A method for preparing a segmented CVD combined double brush coating process of a tantalum carbide coating

Abstract

The application discloses a method for preparing a carbonized tantalum coating by a sectional CVD combined double-brush coating process, and the method comprises the following steps: firstly, brushing a carbonized tantalum slurry on the surface of a pretreated base material and heat treating to form an initial covering layer; then, depositing a dense and smooth carbonized tantalum transition layer by high-temperature CVD; then, forming a carbonized tantalum support layer with a columnar crystal structure by high-temperature and high-pressure CVD rapid deposition; then, filling pores by low-temperature and low-pressure CVD dense repair; and finally, sintering after brushing a carbonized tantalum precursor slurry on the surface of the carbonized tantalum coating, so as to completely seal the residual pores of the carbonized tantalum coating. By means of the process combination of 'pretreatment-section deposition-post treatment', the technical problems of insufficient density of the carbonized tantalum coating, poor bonding force and long preparation period are solved, the obtained coating has no pore defects, has good bonding strength and excellent thermal shock resistance, and the service life of a graphite component under high-temperature corrosion and thermal shock conditions is significantly prolonged.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tantalum carbide coating preparation, and particularly relates to a method for preparing a tantalum carbide coating by using a segmented CVD combined double-brush coating process. BACKGROUND

[0002] The tantalum carbide coating has a wide application prospect in the fields of aerospace, semiconductor industry, high-temperature heat treatment, etc. due to its extremely high melting point, excellent chemical stability, outstanding corrosion resistance and high-temperature mechanical strength. In particular, in a semiconductor crystal growth device, the tantalum carbide coating can effectively prevent the reaction between a graphite matrix and a silicon melt, reduce crystal contamination and improve crystal quality. However, the traditional tantalum carbide coating preparation technology mainly has the following problems:

[0003] (1) Insufficient density: the TaC coating prepared by the conventional chemical vapor deposition technology often has problems of columnar crystal structure, porosity and micro-cracks, and easily becomes a channel for gas penetration and corrosion medium diffusion in a high-temperature service environment;

[0004] (2) Poor adhesion: due to the difference in the thermal expansion coefficient between the tantalum carbide coating and the graphite matrix, interface stress is easily generated under thermal cycling conditions, resulting in peeling failure of the coating;

[0005] (3) Long preparation period: it often takes tens or even hundreds of hours of deposition time to obtain a completely dense tantalum carbide coating, and the production efficiency is low and the cost is high.

[0006] For example, in the prior art, patent CN106699228A proposes a low-cost suspension liquid spraying combined sintering tantalum carbide coating preparation method, which is simple in process, but the coating density and adhesion strength are difficult to meet the high-performance requirements. Patent CN202311049786A introduces a composite phase composition as a microstructure regulator to improve the coating density through solid-phase reaction, but the process control is complex, and it is difficult to realize large-area uniform preparation.

[0007] Therefore, it is urgent to develop a high-quality tantalum carbide coating preparation method which can simultaneously solve the problems of density, adhesion and preparation efficiency. SUMMARY

[0008] The present application aims to solve the technical problems of insufficient density, poor adhesion and long preparation period of the tantalum carbide coating in the prior art, and provides a method for preparing a tantalum carbide coating by using a segmented CVD combined double-brush coating process.

[0009] To achieve the above-mentioned purpose, the present application provides a high-quality tantalum carbide coating preparation method combining segmented CVD and brush coating densification, which comprises the following steps:

[0010] S100, selecting a base material and performing pretreatment, specifically, selecting isostatic pressed graphite as the base material, and sequentially performing ultrasonic cleaning of the isostatic pressed graphite base in deionized water and anhydrous ethanol, and then drying in a vacuum drying oven, wherein the isostatic pressed graphite has a density of ≥1.75 g / cm3, an average pore size of 10-20 μm, a surface roughness of 1-2 μm, an ultrasonic cleaning time of 20-40 min, a temperature in the vacuum drying oven of 110-130 °C, and a drying time of 1-3 h;

[0011] Based on the above step S100, impurities and dust on the surface of the base material can be effectively removed;

[0012] S200, brushing and coating a tantalum carbide slurry on the surface of the pretreated base material to form an initial covering layer, and then placing it in a CVD deposition furnace under high temperature conditions to generate a dense and flat tantalum carbide transition layer, which specifically comprises:

[0013] S210, preparing a tantalum carbide slurry by selecting a tantalum carbide powder with an average particle size of 1-3 μm and a solid content of 60-70 wt%, and then adding 1-3 wt% polyvinyl alcohol, 20-30 wt% anhydrous ethanol, and 0.3-0.5 wt% dispersant, and ball milling for 5-7 h to obtain a uniform tantalum carbide slurry;

[0014] S220, uniformly coating the slurry on the surface of the base material using a brush or ultrasonic spraying method, and obtaining an initial covering layer coated on the surface of the base material after drying, wherein the thickness of the tantalum carbide slurry brushed on the surface of the base material is 1-5 μm, and the drying operation is performed by placing the base material in an oven with a temperature of 180-220 °C for drying for 3-5 h, and then heat treating for 40-80 min under an inert gas atmosphere at a temperature of 750-850 °C;

[0015] S230, placing the base material coated with the initial covering layer in a CVD deposition furnace, and controlling the temperature to be 2100-2400 °C, the pressure to be 40-60 Pa, and the inert atmosphere, and reacting in an Ar mixed atmosphere for 2-5 h to generate a dense and flat tantalum carbide transition layer. 、 、

[0016] In this step, the thickness of the generated tantalum carbide transition layer is 1-5 μm, and the transition layer can provide an excellent nucleation surface for subsequent CVD deposition, thereby improving the bonding force between the tantalum carbide coating and the base material.

[0017] S300, rapidly depositing and forming a tantalum carbide support layer with a columnar crystal structure on the surface of the tantalum carbide transition layer of the base material under high temperature and high pressure conditions;

[0018] ​In this step, the temperature of the CVD deposition furnace is 1300-1400 DEG C, the pressure is controlled to be 10-15 kPa, and Ar mixed gas is introduced into the CVD deposition furnace 、 、 , and the reaction deposition is performed for 4-6 h under the Ar mixed atmosphere, wherein the supply rate of the carbon source is 0.5-1.0 g / min, and the thickness of the tantalum carbide support layer is 30-60 microns. Due to the fast deposition rate in this step, the generated tantalum carbide support layer particles are coarse and have a columnar crystal structure, obvious gaps exist between the grain boundaries, and the overall density is insufficient, but it can be used as a support skeleton.

[0019] S400, under low-temperature and low-pressure conditions, the pores and micro-cracks in the tantalum carbide support layer are densified and repaired.

[0020] In this step, the temperature of the CVD deposition furnace is controlled to be 1000-1100 DEG C, the reaction pressure is controlled to be 100-200 Pa, and the deposition time is 8-12 h. Under the low-temperature and low-pressure conditions, the deposition rate of the tantalum carbide is significantly slowed down, the fine-grained deposits fill and repair the pores and micro-cracks in the tantalum carbide support layer, the number of cavities in the tantalum carbide support layer is greatly reduced, the grain boundary diffusion is enhanced, and thus the density and adhesion of the tantalum carbide coating are effectively improved.

[0021] S500, the tantalum carbide coating after the densification repair is brushed with tantalum carbide precursor slurry again and sintered at high temperature to densify.

[0022] In this step, the tantalum carbide precursor slurry includes: nano-tantalum carbide powder with a particle size of 50-100 nm, organic binder and volatile solvent; or, metal tantalum powder with a D50 particle size of 200 nm, carbon black or organic carbon precursor, and the ratio is stoichiometric.

[0023] In this step, after the tantalum carbide precursor slurry is brushed on the tantalum carbide coating after the densification repair and dried at room temperature, sintering is performed under vacuum ≤100 Pa or inert atmosphere, the sintering temperature is 1800-2200 DEG C, and the sintering time is 10-60 min. Although the number of cavities in the tantalum carbide support layer is greatly reduced after the low-temperature and low-pressure densification repair, there are still some submicron-sized cavities or necking defects, which may become the starting point of gas permeation or thermal cracks under high-temperature service conditions. Therefore, based on the sintering after the brushing of the tantalum carbide precursor slurry, the tantalum carbide precursor slurry particles are sintered and densified or in-situ react to generate tantalum carbide, so that they are combined with the lower tantalum carbide coating through interface diffusion, and finally the residual pores are completely closed, and the integrity and thermal cycle stability of the tantalum carbide coating are further improved.

[0024] Therefore, compared with the prior art, the present application has the following advantages:

[0025] (1) The coating density is significantly improved: through the segmented CVD deposition combined with the post-brushing densification process, the complete densification of the tantalum carbide coating is realized, and there is no any hole defect on the surface, which effectively prevents the gas permeation and the diffusion of the corrosion medium;

[0026] (2) The coating bonding force is enhanced: through the high-temperature interlocking interface formed by the brushing pretreatment and the optimized design of the transition layer, the bonding strength of the tantalum carbide coating to the substrate surface is ≥30 MPa, which is much higher than the 15-20 MPa of the conventional CVD deposited tantalum carbide coating;

[0027] (3) The thermal shock resistance is excellent: the tantalum carbide coating prepared by the method has no peeling after 2000-2400℃ thermal cycle for more than 50 times, which proves the excellent durability of the tantalum carbide coating under extreme temperature change conditions;

[0028] (4) The preparation efficiency is improved: through the optimization of the deposition conditions of the segmented CVD, the overall preparation time can be controlled within a reasonable range while ensuring the quality of the tantalum carbide coating, realizing the balance between efficiency and quality;

[0029] (5) The process has good adaptability: the present application can be implemented on the basis of the existing CVD equipment, the equipment modification cost is low, and it has strong industrialization popularization potential. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings needed to be used in the specific embodiments or the prior art description. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0031] Figure 1 The flow chart of the method for preparing the tantalum carbide coating by the segmented CVD combined with the double-brushing coating process in the present application,

[0032] Figure 2 The SEM image of the tantalum carbide support layer deposited under high temperature and high pressure conditions in Example 1 of the present application,

[0033] Figure 3 The SEM image of the tantalum carbide coating after densification repair under low temperature and low pressure conditions in Example 1 of the present application,

[0034] Figure 4 The SEM image of the tantalum carbide coating obtained by brushing the tantalum carbide precursor slurry and high-temperature sintering in Example 1 of the present application. DETAILED DESCRIPTION

[0035] The application will be described in detail below with specific examples. The following examples will help those skilled in the art to further understand the application, but do not limit the application in any form.

[0036] Example 1

[0037] This embodiment provides a method for preparing high-quality TaC coating by segmented CVD combined with brush coating densification, and the specific steps are as follows:

[0038] (1) Select the substrate material and perform pretreatment: isostatic pressing graphite with a density of 1.75 g / cm³, an average pore size of 20 μm, and a surface roughness of 2 μm is selected as the substrate material, and the isostatic pressing graphite is ultrasonically cleaned with deionized water and anhydrous ethanol for 20 min, and then vacuum dried at 110°C for 1 h;

[0039] (2) Brush coating a layer of tantalum carbide slurry on the surface of the pretreated substrate material, and place it in a CVD deposition furnace for high-temperature deposition to form a dense and smooth tantalum carbide transition layer, which specifically includes: first, taking tantalum carbide powder with an average particle size of 1 μm and a solid content of 60 wt% as the main body, adding 1 wt% of polyvinyl alcohol (PVA) as a binder, 20 wt% of anhydrous ethanol as a solvent, and 0.3 wt% of ammonium polyacrylate as a dispersant, and ball milling for 5 h to obtain a uniform tantalum carbide slurry; then, a brush is used to brush a 1 μm thick cover layer on the surface of the graphite substrate, which is dried in a 180°C oven for 3 h, and then heated at 750°C for 40 min in an argon atmosphere to obtain an initial cover layer; finally, the substrate material with the generated tantalum carbide transition layer is placed in a CVD deposition furnace, heated to 2100°C, and reacted in an argon-hydrogen mixture gas atmosphere for 2 h at a flow rate of 0.5 g / min, i.e. a tantalum carbide transition layer with a thickness of 1 μm is formed; (0.5 g / min supply rate), ,

[0040] (3) Segmented CVD deposition, which specifically includes: first, reduce the temperature of the CVD deposition furnace to 1300°C, control the reaction pressure to 10 kPa, and react and deposit for 6 h to obtain a 30 μm thick tantalum carbide support layer with a columnar crystal structure; then, reduce the temperature of the CVD deposition furnace to 1000°C, adjust the pressure to 200 Pa, and deposit for 8 h to achieve the dense repair of the voids and micro-cracks in the tantalum carbide support layer;

[0041] (4) Post-brush coating densification, which specifically includes: after the completion of the segmented CVD deposition, brush coating the tantalum carbide precursor slurry (nanometer tantalum carbide powder with a particle size of 50-100 nm, with organic binder and volatile solvent) on the surface of the tantalum carbide coating again, dry at room temperature, and then sinter in a vacuum of ≤100 Pa, with a sintering temperature of 1800°C and a sintering time of 60 min. ​

[0042] Electron microscopy was performed on the tantalum carbide transition layer, the densely repaired tantalum carbide coating, and the tantalum carbide coating obtained by high-temperature sintering after brushing with tantalum carbide precursor slurry in Example 1. Figures 2-4 As shown, Figure 2 This is a SEM image of the tantalum carbide support layer in Example 1. Figure 3 This is a SEM image of the tantalum carbide coating after dense repair in Example 1. Figure 4 This is a SEM image of the tantalum carbide coating obtained by brushing with tantalum carbide precursor slurry and then sintering at high temperature in Example 1.

[0043] from Figure 2 As can be seen, the tantalum carbide support layer formed by rapid deposition under high temperature and high pressure conditions has a large number of pores, and its overall density is significantly insufficient; from Figure 3 As can be seen, after low-temperature and low-pressure densification repair, the porosity in the tantalum carbide support layer is significantly reduced, with only a small number of submicron-sized pores remaining. This is because, under low-temperature and low-pressure conditions, the deposits, mainly composed of fine grains, fill and repair the pores and microcracks formed in the tantalum carbide support layer, effectively improving the density of the tantalum carbide coating. Figure 4 As can be seen, after the tantalum carbide precursor slurry is brushed and sintered at high temperature, there are no pore defects on the surface of the tantalum carbide coating. This is because after the tantalum carbide precursor slurry is brushed and sintered, the tantalum carbide precursor slurry particles undergo sintering densification or in-situ reaction to generate tantalum carbide, which then diffuses and combines with the lower tantalum carbide coating through the interface, ultimately completely sealing the residual pores.

[0044] Example 2

[0045] The difference between this embodiment and Embodiment 1 is that:

[0046] In step (1), the density of isostatic graphite is 1.80 g / cm³, the average pore size is 15 μm, the surface roughness is 1.5 μm, the ultrasonic cleaning time is 30 min, the vacuum drying temperature is 120℃, and the drying time is 2 h.

[0047] In step (2), the tantalum carbide powder has an average particle size of 2 μm, a solid content of 65 wt%, a polyvinyl alcohol (PVA) mass percentage of 2 wt%, anhydrous ethanol mass percentage of 25 wt%, and ammonium polyacrylate mass percentage of 0.4 wt%. The ball milling time is 6 h, the oven temperature is 200 °C, the oven drying time is 4 h, the holding temperature under argon atmosphere is 800 °C, the holding time is 60 min, and the CVD deposition furnace temperature is raised to 2200 °C. The feed rate was 0.8 g / min, and the deposition reaction time was 3 h.

[0048] In step (3), the CVD deposition furnace is firstly cooled to 1350℃, the reaction pressure is controlled to be 13 kPa, the reaction deposition time is 5 h, and the thickness of the tantalum carbide support layer is 50 μm; the CVD deposition furnace is secondly cooled to 1050℃, the reaction pressure is controlled to be 150 Pa, and the reaction deposition time is 10 h;

[0049] In step (4), the slurry adopts scheme B: metal Ta powder (D50 200 nm) + carbon black, the ratio is the stoichiometric ratio, the sintering temperature is 2000℃, and the sintering time is 30 min.

[0050] Example 3

[0051] The difference between this example and example 1 is that:

[0052] In step (1), the isostatic pressing graphite has a density of 1.85 g / cm3, an average pore size of 10 μm, and a surface roughness of 1 μm, the ultrasonic cleaning time is 40 min, the vacuum drying temperature is 130℃, and the drying time in the oven is 3 h;

[0053] In step (2), the average particle size of the tantalum carbide powder is 3 μm, the solid content is 70 wt%, the mass percentage of polyvinyl alcohol (PVA) is 3 wt%, the mass percentage of anhydrous ethanol is 30 wt%, the mass percentage of ammonium polyacrylate is 0.5 wt%, the ball milling time is 7 h, the oven drying temperature is 220℃, the oven drying time is 3 h, the holding temperature under argon atmosphere is 850℃, the holding time is 80 min, the CVD deposition furnace is heated to 2400℃, The feeding rate is 1.0 g / min, and the deposition reaction time is 5 h;

[0054] In step (3), the CVD deposition furnace is firstly cooled to 1400℃, the reaction pressure is controlled to be 15 kPa, the reaction deposition time is 4 h, and the thickness of the tantalum carbide support layer is 60 μm; the CVD deposition furnace is secondly cooled to 1100℃, the reaction pressure is controlled to be 100 Pa, and the reaction deposition time is 12 h;

[0055] In step (4), the slurry adopts scheme B: metal Ta powder (D50 200 nm) + carbon black, the ratio is the stoichiometric ratio, the sintering temperature is 2200℃, and the sintering time is 10 min.

[0056] Comparative Example 1

[0057] Comparative Example 1 adopts a traditional single CVD process: directly depositing a tantalum carbide coating on a graphite substrate at 1300℃ under normal pressure for 26 hours, and other conditions are the same as those in Example 1.

[0058] Performance test

[0059] The carbonized tantalum coating prepared by the examples 1-3 and the comparative example 1 was tested for performance, and the test results are shown in Table 1.

[0060] Table 1: Performance test results of the carbonized tantalum coating prepared by the examples 1-3 and the comparative example 1

[0061] Test item Example 1 Example 2 Example 3 Comparative Example 1 Coating thickness (pm) 32 53 63 45 Porosity (%) ＜0.01 ＜0.01 ＜0.01 8-12 Bonding strength (MPa) 35 32 33 16 Number of thermal cycles at 2000°C (times) ＞50 ＞50 ＞50 12 Preparation time (h) 15 15.5 16.2 26

[0062] As can be seen from Table 1, the carbonized tantalum coating prepared by the examples 1-3 of the present application is significantly better than the traditional single CVD process of the comparative example 1 in terms of compactness, bonding strength and thermal shock resistance, and the deposition reaction time of the examples 1-3 is also much shorter than that of the single CVD process. Therefore, the method provided by the present application effectively solves the technical problems of insufficient compactness, poor bonding strength and long preparation period of the carbonized tantalum coating in the prior art.

[0063] The above describes in detail the method for preparing the carbonized tantalum coating by the sectional CVD combined double-brush coating process provided by the present application. The principles and implementation manners of the present application are described by applying specific examples, and the above description of the examples is only for helping to understand the core idea of the present application. It should be pointed out that, for those skilled in the art, some improvements and modifications can be made to the present application without departing from the principles of the present application, and these improvements and modifications also fall within the protection scope of the claims of the present application.

Claims

1. A method for producing a coating of tantalum carbide by a segmented CVD combined double brush coating process, characterized in that The method comprises the following steps: S100, selecting a base material and pre-treating; S200, brushing a tantalum carbide slurry on the surface of the pre-treated base material to form an initial covering layer, and then placing it in a CVD deposition furnace at a temperature of 2100-2400℃ to generate a dense and flat tantalum carbide transition layer; S300, rapidly depositing and forming a tantalum carbide support layer with a columnar crystal structure on the surface of the tantalum carbide transition layer of the base material at a temperature of 1300-1400℃ and a pressure of 10-15 kPa; S400, densifying and repairing the pores and micro-cracks in the tantalum carbide support layer at a temperature of 1000-1100℃ and a pressure of 100-200 Pa; S500, re-brushing the tantalum carbide precursor slurry on the densified tantalum carbide coating and sintering it at a temperature of 1800-2200℃.

2. The method of claim 1, wherein, The step S100 specifically comprises: selecting isostatic graphite as the base material, and sequentially performing ultrasonic cleaning of the isostatic graphite base in deionized water and anhydrous ethanol, and then drying it in a vacuum drying box, wherein the isostatic graphite has a density of ≥1.75 g / cm³, an average pore size of 10-20μm, a surface roughness of 1-2μm, an ultrasonic cleaning time of 20-40min, a vacuum drying box temperature of 110-130℃, and a drying time of 1-3h.

3. The method of claim 1, wherein, The step S200 comprises: S210, preparing a tantalum carbide slurry; S220, uniformly coating the slurry on the surface of the base material using a brush or ultrasonic spraying method, and obtaining an initial covering layer on the surface of the base material after drying; S230, placing the base material coated with the initial covering layer in a CVD deposition furnace, controlling the temperature to be 2100-2400℃, the pressure to be 40-60Pa, and the inert atmosphere, and reacting in a TaCl5, CH4, H2, Ar mixed atmosphere for 2-5h to generate a dense and flat tantalum carbide transition layer.

4. The method of claim 3, wherein, The step S210 specifically comprises: selecting a tantalum carbide powder with an average particle size of 1-3μm and a solid content of 60-70wt%, and then adding 1-3wt% polyvinyl alcohol, 20-30wt% anhydrous ethanol, and 0.3-0.5wt% dispersant, and ball milling for 5-7h to obtain a uniform tantalum carbide slurry.

5. The method of claim 4, wherein, The step S220 specifically comprises: uniformly coating the prepared tantalum carbide slurry on the surface of the pre-treated base material using a brush or ultrasonic spraying method, and the thickness of the tantalum carbide slurry is 1-5μm, then placing the base material in an oven at a temperature of 180-220℃ for drying for 3-5h, and heat treating in an inert gas atmosphere at a temperature of 750-850℃ for 40-80min to obtain the base material coated with the initial covering layer.

6. The method of claim 1, wherein, The step S300 comprises: reducing the temperature of the CVD deposition furnace to 1300-1400℃, controlling the reaction pressure to be 10-15 kPa, and reacting and depositing in a TaCl5, CH4, H2, Ar mixed atmosphere for 4-6h to form a tantalum carbide support layer with a thickness of 30-60μm and a columnar crystal structure.

7. The method of claim 6, wherein, The step S400 comprises: reducing the temperature of the CVD deposition furnace to 1000-1100 ℃, controlling the reaction pressure to 100-200 Pa, maintaining deposition for 8-12 h, filling the pores and micro-cracks in the tantalum carbide support layer with fine grains, so as to improve the compactness and bonding force of the tantalum carbide coating, and obtaining a high-density tantalum carbide coating with a thickness of 30-60 μm.

8. The method of claim 7, wherein, The step S500 comprises: taking out the substrate material after CVD deposition, uniformly brushing a layer of tantalum carbide precursor slurry on the surface of the tantalum carbide coating after densification repair, drying at room temperature, and then sintering under vacuum ≤100 Pa or inert atmosphere to seal the residual pores of the tantalum carbide coating, wherein the sintering temperature is 1800-2200 ℃, and the sintering time is 10-60 min.

9. The method of claim 8, wherein, In the step S500, the tantalum carbide precursor slurry adopts one of the following schemes: Scheme A: nano-tantalum carbide powder with a particle size of 50-100 nm, mixed with an organic binder and a volatile solvent; Scheme B: metal tantalum powder with a D50 particle size of 200 nm, mixed with carbon black or an organic carbon precursor in a stoichiometric ratio.

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