A two-step method for preparing TaSi2 coatings using chemical vapor deposition and powder embedding.

Abstract

This invention relates to the field of coating materials technology, and provides a two-step method for preparing TaSi2 coatings using chemical vapor deposition (CVD) and powder embedding. The invention employs CVD to prepare a Ta layer on the surface of an alloy substrate, obtaining an alloy substrate with the Ta layer deposited. The alloy substrate with the Ta layer deposited is then embedded in silicon-containing powder and heat-treated to obtain a TaSi2 coating. The silicon-containing powder comprises the following components by mass fraction: SiC 65-75%, Si 20-30%, and NaF 4-6%. The TaSi2 coating prepared by this invention has a tight bond with the substrate, with no obvious pores or interface cracks. Furthermore, the method is simple to operate, fast to prepare, suitable for complex workpieces, and the coating thickness and uniformity are easily controlled, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of coating materials technology, and in particular to a two-step method for preparing TaSi2 coatings using chemical vapor deposition-powder embedding. Background Technology

[0002] Nb-based alloys are considered highly competitive high-temperature structural materials due to their high melting point, low density, and excellent mechanical properties at high temperatures. However, Nb-based alloys are prone to oxidation at high temperatures, forming loose and easily peeling niobium oxide products. This ultimately leads to a rapid decline in the mechanical properties of components and a significant reduction in service life, severely limiting the large-scale application of Nb-based alloys under high-temperature conditions.

[0003] Currently, the industry mainly addresses the high-temperature oxidation problem of niobium-based alloys through two major technical routes: alloying modification and surface protective coatings. Alloying modification enhances oxidation resistance by doping the matrix with elements such as silicon, aluminum, and hafnium; however, this method disrupts the original microstructure of the niobium-based alloy, leading to a decline in the material's mechanical properties. Surface coating technology, on the other hand, can construct a protective layer on the component surface to block oxygen penetration without damaging the matrix's mechanical properties, achieving a balance between oxidation resistance and mechanical properties. This is the mainstream technical direction for improving high-temperature service stability.

[0004] Refractory metal silicides, such as TaSi2, have become important coating materials for improving the high-temperature protective performance of Nb-based alloys due to their high melting point, low resistivity, and excellent thermal stability. Currently, methods for preparing TaSi2 coatings include plasma spraying, magnetron sputtering, and slurry brushing. However, coatings prepared by plasma spraying and magnetron sputtering exhibit poor adhesion to the substrate and are difficult to apply to complex workpieces. Slurry brushing requires high-temperature firing, resulting in high costs and long processing times. Summary of the Invention

[0005] In view of this, the present invention provides a two-step method for preparing TaSi2 coatings using chemical vapor deposition and powder embedding. The method provided by the present invention is simple to operate, has a fast preparation speed, can be applied to complex workpieces, and produces coatings with good adhesion to the substrate, with easily controllable coating thickness and uniformity.

[0006] To achieve the above-mentioned objectives, the present invention provides the following technical solution: A two-step method for preparing TaSi2 coatings using chemical vapor deposition-powder embedding includes the following steps: A Ta layer was prepared on the surface of an alloy substrate by chemical vapor deposition, resulting in an alloy substrate with a deposited Ta layer. The alloy substrate with the deposited Ta layer is embedded in silicon-containing powder and heat-treated to obtain a TaSi2 coating; the silicon-containing powder comprises the following components by mass fraction: SiC 65~75%, Si 20~30%, NaF 4~6%; the heat treatment temperature is 1000~1100℃.

[0007] Preferably, the chemical vapor deposition method includes: placing a Ta sheet inside a quartz tube in a chlorination chamber, placing an alloy substrate on a sample stage in a deposition chamber, evacuating the chamber and then introducing hydrogen gas, then starting to heat up, and when the temperature reaches 1100~1200℃, introducing chlorine gas into the chlorination chamber, and holding the temperature for 1~2 hours to obtain a Ta layer.

[0008] Preferably, the flow rate of the hydrogen is 0.5~0.8 L / min.

[0009] Preferably, the flow rate of the chlorine gas is 80~100 mL / min.

[0010] Preferably, the thickness of the Ta layer is 45~65μm.

[0011] Preferably, the silicon-containing powder comprises the following components by mass fraction: SiC 70%, Si 25%, NaF 5%.

[0012] Preferably, the heat treatment time is 8 to 11 hours.

[0013] Preferably, the heating rate to the heat treatment temperature is 3~6℃ / min.

[0014] Preferably, the embedding includes: placing the alloy substrate with the deposited Ta layer into an alumina crucible filled with silicon powder, and encapsulating the alumina crucible with alumina adhesive.

[0015] Preferably, before the heat treatment, the packaged sample is dried at a temperature of 100-120°C for 0.5-2 hours.

[0016] This invention provides a two-step method for preparing a TaSi2 coating using chemical vapor deposition (CVD) and powder embedding. The method includes the following steps: preparing a Ta layer on the surface of an alloy substrate using CVD to obtain an alloy substrate with the Ta layer deposited; embedding the Ta-layered alloy substrate in silicon-containing powder and performing heat treatment to obtain a TaSi2 coating; the silicon-containing powder comprises the following components by mass fraction: SiC 65-75%, Si 20-30%, and NaF 4-6%; the heat treatment temperature is 1000-1100℃. This invention first deposits a pure tantalum layer on the surface of the alloy substrate using CVD. During the CVD process, tantalum atoms form chemical bonds with the substrate, significantly improving the bonding strength between the coating and the substrate. In the subsequent powder embedding stage, silicon diffuses into the tantalum layer and undergoes a chemical reaction to generate TaSi2. The overall coating system has a tight interface bond, with no obvious pores or interface cracks inside the coating. It is not prone to peeling or flaking under high-temperature thermal cycling conditions, effectively extending the high-temperature service life of components.

[0017] Furthermore, the present invention can control the thickness and uniformity of the Ta layer by controlling parameters such as gas flow rate and heat preservation time; the second step of powder embedding adopts the method of powder omnidirectionally covering the substrate, the silicon element diffusion reaction is uniform, and the final TaSi2 coating is uniform in thickness and dense in structure, avoiding the problems of uneven coating thickness and many local defects that are easy to occur in processes such as slurry brushing.

[0018] Furthermore, the powder embedding process relies on the full surface contact between the powder and the workpiece to achieve a diffusion reaction, which is not limited by the workpiece structure. It can be used to prepare coatings for alloy components with various complex shapes, solving the problem that processes such as plasma spraying and magnetron sputtering are difficult to apply to complex workpieces.

[0019] In summary, the method provided by this invention is simple to operate, fast to prepare, applicable to complex workpieces, and has good adhesion between the coating and the substrate, and the coating thickness and uniformity are easy to control, thus having broad application prospects. Attached Figure Description

[0020] Figure 1 The image shows the cross-sectional morphology of the TaSi2 coating prepared in Example 1. Figure 2 The image shows the cross-sectional morphology of the TaSi2 coating prepared in Comparative Example 1. Detailed Implementation

[0021] This invention provides a two-step method for preparing TaSi2 coatings using chemical vapor deposition and powder embedding, comprising the following steps: A Ta layer was prepared on the surface of an alloy substrate by chemical vapor deposition, resulting in an alloy substrate with a deposited Ta layer. The alloy substrate with the deposited Ta layer is embedded in silicon-containing powder and heat-treated to obtain a TaSi2 coating; the silicon-containing powder comprises the following components by mass fraction: SiC 65~75%, Si 20~30%, NaF 4~6%; the heat treatment temperature is 1000~1100℃.

[0022] This invention employs chemical vapor deposition (CVD) to prepare a Ta layer on the surface of an alloy substrate, resulting in an alloy substrate with a deposited Ta layer. In this invention, the alloy substrate is preferably an Nb-based alloy, specifically an Nb521 alloy. Before CVD, the alloy substrate is preferably subjected to sequential polishing and ultrasonic cleaning. The polishing is preferably performed using 400#, 800#, and 1200# SiC sandpaper, and the ultrasonic cleaning is preferably performed using ethanol.

[0023] In this invention, the chemical vapor deposition method preferably includes: placing a Ta sheet inside a quartz tube in a chlorination chamber, placing the alloy substrate on a sample stage in the deposition chamber, evacuating the chamber, introducing hydrogen gas, and then heating the chamber. When the temperature reaches 1100-1200°C, chlorine gas is introduced into the chlorination chamber, and the temperature is maintained for 1-2 hours to obtain a Ta layer. The purity of the Ta sheet is preferably above 99.99%. The flow rate of the hydrogen gas is preferably 0.5-0.8 L / min, specifically 0.8 L / min. The flow rate of the chlorine gas is preferably 80-100 mL / min, specifically 100 mL / min. During the chemical vapor deposition process, chlorine gas reacts with tantalum in the chlorination chamber to produce TaCl5 gas. The TaCl5 gas is carried by the gas flow into the deposition chamber and reacts with hydrogen gas to produce Ta and HCl. The HCl evaporates, and Ta nucleates and grows on the metal substrate. The coating and the substrate form chemical bonds, thereby improving the adhesion between the coating and the substrate. In a specific embodiment of the present invention, when the Ta layer reaches the target thickness, the chlorine gas flow is turned off and the heating of the deposition chamber is stopped, thereby precisely controlling the thickness of the coating.

[0024] In this invention, the thickness of the Ta layer is preferably 45 μm to 65 μm.

[0025] After obtaining an alloy substrate with a deposited Ta layer, the present invention embeds the alloy substrate with the deposited Ta layer in silicon-containing powder and performs heat treatment to obtain a TaSi2 coating. In the present invention, the silicon-containing powder comprises the following components by mass fraction: SiC 65~75%, preferably 70%, Si 20~30%, preferably 25%, NaF 4~6%, preferably 5%; the SiC, Si and NaF are all spherical powder materials, and the average particle size of the SiC, Si and NaF is preferably 30~60 μm. The SiC serves as a supporting framework, enabling the uniform dispersion of Si and NaF, resulting in a good overall powder packing morphology. This ensures the workpiece is uniformly coated by the powder from all directions, preventing localized powder agglomeration and guaranteeing a uniform and stable embedding atmosphere. Simultaneously, SiC is chemically stable and does not react with the tantalum layer or substrate at high temperatures, effectively isolating it from air and inhibiting oxidation of the substrate and coating during high-temperature processes. Si is the core silicon source for preparing the TaSi2 coating. Under high-temperature heat treatment conditions, silicon atoms undergo thermal diffusion, continuously penetrating into the Ta layer on the substrate surface and reacting with Ta in a solid-phase chemical reaction, generating the target phase TaSi2 in situ. NaF acts as an activator, enhancing the gas-phase transport capability of silicon, accelerating the diffusion rate of silicon into the Ta layer, and promoting rapid and uniform coating growth.

[0026] In this invention, the embedding preferably includes: placing the alloy substrate with the deposited Ta layer into an alumina crucible filled with silicon powder, and encapsulating the alumina crucible with alumina adhesive; the alumina adhesive is specifically alumina high-temperature adhesive.

[0027] In this invention, before the heat treatment, it is preferable to further dry the packaged sample. The drying temperature is preferably 100~120℃, specifically 100℃, and the drying time is preferably 0.5~2h, specifically 1h. The drying is carried out in a drying oven.

[0028] In this invention, the heat treatment temperature is 1000~1100℃, specifically 1050℃; the heat treatment time is preferably 8~11h, specifically 10h; the heating rate to the heat treatment temperature is preferably 3~6℃ / min, specifically 5℃ / min; the heat treatment is preferably carried out in a tube furnace. During the heat treatment process, silicon-containing powder fully embeds the alloy substrate with a Ta layer deposited on its surface. Si atoms diffuse from the substrate surface inward and chemically bond with the Ta layer to form a TaSi2 coating. Furthermore, since the silicon-containing powder is in omnidirectional contact with the alloy substrate, it is very suitable for coating preparation of complex structure alloy substrates.

[0029] The TaSi2 coating prepared by this invention has a hexagonal crystal structure, space group P6222 (international designation 180), number of molecules per unit cell Z=3, and Pearson notation (PS) hP9.00. Its unit cell parameters are: lattice constants a=b=4.78351Å, c=6.5698Å, cell angles α=β=90.0°, γ=120.0°; the molecular weight of the phase is 237.12, and the unit cell volume is 130.19Å. 3 The theoretically calculated density is 9.073 g / cm³. 3 X-ray powder diffraction analysis showed that its diffraction quality factor F(30) = 131.1 (0.0059,39 / 0), indicating high phase purity and regular crystal structure.

[0030] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0031] In the following examples, the Ta sheets were purchased from Baoji Yusheng Metal Technology Co., Ltd., and the SiC, Si, and NaF were all spherical powders purchased from Shanghai Qizhi New Materials, with an average particle size of 30~60μm.

[0032] Example 1 The Nb521 alloy matrix was cut into Φ8×8mm cylinders using a wire EDM machine, polished with 400#, 800#, and 1200# SiC sandpaper, and ultrasonically cleaned with ethanol.

[0033] A Ta layer was deposited on the alloy substrate using chemical vapor deposition. The specific steps are as follows: 55g of Ta sheet with a purity of 99.99% was placed in the quartz tube of the chlorination chamber, and the alloy substrate was placed on the sample stage of the deposition chamber. Then, a vacuum was drawn, hydrogen gas was introduced, and the temperature was raised at a flow rate of 0.5L / min. When the temperature reached 1100℃, chlorine gas was introduced at a flow rate of 100mL / min. After holding at this temperature for 1 hour, the deposited Ta layer was obtained.

[0034] The alloy substrate with the deposited Ta layer was placed in an alumina crucible filled with silicon powder (spherical powder of 70wt%SiC-25wt%Si-5wt%NaF), sealed with alumina high-temperature adhesive, dried in a drying oven at 100℃ for 1 hour, and then placed in a tube furnace and heated to 1050℃ at a heating rate of 5℃ / min. After holding at this temperature for 10 hours, the TaSi2 coating was obtained.

[0035] Figure 1This is a cross-sectional morphology image of the TaSi2 coating prepared in Example 1. According to... Figure 1 As can be seen, the coating is uniform and there are no cracks. The coating and the substrate are well bonded together, with no holes or contact boundary cracks.

[0036] Comparative Example 1 The other conditions are the same as in Example 1, except that the temperature of the heat treatment after embedding is changed to 1200°C.

[0037] Figure 2 This is a cross-sectional morphology image of the TaSi2 coating prepared in Comparative Example 1. Figure 2 It can be seen that Si diffuses excessively, forming a composite coating of TaSi2, NbSi2, and Nb5Si3, and penetrating cracks appear.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A two-step method for preparing TaSi2 coatings using chemical vapor deposition-powder embedding, characterized in that, Includes the following steps: A Ta layer was prepared on the surface of an alloy substrate by chemical vapor deposition, resulting in an alloy substrate with a deposited Ta layer. The alloy substrate with the deposited Ta layer is embedded in silicon-containing powder and heat-treated to obtain a TaSi2 coating; the silicon-containing powder comprises the following components by mass fraction: SiC 65~75%, Si 20~30%, NaF 4~6%; the heat treatment temperature is 1000~1100℃.

2. The preparation method according to claim 1, characterized in that, The chemical vapor deposition method includes: placing a Ta sheet inside a quartz tube in a chlorination chamber, placing an alloy substrate on a sample stage in the deposition chamber, evacuating the chamber and then introducing hydrogen gas, followed by heating. When the temperature reaches 1100~1200℃, chlorine gas is introduced into the chlorination chamber, and the Ta layer is obtained after holding the temperature for 1~2 hours.

3. The preparation method according to claim 2, characterized in that, The flow rate of the hydrogen is 0.5~0.8 L / min.

4. The preparation method according to claim 2, characterized in that, The flow rate of the chlorine gas is 80~100 mL / min.

5. The preparation method according to claim 1 or 2, characterized in that, The thickness of the Ta layer is 45~65μm.

6. The preparation method according to claim 1, characterized in that, The silicon-containing powder comprises the following components by mass fraction: SiC 70%, Si 25%, NaF 5%.

7. The preparation method according to claim 1, characterized in that, The heat treatment time is 8~11 hours.

8. The preparation method according to claim 1, characterized in that, The heating rate to the heat treatment temperature is 3~6℃ / min.

9. The preparation method according to claim 1, characterized in that, The embedding process includes: placing the alloy substrate with the deposited Ta layer into an alumina crucible filled with silicon powder, and encapsulating the alumina crucible with alumina adhesive.

10. The preparation method according to claim 9, characterized in that, Before the heat treatment, the packaged sample is dried at a temperature of 100-120°C for 0.5-2 hours.

Images