A nano-carbon material modified aluminum trioxide / chromium trioxide composite coating, a preparation method and application thereof

Abstract

The application belongs to the technical field of coating, and discloses a nano-carbon material modified aluminum oxide / chromium trioxide composite coating, a preparation method and application thereof, wherein the composite coating is prepared by first spraying NiCrAlY powder on a base to obtain a transition layer, and then spraying nano-carbon material modified Al2O3-Cr2O3 composite powder on the transition layer by plasma spraying; the nano-carbon material modified Al2O3-Cr2O3 composite powder is prepared by mixing Cr2O3 nano-powder, Al2O3 nano-powder, nano-carbon material and an organic binder, and then screening after spray granulation. The composite powder is spherical particles with a particle size of 15-80 microns, and the microstructure of the composite powder is a three-dimensional network nanostructure; the composite coating has high phase stability and wear resistance, and provides an important way for the preparation of Al2O3-based composite coatings with high phase stability and high performance.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coating, more particularly, relates to a nano-carbon material modified Al2O3-Cr2O3 composite coating and a preparation method and application thereof. TECHNICAL BACKGROUND

[0002] Al2O3 and its composite coating generally have excellent insulation performance, high hardness, high wear resistance and high corrosion resistance, and have broad application prospects in the field of wear resistance, corrosion resistance and oxidation resistance protection of metal parts. However, since Al2O3 has various crystal structures such as α-Al2O3, κ-Al2O3, θ-Al2O3, γ-Al2O3, δ-Al2O3 and η-Al2O3, and the α-Al2O3 phase is a stable phase, different metastable Al2O3 phases such as θ-Al2O3 and γ-Al2O3 phases are easily formed in the coating during spraying due to high cooling rate, which reduces the performance of the coating. Researchers introduce TiO2 and YSZ into Al2O3, which effectively improves the mechanical properties of Al2O3 coating, and prepares Al2O3-TiO2 and Al2O3-YSZ composite coatings with high fracture toughness. However, TiO2 and YSZ do not have obvious stabilizing effect on high-temperature α-Al2O3 phase.

[0003] Cr2O3 has the same crystal structure as high-temperature α-Al2O3, which can effectively stabilize the high-temperature α-Al2O3 phase, reduce the content of metastable Al2O3 phase in the coating, and improve the comprehensive performance of the coating. Al2O3-Cr2O3 composite coating has high hardness, wear resistance and corrosion resistance. However, current Al2O3-Cr2O3 composite coatings are generally prepared by using micron-sized Al2O3 and Cr2O3 particles, and Al2O3 and Cr2O3 cannot fully contact and solid solution during spraying, which leads to the fact that α-Al2O3 phase cannot be effectively stabilized. Therefore, there are still a large number of metastable Al2O3 phases in traditional micron-structured Al2O3-Cr2O3 composite coatings. In addition, similar to other ceramic coatings, Al2O3-Cr2O3 composite coating also has high friction coefficient, and the wear resistance under high contact stress is insufficient. SUMMARY

[0004] In order to solve the above-mentioned problems in the prior art, the present application is aimed at providing a nano-carbon material modified Al2O3-Cr2O3 composite coating. The composite coating uses nano-carbon material in the composite powder to endow the coating with low friction coefficient and high wear resistance, so as to have better comprehensive performance.

[0005] Another object of the present application is to provide a preparation method of the nano-carbon material modified Al2O3-Cr2O3 composite coating. By using the nano-carbon material modified Al2O3-Cr2O3 composite powder, the nano-Al2O3 and Cr2O3 can be fully contacted and solid-solved during spraying, the high-temperature Al2O3 phase can be effectively stabilized, the Al2O3-Cr2O3 composite coating with high phase stability can be obtained, the friction coefficient of the Al2O3-Cr2O3 composite coating can be reduced, and the wear resistance of the composite coating can be improved.

[0006] Still another object of the present application is to provide an application of the nano-carbon material modified Al2O3-Cr2O3 composite coating.

[0007] The object of the present application is achieved by the following technical solutions.

[0008] The nano-carbon material modified Al2O3-Cr2O3 composite coating is prepared by first spraying NiCrAlY powder on a substrate to form a transition layer, and then plasma spraying nano-carbon material modified Al2O3-Cr2O3 composite powder on the transition layer. The nano-carbon material modified Al2O3-Cr2O3 composite powder is prepared by mixing Cr2O3 nano-powder, Al2O3 nano-powder, nano-carbon material, organic binder and deionized water, and then sieving the spray granules. The mass ratio of the Cr2O3 nano-powder to the Al2O3 nano-powder is 1:(0.5-2). The content of the nano-carbon material is 0.5-10% of the total mass of the Al2O3 nano-powder and the Cr2O3 nano-powder. The addition amount of the organic binder is 0.5-1.5% of the total mass of the Al2O3 nano-powder, the Cr2O3 nano-powder and the nano-carbon material. The ratio of the deionized water to the total mass of the Al2O3 nano-powder and the Cr2O3 nano-powder is (0.3-0.6):1. The composite powder is spherical particles with a particle size of 15-80 μm, and the microstructure of the composite powder is a three-dimensional network nanostructure.

[0009] Preferably, the nano-carbon material is one or more of carbon nanotubes, graphene, graphene oxide, fullerene, nano-porous carbon and nano-carbon fiber. The organic binder is sodium carboxymethyl cellulose, carboxymethyl cellulose, polyvinyl alcohol or polypropylene alcohol.

[0010] More preferably, the carbon nanotubes have a tube diameter of 5-15 nm. The graphene has 1-10 layers of carbon atom layers and a particle size of 5-8 μm. The graphene oxide has a lateral size of 50-100 nm. The nano-carbon fiber has a diameter of 50-100 nm and a length of 10-20 μm. The fullerene has a diameter of 10-20 nm. The nano-porous carbon has a pore size of 10-20 nm.

[0011] Preferably, the average particle size of the Cr2O3 nanopowder is 50-100 nm; the average particle size of the Al2O3 nanopowder is 20-50 nm.

[0012] Preferably, the thickness of the transition layer is 60-100 μm, and the thickness of the composite coating is 150-300 μm.

[0013] Preferably, the substrate is pure metal, iron-based alloy, nickel-based alloy, cobalt-based alloy or hard alloy.

[0014] The preparation method of the nanocarbon material modified Al2O3-Cr2O3 composite coating comprises the following specific steps:

[0015] S1. After mixing the nanocarbon material and deionized water, ball milling is performed for 1-2 h, then Cr2O3 nanopowder is added and ball milling is continued for 3-6 h; then Al2O3 nanopowder is added and ball milling is continued for 12-24 h; finally, an organic binder is added and ball milling is continued for 0.5-1 h, after separation, a mixed slurry is prepared;

[0016] S2. The mixed slurry is continuously stirred, and a peristaltic pump is used to guide the mixed slurry into a spray granulation device for spray granulation, the inlet temperature is 255-260℃, and the outlet temperature is 105-110℃, after screening, a nanocarbon material modified Al2O3-Cr2O3 composite powder is prepared;

[0017] S3. The NiCrAlY powder and the nanocarbon material modified Al2O3-Cr2O3 composite powder are plasma sprayed on the substrate, and a NiCrAlY transition layer and a nanocarbon material modified Al2O3-Cr2O3 composite coating are sequentially prepared on the substrate.

[0018] The function of the transition layer is to reduce the thermal stress between the surface layer and the metal substrate due to the large difference in the thermal expansion coefficient, and to avoid the peeling of the coating.

[0019] Preferably, the process parameters of the plasma spraying in step S3 are as follows: the main gas flow rate is 30-50 L / min, the current is 500-650 A, the power is 30-40 kW, the rotation speed of the disc is 28%, the powder feeding rate is 30-40 g / min, and the spraying distance is 80-110 mm.

[0020] Preferably, the particle size of the NiCrAlY powder in step S3 is 45-105 μm.

[0021] The nanocarbon material modified Al2O3-Cr2O3 composite coating is used in the protection field of parts such as aero-engine, automobile engine, bearing, cutter, blast furnace tuyere and graphite electrode, and is used as a heat-insulating, wear-resistant, ablation-resistant and oxidation-resistant coating.

[0022] The present application adopts nano carbon material to modify Al2O3-Cr2O3 nano structure spherical powder for spraying, and the particle size of the powder used is between 15-80 microns. Because the nano particles are lighter in mass, they cannot be directly used as the spraying feed, and after spray granulation, the nano particles are agglomerated to form larger size spherical particles, and then the spraying can be carried out. During the spraying, part of the particles are not fully melted. In addition, the molten particles have a fast cooling speed, and the grains are not fully grown. Therefore, the nano structure composite coating can be obtained by using the nano carbon material modified Al2O3-Cr2O3 nano structure composite powder as the feed. By using the modification of the nano carbon material, the self-lubricating property is given to the coating, the friction coefficient of the coating is reduced, and the wear resistance of the coating is improved.

[0023] The present application adopts the spray granulation method to prepare the nano carbon material modified Al2O3-Cr2O3 composite powder, and the powder structure is a three-dimensional network nano structure, which has the following main advantages: (1) the Al2O3 nano particles and the Cr2O3 nano particles are fully contacted, melted and solid-solved, which can effectively stabilize the high temperature alpha-Al2O3 phase and reduce the content of the metastable Al2O3 phase in the coating; (2) the nano structure coating has higher compactness and mechanical properties. The main effects of the nano carbon material modification are: (1) giving the self-lubricating property to the coating, reducing the friction coefficient of the coating; (2) improving the wear resistance of the coating.

[0024] The molten droplets of the micron level powder particles do not have sufficient contact with each other during the thermal spraying process, and therefore the full solid solution cannot be formed between the particles of different components, and the stabilizing effect of Cr2O3 on the alpha-Al2O3 phase cannot be effectively realized. By using the nano level powder, the powder particles with uniform components can be prepared through the ball milling and spray granulation. When the powder particles are melted, the nano Cr2O3 and Al2O3 particles in the same particle are simultaneously melted to form a good solid solution in the liquid state, which plays a role in stabilizing the alpha-Al2O3 phase.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] 1. The composite coating of the present application uses the nano carbon material modified Al2O3-Cr2O3 composite powder, and the full solid solution of the Al2O3 nano particles and the Cr2O3 nano particles is realized during the spraying, which effectively stabilizes the alpha-Al2O3 phase in the composite coating, reduces the content of the metastable Al2O3 phase in the coating, and can obtain the Al2O3-Cr2O3 composite coating with high phase stability, while reducing the friction coefficient of the Al2O3-Cr2O3 composite coating and improving the wear resistance of the composite coating.

[0027] 2. The nano carbon material modified Al2O3-Cr2O3 nano structure composite powder of the present application inhibits the generation of metastable phase in the Al2O3 coating, improves the phase stability of the Al2O3-Cr2O3 composite coating, effectively reduces the friction coefficient of the composite coating by the nano carbon material, so that the composite coating has self-lubricating performance, improves the wear resistance of the composite coating, and provides an important way for the preparation of high phase stability and high performance Al2O3-based composite coating. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 are morphology photos of the Al2O3-40% Cr2O3 nano structure powder prepared in Comparative Example 1 and the graphene modified Al2O3-40% Cr2O3 nano structure composite powder prepared in Examples 1-3;

[0029] Figure 2 are morphologies of the Al2O3-40% Cr2O3 nano structure coating prepared in Comparative Example 1 and the graphene modified Al2O3-40% Cr2O3 nano structure composite coating prepared in Examples 1-3;

[0030] Figure 3 are XRD diffraction patterns of the Al2O3-40% Cr2O3 nano structure coating prepared in Comparative Example 1 and the graphene modified Al2O3-40% Cr2O3 nano structure composite coating prepared in Examples 1-3.

[0031] Figure 4 are changes of the friction coefficient of the Al2O3-40% Cr2O3 nano structure coating prepared in Comparative Example 1 and the graphene modified Al2O3-40% Cr2O3 nano structure composite coating prepared in Examples 1-3 with time.

[0032] Figure 5 are wear rates of the Al2O3-40% Cr2O3 nano structure coating prepared in Comparative Example 1 and the graphene modified Al2O3-40% Cr2O3 nano structure composite coating prepared in Examples 1-3. DETAILED DESCRIPTION

[0033] The present application will be further described in conjunction with specific examples, but should not be understood as a limitation of the present application. If not specifically indicated, the technical means used in the examples are conventional means known to those skilled in the art. Unless specifically indicated, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the technical field.

[0034] Example 1

[0035] 1. Weigh 200g of deionized water, 120g of Cr2O3 nanoparticles (average particle size 100nm), 180g of Al2O3 nanoparticles (average particle size 50nm), 3g of graphene (1-10 carbon atom layers, particle size 5-8μm), and 30g of 5% sodium carboxymethyl cellulose solution. Weigh grinding balls with diameters of 5mm, 10mm, and 15mm, prepare a mixture in a mass ratio of 6:3:1, and load it into a ball mill jar. Then, add deionized water and graphene sequentially, and ball mill at 350r / min for 1 hour. Next, add Cr2O3 and ball mill at the same speed for 3 hours. Then, add Al2O3 and ball mill at the same speed for 12 hours. Finally, add the organic binder solution and ball mill for 1 hour. After ball milling, separate the grinding balls and the slurry to obtain a mixed slurry.

[0036] 2. Place the mixed slurry in a container, stir and spray granulate. Control the inlet temperature at 255-260℃ and the outlet temperature at 105-110℃. Sieve the spray-granulated powder to obtain graphene-modified Al2O3-Cr2O3 nanostructured composite powder with a particle size of 15-80μm.

[0037] 3. Using the SULZER METCO 9MC device, to Using 45# steel as the substrate, NiCrAlY powder (45–105 μm) and graphene-modified Al2O3-Cr2O3 nanostructured composite powder were sequentially sprayed onto the substrate to form a NiCrAlY transition layer and a graphene-modified Al2O3-Cr2O3 composite coating. The thickness of the NiCrAlY transition layer was 80 ± 20 μm, and the thickness of the graphene-modified Al2O3-Cr2O3 composite coating was 200 ± 20 μm.

[0038] Example 2

[0039] 1. Weigh 200g of deionized water, 120g of Cr2O3 nanoparticles (average particle size 100nm), 180g of Al2O3 nanoparticles (average particle size 50nm), 9g of graphene (1-10 carbon atom layers, particle size 5-8μm), and 30g of 5% sodium carboxymethyl cellulose solution. Weigh grinding balls with diameters of 5, 10, and 15mm, prepare a mixture in a mass ratio of 6:3:1, and load it into a ball mill jar. Then, add deionized water and graphene sequentially, and ball mill at 350r / min for 1 hour. Add Cr2O3 and continue ball milling at the same speed for 3 hours, then add Al2O3 and continue ball milling at the same speed for 12 hours. After ball milling, separate the grinding balls and the slurry to obtain a mixed slurry.

[0040] 2. Put the mixed slurry into a container and stir and spray granulate, control the inlet temperature at 255-260°C and the outlet temperature at 105-110°C, sieve the powder after spray granulation to obtain graphene modified Al2O3-Cr2O3 nano-structured composite powder with a particle size of 15-80 μm.

[0041] 3. Use SULZER METCO 9MC equipment, take 45# steel as the substrate, and spray NiCrAlY powder and graphene modified Al2O3-Cr2O3 nano-structured composite powder in sequence to obtain NiCrAlY transition layer and graphene modified Al2O3-Cr2O3 composite coating on the substrate in sequence. The thickness of the transition layer NiCrAlY is 80±20 μm, and the thickness of the graphene modified Al2O3-Cr2O3 composite coating is 200±20 μm.

[0042] Example 3

[0043] 1. Take 200 g of deionized water, 120 g of Cr2O3 nano-powder (average particle size 100 nm), 180 g of Al2O3 nano-powder (average particle size 50 nm), 18 g of graphene (1-10 layers of carbon atom layers, particle size 5-8 μm), and 30 g of a 5% mass concentration carboxymethyl cellulose sodium solution. Take grinding balls with diameters of 5, 10, and 15 mm, and prepare them according to a mass ratio of 6:3:1, and load them into a ball mill jar. Then add deionized water and graphene in sequence, control the rotation speed of the ball mill at 350 r / min, and ball mill for 1 h. Then add Cr2O3 and keep the rotation speed unchanged for continuous ball milling for 3 h; then add Al2O3 and keep the rotation speed unchanged for continuous ball milling for 12 h. After ball milling, separate the grinding balls and the slurry to obtain a mixed slurry;

[0044] 2. Put the mixed slurry into a container and stir and spray granulate, control the inlet temperature at 255-260°C and the outlet temperature at 105-110°C, sieve the powder after spray granulation to obtain graphene modified Al2O3-Cr2O3 nano-structured composite powder with a particle size of 15-80 μm.

[0045] 3. Use SULZER METCO 9MC equipment, take 45# steel as the substrate, and spray NiCrAlY powder and graphene modified Al2O3-Cr2O3 nano-structured composite powder in sequence to obtain NiCrAlY transition layer and graphene modified Al2O3-Cr2O3 composite coating on the substrate in sequence. The thickness of the transition layer NiCrAlY is 80±20 μm, and the thickness of the graphene modified Al2O3-Cr2O3 composite coating is 200±20 μm. 3. Use SULZER METCO 9MC equipment, take 45# steel as the substrate, and spray NiCrAlY powder and graphene modified Al2O3-Cr2O3 nano-structured composite powder in sequence to obtain NiCrAlY transition layer and graphene modified Al2O3-Cr2O3 composite coating on the substrate in sequence. The thickness of the transition layer NiCrAlY is 80±20 μm, and the thickness of the graphene modified Al2O3-Cr2O3 composite coating is 200±20 μm.​

[0046] Comparative Example 1

[0047] 1. Weigh 200g of deionized water, 120g of Cr2O3 nanoparticles (average particle size 100nm), 180g of Al2O3 nanoparticles (average particle size 50nm), and 30g of 5% sodium carboxymethyl cellulose solution. Weigh grinding balls with diameters of 5, 10, and 15mm, prepare the mixture in a mass ratio of 6:3:1, and load it into a ball mill jar. Maintain a constant rotation speed of 350r / min throughout the process. Then, add deionized water and Cr2O3 sequentially, and maintain the rotation speed for 3 hours. Next, add Al2O3 and maintain the rotation speed for 12 hours. After ball milling, separate the grinding balls and the slurry to obtain a mixed slurry.

[0048] 2. Place the mixed slurry into a mixer and continuously stir and spray granulate. Control the inlet temperature to 255-260℃ and the outlet temperature to 105-110℃. Sieve the spray-granulated powder to obtain Al2O3-Cr2O3 nanostructured composite powder with a particle size of 15-80μm.

[0049] 3. Using the SULZERMETCO 9MC device, to Using 45# steel as the substrate, NiCrAlY powder (45-105μm) and Al2O3-Cr2O3 nanostructured composite powder were sequentially sprayed onto the substrate to form a NiCrAlY transition layer and an Al2O3-Cr2O3 composite coating. The thickness of the NiCrAlY transition layer was 80±20μm, and the thickness of the Al2O3-Cr2O3 composite coating was 200±20μm.

[0050] Figure 1 These are morphological photographs of the Al2O3-40%Cr2O3 nanostructure powder in Comparative Example 1 and the graphene-modified Al2O3-40%Cr2O3 nanostructure composite powder prepared in Examples 1-3. Specifically, (a) and (b) show the Al2O3-Cr2O3 composite powder and its microstructure in Comparative Example 1, respectively; (c) and (d) show the graphene-modified Al2O3-Cr2O3 composite powder and its microstructure in Example 1, respectively; (e) and (f) show the graphene-modified Al2O3-Cr2O3 composite powder and its microstructure in Example 2, respectively; and (g) and (h) show the graphene-modified Al2O3-Cr2O3 composite powder and its microstructure in Example 3, respectively. Figure 1It can be seen that the Al2O3-40%Cr2O3 nanostructured powder prepared in Comparative Example 1 and the graphene modified Al2O3-40%Cr2O3 nanostructured composite powder prepared in Examples 1-3 both have good sphericity and the powder is dense. From the microstructure, the composite powder is a three-dimensional network nanostructure, but as the amount of graphene increases, the density of the powder particles decreases; from the morphology, the sphericity of the powder slightly decreases. Figure 2 are the morphologies of the Al2O3-40%Cr2O3 composite coating prepared in Comparative Example 1 and the graphene modified Al2O3-40%Cr2O3 nanostructured composite coating prepared in Examples 1-3. Among them, (a) is the Al2O3-Cr2O3 composite coating prepared in Comparative Example 1, (b) is the graphene modified Al2O3-Cr2O3 composite coating prepared in Example 1, (c) is the graphene modified Al2O3-Cr2O3 composite coating prepared in Example 2, and (d) is the graphene modified Al2O3-Cr2O3 composite coating prepared in Example 3. From the Figure 2 It can be seen that the composite coatings of Comparative Example 1 and Examples 1-3 are all stacked structures of lamellar. Figure 1 and Figure 2 The results prove that the sprayable nanostructured composite powder and the composite coating thereof are prepared.

[0051] Figure 3 are the XRD diffraction patterns of the Al2O3-40%Cr2O3 nanostructured composite coating prepared in Comparative Example 1 and the graphene modified Al2O3-40%Cr2O3 nanostructured composite coating prepared in Examples 1-3. From the Figure 3 It can be seen in the 0.9 Cr 0.1 )2O3 diffraction peak is relatively obvious, indicating that the Cr2O3 and Al2O3 in the composite coating form (Al 0.9 Cr 0.1 )2O3 solid solution; the intensity of the α-Al2O3 and (Al 0.9 Cr 0.1 )2O3 diffraction peaks is strong, and the intensity of the γ-Al2O3 diffraction peak is relatively weak; both the α-Al2O3 and (Al 0.9 Cr 0.1 )2O3 are hexagonal crystals, indicating that the Cr2O3 effectively stabilizes the α-Al2O3 phase.

[0052] The tribological properties of the coatings were tested using an HT-1000 high-temperature tribological testing machine. Silicon nitride balls with a diameter of 6 mm were used as the wear targets. During the test, the sample rotation speed was 400 r / min, the wear radius was 8 mm, and the sliding time was 20 min. A normal load of 15 N was applied to the wear targets. Data was collected and the change curve of the friction coefficient over time was recorded using a computer-controlled program. The cross-sectional area of ​​the wear track was measured using a laser confocal microscope, and the wear volume was calculated. Three samples were tested for each coating type, and the average value was taken. Figure 4 The coefficient of friction of the Al2O3-40%Cr2O3 nanostructured composite coating prepared in Comparative Example 1 and the graphene-modified Al2O3-40%Cr2O3 nanostructured composite coating prepared in Examples 1-3 changes over time. Figure 4 As can be seen, with the increase of graphene content, the friction coefficient of the composite coatings in Examples 1-3 first decreases and then increases during the break-in period. The composite coating exhibits the lowest friction coefficient when the graphene content is 3%. The addition of graphene reduces the friction coefficient of the coating.

[0053] Figure 5 The wear rates are compared between the Al2O3-40%Cr2O3 nanostructured composite coating prepared in Example 1 and the graphene-modified Al2O3-40%Cr2O3 nanostructured composite coating prepared in Examples 1-3. Figure 5 As can be seen, compared with the composite coating without graphene in Comparative Example 1, the composite coatings containing graphene in Examples 1-3 have a lower wear rate. Graphene effectively improves the wear resistance of the composite coating by more than 37%, especially when the graphene content is 3%, the wear resistance of the composite coating is the best.

[0054] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A nanocarbon material-modified aluminum trioxide / chromium trioxide composite coating, characterized by, The composite coating is prepared by first spraying NiCrAlY powder on the substrate to form a transition layer, and then plasma spraying nano-carbon material modified Al2O3-Cr2O3 composite powder on the transition layer to form the composite coating. The nano-carbon material modified Al2O3-Cr2O3 composite powder is prepared by mixing 120 g of Cr2O3 nano-powder, 180 g of Al2O3 nano-powder, 9 g of nano-carbon material, an organic binder and 200 g of deionized water, then spray granulating and sieving; wherein the organic binder is 30 g of a 5% carboxymethyl cellulose sodium solution; the composite powder is spherical particles with a particle size of 15-80 μm, and the microstructure of the composite powder is a three-dimensional network nanostructure. The nano-carbon material is graphene, which is 1-10 layers of carbon atom layers with a particle size of 5-8 μm; the average particle size of the Cr2O3 nano-powder is 50-100 nm; the average particle size of the Al2O3 nano-powder is 20-50 nm; the thickness of the transition layer is 60-100 μm, and the thickness of the composite coating is 150-300 μm.

2. The nanocarbon material-modified alumina / chromia composite coating according to claim 1, characterized by, The substrate is pure metal, iron-based alloy, nickel-based alloy, cobalt-based alloy or hard alloy.

3. The method for producing a nanocarbon material-modified alumina / chromia composite coating according to claim 1 or 2, characterized by, The specific steps are as follows: S1. Mix the nano-carbon material and deionized water, then ball mill for 1-2 h, then add the Cr2O3 nano-powder and continue to ball mill for 3-6 h; then add the Al2O3 nano-powder and continue to ball mill for 12-24 h; finally add the organic binder and continue to ball mill for 0.5-1 h, then separate to obtain the mixed slurry; S2. Continuously stir the mixed slurry, use a peristaltic pump to introduce the mixed slurry into a spray granulation device for spray granulation, the inlet temperature is 255-260 °C, and the outlet temperature is 105-110 °C, then sieve to obtain the nano-carbon material modified Al2O3-Cr2O3 composite powder; S3. Plasma spray the NiCrAlY powder and the nano-carbon material modified Al2O3-Cr2O3 composite powder on the substrate to form a NiCrAlY transition layer and a nano-carbon material modified Al2O3-Cr2O3 composite coating on the substrate in sequence.

4. The method of claim 3, wherein the nanocarbon-modified alumina / chromia composite coating is prepared by the steps of: (a) preparing a slurry by mixing alumina, chromia, and a nanocarbon material; (b) applying the slurry to a substrate; and (c) sintering the slurry. The process parameters of the plasma spraying in step S3 are as follows: the main gas flow rate is 30-50 L / min, the current is 500-650 A, the power is 30-40 kW, the powder feeding rate is 30-40 g / min, and the spraying distance is 80-110 mm.

5. The method of claim 3, wherein the nanocarbon-modified alumina / chromia composite coating is prepared by the steps of: (a) preparing a slurry by mixing alumina, chromia, and a nanocarbon material; (b) applying the slurry to a substrate; and (c) sintering the slurry. The particle size of the NiCrAlY powder in step S3 is 45-105 μm.

6. The nano-carbon material modified aluminum oxide / chromium oxide composite coating of claim 1 or 2 is used in the protection field of aero-engine, automobile engine, bearing, cutter, blast furnace tuyere, and graphite electrode parts.

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