A hot pressing rapid sintering preparation (Zr x Ta 1-x B2) - Method of SiC oxidation resistant ceramics

Abstract

The present invention belongs to the technical field of ultra-high temperature ceramic design and preparation, and is specifically a method for preparing (Zr x Ta 1‑x The method comprises the following steps: modeling a unit cell and optimizing the geometric structure, calculating the state density and population of Si-O bonds in the unit cell and optimizing the composition; weighing three ultrafine powders of ZrB2, α-SiC and TaB2; mixing the powders uniformly and performing pretreatment on the powders using a planetary ball mill to obtain a mixed powder; and sintering the powders using a step-by-step temperature increase process and maintaining the temperature at a predetermined temperature for degassing to obtain (ZrB2). x Ta 1‑x )B2-SiC oxidation resistant ceramics. The present invention forms (Zr x Ta 1‑x )B2 solid solution, optimized the composition of the ceramic system; and designed powder pretreatment and spark plasma sintering to achieve high density, fine grain and high purity (Zr x Ta 1‑x B2) Rapid preparation of SiC ceramics to further enhance their oxidation protection capabilities.

Description

Technical Field

[0001] The present invention belongs to the field of ultra-high temperature ceramic design and preparation technology. More specifically, by synthesizing (Zr x Ta 1-x )B2 ultra-high temperature ceramic boride solid solution, combined with the introduction of SiC phase, improves the oxidation resistance of composite ceramics, and adopts wet ball milling and spark plasma sintering process to achieve (Zr x Ta 1-x ) Preparation of B2-SiC oxidation-resistant ceramics by hot pressing and rapid sintering. Background Art

[0002] Ultra-high temperature ceramics (UHTCs) have excellent properties such as high melting point (>3000℃), low density, high hardness, high specific strength, medium thermal expansion coefficient, good oxidation resistance and mechanical properties. They are high-temperature thermal protection materials with great application potential in the aerospace field. Among them, the introduction of SiC phase into ZrB2 forms ZrB2-SiC composite ceramics. The borosilicate glass layer generated after oxidation can effectively improve the oxidation resistance of ceramics in a wide temperature range. It is one of the ultra-high temperature oxidation-resistant ceramic systems with the most application potential. However, under high temperature, long-term oxidation and airflow scouring environments, the SiO2-rich glass film on the surface of ZrB2-SiC ceramics will accelerate volatilization, resulting in a significant decrease in oxidation resistance and mechanical properties. At present, domestic and foreign researchers mostly use the method of introducing additives to regulate the structure and stability of the glass film to improve the oxidation resistance of ZrB2-SiC ceramics. Studies have shown that by introducing a high cation field strength (E=Z / r 2 , where Z is the cation valence and r is the ionic radius) element compound TaB2 promotes the phase separation of the surface glass film, reduces the volatilization rate of the glass film, increases the viscosity of the glass film, and thus improves the antioxidant capacity of the ceramic. At the same time, ZrB2 and TaB2 have similar crystal structures and can form (Zr x Ta 1-x )B2 solid solution, Ta after oxidation 5+ Can partially replace Zr in ZrO2 4+ , reducing the oxygen vacancy concentration in ZrO2 and the oxygen diffusion rate in the oxide layer, thereby improving the ceramic's oxidation protection ability.

[0003] However, the current preparation (Zr x Ta 1-x B2) -SiC ceramics are less studied, and are mostly prepared by pressureless reaction sintering or conventional hot pressing sintering, which takes a long time. At the same time, in the existing preparation technology, the chemical reaction process leads to the formation of Zr x Ta 1- xThe purity and relative content of B2 solid solution phase are difficult to control, resulting in insufficient density of ceramics, and excessive sintering time will also cause coarse grains, decreased mechanical properties and antioxidant properties of ceramics. Therefore, it is necessary to develop a preparation method to achieve fine-grained high-purity (Zr x Ta 1-x B2) Precise control and rapid preparation of SiC ceramic composition. Summary of the Invention

[0004] The present invention aims to optimize the oxidation resistance of ZrB2-SiC ceramic system. In order to overcome the shortcomings of the existing high temperature oxidation resistance of ZrB2-SiC ceramics, TaB2 is introduced to form (Zr x Ta 1-x )B2 solid solution, through the unit cell modeling and calculation of state density and population number, the composition optimization design of the ceramic system is completed; at the same time, through ball milling mixing and sintering process optimization, fine grain high purity (Zr x Ta 1-x B2)-SiC composite ceramics, rapid preparation, density improvement, and dispersion and uniform mixing of various phases in the composite ceramics. Specifically, by introducing TaB2 to form (Zr x Ta 1-x )B2 solid solution, and optimize the antioxidant components of ZrB2-SiC; use ultrafine powder and all-round wet ball milling process to achieve dispersed distribution and uniform mixing of each phase in the composite ceramic powder; use spark plasma hot pressing rapid sintering technology, by setting the appropriate heating method, sintering temperature, sintering pressure and holding time, so that the mixed powder is fully sintered to achieve high density, fine grain and high purity (Zr x Ta 1-x B2) Rapid preparation of SiC ceramics to further enhance their oxidation protection capabilities.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A hot pressing rapid sintering preparation (Zr x Ta 1-x ) A method for producing B2-SiC oxidation-resistant ceramics, comprising the following steps:

[0007] S1: Component design, including:

[0008] S1.1: Unit cell modeling, using high-temperature quartz β-SiO2 as the basic calculation model, expanding the primary cell to a 2x2x1 stacking model to form a supercell, and introducing B, Ta, and Zr atoms into the unit cell to form a doping structure;

[0009] S1.2 performs structural optimization on the unit cell system after doping. The structural optimization parameters during the geometric structure optimization process are:

[0010] The functionals used are GGA, PW91, BFGS rule and ultrasoft pseudopotential, with a cutoff energy of 350 eV, which meets the convergence requirements of doping atoms and system structure. The total energy of the convergence parameter system is set to be less than 10 -6 eV / atom, the minimum atomic force is

[0011] The k-point grid is smaller than 0.001eV / 1×1 supercell;

[0012] S1.3: Calculate the density of states and population of Si-O bonds in the unit cell, including:

[0013] S1.3.1: Optimize the structural stability of B-SiO2 unit cells with different Zr doping methods until the unit cell structure is stable. Use the optimized results to calculate the dissolution energy.

[0014] S1.3.2: Optimize the structural stability of B-SiO2 unit cells with different Ta doping methods until the unit cell structure is stable, and use the optimized results to calculate the dissolution energy;

[0015] S1.3.3: Analyze the effect of Ta doping on the stability of B-Si-O glass. Calculate the population and density of states of B-SiO2 unit cells and Ta substitutionally doped B-SiO2 unit cells.

[0016] S1.4 Based on the calculation results, the optimized composition of the ZrB2-SiC system antioxidant ceramics is obtained;

[0017] S2: Based on the components designed in S1, (Zr x Ta 1-x ) Preparation of B2-SiC oxidation-resistant ceramics, including:

[0018] S2.1 Mixed powder pretreatment: Weigh three ultrafine powders of ZrB2, α-SiC, and TaB2, maintaining a volume ratio of ZrB2 to SiC powder of 4:1 and a particle size ratio of ZrB2 to α-SiC powder of 3:1, add TaB2 powder, and mix the powders uniformly using an omnidirectional planetary ball mill to obtain a mixed powder, wherein the proportion of TaB2 powder in the mixed powder is 10 vol.%;

[0019] S2.2 Sintering pretreatment: Prepare the mold required for spark plasma sintering, make the indenter fit tightly with the inner wall of the mold, pour the pretreated mixed powder into the mold and spread it evenly;

[0020] S2.3 Ceramic preparation: The assembled mold was placed in a spark plasma sintering furnace for sintering. The sintering temperature was set to 1600-1900℃, the heating rate was 50-100℃ / min, the sintering pressure was 30-50MPa, and a step-by-step heating process was adopted. The first stage was to heat to 800℃ and keep warm for 5-30min, the second stage was to heat to 1400℃ and keep warm for 5-30min, and the third stage was to heat to 1600-1900℃ and keep warm for 5-30min. After the sintering was completed, the temperature in the furnace was cooled to below 40℃ and then taken out to obtain (Zr x Ta 1-x )B2-SiC oxidation-resistant ceramics.

[0021] Furthermore, in step S2.3, degassing is performed simultaneously while maintaining the temperature at 800°C and 1400°C.

[0022] Furthermore, in the mixed powder pretreatment step, the ultrafine powder is placed in a ball mill and anhydrous ethanol is added. The ball mill speed is set to 130-150 rpm, and a forward and reverse ball milling process is used to fully break up and mix the powder. After ball milling, the liquid and grinding balls are poured out, and the powder is placed in a drying box for drying. The dried agglomerated powder is then broken up to finally obtain a mixed powder.

[0023] Furthermore, the ball mill jar is a polytetrafluoroethylene jar, and anhydrous ethanol is poured into the jar and does not cover the surface of the powder.

[0024] Furthermore, the drying temperature is 70° C. and the time is 12 h.

[0025] Furthermore, the agglomerated powder was ground and crushed using an agate mortar.

[0026] Furthermore, in step S2.2, the mold is a graphite mold.

[0027] Furthermore, in step S2.2, the inner wall of the graphite mold is completely wrapped with graphite paper so that the pressing head fits tightly with the inner wall of the mold.

[0028] Furthermore, the (Zr x Ta 1-x )B2-SiC oxidation resistant ceramics, the (Zr x Ta 1-x )B2-SiC oxidation resistant ceramics are formed with (Zr x Ta 1-x )B2 solid solution, the phase composition is SiC and (Zr x Ta 1-x )B2.

[0029] Furthermore, (Zr x Ta 1-x) The relative density of B2-SiC ceramics is not less than 97%, and after oxidation at 1400℃ for 20h, the oxidation weight gain is not higher than 10mg / mm 2 , the residual strength retention rate is not less than 92%.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) By adding TaB2, an element compound with high cationic field strength (Zr x Ta 1-x )B2 solid solution, and the antioxidant composition of ZrB2-SiC was optimized. Combined with the unit cell modeling of doped Zr and Ta and the calculation of state density and population number, the composition optimization design of the ceramic system was completed, and the TaB2 addition amount for the optimal antioxidant performance was obtained. The results show that for the optimized composition (Zr x Ta 1-x )B2-SiC ceramics, which form Ta-Zr-Si-O bonds in the outermost SiO2-rich glass generated after oxidation, improving the stability and oxygen barrier capacity of the glass film.

[0032] (2) The use of high-purity boride powder avoids the introduction of oxide impurities that are inevitable in the process of synthesizing boride powder through chemical reaction using oxide powder, and improves the ceramic oxidation resistance by optimizing the ceramic phase composition and purity.

[0033] (3) The powder is pretreated using a full range of wet ball milling technology, which avoids the stratification phenomenon caused by different powder densities in the traditional planetary ball milling process, making the powder more fully dispersed and mixed more evenly, improving the uniformity of the distribution of each phase of the ceramic and reducing powder agglomeration, thereby improving the uniformity of the oxide film composition and thickness and enhancing the antioxidant performance.

[0034] (4) By optimizing the heating process of spark plasma rapid sintering technology, a step-by-step heating process was adopted, combined with the mixed sintering exhaust process and system experiments of ZrB2, SiC, and TaB2 powders with different particle sizes, heat preservation and degassing were carried out at 800℃ and 1400℃ respectively, and the heating rate in the high temperature zone was reasonably controlled to promote the full sintering of ceramic powder, increase the density of ceramics, and thus enhance the antioxidant performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the PDOS diagram before and after Ta doping.

[0036] Figure 2 Isothermal oxidation curves of ZrB2-SiC ceramics containing different amounts of TaB2 powder at 1400℃.

[0037] Figure 3The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x )XRD pattern of B2-SiC ceramics.

[0038] Figure 4 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x )SEM image of B2-SiC ceramic surface.

[0039] Figure 5 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x ) Oxidation curve of B2-SiC ceramics at 1400℃.

[0040] Figure 6 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x ) Oxidation morphology of B2-SiC ceramics after oxidation at 1400℃ for 20h.

[0041] Figure 7 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x ) Comparison of the flexural strength of B2-SiC ceramics before and after oxidation at 1400℃ for 20h.

[0042] Figure 8 This is a TEM image of the surface glass layer of the ZrB2-SiC ceramic prepared in the comparative example of the present invention after oxidation for 20 hours.

[0043] Figure 9 (Zr prepared in the embodiment of the present invention x Ta 1-x )TEM image of the surface glass layer of B2-SiC ceramic after 20h of oxidation. DETAILED DESCRIPTION

[0044] The technical solution of the present invention is further described in detail below. Obviously, the described embodiments are only for illustration and are not intended to limit this application.

[0045] The present invention discloses a method for preparing (Zr x Ta 1-x)B2-SiC oxidation-resistant ceramics. First, in order to explore the effect of the introduction of TaB2 on the structure and oxygen barrier effect of the outermost oxidized B-Si-O glass film, the solubility of Ta and Zr in B-Si-O glass and the effect of Ta doping on the stability of B-Si-O glass film were analyzed, in order to facilitate (Zr x Ta 1-x ) Optimized component design of B2-SiC oxidation-resistant ceramics, including:

[0046] (1) Unit cell modeling: β-SiO2 (high-temperature quartz) is selected as the basic calculation model. The primary cell is expanded to a 2x2x1 stacking model to form a supercell. Appropriate sites are selected to introduce B, Ta, and Zr atoms into the unit cell to form a doping structure.

[0047] (2) Parameter setting: Since the selected doping site cannot guarantee that it is the lowest energy in the system and forms a stable structure, it is necessary to optimize the structure of the unit cell system after doping to ensure that it is a stable form and provide a correct basic system for subsequent physical calculations. The structural optimization parameters in the geometric structure optimization process are: GGA, PW91 functionals, BFGS rule and ultrasoft pseudopotential, 350ev cutoff energy, in line with the convergence requirements of doping atoms and system structure, to ensure the accuracy of the calculation results; the set convergence parameter system total energy is less than 10 -6 eV / atom, the minimum atomic force is The k-point grid is smaller than 0.001eV / 1×1 supercell;

[0048] (3) Calculation of physical parameters:

[0049] Calculate the density of states and population of Si-O bonds in the unit cell to determine the structural stability. An example is shown below:

[0050] 3.1) The structural stability of B-SiO2 unit cells with different Zr doping methods was optimized, and the dissolution energy was calculated using the optimized results. The dissolution energy calculation results are as follows:

[0051]

[0052]

[0053] 3.2) The structural stability of B-SiO2 unit cells with different Ta doping methods was optimized, and the optimized results were used to calculate the dissolution energy. The dissolution energy calculation results are as follows:

[0054]

[0055]

[0056] Calculations show that the dissolution energy of Ta doped in the B-SiO2 unit cell as a substitutional doping is -1.16 eV, and the dissolution energy of Ta doped in B-SiO2 as an interstitial doping is 3.04 eV, indicating that Ta is more likely to exist in B-SiO2 glass in the form of substitutional doping, with a corresponding dissolution energy of -1.16 eV. Compared with the dissolution energy of Zr-doped B-SiO2 glass (-0.76 eV), the dissolution energy of Ta-doped B-SiO2 glass is lower, indicating that Ta has a higher solubility in the B-SiO2 structure. The dissolution of Ta ions will form a huge and complex network structure in the B-Si-O glass, thereby effectively improving the oxygen barrier effect of the glass film.

[0057] Subsequently, the effect of Ta doping on the stability of B-Si-O glass was analyzed, and the B-SiO2 unit cell and Ta-doped B-SiO2 unit cell were selected to calculate the population and state density. The calculation results are shown in Table 1. It can be seen from the results that after Ta occupies the Si atomic site in the B-SiO2 unit cell, it will affect the bond strength of the surrounding BO bonds and Si-O bonds: the population of BO bonds around the Ta-doped ions increases, the BO bond energy is enhanced, and the glass stability is improved; at the same time, although the population of adjacent Si-O bonds affected by the Ta-doped ions decreases from 0.53 to 0.50, the population of Si-O bonds within a certain range around them increases (from 0.53 to 0.56 and 0.54), indicating that the bond energy of the Si-O bond is also enhanced. Figure 1 As shown in the PDOS diagram, the 3s and 3p orbital peaks of Si atoms in the suTa-B-SiO2 structure shift to lower energy positions, making the Si-O bond structure more stable. Therefore, the above calculation results show that Ta doping will increase the bond strength of the B-O bond and the Si-O bond in the B-SiO2 unit cell, resulting in improved structural stability of the B-Si-O glass and thus better antioxidant effect.

[0058] Table 1 Calculation of population of suTa-B-SiO2 structure

[0059]

[0060]

[0061] Based on the calculation results and combined with the previous test data, the optimal composition of ZrB2-SiC system antioxidant ceramics is obtained, and the ZrB2-SiC system antioxidant ceramics are prepared based on this composition. Including:

[0062] (1) Pretreatment of mixed powders: Weigh three ultrafine powders of ZrB2, α-SiC and TaB2, and maintain a volume ratio of ZrB2 to SiC powder of 4:1. Studies have shown that the oxidation behavior of ceramics is closely related to the ceramic composition. The presence of oxide impurities will change the composition of the high oxygen barrier glass film and affect the continuity of the formed glass film to a certain extent, thereby causing a decrease in the oxidation resistance of the ceramic. The present invention directly uses boride powder as the raw material, avoiding the introduction of oxide impurities that are inevitable in the process of synthesizing boride powder by chemical reaction using oxide powder, which is beneficial to the improvement of the oxidation resistance of sintered ceramics. At the same time, studies have shown that for the ZrB2-SiC ceramic system, when the larger particle size ZrB2 raw material powder (particle size 200-500nm) is mixed and sintered with the smaller particle size SiC powder (particle size 50-150nm), the mixing effect of the coarse and fine powders is good, and it is easy to obtain ZrB2-SiC ceramics with uniform distribution of each phase and dense structure. Therefore, the particle size ratio of ZrB2 powder to α-SiC powder is selected to be 3:1. Then, TaB2 powder is added, accounting for 10 vol.% of the total powder; the powder is mixed evenly using an omnidirectional planetary ball mill. The ultrafine powder is placed in a polytetrafluoroethylene tank, and about half of the volume of the tank is poured into anhydrous ethanol (covering the surface of the powder). The ball mill speed is set to 130-150 rpm, and the forward and reverse ball milling process is used to fully break up and mix the powder evenly. After ball milling, the liquid and grinding balls are poured out, and the powder is placed in a drying oven for drying at a temperature of 70°C for 12 hours. Finally, the dried agglomerated powder is ground and broken up using an agate mortar to obtain a mixed powder.

[0063] (2) Sintering pretreatment: prepare the mold required for spark plasma sintering, make the indenter fit tightly with the inner wall of the mold, pour the mixed powder obtained after the treatment in step (1) into the mold and spread it evenly;

[0064] (3) Ceramic preparation: Place the assembled mold into a spark plasma sintering furnace for sintering.

[0065] The sintering temperature is set at 1600-1900℃, the heating rate is 50-100℃ / min, the sintering pressure is 30-50MPa, and a step-by-step heating process is adopted. The first stage is to heat to 800℃ and keep it for 5-30min, and degas at the same time. The second stage is to heat to 1400℃ and keep it for 5-30min, and degas at the same time. The third stage is to heat to 1600-1900℃ and keep it for 5-30min. After the sintering is completed, the temperature in the furnace is cooled to below 40℃ and then taken out to obtain (Zr x Ta 1-x)B2-SiC oxidation-resistant ceramics. Studies have shown that during the rapid sintering of ultrafine ceramic powders, due to the low bulk density of the powder in the graphite mold, the presence of more pores between the powders and the failure to remove gas in time, a stage of rapid vacuum increase is likely to occur during the sintering process, resulting in a low density of the final sintered ceramic material. In order to avoid this problem, a heat preservation and degassing step is designed in the sintering process described in the present invention. Experimental results show that heat preservation and degassing at 800°C and 1400°C can effectively improve the sintering density of the ZrB2-SiC ceramic system.

[0066] The present invention is further described below using specific examples.

[0067] Example 1

[0068] (1) Theoretical analysis and experimental results of Zr and Ta solid solubility ( Figure 2 ) showed that the ZrB2-SiC-10vol.%TaB2 mixed powder was prepared (Zr x Ta 1-x )B2-SiC ceramics have the best oxidation resistance, so this composition ratio is used. 29g of ZrB2 powder (particle size 300nm), 3.84g of α-SiC powder (particle size 100nm), and 9.37g of TaB2 powder (particle size 1-3μm) were weighed and wet-milled using an omnidirectional planetary ball mill. The powders were placed in a polytetrafluoroethylene jar, and approximately half the jar was filled with anhydrous ethanol (approximately 170ml) to cover the powder surface. The ball-to-material ratio was 3:1, and the ball mill speed was set to 130 rpm. The mill was rotated forward for 30 minutes, reversed for 30 minutes, and rested for 10 minutes, for a total of 300 minutes. The powder was dried in a 70°C oven for 12 hours. The dried powder was ground and broken into pieces using an agate mortar, ultimately obtaining a uniformly mixed ZrB2 / TaB2 / SiC powder.

[0069] (2) The inner wall of the graphite mold is fully wrapped with graphite paper so that the indenter fits tightly against the inner wall of the mold. 15.58 g of the ZrB2 / TaB2 / SiC mixed powder processed in step (1) is placed in the graphite mold. The upper and lower indenters are adjusted to compact the powder and complete the mold assembly.

[0070] (3) Place the assembled graphite mold into a spark plasma sintering furnace for sintering, and set the sintering pressure to 40 MPa. Use a step-by-step heating process: the heating rate from room temperature to 800°C is 100°C / min, and the temperature is kept at 800°C for 1 minute; the heating rate from 800°C to 1400°C is 100°C / min, and the temperature is kept at 1400°C for 1 minute; the heating rate from 1400°C to 1850°C is 50°C / min, and the temperature is kept at 1850°C for 5 minutes. After sintering, wait until the temperature in the furnace drops below 40°C and take it out to obtain (Zr x Ta 1-x )B2-SiC ceramics. x Ta 1-x )The relative density of B2-SiC ceramics is 97.3%.

[0071] Comparative Example 1

[0072] (1) Weigh 26.84 g of ZrB2 powder (particle size 300 nm) and 3.55 g of α-SiC powder (particle size 100 nm) respectively, and wet-mill the mixed powders using an omnidirectional planetary ball mill. Place the powders in a polytetrafluoroethylene jar, and pour about half the volume of anhydrous ethanol into the jar (covering the surface of the powder, about 170 ml). The ball-to-material ratio is 3:1. The ball mill speed is set to 130 rpm, and the mill is rotated forward for 30 minutes, reversed for 30 minutes, and rested for 10 minutes, for a total of 300 minutes. The powders are placed in a drying oven at 70°C and dried for 12 hours. The dried powders are ground and broken into pieces using an agate mortar to obtain a uniformly mixed high-purity ZrB2 / SiC powder.

[0073] (2) The inner wall of the graphite mold is fully wrapped with graphite paper so that the indenter fits tightly against the inner wall of the mold. 13.6 g of the ZrB2 / SiC mixed powder processed in step (1) is placed in the graphite mold. The upper and lower indenters compact the powder, maintaining a tight fit between the indenter and the inner wall of the mold. The mold assembly is completed.

[0074] (3) Place the assembled graphite mold in a spark plasma sintering furnace for sintering. Set the equipment sintering pressure to 40 MPa, and adopt a step-by-step heating process: the heating rate from room temperature to 800°C is 100°C / min, and the temperature is kept at 800°C for 1 minute; the heating rate from 800°C to 1400°C is 100°C / min, and the temperature is kept at 1400°C for 1 minute; the heating rate from 1400°C to 1850°C is 50°C / min, and the temperature is kept at 1850°C for 5 minutes. After sintering, wait until the temperature in the furnace drops below 40°C and take it out to obtain ZrB2-SiC ceramics. After measurement, the relative density of the prepared ZrB2-SiC ceramics is 96.5%.

[0075] Figure 2The isothermal oxidation curves of ZrB2-SiC ceramics containing different amounts of TaB2 powder at 1400℃ are shown in Figure 2. The results verify the rationality of the component structure design of the present invention. The results show that when the amount of TaB2 powder added is 10vol.%, the prepared (Zr x Ta 1-x )B2-SiC has the best antioxidant properties.

[0076] Figure 3 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x )B2-SiC ceramic XRD spectrum. Among them, the phase composition of ZrB2-SiC ceramic sample is SiC and ZrB2; in (Zr x Ta 1-x )B2-SiC ceramics XRD spectrum, it can be observed that the diffraction peaks of the ZrB2 position are shifted to the large angle direction, so it is inferred that the (Zr x Ta 1-x )B2 solid solution, the ceramic sample phase composition is SiC and (Zr x Ta 1-x )B2.

[0077] Figure 4 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x ) SEM photo of B2-SiC ceramic surface. Figure 4 (a) is the SEM photo of the ZrB2-SiC ceramic surface. Figure 4 (b) is (Zr x Ta 1-x ) SEM image of the B2-SiC surface. As can be seen from the image, the composite ceramics produced through omnidirectional wet ball milling and spark plasma sintering exhibit uniform distribution and tight bonding of all phases, with no apparent holes or cracks on the surface and high density.

[0078] Figure 5 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x )B2-SiC ceramic 1400℃ oxidation curve. As can be seen from the figure, (Zr x Ta 1-x The oxidation weight gain of )B2-SiC ceramics is significantly smaller than that of ZrB2-SiC ceramics, and the oxidation resistance is significantly improved.

[0079] Figure 6 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x ) Oxidation morphology of B2-SiC ceramics after oxidation at 1400℃ for 20h. Figure 6 (a) and Figure 6 (b) are SEM photos of the oxidation surface and cross section of ZrB2-SiC ceramics. Figure 6 (c) and (d) are (Zr x Ta 1-x )B2-SiC ceramic oxidation surface and cross-section SEM photos. As can be seen from the figure, compared with ZrB2-SiC ceramic samples, (Zr x Ta 1-x )After the B2-SiC ceramic samples were oxidized for the same time, the thickness of the outermost SiO2-rich glass layer (i.e., B-Si-O glass containing some ZrO2 / Ta2O5 precipitates) decreased slightly (from 70μm to 60μm), and the oxygen penetration depth of the ceramic decreased significantly (from 220μm to 120μm), indicating that the volatility of the glass film decreased and the oxygen barrier effect improved.

[0080] Figure 7 The ZrB2-SiC and TaB2 powders prepared in the examples and comparative examples of the present invention are added in an amount of 10 vol.% (Zr x Ta 1-x )B2-SiC ceramics flexural strength comparison before and after oxidation at 1400℃ for 20h. As shown in the figure, after oxidation at 1400℃ for 20h, the residual strength retention rate of ZrB2-SiC ceramics is 74%, while (Zr x Ta 1-x )B2-SiC ceramics have a residual strength retention rate of 92.6%. Compared with ZrB2-SiC ceramics, (Zr x Ta 1-x )The oxidation resistance of B2-SiC ceramics is significantly improved.

[0081] Figure 8 This is a TEM image of the composite glass layer on the surface of a ZrB2-SiC ceramic oxidized at 1400°C for 20 hours. The B-Si-O glass layer is composed of an amorphous glass phase and dispersed nanocrystals. Combined with HRTEM analysis, the nanocrystals are primarily ZrO2, approximately 20-30 nm in size. Zr oxide has a low solubility in B-Si-O glass, and a large amount of it precipitates on the surface of the glass layer.

[0082] Figure 9 As shown in (Zr x Ta 1-xTEM image of the composite glass layer on the surface of a B2-SiC ceramic oxidized at 1400°C for 20 hours. The B-SiO2 glass layer is composed of an amorphous glass phase and dispersed nanocrystals. A magnified TEM image reveals that a large number of dispersed nanocrystals have dissolved into the glass layer, resulting in smaller particle sizes. HRTEM analysis reveals that the nanocrystals are composed of ZrO2 and Ta2O5 phases, with sizes of approximately 2-5 nm. The introduction of Ta as a doping element increases the solubility of oxides in the B-Si-O glass and significantly reduces the size of the precipitated grains.

[0083] TEM analysis shows that the introduction of TaB2 significantly increases the solubility of oxides in the outermost B-Si-O oxide film, forming a large and complex network structure within the B-Si-O glass, thereby improving the ceramic's oxidation resistance. These characterization results are consistent with the calculated results.

[0084] The above description is merely an embodiment of the present application and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present invention description 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 hot pressing rapid sintering preparation (Zr x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, The following steps are involved: S1: Component design, including: S1.1: Unit cell modeling, using high-temperature quartz β-SiO2 as the basic calculation model, expanding the primary cell to a 2×2×1 stacking model to form a supercell, and introducing B, Ta, and Zr atoms into the unit cell to form a doping structure; S1.2: Optimize the geometric structure of the doped unit cell system, using GGA, PW91 functionals, BFGS rule and ultrasoft pseudopotential, 350eV cutoff energy, in line with the convergence requirements of doped atoms and system structure, and set the convergence parameter system total energy to be less than 10 -6 eV / atom, the minimum atomic force is The k-point grid is smaller than 0.001eV / 1×1 supercell; S1.3: Calculate the density of states and population of Si-O bonds in the unit cell, including: S1.3.1: Optimize the structural stability of B-SiO2 unit cells with different Zr doping methods and use the optimized results to calculate the dissolution energy; S1.3.2: Optimize the structural stability of B-SiO2 unit cells with different Ta doping methods and use the optimized results to calculate the dissolution energy; S1.3.3: Analyze the effect of Ta doping on the stability of B-Si-O glass. Calculate the population and density of states of B-SiO2 unit cells and Ta substitutionally doped B-SiO2 unit cells. S1.4: Based on the calculation results, obtain the optimized composition of the ZrB2-SiC system antioxidant ceramics; S2: Based on the components designed in S1, (Zr x Ta 1-x ) Preparation of B2-SiC oxidation-resistant ceramics, including: S2.1 Mixed powder pretreatment: Weigh three ultrafine powders of ZrB2, α-SiC, and TaB2, maintaining a volume ratio of ZrB2 to SiC powder of 4:1 and a particle size ratio of ZrB2 to α-SiC powder of 3:1, add TaB2 powder, and mix the powders uniformly using an omnidirectional planetary ball mill to obtain a mixed powder, wherein the proportion of TaB2 powder in the mixed powder is 10 vol.%; S2.2 Sintering pretreatment: Prepare the mold required for spark plasma sintering, so that the pressure head fits tightly with the inner wall of the mold. Pour the mixed powder obtained after pretreatment into a mold and spread it evenly; S2.3 Ceramic preparation: Place the assembled mold into a spark plasma sintering furnace for sintering. Set the sintering temperature to 1600-1900℃, the heating rate to 50-100℃ / min, the sintering pressure to 30-50MPa, and use a step-by-step heating process. The first stage is to heat up to 800℃ and keep it for 5-30min, the second stage is to heat up to 1400℃ and keep it for 5-30min, the third stage is to heat up to 1600-1900℃ and keep it for 5-30min, after sintering, wait for the temperature in the furnace to cool down to below 40℃ and take it out to obtain (Zr x Ta 1-x )B2-SiC oxidation-resistant ceramics.

2. A method of preparing (Zr by hot pressing and rapid sintering according to claim 1 x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, In step S2.3, degassing is performed simultaneously while maintaining at 800°C and 1400°C.

3. A hot pressing rapid sintering preparation according to claim 1 or 2 (Zr x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, In the mixed powder pretreatment step, the ultrafine powder is placed in a ball mill and anhydrous ethanol is added. The ball mill speed is set to 130-150 rpm, and a forward and reverse ball milling process is used to fully break up and mix the powder. After ball milling, the liquid and grinding balls are poured out, and the powder is placed in a drying oven for drying. The dried agglomerated powder is then broken up to finally obtain a mixed powder.

4. A method of preparing (Zr by hot pressing and rapid sintering according to claim 3 x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, The ball mill jar is a polytetrafluoroethylene jar, and anhydrous ethanol is poured into the jar and does not cover the surface of the powder.

5. A method of preparing (Zr by hot pressing and rapid sintering according to claim 4 x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, The drying temperature is 70℃ and the time is 12h.

6. A method of preparing (Zr by hot pressing and rapid sintering according to claim 5 x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, The agglomerated powder was ground and broken using an agate mortar.

7. A method of preparing (Zr) by hot pressing and rapid sintering according to claim 1 or 2 x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, In step S2.2, the mold is a graphite mold.

8. A method of preparing (Zr) by hot pressing and rapid sintering according to claim 1 or 2 x Ta 1-x ) B2-SiC oxidation resistant ceramic method, characterized in that, In step S2.2, the inner wall of the graphite mold is completely wrapped with graphite paper so that the pressing head fits tightly with the inner wall of the mold.

9. (Zr prepared according to any one of claims 1 to 8 x Ta 1-x ) B2-SiC oxidation-resistant ceramics, characterized in that The (Zr x Ta 1-x )B2-SiC oxidation resistant ceramics are formed with (Zr x Ta 1-x )B2 solid solution, the phase composition is SiC and (Zr x Ta 1-x )B2.

10. (Zr prepared according to any one of claims 1 to 8 x Ta 1-x ) B2-SiC oxidation-resistant ceramics, characterized in that (Zr x Ta 1-x ) The relative density of B2-SiC ceramics is not less than 97%, and after oxidation at 1400℃ for 20h, the oxidation weight gain is not higher than 10mg / mm 2 , the residual strength retention rate is not less than 92%.

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