WO2022041415A1 - 一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法 - Google Patents

一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法 Download PDF

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WO2022041415A1
WO2022041415A1 PCT/CN2020/121774 CN2020121774W WO2022041415A1 WO 2022041415 A1 WO2022041415 A1 WO 2022041415A1 CN 2020121774 W CN2020121774 W CN 2020121774W WO 2022041415 A1 WO2022041415 A1 WO 2022041415A1
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silicon nitride
preparation
powder
spray drying
sintering aid
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French (fr)
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张晶
王文雪
刘璐
孙峰
颜家森
宋健
杨文武
杨凯宁
刘富兵
于安乐
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中材高新氮化物陶瓷有限公司
中国航发哈尔滨轴承有限公司
中国航发湖南动力机械研究所
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Publication of WO2022041415A1 publication Critical patent/WO2022041415A1/zh

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    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
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    • C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
    • C04B35/584—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on silicon nitride
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    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
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    • C04B2235/00—Aspects relating to ceramic starting mixtures or sintered ceramic products
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    • C04B2235/30—Constituents and secondary phases not being of a fibrous nature
    • C04B2235/44—Metal salt constituents or additives chosen for the nature of the anions, e.g. hydrides or acetylacetonate
    • C04B2235/449—Organic acids, e.g. EDTA, citrate, acetate, oxalate
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Definitions

  • the invention relates to the technical field of manufacture of silicon nitride ceramic balls, in particular to a preparation method of a high-reliability and long-life silicon nitride ceramic ball for aviation bearings.
  • Aviation bearings are one of the key core components of aero-engines, which need to deal with extremely harsh environments and working conditions such as high speed, high temperature, large maneuvering, large overload, and lean oil lubrication in the aviation field.
  • the performance and quality of aviation bearings directly affect the service life and reliability of aero-engines, and are also one of the main factors affecting the combat effectiveness of aircraft equipment.
  • Silicon nitride ceramics have the characteristics of light specific gravity, high rigidity, high temperature resistance, corrosion resistance, wear resistance, self-lubrication and electrical insulation, etc., and have excellent comprehensive performance.
  • the hybrid ceramic ball bearing with silicon nitride ceramic ball as the rolling element and M50 bearing steel as the ferrule has been used as the main shaft bearing of aero-engine in the United States.
  • the manufacturing technology of high-reliability and long-life silicon nitride ceramic balls for domestic aviation bearings is still a "stuck neck" technology that restricts the development of aero-engines.
  • the sintering of silicon nitride ceramic balls belongs to liquid phase sintering, and a certain amount of sintering aids needs to be added to achieve sintering densification.
  • the sintering aid powder and the silicon nitride powder are usually mixed by mechanical ball milling. Although this method is simple to operate, it is difficult to achieve uniform mixing of the silicon nitride powder and the sintering aid powder. agglomeration phenomenon.
  • the agglomerated sintering aids segregate during the sintering process, resulting in defects such as "white spots" and "snowflakes" in the prepared ceramic balls. These defects will become the source of spalling during the service of the ceramic balls. Therefore, the agglomeration and segregation of sintering aids not only reduce the strength, hardness and other mechanical properties of silicon nitride ceramic balls, but also seriously affect the reliability and fatigue life of the ceramic balls.
  • the purpose of the present invention is to provide a preparation method of high reliability and long life silicon nitride ceramic balls for aviation bearings, so as to realize uniform dispersion of sintering aids in silicon nitride, and the prepared silicon nitride ceramic balls have high reliability and fatigue life. long.
  • the invention provides a preparation method of high-reliability and long-life silicon nitride ceramic balls for aviation bearings, comprising the following steps:
  • the sintering aid-coated silicon nitride powder is ground, mixed with a binder, and subjected to second spray drying to obtain granulated powder;
  • the granulated powder is sequentially shaped, de-bonded and sintered to obtain silicon nitride ceramic balls.
  • the particle size D 50 of the silicon nitride powder is 0.5-1.5 ⁇ m, the content of ⁇ -Si 3 N 4 is more than 85%, and the content of oxygen is less than 2%.
  • the metal acetate in the metal acetate aqueous solution includes one or more of yttrium acetate, magnesium acetate, lanthanum acetate, neodymium acetate and lutetium acetate.
  • the concentration of the metal acetate aqueous solution is 100-500 g/L.
  • the amount of aluminum isopropoxide added is 2-8% of the total mass of the sintering aid-coated silicon nitride powder in terms of the amount of alumina produced; in terms of the amount of metal oxides produced, the The addition amount of the metal acetate is 2-8% of the total mass of the sintering aid-coated silicon nitride powder; the addition amount of the silicon nitride powder is the total amount of the sintering aid-coated silicon nitride powder. 85 to 95% of the mass.
  • the organic solvent is absolute ethanol and/or isopropanol.
  • the first spray drying method is nitrogen protection pressure spray drying or centrifugal spray drying.
  • the calcination temperature is 400-600° C., and the time is 1-10 h.
  • the binder includes polyvinyl butyral and/or polyacrylic acid emulsion.
  • the addition amount of the binder is 0.5-4% of the total mass of the silicon nitride powder coated by the sintering aid.
  • the solid content of the slurry used in the second spray drying is 40-50%.
  • the second spray drying method is nitrogen protection pressure spray drying or centrifugal spray drying.
  • the particle size D50 of the granulated powder is 30-150 ⁇ m.
  • the forming method includes cold isostatic pressing, and the pressure of the cold isostatic pressing is 120-300 MPa.
  • the temperature of the degumming is 400-600° C.
  • the holding time is 1-10 h.
  • the sintering method is gas pressure sintering, the sintering temperature is 1600-1900° C., the holding time is 1-6 h, and the pressure is 0.3-10 MPa.
  • the invention provides a preparation method of high reliability and long life silicon nitride ceramic balls for aviation bearings, which comprises the following steps: mixing aluminum isopropoxide, organic solvent, silicon nitride powder and metal acetate aqueous solution, and sequentially performing the following steps: hydrolysis and first spray drying to obtain a mixed powder; calcining the mixed powder to obtain a sintering aid-coated silicon nitride powder; grinding the sintering aid-coated silicon nitride powder with a binder Mixing, and performing the second spray drying to obtain granulated powder; the granulated powder is sequentially shaped, degummed and sintered to obtain silicon nitride ceramic balls.
  • metal organic salts aluminum isopropoxide and metal acetate
  • the sintering aids can be coated on the surface of silicon nitride through hydrolysis, spray drying and calcination, so as to realize sintering aids.
  • the uniform dispersion of the agent in the silicon nitride can avoid the decrease of the reliability and fatigue life of the ceramic ball due to the agglomeration and segregation of the sintering aid.
  • the results of the examples show that the density of the silicon nitride ceramic balls prepared by the method of the present invention reaches more than 99.9%, the Vickers hardness (HV10) is greater than 1500, the crushing load ratio is greater than 45%, and the Weibull modulus is greater than 15.
  • the rolling contact fatigue life (RCF) is more than 400h, which is especially suitable for the manufacture of rolling elements for aviation bearings.
  • the invention provides a preparation method of high-reliability and long-life silicon nitride ceramic balls for aviation bearings, comprising the following steps:
  • the sintering aid-coated silicon nitride powder is ground, mixed with a binder, and subjected to second spray drying to obtain granulated powder;
  • the granulated powder is sequentially shaped, de-bonded and sintered to obtain silicon nitride ceramic balls.
  • the required preparation raw materials are all commercially available products well known to those skilled in the art.
  • the purity of the aluminum isopropoxide is preferably ⁇ 99.9%.
  • the particle size D 50 of the silicon nitride powder is preferably 0.5-1.5 ⁇ m, the content of ⁇ -Si 3 N 4 is > 85%, more preferably > 90%, the content of oxygen is ⁇ 2%, more preferably ⁇ 1.5 %.
  • the metal acetate in the metal acetate aqueous solution preferably includes one or more of yttrium acetate, magnesium acetate, lanthanum acetate, neodymium acetate and lutetium acetate, more preferably yttrium acetate or magnesium acetate ;
  • the metal acetate is several of the above, the present invention has no special limitation on the proportioning of different types of metal acetate, and any proportioning can be used.
  • the purity of the metal acetate is preferably ⁇ 99.9%.
  • the concentration of the metal acetate aqueous solution is preferably 100-500 g/L, more preferably 200-300 g/L.
  • the organic solvent is preferably anhydrous ethanol and/or isopropanol; when the organic solvent is preferably anhydrous ethanol and isopropanol, the volume ratio of the present invention to anhydrous ethanol and isopropanol There is no special restriction, any ratio can be used.
  • the amount of the organic solvent is not particularly limited, as long as the raw materials can be fully dissolved.
  • the addition amount of the aluminum isopropoxide is preferably 2-8% of the total mass of the sintering aid-coated silicon nitride powder, more preferably 3-7% ;
  • the addition amount of the metal acetate is preferably 2-8% of the total mass of the sintering aid-coated silicon nitride powder, more preferably 3-7%;
  • the The amount of silicon nitride powder added is preferably 85-95% of the total mass of the silicon nitride powder coated with the sintering aid, more preferably 90%.
  • the process of mixing the aluminum isopropoxide, the organic solvent, the silicon nitride powder and the metal acetate aqueous solution is preferably to first dissolve the aluminum isopropoxide in the organic solvent, and then add silicon nitride to the obtained solution. powder, stirring for more than 3 hours, so that the silicon nitride powder is dispersed in the organic solvent, and then the metal acetate aqueous solution is added, and the mixture is stirred for more than 0.5 hours to obtain a mixed solution.
  • the aluminum isopropoxide is completely hydrolyzed to form a metal hydroxide.
  • the present invention does not have a special limitation on the stirring process and specific time, and the materials can be uniformly mixed according to a process well known in the art.
  • the mixed solution is immediately subjected to the first spray drying without any stoppage to obtain the mixed powder.
  • the method of the first spray drying is preferably nitrogen protection pressure spray drying or centrifugal spray drying; the present invention does not specifically limit the specific parameters of the first spray drying, according to the process well known in the art Just do it.
  • the mixed powder is a mixed powder of silicon nitride and a sintering aid precursor.
  • the present invention does not specifically limit the particle size of the mixed powder, and the particle size well known in the art may be sufficient.
  • the mixed powder is calcined to obtain the sintering aid-coated silicon nitride powder.
  • the temperature of the calcination is preferably 400-600° C., and the time is preferably 1-10 h.
  • the precursor of the sintering aid is thermally decomposed to obtain the metal oxide-coated silicon nitride powder, that is, the sintering aid-coated silicon nitride powder.
  • the sintering aid-coated silicon nitride powder is ground, mixed with a binder, and subjected to second spray drying to obtain granulated powder.
  • anhydrous ethanol is preferably used as a solvent
  • silicon nitride balls are used as grinding media balls, and grinding is performed until the powder particle size D 50 ⁇ 0.6 ⁇ m to obtain a grinding slurry.
  • the equipment used for the grinding is preferably a horizontal ball mill, a stirring ball mill or a sand mill.
  • the present invention has no special limitation on the specifications of the grinding media balls, and no special limitation on the specific parameters of the grinding, as long as the powder can reach the above-mentioned particle size range.
  • the present invention preferably adds a binder to the grinding slurry, stirs for more than 3 hours, and performs the second spray drying on the obtained mixture.
  • the binder preferably includes polyvinyl butyral (PVB) and/or polyacrylic acid emulsion.
  • PVB polyvinyl butyral
  • the present invention is suitable for the PVB and polyacrylic acid emulsion.
  • the dosage ratio of the acrylic emulsion is not particularly limited, and can be adjusted according to actual needs; the addition amount of the binder is preferably 0.5-4% of the total mass of the silicon nitride powder coated by the sintering aid, more preferably 1 to 3%.
  • the present invention has no special limitation on the stirring process and specific time, and the raw materials can be uniformly mixed according to the well-known process in the art.
  • the solid content of the slurry used for the second spray drying is preferably 40-50%, more preferably 45%.
  • the method of the second spray drying is preferably nitrogen protection pressure spray drying or centrifugal spray drying; the present invention does not specifically limit the specific parameters of the second spray drying, according to the process well known in the art What is necessary is just to carry out so that the granulated powder can reach the following particle size.
  • the particle size D50 of the granulated powder is preferably 30 to 150 ⁇ m, more preferably 50 to 120 ⁇ m.
  • the present invention sequentially performs molding, debinding and sintering of the granulated powder to obtain silicon nitride ceramic balls.
  • the molding method is preferably dry pressing first and then cold isostatic pressing, or only cold isostatic pressing; the present invention forms the granulated powder into ceramic balls by molding.
  • the process of the dry pressing is not specifically limited in the present invention, and can be performed according to a process well known in the art.
  • the pressure of the cold isostatic pressing is preferably 120-300 MPa, more preferably 150-250 MPa; the present invention does not have any special limitations on other parameters of the cold isostatic pressing, and the process is carried out according to well-known procedures in the art That's it.
  • the present invention preferably debonds the obtained ceramic balls, and the debonding is preferably performed in a flowing air atmosphere, or preferably in a vacuum or an inert atmosphere.
  • the flow rate of the air atmosphere is not particularly limited, and it can be carried out according to a process well known in the art.
  • the temperature of the degumming is preferably 400-600°C, more preferably 450-550°C, and the holding time is preferably 1-10h, more preferably 2-8h.
  • the organic matter (binder) in the ceramic ball is fully eliminated by debinding, thereby reducing the carbon content.
  • the present invention sinters the obtained ceramic balls.
  • the sintering method is preferably gas pressure sintering, the atmosphere in the furnace is preferably nitrogen, the sintering temperature is preferably 1600-1900°C, more preferably 1700-1800°C, and the holding time is preferably 1-6h, More preferably, it is 2 to 5 hours, and the pressure is preferably 0.3 to 10 MPa.
  • the present invention has no special limitation on the furnace used for the sintering, and a sintering furnace well known in the art can be selected.
  • the present invention realizes the densification of silicon nitride ceramic balls by sintering.
  • the obtained silicon nitride blank balls are preferably ground and polished in sequence, so that the machining accuracy of the silicon nitride blank balls can reach the silicon nitride ceramics above G5 level specified in GBT 308.2-2010. ball.
  • the present invention does not have a special limitation on the grinding and polishing processes, and the above-mentioned requirements can be achieved by performing the processes well known in the art.
  • the metal organic salt is used as the precursor of the sintering aid, and the sintering aid is coated on the surface of the silicon nitride through hydrolysis, spray drying and calcination, so as to realize the uniform dispersion of the sintering aid in the silicon nitride, thereby avoiding the The agglomeration and segregation of sintering aids lead to a decrease in the reliability and fatigue life of ceramic balls.
  • the purity of the aluminum isopropoxide used is 99.99%
  • the purity of the metal acetate used is 99.99%
  • the particle size D 50 of the silicon nitride powder used is 0.8 ⁇ m
  • the content of ⁇ -Si 3 N 4 is 93 %
  • the oxygen content is 1.2%
  • the spray drying process is nitrogen protection pressure spray drying.
  • deionized water of yttrium acetate (Y(C 2 H 3 O 2 ) 3 ⁇ 4H 2 O) (the concentration of the yttrium acetate aqueous solution is 200 g/L), stirred for 1.5 hours, and then Immediately spray-drying to obtain a mixed powder of silicon nitride and sintering aid precursor, and calcining the mixed powder at 450° C. for 3 hours to obtain alumina and yttria-coated silicon nitride powder (100 kg);
  • the alumina and yttrium oxide-coated silicon nitride powder was ground in a stirring ball mill for 6 hours, so that the particle size D50 of the powder reached 0.6 microns or less, and then 1.5 kg of binder PVB and 1 kg of polyacrylic acid emulsion were added to the slurry obtained by grinding, and stirred for 3 hours to obtain a slurry with a solid content of 45%. After the second spray drying, a granulated powder was obtained.
  • the diameter D 50 is about 100 ⁇ m;
  • the granulated powder is dry-pressed into ceramic balls with a diameter of 9.525 mm, and then subjected to cold isostatic pressing at a pressure of 250 MPa; the shaped ceramic balls are degummed in a flowing air atmosphere, and the degumming temperature is 450°C, the holding time is 5h;
  • the debinding ceramic balls are sintered by air pressure sintering, the sintering temperature is 1800°C, the holding time is 2h, the atmosphere in the furnace is nitrogen, and the nitrogen pressure is 3MPa, to obtain a silicon nitride rough ball with a diameter of 9.525mm;
  • the silicon nitride rough balls are ground and polished in turn to obtain silicon nitride ceramic fine balls with a machining accuracy of G5 level specified in GBT 308.2-2010.
  • yttrium acetate (Y(C 2 H 3 O 2 ) 3 ⁇ 4H 2 O) in deionized water (the concentration of the yttrium acetate aqueous solution is 200 g/L), stirred for 2 hours, and then immediately spray-drying to obtain a mixed powder of silicon nitride and sintering aid precursor, and calcining the mixed powder at 500° C. for 2 h to obtain alumina and yttria-coated silicon nitride powder (100 kg);
  • the alumina and yttrium oxide-coated silicon nitride powder was ground in a stirring ball mill for 6 hours, so that the particle size D50 of the powder reached 0.6 microns or less, and then 1.5 kg of binder PVB and 1 kg of polyacrylic acid emulsion were added to the slurry obtained by grinding, and stirred for 3 hours to obtain a slurry with a solid content of 45%. After the second spray drying, a granulated powder was obtained.
  • the diameter D 50 is about 100 ⁇ m;
  • the granulated powder is dry-pressed into ceramic balls with a diameter of 9.525 mm, and then subjected to cold isostatic pressing at a pressure of 200 MPa; the shaped ceramic balls are degummed in a flowing air atmosphere, and the degumming temperature is 500°C, the holding time is 3h;
  • the debinding ceramic balls are sintered by air pressure sintering, the sintering temperature is 1750°C, the holding time is 4h, the atmosphere in the furnace is nitrogen, and the nitrogen pressure is 5MPa, to obtain a silicon nitride blank ball with a diameter of 9.525mm;
  • the silicon nitride rough balls are ground and polished in turn to obtain silicon nitride ceramic fine balls with a machining accuracy of G5 level specified in GBT 308.2-2010.
  • the alumina and magnesium oxide-coated silicon nitride powders were ground in a stirring ball mill for 6 hours, so that the particle size D50 of the powder reached below 0.6 microns, and then 1.5 kg of binder PVB and 1 kg of polyacrylic acid emulsion were added to the slurry obtained by grinding, and stirred for 3 hours to obtain a slurry with a solid content of 45%. After the second spray drying, a granulated powder was obtained.
  • the diameter D 50 is about 100 ⁇ m;
  • the granulated powder is dry-pressed into ceramic balls with a diameter of 9.525 mm, and then subjected to cold isostatic pressing at a pressure of 150 MPa; the shaped ceramic balls are degummed in a flowing air atmosphere, and the degumming temperature is 550°C, the holding time is 2h;
  • the debonded ceramic balls are sintered by air pressure sintering, the sintering temperature is 1700°C, the holding time is 6h, the atmosphere in the furnace is nitrogen, and the nitrogen pressure is 8MPa, to obtain a silicon nitride rough ball with a diameter of 9.525mm;
  • the silicon nitride rough balls are ground and polished in turn to obtain silicon nitride ceramic fine balls with a machining accuracy of G5 grade specified in GBT 308.2-2010.
  • alumina powder and yttrium oxide powder are directly used as sintering aids.
  • the purity of the yttrium powder is 99.99%, and the particle size D 50 is 0.8 ⁇ m; the sintering aid powder and the silicon nitride powder are mixed and ground by mechanical ball milling, and the mixing and grinding time is 6 hours.
  • a binder (same as Example 1) was added to the slurry obtained by grinding, stirred for 3h, and spray-dried to obtain granulated powder.
  • Other process conditions were the same as those in Example 1.
  • alumina powder and yttrium oxide powder are directly used as sintering aids, and the amount of sintering aids added is the same as that in Example 2.
  • the purity of the alumina powder is 99.99%, and the particle size D50 is 0.5 microns, the purity of the yttrium oxide powder is 99.99%, and the particle size D 50 is 0.8 microns.
  • the sintering aid powder and the silicon nitride powder were mixed and ground by mechanical ball milling. The mixing and grinding time was 6 hours. After the particle size D 50 of the test powder reached the same level as in Example 2 (below 0.6 microns), the powder was ground.
  • the obtained slurry was added with a binder (same as in Example 2), stirred for more than 3 hours, and spray-dried to obtain granulated powder.
  • Other process conditions were the same as those in Example 2.
  • alumina powder and magnesia powder are used as sintering aids, and the amount of sintering aids added is the same as that in Example 3; the purity of the alumina powder is 99.99%, and the particle size D50 is 0.5 The purity of the magnesium oxide powder is 99.9%, and the particle size D 50 is 0.5 microns; the sintering aid powder and the silicon nitride powder are mixed and ground by mechanical ball milling, and the mixing and grinding time is 6h.
  • Example 3 After the diameter D 50 reaches the same level (below 0.6 microns) in Example 3, add a binder (same as Example 3) to the slurry obtained by grinding, stir for more than 3h, obtain granulated powder by spray drying, and other process conditions The process conditions were the same as in Example 3.
  • the densities of the silicon nitride ceramic balls in Examples 1-3 and Comparative Examples 1-3 were measured by the Archimedes drainage method, and their relative densities were calculated.
  • the Vickers hardness (HV10) of the ceramic balls was measured by the method specified in GBT 16534-2009, and the fracture toughness was measured according to the indentation method proposed by Niihara.

Abstract

航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法，属于氮化硅陶瓷球制造技术领域，以金属有机盐(异丙醇铝和金属醋酸盐)作为烧结助剂的前驱体，通过水解、喷雾干燥和煅烧工艺，能够使烧结助剂包覆在氮化硅表面，实现烧结助剂在氮化硅中的均匀分散，从而避免因烧结助剂的团聚和偏析而导致陶瓷球可靠性及疲劳寿命的下降，所制备的氮化硅陶瓷球致密度达到了99.9％以上，维氏硬度(HV10)大于1500，压碎载荷比大于45％，韦布尔模数大于15，滚动接触疲劳寿命(RCF)在400h以上，特别适合用来制造航空轴承用滚动元件。

Description

一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法
本申请要求于2020年8月24日提交中国专利局、申请号为CN202010855055.6、发明名称为“一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本发明涉及氮化硅陶瓷球制造技术领域，尤其涉及一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法。
背景技术
航空轴承是航空发动机的关键核心部件之一，需要应对航空领域高速、高温、大机动、大过载、贫油润滑等极端苛刻的环境和工况条件。航空轴承的性能和质量直接影响航空发动机的使用寿命和可靠性，也是影响飞机装备战斗力的主要因素之一。
氮化硅陶瓷具有比重轻、刚度大、耐高温、耐腐蚀、耐磨损、自润滑和电绝缘等特点，综合性能优异，是用来制造航空轴承用滚动体的首选材料。目前以氮化硅陶瓷球为滚动体，M50轴承钢为套圈的混合陶瓷球轴承在美国已经作为航空发动机的主轴轴承被使用。然而，在国内航空轴承用高可靠性长寿命氮化硅陶瓷球的制造技术仍是一项制约航空发动机发展的“卡脖子”技术。
氮化硅陶瓷球的烧结属于液相烧结，需要加入一定量的烧结助剂来实现烧结致密化。烧结助剂粉末和氮化硅粉末通常采用机械球磨的方式混合，这种方式虽然操作简单但很难实现氮化硅粉末和烧结助剂粉末的均匀混合，使得混合粉体中存在烧结助剂的团聚现象。团聚的烧结助剂在烧结过程中产生偏析，导致制备的陶瓷球出现“白点”、“雪花”等缺陷，这些缺陷会成为陶瓷球服役过程中剥落产生的源头。因此，烧结助剂的团聚和偏析不仅降低了氮化硅陶瓷球的强度、硬度等力学性能，还严重影响了陶瓷球的可靠性和疲劳寿命。
发明内容
本发明的目的在于提供一种航空轴承用高可靠性长寿命氮化硅陶瓷 球的制备方法，实现烧结助剂在氮化硅中均匀分散，制备的氮化硅陶瓷球可靠性高、疲劳寿命长。
为了实现上述发明目的，本发明提供以下技术方案：
本发明提供了一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法，包括以下步骤：
将异丙醇铝、有机溶剂、氮化硅粉和金属醋酸盐水溶液混合，依次进行水解和第一喷雾干燥，得到混合粉体；
将所述混合粉体进行煅烧，得到烧结助剂包覆氮化硅粉；
将所述烧结助剂包覆氮化硅粉研磨后与粘结剂混合，进行第二喷雾干燥，得到造粒粉；
将所述造粒粉依次进行成型、排胶和烧结，得到氮化硅陶瓷球。
优选的，所述氮化硅粉的粒径D 50为0.5～1.5μm，α-Si 3N 4含量＞85％，氧含量＜2％。
优选的，所述金属醋酸盐水溶液中的金属醋酸盐包括醋酸钇、醋酸镁、醋酸镧、醋酸钕和醋酸镥中的一种或几种。
优选的，所述金属醋酸盐水溶液的浓度为100～500g/L。
优选的，以产生氧化铝的量计，所述异丙醇铝的加入量为所述烧结助剂包覆氮化硅粉总质量的2～8％；以产生金属氧化物的量计，所述金属醋酸盐的加入量为所述烧结助剂包覆氮化硅粉总质量的2～8％；所述氮化硅粉的加入量为所述烧结助剂包覆氮化硅粉总质量的85～95％。
优选的，所述有机溶剂为无水乙醇和/或异丙醇。
优选的，所述第一喷雾干燥的方式为氮气保护压力式喷雾干燥或离心式喷雾干燥。
优选的，所述煅烧的温度为400～600℃，时间为1～10h。
优选的，所述粘结剂包括聚乙烯醇缩丁醛和/或聚丙烯酸乳液。
优选的，所述粘结剂的添加量为所述烧结助剂包覆氮化硅粉总质量的0.5～4％。
优选的，所述第二喷雾干燥所用料浆的固含量为40～50％。
优选的，所述第二喷雾干燥的方式为氮气保护压力式喷雾干燥或离心式喷雾干燥。
优选的，所述造粒粉的粒径D 50为30～150μm。
优选的，所述成型的方式包括冷等静压，所述冷等静压的压力为120～300MPa。
优选的，所述排胶的温度为400～600℃，保温时间为1～10h。
优选的，所述烧结的方式为气压烧结，所述烧结的温度为1600～1900℃，保温时间为1～6h，压力为0.3～10MPa。
本发明提供了一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法，包括以下步骤：将异丙醇铝、有机溶剂、氮化硅粉和金属醋酸盐水溶液混合，依次进行水解和第一喷雾干燥，得到混合粉体；将所述混合粉体进行煅烧，得到烧结助剂包覆氮化硅粉；将所述烧结助剂包覆氮化硅粉研磨后与粘结剂混合，进行第二喷雾干燥，得到造粒粉；将所述造粒粉依次进行成型、排胶和烧结，得到氮化硅陶瓷球。本发明以金属有机盐(异丙醇铝和金属醋酸盐)作为烧结助剂的前驱体，通过水解、喷雾干燥和煅烧工艺，能够使烧结助剂包覆在氮化硅表面，实现烧结助剂在氮化硅中的均匀分散，从而避免因烧结助剂的团聚和偏析导致陶瓷球可靠性及疲劳寿命的下降。实施例的结果表明，本发明所述方法制备的氮化硅陶瓷球致密度达到了99.9％以上，维氏硬度(HV10)大于1500，压碎载荷比大于45％，韦布尔模数大于15，滚动接触疲劳寿命(RCF)在400h以上，特别适合用来制造航空轴承用滚动元件。
具体实施方式
本发明提供了一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法，包括以下步骤：
将异丙醇铝、有机溶剂、氮化硅粉和金属醋酸盐水溶液混合，依次进行水解和第一喷雾干燥，得到混合粉体；
将所述混合粉体进行煅烧，得到烧结助剂包覆氮化硅粉；
将所述烧结助剂包覆氮化硅粉研磨后与粘结剂混合，进行第二喷雾干燥，得到造粒粉；
将所述造粒粉依次进行成型、排胶和烧结，得到氮化硅陶瓷球。
在本发明中，若无特殊说明，所需制备原料均为本领域技术人员熟知的市售商品。
本发明将异丙醇铝、有机溶剂、氮化硅粉和金属醋酸盐水溶液混合，依次进行水解和第一喷雾干燥，得到混合粉体。在本发明中，所述异丙醇铝的纯度优选≥99.9％。在本发明中，所述氮化硅粉的粒径D 50优选为0.5～1.5μm，α-Si 3N 4含量＞85％，更优选＞90％，氧含量＜2％，更优选＜1.5％。
在本发明中，所述金属醋酸盐水溶液中的金属醋酸盐优选包括醋酸钇、醋酸镁、醋酸镧、醋酸钕和醋酸镥中的一种或几种，更优选为醋酸钇或醋酸镁；当所述金属醋酸盐为上述中的几种时，本发明对不同种类金属醋酸盐的配比没有特殊的限定，任意配比均可。在本发明中，所述金属醋酸盐的纯度优选≥99.9％。本发明中，所述金属醋酸盐水溶液的浓度优选为100～500g/L，更优选为200～300g/L。
在本发明中，所述有机溶剂优选为无水乙醇和/或异丙醇；当所述有机溶剂优选为无水乙醇和异丙醇时，本发明对无水乙醇和异丙醇的体积比没有特殊的限定，任意配比均可。本发明对所述有机溶剂的用量没有特殊的限定，能够将原料充分溶解即可。
在本发明中，以产生氧化铝的量计，所述异丙醇铝的加入量优选为所述烧结助剂包覆氮化硅粉总质量的2～8％，更优选为3～7％；以产生金属氧化物的量计，所述金属醋酸盐的加入量优选为所述烧结助剂包覆氮化硅粉总质量的2～8％，更优选为3～7％；所述氮化硅粉的加入量优选为所述烧结助剂包覆氮化硅粉总质量的85～95％，更优选为90％。
在本发明中，所述异丙醇铝、有机溶剂、氮化硅粉和金属醋酸盐水溶液混合的过程优选为先将异丙醇铝溶解于有机溶剂中，向所得溶液中加入氮化硅粉，搅拌3h以上，使氮化硅粉分散在有机溶剂中，然后加入金属醋酸盐水溶液，搅拌0.5h以上，得到混合液。在所述加入金属醋酸盐水溶液后搅拌过程中，异丙醇铝完全水解，形成金属氢氧化物。本发明对所述搅拌的过程和具体时间没有特殊的限定，按照本领域熟知的过程能够将物料混合均匀即可。
得到混合液后，本发明优选不作任何停留，立即将所述混合液进行第一喷雾干燥，得到混合粉体。在本发明中，所述第一喷雾干燥的方式优选为氮气保护压力式喷雾干燥或离心式喷雾干燥；本发明对所述第一喷雾干 燥的具体参数没有特殊的限定，按照本领域熟知的过程进行即可。
在本发明中，所述混合粉体为氮化硅和烧结助剂前驱体的混合粉体。本发明对所述混合粉体的粒径没有特殊的限定，本领域熟知的粒径即可。
得到混合粉体后，本发明将所述混合粉体进行煅烧，得到烧结助剂包覆氮化硅粉。在本发明中，所述煅烧的温度优选为400～600℃，时间优选为1～10h。在所述煅烧过程中，烧结助剂前驱体发生热分解，得到金属氧化物包覆氮化硅粉，即烧结助剂包覆氮化硅粉。
得到烧结助剂包覆氮化硅粉后，本发明将所述烧结助剂包覆氮化硅粉研磨后与粘结剂混合，进行第二喷雾干燥，得到造粒粉。本发明优选以无水乙醇为溶剂，以氮化硅球为磨介球，进行研磨，直至粉体粒径D 50≤0.6μm，得到研磨料浆。在本发明中，所述研磨所用设备优选为卧式球磨机、搅拌式球磨机或砂磨机。本发明对所述磨介球的规格没有特殊的限定，对所述研磨的具体参数没有特殊的限定，能够使得粉体达到上述粒径范围即可。
得到研磨料浆后，本发明优选向所述研磨料浆中加入粘结剂，搅拌3h以上，将所得混合物料进行第二喷雾干燥。在本发明中，所述粘结剂优选包括聚乙烯醇缩丁醛(PVB)和/或聚丙烯酸乳液，当所述粘结剂为PVB和聚丙烯酸乳液时，本发明对所述PVB和聚丙烯酸乳液的用量比没有特殊的限定，根据实际需求进行调整即可；所述粘结剂的添加量优选为所述烧结助剂包覆氮化硅粉总质量的0.5～4％，更优选为1～3％。本发明对所述搅拌的过程和具体时间没有特殊的限定，按照本领域熟知的过程能够将原料混合均匀即可。
在本发明中，所述第二喷雾干燥所用料浆(即上述混合物料)的固含量优选为40～50％，更优选为45％。在本发明中，所述第二喷雾干燥的方式优选为氮气保护压力式喷雾干燥或离心式喷雾干燥；本发明对所述第二喷雾干燥的具体参数没有特殊的限定，按照本领域熟知的过程进行能够使得造粒粉达到下述粒径即可。
在本发明中，所述造粒粉的粒径D 50优选为30～150μm，更优选为50～120μm。
得到造粒粉后，本发明将所述造粒粉依次进行成型、排胶和烧结，得 到氮化硅陶瓷球。在本发明中，所述成型的方式优选为先干压再冷等静压，或者仅采用冷等静压；本发明通过成型将造粒粉成型为陶瓷球。
本发明对所述干压的过程没有具体的限定，按照本领域熟知的过程进行即可。在本发明中，所述冷等静压的压力优选为120～300MPa，更优选为150～250MPa；本发明对所述冷等静压的其他参数没有特殊的限定，按照本领域熟知的过程进行即可。
完成所述成型后，本发明优选将所得陶瓷球进行排胶，所述排胶优选在流动的空气气氛中排胶，或者优选在真空或惰性气氛中进行排胶。本发明对所述空气气氛的流量没有特殊的限定，按照本领域熟知的过程进行即可。在本发明中，所述排胶的温度优选为400～600℃，更优选为450～550℃，保温时间优选为1～10h，更优选为2～8h。本发明通过排胶使得陶瓷球中的有机物(粘结剂)充分排除，从而降低碳含量。
完成所述排胶后，本发明将所得陶瓷球进行烧结。在本发明中，所述烧结的方式优选为气压烧结，炉内气氛优选为氮气，所述烧结的温度优选为1600～1900℃，更优选为1700～1800℃，保温时间优选为1～6h，更优选为2～5h，压力优选为0.3～10MPa。本发明对所述烧结所用炉没有特殊的限定，选用本领域熟知的烧结炉即可。本发明通过烧结来实现氮化硅陶瓷球的致密化。
完成所述烧结后，本发明优选将所得氮化硅毛坯球依次进行研磨和抛光加工，使所述氮化硅毛坯球的加工精度达到GBT 308.2-2010中规定的G5级以上的氮化硅陶瓷球。本发明对所述研磨和抛光加工的过程没有特殊的限定，按照本领域熟知的过程进行能够达到上述要求即可。
本发明以金属有机盐作为烧结助剂的前驱体，通过水解、喷雾干燥和煅烧，使烧结助剂包覆在氮化硅表面，实现烧结助剂在氮化硅中的均匀分散，从而避免因烧结助剂的团聚和偏析而导致陶瓷球可靠性及疲劳寿命的下降。
下面将结合本发明中的实施例，对本发明中的技术方案进行清楚、完整地描述。显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
以下实施例中，所用异丙醇铝的纯度为99.99％，所用金属醋酸盐的纯度为99.99％，所用氮化硅粉的粒径D 50为0.8μm，α-Si 3N 4含量为93％，氧含量为1.2％；所述喷雾干燥工艺的方式为氮气保护压力式喷雾干燥。
实施例1
将12kg(换算为氧化铝的量为3kg)的异丙醇铝(C 9H 21AlO 3)溶解于无水乙醇(100kg)中，加入92kg氮化硅粉，搅拌3h，然后加入溶解有15kg(换算为氧化钇的量为5kg)的醋酸钇(Y(C 2H 3O 2) 3·4H 2O)的去离子水(醋酸钇水溶液的浓度为200g/L)，搅拌1.5h，随后立即进行喷雾干燥，得到氮化硅和烧结助剂前驱体的混合粉体，将所述混合粉体在450℃下煅烧3h，得到氧化铝和氧化钇包覆氮化硅粉(100kg)；
以无水乙醇为溶剂，氮化硅为磨介球，将所述氧化铝和氧化钇包覆氮化硅粉在搅拌式球磨机中研磨6h，使粉体的粒度D 50达到0.6微米以下，之后向研磨所得料浆中加入1.5kg粘结剂PVB和1kg聚丙烯酸乳液，搅拌3h，得到料浆的固含量为45％，进行第二喷雾干燥后，得到造粒粉，所述造粒粉粒径D 50约为100μm；
将所述造粒粉进行干压成型为直径9.525mm的陶瓷球，再进行冷等静压处理，压力为250MPa；将成型后的陶瓷球在流动的空气气氛中进行排胶，排胶温度为450℃，保温时间为5h；
将排胶后的陶瓷球采用气压烧结的方式进行烧结，烧结温度为1800℃，保温时间为2h，炉内气氛为氮气，氮气压力为3MPa，得到直径为9.525mm的氮化硅毛坯球；
将所述氮化硅毛坯球依次进行研磨和抛光加工，得到加工精度为GBT 308.2-2010中规定的G5级的氮化硅陶瓷精球。
实施例2
将20kg(换算为氧化铝的量为5kg)的异丙醇铝(C 9H 21AlO 3)溶解于无水乙醇(120kg)中，加入92kg氮化硅粉，搅拌3h，然后加入溶解有9kg(换算为氧化钇的量为3kg)的醋酸钇(Y(C 2H 3O 2) 3·4H 2O)的去离子水(醋酸钇水溶液的浓度为200g/L)，搅拌2h，随后立即进行喷雾干燥，得到氮化硅和烧结助剂前驱体的混合粉体，将所述混合粉体在500℃下煅烧2h，得到氧化铝和氧化钇包覆氮化硅粉(100kg)；
以无水乙醇为溶剂，氮化硅为磨介球，将所述氧化铝和氧化钇包覆氮 化硅粉在搅拌式球磨机中研磨6h，使粉体的粒度D 50达到0.6微米以下，之后向研磨所得料浆中加入1.5kg粘结剂PVB和1kg聚丙烯酸乳液，搅拌3h，得到料浆的固含量为45％，进行第二喷雾干燥后，得到造粒粉，所述造粒粉粒径D 50约为100μm；
将所述造粒粉进行干压成型为直径9.525mm的陶瓷球，再进行冷等静压处理，压力为200MPa；将成型后的陶瓷球在流动的空气气氛中进行排胶，排胶温度为500℃，保温时间为3h；
将排胶后的陶瓷球采用气压烧结的方式进行烧结，烧结温度为1750℃，保温时间为4h，炉内气氛为氮气，氮气压力为5MPa，得到直径为9.525mm的氮化硅毛坯球；
将所述氮化硅毛坯球依次进行研磨和抛光加工，得到加工精度为GBT 308.2-2010中规定的G5级的氮化硅陶瓷精球。
实施例3
将20kg(换算为氧化铝的量为5kg)的异丙醇铝(C 9H 21AlO 3)溶解于无水乙醇(120L)中，加入92kg氮化硅粉，搅拌3h，然后加入溶解有16.8kg(换算为氧化镁的量为3kg)的醋酸镁(Mg(C 2H 3O 2) 2·4H 2O)的去离子水(醋酸镁水溶液的浓度为300g/L)，搅拌2.5h，随后立即进行喷雾干燥，得到氮化硅和烧结助剂前驱体的混合粉体，将所述混合粉体在550℃下煅烧1h，得到氧化铝和氧化镁包覆氮化硅粉(100kg)；
以无水乙醇为溶剂，氮化硅为磨介球，将所述氧化铝和氧化镁包覆氮化硅粉在搅拌式球磨机中研磨6h，使粉体的粒度D 50达到0.6微米以下，之后向研磨所得料浆中加入1.5kg粘结剂PVB和1kg聚丙烯酸乳液，搅拌3h，得到料浆的固含量为45％，进行第二喷雾干燥后，得到造粒粉，所述造粒粉粒径D 50约为100μm；
将所述造粒粉进行干压成型为直径9.525mm的陶瓷球，再进行冷等静压处理，压力为150MPa；将成型后的陶瓷球在流动的空气气氛中进行排胶，排胶温度为550℃，保温时间为2h；
将排胶后的陶瓷球采用气压烧结的方式进行烧结，烧结温度为1700℃，保温时间为6h，炉内气氛为氮气，氮气压力为8MPa，得到直径为9.525mm的氮化硅毛坯球；
将所述氮化硅毛坯球依次进行研磨和抛光加工，得到加工精度为 GBT 308.2-2010中规定的G5级的氮化硅陶瓷精球。
对比例1
本对比例直接以氧化铝粉末和氧化钇粉末作为烧结助剂，烧结助剂的加入量与实施例1相同，所述氧化铝粉末纯度为99.99％，粒径D 50为0.5μm，所述氧化钇粉末纯度为99.99％，粒径D 50为0.8μm；采用机械球磨的方式将烧结助剂粉末和氮化硅粉末进行混合和研磨，混合研磨时间为6h，测试粉体粒径D 50达到实施例1中的相同水平(0.6微米以下)后，向研磨所得料浆中加入粘结剂(同实施例1)，搅拌3h，通过喷雾干燥得到造粒粉，其他工艺条件与实施例1相同。
对比例2
本对比例直接以氧化铝粉末和氧化钇粉末作为烧结助剂，烧结助剂加入量与实施例2中烧结助剂的加入量相同，所述氧化铝粉末纯度为99.99％，粒径D 50为0.5微米，所述氧化钇粉末纯度为99.99％，粒径D 50为0.8微米。采用机械球磨的方式将烧结助剂粉末和氮化硅粉末进行混合和研磨，混合研磨时间为6h，测试粉体粒径D 50达到实施例2中的相同水平(0.6微米以下)后，向研磨所得料浆中加入粘结剂(同实施例2)，搅拌3h以上，通过喷雾干燥得到造粒粉，其他工艺条件与实施例2中的工艺条件相同。
对比例3
本对比例以氧化铝粉末和氧化镁粉末作为烧结助剂，烧结助剂加入量和实施例3中烧结助剂的加入量相同；所述氧化铝粉末纯度为99.99％，粒径D 50为0.5微米，所述氧化镁粉末纯度为99.9％，粒径D 50为0.5微米；采用机械球磨的方式将烧结助剂粉末和氮化硅粉末进行混合和研磨，混合研磨时间为6h，测试粉体粒径D 50达到实施例3中的相同水平(0.6微米以下)后，向研磨所得料浆中加入粘结剂(同实施例3)，搅拌3h以上，通过喷雾干燥得到造粒粉，其他工艺条件与实施例3中的工艺条件相同。
性能测试
采用阿基米德排水法测量实施例1～3及对比例1～3中氮化硅陶瓷球的密度，并计算其相对密度。采用GBT 16534-2009中规定的方法测量陶瓷球的维氏硬度(HV10)，并根据Niihara提出的压痕法测量断裂韧性。按照JB/T 1255-2001标准规定的三球试验方法测试陶瓷球的压碎载荷， 并计算压碎载荷比(陶瓷球所能承受的压碎载荷与同规格钢球所承受的压碎载荷的比值)。每个案例测试30组压碎载荷数据，对这30组压碎载荷数据进行拟合得出韦布尔模数，并以此作为陶瓷球可靠性的评价依据。采用专利CN102951905A中描述的方法对陶瓷球的滚动接触疲劳寿命进行测试(最大接触应力为5.9GPa，转速为1200rpm)。表1为测量所得各项测试数据。
表1 实施例1～3和对比例1～3制备的氮化硅陶瓷球的性能数据
Figure PCTCN2020121774-appb-000001
从表1可以看出，在其他工艺条件相同的情况下，采用烧结助剂包覆氮化硅的方式制备的陶瓷球致密度达到了99.9％以上，维氏硬度(HV10)大于1500，压碎载荷比大于45％，韦布尔模数大于15，滚动接触疲劳寿命在400h以上。对比来看，采用烧结助剂包覆氮化硅的方式制备的陶瓷球各项性能均优于采用直接加入烧结助剂粉末的方式制备的陶瓷球，尤其可靠性和疲劳寿命均有了较大幅度的提升。
以上实施例的说明只是用于帮助理解本发明的方法及其核心思想。应当指出，对于本技术领域的普通技术人员来说，在不脱离本发明原理的前 提下，还可以对本发明进行若干改进和修饰，这些改进和修饰也落入本发明权利要求的保护范围内。对这些实施例的多种修改对本领域的专业技术人员来说是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下在其它实施例中实现。因此，本发明将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (16)

  1. 一种航空轴承用高可靠性长寿命氮化硅陶瓷球的制备方法，包括以下步骤：
    将异丙醇铝、有机溶剂、氮化硅粉和金属醋酸盐水溶液混合，依次进行水解和第一喷雾干燥，得到混合粉体；
    将所述混合粉体进行煅烧，得到烧结助剂包覆氮化硅粉；
    将所述烧结助剂包覆氮化硅粉研磨后与粘结剂混合，进行第二喷雾干燥，得到造粒粉；
    将所述造粒粉依次进行成型、排胶和烧结，得到氮化硅陶瓷球。
  2. 根据权利要求1所述的制备方法，其特征在于，所述氮化硅粉的粒径D 50为0.5～1.5μm，α-Si 3N 4含量＞85％，氧含量＜2％。
  3. 根据权利要求1所述的制备方法，其特征在于，所述金属醋酸盐水溶液中的金属醋酸盐包括醋酸钇、醋酸镁、醋酸镧、醋酸钕和醋酸镥中的一种或几种。
  4. 根据权利要求1或3所述的制备方法，其特征在于，所述金属醋酸盐水溶液的浓度为100～500g/L。
  5. 根据权利要求1所述的制备方法，其特征在于，以产生氧化铝的量计，所述异丙醇铝的加入量为所述烧结助剂包覆氮化硅粉总质量的2～8％；以产生金属氧化物的量计，所述金属醋酸盐的加入量为所述烧结助剂包覆氮化硅粉总质量的2～8％；所述氮化硅粉的加入量为所述烧结助剂包覆氮化硅粉总质量的85～95％。
  6. 根据权利要求1所述的制备方法，其特征在于，所述有机溶剂为无水乙醇和/或异丙醇。
  7. 根据权利要求1所述的制备方法，其特征在于，所述第一喷雾干燥的方式为氮气保护压力式喷雾干燥或离心式喷雾干燥。
  8. 根据权利要求1所述的制备方法，其特征在于，所述煅烧的温度为400～600℃，时间为1～10h。
  9. 根据权利要求1所述的制备方法，其特征在于，所述粘结剂包括聚乙烯醇缩丁醛和/或聚丙烯酸乳液。
  10. 根据权利要求1或9所述的制备方法，其特征在于，所述粘结剂的添加量为所述烧结助剂包覆氮化硅粉总质量的0.5～4％。
  11. 根据权利要求1所述的制备方法，其特征在于，所述第二喷雾干燥所用料浆的固含量为40～50％。
  12. 根据权利要求1或11所述的制备方法，其特征在于，所述第二喷雾干燥的方式为氮气保护压力式喷雾干燥或离心式喷雾干燥。
  13. 根据权利要求1所述的制备方法，其特征在于，所述造粒粉的粒径D 50为30～150μm。
  14. 根据权利要求1所述的制备方法，其特征在于，所述成型的方式包括冷等静压，所述冷等静压的压力为120～300MPa。
  15. 根据权利要求1所述的制备方法，其特征在于，所述排胶的温度为400～600℃，保温时间为1～10h。
  16. 根据权利要求1所述的制备方法，其特征在于，所述烧结的方式为气压烧结，所述烧结的温度为1600～1900℃，保温时间为1～6h，压力为0.3～10MPa。
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