Ultrahigh-temperature anti-oxidation thermal-shock-resistant composite coating and preparation method thereof

Abstract

The invention discloses an ultrahigh-temperature anti-oxidation thermal-shock-resistant composite coating which is composed of a silicide-boride composite ceramic surface layer, a Ta5Si3 middle layer, a TaSi2 equiaxed crystal layer, a TaSi2 layer columnar crystal layer and a Ta5Si3 interface reaction layer, wherein the silicide-boride composite ceramic surface layer, the Ta5Si3 middle layer, the TaSi2 equiaxed crystal layer and the TaSi2 layer columnar crystal layer are sequentially deposited on a tantalum alloy matrix from top to bottom, and the Ta5Si3 interface reaction layer is located at the interface of the tantalum alloy matrix. The composite coating is prepared by adopting a one-step vacuum reaction sintering method. According to the composite coating, through structural and composition design, a composite oxidation film similar to a'sand-stone 'concrete structure is generated in a high-temperature oxidation environment, and the composite coating has more excellent thermal scouring resistance, thermal shock resistance and ultrahigh-temperature oxidation resistance; according to the preparation method, it is guaranteed that all layers and interlayer interfaces in the composite coating are generated through in-situ reaction, the interlayer binding force is good, and the composite coating has excellent thermal shock resistance, is high in preparation efficiency and low in cost and is suitable for the field of ultra-high-temperature protective coatings.

Description

Technical Field

[0001] The present invention belongs to the technical field of high temperature protection, and in particular relates to an ultra-high temperature anti-oxidation and anti-thermal shock composite coating and a preparation method thereof. Background Art

[0002] Tantalum and its alloys have excellent properties such as high density, high melting point, corrosion resistance, excellent high temperature strength, good processability and weldability, and low toughness / brittle transition temperature. Since the 1930s, the United States and the Soviet Union have begun to vigorously develop tantalum and its alloys. They are mainly used in the fields of reinforced structural materials of space nuclear power systems, combustion chambers of Jin Ajina spacecraft and nose cones of missiles (using temperature is about 2500℃), gas spoilers of rocket engine nozzles, combustion chambers of Apollo, and nozzles of liquid rocket nozzles. However, tantalum and its alloys will quickly oxidize and fail under high temperature (above 500℃) oxygen-containing conditions, and "pesting" powdering phenomenon will occur. This is because the main oxide of tantalum and its alloys is porous and brittle oxide Ta2O5, which has no barrier effect on oxygen diffusion, so that the matrix directly contacts oxygen and oxidizes and fails. At the same time, its PBR value is 2.47, which is much greater than 1. Therefore, the oxide film will produce a large growth stress during the growth process, resulting in a serious decrease in the bonding force between the oxide film layer and the substrate, and even causing the oxide film layer to peel off.

[0003] The high-temperature protective coating for tantalum-based alloys is mainly silicide coating. A few researchers use iridium coating and high-entropy silicide ceramic coating to protect tantalum-based alloys. However, the preparation of these two coatings faces problems such as immature process, high cost and insufficient bonding strength. At present, the protection temperature of the mature silicide high-temperature protective coating widely used on the surface of tantalum alloy is mostly below 1700℃. As the service temperature of tantalum alloy further increases (>1750℃) and the service life further extends, the existing silicide coating can no longer meet the high-temperature protection needs of tantalum alloy in extremely harsh environments: (1) When the ambient temperature is higher than the melting point of SiO2 (1710℃), the viscosity of the SiO2 glass protective film drops sharply, and the barrier effect on the inward diffusion of oxygen is weakened; (2) Above its melting point (1710℃), the protective effect is limited. When the operating temperature is further increased to 1800℃, the vapor pressure of SiO at the silicide / SiO2 glass film interface exceeds one atmosphere, and the high-temperature protection ability of the SiO2 glass protective film is lost; (3) There is a large mismatch in thermal expansion coefficients among the substrate, coating and oxide film. The silicide coating (~8×10 -6 K -1 ) and the thermal expansion coefficient of the tantalum-based alloy matrix (5.6×10 -6 K -1 ) is too different, and the thermal expansion coefficient of glassy SiO2 (0.55×10 -6 K -1) is much lower than the main body of the coating. Under the action of ultra-high temperature and strong thermal shock, it is very easy to produce cracks in the coating caused by the accumulation of thermal stress, thereby accelerating the failure process of the coating. Element modification and ceramic particle modification of silicide coatings can improve the oxidation resistance of silicide coatings in medium and low temperature environments to a certain extent, but it is still difficult to meet the use requirements of the coating under ultra-high temperature conditions above 1750℃.

[0004] With the rapid development of aerospace, nuclear industry and other fields, there is an urgent need to develop ultra-high temperature protective coatings suitable for tantalum alloys. It is urgent to develop ultra-high temperature (≥1750℃) anti-oxidation, erosion-resistant, thermal shock-resistant and long-life protective coatings. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide an ultra-high temperature anti-oxidation and anti-thermal shock composite coating in view of the deficiencies of the above-mentioned prior art. The coating designs the composite coating structure and composition on the surface of tantalum alloy, generates a composite oxide film similar to a "sand-stone" concrete structure in a high-temperature oxidation environment, has a stronger barrier effect on oxygen at ultra-high temperatures, and can effectively resist the scouring of high-temperature and high-speed airflow, thus having excellent ultra-high temperature oxidation resistance, thermal shock resistance and thermal scouring resistance, solving the problem of rapid volatilization failure and insufficient oxygen barrier capacity of traditional silicide coatings under ultra-high temperature conditions (≥1750℃).

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: an ultra-high temperature anti-oxidation and anti-thermal shock composite coating, characterized in that it is composed of a silicide-boride composite ceramic surface layer, a Ta5Si3 intermediate layer, a TaSi2 equiaxed crystal layer, a TaSi2 columnar crystal layer and a Ta5Si3 interface reaction layer at the interface with the tantalum alloy substrate, which are sequentially deposited on the tantalum alloy substrate from top to bottom;

[0007] The thickness of the silicide-boride composite ceramic surface layer is 15 μm to 30 μm, the thickness of the Ta5Si3 intermediate layer is 3 μm to 8 μm, the thickness of the TaSi2 equiaxed crystal layer is 15 μm to 20 μm, the thickness of the TaSi2 columnar crystal layer is 35 μm to 45 μm, and the thickness of the Ta5Si3 interface reaction layer is 3 μm to 10 μm;

[0008] The composite coating has a constant temperature anti-oxidation life of not less than 5 hours in an atmospheric environment of 1700°C, a constant temperature anti-oxidation life of not less than 400 seconds in an atmospheric environment of 1900°C, a thermal shock life of not less than 150 times under water-cooling conditions of room temperature to 1700°C, and a thermal shock life of not less than 50 times under water-cooling conditions of room temperature to 1800°C; the composite coating provides effective protection for tantalum alloy materials under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C.

[0009] Aiming at the service condition of tantalum alloy under ultra-high temperature conditions, the present invention constructs an ultra-high temperature anti-oxidation and thermal shock resistant composite coating in situ on the surface of tantalum alloy by designing the structure of the coating and the functions of each layer. In the composite coating, the oxidation resistance of the composite coating and the formation of the composite oxide film mainly come from the uppermost silicide-boride composite ceramic surface layer. Through the physical phase design of the surface layer, on the one hand, the composite coating can form a composite oxide film under oxidation conditions, which has both oxidation resistance and thermal erosion resistance. On the other hand, the composite coating has better mechanical properties than a single silicide coating, thereby having higher thermal shock resistance. At the same time, the silicide-boride composite ceramic surface layer contains a small amount of Ta5Si3. By setting a Ta5Si3 intermediate layer, the Ta5Si3 intermediate layer contains the same components as the silicide-boride composite ceramic surface layer and the same elemental composition as the TaSi2 equiaxed crystal layer, and the Ta5Si3 intermediate layer has Hf and Zr elements dissolved therein and contains a Cr-containing phase, so that a good interface bonding is formed between the three, thereby effectively connecting the upper silicide-boride composite ceramic surface layer and the lower TaSi2 equiaxed crystal layer through the Ta5Si3 intermediate layer to form a stable structure. Next, the present invention sets a TaSi2 equiaxed crystal layer and a TaSi2 columnar crystal layer. On the one hand, both TaSi2 layers can store a large amount of Si elements, thereby maintaining the stable growth of the SiO2 glass film on the surface of the composite coating, providing the composite coating with a longer high-temperature anti-oxidation life. On the other hand, the TaSi2 equiaxed crystal layer contains a certain amount of Hf, Zr, and Cr phases, which is conducive to forming a good interface with the Ta5Si3 intermediate layer, and the presence of the TaSi2 columnar crystal layer can increase the deformation capacity of the composite coating, which is conducive to improving the thermal shock resistance of the composite coating. Finally, by setting a Ta5Si3 interface reaction layer at the interface between the composite coating and the tantalum alloy substrate, it is conducive to improving the interface bonding performance between the composite coating and the tantalum alloy substrate. The present invention limits the thickness of each layer so that the layers work together. Under the premise of ensuring the high-temperature protection performance of the composite coating, the composite coating is prevented from cracking and peeling under internal stress or thermal stress conditions. Therefore, the composite coating can provide effective protection for the tantalum alloy material under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C. In particular, the composite coating has a constant temperature anti-oxidation life of not less than 5 hours in an atmospheric environment of 1800°C, thereby providing ultra-high temperature protection for tantalum alloy hot end components of advanced attitude and orbit control rocket engines and hypersonic aircraft.

[0010] The above-mentioned ultra-high temperature anti-oxidation and anti-thermal shock composite coating is characterized in that each layer in the composite coating is formed during the high-temperature vacuum reaction firing process, and the interfaces between the layers are all in-situ reaction self-generated interfaces. Since each layer and the interface between the layers in the composite coating are generated by in-situ reaction during the vacuum reaction firing process, it has good interface bonding performance, avoiding cracking and peeling of the composite coating under internal stress or thermal stress conditions, so that the composite coating has good thermal shock resistance.

[0011] The above-mentioned ultra-high temperature anti-oxidation and thermal shock resistant composite coating is characterized in that the silicide-boride composite ceramic surface layer is mainly composed of HfCrSi2, (Hf, Zr)B2, HfB, (Hf, Zr)Si ceramics, and contains a small amount of HfTa, Hf and Ta5Si3.

[0012] The composition and phase of the surface layer in the composite coating directly determine the structure and phase of the oxide film, thereby determining the antioxidant performance of the composite coating. The present invention adopts an ultra-high temperature boride ceramic phase as a surface layer component to ensure the ultra-high temperature protection performance of the surface layer, and introduces a Si-containing ceramic phase to reduce the high temperature oxidation rate of the surface layer and improve the antioxidant performance of the surface layer. The Si-containing ceramic phase in the surface layer is a phase that forms a SiO2 glass film, the Hf and Zr-containing ceramic phase is a phase that forms a high melting point oxide or silicate in the oxide film, and the B-containing ceramic phase is an important phase that forms B2O3. Therefore, the composite coating of the present invention forms a composite oxide film with high melting point oxides or silicates such as ZrO2, HfO2, (Zr, Hf)SiO4 as the "skeleton" reinforcement phase and Hf-Zr-Ta-B-Si-O glass as the filler during the ultra-high temperature oxidation process. This composite oxide film with a "sand-stone" concrete structure can have both oxygen barrier properties and thermal erosion resistance. It not only makes up for the rapid volatilization failure and insufficient oxygen barrier capacity of traditional silicide coatings under ultra-high temperature conditions (≥1750°C), but also effectively improves the thermal erosion resistance and thermal shock resistance of the coating. At the same time, the HfCrSi2 phase in the surface layer greatly improves the density of the surface layer, which is beneficial to reduce the oxidation rate of the composite coating and further improve the anti-oxidation performance of the composite coating. In addition, the metal phases HfTa and Hf in the surface layer can improve the toughness of the surface layer.

[0013] The above-mentioned ultra-high temperature anti-oxidation and thermal shock resistant composite coating is characterized in that the Ta5Si3 intermediate layer is composed of t-Ta5Si3 and h-Ta5Si3 in which Hf and Zr elements are solid dissolved, and Ta2Cr4Si5 phase. The atomic percentage of Hf element in t-Ta5Si3 is not less than 12%, the atomic percentage of Zr element is not less than 11%, and the atomic percentage of Cr element is not less than 5%. The atomic percentage of Hf element in h-Ta5Si3 is not less than 5%, the atomic percentage of Zr element is not less than 2%, and the atomic percentage of Cr element is not less than 10%. By limiting the composition and element content of the Ta5Si3 middle layer, a gradient transition of Si element content is formed in its composition with the upper ceramic layer and the lower TaSi2 layer, forming a more stable interface bond with the upper silicide-boride composite ceramic surface layer and the lower TaSi2 equiaxed crystal layer, thereby playing a better connecting role; at the same time, since the formation of the TaSi2 equiaxed crystal layer is the result of the downward diffusion of metal elements in the Ta5Si3 middle layer and the interruption of the growth of columnar crystals TaSi2, the formation of the TaSi2 equiaxed crystal layer is guaranteed by this limitation, and the interlayer interface bonding between the Ta5Si3 middle layer and the TaSi2 equiaxed crystal layer is further improved, avoiding longitudinal cracks caused by excessive thickness of the TaSi2 equiaxed crystal layer.

[0014] The above-mentioned ultra-high temperature anti-oxidation and anti-thermal shock composite coating is characterized in that the TaSi2 equiaxed crystal layer is composed of equiaxed crystal TaSi2 and Hf5Si4 and Ta3(CrSi)8 distributed at the grain boundaries of TaSi2 equiaxed crystals. The silicon phase in Hf5Si4 and Ta3(CrSi)8 distributed at the grain boundaries of TaSi2 equiaxed crystals is beneficial to reducing the grain size of TaSi2 and improving the toughness of the TaSi2 equiaxed crystal layer, thereby improving the thermal shock resistance of the composite coating. On the other hand, the presence of Cr and Hf elements can form a better interface bonding between the TaSi2 equiaxed crystal layer and the Ta5Si3 intermediate layer.

[0015] The above-mentioned ultra-high temperature anti-oxidation and thermal shock resistant composite coating is characterized in that the tantalum alloy substrate is Ta10W or Ta12W tantalum alloy. By selecting Ta10W or Ta12W tantalum alloy as the substrate, Ta element is provided for Ta phase-containing ceramics (Ta5Si3, TaSi2 Ta2Cr4Si5, Ta3(CrSi)8) in the composite coating; at the same time, the preferred tantalum alloy is used as the substrate in the vacuum high temperature sintering preparation process and ultra-high temperature service process of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating, and its mechanical properties will not be significantly reduced, and its service temperature range is greater than the protection temperature range of the composite coating, which is suitable for the preparation method of the present invention.

[0016] At the same time, the present invention also discloses a method for preparing the ultra-high temperature anti-oxidation and thermal shock resistant composite coating as mentioned above, which is characterized in that the method is prepared by a one-step vacuum reaction sintering method.

[0017] The above method is characterized in that the method comprises the following steps:

[0018] Step 1: Perform surface pretreatment of the tantalum alloy by grinding, sandblasting, pickling and degreasing in sequence, so that the oxide and oxygen absorption layer on the tantalum alloy are removed and the surface is in a "pitted" state;

[0019] Step 2: Place the raw material powders Si powder, Hf powder, Cr powder, HfB2 ceramic particles and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle sizes of the Si powder, Hf powder and Cr powder are all 1μm to 5μm, the particle size of the HfB2 ceramic particles is 1μm to 10μm, the mass purity of each raw material powder is not less than 99%, and the mass percentage of Si powder in the raw material powder is not less than 40%, the mass percentage of Cr powder is not less than 3%, and the mass percentage of HfB2 ceramic particles is not less than 8%;

[0020] Step 3: pre-coat the composite suspension slurry obtained in step 2 on the surface of the tantalum alloy that has been surface pretreated in step 1 by dipping or pneumatic spraying, and obtain a pre-coated layer on the surface of the tantalum alloy after drying. Then, place the tantalum alloy with the pre-coated layer in a vacuum sintering furnace at a vacuum degree of 8.0×10 -3 Pa~7.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and an ultra-high temperature anti-oxidation and thermal shock resistant composite coating is prepared on the surface of the tantalum alloy after cooling with the furnace; the specific process of the high-temperature firing is: firstly heating to 700°C~900°C at a rate of 5°C / min~20°C / min and keeping warm for 30min~60min, and then heating to 1350°C~1700°C at a rate of 5°C / min~10°C / min and keeping warm for 30min~120min.

[0021] The present invention adopts a high-energy ball milling process to make the raw material powders Si powder, Hf powder, Cr powder, and HfB2 ceramic particles uniformly dispersed in the dispersant, and 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 preset layer, and the particle size of the selected raw material powder is beneficial to promoting the silicification reaction between Si and the metal powder and the tantalum alloy matrix during the vacuum high-temperature sintering process. By limiting the mass purity of the raw material powder, the introduction of impurity elements is reduced, thereby reducing the influence of impurity elements on the high-temperature protection performance of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating. At the same time, by limiting the mass content of HfB2 ceramic particles, the thickness and phase composition of the surface layer in the composite coating can be effectively controlled. By limiting the mass content of Si powder and Cr powder, the density, thickness and interlayer bonding performance of the composite coating can be effectively controlled. In addition, the high-temperature sintering process under vacuum of the present invention can not only ensure sufficient reaction between the Si element in the pre-deposited layer and the metal Hf, Cr and tantalum alloy matrix, but also avoid the problem of low content of antioxidant Si element in the composite coating due to excessive reaction with the tantalum alloy matrix, and at the same time significantly reduce the adverse effects of the dispersant in the pre-deposited layer on the quality of the composite coating.

[0022] The present invention controls the composition and firing process of the slurry, and adopts a one-step vacuum reaction sintering method to realize the in-situ composite of ultra-high temperature boride ceramics and silicide ceramics on the surface of tantalum-tungsten alloy, and the interlayer interface of the obtained composite coating is in-situ self-generated, which overcomes the problem of insufficient bonding performance between the layers of the layered ceramic coating and the interface between the ceramic coating and the metal substrate, and significantly improves the ability of the composite coating to resist cracking and peeling under thermal scouring or strong thermal shock conditions. At the same time, the present invention designs the chemical reaction process of the raw materials Si, Hf, Cr, HfB2, and the tantalum-tungsten alloy substrate under vacuum and high temperature conditions, and adopts a one-step vacuum reaction sintering method to obtain a layered composite coating, thereby avoiding the grain growth of the tantalum alloy substrate during multiple sintering processes, and reducing the adverse effects on the microstructure and mechanical properties of the tantalum alloy substrate. In addition, the slurry pre-layer preparation-vacuum reaction firing method of the present invention is suitable for tantalum-tungsten alloy engineering parts with complex shapes, and can overcome the problems of line of sight effect, low deposition efficiency, and difficult control of coating composition in the preparation of layered composite ceramic coatings by thermal spraying, physical vapor deposition (PVD), chemical vapor deposition (CVD), laser cladding and other methods.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] 1. The present invention designs the structure and composition of the composite coating on the surface of the tantalum alloy so that the composite coating can generate a composite oxide film with high melting point oxide (HfO2, ZrO2) or silicate (HfSiO4, ZrSiO4) particles as the "skeleton" and Hf-Zr-Ta-Si-BO glass as the filler in a high-temperature oxidizing environment. The composite oxide film has a "sand-stone" concrete structure, which can effectively resist the erosion of high-temperature and high-speed airflow, and has better anti-stripping performance under strong thermal shock conditions than a single amorphous oxide film, and has more excellent thermal erosion resistance and thermal shock resistance.

[0025] 2. Compared with the most commonly used silicide coating for tantalum alloy, the glassy oxide film formed on the surface of the composite coating of the present invention under ultra-high temperature oxidation conditions is Hf-Zr-Ta-Si-BO glass. Compared with the SiO2 glass film and Si-BO glass film formed by oxidation of traditional silicide coatings, it has better high-temperature stability and higher high-temperature viscosity, stronger barrier effect against oxygen under ultra-high temperature (>1750℃) conditions, and has more excellent ultra-high temperature oxidation resistance.

[0026] 3. Each layer and the interface between layers in the composite coating of the present invention are generated by in-situ reaction during vacuum high-temperature firing. The interlayer bonding force is good and has better resistance to cracking and peeling than artificial interfaces. It effectively avoids interface cracking and peeling of the composite coating under thermal scouring or strong thermal shock conditions, making the composite coating have excellent thermal shock resistance.

[0027] 4. The present invention designs the components and morphological structures of each layer in the composite coating so that each layer has higher mechanical properties or greater deformation capacity, further ensuring good interlayer bonding performance between the coating layers and the substrate, and having better thermal shock resistance than a single silicide coating.

[0028] 5. Since the melting points of ZrB2, HfB2, and HfB ultra-high temperature ceramic particles are very high, their sintering densification temperatures are also very high. The prior art generally adopts CVD or plasma spraying methods to prepare coatings, which makes it difficult to adjust the composition of the coatings or the interface bonding performance is insufficient, making it difficult to meet the aerospace industry's requirements for coating preparation of tantalum-tungsten alloy high-temperature components. The present invention designs the slurry composition, combines the control of the chemical reaction process during vacuum high-temperature firing, and adopts a one-step vacuum reaction sintering method to prepare an ultra-high temperature anti-oxidation and thermal shock resistant composite coating on the surface of the tantalum alloy. The ultra-high temperature ceramic layer of the surface layer of the composite coating has good density.

[0029] 6. Compared with the existing single ultra-high temperature boride ceramic coating prepared by thermal spraying, CVD and other methods, the present invention uses Si, Cr, Hf and HfB2 to react chemically under vacuum and high temperature conditions to form a composite ceramic surface layer with (Hf, Zr) B2, HfB, (Zr, Hf) Si and HfCrSi2 as the main phases. The oxidation rate of the surface layer composed of this phase is significantly reduced, further improving the anti-oxidation performance of the composite coating.

[0030] 7. Compared with the method of preparing layered composite coatings by multiple sintering processes, the present invention adopts a one-step vacuum reaction sintering method to prepare ultra-high temperature anti-oxidation and thermal shock resistant composite coatings on the surface of tantalum alloys, which significantly reduces the adverse effects of the sintering process on the microstructure and mechanical properties of the tantalum alloy matrix.

[0031] 8. The present invention adopts a vacuum high-temperature sintering process to prepare an ultra-high temperature anti-oxidation and thermal shock resistant composite coating on the surface of tantalum alloy, avoiding the problem that conventional thermal spraying, PVD, CVD and other processes are difficult to prepare ultra-high temperature ceramic coatings on the surface of tantalum alloy components with complex shapes. Compared with traditional chemical vapor deposition methods, it has higher coating deposition efficiency and lower cost.

[0032] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a macroscopic morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in Example 1 of the present invention.

[0034] Figure 2 This is a surface morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in Example 1 of the present invention.

[0035] Figure 3 This is a cross-sectional morphology diagram of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in Example 1 of the present invention.

[0036] Figure 4 This is a cross-sectional morphology diagram of the ultra-high temperature anti-oxidation and anti-thermal shock composite coating prepared in Example 2 of the present invention after being oxidized in an atmospheric environment at 1700°C for 5 hours.

[0037] Figure 5 This is a cross-sectional morphology of the oxide film of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in Example 3 of the present invention after being oxidized at 1900°C for 400s.

[0038] Figure 6 This is a surface morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in Example 4 of the present invention after 150 thermal shocks under water cooling conditions at room temperature to 1700°C.

[0039] Figure 7This is a surface morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in Example 5 of the present invention after 50 thermal shocks under water cooling conditions at room temperature to 1800°C. DETAILED DESCRIPTION

[0040] Example 1

[0041] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is composed of a silicide-boride composite ceramic surface layer with a thickness of 22 μm, a Ta5Si3 intermediate layer with a thickness of 6 μm, a TaSi2 equiaxed crystal layer with a thickness of 17 μm, a TaSi2 columnar crystal layer with a thickness of 39 μm, and a Ta5Si3 interface reaction layer with a thickness of 5 μm at the interface with the Ta12W tantalum alloy substrate, which are deposited sequentially from top to bottom.

[0042] Each layer in the composite coating is formed during high-temperature vacuum reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces;

[0043] The silicide-boride composite ceramic surface layer is mainly composed of HfCrSi2, (Hf, Zr)B2, HfB, (Hf, Zr)Si ceramics, and contains a small amount of HfTa, Hf and Ta5Si3;

[0044] The Ta5Si3 intermediate layer is composed of t-Ta5Si3 and h-Ta5Si3 in which Hf and Zr elements are solid-dissolved, and Ta2Cr4Si5 phases. The atomic percentage of Hf element in t-Ta5Si3 is 12.5%, the atomic percentage of Zr element is 11.4%, and the atomic percentage of Cr element is 5.6%. The atomic percentage of Hf element in h-Ta5Si3 is 5%, the atomic percentage of Zr element is 2.2%, and the atomic percentage of Cr element is 11.2%.

[0045] The TaSi2 equiaxed crystal layer is composed of equiaxed TaSi2 crystals and Hf5Si4 and Ta3(CrSi)8 distributed on the grain boundaries of the TaSi2 equiaxed crystals.

[0046] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which comprises the following steps:

[0047] Step 1: Perform surface pretreatment of the Ta12W tantalum alloy by grinding, sandblasting, pickling and degreasing in sequence, so that the oxide and oxygen absorption layer on the Ta12W tantalum alloy are removed, and the surface is in a "pitted" state;

[0048] Step 2: Place the raw material powders Si powder, Hf powder, Cr powder, HfB2 ceramic particles and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle sizes of the Si powder, Hf powder and Cr powder are all 1μm to 5μm, the particle size of the HfB2 ceramic particles is 1μm to 10μm, the mass purity of each raw material powder is not less than 99%, and the mass percentage of Si powder in the mixed powder is 40%, the mass percentage of Cr powder is 5%, and the mass percentage of HfB2 ceramic particles is 20%;

[0049] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Ta12W tantalum alloy that has been surface pretreated in step 1 by dipping or pneumatic spraying, and a pre-applied layer is obtained on the surface of the tantalum alloy after drying, and then the Ta12W tantalum alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 7.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and an ultra-high temperature anti-oxidation and thermal shock resistant composite coating is prepared on the surface of Ta12W tantalum alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 800°C at a rate of 10°C / min and keeping warm for 30 minutes, then heating to 1420°C at a rate of 10°C / min and keeping warm for 60 minutes.

[0050] Figure 1 This is the macroscopic morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in this example. Figure 1 It can be seen that the coating macroscopic morphology of the composite coating surface is consistent, the coating surface is in good condition, and no peeling or bulging is found.

[0051] Figure 2 This is the surface morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in this example. Figure 2 It can be seen that the composite coating exhibits typical morphological characteristics of vacuum reaction fired coatings, and the coating surface is flat.

[0052] Figure 3 This is a cross-sectional morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in this embodiment. Figure 3 It can be seen that the composite coating is divided into five layers from top to bottom, namely, a silicide-boride composite ceramic surface layer, a Ta5Si3 intermediate layer, a TaSi2 equiaxed crystal layer, a TaSi2 columnar crystal layer, and a Ta5Si3 interface reaction layer at the interface with the tantalum alloy substrate, and the interfaces between the layers are well bonded.

[0053] After testing, the composite coating of this embodiment did not fail after isothermal oxidation for 5 hours in an atmospheric environment of 1700°C, did not fail after isothermal oxidation for 550 seconds in an atmospheric environment of 1900°C, did not fail after 160 thermal shocks under water-cooling conditions at room temperature to 1700°C, and did not fail after 57 thermal shocks under water-cooling conditions at room temperature to 1800°C. The composite coating provides effective protection for tantalum alloy materials under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C.

[0054] Example 2

[0055] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is composed of a 15 μm thick silicide-boride composite ceramic surface layer, an 8 μm thick Ta5Si3 intermediate layer, a 20 μm thick TaSi2 equiaxed crystal layer, a 35 μm thick TaSi2 columnar crystal layer, and a 3 μm thick Ta5Si3 interface reaction layer at the interface with the Ta12W tantalum alloy substrate, which are sequentially deposited from top to bottom on the Ta12W tantalum alloy substrate;

[0056] Each layer in the composite coating is formed during high-temperature vacuum reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces;

[0057] The silicide-boride composite ceramic surface layer is mainly composed of HfCrSi2, (Hf, Zr)B2, HfB, (Hf, Zr)Si ceramics, and contains a small amount of HfTa, Hf and Ta5Si3;

[0058] The Ta5Si3 intermediate layer is composed of t-Ta5Si3 and h-Ta5Si3 in which Hf and Zr elements are solid-dissolved, and Ta2Cr4Si5 phases. The atomic percentage of Hf element in t-Ta5Si3 is 13.1%, the atomic percentage of Zr element is 11.6%, and the atomic percentage of Cr element is 5.4%. The atomic percentage of Hf element in h-Ta5Si3 is 5.5%, the atomic percentage of Zr element is 2.8%, and the atomic percentage of Cr element is 10%.

[0059] The TaSi2 equiaxed crystal layer is composed of equiaxed TaSi2 crystals and Hf5Si4 and Ta3(CrSi)8 distributed on the grain boundaries of the TaSi2 equiaxed crystals.

[0060] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which comprises the following steps:

[0061] Step 1: Perform surface pretreatment of the Ta12W tantalum alloy by grinding, sandblasting, pickling and degreasing in sequence, so that the oxide and oxygen absorption layer on the Ta12W tantalum alloy are removed, and the surface is in a "pitted" state;

[0062] Step 2: Place the raw material powders Si powder, Hf powder, Cr powder, HfB2 ceramic particles and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle sizes of the Si powder, Hf powder and Cr powder are all 1μm to 5μm, the particle size of the HfB2 ceramic particles is 1μm to 10μm, the mass purity of each raw material powder is not less than 99%, and the mass percentage of Si powder in the mixed powder is 50%, the mass percentage of Cr powder is 6%, and the mass percentage of HfB2 ceramic particles is 10%;

[0063] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Ta12W tantalum alloy that has been surface pretreated in step 1 by dipping or pneumatic spraying, and a pre-applied layer is obtained on the surface of the tantalum alloy after drying, and then the Ta12W tantalum alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 2.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and an ultra-high temperature anti-oxidation and thermal shock resistant composite coating is prepared on the surface of Ta12W tantalum alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 700°C at a rate of 15°C / min and keeping warm for 60 minutes, and then heating to 1600°C at a rate of 8°C / min and keeping warm for 30 minutes.

[0064] Figure 4 This is a cross-sectional morphology of the ultra-high temperature anti-oxidation and anti-thermal shock composite coating prepared in this example after being oxidized for 5 hours in an atmospheric environment at 1700°C. Figure 4 It can be seen that after oxidation, a composite oxide film with high melting point oxides and silicates as the reinforcing phase and Hf-Zr-Ta-Si-BO as the main body is generated on the surface of the composite coating. The oxide film has a good interface with the coating, and the oxide film is uniform and continuous as a whole, showing excellent resistance to ultra-high temperature oxidation.

[0065] After testing, the composite coating of this embodiment did not fail after isothermal oxidation for 5 hours in an atmospheric environment of 1700°C, did not fail after isothermal oxidation for 400 seconds in an atmospheric environment of 1900°C, did not fail after 170 thermal shocks under water-cooling conditions at room temperature to 1700°C, and did not fail after 70 thermal shocks under water-cooling conditions at room temperature to 1800°C. The composite coating provides effective protection for tantalum alloy materials under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C.

[0066] Example 3

[0067] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is composed of a 30 μm thick silicide-boride composite ceramic surface layer, a 3 μm thick Ta5Si3 intermediate layer, a 15 μm thick TaSi2 equiaxed crystal layer, a 45 μm thick TaSi2 columnar crystal layer, and a 10 μm thick Ta5Si3 interface reaction layer at the interface with the Ta12W tantalum alloy substrate, which are sequentially deposited from top to bottom on the Ta12W tantalum alloy substrate;

[0068] Each layer in the composite coating is formed during high-temperature vacuum reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces;

[0069] The silicide-boride composite ceramic surface layer is mainly composed of HfCrSi2, (Hf, Zr)B2, HfB, (Hf, Zr)Si ceramics, and contains a small amount of HfTa, Hf and Ta5Si3;

[0070] The Ta5Si3 intermediate layer is composed of t-Ta5Si3 and h-Ta5Si3 in which Hf and Zr elements are solid-dissolved, and Ta2Cr4Si5 phases. The atomic percentage of Hf element in t-Ta5Si3 is 13.2%, the atomic percentage of Zr element is 11.7%, and the atomic percentage of Cr element is 6.7%. The atomic percentage of Hf element in h-Ta5Si3 is 5.3%, the atomic percentage of Zr element is 2.9%, and the atomic percentage of Cr element is 11.4%.

[0071] The TaSi2 equiaxed crystal layer is composed of equiaxed TaSi2 crystals and Hf5Si4 and Ta3(CrSi)8 distributed on the grain boundaries of the TaSi2 equiaxed crystals.

[0072] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which comprises the following steps:

[0073] Step 1: Perform surface pretreatment of the Ta12W tantalum alloy by grinding, sandblasting, pickling and degreasing in sequence, so that the oxide and oxygen absorption layer on the Ta12W tantalum alloy are removed, and the surface is in a "pitted" state;

[0074] Step 2: Place the raw material powders Si powder, Hf powder, Cr powder, HfB2 ceramic particles and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle sizes of the Si powder, Hf powder and Cr powder are all 1μm to 5μm, the particle size of the HfB2 ceramic particles is 1μm to 10μm, the mass purity of each raw material powder is not less than 99%, and the mass percentage of Si powder in the mixed powder is 70%, the mass percentage of Cr powder is 8%, and the mass percentage of HfB2 ceramic particles is 15%;

[0075] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Ta12W tantalum alloy that has been surface pretreated in step 1 by dipping or pneumatic spraying, and a pre-applied layer is obtained on the surface of the tantalum alloy after drying, and then the Ta12W tantalum alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 8.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and an ultra-high temperature anti-oxidation and thermal shock resistant composite coating is prepared on the surface of Ta12W tantalum alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 900°C at a rate of 5°C / min and keeping warm for 45 minutes, and then heating to 1350°C at a rate of 5°C / min and keeping warm for 120 minutes.

[0076] Figure 5 This is a cross-sectional morphology of the oxide film of the ultra-high temperature anti-oxidation and anti-thermal shock composite coating prepared in Example 3 of the present invention after oxidation at 1900°C for 400s. Figure 5 It can be seen that after oxidation, the composite coating also generates a composite oxide film with a sand-stone concrete structure, which has better resistance to high-temperature oxidation, thermal shock and thermal erosion than a single SiO2 glass film.

[0077] After testing, the composite coating of this embodiment did not fail after isothermal oxidation for 6 hours in an atmospheric environment of 1800°C, did not fail after isothermal oxidation for 400 seconds in an atmospheric environment of 1900°C, did not fail after 160 thermal shocks under water-cooling conditions of room temperature to 1700°C, and did not fail after 80 thermal shocks under water-cooling conditions of room temperature to 1800°C. The composite coating provides effective protection for tantalum alloy materials under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C.

[0078] Example 4

[0079] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is composed of a silicide-boride composite ceramic surface layer with a thickness of 28 μm, a Ta5Si3 intermediate layer with a thickness of 5 μm, a TaSi2 equiaxed crystal layer with a thickness of 18 μm, a TaSi2 columnar crystal layer with a thickness of 37 μm, and a Ta5Si3 interface reaction layer with a thickness of 7 μm at the interface with the Ta12W tantalum alloy substrate, which are deposited sequentially from top to bottom.

[0080] Each layer in the composite coating is formed during high-temperature vacuum reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces;

[0081] The silicide-boride composite ceramic surface layer is mainly composed of HfCrSi2, (Hf, Zr)B2, HfB, (Hf, Zr)Si ceramics, and contains a small amount of HfTa, Hf and Ta5Si3;

[0082] The Ta5Si3 intermediate layer is composed of t-Ta5Si3 and h-Ta5Si3 in which Hf and Zr elements are solid-dissolved, and Ta2Cr4Si5 phases. The atomic percentage of Hf element in t-Ta5Si3 is 14.1%, the atomic percentage of Zr element is 11%, and the atomic percentage of Cr element is 6.2%. The atomic percentage of Hf element in h-Ta5Si3 is 5.5%, the atomic percentage of Zr element is 2.3%, and the atomic percentage of Cr element is 11.4%.

[0083] The TaSi2 equiaxed crystal layer is composed of equiaxed TaSi2 crystals and Hf5Si4 and Ta3(CrSi)8 distributed on the grain boundaries of the TaSi2 equiaxed crystals.

[0084] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which comprises the following steps:

[0085] Step 1: Perform surface pretreatment of the Ta12W tantalum alloy by grinding, sandblasting, pickling and degreasing in sequence, so that the oxide and oxygen absorption layer on the Ta12W tantalum alloy are removed, and the surface is in a "pitted" state;

[0086] Step 2: Place the raw material powders Si powder, Hf powder, Cr powder, HfB2 ceramic particles and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle sizes of the Si powder, Hf powder and Cr powder are all 1μm to 5μm, the particle size of the HfB2 ceramic particles is 1μm to 10μm, the mass purity of each raw material powder is not less than 99%, and the mass percentage of Si powder in the mixed powder is 67%, the mass percentage of Cr powder is 6%, and the mass percentage of HfB2 ceramic particles is 18%;

[0087] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Ta12W tantalum alloy that has been surface pretreated in step 1 by dipping or pneumatic spraying, and a pre-applied layer is obtained on the surface of the tantalum alloy after drying, and then the Ta12W tantalum alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 1.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and an ultra-high temperature anti-oxidation and thermal shock resistant composite coating is prepared on the surface of Ta12W tantalum alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 850°C at a rate of 20°C / min and keeping warm for 40 minutes, and then heating to 1700°C at a rate of 6°C / min and keeping warm for 60 minutes.

[0088] Figure 6 This is the surface morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in this embodiment after 150 thermal shocks under water cooling conditions at room temperature to 1700°C. Figure 6 It can be seen that after thermal shock, the oxide film on the surface of the composite coating presents typical sand-stone concrete morphology characteristics, is intact as a whole, and does not crack or peel off, showing excellent thermal shock resistance.

[0089] After testing, the composite coating of this embodiment did not fail after isothermal oxidation for 8 hours in an atmospheric environment of 1700°C, did not fail after isothermal oxidation for 640 seconds in an atmospheric environment of 1900°C, did not fail after 150 thermal shocks under water-cooling conditions at room temperature to 1700°C, and did not fail after 64 thermal shocks under water-cooling conditions at room temperature to 1800°C. The composite coating provides effective protection for tantalum alloy materials under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C.

[0090] Example 5

[0091] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is composed of a silicide-boride composite ceramic surface layer with a thickness of 24 μm, a Ta5Si3 intermediate layer with a thickness of 7 μm, a TaSi2 equiaxed crystal layer with a thickness of 17 μm, a TaSi2 columnar crystal layer with a thickness of 34 μm, and a Ta5Si3 interface reaction layer with a thickness of 6 μm at the interface with the Ta12W tantalum alloy substrate, which are deposited sequentially from top to bottom on the Ta10W tantalum alloy substrate;

[0092] Each layer in the composite coating is formed during high-temperature vacuum reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces;

[0093] The silicide-boride composite ceramic surface layer is mainly composed of HfCrSi2, (Hf, Zr)B2, HfB, (Hf, Zr)Si ceramics, and contains a small amount of HfTa, Hf and Ta5Si3;

[0094] The Ta5Si3 intermediate layer is composed of t-Ta5Si3 and h-Ta5Si3 in which Hf and Zr elements are solid-dissolved, and Ta2Cr4Si5 phases. The atomic percentage of Hf element in t-Ta5Si3 is 12%, the atomic percentage of Zr element is 11.4%, and the atomic percentage of Cr element is not less than 5.1%. The atomic percentage of Hf element in h-Ta5Si3 is 6.4%, the atomic percentage of Zr element is 2.3%, and the atomic percentage of Cr element is 10.5%.

[0095] The TaSi2 equiaxed crystal layer is composed of equiaxed TaSi2 crystals and Hf5Si4 and Ta3(CrSi)8 distributed on the grain boundaries of the TaSi2 equiaxed crystals.

[0096] The ultra-high temperature anti-oxidation and anti-thermal shock composite coating of this embodiment is prepared by a one-step vacuum reaction sintering method, which comprises the following steps:

[0097] Step 1: Perform surface pretreatment of the Ta10W tantalum alloy by grinding, sandblasting, pickling and degreasing in sequence, so that the oxide and oxygen absorption layer on the Ta10W tantalum alloy are removed, and the surface is in a "pitted" state;

[0098] Step 2: Place the raw material powders Si powder, Hf powder, Cr powder, HfB2 ceramic particles and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle sizes of the Si powder, Hf powder and Cr powder are all 1μm to 5μm, the particle size of the HfB2 ceramic particles is 1μm to 10μm, the mass purity of each raw material powder is not less than 99%, and the mass percentage of Si powder in the mixed powder is 64%, the mass percentage of Cr powder is 6%, and the mass percentage of HfB2 ceramic particles is 25%;

[0099] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Ta10W tantalum alloy that has been surface pretreated in step 1 by dipping or pneumatic spraying, and a pre-applied layer is obtained on the surface of the tantalum alloy after drying, and then the Ta10W tantalum alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 9.0×10 -3 High-temperature firing is carried out under the conditions of Pa, and an ultra-high temperature anti-oxidation and thermal shock resistant composite coating is prepared on the surface of Ta10W tantalum alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 750°C at a rate of 15°C / min and keeping warm for 45 minutes, and then heating to 1550°C at a rate of 8°C / min and keeping warm for 80 minutes.

[0100] Figure 7 This is the surface morphology of the ultra-high temperature anti-oxidation and thermal shock resistant composite coating prepared in this embodiment after 50 thermal shocks under water cooling conditions at room temperature to 1800°C. Figure 7 It can be seen that some bubbles appeared on the surface of the composite coating after thermal shock, which was caused by the volatilization and overflow of CrO3 generated by oxidation in the composite coating, but the oxide film was intact as a whole, without cracking or peeling, showing excellent thermal shock resistance.

[0101] After testing, the composite coating of this embodiment did not fail after isothermal oxidation for 6 hours in an atmospheric environment of 1700°C, did not fail after isothermal oxidation for 450 seconds in an atmospheric environment of 1900°C, did not fail after 172 thermal shocks under water-cooling conditions at room temperature to 1700°C, and did not fail after 50 thermal shocks under water-cooling conditions at room temperature to 1800°C. The composite coating provides effective protection for tantalum alloy materials under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C.

[0102] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. An ultra-high temperature anti-oxidation and thermal shock resistant composite coating, characterized in that: It is composed of a silicide-boride composite ceramic surface layer, a Ta5Si3 intermediate layer, a TaSi2 equiaxed crystal layer, a TaSi2 columnar crystal layer and a Ta5Si3 interface reaction layer at the interface with the tantalum alloy substrate, which are deposited on the tantalum alloy substrate from top to bottom. The thickness of the silicide-boride composite ceramic surface layer is 15 μm to 30 μm, the thickness of the Ta5Si3 intermediate layer is 3 μm to 8 μm, the thickness of the TaSi2 equiaxed crystal layer is 15 μm to 20 μm, the thickness of the TaSi2 columnar crystal layer is 35 μm to 45 μm, and the thickness of the Ta5Si3 interface reaction layer is 3 μm to 10 μm; The composite coating has a constant temperature anti-oxidation life of not less than 5 hours in an atmospheric environment of 1700°C, a constant temperature anti-oxidation life of not less than 400 seconds in an atmospheric environment of 1900°C, a thermal shock life of not less than 150 times under water-cooling conditions of room temperature to 1700°C, and a thermal shock life of not less than 50 times under water-cooling conditions of room temperature to 1800°C; the composite coating provides effective protection for tantalum alloy materials under ultra-high temperature aerobic, strong oxidation and thermal scouring conditions not exceeding 1900°C.

2. The ultra-high temperature anti-oxidation and thermal shock resistant composite coating according to claim 1, characterized in that: Each layer in the composite coating is formed during high-temperature vacuum reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces.

3. The ultra-high temperature anti-oxidation and thermal shock resistant composite coating according to claim 1, characterized in that: The silicide-boride composite ceramic surface layer has HfCrSi2, (Hf, Zr)B2, HfB, (Hf, Zr)Si ceramics as main phases, and contains a small amount of HfTa, Hf and Ta5Si3.

4. The ultra-high temperature anti-oxidation and thermal shock resistant composite coating according to claim 1, characterized in that: The Ta5Si3 intermediate layer is composed of t-Ta5Si3 and h-Ta5Si3 in which Hf and Zr elements are solid dissolved, and Ta2Cr4Si5 phase. The atomic percentage of Hf element in t-Ta5Si3 is not less than 12%, the atomic percentage of Zr element is not less than 11%, and the atomic percentage of Cr element is not less than 5%. The atomic percentage of Hf element in h-Ta5Si3 is not less than 5%, the atomic percentage of Zr element is not less than 2%, and the atomic percentage of Cr element is not less than 10%.

5. The ultra-high temperature anti-oxidation and thermal shock resistant composite coating according to claim 1, characterized in that: The TaSi2 equiaxed crystal layer is composed of equiaxed TaSi2 crystals and Hf5Si4 and Ta3(CrSi)8 distributed on the grain boundaries of the TaSi2 equiaxed crystals.

6. The ultra-high temperature anti-oxidation and thermal shock resistant composite coating according to claim 1, characterized in that: The tantalum alloy substrate is Ta10W or Ta12W tantalum alloy.

7. A method for preparing the ultra-high temperature anti-oxidation and anti-thermal shock composite coating according to any one of claims 1 to 6, characterized in that: The preparation was carried out by a one-step vacuum reaction sintering method.

8. The method according to claim 7, characterized in that The method comprises the following steps: Step 1: Perform surface pretreatment of the tantalum alloy by grinding, sandblasting, pickling and degreasing in sequence, so that the oxide and oxygen absorption layer on the tantalum alloy are removed and the surface is in a "pitted" state; Step 2: Place the raw material powders Si powder, Hf powder, Cr powder, HfB2 ceramic particles and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle sizes of the Si powder, Hf powder and Cr powder are all 1μm to 5μm, the particle size of the HfB2 ceramic particles is 1μm to 10μm, the mass purity of each raw material powder is not less than 99%, and the mass percentage of Si powder in the raw material powder is not less than 40%, the mass percentage of Cr powder is not less than 3%, and the mass percentage of HfB2 ceramic particles is not less than 8%; Step 3: pre-coat the composite suspension slurry obtained in step 2 on the surface of the tantalum alloy that has been surface pretreated in step 1 by dipping or pneumatic spraying, and obtain a pre-coated layer on the surface of the tantalum alloy after drying. Then, place the tantalum alloy with the pre-coated layer in a vacuum sintering furnace at a vacuum degree of 8.0×10 -3 Pa~7.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and an ultra-high temperature anti-oxidation and thermal shock resistant composite coating is prepared on the surface of the tantalum alloy after cooling with the furnace; the specific process of the high-temperature firing is: firstly heating to 700°C~900°C at a rate of 5°C / min~20°C / min and keeping warm for 30min~60min, and then heating to 1350°C~1700°C at a rate of 5°C / min~10°C / min and keeping warm for 30min~120min.

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