A micro-arc oxidation film and a method for preparing the same

Abstract

The present application relates to a micro-arc oxidation film and a preparation method thereof, the micro-arc oxidation film comprising boron nitride particles and silicon nitride particles. The micro-arc oxidation film of an embodiment of the present application has high emissivity and good wear resistance.

Description

Technical Field

[0001] The present invention relates to micro-arc oxidation, in particular to a micro-arc oxidation film with high emissivity and good wear resistance. Background Art

[0002] Titanium alloys have many advantages, such as high specific strength and excellent corrosion resistance, and have great potential in core manufacturing fields such as aircraft and marine vessels. As the speed of aircraft continues to increase, the friction between the titanium alloy surface and the air during flight generates a large amount of aerodynamic heat. This heat is conducted through the metal and causes a sharp increase in the temperature inside the aircraft. In order to ensure that the temperature of the aircraft cavity can be controlled within the allowable range, effective methods are needed to control the energy dissipation of aerodynamic heat. Based on the principle of heat transfer, heat conduction and heat convection cannot completely offset all heat. Therefore, it is usually adopted to prepare a coating with high emissivity on the metal surface to enhance heat dissipation by thermal radiation.

[0003] Micro-arc oxidation coatings are ceramic films primarily composed of a base oxide, formed by increasing the breakdown voltage of the existing anodic oxidation process. These coatings offer advantages such as good wear resistance and high emissivity. However, the microscopic molten pores formed by high-voltage discharge increase the surface roughness of the coating, resulting in a high coefficient of friction and low surface hardness. This hinders the reduction of aerodynamic heat generated by friction between the coating and air, as well as friction and wear during long-term cyclic use. Summary of the Invention

[0004] To overcome at least one of the above-mentioned defects of the prior art, in a first aspect, one embodiment of the present invention provides a micro-arc oxidation film comprising boron nitride particles and silicon nitride particles.

[0005] According to one embodiment of the present invention, the particle size of the boron nitride particles is 10 to 20 nm; and / or the particle size of the silicon nitride particles is 300 to 500 nm.

[0006] According to one embodiment of the present invention, the mass ratio of the boron nitride particles to the silicon nitride particles is (3-10):5.

[0007] In a second aspect, an embodiment of the present invention provides a micro-arc oxidation metal, comprising a metal substrate and the above-mentioned micro-arc oxidation film disposed on the metal substrate.

[0008] In a third aspect, an embodiment of the present invention provides a method for preparing a micro-arc oxidation film, comprising forming a micro-arc oxidation film on a metal substrate through a micro-arc oxidation process; wherein the electrolyte used in the micro-arc oxidation process comprises boron nitride particles and silicon nitride particles.

[0009] According to one embodiment of the present invention, the particle size of the boron nitride particles is 10 to 20 nm, and the particle size of the silicon nitride particles is 300 to 500 nm; and / or,

[0010] The mass ratio of the boron nitride particles to the silicon nitride particles is (3-10):5.

[0011] According to one embodiment of the present invention, in the electrolyte, the total mass concentration of the boron nitride particles and the silicon nitride particles is 1.0 to 4.0 g / L.

[0012] According to one embodiment of the present invention, the electrolyte contains phosphate, silicate and aluminate.

[0013] According to one embodiment of the present invention, the micro-arc oxidation process includes: oxidation at a voltage of 300-350V for 20-30min and oxidation at a voltage of 550-650V for 15-20min under the conditions of a frequency of 300-500Hz and a duty cycle of 5%-20%.

[0014] According to one embodiment of the present invention, the metal substrate is a titanium alloy.

[0015] The micro-arc oxidation film according to one embodiment of the present invention has high emissivity and good wear resistance.

[0016] In the present invention, the above-mentioned technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of the present invention will be described in the following description, and some advantages will become apparent from the description or be learned through practice of the present invention. The objectives and other advantages of the present invention can be achieved and obtained through the contents particularly pointed out in the description. DETAILED DESCRIPTION

[0017] The preferred embodiments of the present invention are described in detail below, which are used to illustrate the principles of the present invention but are not used to limit the scope of the present invention.

[0018] One embodiment of the present invention provides a micro-arc oxidation film formed on a metal substrate through a micro-arc oxidation process, wherein the micro-arc oxidation film comprises boron nitride particles and silicon nitride (Si3N4) particles.

[0019] The micro-arc oxidation film of one embodiment of the present invention can increase the density of the film layer and play a self-lubricating role by adding boron nitride particles and silicon nitride particles; at the same time, the rigidity of the silicon nitride particles can increase the hardness of the film, improve the friction and wear performance, and rely on the two nitride nanoparticles to ensure the structural stability of the film layer at high temperatures, so that the emissivity will not be significantly attenuated.

[0020] In one embodiment, the silicon nitride particles may be nano-silicon nitride particles, and the particle size thereof may be 300-500 nm, for example, 350 nm, 400 nm, 450 nm, or 500 nm.

[0021] In one embodiment, the boron nitride particles may be nano boron nitride particles (or powder), and may further be hexagonal boron nitride (HBN) particles, and the particle size may be 10-20 nm, such as 12 nm, 14 nm, 15 nm, 16 nm, or 18 nm.

[0022] In one embodiment, the friction coefficient of the boron nitride particles is 0.1-0.2.

[0023] In one embodiment, the mass ratio of the boron nitride particles to the silicon nitride particles may be (3-10):5 (i.e., (9-30):15), and may further be (24-26):15, for example, 3:5, 1:1, 5:3, or 2:1.

[0024] In one embodiment, the thickness of the micro-arc oxidation film may be 15-25 μm, for example, 16 μm, 18 μm, 19 μm, 20 μm, 22 μm, 23 μm, or 24 μm.

[0025] In one embodiment, the emissivity of the micro-arc oxidation film at room temperature (25°C) may be ≥0.84, and may further be 0.84-0.93, for example, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93; the emissivity at 650°C may be ≥0.80, and may further be 0.80-0.87, for example, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87; the hardness may be 600-1015HV, and further be 850-1000HV, for example, 650HV, 700HV, 750HV, 8 00HV, 830HV, 850HV, 858HV, 860HV, 890HV, 897HV, 900HV, 930HV, 940HV, 950HV, 960HV, 970HV, 975HV, 980HV, 990HV, 995HV, 1000HV, 1015HV; the friction coefficient can be 0.2 to 0.65, and further can be 0.2 to 0.41, for example, 0.21, 0.25, 0.30, 0.33, 0.35, 0.40, 0.41, 0.45, 0.46, 0.48, 0.50, 0.52, 0.58, and 0.62.

[0026] The micro-arc oxidation film of one embodiment of the present invention is a self-lubricating, highly emissive, and highly wear-resistant titanium alloy micro-arc oxidation film layer.

[0027] One embodiment of the present invention provides a micro-arc oxidation metal, comprising a metal substrate and the micro-arc oxidation film disposed on the metal substrate.

[0028] In one embodiment, the metal substrate may be, for example, a titanium alloy.

[0029] One embodiment of the present invention provides a method for preparing the above-mentioned micro-arc oxidation film, comprising forming a micro-arc oxidation layer on a metal substrate through a micro-arc oxidation process; wherein the electrolyte used in the micro-arc oxidation process comprises boron nitride particles and silicon nitride particles.

[0030] In one embodiment, the electrolyte may include conventional phosphoric acid system micro-arc oxidation components and boron nitride particles and silicon nitride particles.

[0031] In one embodiment, in the electrolyte, the mass ratio of the boron nitride particles to the silicon nitride particles can be (3-10):5, and the combined mass concentration of the boron nitride particles and the silicon nitride particles can be 1.0-4.0 g / L, further 1.5-3.0 g / L, for example, 1.5 g / L, 2 g / L, 2.5 g / L, 3 g / L, or 3.5 g / L. The mass ratio of the boron nitride particles to the silicon nitride particles is (3-10):5. If the combined mass concentration of the two particles is below the above range, the boron nitride particle content is low, making it impossible to completely fill the discharge channels and produce sufficient self-lubricating effects. If the combined mass concentration of the two particles is above the above range, excessive silicon nitride accumulation can result, increasing internal stress within the film layer, making the film prone to cracking, and reducing wear resistance. Within this content range, boron nitride particles are encapsulated by the metal oxide within the molten pores due to electrophoretic migration. This improves the porosity and density of the film. Furthermore, the boron nitride particles effectively reduce the friction coefficient of the film surface, acting as a self-lubricating agent. Furthermore, an appropriate amount of rigid silicon nitride particles evenly dispersed throughout the film act as interlayer support, enhancing the strength of the outer surface of the micro-arc oxidation film and, consequently, improving the overall wear resistance of the film.

[0032] In one embodiment, the electrolyte comprises phosphate, silicate, aluminate and an additive; wherein the phosphate content may be 8 to 10 g / L, for example, 8 g / L, 9 g / L; the silicate content may be 2 to 4 g / L, for example, 2 g / L, 3 g / L; the aluminate content may be 0.5 to 1 g / L, for example, 0.5 g / L, 1 g / L; the additive content may be 2 g / L; the main function of the additive is to enhance the conductivity of the electrolyte and adjust the pH, and the additive may be potassium ferrocyanide.

[0033] In one embodiment, a step-by-step voltage boosting process can be used for constant voltage micro-arc oxidation, and the power supply can be a dedicated pulse unipolar micro-arc oxidation power supply. The micro-arc oxidation step-by-step voltage boosting process can be: the first stage of oxidation is carried out at a voltage of 300-350V, and the oxidation time is 20-30min. The voltage can be, for example, 310V, 320V, 330V, or 340V, and the oxidation time can be 22min, 25min, 26min, or 28min; the second stage of oxidation is carried out at a voltage of 550-650V, and the oxidation time is 20-30min. The time is 15 to 20 minutes, the voltage can be, for example, 560V, 580V, 600V, 610V, 630V, and the oxidation time can be 16 minutes, 17 minutes, 18 minutes, or 19 minutes; the frequency of the two stages can be 300 to 500Hz, for example, 350Hz, 400Hz, or 450Hz; the duty cycle can be 5 to 20%, for example, 6%, 8%, 10%, 12%, 14%, 15%, 16%, or 18%; the oxidation electrolyte is circulated by a chiller to ensure that the working state does not exceed 30°C.

[0034] A preparation method for a micro-arc oxidation film according to one embodiment of the present invention adopts a step-by-step voltage boosting method to form molten holes with different diameters through two different voltages. During the first stage of low voltage, the arc discharge degree on the surface of the film layer is low, and the size of the generated molten holes only allows 10-20 nm nano-boron nitride particles to enter and embed and fill the channels; at the same time, the accumulation of nanoparticles will accelerate the rapid cooling of the molten oxide, preventing the pore diameter from further increasing, thereby reducing the roughness of the film layer and providing a certain self-lubricating effect; as the oxidation proceeds, when entering the second stage of high voltage, large-sized nano-silicon nitride particles are gradually embedded into the surface of the film layer from the original accumulation on the surface of the film layer. Compared with oxides, the hardness of the silicon nitride particles effectively enhances the hardness of the film surface and improves the friction and wear performance of the micro-arc oxidation film layer.

[0035] A method for preparing a micro-arc oxidation film according to one embodiment of the present invention adds boron nitride and silicon nitride nanoparticles of different functional types to an electrolyte, and through the combination and proportion of particles of different sizes, ensures that the nano-boron nitride fills the unique molten pore structure in the micro-arc oxidation film layer, increases the density of the film layer, and plays a self-lubricating role; at the same time, it fully relies on the rigidity of nano-silicon nitride to increase the hardness of the film layer, improves the friction and wear performance, and relies on the two nitride nanoparticles to ensure that the structure of the film layer is stable at high temperatures and the emissivity does not significantly attenuate.

[0036] The micro-arc oxidation film of one embodiment of the present invention is a thermal protective coating, which actively reduces the friction coefficient of the film layer, slows down the generation of aerodynamic heat, and ensures that the heat is controllable.

[0037] The micro-arc oxidation film of one embodiment of the present invention utilizes the growth characteristics and structural features of the micro-arc oxidation film layer, introduces hard nano-silicon nitride particles and lubricating nano-hexagonal boron nitride particles, and through the deposition of different functional particles in the film layer, reduces the surface friction coefficient while increasing the hardness of the film layer, thereby achieving the self-lubricating, high-emission, and wear-resistant properties of the micro-arc oxidation film layer in one step, and solving the adverse hidden dangers of aerodynamic heat generation on hypersonic aircraft.

[0038] The micro-arc oxidation film according to one embodiment of the present invention has the characteristics of high emissivity and good wear resistance within a certain temperature range (eg, 25-700° C.).

[0039] The following describes a method for preparing a micro-arc oxidation film according to one embodiment of the present invention, using specific examples. The emissivity is measured using an infrared emissivity meter, the film hardness is measured using a microhardness meter, and the friction coefficient is measured using a universal friction and wear tester. The room-temperature emissivity refers to the emissivity at 25°C.

[0040] Example 1

[0041] S1: First, use acetone to wipe and clean the surface of the titanium alloy parts, connect the cleaned parts to the power anode wire and place them into the oxidation tank.

[0042] S2: The electrolyte in the oxidation tank includes 8g / L of trisodium phosphate, 2g / L of sodium silicate, 0.5g / L of sodium aluminate, 2g / L of potassium ferrocyanide, boron nitride and silicon nitride. The sum of the concentrations of boron nitride and silicon nitride is 1.5g / L, and the mass ratio of the two is HBN:Si3N4=5:3. The particle size of the boron nitride particles is 10nm, and the particle size of the silicon nitride particles is 300nm. A step-by-step voltage boost method is used for constant voltage micro-arc oxidation. The specific oxidation process parameters are: frequency 500Hz, duty cycle 5%, first stage voltage 300V, oxidation time 20min; second stage voltage 550V, oxidation time 15min.

[0043] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 18μm, an emissivity of 0.90 at room temperature, an emissivity of 0.86 at 650℃, a film hardness of 858HV, and a friction coefficient of 0.33.

[0044] Example 2

[0045] S1: First, use acetone to wipe and clean the surface of the titanium alloy parts, connect the cleaned parts to the power anode wire and place them into the oxidation tank.

[0046] S2: The electrolyte in the oxidation tank includes 8g / L of trisodium phosphate, 2g / L of sodium silicate, 0.5g / L of sodium aluminate, 2g / L of potassium ferrocyanide, boron nitride and silicon nitride. The sum of the concentrations of boron nitride and silicon nitride is 3.0g / L, and the mass ratio of the two is HBN:Si3N4=5:3. The particle size of the boron nitride particles is 20nm, and the particle size of the silicon nitride particles is 300nm. A step-by-step boost method is used for constant-voltage micro-arc oxidation. The specific oxidation process parameters are: frequency 500Hz, duty cycle 20%, first-stage voltage 350V, oxidation time 30min; second-stage voltage 650V, oxidation time 20min.

[0047] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 24μm, an emissivity of 0.93 at room temperature, an emissivity of 0.87 at 650℃, a film hardness of 975HV, and a friction coefficient of 0.21.

[0048] Example 3

[0049] S1: First, use acetone to wipe and clean the surface of the titanium alloy parts, connect the cleaned parts to the power anode wire and place them into the oxidation tank.

[0050] S2: The electrolyte in the oxidation tank includes 8g / L of trisodium phosphate, 2g / L of sodium silicate, 0.5g / L of sodium aluminate, 2g / L of potassium ferrocyanide, boron nitride and silicon nitride. The sum of the concentrations of boron nitride and silicon nitride is 4.0g / L, and the mass ratio of the two is HBN:Si3N4=1:1. The particle size of the boron nitride particles is 20nm, and the particle size of the silicon nitride particles is 300nm. A step-by-step voltage boost method is used for constant voltage micro-arc oxidation. The specific oxidation process parameters are: frequency 500Hz, duty cycle 20%, first stage voltage 350V, oxidation time 30min; second stage voltage 650V, oxidation time 20min.

[0051] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 20μm, an emissivity of 0.88 at room temperature, an emissivity of 0.83 at 650℃, a film hardness of 830HV, and a friction coefficient of 0.41.

[0052] Example 4-1

[0053] This embodiment uses substantially the same raw materials and steps as those in Example 2 to prepare a micro-arc oxidation film on the surface of a titanium alloy part, with the only difference being that the particle size of the boron nitride particles in the electrolyte in step S2 is 5 nm.

[0054] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 20μm, an emissivity of 0.89 at room temperature, an emissivity of 0.85 at 650℃, a film hardness of 940HV, and a friction coefficient of 0.48.

[0055] Example 4-2

[0056] This embodiment uses substantially the same raw materials and steps as those in Example 2 to prepare a micro-arc oxidation film on the surface of a titanium alloy part, with the only difference being that the particle size of the boron nitride particles in the electrolyte in step S2 is 15 nm.

[0057] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 16μm, an emissivity of 0.87 at room temperature, an emissivity of 0.82 at 650℃, a film hardness of 897HV, and a friction coefficient of 0.35.

[0058] Example 5

[0059] This embodiment uses substantially the same raw materials and steps as those of embodiment 2 to prepare a micro-arc oxidation film on the surface of a titanium alloy part, with the only difference being that the mass ratio of boron nitride to silicon nitride is HBN:Si3N4=1:1.

[0060] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 16μm, an emissivity of 0.86 at room temperature, an emissivity of 0.83 at 650℃, a film hardness of 960HV, and a friction coefficient of 0.46.

[0061] Example 6-1

[0062] This embodiment uses substantially the same raw materials and steps as those in Example 2 to prepare a micro-arc oxidation film on the surface of a titanium alloy part, with the only difference being that the sum of the concentrations of boron nitride and silicon nitride in the electrolyte in step S2 is 0.5 g / L.

[0063] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 19μm, an emissivity of 0.88 at room temperature, an emissivity of 0.82 at 650℃, a film hardness of 860HV, and a friction coefficient of 0.41.

[0064] Example 6-2

[0065] This embodiment uses substantially the same raw materials and steps as those in Example 2 to prepare a micro-arc oxidation film on the surface of a titanium alloy part, with the only difference being that the sum of the concentrations of boron nitride and silicon nitride in the electrolyte of step S2 is 5 g / L.

[0066] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray, with a thickness of about 22μm, an emissivity of 0.90 at room temperature, an emissivity of 0.83 at 650℃, a film hardness of 995HV, and a friction coefficient of 0.52.

[0067] Example 6-3

[0068] This embodiment uses substantially the same raw materials and steps as those in Example 2 to prepare a micro-arc oxidation film on the surface of a titanium alloy part, with the only difference being that the sum of the concentrations of boron nitride and silicon nitride in the electrolyte in step S2 is 10 g / L.

[0069] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is grayish white, with a thickness of about 23 μm, an emissivity of 0.84 at room temperature, an emissivity of 0.80 at 650°C, a film hardness of 1015 HV, and a friction coefficient of 0.58.

[0070] Example 7

[0071] This embodiment uses substantially the same raw materials and steps as those in Example 2 to prepare a micro-arc oxidation film on the surface of a titanium alloy part, with the only difference being that in step S2, a step-by-step voltage-boosting method is not used for micro-arc oxidation, but a constant voltage 650V micro-arc oxidation method is used.

[0072] The micro-arc oxidation film prepared on the outer surface of the titanium alloy part is gray-brown, with a thickness of about 24μm, an emissivity of 0.85 at room temperature, an emissivity of 0.81 at 650℃, a film hardness of 860HV, and a friction coefficient of 0.62.

[0073] The performance parameters of the micro-arc oxidation films prepared in Examples 1 to 7 are shown in Table 1.

[0074] Table 1

[0075]

[0076]

[0077] According to the descriptions of Examples 2, 4-1, and 4-2, the difference between Example 2 and Examples 4-1 and 4-2 lies in the size of the boron nitride particles. The particle sizes of the boron nitride particles in Examples 2, 4-1, and 4-2 are 20 nm, 5 nm, and 15 nm, respectively. Comparing the various performance parameters of the micro-arc oxidation films of the above three examples in Table 1, it can be seen that the friction coefficient of Example 4-1 is 0.48, which is much higher than the friction coefficients of 0.21 and 0.35 of Examples 2 and 4-2, respectively, indicating that the micro-arc oxidation films of Examples 2 and 4-2 have better wear resistance. In addition, although the room temperature emissivity, 650°C emissivity, and film hardness of Example 4-1 are slightly higher than those of Example 4-2, they are lower than those of Example 2. In addition, the particle size of the boron nitride particles in Example 1 is 10 nm, and the friction coefficient of its film layer is 0.33, which is also lower than 0.48. Therefore, overall, the film layers of Examples 1, 2, and 4-2 have better comprehensive performance, and the particle size of the boron nitride particles is preferably 10 to 20 nm, and more preferably 20 nm.

[0078] According to the descriptions of Examples 2 and 5, the difference between the two lies in the mass ratio of boron nitride to silicon nitride. In Examples 2 and 5, the mass ratios of boron nitride to silicon nitride are 5:3 and 1:1, respectively. Comparing the various performance parameters of the micro-arc oxidation films of the above two examples in Table 1, it can be seen that the friction coefficient of Example 2 (0.21) is much lower than the friction coefficient of Example 5 (0.46), indicating that the film layer of Example 2 has better wear resistance. At the same time, the room temperature emissivity, 650°C emissivity, and film hardness of Example 2 are all higher than those of Example 5. Therefore, the film layer of Example 2 has better comprehensive performance than that of Example 5. The mass ratio of boron nitride to silicon nitride is preferably (24-26):15, and more preferably 25:15 (5:3).

[0079] According to the description of Examples 2, 6-1, 6-2, and 6-3, the difference between Example 2 and Examples 6-1, 6-2, and 6-3 lies in the sum of the concentrations of boron nitride and silicon nitride in the electrolyte. In Examples 2, 6-1, 6-2, and 6-3, the sum of the concentrations of boron nitride and silicon nitride in the electrolyte is 3.0 g / L, 0.5 g / L, 5 g / L, and 10 g / L, respectively. Comparing the various performance parameters of the micro-arc oxidation films of the above four examples in Table 1, it can be seen that the friction coefficient of Example 6-3 is 0.58, which is much higher than the friction coefficients of Examples 2, 6-1, and 6-2, which are 0.21, 0.41, and 0.52, respectively. This shows that Examples 2, 6-1, and 6-2 have better wear resistance than Example 6-3. Furthermore, Examples 2 and 6-1 have better wear resistance than Example 6-2.

[0080] In addition, the sum of the boron nitride and silicon nitride concentrations in the electrolytes of Examples 1 and 3 was 1.5 g / L and 4.0 g / L, respectively. The wear resistance and emissivity of the films of these two examples were superior to those of the film of Example 6-3. Therefore, overall, the sum of the boron nitride and silicon nitride concentrations in the electrolyte is preferably 0.5 to 4.0 g / L, more preferably 1.0 to 4.0 g / L, and even more preferably 1.5 to 3.0 g / L.

[0081] The descriptions of Examples 2 and 7 show that the difference between Example 2 and Example 7 lies in the different micro-arc oxidation processes. Comparing the various performance parameters of the micro-arc oxidation films of the two examples in Table 1 shows that the friction coefficient of Example 2 (0.21) is significantly lower than the friction coefficient of Example 7 (0.62), indicating that the film of Example 2 has better wear resistance. Furthermore, the room-temperature emissivity, 650°C emissivity, and film hardness of Example 2 are all higher than those of Example 7, indicating that the use of a stepped pressure-increasing method for micro-arc oxidation can produce a film with better overall performance.

[0082] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with this technical field within the technical scope disclosed by the present invention should be covered by the scope of protection of the present invention.

Claims

1. A self-lubricating, highly emissive titanium alloy micro-arc oxidation film, comprising boron nitride particles and silicon nitride particles, wherein the particle size of the boron nitride particles is 10 to 20 nm, the particle size of the silicon nitride particles is 300 to 500 nm, and the mass ratio of the boron nitride particles to the silicon nitride particles is (3 to 10):5; the micro-arc oxidation film has a thickness of 15 to 25 μm, an emissivity of ≥0.84 at 25°C and ≥0.80 at 650°C, a hardness of 830 to 1015 HV, and a friction coefficient of 0.2 to 0.65; The micro-arc oxidation film is formed on a titanium alloy substrate through a micro-arc oxidation process. The electrolyte used in the micro-arc oxidation process includes boron nitride particles and silicon nitride particles. The total concentration of the boron nitride particles and the silicon nitride particles is 1.0 to 4.0 g / L. The micro-arc oxidation process uses a step-by-step pressure-boosting process to perform constant-pressure micro-arc oxidation, including: Under the conditions of a power frequency of 300-500 Hz and a duty cycle of 5%-20%, oxidation is carried out at a voltage of 300-350 V for 20-30 minutes and at a voltage of 550-650 V for 15-20 minutes.

2. A method for preparing a micro-arc oxidation film according to claim 1, comprising forming a micro-arc oxidation film on a metal substrate by a micro-arc oxidation process; wherein: The electrolyte used in the micro-arc oxidation process includes phosphate, silicate and aluminate, as well as boron nitride particles and silicon nitride particles.

3. The method according to claim 2, wherein: The particle size of the boron nitride particles is 10 to 20 nm, and the particle size of the silicon nitride particles is 300 to 500 nm; The mass ratio of the boron nitride particles to the silicon nitride particles is (3-10):

5.

4. The method according to claim 2, wherein: In the electrolyte, the total mass concentration of the boron nitride particles and the silicon nitride particles is 1.0 to 4.0 g / L.

5. The method according to any one of claims 2 to 4, wherein The micro-arc oxidation process includes: oxidation at a voltage of 300-350V for 20-30min and oxidation at a voltage of 550-650V for 15-20min under the conditions of a frequency of 300-500Hz and a duty cycle of 5%-20%.

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