is the minimum and is 47.07MPa, the bonding strength of the examples 1-4 and the comparative example 1 is 47 MPa-53 MPa, and the 5 groups of examples have higher bonding strength.

The coating prepared in example 1 was at 0.5mol/L H₂SO₄Corrosion resistance tests were performed in solutions of 1mol/L NaOH and 3.5 wt.% NaCl, and the results are shown in fig. 6, fig. 7, fig. 8, fig. 6 being polarization curves in sulfuric acid solution, fig. 7 being polarization curves in alkaline solution, fig. 8 being polarization curves in saline solution. From the figure, the corrosion resistance of each coating to acid, sulfate ions, alkali and chloride ions is higher than that of a #45 steel substrate.

SEM characterization tests were performed on the surface topography of example 1, as shown in fig. 9. It can be seen that the surfaces all show better melting state, the distribution is more uniform, and the characteristic state of the coating surface shows better.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and should not be taken as limiting the invention, and all modifications, equivalents, improvements, etc. that are made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A preparation method of an alumina coating doped with graphene nanosheets is characterized by comprising the following steps: the preparation method comprises the following specific steps:

(1) preparing nano aluminum oxide composite powder doped with graphene nano sheets for plasma spraying;

the preparation method of the composite powder comprises the following steps: ball-milling the graphene nanosheets and the alumina powder for 4 hours by using a ball mill according to the proportion, promoting the uniform mixing of the graphene nanosheets and the alumina powder, adding a PVA solution for granulation to enable the nano alumina powder to wrap the surfaces of the graphene nanosheets, and finally obtaining composite powder with good fluidity;

(3) and (3) preparing a coating, namely melting the powder prepared in the step (1) through plasma thermal spraying by using a 9MB plasma spray gun, depositing the melted powder on the substrate treated in the step (2) in batches to obtain the graphene-doped nanosheet alumina coating, wherein the substrate is arranged on a plate-shaped fixture and fixed on a rotary worktable.

2. The preparation method of the graphene nanoplatelet doped alumina coating according to claim 1, which is characterized in that: in the composite powder in the step (1), the graphene nanosheet and the nano-alumina are in mass percent: 0.1-1% of graphene nano-sheets, 99-99.9 wt.% of nano-alumina.

3. The preparation method of the graphene nanoplatelet doped alumina coating according to claim 1, which is characterized in that: the substrate in the step (2) includes but is not limited to titanium alloy, stainless steel, carbon steel or copper alloy.

4. The preparation method of the graphene nanoplatelet doped alumina coating according to claim 1, which is characterized in that: and (3) soaking the oil and stain removal in acetone solution, and then carrying out ultrasonic cleaning by using absolute ethyl alcohol, wherein the sand blasting is carried out by using 24-80 # brown corundum, and the pressure of the sand blasting is 0.4-0.6 MPa.

5. The preparation method of the graphene nanoplatelet doped alumina coating according to claim 1, which is characterized in that: the plasma spraying conditions in the step (3) are as follows: h₂The flow rate is 8slpm, the Ar flow rate is 40slpm, the spraying power is 30-45 Kw, the spraying distance is 60-120 mm, and the powder feeding rate is 30 g/min.

6. The preparation method of the graphene nanoplatelet doped alumina coating according to claim 1, which is characterized in that: the diameter of the rotary worktable in the step (3) is 50-300 mm, and the rotating speed is 80-300 rpm.

7. The preparation method of the graphene nanoplatelet doped alumina coating according to claim 1, which is characterized in that: the thickness of the composite coating in the step (3) is 200-300 μm.