Preparation method of 3D printing niobium-tungsten alloy high-temperature oxidation resistant coating

Abstract

A preparation method of a 3D printing niobium-tungsten alloy high-temperature oxidation resistant coating belongs to the field of niobium-tungsten alloy coating preparation.The preparation method adopts a two-step method to prepare a MoSi2 coating, firstly, a Mo coating is prepared on a substrate through a slurry method, and then the MoSi2 coating is obtained by embedding and permeating Si. For Mo coating slurry, the content of a binder in the slurry is adjusted to 0.8-1.3 wt.%, and a multi-time spraying mode is adopted, so that the surface of a matrix is better wetted, the slurry is completely permeated into a microcosmic recess, and hole defects caused by interface air residues are reduced. Secondly, the residual stress of the base body is large, the thickness of the sprayed coating should be controlled to be 100 microns or below, the temperature rise rate is adjusted, the temperature is slowly increased to 800-1000 DEG C, and a heat preservation platform is arranged so that internal stress can be slowly released, and good combination of the coating and the base body can be maintained; the thickness of the Mo coating ranges from 40 micrometers to 90 micrometers, and the Mo coating can be well combined with a base body. The thickness of the MoSi2 anti-oxidation coating is 50-100 microns, and the static anti-oxidation service life of the anti-oxidation coating on the surface of the 3D printing niobium-tungsten alloy in the air at the temperature of 1200 DEG C can reach more than 75 hours.

Description

Technical Field

[0001] This invention belongs to the field of powder metallurgy and high-temperature anti-oxidation coating technology, and relates to a method for preparing a high-temperature anti-oxidation coating of niobium-tungsten alloy, and more particularly to a method for preparing a 3D printed molybdenum disilicide (MoSi2) coating of niobium-tungsten alloy. Technical Background

[0002] Niobium and niobium alloys are key materials for extreme environments due to their high melting point, excellent high-temperature strength and specific strength, outstanding weldability, and corrosion resistance. 3D printing technology enables near-net-shape forming of high-performance, complex-shaped, lightweight structural components, driving the large-scale application of niobium alloys in high-end fields such as rocket engine thrust chambers and corrosion-resistant components in nuclear reactors. However, niobium-tungsten alloys, a typical example of niobium alloys, have a strong affinity for oxygen and undergo severe oxidation at 600°C, generating powdery oxides that lead to catastrophic failure of structural components. Therefore, coatings are typically applied to the surface of niobium-tungsten alloys to improve their oxidation resistance, meeting the needs of modern aerospace and other fields. MoSi2, with its low density, high melting point, and similar coefficient of thermal expansion to niobium-tungsten alloys, rapidly forms a continuous and dense silicon oxide (SiO2) protective film on the coating surface at high temperatures, preventing oxidation of the substrate and making it the preferred material for anti-oxidation coatings on niobium-tungsten alloys.

[0003] The non-equilibrium solidification process in 3D printing leads to uneven microstructure and significant residual stress in the matrix. This affects the diffusion and reaction between the coating and the matrix during sintering, and the stress release and deformation within the matrix during sintering disrupts the bond between the coating and the matrix. Compared to traditional castings and forgings, 3D-printed niobium-tungsten alloy samples exhibit higher surface roughness, greater internal stress, and poorer microstructure uniformity. These factors result in variations in coating application, growth rate, phase composition, and even the number of defects in different regions, significantly increasing the difficulty of process control. Furthermore, the layer-by-layer molding characteristic of 3D printing easily leads to defects such as incomplete fusion and porosity, forming deep and sharp depressions on the surface, which hinders complete filling of the coating slurry. Uneven coating thickness exacerbates stress imbalance, causing localized cracking due to stress concentration, ultimately leading to overall failure. Therefore, traditional coating preparation processes are unsuitable for 3D-printed alloy systems, necessitating the development of a MoSi2 coating preparation process suitable for 3D-printed niobium-tungsten alloys. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a high-temperature oxidation-resistant coating for niobium-tungsten alloy using 3D printing, thereby improving its high-temperature oxidation resistance and extending its service life. Based on the above research background, collaborative improvements are needed in areas such as 3D printing process adjustment, surface finishing, coating slurry viscosity control, slurry coating thickness and uniformity control, and sintering process optimization. A two-step method for preparing the MoSi2 coating is considered.

[0005] The technical problem solved by this invention is achieved by the following technical solution:

[0006] The substrate used in this invention is a 3D printed niobium-tungsten alloy. During the printing process, the sample surface is remelted once. By reducing the laser power and scanning speed, the stability of the molten pool is improved, the defect density on the surface of the formed part is reduced, and the surface density and precision are improved. After printing, the substrate surface is sanded and sandblasted to reduce the surface roughness.

[0007] This invention employs a two-step method to prepare a MoSi2 coating. First, a Mo coating is prepared on the substrate using a slurry method, followed by Si embedding to obtain the MoSi2 coating. For the Mo coating slurry, the binder content is adjusted to 0.8–1.3 wt.%, and multiple sprayings are used to better wet the substrate surface, ensuring complete penetration of the slurry into microscopic depressions and reducing porosity defects caused by residual air at the interface. Secondly, given the high residual stress in the substrate, the coating thickness should be controlled below 100 μm, and the heating rate should be adjusted to slowly raise the temperature to 800–1000 °C, with a heat preservation platform set up to slowly release internal stress and maintain good adhesion between the coating and the substrate.

[0008] A method for preparing a 3D-printed niobium-tungsten alloy high-temperature oxidation resistant coating includes the following steps:

[0009] Step 1) The surface of the niobium-tungsten alloy sample is remelted once during 3D printing. By reducing the laser power and scanning speed, the stability of the molten pool is improved, the defect density on the surface of the 3D printed niobium-tungsten alloy part is reduced, and the surface density and accuracy are improved. The surface of the 3D printed niobium-tungsten alloy block is rough ground with sandpaper, then ultrasonically cleaned with anhydrous ethanol, and finally dried and sandblasted for later use.

[0010] Step 2) Molybdenum powder, anhydrous ethanol and polyvinyl butyral are mixed using a planetary ball mill to prepare a uniform slurry for later use.

[0011] Step 3) Apply a molybdenum (Mo) coating to the niobium-tungsten alloy surface treated in Step 1) using a spray gun. After natural drying and vacuum drying, the surface is sintered in a vacuum sintering furnace to obtain the Mo coating.

[0012] Step 4) Use a mixer to mix silicon powder, sodium fluoride and alumina to obtain a mixed powder, and dry it for later use;

[0013] Step 5) Pour the dried mixed powder from Step 4) into a crucible of appropriate size and spread it evenly. Place the niobium-tungsten alloy with Mo coating obtained in Step 3) into the crucible, then pour the remaining mixed powder into the crucible and spread it evenly. Seal the crucible lid.

[0014] Step 6) Place the sealed crucible from step 5) into a high-temperature tubular sintering furnace for silicon infiltration treatment, and protect it with an argon atmosphere to obtain a molybdenum disilicide (MoSi2) coating.

[0015] Furthermore, in step 1), the parameters for remelting the sample surface are a laser power of 150–180 W and a scanning speed of 400–600 mm / s.

[0016] Furthermore, in step 2), the particle size distribution of the Mo powder is 1–20 μm.

[0017] Further, in step 2), the ratio of molybdenum powder to anhydrous ethanol is 1.0:0.5-1 (wt.%), and the polyvinyl butyral is 0.8-1.3 wt.% of the total slurry.

[0018] Furthermore, in step 2), the ball-to-material ratio is 10:1, the rotation speed is 300 r / min, and the mixing time of the ball mill is 12-15 h.

[0019] Furthermore, in step 3), natural drying takes 1.5-2.5 hours, followed by vacuum drying at 80°C for 1.5-2.5 hours.

[0020] Further, in step 3), during sintering, the temperature is increased from room temperature to 800-1000℃ at a heating rate of 5℃ / min, held for 0.5-1.5h, and then increased from 800℃ to the sintering temperature of 1500-1550℃ at a heating rate of 3℃ / min, held for 1.5-2.5h.

[0021] Further, in the mixed powder described in step 4), silicon powder: 30-40 wt.%, sodium fluoride: 2-5 wt.%, and the remainder is alumina.

[0022] Further, in step 4), the ball-to-material ratio is 1:5, the rotation speed is 60 r / min, and the ball milling time is 4.5-5.5 h; the drying is carried out in a constant temperature vacuum drying oven at 80℃ for 1.5-2.5 h.

[0023] Furthermore, in step 6), during sintering, the temperature is increased from room temperature to 800°C at a heating rate of 5°C / min, and then increased from 800°C to the sintering temperature of 1100°C to 1200°C at a heating rate of 3°C / min and held at that temperature.

[0024] Note: The number of claims is generally limited to no more than 10. Each additional claim will incur an extra 150 yuan fee, which I personally believe is unnecessary. Moreover, your last two claims pertain to effects, which are guaranteed by the manufacturing process. Individual effects are not protected and should be included in the specification.

[0025] The Mo coating of the present invention has a thickness of 40-90 μm and good adhesion to the substrate.

[0026] The MoSi2 anti-oxidation coating has a thickness of 50-100 μm. The anti-oxidation coating on the surface of the 3D printed niobium-tungsten alloy can achieve a static anti-oxidation life of more than 75 hours in air at 1200℃. Its anti-oxidation performance is significantly better than the traditional method of preparing niobium-tungsten alloy coatings (about 5 hours).

[0027] The technical effects of this invention are as follows:

[0028] (1) The 3D printed niobium-tungsten alloy anti-high temperature oxidation coating obtained by the present invention has good bonding with the substrate and is not easy to crack or fall off;

[0029] (2) The 3D printed niobium-tungsten alloy anti-high temperature oxidation coating obtained by the present invention has a high coating density, reaching more than 90%;

[0030] (3) The 3D printed niobium-tungsten alloy anti-high temperature oxidation coating obtained by the present invention has excellent anti-oxidation performance, and the static anti-oxidation life in air at 1200℃ is more than 75h. Attached Figure Description

[0031] The advantages and benefits of the present invention will be better understood by those skilled in the art through the detailed description of preferred embodiments below.

[0032] In the attached diagram:

[0033] Figure 1 The images show surface and cross-sectional SEM images of the MoSi2 anti-oxidation coating on the niobium alloy surface prepared in Example 1 of this invention. (a) is a surface SEM image of the coating, and (b) is a cross-sectional SEM image of the coating.

[0034] Figure 2 The images show surface and cross-sectional SEM images of the MoSi2 anti-oxidation coating on the niobium alloy surface prepared in Example 2 of this invention. (a) is a surface SEM image of the coating, and (b) is a cross-sectional SEM image of the coating.

[0035] Figure 3 The images show surface and cross-sectional SEM images of the MoSi2 anti-oxidation coating on the niobium alloy surface prepared in Example 3 of this invention. (a) is a surface SEM image of the coating, and (b) is a cross-sectional SEM image of the coating.

[0036] Figure 4 These are comparative photos of the samples from Example 3 of the present invention after oxidation in air at 1200°C for different times. (a) is a comparison photo of the sample before oxidation with and without coating. (b) is a comparison photo of the sample after oxidation for 20 min with and without coating. (c) is a photo of the sample after oxidation for 75 h with coating. Detailed Implementation

[0037] Example 1

[0038] 1. Use 240-600# sandpaper to rough grind the surface of the 3D printed niobium-tungsten alloy block, then use anhydrous ethanol for ultrasonic cleaning, and finally blow dry and sandblast for later use.

[0039] 2. A planetary ball mill was used to mix molybdenum powder, anhydrous ethanol, and polyvinyl butyral to prepare a homogeneous slurry for later use. The molybdenum powder:anhydrous ethanol ratio was 1:2 (wt.%), polyvinyl butyral was 0.8 wt.%, the ball-to-powder ratio was 10:1, the milling speed was 300 r / min, and the mixing time was 10 h. The prepared slurry was sprayed onto the treated alloy surface using a spray gun, and after natural drying, it was placed in an 80℃ constant temperature vacuum oven for 2 h. Then, it was placed in a vacuum sintering furnace and held at 1500℃ for 2 h to obtain a Mo coating for later use.

[0040] 3. A mixer is used to mix silicon powder, sodium fluoride, and alumina, wherein the silicon powder content is 30 wt.%, sodium fluoride content is 5 wt.%, and the remainder is alumina. The mixture is then dried in an 80℃ constant temperature vacuum oven for 2 hours. A portion of the dried powder mixture is poured into a suitably sized crucible and leveled. A Mo-coated niobium-tungsten alloy is then added, and the remaining powder mixture is gradually poured into the crucible and leveled. The crucible is then sealed. The crucible is then placed in a high-temperature tube furnace and heated from room temperature to 1200℃ for 3 hours to obtain a MoSi2 coating.

[0041] 4. SEM images of the surface and cross-section of the MoSi2 anti-oxidation coating on the prepared niobium alloy surface are shown below. Figure 1 As shown (the left side is the surface SEM image, and the right side is the cross-sectional SEM image), the coating surface is relatively smooth and no obvious cracks were found; due to the short silicon infiltration time, the Mo layer was not completely siliconized, and the coating consists of a MoSi2 layer and a Mo layer, and the coating is dense.

[0042] Example 2

[0043] 1. Use 240-600# sandpaper to rough grind the surface of the 3D printed niobium-tungsten alloy block, then use anhydrous ethanol for ultrasonic cleaning, and finally blow dry and sandblast for later use.

[0044] 2. A planetary ball mill was used to mix molybdenum powder, anhydrous ethanol, and polyvinyl butyral to prepare a homogeneous slurry for later use. The molybdenum powder:anhydrous ethanol ratio was 1:2 (wt.%), polyvinyl butyral was 0.9 wt.%, the ball-to-powder ratio was 10:1, the milling speed was 300 r / min, and the mixing time was 10 h. The prepared slurry was sprayed onto the treated alloy surface using a spray gun, allowed to dry naturally, and then dried in an 80℃ constant temperature vacuum oven for 2 h. Afterward, it was placed in a vacuum sintering furnace and held at 1550℃ for 2 h to obtain a Mo coating for later use.

[0045] 3. A mixing machine is used to mix silicon powder, sodium fluoride, and alumina, wherein silicon powder: 35 wt.%, sodium fluoride: 5 wt.%, and the remainder is alumina. The mixture is then dried in an 80℃ constant temperature vacuum oven for 2 hours for later use. The dried mixed powder is poured into a crucible of appropriate size and spread evenly. Then, a niobium-tungsten alloy with a Mo coating is placed in the crucible. The remaining mixed powder is gradually poured into the crucible and spread evenly. The crucible is then sealed. The crucible is then placed in a high-temperature tube sintering furnace and heated from room temperature to 1200℃ for 4 hours to obtain a MoSi2 coating.

[0046] 4. SEM images of the surface and cross-section of the MoSi2 anti-oxidation coating on the prepared niobium alloy surface are shown below. Figure 2 As shown (the left side is the surface SEM image, and the right side is the cross-sectional SEM image), in this embodiment, the Mo layer is completely siliconized, and the coating consists of a complete MoSi2 layer. The bonding effect is good, and the coating is dense and uniform internally.

[0047] Example 3

[0048] 1. Use 240-600# sandpaper to rough grind the surface of the 3D printed niobium-tungsten alloy block, then use anhydrous ethanol for ultrasonic cleaning, and finally blow dry and sandblast for later use.

[0049] 2. A uniform slurry was prepared by mixing molybdenum powder, anhydrous ethanol, and polyvinyl butyral using a planetary ball mill. The molybdenum powder:anhydrous ethanol ratio was 1:2 (wt.%), and polyvinyl butyral was 1.0 wt.%, with a ball-to-powder ratio of 10:1. The milling speed was 300 r / min, and the mixing time was 10 h. The prepared slurry was sprayed onto the treated alloy surface using a spray gun. After natural drying, it was placed in an 80℃ constant temperature vacuum oven for 2 h. Then, it was placed in a vacuum sintering furnace and held at 1550℃ for 2 h to obtain a Mo coating.

[0050] 3. A mixing machine is used to mix silicon powder, sodium fluoride, and alumina. The silicon powder content is 40 wt.%, the sodium fluoride content is 5 wt.%, and the remainder is alumina. The mixture is then dried in a vacuum oven at 80°C for 2 hours. The dried mixed powder is poured into a crucible of appropriate size and spread evenly. Then, a niobium-tungsten alloy with a Mo coating is placed in the crucible. The remaining mixed powder is gradually poured into the crucible and spread evenly. The crucible is then sealed. The crucible is then placed in a high-temperature tube sintering furnace and heated from room temperature to 1200°C for 5 hours to obtain a MoSi2 coating.

[0051] 4. SEM images of the surface and cross-section of the MoSi2 anti-oxidation coating on the prepared niobium alloy surface are shown below. Figure 3 As shown (the left side is the surface SEM image, and the right side is the cross-sectional SEM image), the coating surface is relatively smooth and no obvious cracks were found; the coating consists of a MoSi2 coating and a NbSi2 diffusion layer, and the coating has good bonding with the diffusion layer and the substrate, and the coating is dense and uniform inside.

[0052] 5. Place the uncoated sample and the coated sample into the crucible respectively, mark them, and record their appearance.

[0053] 6. After heating the high-temperature furnace to 1200℃ and maintaining the temperature, place two crucibles inside. After a period of time, take them out and observe whether the samples have changed, and record the results.

[0054] After 20 minutes of oxidation, the uncoated sample showed oxide formation on its surface and failed, while the coated sample remained intact without cracking. After 75 hours of oxidation in air at 1200℃, the coated sample showed no signs of peeling or cracking and still exhibited excellent oxidation resistance.

Claims

1. A method for preparing a 3D-printed niobium-tungsten alloy high-temperature oxidation resistant coating, characterized by comprising the following steps: Step 1) The surface of the niobium-tungsten alloy sample is remelted once during 3D printing. By reducing the laser power and scanning speed, the stability of the molten pool is improved, the defect density on the surface of the 3D printed niobium-tungsten alloy part is reduced, and the surface density and accuracy are improved. The surface of the 3D printed niobium-tungsten alloy block is rough ground with sandpaper, then ultrasonically cleaned with anhydrous ethanol, and finally dried and sandblasted for later use. Step 2) Molybdenum powder, anhydrous ethanol and polyvinyl butyral are mixed using a planetary ball mill to prepare a uniform slurry for later use. Step 3) Apply a molybdenum (Mo) coating to the niobium-tungsten alloy surface treated in Step 1) using a spray gun. After natural drying and vacuum drying, the surface is sintered in a vacuum sintering furnace to obtain the Mo coating. Step 4) Use a mixer to mix silicon powder, sodium fluoride and alumina to obtain a mixed powder, and dry it for later use; Step 5) Pour the dried mixed powder from Step 4) into a crucible of appropriate size and spread it evenly. Place the niobium-tungsten alloy with Mo coating obtained in Step 3) into the crucible, then pour the remaining mixed powder into the crucible and spread it evenly. Seal the crucible lid. Step 6) Place the sealed crucible from step 5) into a high-temperature tubular sintering furnace for silicon infiltration treatment, and protect it with an argon atmosphere to obtain a molybdenum disilicide (MoSi2) coating.

2. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In step 1), the parameters for remelting the sample surface are laser power of 150-180W and scanning speed of 400-600 mm / s.

3. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In step 2), the particle size distribution of the Mo powder is 1–20 μm.

4. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In step 2), the ratio of molybdenum powder to anhydrous ethanol is 1.0:0.5-1 (wt.%), and the polyvinyl butyral is 0.8-1.3 wt.% of the total slurry.

5. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In step 2), the ball-to-material ratio is 10:1, the rotation speed is 300 r / min, and the mixing time of the ball mill is 12-15 h.

6. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In step 3), natural drying takes 1.5-2.5 hours, followed by vacuum drying at 80°C for 1.5-2.5 hours.

7. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In step 3), during sintering, the temperature is increased from room temperature to 800-1000℃ at a heating rate of 5℃ / min, held for 0.5-1.5h, and then increased from 800℃ to sintering temperature of 1500-1550℃ at a heating rate of 3℃ / min, held for 1.5-2.5h.

8. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In the mixed powder described in step 4), silicon powder: 30-40 wt.%, sodium fluoride: 2-5 wt.%, and the remainder is alumina.

9. The method for preparing a 3D-printed niobium-tungsten alloy high-temperature oxidation resistant coating according to claim 1, characterized in that, In step 4), the ball-to-material ratio is 1:5, the rotation speed is 60 r / min, and the ball milling time is 4.5-5.5 h; the drying is carried out in a constant temperature vacuum drying oven at 80℃ for 1.5-2.5 h.

10. The method for preparing a high-temperature oxidation-resistant coating for 3D-printed niobium-tungsten alloy according to claim 1, characterized in that, In step 6), during sintering, the temperature is increased from room temperature to 800°C at a heating rate of 5°C / min, and then increased from 800°C to the sintering temperature of 1100°C to 1200°C at a heating rate of 3°C / min and held at that temperature.

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