Multi-layer composite silicide high-temperature coating with tissue degradation resistance and preparation method of multi-layer composite silicide high-temperature coating

Abstract

The invention discloses a multi-layer composite silicide high-temperature coating with tissue degradation resistance. The multi-layer composite silicide high-temperature coating sequentially comprises a MoSi2 surface layer, an NbSi2-Zr5Si4 main body layer, a Zr5Si4 diffusion-resistant layer, an NbSi2 lower layer and an Nb5Si3 interface reaction layer between the NbSi2 lower layer and a matrix from outside to inside, the coating is prepared by adopting a one-step vacuum reaction firing method. According to the coating, the NbSi2-Zr5Si4 main body layer is arranged to delay diffusion of the Si element to the substrate side, the NbSi2 lower layer is arranged to avoid diffusion of the Zr element to the substrate side, the structure degradation resistance of the coating is improved, the high-temperature protection performance of the coating is guaranteed, cracking and stripping of the coating are avoided, and the service life of the coating is prolonged; all layers and interlayer interfaces are generated in situ by adopting a one-step vacuum reaction sintering method, the interlayer bonding force is good, and the coating has excellent thermal shock resistance and is suitable for the field of high-temperature coatings.

Description

Technical Field

[0001] The present invention belongs to the technical field of high temperature protection, and in particular relates to a multilayer composite silicide high temperature coating with tissue degradation resistance and a preparation method thereof. Background Art

[0002] Among refractory metals, niobium and its alloys have the advantages of excellent high-temperature strength, good processing plasticity, and good corrosion resistance. They are important high-temperature structural materials and have been widely used in the aerospace industry. However, niobium and its alloys have high oxygen affinity and are easily oxidized. Applying a silicide coating can significantly improve the high-temperature oxidation resistance of niobium and niobium alloys. The silicide coating will form a continuous SiO2 glass protective film in a high-temperature oxygen-containing environment, which can effectively prevent the diffusion of oxygen to one side of the substrate. The SiO2 glass film has good fluidity at high temperatures and can promptly repair defects such as cracks and pores on the coating surface, showing a certain "self-healing property" that can continuously and effectively protect the niobium alloy substrate.

[0003] However, the silicide coating on the surface of niobium alloy has the following problems during high temperature service: (1) There is a large mismatch in thermal expansion coefficients between the substrate, coating and oxide film. -6 K -1 ) and the thermal expansion coefficient of the niobium 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. (2) There is a significant difference in chemical composition between the coating and the substrate. During the high-temperature service process, high-temperature diffusion reaction at the interface is inevitable, which causes the Si element in the coating to be quickly consumed, resulting in the coating being unable to maintain the stable growth of the SiO2 amorphous oxide film. In addition, the Nb element in the niobium alloy substrate will also diffuse into the coating and participate in the high-temperature oxidation reaction, thereby changing the structure and composition of the oxide film and reducing the high-temperature oxidation resistance of the coating.

[0004] In addition, among the many silicide coating preparation methods applicable to niobium alloys, the slurry vacuum reaction firing method has the advantages of easy control of coating thickness, easy adjustment of coating composition, and applicability to complex-shaped workpieces, and has been widely used in the aerospace industry. However, in the process of preparing silicide coatings using the vacuum reaction sintering method, the alloy matrix elements will participate in the chemical reactions that occur during the vacuum firing process, resulting in the coating composition and phase being greatly affected by the matrix chemical composition, which in turn causes the matrix element oxides to appear in the coating oxide film, significantly reducing the high-temperature oxidation resistance of the coating. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a multilayer composite silicide high-temperature coating with resistance to structural degradation in view of the deficiencies of the above-mentioned prior art. The coating of this method delays the diffusion of Si element to the substrate side by setting a NbSi2-Zr5Si4 main layer under the MoSi2 surface layer, and sets a NbSi2 lower layer to connect the Zr5Si4 diffusion barrier layer and the Nb5Si3 interface reaction layer, so as to avoid the rapid degradation of Zr element due to diffusion to the substrate side, thereby improving the structural degradation resistance of the multilayer composite silicide high-temperature coating, ensuring the high-temperature protective performance of the coating, and solving the problem that the Si element is easily consumed and the Nb element enters the coating during high-temperature service due to poor structural degradation resistance of the silicide coating on the surface of the niobium alloy, thereby reducing the high-temperature oxidation resistance of the coating.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a multilayer composite silicide high-temperature coating with resistance to tissue degradation, characterized in that the coating consists of 5 layers, and the layered structure is MoSi2 / NbSi2-Zr5Si4 / Zr5Si4 / NbSi2 / Nb5Si3, which are MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer between the substrate and the coating from the outside to the inside; The thickness of the MoSi2 surface layer is 20μm to 35μm, the thickness of the NbSi2-Zr5Si4 main layer is 90μm to 100μm, the thickness of the Zr5Si4 diffusion barrier layer is 3μm to 7μm, the thickness of the NbSi2 lower layer is 12μm to 18μm, and the thickness of the Nb5Si3 interface reaction layer is 7μm to 12μm; the anti-oxidation life of the multi-layer composite silicide high-temperature coating at 1500°C is not less than 60h, and the anti-oxidation life at 1600°C is not less than 10h.

[0007] The multilayer composite silicide high-temperature coating with tissue degradation resistance of the present invention has a layered structure designed to clarify the functions of each layer, so that the coating has both excellent resistance to isothermal oxidation and excellent resistance to high-temperature tissue degradation. Specifically, by setting a MoSi2 surface layer on the outermost layer of the coating, it is ensured that a protective SiO2 protective film can be generated on the surface of the coating under high-temperature isothermal or thermal shock conditions, thereby providing the coating with antioxidant properties; by setting the thickest NbSi2-Zr5Si4 main layer as a "storage pool" for the antioxidant element Si in the coating, the diffusion rate of the Si element in the Zr5Si4 diffusion barrier layer is slow, effectively alleviating the diffusion of the Si element to the substrate side, thereby delaying the high-temperature degradation rate of the coating tissue, and the Zr5Si4 diffusion barrier layer is located in the NbSi2-Zr5S Between the i4 main layer and the NbSi2 lower layer, the stress between the two layers of high silicon phases is effectively relieved, and the high silicon phase layer is prevented from cracking due to its large thickness; by setting the NbSi2 lower layer to connect the Zr5Si4 diffusion barrier layer and the Nb5Si3 interface reaction layer, it mainly plays the role of storing Si elements. At the same time, the solubility of Zr elements in NbSi2 is small, which can prevent the Zr elements in the Zr5Si4 diffusion barrier layer from diffusing to the side of the substrate and causing rapid degradation; by setting the Nb5Si3 interface reaction layer, it mainly plays the role of connecting the coating and the substrate, and improves the tightness of the connection between the two. In the present invention, by limiting the thickness of each layer in the coating, the coating is prevented from cracking and peeling under internal stress or thermal stress conditions while ensuring the high temperature protection performance of the coating. Finally, the anti-oxidation life of the multilayer composite silicide high temperature coating with resistance to tissue degradation in the present invention is not less than 60h at 1500℃, and the anti-oxidation life is not less than 10h at 1600℃.

[0008] The above-mentioned multi-layer composite silicide high-temperature coating with resistance to tissue degradation is characterized in that the MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer are all in-situ generated during vacuum high-temperature reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces with good interface bonding performance; the thermal shock life of the multi-layer composite silicide high-temperature coating under water-cooling conditions of room temperature to 1500°C is not less than 500 times, and the thermal shock life under water-cooling conditions of room temperature to 1600°C is not less than 400 times.

[0009] As the service temperature of niobium alloy coating is above 1400°C, the use of physical vapor deposition (PVD), chemical vapor deposition CVD or other methods to deposit multi-layer ceramic coatings on its surface will face the problems of insufficient interlayer or coating / substrate interface bonding performance and easy cracking and peeling under strong thermal shock conditions. The present invention forms various functional component layers on the surface of the niobium alloy substrate in situ by designing the composition of each layer and the firing process, and the interfaces between the layers are all formed in situ during the reaction, which has good interlayer and coating / substrate interface bonding performance.

[0010] The above-mentioned multi-layer composite silicide high-temperature coating with resistance to tissue degradation is characterized in that the MoSi2 on the surface of the MoSi2 surface layer mainly exists in the form of short rods and is in a "interlaced" form, and the atomic percentage of the impurity element Nb is less than 2%, and the atomic percentage of the Si element is not less than 66%. The MoSi2 surface layer in the present invention is located at the outermost layer of the coating, and is preferentially oxidized to form an oxide film under high-temperature oxidation conditions. Since the oxide of Mo is gaseous under high-temperature conditions, and the main element Nb in the matrix is ​​easily dissolved into the MoSi2 surface layer, the purity of the surface amorphous SiO2 oxide film is controlled by controlling the content of the impurity element Nb contained in MoSi2, and the excellent high-temperature oxygen barrier performance of the high-purity SiO2 oxide film is used to improve the coating's resistance to isothermal oxidation. By controlling the Si element content in MoSi2, the formation of the silicon phase in Mo5Si3 is avoided, the content of the high silicon phase on the surface is guaranteed, and the stable growth of the SiO2 oxide film is guaranteed. In addition, since the thermal expansion coefficient of the amorphous SiO2 oxide film is much smaller than that of MoSi2, it is very easy to peel off during the hot and cold cycle. The short rod-shaped MoSi2 particles on the surface of the MoSi2 surface layer of the present invention can pin the SiO2 glass film that does not contain other condensed oxide particles generated by oxidation of the coating under high temperature conditions, thereby preventing the oxide film from peeling off during the hot and cold cycle.

[0011] The above-mentioned multi-layer composite silicide high-temperature coating with resistance to structural degradation is characterized in that Zr5Si4 in the NbSi2-Zr5Si4 main layer is mainly distributed at the grain boundaries of NbSi2 grains. Since the MoSi2 surface layer of the outermost layer of the coating is relatively thin and the Si element content is limited, the NbSi2-Zr5Si4 main layer with high silicon phase NbSi2 as the main phase is provided. On the one hand, Si elements are provided to maintain the coating to avoid the stable growth of SiO2 protective oxide film. On the other hand, Zr5Si4 mainly distributed at the grain boundaries of NbSi2 grains slows down the diffusion of Si elements in the main layer to the substrate side, thereby reducing the degradation rate of the coating, improving the structural degradation resistance of the coating, and extending the high-temperature service life of the coating.

[0012] The above-mentioned multi-layer composite silicide high-temperature coating with resistance to tissue degradation is characterized in that the NbSi2 lower layer contains a small amount of Nb5Si3, and the Nb5Si3 layer is mainly distributed in the middle and lower part of the NbSi2 layer. Since the high-silicon phase of NbSi2 is brittle, a small amount of Nb5Si3 is mixed in the middle and lower part of the NbSi2 layer to form a gradient structure in composition, which is conducive to relieving interlayer stress and improving the thermal shock resistance of the coating.

[0013] The above-mentioned multi-layer composite silicide high-temperature coating with resistance to tissue degradation is characterized in that the coating is coated on the surface of a niobium alloy substrate. By selecting a niobium alloy as a substrate, Nb elements are provided for the NbSi2 high-silicon phase and the Nb5Si3 medium-silicon phase in the multi-layer composite silicide high-temperature coating with resistance to tissue degradation; at the same time, the mechanical properties of the niobium alloy as a substrate will not be significantly reduced during the vacuum high-temperature sintering preparation process and high-temperature service process of the multi-layer composite silicide high-temperature coating, and the niobium alloy is suitable for the preparation method of the present invention.

[0014] In addition, the present invention also discloses a method for preparing the above-mentioned multi-layer composite silicide high-temperature coating with resistance to tissue degradation, which is characterized in that it is prepared by a one-step vacuum reaction firing method.

[0015] The above method is characterized in that the method comprises the following steps:

[0016] Step 1: Pre-treating the niobium alloy substrate in sequence, including grinding, sandblasting, pickling and degreasing, so that the oxide and oxygen absorption layer on the niobium alloy are removed and the surface is in a "pitted" state;

[0017] Step 2: placing Si powder, Zr powder, Mo powder and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, Zr powder and Mo powder is 500nm-10μm, the mass purity is not less than 99%, and the mass percentage of Si powder in the Si powder, Zr powder and Mo powder is not less than 60%, and the mass percentage of Zr powder is not less than 8%;

[0018] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the niobium 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 niobium alloy after drying. The niobium alloy with the pre-applied layer is then placed in a vacuum sintering furnace at a vacuum degree of 4.0×10 -3 Pa~7.0×10 -2Pa, and a multilayer composite silicide high-temperature coating with resistance to tissue degradation is prepared on the surface of the niobium alloy after cooling in the furnace; the specific process of the high-temperature firing is: firstly heating to 750°C to 850°C at a rate of 5°C / min to 20°C / min and keeping warm for 30min to 60min, and then heating to 1300°C to 1600°C at a rate of 5°C / min to 10°C / min and keeping warm for 30min to 90min.

[0019] The present invention prepares raw materials Si powder, Zr powder, Mo powder and dispersant by high-energy ball milling to form a composite suspension slurry, and then pre-places it on the surface of the niobium alloy after surface pretreatment, and successively obtains a multi-layer composite silicide high-temperature coating with resistance to tissue degradation by drying and one-step vacuum reaction sintering. Each layer and the interface between the layers in the coating are formed in situ during the vacuum high-temperature sintering process, and the interface interlayer bonding force is good, so that the multi-layer composite silicide high-temperature coating with resistance to tissue degradation has excellent thermal shock resistance. In addition, the present invention adopts a one-step vacuum reaction sintering method to avoid the grain growth of the niobium alloy matrix during multiple sintering processes, and reduces the adverse effects on the microstructure and mechanical properties of the niobium alloy matrix.

[0020] The present invention removes impurities adsorbed on the surface of the niobium alloy due to its high oxygen affinity and the oxide scale generated by pre-treating the surface of the niobium alloy, and increases the roughness of the surface of the niobium alloy substrate, which is conducive to the formation of a good interface between the coating and the niobium alloy substrate, and is conducive to improving the firing quality of the subsequent coating. Then, the present invention controls the particle size of the raw material powder to obtain a uniformly mixed composite suspension slurry without significantly changing the particle size of the metal powder, ensuring the spraying and dipping performance of the slurry, which is conducive to improving the uniformity of the coating, and then combines the control of drying and vacuum high-temperature sintering process to regulate the mass transfer and chemical reaction process on the surface of the niobium alloy during vacuum sintering, and forms a multi-layer composite silicide high-temperature coating with resistance to tissue degradation on the surface of the niobium alloy. At the same time, the particle sizes of Si powder, Zr powder and Mo powder defined in the present invention are beneficial to promoting the silicidation reaction between Si and the metal elements Zr and Mo and the niobium alloy matrix during vacuum high-temperature sintering. The mass purity of Si powder, Zr powder and Mo powder is limited to reduce the introduction of impurity elements, thereby reducing the influence of impurity elements on the high-temperature protective performance of the multi-layer composite silicide high-temperature coating with resistance to tissue degradation. In addition, the mass percentage of Si powder in the raw material powder is also limited to not less than 60%, which is beneficial to improving the continuity and density of the multi-layer composite silicide high-temperature coating with resistance to tissue degradation, thereby helping to improve the oxidation resistance of the coating.

[0021] The present invention controls the high-temperature sintering process, thereby ensuring that the Si element in the coating reacts fully with other metal powders and the alloy matrix to form various functional layers and form a target coating structure, while avoiding the problem of low content of antioxidant Si element in the coating due to excessive reaction between the coating and the matrix.

[0022] Compared with the prior art, the present invention has the following advantages:

[0023] 1. The layered structure and composition of the multilayer composite silicide high-temperature coating of the present invention are designed. The diffusion of Si element to the substrate side is delayed by arranging a NbSi2-Zr5Si4 main layer under the MoSi2 surface layer, thereby delaying the high-temperature degradation rate of the coating structure. The diffusion of Zr element to the substrate side and rapid degradation are avoided by arranging a NbSi2 lower layer to connect the Zr5Si4 diffusion barrier layer and the Nb5Si3 interface reaction layer, thereby improving the structural degradation resistance of the multilayer composite silicide high-temperature coating, ensuring the high-temperature protection performance of the coating, avoiding cracking and peeling of the coating, and extending the service life of the coating.

[0024] 2. The multi-layer composite silicide high-temperature coating of the present invention has a MoSi2 surface layer on the outermost layer. The MoSi2 in the MoSi2 surface layer mainly exists in the form of short rods and has a "jigs and needles" shape, which effectively pins the SiO2 glass protective film generated by oxidation of the coating under high temperature conditions, thereby preventing it from peeling off during the hot and cold cycle due to a large mismatch in the thermal expansion coefficient with the coating.

[0025] 3. Compared with the silicide coating commonly used in niobium alloys, the multilayer composite silicide high-temperature coating of the present invention significantly slows down the diffusion of Si element in the coating to the substrate side by setting a Zr5Si4 diffusion barrier layer between the NbSi2-Zr5Si4 main layer and the NbSi2 lower layer, and Zr5Si4 distributed at the NbSi2 grain boundary in the NbSi2-Zr5Si4 main layer, thereby reducing the degradation rate of the coating, improving the coating's resistance to structural degradation, and extending the high-temperature service life of the coating, thereby solving the problem that the chemical composition of the silicide coating and the refractory alloy substrate is quite different and high-temperature diffusion reaction is inevitable under high-temperature service conditions.

[0026] 4. Compared with the silicide coating prepared on the surface of niobium alloy by vacuum reaction sintering of slurry, the chemical composition and high-temperature oxidation resistance of the multilayer composite silicide high-temperature coating with resistance to tissue degradation in the present invention are less affected by the composition of the niobium alloy matrix. The MoSi2 surface layer on the coating surface is oxidized to generate a high-purity SiO2 oxide film, which has better oxygen barrier properties than the oxide film mixed with Nb2O5 generated by oxidation of the sintered silicide coating, so that the high-temperature oxidation rate of the coating is lower and it has excellent high-temperature oxidation resistance.

[0027] 5. The present invention adopts a one-step vacuum reaction sintering method to prepare a multilayer composite silicide high-temperature coating with resistance to tissue degradation on the surface of a niobium alloy. The coating layers and the interfaces between the layers are in-situ generated during the high-temperature vacuum reaction sintering process. The interlayer bonding force is good, which effectively avoids interface cracking and peeling of the coating under thermal scouring or strong thermal shock conditions. Compared with multilayer composite coatings prepared by thermal spraying, CVD, PVD and other methods, the coating has more excellent thermal shock resistance.

[0028] 6. The present invention adopts a vacuum high-temperature sintering process to prepare a multilayer composite silicide high-temperature coating with resistance to tissue degradation on the surface of the niobium alloy, avoiding 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 complex-shaped niobium alloy components, and has higher coating deposition efficiency and lower cost than traditional chemical vapor deposition methods. In addition, the present invention adopts a one-step sintering process, which reduces the adverse effects of the sintering process on the microstructure and mechanical properties of the niobium alloy matrix compared to multiple sintering processes.

[0029] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a surface morphology of a multilayer composite silicide high-temperature coating with resistance to tissue degradation prepared in Example 1 of the present invention.

[0031] Figure 2 This is a cross-sectional morphology of a multilayer composite silicide high-temperature coating with resistance to tissue degradation prepared in Example 1 of the present invention.

[0032] Figure 3 This is a surface morphology of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in Example 1 of the present invention after constant temperature oxidation at 1500° C. for 10 hours.

[0033] Figure 4 This is a cross-sectional morphology of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in Example 2 of the present invention after constant temperature oxidation in an atmospheric environment at 1600°C for 3 hours.

[0034] Figure 5 This is a cross-sectional morphology diagram of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in Example 3 of the present invention after 500 thermal shocks at room temperature to 1500°C.

[0035] Figure 6 This is a cross-sectional morphology diagram of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in Example 4 of the present invention after being oxidized 400 times at room temperature to 1600°C. DETAILED DESCRIPTION

[0036] Example 1

[0037] The multilayer composite silicide high temperature coating with resistance to tissue degradation in this embodiment is composed of 5 layers, and the layered structure is MoSi2 / NbSi2-Zr5Si4 / Zr5Si4 / NbSi2 / Nb5Si3, which are, from outside to inside, a MoSi2 surface layer with a thickness of 35 μm, a NbSi2-Zr5Si4 main layer with a thickness of 85 μm, a Zr5Si4 diffusion barrier layer with a thickness of 6 μm, a NbSi2 lower layer with a thickness of 15 μm, and a Nb5Si3 interface reaction layer with a thickness of 12 μm between the Nb521 alloy substrate;

[0038] The MoSi2 on the surface of the MoSi2 surface layer mainly exists in the form of short rods and presents a "tooth-interlaced" shape, and the atomic percentage of the impurity element Nb is 1.8%, the atomic percentage of the Si element is 66.2%, and the Zr5Si4 in the NbSi2-Zr5Si4 main layer is mainly distributed at the grain boundaries of the NbSi2 grains; the NbSi2 lower layer contains a small amount of Nb5Si3, and the Nb5Si3 layer is mainly distributed in the middle and lower parts of the NbSi2 layer;

[0039] The MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer are all in-situ generated during vacuum high-temperature reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces with good interface bonding performance.

[0040] The multilayer composite silicide high-temperature coating with tissue degradation resistance of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0041] Step 1: performing surface pretreatment on the Nb521 alloy substrate in sequence, including grinding, sandblasting, pickling and degreasing, so that the oxide and oxygen absorption layer on the Nb521 alloy are removed and the surface is in a "pitted" state;

[0042] Step 2: placing Si powder, Zr powder, Mo powder and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, Zr powder and Mo powder is 500nm-10μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 65% and the mass percentage of Zr powder is 10% among the Si powder, Zr powder and Mo powder;

[0043] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Nb521 alloy that has been surface pretreated in step 1 by pneumatic spraying, and a pre-applied layer is obtained on the surface of the Nb521 alloy after drying, and then the Nb521 alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 4.0×10-3 Pa, and a multilayer composite silicide high-temperature coating with resistance to tissue degradation is prepared on the surface of the Nb521 alloy after cooling in the furnace; the specific process of the high-temperature firing is: firstly heating to 800°C at a rate of 15°C / min and keeping warm for 45min, and then heating to 1420°C at a rate of 8°C / min and keeping warm for 60min.

[0044] Figure 1 This is the surface morphology of the multilayer composite silicide high temperature coating with tissue degradation resistance prepared in this embodiment. Figure 1 It can be seen that the MoSi2 generated in situ on the surface of the coating is in the shape of short rods and presents a "jagged" state. MoSi2 with this morphological feature can effectively pin the amorphous SiO2 protective film formed during the oxidation process to prevent it from cracking and peeling under hot and cold cycling conditions.

[0045] Figure 2 This is a cross-sectional morphology of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in this embodiment. Figure 2 It can be seen that the coating forms a five-layer stacked structure, and the phases of each layer are MoSi2, NbSi2-Zr5Si4, Zr5Si4, NbSi2 and Nb5Si3 respectively.

[0046] Figure 3 This is a surface morphology of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in this embodiment after constant temperature oxidation at 1500°C for 10 hours. Figure 3 It can be seen that after a short period of oxidation, the coating surface still maintains a rod-shaped staggered morphology, but the rod-shaped MoSi2 surface is oxidized to form a thin glass film, which is significantly different from the morphology of the coating after oxidation prepared by PVD or CVD method; the characteristic structure of MoSi2 on the coating surface changes the existence form of the amorphous SiO2 film generated after the coating is oxidized, which is beneficial to improve the thermal shock resistance and thermal erosion resistance of the coating.

[0047] After testing, the multilayer composite silicide high-temperature coating prepared in this embodiment did not fail after constant temperature oxidation at 1500°C for 65 hours, and did not fail after constant temperature oxidation at 1600°C for 12 hours; the multilayer composite silicide high-temperature coating did not fail after 580 thermal shocks under water cooling conditions at room temperature to 1500°C, and did not fail after 460 thermal shocks under water cooling conditions at room temperature to 1600°C.

[0048] Example 2

[0049] The multilayer composite silicide high temperature coating with resistance to tissue degradation in this embodiment is composed of 5 layers, and the layered structure is MoSi2 / NbSi2-Zr5Si4 / Zr5Si4 / NbSi2 / Nb5Si3, which are, from outside to inside, a MoSi2 surface layer with a thickness of 28 μm, a NbSi2-Zr5Si4 main layer with a thickness of 90 μm, a Zr5Si4 diffusion barrier layer with a thickness of 3 μm, a NbSi2 lower layer with a thickness of 12 μm, and a Nb5Si3 interface reaction layer with a thickness of 10 μm between the Nb521 alloy substrate;

[0050] The MoSi2 on the surface of the MoSi2 surface layer mainly exists in the form of short rods and presents a "interlaced" shape, and the atomic percentage of the impurity element Nb is 1.7%, the atomic percentage of the Si element is 67.2%, and the Zr5Si4 in the NbSi2-Zr5Si4 main layer is mainly distributed at the grain boundaries of the NbSi2 grains; the NbSi2 lower layer contains a small amount of Nb5Si3, and the Nb5Si3 layer is mainly distributed in the middle and lower parts of the NbSi2 layer;

[0051] The MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer are all in-situ generated during vacuum high-temperature reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces with good interface bonding performance.

[0052] The multilayer composite silicide high-temperature coating with tissue degradation resistance of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0053] Step 1: performing surface pretreatment on the Nb521 alloy substrate in sequence, including grinding, sandblasting, pickling and degreasing, so that the oxide and oxygen absorption layer on the Nb521 alloy are removed and the surface is in a "pitted" state;

[0054] Step 2: placing Si powder, Zr powder, Mo powder and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, Zr powder and Mo powder is 500nm-10μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 70% and the mass percentage of Zr powder is 15% among the Si powder, Zr powder and Mo powder;

[0055] Step 3: The composite suspension slurry obtained in step 2 is pre-coated on the surface of the Nb521 alloy that has been surface pretreated in step 1 by dipping, and a pre-coated layer is obtained on the surface of the Nb521 alloy after drying, and then the Nb521 alloy with the pre-coated layer is placed in a vacuum sintering furnace at a vacuum degree of 1.0×10 -2High-temperature firing is carried out under the conditions of Pa, and a multilayer composite silicide high-temperature coating with resistance to tissue degradation is prepared on the surface of the Nb521 alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 780°C at a rate of 20°C / min and keeping warm for 60 minutes, and then heating to 1600°C at a rate of 10°C / min and keeping warm for 30 minutes.

[0056] Figure 4 This is a cross-sectional morphology of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in this embodiment after constant temperature oxidation for 3 hours in an atmospheric environment at 1600°C. Figure 4 It can be seen that a continuous and adhesive SiO2 protective film is generated on the surface of the oxidized coating; due to the presence of the Zr5Si4 phase in the coating, the outermost layer of the coating on one side of the oxide film / coating interface is still a high-silicon phase, which can maintain the stable growth of the SiO2 amorphous glass film, and the coating exhibits good resistance to tissue degradation.

[0057] After testing, the multilayer composite silicide high-temperature coating prepared in this embodiment did not fail after constant temperature oxidation at 1500°C for 68 hours, and did not fail after constant temperature oxidation at 1600°C for 15 hours; the multilayer composite silicide high-temperature coating did not fail after 550 thermal shocks under water cooling conditions at room temperature to 1500°C, and did not fail after 470 thermal shocks under water cooling conditions at room temperature to 1600°C.

[0058] Example 3

[0059] The multilayer composite silicide high temperature coating with resistance to tissue degradation in this embodiment is composed of 5 layers, and the layered structure is MoSi2 / NbSi2-Zr5Si4 / Zr5Si4 / NbSi2 / Nb5Si3, which are, from outside to inside, a MoSi2 surface layer with a thickness of 20 μm, a NbSi2-Zr5Si4 main layer with a thickness of 100 μm, a Zr5Si4 diffusion barrier layer with a thickness of 7 μm, a NbSi2 lower layer with a thickness of 18 μm, and a Nb5Si3 interface reaction layer with a thickness of 7 μm to 12 μm between the Nb521 alloy substrate;

[0060] The MoSi2 on the surface of the MoSi2 surface layer mainly exists in the form of short rods and presents a "interlaced" shape, and the atomic percentage of the impurity element Nb is 0.8%, the atomic percentage of the Si element is 67.3%, and the Zr5Si4 in the NbSi2-Zr5Si4 main layer is mainly distributed at the grain boundaries of the NbSi2 grains; the NbSi2 lower layer contains a small amount of Nb5Si3, and the Nb5Si3 layer is mainly distributed in the middle and lower parts of the NbSi2 layer;

[0061] The MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer are all in-situ generated during vacuum high-temperature reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces with good interface bonding performance.

[0062] The multilayer composite silicide high-temperature coating with tissue degradation resistance of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0063] Step 1: performing surface pretreatment on the Nb521 alloy substrate in sequence, including grinding, sandblasting, pickling and degreasing, so that the oxide and oxygen absorption layer on the Nb521 alloy are removed and the surface is in a "pitted" state;

[0064] Step 2: placing Si powder, Zr powder, Mo powder and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, Zr powder and Mo powder is 500nm-10μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 68%, and the mass percentage of Zr powder is 20%;

[0065] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Nb521 alloy that has been surface pretreated in step 1 by pneumatic spraying, and a pre-applied layer is obtained on the surface of the Nb521 alloy after drying, and then the Nb521 alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 7.0×10 -2 Pa, and a multilayer composite silicide high-temperature coating with resistance to tissue degradation is prepared on the surface of the Nb521 alloy after cooling in the furnace; the specific process of the high-temperature firing is: firstly heating to 850°C at a rate of 5°C / min and keeping warm for 30min, and then heating to 1300°C at a rate of 5°C / min and keeping warm for 90min.

[0066] Figure 5 This is a cross-sectional morphology of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in this embodiment after 500 thermal shocks at room temperature to 1500 °C. Figure 5 It can be seen that no obvious microcracks were found on the coating surface after thermal shock. In addition to the amorphous SiO2 glass film generated on the coating surface, MoSi2 protrusions that have not been completely oxidized can also be observed. The presence of these rod-shaped MoSi2 can significantly strengthen the SiO2 glass film and prevent it from peeling off during the cooling process.

[0067] After testing, the multilayer composite silicide high-temperature coating prepared in this embodiment did not fail after constant temperature oxidation at 1500°C for 65 hours, and did not fail after constant temperature oxidation at 1600°C for 12 hours; the multilayer composite silicide high-temperature coating did not fail after 580 thermal shocks under water cooling conditions at room temperature to 1500°C, and did not fail after 460 thermal shocks under water cooling conditions at room temperature to 1600°C.

[0068] Example 4

[0069] The multilayer composite silicide high temperature coating with resistance to tissue degradation in this embodiment is composed of 5 layers, and the layered structure is MoSi2 / NbSi2-Zr5Si4 / Zr5Si4 / NbSi2 / Nb5Si3, which are, from outside to inside, a MoSi2 surface layer with a thickness of 32 μm, a NbSi2-Zr5Si4 main layer with a thickness of 94 μm, a Zr5Si4 diffusion barrier layer with a thickness of 6 μm, a NbSi2 lower layer with a thickness of 15 μm, and a Nb5Si3 interface reaction layer with a thickness of 11 μm between the Nb521 alloy substrate;

[0070] The MoSi2 on the surface of the MoSi2 surface layer mainly exists in the form of short rods and presents a "interlaced" shape, and the atomic percentage of the impurity element Nb is 0.8%, the atomic percentage of the Si element is 66.8%, and the Zr5Si4 in the NbSi2-Zr5Si4 main layer is mainly distributed at the grain boundaries of the NbSi2 grains; the NbSi2 lower layer contains a small amount of Nb5Si3, and the Nb5Si3 layer is mainly distributed in the middle and lower parts of the NbSi2 layer;

[0071] The MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer are all in-situ generated during vacuum high-temperature reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces with good interface bonding performance.

[0072] The multilayer composite silicide high-temperature coating with tissue degradation resistance of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0073] Step 1: performing surface pretreatment on the Nb521 alloy substrate in sequence, including grinding, sandblasting, pickling and degreasing, so that the oxide and oxygen absorption layer on the Nb521 alloy are removed and the surface is in a "pitted" state;

[0074] Step 2: placing Si powder, Zr powder, Mo powder and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, Zr powder and Mo powder is 500nm-10μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 80%, and the mass percentage of Zr powder is 10%;

[0075] Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the Nb521 alloy that has been surface pretreated in step 1 by pneumatic spraying, and a pre-applied layer is obtained on the surface of the Nb521 alloy after drying, and then the Nb521 alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 8.0×10 -3 High-temperature firing is carried out under the conditions of Pa, and a multilayer composite silicide high-temperature coating with resistance to tissue degradation is prepared on the surface of the Nb521 alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 800°C at a rate of 15°C / min and keeping warm for 50 minutes, and then heating to 1550°C at a rate of 8°C / min and keeping warm for 40 minutes.

[0076] Figure 6 This is a cross-sectional morphology of the multilayer composite silicide high-temperature coating with tissue degradation resistance prepared in Example 4 of the present invention after being oxidized 400 times at room temperature to 1600°C. Figure 6 It can be seen that after experiencing strong thermal shock, obvious cracks appeared in the cross section of the coating, but the amorphous SiO2 glass film generated by oxidation of the coating effectively healed these cracks, and the coating did not fail after the thermal shock.

[0077] After testing, the multilayer composite silicide high-temperature coating prepared in this embodiment did not fail after constant temperature oxidation at 1500°C for 65 hours, and did not fail after constant temperature oxidation at 1600°C for 12 hours; the multilayer composite silicide high-temperature coating did not fail after 580 thermal shocks under water cooling conditions at room temperature to 1500°C, and did not fail after 460 thermal shocks under water cooling conditions at room temperature to 1600°C.

[0078] Example 5

[0079] The multilayer composite silicide high temperature coating with resistance to tissue degradation in this embodiment is composed of 5 layers, and the layered structure is MoSi2 / NbSi2-Zr5Si4 / Zr5Si4 / NbSi2 / Nb5Si3, which are, from outside to inside, a MoSi2 surface layer with a thickness of 28 μm, a NbSi2-Zr5Si4 main layer with a thickness of 94 μm, a Zr5Si4 diffusion barrier layer with a thickness of 3 μm to 7 μm, a NbSi2 lower layer with a thickness of 16 μm, and a Nb5Si3 interface reaction layer with a thickness of 10 μm between the Nb521 alloy substrate;

[0080] The MoSi2 on the surface of the MoSi2 surface layer mainly exists in the form of short rods and presents a "interlaced" shape, and the atomic percentage of the impurity element Nb is 1.2%, the atomic percentage of the Si element is 66.8%, and the Zr5Si4 in the NbSi2-Zr5Si4 main layer is mainly distributed at the grain boundaries of the NbSi2 grains; the NbSi2 lower layer contains a small amount of Nb5Si3, and the Nb5Si3 layer is mainly distributed in the middle and lower parts of the NbSi2 layer;

[0081] The MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer are all in-situ generated during vacuum high-temperature reaction firing, and the interfaces between the layers are all in-situ reaction self-generated interfaces with good interface bonding performance.

[0082] The multilayer composite silicide high-temperature coating with tissue degradation resistance of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0083] Step 1: performing surface pretreatment on the Nb521 alloy substrate in sequence, including grinding, sandblasting, pickling and degreasing, so that the oxide and oxygen absorption layer on the Nb521 alloy are removed and the surface is in a "pitted" state;

[0084] Step 2: placing Si powder, Zr powder, Mo powder and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, Zr powder and Mo powder is 500nm-10μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 75% and the mass percentage of Zr powder is 15% among the Si powder, Zr powder and Mo powder;

[0085] Step 3: The composite suspension slurry obtained in step 2 is pre-coated on the surface of the Nb521 alloy that has been surface pretreated in step 1 by dipping, and a pre-coated layer is obtained on the surface of the Nb521 alloy after drying, and then the Nb521 alloy with the pre-coated layer is placed in a vacuum sintering furnace at a vacuum degree of 3.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and a multilayer composite silicide high-temperature coating with resistance to tissue degradation is prepared on the surface of the Nb521 alloy after cooling in the furnace; the specific process of the high-temperature firing is: first heating to 800°C at a rate of 12°C / min and keeping warm for 50 minutes, and then heating to 1450°C at a rate of 8°C / min and keeping warm for 80 minutes.

[0086] After testing, the multilayer composite silicide high-temperature coating prepared in this embodiment did not fail after constant temperature oxidation at 1500°C for 65 hours, and did not fail after constant temperature oxidation at 1600°C for 12 hours; the multilayer composite silicide high-temperature coating did not fail after 580 thermal shocks under water cooling conditions at room temperature to 1500°C, and did not fail after 460 thermal shocks under water cooling conditions at room temperature to 1600°C.

[0087] 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. A multilayer composite silicide high temperature coating with resistance to tissue degradation, characterized in that: The coating consists of 5 layers, and the layered structure is MoSi2 / NbSi2-Zr5Si4 / Zr5Si4 / NbSi2 / Nb5Si3, which are, from outside to inside, a MoSi2 surface layer, a NbSi2-Zr5Si4 main layer, a Zr5Si4 diffusion barrier layer, a NbSi2 lower layer, and a Nb5Si3 interface reaction layer between the substrate; the thickness of the MoSi2 surface layer is 20μm to 35μm, the thickness of the NbSi2-Zr5Si4 main layer is 90μm to 100μm, the thickness of the Zr5Si4 diffusion barrier layer is 3μm to 7μm, the thickness of the NbSi2 lower layer is 12μm to 18μm, and the thickness of the Nb5Si3 interface reaction layer is 7μm to 12μm; the anti-oxidation life of the multi-layer composite silicide high-temperature coating at 1500°C is not less than 60h, and the anti-oxidation life at 1600°C is not less than 10h.

2. The multilayer composite silicide high temperature coating with tissue degradation resistance according to claim 1, characterized in that: The MoSi2 surface layer, NbSi2-Zr5Si4 main layer, Zr5Si4 diffusion barrier layer, NbSi2 lower layer and Nb5Si3 interface reaction layer are all generated in situ during the vacuum high-temperature reaction firing process. The interfaces between the layers are all self-generated interfaces of the in-situ reaction, and the interface bonding performance is good; the thermal shock resistance life of the multi-layer composite silicide high-temperature coating under water-cooling conditions of room temperature to 1500°C is not less than 500 times, and the thermal shock resistance life under water-cooling conditions of room temperature to 1600°C is not less than 400 times.

3. The multilayer composite silicide high temperature coating with tissue degradation resistance according to claim 1, characterized in that: The MoSi2 on the surface of the MoSi2 surface layer mainly exists in the form of short rods and presents a "tooth-interlaced" morphology, and the atomic percentage of the impurity element Nb is less than 2%, and the atomic percentage of the Si element is not less than 66%.

4. The multilayer composite silicide high temperature coating with tissue degradation resistance according to claim 1, characterized in that: In the NbSi2-Zr5Si4 main layer, Zr5Si4 is mainly distributed at the grain boundaries of NbSi2 grains.

5. The multi-layer composite silicide high temperature coating with tissue degradation resistance according to claim 1, characterized in that: The NbSi2 lower layer contains a small amount of Nb5Si3, and the Nb5Si3 layer is mainly distributed in the middle and lower part of the NbSi2 layer.

6. The multi-layer composite silicide high temperature coating with tissue degradation resistance according to claim 1, characterized in that: The coating is coated on the surface of the niobium alloy substrate.

7. A method for preparing a multilayer composite silicide high temperature coating having tissue degradation resistance as claimed in any one of claims 1 to 6, characterized in that: The preparation is 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: Pre-treating the niobium alloy substrate in sequence, including grinding, sandblasting, pickling and degreasing, so that the oxide and oxygen absorption layer on the niobium alloy are removed and the surface is in a "pitted" state; Step 2: placing Si powder, Zr powder, Mo powder and a dispersant in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, Zr powder and Mo powder is 500nm-10μm, the mass purity is not less than 99%, and the mass percentage of Si powder in the Si powder, Zr powder and Mo powder is not less than 60%, and the mass percentage of Zr powder is not less than 8%; Step 3: The composite suspension slurry obtained in step 2 is pre-applied on the surface of the niobium 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 niobium alloy after drying. The niobium alloy with the pre-applied layer is then placed in a vacuum sintering furnace at a vacuum degree of 4.0×10 -3 Pa~7.0×10 -2 Pa, and a multilayer composite silicide high-temperature coating with resistance to tissue degradation is prepared on the surface of the niobium alloy after cooling in the furnace; the specific process of the high-temperature firing is: firstly heating to 750°C to 850°C at a rate of 5°C / min to 20°C / min and keeping warm for 30min to 60min, and then heating to 1300°C to 1600°C at a rate of 5°C / min to 10°C / min and keeping warm for 30min to 90min.

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