A method for preparing a MoSi2 coating on the surface of a niobium alloy by a two-step process

Abstract

The present application relates to the technical field of antioxidant coating, and particularly relates to a method for preparing MoSi2 coating on the surface of niobium alloy through a two-step method. The present application first deposits a dense Mo layer on the surface of niobium alloy by arc ion plating, and then prepares MoSi2 coating on the surface of the Mo layer by embedding silicon, and the "tough Mo layer + antioxidant MoSi2 outer layer" system is constructed by adjusting the process parameters of arc ion plating and embedding. The Mo layer has good mutual solubility with the niobium alloy substrate and strong interface bonding force, the dense Mo layer simultaneously blocks the diffusion of Si inward and Nb outward as a diffusion barrier layer, and the tough Mo layer can reduce the thermal stress caused by the mismatch of the thermal expansion coefficients of MoSi2 and the niobium alloy substrate in the thermal cycle process, thereby avoiding the peeling and failure of the coating. The coating preparation process of the present application is simple and controllable, the coating is dense and continuous, and has no obvious defects, and the high-temperature oxidation resistance of the niobium alloy can be improved.

Description

Technical Field

[0001] This invention relates to the field of antioxidant coating technology, and more particularly to a two-step method for preparing a MoSi2 coating on the surface of a niobium alloy. Background Technology

[0002] In cutting-edge fields such as aerospace, propulsion systems, and nuclear energy, the operating temperature limits of materials directly determine the performance limits of equipment, such as engine thrust-to-weight ratio, flight speed, and energy efficiency.

[0003] Nickel-based / cobalt-based superalloys are currently mature and widely used, but they are approaching their melting point limits, with operating temperatures generally below 1100℃. When the operating temperature exceeds 1100℃, intermetallic compounds (such as TiAl and NiAl) exhibit poor toughness; ceramic matrix composites (such as C / SiC and SiC / SiC) are expensive and have poor environmental stability; and tungsten-based alloys have high density. Niobium-based alloys, with their high melting point, moderate density, good high-temperature specific strength, and excellent processing performance, are currently the most promising candidates for engineering applications, and have broad development prospects in next-generation supersonic cruise vehicles, space shuttle vehicles, and high-performance rocket engines.

[0004] However, niobium-based alloys have extremely poor high-temperature oxidation resistance. In air, they begin to undergo "pest" oxidation (i.e., powdering oxidation) at around 600°C, forming porous, loose, and volatile Nb2O5 oxides. These oxides fail within minutes to hours in high-temperature environments, failing to meet the operational requirements of components such as aerospace engines, which can operate for hundreds or even thousands of hours. Silicide coatings, due to their ability to form a "self-healing SiO2 glass protective film," have become the best choice.

[0005] Embedding silicon, as a chemical vapor deposition (CVD) process, offers excellent coverage, produces dense coatings, and is simple to execute, enabling the fabrication of strong, uniform protective coatings for complex-shaped components. Directly embedding silicon onto niobium alloys results in a silicide layer primarily composed of NbSi2. While this layer offers good oxidation resistance, it is also brittle, and the coefficient of thermal expansion of NbSi2 (approximately 10.5 × 10⁻⁶) is high. -6 / K) and the coefficient of thermal expansion of the niobium alloy matrix (approximately 7-8×10) -6 The difference in thermal expansion coefficient ( / K) is significant, making it prone to cracking during thermal cycling. MoSi2 has a thermal expansion coefficient of approximately 8.5 × 10⁻⁶. -6 Molybdenum (Mo) coatings are similar to niobium alloys and help reduce interfacial thermal stress, making them the most commonly used coatings currently available. Therefore, a molybdenum layer needs to be pre-deposited on the surface of niobium-based alloys before silicon embedding. A dense Mo layer effectively inhibits outward diffusion from the niobium alloy matrix and inward diffusion of oxygen, and also exhibits good chemical compatibility with the subsequently formed MoSi2.

[0006] Methods for depositing Mo layers on niobium-based alloys mainly include physical vapor deposition (PVD), chemical vapor deposition (CVD), electroplating, melt infiltration, and slurry sintering. Among these, CVD requires handling corrosive and toxic exhaust gases; melt infiltration involves extremely high process temperatures (exceeding the melting point of molybdenum, 2610℃), affecting the properties of the niobium alloy matrix and making process control difficult; slurry sintering results in low density and poor interfacial bonding of the sintered Mo layer. Therefore, PVD is currently the most widely used method. Magnetron sputtering, with its low deposition temperature, is also commonly used. However, magnetron sputtering has low deposition efficiency and is not suitable for depositing thicker Mo layers. Furthermore, the Mo layer deposited by magnetron sputtering has low density, and its adhesion to the substrate needs improvement. Summary of the Invention

[0007] In view of this, the object of the present invention is to provide a two-step method for preparing a MoSi2 coating on the surface of a niobium alloy. The present invention improves the interfacial adhesion between the Mo layer and the substrate, and also improves the density of the Mo layer.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a two-step method for preparing a MoSi2 coating on a niobium alloy surface, comprising the following steps: A Mo layer was deposited on the surface of a niobium alloy substrate using arc ion plating to obtain a substrate with a Mo layer deposited on its surface. The conditions for depositing the Mo layer included: using a molybdenum target as the cathode ionization source, introducing argon gas into the vacuum chamber to adjust the vacuum level to 2~5 Pa, using an arc current of 80~160 A, using a substrate pulse bias voltage of -50 V to -200 V, and using an air-pressure ratio of 20~50%. The substrate with the Mo layer deposited on its surface is embedded and infiltrated with silicon to obtain a MoSi2 coating, the bottom of which is a remaining Mo layer; the thickness of the remaining Mo layer is 2~15μm.

[0009] Preferably, by mass percentage, the infiltrating agent used for embedding Si comprises 20-40% silicon powder, 2-5% activator, 0-1% B powder, and the balance Al2O3.

[0010] Preferably, the activator includes NaF or NH4F.

[0011] Preferably, the temperature for embedding and infiltrating Si is 1000~1300℃.

[0012] Preferably, the heat preservation time for the Si embedding and infiltration is 1 to 5 hours.

[0013] Preferably, the rate of heating to the temperature of the embedded Si is ≤5℃ / min.

[0014] Preferably, before depositing the Mo layer, the niobium alloy substrate is subjected to glow discharge cleaning and arc cleaning sequentially using arc ion plating. The glow discharge cleaning conditions include: argon gas is introduced into the vacuum chamber to adjust the vacuum level to 2~5 Pa, the substrate pulse bias voltage is -50V to -200V, the air-pressure ratio is 20~50%, and the cleaning time is 5 min. The arc cleaning is performed while keeping the glow discharge cleaning conditions unchanged, with arc current ignition and an arc current of 80~160A, and the arc cleaning time is 5 min.

[0015] Preferably, before the glow discharge cleaning, the process further includes pretreatment of the niobium alloy substrate; the pretreatment includes sequentially grinding, sandblasting, washing and drying the niobium alloy substrate.

[0016] Preferably, the thickness of the Mo layer deposited on the niobium alloy substrate surface is 70~75μm.

[0017] This invention deposits a Mo layer on the surface of a niobium alloy using arc ion plating. This layer is dense and continuous, exhibiting high bonding strength with the substrate alloy and a defect-free interface. Subsequently, a continuous and dense MoSi2 layer is obtained through silicon infiltration. By controlling process parameters, a coating system of "tough Mo layer + anti-oxidation MoSi2 outer layer" is constructed. The Mo layer exhibits good miscibility with the niobium alloy substrate, strong interfacial bonding, and good toughness, making it insensitive to cracks. This prevents the outer MoSi2 layer from accidentally generating microcracks that propagate into the substrate. Furthermore, during thermal shock and thermal cycling, it can absorb thermal stress caused by the mismatch in thermal expansion coefficients through its own plastic deformation, extending the sample's lifespan under thermal shock and thermal cycling conditions. Simultaneously, the dense Mo layer effectively blocks the inward diffusion of Si and the outward diffusion from the niobium alloy substrate, preventing the formation of brittle Nb5Si3. The overall process of this invention is simple and highly efficient. Subsequent modification of the infiltrator formulation can further enhance the coating, indicating broad prospects for engineering applications. Attached Figure Description

[0018] Figure 1 This is a surface morphology image of the Mo layer deposited by arc ion plating in Example 1; Figure 2 This is a cross-sectional view of the Mo layer deposited by arc ion plating in Example 1; Figure 3 This is a cross-sectional view of the embedded Mo-MoSi2 coating in Example 1. Figure 4 This is a cross-sectional view of the embedded coating in Comparative Example 1. Figure 5 A cross-sectional view of the MoSi2 coating prepared by embedding and infiltrating after the Mo layer is prepared by slurry sintering. Detailed Implementation

[0019] This invention provides a two-step method for preparing a MoSi2 coating on a niobium alloy surface, comprising the following steps: A Mo layer was deposited on the surface of a niobium alloy substrate using arc ion plating to obtain a substrate with a Mo layer deposited on its surface. The conditions for depositing the Mo layer included: using a molybdenum target as the cathode ionization source, introducing argon gas into the vacuum chamber to adjust the vacuum level to 2~5 Pa, using an arc current of 80~160 A, using a substrate pulse bias voltage of -50 V to -200 V, and using an air-pressure ratio of 20~50%. The substrate with the Mo layer deposited on its surface is embedded and infiltrated with silicon to obtain a MoSi2 coating, the bottom of which is the remaining Mo layer.

[0020] In this invention, unless otherwise specified, all raw materials and equipment used are commercially available products well known in the art.

[0021] This invention utilizes arc ion plating to deposit a Mo layer on the surface of a niobium alloy substrate, thereby obtaining a substrate with a Mo layer deposited on its surface.

[0022] Before placing the niobium alloy substrate in the arc ion plating apparatus, the present invention preferably pre-treats the niobium alloy substrate; the pre-treatment preferably includes: sequentially grinding, sandblasting, washing and drying the niobium alloy substrate.

[0023] In this invention, the polishing is preferably done by polishing the substrate surface with 180-grit wet sandpaper and then chamfering all six sides; the sandblasting is preferably done by wet sandblasting with 220-grit white corundum; the washing is preferably done by ultrasonic cleaning with acetone, deionized water, and anhydrous ethanol for 30 minutes in sequence. In this invention, the drying temperature is preferably 100°C, and the drying time is preferably 1 hour. This invention removes contaminants from the surface of the niobium alloy substrate through pretreatment.

[0024] After completing the pretreatment, the present invention places the niobium alloy substrate in an arc ion plating apparatus.

[0025] Before depositing the Mo layer, the present invention preferably first performs glow discharge cleaning and arc cleaning on the niobium alloy substrate by arc ion plating. The preferred conditions for glow discharge cleaning include: argon gas is introduced into the vacuum chamber to adjust the vacuum level to 2~5 Pa, the substrate pulse bias voltage is -50V to -200V, the air-pressure ratio is 20~50%, and the cleaning time is 5 min. The arc cleaning is performed by starting the arc current while keeping the glow discharge cleaning conditions unchanged. The arc current is 80~160A, and the arc cleaning time is 5 min.

[0026] In an embodiment of the present invention, a niobium alloy substrate is suspended in a cavity, and the vacuum level inside the cavity reaches 3×10⁻⁶. -2At a pressure of 2-5 Pa, Ar gas is introduced; after the argon gas pressure reaches 2-5 Pa and the reading stabilizes, a pulsed bias voltage with an air pressure ratio of 20-50% is applied to the substrate, and glow discharge cleaning is performed for 5 minutes; then, the arc current is activated, and the arc current is adjusted to 80-160 A, and the substrate is arc-cleaned for 5 minutes. In specific embodiments, the air pressure ratio of the pulsed bias voltage can be 20%, 30%, 40%, or 50%; the pulsed bias voltage of the substrate during glow discharge cleaning can be -50, -100, -150, or -200 V; and the arc current for arc cleaning can be 80, 90, 100, 120, 140, or 160 A. This invention further removes contaminants adhering to the substrate surface through glow discharge cleaning and arc cleaning.

[0027] After the arc cleaning is completed and the arc stabilizes, the present invention begins to deposit a Mo layer on the surface of the niobium alloy substrate.

[0028] In this invention, the conditions for depositing the Mo layer include: using a molybdenum target as the cathode ionization source, introducing argon gas into the vacuum chamber to adjust the vacuum level to 2~5 Pa, the arc current to 80~160 A, the substrate pulse bias voltage to -50 V to -200 V, and the air-pressure ratio to 20~50%.

[0029] In a specific embodiment, the vacuum chamber is purged with argon gas, and the vacuum level can be adjusted to 2, 3, 4, or 5 Pa. The arc current can be 80, 90, 100, 120, 140, or 160 A, the substrate pulse bias voltage can be -50, -100, -150, or -200 V, and the air-pressure ratio can be 20%, 30%, 40%, or 50%. In this invention, the deposition time of the Mo layer is preferably 2-5 hours, and in a specific embodiment, it can be 2, 3, 4, or 5 hours. In this invention, the thickness of the Mo layer is preferably 70-75 μm.

[0030] This invention utilizes arc ion plating to deposit a Mo layer and controls its deposition conditions, resulting in a Mo layer with higher purity, stronger adhesion to the substrate, and better density compared to other methods. The dense Mo layer can act as a diffusion barrier layer, simultaneously blocking the inward diffusion of Si and the outward diffusion of Nb. At the same time, the tough Mo layer can reduce the thermal stress caused by the mismatch in the coefficients of thermal expansion between MoSi2 and the niobium alloy substrate during thermal cycling, thus preventing coating detachment and failure.

[0031] After obtaining a substrate with a Mo layer deposited on its surface, the present invention embeds and infiltrates silicon into the substrate with the Mo layer deposited on its surface to obtain a MoSi2 coating, wherein the bottom of the MoSi2 coating is the remaining Mo layer.

[0032] In this invention, the infiltrating agent used for embedding Si preferably comprises 20-40% silicon powder, 2-5% activator, 0-1% boron powder, and the balance Al2O3, by mass percentage. Specifically, the silicon powder content in the infiltrating agent can be 20%, 24%, 28%, 30%, 34%, 38%, or 40%; the activator content can be 2%, 2.5%, 3%, 4%, or 5%; and the boron powder content can be 0%, 0.2%, 0.4%, 0.6%, 0.8%, or 1%. Preferably, the activator comprises NaF or NH4F, more preferably NaF.

[0033] In this invention, the preparation method of the infiltrator preferably includes the following steps: first, vacuum drying of silicon powder, B powder, and Al2O3 powder; then, weighing silicon powder, activator, B powder, and Al2O3 according to the mass ratio and ball milling to obtain the infiltrator. In this invention, the ball milling speed is preferably 100 r / min, and the ball milling time is preferably 2 h. This invention uses ball milling to ensure uniform mixing of the components. In this invention, the vacuum drying temperature is preferably 100℃, and the vacuum drying time is preferably 10 h.

[0034] The present invention does not have special requirements for the specific operation of embedding and infiltrating Si; any operation well known in the art can be used. Specifically, the substrate with the Mo layer deposited on its surface and the infiltrating agent are placed into a crucible and compacted to ensure that the substrate with the Mo layer deposited on its surface is surrounded by the infiltrating agent. Then, the crucible is sealed and placed in a sintering furnace for embedding and infiltrating Si. The present invention preferably uses a sealing putty to seal the crucible, and then places it in the air for more than 8 hours to allow the sealing putty to cure.

[0035] In this invention, the Si embedding and infiltration is preferably carried out under argon protection. The Si embedding and infiltration temperature is preferably 1000~1300℃, and in specific embodiments it can be 1000, 1100, 1200 or 1300℃; the heating rate to the Si embedding and infiltration temperature is preferably ≤5℃ / min. The Si embedding and infiltration holding time is preferably 1~5h, and in specific embodiments it can be 1, 2, 3, 4 or 5h.

[0036] After the heat preservation is completed, the present invention preferably cools down with the furnace, and the cooling rate preferably does not exceed 2℃ / min. After cooling to below 100℃, the argon gas is turned off, the product is taken out and ultrasonically cleaned with anhydrous ethanol to remove the seepage agent, and the MoSi2 coating is obtained.

[0037] In this invention, the bottom of the MoSi2 coating is a residual Mo layer; the thickness of the MoSi2 coating is not specifically limited, as long as the thickness of the residual Mo layer is 2~15μm. In specific embodiments, the thickness of the residual Mo layer can be 2, 5, 7, 10, 12 or 15μm.

[0038] This invention significantly improves the high-temperature oxidation resistance of niobium alloys by constructing a "tough Mo layer + oxidation-resistant MoSi2 outer layer". The preparation method of this invention is simple and controllable, and the coating is dense, continuous, and free of obvious defects.

[0039] The following detailed description, in conjunction with embodiments, illustrates the method for preparing a MoSi2 coating on a niobium alloy surface using a two-step approach provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0040] Example 1 ① Substrate pretreatment: Grind the substrate surface with 180-grit wet sandpaper and chamfer all six sides. Perform wet sandblasting with 220-grit white corundum. Then, ultrasonically clean with acetone, deionized water, and anhydrous ethanol for 30 minutes in sequence. Dry in a drying oven at 100℃ for 1 hour for later use.

[0041] ② Arc ion plating deposition of Mo layer: After surface treatment, the sample is suspended in the cavity, and when the vacuum degree in the cavity reaches 3×10 -2 At Pa, Ar gas was introduced. After the argon gas pressure reached 4 Pa ​​and the reading stabilized, a pulse bias voltage of -100V with an air pressure ratio of 30% was applied to the substrate. Glow current cleaning was performed for 5 min. Then, the arc current was turned on to ignite the arc and adjusted to 140A. The substrate was then cleaned with arc light for 5 min to further remove contaminants attached to the substrate surface. After the arc light stabilized, deposition was performed for 5 h. After deposition, the cavity was opened and the sample was taken out.

[0042] ③ Embedding and Infiltration: 34% Si-1% B-2.5% NaF-62.5% Al2O3 by mass percentage was selected as the infiltration agent. Si powder, B powder and Al2O3 powder were dried in a vacuum drying oven at 100℃ for 10 hours in advance. The ingredients were weighed according to the proportion using a high-precision balance to prepare the infiltration agent. The prepared infiltration agent was slowly ball-milled at 100r / min for 2 hours to ensure uniform mixing. The deposited Mo layer sample and the infiltration agent were placed into a corundum crucible and gently compacted to ensure that the sample was filled with infiltration agent. The crucible was sealed with sealing putty and then left in the air for more than 8 hours to allow the sealing putty to cure.

[0043] ④ Reaction sintering: Place the sealed crucible in a vacuum tube furnace, evacuate and fill with argon gas, repeating the above process twice. Set the tube furnace heating temperature to 1200℃ and hold for 5 hours. The heating rate of the tube furnace should not exceed 5℃ / min, and the cooling rate should not exceed 2℃ / min. Argon gas protection should be maintained throughout the process. After the tube furnace cools down to below 100℃, turn off the argon gas, remove the sample, and ultrasonically clean it with anhydrous ethanol for 30 minutes to remove the outer layer of adhering permeating agent.

[0044] Figure 1 This is a surface morphology image of the Mo layer deposited by arc ion plating in Example 1; Figure 2This is a cross-sectional view of the Mo layer deposited by arc ion plating in Example 1; Figure 3 This is a cross-sectional view of the embedded Mo-MoSi2 coating after infiltration. Figures 1-3 It can be seen that the arc ion plating deposits a Mo layer of about 72 μm, and embeds and infiltrates Si to form a dense MoSi2 layer of about 69 μm. There are some Mo / Mo3Si and small pores inside the coating. At the bottom, there is a remaining Mo5Si3 and a dense Mo layer of about 3 μm. The interfacial bonding between the layers is good.

[0045] Example 2 ① Substrate pretreatment: Grind the substrate surface with 180-grit wet sandpaper and chamfer all six sides. Perform wet sandblasting with 220-grit white corundum. Then, ultrasonically clean with acetone, deionized water, and anhydrous ethanol for 30 minutes in sequence. Dry in a drying oven at 100℃ for 1 hour for later use.

[0046] ② Arc ion plating deposition of Mo layer: After surface treatment, the sample is suspended in the cavity, and when the vacuum degree in the cavity reaches 3×10 -2 At Pa, Ar gas was introduced. After the argon gas pressure reached 4 Pa ​​and the reading stabilized, a pulse bias voltage of -100V with an air pressure ratio of 30% was applied to the substrate. Glow current cleaning was performed for 5 min. Then, the arc current was turned on to ignite the arc and adjusted to 140A. The substrate was then cleaned with arc light for 5 min to further remove contaminants attached to the substrate surface. After the arc light stabilized, deposition was performed for 5 h. After deposition, the cavity was opened and the sample was taken out.

[0047] ③ Embedding and Infiltration: Select 34% Si-1% B-5% NaF-60% Al2O3 by mass percentage as infiltration agent. Si powder, B powder and Al2O3 powder are dried in a vacuum drying oven at 100℃ for 10 hours in advance. Weigh each ingredient according to the proportion using a high-precision balance to prepare the infiltration agent. Use a planetary ball mill to slowly ball mill the prepared infiltration agent at 100r / min for 5 hours to make the infiltration agent uniformly mixed. Put the deposited Mo layer sample and the infiltration agent into a corundum crucible and gently compact it to ensure that the sample is filled with infiltration agent. Seal the crucible with sealing putty and then leave it in the air for more than 8 hours to allow the sealing putty to solidify. ④ Reaction sintering: Place the sealed crucible in a vacuum tube furnace, evacuate and fill with argon gas, repeating the above process twice. Set the tube furnace heating temperature to 1200℃ and hold for 3 hours. The heating rate of the tube furnace should not exceed 5℃ / min, and the cooling rate should not exceed 2℃ / min. Argon gas protection should be maintained throughout the process. After the tube furnace cools down to below 100℃, turn off the argon gas, remove the sample, and ultrasonically clean it with anhydrous ethanol for 30 minutes to remove the outer layer of adhering permeating agent.

[0048] The results showed that the arc ion plating deposited a Mo layer of about 72 μm, and the embedded Si infiltration generated a dense MoSi2 layer of about 60 μm. The internal Mo / Mo3Si and small pores were significantly reduced, and about 12 μm of Mo5Si3 and a dense Mo layer remained at the bottom. The interfacial bonding between the layers was good.

[0049] Comparative Example 1 ① Substrate pretreatment: Grind the substrate surface with 180-grit wet sandpaper and chamfer all six sides. Perform wet sandblasting with 220-grit white corundum. Then, ultrasonically clean with acetone, deionized water, and anhydrous ethanol for 30 minutes in sequence. Dry in a drying oven at 100℃ for 1 hour for later use.

[0050] ② Arc ion plating deposition of Mo layer: After surface treatment, the sample is suspended in the cavity, and when the vacuum degree in the cavity reaches 3×10 -2 At Pa, Ar gas was introduced. After the argon gas pressure reached 4 Pa ​​and the reading stabilized, a pulse bias voltage of -100V with an air pressure ratio of 30% was applied to the substrate. Glow current cleaning was performed for 5 min. Then, the arc current was turned on to ignite the arc, and the arc current was adjusted to 120A. The substrate was then cleaned with arc light for 5 min to further remove contaminants attached to the substrate surface. After the arc light stabilized, deposition was performed for 5 h. After deposition, the cavity was opened and the sample was taken out.

[0051] ③ Embedding and Infiltration: 34% Si-1% B-2.5% NaF-62.5% Al2O3 by mass percentage was selected as the infiltration agent. Si powder, B powder and Al2O3 powder were dried in a vacuum drying oven at 100℃ for 10 hours in advance. The ingredients were weighed according to the proportion using a high-precision balance to prepare the infiltration agent. The prepared infiltration agent was slowly ball-milled at 100r / min for 2 hours to ensure uniform mixing. The deposited Mo layer sample and the infiltration agent were placed into a corundum crucible and gently compacted to ensure that the sample was filled with infiltration agent. The crucible was sealed with sealing putty and then left in the air for more than 8 hours to allow the sealing putty to cure.

[0052] ④ Reaction sintering: Place the sealed crucible in a vacuum tube furnace, evacuate and fill with argon gas, repeating the above process twice. Set the tube furnace heating temperature to 1200℃ and hold for 5 hours. The heating rate of the tube furnace should not exceed 5℃ / min, and the cooling rate should not exceed 2℃ / min. Argon gas protection should be maintained throughout the process. After the tube furnace cools down to below 100℃, turn off the argon gas, remove the sample, and ultrasonically clean it with anhydrous ethanol for 30 minutes to remove the outer layer of adhering permeating agent.

[0053] Figure 4 The image shows a cross-sectional view of the coating after embedding and infiltration in Comparative Example 1. The results show that the Mo layer deposited by arc ion plating is about 30 μm thick. The embedded and infiltrated Si layer completely covers the Mo layer deposited by arc ion plating (there is no remaining Mo layer), and continues to diffuse inward to form a NbSi2+Nb5Si3 layer of about 20 μm. The interfacial bonding between the MoSi2 and NbSi2 layers is poor.

[0054] Comparative Example 2 ① Substrate pretreatment: Grind the substrate surface with 180-grit wet sandpaper and chamfer all six sides. Perform wet sandblasting with 220-grit white corundum. Then, ultrasonically clean with acetone, deionized water, and anhydrous ethanol for 30 minutes in sequence. Dry in a drying oven at 100℃ for 1 hour for later use.

[0055] ② Arc ion plating deposition of Mo layer: After surface treatment, the sample is suspended in the cavity, and when the vacuum degree in the cavity reaches 3×10 -2 At Pa, Ar gas was introduced. After the argon gas pressure reached 4 Pa ​​and the reading stabilized, a pulse bias voltage of -100V with an air pressure ratio of 30% was applied to the substrate. Glow current cleaning was performed for 5 min. Then, the arc current was turned on to ignite the arc and adjusted to 140A. The substrate was then cleaned with arc light for 5 min to further remove contaminants attached to the substrate surface. After the arc light stabilized, deposition was performed for 2 h. After deposition, the cavity was opened and the sample was taken out.

[0056] ③ Embedding and Infiltration: A mixture of 34.1% Si, 0.9% B, 5% NaF, and 60% Al2O3 by mass percentage was selected as the infiltration agent. Si powder, B powder, and Al2O3 powder were dried in a vacuum drying oven at 100℃ for 10 hours in advance. The ingredients were weighed according to the proportion using a high-precision balance to prepare the infiltration agent. The prepared infiltration agent was slowly ball-milled at 100 r / min for 2 hours to ensure uniform mixing. The deposited Mo layer sample and the infiltration agent were placed into a corundum crucible and gently compacted to ensure that the sample was filled with infiltration agent. The crucible was then sealed with sealing putty and left in the air for more than 8 hours to allow the sealing putty to cure.

[0057] ④ Reaction sintering: Place the sealed crucible in a vacuum tube furnace, evacuate and fill with argon gas, repeating the above process twice. Set the tube furnace heating temperature to 1200℃ and hold for 2 hours. The heating rate of the tube furnace should not exceed 5℃ / min, and the cooling rate should not exceed 2℃ / min. Argon gas protection should be maintained throughout the process. After the tube furnace cools down to below 100℃, turn off the argon gas, remove the sample, and ultrasonically clean it with anhydrous ethanol for 30 minutes to remove the outer layer of adhering permeating agent.

[0058] The results showed that the arc ion plating deposited a Mo layer of about 15 μm, and the embedded Si infiltration formed a dense MoSi2 layer of about 15 μm (with no remaining Mo layer). After that, the silicon continued to diffuse inward and reacted with the niobium alloy substrate to form an NbSi2+Nb5Si3 layer, with poor interfacial adhesion.

[0059] Comparative Example 3 Mo layer preparation by slurry sintering method ① Substrate pretreatment: The substrate surface is sanded with 180-grit wet sandpaper and chamfered on all six sides. It is then wet-blasted with 220-grit white corundum. It is then pickled for 3 minutes in a pickling solution with a ratio of 60 vol.% distilled water, 30 vol.% HNO3, and 10 vol.% HF. After that, it is ultrasonically cleaned with acetone, deionized water, and anhydrous ethanol for 30 minutes in sequence. Finally, it is dried in a drying oven at 100℃ for 1 hour for later use.

[0060] ② Preparation of Mo layer by slurry sintering method: Mo powder was refined by ball milling using an all-around planetary ball mill, a polytetrafluoroethylene ball mill jar, and zirconia balls. Anhydrous ethanol was used as the solvent. The ball mill speed was 300 r / min, the ball-to-powder ratio was 15:1, and the milling time was 8 h. The ball-milled powder was then thoroughly dried. The slurry was prepared by mixing the refined Mo powder with anhydrous ethanol, with 2.0 wt% hydroxypropyl cellulose added as a binder. The slurry was evenly brushed onto the sample surface, rotating the sample during the brushing process to ensure uniform spreading of the slurry on the substrate surface. The sample was then placed in a vacuum drying oven at 100℃ for 1 h for drying, followed by sintering in a tube furnace at 1200℃ under Ar atmosphere for 3 h. The heating rate of the tube furnace did not exceed 5℃ / min, and the cooling rate did not exceed 2℃ / min. After the tube furnace cooled to below 100℃, the argon gas was turned off, the sample was removed, and the surface was gently sanded smooth with 1000-grit wet sandpaper.

[0061] ③ Embedding and Infiltration: Select 34% Si-1% B-5% NaF-60% Al2O3 by mass percentage as infiltration agent. Si powder, B powder and Al2O3 powder are dried in a vacuum drying oven at 100℃ for 10 hours in advance. Weigh each ingredient according to the proportion using a high-precision balance to prepare the infiltration agent. Use a planetary ball mill to slowly ball mill the prepared infiltration agent at 100r / min for 5 hours to make the infiltration agent uniformly mixed. Put the deposited Mo layer sample and the infiltration agent into a corundum crucible and gently compact it to ensure that the sample is filled with infiltration agent. Seal the crucible with sealing putty and then leave it in the air for more than 8 hours to allow the sealing putty to solidify. ④ Reaction sintering: Place the sealed crucible in a vacuum tube furnace, evacuate and fill with argon gas, repeating the above process twice. Set the tube furnace heating temperature to 1200℃ and hold for 5 hours. The heating rate of the tube furnace should not exceed 5℃ / min, and the cooling rate should not exceed 2℃ / min. Argon gas protection should be maintained throughout the process. After the tube furnace cools down to below 100℃, turn off the argon gas, remove the sample, and ultrasonically clean it with anhydrous ethanol for 30 minutes to remove the outer layer of adhering permeating agent.

[0062] Figure 5 The image shows a cross-sectional view of the MoSi2 coating prepared by slurry sintering followed by embedding and infiltrating. The results show that the Mo layer deposited by slurry method is not dense enough. The embedded Si infiltrating generates a MoSi2 layer of about 210 μm, but it is discontinuous inside and has poor interfacial bonding.

[0063] 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 method for preparing a MoSi2 coating on a niobium alloy surface via a two-step process, characterized in that, Includes the following steps: A Mo layer was deposited on the surface of a niobium alloy substrate using arc ion plating to obtain a substrate with a Mo layer deposited on its surface. The conditions for depositing the Mo layer included: using a molybdenum target as the cathode ionization source, introducing argon gas into the vacuum chamber to adjust the vacuum level to 2~5 Pa, using an arc current of 80~160 A, using a substrate pulse bias voltage of -50 V to -200 V, and using an air-pressure ratio of 20~50%. The substrate with the Mo layer deposited on its surface is embedded and infiltrated with silicon to obtain a MoSi2 coating, the bottom of which is a remaining Mo layer; the thickness of the remaining Mo layer is 2~15μm.

2. The method according to claim 1, characterized in that, The infiltrating agent used for embedding Si, by mass percentage, comprises 20-40% silicon powder, 2-5% activator, 0-1% B powder, and the balance Al2O3.

3. The method according to claim 2, characterized in that, The activator includes NaF or NH4F.

4. The method according to claim 1, characterized in that, The temperature for embedding and infiltrating Si is 1000~1300℃.

5. The method according to claim 1 or 4, characterized in that, The heat preservation time for embedding and infiltrating Si is 1~5h.

6. The method according to claim 1 or 4, characterized in that, The rate of heating to the temperature of the embedded Si is ≤5℃ / min.

7. The method according to claim 1, characterized in that, Before depositing the Mo layer, the niobium alloy substrate is subjected to glow discharge cleaning and arc cleaning sequentially using arc ion plating. The glow discharge cleaning conditions include: argon gas is introduced into the vacuum chamber to adjust the vacuum level to 2~5 Pa, the substrate pulse bias voltage is -50V to -200V, the air-pressure ratio is 20~50%, and the cleaning time is 5 min. The arc cleaning is performed while keeping the glow discharge cleaning conditions unchanged, with arc current ignition and an arc current of 80~160A, and the arc cleaning time is 5 min.

8. The method according to claim 7, characterized in that, Before the glow discharge cleaning, the process also includes pretreatment of the niobium alloy substrate; the pretreatment includes sequentially grinding, sandblasting, washing and drying the niobium alloy substrate.

9. The method according to claim 1, characterized in that, The thickness of the Mo layer deposited on the niobium alloy substrate is 70~75μm.

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