A molybdenum-based composite coating with high temperature stability and low emissivity and a preparation method thereof

Abstract

This invention relates to a molybdenum-based composite coating with high-temperature stability and low emissivity, and its preparation method. The molybdenum-based composite coating sequentially comprises an Al₂O₃ anti-diffusion barrier layer, a PtOx modified transition layer, and a Pt low-emissivity layer formed on the surface of a Mo substrate. The molybdenum-based composite coating obtained by this invention has a uniform microstructure and good density; the layers are well bonded together, and there are no defects such as through cracks. It exhibits excellent high-temperature stability and low emissivity, meeting the performance requirements of high-temperature multilayer thermal insulation reflectors for high-temperature resistance and low emissivity.

Description

Technical Field

[0001] This invention belongs to the field of coating structure design and preparation, and relates to a molybdenum-based composite coating with good high-temperature stability and low emissivity and its preparation method. Background Technology

[0002] In recent years, with the rapid development of high-thrust engines and hypersonic spacecraft, the ambient temperature during engine ignition can exceed 1000℃. Spacecraft propulsion systems and their equipment are extremely susceptible to damage when subjected to the radiant heat of the engine's high-temperature plume. Therefore, more stringent performance requirements have been placed on the thermal protection materials for critical components such as spacecraft propulsion systems.

[0003] Multilayer thermal insulation materials are a core component of spacecraft thermal protection systems. Their performance directly affects the internal temperature balance of the spacecraft, thus determining whether internal equipment and payloads can operate normally. Multilayer thermal insulation materials are thermal insulation components composed of alternating layers of low-emissivity reflective screens and low-thermal-conductivity spacers. Their working principle is that the reflective screens reflect radiant heat layer by layer, forming extremely high thermal resistance. They exhibit excellent thermal insulation performance in a vacuum environment, with a theoretical equivalent thermal conductivity as low as 10. -5 With a strength on the order of W / (m·K), it is known as a super thermal insulation material and has important applications in spacecraft thermal protection systems.

[0004] Conventional multilayer heat-insulating reflective materials, despite their low emissivity, are typically suitable for lower operating temperatures. According to Boltzmann's law, infrared emissivity increases with the fourth power of temperature; the higher the temperature, the more significant the radiative heat transfer. When the temperature exceeds 1000℃, the reduced emissivity of the reflective screen can significantly suppress radiative heat transfer. Currently, high-temperature materials for reflective screens are mainly low-emissivity metal foils, such as gold foil, copper foil, aluminum foil, nickel foil, and stainless steel. However, most metal foil materials (such as gold and aluminum foil) are prone to diffusion, volatilization, oxidation, and structural instability at high temperatures. Therefore, developing reflective screen materials with higher temperature resistance and lower emissivity is key to achieving high-temperature heat insulation materials.

[0005] Numerous researchers both domestically and internationally have explored the preparation of low-emissivity composite coatings from various perspectives to achieve the goal of high-temperature, low-emissivity properties. Studies have found that metal films such as Au foil, Al foil, and stainless steel exhibit good structural stability and low emissivity. However, some shortcomings remain. For example, metal films exhibit some selectivity for high-temperature alloys; for instance, metal films deposited on the surface of single-crystal nickel-based alloys have weaker adhesion and are prone to detachment. Furthermore, the metal film preparation process requires sophisticated equipment, imposes limitations on component size, and has a relatively low temperature resistance (below 800℃). During long-term use, phenomena such as elemental diffusion, film blistering, and easy wear can occur, affecting their long-term performance and stability.

[0006] Molybdenum metal, due to its excellent thermal fatigue resistance, high melting point (2620℃), low coefficient of thermal expansion, and good high-temperature creep resistance, is an ideal choice for reflectors in multilayer thermal insulation materials for high-temperature thermal protection (>1200℃). However, molybdenum foil has a relatively high surface emissivity (approximately 0.1) at high temperatures, affecting its thermal radiation performance. The emissivity of a metal is affected by surface roughness and oxide film; precious metals such as gold (Au), platinum (Pt), and palladium (Pd) are commonly used for low-emissivity coatings. Among them, Pt coatings are widely used on the surfaces of substrates such as stainless steel, titanium alloys, and nickel alloys. Applying a Pt coating to a molybdenum foil substrate can effectively reduce its surface emissivity and improve the thermal radiation performance of the reflector. However, at high temperatures, molybdenum metal easily diffuses into the Pt coating, leading to an increase in the coating's emissivity.

[0007] Furthermore, molybdenum metal readily forms volatile molybdenum oxides (such as MoO3 and MoO2) in high-temperature, oxygen-rich environments. These oxides not only significantly reduce the mechanical properties of molybdenum but also increase its surface emissivity, thereby reducing the radiative thermal performance of the reflector. In summary, directly coating the molybdenum metal surface with a low-emissivity platinum coating is insufficient to meet the low-emissivity performance requirements of reflectors in high-temperature environments. Currently, there are no literature reports on low-emissivity reflectors suitable for multilayer thermal insulation materials used in high-temperature thermal protection (>1200℃) applications such as spacecraft surfaces and propulsion systems. Therefore, research and development of high-temperature resistant, low-emissivity molybdenum-based reflector composite coatings are urgently needed. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a molybdenum-based composite coating with good high-temperature stability and low emissivity, as well as its preparation method. Specifically, this invention constructs a Mo / Al₂O₃ / PtOx / Pt composite coating on the surface of a molybdenum foil (Mo) substrate, comprising an Al₂O₃ diffusion-blocking layer and a PtOx layer, respectively. x A modified transition layer and a Pt low-emissivity surface layer are used to meet the performance requirements of high-temperature multilayer thermal insulation material reflectors for high temperature resistance (>1200℃) and low emissivity.

[0009] In a first aspect, the present invention provides a molybdenum-based composite coating with high temperature stability and low emissivity, comprising, in sequence, an Al2O3 anti-diffusion barrier layer, a PtOx modified transition layer, and a Pt low emissivity layer formed on the surface of a Mo substrate.

[0010] Preferably, the thickness of the Al2O3 anti-diffusion barrier layer is 300–600 nm, and more preferably 530–550 nm.

[0011] Preferably, the thickness of the PtOx modified transition layer is 50–400 nm, and more preferably 200–230 nm.

[0012] Preferably, the thickness of the Pt low emissivity layer is 100–1000 nm, more preferably 200–230 nm.

[0013] Preferably, the total thickness of the composite coating is 0.45–2 μm.

[0014] Compared with existing technologies, the inorganic high-temperature resistant and low infrared emissivity composite coating of the present invention adopts a multi-layer stacked structure design, which can be used in a high-temperature environment of 1200℃, with an emissivity of 0.07. Compared with current yttrium oxide coatings, silicon dioxide coatings, and Au / Ni coatings prepared by magnetron sputtering, its performance is significantly improved in many aspects such as infrared emissivity, operating temperature, and high-temperature stability.

[0015] Based on the principle of functional superposition and complementary advantages of composite coatings, the anti-diffusion barrier layer uses an Al2O3 thin film, which can prevent the high-temperature oxidation of the metal substrate and the diffusion between the substrate material and the Pt thin film at high temperatures, thus avoiding the deterioration of the performance of the low emissivity functional layer. The introduction of the PtOx modified transition layer enhances the bonding force between the Al2O3 layer and the Pt layer, preventing the "dehydration and agglomeration" phenomenon of the composite coating during high-temperature processes and maintaining the stability of the composite coating system at high temperatures. The low emissivity layer Pt is chemically stable and does not oxidize at high temperatures, ensuring stability and low emissivity at high temperatures, while also serving as an anti-oxidation coating to prevent the high-temperature oxidation of the molybdenum substrate. The coatings are tightly bonded with both mechanical and solid-phase diffusion bonding forces. In addition, the matching of the thermal expansion coefficients of the coatings prevents cracking and peeling of the composite coating. Therefore, the molybdenum-based composite coating obtained by this invention has a dense structure, good bonding between layers, and excellent high-temperature stability and low emissivity performance.

[0016] Secondly, the present invention provides a method for preparing a molybdenum-based composite coating with high-temperature stability and low emissivity, comprising: (1) Surface pretreatment of Mo matrix; (2) An Al2O3 anti-diffusion barrier layer was prepared by vacuum deposition of molten alumina onto the surface of a pretreated Mo substrate. (3) A PtOx modified transition layer was prepared on the surface of the Al2O3 anti-diffusion barrier layer by DC magnetron sputtering reaction method; (4) A low emissivity Pt layer was prepared on the surface of the PtOx modified transition layer by DC magnetron sputtering.

[0017] Preferably, in step (1), the surface pretreatment of the Mo substrate includes: ultrasonically cleaning the Mo substrate with acetone, distilled water and ethanol respectively, for cleaning times of 10-30 min, 0-20 min and 0-10 min respectively, and then drying at 80-100°C for 10-20 min.

[0018] Preferably, in step (2), a vacuum coating machine is used to melt alumina crystal particles with a purity of 99.99% and a particle size of 1-3 mm; Preferably, the parameters of the smelting process for the alumina crystal particles include: a vacuum degree of 1×10⁻⁶. -3 ~50×10 -3 Pa, voltage is -1 to -10 kV.

[0019] Preferably, in step (2), the process parameters of the vacuum coating method include: heating temperatures of the workpiece disk, monitoring plate, and sidewall are 100–150°C, 150–300°C, and 50–200°C, respectively; and the cavity vacuum degree is 0.1–1×10⁻⁶. -3 Pa; Thickness monitoring method: crystal control; Ion beam cleaning time: 50-150s; Ion source voltage: 700-900V; Current: 800-1000mA; Oxygen flow rate: 20-100sccm; Argon flow rate: 2-20sccm; Coating thickness: 500-600nm; Coating rate: 0.1-0.8nm / s.

[0020] Preferably, in step (3), the process parameters of the DC magnetron sputtering reaction method include: a vacuum degree of 1.0 × 10⁻⁶. -4 ~5×10 -4 Pa; Target material: Pt (purity 99.99%); Target-substrate distance: 5-20 cm; Working pressure: 0.1-1.0 Pa; Power: 50-200 W; Oxygen flow rate: 1-20 sccm; Argon flow rate: 5-60 sccm; Sputtering temperature: room temperature.

[0021] Preferably, in step (4), the process parameters of the DC magnetron sputtering method include: vacuum degree 1×10⁻⁶. -4 ~5×10 -4 Pa; Target material: Pt (purity 99.99%); Target-substrate distance: 5-20 cm; Working pressure: 0.1-1.0 Pa; Power: 50-200 W; Argon flow rate: 5-100 sccm; Sputtering temperature: room temperature.

[0022] Beneficial effects: (1) A composite coating was prepared by combining vacuum coating and magnetron sputtering. The resulting coating had a uniform microstructure and good density. The layers of the coating were well bonded together and there were no defects such as through cracks. (2) In the coating system designed in this invention, Al2O3 (8.3×10⁻⁶) -6 ℃ -1 PtOx (9.0×10) -6 ℃ -1 ), Pt(8.8×10 -6℃ -1 ) and molybdenum substrate (6.0×10 -6 ℃ -1 The matching thermal expansion coefficient can effectively alleviate thermal stress during thermal cycling. Pt, as the outermost layer, can resist oxygen and high temperature, further protecting the internal coating system and ensuring low emissivity characteristics. (3) Compared with the prepared single molybdenum-based coating Mo / Pt and Mo / Al2O3 / Pt systems, the molybdenum-based composite coating prepared in this invention has better high-temperature stability (>1200℃) and low emissivity (<0.1). (4) The present invention uses a combination of vacuum coating technology and magnetron sputtering technology to prepare composite coatings. This method has the advantages of low process cost, high efficiency, good repeatability, controllable coating thickness, and suitability for large-scale production. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the molybdenum-based composite coating structure prepared in Example 1; Figure 2 The surface morphology of the Mo / Al2O3 / PtOx / Pt composite coating system is shown in (a) before treatment and (b) after high-temperature treatment at 1200℃. Figure 3 Cross-sectional views of the Mo / Al2O3 / PtOx / Pt composite coating system before treatment (a) and after high-temperature treatment at 1200℃ (b); Figure 4 The surface morphology images of the Mo / Pt coating system are shown in (a) before treatment and (b) after high-temperature treatment at 1200℃. Figure 5 Cross-sectional view of the Mo / Pt coating system after high-temperature treatment at 1200℃; Figure 6 The surface morphology of the Mo / Al2O3 / Pt coating system is shown in (a) before treatment and (b) after high-temperature treatment at 1200℃. Figure 7 Cross-sectional view of the Mo / Al2O3 / Pt coating system after high-temperature treatment at 1200℃; Figure 8 The values ​​represent the hemispherical emissivity of different coatings (MAOP, MP, and MAP) before and after high-temperature treatment at 1200℃. MAOP, MP, and MAP are abbreviations for the Mo / Al2O3 / PtOx / Pt composite coating system, the Mo / Pt coating system, and the Mo / Al2O3 / Pt coating system, respectively. Detailed Implementation

[0024] To further illustrate the invention's content, features, and practical effects, the invention will be described in detail below with reference to embodiments. It should be noted that the modification methods of the invention are not limited to these specific implementation methods. Equivalent substitutions and modifications made by those skilled in the art based on their reading of the invention's content, without departing from the spirit and essence of the invention, are also within the scope of protection claimed by this invention.

[0025] First, this invention provides a molybdenum-based composite coating with good high-temperature stability and low emissivity. The molybdenum-based composite coating comprises: an Al2O3 diffusion barrier layer in direct contact with the molybdenum substrate, a PtOx modified transition layer formed on the surface of the diffusion barrier layer, and an outermost Pt layer. The Al2O3 diffusion barrier layer has a high diffusion barrier that can suppress inter-metal diffusion; the introduction of the PtOx modified transition layer enhances the bonding force between the Al2O3 layer and the Pt layer, maintaining the stability of the composite coating system at high temperatures; the Pt layer has low emissivity and antioxidant properties. The coating layers are tightly bonded together with both mechanical bonding and solid-phase diffusion bonding forces. The molybdenum-based composite coating obtained by this invention has a dense structure, good inter-layer bonding, and exhibits good high-temperature stability and low emissivity.

[0026] In this invention, the density and uniformity of each coating are ensured by controlling the process parameters of vacuum coating and magnetron sputtering (such as deposition rate, atmosphere, temperature, etc.); the adhesion between the alumina layer and the low emissivity functional layer Pt is enhanced by selecting a suitable PtOx modified transition layer; and the high-temperature resistance of the composite coating is improved by using high-temperature resistant materials such as alumina and platinum.

[0027] The following exemplarily illustrates the preparation method of the molybdenum-based composite coating with good high-temperature stability and low emissivity provided by the present invention.

[0028] Surface pretreatment of the Mo substrate. The Mo substrate was ultrasonically cleaned with acetone, distilled water, and ethanol for 10–30 min, 0–20 min, and 0–10 min, respectively, and then dried at 80–100 °C for 10–20 min. As an example, a 20 μm pure molybdenum foil was used as the substrate. The Mo foil was cut to a size of 4 × 4 cm, placed in a beaker, and ultrasonically cleaned with 20 mL of acetone, 40 mL of distilled water, and 20 mL of ethanol for 20 min, 10 min, and 5 min, respectively, and then dried in an oven at 80 °C for 10 min.

[0029] An Al2O3 diffusion barrier layer was prepared by vacuum deposition of molten alumina onto the surface of a pretreated Mo substrate.

[0030] In an optional embodiment, a vacuum coating machine is used to melt alumina crystal particles with a purity of 99.99% and a particle size of 1-3 mm. Preferably, the parameters of the melting process for the alumina crystal particles include: a vacuum degree of 1×10⁻⁶. -3 ~50×10 -3 Pa, voltage is -1 to -10 kV.

[0031] In an optional embodiment, the process parameters of the vacuum coating method include: heating temperatures of the workpiece disk, monitoring plate, and sidewall are 100–150°C, 150–300°C, and 50–200°C, respectively; and the cavity vacuum degree is 0.1–1×10⁻⁶. -3 Pa; Thickness monitoring method: crystal control; Ion beam cleaning time: 50-150s; Ion source voltage: 700-900V, current: 800-1000mA; Oxygen flow rate: 20-100sccm, Argon flow rate: 2-20sccm; Coating thickness: 500-600nm; Coating rate: 0.1-0.8nm / s.

[0032] A PtOx modified transition layer was prepared on the surface of an Al2O3 anti-diffusion barrier layer using a DC magnetron sputtering reactive method.

[0033] In an optional embodiment, the process parameters of the DC magnetron sputtering reaction method include: vacuum degree 1×10⁻⁶. -4 ~5×10 -4 Pa; Target material: Pt (purity 99.99%); Target-substrate distance: 5-20 cm; Working pressure: 0.1-1.0 Pa; Power: 50-200 W; Oxygen flow rate: 1-20 sccm; Argon flow rate: 5-60 sccm; Sputtering temperature: room temperature.

[0034] A low emissivity Pt layer was prepared on the surface of PtOx using DC magnetron sputtering.

[0035] In an optional embodiment, the process parameters of the DC magnetron sputtering method include: vacuum degree 1×10⁻⁶. -4 ~5×10 -4 Pa; Target material: Pt (purity 99.99%); Target-substrate distance: 5-20 cm; Working pressure: 0.1-1.0 Pa; Power: 50-200 W; Argon flow rate: 5-100 sccm; Sputtering temperature: room temperature.

[0036] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0037] Example 1

[0038] In Example 1 of this invention, an Al2O3 / PtOx / Pt composite coating was prepared on a Mo substrate (20 μm thick). From the innermost layer to the outermost layer, the coating comprises: an Al2O3 diffusion-blocking layer, a PtOx modified transition layer, and an outermost Pt layer. The preparation method of the composite coating includes the following steps: (1) Mo substrate pretreatment. The Mo substrate was cut into 4×4cm pieces and ultrasonically cleaned in 20mL acetone, 40mL distilled water and 20mL ethanol for 20min, 10min and 5min respectively. Then it was dried in an oven at 80℃ for 10min. (2) A vacuum coating machine was used to melt alumina crystal particles (99.99% purity) with a particle size of 1-3 mm to obtain Al2O3 melt; the melting process parameters included: vacuum degree of 5×10 -3 Pa, voltage is -4.5 kV; (3) The obtained Al2O3 melt was deposited onto the pretreated Mo substrate by vacuum deposition (process parameters are shown in Table 1) to prepare an Al2O3 anti-diffusion barrier layer with a thickness of 544 nm. Table 1. Process parameters for vacuum deposition of Al2O3 coatings. (4) A PtOx layer with a thickness of 220 nm was prepared on the surface of the Al2O3 anti-diffusion barrier layer by DC magnetron sputtering (process parameters are shown in Table 2); Table 2 Process parameters for PtOx coatings sputtered by DC magnetron sputtering Coating temperature room temperature vacuum degree <![CDATA[2.5×10 -4 Well]]> Working air pressure 0.2Pa Target-base distance 12cm Target material Pt target power 80W Oxygen flow rate 10sccm Argon flow rate 40sccm (5) A Pt layer with a thickness of 224 nm was prepared on the surface of the PtOx layer by DC magnetron sputtering (process parameters are shown in Table 3). Table 3 Process parameters for Pt coating sputtering by DC magnetron sputtering Coating temperature room temperature vacuum degree <![CDATA[2.5×10 -4 Well]]> working air pressure 0.2Pa Target-base distance 12cm Target material Pt target power 80W Argon flow rate 80sccm

[0039] Figure 1 This is a schematic diagram of the molybdenum-based composite coating structure prepared in Example 1. As shown in the figure, the molybdenum-based composite coating prepared in Example 1 consists of three layers: the first layer is an Al2O3 anti-diffusion barrier layer in direct contact with the substrate; the second layer is a PtOx modified transition layer on the surface of the Al2O3 anti-diffusion barrier layer; and the third layer (outermost layer) is a Pt layer on the surface of the PtOx layer. The layers are well bonded together.

[0040] Figure 2 (a) and Figure 3 (a) shows the surface morphology and cross-sectional view of the Mo / Al2O3 / PtOx / Pt composite coating system prepared in Example 1. As can be seen from the figure, the coating surface is uniform and dense, the microstructure is uniform, and the coating layers are tightly bonded.

[0041] The high-temperature performance of the Mo / Al2O3 / PtOx / Pt composite coating was evaluated by heat treatment. The conditions were as follows: the sample was placed in a vacuum graphite furnace at 1200℃ and held for 30 minutes, and then cooled to room temperature.

[0042] Figure 2 (b) and Figure 3 (b) shows the surface morphology and cross-sectional view of the composite coating system after heat treatment. Figure 2 (b) It can be seen that after high-temperature treatment at 1200℃, the coating surface is uniform and dense, and still maintains a smooth state. Figure 3 (b) It can be seen that longitudinal cracks are generated in the Al2O3 layer during the heat treatment process, but terminate in the Al2O3 layer. The coating and the substrate are well bonded and no cracking occurs. It can be seen that the coating surface maintains a smooth and dense morphology during the heat treatment process, indicating that the coating system designed in this invention has good high temperature resistance.

[0043] The hemispherical emissivity of the Mo / Al2O3 / PtOx / Pt composite coating before and after heat treatment was measured using an infrared emissivity meter. The results are as follows: Figure 8 As shown, the hemispherical emissivity of the composite coating without high-temperature treatment is 0.06, while that after high-temperature treatment is 0.07, indicating that the Mo / Al2O3 / PtOx / Pt composite coating system prepared in Example 1 has good high-temperature stability and low emissivity performance.

[0044] Comparative Example 1

[0045] A Pt coating with a thickness of 224 nm (Mo / Pt coating) was prepared on a Mo substrate using the same DC magnetron sputtering Pt process conditions as in step (5) of Example 1.

[0046] The resulting coating was subjected to high-temperature heat treatment under the same conditions as in Example 1, and the emissivity after high-temperature heat treatment was tested.

[0047] Figure 4 (a) and (b) are the microstructure images of the Mo / Pt coating before and after heat treatment at 1200℃ for 30 min, respectively. As can be seen from the figures, after heat treatment of the Mo / Pt coating for 30 min, a network of pores appears on the surface of the coating, exposing the substrate.

[0048] Figure 5 The figure shows a cross-sectional view of the Mo / Pt coating system after high-temperature treatment at 1200℃. As can be seen from the figure, significant interlayer fractures occurred in the Mo / Pt coating system after heat treatment at 1200℃.

[0049] like Figure 8 As shown, the infrared emissivity test results of the Mo / Pt coating before and after heat treatment at 1200℃ for 30 min are 0.06 and 0.19, respectively. This indicates that the high-temperature performance and retention of low infrared emissivity of this coating system are far inferior to the Mo / Al2O3 / PtOx / Pt composite coating system prepared in Example 1.

[0050] Comparative Example 2

[0051] An Al2O3 / Pt coating was prepared on a Mo substrate using the same vacuum Al2O3 deposition process conditions in step (3) of Example 1 and the same DC magnetron sputtering Pt process conditions in step (5). The Al2O3 film thickness was 544 nm and the Pt thickness was 224 nm (Mo / Al2O3 / Pt coating).

[0052] The obtained Al2O3 / Pt coating was subjected to high-temperature heat treatment under the same conditions as in Example 1, and the emissivity after high-temperature heat treatment was tested.

[0053] Figure 6 (a) and (b) show the microstructures of the Mo / Al2O3 / Pt coating before and after heat treatment at 1200℃ for 30 min, respectively. As can be seen from the figures, pores appear on the surface of the Mo / Al2O3 / Pt coating after heat treatment for 30 min.

[0054] Figure 7 The figure shows a cross-sectional view of the Mo / Al2O3 / Pt coating system after high-temperature treatment at 1200℃. As can be seen from the figure, obvious porosity occurs in the Pt layer of the coating system after heat treatment at 1200℃.

[0055] like Figure 8 As shown, the infrared emissivity test results of the Mo / Al2O3 / Pt coating before and after heat treatment at 1200℃ for 30 min are 0.06 and 0.15, respectively. This indicates that the high-temperature performance and retention of low infrared emissivity of this coating system are far inferior to the Mo / Al2O3 / PtOx / Pt composite coating system prepared in Example 1.

Claims

1. A molybdenum-based composite coating with high-temperature stability and low emissivity, characterized in that, It consists of an Al2O3 diffusion barrier layer, a PtOx modified transition layer, and a Pt low emissivity layer formed on the surface of a Mo matrix.

2. The molybdenum-based composite coating with high-temperature stability and low emissivity according to claim 1, characterized in that, The thickness of the Al2O3 anti-diffusion barrier layer is 300–600 nm, preferably 530–550 nm.

3. The molybdenum-based composite coating with high-temperature stability and low emissivity according to claim 1 or 2, characterized in that, The thickness of the PtOx modified transition layer is 50–400 nm, preferably 200–230 nm.

4. The molybdenum-based composite coating with high-temperature stability and low emissivity according to any one of claims 1-3, characterized in that, The thickness of the Pt low emissivity layer is 100–1000 nm, preferably 200–230 nm.

5. The molybdenum-based composite coating with high-temperature stability and low emissivity according to any one of claims 1-4, characterized in that, The total thickness of the composite coating is 0.45–2 μm.

6. A method for preparing a molybdenum-based composite coating with high-temperature stability and low emissivity according to any one of claims 1-5, characterized in that, include: (1) Surface pretreatment of Mo matrix; (2) An Al2O3 anti-diffusion barrier layer was prepared by vacuum deposition of molten alumina onto the surface of a pretreated Mo substrate. (3) A PtOx modified transition layer was prepared on the surface of the Al2O3 anti-diffusion barrier layer by DC magnetron sputtering reaction method; (4) A low emissivity Pt layer was prepared on the surface of the PtOx modified transition layer by DC magnetron sputtering.

7. The preparation method according to claim 6, characterized in that, In step (1), the surface pretreatment of the Mo matrix includes: ultrasonic cleaning of the Mo matrix with acetone, distilled water and ethanol respectively for 10-30 min, 0-20 min and 0-10 min respectively, and then drying at 80-100℃ for 10-20 min.

8. The preparation method according to claim 6 or 7, characterized in that, In step (2), a vacuum coating machine is used to melt alumina crystal particles with a purity of 99.99% and a particle size of 1-3 mm; Preferably, the parameters of the smelting process for the alumina crystal particles include: a vacuum degree of 1×10⁻⁶. -3 ~50×10 -3 Pa, voltage is -1 to -10 kV; Preferably, the process parameters of the vacuum coating method include: heating temperatures of the workpiece disk, monitoring plate, and sidewall are 100–150°C, 150–300°C, and 50–200°C, respectively; and the cavity vacuum degree is 0.1–1×10⁻⁶. -3 Pa; Thickness monitoring method: crystal control; Ion beam cleaning time: 50-150s; Ion source voltage: 700-900V; Current: 800-1000mA; Oxygen flow rate: 20-100sccm; Argon flow rate: 2-20sccm; Coating thickness: 500-600nm; Coating rate: 0.1-0.8nm / s.

9. The preparation method according to any one of claims 6-8, characterized in that, In step (3), the process parameters of the DC magnetron sputtering reaction method include: a vacuum degree of 1.0 × 10⁻⁶. -4 ~5×10 -4 Pa; Target material: Pt; Target-substrate distance: 5–20 cm; Working pressure: 0.1–1.0 Pa; Power: 50–200 W; Oxygen flow rate: 1–20 sccm; Argon flow rate: 5–60 sccm; Sputtering temperature: room temperature.

10. The preparation method according to any one of claims 6-9, characterized in that, In step (4), the process parameters of the DC magnetron sputtering method include: vacuum degree 1×10⁻⁶. -4 ~5×10 -4 Pa; Target material: Pt; Target-substrate distance: 5–20 cm; Working pressure: 0.1–1.0 Pa; Power: 50–200 W; Argon flow rate: 5–100 sccm; Sputtering temperature: room temperature.

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