Refractory alloy surface anti-oxidation coating as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of anti-oxidation coatings, and particularly relates to a refractory alloy surface anti-oxidation coating and a preparation method and application thereof.The refractory alloy surface comprises a base layer, a middle layer and a surface layer which are sequentially stacked, and the silicon content in the middle layer is larger than that of the base layer and that of the surface layer. By means of the design concept of a high-entropy alloy, it is proposed that multi-component refractory metal-Ta, W, Zr, Hf and Ti with the high-entropy effect is introduced into a silicide coating to construct the refractory high-entropy silicide coating, and by means of the coupling effect of multi-principal-component alloying, the structure heat stability of the silicide coating is improved, and the temperature resistance of the silicide coating is improved. A secondary slurry sintering process which is simple in process and low in cost is used, and gradient distribution of Si components is realized by adjusting the coating slurry composition and utilizing the Si internal diffusion phenomenon in the sintering process.

Description

Technical Field

[0001] The invention belongs to the technical field of anti-oxidation coatings, and in particular relates to an anti-oxidation coating on the surface of a refractory alloy and a preparation method and application thereof. Background Art

[0002] With the rapid development of aerospace and nuclear industries, the demand for ultra-high temperature structural materials is increasing. Among them, refractory metal-based alloys (such as niobium alloys, tantalum alloys, tungsten alloys, molybdenum alloys, etc.) are widely used due to their excellent high-temperature mechanical properties. However, refractory alloys have poor high-temperature oxidation resistance, and catastrophic "powdering" oxidation generally occurs when oxidized in the range of 500~800 ℃. Therefore, it is necessary to prepare an anti-oxidation coating on its surface to ensure its safe service.

[0003] Among many anti-oxidation coating systems, silicide coating is currently the most widely used coating system on refractory alloy surfaces. However, the antioxidant capacity of a single silicide coating is insufficient, and active elements are generally added for modification. Common active elements include Al, Cr, Ti, B, Ge, Zr, Hf and rare earth elements (Y, Ce). These modified elements either change the selective oxidation activity of Si, or oxidize to form a composite oxide film that coexists with SiO2, which can not only inhibit the "pesting" oxidation phenomenon that occurs in the medium temperature zone of silicide, but also improve the fluidity and adhesion of the SiO2 film at high temperature, and improve the oxygen barrier capacity. However, in the prior art, the heat resistance of the silicide coating modified by active elements is not high. For example, the operating temperature of the Si-Cr-Ti or Si-Cr-Fe silicide coating system generally does not exceed 1400 ℃. In order to reduce the temperature of the thrust chamber wall to an operating temperature that the coating can withstand, the design adopts a combined fuel liquid film / radiation cooling method. The propellant flow of this part of cooling accounts for about 30%~40% of the fuel. Therefore, measures to further improve the heat resistance of the silicide coating and thus reduce propellant consumption have important scientific significance and engineering value.

[0004] In addition, during the actual application of the anti-oxidation coating, its high temperature resistance (temperature resistance) and thermal shock / thermal fatigue resistance (heat resistance) need to be examined. The main principle of the anti-oxidation of the silicide coating is that after SiO2 is generated, a complete and dense layer is formed on the surface to inhibit the penetration of oxygen. The failure of the silicide coating is the result of the combined effect of dynamic factors such as the volatilization of the liquid phase in the form of gas and the high-temperature creep of oxide particles under thermodynamic factors such as high temperature and low oxygen pressure. In the working environment of the engine, the oxygen partial pressure is generally higher than the critical oxygen partial pressure of SiO generation, so the volatilization of high-temperature SiO and SiO2 is an important factor in the failure of the coating. Summary of the invention

[0005] The purpose of the present invention is to provide an anti-oxidation coating on the surface of a refractory alloy and a preparation method and application thereof, so as to overcome the shortcomings of the prior art and obtain an anti-oxidation coating having relatively excellent heat resistance.

[0006] The overall inventive concept adopted by the present invention is: drawing on the design concept of high entropy alloys, it is proposed to introduce multi-component refractory metals with high entropy effect into the silicide coating: Ta, W, Zr, Hf, Ti to construct a refractory high entropy silicide coating, and by means of the coupling effect of multi-principal alloying, the thermal stability of the organization of the silicide coating is increased, and its temperature resistance is improved. A simple and low-cost secondary slurry sintering process is used, and the gradient distribution of Si components is achieved by adjusting the composition of the coating slurry and utilizing the Si internal diffusion phenomenon during the sintering process.

[0007] The anti-oxidation coating on the surface of the refractory alloy is a high entropy silicide gradient anti-oxidation coating, including a base layer, an intermediate layer and a surface layer stacked in sequence, wherein the silicon content in the intermediate layer is greater than that in the base layer and the surface layer. The atomic percentage of Si in the direction away from the refractory alloy part in the coating thickness direction first increases from 30-45% to 50-65%, and then decreases to 35-50%, that is, it presents a gradient distribution of low inside, high middle and low outside. Since the melting point of low silicide is higher than that of high silicide, the temperature resistance of low silicide is better than that of high silicide. In addition, due to the low Si content in the surface layer, a composite oxide film composed of oxide ceramic phase (such as TiO2, ZrO2, HfO2, etc.) and glassy silicon oxide (SiO2) is generated on the surface during oxidation, which can improve the density and oxygen diffusion resistance of the oxide film. At the same time, the presence of the oxide ceramic phase can also play a "pinning effect" on the SiO2 glass phase, reduce the high-temperature volatilization of SiO2, and thus improve the anti-oxidation performance of the coating. The intermediate layer provides silicon source for the continuous generation of SiO2 to maintain its oxygen barrier ability. The base layer reduces the difference in thermal properties between the coating and the base alloy and improves the thermal shock resistance of the coating.

[0008] In order to achieve the above object, the technical solution of the present invention is: In a first aspect, the present invention provides an anti-oxidation coating on the surface of a refractory alloy, wherein the surface of the refractory alloy comprises a base layer, an intermediate layer and a surface layer stacked in sequence, wherein the silicon content in the intermediate layer is greater than that in the base layer and the surface layer.

[0009] In some other embodiments, the silicon atomic percentage in the base layer is 30-45%, the silicon atomic percentage in the middle layer is 50-65%, and the silicon atomic percentage in the surface layer is 35-50%.

[0010] In a second aspect, the present invention provides a method for preparing an anti-oxidation coating on the surface of a refractory alloy as described in the first aspect, comprising the following steps: (1) Using Ta, W, Zr, Hf and Ti single metal powders as raw materials, TaWZrHfTi supersaturated solid solution alloy powder is synthesized; (2) mixing TaWZrHfTi supersaturated solid solution alloy powder with Si powder to obtain coating powder I, and mixing coating powder I with a binder to obtain coating slurry I; (3) coating the coating slurry I on the refractory alloy part, and performing a first sintering to obtain a coating alloy part I; (4) mixing TaWZrHfTi supersaturated solid solution alloy powder with Si powder to obtain coating powder II, and mixing coating powder II with a binder to obtain coating slurry II; (5) The coating slurry II is coated on the coating alloy part I, and after a second sintering, a coating alloy part II is obtained, wherein the surface coating of the refractory alloy part in the coating alloy part II is the refractory alloy surface anti-oxidation coating.

[0011] In some other embodiments, in step (1), the raw material composition of the TaWZrHfTi supersaturated solid solution alloy powder is as follows in atomic percentage: Ta=15~25%, W=15~25%, Zr=15~25%, Hf=15~25%, Ti=15~30%; Alternatively, the particle size of the Ta, W, Zr, Hf, and Ti single-element metal powders is 20 to 100 µm, and the purity is greater than 99.5%.

[0012] In some other embodiments, in the step (1), the preparation method of the TaWZrHfTi supersaturated solid solution alloy powder is a mechanical alloying method, and the mechanical alloying method is: mixing the raw material Ta, W, Zr, Hf, Ti single metal powders with a solvent, ultrasonically dispersing, vacuumizing, and then ball milling with protective gas, and drying to obtain the TaWZrHfTi supersaturated solid solution alloy powder; Preferably, the solvent is anhydrous ethanol; The ultrasonic dispersion time is 5 to 10 min; The vacuuming is to evacuate to below 10 Pa; The protective gas is nitrogen, argon and helium; The protective gas is filled to 1 atmosphere pressure; The ball milling treatment is as follows: the rotation speed is 300-400 r / min, and the ball milling time is 10-30 h; The drying is: vacuum drying, the drying time is 12-24 h, and the drying temperature is 60-80 °C.

[0013] In some other embodiments, in step (2), the molar ratio of the TaWZrHfTi supersaturated solid solution alloy powder to the Si powder is 1:(2-2.5); the mass ratio of the coating powder I to the binder is (1-2.5) g:1 mL; Or, in step (3), the first sintering is carried out under vacuum conditions, the sintering temperature is 1400-1500°C, and the vacuum degree is ≥1.0×10 -2 Pa, sintering time is 20 to 40 min.

[0014] In some other embodiments, in step (4), the molar ratio of the TaWZrHfTi supersaturated solid solution alloy powder to the Si powder is 1:(0.9-1.5); the mass ratio of the coating powder II to the binder is (1-2.5) g:1 mL; Or, in step (5), the second sintering is carried out under vacuum conditions, the sintering temperature is 1450-1550°C, and the vacuum degree is ≥1.0×10 -2 Pa, sintering time is 20 to 40 min.

[0015] In some other embodiments, in step (2), the TaWZrHfTi supersaturated solid solution alloy powder and Si powder are mixed for 5-10 h; the coating powder I and binder are mixed for 1-2 h; Or, in step (4), the TaWZrHfTi supersaturated solid solution alloy powder and Si powder are mixed for 5-10 h; and the coating powder II and binder are mixed for 1-2 h.

[0016] In some other embodiments, in the step (3), before the coating slurry I is coated on the refractory alloy part, the refractory alloy part is also pretreated, wherein the pretreatment is to polish the surface of the refractory alloy part until the metallic luster is exposed, ultrasonically clean the surface in alcohol, and then dry the surface; Alternatively, in the step (5), before the coating slurry II is coated on the coating alloy part I, the coating alloy part I is also pretreated, wherein the pretreatment is to ultrasonically clean the coating alloy part I in alcohol and then dry it; Alternatively, in step (3) or step (5), the ultrasonic cleaning time is 15-25 min, and the drying temperature is 45-55° C. and the drying time is 10-15 min.

[0017] In a third aspect, the present invention provides the use of the anti-oxidation coating on the surface of the refractory alloy described in the first aspect in the preparation of a refractory metal-based alloy.

[0018] Beneficial effects of the present invention: 1. The present invention draws on the design concept of high entropy alloys and proposes to introduce multi-component refractory metals Ta, W, Zr, Hf and Ti with high entropy effect into the silicide coating to construct a refractory high entropy silicide coating. With the help of the coupling effect of multi-principal element alloying, the thermal stability of the silicide coating is increased and its temperature resistance is improved.

[0019] 2. The method of the present invention uses a simple and low-cost secondary slurry sintering process, and by adjusting the coating slurry composition and utilizing the Si internal diffusion phenomenon during the sintering process, a gradient distribution of Si components with low outside, high in the middle and low inside is achieved.

[0020] 3. The refractory alloy surface anti-oxidation coating prepared by the present invention is a high entropy silicide gradient anti-oxidation coating, comprising a refractory alloy surface including a base layer, an intermediate layer and a surface layer stacked in sequence, wherein the silicon content in the intermediate layer is greater than that in the base layer and the surface layer. The Si content in the coating thickness direction along the direction away from the refractory alloy part first increases from 30-45% to 50-65%, and then decreases to 35-50%, that is, presenting a gradient distribution of low inside, high middle and low outside.

[0021] 4. The anti-oxidation coating on the surface of the refractory alloy prepared by the present invention has excellent anti-oxidation performance and can provide effective protection for the refractory alloy parts at 1700°C. For example, after oxidation at 1600°C for 10 h, the weight gain per unit area of ​​the coating reaches 15-18 mg / cm 2 . BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0023] Figure 1 The process flow chart of the method for preparing the anti-oxidation coating on the surface of the refractory alloy in Example 1 of the present invention; Figure 2 A cross-sectional backscattered image of the anti-oxidation coating on the surface of the refractory alloy in Example 1 of the present invention; Figure 3 A gradient diagram of Si content variation along the thickness direction of a cross section of an anti-oxidation coating on the surface of a refractory alloy in Example 1 of the present invention; Figure 4 Secondary electron image of the surface of the anti-oxidation coating on the refractory alloy in Example 1 of the present invention after being oxidized at 1600°C for 10 h; Figure 5 Cross-sectional backscattered image of the anti-oxidation coating on the surface of the refractory alloy in Example 1 of the present invention after being oxidized at 1600°C for 10 h. DETAILED DESCRIPTION

[0024] Example 1 A method for preparing an anti-oxidation coating on the surface of a refractory alloy, the process flow chart of which is as follows Figure 1 As shown, the following steps are included: (1) Synthesis of TaWZrHfTi supersaturated solid solution alloy powder: Ta, W, Zr, Hf, and Ti single metal powders are used as raw materials. The particle size of each metal powder is 50-100 µm, and the purity is greater than 99.5%. According to the following atomic percentages, Ta=15%, W=15%, Zr=20%, Hf=20%, and Ti=30%, TaWZrHfTi supersaturated solid solution alloy powder is synthesized by mechanical alloying method. Specifically, the following steps are included: The raw materials Ta, W, Zr, Hf, and Ti single metal powders are placed in a stainless steel ball mill containing a process control agent (anhydrous ethanol), and after ultrasonic oscillation dispersion for 10 min, the powder is placed in a vacuum glove box and evacuated to below 10 Pa. After the protective gas (such as argon) is filled to 1 atmosphere, the stainless steel ball mill is sealed. The powder is then taken out of the glove box and installed in a ball mill for ball milling (speed of 300 r / min, ball milling time of 30 h). The ball-milled powder is then placed in a vacuum drying oven at 80°C for 12 h to obtain TaWZrHfTi supersaturated solid solution alloy powder. (2) Preparation of coating slurry I: TaWZrHfTi supersaturated solid solution alloy powder and Si powder were mixed in a mixer at a molar ratio of 1:2.1 for 6 h to obtain coating powder I; coating powder I and binder (PVB) were stirred in a magnetic stirrer at a mass ratio of 1.5 g / ml for 1 h to obtain coating slurry I; (3) First sintering: The surface of the refractory alloy NbMoTaWTi high entropy alloy (20Nb-20Mo-20Ta-20W-20Ti) substrate was polished until the metallic luster was exposed, ultrasonically cleaned in alcohol for 20 min, and dried at 50 °C for 10 min to obtain a treated refractory alloy part; the coating slurry I was applied to the surface of the treated refractory alloy part by dipping or brushing; the coated coating sample was placed in a drying oven at 80 °C for 12 h; the dried coating sample was placed in a vacuum high-temperature furnace for sintering, wherein the sintering temperature was 1400 °C and the vacuum degree was better than 1.0×10 -2 Pa, sintering time is 40 min, and coating alloy part I is obtained; (4) Preparation of coating slurry II: TaWZrHfTi supersaturated solid solution alloy powder and Si powder were mixed in a mixer at a molar ratio of 1:1 for 6 h to obtain coating powder II; coating powder II and binder (PVB) were stirred in a magnetic stirrer at a mass ratio of 1.8 g / ml for 1 h to obtain coating slurry II; (5) Second sintering: The coated alloy part I was ultrasonically cleaned in alcohol for 20 min and dried at 50 °C for 10 min to obtain the treated coated alloy part I; the coating slurry II was applied to the surface of the treated coated alloy part I by dipping or brushing; the part was placed in a drying oven and dried at 80 °C for 12 h; the dried coated sample was placed in a vacuum high-temperature furnace for sintering, wherein the sintering temperature was 1450 °C and the vacuum degree was 1.0×10 -2 Pa, the sintering time is 40 min, and the coating alloy part II is obtained; the surface of the coating alloy part II is a high entropy silicide gradient anti-oxidation coating.

[0025] According to tests, the atomic percentage of Si in the high entropy silicide gradient anti-oxidation coating on the surface of the refractory alloy in the direction of its thickness away from the refractory alloy part (i.e. from the inside to the outside) is: 42% for the base layer, 64% for the middle layer, and 37% for the surface layer.

[0026] The cross-sectional structure of the oxidation-resistant coating on the surface of the refractory alloy was characterized. Figure 2 This is a cross-sectional backscattered image of the high entropy silicide gradient anti-oxidation coating on the surface of the refractory alloy in Example 1. Figure 2 It can be seen that the coating has an obvious gradient structure: the surface layer is loose and has large pores; the middle layer is denser, with some bright gray particles scattered on the gray matrix; the bottom layer is dense and continuous, and is metallurgically bonded to the matrix alloy.

[0027] The Si content in the cross-sectional structure of high entropy silicide gradient anti-oxidation coating on the surface of refractory alloy was characterized. Figure 3 The figure is a graph showing the Si content variation gradient along the thickness direction of the cross section of the anti-oxidation coating on the surface of the refractory alloy in Example 1. Figure 3 It can be seen that the surface layer of the coating is low-silicon silicide, the middle layer is high-silicon silicide, and the bottom layer is low-silicon silicide. The oxidized surface of the anti-oxidation coating on the surface of the refractory alloy was characterized. Figure 4 This is the secondary electron image of the surface of the anti-oxidation coating on the refractory alloy in Example 1 after being oxidized at 1600 °C for 10 h. Figure 4 It can be seen that a dense glassy silicon oxide is formed on the surface of the coating, which can block the diffusion of oxygen into the coating; the metal oxide is evenly distributed and embedded in the silicon oxide film, which can act as a skeleton. The formed composite oxide film has excellent heat resistance and ablation resistance.

[0028] Figure 5 This is a cross-sectional backscattered image of the anti-oxidation coating on the surface of the refractory alloy in Example 1 after being oxidized at 1600 °C for 10 h. Figure 5It can be seen that the coating also has a three-layer structure after oxidation, which corresponds to the refractory alloy surface before high-temperature treatment, which still maintains the original base layer, middle layer and surface layer structure, but the surface layer after oxidation is composed of white granular grains and black tissue wrapped together, with a dense structure and no obvious holes and cracks; compared with before high-temperature oxidation treatment, the thickness of the middle layer is significantly increased.

[0029] The test shows that after oxidation at 1600 °C for 10 h, the coating has a unit area weight gain of about 15 mg / cm 2 The thickness of the generated surface layer is 20μm.

[0030] Example 2 A method for preparing an anti-oxidation coating on the surface of a refractory alloy comprises the following steps: (1) Synthesis of TaWZrHfTi supersaturated solid solution alloy powder: Ta, W, Zr, Hf, and Ti single metal powders are used as raw materials. The particle size of each metal powder is 50-100 µm, and the purity is greater than 99.5%. According to the following atomic percentages, Ta=18%, W=18%, Zr=18%, Hf=20%, and Ti=26%, TaWZrHfTi supersaturated solid solution alloy powder is synthesized by mechanical alloying method. Specifically, the following steps are included: The raw materials Ta, W, Zr, Hf, and Ti single metal powders are placed in a stainless steel ball mill containing a process control agent (anhydrous ethanol), and after ultrasonic oscillation dispersion for 10 min, the powder is placed in a vacuum glove box and evacuated to below 10 Pa. After the protective gas (such as argon) is filled to 1 atmosphere, the stainless steel ball mill is sealed. The powder is then taken out of the glove box and installed in a ball mill for ball milling (rotation speed of 350 r / min, ball milling time of 25 h). The ball-milled powder is then placed in a vacuum drying oven at 80°C for 18 h to obtain TaWZrHfTi supersaturated solid solution alloy powder. (2) Preparation of coating slurry I: TaWZrHfTi supersaturated solid solution alloy powder and Si powder were mixed in a mixer at a molar ratio of 1:2.3 for 8 h to obtain coating powder I; coating powder I and binder (PVB) were stirred in a magnetic stirrer at a mass ratio of 2 g / ml for 1.5 h to obtain coating slurry I; (3) First sintering: The surface of the refractory alloy niobium tungsten alloy Nb521 (Nb-5W-2Mo-1Zr) workpiece was polished until the metallic luster was exposed, ultrasonically cleaned in alcohol for 20 min, and dried at 50 °C for 10 min to obtain a treated refractory alloy workpiece; the coating slurry I was applied to the surface of the treated refractory alloy workpiece by dipping or brushing; the coated coating sample was placed in a drying oven at 100 °C for 10 h; the dried coating sample was placed in a vacuum high-temperature furnace for sintering, wherein the sintering temperature was 1450 °C and the vacuum degree was better than 1.0×10 -2 Pa, sintering time is 30 min, and coating alloy part I is obtained; (4) Preparation of coating slurry II: TaWZrHfTi supersaturated solid solution alloy powder and Si powder were mixed in a mixer at a molar ratio of 1:1.3 for 6 h to obtain coating powder II; coating powder II and binder (PVB) were stirred in a magnetic stirrer at a mass ratio of 2.5 g / ml for 1.5 h to obtain coating slurry II; (5) Second sintering: The coated alloy part I was ultrasonically cleaned in alcohol for 20 min and dried at 50 °C for 10 min to obtain the treated coated alloy part I; the coating slurry II was applied to the surface of the treated coated alloy part I by dipping or brushing; the part was placed in a drying oven and dried at 100 °C for 10 h; the dried coated sample was placed in a vacuum high-temperature furnace for sintering, wherein the sintering temperature was 1500 °C and the vacuum degree was 1.0×10 -2 Pa, the sintering time is 30 min, and a coated alloy part II is obtained; the surface of the coated alloy part II is a high entropy silicide gradient anti-oxidation coating; after testing, the atomic percentage of Si in the high entropy silicide gradient anti-oxidation coating on the surface of the refractory alloy in the direction of its thickness away from the refractory alloy part (i.e. from the inside to the outside) is: 37% for the base layer, 62% for the middle layer, and 43% for the surface layer.

[0031] The test shows that after oxidation at 1600 ℃ for 10 h, the unit area weight gain of the anti-oxidation coating on the surface of the refractory alloy is about 18 mg / cm 2 , indicating that it has good antioxidant properties.

[0032] Example 3 A method for preparing an anti-oxidation coating on the surface of a refractory alloy comprises the following steps: (1) Synthesis of TaWZrHfTi supersaturated solid solution alloy powder: Ta, W, Zr, Hf, and Ti single metal powders are used as raw materials. The particle size of each metal powder is 50-100 µm, and the purity is greater than 99.5%. According to the following atomic percentages, Ta=17%, W=17%, Zr=20%, Hf=20%, and Ti=26%, TaWZrHfTi supersaturated solid solution alloy powder is synthesized by mechanical alloying method. Specifically, the following steps are included: The raw materials Ta, W, Zr, Hf, and Ti single metal powders are placed in a stainless steel ball mill containing a process control agent (anhydrous ethanol), and after ultrasonic oscillation dispersion for 10 min, the powder is placed in a vacuum glove box and evacuated to below 10 Pa. After the protective gas (such as argon) is filled to 1 atmosphere, the stainless steel ball mill is sealed. The powder is then taken out of the glove box and installed in a ball mill for ball milling (rotation speed of 400 r / min, ball milling time of 20 h). The ball-milled powder is then placed in a vacuum drying oven at 60°C and dried for 24 h to obtain TaWZrHfTi supersaturated solid solution alloy powder. (2) Preparation of coating slurry I: TaWZrHfTi supersaturated solid solution alloy powder and Si powder were mixed in a mixer at a molar ratio of 1:2.5 for 10 h to obtain coating powder I; coating powder I and binder (PVB) were stirred in a magnetic stirrer at a mass ratio of 1.5 g / ml for 2 h to obtain coating slurry I; (3) First sintering: The surface of the refractory alloy tantalum-tungsten alloy (Ta10W) workpiece was polished until the metallic luster was exposed, ultrasonically cleaned in alcohol for 20 min, and dried at 50 °C for 10 min to obtain a treated refractory alloy workpiece; the coating slurry I was applied to the surface of the treated refractory alloy workpiece by dipping or brushing; the coated coating sample was placed in a drying oven at 120 °C and dried for 8 h; the dried coating sample was placed in a vacuum high-temperature furnace for sintering, wherein the sintering temperature was 1500 °C and the vacuum degree was better than 1.0×10 -2 Pa, sintering time is 20 min, and coating alloy part I is obtained; (4) Preparation of coating slurry II: TaWZrHfTi supersaturated solid solution alloy powder and Si powder were mixed in a mixer at a molar ratio of 1:1.5 for 10 h to obtain coating powder II; coating powder II and binder (PVB) were stirred in a magnetic stirrer at a mass ratio of 2.0 g / ml for 2 h to obtain coating slurry II; (5) Second sintering: The coated alloy part I was ultrasonically cleaned in alcohol for 20 min and dried at 50 °C for 10 min to obtain the treated coated alloy part I; the coating slurry II was applied to the surface of the treated coated alloy part I by dipping or brushing; the part was placed in a drying oven and dried at 120 °C for 8 h; the dried coated sample was placed in a vacuum high-temperature furnace for sintering, wherein the sintering temperature was 1550 °C and the vacuum degree was 1.0×10 -2 Pa, the sintering time is 20 min, and a coated alloy part II is obtained; the surface of the coated alloy part II is a high entropy silicide gradient anti-oxidation coating; after testing, the atomic percentage of Si in the high entropy silicide gradient anti-oxidation coating on the surface of the refractory alloy in the direction of its thickness away from the refractory alloy part (i.e. from the inside to the outside) is: 38% for the base layer, 63% for the middle layer, and 42% for the surface layer.

[0033] According to the test, after oxidation at 1700 ℃ for 5 h, the unit area weight gain of the anti-oxidation coating on the surface of the refractory alloy is about 16 mg / cm 2 , has good antioxidant properties.

[0034] Comparative Example 1 Different from Example 1, steps (2) to (5) are omitted, and only step (1) is performed, that is, the TaWZrHfTi supersaturated solid solution alloy powder is mixed with a binder and then coated on the refractory alloy part, and then sintered for the first time.

[0035] The test showed that after oxidation at 1600 ℃ for 10 h, the coating and the alloy substrate were completely oxidized and destroyed.

[0036] The present application focuses on high-temperature oxidation resistance, and mainly measures the oxidation resistance of the coating by weight gain per unit area. It can be seen from Examples 1-3 and Comparative Example 1 that the method for preparing the oxidation-resistant coating on the surface of the refractory alloy of the present application adjusts the composition of the coating slurry and utilizes the Si internal diffusion phenomenon during the sintering process to achieve a gradient distribution of the Si component with low outside, high in the middle and low inside. It can provide effective protection for refractory alloy parts at 1700°C. For example, after oxidation at 1600°C for 10 hours, the weight gain per unit area of ​​the coating reaches 15~18 mg / cm 2 .

[0037] The above embodiments are only used to explain the technical solutions provided by the present invention and cannot limit the present invention. Any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention fall within the protection scope of the technical solutions of the present invention.

Claims

1. An anti-oxidation coating on the surface of a refractory alloy, characterized in that: The surface of the refractory alloy comprises a base layer, an intermediate layer and a surface layer which are stacked in sequence, and the silicon content in the intermediate layer is greater than that in the base layer and the surface layer.

2. The refractory alloy surface anti-oxidation coating according to claim 1, characterized in that: The silicon atomic percentage in the base layer is 30-45%, the silicon atomic percentage in the middle layer is 50-65%, and the silicon atomic percentage in the surface layer is 35-50%.

3. A method for preparing an anti-oxidation coating on the surface of a refractory alloy according to claim 1 or 2, characterized in that: The following steps are involved: (1) Using Ta, W, Zr, Hf and Ti single metal powders as raw materials, TaWZrHfTi supersaturated solid solution alloy powder is synthesized; (2) mixing TaWZrHfTi supersaturated solid solution alloy powder with Si powder to obtain coating powder I, and mixing coating powder I with a binder to obtain coating slurry I; (3) coating the coating slurry I on the refractory alloy part, and performing a first sintering to obtain a coating alloy part I; (4) mixing TaWZrHfTi supersaturated solid solution alloy powder with Si powder to obtain coating powder II, and mixing coating powder II with a binder to obtain coating slurry II; (5) The coating slurry II is coated on the coating alloy part I, and after a second sintering, a coating alloy part II is obtained, wherein the surface coating of the refractory alloy part in the coating alloy part II is the refractory alloy surface anti-oxidation coating.

4. The method for preparing an anti-oxidation coating on the surface of a refractory alloy according to claim 3, characterized in that: In the step (1), the raw material composition of the TaWZrHfTi supersaturated solid solution alloy powder is as follows: Ta=15~25%, W=15~25%, Zr=15~25%, Hf=15~25%, Ti=15~30% according to the following atomic percentages; Alternatively, the particle size of the Ta, W, Zr, Hf, and Ti single-element metal powders is 20 to 100 µm, and the purity is greater than 99.5%.

5. The method for preparing an anti-oxidation coating on the surface of a refractory alloy according to claim 4, characterized in that: In the step (1), the preparation method of the TaWZrHfTi supersaturated solid solution alloy powder is a mechanical alloying method. The mechanical alloying method comprises: mixing the raw materials Ta, W, Zr, Hf, Ti single metal powders with a solvent, ultrasonically dispersing, evacuating, and then ball milling with protective gas, and drying to obtain TaWZrHfTi supersaturated solid solution alloy powder; The solvent is anhydrous ethanol; The ultrasonic dispersion time is 5 to 10 min; The vacuuming is to vacuumize to below 10 Pa; The protective gas is nitrogen, argon and helium; The protective gas is filled to 1 atmosphere pressure; The ball milling treatment is as follows: the rotation speed is 300-400 r / min, and the ball milling time is 10-30 h; The drying is: vacuum drying, the drying time is 12-24 h, and the drying temperature is 60-80 °C.

6. The method for preparing an anti-oxidation coating on the surface of a refractory alloy according to claim 3, characterized in that: In the step (2), the molar ratio of the TaWZrHfTi supersaturated solid solution alloy powder to the Si powder is 1:(2-2.5); the mass ratio of the coating powder I to the binder is (1-2.5) g:1 mL; Or, in step (3), the first sintering is carried out under vacuum conditions, the sintering temperature is 1400-1500°C, and the vacuum degree is ≥1.0×10 -2 Pa, sintering time is 20 to 40 min.

7. The method for preparing an anti-oxidation coating on the surface of a refractory alloy according to claim 3, characterized in that: In the step (4), the molar ratio of the TaWZrHfTi supersaturated solid solution alloy powder to the Si powder is 1:(0.9-1.5); the mass ratio of the coating powder II to the binder is (1-2.5) g:1 mL; Or, in step (5), the second sintering is carried out under vacuum conditions, the sintering temperature is 1450-1550°C, and the vacuum degree is ≥1.0×10 -2 Pa, sintering time is 20 to 40 min.

8. The method for preparing an anti-oxidation coating on the surface of a refractory alloy according to claim 3, characterized in that: In the step (2), the TaWZrHfTi supersaturated solid solution alloy powder and Si powder are mixed for 5-10 h; the coating powder I and binder are mixed for 1-2 h; Or, in step (4), the TaWZrHfTi supersaturated solid solution alloy powder and Si powder are mixed for 5-10 hours; and the coating powder II and binder are mixed for 1-2 hours.

9. The method for preparing an anti-oxidation coating on the surface of a refractory alloy according to claim 1, characterized in that: In the step (3), before the coating slurry I is coated on the refractory alloy part, the refractory alloy part is pretreated, wherein the pretreatment is to polish the surface of the refractory alloy part until the metallic luster is exposed, ultrasonically clean the surface in alcohol, and then dry the surface; Alternatively, in the step (5), before the coating slurry II is coated on the coating alloy part I, the coating alloy part I is also pretreated, wherein the pretreatment is to ultrasonically clean the coating alloy part I in alcohol and then dry it; Alternatively, in step (3) or step (5), the ultrasonic cleaning time is 15-25 min, and the drying temperature is 45-55° C. and the drying time is 10-15 min.

10. Use of the anti-oxidation coating on the surface of a refractory alloy according to claim 1 or 2 in the preparation of a refractory metal-based alloy.

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