Anti-oxidation coating on surface of refractory metal molybdenum alloy and manufacturing method of anti-oxidation coating

Abstract

The invention discloses an anti-oxidation coating on the surface of refractory metal molybdenum alloy and a manufacturing method of the anti-oxidation coating, and belongs to the technical field of refractory metal protection.The anti-oxidation coating adopts MoSi2 as a main component, a certain proportion of SiO2 powder with the low thermal expansion coefficient and B4C powder with the excellent medium and low temperature anti-oxidation performance are added, and the anti-oxidation coating is prepared. A composite coating is prepared on the surface of the molybdenum alloy through a sintering method; the prepared MoSi2-based composite anti-oxidation coating is uniform, compact, free of cracks, good in interface bonding strength, good in anti-oxidation performance and suitable for being used as the anti-oxidation coating on the surfaces of molybdenum and molybdenum alloy.

Description

Technical Field

[0001] This application belongs to the technical field of refractory metal protection, and particularly relates to an antioxidant coating on the surface of refractory metal molybdenum alloy and a manufacturing method thereof. Background Technique

[0002] Molybdenum disilicide (MoSi 2 ) is a material with excellent high-temperature oxidation resistance. In a high-temperature oxidation environment, on the surface of MoSi 2 , through the selective oxidation of silicon elements, a silica (SiO 2 ) protective layer with self-healing characteristics is formed. This protective layer can effectively inhibit the inward diffusion of oxygen, protect the matrix material from further oxidation, and thus significantly improve the high-temperature oxidation resistance of the material. Therefore, it is widely used in high-temperature protection fields such as aerospace and energy; MoSi 2 is an intermediate phase with the highest Si content in Mo x Si y compounds. It has a relatively high melting point (2030 °C), a relatively low density (6.24 g / cm 3 ), excellent high-temperature oxidation resistance and thermal shock resistance, and can form a good bond with the molybdenum matrix; therefore, MoSi 2 coatings play an important role in the surface protection of molybdenum and its alloys. Preparing high-quality MoSi 2 coatings on the surface of molybdenum and its alloys has become the key to improving the performance of molybdenum alloys.

[0003] In this application background, Patent CN2016104526354 discloses a method for preparing MoSi 2 coatings on the surface of molybdenum-based alloys by in-situ chemical vapor deposition. By mixing silicon powder, sodium fluoride, and alumina, a powder feedstock is obtained; the surface treatment of the molybdenum-based alloy includes sandblasting, ultrasonic cleaning, and degreasing in sequence; the powder feedstock and the molybdenum-based alloy are placed in a tubular furnace and pretreated at 900 - 1000 °C for 10 - 12 h, cooled to room temperature, then ultrasonically cleaned and dried, and a MoSi 2 layer is prepared on the surface of the molybdenum matrix; Patent CN2017107916883 discloses a method for preparing molybdenum disilicide coatings on the surface of molybdenum or molybdenum alloys. Using silicon powder as the raw material, a silicon coating is prepared on the surface of the molybdenum or molybdenum alloy matrix by plasma spraying technology, and then heat-treated in an inert atmosphere at 1000 - 1500 °C for 1 - 10 h, thereby forming a molybdenum disilicide coating on the surface of the molybdenum or molybdenum alloy matrix; Patent CN2017113954045 discloses a Mo 5 Si 3 -MoSi 2 -SiO 2High-temperature protection composite coating and preparation method. This invention combines the vacuum-activated pack cementation method with the high-temperature oxidation process to achieve Mo 5 Si 3 -MoSi 2 -SiO 2 Preparation of the composite coating; First, the vacuum-activated pack cementation method is used to achieve Mo 5 Si 3 -MoSi 2 Preparation of the composite coating. The surface MoSi 2 provides a Si source for the subsequent oxidation process. During the subsequent high-temperature oxidation process, MoSi 2 is oxidized, and a dense SiO 2 coating is formed on the surface, filling the pores and cracks of the MoSi 2 coating, improving the densification of the entire coating system, and further enhancing the high-temperature oxidation resistance of the system.

[0004] However, although the MoSi 2 coating obtained by the element diffusion method has a relatively high density, the coating is mainly composed of a single MoSi 2 phase. Due to the large difference in the thermal expansion coefficients of MoSi 2 (8.1×10- 6 / °C) and molybdenum (5.8×10 -6 / °C), during use, affected by temperature changes, the thermal stress between the MoSi 2 coating and the molybdenum substrate will cause through-cracks in the coating, and even cause the coating to peel off, reducing the coating protection effect; In addition, under medium and low temperature (400 - 600°C) oxidation conditions, the Mo element and Si element in MoSi 2 are oxidized simultaneously. At this temperature, the self-diffusion coefficient of Si is relatively low, and the generated SiO 2 cannot completely cover the substrate surface. The volume expansion of the generated MoO 3 causes the surface layer to be in a loose state or even powdery, making it difficult to play a good protective role. Summary of the Invention

[0005] The purpose of the implementation of this application is to provide an antioxidant coating on the surface of a refractory metal molybdenum alloy and its manufacturing method to solve the problems of thermal mismatch between the molybdenum disilicide coating and the molybdenum substrate and insufficient medium and low temperature antioxidant ability of molybdenum disilicide in the prior art.

[0006] To achieve the above purpose, the technical solution adopted in this application is: Provide a manufacturing method for an antioxidant coating on the surface of a refractory metal molybdenum alloy, specifically including the following steps:

[0007] (1). Process the refractory metal molybdenum alloy, polish its surface, then clean and dry it to obtain a molybdenum alloy substrate;

[0008] (2). Weigh and mix molybdenum disilicide (MoSi 2 ), silicon dioxide (SiO 2 ), and boron carbide (B 4 C) powders in proportion to obtain a mixed powder;

[0009] (3). Coat the molybdenum alloy substrate with the mixed powder and place it in a graphite mold;

[0010] (4). Use hot press sintering to apply pressure and sinter the graphite mold. Through high-temperature chemical reactions, a composite antioxidant coating composed of MoSi 2 , B 4 C, SiO 2 , molybdenum pentaboride (Mo 2 B 5 ), molybdenum diboride (MoB 2 ), and silicon carbide (SiC) phases is obtained on the surface of the molybdenum alloy.

[0011] In one embodiment,

[0012] In step (2), by weight percentage, the MoSi 2 powder accounts for 70 - 95%, the SiO 2 powder accounts for 2 - 15%, the B 4 C powder accounts for 2 - 15%. Preferably, the MoSi 2 powder accounts for 90%, the SiO 2 powder accounts for 5%, and the B 4 C powder accounts for 5%.

[0013] In one embodiment,

[0014] The drying temperature in step (1) is 80 - 120°C. Preferably, the drying temperature is 90°C.

[0015] In one embodiment,

[0016] The mixing in step (2) is carried out by ball milling in a powder mixer.

[0017] In one embodiment,

[0018] The ball-to-powder ratio for mixing is 5 - 10:1, and the ball milling time is 8 - 15 h. Preferably, the ball-to-powder ratio for mixing is 8:1, and the ball milling time is 10 h.

[0019] In one embodiment,

[0020] Step (IV): The temperature of pressure sintering is 1400 - 1600 °C, and the pressure is 20 - 40 MPa. Preferably, the temperature of pressure sintering is 1500 °C and the pressure is 30 MPa.

[0021] In one embodiment,

[0022] After pressure sintering, it is necessary to keep warm for 5 - 30 min. Preferably, keep warm for 10 min.

[0023] In one embodiment,

[0024] In step (III), the diameter of the graphite mold is 30 mm.

[0025] In one embodiment,

[0026] In step (II), the particle size of MoSi 2 powder is 15 μm, and the particle sizes of SiO 2 powder and B 4 C powder are 10 μm.

[0027] This application also provides an antioxidant coating on the surface of a refractory metal molybdenum alloy, which is an antioxidant coating prepared by the manufacturing method according to any one of the above embodiments. An antioxidant composite coating is coated on the surface of the refractory metal molybdenum alloy. The antioxidant composite coating is composed of MoSi 2 , Mo 2 , B 5 , MoB 2 , SiC, B 4 C and SiO 2 .

[0028] Compared with the prior art, this application has significant advantages in the design and performance optimization of the antioxidant coating, which are mainly reflected in the following aspects:

[0029] 1. Reduce thermal mismatch and improve bonding strength: Existing high-temperature antioxidant coating materials are prone to stress concentration due to the mismatch of the coefficient of thermal expansion (CTE) with the matrix material in a high-temperature environment, which may lead to cracking and peeling of the coating; in the design of the coating composition of the present invention, by optimizing the coefficient of thermal expansion of the main components, it is made closer to the matrix material, thus effectively reducing the thermal mismatch problem between the coating and the matrix; using a specific ratio of MoSi, BC and SiO 2 , after high-temperature reaction, phases of Mo 2 B 5 , MoB 2 , SiC are obtained, and a coating mainly composed of MoSi, Mo 2 B 5 , MoB 2 , SiC, BC and SiO 2The composite coating formed enhances the toughness and adhesion of the coating, improves the bonding strength between the coating and the substrate, reduces the cracking risk caused by thermal stress during high-temperature cycling. In contrast, traditional MoSi-based coatings are prone to forming microcracks under thermal cycling conditions, which in turn leads to a decline in antioxidant performance. However, this problem is effectively suppressed by the composition optimization of the present invention;

[0030] 2. Improve the antioxidant performance at medium and low temperatures: The main antioxidant mechanism of MoSi-based coatings relies on the formation of a SiO protective layer at high temperatures. In an environment of medium and low temperatures (400 - 600 °C), the oxidation kinetics of MoSi is slow, and a dense protective layer cannot be formed rapidly, resulting in a relatively fast initial oxidation rate and affecting the overall lifespan of the coating. In this application, by introducing the BC component into the coating and utilizing its preferential reactivity with oxygen at lower temperatures to form low-melting-point oxides such as BO, a dense protective film can be rapidly generated under medium and low temperature conditions to block the further intrusion of oxygen, thereby significantly enhancing the antioxidant performance at medium and low temperatures. In the prior art, a single MoSi coating is vulnerable to oxidation erosion at low temperatures, leading to early oxidation failure;

[0031] 3. Improve the coating density and enhance the antioxidant ability: The antioxidant ability of the coating is closely related to its density. Traditional MoSi coatings may have a relatively high porosity due to insufficient sintering or crack generation during the sintering process, allowing oxygen to diffuse along the defects and reducing the antioxidant performance. In this application, a chemical reaction occurs between BC and MoSi during the high-temperature sintering process, and at the same time, the softening and filling effect of SiO 2 can fill microcracks and pores, improving the density of the coating and further enhancing the antioxidant ability. In addition, the densified coating can also effectively reduce the erosion of the high-temperature gas on the substrate and improve the long-term service performance of the material. In contrast, existing MoSi coatings are prone to local spalling due to the influence of oxidation stress and pores during long-term high-temperature service, while the coating of the present invention significantly reduces this problem due to the increased density.

[0032] In summary, through composition optimization and multiphase synergistic effects, the present invention not only improves the high-temperature stability and antioxidant ability of the coating, but also significantly enhances the antioxidant performance in the medium and low temperature stages and reduces the risk of coating cracking, enabling it to have more excellent comprehensive performance in low-temperature and high-temperature environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0034] Figure 1 It is MoSi 2 、B 4 C, SiO 2 Reaction equation;

[0035] Figure 2 Cross-sectional scanning electron microscope image of the coating prepared by the present invention;

[0036] Figure 3 Phase analysis diagram of the coating prepared by the present invention;

[0037] Figure 4 Cross-sectional scanning electron microscope image of the surface oxide layer of the coating prepared by the present invention after oxidation at 600 °C;

[0038] Figure 5 Cross-sectional scanning electron microscope image of the surface oxide layer of the coating prepared by the present invention after oxidation at 1200 °C. Detailed implementation manners

[0039] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present application clearer and more understandable, the present application will be further described in detail. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0040] Example 1

[0041] A method for manufacturing an antioxidant coating on the surface of a refractory metal molybdenum alloy, specifically including the following steps:

[0042] (1). Process the molybdenum sheet and perform grinding and polishing on the surface, then wash and dry at 90 °C to obtain a prefabricated molybdenum substrate;

[0043] (2). Weigh MoSi 2 powder with an average particle size of 15 μm, B 4 C powder with a particle size of 10 μm, and SiO 2 powder with a particle size of 10 μm in a weight percentage ratio of 90%:5%:5%, and perform ball milling and mixing treatment in a powder mixer for 12 h with a ball-to-material ratio of 8:1 to obtain a mixed powder;

[0044] (3). Coat the prefabricated molybdenum substrate with the mixed powder and put it into a graphite mold with a diameter of 30 mm;

[0045] (4). Put the filled graphite mold into a vacuum hot press furnace for pressure sintering at a sintering temperature of 1500 °C, a pressure of 30 MPa, and hold for 15 min. After high-temperature chemical reaction, obtain MoSi 2 , Mo 2 B 5 , MoB2 , SiC, B 4 C and SiO 2 phase composition of MoSi 2 based composite antioxidant coating on a molybdenum metal sheet, the reaction equation is as Figure 1 shown.

[0046] Example 2

[0047] A method for manufacturing an antioxidant coating on the surface of a refractory metal molybdenum alloy, specifically including the following steps:

[0048] (I). Process the molybdenum sheet and polish the surface, then wash and dry it at 90 °C to obtain a prefabricated molybdenum substrate;

[0049] (II). Weigh MoSi 2 powder with an average particle size of 15 μm, 10 μm of B 4 C powder, 10 μm of SiO 2 powder in a ratio of 80%:10%:10% by weight, and perform ball milling and mixing treatment in a powder mixer for 15 h with a ball-to-material ratio of 10:1 to obtain a mixed powder;

[0050] (III). Coating the prefabricated molybdenum substrate with the mixed powder and putting it into a graphite mold with a diameter of 30 mm;

[0051] (IV). Put the filled graphite mold into a vacuum hot press furnace for pressure sintering at a sintering temperature of 1450 °C, a pressure of 25 MPa, and keep it warm for 20 min. Through high-temperature chemical reactions, obtain a molybdenum metal sheet with a MoSi 2 , Mo 2 B 5 , MoB 2 , SiC, B 4 C and SiO 2 phase composition of MoSi 2 based composite antioxidant coating.

[0052] Example 3

[0053] The difference between this example and Example 1 is that the weight percentages of MoSi 2 powder, B 4 C powder and SiO 2 powder are 70%:2%:2%, and the rest of the operations are the same.

[0054] Example 4

[0055] The difference between this example and Example 1 is that the weight percentages of MoSi 2 powder, B 4 C powder and SiO2 The weight percentages of the powders are 95%:15%:15%, and the remaining operations are the same.

[0056] Example 5

[0057] The difference between this example and Example 1 is that in step (ii), the ball milling mixing time is 8 h, and the ball-to-material ratio for mixing is 5:1, and the remaining operations are the same.

[0058] Example 6

[0059] The difference between this example and Example 1 is that in step (iv), the temperature for pressure sintering is 1400 °C, the pressure is 20 MPa, and the heat preservation time is 5 min, and the remaining operations are the same.

[0060] Example 7

[0061] The difference between this example and Example 1 is that in step (iv), the temperature for pressure sintering is 1600 °C, the pressure is 40 MPa, and the heat preservation time is 30 min, and the remaining operations are the same.

[0062] Example 8

[0063] The difference between this example and Example 1 is that in step (i), the drying temperature is 80 °C, and the remaining operations are the same.

[0064] Example 9

[0065] The difference between this example and Example 1 is that in step (i), the drying temperature is 120 °C, and the remaining operations are the same.

[0066] Example 10

[0067] An antioxidant coating on the surface of a refractory metal molybdenum alloy, comprising a refractory metal molybdenum alloy, and an antioxidant composite coating is coated on the surface of the refractory metal molybdenum alloy. The antioxidant composite coating consists of MoSi 2 , Mo 2 B 5 , MoB 2 , SiC, B 4 C and SiO 2 phase composition.

[0068] As Figure 2 and Figure 3 shown, from the cross-sectional microstructure diagram and the X-ray diffraction phase analysis diagram of the MoSi 2 -based composite antioxidant coating, it can be seen that the thickness of the coating prepared in this application is about 400 μm, the coating structure is uniform and dense, without cracks, and is tightly bonded to the substrate. The coating is mainly composed of MoSi 2 , Mo 2 B 5 , MoB 2, SiC, B 4 C and SiO 2 and other phase compositions; such as Figure 4 and Figure 5 As shown, from the cross-sectional microstructure diagram of the oxidized MoSi 2 -based composite antioxidant coating, it can be seen that in low-temperature and high-temperature oxidation environments, a dense and continuous SiO 2 protective film is formed on the coating surface, and the coating has excellent antioxidant performance.

[0069] This application provides an antioxidant coating on the surface of a refractory metal molybdenum alloy and a manufacturing method thereof. The antioxidant coating uses MoSi 2 as the main component, adds a certain proportion of SiO 2 powder with a low coefficient of thermal expansion and B 4 C powder with excellent medium and low-temperature antioxidant performance, and prepares a composite coating on the surface of the molybdenum alloy by a sintering method; the content range of MoSi 2 powder is 70-95%. Through composition optimization and multiphase synergistic effects, not only the high-temperature stability and antioxidant ability of the coating are improved, but also the antioxidant performance in the medium and low-temperature stages is significantly enhanced, and the risk of coating cracking is reduced, making it have better comprehensive performance in low-temperature and high-temperature environments; In summary, the MoSi 2 -based composite antioxidant coating prepared in this application is uniform, dense, crack-free, has good interfacial bonding strength, has good antioxidant performance, and is suitable for use as an antioxidant coating on the surface of molybdenum and its alloys.

[0070] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of this application, "a plurality" means two or more, unless otherwise specifically defined.

[0071] The above are only the preferred embodiments of this application and are not intended to limit this application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of this application shall be included in the protection scope of this application.

Claims

1. A method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy, characterized in that: The specific steps include: (1) processing a refractory metal molybdenum alloy and grinding and polishing the surface, and then cleaning and drying the surface to obtain a molybdenum alloy matrix; (ii) mixing molybdenum disilicide powder, silicon dioxide powder and boron carbide powder according to a certain proportion to obtain a mixed powder; (iii) coating the molybdenum alloy substrate with the mixed powder and placing the mixed powder into a graphite mold; (iv) The graphite mold is pressurized and sintered by hot pressing, and a composite anti-oxidation coating composed of molybdenum disilicide, molybdenum pentaboride, molybdenum diboride, silicon carbide, boron carbide and silicon dioxide is obtained on the surface of the metal molybdenum alloy through a high-temperature chemical reaction.

2. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 1, characterized in that: In step (ii), according to weight percentage, the molybdenum disilicide powder accounts for 70-95%, the silicon dioxide powder accounts for 2-15%, and the boron carbide powder accounts for 2-15%.

3. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 1, characterized in that: The drying temperature in step (1) is 80-120°C.

4. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 1, characterized in that: The mixing in step (ii) is performed by ball milling in a powder mixer.

5. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 4, characterized in that: The mixed ball-to-material ratio is 5-10:1, and the ball milling time is 8-15h.

6. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 1, characterized in that: The temperature of the pressure sintering in step (iv) is 1400-1600° C. and the pressure is 20-40 MPa.

7. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 6, characterized in that: After pressure sintering, it needs to be kept warm for 5-30 minutes.

8. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 1, characterized in that: The diameter of the graphite mold in step (iii) is 30 mm.

9. The method for manufacturing an anti-oxidation coating on the surface of a refractory metal molybdenum alloy according to claim 1, characterized in that: In step (ii), the particle size of the molybdenum disilicide powder is 15 μm, and the particle size of the silicon dioxide powder and the boron carbide powder is 10 μm.

10. An anti-oxidation coating on the surface of a refractory metal molybdenum alloy, which is an anti-oxidation coating made according to the manufacturing method according to any one of claims 1 to 9, characterized in that: An anti-oxidation composite coating is coated on the surface of a refractory metal molybdenum alloy. The anti-oxidation composite coating mainly consists of molybdenum disilicide, molybdenum pentaboride, molybdenum diboride, silicon carbide, boron carbide and silicon dioxide.

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