Method for preparing MoSi2 coating on molybdenum alloy surface

Abstract

The invention discloses a method for preparing a MoSi2 coating on the surface of molybdenum alloy, which comprises the following steps of: ball-milling silicide alloy powder, hot-pressing and sintering to prepare a target material, and sputtering a high-entropy silicide thin layer on the molybdenum alloy through magnetron sputtering; and then MoSi2 powder is preset on the surface of the molybdenum alloy sputtered with the high-entropy silicide thin layer, and then the MoSi2 coating is prepared through laser scanning. The high-entropy silicide thin layer is firstly sputtered on the surface of the molybdenum alloy, then the MoSi2 coating is prepared on the high-entropy silicide thin layer through the laser scanning technology, the high-entropy silicide thin layer is used for preventing Si elements in a silicide coating body from diffusing into a refractory metal matrix, and the service life of the MoSi2 coating is effectively prolonged.

Description

Technical Field

[0001] The invention relates to a method for preparing a MoSi2 coating on a molybdenum alloy surface, belonging to the technical field of refractory metal surface engineering. Background Art

[0002] Molybdenum-based alloys have high melting points, low thermal expansion coefficients, high elastic modulus, good mechanical stability and excellent high-temperature creep resistance, and have broad applications and development prospects in the field of aerospace engineering. However, molybdenum has poor high-temperature oxidation resistance, and oxides volatilize at 725°C, resulting in "catastrophic" oxidation, which affects its long-term effective use under high-temperature conditions.

[0003] At present, the main method to improve the high-temperature oxidation performance of molybdenum is to prepare a silicide coating on its surface for protection. Among silicide coatings, MoSi2 has excellent high-temperature oxidation resistance. When oxidation occurs at high temperatures, dense amorphous SiO2 is formed on the surface, which can block the diffusion of oxygen into the interior. In addition, amorphous SiO2 has fluidity and can make up for the microcracks that appear during the oxidation process, so that the coating has self-healing ability and can effectively protect the molybdenum substrate from oxidation.

[0004] During the high-temperature service of the refractory metal / silicide coating system, the Si element in the main body of the silicide coating will diffuse into the refractory metal matrix and form a new transition layer at the refractory metal / silicide coating interface. This process will accelerate the organizational degradation and failure of the coating. Therefore, it is crucial to design and construct a refractory metal silicide coating system with diffusion-resistant effect to hinder the diffusion of elements between the main body of the coating and the matrix elements. Summary of the invention

[0005] The purpose of the present invention is to provide a method for preparing a MoSi2 coating on a molybdenum alloy surface. First, a high-entropy silicide thin layer is sputtered on the molybdenum alloy surface, and then the MoSi2 coating is prepared on the high-entropy silicide thin layer by a laser scanning process. The high-entropy silicide thin layer can hinder the Si element in the silicide coating body from diffusing into the interior of the refractory metal matrix, which can effectively improve the service life of the MoSi2 coating.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for preparing a MoSi2 coating on a molybdenum alloy surface comprises the following steps: firstly, silicide alloy powder is ball-milled and then hot-pressed and sintered to form a target material, and then a high-entropy silicide thin layer is sputtered on the molybdenum alloy by magnetron sputtering; and then, MoSi2 powder is pre-placed on the surface of the molybdenum alloy sputtered with the high-entropy silicide thin layer and the MoSi2 coating is obtained by laser scanning.

[0008] Preferably, the high entropy silicide powder is a mixture of any five silicide powders of MoSi2, WSi2, NbSi2, TaSi2, ZrSi2, ReSi2, HfSi2, TiSi2 and VSi2, and the mass proportion of each silicide powder in the alloy powder is 10-30%; the purity of each silicide powder is greater than 99.5%, and the particle diameter is less than 4.5μm.

[0009] Preferably, the ball milling conditions are: rotation speed 100-1000 r / min, 15-30 h.

[0010] Preferably, the hot pressing sintering conditions are: 1450-1750° C., 20-60 min, and a pressure of 20-50 MPa.

[0011] Preferably, the conditions for magnetron sputtering are: argon is used as the sputtering gas, the flow rate is 25-35 sccm, and the sputtering gas pressure is 0.15-0.35 Pa.

[0012] Preferably, the thickness of the high entropy silicide thin layer is 5-30 μm.

[0013] Preferably, the MoSi2 powder is adhered to the surface of the molybdenum alloy sputtered with a high entropy silicide thin layer by acetone or alcohol to form a MoSi2 powder layer, and the thickness of the MoSi2 powder layer is 1-2 mm.

[0014] Preferably, a drying step is performed after the MoSi2 powder is adhered, specifically, the molybdenum alloy adhered with the MoSi2 powder is placed in a heating furnace at 130-180° C. and dried for 30-50 minutes.

[0015] Preferably, the laser scanning conditions are: overlap rate 40-60%, laser power 2-2.5KW, and scanning speed 4-8mm / s.

[0016] Preferably, the molybdenum alloy is polished, cleaned and dried in sequence before sputtering the high entropy silicide thin layer.

[0017] The beneficial effects of the present invention are:

[0018] In order to inhibit or reduce the element diffusion between the refractory metal substrate and the silicide coating, it is a direct and effective solution to reasonably design a diffusion barrier layer that can achieve good interface matching with both the substrate and the silicide. At present, the materials of the diffusion barrier layer are mainly divided into two categories: metal and ceramic. Metals have a weak ability to hinder the diffusion of elements, and they also diffuse and oxidize themselves, and easily form brittle phases at the interface, which reduces the service performance of the coating. In contrast, the ceramic phase has a stronger diffusion barrier ability and can effectively prevent the mutual diffusion of elements in the coating and the substrate, but the interface bonding strength between the coating and the substrate needs to be improved. Since it is often difficult to take both the diffusion barrier effect and the bonding strength into consideration, the traditional alloy design method is difficult to guide the development of the diffusion barrier layer of the coating system.

[0019] High entropy silicide has good interface compatibility with Mo-based alloys and MoSi2. The elastic modulus and thermal expansion coefficient of high entropy silicide have a "cocktail" effect, which can match Mo alloys and MoSi2, and can avoid the peeling of molybdenum silicide coatings when subjected to thermal fatigue or thermal shock due to the difference in elastic modulus and thermal expansion coefficient. Moreover, the dynamic hysteresis diffusion effect of high entropy silicide has a strong diffusion resistance, which can effectively prevent the mutual diffusion of elements between Mo alloys and MoSi2. And because of the use of high entropy silicide diffusion resistance layer, even if the surface coating fails early, the high entropy silicide diffusion resistance layer still has a good protective effect.

[0020] The present application sputters a thin layer of high entropy silicide on the surface of a molybdenum alloy, and then combines the molybdenum alloy, the sputtered thin layer of high entropy silicide and the MoSi2 coating together through laser scanning, thereby hindering the diffusion of Si elements in the main body of the silicide coating into the interior of the molybdenum matrix, thereby effectively improving the service life of the MoSi2 coating.

[0021] In addition, the high entropy silicide thin layer is prepared at the interface of the molybdenum alloy and the MoSi2 coating by magnetron sputtering, which can accurately control the thickness of the high entropy silicide thin layer and effectively inhibit the diffusion of elements between the molybdenum alloy and the MoSi2 coating. When preparing the MoSi2 coating on the surface of the molybdenum alloy, the laser scanning process is used to combine the molybdenum alloy, the sputtered high entropy silicide thin layer, and the pre-set MoSi2 powder coating, which has the characteristics of small dilution, dense organization, and good combination of the coating and the substrate, and can improve the wear resistance, corrosion resistance, heat resistance, and oxidation resistance of the molybdenum alloy surface. DETAILED DESCRIPTION

[0022] Comparative Example 1

[0023] First, the molybdenum alloy was surface polished, ultrasonically cleaned with alcohol, and dried. After that, MoSi2 powder was adhered to the surface of the molybdenum alloy with acetone, and the thickness of the MoSi2 powder was preset to 1.5mm. Then it was placed in a 140℃ heating furnace and dried for 30min. The molybdenum alloy was scanned by a laser, with a laser scanning overlap rate of 40%, a laser power of 2.2kW, and a scanning speed of 8mm / s to form a surface MoSi2 coating. After the coating was oxidized in a static hot oxygen air at 1500℃ for 128h, the mass loss was 1.44%.

[0024] Example 1

[0025] First, the molybdenum alloy is surface polished, ultrasonically cleaned with alcohol, and dried. According to the mass percentage, each silicide accounts for 20%, and the mixed powder of MoSi2, WSi2, NbSi2, TaSi2, and ReSi2 is ball milled for a long time, the ball milling time is 18 hours, and the rotation speed is 300r / min. Then the high entropy silicide target is hot pressed and sintered, the sintering temperature is 1450℃, the holding time is 40min, and the sintering pressure is 50MPa. Then, a 15μm thick high entropy silicide thin layer is sputtered on the molybdenum alloy by magnetron sputtering, and high-purity argon is used as the sputtering gas, the argon gas flow rate is 25sccm, and the argon sputtering pressure is 0.25Pa. Thereafter, acetone is used to adhere MoSi2 powder to the surface of the molybdenum alloy sputtered with a thin layer of high entropy silicide, and the thickness of the alloy powder is preset to 1.0mm, and then it is placed in a 140℃ heating furnace and dried for 30min. The laser scanning was performed on the molybdenum alloy with sputtered high entropy silicide thin layer, the overlap rate of laser scanning was 40%, the laser power was 2.2kW, and the scanning speed was 8mm / s to form a surface MoSi2 coating. The coating was tested to be able to serve effectively in a static hot oxygen air at 1500℃ for 128h, and the mass loss was 0.84%. Compared with comparative example 1, under the same service conditions, the mass loss was significantly reduced.

[0026] The oxidation resistance of molybdenum alloy with single high entropy silicide coating and molybdenum alloy with single MoSi2 coating was tested. The results show that the mass loss of molybdenum alloy with 15μm thick high entropy silicide coating is 1.39% after 128h of service in 1500℃ static hot oxygen air, while the mass loss of molybdenum alloy with MoSi2 coating of the same thickness is 1.25% after 128h of service in 1500℃ static hot oxygen air. The above results show that the high entropy silicide coating has an oxidation resistance close to that of the MoSi2 coating. Therefore, when the surface coating fails early, the high entropy silicide thin layer still has a good protective effect.

[0027] Example 2

[0028] First, the molybdenum alloy is surface polished, ultrasonically cleaned with alcohol, and dried. According to the mass percentage, each silicide accounts for 20%, and the mixed powder of MoSi2, WSi2, TaSi2, ReSi2, and VSi2 is ball milled for a long time, the ball milling time is 21h, and the rotation speed is 350r / min. Then the high entropy silicide target is hot pressed and sintered, the sintering temperature is 1550℃, the holding time is 30min, and the sintering pressure is 40MPa. Then a 15μm thick high entropy silicide thin layer is sputtered on the molybdenum alloy by magnetron sputtering, and high-purity argon is used as the sputtering gas, the argon gas flow rate is 25sccm, and the argon sputtering pressure is 0.25Pa. Thereafter, acetone is used to adhere the MoSi2 powder to the surface of the molybdenum alloy sputtered with a thin layer of high entropy silicide, and the MoSi2 powder thickness is preset to 1.5mm, and then it is placed in a 150℃ heating furnace and dried for 30min. The laser scanning was performed on the molybdenum alloy with sputtered high entropy silicide thin layer, with a laser scanning overlap rate of 40%, a laser power of 2.5kW, and a scanning speed of 6mm / s to form a surface MoSi2 coating. The coating was tested to be able to serve effectively in a static hot oxygen atmosphere of 1500℃ for 128h, with a mass loss of 0.79%.

[0029] Example 3

[0030] First, the molybdenum alloy is surface polished, ultrasonically cleaned with alcohol, and dried. According to the mass percentage, each silicide accounts for 20%, and the mixed powder of MoSi2, WSi2, TaSi2, ReSi2, and CrSi2 is ball milled for a long time, the ball milling time is 24h, and the rotation speed is 400r / min. Then the high entropy silicide target is hot pressed and sintered, the sintering temperature is 1650℃, the holding time is 30min, and the sintering pressure is 30MPa. Then a 20μm thick high entropy silicide thin layer is sputtered on the molybdenum alloy by magnetron sputtering, and high-purity argon is used as the sputtering gas, the argon gas flow rate is 25sccm, and the argon sputtering pressure is 0.25Pa. Thereafter, acetone is used to adhere the MoSi2 powder to the surface of the molybdenum alloy sputtered with a thin layer of high entropy silicide, and the MoSi2 powder thickness is preset to 2.0mm, and then it is placed in a 160℃ heating furnace and dried for 40min. The laser scanning was performed on the molybdenum alloy with sputtered high entropy silicide thin layer, with the overlap rate of 40%, laser power of 2.0kW and scanning speed of 8mm / s to form a surface MoSi2 coating. The coating was tested to be able to serve effectively in static hot oxygen air at 1500℃ for 128h, with a mass loss of 0.72%.

[0031] The above is only a preferred implementation of the patent of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the patent of the present invention. These improvements and modifications should also be regarded as the scope of protection of the patent of the present invention.

Claims

1. A method for preparing a MoSi2 coating on a molybdenum alloy surface, characterized in that: The method comprises the following steps: firstly, the silicide alloy powder is ball-milled and then hot-pressed and sintered to form a target material, and then a high-entropy silicide thin layer is sputtered on the molybdenum alloy by magnetron sputtering; then, MoSi2 powder is pre-placed on the surface of the molybdenum alloy sputtered with the high-entropy silicide thin layer and a MoSi2 coating is obtained by laser scanning.

2. The method for preparing MoSi2 coating on a molybdenum alloy surface according to claim 1, characterized in that: The high entropy silicide powder is a mixture of any five silicide powders of MoSi2, WSi2, NbSi2, TaSi2, ZrSi2, ReSi2, HfSi2, TiSi2 and VSi2, and the mass proportion of each silicide powder in the alloy powder is 10-30% respectively; the purity of each silicide powder is greater than 99.5%, and the particle diameter is less than 4.5μm.

3. The method for preparing MoSi2 coating on the surface of molybdenum alloy according to claim 1, characterized in that, The ball milling conditions are: rotation speed 100-1000r / min, 15-30h.

4. The method for preparing MoSi2 coating on the surface of molybdenum alloy according to claim 1, characterized in that, The conditions for hot pressing sintering are: 1450-1750°C, 20-60min, and pressure 20-50MPa.

5. The method for preparing MoSi2 coating on the surface of molybdenum alloy according to claim 1, characterized in that, The conditions of magnetron sputtering are: argon as sputtering gas, flow rate 25-35sccm, sputtering pressure 0.15-0.35Pa.

6. The method for preparing MoSi2 coating on the surface of molybdenum alloy according to claim 1, characterized in that: The thickness of the high entropy silicide layer is 5-30 μm.

7. The method for preparing MoSi2 coating on the surface of a molybdenum alloy according to claim 1, characterized in that: The MoSi2 powder is adhered to the surface of the molybdenum alloy sputtered with a high entropy silicide thin layer by acetone or alcohol to form a MoSi2 powder layer, and the thickness of the MoSi2 powder layer is 1-2mm.

8. The method for preparing MoSi2 coating on the surface of molybdenum alloy according to claim 1, characterized in that: After the MoSi2 powder is adhered, a drying step is also performed, specifically, the molybdenum alloy adhered with the MoSi2 powder is placed in a heating furnace at 130-180°C and dried for 30-50 minutes.

9. The method for preparing MoSi2 coating on the surface of molybdenum alloy according to claim 1, characterized in that: The conditions for laser scanning are: overlap rate 40-60%, laser power 2-2.5KW, and scanning speed 4-8mm / s.

10. The method for preparing MoSi2 coating on the surface of molybdenum alloy according to claim 1, characterized in that: The molybdenum alloy was polished, cleaned and dried in sequence before sputtering the high entropy silicide thin layer.