Multi-layer complex-phase composite silicide high-temperature coating and preparation method thereof

Abstract

The invention discloses a multilayer complex-phase composite silicide high-temperature coating which is composed of an upper layer, a lower layer and an interface reaction layer, the upper layer and the lower layer are sequentially deposited on a niobium alloy matrix from top to bottom, the interface reaction layer is arranged between the upper layer and the matrix, the upper layer is (Nb, Ti and Cr) Si2-Nb4Cr2Si5, the lower layer is NbSi2-Nb5Si3, and the interface reaction layer is Nb5Si3; the coating is prepared by adopting a one-step vacuum reaction firing method. By designing the components and phase of the coating, the Si element is effectively prevented from diffusing towards the substrate side, the high-temperature degradation rate of the coating is delayed, and a similar sand-stone concrete structure is generated in a high-temperature oxidation environment, so that the coating has better high-temperature stability and higher high-temperature viscosity, and the high-temperature protection performance of the coating is improved; the coating and the interface layer are generated in situ through the one-step vacuum reaction firing method, interface cracking and stripping of the coating are avoided, and the method is suitable for the field of high-temperature alloy protection.

Description

Technical Field

[0001] The invention belongs to the technical field of high temperature protection, and in particular relates to a multi-layer multi-phase composite silicide high temperature coating and a preparation method thereof. Background Art

[0002] With the development of aerospace technology, the requirements of rocket engines and other power systems for the performance of high-temperature structural materials are gradually increasing. They are not only required to have excellent high-temperature mechanical properties, but also to have good high-temperature oxidation resistance and corrosion resistance. The single crystal high-temperature working temperature of the currently used nickel-based high-temperature alloy has reached 1150°C, which is close to 85% of its melting point. Therefore, metals with higher melting points and better resistance to high-temperature corrosion are needed. Refractory metals such as tantalum, niobium, tungsten, molybdenum, rhenium and their alloys have been widely used because of their good high-temperature mechanical properties and room temperature processing properties. Among them, niobium and its alloys have moderate density (7.83g / cm 3 ), has a high melting point (2468℃), has good ductility and thermal conductivity, and has good mechanical properties at high temperatures above 1500℃. It is widely used in key components of rocket engines, spacecraft and nuclear reactors.

[0003] However, due to their high affinity for oxygen and high oxygen solubility, niobium and its alloys will be severely oxidized at temperatures far below the service temperature, resulting in powdery Nb2O5 exfoliation. Niobium alloys are chemically stable at room temperature, but during the heating process, as the temperature rises, Nb will oxidize, causing the mechanical properties of the alloy to drop sharply. Therefore, how to effectively improve the high-temperature oxidation resistance of niobium alloys has become a key issue for their high-temperature applications, and there are two main ways to solve this problem: alloying and coating with a high-temperature oxidation-resistant coating. While alloying improves the oxidation resistance of the alloy, it will inevitably reduce the high-temperature mechanical properties of the alloy. Therefore, coating with a high-temperature oxidation-resistant coating is the main means to improve the oxidation resistance of the alloy at high temperatures at this stage. It can effectively improve the high-temperature oxidation resistance of the alloy without significantly reducing the high-temperature mechanical properties of the substrate.

[0004] For refractory metals, the most widely used high-temperature protective coating is the silicide coating. In a high-oxygen environment, the silicide coating will undergo selective oxidation to generate a molten SiO2 glass protective film with a certain fluidity, which can make up for defects such as voids and microcracks in the coating and block the diffusion of oxygen into the interior, thereby improving the high-temperature oxidation resistance. Traditional silicide coatings are divided into three categories: Si-Cr-Ti (Fe), Si-Mo, and Nb-Si. With the development of science and technology, the service environment of refractory metal high-temperature components has become increasingly harsh, and the shortcomings of traditional silicide coatings have gradually emerged: (1) The oxidation resistance of silicide coatings under high temperature conditions comes from the amorphous SiO2 glass film. However, due to the low thermal expansion coefficient of SiO2 (0.5×10 -6 ℃ -1 ) There is a large mismatch between the thermal expansion coefficient of the coating and that of the substrate, which makes it prone to cracking and peeling under hot and cold cycles or thermal shock conditions; (2) Due to the significant difference in the chemical composition of the coating and the substrate, the coating and the substrate will inevitably undergo a high-temperature diffusion reaction under high-temperature conditions, resulting in rapid consumption of the antioxidant Si element in the coating, significantly reducing the service life of the coating, and the higher the temperature, the faster the coating's retreat rate. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a multi-layer multi-phase composite silicide high-temperature coating in view of the deficiencies of the above-mentioned prior art. The present invention effectively prevents the diffusion of Si elements to the substrate side and slows down the high-temperature degradation rate of the coating by designing the coating composition and phase. It has a more excellent ability to resist tissue degradation under high temperature conditions, and generates a composite oxide film similar to the "sand-stone" concrete structure in a high-temperature oxidation environment. It has better high-temperature stability and higher high-temperature viscosity, and effectively prevents the oxide film on the surface of the coating from peeling off under hot and cold cycles or thermal shock conditions, thereby improving the high-temperature protection performance of the coating, and solving the problem that the existing silicide coating is prone to cracking and peeling at high temperatures, has a fast degradation rate, and has a reduced service life.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: a multi-layer complex phase composite silicide high temperature coating, characterized in that it is composed of an upper layer, a lower layer and an interface reaction layer between the substrate and the substrate deposited in sequence from top to bottom on a niobium alloy substrate, wherein the upper layer is (Nb, Ti, Cr) Si2-Nb4Cr2Si5 with a thickness of 50μm to 100μm, the lower layer is NbSi2-Nb5Si3 with a thickness of 25μm to 35μm, and the interface reaction layer is Nb5Si3 with a thickness of 5μm to 8μm; the anti-oxidation life of the multi-layer complex phase composite silicide high temperature coating at 1500°C is not less than 50h, and the anti-oxidation life at 1600°C is not less than 5h.

[0007] The multilayer multiphase composite silicide high-temperature coating of the present invention regulates the oxide film structure of the coating by designing the coating composition and phase, so that the coating has excellent resistance to high-temperature constant-temperature oxidation and a low degradation rate. The layered structure design of the coating relieves the stress between the coating and the substrate, and improves the bonding performance of the two, so that the coating has excellent thermal shock resistance. Specifically, the main phase NbSi2 in the lower layer NbSi2-Nb5Si3 of the multi-layer multi-phase composite silicide high-temperature coating acts as a "storage pool" for the anti-oxidation element Si in the coating, ensuring that the coating can generate a protective SiO2 protective film on the surface under high-temperature constant temperature or thermal shock conditions, ensuring that the coating has excellent high-temperature anti-oxidation performance; the (Nb, Ti, Cr) Si2 in the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 provides Ti elements for forming a high-temperature anti-oxidation TiO2 oxide film, and the diffusion rate of Si elements in Nb4Cr2Si5 is relatively slow, and its presence can effectively reduce the diffusion of Si elements to the substrate side, thereby delaying the high-temperature degradation rate of the coating structure; at the same time, the interface reaction layer Nb5Si3 between the substrate mainly plays the role of connecting the coating and the substrate, improving the bonding performance of the two. In addition, the thickness design of each layer in the multi-layer multi-phase composite silicide high-temperature coating of the present invention avoids cracking and peeling of the coating under internal stress or thermal stress conditions while ensuring the high-temperature protective performance of the coating, thereby improving the thermal shock resistance of the coating. Finally, the multi-layer multi-phase composite silicide high-temperature coating of the present invention has an anti-oxidation life of not less than 50 hours at 1500°C and an anti-oxidation life of not less than 5 hours at 1600°C.

[0008] In addition, the multilayer multiphase composite silicide high temperature coating of the present invention can also be disposed on other non-niobium alloy surfaces other than the niobium alloy substrate, but a Nb layer needs to be pre-deposited on the other non-niobium alloy surfaces to provide the Nb element required for the reaction of preparing the coating.

[0009] The above-mentioned multi-layer multi-phase composite silicide high-temperature coating is characterized in that the upper layer, the lower layer and the interface reaction layer are all generated by in-situ reaction during vacuum high-temperature firing, and the interfaces between the layers are all self-generated interfaces of in-situ reactions, and the interface bonding performance is good; the thermal shock resistance life of the multi-layer multi-phase composite silicide high-temperature coating under water-cooling conditions of room temperature to 1500°C is not less than 600 times, and the thermal shock resistance life under water-cooling conditions of room temperature to 1600°C is not less than 400 times.

[0010] The service temperature of niobium alloy is generally above 1400℃. Whether thermal spraying, physical vapor deposition (PVD), chemical vapor deposition CVD or other methods are used to deposit multilayer ceramic coatings on its surface, there will be problems such as insufficient interlayer or coating / substrate interface bonding performance and easy cracking and peeling under strong thermal shock conditions. In view of this technical difficulty, the present invention adopts a vacuum high-temperature firing process to in-situ form an upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, a lower layer NbSi2-Nb5Si3 and an interface reaction layer Nb5Si3 on the surface of the niobium alloy, and the interfaces between each layer are in-situ formed during the reaction, which has good interlayer and coating / substrate interface bonding performance, greatly improving the thermal shock resistance of the multilayer multiphase composite silicide high-temperature coating.

[0011] The above-mentioned multi-layer multi-phase composite silicide high-temperature coating is characterized in that the mass percentage of Nb element in the (Nb, Ti, Cr)Si2 ceramic phase of the upper layer (Nb, Ti, Cr)Si2-Nb4Cr2Si5 is not higher than 24%, the mass percentage of Ti element is not lower than 6%, and the mass percentage of Cr element is not lower than 3%.

[0012] The high-temperature oxidation resistance and erosion resistance of the multi-layer multi-phase composite silicide high-temperature coating of the present invention are mainly borne by the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5. The essential reason is that the coating surface is oxidized to form a composite oxide film with non-static SiO2 as the main body and TiO2 as the reinforcement phase. Therefore, the high-temperature oxidation resistance of the coating is guaranteed by regulating the Ti element content in the upper layer (Nb, Ti, Cr) Si2 ceramic phase, and the Nb element content is controlled to avoid the generation of Nb2O5 oxide in the coating to prevent the coating from being oxidized. At the same time, since the slower degradation rate of the multi-layer multiphase composite silicide high-temperature coating comes from the blocking effect of Nb4Cr2Si5 phase in the upper layer (Nb,Ti,Cr)Si2-Nb4Cr2Si5 on the Si element, the content of Cr element is adjusted to ensure that the Cr element reacts with the Nb-Si phase in the coating to generate a sufficient amount of (Nb,Ti,Cr)Si2 ceramic phase, avoiding the decomposition of part of the Nb4Cr2Si5 phase due to insufficient content, thereby reducing the coating's resistance to tissue degradation under high temperature conditions.

[0013] The above-mentioned multi-layer multi-phase composite silicide high-temperature coating is characterized in that (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed in the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, and the physical phase of the lower layer NbSi2-Nb5Si3 is mainly NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2. As mentioned above, the high-temperature oxidation resistance of the multi-layer multi-phase composite silicide high-temperature coating of the present invention mainly comes from the (Nb, Ti, Cr) Si2 phase, and the structural degradation resistance mainly comes from the Nb4Cr2Si5 phase, so the uniform mixing of the two phases is beneficial to taking into account the high-temperature oxidation resistance and structural degradation resistance of the coating; at the same time, due to the high brittleness of the high-silicon phase of NbSi2, by mixing a small amount of NbSi2 in the middle and lower layers of NbSi2, a gradient structure is formed in terms of composition, which is beneficial to relieving the stress between layers and improving the thermal shock resistance of the coating.

[0014] The above-mentioned multi-layer multi-phase composite silicide high-temperature coating is characterized in that the multi-layer multi-phase composite silicide high-temperature coating generates a composite oxide film with SiO2 glass film as the main body and TiO2 spherical particles as the reinforcement phase at 1100°C to 1600°C. The multi-layer multi-phase composite silicide high-temperature coating of the present invention is oxidized under high temperature conditions of 1100°C to 1600°C to form a composite oxide film with SiO2 glass film as the main filler and TiO2 spherical particles as the reinforcement phase, that is, a composite oxide film. The composite oxide film similar to the "sand-stone" structure has both oxygen barrier properties and thermal erosion resistance, better high-temperature stability and higher high-temperature viscosity, and can effectively prevent the oxide film on the surface of the coating from peeling off under hot and cold cycles or thermal shock conditions, thereby improving the high-temperature protection performance of the coating, and providing high-temperature protection for niobium alloy substrates such as advanced attitude and orbit control rocket engines and niobium alloy high-temperature components for hypersonic aircraft.

[0015] The present invention selects a niobium alloy substrate, which, on the one hand, provides Nb elements for (Nb, Ti, Cr)Si2, Nb4Cr2Si5, NbSi2 high silicon phase and Nb5Si3 medium silicon phase in the multi-layer multi-phase composite silicide high temperature coating; on the other hand, the high-temperature alloy niobium alloy is not prone to significant reduction in mechanical properties as a substrate during the vacuum high-temperature firing process of the coating and the subsequent high-temperature service process, and is suitable for the coating preparation method of the present invention.

[0016] At the same time, the present invention also discloses a method for preparing the multi-layer multi-phase composite silicide high-temperature coating as mentioned above, which is characterized in that the coating is prepared by a one-step vacuum reaction firing method.

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

[0018] Step 1: Pre-treating the surface of the base niobium alloy 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;

[0019] Step 2: placing Si powder, Cr powder, Ti 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, Cr powder and Ti powder is 500nm-5μm, the mass purity is not less than 99%, and the mass percentage of Si powder in the Si powder, Cr powder and Ti powder is not less than 65%, and the mass percentage of Cr powder is not less than 10%;

[0020] 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, and then the niobium alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 8.0×10 -4 Pa~2.0×10 -2 Pa, and a multilayer multiphase composite silicide high-temperature coating 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 900°C at a rate of 8°C / min to 15°C / min and keeping warm for 30min to 60min, and then heating to 1300°C to 1550°C at a rate of 5°C / min to 10°C / min and keeping warm for 30min to 90min.

[0021] Since the matrix niobium alloy has high oxygen affinity, the present invention removes impurities and oxide scale on the surface of the niobium alloy through surface pretreatment and increases the roughness of the surface of the niobium alloy, which is beneficial to the formation of a good interface bonding between the coating and the niobium alloy and improves the firing quality of the coating.

[0022] The present invention conducts high-energy ball milling of raw materials silicon powder, chromium powder, titanium powder and dispersant to obtain a uniformly mixed composite suspension slurry without significantly changing the particle size of each metal powder, thereby ensuring the spraying and dipping performance of the composite suspension slurry, which is beneficial to improving the uniformity of the coating. Combined with the controlled drying and vacuum high-temperature firing process, the mass transfer and chemical reaction process on the surface of the niobium alloy during the vacuum firing process are regulated to ensure the smooth preparation of the multi-layer multi-phase composite silicide high-temperature coating.

[0023] The present invention, by limiting the particle size of Si powder, Cr powder, and Ti powder, is conducive to promoting the silicification reaction between Si and Cr, Ti, and the niobium alloy matrix during vacuum high-temperature firing. By limiting the mass purity of Si powder, Cr powder, and Ti powder, the introduction of impurity elements is reduced, thereby reducing the influence of impurity elements on the high-temperature protection performance of the coating. At the same time, the present invention improves the continuity and density of the coating by limiting the mass content of Si powder in the raw material powder, and ensures the formation of the required Cr-containing ceramic phase in the coating by limiting the mass content of Cr powder in the raw material powder, and obtains the target coating structure. In addition, by limiting the specific process of vacuum high-temperature firing, the present invention ensures that the Si powder in the pre-set layer reacts with other metal powders and the matrix niobium alloy to fully form the upper and lower layers, ensuring that the layered structure and composite phase designed by the coating are obtained, and avoiding excessive reaction with the matrix, resulting in a large amount of anti-oxidant Si elements in the coating diffusing to one side of the matrix, resulting in a low content in the coating, and then resulting in insufficient anti-oxidation performance of the coating.

[0024] The present invention prepares the raw materials of the coating, silicon powder, chromium powder, titanium powder and dispersant, into a composite suspension slurry, and then pre-places it on the surface of the pretreated niobium alloy, and successively obtains a multi-layered complex phase composite silicide high temperature coating by drying and one-step vacuum reaction sintering. Since each layer and the interface between the layers in the coating are formed in situ during the vacuum high temperature sintering process, the interface interlayer bonding force is good, so that the multi-layered complex phase composite silicide high temperature coating has excellent high temperature protection performance. At the same time, 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.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. Compared with the conventional silicide coating on the surface of niobium alloy, the multilayer multiphase composite silicide high temperature coating of the present invention designs the coating composition and phase, utilizes the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 to form an oxide film and prevent the Si element from diffusing to the substrate side, thereby delaying the high temperature degradation rate of the coating, and Nb4Cr2Si5 plays a dispersion strengthening role to improve the fracture toughness of the upper layer, so that the coating has higher thermal shock resistance, and utilizes the lower layer NbSi2-Nb5Si3 to ensure that the coating generates a protective SiO2 protective film under high temperature constant temperature or thermal shock conditions, thereby improving the high temperature oxidation resistance of the coating, so that the coating has excellent high temperature constant temperature oxidation resistance and a lower high temperature degradation rate, thereby extending the service life of the coating.

[0027] 2. Compared with conventional silicide coatings on the surface of niobium alloys, the multi-layer multi-phase composite silicide high-temperature coating of the present invention generates a composite oxide film with a "sand-stone" concrete structure similar to that with TiO2 as a reinforcing phase and SiO2 glass as a filler in a high-temperature oxidizing environment. The TiO2 reinforcing phase is used to effectively strengthen and pin the SiO2 glass protective film, thereby effectively resisting the erosion of high-temperature and high-speed airflows. Compared with a single amorphous oxide film, it has better anti-stripping performance under thermal shock or hot and cold cycle conditions, and has more excellent thermal erosion resistance and thermal shock resistance, thereby improving the high-temperature protection performance of the coating.

[0028] 3. The present invention adopts a one-step vacuum reaction firing method to prepare a multilayer multiphase composite silicide high-temperature coating on the surface of a niobium alloy, so that the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, the lower layer NbSi2-Nb5Si3 and the Nb5Si3 interface reaction layer and the interlayer interface in the coating are all generated in situ during the vacuum high-temperature firing process, and the interlayer bonding force is good, which effectively avoids the interface cracking and peeling of the coating under thermal scouring or strong thermal shock conditions. Compared with the multilayer composite coating prepared by thermal spraying, CVD, PVD and other methods, it has more excellent thermal shock resistance.

[0029] 4. The present invention adopts a vacuum high-temperature sintering process to prepare a multi-layer complex phase composite silicide high-temperature coating 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 complex phase and layered composite coatings on the surface of complex-shaped niobium alloy components. Compared with the traditional chemical vapor deposition method, it has higher coating deposition efficiency and lower cost.

[0030] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a surface morphology of the multilayer multiphase composite silicide high-temperature coating prepared in Example 1 of the present invention.

[0032] Figure 2 This is a cross-sectional morphology diagram of the multi-layer multi-phase composite silicide high-temperature coating prepared in Example 1 of the present invention.

[0033] Figure 3 This is an enlarged cross-sectional morphology of the upper layer of the multi-layer multi-phase composite silicide high-temperature coating prepared in Example 1 of the present invention.

[0034] Figure 4 The multilayer multiphase composite silicide high temperature coating prepared in Example 1 of the present invention is

[0035] Surface morphology after 500 thermal shocks at ~1500℃ water cooling conditions.

[0036] Figure 5 This is a surface morphology of the multilayer multiphase composite silicide high-temperature coating prepared in Example 2 of the present invention after being oxidized in an atmospheric environment at 1500°C for 20 hours.

[0037] Figure 6 This is a cross-sectional morphology diagram of the multilayer multiphase composite silicide high-temperature coating prepared in Example 3 of the present invention after being oxidized in an atmospheric environment at 1500°C for 10 hours.

[0038] Figure 7 This is a surface morphology of the multilayer multiphase composite silicide high-temperature coating prepared in Example 4 of the present invention after being thermally shocked 300 times under water cooling conditions at room temperature to 1600°C. DETAILED DESCRIPTION

[0039] Example 1

[0040] The multilayer multiphase composite silicide high temperature coating of this embodiment is composed of an upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 with a thickness of 92 μm, a lower layer NbSi2-Nb5Si3 with a thickness of 34 μm, and an interface reaction layer Nb5Si3 with a thickness of 7 μm deposited on the Nb521 alloy substrate from top to bottom;

[0041] In the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed, and the mass percentage of Nb element in the (Nb, Ti, Cr) Si2 ceramic phase of the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 is 24%, the mass percentage of Ti element is 6.9%, and the mass percentage of Cr element is 3.5%; the physical phase of the lower layer NbSi2-Nb5Si3 is mainly composed of NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2; the upper layer, lower layer and interface reaction layer are all generated by in-situ reaction during vacuum high-temperature firing, and the interfaces between the layers are all self-generated interfaces of in-situ reactions, and the interface bonding performance is good.

[0042] The multilayer multiphase composite silicide high temperature coating of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0043] Step 1: Pre-treating the surface of the base Nb521 alloy 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;

[0044] Step 2: Place Si powder, Cr powder, Ti 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, Cr powder and Ti powder is 500nm-5μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 65% and the mass percentage of Cr powder is 18% among the Si powder, Cr powder and Ti powder;

[0045] 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 2.0×10 -2 The high-temperature firing is carried out under the conditions of Pa, and a multilayer multiphase composite silicide high-temperature coating is prepared on the surface of the Nb521 alloy after cooling with the furnace; the specific process of the high-temperature firing is: firstly heating to 800°C at a rate of 8°C / min and keeping warm for 45min, and then heating to 1400°C at a rate of 8°C / min and keeping warm for 60min.

[0046] Figure 1 This is the surface morphology of the multi-layer composite silicide high temperature coating prepared in this embodiment. Figure 1 It can be seen that the coating surface presents a typical vacuum reaction fired coating morphology. The coating surface is rough, "cauliflower" shaped, and there are holes on the surface. This is the result of the volume shrinkage of the high silicon phase generated on the surface during the firing process.

[0047] Figure 2 This is a cross-sectional morphology of the multi-layer composite silicide high temperature coating prepared in this embodiment. Figure 2 It can be seen that the coating presents obvious layered morphology characteristics, in which the upper layer is composed of two phases and the lower layer is composed of relatively pure NbSi2, but the lower part of the NbSi2 layer is distributed with bright white Nb5Si3, and the interface reaction layer between the coating and the substrate is Nb5Si3.

[0048] Figure 3 This is an enlarged cross-sectional morphology of the upper layer of the multi-layer multi-phase composite silicide high-temperature coating prepared in this embodiment. Figure 3 It can be seen that the upper layer of the coating has an obvious two-phase structure, in which the gray one is (Nb,Ti,Cr)Si2 and the black one is Nb4Cr2Si5.

[0049] Figure 4 The multilayer multiphase composite silicide high temperature coating prepared in Example 1 of the present invention is

[0050] Surface morphology after 500 thermal shocks at 1500℃ water cooling conditions. Figure 4It can be seen that there are no obvious cracks on the coating surface and the coating exhibits good self-healing ability.

[0051] The multilayer multiphase composite silicide high temperature coating of this embodiment generates a composite oxide film with SiO2 glass film as the main body and TiO2 spherical particles as the reinforcement phase under high temperature conditions of 1500°C. According to tests, the multilayer multiphase composite silicide high temperature coating of this embodiment did not fail after constant temperature oxidation at 1500°C for 60 hours, did not fail after constant temperature oxidation at 1600°C for 5 hours, did not fail after resisting thermal shock 700 times under water cooling conditions at room temperature to 1500°C, and did not fail after resisting thermal shock 400 times under water cooling conditions at room temperature to 1600°C.

[0052] Example 2

[0053] The multilayer multiphase composite silicide high temperature coating of this embodiment is composed of an upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 with a thickness of 100 μm, a lower layer NbSi2-Nb5Si3 with a thickness of 25 μm, and an interface reaction layer Nb5Si3 with a thickness of 5 μm deposited on the Nb521 alloy substrate from top to bottom;

[0054] In the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed, and the mass percentage of Nb element in the (Nb, Ti, Cr) Si2 ceramic phase of the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 is 23.4%, the mass percentage of Ti element is 7.2%, and the mass percentage of Cr element is 3.8%; the physical phase of the lower layer NbSi2-Nb5Si3 is mainly composed of NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2; the upper layer, the lower layer and the interface reaction layer are all generated by in-situ reaction during vacuum high-temperature firing, and the interfaces between the layers are all self-generated interfaces of in-situ reactions, and the interface bonding performance is good.

[0055] The multilayer multiphase composite silicide high temperature coating of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0056] Step 1: Pre-treating the surface of the base Nb521 alloy 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;

[0057] Step 2: Place Si powder, Cr powder, Ti 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, Cr powder and Ti powder is 500nm-5μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 68% and the mass percentage of Cr powder is 15% among the Si powder, Cr powder and Ti powder;

[0058] 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 8.0×10 -3 High-temperature firing is carried out under the conditions of Pa, and a multilayer multiphase composite silicide high-temperature coating 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 750°C at a rate of 15°C / min and keeping warm for 60 minutes, and then heating to 1550°C at a rate of 5°C / min and keeping warm for 30 minutes.

[0059] Figure 5 This is the surface morphology of the multi-layer composite silicide high temperature coating prepared in this example after being oxidized in an atmospheric environment at 1500°C for 20 hours. Figure 5 It can be seen that the coating generates a composite oxide film with SiO2 glass film as the main body and TiO2 spherical particles as the reinforcement phase under high temperature conditions of 1500℃.

[0060] After testing, the multilayer multiphase composite silicide high-temperature coating of this embodiment did not fail after isothermal oxidation at 1500°C atmospheric conditions for 50 hours, did not fail after isothermal oxidation at 1600°C for 10 hours, did not fail after resisting thermal shock for 680 times under water-cooling conditions at room temperature to 1500°C, and did not fail after resisting thermal shock for 430 times under water-cooling conditions at room temperature to 1600°C.

[0061] Example 3

[0062] The multilayer multiphase composite silicide high temperature coating of this embodiment is composed of an upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 with a thickness of 50 μm, a lower layer NbSi2-Nb5Si3 with a thickness of 35 μm, and an interface reaction layer Nb5Si3 with a thickness of 8 μm deposited on the Nb521 alloy substrate from top to bottom;

[0063] In the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed, and the mass percentage of Nb element in the (Nb, Ti, Cr) Si2 ceramic phase of the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 is 22.7%, the mass percentage of Ti element is 7.1%, and the mass percentage of Cr element is 4.2%; the physical phase of the lower layer NbSi2-Nb5Si3 is mainly composed of NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2; the upper layer, the lower layer and the interface reaction layer are all generated by in-situ reaction during vacuum high-temperature firing, and the interfaces between the layers are all self-generated interfaces of in-situ reactions, and the interface bonding performance is good.

[0064] The multilayer multiphase composite silicide high temperature coating of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0065] Step 1: Pre-treating the surface of the base Nb521 alloy 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;

[0066] Step 2: Place Si powder, Cr powder, Ti 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, Cr powder and Ti powder is 500nm-5μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 75% and the mass percentage of Cr powder is 10% among the Si powder, Cr powder and Ti powder;

[0067] 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 1.0×10 -2 High-temperature firing is carried out under the conditions of Pa, and a multilayer multiphase composite silicide high-temperature coating 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 900°C at a rate of 12°C / min and keeping warm for 30 minutes, and then heating to 1300°C at a rate of 10°C / min and keeping warm for 90 minutes.

[0068] Figure 6 This is a cross-sectional morphology of the multilayer multiphase composite silicide high-temperature coating prepared in this embodiment after being oxidized in an atmospheric environment at 1500°C for 10 hours. Figure 6It can be seen that the coating generates a composite oxide film with SiO2 glass film as the main body and TiO2 spherical particles as the reinforcement phase under high temperature conditions of 1500℃. The composite oxide film is continuous and well bonded to the coating interface. The upper layer of the coating has slightly degraded due to the selective oxidation of Si element, showing an obvious contrast difference with the high Si phase layer.

[0069] After testing, the multilayer multi-phase composite silicide high-temperature coating of this embodiment did not fail after isothermal oxidation for 68 hours under atmospheric conditions of 1500°C, did not fail after isothermal oxidation for 12 hours at 1600°C, did not fail after resisting thermal shock for 720 times under water-cooling conditions of room temperature to 1500°C, and did not fail after resisting thermal shock for 450 times under water-cooling conditions of room temperature to 1600°C.

[0070] Example 4

[0071] The multilayer multiphase composite silicide high temperature coating of this embodiment is composed of an upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 with a thickness of 70 μm, a lower layer NbSi2-Nb5Si3 with a thickness of 29 μm, and an interface reaction layer Nb5Si3 with a thickness of 6 μm deposited on the Nb521 alloy substrate from top to bottom;

[0072] In the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed, and the mass percentage of Nb element in the (Nb, Ti, Cr) Si2 ceramic phase of the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 is 23.2%, the mass percentage of Ti element is 8.1%, and the mass percentage of Cr element is 3.7%; the physical phase of the lower layer NbSi2-Nb5Si3 is mainly composed of NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2; the upper layer, the lower layer and the interface reaction layer are all generated by in-situ reaction during vacuum high-temperature firing, and the interfaces between the layers are all self-generated interfaces of in-situ reactions, and the interface bonding performance is good.

[0073] The multilayer multiphase composite silicide high temperature coating of this embodiment is prepared by a one-step vacuum reaction firing method, which includes the following steps:

[0074] Step 1: Pre-treating the surface of the base Nb521 alloy 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;

[0075] Step 2: Place Si powder, Cr powder, Ti 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, Cr powder and Ti powder is 500nm-5μm, the mass purity is not less than 99%, and the mass percentage of Si powder is 78% and the mass percentage of Cr powder is 10% among the Si powder, Cr powder and Ti powder;

[0076] 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 9.0×10 -3 High-temperature firing is carried out under the conditions of Pa, and a multilayer multiphase composite silicide high-temperature coating is prepared on the surface of the Nb521 alloy after cooling with the furnace; the specific process of the high-temperature firing is: first heating to 850°C at a rate of 10°C / min and keeping warm for 40 minutes, then heating to 1450°C at a rate of 10°C / min and keeping warm for 80 minutes.

[0077] Figure 7 This is the surface morphology of the multi-layer composite silicide high temperature coating prepared in this embodiment after 300 thermal shocks under the condition of room temperature to 1600°C water cooling. Figure 7 It can be seen that there are no obvious cracks on the surface of the coating, and the coating exhibits good self-healing ability.

[0078] The multi-layer multi-phase composite silicide high temperature coating of this embodiment generates a composite oxide film with SiO2 glass film as the main body and TiO2 spherical particles as the reinforcement phase at 1600°C.

[0079] After testing, the multilayer multiphase composite silicide high-temperature coating of this embodiment did not fail after isothermal oxidation for 68 hours under atmospheric conditions of 1500°C, did not fail after isothermal oxidation for 7 hours at 1600°C, did not fail after resisting thermal shock for 740 times under water-cooling conditions of room temperature to 1500°C, and did not fail after resisting thermal shock for 480 times under water-cooling conditions of room temperature to 1600°C.

[0080] 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 multi-layer multi-phase composite silicide high temperature coating, characterized in that: It consists of an upper layer, a lower layer and an interface reaction layer between the niobium alloy substrate and the substrate, which are deposited in sequence from top to bottom, wherein the upper layer is (Nb, Ti, Cr) Si2-Nb4Cr2Si5 with a thickness of 50μm to 100μm, the lower layer is NbSi2-Nb5Si3 with a thickness of 25μm to 35μm, and the interface reaction layer is Nb5Si3 with a thickness of 5μm to 8μm; the multi-layer multiphase composite silicide high-temperature coating has an anti-oxidation life of not less than 50h at 1500℃ and not less than 5h at 1600℃.

2. The multi-layer multi-phase composite silicide high temperature coating according to claim 1, characterized in that: The upper layer, the lower layer and the interface reaction layer are all generated by in-situ reaction during the vacuum high-temperature firing process. The interfaces between the layers are all self-generated interfaces of in-situ reaction, and the interface bonding performance is good. The thermal shock resistance life of the multi-layer multi-phase composite silicide high-temperature coating under water-cooling conditions of room temperature to 1500°C is not less than 600 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 multi-layer multi-phase composite silicide high temperature coating according to claim 1, characterized in that: The mass percentage of Nb element in the (Nb, Ti, Cr)Si2 ceramic phase of the upper layer (Nb, Ti, Cr)Si2-Nb4Cr2Si5 is not higher than 24%, the mass percentage of Ti element is not lower than 6%, and the mass percentage of Cr element is not lower than 3%.

4. The multi-layer multi-phase composite silicide high temperature coating according to claim 1, characterized in that: In the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed, and the physical phase of the lower layer NbSi2-Nb5Si3 is mainly NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2.

5. The multi-layer multi-phase composite silicide high temperature coating according to claim 1, characterized in that: The multi-layer multi-phase composite silicide high-temperature coating generates a composite oxide film with SiO2 glass film as the main body and TiO2 spherical particles as the reinforcement phase at 1100°C to 1600°C.

6. A method for preparing a multi-layer multi-phase composite silicide high temperature coating 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.

7. The method according to claim 6, characterized in that The method comprises the following steps: Step 1: Pre-treating the surface of the base niobium alloy 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, Cr powder, Ti 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, Cr powder and Ti powder is 500nm-5μm, the mass purity is not less than 99%, and the mass percentage of Si powder in the Si powder, Cr powder and Ti powder is not less than 65%, and the mass percentage of Cr powder is not less than 10%; 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, and then the niobium alloy with the pre-applied layer is placed in a vacuum sintering furnace at a vacuum degree of 8.0×10 -4 Pa~2.0×10 -2 Pa, and a multilayer multiphase composite silicide high-temperature coating 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 900°C at a rate of 8°C / min to 15°C / min and keeping warm for 30min to 60min, and then heating to 1300°C to 1550°C at a rate of 5°C / min to 10°C / min and keeping warm for 30min to 90min.

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