Spacecraft iridium alloy coating and preparation method thereof

Abstract

The invention provides a spacecraft iridium alloy coating and a preparation method thereof, and relates to the technical field of coating preparation. The platinum substrate is sequentially subjected to heat treatment, sand blowing and acid etching, and a treated substrate is obtained; and the alloy is arranged on the surface of the treated base body through laser cladding, and cooling is conducted under the protective atmosphere to obtain the spacecraft iridium alloy coating. The alloy includes iridium and rhenium. By means of the ultrahigh-energy-density laser cladding technology, the iridium alloy and the platinum matrix are metallurgically bonded instantly, the deposition rate is increased to 10 times or above that of a traditional technology, and use of a precious metal salt solution and complex waste liquid treatment are avoided; and the platinum substrate is subjected to surface treatment, and interface bonding is further strengthened through hardness regulation and control, stress counteracting and surface microstructure optimization, so that the bonding strength of the coating and the treated substrate is effectively improved, and the problem of thermal cycle cracking is thoroughly solved.

Description

Technical Field

[0001] This application relates to the technical field of coating preparation, and particularly to an iridium alloy coating for spacecraft and a preparation method thereof. Background Art

[0002] Space attitude and orbit control engines are the core components of modern spacecraft, featuring high operating temperatures and heavy loads. Therefore, materials with high temperature resistance and strong stability are required to ensure their efficient and reliable operation. Currently, high-performance green unit engines are under research, with the combustion temperature of the engine reaching over 1600°C. After testing with traditional metal materials, problems such as metal deformation occur, which cannot meet the requirements of long-term engine operation. Platinum-iridium coatings, with characteristics such as high melting point, stable chemical properties, and strong high-temperature stability, have become the key materials for the development of a new generation of high-temperature core components.

[0003] Conventional methods for preparing iridium coatings: electroplating, electroless plating, sol-gel method, thermal spraying method. Among them, electroplating, electroless plating, and sol-gel method are chemical precipitation methods, where iridium salts are chemically precipitated onto platinum metal, and high-temperature heat treatment methods are used for coating preparation. The thermal spraying method is a physical method. Using thermal spraying technologies such as flame spraying and plasma spraying, iridium powder is heated to a molten or semi-molten state and sprayed onto the surface of the platinum metal substrate at high speed to obtain an iridium coating.

[0004] Conventional methods for cladding iridium alloys on platinum substrates include: electroplating, electroless plating, sol-gel method, thermal spraying method, etc. Among them, electroplating and electroless plating rely on the redox reaction of iridium salt solution on the surface of the platinum substrate to deposit the iridium layer. Although uniform coating can be achieved, the deposition rate is slow, making it difficult to meet the requirements of thick coatings. Moreover, most iridium salts are noble metal compounds, with high costs, complex waste liquid treatment, and in the high-temperature heat treatment process, the coating needs to be heated to over 1000°C to improve crystallinity, which will cause thermal stress due to the difference in thermal expansion coefficients between the coating and the substrate, easily leading to coating cracking or peeling; the sol-gel method is extremely sensitive to environmental humidity and temperature, and small parameter fluctuations will result in poor coating uniformity, with local thickness deviation exceeding 30%. At the same time, a large amount of gas is generated during the gel sintering process. If the gas cannot escape smoothly, pores are easily formed inside the coating, reducing the coating density. The gas expansion at high temperatures may also cause the coating to rupture; the thermal spraying method uses flame or plasma to heat and spray iridium powder onto the substrate. Although the process efficiency is high, large internal stresses (up to over 200 MPa) are easily generated when high-speed particles impact the substrate, resulting in insufficient bonding strength between the coating and the substrate; moreover, the molten iridium particles are easily oxidized to form IrO2 impurities when contacting air during the spraying process, significantly reducing the high-temperature oxidation resistance and mechanical properties of the coating. In addition, the coating formed by thermal spraying has a layered structure and micropores inside, with a porosity of usually 5% - 15%. In extreme environments such as the nozzle of a space engine, high-temperature combustion gas is likely to penetrate through the pores, accelerating the failure of the coating.

[0005] Based on this, there is an urgent need to provide a new preparation method for cladding an iridium alloy on a platinum substrate to solve the above problems. Summary of the Invention

[0006] The purpose of this application is to provide a spacecraft iridium alloy coating and its preparation method to solve the above problems.

[0007] To achieve the above purpose, the first aspect of this application provides a preparation method for a spacecraft iridium alloy coating, including: Heat-treat, sand-blast, and acid-etch the platinum substrate in sequence to obtain a treated substrate; Use laser cladding to set the alloy on the surface of the treated substrate, and cool it under a protective atmosphere to obtain a spacecraft iridium alloy coating; The alloy includes iridium and rhenium.

[0008] Optionally, the preparation method of the spacecraft iridium alloy coating satisfies at least one of the following conditions: A. The heat treatment includes a first heating and a second heating performed in sequence. The temperature of the first heating is 200°C - 250°C, and the holding time is 1h - 2h; the temperature of the second heating is 350°C - 400°C, and the holding time is 2h - 3h; the heating rate for the second heating is 5°C / min - 15°C / min; B. The Vickers hardness of the substrate after the heat treatment is 150HV - 180HV; C. The peak stress of the substrate after the heat treatment is 150MPa - 250MPa.

[0009] Optionally, the pressure of the sand-blast is 0.3 MPa - 0.8MPa.

[0010] Optionally, the preparation method of the spacecraft iridium alloy coating satisfies at least one of the following conditions: A. The acid includes oxalic acid; B. The mass concentration of the acid is 5% - 15%; C. The temperature of the acid-etch is 80°C - 100°C, and the time is 30min - 60min.

[0011] Optionally, the preparation method of the spacecraft iridium alloy coating satisfies at least one of the following conditions: A. The particle size of the alloy is 50μm - 100μm; B. Based on the total mass of the alloy raw materials being 100%, it includes: 5% - 10% rhenium and 90% - 95% iridium.

[0012] Optionally, the energy density of the laser cladding is 1.5×10 4 W / cm 2 -3×10 4 W / cm 2 , the laser power is 80 kW - 100 kW, the focused spot is 0.2 mm - 2.0 mm, the scanning speed is 150 mm / s - 200 mm / s, and the powder feeding rate is 5 g / min - 20 g / min.

[0013] Optionally, the method for preparing the iridium alloy coating of the spacecraft satisfies at least one of the following conditions: A. The cooling rate is 10 3 K / s - 10 4 K / s; B. The gas in the protective atmosphere includes argon and nitrogen. The flow rate of argon is 8 L / min - 12 L / min, and the flow rate of nitrogen is 3 L / min - 5 L / min.

[0014] The second aspect of the present application provides an iridium alloy coating for a spacecraft, which is prepared by the method for preparing the iridium alloy coating of the spacecraft.

[0015] Optionally, the iridium alloy coating of the spacecraft satisfies at least one of the following conditions: A. The thickness of the iridium alloy coating of the spacecraft ≤ 1 mm; B. The hardness of the iridium alloy coating of the spacecraft ≥ 400 HV; C. The shear bonding strength between the platinum substrate and the iridium alloy coating of the spacecraft is 300 MPa - 350 MPa.

[0016] The third aspect of the present application provides a spacecraft, including the iridium alloy coating of the spacecraft.

[0017] Compared with the prior art, the beneficial effects of the present application include: The method for preparing the iridium alloy coating of the spacecraft provided by the present application realizes metallurgical bonding between the iridium alloy and the platinum substrate instantaneously through the laser cladding technology with ultra-high energy density, increases the deposition rate to more than 10 times that of the traditional process, and avoids the use of precious metal salt solutions and complex waste liquid treatment; and performs surface treatment on the platinum substrate, further strengthens the interfacial bonding through hardness regulation, stress cancellation and surface microstructure optimization, effectively improves the bonding strength between the coating and the treated substrate, and completely solves the problem of thermal cycle cracking.

[0018] The iridium alloy coating of the spacecraft provided by the present application has a high bonding strength between the coating and the substrate, no risk of interfacial peeling, excellent wear and corrosion resistance, can withstand heavy loads and complex stress environments, and fully meets the long-term reliable application requirements of harsh environments such as aerospace engine nozzles. Brief Description of the Drawings

[0019] To more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present application and should not be regarded as limiting the scope of the present application.

[0020] Figure 1 Schematic diagram of preparing a coating by laser cladding; Figure 2 Scanning electron micrograph of the iridium alloy coating for spacecraft prepared in Example 1; Figure 3 Scanning electron micrograph of the iridium alloy coating for spacecraft prepared in Comparative Example 1; Figure 4 Scanning electron micrograph of the iridium alloy coating for spacecraft prepared in Comparative Example 2.

[0021] Description of the main element symbols: 1 - Platinum substrate, 2 - Laser, 3 - Laser alloy jet, 4 - Melting zone, 5 - Platinum-iridium coating. Detailed Description of the Embodiments

[0022] As used herein, the terms: "Prepared from" is synonymous with "comprising". As used herein, the terms "comprising", "including", "having", "containing" or any other variation thereof are intended to cover non-exclusive inclusion. For example, a composition, step, method, article or device containing the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article or device.

[0023] The connecting word "consisting of" excludes any unstated element, step or component. If used in a claim, this phrase will render the claim closed, excluding materials other than those described, except for conventional impurities associated therewith. When the phrase "consisting of" appears in a clause of the claim body rather than immediately following the subject, it only limits the elements described in that clause; other elements are not excluded from the claim as a whole.

[0024] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed individually. For example, when the range "1 to 5" is disclosed, the described range should be interpreted as including the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise specified, the range is intended to include its end values and all integers and fractions within the range.

[0025] In these examples, unless otherwise specified, the parts and percentages are by mass.

[0026] "Parts by mass" refers to the basic measurement unit representing the mass ratio relationship of multiple components. 1 part can represent any unit mass, such as 1 g or 2.689 g, etc. If we say that the mass of component A is a parts by mass and the mass of component B is b parts by mass, it means the mass ratio of component A to component B is a:b. Or, it means the mass of component A is aK and the mass of component B is bK (K is any number representing a multiple factor). It should not be misunderstood that, different from the number of parts by mass, the sum of the parts by mass of all components is not limited to 100 parts.

[0027] "And / or" is used to indicate that either or both of the stated situations may occur. For example, A and / or B includes (A and B) and (A or B).

[0028] The first aspect of the present application provides a method for preparing an iridium alloy coating for a spacecraft, comprising: Successively subjecting a platinum substrate to heat treatment, sandblasting, and acid etching to obtain a treated substrate; It should be noted that in the preparation process of iridium alloy coatings for extreme environments of spacecraft, the process sequence of "heat treatment followed by sand blasting and acid etching" is the key to solving the problem of interface bonding between platinum substrate and iridium alloy; first, the platinum substrate is heat treated. This process can release the residual stress inside the substrate through thermal expansion, thereby avoiding cracking or peeling due to stress concentration during subsequent coating preparation; at the same time, heat treatment will make the originally dense oxide film (such as PtO2) on the platinum surface become loose or even partially decomposed, making it easier for subsequent treatment to remove the oxide layer more efficiently, and heating can increase the surface mobility of platinum atoms and enhance surface activity, creating ideal conditions for subsequent processes; secondly, sand blasting is performed after heat treatment, using the impact of high-speed sand particles (such as Al2O3 or ZrO2 sand) to thoroughly remove residual oil stains, particulate impurities and loose oxide layers on the substrate surface. On the other hand, a micron-scale concave-convex structure is formed on the surface of platinum, and the bonding strength of the coating is significantly improved through the "mechanical anchoring effect". The sand blasting step is performed after the heat treatment, which can avoid the risk of forming a dense oxide layer on the surface again when sand blasting is performed first and then heat treated, thereby ensuring the maximum cleaning effect; finally, an acid solution is used for acid etching after sand blasting. For example, the acid solution includes oxalic acid. Oxalic acid, as a medium-strong acid, can react with the residual oxide film on the surface of platinum to completely dissolve the nano-scale oxide layer and trace impurities (such as Fe, Ni, etc.), exposing the highly active metal surface; at the same time, the etching action will form nano-scale pits or grooves on the surface of platinum, which will form a "multi-level anchoring structure" with the micron-scale roughness generated by sand blasting, further strengthening the mechanical interlocking effect of the interface; the electron-rich state of the substrate surface after acid etching can also slow down the reoxidation rate, thereby gaining a cleaning window period for subsequent cladding; It should also be noted that the process sequence of "sand blasting and acid etching after heat treatment" is irreplaceable. If sand blasting is performed first and then heat treatment is performed, the fresh metal exposed after sand blasting is prone to quickly form a dense oxide film during preheating, which increases the difficulty of acid etching and may over-corrode the substrate. The superposition of thermal stress and sand blasting stress can easily lead to deformation of the substrate. If heat treatment is omitted and sand blasting is performed directly, the internal stress of the substrate is not released. During cladding, the rapid cooling of the high-energy density process can easily cause cracking of the coating. At the same time, the dense oxide film at room temperature requires stronger processing intensity, which may damage the substrate or reduce efficiency. The above-mentioned pretreatment steps are adopted to systematically improve the interface bonding strength and thermal damage resistance through the synergistic effects of stress release, physical roughening and cleaning, and chemical activation, ensuring that the coating can serve stably in extreme environments such as aerospace engine nozzles. The alloy is disposed on the surface of the treated substrate by laser cladding, and cooled in a protective atmosphere to obtain a spacecraft iridium alloy coating; The schematic diagram of laser cladding coating preparation is as follows Figure 1 shown.

[0029] The alloy includes iridium and rhenium.

[0030] It should be noted that rhenium atoms are dissolved in iridium, which can improve the high-temperature strength and creep resistance, allow a higher scanning speed (reduce heat input) without causing the collapse of the molten pool. In addition, rhenium segregates at grain boundaries, which can inhibit the migration of high-temperature grain boundaries and synergistically improve the high-temperature oxidation resistance of the coating with rapid solidification (grain size <5μm); rhenium enhances the thermal stability of the alloy, reduces the risk of microcracks caused by thermal cycling during high-speed machining, and the solid solution effect of rhenium improves the hot cracking resistance of the alloy, enabling the coating integrity to be maintained under extreme cooling rates.

[0031] In some embodiments, the method for preparing the iridium alloy coating of the spacecraft satisfies at least one of the following conditions: A. The heat treatment includes a first heating and a second heating performed in sequence. The temperature of the first heating is 200°C - 250°C, and the holding time is 1h - 2h; the temperature of the second heating is 350°C - 400°C, and the holding time is 2h - 3h; the heating rate for the second heating is 5°C / min - 15°C / min; Optionally, the temperature of the first heating can be 200°C, 210°C, 220°C, 230°C, 240°C, 250°C or any value between 200°C - 250°C, the holding time can be 1h, 1.5h, 2h or any value between 1h - 2h, the temperature of the second heating can be 350°C, 360°C, 370°C, 380°C, 390°C, 400°C or any value between 350°C - 400°C, the holding time can be 2h, 2.5h, 3h or any value between 2h - 3h, and the heating rate for the second heating can be 5°C / min, 10°C / min, 15°C / min or any value between 5°C / min - 15°C / min; It should be noted that the heat treatment is carried out before the sandblasting treatment, and its core role is reflected in the dual optimization of mechanical property regulation and surface treatment adaptability. During the heat treatment process, the platinum matrix undergoes partial recovery due to the enhanced atomic diffusion ability, and the Vickers hardness moderately decreases from 200HV at room temperature to 150 - 180HV. This hardness range enables the high-speed sand grains to impact the surface of the matrix more evenly during sandblasting, forming a micron-scale rough structure with a deviation ≤±10% (the Ra value can be controlled within 2 - 5μm), avoiding uneven surface topography after sandblasting due to excessive matrix hardness, such as local over-etching or differences in the depth of scratches; at the same time, the thermal expansion effect generated by preheating can offset 30 - 50% of the sandblasting cold working stress, reducing the peak surface stress of the matrix from 300 - 400MPa in the non-heat-treated state to 150 - 250MPa, significantly reducing the risk of microcracks caused by stress concentration. After actual measurement, the cracking probability decreases by more than 70% compared with the non-preheated process; The scientific definition of the temperature threshold is the key innovation point of the heat treatment process. Taking 200°C as the starting temperature ensures that platinum atoms have a minimum diffusion ability to release internal stress. When the temperature is lower than this, the stress release is insufficient, and sandblasting is likely to cause sudden changes in interface stress. Taking 400°C as the upper limit is based on the recrystallization kinetics characteristics of platinum. This temperature is close to but does not reach the recrystallization critical temperature of platinum (about 450°C). The grain boundary diffusion coefficient is only 1% of that at the recrystallization temperature, which can avoid excessive grain coarsening (when the grain size increases from 50μm at room temperature to more than 200μm, the tensile strength at 1370°C will decrease by 25%). At the same time, it can inhibit creep deformation caused by coarse grains during high-temperature service (the steady-state creep rate can be increased by 3 times). It can be understood that heat-treating the substrate within the range of 200 - 400°C is not a random temperature increase, but a precise control system based on material properties, process requirements, and thermophysical laws. The setting of this temperature range should not only ensure good metallurgical bonding between the substrate and the iridium alloy under the action of laser, but also avoid tissue deterioration or oxidation of the substrate due to overheating. Exemplarily, the softening temperature of platinum is about 1200°C, and the heat treatment temperature is much lower than this. The surface activity is mainly enhanced by moderately increasing the substrate temperature, reducing the cooling rate of the molten pool, and reducing thermal stress. The heating process follows strict rate and time control. Usually, it is linearly heated at a rate of 5 - 15°C per minute, adjusted specifically according to the substrate thickness. Thin sheets (<3mm) can be quickly heated to reduce the oxidation risk, while thick-walled parts (>20mm) need to be slowly heated to ensure uniform internal heating. When approaching the target temperature, the heating rate is reduced to 1 - 2°C per minute to prevent temperature overshoot. And after reaching the target temperature, heat preservation is also required according to the substrate thickness and cross-sectional temperature difference to ensure that the overall temperature uniformity is within ±5°C, avoiding local overheating leading to grain coarsening or thermal stress concentration. Exemplarily, the entire heat treatment process monitors the temperature field in real time through an infrared thermal imager and thermocouples. If the local temperature difference exceeds 15°C, the power or position of the heating source needs to be adjusted immediately. This precise control is in sharp contrast to the traditional process. When no heat treatment is carried out or only simply heated to below 100°C, the thermal stress problem cannot be solved, and the existing chemical method has no preheating link and it is difficult to achieve effective metallurgical bonding. The heat treatment of this application, through systematic regulation of temperature, rate, and uniformity, pre-accumulates about 50MPa of compressive stress in the substrate to offset the tensile stress generated by laser cladding, while reducing the wetting angle between the platinum matrix and the iridium alloy, significantly improving the bonding strength, and finally achieving high-quality coating preparation. It should also be noted that by advancing the pretreatment process and precisely controlling the temperature range, this process has achieved three major technological breakthroughs: "hardness matching for sandblasting efficiency - stress resistance to prevent cracking - grain stability to ensure strength". Compared with the traditional sandblasting process after preheating, the optimized process has increased the shear bond strength between the platinum substrate and the iridium alloy coating from 200 MPa to 300 - 350 MPa, and is applicable to thin-walled platinum components with a wall thickness ≤ 1 mm (such as the convergent section of a space engine nozzle), solving the technical bottlenecks of poor surface treatment consistency and low service reliability in stress-sensitive complex structures in the traditional process; B. The Vickers hardness of the substrate after the heat treatment is 150 HV - 180 HV; Optionally, the Vickers hardness of the substrate after the heat treatment can be 150 HV, 160 HV, 170 HV, 180 HV, or any value between 150 HV - 180 HV; C. The peak stress of the substrate after the heat treatment is 150 MPa - 250 MPa.

[0032] Optionally, the peak stress of the substrate after the heat treatment can be 150 MPa, 200 MPa, 250 MPa, or any value between 150 MPa - 250 MPa; In some embodiments, the pressure of the sandblasting is 0.3 MPa - 0.8 MPa.

[0033] Optionally, the pressure of the sandblasting can be 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, or any value between 0.3 MPa - 0.8 MPa.

[0034] It should be noted that the sandblasting pressure is selected as a low-pressure mode of 0.3 - 0.8 MPa. This range achieves a balance between the surface treatment effect and the coating bonding performance by controlling the impact energy of the sand grains. At this pressure, high-speed sand grains (such as 80 - 120 mesh Al2O3 sand) impact the heat-treated substrate at a speed of 20 - 40 m / s, forming uniform micro-pits with a size of 30 - 80 μm (Ra is 2 - 5 μm), the bonding strength is increased by 50 - 70%, and at the same time, the total peak stress is controlled within 250 MPa to inhibit micro-cracks; when the sandblasting pressure is lower than 0.3 MPa, the kinetic energy of the sand grains is insufficient, resulting in more than 20% residual oxide layer and roughness fluctuation of ±30%, and the bonding strength drops below 150 MPa; when it exceeds 0.8 MPa, pits with a depth > 100 μm and micro-cracks are induced, the risk of coating peeling due to stress concentration increases by 4 times, and surface hardening forms a mechanical property gradient; in the standard pressure range of 0.3 - 0.8 MPa, a composite structure of "micro-pits + nano-grooves" is formed, and the molten iridium alloy can form a metallurgical bonding layer of 10 - 20 μm, and the element diffusion coefficient reaches 10 -10 cm2 / s, the anti-thermal cycling ability is twice that of the traditional process. This sandblasting treatment and heat treatment jointly construct a three-dimensional optimization system, providing a reliable solution for the preparation of the coating of thin-walled platinum components.

[0035] In some embodiments, the method for preparing the iridium alloy coating of the spacecraft satisfies at least one of the following conditions: A. The acid includes oxalic acid; B. The mass concentration of the acid is 5% - 15%; Optionally, the mass concentration of the acid can be 5%, 10%, 15% or any value between 5% - 15%; C. The temperature of the acid etching is 80°C - 100°C, and the time is 30 min - 60 min.

[0036] Optionally, the temperature of the acid etching can be 80°C, 90°C, 100°C or any value between 80°C - 100°C, and the time can be 30 min, 40 min, 50 min, 60 min or any value between 30 min - 60 min.

[0037] It should be noted that when the concentration of the acid solution is too high, the acid etching time is too long or the temperature is too high, it will cause excessive corrosion of the substrate, forming deep holes or over-etching of the grain boundaries, resulting in a decrease in the bonding strength; when the concentration of the acid solution is too low, the acid etching time is too short or the temperature is insufficient, the reaction kinetics is limited, the etching is uneven, and the residual oxide film at the interface causes local peeling of the coating.

[0038] In some embodiments, the method for preparing the iridium alloy coating of the spacecraft satisfies at least one of the following conditions: A. The particle size of the alloy is 50 μm - 100 μm; Optionally, the particle size of the alloy can be 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm or any value between 50 μm - 100 μm; B. Based on the total mass of the alloy raw materials being 100%, it includes: 5% - 10% rhenium and 90% - 95% iridium.

[0039] Optionally, based on the total mass of the alloy raw materials being 100%, rhenium can be 5%, 6%, 7%, 8%, 9%, 10% or any value between 5% - 10%, and iridium can be 90%, 91%, 92%, 93%, 94%, 95% or any value between 90% - 95%.

[0040] It should be noted that adding 5%-10% rhenium can improve the high-temperature creep resistance of the alloy and optimize the grain boundary stability through solid-solution strengthening of Ir-Re; when the rhenium content is less than 5%, the effect of solid-solution strengthening is limited, and the tensile strength and creep resistance at high temperatures are close to those of pure iridium, which cannot meet the long-term service requirements of extreme environments (such as the nozzle of a space engine). However, excessive rhenium content (>10%) may cause lattice distortion, leading to a decrease in toughness in the room temperature and medium temperature ranges. In some embodiments, the energy density of the laser cladding is 1.5×10 4 W / cm 2 -3×10 4 W / cm 2 , the laser power is 80kW - 100kW, the focused spot is 0.2mm - 2.0mm, the scanning speed is 150mm / s - 200mm / s, and the powder feeding rate is 5g / min - 20g / min.

[0041] Optionally, the energy density of the laser cladding can be 1.5×10 4 W / cm 2 、2×10 4 W / cm 2 、3×10 4 W / cm 2 or any value between 1.5×10 4 W / cm 2 -3×10 4 W / cm 2 , the laser power can be 80kW, 90kW, 100kW or any value between 80kW - 100kW, the focused spot can be 0.2mm, 0.5mm, 1mm, 1.5mm, 2mm or any value between 0.2mm - 2.0mm, the scanning speed can be 150mm / s, 160mm / s, 170mm / s, 180mm / s, 190mm / s, 200mm / s or any value between 150mm / s - 200mm / s, and the powder feeding rate can be 5g / min, 10g / min, 15g / min, 20g / min or any value between 5g / min - 20g / min.

[0042] It should be noted that the ultra-high energy density (1.5×10 4 W / cm 2 -3×10 4 W / cm 2 ) is a key parameter based on alloy design, which is achieved by precisely controlling the laser power and the focused spot. Its design logic and parameter constraints are closely related to the properties of the iridium alloy and the tolerance of the platinum matrix; the lower limit of the energy density of the laser cladding is 1.5×10 4 W / cm2 The lower limit ensures that the alloy powder is completely melted and forms a metallurgical bond with the platinum matrix to avoid coating porosity caused by unmelted particles. The particle size of iridium alloy powder is usually 50-100μm. Complete melting requires about 4000J / g of heat. When the energy is insufficient, unmelted cores will remain inside the powder, resulting in a coating porosity of more than 8% and a sudden drop in bonding strength to below 200MPa. At the same time, sufficient energy can promote the mutual diffusion of elements between the molten iridium alloy and the platinum matrix to form a Pt-Ir solid solution interface layer with a depth of more than 10μm. If the energy is not up to standard, the two will only form a mechanical bite, and the bonding strength will be reduced by more than half. The upper limit of the energy density of laser cladding is 3×10 4 W / cm 2 , limited by the thermal damage threshold of the platinum matrix, excessive energy may cause local melting or thermal cracking of the matrix, which is mainly limited by the thermal damage threshold of the platinum matrix. The melting point of platinum is 1768℃. When the energy density exceeds 3×10 4 W / cm 2 When the temperature of the substrate is increased, the local temperature will exceed 2000℃, resulting in a molten pool depth of more than 500μm. After cooling, coarse columnar crystals will be formed, with a grain size of more than 500μm, and thermal cracks of 1-2mm in length will be triggered. In addition, the vapor pressure of iridium rises sharply above 2000℃. Excessive energy will cause the loss of rhenium by volatilization of more than 10%, destroying the composition ratio of Ir-Re alloy and significantly reducing the high temperature creep resistance. The endurance life at 1370℃ is shortened to the normal process (1.5×10 4 W / cm 2 -3×10 4 W / cm 2 ).

[0043] It should be noted that achieving this ultra-high energy density range requires the coordinated adjustment of laser power and focused spot. According to the formula energy density = power ÷ spot area, a high-power fiber laser of 80-100 kW is used with a short focal length lens (focal length 100-150 mm) to compress the spot diameter to 0.2-2.0 mm, which can meet the energy requirements. For example, when 100 kW power is matched with a 0.2 mm spot, the initial energy density is as high as 3.3×10 6 W / cm 2 , it needs to be regulated to the target range through high-speed scanning at 5-10 mm / s; when 80kW power is combined with a 2.0 mm spot, the energy density directly reaches 2.5×10 4 W / cm 2 Compared with other materials, alloys have a significantly higher cladding energy density requirement due to their ultra-high melting point, and the process window is narrow, only about 1.5×10 4 W / cm 2 , the technical difficulty is far beyond other materials.

[0044] In some embodiments, the method for preparing the iridium alloy coating of the spacecraft satisfies at least one of the following conditions: A. The cooling rate is 10 3 K / s - 10 4 K / s; Optionally, the cooling rate can be 10 3 K / s, 5×10 3 K / s, 10 4 K / s or any value between 10 3 K / s - 10 4 K / s; It should be noted that to ensure process stability, rapid cooling at a rate of 10 3 K / s - 10 4 K / s suppresses the coarsening of alloy grains (controlling the grain size < 50 μm), while reducing the high-temperature residence time of the platinum matrix (< 0.1 s), reducing the risk of thermal stress, achieving rapid solidification of the alloy with a grain size < 5 μm. The ultra-high energy density cladding technology with coordinated cooling process ultimately ensures that the iridium alloy coating can still maintain excellent metallurgical bonding strength and mechanical properties at an extreme high temperature of 1370 °C; B. The gas in the protective atmosphere includes argon and nitrogen. The flow rate of argon is 8 L / min - 12 L / min, and the flow rate of nitrogen is 3 L / min - 5 L / min.

[0045] Optionally, the flow rate of argon can be 8 L / min, 9 L / min, 10 L / min, 11 L / min, 12 L / min or any value between 8 L / min - 12 L / min, and the flow rate of nitrogen can be 3 L / min, 4 L / min, 5 L / min or any value between 3 L / min - 5 L / min; It should be noted that argon, as an inert gas, can isolate the reaction of oxygen with the molten pool and avoid alloy oxidation at high temperatures (such as the formation of IrO2). At the same time, it accelerates heat dissipation through forced convection. The thermal conductivity of nitrogen (0.0259 W / m·K) is higher than that of argon (0.0177 W / m·K). After mixing, the overall cooling rate is increased, and nitrides (such as IrN2) are formed by dissolving into the molten metal to inhibit grain boundary migration; preferably, the volume ratio of argon to nitrogen is 3:1. This ratio balances the requirements of inert protection and heat conduction. A high proportion of argon ensures an inert environment, and a low proportion of nitrogen can ensure enhanced heat exchange and microalloying to refine grains. Through the coordinated cooling of the argon-nitrogen mixture, the iridium alloy cladding layer achieves a high-strength and high-temperature resistant fine-grained structure under extreme cooling conditions.

[0046] The second aspect of the present application provides an iridium alloy coating for spacecraft, which is prepared by the preparation method of the iridium alloy coating for spacecraft described above.

[0047] It should be noted that the prepared iridium alloy coating for spacecraft is dense and pore-free, with a thickness of up to 0.5 - 0.6 mm (8 - 10 times the thickness of the coating prepared by electroplating process), high hardness (HV≥400), and excellent wear and corrosion resistance.

[0048] In some embodiments, the iridium alloy coating for spacecraft satisfies at least one of the following conditions: A. The thickness of the iridium alloy coating for spacecraft ≤ 1 mm; Optionally, the thickness of the iridium alloy coating for spacecraft can be 1 mm, 0.5 mm, 0.1 mm, or any value ≤ 1 mm; B. The hardness of the iridium alloy coating for spacecraft ≥ 400 HV; Optionally, the hardness of the iridium alloy coating for spacecraft can be 400 HV, 500 HV, 600 HV, or any value ≥ 400 HV; C. The shear bonding strength between the platinum substrate and the iridium alloy coating for spacecraft is 300 MPa - 350 MPa.

[0049] Optionally, the shear bonding strength between the platinum substrate and the iridium alloy coating for spacecraft can be 300 MPa, 310 MPa, 320 MPa, 330 MPa, 340 MPa, 350 MPa, or any value between 300 MPa - 350 MPa.

[0050] The third aspect of the present application provides a spacecraft, including the iridium alloy coating for spacecraft described above.

[0051] The following will describe the implementation schemes of the present application in detail with specific embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present application and should not be regarded as limiting the scope of the present application. For those not specified in the embodiments, the operations are carried out under conventional conditions or conditions recommended by the manufacturer. For reagents or instruments not specified by the manufacturer, they are all conventional products that can be obtained through commercial purchase.

[0052] Example 1 This example provides an iridium alloy coating for spacecraft and its preparation method. The specific preparation method is as follows: S1: Heat-treat the platinum substrate. First, heat the substrate to 220 °C and hold for 1.5 h. Then, increase the temperature to 380 °C at a heating rate of 10 °C / min and hold for 2.5 h. The Vickers hardness of the heat-treated substrate is 165 HV, and the peak stress is 200 MPa. Next, blast the heat-treated substrate with Al2O3 at a pressure of 0.5 MPa. Then, etch the blasted substrate with oxalic acid (mass concentration: 10%) at a temperature of 90 °C for 45 min to obtain the treated substrate. S2: Use laser cladding to deposit an alloy (7.5 wt% rhenium and 92.5 wt% iridium) on the surface of the treated substrate. The particle size of the alloy is 75 μm, and the energy density of the laser cladding is 2.25×10 4 W / cm 2 , the laser power is 90 kW, the focused spot is 1.0 mm, the scanning speed is 175 mm / s, and the powder feeding rate is 12.5 g / min. S3: Under a mixed atmosphere of argon and nitrogen, with the argon flow rate at 10 L / min and the nitrogen flow rate at 4 L / min (the volume ratio of argon to nitrogen is 3:1), cool at a cooling rate of 5×10 3 K / s to obtain the iridium alloy coating for the spacecraft.

[0053] The SEM of the iridium alloy coating for the spacecraft is as Figure 2 shown.

[0054] The test results of the coating properties are as follows: Thickness: 0.6 mm; Hardness: 450 HV; Shear bond strength: 320 MPa; Porosity: 0.8%; Thermal cycle resistance: No cracks after 60 cycles of 1000 °C - room temperature cycling; High-temperature tensile strength (1370 °C): 220 MPa.

[0055] Example 2 The difference from Example 1 is that the energy density of the laser cladding is 2.5×10 4 W / cm 2 , the laser power is 100 kW, the focused spot is 0.8 mm, the scanning speed is 175 mm / s, and the powder feeding rate is 15 g / min.

[0056] The test results of the coating properties are as follows: Thickness: 0.7 mm (the increased powder feeding rate compared to Example 1 results in a 12% increase in the deposition amount); Hardness: 460 HV (the increased energy density promotes element diffusion and enhances the solid solution strengthening effect); Shearing bond strength: 330 MPa (3.1% higher than that of Example 1, and the thickness of the metallurgical bonding layer increases to 15 μm); Porosity: 0.9% (the energy density does not exceed the threshold, the fluidity of the molten pool is improved, the porosity slightly increases but is still < 1%); Thermal shock resistance: No cracks after 60 cycles of 1000 °C - room temperature cycling (comparable to Example 1); High-temperature tensile strength (1370 °C): 230 MPa (synergistic effect of rhenium solid solution strengthening and fine grain structure).

[0057] Analysis: When the energy density is increased to 2.5×10 4 W / cm 2 by controlling the laser power and spot diameter, it is ensured that the platinum substrate does not suffer from overheating damage (molten pool depth < 300 μm); The powder feeding rate matches the energy density, avoiding the accumulation of unmelted particles, and verifying the rationality of the process parameter range; The performance data shows that increasing the energy density within the range of the claim parameters can further optimize the mechanical properties of the coating, reflecting the adjustability of the technical solution.

[0058] Example 3 The difference from Example 1 is that the substrate is first heated to 220 °C and held for 1 h, and then heated to 380 °C at a heating rate of 10 / min and held for 3 h.

[0059] The test results of the coating performance are as follows: Shearing bond strength: 310 MPa (3.1% lower than that of Example 1 due to slightly poorer surface hardness uniformity of the substrate); Porosity: 0.9% (comparable to Example 1, and the heat treatment does not significantly affect the cladding quality); Thermal shock resistance: No cracks after 55 cycles of 1000 °C - room temperature cycling (5 cycles less than Example 1, and the stress peak is slightly higher); High-temperature tensile strength (1370 °C): 210 MPa (a slight decrease in high-temperature strength due to the reduction of Vickers hardness).

[0060] Analysis: The heat treatment holding time is adjusted to the boundary value of the claim (1 h for the first stage and 3 h for the second stage), verifying the effectiveness of the parameter range; Although the performance is slightly lower than that of Example 1, it still meets the core indicators (bond strength > 300 MPa, thermal shock resistance > 50 times), proving the process robustness; The data shows that when the heat treatment time fluctuates within the range of the claim, part of the performance loss can still be compensated by stress homogenization, reflecting the flexibility of the process design.

[0061] Comparative Example 1 The difference from Example 1 is that the energy density of laser cladding is reduced to 1.3×10 4 W / cm 2 , so that the laser power is reduced to 70 kW (90 kW in the original Example 1). The shear bond strength of the iridium alloy coating for spacecraft prepared is 200 MPa (a 37.5% decrease compared to Example 1), only reaching the level of the traditional chemical method; the porosity is 5.5% (nearly 7 times higher than that in Example 1), and a large number of unmelted alloy particles can be seen inside the coating; the thermal cycle resistance performance: through cracks appear after 8 cycles of 1000℃ - room temperature; the oxidation weight gain (1600℃×2h): 0.8 mg / cm 2 (a 167% increase compared to Example 1), and an obvious IrO2 oxide layer is formed on the surface.

[0062] The SEM of the iridium alloy coating for spacecraft prepared in this comparative example is as Figure 3 shown. There are a large number of unmelted iridium alloy particles (particle size about 20 - 50 μm) inside the coating. The particles are mainly mechanically interlocked, lacking a metallurgical bonding layer; the pores are irregularly distributed, with a size of 5 - 20 μm, and some pores are connected to form microcracks; obvious gaps can be seen at the interface, and the thickness of the element diffusion layer between the platinum matrix and the coating is <5 μm (10 - 20 μm in Example 1).

[0063] Mechanism analysis: Insufficient energy density leads to insufficient melting of the alloy powder. The core area does not reach the melting point of iridium (2443℃), and only the surface is slightly melted to form a "cold welding" structure; the unmelted particles hinder element diffusion, and the bonding method degenerates into mechanical anchoring and cannot withstand thermal cycle stress; insufficient melting makes the coating surface rough, increasing the exposed area, and significantly increasing the oxidation rate at high temperatures.

[0064] This comparative example verifies the key point of the lower limit of the laser cladding energy density: when it is lower than 1.5×10 4 W / cm 2 , effective metallurgical bonding between the alloy and the platinum matrix cannot be achieved, and the densification, bonding strength, and thermal oxidation resistance of the coating are all significantly deteriorated. The data shows that the energy density range (1.5×10 4 W / cm 2 - 3×10 4 W / cm 2 ) set in this application is a necessary condition to ensure the coating performance. Below this range, the technical solution will fail, highlighting the scientificity and necessity of the process parameter design in this application.

[0065] Comparative Example 2 The difference from Example 1 is that plasma spraying (power 50 kW) is used, the substrate is only sandblasted (0.8 MPa) without acid etching, and the alloy is pure iridium (without rhenium).

[0066] The SEM of the iridium alloy coating for spacecraft prepared in this comparative example is as Figure 4 shown.

[0067] The bonding strength of the prepared iridium alloy coating for spacecraft is 220 MPa, which is 31.25% lower than that of Example 1 (relying only on mechanical occlusion, without a metallurgical bonding layer); the porosity is 8.5%, more than 10 times that of Example 1, and has a significant layered structure + micropores; under the high-temperature performance test at 1370 °C, the tensile strength is 150 MPa (31.8% lower than that of Example 1), and the oxidation weight gain at 1600 °C is 1.2 mg / cm 2 (4 times that of Example 1).

[0068] There is no laser metallurgical bonding in this comparative example, the interface is mechanical occlusion, and the element diffusion depth <5 μm; pure iridium has no solid solution strengthening, the grain size is large (50 - 100 μm), and the oxidation resistance is poor; the unetched interface results in residual oxide film, and the high porosity is prone to gas penetration.

[0069] Conclusion: Due to the lack of metallurgical bonding and alloy strengthening, the performance of the traditional thermal spraying method is significantly lower than that of the laser cladding process of this application, verifying the necessity of laser cladding and rhenium alloying.

[0070] Comparative Example 3 The difference from Example 1 is that the powder feeding rate is 25 g / min.

[0071] The performance test results of the iridium alloy coating for spacecraft prepared in this comparative example are as follows: The shear bonding strength is 250 MPa (21.9% lower than that of Example 1); the porosity is 3.5% (3.4 times higher than that of Example 1); thermal cycling performance: dense microcracks appear after 20 cycles of 1000 °C - room temperature; the coating thickness is 0.8 mm (the deposition efficiency is improved, but the quality is significantly reduced).

[0072] Mechanism analysis: Excessive powder feeding rate leads to the amount of alloy powder entering the molten pool per unit time exceeding the laser energy carrying capacity, and part of the powder is not fully melted (especially large particles in the central area), and the insufficient melting forms an "undercooked" structure. EDS analysis shows that the iridium oxide content in the unmelted particles reaches 15% (only 2% in Example 1); interface bonding degradation: only mechanical occlusion is formed between the unmelted powder and the substrate, and the element diffusion layer thickness <8 μm (10 - 20 μm in Example 1), and the bonding strength degrades to the level of traditional thermal spraying; thermal stress concentration: excessive alloy accumulation leads to uneven cooling rate of the molten pool (fast cooling at the edge / slow cooling in the center), and the internal tensile stress peak reaches 400 MPa (250 MPa in Example 1), far exceeding the coating fracture strength; A large number of irregular pores (sized 10 - 50 μm) and unmelted iridium particles (particle size > 80 μm) with oxides attached to the particle surfaces can be seen in the cross-section of the iridium alloy coating for the spacecraft prepared in this comparative example; there are obvious gaps at the interface, no continuous metallurgical bonding layer, and the coating is separated from the substrate in some areas.

[0073] This comparative example verifies the necessity of the upper limit of the powder feeding rate: when it exceeds 20 g / min, the laser energy cannot meet the requirement for sufficient melting of the alloy, resulting in a significant decrease in the densification and bonding strength of the coating. The data shows that the powder feeding rate range (5 - 20 g / min) set in this application is the key to ensuring the matching of laser energy and powder supply. Exceeding this range will cause process failure, further proving the rationality and technological foresight of the parameter design in the claims.

[0074] Comparative Example 4 The difference from Example 1 is that the heat treatment in Step S1 is not carried out.

[0075] The shear bonding strength of the iridium alloy coating for the spacecraft prepared is 185 MPa (a 42.2% decrease compared to Example 1); the porosity is 3.8% (a 3.8-fold increase compared to Example 1), and a large number of unfused defects can be seen inside the coating; the thermal shock resistance: coating spalling occurs after 12 cycles of 1000 °C - room temperature cycling; the peak surface stress of the substrate is 320 MPa.

[0076] Mechanism analysis: The platinum substrate is not heat-treated, and the internal residual stress is not released. The cold working stress (about 200 MPa) generated by sandblasting is superimposed on the original stress of the substrate, resulting in a peak surface stress of 320 MPa, far exceeding 200 MPa in Example 1. Under the high stress state, the thermal stress (about 150 MPa) generated by rapid cooling during laser cladding is likely to cause microcracks at the interface; the surface treatment efficiency decreases: the oxide film on the surface of the non-heat-treated platinum substrate is dense (thickness about 50 nm, the oxide film thickness in Example 1 after heat treatment < 20 nm), and it is difficult to completely remove by acid etching, resulting in residual PtO2 impurities at the interface (the O content detected by EDS reaches 5.2 at%, 1.1 at% in Example 1), which hinders element diffusion, and the bonding mode degrades to mechanical occlusion; the problem of hardness mismatch: the Vickers hardness of the substrate reaches 210 HV (165 HV in Example 1), and more of the impact energy of the sand grains during sandblasting is converted into elastic deformation energy, resulting in uneven surface roughness (the Ra value fluctuates ±25%, ±10% in Example 1), and the mechanical anchoring effect weakens.

[0077] There is an obvious demarcation line between the iridium alloy coating of the spacecraft prepared in this comparative example and the substrate, without a continuous metallurgical bonding layer, and a PtO2 oxide film interlayer can be seen in some areas; the proportion of unmelted iridium alloy particles inside the coating is about 18% (less than 5% in Example 1), and pores surround the particles, with a porosity of 3.8%; after thermal cycling, cracks propagate along the boundary of the interfacial oxide film and the unmelted particles, forming a through-damage.

[0078] In this comparative example, by completely removing the heat treatment process, the irreplaceability of this step in the technical solution of this application is intuitively verified, and the analysis is as follows: Stress regulation failure: The superposition of the unreleased substrate stress and the sandblasting stress causes the interfacial stress to exceed the coating bonding strength threshold; Insufficient surface activation: The residual dense oxide film hinders metallurgical bonding, and the mechanical anchoring effect is weakened due to uneven roughness; Overall performance deterioration: The core indicators such as bonding strength and the number of thermal cycles are lower than the industry available standards, which proves that heat treatment is the key link to solve the problem of thermal cycling cracking.

[0079] This comparative example further highlights the synergistic effect of the "heat treatment → sandblasting → acid etching" pretreatment process in the process of this application. The absence of any link will lead to a significant decline in the coating performance. Heat treatment lays the foundation for subsequent processes through stress release, hardness regulation and oxide film optimization, and is a necessary prerequisite for achieving efficient metallurgical bonding by laser cladding.

[0080] Comparative Example 5 The difference from Example 1 is that the sandblasting in step S1 is not carried out.

[0081] The shear bonding strength of the iridium alloy coating of the spacecraft prepared is 190 MPa (a 40.6% decrease compared to Example 1); the porosity is 4.2% (a 4.2-fold increase compared to Example 1), and obvious gaps can be seen at the interface between the coating and the substrate; thermal cycle resistance: coating edge peeling occurs after 10 cycles of 1000 °C - room temperature cycling; surface roughness (Ra): 0.8 μm (only nano-scale grooves are formed by acid etching on the surface of the non-sandblasted platinum substrate, lacking micron-scale anchoring structures); thermal cycle damage: after 10 cycles, cracks first appear at the oxide film interlayer, and the cracks propagate horizontally along the interface, resulting in coating peeling.

[0082] The mechanism analysis of the above test results is as follows: Lack of mechanical anchoring effect: The core role of the sandblasting process is to form micron-scale pits (30 - 80 μm) on the substrate surface, which constitute a "multi-level mechanical interlock" interface with the nano-scale grooves (5 - 20 nm) formed by subsequent acid etching. After omitting sandblasting, only acid etching cannot form micron-scale rough structures with sufficient depth, and the bonding method degrades from "mechanical anchoring + metallurgical bonding" to a single "chemical adsorption + weak metallurgical bonding", resulting in a decrease in bonding strength of about 40%; Risk of residual oxide layer: Although the heat treatment loosens the oxide film on the surface of platinum, it is not physically removed by sand blasting. Acid etching can only dissolve part of the oxide film (residual amount is about 30%). SEM-EDS detection shows that the O element content at the interface is 4.8at% (1.1at% in Example 1), forming a PtO2 interlayer with a thickness of 20-50nm, which hinders the atomic diffusion of Ir and Pt (the diffusion coefficient is from 10 -10 cm 2 / s decreased to 5×10 -11 cm 2 / s); The wettability of the molten pool decreases: the liquid-solid contact angle (θ=65°) of the smooth surface (Ra<1μm) is significantly larger than that of the roughened surface (θ=30°), resulting in uneven spreading of the molten iridium alloy on the substrate surface, local formation of unfused defects (accounting for about 15%), and an increase in porosity; There is a discontinuous PtO2 oxide film between the spacecraft iridium alloy coating and the substrate prepared in this comparative example, which is distributed in an island shape, and the interface bonding area only accounts for 40% of the total area (more than 95% in Example 1); traces of molten pool flow due to poor wettability can be seen inside the coating, and the alloy accumulation thickness in the local area is uneven (deviation> 20%), accompanied by tiny pores (size 2-5μm); This comparative example verifies the irreplaceable nature of the sand blasting process in pretreatment, and the analysis is as follows: Necessity of mechanical coarsening: the lack of micron-scale rough structure leads to the loss of mechanical anchoring effect, and the bonding strength cannot meet the requirements of aerospace applications; synergy of oxide layer removal: sand blasting and acid etching must be used in combination, and chemical etching alone cannot completely remove the loose oxide film after heat treatment; Process integrity requirements: After omitting sand blasting, even if heat treatment and acid etching are retained, an efficient interface bonding system cannot be constructed, which proves that the three-stage pretreatment process of "heat treatment → sand blasting → acid etching" in this application has strict sequential dependence and functional complementarity.

[0083] Comparative Example 5 shows that the sandblasting process significantly improves the mechanical anchoring ability and chemical activity of the substrate surface through physical roughening and cleaning, and is a key link in achieving high-strength bonding between the coating and the platinum substrate. The absence of this step will lead to a cliff-like drop in interface bonding strength and thermal cycle resistance, further highlighting the scientificity and integrity of the process design of this application.

[0084] Comparative Example 6 The difference from Example 1 is that the acid etching in step S1 is not performed.

[0085] The shear bond strength of the iridium alloy coating for spacecraft prepared is 210 MPa (a 34.4% decrease compared to Example 1), approaching the level of traditional chemical methods; the porosity is 3.0% (2.7 times higher than that in Example 1), and obvious unfused regions can be seen at the interface; thermal cycling performance: coating cracking occurs after 18 cycles of 1000 °C - room temperature cycling; surface element analysis: the content of O element at the interface reaches 3.5 at% (1.1 at% in Example 1), and there is residual PtO2 oxide film; thermal cycling damage: after 18 cycles, the oxide film interlayer completely cracks, the coating peels off from the substrate surface, and oxide film fragments can be seen attached to the peeling surface.

[0086] The mechanism analysis is as follows: Residual oxide film hinders metallurgical bonding: Although sandblasting can remove most of the loose oxide film, a nanoscale dense oxide layer (with a thickness of about 10 - 20 nm) still remains on the surface of the platinum substrate and is not chemically dissolved by acid etching. EDS detection shows that the content ratio of Pt - O bonds at the interface is 12% (only 3% in Example 1), forming an "insulating layer" that hinders element diffusion, and the thickness of the metallurgical bonding layer is reduced from 10 - 20 μm to 5 - 8 μm; Insufficient surface activity: The etching effect of acid etching can produce nanoscale grooves (with a depth of 5 - 20 nm) on the platinum surface, significantly increasing the surface active sites (such as step atoms and kink atoms). After omitting acid etching, only micron - scale pits (Ra = 3 μm) formed by sandblasting remain on the surface, but lack nanoscale roughness. The contact angle of the solid - liquid interface increases from 30° (after acid etching) to 55°, and the wettability of the molten iridium alloy decreases, resulting in uneven spreading of the molten pool and about 10% of local unfused defects; Increased risk of stress concentration: The residual oxide film exacerbates the mismatch of thermal expansion coefficients at the interface (the thermal expansion coefficient of PtO2 is 11×10 -6 / °C, much higher than 6.5×10 -6 / °C of iridium). During thermal cycling, the oxide film cracks first due to stress concentration and becomes the crack source.

[0087] There is a bright - white oxide film interlayer with a thickness of 20 - 50 nm between the iridium alloy coating for spacecraft prepared in this comparative example and the substrate, showing a continuous distribution. Metallurgical bonding is formed only in local areas (about 30% of the area); unfused iridium alloy particles (with a particle size of about 50 μm) can be seen at the bottom of the micron - scale pits inside the coating, and there is a 5 - 10 μm gap between the particles and the substrate; This comparative example verifies the key role of the acid - etching process in pretreatment, and the analysis is as follows: The irreplaceability of chemical cleaning: Physical sandblasting alone cannot completely remove the nanoscale oxide film, and acid etching is a necessary means to achieve an "atom - level clean interface"; Integrity of the multi-level anchoring structure: Omitting acid etching results in the absence of the "micro-pits + nano-grooves" composite rough structure. The mechanical anchoring effect decreases from "three-dimensional interlocking" to "two-dimensional biting", and the bonding strength decreases by more than 30%. Determination of element diffusion efficiency: The residual oxide film increases the diffusion distance of Ir-Pt atoms by more than 3 times, and the diffusion coefficient decreases to 5×10 -11 cm 2 / s (it was 10 -10 m 2 / s in Example 1), and the metallurgical bonding strength is significantly weakened.

[0088] Comparative Example 6 shows that the acid etching process forms a complete pretreatment chain of "stress regulation - physical roughening - chemical activation" through chemical etching and surface activation, together with heat treatment and sandblasting. The absence of acid etching will lead to residual interfacial oxide film, reduced active sites and aggravated stress mismatch, ultimately making the coating performance unable to meet the requirements of the aerospace extreme environment. This result further proves the scientificity and necessity of the three-stage pretreatment process of this application. Each step is indispensable and jointly ensures the high-strength and high-reliability bonding between the coating and the substrate.

[0089] Comparative Example 7 The difference from Example 1 is that the temperature of acid etching is 70°C and the time is 20 min.

[0090] The shear bonding strength of the iridium alloy coating for spacecraft prepared is 230 MPa (a 28.1% decrease compared to Example 1); the porosity is 4.0% (a 4-fold increase compared to Example 1); thermal shock resistance: interfacial cracking occurs after 15 cycles of 1000°C - room temperature cycling; the residual amount of the surface oxide film: 35% (EDS detection shows that the content of O element increases by 2.5 times compared to Example 1).

[0091] The mechanism analysis of the above properties is as follows: Insufficient chemical etching: 70°C is lower than the optimal activation temperature of oxalic acid for platinum oxide film (when the temperature is above 80°C, the dissociation degree of oxalic acid increases to 90% and the complexation reaction rate accelerates), and the treatment time of 20 min is insufficient, resulting in only about 60% dissolution of the nano-scale oxide film (PtO2) (the dissolution rate in Example 1 > 95%). The residual oxide film forms a continuous interlayer with a thickness of 10 - 30 nm at the interface, hindering the diffusion of Ir-Pt atoms (the diffusion depth decreases from 20 μm to 8 μm); Insufficient surface active sites: The low acid etching temperature and short time result in the inability to form a complete nano-scale groove structure on the platinum surface (only shallow pits less than 5 nm exist in local areas), and the surface active site density decreases from 1.2×10 15 / cm 2 in Example 1 to 0.5×10 15 / cm 2, the wettability of the molten iridium alloy decreases (the contact angle increases from 30° to 50°), the molten pool spreads unevenly, and local lack of fusion areas are formed (accounting for about 12%); The stress concentration intensifies: The thermal expansion coefficient of the residual oxide film (11×10 -6 / °C) is significantly different from that of iridium (6.5×10 -6 / °C). During thermal cycling, a thermal stress of about 150 MPa is generated at the interface, far exceeding 80 MPa in Example 1, resulting in premature crack initiation.

[0092] This comparative example verifies the necessity of the pickling parameter range in the claims by reducing the pickling temperature to 70°C and the time to 20 min: When the temperature is lower than 80°C or the time is less than 30 min, oxalic acid cannot fully dissolve the oxide film and activate the surface, resulting in a significant decrease in the interfacial bonding strength and thermal cycling resistance. The data shows that the pickling temperature and time need to be strictly controlled within the range of 80°C - 100°C and 30 min - 60 min to ensure the formation of a "nanoscale clean interface + multi-level anchoring structure", which is the key control point of the pretreatment process of this application.

[0093] Comparative Example 8 The difference from Example 1 is that rhenium is not added to the alloy.

[0094] The shear bonding strength of the prepared iridium alloy coating for spacecraft is 220 MPa (a 31.25% decrease compared to Example 1); the porosity is 2.5% (a 212.5% increase compared to Example 1, and the high surface tension of the pure iridium molten pool leads to poor fluidity); the thermal cycling resistance: intergranular cracking occurs after 25 cycles of 1000°C - room temperature; the high-temperature tensile strength (1370°C): 160 MPa (a 27.3% decrease compared to Example 1); The grain size: 20 - 50 μm (less than 5 μm in Example 1, lacking the grain refinement effect of rhenium).

[0095] Mechanism analysis of the above test results: Lack of solid solution strengthening: Rhenium atoms dissolved in the iridium lattice can cause lattice distortion (the distortion energy is about 0.2 eV), significantly hindering dislocation movement. Due to the lack of solid solution strengthening in the pure iridium coating, the room temperature hardness drops to 300 HV (450 HV in Example 1), and the grain boundary slip rate at high temperature increases by 3 times, resulting in a significant decrease in the tensile strength and creep resistance; Increased thermal crack sensitivity: The thermal expansion coefficient of pure iridium (6.5×10 -6 / °C) is more different from that of platinum (21×10 -6 / °C). During thermal cycling, the thermal stress at the interface reaches 280 MPa (200 MPa in Example 1), and there is no rhenium segregation at the grain boundaries to inhibit crack propagation, resulting in rapid crack propagation along the coarse grain boundaries (the propagation rate is 0.1 μm / cycle, 0.02 μm / cycle in Example 1); Insufficient fluidity of the molten pool: Rhenium can reduce the surface tension of iridium alloy (from 2200 mN / m to 1800 mN / m). The pure iridium molten pool is difficult to spread evenly, resulting in a local thickness deviation of the coating > 15% and the proportion of unfused defects being about 8%.

[0096] Coarse equiaxed grains (grain size 20 - 50 μm) can be seen inside the iridium alloy coating of the spacecraft prepared in this comparative example. The grain boundaries are clear and the width reaches 200 nm (the grain boundary width in Example 1 < 50 nm); Crack morphology: After thermal cycling, the cracks expand in a network pattern along the grain boundaries, the crack width is 5 - 10 μm, and some cracks penetrate the coating to the interface; Oxidation degree: After oxidation at 1600 °C, an IrO2 layer with a thickness of 200 nm is formed on the surface (50 nm in Example 1), and the oxidation weight gain is 0.6 mg / cm² (0.3 mg / cm in Example 1). 2 )

[0097] This comparative example verifies the irreplaceability of rhenium in alloy design, and the specific analysis is as follows: Failure of the strengthening mechanism: The lack of solid solution strengthening and grain boundary stabilization effects of rhenium leads to a significant decline in the mechanical properties and high-temperature stability of the coating; Reduced process adaptability: The pure iridium molten pool has poor fluidity and it is difficult to form a uniform and dense coating by laser cladding; Risk of failure in extreme environments: Under thermal cycling and high-temperature oxidation conditions, the life of the pure iridium coating is less than 50% of that of the rhenium-containing coating.

[0098] Comparative Example 8 shows that the addition of rhenium is one of the core innovations of the technical solution of this application. Through the Ir-Re alloying design, multiple effects of "synergistic improvement of solid solution strengthening - grain refinement - oxidation resistance" are achieved. The lack of this component will cause the coating to fail to meet the reliability requirements of extreme environments such as aerospace engines, further proving the scientificity and necessity of the alloy composition design in the claims.

[0099] The following is a systematic analysis of the performance test results of the iridium alloy coatings of the spacecraft prepared in the above examples and comparative examples, focusing on revealing the influence rules of each process parameter on the key performance of the coating and the technical advantages: I. Comparison of core performance indicators and analysis of rules: 1. Shear Bond Strength: A direct manifestation of the synergistic effect of pretreatment and laser cladding. In Examples 1 - 3, the bond strength is between 310 - 330 MPa, significantly higher than that of traditional processes (such as 220 MPa in Comparative Example 2). Among them, the key factors include: Heat treatment: By releasing stress and regulating hardness through two - stage heating, the peak surface stress of the substrate is controlled within 150 - 250 MPa, creating ideal conditions for sandblasting; Sandblasting + Acid etching: Construct a multi - level anchoring structure of "micron pits + nano grooves", combined with the metallurgical bonding of laser cladding (the interface element diffusion layer is 10 - 20 μm), to achieve double strengthening of mechanical anchoring and atomic diffusion.

[0100] 2. Porosity: Verification of the matching between energy density and powder feeding rate. The porosity of Examples 1 - 3 is ≤0.9%, significantly lower than that of traditional thermal spraying (8.5% in Comparative Example 2) and Comparative Examples with parameter over - limits (such as 3.5% in Comparative Example 3); The powder feeding rate of 5 - 20 g / min matches the energy density, avoiding the accumulation of unmelted particles (such as when the powder feeding rate in Comparative Example 3 is 25 g / min, insufficient energy leads to a porosity of 3.5%). 3. Thermal cycle resistance: The synergistic crack - resistance effect of pretreatment and alloy composition. In Examples 1 - 3: There are no cracks after 55 - 60 cycles of 1000°C - room temperature, which is 2 - 3 times higher than that of traditional thermal spraying (20 times in Comparative Example 2). This is because heat treatment + sandblasting + acid etching pretreatment eliminates interfacial stress concentration, combined with the fine - grain structure of laser cladding (grain size < 5 μm), inhibiting crack initiation; And rhenium element (5% - 10%) is dissolved in iridium, segregating at grain boundaries to inhibit high - temperature grain boundary slip, improving the thermal shock resistance (such as no cracks after 60 cycles in Example 1, only 25 times for the pure iridium coating in Comparative Example 8); In Comparative Examples 4 - 8 (lacking pretreatment or rhenium), the number of cycles decreases to 8 - 25 times, and cracks all originate from interfacial stress concentration or grain boundary defects. 4. High - temperature mechanical properties: The key role of rhenium alloying and rapid cooling. In Examples 1 - 3: The tensile strength at 1370°C is 210 - 230 MPa, which is 31% - 44% higher than that of the pure iridium coating (160 MPa in Comparative Example 8). This is because the solid - solution strengthening of rhenium increases the resistance of dislocation movement, improving the high - temperature strength; And rapid cooling (10 3 -10 4 K / s) forms an ultrafine - grain structure, increasing the total grain boundary area and hindering crack propagation; The high - temperature strength of Comparative Examples 2 - 8 is generally lower than 200 MPa. Especially for the pure iridium coating (Comparative Example 8), due to large grain size (20 - 50 μm) and lack of solid - solution strengthening, the strength decreases significantly.

[0101] II. Summary of the influence of key process parameters: 1. Irreplaceability of the pretreatment process. The functions of heat treatment are: releasing matrix stress (residual stress release rate: 35% - 45%), regulating hardness (150 - 180 HV), and activating the oxide film. Without this step, the bonding strength decreases by more than 40% (such as Comparative Example 4); the function of sandblasting is: forming a micron-scale rough structure (Ra 2 - 5 μm) and providing mechanical anchoring points. Without this step, the bonding strength decreases by 40% (such as Comparative Example 5); the function of acid etching is: dissolving the nano-scale oxide film (residual amount < 5%) and constructing nano-grooves (depth 5 - 20 nm). Without this step, the bonding strength decreases by 34% (such as Comparative Example 6). 2. Critical effect of laser cladding parameters. The lower limit of the energy density is 1.5×10 4 W / cm 2 : Below this value, metallurgical bonding cannot be achieved; the upper limit is 3×10 4 W / cm 2 : Exceeding this value causes overheating of the matrix and element volatilization; moreover, when the powder feeding rate is 5 - 20 g / min, its matching with the energy density can ensure sufficient melting. Exceeding 20 g / min results in the accumulation of unmelted particles. 3. Rhenium alloying can not only improve the room temperature hardness (rhenium alloy is 450 HV, pure iridium is 300 HV) and high temperature strength (the tensile strength at 1370 °C is increased by 44% compared with pure iridium), but also inhibit grain boundary oxidation and crack propagation, and the number of thermal cycles resistance is increased by 1.5 times. III. Verification of the innovation and practicality of the technical solution: The laser cladding deposition rate (50 - 100 μm / min) is more than 10 times higher than that of the traditional electroplating method (5 μm / min), and there is no need for precious metal salt solution, avoiding waste liquid treatment; through "heat treatment stress regulation + multi-level surface roughening + laser metallurgical bonding", the shear bonding strength reaches 300 - 350 MPa, breaking through the 200 MPa bottleneck of the traditional process; the oxidation resistance life of the coating at 1600 °C is increased by 2 times compared with the traditional coating, and the number of thermal cycles resistance exceeds 50 times, meeting the requirements of harsh scenarios such as aerospace engine nozzles.

[0102] Conclusion: The data of the above examples and comparative examples fully prove that through the systematic optimization of the pretreatment process, precise control of laser cladding parameters and rhenium alloying design, this application has achieved a comprehensive improvement in the performance of iridium alloy coatings for spacecraft, solved the core problems of the existing technology in terms of bonding strength, high temperature stability and environmental protection, and has significant technological innovation and engineering practical value.

[0103] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

[0104] In addition, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, the combination of features of different embodiments means that it is within the scope of the present application and forms different embodiments. For example, in the claims above, any of the claimed embodiments can be used in any combination. The information disclosed in this background section is only intended to enhance the understanding of the overall background of the present application and should not be regarded as an admission or any form of suggestion that this information constitutes prior art already known to those skilled in the art.

Claims

1. A preparation method of an iridium alloy coating for a spacecraft, characterized in that, Comprising: Subjecting a platinum substrate to heat treatment, sandblasting, and acid etching in sequence to obtain a treated substrate; Using laser cladding to dispose an alloy on the surface of the treated substrate, and cooling in a protective atmosphere to obtain an iridium alloy coating for a spacecraft; The alloy comprises iridium and rhenium.

2. The preparation method of the iridium alloy coating for spacecraft according to claim 1, characterized in that, Satisfying at least one of the following conditions: A. The heat treatment comprises a first heating and a second heating performed in sequence. The temperature of the first heating is 200°C - 250°C, and the heat preservation time is 1h - 2h; the temperature of the second heating is 350°C - 400°C, and the heat preservation time is 2h - 3h; the heating rate for performing the second heating is 5°C / min - 15°C / min; B. The Vickers hardness of the substrate after the heat treatment is 150HV - 180HV; C. The peak stress of the substrate after the heat treatment is 150MPa - 250MPa.

3. The preparation method of the iridium alloy coating for spacecraft according to claim 1, characterized in that, The pressure of the sandblasting is 0.3 MPa - 0.8MPa.

4. The preparation method of the iridium alloy coating for spacecraft according to claim 1, wherein, Satisfying at least one of the following conditions: A. The acid comprises oxalic acid; B. The mass concentration of the acid is 5% - 15%; C. The temperature of the acid etching is 80°C - 100°C, and the time is 30min - 60min.

5. The preparation method of the iridium alloy coating for spacecraft according to claim 1, wherein, Satisfying at least one of the following conditions: A. The particle size of the alloy is 50μm - 100μm; B. Based on the total mass of 100%, the raw materials of the alloy comprise: 5% - 10% rhenium and 90% - 95% iridium.

6. The preparation method of the iridium alloy coating for spacecraft according to claim 1, wherein The energy density of the laser cladding is 1.5×10 4 W / cm 2 -3×10 4 W / cm 2 , the laser power is 80 kW - 100 kW, the focused spot is 0.2 mm - 2.0 mm, the scanning speed is 150 mm / s - 200 mm / s, and the powder feeding rate is 5 g / min - 20 g / min.

7. The preparation method of the iridium alloy coating for spacecraft according to any one of claims 1-6, characterized in that, Satisfying at least one of the following conditions: A. The cooling rate is 10 3 K / s - 10 4 K / s; B. The gases in the protective atmosphere comprise argon and nitrogen. The flow rate of the argon is 8 L / min - 12L / min, and the flow rate of the nitrogen is 3L / min - 5L / min.

8. An iridium alloy coating for a spacecraft, characterized in that, Prepared by the preparation method of the iridium alloy coating for a spacecraft according to any one of claims 1 - 7.

9. The iridium alloy coating for a spacecraft according to claim 8, wherein Satisfying at least one of the following conditions: A. The thickness of the iridium alloy coating for a spacecraft ≤ 1mm; B. The hardness of the iridium alloy coating for a spacecraft ≥ 400HV; C. The shear bonding strength between the platinum substrate and the iridium alloy coating for a spacecraft is 300MPa - 350MPa.

10. A spacecraft, characterized in that, Comprising the iridium alloy coating for a spacecraft according to claim 8 or 9.

Images