Method for improving high-temperature chemical stability and mechanical compatibility of transition metal silicide boride coatings

Abstract

The application discloses a method for improving high-temperature chemical stability and mechanical compatibility of a transition metal silicon boride coating, which comprises the following steps: obtaining a boride layer on the surface of a transition metal by chemical vapor deposition; obtaining a boron-doped transition metal silicide layer by chemical vapor deposition; and finally obtaining a boron-doped silicon dioxide layer through pre-oxidation treatment, thereby obtaining a composite structure of three-layer boron-doped transition metal silicide layer, two-layer transition metal boride layer and a molybdenum matrix. The application introduces a dense and continuous boride layer by two-step chemical vapor deposition technology, and the boride layer is matched with a subsequent ordered multilayer structure formed by silicon-boron co-deposition and pre-oxidation to improve mechanical compatibility. In addition, the application provides abundant boron sources and a silicide layer to form a transition metal silicon boride layer with good element diffusion resistance, so as to improve the chemical stability of the coating.

Description

Technical Field

[0001] This invention relates to a new material coating technology, specifically a method for improving the high-temperature chemical stability and mechanical compatibility of transition metal borosilicate coatings. Background Technology

[0002] Existing technologies typically employ multilayer borosilicate coatings to provide protection for refractory metals, high-entropy refractory alloys (RHEAs), or multi-principal-element alloys (RMPEAs) at high temperatures (1600℃). However, multilayer borosilicate coatings cannot simultaneously enhance the oxidation resistance and diffusion barrier properties of the silicide layer, and they do not consider the high-temperature mechanical compatibility of the multilayer structure. Furthermore, silicide coatings without boron doping do not provide protection over a wide temperature range, and the multilayer silicide layers formed after oxidation do not exhibit good oxidation resistance at high temperatures. Summary of the Invention

[0003] This invention addresses the shortcomings of existing borosilicate coatings, which cannot simultaneously possess antioxidant and diffusion-blocking properties, and whose differences in thermal expansion coefficients and Young's modulus with the substrate can lead to cracking and even peeling. It proposes a method to improve the high-temperature chemical stability and mechanical compatibility of transition metal borosilicate coatings. This method employs a two-step chemical vapor deposition technique. The first step, boron deposition, introduces a dense and continuous boride layer, which, combined with the ordered multilayer structure obtained from subsequent silicon-boron co-deposition and pre-oxidation, forms a good performance match to improve mechanical compatibility. Furthermore, it provides an abundant boron source to form a transition metal borosilicate layer with good elemental diffusion-blocking capabilities, thereby improving the coating's chemical stability.

[0004] This invention is achieved through the following technical solution:

[0005] This invention relates to a method for improving the high-temperature chemical stability and mechanical compatibility of transition metal borosilicate coatings. The method involves obtaining a boride layer on the surface of a transition metal by chemical vapor deposition; then obtaining a boron-doped transition metal silicide layer by chemical vapor deposition; and finally obtaining a composite structure consisting of a boron-doped silicon dioxide layer, three boron-doped transition metal silicide layers, two transition metal boride layers, and a molybdenum substrate through pre-oxidation treatment.

[0006] The transition metals mentioned are molybdenum, niobium, tantalum, and tungsten.

[0007] The boride layer obtained by chemical vapor deposition refers to the process of filling the transition metal with boron deposition diffusion source powder and then heating and holding it at a temperature in an inert gas atmosphere.

[0008] The boron-doped transition metal silicide layer obtained by chemical vapor deposition refers to the process of filling the transition metal containing the boricide layer with silicon-boron co-deposited diffusion source powder, followed by heating and holding in an inert gas atmosphere.

[0009] The silicon-boron co-deposited diffusion source powder is preferably of silicon / boron mass fraction ratio of 45:1-2.5:1, and more preferably 34:1.

[0010] The aforementioned pre-oxidation treatment refers to heating the transition metal containing a boron-doped transition metal silicide layer to a pre-oxidation temperature below the service temperature in an air atmosphere and holding it at that temperature.

[0011] The present invention relates to a transition metal silicoboride coating prepared by the above method, comprising: a boron-doped silicon dioxide layer from the outside to the inside, a boron-doped transition metal silicoboride antioxidant layer, a first transition metal silicoboride diffusion barrier layer, and a second transition metal boride diffusion barrier layer.

[0012] This invention relates to the application of the aforementioned transition metal borosilicate coating, specifically its use in the high-temperature oxygen-containing environment protection of novel high-temperature structural materials.

[0013] Technical effect

[0014] This invention involves a first-step boron infiltration followed by silicon-boron co-infiltration on the surface of a refractory transition metal alloy, followed by pre-oxidation treatment. The resulting thick and dense boride layer acts as an initial element diffusion barrier before the formation of the diffusion barrier layer (silicon-boron layer), preventing the entry of the antioxidant silicon into the substrate and improving the thickness and density of the diffusion barrier layer (silicon-boron layer), thereby enhancing the thermochemical stability of the coating throughout its entire lifecycle. The second step, silicon-boron co-infiltration, yields a boron-doped silicide layer, improving its self-healing and oxidation resistance. The pre-oxidation process results in a gradient coating composed of a boron-doped silicon dioxide layer, a layered boron-doped silicide layer, a silicon-boron diffusion barrier layer, and a layered boride layer, improving the overall mechanical compatibility of the coating. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the coating structure of the present invention;

[0016] Figure 2 (a) is the X-ray diffraction pattern of the sample surface after boron deposition in the example; (b) is the backscattered electron image of the cross-section of the sample after boron deposition.

[0017] Figure 3 (a) is a cross-sectional backscattered electron image of the sample after silicon-boron co-deposition in the example; (b) is a cross-sectional backscattered electron image of the sample after pre-oxidation; the inset is a magnified cross-sectional backscattered electron image.

[0018] Figure 4This is the mass change curve of the sample during the isothermal oxidation test at 1500℃ in the example;

[0019] Figure 5 The image shows the phase distribution of a cross-section of a sample after isothermal oxidation at 1500℃ for 100 hours in the example.

[0020] Figure 6 (a) shows the mass change of the sample in the example after isothermal oxidation at 1600℃ for 20h; (b) shows the phase distribution image of the corresponding sample cross-section.

[0021] Figure 7 The image shows the cross-sectional phase distribution of a sample without boron deposition in the examples after isothermal oxidation at 1600℃ for 20 hours.

[0022] Figure 8 The delamination driving force curve of the multilayer coating in the early stage of oxidation.

[0023] Figure 9 The delamination driving force curve of the multilayer coating in the later stage of oxidation;

[0024] Figure 10 This is a schematic diagram illustrating the effect of different proportions of silicon-boron co-deposited diffusion source powder. Detailed Implementation

[0025] like Figure 1 As shown, this embodiment relates to a method for improving the high-temperature chemical stability and mechanical compatibility of transition metal borosilicate coatings, comprising:

[0026] Step 1, prepare boron deposition diffusion source powder: grind 5 wt.% boron powder, 2.5 wt.% sodium fluoride powder as activator and 92.5 wt.% alumina powder for 20 min and mix evenly;

[0027] Step two, chemical vapor deposition (boron deposition), specifically includes:

[0028] 2.1 The pure molybdenum sample was polished step by step with sandpaper of 400#, 800#, 1500#, 2000#, 3000#, 5000# and 7000#. It was ultrasonically cleaned in anhydrous ethanol for 10 minutes, dried with cold air, placed in the middle of the corundum crucible, filled and compacted with the powder prepared in step 1, and placed in a tube furnace.

[0029] 2.2 Under an argon atmosphere, the heating rate was set to 10℃ / min. When the temperature reached 1000℃, it was held for 3 hours. Then, the furnace was cooled. After the temperature dropped to room temperature, the furnace was removed, ultrasonically cleaned in alcohol for 30 minutes, and dried with cold air to obtain the product shown below. Figure 2 (a) and (b) show molybdenum boride (MoB) layers with a thickness of approximately 19 μm;

[0030] Step 3, prepare silicon-boron co-deposition diffusion source powder: grind 34wt.% silicon powder, 1wt.% boron powder, 2.5wt.% sodium fluoride powder as activator and 62.5wt.% alumina powder for 20 minutes and mix evenly;

[0031] Step four, chemical vapor deposition (silicon-boron co-deposition), specifically includes:

[0032] 4.1 Place the sample treated in step two in the middle of the corundum crucible, fill and compact the powder prepared in step three around it, and place it in a tube furnace.

[0033] 4.2 Under an argon atmosphere, the heating rate was set to 10℃ / min. When the temperature reached 1000℃, it was held for 50 hours. Then, the furnace was cooled. After the temperature dropped to room temperature, the furnace was removed, ultrasonically cleaned in alcohol for 30 minutes, and dried with cold air to obtain the product shown below. Figure 3 (a) shows a molybdenum disilicide (MoSi2) layer with a thickness of approximately 64 μm and a MoB layer of approximately 23 μm between the MoSi2 layer and the molybdenum substrate;

[0034] Step 5, Pre-oxidation treatment: Place the sample treated in Step 4 in a corundum crucible and then in a tube furnace; in an air atmosphere, set the heating rate to 10℃ / min, and when the temperature reaches 1500℃, hold for 10 hours; then cool with the furnace until the temperature drops to room temperature to obtain the sample as shown. Figure 3 (b) and Figure 1 The structure shown, from the outside in, consists of a boron-doped silicon dioxide layer, a boron-doped MoSi2 layer, a boron-doped Mo5Si3 antioxidant layer T1, a Mo5SiB2 diffusion barrier layer T2, a MoB layer, a Mo2B layer, and a molybdenum substrate.

[0035] Performance testing:

[0036] A) Multiple composite structures obtained through steps one to five were subjected to isothermal oxidation at 1500℃, and the resulting oxidation mass change curves are shown below. Figure 4 As shown, the average mass gain per unit surface area after oxidation at 1500℃ for 100 hours was 2.23 mg / cm³. 2 ;

[0037] like Figure 5 As shown, the phase analysis results show that the diffusion barrier layer T2 is dense and continuous, and there is a dense and continuous Mo2B layer between it and the substrate. There is no phenomenon of the antioxidant element Si entering the substrate, indicating that the coating has good chemical stability.

[0038] B) The two composite structures obtained in steps one through five were subjected to isothermal oxidation at 1600℃ for 20 hours. The resulting mass change after oxidation is as follows: Figure 6As shown in (a), the mass gain per unit surface area after oxidation was 1.47 mg / cm³. 2 and 1.96 mg / cm 2 ;

[0039] like Figure 6 As shown in (b), the phase composition of the coating cross-section after isothermal oxidation at 1600℃ for 20 h is similar to that shown in (b). Figure 5 Similarly, no Si element diffusion into the substrate was observed, further indicating that the coating has excellent high-temperature chemical stability.

[0040] C) Samples that underwent only silicon-boron deposition (one-step sample) without boron deposition were subjected to isothermal oxidation at 1600℃ for 20 h. The phase distribution image of the cross-section of the sample is shown below. Figure 7 As shown, compared to Figure 6 (b) The two-step sample has a significantly thinner and discontinuous diffusion barrier layer T2; there is an obvious antioxidant layer T1 and a Mo3Si layer between the diffusion barrier layer T2 and the substrate, which means that Si diffuses into the molybdenum substrate, indicating that this coating does not have good chemical stability at high temperature.

[0041] like Figure 8 As shown, the maximum delamination driving force for both samples in the early stage of oxidation (with a MoSi2 layer present) was 267 J / m. 2 However, the maximum value of the one-step sample appeared at the coating / substrate interface, while that of the two-step sample appeared at the Mo2B layer / diffusion barrier layer T2 interface; the delamination driving force at the coating / substrate interface of the two-step sample was only 237 J / m. 2 Compared to the one-step sample, the two-step method reduced the coating by 11.2%, indicating that the coating prepared by the two-step method has better mechanical compatibility and a lower tendency to delamination.

[0042] like Figure 9 As shown, the maximum delamination driving force of the one-step sample in the later stage of oxidation (when all MoSi2 is converted to T1) is 224 J / m. 2 The maximum delamination driving force for the two-step sample is only 206 J / m. 2 The delamination rate was reduced by 8.0%, and the location was also at the Mo2B layer / diffusion barrier layer T2 interface; the delamination driving force at the coating / matrix interface of the two-step sample was only 172 J / m. 2 The two-step method reduced the mechanical compatibility by 23.2% compared to the one-step method, which further indicates that the coating prepared by the two-step method has stronger mechanical compatibility.

[0043] like Figure 10As shown, this diagram illustrates the effect of different proportions of silicon-boron co-deposited diffusion source powder on the performance of the final MoB product. Among them, 30 / 5 and 25 / 10 cannot significantly improve the thickness and density of the MoB layer between the substrate and MoSi2, and will significantly increase the number of MoB particles in the MoSi2 layer, resulting in a decrease in coating viscosity and a deterioration in stability.

[0044] In summary, this invention utilizes a two-step chemical vapor deposition technique to introduce a continuous and dense transition metal boride layer between the transition metal-silicon-boron coating and the substrate. This layer can act as a diffusion barrier layer before the formation of the transition metal-silicon-boron barrier layer and provides an abundant boron source during long-term service, improving the thickness and density of the transition metal-silicon-boron barrier layer, thereby enhancing the high-temperature chemical stability of the coating. The small difference in the coefficients of thermal expansion between the transition metal boride layer and the substrate enhances the high-temperature mechanical compatibility of the coating.

[0045] The above-described specific implementations can be partially adjusted by those skilled in the art in different ways without departing from the principles and purpose of the present invention. The scope of protection of the present invention is defined by the claims and is not limited to the above-described specific implementations. All implementation schemes within the scope of the claims are bound by the present invention.

Claims

1. A method for improving high temperature chemical stability and mechanical compatibility of transition metal silicide boride coatings, characterized in that, The gradient microstructure of three layers of boron-doped transition metal silicide layers, two layers of transition metal boride layers and a molybdenum substrate is obtained by the following steps: obtaining a boride layer on the surface of the transition metal by chemical vapor deposition; obtaining a boron-doped transition metal silicide layer by chemical vapor deposition; and finally obtaining a boron-doped silicon dioxide layer by pre-oxidation treatment. The pre-oxidation treatment refers to heating the transition metal containing the boron-doped transition metal silicide layer to a pre-oxidation temperature below the service temperature in an air atmosphere and holding the temperature. The boride layer is obtained by filling the transition metal with boron deposition diffusion source powder and heating and holding in an inert gas atmosphere. The boron-doped transition metal silicide layer is obtained by filling the transition metal containing the boride layer with silicon-boron co-deposition diffusion source powder and heating and holding in an inert gas atmosphere. The gradient microstructure, from the outside to the inside, is a boron-doped silicon dioxide layer, a boron-doped MoSi2 layer, an oxidation-resistant layer T1 of boron-doped Mo5Si3, a diffusion-resistant layer T2 of Mo5SiB2, a MoB layer, a Mo2B layer and a molybdenum substrate.

2. The method of claim 1, wherein the method is characterized by: The boron deposition diffusion source powder includes boron powder, sodium fluoride activator powder and alumina powder.

3. The method of claim 1, wherein the method is characterized by: The silicon-boron co-deposition diffusion source powder includes silicon powder, boron powder, sodium fluoride activator powder and alumina powder.

4. The method of claim 1 or 3, wherein the method is characterized by, The silicon-boron co-deposition diffusion source powder has a silicon / boron mass fraction ratio of 45:1-2.5:

1.

5. The method of claim 1 or 2, wherein the method is characterized by, The heating and holding in an inert gas atmosphere refers to setting the heating rate to 10℃ / min in an argon atmosphere, holding the temperature for 50h when the temperature rises to 1000℃, and then cooling with the furnace.

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