A multilayer multiphase composite silicide high-temperature coating and a preparation method thereof

Abstract

The application discloses a multilayer composite composite silicide high-temperature coating, which is composed of an upper layer, a lower layer and an interface reaction layer between the upper layer and the lower layer which are sequentially deposited on a niobium alloy substrate from top to bottom, wherein the upper layer is (Nb, Ti, Cr)Si2-Nb4Cr2Si5, the lower layer is NbSi2-Nb5Si3, and the interface reaction layer is Nb5Si3; the coating is prepared by using a one-step vacuum reaction sintering method. Through the design of the coating composition and phase, the application effectively prevents the diffusion of Si elements to the substrate side, delays the high-temperature degradation rate of the coating, and generates a structure similar to "sand-stone" concrete in a high-temperature oxidation environment, so that the coating has better high-temperature stability and higher high-temperature viscosity, thereby improving the high-temperature protection performance of the coating; the application generates the coating and the interface layer in situ by using the one-step vacuum reaction sintering method, avoids the interface cracking and peeling of the coating, and is suitable for the high-temperature alloy protection field.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high-temperature protection, and particularly relates to a multilayer composite silicide high-temperature coating and a preparation method thereof. BACKGROUND

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

[0003] However, niobium and its alloys have a high affinity for oxygen and a large oxygen solubility. They will oxidize severely at temperatures much lower than the service temperature, forming powdery Nb2O5 that peels off. Niobium alloys are chemically stable at room temperature, but during heating, as the temperature rises, Nb will oxidize, causing the mechanical properties of the alloy to decrease sharply. Therefore, how to effectively improve the high-temperature oxidation resistance of niobium alloys has become a key problem for their high-temperature application. The main methods to solve this problem are alloying and coating a high-temperature oxidation-resistant coating. Alloying can improve the oxidation resistance of the alloy, but it inevitably reduces the high-temperature mechanical properties of the alloy. Therefore, coating a high-temperature oxidation-resistant coating is the main means to improve the oxidation resistance of alloys at high temperatures at the present stage. It can effectively improve the high-temperature oxidation resistance of alloys while not significantly reducing the high-temperature mechanical properties of the substrate.

[0004] For refractory metals, the most widely used high-temperature protective coating is silicide coating. In a high-oxygen environment, the silicide coating will selectively oxidize to form a molten SiO2 glass protective film with a certain fluidity, which can fill the defects such as holes and microcracks in the coating and block the diffusion of oxygen to the inside, thereby improving the high-temperature oxidation resistance. Traditional silicide coatings are divided into Si-Cr-Ti(Fe) system, Si-Mo system and Nb-Si system. With the development of science and technology, the service environment of refractory metal high-temperature components is becoming more and more harsh, and the shortcomings of traditional silicide coatings are gradually emerging: (1) The oxidation resistance of silicide coating at high temperature comes from the amorphous SiO2 glass film. However, due to the low thermal expansion coefficient of SiO2 (0.5*10 -6 ℃ -1 ), the mismatch degree of the thermal expansion coefficient with the coating is large, and cracking and peeling are easy to occur under cold and hot cycle or thermal shock conditions; (2) Due to the significant difference in chemical composition between the coating and the substrate, high-temperature diffusion reaction between the coating and the substrate is inevitable under high-temperature conditions, which leads to rapid consumption of the oxidation-resistant Si element in the coating, significantly reducing the service life of the coating, and the higher the temperature, the faster the coating degradation rate. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a multi-layer complex composite silicide high-temperature coating to solve the above-mentioned problems of the prior art. By designing the composition and phase of the coating, the present application effectively prevents the diffusion of Si element to the substrate side, delays the high-temperature degradation rate of the coating, has more excellent anti-organizational degradation ability under high-temperature conditions, and generates a composite oxidation film similar to a "sand-stone" concrete structure in a high-temperature oxidation environment, which has better high-temperature stability and higher high-temperature viscosity, effectively avoiding the peeling of the oxidation film on the surface of the coating under cold and hot cycle or thermal shock conditions, thereby improving the high-temperature protection performance of the coating, and solving the problems of easy cracking and peeling of the existing silicide coating under high temperature, fast degradation rate and reduced service life.

[0006] To solve the above technical problems, the technical scheme adopted by the present application is as follows: a multi-layer complex composite silicide high-temperature coating, characterized in that it is composed of an upper layer, a lower layer and an interfacial reaction layer between the substrate, which are sequentially deposited on the niobium alloy substrate from top to bottom, wherein the upper layer is (Nb, Ti, Cr)Si2-Nb4Cr2Si5, the thickness is 50-100 μm, the lower layer is NbSi2-Nb5Si3, the thickness is 25-35 μm, and the interfacial reaction layer is Nb5Si3, the thickness is 5-8 μm; the anti-oxidation life of the multi-layer complex composite silicide high-temperature coating at 1500℃ is not less than 50h, and the anti-oxidation life at 1600℃ is not less than 5h.

[0007] The multilayer complex composite silicide high-temperature coating of the present application has excellent high-temperature isothermal oxidation resistance and low degradation rate by designing the coating composition and phase to control the oxide film structure of the coating, and has excellent thermal shock resistance by designing the layered structure of the coating to relieve the stress between the coating and the substrate and improve the bonding performance between the coating and the substrate. Specifically, the main phase NbSi2 in the lower layer NbSi2-Nb5Si3 of the multilayer complex composite silicide high-temperature coating of the present application acts as a "storage pool" of the oxidation-resistant element Si in the coating, ensuring that a protective SiO2 protective film can be generated on the surface of the coating under high-temperature isothermal or thermal shock conditions, thereby ensuring excellent high-temperature oxidation resistance of the coating; the (Nb,Ti,Cr)Si2 in the upper layer (Nb,Ti,Cr)Si2-Nb4Cr2Si5 provides Ti element for forming TiO2 oxidation film with high-temperature oxidation resistance, and the diffusion rate of Si element in Nb4Cr2Si5 is slow, so the presence of Nb4Cr2Si5 can effectively reduce the diffusion of Si element 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 coating and the substrate mainly serves to connect the coating and the substrate and improve the bonding performance between the coating and the substrate. In addition, the thickness of each layer in the multilayer complex composite silicide high-temperature coating of the present application is designed to ensure the high-temperature protection performance of the coating under the premise of avoiding cracking and peeling of the coating under internal stress or thermal stress conditions, thereby improving the thermal shock resistance of the coating. Finally, the multilayer complex composite silicide high-temperature coating of the present application has an oxidation resistance life of not less than 50 h at 1500℃ and an oxidation resistance life of not less than 5 h at 1600℃.

[0008] In addition, the multilayer complex composite silicide high-temperature coating of the present application can also be provided on the surface of other non-niobium alloy substrates, but a Nb layer needs to be pre-deposited on the surface of other non-niobium alloy substrates to provide the required Nb element for the preparation of the coating.

[0009] The multilayer complex composite silicide high-temperature coating has the following characteristics: the upper layer, the lower layer and the interface reaction layer are all generated in situ during the vacuum high-temperature firing process, the interfaces between the layers are all in-situ reaction interfaces, and the interface bonding performance is good; the multilayer complex composite silicide high-temperature coating has a thermal shock resistance life of not less than 600 times under room temperature-1500℃ water cooling conditions and a thermal shock resistance life of not less than 400 times under room temperature-1600℃ water cooling conditions.

[0010] The service temperature of the niobium alloy is generally above 1400 DEG C, and no matter whether the multilayer ceramic coating is deposited on the surface of the niobium alloy by using thermal spraying, physical vapor deposition (PVD), chemical vapor deposition (CVD) or other methods, the problems of insufficient interlayer or coating / substrate interface bonding performance and easy cracking and peeling under strong thermal shock conditions will be faced. In view of the technical problems, the vacuum high-temperature firing process is adopted to form the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, the lower layer NbSi2-Nb5Si3 and the interface reaction layer Nb5Si3 on the surface of the niobium alloy in situ, and the interfaces between the layers are formed in situ in the reaction, so that the interlayer and the coating / substrate interface bonding performance are good, and the thermal shock resistance of the multilayer composite silicide high-temperature coating is greatly improved.

[0011] The multilayer composite silicide high-temperature coating has the characteristics that the mass percentage content 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 content of Ti element is not less than 6%, and the mass percentage content of Cr element is not less than 3%.

[0012] The high-temperature oxidation resistance and erosion resistance protection performance of the multilayer composite silicide high-temperature coating of the application are mainly borne by the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, and the essential reason is that the oxidation of the coating surface generates a composite oxide film mainly composed of non-static SiO2 and reinforced by TiO2, so that the content of Ti element in the (Nb, Ti, Cr) Si2 ceramic phase of the upper layer is adjusted to ensure the high-temperature oxidation resistance of the coating, and the content of Nb element is controlled to avoid the adverse effect of the Nb2O5 oxide generated in the coating on the oxidation resistance of the coating. At the same time, since the slow degradation rate of the multilayer composite silicide high-temperature coating is derived from the blocking effect of the Nb4Cr2Si5 phase in the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 on 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, so as to avoid the decomposition of part of the Nb4Cr2Si5 phase due to insufficient content, and reduce the microstructure degradation resistance of the coating under high temperature conditions.

[0013] The multilayer complex composite silicide high-temperature coating has the characteristics that (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed in the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, and the phase of the lower layer NbSi2-Nb5Si3 is mainly NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2. As described above, the high-temperature oxidation resistance of the multilayer complex composite silicide high-temperature coating of the application is mainly from the (Nb, Ti, Cr) Si2 phase, and the resistance to microstructure degradation is mainly from the Nb4Cr2Si5 phase, so the uniform mixing of the two phases is beneficial to the high-temperature oxidation resistance and the resistance to microstructure degradation of the coating; at the same time, since the NbSi2 high-silicon phase is brittle, by mixing a small amount of NbSi2 in the middle and lower layers of NbSi2, a gradient structure is formed in the composition, which is beneficial to relieving the stress between the layers and improving the thermal shock resistance of the coating.

[0014] The multilayer complex composite silicide high-temperature coating has the characteristics that (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 are uniformly mixed in the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5, and the phase of the lower layer NbSi2-Nb5Si3 is mainly NbSi2, and Nb5Si3 is mainly distributed in the middle and lower layers of NbSi2. As described above, the high-temperature oxidation resistance of the multilayer complex composite silicide high-temperature coating of the application is mainly from the (Nb, Ti, Cr) Si2 phase, and the resistance to microstructure degradation is mainly from the Nb4Cr2Si5 phase, so the uniform mixing of the two phases is beneficial to the high-temperature oxidation resistance and the resistance to microstructure degradation of the coating; at the same time, since the NbSi2 high-silicon phase is brittle, by mixing a small amount of NbSi2 in the middle and lower layers of NbSi2, a gradient structure is formed in the composition, which is beneficial to relieving the stress between the layers and improving the thermal shock resistance of the coating.

[0015] The application selects a niobium alloy substrate, which provides Nb elements for (Nb, Ti, Cr) Si2, Nb4Cr2Si5, NbSi2 high-silicon phase and Nb5Si3 medium-silicon phase in the multilayer complex composite silicide high-temperature coating, and the mechanical properties of the high-temperature alloy niobium alloy as the substrate are not easily reduced significantly during the vacuum high-temperature sintering process of the coating and the subsequent high-temperature service process, so the coating preparation method of the application is suitable.

[0016] Meanwhile, the application also discloses a method for preparing the multilayer complex composite silicide high-temperature coating as described above, which has the characteristics that the one-step vacuum reaction sintering method is used for preparation.

[0017] The method has the characteristics that the method comprises the following steps:

[0018] Step one, the base niobium alloy is sequentially subjected to surface pretreatment, including polishing treatment, sand blasting treatment, pickling and degreasing treatment, so that the oxides and oxygen absorption layer on the niobium alloy are removed, and the surface is in a "pitted" state;

[0019] Step two, the Si powder, Cr powder, Ti powder and dispersant are placed 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-5um, 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 three, the composite suspension slurry obtained in step two is pre-placed on the surface of the niobium alloy subjected to surface pretreatment in step one by using dip coating or pneumatic spraying, and after drying, a pre-placed layer is obtained on the surface of the niobium alloy, and then the niobium alloy with the pre-placed layer is placed in a vacuum sintering furnace, and high-temperature sintering is carried out under the condition that the vacuum degree is 8.0*10 -4 Pa-2.0*10 -2 Pa, and after furnace cooling, a multilayer composite silicide high-temperature coating is prepared on the surface of the niobium alloy; the specific process of high-temperature sintering is: first, heat to 750-900℃ at a rate of 8-15℃ / min and keep for 30-60min, then heat to 1300-1550℃ at a rate of 5-10℃ / min and keep for 30-90min.

[0021] Since the oxygen affinity potential of the base niobium alloy is high, the surface pretreatment is used to remove impurities and oxide scale on the surface of the niobium alloy, and the roughness of the surface of the niobium alloy is increased, which is beneficial to the formation of good interface bonding between the coating and the niobium alloy and improves the sintering quality of the coating.

[0022] The raw materials silicon powder, chromium powder and titanium powder are subjected to high-energy ball milling with a dispersant, and a uniformly mixed composite suspension slurry is obtained without significantly changing the particle size of each metal powder, which ensures the spraying and dipping performance of the composite suspension slurry and is beneficial to improving the uniformity of the coating, and in combination with the control of drying and vacuum high-temperature sintering process, the mass transfer and chemical reaction process on the surface of the niobium alloy during vacuum sintering is controlled, and the smooth preparation of the multilayer composite silicide high-temperature coating is ensured.

[0023] The application is beneficial to promote the silicidation reaction between Si and Cr, Ti and the niobium alloy substrate in the vacuum high-temperature sintering process by limiting the particle size of Si powder, Cr powder and Ti powder, and reduces the introduction of impurity elements by limiting the mass purity of Si powder, Cr powder and Ti powder, thereby reducing the influence of impurity elements on the high-temperature protection performance of the coating. Meanwhile, the application 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 and obtains the purpose coating structure by limiting the mass content of Cr powder in the raw material powder. In addition, the application ensures the full reaction between Si powder in the preposition layer and other metal powders and the substrate niobium alloy to form the upper layer and the lower layer, ensures the layered structure and composite phase of the coating design, and avoids the problem that the oxidation-resistant Si element in the coating diffuses to the substrate side in large quantities due to excessive reaction with the substrate, which leads to a low content in the coating and further leads to insufficient oxidation resistance of the coating.

[0024] The application prepares the raw materials silicon powder, chromium powder and titanium powder of the coating into a composite suspension slurry with a dispersant, and then prepositions on the surface of the pretreated niobium alloy, and then obtains the multilayer composite silicide high-temperature coating by drying and one-step vacuum reaction sintering. Since each layer and the interfacial layer in the coating are formed in situ during the vacuum high-temperature sintering process, the interfacial bonding force is good, so that the multilayer composite silicide high-temperature coating has excellent high-temperature protection performance. Meanwhile, the one-step vacuum reaction sintering method avoids the grain growth of the niobium alloy substrate in the multiple melting and sintering process, and reduces the adverse effects on the microstructure and mechanical properties of the niobium alloy substrate.

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

[0026] 1. Compared with the conventional silicide coating on the surface of the niobium alloy, the multilayer composite silicide high-temperature coating of the application utilizes the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 to form an oxidation film and prevent the diffusion of Si elements to the substrate side, delays the high-temperature degradation rate of the coating, and the Nb4Cr2Si5 plays a dispersion strengthening role to improve the fracture toughness of the upper layer, so that the coating has higher thermal shock resistance. The lower layer NbSi2-Nb5Si3 ensures the formation of a protective SiO2 film in the coating under high-temperature constant temperature or thermal shock conditions, and improves the high-temperature oxidation resistance of the coating, so that the coating has excellent high-temperature constant oxidation resistance and a lower high-temperature degradation rate, prolonging the service life of the coating.

[0027] 2、Compared with the conventional silicide coating on the surface of niobium alloy, the multilayer composite silicide high-temperature coating of the application generates a composite oxidation film with a "sand-stone" concrete structure similar to TiO2 as a reinforcing phase and SiO2 glass as a filler in a high-temperature oxidation environment, effectively strengthens and pins the SiO2 glass protective film with the TiO2 reinforcing phase, thereby effectively resisting the erosion of high-temperature high-speed airflow, and has better anti-peeling performance than a single amorphous oxidation film under thermal shock or cold-hot cycle working conditions, and has more excellent anti-thermal erosion performance and thermal shock resistance, thereby improving the high-temperature protection performance of the coating.

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

[0029] 4、The application adopts a vacuum high-temperature melting and firing process to prepare a multilayer composite silicide high-temperature coating on the surface of niobium alloy, which avoids the problem that the conventional thermal spraying or electron beam physical vapor deposition process is difficult to prepare a composite, layered composite coating on the surface of a complex-shaped niobium alloy component, and has higher coating deposition efficiency and lower cost than the traditional chemical vapor deposition method.

[0030] The technical solutions of the application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The surface morphology diagram of the multilayer composite silicide high-temperature coating prepared for the example 1 of the application.

[0032] Figure 2 The cross-sectional morphology diagram of the multilayer composite silicide high-temperature coating prepared for the example 1 of the application.

[0033] Figure 3 The upper layer cross-sectional magnified morphology diagram of the multilayer composite silicide high-temperature coating prepared for the example 1 of the application.

[0034] Figure 4 The surface morphology diagram of the multilayer composite silicide high-temperature coating prepared for the example 1 of the application at room temperature

[0035] The surface morphology diagram of the multilayer composite silicide high-temperature coating prepared for the example 1 of the application after thermal shock for 500 times under the condition of room temperature

[0036] Figure 5 The surface morphology diagram of the multilayer composite silicide high-temperature coating prepared in Embodiment 2 of the present application after oxidation at 1500℃ in an atmospheric environment for 20h.

[0037] Figure 6 The cross-section morphology diagram of the multilayer composite silicide high-temperature coating prepared in Embodiment 3 of the present application after oxidation at 1500℃ in an atmospheric environment for 10h.

[0038] Figure 7 The surface morphology diagram of the multilayer composite silicide high-temperature coating prepared in Embodiment 4 of the present application after thermal shock for 300 times under room temperature-1600℃ water cooling conditions. DETAILED DESCRIPTION

[0039] Embodiment 1

[0040] The multilayer composite silicide high-temperature coating of the present embodiment is composed of an upper layer (Nb,Ti,Cr)Si2-Nb4Cr2Si5 with a thickness of 92μm, a lower layer NbSi2-Nb5Si3 with a thickness of 34μm and an interface reaction layer Nb5Si3 with a thickness of 7μm between the Nb521 alloy substrate, which are sequentially 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, 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 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 in situ during the vacuum high-temperature firing process, the interface between each layer is an in-situ reaction interface, and the interface bonding performance is good.

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

[0043] Step one, sequentially performing surface pretreatment on the substrate Nb521 alloy, including polishing treatment, sand blasting treatment, pickling and degreasing treatment, so that the oxides and oxygen absorption layer on the Nb521 alloy are removed, and the surface is in a "rough surface" state;

[0044] Step two, put Si powder, Cr powder, Ti powder and dispersant into 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 500 nm-5 μm, 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 65%, and the mass percentage of Cr powder is 18%;

[0045] Step three, the composite suspension slurry obtained in step two is pre-placed on the surface of the Nb521 alloy after surface pretreatment in step one by using a pneumatic spraying method, and a pre-placed layer is obtained on the surface of the Nb521 alloy after drying, and then the Nb521 alloy with the pre-placed layer is placed in a vacuum sintering furnace for high-temperature sintering under the condition of a vacuum degree of 2.0*10 -2 Pa, and after furnace cooling, a multilayer composite silicide high-temperature coating is prepared on the surface of the Nb521 alloy; the specific process of high-temperature sintering is as follows: first, heat to 800℃ at a rate of 8℃ / min and keep for 45 min, then heat to 1400℃ at a rate of 8℃ / min and keep for 60 min.

[0046] Figure 1 The surface morphology of the multilayer composite silicide high-temperature coating prepared in this embodiment is shown in Figure 1, from which Figure 1 It can be seen that the surface of the coating presents a typical vacuum reaction sintering coating morphology, the coating surface is rough and presents a "cauliflower" shape, and there are holes on the surface, which is the result of volume shrinkage of the high-silicon phase generated on the surface during sintering.

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

[0048] Figure 3 The upper layer cross-sectional magnified morphology of the multilayer composite silicide high-temperature coating prepared in this embodiment is shown in Figure 3, from which Figure 3 It can be seen that the upper layer of the coating has a clear two-phase structure, in which the gray color is (Nb, Ti, Cr) Si2, and the black color is Nb4Cr2Si5.

[0049] Figure 4 The surface morphology of the multilayer composite silicide high-temperature coating prepared in Example 1 of the present application after thermal shock for 500 times at room temperature

[0050] ~1500℃ water cooling is shown in Figure 4, from which Figure 4It can be seen that the coating surface does not appear obvious cracks, and the coating exhibits good self-healing ability.

[0051] The multilayer composite silicide high-temperature coating of the embodiment generates a composite oxide film mainly composed of SiO2 glass film and reinforced by TiO2 spherical particles under high-temperature conditions of 1500℃. It is detected that the multilayer composite silicide high-temperature coating of the embodiment does not fail after being thermostated for 60h under atmospheric conditions of 1500℃, does not fail after being thermostated for 5h at 1600℃, does not fail after being subjected to thermal shock for 700 times under water cooling conditions of room temperature-1500℃, and does not fail after being subjected to thermal shock for 400 times under water cooling conditions of room temperature-1600℃.

[0052] Embodiment 2

[0053] The multilayer composite silicide high-temperature coating of the embodiment is composed of an upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 with a thickness of 100μm, a lower layer NbSi2-Nb5Si3 with a thickness of 25μm, and an interface reaction layer Nb5Si3 with a thickness of 5μm between the Nb521 alloy substrate, which are sequentially 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, 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 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 in situ during vacuum high-temperature firing, the interfaces between the layers are all in-situ reaction interfaces, and the interface bonding performance is good.

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

[0056] Step one, the substrate Nb521 alloy is sequentially subjected to surface pretreatment including polishing treatment, sand blasting treatment, pickling and degreasing treatment, so that the oxides and oxygen absorption layer on the Nb521 alloy are removed, and the surface is in a “rough surface” state;

[0057] Step two, put Si powder, Cr powder, Ti powder and dispersant into a ball mill for high energy ball milling to obtain a composite slurry; the particle size of the Si powder, Cr powder and Ti powder is 500 nm to 5 μm, 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 68%, and the mass percentage of Cr powder is 15%;

[0058] Step three, the composite slurry obtained in step two is pre-deposited on the surface of the Nb521 alloy after surface pretreatment in step one by dip coating, dried to obtain a pre-deposited layer on the surface of the Nb521 alloy, and then the Nb521 alloy with the pre-deposited layer is placed in a vacuum sintering furnace for high temperature sintering under the condition of a vacuum degree of 8.0 x 10 -3 Pa, and after cooling in the furnace, a multilayer composite silicide high temperature coating is prepared on the surface of the Nb521 alloy; the specific process of high temperature sintering is: first, heat to 750℃ at a rate of 15℃ / min and keep for 60 min, then heat to 1550℃ at a rate of 5℃ / min and keep for 30 min.

[0059] Figure 5 The surface morphology of the multilayer composite silicide high temperature coating prepared in this embodiment after oxidation at 1500℃ in air for 20 h is shown in Figure 6. Figure 5 It can be seen that the coating generates a composite oxidation film mainly composed of SiO2 glass film and TiO2 spherical particles as reinforcing phase under high temperature conditions of 1500℃.

[0060] After detection, the multilayer composite silicide high temperature coating of this embodiment does not fail after constant temperature oxidation at 1500℃ in air for 50 h, does not fail after constant temperature oxidation at 1600℃ for 10 h, does not fail after thermal shock resistance of 680 times under room temperature-1500℃ water cooling conditions, and does not fail after thermal shock resistance of 430 times under room temperature-1600℃ water cooling conditions.

[0061] Example 3

[0062] The multilayer 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 between the Nb521 alloy substrate;

[0063] The (Nb, Ti, Cr)Si2 and Nb4Cr2Si5 in the upper layer (Nb, Ti, Cr)Si2-Nb4Cr2Si5 are uniformly mixed, 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 phase of the lower layer NbSi2-Nb5Si3 is mainly 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 in-situ reaction generated in the vacuum high-temperature sintering process, the interface between the layers is an in-situ reaction interface, and the interface bonding performance is good.

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

[0065] Step one, the substrate Nb521 alloy is sequentially subjected to surface pretreatment, including polishing treatment, sand blasting treatment, pickling and degreasing treatment, so that the oxides and oxygen absorption layer on the Nb521 alloy are removed, and the surface is in a "rough surface" state;

[0066] Step two, Si powder, Cr powder, Ti powder and a dispersing agent are placed in a ball mill for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, the Cr powder and the Ti powder is 500 nm to 5 μm, and the mass purity of each is not less than 99%, and the mass percentage of Si powder in the Si powder, the Cr powder and the Ti powder is 75%, and the mass percentage of Cr powder is 10%;

[0067] Step three, the composite suspension slurry obtained in step two is pre-placed on the surface of the Nb521 alloy subjected to surface pretreatment in step one by means of pneumatic spraying, and a pre-placed layer is obtained on the surface of the Nb521 alloy after drying, then the Nb521 alloy with the pre-placed layer is placed in a vacuum sintering furnace, and high-temperature sintering is carried out under the condition of vacuum degree of 1.0×10 -2 Pa, and the multilayer composite silicide high-temperature coating is prepared on the surface of the Nb521 alloy after furnace cooling; the specific process of high-temperature sintering is: first, heat to 900℃ at a rate of 12℃ / min and keep for 30 min, then heat to 1300℃ at a rate of 10℃ / min and keep for 90 min.

[0068] Figure 6 The cross-sectional morphology of the multilayer composite silicide high-temperature coating prepared in the embodiment after oxidation at 1500℃ in an atmospheric environment for 10 h, from Figure 6It can be seen that the coating generates a composite oxide film mainly composed of SiO2 glass film and TiO2 spherical particles as reinforcing phase under high temperature of 1500℃, the composite oxide film is continuous and well combined with the interface of the coating, the upper layer of the coating slightly degrades due to selective oxidation of Si element, and presents obvious contrast difference with the high Si phase layer.

[0069] It is detected that the multilayer composite silicide high temperature coating of the embodiment does not fail after constant temperature oxidation for 68h under atmospheric condition at 1500℃, does not fail after constant temperature oxidation for 12h at 1600℃, does not fail after thermal shock for 720 times under water cooling condition at room temperature-1500℃, and does not fail after thermal shock for 450 times under water cooling condition at room temperature-1600℃.

[0070] Example 4

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

[0072] (Nb, Ti, Cr) Si2 and Nb4Cr2Si5 in the upper layer (Nb, Ti, Cr) Si2-Nb4Cr2Si5 are uniformly mixed, 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 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 in situ during vacuum high temperature sintering, the interfaces between the layers are all in-situ reaction interfaces, and the interface bonding performance is good.

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

[0074] Step one, the substrate Nb521 alloy is sequentially subjected to surface pretreatment including polishing treatment, sand blasting treatment, pickling and degreasing treatment, so that the oxides and oxygen absorption layer on the Nb521 alloy are removed, and the surface is in a "rough surface" state;

[0075] Step two, the Si powder, Cr powder, Ti powder and dispersant are placed in a ball mill for high-energy ball milling to obtain a composite 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 78%, and the mass percentage of Cr powder is 10%;

[0076] Step three, the composite slurry obtained in step two is pre-placed on the surface of the Nb521 alloy after surface pretreatment in step one by using a pneumatic spraying method, and a pre-placed layer is obtained on the surface of the Nb521 alloy after drying, and then the Nb521 alloy with the pre-placed layer is placed in a vacuum sintering furnace, and high-temperature sintering is carried out under the condition that the vacuum degree is 9.0×10 -3 Pa, and the Nb521 alloy is cooled in the furnace to prepare a multilayer composite silicide high-temperature coating on the surface of the Nb521 alloy; the specific process of high-temperature sintering is as follows: first, heat to 850℃ at a rate of 10℃ / min and keep for 40min, then heat to 1450℃ at a rate of 10℃ / min and keep for 80min.

[0077] Figure 7 The surface morphology of the multilayer composite silicide high-temperature coating prepared in this embodiment after thermal shock 300 times under room temperature-1600℃ water cooling conditions can be seen from Figure 7 It can be seen that the coating surface has no obvious cracks, and the coating shows good self-healing ability.

[0078] The multilayer composite silicide high-temperature coating of this embodiment generates a composite oxide film mainly composed of SiO2 glass film and TiO2 spherical particles as reinforcing phase at 1600℃.

[0079] After detection, the multilayer composite silicide high-temperature coating of this embodiment does not fail after constant temperature oxidation for 68h at 1500℃ in the atmosphere, does not fail after constant temperature oxidation for 7h at 1600℃, does not fail after thermal shock for 740 times under room temperature-1500℃ water cooling conditions, and does not fail after thermal shock for 480 times under room temperature-1600℃ water cooling conditions.

[0080] The above is only a preferred embodiment of the present application, and does not limit the present application. Any simple modification, change and equivalent change made according to the technical essence of the present application to the above embodiment are still within the protection scope of the technical solution of the present application.

Claims

1. A multilayer multiphase composite silicide high temperature coating, characterized in that, The multilayer composite silicide high-temperature coating is composed of an upper layer, a lower layer and an interface reaction layer deposited on a niobium alloy substrate from top to bottom, wherein the upper layer is (Nb,Ti,Cr)Si2-Nb4Cr2Si5, the thickness is 50-100 microns, the lower layer is NbSi2-Nb5Si3, the thickness is 25-35 microns, and the interface reaction layer is Nb5Si3, the thickness is 5-8 microns; the multilayer composite silicide high-temperature coating has an oxidation resistance life of not less than 50 hours at 1500 DEG C and not less than 5 hours at 1600 DEG C.

2. The multilayer, multiphase, composite silicide high-temperature coating of claim 1, wherein, The upper layer, the lower layer and the interface reaction layer are all generated in-situ during vacuum high-temperature firing, the interfaces between the layers are all in-situ reaction self-birth interfaces, and the interface bonding performance is good; the multilayer composite silicide high-temperature coating has a thermal shock resistance life of not less than 600 times under room temperature-1500 DEG C water cooling condition and not less than 400 times under room temperature-1600 DEG C water cooling condition.

3. The multilayer, multiphase, composite silicide high-temperature coating of claim 1, wherein, 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 less than 6%, and the mass percentage of Cr element is not less than 3%.

4. The multilayer, multiphase, composite silicide high-temperature coating of claim 1, wherein, The (Nb,Ti,Cr)Si2 and Nb4Cr2Si5 in the upper layer (Nb,Ti,Cr)Si2-Nb4Cr2Si5 are uniformly mixed, the 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 multilayer, multiphase, composite silicide high-temperature coating of claim 1, wherein, The multilayer composite silicide high-temperature coating generates a composite oxide film mainly composed of SiO2 glass film and TiO2 spherical particles as reinforcing phase at 1100 DEG C-1600 DEG C.

6. A method of making a multilayer, multiphase, composite silicide high- temperature coating according to any one of claims 1 to 5, characterized in that, The multilayer composite silicide high-temperature coating is prepared by one-step vacuum reaction firing method.

7. The method of claim 6, wherein, The method comprises the following steps: Step one, the substrate niobium alloy is sequentially subjected to surface pretreatment including polishing treatment, sand blasting treatment, pickling and degreasing treatment, so that the oxides and oxygen absorption layer on the niobium alloy are removed, and the surface is in a "rough surface" state; Step two, Si powder, Cr powder and Ti powder are placed in a ball mill together with a dispersing agent for high-energy ball milling to obtain a composite suspension slurry; the particle size of the Si powder, the Cr powder and the Ti powder is 500 nm-5 microns, the mass purity is not less than 99%, and the mass percentage of Si powder in the Si powder, the Cr powder and the Ti powder is not less than 65%, and the mass percentage of Cr powder is not less than 10%. Step three, the composite suspension slurry obtained in step two is prepositioned on the surface of the niobium alloy after surface pretreatment in step one by dipping or pneumatic spraying, and a prepositioned layer is obtained on the surface of the niobium alloy after drying, and then the niobium alloy with the prepositioned layer is placed in a vacuum sintering furnace to perform high-temperature sintering under the condition of a vacuum degree of 8.0*10 -4 Pa~2.0*10 -2 Pa, and a multilayer composite silicide high-temperature coating is prepared on the surface of the niobium alloy after furnace cooling. The specific process of the high-temperature sintering is as follows: first, the temperature is increased to 750~900℃ at a rate of 8~15℃ / min and kept for 30~60min, and then the temperature is increased to 1300~1550℃ at a rate of 5~10℃ / min and kept for 30~90min.

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