Method for preparing conductive and thermal conductive composite coating on the surface of alumina ceramics

Abstract

A method for preparing a conductive and thermally conductive composite coating on the surface of an alumina ceramic. It belongs to the field of material surface engineering technology. In order to solve the problem of poor conductive and thermal conductivity of alumina ceramics and the problem of mismatch in thermal expansion coefficient of metal coatings prepared on the surface of alumina ceramics, the present invention uses alumina powder and aluminum powder through low-energy ball milling and high-pressure cold spraying technology to prepare a composite coating with excellent conductive and thermal conductivity on the surface of alumina ceramics. The preparation method comprises: mixing alumina powder and aluminum powder in a certain proportion and then performing low-energy ball milling to obtain a mixed powder; using high-pressure cold spraying technology to spray the mixed powder on the alumina ceramic to form a transition coating; and then spraying pure aluminum powder on the transition coating to form a composite coating. The preparation method of the present invention has the advantages of high efficiency and simple and easy operation. The prepared composite coating can give the surface of the alumina ceramic good electrical conductivity and thermal conductivity, thereby broadening the application field of alumina ceramics.

Description

Technical Field

[0001] The invention belongs to the technical field of material surface engineering, and in particular relates to a method for preparing an electrically conductive and thermally conductive composite coating on the surface of an alumina ceramic. Background Art

[0002] Alumina ceramics have broad application prospects in many industries such as aerospace, electronics and power, chemical industry, etc. due to their high strength, high hardness, excellent high temperature resistance, corrosion resistance and wear resistance. However, the inherent limitations of alumina ceramics, such as poor electrical conductivity, limited thermal conductivity and weak impact resistance, have restricted the further application of alumina ceramics. In contrast, metal materials generally have excellent electrical conductivity, thermal conductivity, ductility and excellent machinability. In order to fully utilize the advantages of these two materials, a metal coating can be prepared on the surface of alumina ceramics to give the surface of alumina ceramics good electrical conductivity and efficient thermal conductivity. This technology can combine the advantages of ceramics and metals, greatly broaden the application field of alumina ceramics, and promote the further development of materials science.

[0003] Cold spraying is a material surface coating technology based on the principles of aerodynamics. Cold spraying technology uses supersonic airflow to drive the spray powder particles to collide with the substrate surface at high speed in a gas-solid bidirectional flow. The particles undergo strong plastic deformation and form a mechanical bond with the substrate, thereby being deposited on the substrate surface to form a coating. Due to the short contact time with the gas, the particle temperature is much lower than the melting point of the particles, and the particles always remain in a solid state. The continuous high-speed impact of the particles may produce a shot peening or "tamping" effect, resulting in the densification of the coating, and its density is close to the theoretical density. The cold spray process is expected to become a method for efficiently and quickly preparing metal coatings on ceramic surfaces. CN115874173A discloses a cold-sprayed metal coating for improving the anti-multi-shot performance of ceramic armor and a preparation method thereof. The method uses cold spraying technology to directly deposit an aluminum or copper metal coating on a roughened ceramic surface. CN114075664B discloses a method for cold spraying to produce patterned ceramic copper-clad laminates. This method first uses cold spraying equipment to spray metal powder onto the surface of a ceramic substrate under certain conditions to form a transition layer. High-purity copper powder is then sprayed onto the prepared transition layer to obtain a pure copper coating on the ceramic substrate. Both methods produce a metal coating on the ceramic surface, but CN115874173A directly deposits metal powder on the ceramic surface. The difference in thermal expansion coefficients between the two materials is significant, resulting in high stress at the interface between the coating and the substrate. While CN114075664B uses a transition layer, the composition of the transition layer is pure metal, a binary metal mixture, a ternary metal mixture, a binary alloy, or a ternary alloy, which still has significant differences in physical properties from the ceramic substrate. Summary of the Invention

[0004] In order to address the deficiencies of the above-mentioned prior art, the present invention proposes a method for preparing a conductive and thermally conductive composite coating on the surface of alumina ceramics. High-pressure cold spraying is innovatively used to spray a mixed powder of alumina and aluminum on the surface of alumina ceramics to prepare a transition coating. The physical properties of the transition coating are similar to those of alumina ceramics, which can solve the problem of thermal expansion coefficient mismatch between the coating and the substrate, relieve stress, and achieve continuous changes in composition, structure and performance from the ceramic substrate to the surface metal layer.

[0005] The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics of the present invention is carried out according to the following steps:

[0006] Step 1: Using a ball mill to perform low-energy ball milling on alumina powder and aluminum powder, so that the alumina powder particles are evenly distributed in the aluminum powder to obtain a mixed powder; the mass ratio of the aluminum powder to the alumina powder is (2-4):1;

[0007] The low-energy ball milling process comprises: weighing alumina powder and aluminum powder, mixing them and then loading them into a ball mill, evacuating the ball mill, and then introducing an inert gas; the ball milling process adopts a dry milling method, controlling the ball-to-material mass ratio to be (3-4):1, setting the ball mill speed to 150-200 r / min, and setting the ball milling time to 2-4 hours. During the ball milling, the ball mill rotates in a unidirectional manner, and the ball mill stops rotating for 5-10 minutes after each 0.5-1 hour of ball milling;

[0008] Step 2: spraying the mixed powder obtained in step 1 onto an alumina ceramic substrate by cold spraying to obtain an Al-Al2O3 transition coating;

[0009] The cold spraying process comprises: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol, placing the alumina ceramic substrate in a drying oven for drying after ultrasonic cleaning, and fixing the alumina ceramic substrate on a fixture after drying; before spraying, loading the mixed powder obtained in step 1 into a powder feeder, using nitrogen as a working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2-3 mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun moving speed is 150-200 mm / s, the vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed is 40-45 mm, the working gas pressure is 5-7 MPa, the working gas temperature is 600-900°C, and the number of spray layers is 1-2;

[0010] Step 3: cold spraying aluminum powder onto the Al-Al2O3 transition coating obtained in step 2 to obtain a composite coating of the Al-Al2O3 transition coating and the pure Al coating;

[0011] The cold spraying process comprises the following steps: loading aluminum powder into a powder feeder, fixing the alumina ceramic substrate with an Al-Al2O3 transition coating deposited on its surface obtained in step 2 on a fixture; using nitrogen as the working gas during spraying, an S-shaped spraying trajectory, a line spacing of 2-3 mm, an angle of 90° between the spray beam and the surface to be sprayed, a spray gun moving speed of 150-200 mm / s, a vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed of 40-45 mm, a working gas pressure of 3.5-4.5 MPa, a working gas temperature of 550-650°C, and 2-6 spray layers.

[0012] Principles and beneficial effects of the present invention:

[0013] 1. This invention utilizes a cold spray process, enabling coating deposition at relatively low temperatures (hundreds of degrees Celsius) and at high deposition rates (coating deposition rates can reach millimeters per minute). The low temperatures during cold spraying avoid the risk of substrate deformation or damage due to high temperatures. The mixed powder is less affected by heat, and no phase transition occurs during the spraying process, significantly suppressing the generation of thermal defects in the coating. The coating exhibits excellent microstructure and mechanical properties.

[0014] 2. This invention utilizes a composite coating designed by combining an Al-Al2O3 transition layer and a pure Al coating. The Al-Al2O3 transition coating, serving as the intermediate layer, possesses physical properties similar to those of alumina ceramics, resolving the thermal expansion coefficient mismatch between the coating and the substrate, mitigating stress, and achieving a gradient transition in composition, structure, and performance from the ceramic substrate to the surface metal layer. The pure Al coating, serving as the outer surface layer, possesses excellent electrical and thermal conductivity, endowing the alumina ceramic surface with both excellent electrical conductivity and efficient thermal conductivity.

[0015] 3. When spraying a mixed powder containing alumina ceramic particles to prepare a transition coating, the present invention utilizes high gas pressure and temperature for cold spraying, with the gas pressure reaching 5-7 MPa and the gas temperature being 600-900°C. This high gas pressure and temperature achieve high-quality deposition of the mixed powder containing alumina ceramic particles, thereby forming an Al-Al2O3 transition coating on the alumina ceramic surface. Higher spraying pressures enable the powder particles to acquire greater kinetic energy within the accelerated airflow, resulting in more significant particle bombardment and compaction, and a higher coating density. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a cross-sectional morphology of the composite coating prepared in step 3 of Example 1;

[0017] Figure 2This is a diagram showing the transition change in Vickers hardness of the composite coating prepared in step 3 of Example 1. DETAILED DESCRIPTION

[0018] The technical solution of the present invention is not limited to the specific implementation methods listed below, but also includes any reasonable combination of the specific implementation methods.

[0019] Specific embodiment 1: The preparation method of the conductive and thermal conductive composite coating on the surface of alumina ceramics in this embodiment is carried out according to the following steps:

[0020] Step 1: Using a ball mill to perform low-energy ball milling on alumina powder and aluminum powder, so that the alumina powder particles are evenly distributed in the aluminum powder to obtain a mixed powder; the mass ratio of the aluminum powder to the alumina powder is (2-4):1;

[0021] The low-energy ball milling process comprises: weighing alumina powder and aluminum powder, mixing them and then loading them into a ball mill, evacuating the ball mill, and then introducing an inert gas; the ball milling process adopts a dry milling method, controlling the ball-to-material mass ratio to be (3-4):1, setting the ball mill speed to 150-200 r / min, and setting the ball milling time to 2-4 hours. During the ball milling, the ball mill rotates in a unidirectional manner, and the ball mill stops rotating for 5-10 minutes after each 0.5-1 hour of ball milling;

[0022] Step 2: spraying the mixed powder obtained in step 1 onto an alumina ceramic substrate by cold spraying to obtain an Al-Al2O3 transition coating;

[0023] The cold spraying process comprises: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol, placing the alumina ceramic substrate in a drying oven for drying after ultrasonic cleaning, and fixing the alumina ceramic substrate on a fixture after drying; before spraying, loading the mixed powder obtained in step 1 into a powder feeder, using nitrogen as a working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2-3 mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun moving speed is 150-200 mm / s, the vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed is 40-45 mm, the working gas pressure is 5-7 MPa, the working gas temperature is 600-900°C, and the number of spray layers is 1-2;

[0024] Step 3: cold spraying aluminum powder onto the Al-Al2O3 transition coating obtained in step 2 to obtain a composite coating of the Al-Al2O3 transition coating and the pure Al coating;

[0025] The cold spraying process comprises the following steps: loading aluminum powder into a powder feeder, fixing the alumina ceramic substrate with an Al-Al2O3 transition coating deposited on its surface obtained in step 2 on a fixture; using nitrogen as the working gas during spraying, an S-shaped spraying trajectory, a line spacing of 2-3 mm, an angle of 90° between the spray beam and the surface to be sprayed, a spray gun moving speed of 150-200 mm / s, a vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed of 40-45 mm, a working gas pressure of 3.5-4.5 MPa, a working gas temperature of 550-650°C, and 2-6 spray layers.

[0026] 1. This embodiment utilizes a cold spray process, enabling coating deposition at relatively low temperatures (hundreds of degrees Celsius) and at high deposition rates (coating deposition rates can reach millimeters per minute). The low temperatures during cold spraying avoid the risk of substrate deformation or damage due to high temperatures. The mixed powder is less affected by heat, and no phase transition occurs during the spraying process, significantly suppressing the generation of thermal defects in the coating. The coating exhibits excellent microstructure and mechanical properties.

[0027] 2. This embodiment utilizes a composite coating designed by combining an Al-Al2O3 transition layer and a pure Al coating. The Al-Al2O3 transition coating, serving as the intermediate layer, possesses physical properties similar to those of alumina ceramics, resolving the thermal expansion coefficient mismatch between the coating and the substrate, mitigating stresses and achieving a gradient transition in composition, structure, and performance from the ceramic substrate to the surface metal layer. The pure Al coating, serving as the outer surface layer, possesses excellent electrical and thermal conductivity, endowing the alumina ceramic surface with both excellent electrical conductivity and efficient thermal conductivity.

[0028] 3. In this embodiment, when spraying a mixed powder containing alumina ceramic particles to form a transition coating, deposition is difficult due to the poor plastic deformation ability of alumina ceramic particles. Therefore, the present invention utilizes high gas pressure and high gas temperature for cold spraying of the transition coating, with the gas pressure reaching 5-7 MPa and the gas temperature being 600-900°C. This high gas pressure and high temperature achieve high-quality deposition of the mixed powder containing alumina ceramic particles, forming an Al-Al2O3 transition coating on the alumina ceramic surface. Higher spraying pressures enable the powder particles to acquire greater kinetic energy in the accelerated airflow, resulting in more significant particle bombardment and compaction, and a higher coating density.

[0029] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that: the purity of the aluminum powder in step 1 is 99.9%, the particles are spherical, and the particle size is 20-35 μm.

[0030] Specific embodiment three: This embodiment differs from specific embodiment one or two in that: the purity of the aluminum oxide powder in step one is 99.9%, the particles are irregular in shape, and the particle size is 20-60 μm.

[0031] Specific embodiment 4: This embodiment differs from any one of specific embodiments 1 to 3 in that: the ball mill in step 1 is a planetary ball mill.

[0032] Specific embodiment 5: This embodiment differs from any one of specific embodiments 1 to 4 in that the inert gas in step 1 is argon.

[0033] Specific embodiment six: This embodiment differs from any one of specific embodiments one to five in that: the process of low-energy ball milling is: the weighed alumina powder and aluminum powder are mixed and loaded into a ball mill jar, the ball mill jar is vacuumed, and then argon gas is introduced; the ball milling process adopts dry milling method, the ball-material mass ratio is controlled to 3:1, the ball mill speed is set to 200r / min, the ball milling time is set to 2h, the ball mill jar is rotated in a unidirectional manner during the ball milling, and the ball mill stops rotating for 5min after each 0.5h of ball milling.

[0034] Specific embodiment seven: This embodiment differs from any one of specific embodiments one to six in that: the ultrasonic cleaning time in step two is 10-30 min, the ultrasonic frequency is 20-80 KHz, the drying temperature is 50-80° C., and the drying time is 10-30 min.

[0035] Specific embodiment eight: The difference between this embodiment and any one of specific embodiments one to seven is that: the cold spraying process described in step two includes the following steps: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol, placing the alumina ceramic substrate in a drying oven for drying after ultrasonic cleaning, and fixing the alumina ceramic substrate on a fixture after drying; before spraying, loading the mixed powder obtained in step one into a powder feeder, using nitrogen as the working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun moving speed is 200mm / s, the vertical distance between the end of the spray gun and the surface of the alumina ceramic substrate to be sprayed is 40mm, the working gas pressure is 5MPa, the working gas temperature is 650℃, and the number of spray layers is 2 layers.

[0036] Specific embodiment 9: This embodiment differs from any one of specific embodiments 1 to 8 in that: the purity of the aluminum powder in step 3 is 99.9%, the particles are spherical, and the particle size is 20-35 μm.

[0037] Specific embodiment ten: This embodiment differs from any one of specific embodiments one to nine in that: the cold spraying process described in step three includes the following steps: loading aluminum powder into a powder feeder, and fixing the alumina ceramic substrate with an Al-Al2O3 transition coating deposited on the surface obtained in step two on a fixture; nitrogen is used as the working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun moving speed is 200mm / s, the vertical distance between the end of the spray gun and the surface of the alumina ceramic substrate to be sprayed is 40mm, the working gas pressure is 4MPa, the working gas temperature is 600℃, and the number of spray layers is 4.

[0038] Example 1:

[0039] The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics in this embodiment is carried out according to the following steps:

[0040] Step 1: Using a ball mill to perform low-energy ball milling on alumina powder and aluminum powder, so that the alumina powder particles are evenly distributed in the aluminum powder, to obtain a mixed powder; the mass ratio of the aluminum powder to the alumina powder is 4:1;

[0041] The low-energy ball milling process comprises: weighing alumina powder and aluminum powder, mixing them and then loading them into a ball mill jar, evacuating the jar, and then introducing an inert gas; the ball milling process adopts a dry milling method, controlling the ball-to-material mass ratio to be 3:1, setting the ball mill speed to 200 rpm, and setting the ball milling time to 2 hours. During the ball milling process, the ball mill jar is rotated in a unidirectional manner, and the ball mill is stopped for 5 minutes after each 0.5 of ball milling;

[0042] The purity of the aluminum powder is 99.9%, the particles are spherical, and the particle size is 20-35 μm;

[0043] The purity of the aluminum oxide powder is 99.9%, the particles are irregular in shape, and the particle size is 20-60 μm;

[0044] The ball mill is a planetary ball mill;

[0045] The inert gas is argon;

[0046] Step 2: spraying the mixed powder obtained in step 1 onto an alumina ceramic substrate by cold spraying to obtain an Al-Al2O3 transition coating;

[0047] The cold spraying process comprises: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol for 30 minutes at an ultrasonic frequency of 50 kHz; drying the alumina ceramic substrate in a drying oven for 30 minutes at a drying temperature of 70° C.; and fixing the alumina ceramic substrate on a fixture after drying; loading the mixed powder obtained in step 1 into a powder feeder before spraying; using nitrogen as the working gas during spraying; an S-shaped spraying trajectory; a line spacing of 2 mm between the spraying trajectory; an angle of 90° between the spray beam and the surface to be sprayed; a spray gun moving speed of 200 mm / s; a vertical distance of 40 mm between the end of the spray gun and the surface of the alumina ceramic substrate to be sprayed; a working gas pressure of 5 MPa; a working gas temperature of 650° C.; and two spray layers.

[0048] Step 3: cold spraying aluminum powder onto the Al-Al2O3 transition coating obtained in step 2 to obtain a composite coating of the Al-Al2O3 transition coating and the pure Al coating;

[0049] The cold spraying process comprises: loading aluminum powder into a powder feeder, fixing the alumina ceramic substrate with the Al-Al2O3 transition coating deposited on the surface obtained in step 2 on a fixture; using nitrogen as the working gas during spraying, an "S"-shaped spraying trajectory, a spraying trajectory line spacing of 2 mm, an angle of 90° between the spray beam and the surface to be sprayed, a spray gun moving speed of 200 mm / s, a vertical distance of 40 mm between the spray gun end and the surface of the alumina ceramic substrate to be sprayed, a working gas pressure of 4.5 MPa, a working gas temperature of 600°C, and four spray layers;

[0050] The purity of the aluminum powder is 99.9%, the particles are spherical, and the particle size is 20-35 μm.

[0051] The thermal diffusion coefficient of the composite coating of Al-Al2O3 transition coating and pure Al coating obtained in this example is 70.951 mm 2 / s, and the thermal conductivity is 149.462W / (m·K). The Hall coefficient of the composite coating is 31.67×10 3 cm 3 / C, and the Hall mobility is 2.61 cm 3 / V·s, the resistance is 6.89Ω, and the conductivity is 203.60×10 3 S / cm. The porosity of the composite coating is 0.55%.

[0052] Figure 1This is a cross-sectional morphology of the composite coating prepared in step 3 of Example 1. The figure shows no distinct boundary between the Al-Al2O3 transition coating and the pure Al coating, produced by cold spraying on the alumina ceramic substrate. Al2O3 particles are evenly distributed throughout the Al-Al2O3 transition coating. The composite coating exhibits good internal interface bonding, resulting in a dense coating with no apparent pores or cracks. Figure 2 This is a graph showing the Vickers hardness transition of the composite coating prepared in step 3 of Example 1. As can be seen from the graph, the coating hardness changes relatively smoothly when measured at points perpendicular to the Al2O3 ceramic substrate, from the interface between the ceramic substrate and the composite coating to the surface of the composite coating. This demonstrates that the Al-Al2O3 transition coating prepared on the alumina ceramic substrate via cold spraying achieves a continuous change in hardness from the ceramic substrate to the surface metal layer.

[0053] Example 2:

[0054] The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics in this embodiment is carried out according to the following steps:

[0055] Step 1: Using a ball mill to perform low-energy ball milling on alumina powder and aluminum powder, so that the alumina powder particles are evenly distributed in the aluminum powder, to obtain a mixed powder; the mass ratio of the aluminum powder to the alumina powder is 4:1;

[0056] The low-energy ball milling process comprises: weighing alumina powder and aluminum powder, mixing them and then loading them into a ball mill jar, evacuating the jar, and then introducing an inert gas; the ball milling process adopts a dry milling method, controlling the ball-to-material mass ratio to be 3:1, setting the ball mill speed to 200 rpm, and setting the ball milling time to 2 hours. During the ball milling, the ball mill jar is rotated in a unidirectional manner, and the ball mill is stopped for 5 minutes after each 0.5 hour of ball milling;

[0057] The purity of the aluminum powder is 99.9%, the particles are spherical, and the particle size is 20-35 μm;

[0058] The purity of the aluminum oxide powder is 99.9%, the particles are irregular in shape, and the particle size is 20-60 μm;

[0059] The ball mill is a planetary ball mill;

[0060] The inert gas is argon;

[0061] Step 2: spraying the mixed powder obtained in step 1 onto an alumina ceramic substrate by cold spraying to obtain an Al-Al2O3 transition coating;

[0062] The cold spraying process comprises: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol for 20 minutes at an ultrasonic frequency of 50 kHz; drying the alumina ceramic substrate in a drying oven for 10 minutes at a drying temperature of 70° C.; and fixing the alumina ceramic substrate on a fixture after drying; loading the mixed powder obtained in step 1 into a powder feeder before spraying; using nitrogen as the working gas during spraying; an S-shaped spraying trajectory; a line spacing of 2 mm between the spraying trajectory; an angle of 90° between the spray beam and the surface to be sprayed; a spray gun moving speed of 200 mm / s; a vertical distance of 40 mm between the end of the spray gun and the surface of the alumina ceramic substrate to be sprayed; a working gas pressure of 5 MPa; a working gas temperature of 650° C.; and two spray layers.

[0063] Step 3: cold spraying aluminum powder onto the Al-Al2O3 transition coating obtained in step 2 to obtain a composite coating of the Al-Al2O3 transition coating and the pure Al coating;

[0064] The cold spraying process comprises: loading aluminum powder into a powder feeder, fixing the alumina ceramic substrate with the Al-Al2O3 transition coating deposited on the surface obtained in step 2 on a fixture; using nitrogen as the working gas during spraying, an "S"-shaped spraying trajectory, a spraying trajectory line spacing of 2 mm, an angle of 90° between the spray beam and the surface to be sprayed, a spray gun moving speed of 200 mm / s, a vertical distance of 40 mm between the spray gun end and the surface of the alumina ceramic substrate to be sprayed, a working gas pressure of 4 MPa, a working gas temperature of 600°C, and four spray layers;

[0065] The purity of the aluminum powder is 99.9%, the particles are spherical, and the particle size is 20-35 μm.

[0066] The thermal diffusivity of the composite coating of Al-Al2O3 transition coating and pure Al coating obtained in this example is 61.532 mm 2 / s, and the thermal conductivity is 131.654W / (m·K). The Hall coefficient of the composite coating is 25.12×10 3 cm 3 / C, and the Hall mobility is 1.83 cm 3 / V·s, the resistance is 7.22Ω, and the conductivity is 153.30×10 3 S / cm. The porosity of the composite coating is 0.87%.

[0067] Example 3:

[0068] The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics in this embodiment is carried out according to the following steps:

[0069] Step 1: Using a ball mill to perform low-energy ball milling on alumina powder and aluminum powder, so that the alumina powder particles are evenly distributed in the aluminum powder, to obtain a mixed powder; the mass ratio of the aluminum powder to the alumina powder is 4:1;

[0070] The low-energy ball milling process comprises: weighing alumina powder and aluminum powder, mixing them and then loading them into a ball mill jar, evacuating the jar, and then introducing an inert gas; the ball milling process adopts a dry milling method, controlling the ball-to-material mass ratio to be 3:1, setting the ball mill speed to 200 rpm, and setting the ball milling time to 2 hours. During the ball milling, the ball mill jar is rotated in a unidirectional manner, and the ball mill is stopped for 5 minutes after each 0.5 hour of ball milling;

[0071] The purity of the aluminum powder is 99.9%, the particles are spherical, and the particle size is 20-35 μm;

[0072] The purity of the aluminum oxide powder is 99.9%, the particles are irregular in shape, and the particle size is 20-60 μm;

[0073] The ball mill is a planetary ball mill;

[0074] The inert gas is argon;

[0075] Step 2: spraying the mixed powder obtained in step 1 onto an alumina ceramic substrate by cold spraying to obtain an Al-Al2O3 transition coating;

[0076] The cold spraying process comprises: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol for 30 minutes at an ultrasonic frequency of 50 kHz; drying the alumina ceramic substrate in a drying oven for 10 minutes at a drying temperature of 70° C.; and fixing the alumina ceramic substrate on a fixture after drying; loading the mixed powder obtained in step 1 into a powder feeder before spraying; using nitrogen as the working gas during spraying; the spraying trajectory is "S"-shaped; the spraying trajectory line spacing is 2 mm; the angle between the spray beam and the surface to be sprayed is 90°; the spray gun moving speed is 200 mm / s; the vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed is 40 mm; the working gas pressure is 5 MPa; the working gas temperature is 650° C.; and the number of spray layers is 2;

[0077] Step 3: cold spraying aluminum powder onto the Al-Al2O3 transition coating obtained in step 2 to obtain a composite coating of the Al-Al2O3 transition coating and the pure Al coating;

[0078] The cold spraying process is as follows: aluminum powder is loaded into a powder feeder, and the alumina ceramic substrate with an Al-Al2O3 transition coating deposited on the surface obtained in step 2 is fixed on a fixture; nitrogen is used as the working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2 mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun movement speed is 200 mm / s, the vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed is 40 mm, the working gas pressure is 3.5 MPa, the working gas temperature is 600°C, and the number of spray layers is 4.

[0079] The purity of the aluminum powder is 99.9%, the particles are spherical, and the particle size is 20-35 μm;

[0080] The thermal diffusivity of the composite coating of Al-Al2O3 transition coating and pure Al coating obtained in this example is 52.698 mm 2 / s, and the thermal conductivity is 114.154W / (m·K). The Hall coefficient of the composite coating is 15.33×10 3 cm 3 / C, and the Hall mobility is 1.02 cm 3 / V·s, the resistance is 7.37Ω, and the conductivity is 120.20×10 3 S / cm. The porosity of the composite coating is 1.32%.

Claims

1. A method for preparing a conductive and thermal conductive composite coating on the surface of an alumina ceramic, characterized by: The preparation method of the conductive and thermal conductive composite coating on the surface of alumina ceramics is carried out according to the following steps: Step 1: Using a ball mill to perform low-energy ball milling on alumina powder and aluminum powder, so that the alumina powder particles are evenly distributed in the aluminum powder to obtain a mixed powder; the mass ratio of the aluminum powder to the alumina powder is (2-4):1; The low-energy ball milling process comprises: weighing alumina powder and aluminum powder, mixing them and then loading them into a ball mill, evacuating the ball mill, and then introducing an inert gas; the ball milling process adopts a dry milling method, controlling the ball-to-material mass ratio to be (3-4):1, setting the ball mill speed to 150-200 r / min, and setting the ball milling time to 2-4 hours. During the ball milling, the ball mill rotates in a unidirectional manner, and the ball mill stops rotating for 5-10 minutes after each 0.5-1 hour of ball milling; Step 2: spraying the mixed powder obtained in step 1 onto an alumina ceramic substrate by cold spraying to obtain an Al-Al2O3 transition coating; The cold spraying process comprises: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol, placing the alumina ceramic substrate in a drying oven for drying after ultrasonic cleaning, and fixing the alumina ceramic substrate on a fixture after drying; before spraying, loading the mixed powder obtained in step 1 into a powder feeder, using nitrogen as a working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2-3mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun moving speed is 150-200mm / s, the vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed is 40-45mm, the working gas pressure is 5-7MPa, the working gas temperature is 600-900℃, and the number of spray layers is 1-2; Step 3: cold spraying aluminum powder onto the Al-Al2O3 transition coating obtained in step 2 to obtain a composite coating of the Al-Al2O3 transition coating and the pure Al coating; The cold spraying process comprises: loading aluminum powder into a powder feeder, fixing the alumina ceramic substrate with an Al-Al2O3 transition coating deposited on its surface obtained in step 2 on a fixture; using nitrogen as the working gas during spraying, an "S"-shaped spraying trajectory, a spraying trajectory line spacing of 2-3 mm, an angle of 90° between the spray beam and the surface to be sprayed, a spray gun movement speed of 150-200 mm / s, a vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed of 40-45 mm, a working gas pressure of 3.5-4.5 MPa, a working gas temperature of 550-650°C, and a number of spray layers of 2-6.

2. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramic according to claim 1, characterized in that: The purity of the aluminum powder in step 1 is 99.9%, the particles are spherical, and the particle size is 20-35 μm.

3. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramic according to claim 1, characterized in that: The purity of the aluminum oxide powder in step 1 is 99.9%, the particles are irregular in shape, and the particle size is 20-60 μm.

4. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramic according to claim 1, characterized in that: The ball mill in step 1 is a planetary ball mill.

5. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics according to claim 1, characterized in that: The inert gas in step 1 is argon.

6. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics according to claim 1, characterized in that: The low-energy ball milling process is as follows: weighed alumina powder and aluminum powder are mixed and loaded into a ball mill jar, the ball mill jar is vacuumed, and then argon gas is introduced; the ball milling process adopts a dry milling method, the ball-to-material mass ratio is controlled to be 3:1, the ball mill speed is set to 200 r / min, the ball milling time is set to 2 hours, the ball mill jar is rotated in a unidirectional manner during the ball milling, and the ball mill stops rotating for 5 minutes after each 0.5 hour of ball milling.

7. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics according to claim 1, characterized in that: The ultrasonic cleaning time in step 2 is 10-30 minutes, the ultrasonic frequency is 20-80KHz, the drying temperature is 50-80°C, and the drying time is 10-30 minutes.

8. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics according to claim 1, characterized in that: The cold spraying process in step 2 includes the following steps: ultrasonically cleaning the alumina ceramic substrate to be sprayed with anhydrous ethanol, placing the alumina ceramic substrate in a drying oven for drying after ultrasonic cleaning, and fixing the alumina ceramic substrate on a fixture after drying; before spraying, loading the mixed powder obtained in step 1 into a powder feeder, using nitrogen as the working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun moving speed is 200mm / s, the vertical distance between the spray gun end and the surface of the alumina ceramic substrate to be sprayed is 40mm, the working gas pressure is 5MPa, the working gas temperature is 650℃, and the number of spray layers is 2.

9. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics according to claim 1, characterized in that: The purity of the aluminum powder in step 3 is 99.9%, the particles are spherical, and the particle size is 20-35 μm.

10. The method for preparing the conductive and thermal conductive composite coating on the surface of alumina ceramics according to claim 1, characterized in that: The cold spraying process described in step 3 includes the following steps: loading aluminum powder into a powder feeder, fixing the alumina ceramic substrate with an Al-Al2O3 transition coating deposited on the surface obtained in step 2 on a fixture; using nitrogen as the working gas during spraying, the spraying trajectory is "S"-shaped, the spraying trajectory line spacing is 2mm, the angle between the spray beam and the surface to be sprayed is 90°, the spray gun moving speed is 200mm / s, the vertical distance between the end of the spray gun and the surface of the alumina ceramic substrate to be sprayed is 40mm, the working gas pressure is 4MPa, the working gas temperature is 600℃, and the number of spray layers is 4.

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