CN117586023A - Hot-pressing rapid sintering preparation (Zr) x Ta 1-x B 2 ) Method for preparing-SiC antioxidant ceramic - Google Patents
Hot-pressing rapid sintering preparation (Zr) x Ta 1-x B 2 ) Method for preparing-SiC antioxidant ceramic Download PDFInfo
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- 239000000919 ceramic Substances 0.000 title claims abstract description 110
- 238000005245 sintering Methods 0.000 title claims abstract description 56
- 238000002360 preparation method Methods 0.000 title claims abstract description 24
- 238000007731 hot pressing Methods 0.000 title claims abstract description 8
- 238000000034 method Methods 0.000 title claims description 41
- 239000003963 antioxidant agent Substances 0.000 title claims description 9
- 230000003078 antioxidant effect Effects 0.000 title claims description 9
- 229910010271 silicon carbide Inorganic materials 0.000 claims abstract description 110
- 239000000843 powder Substances 0.000 claims abstract description 92
- 238000007254 oxidation reaction Methods 0.000 claims abstract description 69
- 230000003647 oxidation Effects 0.000 claims abstract description 65
- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Inorganic materials [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 claims abstract description 30
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Abstract
The invention belongs to the technical field of superhigh temperature ceramic design and preparation, and particularly relates to a hot-pressing rapid sintering preparation (Zr) x Ta 1‑x )B 2 A process for preparing an oxidation-resistant SiC ceramic, which comprises modeling and geometry optimization of the unit cells, calculation of the density of states and the number of clusters of Si-O bonds in the unit cells and composition optimization, and weighing ZrB 2 alpha-SiC and TaB 2 Mixing the three superfine powders uniformly by using a planetary ball mill, and preprocessing to obtain mixed powder; sintering by spark plasma sintering, sintering by a step heating process, and preserving heat and degassing at a preset temperature to obtain (Zr) x Ta 1‑x )B 2 -SiC oxidation resistant ceramic. The invention is realized by introducing TaB 2 Formation (Zr) x Ta 1‑x )B 2 Solid solution, carrying out component optimization design on a ceramic system; and design the powder pretreatment and spark plasma sintering to realize high density, fine crystal and high purity (Zr) x Ta 1‑x B 2 ) The rapid preparation of the SiC ceramic further improves the oxidation protection capability.
Description
Technical Field
The invention belongs to the technical field of ultrahigh temperature ceramic design and preparation. More specifically, by synthesis (Zr x Ta 1-x )B 2 The ultra-high temperature ceramic boride solid solution, combined with the introduction of SiC phase, improves the oxidation resistance of the complex phase ceramic, and is realized by adopting wet ball milling and spark plasma sintering processes (Zr) x Ta 1-x )B 2 Hot pressing and rapid sintering of the SiC antioxidant ceramic.
Background
Ultra-high temperature ceramics (UHTCs) have a high melting point>3000 ℃, low density, high hardness, high specific gravity, medium thermal expansion coefficient, good oxidation resistance, mechanical property and other excellent properties, and is a high-temperature thermal protection material with great application potential in the aerospace field. Wherein in ZrB 2 After the SiC phase is introduced, zrB is formed 2 The borosilicate glass layer generated after oxidation of the SiC complex phase ceramic can effectively improve the oxidation resistance of the ceramic in a wide temperature range, and is one of the ultrahigh temperature oxidation resistant ceramic systems with the most application potential. However, zrB 2 SiC ceramics are oxidized at high temperature and in the environment of airflow scouring, and the surface of the SiC ceramics is rich in SiO 2 The glass film can accelerate volatilization, so that the oxidation resistance and mechanical property are obviously reduced. At present, researchers at home and abroad mostly adopt a method for introducing additives to regulate and control the structure and stability of the glass film to promote ZrB 2 -oxidation resistance of SiC ceramics. Studies have shown that the field strength can be increased by introducing cations (e=z/r 2 An elemental compound TaB wherein Z is a cationic valence and r is an ionic radius) 2 Promote the phase separation of the surface glass film, reduce the volatilization rate of the glass film, improve the viscosity of the glass film and further improve the oxidation resistance of the ceramic. Simultaneous ZrB 2 And TaB 2 Has a similar crystal structure, can form (Zr x Ta 1-x )B 2 Solid solution, post-oxidation Ta 5+ Can partially replace ZrO 2 Zr in (b) 4+ Reduce ZrO 2 The oxygen vacancy concentration in the oxide layer is reduced, so that the oxygen diffusion rate in the oxide layer is reduced, and the oxidation protection capability of the ceramic is improved.
However, the current preparation (Zr x Ta 1-x B 2 ) The related research of the SiC ceramic is less, and the SiC ceramic is prepared by adopting a pressureless reaction sintering method or a conventional hot press sintering method, so that the sintering time is longer. Meanwhile, in the prior art, zr is caused in the chemical reaction process x Ta 1- x B 2 The purity and relative content of the solid solution phase are difficult to control, the density of the ceramic is insufficient, and the overlength sintering time can cause coarse grains, and the mechanical property and oxidation resistance of the ceramic are reduced. Therefore, it is necessary to develop a preparation method for achieving fine-grained high purity (Zr x Ta 1-x B 2 ) -precise regulation and rapid preparation of SiC ceramic components.
Disclosure of Invention
The present invention is directed to ZrB 2 The problem of optimizing the oxidation resistance of the SiC ceramic system is solved to overcome the prior ZrB 2 The high-temperature oxidation resistance of the SiC ceramic is insufficient by introducing TaB 2 Formation (Zr) x Ta 1-x )B 2 The solid solution is modeled through unit cells, the state density and the population number are calculated, and the component optimization design of a ceramic system is completed; meanwhile, through ball milling mixing and sintering process optimization, fine-grain high-purity (Zr) is realized x Ta 1-x B 2 ) Quick preparation of SiC complex phase ceramic, density improvement and dispersion distribution and uniform mixing of each phase in the complex phase ceramic. In particular by introducing TaB 2 Formation (Zr) x Ta 1-x )B 2 Solid solution of ZrB 2 -the oxidation resistant composition of SiC is optimised; adopting superfine powder, and realizing dispersion distribution and uniform mixing of each phase in the complex phase ceramic powder by utilizing an omnibearing wet ball milling process; by adopting a discharge plasma hot-pressing rapid sintering technology and setting a proper heating mode, sintering temperature, sintering pressure and heat preservation time, the mixed powder is fully sintered, and the high-density, fine-grain and high-purity (Zr) is realized x Ta 1-x B 2 ) The rapid preparation of the SiC ceramic further improves the oxidation protection capability.
The aim of the invention is achieved by the following technical scheme:
hot-pressing rapid sintering preparation (Zr) x Ta 1-x )B 2 -a method of SiC oxidation resistant ceramic comprising the steps of:
s1: the composition design comprises:
s1.1: modeling unit cell, selecting high-temperature quartz beta-SiO 2 Expanding the primary cells to a 2x2x1 stacked model to form supercells, and introducing B, ta and Zr atoms into the unit cells to form a doped structure;
s1.2, carrying out structural optimization on the doped unit cell system, wherein the structural optimization parameters in the geometric structure optimization process are as follows:
the functional functions are GGA and PW91, BFGS rule and ultra-soft pseudo potential are selected, the 350ev cutoff energy accords with the convergence requirement of doping atoms and a system structure, and the total energy of a set convergence parameter system is less than 10 -6 eV/atom, minimum atomic force of The k-point grid is less than 0.001eV/1 x1 super cell;
s1.3: the calculation of the density of states and the population of si—o bonds in the unit cell comprises:
s1.3.1: B-SiO for different Zr doping modes 2 The structural stability of the unit cell is optimized and adjusted until the structure of the unit cell is stable, and the dissolution energy is calculated by adopting the optimized result;
s1.3.2: B-SiO for different Ta doping modes 2 The structural stability of the unit cell is optimized and adjusted until the structure of the unit cell is stable, and the dissolution energy is calculated by adopting the optimized result;
s1.3.3: analyzing the influence on the stability of the glass after the Ta is doped with the B-Si-O glass, and selecting B-SiO 2 Unit cell, ta substituted doped B-SiO 2 Calculating the population number and the density of states of the unit cells;
s1.4 obtaining ZrB according to the calculation result 2 -optimized components of an oxidation-resistant ceramic of SiC system;
s2: according to the composition designed for S1 (Zr) x Ta 1-x )B 2 -SiC oxidation resistant ceramic preparation, comprising:
s2.1, pretreatment of mixed powder: weighing ZrB 2 alpha-SiC and TaB 2 Three ultrafine powders, zrB is maintained 2 SiC powder volume ratio 4:1, zrB 2 The particle size ratio of the powder to the alpha-SiC powder is 3:1, and TaB is added 2 Powder, uniformly mixing the powder by using an omnibearing planetary ball mill to obtain mixed powder, and TaB 2 The ratio of the powder to the mixed powder is 10vol.%;
s2.2, sintering pretreatment: preparing a die required by spark plasma sintering, enabling a pressure head to be tightly matched with the inner wall of the die, pouring the mixed powder obtained after pretreatment into the die, and uniformly spreading;
s2.3, ceramic preparation: placing the assembled mold into a discharge plasma sintering furnace for sintering, setting the sintering temperature to 1600-1900 ℃, the heating rate to 50-100 ℃/min, the sintering pressure to 30-50MPa, adopting a step heating process, wherein the first stage is to heat up to 800 ℃ and then keep the temperature for 5-30min, the second stage is to heat up to 1400 ℃ and then keep the temperature for 5-30min, the third stage is to heat up to 1600-1900 ℃ and then keep the temperature for 5-30min, and taking out after the sintering is completed and the temperature in the furnace is cooled to below 40 ℃, thus obtaining (Zr) x Ta 1-x )B 2 -SiC oxidation resistant ceramic.
Further, in step S2.3, degassing is performed simultaneously while maintaining the temperature at 800℃and 1400 ℃.
Further, in the step of preprocessing the mixed powder, the superfine powder is placed in a ball milling tank, absolute ethyl alcohol is added, the rotating speed of the ball mill is set to be 130-150rmp, and the powder is fully scattered and uniformly mixed by adopting a forward and reverse ball milling process; pouring out the liquid and the grinding balls after ball milling, putting the powder into a drying box for drying, and then crushing the dried agglomerated powder to obtain mixed powder.
Furthermore, the ball milling tank is a polytetrafluoroethylene tank, and absolute ethyl alcohol is poured into the tank and does not pass through the surface of the powder.
Further, the drying temperature is 70 ℃ and the time is 12 hours.
Further, the agglomerated powder was ground with an agate mortar and crushed.
Further, in step S2.2, the mold is a graphite mold.
Further, in step S2.2, after the inner wall of the graphite mold is completely wrapped with graphite paper, the pressing head is tightly matched with the inner wall of the mold.
Further, the (Zr) prepared according to the method x Ta 1-x )B 2 -SiC oxidation resistant ceramic, said (Zr x Ta 1-x )B 2 the-SiC oxidation-resistant ceramic is formed with (Zr) x Ta 1-x )B 2 Solid solution of phase composition of SiC and (Zr x Ta 1-x )B 2 。
Further, (Zr) x Ta 1-x )B 2 The relative density of the SiC ceramic is not lower than 97%, and the oxidation weight gain is not higher than 10mg/mm after being oxidized at 1400 ℃ for 20 hours 2 The retention of residual strength is not less than 92%.
Compared with the prior art, the invention has the beneficial effects that:
(1) By adding the element compound TaB with higher cation field intensity 2 Formation (Zr) x Ta 1-x )B 2 Solid solution of ZrB 2 -SiC is subjected to antioxidant composition optimization. Combining with unit cell modeling doped with Zr and Ta, calculating state density and population number, and completing component optimization design of a ceramic system to obtain TaB with optimal oxidation resistance 2 The addition amount. The results showed that for the composition-optimized (Zr x Ta 1-x )B 2 -SiC ceramic, the outermost layer of which is SiO-rich after oxidation 2 Ta-Zr-Si-O bond is formed in the glass, and the stability and oxygen barrier capability of the glass film are improved.
(2) The adoption of the high-purity boride powder avoids the introduction of unavoidable oxide impurities in the process of synthesizing the boride powder by using the oxide powder through chemical reaction, and improves the oxidation resistance of the ceramic by optimizing the composition and purity of the ceramic phase.
(3) The powder is pretreated by using an omnibearing wet ball milling process, so that layering phenomenon caused by different powder densities in the traditional planetary ball milling process is avoided, the powder is more fully dispersed and uniformly mixed, the distribution uniformity of each phase of ceramic is improved, the aggregation of the powder is reduced, the oxide film components and thickness uniformity are improved, and the oxidation resistance is improved.
(4) The temperature rising process of the discharge plasma rapid sintering technology is optimized, a stepped temperature rising process is adopted, and ZrB with different particle sizes is combined 2 、SiC、TaB 2 And the mixed sintering exhaust process and system experiment of the powder are respectively carried out at 800 ℃ and 1400 ℃ to carry out heat preservation and degassing, and the temperature rising rate of a high-temperature area is reasonably regulated and controlled, so that the full sintering of the ceramic powder is promoted, the ceramic density is improved, and the oxidation resistance is improved.
Drawings
Fig. 1 is a PDOS diagram before and after Ta doping.
FIG. 2 is a schematic diagram of a cell containing different TaBs 2 ZrB in powder addition 2 Isothermal oxidation profile of SiC ceramic at 1400 ℃.
FIG. 3 is ZrB prepared according to the examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -SiC ceramic XRD pattern.
FIG. 4 is ZrB prepared in examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -SEM photograph of the SiC ceramic surface.
FIG. 5 is ZrB prepared according to examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -1400 ℃ oxidation profile of SiC ceramic.
FIG. 6 is ZrB prepared according to examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -oxidation morphology of SiC ceramic after 20h oxidation at 1400 ℃.
FIG. 7 shows ZrB prepared in examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 Flexural strength comparison of SiC ceramic before and after oxidation at 1400℃for 20 h.
FIG. 8 shows ZrB prepared according to the comparative example of the present invention 2 -surface glass layer TEM image after 20h oxidation of SiC ceramic.
FIG. 9 shows the results of the preparation of (Zr) x Ta 1-x )B 2 -surface glass layer TEM image after 20h oxidation of SiC ceramic.
Detailed Description
The following further details the technical solution of the present invention, and it is obvious that the described embodiments are only illustrative and not limiting of the present application.
The invention discloses a hot-pressing rapid sintering preparation (Zr) x Ta 1-x )B 2 Method for preparing-SiC antioxidant ceramic, firstly, taB is added for exploration 2 The influence of the introduction of the (B-Si-O) oxide on the structure and the oxygen barrier effect of the B-Si-O glass film on the outermost layer, and the influence of the dissolution energy of Ta and Zr in the B-Si-O glass and the Ta doping on the stability of the B-Si-O glass film are analyzed to be favorable for (Zr x Ta 1-x )B 2 -optimized component design of SiC oxidation resistant ceramic, comprising:
(1) Unit cell modeling: beta-SiO is selected for use 2 And (3) taking high-temperature quartz as a basic calculation model, expanding the primary cells to a 2x2x1 stacking model to form supercells, and selecting proper positions to introduce B, ta and Zr atoms into the unit cells to form a doping structure.
(2) Parameter setting: since the selected doping sites cannot ensure that the doping sites are the lowest energy in the system to form a stable structure, the doped unit cell system needs to be structurally optimized to ensure that the doping sites are in a stable existence form, and a correct basic system is provided for subsequent physical calculation. The structural optimization parameters in the geometric structure optimization process are as follows: the functional functions are GGA and PW91, BFGS rule and ultra-soft pseudo potential are selected, the cutoff energy is 350ev, the doping atom and architecture convergence requirements are met, and the accuracy of the calculation result is ensured; the total energy of the set convergence parameter system is less than 10 -6 eV/atom, minimum atomic force ofThe k-point grid is less than 0.001eV/1 x1 super cell;
(3) And (3) calculating physical parameters:
and calculating the state density and population number of Si-O bonds in the unit cell, and judging the structural stability of the unit cell. Examples are as follows:
3.1 B-SiO for different Zr doping modes 2 And optimizing the structural stability of the unit cell, and calculating the dissolution energy by adopting the optimized result. The results of the dissolution energy calculations are as follows:
3.2 B-SiO for different Ta doping modes 2 And optimizing the structural stability of the unit cell, and calculating the dissolution energy by adopting the optimized result. The results of the dissolution energy calculations are as follows:
as can be seen from calculation, ta is doped in B-SiO in a substitution doping manner 2 The dissolution energy in the unit cell is-1.16 ev, ta is doped in the B-SiO in a gap doping way 2 The dissolution energy in (a) was 3.04ev, indicating that Ta is more readily present in the B-SiO in a substitutional doped form 2 In glass, the corresponding dissolution energy was-1.16 ev. Doping with Zr B-SiO 2 Ta-doped B-SiO compared to the glass dissolution energy (-0.76 ev) 2 The dissolution energy of the glass is lower, indicating that Ta is in B-SiO 2 The solubility in the structure is higher. The dissolution of Ta ions can form a huge and complex network structure in the B-Si-O glass, thereby effectively improving the oxygen barrier effect of the glass film.
Subsequently, analyzing the influence on the stability of the glass after the Ta-doped B-Si-O glass, and selecting B-SiO 2 Unit cell, ta substituted doped B-SiO 2 And (5) calculating the population number and the density of states of the unit cells. As shown in Table 1, ta occupies B-SiO 2 After Si atom sites in the unit cell, the bond strengths of the surrounding B-O bonds, si-O bonds are affected: the population number of B-O bonds around Ta doped ions is increased, the B-O bond energy is enhanced, and the glass stability is improved; meanwhile, although the population of adjacent Si-O bonds affected by the Ta doping ions was reduced from 0.53 to 0.50, the population of Si-O bonds was increased within a certain range around (from 0.53 to 0.56 and 0.54), indicating that the bond energy of Si-O bonds was also enhanced. As can be seen from the PDOS diagram shown in FIG. 1, in the case of suTa-B-SiO 2 The Si atom 3s and 3p orbit peaks in the structure shift to lower energy positions, so that the Si-O bond structure is more stable. Thus, the above calculation shows that the doping of Ta promotes B-SiO 2 The bond between the B-O bond and the Si-O bond in the unit cell is strong, so that the structural stability of the B-Si-O glass is improved, and the unit cell has better antioxidation effect.
TABLE 1SuTa-B-SiO 2 Structure population count calculation
According to the calculation result and combining with the early test data, zrB is obtained 2 -optimal composition of an oxidation-resistant ceramic of SiC system and ZrB according to this composition 2 -preparing an oxidation resistant ceramic of a SiC system. Comprising the following steps:
(1) Pretreatment of mixed powder: weighing ZrB 2 alpha-SiC and TaB 2 Three ultrafine powders, zrB is maintained 2 SiC powder volume ratio 4:1, researches show that the oxidation behavior of ceramics is closely related to the ceramic components, and the existence of oxide impurities can change the components of the high oxygen barrier glass film and influence the continuity of the formed glass film to a certain extent, thereby guidingLeading to a decrease in the oxidation resistance of the ceramic. The invention directly adopts boride powder as raw material, avoids the introduction of unavoidable oxide impurities in the process of synthesizing boride powder by using oxide powder through chemical reaction, and is beneficial to the improvement of the oxidation resistance of sintered ceramics. Meanwhile, the research shows that for ZrB 2 SiC ceramic system, zrB with larger grain size 2 When the raw material powder (particle size of 200-500 nm) and the SiC powder (particle size of 50-150 nm) with smaller particle size are mixed and sintered, the mixing effect of the coarse powder and the fine powder is good, and ZrB with uniform distribution of each phase and compact structure can be easily obtained 2 -SiC ceramic. Thus, zrB is selected 2 The particle size ratio of the powder to the alpha-SiC powder was 3:1. Subsequent TaB addition 2 Powder, taB 2 The ratio of powder to total powder is 10vol.%; the powder was mixed uniformly using an omnibearing planetary ball mill. Placing superfine powder into polytetrafluoroethylene tank, pouring anhydrous ethanol (which is half of the volume of the tank and is not over the surface of the powder), setting the rotation speed of the ball mill to 130-150rmp, and fully scattering and uniformly mixing the powder by matching with a forward and reverse ball milling process. Pouring out the liquid and the grinding balls after ball milling, and putting the powder into a drying box for drying at 70 ℃ for 12 hours. And finally, grinding and crushing the dried agglomerated powder by an agate mortar to obtain mixed powder.
(2) And (3) sintering pretreatment: preparing a die required by spark plasma sintering, enabling a pressure head to be tightly matched with the inner wall of the die, pouring the mixed powder obtained after the treatment in the step (1) into the die, and uniformly tiling;
(3) Preparing ceramics: placing the assembled mould into a discharge plasma sintering furnace for sintering,
setting sintering temperature to 1600-1900 ℃, heating up to 50-100 ℃/min, sintering pressure to 30-50MPa, adopting a step heating up process, wherein the first stage is to heat up to 800 ℃ and then keep the temperature for 5-30min, simultaneously degassing, the second stage is to heat up to 1400 ℃ and then keep the temperature for 5-30min, simultaneously degassing, the third stage is to heat up to 1600-1900 ℃ and then keep the temperature for 5-30min, and taking out after sintering is completed and cooling the temperature in the furnace to below 40 ℃ to obtain (Zr) x Ta 1-x )B 2 -SiC oxidation resistant ceramic. Studies have shown that superelevationIn the rapid sintering process of fine ceramic powder, the loose density of the powder in the graphite mold is low, more pores exist among the powder and gas cannot be removed in time, so that the stage of rapid vacuum rise easily occurs in the sintering process, and the density of the finally sintered ceramic material is low. In order to avoid the problem, the sintering process of the invention is designed with a heat preservation and degassing step. Experimental results show that the ZrB can be effectively improved by carrying out heat preservation and degassing at 800 ℃ and 1400 DEG C 2 -sintered densification of SiC ceramic system.
The invention will be further illustrated by the following examples.
Example 1
(1) As shown by the theoretical analysis and experimental results (FIG. 2) of the solid solubility of Zr and Ta, zrB is adopted 2 -SiC-10vol.％TaB 2 (Zr) prepared from the mixed powder of the component proportions x Ta 1-x )B 2 The oxidation resistance of the SiC ceramic is most excellent, so that the component proportion is adopted. ZrB is respectively weighed 2 29g of powder (particle size 300 nm), 3.84g of alpha-SiC powder (particle size 100 nm) and TaB 2 9.37g of powder (particle size 1-3 μm) was subjected to wet ball milling with an omnibearing planetary ball mill. The powder was placed in a polytetrafluoroethylene can into which about half the volume of absolute ethanol (about 170ml above the powder surface) was poured, ball to ball ratio 3:1, the rotating speed of the ball mill is set to 130rmp, the ball mill rotates forward for 30min, rotates reversely for 30min and is intermittent for 10min, and the total ball milling time is 300min. And (5) placing the powder into a drying box at 70 ℃ for drying for 12 hours. Grinding the dried powder by an agate mortar and crushing the block to finally obtain ZrB which is uniformly mixed 2 /TaB 2 SiC powder.
(2) The inner wall of the graphite mold is fully wrapped by graphite paper, so that the pressure head is tightly matched with the inner wall of the mold, and the ZrB treated by the step (1) is taken out 2 /TaB 2 15.58g of SiC mixed powder is placed in a graphite mold. And (5) adjusting the positions of the upper pressure head and the lower pressure head, compacting powder and finishing die assembly.
(3) And placing the assembled graphite mold into a discharge plasma sintering furnace for sintering, wherein the sintering pressure is set to be 40MPa. The step heating process is adopted: the temperature rising rate from room temperature to 800 ℃ is 100 ℃/min,800 DEG CPreserving heat for 1min; the temperature rising rate of 800 ℃ to 1400 ℃ is 100 ℃/min, and the temperature is kept at 1400 ℃ for 1min; the temperature rising rate is 50 ℃/min at 1400-1850 ℃ and the temperature is kept for 5min at 1850 ℃. After sintering, taking out after the temperature in the furnace is reduced to below 40 ℃ to obtain (Zr) x Ta 1-x )B 2 -SiC ceramic. Measured, prepared (Zr x Ta 1-x )B 2 The relative density of the SiC ceramic is 97.3%.
Comparative example 1
(1) ZrB is respectively weighed 2 26.84g of powder (particle size 300 nm) and 3.55g of alpha-SiC powder (particle size 100 nm) were subjected to wet ball milling by using an omnibearing planetary ball mill. The powder was placed in a polytetrafluoroethylene can into which about half the volume of absolute ethanol (about 170ml above the powder surface) was poured, ball to ball ratio 3:1, the rotating speed of the ball mill is set to 130rmp, the ball mill rotates forward for 30min, rotates reversely for 30min and is intermittent for 10min, and the total ball milling time is 300min. And (5) placing the powder into a drying box at 70 ℃ for drying for 12 hours. Grinding the dried powder by an agate mortar and crushing the block to finally obtain the uniformly mixed high-purity ZrB 2 SiC powder.
(2) The inner wall of the graphite mold is fully wrapped by graphite paper, so that the pressure head is tightly matched with the inner wall of the mold, and the ZrB treated by the step (1) is taken out 2 13.6g of SiC mixed powder is placed in a graphite mold. The upper pressure head and the lower pressure head compact the powder, keep the tight fit between the pressure head and the inner wall of the die and avoid loosening, and complete the die assembly.
(3) And placing the assembled graphite mold into a discharge plasma sintering furnace for sintering. Setting the sintering pressure of the equipment to 40MPa, and adopting a step heating process: the temperature rising rate from room temperature to 800 ℃ is 100 ℃/min, and the temperature is kept at 800 ℃ for 1min; the temperature rising rate of 800 ℃ to 1400 ℃ is 100 ℃/min, and the temperature is kept at 1400 ℃ for 1min; the temperature rising rate of 1400 ℃ to 1850 ℃ is 50 ℃/min, and the temperature is kept at 1850 ℃ for 5min. After sintering is completed, taking out after the temperature in the furnace is reduced to below 40 ℃ to obtain ZrB 2 -SiC ceramic. Measured, zrB prepared 2 The relative density of the SiC ceramic is 96.5%.
FIG. 2 is a schematic diagram of a cell containing different TaBs 2 ZrB in powder addition 2 Isothermal oxidation profile of SiC ceramic at 1400 ℃. Results prove that the invention combines the structural design of the componentsAnd (5) rationality. The results showed that TaB 2 When the powder addition amount was 10 vol% x Ta 1-x )B 2 SiC has the most excellent oxidation resistance.
FIG. 3 is ZrB prepared according to the examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -SiC ceramic XRD pattern. Wherein ZrB 2 The phase composition of the SiC ceramic sample is SiC and ZrB 2 The method comprises the steps of carrying out a first treatment on the surface of the In (Zr) x Ta 1-x )B 2 ZrB can be observed in the XRD pattern of the SiC ceramic 2 Since diffraction peaks at positions are shifted in a large angle direction, it is estimated that (Zr x Ta 1-x )B 2 Solid solution, ceramic sample phase composition of SiC and (Zr x Ta 1-x )B 2 。
FIG. 4 is ZrB prepared in examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -SEM photograph of the SiC ceramic surface. Wherein (a) in FIG. 4 is ZrB 2 SEM photograph of the surface of SiC ceramic, and (b) in FIG. 4 is (Zr) x Ta 1-x )B 2 -SEM pictures of SiC surface. The figure shows that the complex phase ceramic prepared by the omnibearing wet ball milling and spark plasma sintering process has the advantages of uniform distribution and tight combination of phases, no obvious hole crack on the surface and higher compactness.
FIG. 5 is ZrB prepared according to examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -1400 ℃ oxidation profile of SiC ceramic. As can be seen from the figure, (Zr) x Ta 1-x )B 2 The oxidation weight gain of the SiC ceramic is obviously smaller than that of the ZrB2-SiC ceramic, and the oxidation resistance is obviously improved.
FIG. 6 is ZrB prepared according to examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 -oxidation morphology of SiC ceramic after 20h oxidation at 1400 ℃. Wherein (a) in FIG. 6 and (b) in FIG. 6 are ZrB, respectively 2 -SiC ceramicSEM photograph of oxidized surface and cross section, and FIGS. 6 (c) and (d) are (Zr) x Ta 1-x )B 2 -SEM pictures of the oxidized surface of SiC ceramic and cross-section. As can be seen from the figure, compared with ZrB 2 -SiC ceramic sample, (Zr) x Ta 1-x )B 2 After the same time of oxidation of the SiC ceramic sample, the outermost layer is rich in SiO 2 Glass layer (i.e. containing part of ZrO 2 /Ta 2 O 5 The thickness of the B-Si-O glass of the precipitate was slightly reduced (from 70 μm to 60 μm), and the oxygen permeation depth of the ceramic was significantly reduced (from 220 μm to 120 μm), indicating that the volatility of the glass film was reduced and the oxygen barrier effect was improved.
FIG. 7 shows ZrB prepared in examples and comparative examples of the present invention 2 -SiC、TaB 2 When the powder addition amount was 10 vol% (Zr) x Ta 1-x )B 2 Flexural strength comparison of SiC ceramic before and after oxidation at 1400℃for 20 h. As can be seen from the graph, zrB was oxidized at 1400℃for 20 hours 2 The residual strength retention of the SiC ceramic is 74% and (Zr) x Ta 1-x )B 2 The residual strength retention of the SiC ceramic was 92.6%. Compared with ZrB 2 -SiC ceramic, (Zr) x Ta 1-x )B 2 The oxidation resistance of the SiC ceramic is obviously improved.
FIG. 8 is ZrB 2 TEM image of composite glass layer on surface after 1400 ℃ oxidation of SiC ceramic for 20h, and it can be observed from the image that the B-Si-O glass layer consists of amorphous glass phase and dispersed nanocrystals, and the nanocrystals are mainly ZrO by combining with the analysis result of HRTEM 2 The phase is about 20-30nm in size. The solubility of Zr oxide in the B-Si-O glass is low, and a large amount of oxide is precipitated on the surface of the glass layer.
FIG. 9 is a diagram showing (Zr) x Ta 1-x )B 2 TEM image of surface composite glass layer after 1400 ℃ oxidation of SiC ceramic for 20h, from which B-SiO can be observed 2 The glass layer consists of amorphous glass phase and dispersed nanocrystals, and a large number of dispersed nanocrystals are dissolved into the glass layer and have smaller particle size as can be seen by combining an enlarged TEM image. In combination with the analysis result of HRTEM, the nanocrystalline is formed by ZrO 2 Phase of Ta 2 O 5 Phase composition, size about 2-5nm. Introducing Ta elementsAfter doping, the solubility of oxide in the B-Si-O glass is improved, and the size of precipitated crystal grains is obviously reduced.
TEM analysis showed the introduction of TaB 2 After that, the solubility of the oxide in the B-Si-O oxide film at the outermost layer is obviously improved, and a huge complex network structure can be formed in the B-Si-O glass, so that the oxidation resistance of the ceramic is improved. The correlation characterization result is consistent with the calculated result.
The foregoing description is only exemplary embodiments of the present application and is not intended to limit the scope of the present application, and all equivalent structures or equivalent processes using the descriptions and the drawings of the present application, or direct or indirect application in other related technical fields are included in the scope of the present application.
Claims (10)
1. Hot-pressing rapid sintering preparation (Zr) x Ta 1-x )B 2 -a method of oxidation-resistant SiC ceramic, characterized in that it comprises the steps of:
s1: the composition design comprises:
s1.1: modeling unit cell, selecting high-temperature quartz beta-SiO 2 Expanding the primary cells to a 2x2x1 stacked model to form supercells, and introducing B, ta and Zr atoms into the unit cells to form a doped structure;
s1.2, performing geometric structure optimization on the doped unit cell system, selecting functional functions of GGA and PW91, BFGS rule and ultra-soft pseudopotential, and cutting off energy of 350ev, wherein the total energy of a set convergence parameter system is less than 10 according to convergence requirements of doping atoms and a system structure -6 eV/atom, minimum atomic force ofThe k-point grid is less than 0.001eV/1 x1 super cell;
s1.3: the calculation of the density of states and the population of si—o bonds in the unit cell comprises:
s1.3.1: B-SiO for different Zr doping modes 2 The unit cell is subjected to structural stability optimization adjustment, and the dissolution energy calculation is performed by adopting the optimized result;
S1.3.2：B-SiO for different Ta doping modes 2 The unit cell is subjected to structural stability optimization adjustment, and the dissolution energy calculation is performed by adopting the optimized result;
s1.3.3: analyzing the influence on the stability of the glass after the Ta is doped with the B-Si-O glass, and selecting B-SiO 2 Unit cell, ta substituted doped B-SiO 2 Calculating the population number and the density of states of the unit cells;
s1.4 obtaining ZrB according to the calculation result 2 -optimized components of an oxidation-resistant ceramic of SiC system;
s2: according to the composition designed for S1 (Zr) x Ta 1-x )B 2 -SiC oxidation resistant ceramic preparation, comprising:
s2.1, pretreatment of mixed powder: weighing ZrB 2 alpha-SiC and TaB 2 Three ultrafine powders, zrB is maintained 2 SiC powder volume ratio 4:1, zrB 2 The particle size ratio of the powder to the alpha-SiC powder is 3:1, and TaB is added 2 Powder, uniformly mixing the powder by using an omnibearing planetary ball mill to obtain mixed powder, and TaB 2 The ratio of the powder to the mixed powder is 10vol.%;
s2.2, sintering pretreatment: preparing a die required by spark plasma sintering, enabling the pressure head to be tightly matched with the inner wall of the die,
pouring the mixed powder obtained after pretreatment into a mold and uniformly spreading;
s2.3, ceramic preparation: placing the assembled mould into a discharge plasma sintering furnace for sintering, setting the sintering temperature to 1600-1900 ℃, the heating rate to 50-100 ℃/min, the sintering pressure to 30-50MPa, adopting a step heating process,
the first stage is to heat up to 800 deg.C and keep warm for 5-30min, the second stage is to heat up to 1400 deg.C and keep warm for 5-30min, the third stage is to heat up to 1600-1900 deg.C and keep warm for 5-30min, and take out after sintering is completed and the temperature in the furnace is cooled to below 40 deg.C to obtain (Zr) x Ta 1-x )B 2 -SiC oxidation resistant ceramic.
2. A hot pressed rapid sintering preparation (Zr x Ta 1-x )B 2 Formula of-SiC antioxidant ceramicThe method is characterized in that in step S2.3, degassing is carried out simultaneously while maintaining the temperature at 800 ℃ and 1400 ℃.
3. Hot pressed rapid sintering preparation (Zr x Ta 1-x )B 2 The method for preparing the SiC antioxidant ceramic is characterized in that in the step of preprocessing mixed powder, superfine powder is placed in a ball milling tank, absolute ethyl alcohol is added, the rotating speed of a ball mill is set to be 130-150rmp, and the powder is fully scattered and uniformly mixed by adopting a forward and reverse ball milling process; pouring out the liquid and the grinding balls after ball milling, putting the powder into a drying box for drying, and then crushing the dried agglomerated powder to obtain mixed powder.
4. A hot pressed rapid sintering preparation (Zr x Ta 1-x )B 2 The method for preparing the SiC antioxidant ceramic is characterized in that the ball milling tank is a polytetrafluoroethylene tank, and absolute ethyl alcohol is poured into the tank and does not overflow the surface of the powder.
5. A hot pressed rapid sintering process (Zr) according to claim 4 x Ta 1-x )B 2 The method for preparing the SiC antioxidant ceramic is characterized in that the drying temperature is 70 ℃ and the time is 12 hours.
6. A hot pressed rapid sintering process (Zr) according to claim 5 x Ta 1-x )B 2 -a method of oxidation-resistant SiC ceramic, characterized in that the agglomerated powder is ground with an agate mortar and crushed.
7. Hot pressed rapid sintering preparation (Zr x Ta 1-x )B 2 -a method of oxidation-resistant SiC ceramic, characterized in that in step S2.2, the mould is a graphite mould.
8. Hot pressed rapid sintering preparation (Zr x Ta 1-x )B 2 The method of the SiC oxidation resistant ceramic is characterized in that in the step S2.2, after the inner wall of a graphite mold is completely wrapped by graphite paper, the pressure head is tightly matched with the inner wall of the mold.
9. (Zr) prepared by a process according to any of claims 1 to 8 x Ta 1-x )B 2 -SiC oxidation resistant ceramic, characterized in that said (Zr x Ta 1-x )B 2 the-SiC oxidation-resistant ceramic is formed with (Zr) x Ta 1-x )B 2 Solid solution of phase composition of SiC and (Zr x Ta 1-x )B 2 。
10. (Zr) prepared by a process according to any of claims 1 to 8 x Ta 1-x )B 2 An oxidation-resistant SiC ceramic, characterized in that (Zr) x Ta 1-x )B 2 The relative density of the SiC ceramic is not lower than 97%, and the oxidation weight gain is not higher than 10mg/mm after being oxidized at 1400 ℃ for 20 hours 2 The retention of residual strength is not less than 92%.
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