CN116217235B - Silicon nitride large-size high-temperature structural member and preparation method thereof - Google Patents
Silicon nitride large-size high-temperature structural member and preparation method thereof Download PDFInfo
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- 229910052581 Si3N4 Inorganic materials 0.000 title claims abstract description 89
- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 78
- 238000002360 preparation method Methods 0.000 title claims abstract description 13
- 239000000843 powder Substances 0.000 claims abstract description 66
- 238000005245 sintering Methods 0.000 claims abstract description 62
- 239000011812 mixed powder Substances 0.000 claims abstract description 31
- 238000000034 method Methods 0.000 claims abstract description 30
- 238000002156 mixing Methods 0.000 claims abstract description 26
- 239000002994 raw material Substances 0.000 claims abstract description 18
- 229910001404 rare earth metal oxide Inorganic materials 0.000 claims abstract description 12
- 239000003292 glue Substances 0.000 claims abstract description 10
- 239000011863 silicon-based powder Substances 0.000 claims abstract description 10
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 9
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims abstract description 9
- 229910002804 graphite Inorganic materials 0.000 claims abstract description 9
- 239000010439 graphite Substances 0.000 claims abstract description 9
- 229910052814 silicon oxide Inorganic materials 0.000 claims abstract description 7
- 238000007599 discharging Methods 0.000 claims abstract description 6
- ZVWKZXLXHLZXLS-UHFFFAOYSA-N zirconium nitride Chemical compound [Zr]#N ZVWKZXLXHLZXLS-UHFFFAOYSA-N 0.000 claims abstract description 5
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims abstract description 4
- 239000003086 colorant Substances 0.000 claims abstract description 3
- 238000000465 moulding Methods 0.000 claims abstract description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 51
- 239000000523 sample Substances 0.000 claims description 33
- 238000000498 ball milling Methods 0.000 claims description 27
- 238000004321 preservation Methods 0.000 claims description 27
- 229910052757 nitrogen Inorganic materials 0.000 claims description 25
- 238000010438 heat treatment Methods 0.000 claims description 15
- 239000000243 solution Substances 0.000 claims description 15
- 238000000227 grinding Methods 0.000 claims description 14
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 claims description 12
- 239000012298 atmosphere Substances 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 8
- 238000001035 drying Methods 0.000 claims description 7
- 238000002474 experimental method Methods 0.000 claims description 7
- 239000000203 mixture Substances 0.000 claims description 7
- 238000003825 pressing Methods 0.000 claims description 7
- 229910052710 silicon Inorganic materials 0.000 claims description 7
- 238000001291 vacuum drying Methods 0.000 claims description 7
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 6
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 claims description 6
- 239000002904 solvent Substances 0.000 claims description 6
- 229910001928 zirconium oxide Inorganic materials 0.000 claims description 6
- 239000013078 crystal Substances 0.000 claims description 5
- 238000000280 densification Methods 0.000 claims description 5
- 238000005303 weighing Methods 0.000 claims description 5
- MRELNEQAGSRDBK-UHFFFAOYSA-N lanthanum(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[La+3].[La+3] MRELNEQAGSRDBK-UHFFFAOYSA-N 0.000 claims description 4
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 4
- 238000012360 testing method Methods 0.000 claims description 4
- 239000007789 gas Substances 0.000 claims description 3
- UZLYXNNZYFBAQO-UHFFFAOYSA-N oxygen(2-);ytterbium(3+) Chemical compound [O-2].[O-2].[O-2].[Yb+3].[Yb+3] UZLYXNNZYFBAQO-UHFFFAOYSA-N 0.000 claims description 3
- -1 polytetrafluoroethylene Polymers 0.000 claims description 3
- 229910003454 ytterbium oxide Inorganic materials 0.000 claims description 3
- 229940075624 ytterbium oxide Drugs 0.000 claims description 3
- 239000011324 bead Substances 0.000 claims description 2
- 239000012496 blank sample Substances 0.000 claims description 2
- 238000009694 cold isostatic pressing Methods 0.000 claims description 2
- 239000011521 glass Substances 0.000 claims description 2
- 239000011259 mixed solution Substances 0.000 claims description 2
- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 claims description 2
- 229920001343 polytetrafluoroethylene Polymers 0.000 claims description 2
- 239000004810 polytetrafluoroethylene Substances 0.000 claims description 2
- 238000012545 processing Methods 0.000 claims description 2
- 230000000630 rising effect Effects 0.000 claims description 2
- 239000012856 weighed raw material Substances 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 3
- 239000000919 ceramic Substances 0.000 abstract description 28
- 238000005452 bending Methods 0.000 abstract description 8
- RKTYLMNFRDHKIL-UHFFFAOYSA-N copper;5,10,15,20-tetraphenylporphyrin-22,24-diide Chemical compound [Cu+2].C1=CC(C(=C2C=CC([N-]2)=C(C=2C=CC=CC=2)C=2C=CC(N=2)=C(C=2C=CC=CC=2)C2=CC=C3[N-]2)C=2C=CC=CC=2)=NC1=C3C1=CC=CC=C1 RKTYLMNFRDHKIL-UHFFFAOYSA-N 0.000 abstract description 3
- 229910052582 BN Inorganic materials 0.000 abstract 1
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 abstract 1
- 239000002002 slurry Substances 0.000 description 10
- 238000010304 firing Methods 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 7
- 239000007791 liquid phase Substances 0.000 description 7
- 239000000463 material Substances 0.000 description 7
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 6
- 239000012071 phase Substances 0.000 description 6
- 238000005238 degreasing Methods 0.000 description 5
- XTLNYNMNUCLWEZ-UHFFFAOYSA-N ethanol;propan-2-one Chemical compound CCO.CC(C)=O XTLNYNMNUCLWEZ-UHFFFAOYSA-N 0.000 description 5
- 239000012046 mixed solvent Substances 0.000 description 5
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 4
- 238000000354 decomposition reaction Methods 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 239000000654 additive Substances 0.000 description 3
- 230000000996 additive effect Effects 0.000 description 3
- 238000005070 sampling Methods 0.000 description 3
- 230000009286 beneficial effect Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000002425 crystallisation Methods 0.000 description 2
- 230000008025 crystallization Effects 0.000 description 2
- 239000010703 silicon Substances 0.000 description 2
- KRHYYFGTRYWZRS-UHFFFAOYSA-M Fluoride anion Chemical compound [F-] KRHYYFGTRYWZRS-UHFFFAOYSA-M 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- 239000012752 auxiliary agent Substances 0.000 description 1
- 229910010293 ceramic material Inorganic materials 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000009770 conventional sintering Methods 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 229910001873 dinitrogen Inorganic materials 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 230000003993 interaction Effects 0.000 description 1
- 238000000462 isostatic pressing Methods 0.000 description 1
- 229910044991 metal oxide Inorganic materials 0.000 description 1
- 150000004706 metal oxides Chemical class 0.000 description 1
- 239000012299 nitrogen atmosphere Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 230000035939 shock Effects 0.000 description 1
- 239000007790 solid phase Substances 0.000 description 1
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- C04B2235/32—Metal oxides, mixed metal oxides, or oxide-forming salts thereof, e.g. carbonates, nitrates, (oxy)hydroxides, chlorides
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Abstract
The invention belongs to the field of ceramic preparation, and relates to a large-size thick-wall silicon nitride high-temperature ceramic component and a preparation method thereof. The method comprises the steps of mixing silicon nitride powder with a sintering aid, adopting alpha-silicon nitride powder, beta-silicon nitride whisker, alumina powder, rare earth oxide and silicon powder as raw materials, granulating, molding, discharging glue, presintering at low temperature and low pressure, then sintering at medium temperature under high pressure, and finally sintering at high temperature and low pressure, wherein the whole sintering process adopts double-layer buried powder, mixed powder of BN and graphite in the inner layer and mixed powder of SiON and boron nitride in the outer layer. The large-size thick-wall (more than 30 mm) silicon nitride high-temperature structural ceramic prepared by adopting the process is prepared by the following steps: the inner and outer colors are uniform and have no sandwich; the grain diameter of the sintered body beta-silicon nitride is 1-1.5um, the length-diameter ratio range is 4-8, and the diameter of tetragonal zirconium nitride embedded in the network structure is 2-3um; HV hardness is more than 15GPa, room temperature bending strength is more than 800MPa, bending strength at 900 ℃ is more than 600MPa, and fracture toughness is more than 7MPa.m 1/2 Coefficient of thermal expansion of 2.8-3.1X10 ‑6 。
Description
Technical Field
The invention belongs to the technical field of ceramic preparation, and particularly relates to a large-size thick-wall silicon nitride high-temperature ceramic component and a preparation method thereof.
Background
Silicon nitride is a ceramic with excellent comprehensive properties, and is widely applied to complex structural members in the fields of aerospace and the like at present due to higher mechanical property, high-temperature mechanical property, good thermal shock resistance and excellent corrosion resistance. Si (Si) 3 N 4 It is a strong covalent bond compound, it is difficult to sinter by solid phase diffusion, it is necessary to add sintering aid, and densification is performed by liquid phase sintering mechanism. Si after sintering 3 N 4 The mechanical property of the ceramic is mainly composed of alpha-Si 3 N 4 And beta-Si 3 N 4 The proportion of phases and the number and composition of the inter-crystalline phases (glassy or partially crystalline) are determined depending on the sintering additive and the sintering process.
Composition and content of sintering aid to Si 3 N 4 Densification and mechanical properties of the ceramic have important effects. Common sintering aids are metal oxides (MgO, caO, al) 2 O 3 ) Rare earthOxide (Yb) 2 O 3 、Y 2 O 3 、Lu 2 O 3 、CeO 2 ) And fluoride (LiF, mgF) 2 、YF 3 ) Etc. To reduce the formation temperature of the liquid phase and improve the properties of the grain boundary phase, binary or multi-element sintering aid systems are generally employed. At present, the common additive Y 2 O 3 -Al 2 O 3 、Y 2 O 3 -SiO 2 、MgO-CeO 2 And the like, the effect is obvious in the aspects of liquid phase formation and densification, but the crystallization of the second phase is incomplete, so that the high-temperature performance of the material is weakened. Researchers in recent years have found that adding Yb to silicon nitride 2 O 3 Has certain effects on crystallization of grain boundary phase and improvement of material strength; adding ZrO 2 Can toughen and strengthen Si 3 N 4 Based on ceramic materials and increasing Si 3 N 4 Base ceramic oxidation resistance. How to select proper additive type and content, and make Si while maintaining good sintering property 3 N 4 The base ceramic has good comprehensive mechanical and thermal properties, and is always a hot spot for the study of domestic and foreign scholars.
Due to Si 3 N 4 Decomposition starts after 1700 ℃, and air pressure sintering under nitrogen atmosphere is the most commonly used sintering process for producing high-performance silicon nitride ceramics. However, due to the interaction between the sintering atmosphere and the silicon nitride, the problems of decomposition of the silicon nitride and volatilization of the silicon result in the fact that the sintered large-size thick-wall (thickness greater than 30 mm) silicon nitride structural member often shows a sandwich phenomenon that the near surface is light and the inner layer is dark. This non-uniform color is due to differences in density and microstructure of the inner and outer layers caused by different degrees of sintering within and outside the sample. The sandwich phenomenon after sintering directly affects the deterioration of mechanical and physical properties of the silicon nitride ceramic member, resulting in that the size of the sintered body has to be reduced when producing the silicon nitride member, thereby limiting the application of silicon nitride.
Preparation of large-size thick-wall Si 3 N 4 When the ceramic-based high-temperature structural member is used, the problems of excellent bending strength, high-temperature bending strength, higher hardness, fracture toughness and other mechanical properties are solvedThe sandwich phenomenon of large-size silicon nitride ceramics after sintering has been a difficult problem. Aiming at the situation, the invention designs a multi-element sintering auxiliary agent, a double-layer buried powder and a step sintering process, and obtains large-size Si with good comprehensive performance 3 N 4 A preparation method of a base ceramic high-temperature structural member.
Disclosure of Invention
The invention aims to overcome the defects of the existing large-size silicon nitride high-temperature structural member in performance and preparation, designs a Zr-containing multi-element sintering aid and a hierarchical presintering air pressure sintering process, prepares the large-size thick-wall silicon nitride high-temperature structural member with higher high-temperature bending strength and good hardness and fracture toughness, and solves the sandwich problem of thick-wall silicon nitride after sintering.
The specific technical scheme of the invention is as follows: the silicon nitride large-size thick-wall high-temperature structural member is prepared from (by weight) silicon nitride powder 78-82% and beta-Si 3 N 4 6-8%, alumina powder 3-5%, rare earth oxide 6-8% and silicon powder 1-2%
Preferably, the rare earth oxide is a mixture of one or two of yttrium oxide, ytterbium oxide and lanthanum oxide and zirconium oxide, and the proportion of the zirconium oxide to the rare earth oxide is 10-25%.
The silicon nitride powder is alpha-silicon nitride powder d 50 ＝500nm,α-Si 3 N 4 >95％；
The beta-silicon nitride is beta-Si 3 N 4 Whisker, d=150-300 nm, length 2-4 μm;
the alumina powder d 50 ＝300nm；
The ytterbium oxide powder d 50 ＝2μm；
The zirconia powder is 8wt% of Y 2 O 3 Stable tetragonal ZrO 2 ，d 50 ＝1μm；
The preparation method of the silicon nitride large-size thick-wall high-temperature structural member specifically comprises the following steps:
(1) Mixing: weighing aluminum oxide, rare earth oxide and silicon powder in proportion by an electronic balance, pouring the weighed raw materials into a polytetrafluoroethylene ball milling tank, putting zirconium oxide ball milling beads with different sizes into the ball milling tank in proportion, adding a certain amount of absolute ethyl alcohol acetone mixing medium, and putting the ball milling tank filled with the raw materials into a planetary ball mill for full mixing; weighing silicon nitride powder and silicon nitride whisker by an electronic balance according to a proportion, adding a certain amount of absolute ethyl alcohol acetone mixed medium to prepare silicon nitride powder and silicon nitride whisker mixed solution, mixing the mixed aluminum oxide, rare earth oxide and silicon powder solution with the silicon nitride powder and silicon nitride whisker solution, fully ball-milling according to the ball-milling process, pouring the mixed raw materials into a beaker, and putting the beaker into a vacuum drying oven to fully volatilize the solvent to obtain fully dried mixed powder;
(2) Granulating, forming and discharging glue: pouring the dried powder into a grinding pot, adding a proper amount of PVA solution prepared in advance, and fully grinding to obtain mixed powder with good fluidity. Pouring the granulated powder with certain fluidity into a die according to a certain weight, performing dry pressing molding by a pressure tester, processing a sample by a soft sheath, and performing cold isostatic pressing to obtain a high-density primary blank sample. And placing the molded sample into an experiment box type electric furnace for glue discharging, and then cooling to room temperature along with the furnace.
(3) Sintering buried powder: and placing the sample after the glue discharge into a BN crucible, and then placing the sample into a pneumatic sintering furnace for powder burying and sintering. In order to control the sintering atmosphere and suppress the decomposition of silicon nitride, a double-layer powder burying method as shown in fig. 1 is adopted. The inner layer is a mixed powder bed of BN and graphite to form a reducing atmosphere containing N; the outer layer is Si 3 N 4 Mixed powder bed of BN and SiON, forming a volatile atmosphere containing Si.
(4) The sintering process comprises the following steps: and (3) raising the temperature to the set temperature under low pressure, presintering, preserving heat, increasing the nitrogen flow to increase the gas pressure after the heat preservation is finished, quickly raising the temperature to a medium-temperature sintering stage, preserving heat, continuing raising the temperature to a high-temperature sintering stage after the heat preservation is finished, preserving heat, and cooling to the room temperature along with a gas pressure furnace after the heating is stopped.
Si powder, beta-Si in the raw material formula of the patent 3 N 4 Whisker ZrO 2 The function of (3): si powder is initially burnedAnd the middle burning stage reacts with nitrogen to form silicon nitride, and the silicon nitride reacts with beta-Si separated out from liquid phase 3 N 4 Together filled in beta-Si 3 N 4 beta-Si overlapped with each other is constructed between whiskers 3 N 4 The network structure is favorable for inhibiting the problem of microstructure and color non-uniformity caused by silicon volatilization, and improves the mechanical property of silicon nitride. The addition of zirconia not only plays a role in helping sintering to reduce sintering temperature, but also helps to solve the sandwich problem caused by sintering at too high sintering temperature, and reacts with nitrogen to separate out high-temperature resistant tetragonal ZrN in the sintering process, so that the high-temperature bending strength of silicon nitride is improved. The double-layer powder burying and multi-step sintering play an important role in overcoming the sandwich phenomenon of large-size thick-wall silicon nitride. The double-layer buried powder inner layer forms a reducing atmosphere containing N, and the outer layer forms a volatilizing atmosphere containing Si, so that the decomposition of silicon nitride can be inhibited. The low nitrogen pressure in the primary sintering stage can reduce the N content in the liquid phase, reduce the viscosity of the liquid phase and is beneficial to beta-Si 3 N 4 Precipitation from the liquid phase promotes beta-Si in the core region 3 N 4 And the formed closed air holes are formed by fully separating out and forming a skeleton structure, and the low nitrogen concentration in the holes is beneficial to removing in the press-firing stage, so that the primary blank reaches higher density. In the later stage of high-temperature sintering, under the conditions of high temperature and high nitrogen pressure, the crystal grains continue to grow up through the Oswald curing process, and air holes are removed, so that high-density Si is obtained 3 N 4 And (3) ceramics.
Preferably, the mass ratio of the raw materials to the balls in the step 1 is 1:3-1:5, the volume ratio of the acetone to the absolute ethyl alcohol is 0.7-1.0:1, and the ball milling is carried out for 2-6 hours at the rotating speed of 200-300 r/min. Drying at 80-120deg.C for 10-12 hr.
Preferably, the mechanical pressure in the step 2 is 40-60MPa, the pressurizing speed is 1-2KN/s, the pressure is maintained for 5-10min, the cold isostatic pressure is 200-220MPa, and the pressure is maintained for 5-10min; heating to 600 deg.C at 2-3 deg.C/min, and maintaining for 120-180min.
Preferably, the step 3 is characterized in that the inner layer of the buried powder is a mixed powder bed of BN and graphite, the BN accounts for 80-90wt% and the thickness of the buried powder is 1.2-1.5 times of the height of the sample, so that a reducing atmosphere containing N is formed; the outer layer is 5-10wt% Si 3 N 4 The mixed powder bed of BN 60-70wt% and SiON 20-30wt% has buried powder thickness 0.4-0.8 times the sample height, and forms a volatile atmosphere containing Si.
Preferably, the temperature rising rate of the step 4 is 2-4 ℃/min in the presintering stage, the presintering temperature is 1550-1580 ℃, the heat preservation time is 1-4h, and the nitrogen pressure is 0.3-0.5MPa; the pressure of the nitrogen gas is 3-5MPa,15-20 ℃/min is raised to the pressure temperature for heat preservation, the pressure temperature is 1680-1700 ℃, the heat preservation time is 2-4h, and the beta-Si is formed at the temperature 3 N 4 Is a lap joint structure; the high temperature sintering temperature zone is 1800-1820 ℃, the heat preservation time is 4-6h, the heating rate is 2-4 ℃/min, the nitrogen pressure is 0.3-0.5MPa, and the beta-Si is 3 N 4 The grains further grow and the densification process is completed.
The microstructure diameter of the silicon nitride thick-wall high-temperature structural member prepared by the method is 1-1.5um, the beta-silicon nitride crystal grains with the length-diameter ratio of 4-8 are combined with the glass phase to form a network structure by mutually lap joint, square zirconium nitride with the diameter of 2-3um is embedded in the network structure, and the quantity of the zirconium nitride and the silicon nitride crystal grains accounts for 2-4%.
The silicon nitride thick-wall high-temperature structural member prepared by the method is characterized in that the wall thickness is larger than 30mm, the diameter is larger than 100mm, the internal and external colors are uniform and sandwich-free, the HV hardness is larger than 15GPa, the room temperature bending strength is larger than 800MPa, the bending strength at 900 ℃ is larger than 600MPa, and the fracture toughness is larger than 7MPa.m 1/2 Coefficient of thermal expansion of 2.8-3.1X10 -6 。
Drawings
FIG. 1 is a schematic diagram of a double-layer powder burying method of example 1, example 2 and comparative example 1;
FIG. 2 is a macroscopic cross-sectional view of the silicon nitride ceramic prepared in example 1;
FIG. 3 is a macroscopic cross-sectional view of the silicon nitride ceramic prepared in example 2;
FIG. 4 is a macroscopic cross-sectional view of the silicon nitride ceramic prepared in comparative example 1;
FIG. 5 is a macroscopic cross-sectional view of the silicon nitride ceramic prepared in comparative example 2;
FIG. 6 is a macroscopic cross-sectional view of the silicon nitride ceramic prepared in comparative example 3;
FIG. 7 is a microstructure of the silicon nitride ceramics prepared in example 1.
Detailed Description
In order to further illustrate the technical means and effects adopted by the invention to achieve the preset aim, the following detailed description is given to the specific implementation mode, the steps and the characteristics of the preparation method of the large-size thick-wall silicon nitride high-temperature structural part according to the invention by combining with a preferred example.
Example 1:
1. according to alpha-Si 3 N 4 :β-Si 3 N 4 :Si:Al 2 O 3 :ZrO 2 :Yb 2 O 3 500g of raw material was weighed in a ratio of =82:6:1:4:1:6, si, al 2 O 3 、ZrO 2 And Yb 2 O 3 Ball milling the powder in an ethanol-acetone mixed solvent (volume ratio is 1:1) at a rotating speed of 300r/min for 4 hours, wherein the mass ratio of the raw materials to the balls is 1:4, and uniformly mixing to obtain slurry; by reacting alpha-Si 3 N 4 And beta-Si 3 N 4 Mixing according to the same ball milling process, mixing the mixed auxiliary solvent with silicon nitride solution (comprising silicon nitride powder and silicon nitride whisker), and fully mixing according to the ball milling process.
2. Drying the slurry in a vacuum drying oven at 80 ℃ for 12 hours to obtain completely dried mixed powder;
3. pouring the powder into a grinding body, adding a proper amount of PVA solution prepared in advance, and fully grinding to obtain mixed powder with good fluidity;
4. pressing the granulating material into a primary blank with phi of 100mm, wherein the mechanical pressure is 40MPa, the pressurizing speed is 1KN/s, the pressure is maintained for 5min, the cold isostatic pressure is 200MPa, and the pressure is maintained for 5min;
5. placing the molded sample into an experiment box type electric furnace, heating to 600 ℃ at a speed of 2 ℃/min, and preserving heat for 180min for degreasing;
6. placing the sample after the rubber discharge into a BN crucible, adopting a double-layer powder burying mode shown in figure 1, wherein the inner layer of the buried powder is a mixed powder bed of BN and graphite, the BN accounts for 85wt% of the mixed powder bed, the thickness of the buried powder is 1.2 times of the height of the sample, and the outer layer of the buried powder is 6wt% of Si 3 N 4 Mixed powder bed of 70wt% BN and 24wt% SiON, buried powderThe thickness was 0.6 times the height of the sample. Then placing the mixture into a pneumatic sintering furnace for sintering, presintering at the preset temperature of 4 ℃/min, and preserving heat, wherein the presintering temperature is 1580 ℃, the preserving heat time is 2 hours, and the nitrogen pressure is 0.3MPa; after the heat preservation is finished, increasing the flow of nitrogen to increase the pressure to 4MPa, and simultaneously raising the pressure to the pressure-firing temperature at 15 ℃/min for heat preservation, wherein the pressure-firing temperature is 1700 ℃, and the heat preservation time is 3 hours; and after the heat preservation is finished, continuously heating to 1820 ℃, preserving heat for 6 hours, and cooling to room temperature along with the furnace under the nitrogen pressure of 0.4 MPa.
7. The sintered silicon nitride ceramic had no sandwich phenomenon (see FIG. 2) and the properties are shown in Table 1, wherein all samples were tested for hardness under a load of 10Kg for 15s under pressure.
Example 2:
1. according to alpha-Si 3 N 4 :β-Si 3 N 4 :Si:Al 2 O 3 :ZrO 2 :Yb 2 O 3 500g of raw material was weighed in a ratio of =80:4:1.5:4.5:2:8. Si, al 2 O 3 、ZrO 2 And Yb 2 O 3 Ball milling the powder in an ethanol-acetone mixed solvent (volume ratio is 1:1) at a rotating speed of 300r/min for 4 hours, wherein the mass ratio of the raw materials to the balls is 1:4, and uniformly mixing to obtain slurry; by reacting alpha-Si 3 N 4 And beta-Si 3 N 4 Mixing according to the same ball milling process, mixing the mixed auxiliary solvent with silicon nitride solution (comprising silicon nitride powder and silicon nitride whisker), and fully mixing according to the ball milling process.
2. Drying the slurry in a vacuum drying oven at 80 ℃ for 12 hours to obtain completely dried mixed powder;
3. pouring the powder into a grinding body, adding a proper amount of PVA solution prepared in advance, and fully grinding to obtain mixed powder with good fluidity;
4. pressing the granulating material into a primary blank with phi of 100mm, wherein the mechanical pressure is 40MPa, the pressurizing speed is 1KN/s, the pressure is maintained for 5min, the cold isostatic pressure is 200MPa, and the pressure is maintained for 5min;
5. placing the molded sample into an experiment box type electric furnace, heating to 600 ℃ at a speed of 2 ℃/min, and preserving heat for 180min for degreasing;
6. sample after completing glue dischargingPutting into BN crucible, adopting double-layer powder-embedding mode shown in figure 1, wherein the inner layer of the embedded powder is a mixed powder bed of BN and graphite, the BN accounts for 80wt%, the thickness of the embedded powder is 1.5 times of the height of the sample, and the outer layer is 8wt% Si 3 N 4 The mixed powder bed of 70wt% BN and 22wt% SiON has buried powder thickness 0.6 times the height of the sample. Then placing the mixture into a pneumatic sintering furnace for sintering, presintering at the preset temperature of 4 ℃/min, and preserving heat, wherein the presintering temperature is 1560 ℃, the preserving heat time is 2 hours, and the nitrogen pressure is 0.3MPa; after the heat preservation is finished, increasing the flow of nitrogen to increase the pressure to 4MPa, and simultaneously raising the pressure to the pressure-firing temperature at 15 ℃/min for heat preservation, wherein the pressure-firing temperature is 1680 ℃, and the heat preservation time is 3 hours; and after the heat preservation is finished, continuously heating to 1800 ℃, preserving heat for 5 hours, and cooling to room temperature along with a furnace under the nitrogen pressure of 0.4 MPa.
7. The sintered silicon nitride ceramic was free of sandwiches (see fig. 3) and the properties are shown in table 1. All samples were tested for hardness under a load of 10Kg for 15s.
Comparative example 1 (without addition of beta- -Si) 3 N 4 Whisker, si powder and ZrO 2 Sintering aid):
1. according to alpha-Si 3 N 4 :Al 2 O 3 :Yb 2 O 3 The preparation method comprises the steps of (1) weighing 500g of raw materials in an ethanol-acetone mixed solvent (volume ratio is 1:1) and ball-milling for 4 hours at a rotating speed of 300r/min in a ratio of 88:5:7, and uniformly mixing to obtain slurry;
2. drying the slurry in a vacuum drying oven at 80 ℃ for 12 hours to obtain completely dried mixed powder;
3. pouring the powder into a grinding body, adding a proper amount of PVA solution prepared in advance, and fully grinding to obtain mixed powder with good fluidity;
4. pressing the granulating material into a primary blank with phi of 100mm, wherein the mechanical pressure is 40MPa, the pressurizing speed is 1KN/s, the pressure is maintained for 5min, the cold isostatic pressure is 200MPa, and the pressure is maintained for 5min;
5. placing the molded sample into an experiment box type electric furnace, heating to 600 ℃ at a speed of 2 ℃/min, and preserving heat for 180min for degreasing;
6. placing the sample after the rubber discharge into BN crucible, adopting double-layer powder-burying method shown in figure 1, wherein the inner layer of the buried powder is BN andthe mixed powder bed of graphite has BN content of 85wt%, buried powder thickness of 1.2 times the sample height and outer layer of 6wt% Si 3 N 4 The mixed powder bed of 70wt% BN and 24wt% SiON has buried powder thickness 0.6 times the height of the sample. Then placing the mixture into a pneumatic sintering furnace for sintering, presintering at the preset temperature of 4 ℃/min, and preserving heat, wherein the presintering temperature is 1580 ℃, the preserving heat time is 2 hours, and the nitrogen pressure is 0.3MPa; after the heat preservation is finished, increasing the flow of nitrogen to increase the pressure to 4MPa, and simultaneously raising the pressure to the pressure-firing temperature at 15 ℃/min for heat preservation, wherein the pressure-firing temperature is 1700 ℃, and the heat preservation time is 3 hours; and after the heat preservation is finished, continuously heating to 1820 ℃, preserving heat for 6 hours, and cooling to room temperature along with the furnace under the nitrogen pressure of 0.4 MPa.
7. The sintered silicon nitride ceramic has a sandwich phenomenon (as shown in fig. 4), and the sampling area of the test sample strip is a non-sandwich part, and the performance of the non-sandwich part is shown in table 1.
Comparative example 2 (conventional embedding powder and conventional sintering):
1. according to alpha-Si 3 N 4 :β-Si 3 N 4 :Si:Al 2 O 3 :ZrO 2 :Yb 2 O 3 500g of raw material was weighed in a ratio of =82:6:1:4:1:6, si, al 2 O 3 、ZrO 2 And Yb 2 O 3 Ball milling the powder in an ethanol-acetone mixed solvent (volume ratio is 1:1) at a rotating speed of 300r/min for 4 hours, wherein the mass ratio of the raw materials to the balls is 1:4, and uniformly mixing to obtain slurry; by reacting alpha-Si 3 N 4 And beta-Si 3 N 4 Mixing according to the same ball milling process, mixing the mixed auxiliary solvent with silicon nitride solution (comprising silicon nitride powder and silicon nitride whisker), and fully mixing according to the ball milling process.
2. Drying the slurry in a vacuum drying oven at 80 ℃ for 12 hours to obtain completely dried mixed powder;
3. pouring the powder into a grinding body, adding a proper amount of PVA solution prepared in advance, and fully grinding to obtain mixed powder with good fluidity;
4. pressing the granulating material into a primary blank with phi of 100mm, wherein the mechanical pressure is 40MPa, the pressurizing speed is 1KN/s, the pressure is maintained for 5min, the cold isostatic pressure is 200MPa, and the pressure is maintained for 5min;
5. placing the molded sample into an experiment box type electric furnace, heating to 600 ℃ at a speed of 2 ℃/min, and preserving heat for 180min for degreasing;
6. placing the sample after the glue discharging into a BN crucible, adopting a mixed powder bed of 50wt% of BN and 50wt% of graphite to perform powder burying sintering, raising the temperature to 1860 ℃ at 8 ℃/min, preserving the temperature for 16 hours, and cooling to room temperature along with a furnace under the nitrogen pressure of 3 MPa.
7. The sintered silicon nitride ceramic has a sandwich phenomenon (as shown in fig. 5), the sampling area of the test sample strip is a non-sandwich part, and the performance is shown in table 1.
Comparative example 3 (conventional powder-embedding multi-step sintering):
1. according to alpha-Si 3 N 4 :β-Si 3 N 4 :Si:Al 2 O 3 :ZrO 2 :Yb 2 O 3 500g of raw material was weighed in a ratio of =82:6:1:4:1:6, si, al 2 O 3 、ZrO 2 And Yb 2 O 3 Ball milling the powder in an ethanol-acetone mixed solvent (volume ratio is 1:1) at a rotating speed of 300r/min for 4 hours, wherein the mass ratio of the raw materials to the balls is 1:4, and uniformly mixing to obtain slurry; by reacting alpha-Si 3 N 4 And beta-Si 3 N 4 Mixing according to the same ball milling process, mixing the mixed auxiliary solvent with silicon nitride solution (comprising silicon nitride powder and silicon nitride whisker), and fully mixing according to the ball milling process.
2. Drying the slurry in a vacuum drying oven at 80 ℃ for 12 hours to obtain completely dried mixed powder;
3. pouring the powder into a grinding body, adding a proper amount of PVA solution prepared in advance, and fully grinding to obtain mixed powder with good fluidity;
4. pressing the granulating material into a primary blank with the diameter of 100mm, and carrying out isostatic pressing for 15min under 200MPa to obtain a green body;
5. placing the molded sample into an experiment box type electric furnace, heating to 600 ℃ at a speed of 3 ℃/min, and preserving heat for 180min for degreasing;
6. placing the sample after the glue discharging is completed into a BN crucible, adopting a mixed powder bed of 50wt% of BN and 50wt% of graphite to perform powder burying sintering, then placing the sample into a pneumatic sintering furnace to perform sintering, pre-sintering the sample at a set temperature at 4 ℃/min, and preserving heat, wherein the pre-sintering temperature is 1580 ℃, the preserving heat time is 2h, and the nitrogen pressure is 0.3MPa; after the heat preservation is finished, increasing the flow of nitrogen to increase the pressure to 4MPa, and simultaneously raising the pressure to the pressure-firing temperature at 15 ℃/min for heat preservation, wherein the pressure-firing temperature is 1700 ℃, and the heat preservation time is 3 hours; and after the heat preservation is finished, continuously heating to 1820 ℃, preserving heat for 6 hours, and cooling to room temperature along with the furnace under the nitrogen pressure of 0.4 MPa.
7. The sintered silicon nitride ceramic has a sandwich phenomenon (as shown in fig. 6), the sampling area of the test sample strip is a non-sandwich part, and the performance is shown in table 1.
Table 1 comparison of properties of silicon nitride ceramics
Claims (5)
1. The preparation method of the silicon nitride large-size thick-wall high-temperature structural member is characterized by comprising the following steps of:
(1) Mixing: weighing aluminum oxide, rare earth oxide and silicon powder in proportion by an electronic balance, pouring the weighed raw materials into a polytetrafluoroethylene ball milling tank, putting zirconium oxide ball milling beads with different sizes into the ball milling tank in proportion, adding a certain amount of absolute ethyl alcohol acetone mixing medium, and putting the ball milling tank filled with the raw materials into a planetary ball mill for full mixing; weighing silicon nitride powder and silicon nitride whisker by an electronic balance according to a proportion, adding a certain amount of absolute ethyl alcohol acetone mixed medium to prepare silicon nitride powder and silicon nitride whisker mixed solution, mixing the mixed aluminum oxide, rare earth oxide and silicon powder solution with the silicon nitride powder and silicon nitride whisker solution, fully ball-milling according to the ball-milling process, pouring the mixed raw materials into a beaker, and putting the beaker into a vacuum drying oven to fully volatilize the solvent to obtain fully dried mixed powder;
(2) Granulating, forming and discharging glue: pouring the dried powder into a grinding pot, adding a proper amount of PVA solution prepared in advance, fully grinding to obtain mixed powder with good fluidity, pouring the granulated powder with certain fluidity into a die according to a certain weight, performing dry pressing molding by a pressure testing machine, processing a sample by a soft sheath, performing cold isostatic pressing to obtain a high-density primary blank sample, placing the molded sample into an experiment box type electric furnace for removing glue, and then cooling to room temperature;
(3) Sintering buried powder: placing the sample after the glue discharge into a BN crucible, then placing the crucible into a pneumatic sintering furnace for powder burying and sintering, and forming a reducing atmosphere containing N by adopting a double-layer powder burying mode, wherein the inner layer is a mixed powder bed of BN and graphite, the BN accounts for 80-90wt% and the powder burying thickness is 1.2-1.5 times of the height of the sample; the outer layer is 5-10wt% Si 3 N 4 Mixed powder beds of 60-70wt% of BN and 20-30wt% of SiON, wherein the thickness of buried powder is 0.4-0.8 times of the height of a sample, so as to form a volatile atmosphere containing Si;
(4) The sintering process comprises the following steps: the low-pressure temperature rise is carried out to the set temperature for presintering and heat preservation, after heat preservation is finished, the nitrogen flow is increased to increase the gas pressure, meanwhile, the temperature is quickly raised to a medium-temperature sintering stage and is preserved, after heat preservation is finished, the temperature is continuously raised to a high-temperature sintering stage and is preserved, and after heating is stopped, the air pressure furnace is cooled to the room temperature;
the step (4) is specifically as follows:
the temperature rising rate of the presintering stage is 2-4 ℃/min, the presintering temperature is 1550-1580 ℃, the heat preservation time is 1-4h, and the nitrogen pressure is 0.3-0.5MPa; then raising the temperature to the medium-temperature sintering temperature of 1680-1700 ℃ at 15-20 ℃/min, preserving the heat for 2-4h, and keeping the nitrogen pressure at 3-5MPa; finally, the temperature is increased to the high-temperature sintering temperature of 1800-1820 ℃ at the heating rate of 2-4 ℃/min, the heat preservation time is 4-6h, and the nitrogen pressure is 0.3-0.5MPa, so as to finish the densification process;
the raw materials of the thick-wall high-temperature structural member consist of, by weight, 78-82% of silicon nitride powder, 6-8% of beta-silicon nitride, 3-5% of alumina powder, 6-8% of rare earth oxide and 1-2% of silicon powder;
the rare earth oxide is a mixture of one or two of yttrium oxide, ytterbium oxide and lanthanum oxide and zirconium oxide, and the proportion of the zirconium oxide to the rare earth oxide is 10-25%;
the silicon nitride powder is alpha-silicon nitride powder d 50 =500 nm,α-Si 3 N 4 >95%;
The beta-silicon nitride is beta-silicon nitride whisker, d=150-300 nm and the length is 2-4 mu m.
2. The method for preparing the silicon nitride large-size thick-wall high-temperature structural member according to claim 1, wherein the mass ratio of raw materials to balls in the step 1 is 1:3-1:5, the volume ratio of acetone to absolute ethyl alcohol is 0.7-1.0:1, ball milling is carried out for 2-6h at a rotating speed of 200-300r/min, and drying is carried out for 10-12h at a set temperature of 80-120 ℃.
3. The method for manufacturing a silicon nitride large-size thick-wall high-temperature structural member according to claim 1, wherein the mechanical pressure in the step 2 is 40-60MPa, the pressurizing speed is 1-2KN/s, the pressure is maintained for 5-10min, the cold isostatic pressure is 200-220MPa, and the pressure is maintained for 5-10min; heating to 600 deg.C at 2-3 deg.C/min, and maintaining for 120-180min.
4. The method for producing a silicon nitride large-size thick-wall high-temperature structural member according to claim 1, wherein the thick-wall high-temperature structural member is characterized in that: the microstructure is a network structure formed by mutually overlapping beta-silicon nitride crystal grains with the diameter of 1-1.5um and the length-diameter ratio of 4-8 and glass phases, square zirconium nitride with the diameter of 2-3um is embedded in the network structure, and the quantity of the zirconium nitride and the silicon nitride crystal grains accounts for 2-4 percent.
5. The method for producing a silicon nitride large-size thick-wall high-temperature structural member according to claim 1, wherein the thick-wall high-temperature structural member is characterized in that the wall thickness is greater than 30mm, the diameter is greater than 100mm, the internal and external colors are uniform without sandwich, the HV hardness is greater than 15GPa, the room-temperature flexural strength is greater than 800MPa, the 900 ℃ flexural strength is greater than 600MPa, and the fracture toughness is greater than 7MPa.m 1/2 Coefficient of thermal expansion of 2.8-3.1X10 -6 。
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