Preparation method for thermal control coating

Abstract

A preparation method for a thermal control coating, comprising the following steps: A) cleaning a substrate and then carrying out sandblasting treatment; B) preheating the substrate obtained in step A); C) spraying a NiCrCoAlY transition layer on the surface of the substrate obtained in step B); and D) carrying out plasma spraying on the surface of the substrate obtained in step C) to obtain an aluminum oxide coating. Compared with existing electrochemical aluminum oxide thermal control coatings, the aluminum oxide coating prepared by means of plasma spraying has high binding strength, high hardness, good wear resistance, and high spectral reflection performance and infrared emission performance.

Description

A method for preparing a thermal control coating

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 30, 2023, with application number 2023107985978 and invention name “A Method for Preparing a Thermal Control Coating”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present invention relates to the technical field of thermal control coatings, and in particular to a method for preparing a thermal control coating. Background Art

[0003] 2A12 aluminum alloy is widely used in structures such as spacecraft shells, brackets, and rotating deployment mechanisms due to its low manufacturing cost, high specific strength, low density, and easy machining. However, during space operations, spacecraft can only achieve heat exchange through thermal radiation. Under the influence of solar radiation and its own internal heat sources, the low-emissivity aluminum alloy surface is subjected to excessive heat loads, which can seriously affect the normal operation of the spacecraft. By forming a thermal control coating on the surface, the aluminum alloy surface can reduce its absorption of solar radiation and enhance its ability to radiate heat to the external space, thereby lowering the thermal equilibrium temperature of the spacecraft and ensuring that the spacecraft and its internal instruments and equipment remain within the normal operating temperature range.

[0004] Currently, commonly used thermal control coatings for aluminum alloy surfaces are mainly divided into white paint-based thermal control coatings, electrochemical ceramic-based thermal control coatings, and secondary surface mirror-based thermal control coatings. White paints primarily consist of white powders (such as ZnO, TiO2, and Al2O3) and binders (epoxy resins, acrylic resins, and silicates). The coatings are deposited on the substrate surface by coating or air spraying and then cured to form thermal control coatings. Paint-based thermal control coatings offer advantages such as simple preparation, high efficiency, and easy maintenance. However, the binder degrades in ultra-vacuum and alternating hot and cold environments, causing the coating to harden, thereby reducing the adhesion between the coating and the substrate. Electrochemical ceramic-based thermal control coatings are aluminum oxide coatings formed on aluminum alloy surfaces via anodic oxidation or plasma electrolytic oxidation (PEO). In recent years, researchers have achieved tunable microstructure and composition of the coatings by adjusting the electrolyte composition and optimizing electrical parameters, thereby improving their performance. However, the coatings suffer from poor high-temperature resistance and pose pollution issues during production. Secondary surface mirror-type thermal control coatings, generally referring to silver-plated films and optical solar reflectors (OSRs), have high infrared emissivity and low solar absorptivity, and exhibit good stability in practical applications. However, vacuum silver plating as a second surface mirror is expensive and complex to prepare, making it unsuitable for thermal control coatings on the surfaces of large and complex components. In addition, secondary surface mirror-type coatings have poor wear resistance and are easily worn or even peeled off in harsh space environments, resulting in a decrease in coating performance. In summary, due to the limitations of the preparation process and material properties, the mechanical properties and wear resistance of traditional thermal control coatings still need to be improved.

[0005] Plasma spraying is a mature and widely used surface treatment technology, offering advantages such as high deposition efficiency, minimal surface restrictions on the workpiece surface, and strong bonding strength with the substrate. In recent years, plasma-sprayed alumina coatings have been widely used in various fields due to their high hardness, excellent corrosion and wear resistance, and outstanding chemical stability.

[0006] At present, there are few studies on the thermal control performance of plasma sprayed alumina coatings at home and abroad, and the thermal control performance of the coating (solar absorption ratio (α s ) and infrared emissivity (ε) are usually determined by its microstructure and composition. Therefore, the use of plasma spraying technology to prepare aluminum oxide coatings to achieve improved mechanical properties and thermal control properties is of great significance for thermal control coatings.

[0007] Summary of the Invention

[0008] The technical problem solved by the present invention is to provide a method for preparing a thermal control coating, which has high bonding strength, high hardness, good wear resistance, and good spectral reflection performance and infrared emission performance.

[0009] In view of this, the present application provides a method for preparing a thermal control coating, comprising the following steps:

[0010] A) Clean the substrate and then perform sandblasting;

[0011] B) preheating the substrate obtained in step A);

[0012] C) spraying a NiCrCoAlY transition layer on the surface of the substrate obtained in step B);

[0013] D) Plasma spraying an aluminum oxide coating on the surface of the substrate obtained in step C).

[0014] Preferably, the cleaning method is ultrasonic cleaning, silica quartz sand is used for the sandblasting, and the pressure of the sandblasting is 0.5 to 1.5 MPa.

[0015] Preferably, the preheating treatment adopts plasma flame scanning preheating.

[0016] Preferably, the temperature of the preheating treatment is such that the temperature of the substrate is 120-180°C.

[0017] Preferably, the NiCrCoAlY transition layer is prepared by plasma spraying, and the thickness of the NiCrCoAlY transition layer is 80-150 μm.

[0018] Preferably, in the preparation of the NiCrCoAlY transition layer, the argon flow rate of the plasma spraying is 45-55 L / min, the hydrogen flow rate is 8-10 L / min, the arc current is 500-550 A, the arc voltage is 60-70 V, the spraying power is 30-40 kW, the spraying distance is 120-140 mm, and the powder feeding rate is 20-40 g / min.

[0019] Preferably, in the preparation of the alumina coating, the argon flow rate of the plasma spraying is 40-45 L / min, the hydrogen flow rate is 12-15 L / min, the arc current is 460-580 A, the arc voltage is 71-80 V, the spraying power is 32-41 kW, the spraying distance is 110-130 mm, and the powder feeding rate is 10-30 g / min.

[0020] Preferably, the thickness of the aluminum oxide coating is 100 to 300 μm.

[0021] Preferably, the substrate is 2A12 aluminum alloy.

[0022] The present application provides a method for preparing a thermal control coating, which first pre-treats the surface of a substrate, then pre-heats the obtained substrate, then sprays a NiCrCoAlY transition layer on the obtained substrate surface, and finally plasma sprays an alumina coating on the substrate surface. In the preparation process of the thermal control coating, the present application introduces a NiCrCoAlY alloy layer as a transition layer before spraying the alumina ceramic coating, which reduces the residual thermal stress caused by the huge difference in thermal expansion coefficient between the ceramic coating and the substrate. By plasma spraying the alumina coating, a coating with high bonding strength, high hardness, good wear resistance, high spectral reflection performance and infrared emission performance can be prepared; in addition, the thickness of the coating prepared by this method is controllable, and the environmental harm is relatively weak, and the alumina raw material has strong resistance to proton and electron radiation. The service life of the alumina coating prepared by plasma spraying is less affected by the space environment. On the other hand, the present application optimizes the process parameters in plasma spraying so that the problems of pores, cracks and unmelted particles in the coating are solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a physical photo of the plasma spraying equipment of the present invention;

[0024] FIG2 is a light microscopic morphology photograph of the coatings prepared under different spraying currents according to an embodiment of the present invention;

[0025] FIG3 is an XRD pattern of the coatings prepared under different spraying currents according to an embodiment of the present invention, wherein 2θ in FIGa is 0-90° and 2θ in FIGb is 41-48°;

[0026] FIG4 is a cross-sectional morphology photograph of a sample with and without preheating treatment before spraying a transition layer on the substrate according to the present invention;

[0027] FIG5 is a bar graph showing the hardness, fracture toughness, and bonding strength of an Al2O3 coating prepared according to an embodiment of the present invention;

[0028] FIG6 shows the friction coefficient curve, wear volume and specific wear rate of the Al2O3 coating prepared in an embodiment of the present invention under different loads;

[0029] FIG7 is a bar graph showing the reflectance spectra and emissivity of Al2O3 coatings with different thicknesses prepared according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0031] In view of the problems of weak bonding strength between ceramic coatings and substrates and various defects in the prior art, the present application provides a method for preparing a thermal control coating. The method uses plasma spraying to prepare an aluminum oxide coating, which has high bonding strength, high hardness, good wear resistance, and high spectral reflectivity and infrared emission performance. Specifically, the embodiment of the present invention discloses a method for preparing a thermal control coating, comprising the following steps:

[0032] A) Clean the substrate and then perform sandblasting;

[0033] B) preheating the substrate obtained in step A);

[0034] C) spraying a NiCrCoAlY transition layer on the surface of the substrate obtained in step B);

[0035] D) Plasma spraying an aluminum oxide coating on the surface of the substrate obtained in step C).

[0036] In the process of preparing the thermal control coating, the present application first cleans the substrate and then performs sandblasting to pre-treat the substrate. In the present application, the substrate is selected from an aluminum alloy substrate, more specifically 2A12 aluminum alloy. The cleaning can specifically be performed by ultrasonic cleaning to remove oil stains on the surface of the substrate, and the cleaning agent in the present application is acetone. The specific operation of the sandblasting is carried out in a manner well known to those skilled in the art. The sandblasting is to increase the surface roughness of the substrate and improve the mechanical anchoring between the coating and the substrate; in the present application, the sandblasting is selected from silica quartz sand, and the sandblasting pressure is 0.5 to 1.5 MPa, more specifically, the sandblasting pressure is 0.5 to 1.0 MPa. The surface of the substrate is repeatedly and evenly sandblasted until it is rough and non-reflective.

[0037] The present application then preheats the substrate. This preheating treatment increases the substrate temperature. This preheating treatment reduces the temperature difference between the substrate and the coating, preventing cracking and flaking of the coating caused by thermal stress due to excessive temperature differences. It also promotes the growth of columnar grains in the coating, hindering crack propagation and thereby enhancing the bonding strength between the coating and the substrate. The present application uses a plasma flame to scan and preheat the substrate surface, bringing the substrate temperature to 120-180°C. More specifically, the preheating treatment brings the substrate temperature to 130-160°C.

[0038] According to the present invention, a NiCrCoAlY transition layer is then sprayed on the preheated substrate surface to reduce the residual stress caused by the huge difference in thermal expansion coefficient between the substrate and the alumina coating. The NiCrCoAlY transition layer is prepared by plasma spraying NiCrCoAlY powder; in this process, the particle size of the NiCrCoAlY powder is 35 to 80 μm; the argon flow rate of the plasma spraying is 45 to 55 L / min, the hydrogen flow rate is 8 to 10 L / min, the arc current is 500 to 550 A, the arc voltage is 60 to 70 V, the spraying power is 30 to 40 kW, the spraying distance is 120 to 140 mm, and the powder feeding rate is 20 to 40 g / min; specifically, the argon flow rate of the plasma spraying is 48 to 52 L / min, the hydrogen flow rate is 9 to 10 L / min, the arc current is 510 to 530 A, the arc voltage is 62 to 68 V, the spraying power is 33 to 38 kW, the spraying distance is 128 to 132 mm, and the powder feeding rate is 28 to 35 g / min. The thickness of the NiCrCoAlY transition layer is 80 to 150 μm. Specifically, the thickness of the NiCrCoAlY transition layer is 90 to 120 μm.

[0039] Finally, an aluminum oxide coating is plasma-sprayed onto the substrate surface. Specifically, the aluminum oxide coating is obtained by plasma-spraying aluminum oxide powder onto the substrate surface. The aluminum oxide powder has a particle size of 20 to 80 μm. The plasma spraying is performed in a manner well known to those skilled in the art and is not particularly limited in this application. The argon flow rate of the plasma spraying is 40-45 L / min, the hydrogen flow rate is 12-15 L / min, the arc current is 460-580 A, the arc voltage is 71-80 V, the spraying power is 32-41 kW, the spraying distance is 110-130 mm, and the powder feeding rate is 10-30 g / min; specifically, the argon flow rate of the plasma spraying is 41-43 L / min, the hydrogen flow rate is 13-14 L / min, the arc current is 500-580 A, the arc voltage is 71-78 V, the spraying power is 35-41 kW, the spraying distance is 120-130 mm, and the powder feeding rate is 20-30 g / min. This application solves coating defect problems such as pores, cracks, and unmelted particle distribution by optimizing the above-mentioned parameters of plasma spraying. The thickness of the alumina coating of this application is 100-300 μm.

[0040] Compared to existing electrochemical alumina thermal control coatings, the plasma-sprayed alumina coating produced by this method exhibits high bonding strength, high hardness, excellent wear resistance, and high spectral reflectance and infrared emission properties. Furthermore, the coating thickness produced by this method is controllable, poses minimal environmental hazards, and the alumina raw material exhibits strong resistance to proton and electron radiation. The service life of the alumina coating produced by plasma spraying is minimally affected by the space environment. Therefore, this method is of great significance for the design of long-life, highly reliable spacecraft.

[0041] In order to further understand the present invention, the preparation method of the thermal control coating provided by the present invention is described in detail below with reference to the examples. The protection scope of the present invention is not limited by the following examples.

[0042] Example

[0043] 1) Matrix selection

[0044] The aluminum alloy matrix used in this experiment is 2A12, which is a high-strength hard aluminum alloy. Its technical standard is GB / T 3191-2010. The original size of the experimental specimen is 40 mm × 40 mm × 5 mm plate. The chemical composition and content of the aluminum alloy are shown in Table 1.

[0045] Table 1 Chemical composition of 2A12 aluminum alloy (wt%)

[0046] 2) Powder selection

[0047] The powder materials used for plasma spraying are: alumina powder and NiCrCoAlY powder. Alumina powder and NiCrCoAlY powder are both produced by Beikuang New Material Technology Co., Ltd., with particle sizes of 20-80 μm and 35-80 μm respectively.

[0048] 3) Spraying equipment

[0049] The plasma spraying equipment used was the F6 plasma spray equipment produced by GTV GmbH of Germany. The equipment consists of a Meike F4 plasma spray gun, a manipulator console, a powder feeder, a spray gun control system, and a cooling system, as shown in Figure 1. During the plasma spraying process, powder is fed into the plasma flame of the spray gun through an external powder feeding method. The powder feeding rate can be controlled by adjusting the air flow of the double-barrel gas-carrying powder feeder. During the spraying process, the spray power is controlled by adjusting the primary gas argon flow, the secondary gas hydrogen flow, and the operating current. The temperature of the plasma jet is closely related to the spray power, so the degree of particle melting in the jet can be controlled by adjusting the spray power.

[0050] 4) Coating preparation

[0051] Before spraying, the substrate is ultrasonically cleaned with acetone to remove surface oil stains; then the substrate surface roughness is increased by sandblasting, thereby improving the mechanical anchoring between the coating and the substrate. Silica quartz sand is used for sandblasting, and the sandblasting pressure is 0.5 MPa. The substrate surface is repeatedly and evenly sandblasted until it is rough and non-reflective.

[0052] The substrate surface is then preheated using a plasma flame to a scan pattern, raising the substrate temperature to approximately 150°C. This preheating treatment reduces the temperature difference between the substrate and the coating, as excessive temperature differences can cause thermal stresses that can lead to cracking and peeling in the coating. It also promotes the growth of columnar grains in the coating, hindering crack propagation and thereby enhancing the bonding strength between the coating and the substrate.

[0053] Before depositing the alumina coating, a NiCrCoAlY transition layer with a thickness of about 100 μm was plasma sprayed on the pretreated substrate surface by selecting appropriate process parameters to reduce the damage caused by the aluminum alloy substrate (24×10 -6 K -1 ) and alumina coating (7×10 -6 K -1 ) to reduce the residual stress caused by the huge difference in thermal expansion coefficient between the two layers; finally, an aluminum oxide coating was plasma sprayed on the transition layer. The plasma spraying parameters are shown in Table 2;

[0054] Table 2 Spraying process parameter data table

[0055] Figures 2(a-d) show the cross-sectional metallographic microscopy morphologies of Al2O3 coatings at currents of 400A, 460A, 520A, and 580A, respectively. As can be seen in Figure 2(a), at a current of 400A, a large number of unmelted particles are present in the coating, the coating has fewer completely melted areas, and the deposited coating is thin. This is because at low currents, the plasma flame temperature is low, the degree of melting of the alumina powder is poor, resulting in low deposition efficiency and the appearance of a large number of unmelted particles, pores, cracks, and other defects in the coating. When the spray current is increased to 460A, the spray power increases, the plasma arc has greater heat, and the powder is fully melted. Figure 2(b) shows a significant increase in the thickness of the deposited coating, a significant increase in the completely melted areas in the microstructure, and a gradual decrease in defects such as unmelted particles, pores, and cracks. As the current is further increased, it can be clearly observed that the coating structure becomes denser, as shown in Figures 2(c, d).

[0056] Figure 3 shows the XRD diffraction patterns of plasma sprayed Al2O3 coatings at different spraying currents. As can be seen from Figure 3(a), the Al2O3 coatings not only have the diffraction peaks of the stable α-Al2O3 phase with the same composition as the original powder, but also have the diffraction peaks of the unstable γ-Al2O3 phase. As shown in Figure 3(b), when the current is 400A, the diffraction peak of α-Al2O3 (113) in the plasma sprayed Al2O3 coating is relatively higher than the diffraction peak of γ-Al2O3 (400). This is because the plasma flame temperature is low under low current and only melts the surface of the Al2O3 particles. The deposited coating contains a large number of unmelted particles and incompletely melted areas. Therefore, the coating retains a large amount of original α-Al2O3 phase. The weak diffraction peak of γ-Al2O3 phase in the coating comes from the non-equilibrium solidification of molten alumina at a large cooling rate. Compared with the stable α-Al2O3, the metastable γ-Al2O3 with lower critical free energy is formed during the rapid solidification process (about 10 6 K / s) is easier to nucleate. As the current increases to 460A, that is, the spraying power reaches 32kW, the height of the α-Al2O3 (113) diffraction peak decreases significantly, and the γ-Al2O3 (400) diffraction peak increases significantly. The γ-Al2O3 phase gradually becomes the dominant phase of the alumina coating. This is because the heat of the plasma arc increases with the increase in power, and the Al2O3 powder melts more fully in the plasma arc. Therefore, the droplets form more non-stable γ-Al2O3 phases during the deposition and solidification process. This corresponds to the metallographic micromorphology results of the coating, that is, the greater the relative content of the γ-Al2O3 phase in the coating, the larger the area of ​​the completely melted area in the coating morphology, and the larger the unmelted particles are. The smaller the area of ​​the partially melted area, the weaker the change trend of the α-Al2O3(113) diffraction peak and the γ-Al2O3(400) diffraction peak in the coating with the increase of current. This may be caused by the following two aspects: on the one hand, when the current increases to 460A, the ion arc temperature basically reaches the complete melting temperature of the Al2O3 particles. Increasing the current again has little effect on the melting state of the Al2O3 particles in the jet. Therefore, the γ-Al2O3(400) diffraction peak in the coating is gradually reduced by the current; on the other hand, the residual stress in the coating will reduce the phase transition temperature of γ-Al2O3 to α-Al2O3. Under the action of a higher temperature plasma jet, the Al2O3 coating has a stress-induced transformation of the γ-Al2O3 phase to the α-Al2O3 phase, which is conducive to the increase of the relative content of the α-Al2O3 phase in the coating. Therefore, when the current exceeds 460A, the change trend of the α-Al2O3(113) diffraction peak in the coating is small.

[0057] Comparing the metallographic structures and X-ray diffraction patterns of Al2O3 coatings produced at different spray currents reveals that as the spray current increases, defects such as pores, cracks, and unmelted particles decrease, while the area of ​​complete melting increases. Furthermore, the relative content of γ-Al2O3 and α-Al2O3 phases in the coating also changes with current. Therefore, 580A is the preferred spraying parameter. The following performance data is based on the coatings produced at a fixed arc current of 580A and a fixed spray power of 41kW, as shown in Table 2.

[0058] The coating preparation method is the same as above, but no preheating is performed before spraying the transition layer. Figure 4 shows the cross-sectional morphologies of the substrates with and without preheating before spraying. Figure 4(a) shows the cross-sectional morphology of the sample without preheating, and Figure 4(b) shows the cross-sectional morphology of the sample with preheating. As shown in Figure 4, a clear crack exists between the transition layer and the substrate in the sample without preheating. Due to the low surface temperature, the molten droplet cools and shrinks rapidly during deposition, unable to spread out in time and form a gap between the substrate and the substrate. Preheating the sample before spraying significantly improves the bonding at the interface, making the adhesion between the transition layer and the substrate closer. Compared to the bonding strength of 34.41 MPa for the coating without preheating, the bonding strength of the coating after preheating increased by 21%. The microhardness values ​​of the coatings were measured using a Vickers microhardness tester. The indenter applied a load of 0.9807 N to the polished section of the coating for 15 seconds. The fracture toughness of the alumina coating was determined by calculating the diagonal length of the indentation and the crack length. Figure 5 is a bar chart of the hardness, fracture toughness, and bonding strength of the Al2O3 coating. As shown in Figure 5, the average microhardness of the Al2O3 coating is 1080 HV, and the fracture toughness of the coating is 1.76 MPa·m 0.5 The strength of the bond between the top ceramic layer and the substrate is a key performance indicator of its service life. This application improves the bonding strength between the coating and the substrate by preheating the substrate and introducing NiCrCoAlY as a transition layer to buffer the thermal expansion coefficient between the aluminum alloy substrate and the Al2O3 ceramic top layer, reducing the generation of thermal stress. The average bonding strength of the coating is 41.77 MPa.

[0059] Figure 6 shows the relationship between the friction coefficient, wear volume and specific wear rate of the plasma sprayed Al2O3 coating and the load. As shown in Figure 6(a), the average friction coefficients of the coating under loads of 5N, 10N, 20N and 30N are 0.757, 0.749, 0.724 and 0.682, respectively. The friction coefficient curves under different loads all increase rapidly in a short period of time. This is because at the beginning of the friction test, the Si3N4 grinding ball only collides with the micro-protrusions on the surface of the Al2O3 coating, resulting in a local increase in contact stress. As the friction process continues, the sharp micro-protrusions are worn away, the actual contact area between the coating and the grinding ball increases, the contact stress decreases, and the friction coefficient tends to be stable. As shown in Figure 6(b), when the load increases from 5N to 30N, the wear volume of the micronized Al2O3 coating after 30 minutes of wear increases from 8.17×10 -3 mm 3 Increased to 36.82×10 -3 mm 3 The specific wear rate of the coating is basically maintained at 4×10 -6 mm 3 / N·m, and has good wear resistance, which is related to the inherent high hardness of alumina and the dense microstructure of the prepared coating.

[0060] As shown in Figure 7(a), at thicknesses of 100μm, 200μm, and 300μm, the average reflectivity of the aluminum oxide coating is 54.53%, 61.02%, and 67.58%, respectively. In the ultraviolet band (wavelength less than 380nm), the coating's reflectivity is less affected by thickness. However, as the wavelength of the irradiated light increases into the visible and near-infrared bands (wavelength range 380-2500nm), the coating's reflectivity significantly increases with increasing thickness. Furthermore, when the wavelength exceeds 760nm and enters the near-infrared band, the aluminum oxide coating's reflectivity decreases with increasing wavelength. This is because as the wavelength of the irradiated light increases, its diffraction barrier becomes stronger, weakening the scattering of light in the coating and increasing the amount of transmitted light, resulting in a decrease in the coating's reflectivity. However, as the coating thickness increases, the distance traveled by the transmitted light increases, enhancing the coating's ability to scatter light, which in turn increases the coating's reflectivity.

[0061] As shown in Figure 7(b), when the thickness of the aluminum oxide coating increases from 100 μm to 300 μm, the infrared emissivity of the coating varies from 0.86 to 0.88. The increase in the coating emissivity may be related to the surface roughness of the coating. On the one hand, the rougher the coating surface, the larger the actual radiation area, thereby increasing the coating emissivity; on the other hand, the infrared radiation light undergoes multiple diffuse reflections on the uneven surface, which is conducive to the absorption and capture of infrared radiation by the coating surface, increasing the number of times the coating absorbs infrared radiation, and thus improving the coating emissivity.

[0062] This application can produce aluminum oxide coatings with thicknesses of 100μm, 200μm, and 300μm, each with a white appearance. Testing has shown that the coatings have average reflectivities of 54.53%, 61.02%, and 67.58% within the 200-2500nm wavelength range, respectively, demonstrating high reflectivity. Their infrared emissivities range from 0.86 to 0.88, exceeding 0.85 and demonstrating high emissivity.

[0063] The average hardness of the coating is 1080HV, and the average fracture toughness is 1.76MPa·m 0.5 The average bonding strength is 41.77MPa, which has good mechanical properties.

[0064] The average friction coefficients of the coating under four loads of 5N, 10N, 20N and 30N are 0.757, 0.749, 0.724 and 0.682 respectively, and the wear volume of the coating increases from 8.17×10 -3 mm 3 Increased to 36.82×10 -3 mm 3 , with good wear resistance (using Si3N4 ceramic balls with a diameter of 6mm as the friction object, the sliding friction and wear test was carried out for 30min at room temperature, frequency 10HZ, and stroke 5mm).

[0065] The above embodiments are only intended to help understand the method and core concept of the present invention. It should be noted that, without departing from the principles of the present invention, a number of improvements and modifications may be made to the present invention by those skilled in the art, and such improvements and modifications also fall within the scope of protection of the claims of the present invention.

[0066] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing a thermal control coating, comprising the following steps: A) cleaning the substrate and then performing sandblasting; B) preheating the substrate obtained in step A); C) spraying a NiCrCoAlY transition layer on the surface of the substrate obtained in step B); D) Plasma spraying an aluminum oxide coating on the surface of the substrate obtained in step C).

2. The preparation method according to claim 1, characterized in that: The cleaning method is ultrasonic cleaning, silicon dioxide quartz sand is used for sandblasting, and the pressure of the sandblasting is 0.5-1.5 MPa.

3. The preparation method according to claim 1, characterized in that: The preheating treatment adopts plasma flame scanning preheating.

4. The preparation method according to claim 1, characterized in that: The preheating temperature is such that the temperature of the substrate is 120-180°C.

5. The preparation method according to claim 1, characterized in that: The NiCrCoAlY transition layer is prepared by plasma spraying, and the thickness of the NiCrCoAlY transition layer is 80-150 μm.

6. The preparation method according to claim 5, characterized in that: In the preparation of the NiCrCoAlY transition layer, the argon flow rate of the plasma spraying is 45-55 L / min, the hydrogen flow rate is 8-10 L / min, the arc current is 500-550 A, the arc voltage is 60-70 V, the spraying power is 30-40 kW, the spraying distance is 120-140 mm, and the powder feeding rate is 20-40 g / min.

7. The preparation method according to claim 1, characterized in that: In the preparation of the alumina coating, the argon flow rate of the plasma spraying is 40-45 L / min, the hydrogen flow rate is 12-15 L / min, the arc current is 460-580 A, the arc voltage is 71-80 V, the spraying power is 32-41 kW, the spraying distance is 110-130 mm, and the powder feeding rate is 10-30 g / min.

8. The preparation method according to claim 1, characterized in that: The thickness of the aluminum oxide coating is 100-300 μm.

9. The preparation method according to claims 1 to 8, characterized in that: The substrate is 2A12 aluminum alloy.

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