Nb alloy surface compact MoSi2 coating prepared through single-step slurry melting firing as well as preparation method and application of Nb alloy surface compact MoSi2 coating

Abstract

The invention discloses an Nb alloy surface compact MoSi2 coating prepared through single-step slurry melting firing and a preparation method and application, and particularly relates to the field of high-temperature alloys. Comprising the steps that Si powder, Cr powder, Fe powder and Ti powder are prepared into Si-Cr-Fe-Ti slurry; mo powder and Si powder are prepared into Mo-Si slurry; the preparation method comprises the following steps: sequentially coating the Si-Cr-Fe-Ti slurry and the Mo-Si slurry on the surface of an Nb alloy matrix; and the coated Nb alloy matrix is subjected to heat treatment, and the compact MoSi2 coating is obtained on the surface of the Nb alloy matrix. Compared with a molybdenum silicide coating prepared by only brushing Mo-Si slurry under a single-step slurry sintering method, the compact structure of the MoSi2 coating can block the occurrence of oxidation reaction on the surface of the coating, a compact and continuous SiO2 oxidation film is generated after oxidation, and internal diffusion of oxygen in the environment is effectively blocked; the process is simple, short in period and low in cost.

Description

Technical Field

[0001] The present application relates to the field of high-temperature alloys, and in particular to a method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering, and a preparation method and application thereof. Background Art

[0002] Due to its high melting point (2468℃), low density (8.57g / cm3) and excellent high and low temperature mechanical properties, Nb has been developed into various grades of Nb-based alloys, which are widely used in the manufacture of key components of rocket engines and nuclear reactors. In addition, the development of Nb-based alloys has been oriented towards multi-component alloys, such as Nb-Si-based alloys composed of niobium-based solid solutions and niobium silicides, to meet the demand for higher mechanical properties. With the development of aerospace technology, higher requirements have been placed on the operating temperature and life of Nb-based alloys. The traditional "056" niobium silicide coating can no longer meet future usage needs. Therefore, there is an urgent need to develop an anti-oxidation coating with better performance on the surface of Nb-based alloys.

[0003] MoSi2 coating has a high melting point, excellent oxidation resistance and a thermal expansion coefficient that matches that of Nb-based alloys. It is considered to be an important antioxidant coating material on Nb-based alloys. For the preparation of MoSi2 coating on the surface of Nb-based alloys, the commonly used preparation method is a two-step method, that is, firstly depositing a Mo layer on the surface of the Nb alloy by arc ion plating and other methods, and then converting the Mo layer into a MoSi2 coating by diffusion Si infiltration. However, due to the complexity of the preparation process and the long cycle, the preparation cost of the coating is relatively high. The slurry sintering method has low cost, short cycle, and small restrictions on the size of the workpiece. It has been widely used in the preparation of surface antioxidant coatings in the fields of Ni-based alloys, Nb-based alloys and C / C composites. Therefore, it is of great significance to use the slurry sintering method to achieve the preparation of high-performance MoSi2 coatings on the surface of Nb-based alloys.

[0004] At present, there have been research results that have achieved the method of directly brushing Mo-Si slurry and sintering to prepare MoSi2 coating on the surface of Nb-based alloy, and the coating has a certain high-temperature anti-oxidation protection ability. However, the porosity of the MoSi2 coating prepared by this method is relatively high, and the existing pores will accelerate the consumption of the coating during the oxidation process, seriously limiting the antioxidant performance of the MoSi2 coating. Although the antioxidant performance of the MoSi2 coating has been successfully improved by adding modifying elements, the porosity of the coating has not been effectively reduced. In addition, although a dense MoSi2 coating can be further prepared on the surface by pre-fabricating a diffusion barrier layer on the surface of the Nb-based alloy, this method obviously increases the complexity of the process flow. Summary of the invention

[0005] The main purpose of the present application is to provide a method and application for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering, aiming to solve the problem of large porosity of the coating obtained by the existing method.

[0006] To achieve the above-mentioned objectives, the present application provides a method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering, comprising: mixing Si powder, Cr powder, Fe powder and Ti powder to obtain Si-Cr-Fe-Ti powder, and preparing the Si-Cr-Fe-Ti powder into Si-Cr-Fe-Ti slurry; mixing Mo powder and Si powder to obtain Mo-Si powder, and preparing the Mo-Si powder into Mo-Si slurry; coating the Si-Cr-Fe-Ti slurry and the Mo-Si slurry on the surface of a Nb alloy substrate in sequence; heat treating the coated Nb alloy substrate at a temperature of 1300~1550℃ for 10~60min to obtain a dense MoSi2 coating on the surface of the Nb alloy substrate.

[0007] Optionally, before heat treating the coated Nb alloy substrate, the method further comprises: drying the coated Nb alloy substrate at temperatures of 40-60° C. and 100-120° C. in sequence, with the drying time being 0.8-1.2 h.

[0008] Optionally, the mass ratio of Si powder, Cr powder, Fe powder and Ti powder is 1:(0.5~1.5):(0.1~0.5):(0.2~0.8).

[0009] Optionally, the atomic ratio of Mo powder to Si powder is 1:2~3.

[0010] Optionally, the preparation method of Si-Cr-Fe-Ti slurry is: adding a binder and a solvent to Si-Cr-Fe-Ti powder, and ball milling to obtain Si-Cr-Fe-Ti slurry; wherein the ball milling speed is 300~500r / min, and the ball milling time is 1~8h.

[0011] Optionally, the preparation method of Mo-Si slurry is: adding a binder and a solvent to Mo-Si powder, and performing ball milling to obtain Mo-Si slurry; wherein the ball milling speed is 300-500 r / min, and the ball milling time is 1-8 h.

[0012] Optionally, the binder is polyvinyl butyral; and the solvent is ethanol.

[0013] Optionally, the coating thickness of the Si—Cr—Fe—Ti slurry is 50 to 200 μm, and the coating thickness of the Mo—Si slurry is 200 to 600 μm.

[0014] A dense MoSi2 coating on the surface of a Nb alloy is obtained by the above-mentioned method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering; wherein the coating comprises an inner layer, an intermediate layer and a MoSi2 phase layer arranged in sequence from bottom to top; the intermediate layer comprises a Mo5Si3 phase, and the inner layer comprises a (Nb, Ti, Cr)5Si3 and a Cr, Fe-rich phase; the thickness of the coating is 50~150μm, and the area porosity is less than 5%.

[0015] An application of the above-mentioned dense MoSi2 coating on the surface of the Nb alloy in high-temperature equipment.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In the method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering of the present invention, the elements in the Si-Cr-Fe-Ti slurry applied first can compete and diffuse with the elements in the outer Mo-Si slurry during the sintering process; at high temperature, although the elements in the Si-Cr-Fe-Ti slurry and the elements in the Mo-Si slurry both have a tendency to diffuse into the matrix. However, due to the spatial advantage of the Si-Cr-Fe-Ti slurry and the faster diffusion ability into the matrix, the elements in the Si-Cr-Fe-Ti slurry are in a leading position in the competition with the elements in the Mo-Si slurry for internal diffusion. Therefore, the competitive diffusion significantly reduces the internal diffusion loss of the elements in the Mo-Si slurry, thereby achieving the densification of the MoSi2 coating; on the other hand, the diffusion of elements between the Mo-Si slurry, the Si-Cr-Fe-Ti slurry and the matrix generates a transition layer composed of a low silicide phase between the MoSi2 coating and the matrix. The dense MoSi2 coating, transition layer and substrate achieve metallurgical bonding, and the coating has strong bonding strength. Compared with the molybdenum silicide coating prepared by only brushing Mo-Si slurry under the single-step slurry sintering method, the dense structure of the MoSi2 coating can block the occurrence of oxidation reaction on the coating surface, and after oxidation, a dense and continuous SiO2 oxide film is generated, which effectively blocks the internal diffusion of oxygen in the environment. The process is simple, the cycle is short and the cost is low.

[0017] The dense MoSi2 coating on the surface of the Nb alloy of the present invention has a coating porosity of less than 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A flow chart of a method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering in this application; Figure 2 This is a cross-sectional BSE morphology image of the coating obtained in Example 1 of the present application; Figure 3 This is a cross-sectional BSE morphology image of the coating obtained in Example 2 of the present application; Figure 4The oxidation kinetic curves of the coatings obtained in Example 1 of the present application and the comparative example; Figure 5 It is the cross-sectional BSE morphology image of the coating after oxidation obtained in Example 1 of the present application and the comparative example.

[0019] The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0020] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0021] The first embodiment of the present invention provides a method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering, which specifically includes the following steps: Step S1, mixing Si powder, Cr powder, Fe powder and Ti powder in a mass ratio of 1: (0.5~1.5): (0.1~0.5): (0.2~0.8) to obtain Si-Cr-Fe-Ti powder, adding a binder and a solvent to the Si-Cr-Fe-Ti powder, and ball milling to obtain the Si-Cr-Fe-Ti slurry; wherein the ball milling speed is 300~500r / min, and the ball milling time is 1~8h.

[0022] Step S2, mixing Mo powder and Si powder according to an atomic ratio of 1:2~3 to obtain Mo-Si powder, adding a binder with a content of 0.1~5wt.% and a solvent with a content of 30~80wt.% to the Mo-Si powder, and ball milling to obtain the Mo-Si slurry; wherein the ball milling speed is 300~500r / min, and the ball milling time is 1~8h.

[0023] Exemplarily, the binder is polyvinyl butyral (PVB), and the solvent is ethanol.

[0024] Step S3, coating the Si-Cr-Fe-Ti slurry and the Mo-Si slurry on the surface of the Nb alloy substrate in sequence; wherein the coating thickness of the Si-Cr-Fe-Ti slurry is 50-200 μm, and the coating thickness of the Mo-Si slurry is 200-600 μm.

[0025] Before heat treatment of the coated Nb alloy substrate, in order to completely volatilize the solvent ethanol, the coated Nb alloy substrate is dried at 40-60°C and 100-120°C in turn, with the drying time being 0.8-1.2h. Compared with directly heating to above 100°C, gradient heating can reduce the risk of slurry cracking.

[0026] Step S4, heat treating the coated Nb alloy substrate at a temperature of 1300-1550° C. for 10-60 min in an Ar gas protective atmosphere, cooling the substrate in the furnace, and obtaining a dense MoSi2 coating on the surface of the Nb alloy substrate.

[0027] In this embodiment, the elements in the first-coated Si-Cr-Fe-Ti slurry can compete with the elements in the outer Mo-Si slurry for diffusion during the sintering process. This competitive diffusion significantly reduces the internal diffusion loss of elements in the Mo-Si slurry, thereby ensuring sufficient Mo and Si for the reaction of Mo and Si to form the MoSi2 coating, thereby achieving the densification of the MoSi2 coating; in addition, the element diffusion between the Mo-Si slurry, the Si-Cr-Fe-Ti slurry and the substrate generates a transition layer composed of (Nb, Ti, Cr)5Si3 phase and Cr, Fe-rich phase between the MoSi2 coating and the substrate.

[0028] The second embodiment of the present invention provides a dense MoSi2 coating on the surface of a Nb alloy, which is obtained by using the above-mentioned method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering; The coating comprises a Nb5Si3 phase layer, a Mo5Si3 phase layer and a MoSi2 phase layer arranged in sequence from bottom to top; the thickness of the coating is 50-150 μm, and the area porosity is less than 5%.

[0029] A third embodiment of the present invention provides an application of a dense MoSi2 coating on a Nb alloy surface in a high-temperature device.

[0030] Example 1 Step S1, using electric spark cutting to cut Nb521 alloy into a matrix sample with a size of 7mm×6mm×3.5mm. Use 80~800# SiC sandpaper to polish the sample surface and chamfer the edges. Then, ultrasonically clean the smooth matrix sample in anhydrous ethanol and dry it for later use; Step S2, mixing Si powder, Cr powder, Fe powder and Ti powder in a mass ratio of 1:1:0.2:0.2 to obtain Si-Cr-Fe-Ti powder, adding 1wt.% PVB and 50wt.% anhydrous ethanol to the Si-Cr-Fe-Ti powder, and ball milling for 6h at a rotation speed of 300r / min to obtain the Si-Cr-Fe-Ti slurry; Step S2, mixing Mo powder and Si powder according to an atomic ratio of 1:3 to obtain Mo-Si powder, adding 1wt.% PVB and 50wt.% anhydrous ethanol to the Mo-Si powder, and ball milling for 6h at a rotation speed of 300r / min to obtain the Mo-Si slurry; Step S3, brushing 60μm Si-Cr-Fe-Ti slurry and 300μm Mo-Si slurry on the surface of the Nb521 alloy substrate in turn; placing the coated Nb521 alloy substrate in a drying oven, and drying it at temperatures of 50°C and 110°C in turn, with a drying time of 1h.

[0031] Step S4, heat treating the coated Nb alloy substrate at 1500° C. for 30 min in an Ar gas protective atmosphere, cooling the substrate in the furnace, and obtaining a dense MoSi2 coating on the surface of the Nb521 alloy substrate.

[0032] The cross-sectional BSE image of the dense MoSi2 coating obtained in this example is as follows: Figure 2 As shown in the figure, it can be seen that the coating is well bonded to the substrate. The porosity of the coating obtained by image analysis is about 2%.

[0033] Example 2 Step S1, using electric spark cutting to cut the Nb-Si based alloy into a matrix sample with a size of 7mm×6mm×3.5mm. Use 80~800# SiC sandpaper to polish the sample surface and chamfer the edges. Then, the smooth matrix sample is ultrasonically cleaned in anhydrous ethanol and dried for later use; Step S2, mixing Si powder, Cr powder, Fe powder and Ti powder in a mass ratio of 1:1.5:0.2:0.5 to obtain Si-Cr-Fe-Ti powder, adding 0.5wt.% PVB and 30wt.% anhydrous ethanol to the Si-Cr-Fe-Ti powder, and ball milling for 4h at a rotation speed of 400r / min to obtain the Si-Cr-Fe-Ti slurry; Step S2, mixing Mo powder and Si powder according to an atomic ratio of 1:3 to obtain Mo-Si powder, adding 0.5wt.% PVB and 30wt.% anhydrous ethanol to the Mo-Si powder, and ball milling for 4h at a rotation speed of 400r / min to obtain the Mo-Si slurry; Step S3, brushing 100 μm Si-Cr-Fe-Ti slurry and 400 μm Mo-Si slurry on the surface of the Nb-Si based alloy in turn; placing the coated Nb521 alloy substrate in a drying oven, and drying it at temperatures of 40°C and 120°C in turn, with the drying time being 1 hour.

[0034] Step S4, heat treating the coated Nb alloy substrate at 1450° C. for 40 min in an Ar gas protective atmosphere, cooling the substrate in the furnace, and obtaining a dense MoSi2 coating on the surface of the Nb521 alloy substrate.

[0035] The cross-sectional BSE morphology of the dense MoSi2 coating obtained in this example is as follows: Figure 3 As shown in the figure, it can be seen that the coating consists of a MoSi2 layer and a transition layer. The MoSi2 layer is basically densified, with a porosity of about 2%. The black area marked in the coating is SiO2, which is formed by the oxidation of excess Si in the slurry during the slurry sintering process. The transition layer includes a Mo5Si3 intermediate layer and an inner layer composed of (Nb,Ti,Cr)5Si3 and Cr-rich, Fe phases.

[0036] Comparative Example The Si-Cr-Fe-Ti slurry is not brushed on the surface of the Nb-Si based alloy, and the rest of the method is the same as that of Example 2.

[0037] The oxidation kinetic curves of the coating obtained in Example 2 and the MoSi2 coating prepared by only brushing Mo-Si slurry in the comparative example are shown in FIG. Figure 4 As shown in the figure, it can be seen that the oxidation weight gain of the dense MoSi2 coating in this embodiment is significantly lower than that of the MoSi2 coating prepared in the comparative example. The cross-sectional morphology of the MoSi2 coating prepared in the comparative example and the dense MoSi2 coating obtained in this embodiment after oxidation at 1250°C for 100h and 200h respectively is as follows: Figure 5 As shown. Figure 5 It can be seen from a that due to the high porosity of the MoSi2 coating prepared in the comparative example, the coating is oxidized as a whole, and the oxidation products generated by oxidation are present in the pores of the coating. Figure 5 As can be seen from Fig. 2b, the dense structure of the MoSi2 coating in this embodiment can block the oxidation reaction on the coating surface to a great extent, and a dense and continuous oxide film is generated on the coating surface, and the degradation rate of the coating is significantly reduced.

[0038] Example 3 Step S1, using electric spark cutting to cut the Nb-based alloy into a matrix sample with a size of 7mm×6mm×3.5mm. Use 80~800# SiC sandpaper to polish the sample surface and chamfer the edges. Then, ultrasonically clean the smooth matrix sample in anhydrous ethanol and dry it for later use; Step S2, mixing Si powder, Cr powder, Fe powder and Ti powder in a mass ratio of 1:0.5:0.5:0.2 to obtain Si-Cr-Fe-Ti powder, adding 2wt.% PVB and 40wt.% anhydrous ethanol to the Si-Cr-Fe-Ti powder, and ball milling for 3h at a rotation speed of 500r / min to obtain the Si-Cr-Fe-Ti slurry; Step S2, mixing Mo powder and Si powder according to an atomic ratio of 1:2 to obtain Mo-Si powder, adding 2wt.% PVB and 40wt.% anhydrous ethanol to the Mo-Si powder, and ball milling for 3h at a rotation speed of 500r / min to obtain the Mo-Si slurry; Step S3, brushing 120 μm Si-Cr-Fe-Ti slurry and 300 μm Mo-Si slurry on the surface of the Nb-Si based alloy in turn; placing the coated Nb521 alloy substrate in a drying oven, and drying it at temperatures of 60°C and 100°C in turn, with the drying time being 1 hour.

[0039] Step S4, heat treating the coated Nb alloy substrate at 1400° C. for 60 min in an Ar gas protective atmosphere, cooling the substrate in the furnace, and obtaining a dense MoSi2 coating on the surface of the Nb521 alloy substrate.

[0040] The Nb521 alloy substrate obtained in this example was tested, and it was found that the coating porosity was 2%, and the interface between the coating and the substrate was metallurgically bonded.

[0041] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering, characterized in that: include: Mixing Si powder, Cr powder, Fe powder and Ti powder to obtain Si-Cr-Fe-Ti powder, and preparing Si-Cr-Fe-Ti slurry with the Si-Cr-Fe-Ti powder; Mixing Mo powder and Si powder to obtain Mo-Si powder, and preparing the Mo-Si powder into Mo-Si slurry; The Si-Cr-Fe-Ti slurry and the Mo-Si slurry are sequentially coated on the surface of the Nb alloy substrate; The coated Nb alloy substrate is heat treated at a temperature of 1300-1550°C for 10-60 min to obtain a dense MoSi2 coating on the surface of the Nb alloy substrate.

2. The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering according to claim 1, characterized in that: Before heat treating the coated Nb alloy substrate, the method further comprises: The coated Nb alloy substrate is dried at temperatures of 40-60° C. and 100-120° C. in sequence, with the drying time being 0.8-1.2 h.

3. The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering according to claim 1, characterized in that: The mass ratio of the Si powder, Cr powder, Fe powder and Ti powder is 1: (0.5-1.5): (0.1-0.5): (0.2-0.8).

4. The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering according to claim 1, characterized in that: The atomic ratio of the Mo powder to the Si powder is 1:2-3.

5. The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering according to claim 1, characterized in that: The preparation method of the Si-Cr-Fe-Ti slurry is: Adding a binder and a solvent to the Si-Cr-Fe-Ti powder, and performing ball milling to mix to obtain the Si-Cr-Fe-Ti slurry; Among them, the ball milling speed is 300~500r / min, and the ball milling time is 1~8h.

6. The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering according to claim 1, characterized in that: The preparation method of the Mo-Si slurry is: Adding a binder and a solvent to the Mo-Si powder, and performing ball milling to mix to obtain the Mo-Si slurry; Among them, the ball milling speed is 300~500r / min, and the ball milling time is 1~8h.

7. The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering according to claim 5 or 6, characterized in that: The binder is polyvinyl butyral; the solvent is ethanol.

8. The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering according to claim 1, characterized in that: The coating thickness of the Si-Cr-Fe-Ti slurry is 50-200 μm, and the coating thickness of the Mo-Si slurry is 200-600 μm.

9. A dense MoSi2 coating on a Nb alloy surface, characterized in that: The method for preparing a dense MoSi2 coating on the surface of a Nb alloy by single-step slurry sintering as described in any one of claims 1 to 8 is adopted; Wherein, the coating comprises an inner layer, an intermediate layer and a MoSi2 phase layer arranged in sequence from bottom to top; The middle layer includes a Mo5Si3 phase, and the inner layer includes a (Nb, Ti, Cr)5Si3 and a Cr-rich, Fe phase; The coating has a thickness of 50-150 μm and an area porosity of less than 5%.

10. Use of the dense MoSi2 coating on the surface of the Nb alloy as claimed in claim 9 in high-temperature equipment.

Images