Whisker and MAX phase toughened rare earth silicate material and preparation method thereof
阅读说明：本技术 晶须协同max相增韧的稀土硅酸盐材料及其制备方法 (Whisker and MAX phase toughened rare earth silicate material and preparation method thereof ) 是由 王天颖 张昂 郭孟秋 王长亮 高俊国 崔永静 田浩亮 于 2020-12-24 设计创作，主要内容包括：本发明涉及材料技术领域,涉及一种晶须协同MAX相增韧的稀土硅酸盐材料及其制备方法；首先以含稀土元素的水溶性盐类、正硅酸四乙酯(TEOS)为原材料采用溶胶凝胶法和烧结工艺制备出稀土硅酸盐粉体材料(RE-2Si-2O-7),然后将MAX相材料与RE-2Si-2O-7采用湿磨的方式进行共混,再将分散好的SiC晶须加入,三种材料通过充分球磨混合后,经过干燥模压预烧结、喷雾造粒、筛分和烧结形成球形环境自适应性稀土硅酸盐材料；SiC晶须和MAX相的协同增韧改性,改善稀土硅酸盐材料的环境自适应和自修复能力,全面提高其制备成涂层的综合性能；所涉及的制备技术能够制备出成分均匀分布,形貌和粒径可控的粉末材料,适合用于热喷涂和激光熔覆等工艺技术。(The invention relates to the technical field of materials, in particular to a rare earth silicate material toughened by whiskers in cooperation with MAX phase and a preparation method thereof; firstly, using water-soluble salt containing rare earth element and tetraethyl orthosilicate (TEOS) as raw materials, and adopting sol-gel method and sintering process to prepare rare earth silicate powder material (RE) 2 Si 2 O 7 ) Then the MAX phase material is mixed with RE 2 Si 2 O 7 Blending by adopting a wet grinding mode, adding the dispersed SiC whiskers, fully ball-milling and mixing the three materials, and then forming the spherical environment adaptive rare earth silicate material by drying, mould pressing, pre-sintering, spray granulation, screening and sintering; synergistic enhancement of SiC whiskers and MAX phasesToughness modification is carried out, the environment self-adaption and self-repairing capability of the rare earth silicate material is improved, and the comprehensive performance of the coating prepared from the rare earth silicate material is comprehensively improved; the related preparation technology can prepare the powder material with uniformly distributed components and controllable appearance and particle size, and is suitable for the process technologies such as thermal spraying, laser cladding and the like.)
1. A rare earth silicate material toughened by whiskers in cooperation with MAX phase is characterized in that: the rare earth silicate material comprises the following components in percentage by mass:
the mass ratio of the rare earth silicate to the MAX phase material is 8: 1-8: 2;
the mass of the SiC whisker is 0.2-2% of the sum of the mass of the rare earth silicate and the mass of the MAX phase material;
the rare earth silicate material has the component proportion of RE2Si2O7；
The MAX phase material is MAX phase material containing Si;
the rare earth silicate material is a composite powder material.
2. A method of preparing a whisker co-mingled MAX phase toughened rare earth silicate material according to claim 1, characterized in that: the method comprises the following steps:
step one, taking water-soluble salts of rare earth metal RE and tetraethoxysilane as raw materials, and preparing a rare earth silicate powder material by a sol-gel method and a calcination process;
step two, taking KH560 as a surfactant, adding a dispersion medium, and dispersing the SiC whiskers;
and step three, carrying out wet grinding and mixing, drying, mould pressing and pre-sintering, preparing slurry, spraying and granulating and calcining on the rare earth silicate, the MAX phase material and the SiC crystal whisker to obtain the composite powder.
3. The method of claim 2, wherein: in the first step, the molar ratio of the water-soluble salts of the rare earth metal RE to the tetraethyl orthosilicate element is RE: si is 1: 1-1: 1.2; the molar ratio of RE to ethanol is 1: 9-1: 11, the pH value of the solution is 2-2.5, the temperature for forming sol is 70-90 ℃, and the gel drying temperature is 60-200 ℃ for drying for 4-6 h;
in the first step, the temperature of the calcining process is 1100-1300 ℃, and the calcining time is 4-8 h.
4. The method of claim 2, wherein: and in the second step, the content of the surfactant is 0.01-0.1%.
5. The method of claim 2, wherein: in the second step, absolute ethyl alcohol is used as a dispersion medium, and the SiC crystal whiskers are dispersed by ultrasonic vibration; the ultrasonic vibration dispersion time of the SiC crystal whisker is 30-60 min, the drying temperature is 60-80 ℃, and the drying time is 0.5-1.5 h.
6. The method of claim 2, wherein: the wet milling and mixing process comprises the following steps:
ball milling in the first stage: mixing and ball-milling rare earth silicate and MAX phase material in an absolute ethyl alcohol medium, wherein the ball-to-material ratio is 2: 1-4: 1, vinyl distearamide is used as a dispersing agent, and the adding mass ratio of the dispersing agent is 0.5-1.0% of that of ethyl alcohol; the ball milling time is about 3-6h, and the rotating speed is 100 and 200 rpm/min;
ball milling in the second stage: adding the dispersed SiC crystal whiskers to continue to carry out wet grinding and mixing; the ball milling time is 1-3h, and the ball milling rotating speed is 25-60 rpm/min.
7. The method of claim 2, wherein: the mold pressing pre-sintering pressure is 20-40 MPa, the pressure maintaining time is 20-60 min, and the pre-sintering temperature of the obtained block is 600-800 ℃.
8. The method of claim 2, wherein: the slurry preparation process comprises the following steps: crushing and grinding the block subjected to die pressing and pre-sintering to form micron-level prefabricated powder, taking deionized water as a medium of slurry, taking polyvinyl alcohol as a binder and JA281 as a dispersant;
the mass ratio of the prefabricated powder to the deionized water is 1:3,
the addition amount of the polyvinyl alcohol is 3-8% of the mass of the prefabricated powder,
the addition amount of the dispersant is 1 to 1.5 percent of the mass of the prefabricated powder,
adding zirconia grinding balls according to the ball material mass ratio of 3: 1-5: 1, wherein the ball milling speed is 50-100 r/min, and discharging after ball milling for 10-30 h.
9. The method of claim 2, wherein: the technological parameters of the spray granulation are as follows:
the inlet temperature is 230-330 ℃, the outlet temperature is 125-150 ℃, the air temperature of the cavity is 140-160 ℃, and the atomization air flow is 10m3/h-14m3The rotation speed of the centrifugal atomizer is 12000r/min-15000r/min, and the slurry pumping speed is 40g/min-80 g/min.
10. The method of claim 2, wherein: the calcining process in the third step comprises the following steps:
firstly, the temperature is maintained at 400 ℃ for 2h through 200-plus-one treatment, and then the composite powder material of the MAX phase and SiC whisker synergistic modified rare earth silicate is obtained through sintering for 3-6h in a vacuum furnace at 1400 ℃ through 1200-plus-one treatment.
Technical Field
The invention belongs to the technical field of materials, and particularly relates to a rare earth silicate material toughened by whiskers in cooperation with MAX phase and a preparation method thereof.
Background
The silicon-based ceramic matrix composite is a candidate material for hot end parts of a new generation of aeroengines, has excellent comprehensive performance in a dry high-temperature environment, but is oxidized to form SiO on the surface in a high-temperature environment containing water vapor2The protective layer is eroded by water vapor to form gaseous Si (OH)4And is continuously washed away by airflow, and the surface stability and the comprehensive performance are sharply reduced. The environmental barrier coating is a protective coating for protecting the SiC ceramic matrix composite material from environmental corrosion and preventing the performance of the SiC ceramic matrix composite material from cliff type attenuation, and is a key technology for prolonging the service life of the SiC ceramic matrix composite material and ensuring the reliable application of the SiC ceramic matrix composite material on aeroengines. After more than thirty years of research, the environmental barrier coating generally goes through four stages, namely a third-stage Si/mullite/rare earth silicate developed by a first-stage mullite/YSZ system and a second-stage Si/mullite/BSAS system and a fourth-stage thermal/environmental barrier coating system.
The rare earth silicate has the advantages of high heat resistance, low thermal conductivity, small thermal expansion coefficient, good corrosion resistance, low reactivity of silicon and the like, and is the research focus of the coating material of the surface layer of the current environmental barrier coating. Research shows that the service life of the SiC composite material protected by the rare earth silicate system coating can be prolonged by more than 1 time compared with the service life of the material protected by the BSAS coating. However, rare earth silicates are typical ceramic materials, have a brittle nature, and are extremely easy to be subjected to high-temperature environmentsCracks occur due to stress generated by temperature change and mismatch of thermal expansion coefficients of the coating system, and corrosive gases such as water vapor and the like are formed to provide channels for invading the matrix. In addition, research shows that the rare earth silicate coating can be slowly decomposed in a high-temperature water vapor environment and contains SiO2The volatile overflow from the surface of the coating causes a porous layer to be formed on the surface of the coating, which also becomes a safety hazard when the coating is used as a protective coating. Therefore, in order to ensure the stability and reliability of the environmental barrier coating at high temperature, the development of a new surface material of the environmental barrier coating is urgently needed.
Disclosure of Invention
The purpose of the invention is: provides a rare earth silicate material toughened by crystal whiskers and MAX phase and a preparation method thereof, aiming at solving the problem of rare earth silicate (Yb) of the existing environmental barrier coating2Si2O7、Lu2Si2O7、Er2Si2O7、Sc2Si2O7Etc.) the surface layer is easy to crack under high temperature environment and is slowly decomposed under water vapor, etc.
In order to solve the technical problem, the technical scheme of the invention is as follows:
on the one hand, the rare earth silicate material toughened by the whiskers in cooperation with the MAX phase is provided, and comprises the following components in percentage by mass:
the mass ratio of the rare earth silicate to the MAX phase material is 8: 1-8: 2;
the rare earth silicate material has the component proportion of RE2Si2O7；
The MAX phase material refers to: si-containing MAX-phase materials, e.g. Ti3SiC2、Ti4SiC3Etc.;
the mass of the SiC whisker is 0.2-2% of the sum of the mass of the rare earth silicate and the mass of the MAX phase material;
the rare earth silicate material is a composite powder material and is used for a thermal spraying process.
In another aspect, there is provided a method of preparing a rare earth silicate material toughened with whiskers in conjunction with a MAX phase, the method comprising the steps of:
step one, taking water-soluble salts of rare earth metal RE and tetraethoxysilane as raw materials, and preparing a rare earth silicate powder material by a sol-gel method and a calcination process;
step two, taking KH560 as a surfactant, adding a dispersion medium, and dispersing the SiC whiskers;
and step three, carrying out wet grinding and mixing, drying, mould pressing and pre-sintering, preparing slurry, spraying and granulating and calcining on the rare earth silicate, the MAX phase material and the SiC crystal whisker to obtain the composite powder.
The conventional process for preparing the powder in the third step comprises the following steps: the invention increases the mixing of three materials with different rotating speeds by a wet method, can avoid the agglomeration of SiC whiskers and MAX phase materials, and simultaneously reduces the risk of SiC whisker grinding. The step of die pressing and pre-sintering can avoid component segregation caused by different densities of the materials, and ensure the uniform dispersion and distribution of the three materials when the spray granulation slurry is prepared. Meanwhile, the density and the fluidity of the powder material are improved by the calcination after granulation, which is beneficial to obtaining a more compact coating by spraying.
In the first step, the molar ratio of the water-soluble salts of the rare earth metal RE to the tetraethyl orthosilicate element is RE: si is 1: 1-1: 1.2; the molar ratio of RE to ethanol is 1: 9-1: 11, the pH value of the solution is 2-2.5, the temperature for forming sol is 70-90 ℃, and the gel drying temperature is 60-200 ℃ for drying for 4-6 h;
in the first step, the temperature of the calcining process is 1100-1300 ℃, and the calcining time is 4-8 h.
And in the second step, the content of the surfactant is 0.01-0.1%.
In the second step, absolute ethyl alcohol is used as a dispersion medium, and the SiC crystal whiskers are dispersed by ultrasonic vibration; the ultrasonic vibration dispersion time of the SiC crystal whisker is 30-60 min, the drying temperature is 60-80 ℃, and the drying time is 0.5-1.5 h.
The wet milling and mixing process comprises the following steps:
ball milling in the first stage: mixing and ball-milling rare earth silicate and MAX phase material in an absolute ethyl alcohol medium, wherein the ball-to-material ratio is 2: 1-4: 1, vinyl distearamide is used as a dispersing agent, and the adding mass ratio of the dispersing agent is 0.5-1.0% of that of ethyl alcohol; the ball milling time is about 3-6h, and the rotating speed is 100 and 200 rpm/min;
ball milling in the second stage: adding the dispersed SiC whiskers into a ball milling tank to continuously carry out wet milling and mixing; the ball milling time is 1-3h, and the ball milling rotating speed is 25-60 rpm/min.
The mold pressing pre-sintering pressure is 20-40 MPa, the pressure maintaining time is 20-60 min, and the pre-sintering temperature of the obtained block is 600-800 ℃.
The slurry preparation process comprises the following steps: crushing and grinding the block subjected to die pressing and pre-sintering to form micron-level prefabricated powder, taking deionized water as a medium of slurry, taking polyvinyl alcohol (PVA) as a binder and JA281 as a dispersant;
the mass ratio of the prefabricated powder to the deionized water is 1:3,
the addition amount of the polyvinyl alcohol is 3-8% of the mass of the prefabricated powder,
the addition amount of the dispersant is 1 to 1.5 percent of the mass of the prefabricated powder,
adding zirconia grinding balls according to the ball material mass ratio of 3: 1-5: 1, wherein the ball milling speed is 50-100 r/min, and discharging after ball milling for 10-30 h.
The technological parameters of the spray granulation are as follows:
the inlet temperature is 230-330 ℃, the outlet temperature is 125-150 ℃, the air temperature of the cavity is 140-160 ℃, and the atomization air flow is 10m3/h-14m3The rotation speed of the centrifugal atomizer is 12000r/min-15000r/min, and the slurry pumping speed is 40g/min-80 g/min.
The calcining process in the third step comprises the following steps:
firstly, the temperature is maintained at 400 ℃ for 2h through 200-plus-one treatment, and then the composite powder material of the MAX phase and SiC whisker synergistic modified rare earth silicate is obtained through sintering for 3-6h in a vacuum furnace at 1400 ℃ through 1200-plus-one treatment.
The invention has the beneficial effects that:
the method of the invention utilizes MAX phase (Ti)3SiC2、Ti4SiC3Etc.) by high temperature oxidation2And SiO2The healing factor is filled to repair microcrack, and simultaneously, Si source is provided for the rare earth silicate, so that the rare earth silicate is reduced in waterDecomposing in oxygen environment to improve its water-oxygen corrosion resistance. The synergistic toughening modification of the SiC whisker and the MAX phase improves the environment self-adaptation and self-repair capability of the rare earth silicate material and comprehensively improves the comprehensive performance of the coating prepared from the rare earth silicate material. The related preparation technology can prepare the powder material with uniformly distributed components and controllable appearance and particle size, and is suitable for the process technologies such as thermal spraying, laser cladding and the like. Has the following advantages:
1. the SiC crystal whisker and MAX phase material synergistically modify and toughen the material system of the rare earth silicate, which is designed by the invention, improves the toughness and the high-temperature water-oxygen corrosion resistance of the rare earth silicate coating material, reduces the decomposition speed of the rare earth silicate material in a high-temperature water-oxygen environment, and the coating prepared by adopting the material has the self-adaptive repair characteristic of the coating defects caused by environmental changes such as crack deflection, bridging, crack termination, crack filling repair and the like, and prolongs the service life and the reliability of the coating.
2. According to the invention, the rare earth silicate is prepared by adopting a liquid phase sol process, and the reaction can be fully carried out by controlling the molar ratio of the raw materials, so that the powder with accurate and controllable components and complete crystal grain development is obtained. Through dispersion of the SiC whiskers and mixing of three materials with different wet methods and rotating speeds, agglomeration of the SiC whiskers and the MAX phase material can be avoided, and meanwhile, the risk of grinding the SiC whiskers is reduced. The design of the mould pressing pre-sintering step can avoid the component segregation of the materials caused by different densities, ensure the uniform dispersion and distribution of the three materials when preparing the spray granulation slurry, and prepare the powder material with accurate and controllable components and uniform appearance and particle size through spray granulation and screening. Finally, the high-temperature calcination process treatment of the obtained composite powder can promote the interactive flow and material transmission of three micro powder components, enhance the strength and compactness of the composite powder, fully ensure the deposition efficiency and coating quality of the powder material, and is suitable for the process technologies such as thermal spraying, laser cladding and the like.
Drawings
In order to more clearly illustrate the technical solution of the present invention, the drawings used in the embodiment of the present invention will be briefly explained. It is obvious that the drawings described below are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be obtained from these drawings without inventive effort.
FIG. 1 is SEM image of surface of SiC whisker
FIG. 2 shows a Max phase (Ti)3SiC2) SEM image of powder surface
FIG. 3 shows SiC whisker co-calcined toughened rare earth silicate composite powder with Max phase after spray granulation
FIG. 4 is an SEM comparison of the environmental barrier coating prepared from the composite powder before and after crack self-healing at 1450 ℃.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Features of various aspects of embodiments of the invention will be described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. The following description of the embodiments is merely intended to better understand the present invention by illustrating examples thereof. The present invention is not limited to any particular arrangement or method provided below, but rather covers all product structures, any modifications, alterations, etc. of the method covered without departing from the spirit of the invention.
In the drawings and the following description, well-known structures and techniques are not shown to avoid unnecessarily obscuring the present invention.
Example one
Step oneAnd preparing the rare earth silicate powder material. In Yb (NO)3)3·H2O and tetraethyl orthosilicate as raw materials, in terms of Yb: the two raw materials were weighed out with a molar ratio of Si to 1:1.2 element and added to absolute ethanol, wherein the molar ratio of Yb to ethanol was 1: 10. Diluting HCl 1 times with deionized water, adding into the solution, adjusting pH to 2, and stirring at 70 deg.C for 8 hr to obtain transparent sol. And ageing the transparent sol to form gel, drying the gel at 60 ℃ for 2h, and drying the gel at 200 ℃ for 2 h. And then grinding the dried gel into fine powder, and roasting at 1300 ℃ for 4h to obtain the rare earth silicate material.
And step two, dispersing the SiC whiskers by using KH560 as a surfactant and absolute ethyl alcohol as a dispersion medium, wherein the content of KH560 is 0.05%, and dispersing the SiC whiskers under super-frequency vibration for 40min until the whiskers are in a non-agglomeration state. Completely volatilizing the completely dispersed SiC crystal whiskers in a high-temperature drying oven by using absolute ethyl alcohol, wherein the drying temperature is 60 ℃, and the drying time is 1 h.
And step three, mixing the powder, namely mixing the rare earth silicate, the MAX phase material and the SiC whisker. Firstly, weighing rare earth silicate and MAX phase material according to the mass ratio of 8:1, then taking absolute ethyl alcohol as a dispersion medium, taking vinyl bisstearamide as a dispersant, and adding the dispersant in an amount of 0.5% of the ethyl alcohol. Adding the two materials into a ball milling tank for fully mixing and ball milling, wherein the ball milling adopts zirconia balls, the ball-material ratio is 3:1, and the ball milling time is about 4 hours at the rotating speed of 150 rpm/min. And adding the SiC whiskers dispersed in the step two into a ball milling tank, wherein the addition amount of the whiskers is 0.5% of the mass of the rare earth silicate and MAX phase material, and continuing ball milling for 1.5h, wherein the ball milling speed is 30 rpm/min.
And step four, mould pressing and pre-sintering, drying the uniformly mixed powder obtained in the step three in a rotary evaporator, wherein the rotating speed of the rotary evaporator is 15r/min, the temperature of a water area is 80 ℃, the vacuum degree of a drying chamber is controlled to be-0.07 MPa, completely evaporating ethanol in the mixed powder, and keeping the dried mixed powder for later use. And putting the dried powder into a graphite mold, applying 25MPa pressure to the upper surface of the mold, maintaining the pressure for 30min, and presintering the block obtained by pressing at 600 ℃.
Step five, preparing a material paddle, crushing and grinding the block pre-sintered by die pressing in the step four to form micro-nano composite powder, and weighing deionized water as a medium of the material paddle according to the mass ratio of 1: 3. Weighing PVA accounting for 4% of the mass of the composite powder as a binder, taking JA281 as a dispersing agent accounting for 1.2% of the mass of the powder, adding zirconia grinding balls according to the ball-to-material mass ratio of 3:1, placing the mixture on a stirring ball mill for stirring and ball milling, wherein the ball milling speed is 60r/min, and discharging after ball milling for 12 hours.
And sixthly, spray granulation, namely selecting a centrifugal spray dryer to spray granulate the obtained slurry, wherein the spray drying conditions are that the inlet temperature of hot air is 230 ℃, the outlet temperature is 125 ℃, the air temperature of a cavity is 140 ℃, and the flow of atomized air is 10m3The rotation speed of the centrifugal atomizer is 12000r/min, and the slurry pumping speed is 50 g/min.
And seventhly, screening, namely screening the powder obtained in the sixth step by adopting a molecular vibration sieve to obtain composite powder particles with the particle size range of 30-120 mu m for later use.
And step eight, calcining the powder, sintering the powder obtained in the step seven in a vacuum sintering furnace, firstly preserving the heat at 200 ℃ for 2h, and then sintering the powder in a 1200 ℃ vacuum furnace for 5h to obtain the MAX phase and SiC whisker synergistically modified rare earth silicate composite powder material.
Example two
Step one, preparing the rare earth silicate powder material. With Er (NO)3)3·H2O and tetraethoxysilane are used as raw materials, the two raw materials are weighed according to the molar ratio of Er to Si which is 1:1, and are added into absolute ethyl alcohol, wherein the molar ratio of RE to the ethyl alcohol is 1: 10. Diluting HCl by 1 time with deionized water, adding into the solution, adjusting pH to about 2, and stirring at 80 deg.C for 8 hr to obtain transparent sol. The transparent sol is aged to form gel, and the gel is dried at 60 ℃ for 3h and then at 200 ℃ for 2 h. And grinding the dried gel into fine powder, and roasting at the high temperature of 1200 ℃ for 5h to obtain the rare earth silicate material.
And step two, dispersing the SiC crystal whiskers by using KH560 as a surfactant and absolute ethyl alcohol as a dispersion medium, wherein the content of KH560 is 0.06%, and dispersing the SiC crystal whiskers under ultrasonic vibration for 40min until the crystal whiskers are in a non-agglomeration state. Completely volatilizing the completely dispersed SiC crystal whiskers in a high-temperature drying oven by absolute ethyl alcohol, wherein the drying temperature is 80 ℃, and the drying time is 0.5 h.
And step three, mixing the powder, namely mixing the rare earth silicate, the MAX phase material and the SiC whisker. Firstly, weighing rare earth silicate and MAX phase material according to the mass ratio of 8:2, then taking absolute ethyl alcohol as a dispersion medium, taking vinyl bisstearamide as a dispersant, and adding the dispersant in an amount of 0.8% of the ethyl alcohol. And adding the two materials into a ball milling tank for fully mixing and ball milling, wherein the ball milling adopts zirconia balls, the ball-material ratio is 4:1, and the ball milling time is about 3 hours at the rotating speed of 180 rpm/min. And adding the SiC whiskers dispersed in the step two into a ball milling tank, wherein the addition amount of the whiskers is 0.3% of the mass of the rare earth silicate and MAX phase material, and continuing ball milling for 1h, wherein the ball milling speed is 35 rpm/min.
And step four, mould pressing and pre-sintering, in order to avoid the phenomenon of uneven component mixing caused by density difference in the drying process of the mixed powder, drying the uniformly mixed powder obtained in the step three in a rotary evaporator, wherein the rotating speed of the rotary evaporator is 15r/min, the temperature of a water area is 70 ℃, the vacuum degree of a drying chamber is controlled to be below-0.09 MPa, completely evaporating ethanol in the mixed powder, and keeping the dried mixed powder for later use. And putting the dried powder into a graphite mold, applying 28MPa pressure to the upper surface of the mold, maintaining the pressure for 40min, pre-sintering the block obtained by pressing at 700 ℃, removing the dispersing agent on the surface of the SiC whisker, and simultaneously preventing the component segregation of the mixed components during preparation of the slurry.
Step five, preparing a material paddle, crushing and grinding the block pre-sintered by die pressing in the step four to form micro-nano composite powder, and weighing deionized water as a medium of the material paddle according to the mass ratio of 1: 3. Weighing PVA (polyvinyl alcohol) accounting for 5% of the mass of the composite powder as a binder, taking JA281 as a dispersing agent and accounting for 1% of the mass of the powder, adding zirconia grinding balls according to the ball-to-material mass ratio of 3:1, placing the mixture on a stirring ball mill for stirring and ball milling, wherein the ball milling speed is 50r/min, and discharging the mixture after ball milling for 15 hours.
And sixthly, spray granulation, namely selecting a centrifugal spray dryer to spray granulate the obtained slurry, wherein the spray drying conditions are that the inlet temperature of hot air is 250 ℃, the outlet temperature is 135 ℃, the air temperature of a cavity is 155 ℃, and the flow of atomized air is 12m3The rotation speed of the centrifugal atomizer is 14000r/min, and the slurry pumping speed is 55 g/min.
And seventhly, screening, namely screening the powder obtained in the sixth step by adopting a molecular vibration sieve to obtain composite powder particles with the particle size range of 30-120 mu m for later use.
And step eight, calcining the powder, sintering the powder obtained in the step seven in a vacuum sintering furnace, firstly preserving the heat for 2 hours at 250 ℃, and then sintering the powder in a vacuum furnace at 1400 ℃ for 3 to obtain the MAX phase and SiC whisker synergistically modified rare earth silicate composite powder material.
EXAMPLE III
Step one, preparing the rare earth silicate powder material. With Sc (NO)3)3·H2O and tetraethoxysilane are used as raw materials, the two raw materials are weighed according to the element molar ratio of Sc to Si of 1:1.2, and the raw materials are added into absolute ethyl alcohol, wherein the molar ratio of RE to the ethyl alcohol is 1: 9. Diluting HCl 1.5 times with deionized water, adding into the solution, adjusting pH to about 2.5, and stirring at 90 deg.C for 8 hr to obtain transparent sol. And ageing the transparent sol to form gel, drying the gel at 80 ℃ for 3h, drying the gel at 180 ℃ for 6h, grinding the dried gel into fine powder, and roasting at 1150 ℃ for 8h to obtain the rare earth silicate material.
And step two, dispersing the SiC whiskers by using KH560 as a surfactant and absolute ethyl alcohol as a dispersion medium, wherein the content of KH560 is 0.08%, and dispersing the SiC whiskers under ultrasonic vibration for 35min until the whiskers are in a non-agglomeration state. Completely volatilizing the completely dispersed SiC crystal whiskers in a high-temperature drying oven by using absolute ethyl alcohol, wherein the drying temperature is 80 ℃, and the drying time is 1 h.
And step three, mixing the powder, namely mixing the rare earth silicate, the MAX phase material and the SiC whisker. Firstly, weighing rare earth silicate and MAX phase material according to the mass ratio of 8:2, then taking absolute ethyl alcohol as a dispersion medium, taking vinyl bisstearamide as a dispersant, and adding the dispersant in an amount of 1.0% of the ethyl alcohol. And adding the two materials into a ball milling tank for fully mixing and ball milling, wherein the ball milling adopts zirconia balls, the ball-material ratio is 3:1, the rotating speed is 120rpm/min, and the ball milling time is about 6 hours. And adding the SiC whiskers dispersed in the step two into a ball milling tank, wherein the addition amount of the whiskers is 1.2% of the mass of the rare earth silicate and MAX phase material, and continuing ball milling for 2.5 hours, wherein the ball milling speed is 50 rpm/min.
And step four, mould pressing and pre-sintering, in order to avoid the phenomenon of uneven component mixing caused by density difference in the drying process of the mixed powder, drying the uniformly mixed powder obtained in the step three in a rotary evaporator, wherein the rotating speed of the rotary evaporator is 30r/min, the temperature of a water area is 70 ℃, the vacuum degree of a drying chamber is controlled to be below 0.08MPa, completely evaporating ethanol in the mixed powder, and keeping the dried mixed powder for later use. And putting the dried powder into a graphite mold, applying 40MPa pressure to the upper surface of the mold, maintaining the pressure for 40min, and presintering the block obtained by pressing at 750 ℃.
Step five, preparing a material paddle, crushing and grinding the block pre-sintered by die pressing in the step four to form micro-nano composite powder, and weighing deionized water as a medium of the material paddle according to the mass ratio of 1: 3. Weighing PVA (polyvinyl alcohol) accounting for 6% of the mass of the composite powder as a binder, taking JA281 as a dispersing agent and accounting for 1.4% of the mass of the powder, adding zirconia grinding balls according to the ball-to-material mass ratio of 3:1, placing the mixture on a stirring ball mill for stirring and ball milling, wherein the ball milling speed is 80r/min, and discharging the mixture after ball milling for 20 hours.
And sixthly, spray granulation, namely selecting a centrifugal spray dryer to spray granulate the obtained slurry, wherein the spray drying conditions are that the inlet temperature of hot air is 330 ℃, the outlet temperature of hot air is 150 ℃, the air temperature of a cavity is 160 ℃, and the flow of atomized air is 14m3The rotation speed of the centrifugal atomizer is 13000r/min, and the slurry pumping speed is 70 g/min.
And seventhly, screening, namely screening the powder obtained in the sixth step by adopting a molecular vibration sieve to obtain composite powder particles with the particle size range of 30-120 mu m for later use.
And step eight, calcining the powder, namely sintering the powder obtained in the step seven in a vacuum sintering furnace, firstly preserving the heat at 400 ℃ for 2h, and then sintering the powder in a vacuum furnace at 1400 ℃ for 3h to obtain the MAX phase and SiC whisker synergistically modified rare earth silicate composite powder material.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive various equivalent modifications or substitutions within the technical scope of the present invention, and these modifications or substitutions should be covered within the scope of the present invention.
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