An oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating and its preparation method

Abstract

The application discloses an oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, which is composed of a silicide layer bottom layer with NbSi2 as a main phase and a ceramic layer surface layer with ZrB2 ultra-high-temperature ceramic as a main phase, and provides effective protection for niobium alloy materials under the condition of oxygen thermal erosion at 1000 DEG C to 1700 DEG C; the preparation method of the coating is as follows: raw material powder is made into a composite suspension slurry, and then is prepositioned on the surface of a pretreated niobium alloy; after one-step vacuum reaction sintering, the coating is obtained on the surface of the niobium alloy. The coating has more excellent thermal erosion resistance and thermal shock resistance than the silicide coating, and has a lower oxidation rate than the ultra-high-temperature ceramic coating; the preparation method avoids the problem that the processes such as thermal spraying or electron beam physical vapor deposition are difficult to prepare the coating on the surface of a niobium alloy component with a complex shape, and has higher coating deposition efficiency and lower cost compared with the chemical vapor deposition method.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature protection technology, specifically relating to an oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating and its preparation method. Background Technology

[0002] Niobium alloys possess high melting points, excellent corrosion resistance, and high high-temperature strength, making them important high-temperature structural materials widely used in high-temperature components of propulsion systems for rockets, spacecraft, missiles, and hypersonic vehicles. However, niobium alloys have poor oxidation resistance, undergoing severe oxidation even in oxygen-rich environments far below their service temperatures, limiting their high-temperature applications. There are two main approaches to improving the oxidation resistance of niobium alloys and their alloys: one is alloying, which involves adding elements such as Si, Cr, Al, Hf, V, and Zr to niobium alloys and their alloys to form a protective oxide film on the surface under high-temperature oxidation conditions. However, excessive alloying can significantly reduce the high-temperature mechanical properties of niobium alloys, offering limited improvement in oxidation resistance. The other approach is to coat the surface of niobium alloys with high-temperature anti-oxidation coatings. Currently developed coating types include metallic coatings, silicide coatings, and noble metal coatings, with silicide coatings being the most widely used. Under high-temperature oxidation conditions, the silicide coating generates a SiO2 glass protective film through selective oxidation of Si, providing protection for the substrate and exhibiting good resistance to high-temperature (1000℃~1700℃) oxidation. Moreover, the SiO2 glass film softens at high temperatures and can flow viscously, which can compensate for defects such as cracks and pores formed during the coating preparation or oxidation process, demonstrating good "self-healing" ability.

[0003] However, the service environment of niobium alloy high-temperature components for aerospace vehicles is extremely harsh. The silicide coating on its surface not only needs to withstand strong oxidation, but also often needs to withstand the thermal erosion of high-temperature and high-speed airflow and strong thermal shock. However, the silicide coating on the surface of niobium alloy has significant shortcomings in high-temperature (>1600℃) thermal shock / thermal erosion environments: (1) The protective SiO2 oxide layer formed by the oxidation of the silicide coating softens at temperatures above 1400℃, and its shear resistance is insufficient under thermal shock conditions, resulting in rapid loss and a significant decrease in the coating's protective performance and lifespan; (2) The silicide coating has poor toughness and a large mismatch in thermal expansion coefficient with the refractory alloy matrix, making it prone to cracking under strong thermal shock conditions, leading to rapid coating failure. Traditional methods can effectively improve the oxidation resistance of the silicide coating by adding elements such as Ce, W, and Ge. However, this method has limited improvement on the thermal erosion resistance and thermal shock resistance of the silicide coating.

[0004] Therefore, modifying the silicide coating, controlling the microstructure and chemical composition of the sintered silicide coating, and thus regulating the microstructure and phase composition of the oxide film on the surface of the silicide coating, is the key to improving the protective performance of silicide high-temperature protective coatings and the service performance of niobium alloy high-temperature components. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing an oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating. This coating forms a composite oxide film with a "sand-stone" concrete-like structure in a high-temperature oxidizing environment, effectively resisting the erosion of high-temperature, high-speed airflow and exhibiting excellent oxygen barrier properties. This allows the coating to possess both the oxidation resistance of silicide coatings and the excellent thermal erosion resistance of ultra-high-temperature ceramics, resulting in superior thermal shock resistance compared to traditional silicide coatings. It can provide effective protection for niobium alloy materials under aerobic thermal erosion conditions at 1000℃~1700℃.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: an oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, characterized in that the coating consists of a bottom layer and a top layer, the bottom layer being a silicide layer with NbSi2 as the main phase, and the top layer being a ceramic layer with ZrB2 ultra-high temperature ceramic as the main phase; the thickness of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 40μm to 200μm, providing effective protection for niobium alloy materials under oxygen thermal erosion conditions of 1000℃ to 1700℃.

[0007] Silicide coatings exhibit good isothermal oxidation resistance due to their ability to form an amorphous SiO2 protective film in high-temperature and oxygen-rich environments. However, this protective amorphous SiO2 film is prone to rapid loss under high-temperature thermal erosion conditions, resulting in insufficient thermal erosion resistance. Ultra-high temperature ceramic layers, represented by ZrB2, exhibit good thermal erosion resistance because they can form a composite oxide film with high-melting-point oxides as the "skeleton" and amorphous B2O3 as the filler. However, due to the very low viscosity of B2O3 under ultra-high temperature conditions, its oxygen barrier capacity is insufficient, and it cannot effectively reduce the oxidation rate of niobium alloys. The NbSi2 / ZrB2 layered composite high-temperature protective coating of this invention can form a composite oxide film under high-temperature and oxygen-containing conditions. This film consists of a high-melting-point oxide or silicate particle "skeleton" and a borosilicate glass film as a filler. Because this oxide film has a structure similar to "sand-stone" concrete, it can effectively resist the erosion of high-temperature, high-speed airflow. Furthermore, since the viscosity of borosilicate glass is significantly higher than that of amorphous B2O3, the resulting oxide film has excellent oxygen barrier properties, significantly improving the high-temperature oxidation resistance of the niobium alloy substrate. Simultaneously, because the coefficient of thermal expansion of the ZrB2 ceramic particles in the coating is between that of the niobium alloy substrate and the silicide coating, this NbSi2 / ZrB2 layered composite coating exhibits superior thermal shock resistance compared to the silicide coating. In addition, the coating thickness ensures high-temperature protective performance while preventing cracking and peeling under internal or thermal stress conditions. In summary, these superior properties enable the coating provided by this invention to provide effective protection for niobium alloy materials under oxygen-containing thermal erosion conditions at 1000℃ to 1700℃.

[0008] The aforementioned oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is characterized in that the silicide layer with NbSi2 as the main phase is a medium-entropy ceramic, and the phase is (Nb,Cr,Ti)Si2, (Nb,Mo,Zr)Si2 or (Nb,Cr,Ti,Zr)Si2, and the atomic percentage content of Si element in the silicide layer with NbSi2 as the main phase is 60% to 70%, and the atomic percentage content of Nb element is 22% to 30%. The oxidation resistance of the NbSi2 / ZrB2 layered composite high-temperature protective coating of the present invention is mainly borne by the silicide layer with NbSi2 as the main phase. The oxidation resistance of the silicide coating originates from the amorphous SiO2 protective film generated by the selective oxidation of Si elements in the coating under high-temperature oxidation conditions. However, as Si elements are consumed, the relative content of Nb elements in the coating will continue to rise. Once the content of Si elements is lower than the critical content for selective oxidation, Nb elements begin to oxidize to form Nb2O5. Since Nb2O5 has a high growth rate and is loose and porous, its formation will destroy the integrity of the oxide film, thereby reducing the high-temperature protection effect of the coating. Therefore, the present invention introduces Ti, Cr, Mo, and Zr metal elements into the bottom silicide coating to form a (Nb,Cr,Ti)Si2, (Nb,Mo,Zr)Si2, or (Nb,Cr,Ti,Zr)Si2 medium-entropy ceramic phase, which effectively improves the oxidation resistance of the bottom layer of the silicide layer. Meanwhile, since the oxidation rate of ultra-high temperature ceramics is faster than that of silicides, the present invention can effectively reduce the high-temperature oxidation rate of the coating by introducing an appropriate NbSi2 phase into the ceramic surface layer.

[0009] The aforementioned oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is characterized in that the ceramic layer, with ZrB2 ultra-high temperature ceramic as the main phase, is composed of ZrB2, NbSi2, and other silicide phases, wherein the mass percentage content of Zr element is not less than 70%. The thermal erosion resistance of the NbSi2 / ZrB2 layered composite high-temperature protective coating provided by this invention is mainly borne by the ceramic surface layer with ZrB2 as the main phase. Therefore, this invention ensures the content of the ZrB2 main phase by limiting the mass percentage content of Zr element to not less than 70%, thereby guaranteeing the thermal erosion resistance of the coating.

[0010] The aforementioned oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is characterized in that the coating is applied to the surface of a C103, Nb521, or Nb6621 niobium alloy. In the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of the present invention, the niobium element in the silicide underlayer with NbSi2 as the main phase is derived from a niobium alloy. The preferred niobium alloy ensures the smooth formation of the coating, and simultaneously, the mechanical properties of the preferred niobium alloy as a substrate do not significantly decrease during the vacuum high-temperature sintering process in preparing the NbSi2 / ZrB2 layered composite high-temperature protective coating.

[0011] Meanwhile, the present invention also discloses a method for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating as described above, characterized in that it is prepared by a one-step vacuum reaction sintering method.

[0012] The above method is characterized by comprising the following steps:

[0013] Step 1: Surface pretreatment of niobium alloy: grinding, sandblasting, pickling and degreasing are performed in sequence;

[0014] Step 2: The raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, namely Si powder, metal element powder, ZrB2 ceramic particles and dispersant, are placed in a ball mill for high-energy ball milling to obtain a composite suspension slurry.

[0015] Step 3: The composite suspension slurry obtained in Step 2 is pre-placed on the surface of the niobium alloy that underwent surface pretreatment in Step 1. After drying, a pre-placed layer is formed on the surface of the niobium alloy. Then, the niobium alloy with the pre-placed layer is placed in a vacuum sintering furnace at a vacuum degree of 1.0 × 10⁻⁶. -3 Pa ~ 4.0 × 10 -2 Under the condition of Pa, high-temperature melting was carried out, and after furnace cooling, a NbSi2 / ZrB2 layered composite high-temperature protective coating was prepared on the surface of the niobium alloy.

[0016] This invention prepares a composite suspension slurry from Si powder, metal element powder, ZrB2 ceramic particles, and a dispersant to form an oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating. This slurry is then pre-placed on a pretreated niobium alloy surface and subjected to drying and a one-step vacuum reaction sintering method to obtain the NbSi2 / ZrB2 layered composite high-temperature protective coating. This invention uses a one-step vacuum reaction sintering method to prepare the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating on the niobium alloy surface. The interface formed between the silicide underlayer and the ultra-high temperature ceramic surface layer is an in-situ self-generated interface, resulting in good adhesion between the two layers and effectively preventing interface cracking and peeling of the coating under thermal erosion or strong thermal shock conditions. Furthermore, the one-step sintering method avoids the adverse effects of multiple melting processes on the microstructure and mechanical properties of the niobium alloy matrix. Meanwhile, since ZrB2 is an ultra-high temperature ceramic with a very high sintering temperature, this invention utilizes the ceramic phase formed by the chemical reaction of silicified material slurry under vacuum and high temperature conditions to bond ZrB2 ultra-high temperature ceramic, thus avoiding the adverse effects of excessively high sintering temperature on the niobium alloy substrate.

[0017] The above method is characterized in that, in step one, the sandblasting process uses corundum sand or zirconium oxide sand, the sandblasting pressure is 0.2 MPa to 0.6 MPa, and the time is 2 min to 6 min; the pickling process uses an acid solution composed of concentrated nitric acid (63% to 69% by mass) and hydrofluoric acid (37% to 49% by mass) mixed in a volume ratio of 1:2.5 to 3.5, and the pickling time is 1 min to 5 min. The above-mentioned preferred sandblasting process can effectively remove impurities and oxide scale from the niobium alloy surface and increase the surface roughness of the niobium alloy substrate. Niobium alloys have good acid resistance and will passivate in the acid solution. By controlling the ratio of the strong acid hydrofluoric acid and the strong oxidizing nitric acid, the situation where the niobium alloy cannot obtain a clean surface due to the formation of a passivation film during the pickling process is effectively avoided. Therefore, the above pretreatment process is beneficial for further removing the oxygen-absorbing layer on the niobium alloy surface and increasing the surface roughness of the niobium alloy, thereby making it more conducive to the formation of a good interfacial bond between the coating and the niobium alloy substrate.

[0018] The above method is characterized in that the metal element powder in step two includes titanium powder, chromium powder, zirconium powder, and molybdenum powder, and the particle size of the Si powder, titanium powder, chromium powder, zirconium powder, and molybdenum powder is all less than 30 μm, and the mass purity is not less than 98%. Furthermore, the mass percentage of Si powder in the raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is not less than 65%, and the particle size of the ZrB2 ceramic particles is less than 10 μm, with a mass purity of not less than 99%. This preferred Si powder and metal element powder, along with their particle size, facilitates the silanization reaction between Si and metal elements during vacuum high-temperature sintering. By limiting the mass purity of the powders, the introduction of impurity elements is reduced, thereby reducing the impact of impurity elements on the high-temperature oxidation resistance of the NbSi2 / ZrB2 layered composite high-temperature protective coating. Simultaneously, by limiting the mass percentage of Si powder, continuous coating formation is facilitated, increasing the density of the NbSi2 / ZrB2 layered composite high-temperature protective coating and improving its oxidation resistance.

[0019] The above method is characterized in that, in step two, the high-energy ball milling speed is 300 r / min to 500 r / min, the time is 4 h to 8 h, the ball-to-material ratio is 3:1, the dispersant is a mixture of varnish and ethyl acetate in a volume ratio of 1:3 to 10, and the volume of the dispersant is 5 to 10 times the total mass of Si powder, metal element powder, and ZrB2 ceramic particles, wherein the unit of volume is mL and the unit of mass is g. This invention significantly reduces the "sinking" phenomenon of particles of different densities in the composite suspension slurry by optimizing the dispersant ratio to control the dispersant viscosity, thus ensuring the spraying and dipping performance of the composite suspension slurry. Combined with high-energy ball milling, it promotes the uniform distribution of Si powder, metal powder, and zirconium boride ceramic particles in the dispersant and further refines the size of the added zirconium boride ceramic particles. A uniformly mixed composite suspension slurry is obtained without significantly changing the particle size of the metal powder, which is beneficial to improving the uniformity of the coating. Furthermore, by controlling the drying and vacuum high-temperature melting processes, the mass transfer and chemical reaction processes on the niobium alloy surface during vacuum melting are regulated, forming an NbSi2 / ZrB2 layered composite high-temperature protective coating on the niobium alloy surface.

[0020] The above method is characterized in that, in step three, the composite suspension slurry is uniformly pre-placed on the surface of the niobium alloy after surface pretreatment by dip coating or pneumatic spraying, and the spraying air pressure of pneumatic spraying is 0.2MPa~0.4MPa, and the spraying distance is 10cm~30cm; the drying temperature is 80℃~200℃, and the time is 8h~24h; the specific process of high-temperature melting is as follows: first, the temperature is raised to 700℃~900℃ at a rate of 10℃ / min~30℃ / min and held for 30min~60min, and then the temperature is raised to 1450℃~1550℃ at a rate of 10℃ / min~15℃ / min and held for 30min~90min. This invention effectively prevents significant deviations between the composition of the pre-placed layer on the niobium alloy substrate surface and the composition of the slurry due to differences in particle density in the atomized composite suspension slurry by controlling the spraying air pressure and spraying distance of the pneumatic spraying. The above-mentioned preferred drying process significantly reduces the content of varnish in the pre-placed layer, thereby reducing the adverse effects of excessively high vacuum inside the vacuum sintering furnace on the high-temperature heating process caused by varnish volatilization during vacuum high-temperature melting. The above-mentioned preferred high-temperature melting process can ensure sufficient reaction between Si elements in the coating and metal powder, coating and alloy substrate, and bottom layer and top layer, while avoiding the problem of low content of antioxidant Si elements in the coating due to excessive reaction between the coating and the substrate. At the same time, it significantly reduces the adverse effects of dispersants in the coating on the coating quality.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] 1. The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of the present invention can generate a composite oxide film with high-melting-point oxides or silicate particles as the "skeleton" and borosilicate glass film as the filler in a high-temperature oxidizing environment. This oxide film has a structure similar to "sand-stone" concrete, which can effectively resist the erosion of high-temperature and high-speed airflow. Moreover, since the viscosity of borosilicate glass is significantly higher than that of amorphous B2O3, the formed oxide film has excellent oxygen barrier ability. Therefore, the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating has better thermal erosion resistance than traditional silicide coatings and a lower oxidation rate than ultra-high temperature ceramic coatings.

[0023] 2. The coefficient of thermal expansion of the ZrB2 ceramic particles in the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of the present invention is between that of the niobium alloy matrix and the silicide coating. This makes the thermal expansion coefficient mismatch of the NbSi2 / ZrB2 layered composite coating smaller than that of the silicide coating and the matrix, thus making its thermal shock resistance performance superior to that of traditional silicide coatings.

[0024] 3. The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of the present invention introduces Ti, Cr, Mo, and Zr metal elements into the bottom silicide coating, forming a medium-entropy ceramic phase of (Nb,Cr,Ti)Si2, (Nb,Mo,Zr)Si2, or (Nb,Cr,Ti,Zr)Si2. This effectively inhibits the formation of Nb2O5 oxide, which has poor oxidation resistance, and effectively improves the oxidation resistance of the silicide bottom layer. Compared with the single-diffusion Si coating bottom layer, it has superior oxidation resistance.

[0025] 4. This invention employs a one-step vacuum reaction sintering method to prepare an oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating on the surface of niobium alloy. The interface formed between the silicide bottom layer and the ultra-high temperature ceramic top layer is an in-situ self-generated interface, with good adhesion between the two layers. This effectively avoids interface cracking and peeling of the coating under thermal erosion or strong thermal shock conditions. Compared with preparing ultra-high temperature ceramic coatings directly on the surface of silicide coatings using methods such as thermal spraying, this invention exhibits superior thermal shock resistance. Furthermore, the one-step sintering process of this invention avoids the adverse effects of multiple melting processes on the microstructure and mechanical properties of the niobium alloy matrix.

[0026] 5. This invention uses a vacuum high-temperature melting process to prepare a layered composite high-temperature protective coating of NbSi2 / ZrB2 on the surface of niobium alloy. This avoids the problem that conventional thermal spraying or electron beam physical vapor deposition processes are difficult to prepare ultra-high temperature ceramic coatings on the surface of niobium alloy components with complex shapes. Moreover, it has higher coating deposition efficiency and lower cost compared with traditional chemical vapor deposition methods.

[0027] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0028] Figure 1 The image shows the XRD pattern of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in Example 1 of this invention.

[0029] Figure 2 This is a surface morphology diagram of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in Example 1 of the present invention.

[0030] Figure 3 This is a cross-sectional morphology diagram of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in Example 1 of the present invention.

[0031] Figure 4 This is a cross-sectional elemental analysis diagram of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in Example 1 of the present invention.

[0032] Figure 5The image shows the surface cross-sectional morphology of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in Example 1 of this invention.

[0033] Figure 6 The image shows the cross-sectional morphology of the surface layer of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in Example 1 of this invention after oxidation at 1500℃ for 10 hours in an atmospheric environment. Detailed Implementation

[0034] Example 1

[0035] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment consists of a bottom layer and a top layer. The bottom layer is a medium-entropy ceramic silicide layer with NbSi2 as the main phase, and the phase is (Nb,Cr,Ti)Si2, wherein the atomic percentage of Si element is 70% and the atomic percentage of Nb element is 22%. The top layer is a ceramic layer with ZrB2 ultra-high temperature ceramic as the main phase, composed of ZrB2, NbSi2 and other silicide phases, wherein the mass percentage of Zr element is 80.8%. The thickness of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 133μm. The coating is applied to the surface of Nb521 niobium alloy and provides effective protection for Nb521 niobium alloy under aerobic thermal erosion conditions of 1000℃~1700℃.

[0036] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which includes the following steps:

[0037] Step 1: Surface pretreatment of Nb521 niobium alloy: Grinding, sandblasting, pickling, and degreasing are performed sequentially. The sandblasting uses corundum abrasive, with a pressure of 0.2 MPa and a time of 6 minutes. The pickling solution is a mixture of 63% concentrated nitric acid and 45% hydrofluoric acid at a volume ratio of 1:3.5, and the pickling time is 3 minutes.

[0038] Step 2: The raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, namely Si powder, titanium powder, chromium powder, ZrB2 ceramic particles, and dispersant, are placed in a ball mill for high-energy ball milling to obtain a composite suspension slurry. The particle size of the metal element powders, titanium powder, chromium powder, and Si powder is all less than 20 μm, and the mass purity is not less than 99.9%. The mass percentage of Si powder in the raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 75%, and the particle size of the ZrB2 ceramic particles is less than 10 μm, with a mass purity of not less than 99%. The high-energy ball milling speed is 300 r / min, the time is 8 h, and the ball-to-material ratio is 3:1. The dispersant is a mixture of varnish and ethyl acetate in a volume ratio of 1:7, and the volume of the dispersant is 10 times the total mass of Si powder, metal element powder, and ZrB2 ceramic particles. The unit of volume is mL, and the unit of mass is g.

[0039] Step 3: The composite suspension slurry obtained in Step 2 is pre-placed on the surface of the Nb521 niobium alloy that underwent surface pretreatment in Step 1 using pneumatic spraying. The spraying pressure is 0.3 MPa, and the spraying distance is 20 cm. After drying at 120℃ for 8 hours, a pre-formed layer is obtained on the surface of the Nb521 niobium alloy. Then, the Nb521 niobium alloy with the pre-formed layer is placed in a vacuum sintering furnace at a vacuum degree of 1.0 × 10⁻⁶. -3 Under the condition of Pa, high-temperature sintering was carried out, and after furnace cooling, a NbSi2 / ZrB2 layered composite high-temperature protective coating was prepared on the surface of Nb521 niobium alloy; the specific process of the high-temperature sintering was as follows: first, the temperature was raised to 700℃ at a rate of 10℃ / min and held for 60min, and then the temperature was raised to 1450℃ at a rate of 15℃ / min and held for 60min.

[0040] Figure 1 The XRD pattern of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment is shown below. Figure 1 It can be seen that the surface of the coating consists of ZrB2, NbSi2 and a small amount of ZrSi phase.

[0041] Figure 2 The image shows the surface morphology of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment. Figure 2 As can be seen, the surface of the coating is continuous and flat, exhibiting the characteristics of a typical vacuum reactive sintering coating.

[0042] Figure 3 This is a cross-sectional morphology image of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment. Figure 4This is a cross-sectional elemental analysis diagram of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment, combined with... Figure 3 and Figure 4 It can be seen that the coating exhibits a distinct layered structure, with Zr and B elements predominating on the surface layer and Nb and Si elements predominating on the bottom layer.

[0043] Figure 5 This is a cross-sectional morphology image of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment. Figure 5 It can be seen that the ceramic surface layer of the coating is mainly composed of ZrB2 ceramic particles, containing a small amount of NbSi2 phase.

[0044] Figure 6 This is a cross-sectional morphology image of the surface layer of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment after oxidation at 1500℃ for 10 hours in an atmospheric environment. Figure 6 It can be seen that a continuous protective oxide film is formed on the surface of the coating after oxidation, and the protective film is well bonded to the coating, and the coating exhibits good high-temperature protection performance.

[0045] Example 2

[0046] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment consists of a bottom layer and a top layer. The bottom layer is a medium-entropy ceramic silicide layer with NbSi2 as the main phase, and the phase is (Nb,Mo,Zr)Si2, wherein the atomic percentage of Si element is 64% and the atomic percentage of Nb element is 25%. The top layer is a ceramic layer with ZrB2 ultra-high temperature ceramic as the main phase, composed of ZrB2, NbSi2 and other silicide phases, wherein the mass percentage of Zr element is 77%. The thickness of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 200μm. The coating is applied to the surface of Nb6621 niobium alloy and provides effective protection for Nb6621 niobium alloy under aerobic thermal erosion conditions of 1000℃~1700℃.

[0047] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which includes the following steps:

[0048] Step 1: Surface pretreatment of Nb6621 niobium alloy: Grinding, sandblasting, pickling, and degreasing are performed sequentially. The sandblasting uses zirconium oxide sand at a pressure of 0.4 MPa for 3 minutes. The pickling solution is a mixture of 66% concentrated nitric acid and 37% hydrofluoric acid at a volume ratio of 1:2.5, and the pickling time is 1 minute.

[0049] Step 2: The raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, namely Si powder, chromium powder, molybdenum powder, ZrB2 ceramic particles, and dispersant, are placed in a ball mill for high-energy ball milling to obtain a composite suspension slurry. The particle size of the metal element powders, namely chromium powder, molybdenum powder, and Si powder, is all less than 10 μm, and the mass purity is not less than 99%. The mass percentage of Si powder in the raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 80%, and the particle size of the ZrB2 ceramic particles is less than 5 μm, with a mass purity of not less than 99%. The high-energy ball milling speed is 400 r / min, the time is 6 h, and the ball-to-material ratio is 3:1. The dispersant is a mixture of varnish and ethyl acetate in a volume ratio of 1:3, and the volume of the dispersant is 8 times the total mass of Si powder, metal element powder, and ZrB2 ceramic particles. The unit of volume is mL, and the unit of mass is g.

[0050] Step 3: The composite suspension slurry obtained in Step 2 is pre-placed on the surface of the Nb6621 niobium alloy that underwent surface pretreatment in Step 1 using pneumatic spraying. The spraying pressure is 0.2 MPa, and the spraying distance is 10 cm. After drying at 80℃ for 24 hours, a pre-formed layer is obtained on the surface of the Nb6621 niobium alloy. Then, the Nb6621 niobium alloy with the pre-formed layer is placed in a vacuum sintering furnace at a vacuum degree of 4.0 × 10⁻⁶. -2 Under the condition of Pa, high-temperature sintering was carried out, and after furnace cooling, a NbSi2 / ZrB2 layered composite high-temperature protective coating was prepared on the surface of Nb6621 niobium alloy; the specific process of the high-temperature sintering was as follows: first, the temperature was raised to 800℃ at a rate of 15℃ / min and held for 40min, and then the temperature was raised to 1500℃ at a rate of 12℃ / min and held for 30min.

[0051] Testing showed that the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment did not fail after oxidation at 1700℃ for 10 hours in an atmospheric environment.

[0052] Example 3

[0053] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment consists of a bottom layer and a top layer. The bottom layer is a medium-entropy ceramic silicide layer with NbSi2 as the main phase, and the phase is (Nb,Cr,Ti,Zr)Si2, wherein the atomic percentage of Si element is 60% and the atomic percentage of Nb element is 30%. The top layer is a ceramic layer with ZrB2 ultra-high temperature ceramic as the main phase, composed of ZrB2, NbSi2 and other silicide phases, wherein the mass percentage of Zr element is 70%. The thickness of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 40μm. The coating is applied to the surface of C103 niobium alloy and provides effective protection for C103 niobium alloy under aerobic thermal erosion conditions of 1000℃~1700℃.

[0054] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which includes the following steps:

[0055] Step 1: Surface pretreatment of C103 niobium alloy: Grinding, sandblasting, pickling, and degreasing are performed sequentially. The sandblasting uses corundum abrasive, with a pressure of 0.6 MPa and a time of 2 minutes. The pickling solution is a mixture of 69% concentrated nitric acid and 40% hydrofluoric acid in a 1:3 volume ratio, and the pickling time is 5 minutes.

[0056] Step 2: The raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, namely Si powder, titanium powder, chromium powder, zirconium powder, ZrB2 ceramic particles, and dispersant, are placed in a ball mill for high-energy ball milling to obtain a composite suspension slurry. The particle size of the metal element powders—titanium powder, chromium powder, zirconium powder, and Si powder—is all less than 5 μm, and their purity is not less than 99.5%. This process is necessary for the preparation of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating. The raw material contains 65% Si powder by mass, and the ZrB2 ceramic particles have a particle size of less than 5 μm and a purity of not less than 99%. The high-energy ball mill is used at a speed of 500 r / min for 4 hours, with a ball-to-material ratio of 3:1. The dispersant is a mixture of varnish and ethyl acetate at a volume ratio of 1:10, and the volume of the dispersant is 5 times the total mass of the Si powder, metal element powder, and ZrB2 ceramic particles. The unit of volume is mL, and the unit of mass is g.

[0057] Step 3: The composite suspension slurry obtained in Step 2 is pre-placed on the surface of the C103 niobium alloy that underwent surface pretreatment in Step 1 using pneumatic spraying. The spraying pressure is 0.4 MPa, and the spraying distance is 30 cm. After drying at 200℃ for 16 hours, a pre-formed layer is obtained on the surface of the C103 niobium alloy. Then, the C103 niobium alloy with the pre-formed layer is placed in a vacuum sintering furnace at a vacuum degree of 2.0 × 10⁻⁶. -2 Under the condition of Pa, high-temperature sintering was carried out, and after furnace cooling, a NbSi2 / ZrB2 layered composite high-temperature protective coating was prepared on the surface of C103 niobium alloy; the specific process of the high-temperature sintering was as follows: first, the temperature was raised to 900℃ at a rate of 30℃ / min and held for 30min, and then the temperature was raised to 1550℃ at a rate of 10℃ / min and held for 90min.

[0058] Testing showed that the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment did not fail after 600 thermal shocks at 1700℃ in an atmospheric environment.

[0059] Example 4

[0060] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment consists of a bottom layer and a top layer. The bottom layer is a medium-entropy ceramic silicide layer with NbSi2 as the main phase, and the phase is (Nb,Cr,Ti,Zr)Si2, wherein the atomic percentage of Si element is 64% and the atomic percentage of Nb element is 23%. The top layer is a ceramic layer with ZrB2 ultra-high temperature ceramic as the main phase, composed of ZrB2, NbSi2 and other silicide phases, wherein the mass percentage of Zr element is 84%. The thickness of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 160μm. The coating is applied to the surface of C103 niobium alloy and provides effective protection for C103 niobium alloy under aerobic thermal erosion conditions of 1000℃~1700℃.

[0061] The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which includes the following steps:

[0062] Step 1: Surface pretreatment of Nb521 niobium alloy: Grinding, sandblasting, pickling, and degreasing are performed sequentially. The sandblasting uses corundum abrasive, with a pressure of 0.3 MPa and a time of 3 minutes. The pickling solution is a mixture of 65% concentrated nitric acid and 49% hydrofluoric acid at a volume ratio of 1:2.5, and the pickling time is 4 minutes.

[0063] Step 2: The raw materials for forming the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, namely Si powder, titanium powder, chromium powder, zirconium powder, ZrB2 ceramic particles, and dispersant, are placed in a ball mill for high-energy ball milling to obtain a composite suspension slurry. The particle size of the metal element powders—titanium powder, chromium powder, zirconium powder, and Si powder—is all less than 10 μm, and their purity is not less than 99.5%. Furthermore, the materials are suitable for forming the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating. The raw materials contain 68% Si powder by mass, and the ZrB2 ceramic particles have a particle size of less than 5 μm and a purity of not less than 99%. The high-energy ball mill is used at a speed of 460 r / min for 6 hours, with a ball-to-material ratio of 3:1. The dispersant is a mixture of varnish and ethyl acetate in a volume ratio of 1:8, and the volume of the dispersant is 7 times the total mass of the Si powder, metal element powder, and ZrB2 ceramic particles. The unit of volume is mL, and the unit of mass is g.

[0064] Step 3: The composite suspension slurry obtained in Step 2 is pre-coated onto the surface of the C103 niobium alloy that underwent surface pretreatment in Step 1 using a dip-coating method. After drying at 150℃ for 12 hours, a pre-coated layer is formed on the surface of the C103 niobium alloy. Then, the C103 niobium alloy with the pre-coated layer is placed in a vacuum sintering furnace at a vacuum degree of 1.0 × 10⁻⁶. -2 Under the condition of Pa, high-temperature sintering was carried out, and after furnace cooling, a NbSi2 / ZrB2 layered composite high-temperature protective coating was prepared on the surface of C103 niobium alloy; the specific process of the high-temperature sintering was as follows: first, the temperature was raised to 800℃ at a rate of 20℃ / min and held for 30min, and then the temperature was raised to 1450℃ at a rate of 10℃ / min and held for 90min.

[0065] Testing showed that the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating prepared in this embodiment did not fail after being subjected to flame erosion at 1700℃ and Mach number 1 for 3600 seconds.

[0066] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A layered composite high-temperature protective coating of NbSi2 / ZrB2 that is resistant to oxidation and erosion, characterized in that, The coating consists of a base layer and a top layer. The base layer is a silicide layer with NbSi2 as the main phase, and the top layer is a ceramic layer with ZrB2 ultra-high temperature ceramic as the main phase. The NbSi2-based silicide layer is a medium-entropy ceramic with phases of (Nb,Cr,Ti)Si2, (Nb,Mo,Zr)Si2, or (Nb,Cr,Ti,Zr)Si2, and the atomic percentage of Si in the NbSi2-based silicide layer is 60%~70%. The atomic percentage of Nb is 22%~30%; the ceramic layer with ZrB2 ultra-high temperature ceramic as the main phase is composed of ZrB2, NbSi2 and other silicide phases, wherein the mass percentage of Zr is not less than 70%; the thickness of the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is 40μm~200μm, providing effective protection for niobium alloy materials under aerobic thermal erosion conditions of 1000℃~1700℃.

2. The oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating according to claim 1, characterized in that, The coating is applied to the surface of a C103, Nb521, or Nb6621 niobium alloy.

3. A method for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating as described in claim 1 or 2, characterized in that, It was prepared using a one-step vacuum reaction sintering method.

4. The method according to claim 3, characterized in that, The method includes the following steps: Step 1: Surface pretreatment of niobium alloy: grinding, sandblasting, pickling and degreasing are performed in sequence; Step 2: The raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating, namely Si powder, metal element powder, ZrB2 ceramic particles and dispersant, are placed in a ball mill for high-energy ball milling to obtain a composite suspension slurry. Step 3: The composite suspension slurry obtained in Step 2 is pre-placed on the surface of the niobium alloy that underwent surface pretreatment in Step 1. After drying, a pre-placed layer is formed on the surface of the niobium alloy. Then, the niobium alloy with the pre-placed layer is placed in a vacuum sintering furnace at a vacuum degree of 1.0 × 10⁻⁶. -3 Pa ~ 4.0 × 10 -2 Under the condition of Pa, high-temperature melting was carried out, and after furnace cooling, a NbSi2 / ZrB2 layered composite high-temperature protective coating was prepared on the surface of the niobium alloy.

5. The method according to claim 4, characterized in that, The sand used in step one is corundum sand or zirconium oxide sand. The sandblasting pressure is 0.2MPa~0.6MPa and the time is 2min~6min. The acid solution used in the pickling is a mixture of concentrated nitric acid with a mass concentration of 63%~69% and hydrofluoric acid with a mass concentration of 37%~49% in a volume ratio of 1:2.5~3.

5. The pickling time is 1min~5min.

6. The method according to claim 4, characterized in that, The metal element powders mentioned in step two include titanium powder, chromium powder, zirconium powder, and molybdenum powder. The particle size of Si powder, titanium powder, chromium powder, zirconium powder, and molybdenum powder is less than 30 μm, and the mass purity is not less than 98%. The mass percentage of Si powder in the raw materials for preparing the oxidation-resistant and erosion-resistant NbSi2 / ZrB2 layered composite high-temperature protective coating is not less than 65%, and the particle size of the ZrB2 ceramic particles is less than 10 μm, with a mass purity of not less than 99%.

7. The method according to claim 4, characterized in that, The high-energy ball milling in step two uses a rotation speed of 300 r / min to 500 r / min and a time of 4 h to 8 h, with a ball-to-material ratio of 3:

1. The dispersant is a mixture of varnish and ethyl acetate in a volume ratio of 1:3 to 10, and the volume of the dispersant is 5 to 10 times the total mass of Si powder, metal element powder, and ZrB2 ceramic particles. The unit of volume is mL, and the unit of mass is g.

8. The method according to claim 4, characterized in that, In step three, the composite suspension slurry is uniformly pre-placed on the surface of the niobium alloy after surface pretreatment by dip coating or pneumatic spraying. The spraying pressure of pneumatic spraying is 0.2MPa~0.4MPa, and the spraying distance is 10cm~30cm. The drying temperature is 80℃~200℃, and the time is 8h~24h. The specific process of high-temperature melting is as follows: first, the temperature is raised to 700℃~900℃ at a rate of 10℃ / min~30℃ / min and held for 30min~60min, and then the temperature is raised to 1450℃~1550℃ at a rate of 10℃ / min~15℃ / min and held for 30min~90min.

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