A laser surface coating method for refractory metals

Abstract

This invention relates to the field of metal surface coating technology, and discloses a laser surface coating method for refractory metals, comprising: pretreatment of the refractory metal substrate; preparation of a composite coating powder; gradient coating of the composite coating powder onto the refractory metal substrate using a laser-plasma composite heat source; and subsequent post-treatment to obtain a refractory metal surface coating. This invention thoroughly removes the oxide layer on the refractory metal surface and forms a roughened surface through plasma bombardment pretreatment, combined with high-temperature diffusion treatment, significantly improving the interfacial bonding strength between the coating and the substrate; by using gradient composition coating, it reduces interfacial stress caused by differences in thermal expansion coefficients, and with low-temperature aging treatment, it reduces the coating cracking rate; the titanium carbide in this invention increases the coating hardness, alumina enhances wear resistance, and Y2O3 refines the grains and improves high-temperature oxidation resistance, resulting in a significant improvement in the overall performance of the coating.

Description

Technical Field

[0001] This invention relates to the field of metal surface coating technology, and more specifically, to a method for laser surface coating of refractory metals. Background Technology

[0002] Refractory metals (such as tungsten, molybdenum, tantalum, and niobium) are widely used in high-end fields such as aerospace, nuclear energy, and metallurgy due to their excellent properties such as high melting point and high strength. However, these metals are prone to oxidation and corrosion in high-temperature environments, and their low surface hardness and poor wear resistance severely limit their service life under harsh working conditions.

[0003] Existing laser surface coating technology has the following key problems when applied to refractory metals:

[0004] Weak adhesion between coating and substrate: A dense oxide layer is easily formed on the surface of refractory metals, which is difficult to remove completely by traditional pretreatment methods, resulting in low bonding strength between the coating and the substrate and easy peeling.

[0005] Coatings are prone to cracking: The thermal expansion coefficients of refractory metals and coating materials differ greatly. The thermal stress generated during laser heating and cooling can easily lead to micro-cracks in the coating, affecting the overall protective performance.

[0006] Poor composition uniformity: Traditional laser coating often uses single powder or simple mixed powder, which easily leads to powder agglomeration and element segregation during the coating process, resulting in unstable coating performance.

[0007] Insufficient high-temperature oxidation resistance: Existing coatings oxidize rapidly at temperatures above 1000℃, failing to provide effective protection for refractory metal substrates over a long period.

[0008] Therefore, proposing a laser surface coating method for refractory metals has significant practical implications. Summary of the Invention

[0009] In view of this, the present invention proposes a laser surface coating method for refractory metals, aiming to solve at least one of the problems in the background art.

[0010] This invention proposes a laser surface coating method for refractory metals, comprising the following steps:

[0011] The refractory metal matrix is ​​pretreated, then ultrasonically cleaned and subjected to plasma bombardment before being put into use.

[0012] Tungsten-based powder, titanium carbide powder, alumina powder and Y2O3 powder were ball-milled and mixed, then vacuum dried and sieved to obtain composite coating powder;

[0013] The composite coating powder is gradient coated onto a refractory metal substrate using a laser-plasma composite heat source. After the coating is completed, the refractory metal substrate is subjected to low-temperature aging treatment, laser remelting, and high-temperature diffusion treatment to obtain a refractory metal surface coating.

[0014] Preferably, the ultrasonic cleaning solution is an ethanol-acetone mixture, the ultrasonic frequency is 40kHz, the temperature is 50℃, and the cleaning time is 30 minutes.

[0015] Preferably, the working gas for the plasma bombardment treatment is argon, and the vacuum level of the treatment environment is 5 × 10⁻⁶. -3 Pa, plasma power of 300W, bombardment time of 15 minutes.

[0016] Preferably, the mass fractions of each component in the composite coating powder are: 63-70% tungsten-based powder, 14-20% titanium carbide powder, 8-12% alumina powder, and 2-5% Y2O3 powder.

[0017] Preferably, the grinding media used in the ball milling mixture is tungsten carbide balls, the ball-to-material ratio is 8:1, the rotation speed is 300-400 r / min, the wet grinding media is anhydrous ethanol, and the wet grinding time is 6-8 hours.

[0018] Preferably, the laser power for gradient coating is 2500-3500W, the plasma torch power is 1200W, the powder feeding rate is 8-12g / min, the powder feeding gas is argon, and the protective gas is an argon-hydrogen mixture.

[0019] Preferably, the gradient coating is performed by using a laser-plasma composite heat source to gradient coat the composite coating powder onto a refractory metal substrate for the first layer coating. After the first layer coating is performed, the titanium carbide content in the composite coating powder is reduced by 2% and the alumina content is reduced by 1% for the second layer coating. A total of 3-5 layers are coated, with a single layer thickness of 50-80 μm.

[0020] Preferably, the low-temperature aging treatment is performed at a temperature of 300°C for 2 hours.

[0021] Preferably, the laser power of the laser remelting is 1500-2000W, the spot diameter is 2-3mm, and the remelting depth is 30-50μm.

[0022] Preferably, the high-temperature diffusion treatment is performed at a temperature of 800°C and a vacuum degree of 1×10⁻⁶. -4 Pa, processing time is 4 hours.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) Significantly improved coating adhesion: The present invention thoroughly removes the oxide layer on the surface of refractory metals and forms a roughened surface through plasma bombardment pretreatment, combined with high temperature diffusion treatment, which greatly improves the interfacial bonding strength between the coating and the substrate.

[0025] (2) Reduced risk of coating cracking: The present invention adopts a gradient composition coating design, with the composition of adjacent coatings gradually changing, reducing the interfacial stress caused by the difference in thermal expansion coefficients. Combined with low temperature aging treatment, the coating cracking rate is much lower than that of traditional methods.

[0026] (3) Excellent and stable coating performance: Titanium carbide in the composite powder increases the hardness of the coating, aluminum oxide enhances the wear resistance, and rare earth oxide Y2O3 refines the grains and improves the high-temperature oxidation resistance, which greatly improves the overall performance of the coating.

[0027] (4) High process stability: The present invention achieves precise control of the coating temperature field through laser-plasma composite heat source, resulting in good powder dispersion uniformity and automated continuous operation of the coating process. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0029] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0031] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0032] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0033] This invention provides a method for laser surface coating of refractory metals, comprising the following steps:

[0034] The refractory metal matrix is ​​pretreated, then ultrasonically cleaned and subjected to plasma bombardment before being put into use.

[0035] Tungsten-based powder, titanium carbide powder, alumina powder and Y2O3 powder were ball-milled and mixed, then vacuum dried and sieved to obtain composite coating powder;

[0036] The composite coating powder is gradient coated onto a refractory metal substrate using a laser-plasma composite heat source. After the coating is completed, the refractory metal substrate is subjected to low-temperature aging treatment, laser remelting, and high-temperature diffusion treatment to obtain a refractory metal surface coating.

[0037] Specifically, the pretreatment is preferably performed by alternating wet and dry polishing of the refractory metal substrate surface with 400-mesh, 800-mesh, and 1200-mesh silicon carbide sandpaper until the surface roughness Ra ≤ 0.8 μm.

[0038] Specifically, the laser-plasma composite heat source is a composite heat source system consisting of a fiber laser (wavelength 1064nm, maximum power 5000W) and a plasma torch (output power 1000-1500W). The diameter of the laser spot is adjusted to 3-5mm, the angle between the plasma torch and the laser beam is 45°, and the focal points of the two coincide at 2mm above the surface of the substrate.

[0039] It is understood that the present invention thoroughly removes the oxide layer on the surface of refractory metals and forms a roughened surface through plasma bombardment pretreatment, and combined with high-temperature diffusion treatment, the interfacial bonding strength between the coating and the substrate is greatly improved.

[0040] It is understood that the present invention adopts a gradient composition coating design, with the composition of adjacent coatings gradually changing, reducing the interfacial stress caused by the difference in thermal expansion coefficients. Combined with low-temperature aging treatment, the cracking rate of the coating is much lower than that of traditional methods.

[0041] Understandably, in composite powder, titanium carbide increases coating hardness, alumina enhances wear resistance, and rare earth oxide Y2O3 refines grains and improves high-temperature oxidation resistance, resulting in a significant improvement in the overall performance of the coating.

[0042] It is understood that the present invention achieves precise control of the coating temperature field through a laser-plasma composite heat source, resulting in good powder dispersion uniformity and enabling automated continuous operation of the coating process.

[0043] In this invention, the ultrasonic cleaning solution is an ethanol-acetone mixture, the ultrasonic frequency is 40kHz, the temperature is 50℃, and the cleaning time is 30 minutes.

[0044] Specifically, the polished substrate is placed in an ethanol-acetone mixed solution (volume ratio 3:1) and ultrasonically cleaned at a frequency of 40kHz and a temperature of 50℃ for 30 minutes, and then transferred to deionized water for ultrasonic cleaning for 20 minutes.

[0045] Understandably, the ethanol-acetone mixed solution (volume ratio 3:1) combines the good solubility of ethanol with the strong degreasing ability of acetone, effectively removing residual oil and debris from the substrate surface after polishing. The combination of 40kHz frequency and 50℃ temperature optimizes the ultrasonic vibration energy, ensuring cleaning effectiveness while avoiding damage to the substrate surface. The two-step process of first cleaning with the mixed solution and then rinsing with deionized water thoroughly removes contaminants and rinses away residual organic solutions, ensuring the cleanliness and activity of the substrate surface. This lays a good foundation for subsequent plasma bombardment and coating processes, and helps improve the interfacial bonding stability between the coating and the substrate.

[0046] In this invention, the working gas for the plasma bombardment treatment is argon, and the vacuum level in the treatment environment is 5 × 10⁻⁶. -3 Pa, plasma power of 300W, bombardment time of 15 minutes.

[0047] Specifically, the cleaned substrate is placed in a vacuum plasma cleaner, and argon gas (purity ≥ 99.999%) is introduced as the working gas, with the vacuum level set to 5 × 10⁻⁶. -3 Pa, plasma power of 300W, bombardment time of 15min.

[0048] Understandably, the vacuum level is 5×10 -3 The Pa environment, combined with argon gas of ≥99.999% purity as the working gas, can prevent secondary oxidation of the substrate surface during the treatment process. The reasonable matching of 300W plasma power and 15min bombardment time can not only thoroughly remove the trace oxide layer and adsorbed impurities remaining after ultrasonic cleaning, but also moderately roughen the substrate surface, increasing the surface roughness Ra to 1.2-1.5μm. This effectively increases the contact area and interfacial bonding sites between the coating and the substrate, laying a key foundation for improving the coating adhesion in subsequent coating processes.

[0049] In this invention, the mass fractions of each component of the composite coating powder are: 63-70% tungsten-based powder, 14-20% titanium carbide powder, 8-12% alumina powder, and 2-5% Y2O3 powder.

[0050] Specifically, by mass fraction, 63-70% of tungsten-based powder (particle size 5-20μm), 14-20% of titanium carbide powder (particle size 3-10μm), 8-12% of alumina powder (particle size 1-5μm), and 2-5% of rare earth oxide Y2O3 powder (particle size 0.5-3μm) are mixed.

[0051] Understandably, using 63-70% tungsten-based powder with a particle size of 5-20 μm as the main component ensures the compatibility of the coating with the refractory metal matrix and the stability of the basic structure. 15-20% titanium carbide powder (particle size 3-10 μm) can significantly improve the coating's hardness and wear resistance. 8-12% alumina powder (particle size 1-5 μm) further enhances the coating's wear resistance and chemical stability. 2-5% rare earth oxide Y2O3 powder (particle size 0.5-3 μm) can refine the coating grains and inhibit high-temperature oxidation. The gradient combination of particle size and optimized combination of mass fractions of each component not only achieves complementary and synergistic performance but also avoids the coating brittleness or performance imbalance caused by excessive amounts of a single component, providing a high-quality raw material foundation for subsequent coating to form a coating with excellent comprehensive performance.

[0052] In this invention, the grinding media for ball milling is tungsten carbide balls, the ball-to-material ratio is 8:1, the rotation speed is 300-400 r / min, the wet grinding media is anhydrous ethanol, and the wet grinding time is 6-8 hours.

[0053] Specifically, the composite coating powder is placed in a planetary ball mill, using tungsten carbide balls as the grinding medium, with a ball-to-material ratio of 8:1 and a rotation speed of 300-400 r / min. It is then wet-milled for 6-8 hours under argon protection, with anhydrous ethanol as the wet grinding medium. The milled slurry is then dried in a vacuum drying oven at 60°C for 12 hours, and subsequently sieved through a 200-mesh sieve to obtain a uniformly dispersed composite coating powder.

[0054] Understandably, planetary ball mills paired with tungsten carbide ball grinding media, leveraging the high hardness and wear resistance of tungsten carbide, can prevent impurities from being introduced during grinding due to media wear, while ensuring grinding efficiency. The reasonable setting of a ball-to-material ratio of 8:1 and a rotation speed of 300-400 r / min provides sufficient and appropriate grinding kinetic energy, promoting the thorough refinement and uniform mixing of powders of different particle sizes, and preventing excessive powder agglomeration. The argon protective atmosphere effectively isolates the powder from air, preventing oxidation and deterioration during grinding. The anhydrous ethanol in the wet grinding media not only disperses the powder and lowers the grinding temperature, preventing changes in powder properties due to high temperatures, but also facilitates subsequent drying. The 6-8 hour wet grinding time further ensures the uniformity of the powder mixture, providing a key guarantee for the subsequent coating process to prepare composite coating powders with uniform composition and stable performance.

[0055] Understandably, the 60℃ vacuum drying oven not only prevents oxidation of the powder in the ball-milled slurry during drying through a vacuum environment, but also prevents powder agglomeration or performance changes due to high temperature by using a low-temperature drying method. The 12-hour drying time ensures that the moisture in the slurry is fully removed. Subsequently, sieving through a 200-mesh sieve can effectively screen out powder with uniform particle size, remove any possible small lumps, and finally obtain a uniformly dispersed composite coating powder. This provides a reliable guarantee for the stable powder feeding, uniformity of coating composition, and stability of coating performance in the subsequent laser coating process.

[0056] In this invention, the laser power for gradient coating is 2500-3500W, the plasma torch power is 1200W, the powder feeding rate is 8-12g / min, the powder feeding gas is argon, and the protective gas is an argon-hydrogen mixture.

[0057] In this invention, the gradient coating is performed by using a laser-plasma composite heat source to gradient coat the composite coating powder onto a refractory metal substrate for the first layer coating. After the first layer coating is performed, the titanium carbide content and alumina content in the composite coating powder are reduced by 2% and 1% respectively for the second layer coating. A total of 3-5 layers are coated, with a single layer thickness of 50-80 μm.

[0058] Specifically, the stage moving speed is set to 5-8 mm / s, the laser power to 2500-3500 W, and the plasma torch power to 1200 W. The pretreated substrate is fixed on the stage for laser-plasma composite heat source coating. After the first coating is completed, the titanium carbide content in the composite powder is reduced by 2% and the alumina content is reduced by 1% for the second coating. A total of 3-5 layers are coated, with the angle between the coating directions of adjacent layers being 90°.

[0059] Understandably, the precise setting of the worktable movement speed, laser power, and plasma torch power ensures stable heat source energy and uniform and controllable coating thickness during each coating process. By adjusting the content of titanium carbide and alumina in the composite powder layer by layer to form a gradient composition design, the thermal stress caused by the difference in thermal expansion coefficients between the coating and the substrate and between layers is effectively alleviated. The combination of 3-5 coating layers and a total thickness of 200-300μm ensures the protective effect of the coating while avoiding the risk of cracking caused by excessive thickness. The 90° coating direction angle between adjacent layers further optimizes the internal stress distribution of the coating and improves the overall structural integrity and mechanical performance stability of the coating.

[0060] In this invention, the temperature of the low-temperature aging treatment is 300°C, and the aging time is 2 hours.

[0061] Specifically, the coated substrate is placed in a box-type resistance furnace and kept at 300°C for 2 hours, and then cooled to room temperature with the furnace.

[0062] Understandably, the 300℃ low-temperature insulation environment can effectively activate the release process of residual stress inside the coating and substrate, and avoid adverse phase transformation of the coating microstructure caused by excessively high temperature. The 2-hour insulation time provides sufficient time for the stress to be fully released. The subsequent furnace cooling can achieve slow cooling, preventing the generation of new thermal stress inside the workpiece due to excessively rapid cooling rate. This significantly eliminates the residual stress formed during the laser-plasma coating process. Combined with the gradient coating design, it further reduces the risk of coating cracking and ensures the overall structural stability of the coating.

[0063] In this invention, the laser power of the laser remelting is 1500-2000W, the spot diameter is 2-3mm, and the remelting depth is 30-50μm.

[0064] Specifically, the same fiber laser is used, with the laser power adjusted to 1500-2000W, the spot diameter to 2-3mm, and the stage moving speed to 10-15mm / s, to perform laser remelting on the coating surface, with the remelting depth controlled to 30-50μm.

[0065] Understandably, using the same fiber laser ensures equipment compatibility and process continuity, avoiding parameter errors caused by equipment switching. The compatibility of 1500-2000W laser power, 2-3mm spot diameter, and 10-15mm / s stage movement speed allows for precise control of heat input, achieving surface melting of the coating while avoiding excessive heat effects. A remelting depth of 30-50μm can specifically refine the surface grains of the coating, eliminate surface micropores and defects, and optimize the surface microstructure. This not only reduces the surface roughness Ra to below 0.5μm but also further improves the surface hardness and wear resistance of the coating, enhancing the overall stability of the coating's protective performance.

[0066] In this invention, the high-temperature diffusion treatment is performed at a temperature of 800°C and a vacuum degree of 1×10⁻⁶. -4 Pa, processing time is 4 hours.

[0067] Specifically, the remelted substrate is placed in a vacuum diffusion furnace at 800°C and a vacuum degree of 1×10⁻⁶. -4 Incubate at Pa for 4 hours.

[0068] Understandably, a vacuum degree of 1×10 Pa -4The high vacuum environment can prevent the workpiece from oxidizing during high-temperature processing. The temperature setting of 800℃ can provide sufficient kinetic energy for element interdiffusion at the interface between the coating and the substrate, without causing adverse changes in the microstructure of the coating or the substrate. The 4-hour holding time ensures sufficient element diffusion, forming a continuous and gradient-distributed transition layer at the interface, effectively reducing the difference in interface performance, further improving the bonding strength between the coating and the substrate, and significantly enhancing the stability of the interface bonding.

[0069] Example 1

[0070] Refractory metal substrate: Tungsten metal plate (size 100mm×100mm×5mm, purity ≥99.95%).

[0071] Composite coating powder: 66% tungsten-based powder (particle size 5-20μm), 19% titanium carbide powder (particle size 3-10μm), 10% alumina powder (particle size 1-5μm), and 5% rare earth oxide Y2O3 powder (particle size 0.5-3μm) were mixed and placed in a planetary ball mill. Tungsten carbide balls were used as the grinding medium, the ball-to-material ratio was 8:1, the rotation speed was 350 r / min, and wet milling was carried out for 7 hours under argon protection. The wet milling medium was anhydrous ethanol. The slurry after ball milling was dried in a vacuum drying oven at 60℃ for 12 hours, and then sieved through a 200-mesh sieve to obtain a uniformly dispersed composite coating powder.

[0072] Equipment: A composite heat source system is composed of a fiber laser (wavelength 1064nm, maximum power 5000W) and a plasma torch (output power 1200W). The laser spot diameter is 4mm, the angle between the plasma torch and the laser beam is 45°, and the focal points of the two coincide 2mm above the surface of the tungsten substrate.

[0073] Preparation method:

[0074] S1. The surface of the tungsten substrate is sequentially polished with alternating wet and dry sandpaper using 400-grit, 800-grit, and 1200-grit silicon carbide sandpaper until the final surface roughness Ra = 0.6 μm. The cleaned tungsten substrate is then placed in a vacuum plasma cleaner, and 99.999% pure argon gas is introduced, with the vacuum level set to 5 × 10⁻⁶. -3 Pa, plasma power of 300 W, bombardment for 15 min;

[0075] S2. Fix the bombarded tungsten substrate on the worktable, set the worktable moving speed to 6 mm / s, the laser power to 3000 W, the plasma torch power to 1200 W, the powder feeding rate to 10 g / min, the powder feeding gas to argon (flow rate 12 L / min), and the protective gas to an argon-hydrogen mixture (volume ratio 95:5, flow rate 22 L / min) for the first coating, with a coating thickness of 65 μm.

[0076] S3. After completing the first coating, adjust the titanium carbide content in the composite powder to 17% and the alumina content to 9% and apply the second coating with the same parameters as in S2. Then adjust the titanium carbide content to 15% and the alumina content to 8% and apply the third coating.

[0077] S4. Place the coated tungsten substrate in a box-type resistance furnace and hold it at 300℃ for 2 hours. Then, cool it to room temperature with the furnace. Next, using the same fiber laser, adjust the laser power to 1800W, the spot diameter to 2.5mm, and the stage movement speed to 12mm / s to perform laser remelting on the coating surface. The remelting depth is 40μm. Finally, place the remelted tungsten substrate in a vacuum diffusion furnace and heat it at 800℃ and a vacuum degree of 1×10⁻⁶. -4 Incubate at Pa for 4 hours.

[0078] Example 2

[0079] Refractory metal substrate: Tungsten metal plate (size 100mm×100mm×5mm, purity ≥99.95%).

[0080] Composite coating powder: 63% tungsten-based powder (particle size 5-20μm), 20% titanium carbide powder (particle size 3-10μm), 12% alumina powder (particle size 1-5μm), and 5% rare earth oxide Y2O3 powder (particle size 0.5-3μm) were mixed and placed in a planetary ball mill. Tungsten carbide balls were used as the grinding medium, the ball-to-material ratio was 8:1, the rotation speed was 300 r / min, and wet milling was carried out for 6 hours under argon protection. The wet milling medium was anhydrous ethanol. The slurry after ball milling was dried in a vacuum drying oven at 60℃ for 12 hours, and then sieved through a 200-mesh sieve to obtain a uniformly dispersed composite coating powder.

[0081] Equipment: A composite heat source system is composed of a fiber laser (wavelength 1064nm, maximum power 5000W) and a plasma torch (output power 1200W). The laser spot diameter is 3mm, the angle between the plasma torch and the laser beam is 45°, and the focal points of the two coincide 2mm above the surface of the tungsten substrate.

[0082] Preparation method:

[0083] S1. The surface of the tungsten substrate is sequentially polished with alternating wet and dry sandpaper using 400-grit, 800-grit, and 1200-grit silicon carbide sandpaper until the final surface roughness Ra = 0.7 μm. The cleaned tungsten substrate is then placed in a vacuum plasma cleaner, and 99.999% pure argon gas is introduced, with the vacuum level set to 5 × 10⁻⁶. -3 Pa, plasma power of 300 W, bombardment for 15 min;

[0084] S2. Fix the bombarded tungsten substrate on the worktable, set the worktable moving speed to 5 mm / s, the laser power to 2500 W, the plasma torch power to 1200 W, the powder feeding rate to 8 g / min, the powder feeding gas to argon (flow rate 10 L / min), and the protective gas to an argon-hydrogen mixture (volume ratio 95:5, flow rate 20 L / min) for the first coating, with a coating thickness of 50 μm.

[0085] S3. After completing the first coating, adjust the titanium carbide content in the composite powder to 18% and the alumina content to 11% and apply the second coating with the same parameters as in S2. Then, adjust the titanium carbide content to 16% and the alumina content to 10% and apply the third coating.

[0086] S4. Place the coated tungsten substrate in a box-type resistance furnace and hold it at 300℃ for 2 hours. Then, cool it to room temperature with the furnace. Next, using the same fiber laser, adjust the laser power to 1500W, the spot diameter to 2mm, and the stage movement speed to 10mm / s to perform laser remelting on the coating surface. The remelting depth is 30μm. Finally, place the remelted tungsten substrate in a vacuum diffusion furnace and heat it at 800℃ and a vacuum degree of 1×10⁻⁶. -4 Incubate at Pa for 4 hours.

[0087] Example 3

[0088] Refractory metal substrate: Tungsten metal plate (size 100mm×100mm×5mm, purity ≥99.95%).

[0089] Composite coating powder: 70% tungsten-based powder (particle size 5-20μm), 18% titanium carbide powder (particle size 3-10μm), 10% alumina powder (particle size 1-5μm), and 2% rare earth oxide Y2O3 powder (particle size 0.5-3μm) were mixed and placed in a planetary ball mill. Tungsten carbide balls were used as the grinding medium, the ball-to-material ratio was 8:1, the rotation speed was 400 r / min, and wet milling was carried out for 8 hours under argon protection. The wet milling medium was anhydrous ethanol. The slurry after ball milling was dried in a vacuum drying oven at 60℃ for 12 hours, and then sieved through a 200-mesh sieve to obtain a uniformly dispersed composite coating powder.

[0090] Equipment: A composite heat source system is composed of a fiber laser (wavelength 1064nm, maximum power 5000W) and a plasma torch (output power 1200W). The laser spot diameter is 5mm, the plasma torch and the laser beam are at an angle of 45°, and their focal points coincide 2mm above the tungsten substrate surface.

[0091] Preparation method:

[0092] S1. The surface of the tungsten substrate is sequentially polished with alternating wet and dry sandpaper using 400-grit, 800-grit, and 1200-grit silicon carbide sandpaper until the final surface roughness Ra = 0.8 μm. The cleaned tungsten substrate is then placed in a vacuum plasma cleaner, and 99.999% pure argon gas is introduced, with the vacuum level set to 5 × 10⁻⁶. -3 Pa, plasma power of 300 W, bombardment for 15 min;

[0093] S2. Fix the bombarded tungsten substrate on the worktable, set the worktable moving speed to 8 mm / s, the laser power to 3500 W, the plasma torch power to 1200 W, the powder feeding rate to 12 g / min, the powder feeding gas to argon (flow rate 15 L / min), and the protective gas to an argon-hydrogen mixture (volume ratio 95:5, flow rate 25 L / min) for the first coating, with a coating thickness of 80 μm.

[0094] S3. After completing the first coating, adjust the titanium carbide content in the composite powder to 16% and the alumina content to 9% and apply the second coating with the same parameters as in S2. Then, adjust the titanium carbide content to 14% and the alumina content to 8% and apply the third coating.

[0095] S4. Place the coated tungsten substrate in a box-type resistance furnace and hold it at 300℃ for 2 hours. Then, cool it to room temperature with the furnace. Next, using the same fiber laser, adjust the laser power to 2000W, the spot diameter to 3mm, and the stage movement speed to 15mm / s to perform laser remelting on the coating surface. The remelting depth is 50μm. Finally, place the remelted tungsten substrate in a vacuum diffusion furnace and heat it at 800℃ and a vacuum degree of 1×10⁻⁶. -4 Incubate at Pa for 4 hours.

[0096] Effect test

[0097] Test sample

[0098] The tungsten metal substrate coating prepared in Example 1 was used as an experimental example;

[0099] Using conventional single-fiber laser coating to prepare a tungsten substrate coating as a control example, the conventional single-fiber laser coating has a laser power of 3000W, a spot diameter of 4mm, a stage moving speed of 6mm / s, a powder feeding rate of 10g / min, and a coating thickness of the same as in Example 1. The coating powder is a single tungsten-based powder (particle size 5-20μm) with 10% titanium carbide powder (particle size 3-10μm).

[0100] Test method:

[0101] Interface bond strength: Tested by tensile test according to GB / T 8642-2002 "Determination of Bond Strength of Thermal Spray Coatings" standard;

[0102] High-temperature oxidation resistance: The weight gain of the sample before and after oxidation was tested after static oxidation in a muffle furnace at 1200℃ for 100h.

[0103] Coating hardness: HV-1000 Vickers hardness tester, load 200g, holding pressure for 10s;

[0104] Wear rate: MMW-1 type pin-disc wear tester was used, with a load of 5N, a rotation speed of 300r / min, and a wear time of 60min;

[0105] Coating cracking rate: The surface and cross-section of the coating were observed by scanning electron microscopy (SEM), and the proportion of cracked areas was statistically analyzed.

[0106] The test results are shown in Table 1:

[0107] Table 1 Test Results

[0108]

[0109] The comparative test data shows that the tungsten metal workpiece prepared in this embodiment far surpasses the traditional process samples in terms of interfacial bonding strength, high-temperature oxidation resistance, coating hardness, wear resistance, and crack resistance.

[0110] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method of laser surface coating of refractory metals, characterized in that, It comprises the following steps: The refractory metal matrix is pretreated, ultrasonically cleaned, and subjected to plasma bombardment treatment and then stored; The tungsten-based powder, titanium carbide powder, aluminum oxide powder, and Y2O3 powder are ball-mixed, vacuum-dried, and sieved to obtain a composite coating powder; The composite coating powder is gradient-coated on the refractory metal matrix by using a laser-plasma composite heat source, and after the coating process, the coated refractory metal matrix is subjected to low-temperature aging treatment, laser remelting, and high-temperature diffusion treatment to obtain a refractory metal surface coating; The mass fraction of each component of the composite coating powder is: tungsten-based powder 63-70%, titanium carbide powder 14-20%, aluminum oxide powder 8-12%, and Y2O3 powder 2-5%; The gradient coating is: the composite coating powder is gradient-coated on the refractory metal matrix by using a laser-plasma composite heat source to perform first layer coating, and after the coating process, the titanium carbide content in the composite coating powder is reduced by 2% and the aluminum oxide content is reduced by 1% to perform second coating, a total of 3-5 layers, and the thickness of a single layer is 50-80 μm; The temperature of the low-temperature aging treatment is 300°C, and the aging time is 2 hours; The laser remelting has a laser power of 1500-2000 W, a spot diameter of 2-3 mm, and a remelting depth of 30-50 μm; The high-temperature diffusion treatment has a temperature of 800℃, a vacuum degree of 1x10 -4 Pa, and a treatment time of 4 hours.

2. The refractory metal laser surface coating method of claim 1, wherein, The cleaning solution for the ultrasonic cleaning is an ethanol-acetone mixed solution, the ultrasonic frequency is 40 kHz, the temperature is 50°C, and the cleaning time is 30 minutes.

3. The refractory metal laser surface coating method according to claim 2, characterized in that The working gas of the plasma bombardment treatment is argon, and the vacuum degree in the treatment environment is 5x10 -3 Pa, the plasma power is 300 W, and the bombardment time is 15 minutes.

4. The refractory metal laser surface coating method of claim 3, wherein, The grinding medium for the ball-mixing is tungsten carbide balls, the ball-to-material ratio is 8:1, the rotation speed is 300-400 r / min, the wet grinding medium is anhydrous ethanol, and the wet grinding time is 6-8 hours.

5. The refractory metal laser surface coating method of claim 4, wherein, The laser power for the gradient coating is 2500-3500 W, the power of the plasma torch is 1200 W, the powder feeding rate is 8-12 g / min, the powder feeding gas is argon, and the protective gas is argon-hydrogen mixed gas.

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