CN117185821B - Silicon nitride ceramic and preparation method thereof - Google Patents
Silicon nitride ceramic and preparation method thereof Download PDFInfo
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- CN117185821B CN117185821B CN202311460831.2A CN202311460831A CN117185821B CN 117185821 B CN117185821 B CN 117185821B CN 202311460831 A CN202311460831 A CN 202311460831A CN 117185821 B CN117185821 B CN 117185821B
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- HQVNEWCFYHHQES-UHFFFAOYSA-N silicon nitride Chemical compound N12[Si]34N5[Si]62N3[Si]51N64 HQVNEWCFYHHQES-UHFFFAOYSA-N 0.000 title claims abstract description 125
- 229910052581 Si3N4 Inorganic materials 0.000 title claims abstract description 124
- 239000000919 ceramic Substances 0.000 title claims abstract description 123
- 238000002360 preparation method Methods 0.000 title claims abstract description 25
- 238000005245 sintering Methods 0.000 claims abstract description 70
- 238000000034 method Methods 0.000 claims abstract description 60
- 230000008569 process Effects 0.000 claims abstract description 41
- 238000012545 processing Methods 0.000 claims abstract description 35
- 235000015895 biscuits Nutrition 0.000 claims abstract description 34
- 239000002002 slurry Substances 0.000 claims abstract description 23
- 238000003825 pressing Methods 0.000 claims abstract description 14
- 238000009694 cold isostatic pressing Methods 0.000 claims abstract description 12
- 238000010304 firing Methods 0.000 claims abstract description 8
- 239000000853 adhesive Substances 0.000 claims abstract description 3
- 230000001070 adhesive effect Effects 0.000 claims abstract description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 72
- 238000000227 grinding Methods 0.000 claims description 49
- 238000003754 machining Methods 0.000 claims description 41
- 238000010438 heat treatment Methods 0.000 claims description 38
- 229910052757 nitrogen Inorganic materials 0.000 claims description 36
- 239000000843 powder Substances 0.000 claims description 31
- 238000001816 cooling Methods 0.000 claims description 20
- 239000003292 glue Substances 0.000 claims description 15
- 239000002609 medium Substances 0.000 claims description 15
- 239000011230 binding agent Substances 0.000 claims description 14
- 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 14
- 238000002156 mixing Methods 0.000 claims description 13
- 239000000463 material Substances 0.000 claims description 11
- 229910003460 diamond Inorganic materials 0.000 claims description 10
- 239000010432 diamond Substances 0.000 claims description 10
- 238000003756 stirring Methods 0.000 claims description 10
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 7
- CPLXHLVBOLITMK-UHFFFAOYSA-N magnesium oxide Inorganic materials [Mg]=O CPLXHLVBOLITMK-UHFFFAOYSA-N 0.000 claims description 7
- 239000000395 magnesium oxide Substances 0.000 claims description 7
- AXZKOIWUVFPNLO-UHFFFAOYSA-N magnesium;oxygen(2-) Chemical compound [O-2].[Mg+2] AXZKOIWUVFPNLO-UHFFFAOYSA-N 0.000 claims description 7
- SIWVEOZUMHYXCS-UHFFFAOYSA-N oxo(oxoyttriooxy)yttrium Chemical compound O=[Y]O[Y]=O SIWVEOZUMHYXCS-UHFFFAOYSA-N 0.000 claims description 7
- MTPVUVINMAGMJL-UHFFFAOYSA-N trimethyl(1,1,2,2,2-pentafluoroethyl)silane Chemical compound C[Si](C)(C)C(F)(F)C(F)(F)F MTPVUVINMAGMJL-UHFFFAOYSA-N 0.000 claims description 7
- 238000000498 ball milling Methods 0.000 claims description 5
- 238000013461 design Methods 0.000 claims description 5
- 239000002612 dispersion medium Substances 0.000 claims description 5
- 238000001694 spray drying Methods 0.000 claims description 5
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- 238000004321 preservation Methods 0.000 abstract description 8
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- 238000007599 discharging Methods 0.000 description 10
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- 239000000047 product Substances 0.000 description 10
- 229910052582 BN Inorganic materials 0.000 description 8
- PZNSFCLAULLKQX-UHFFFAOYSA-N Boron nitride Chemical compound N#B PZNSFCLAULLKQX-UHFFFAOYSA-N 0.000 description 8
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 7
- 229910002804 graphite Inorganic materials 0.000 description 7
- 239000010439 graphite Substances 0.000 description 7
- 238000001513 hot isostatic pressing Methods 0.000 description 7
- 230000009467 reduction Effects 0.000 description 7
- 238000011161 development Methods 0.000 description 6
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- 239000011268 mixed slurry Substances 0.000 description 6
- 238000005452 bending Methods 0.000 description 5
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- 229920002037 poly(vinyl butyral) polymer Polymers 0.000 description 5
- 230000007547 defect Effects 0.000 description 4
- 238000000280 densification Methods 0.000 description 4
- 241000220225 Malus Species 0.000 description 3
- 235000021016 apples Nutrition 0.000 description 3
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Abstract
The invention discloses silicon nitride ceramics and a preparation method thereof, which relate to the field of silicon nitride ceramics, and the specific preparation method comprises the steps of preparing slurry; granulating the slurry, and then pressing the slurry into a silicon nitride ceramic ball biscuit; cold isostatic pressing after removing the adhesive from the ceramic ball biscuit; semi-firing the ceramic ball biscuit subjected to cold isostatic pressing to obtain a semi-fired blank; re-sintering the semi-sintered blank to obtain a sintered blank; and processing the sintered blank to obtain the silicon nitride ceramic. According to the invention, the semi-sintering process and the semi-sintering blank re-sintering process are combined on the premise of ensuring the high performance of the silicon nitride ceramic, so that the atmosphere sintering temperature and the heat preservation time are reduced, the processing efficiency of the silicon nitride ceramic is obviously improved, the preparation cost is reduced, and compared with the traditional sintering process, the semi-sintering and re-sintering process is more obvious in improving the performance of the silicon nitride ceramic, and a feasible scheme is provided for low-cost and large-scale preparation of the high-performance silicon nitride ceramic.
Description
Technical Field
The invention relates to the field of silicon nitride ceramics, in particular to silicon nitride ceramics and a preparation method thereof.
Background
The silicon nitride ceramic has excellent physical and chemical properties, is one of the most popular high-performance ceramic materials in the market at present, but has the advantages of high raw material price, complex preparation and processing methods, long preparation period, low efficiency and high cost. At present, the high-performance silicon nitride ceramics are mostly prepared by adopting a dry pressing molding method, an atmosphere presintering heating isostatic pressing sintering method and a grinding processing method. Compared with other forming modes, the dry pressing forming die is simple, high in pressing efficiency and suitable for batch preparation, but is greatly influenced by the powder performance, and the processing allowance of the dry pressing biscuit is large; the silicon nitride blank has high brittleness, is machined, is easy to crack and break edges, is easy to generate microcracks on the surface, and gradually expands to form defects such as opening cracks in the processes of glue discharging and sintering densification after that, and the silicon nitride ceramic has a scrapping risk when the crack depth exceeds the machining allowance; the densified sintered blank has high hardness and toughness, difficult processing, high processing cost and long period. The open pores on the surface of the green body after the atmosphere presintering are basically eliminated, the silicon nitride forms an interlocking structure with very strong rigidity, the densification degree reaches 96% -98% of theoretical density, the effect of improving the density and performance of the blank by the hot isostatic pressing after-treatment is weak, and the advantage of improving the material performance can not be fully exerted.
Disclosure of Invention
Therefore, the invention aims to solve the technical problems that in the preparation of the existing silicon nitride ceramics, the processing allowance of the silicon nitride ceramics formed by dry pressing is large, the mechanical processing difficulty is high, the time is long and the processing cost is high; the hot isostatic pressing sintering post-treatment has weak effect on improving the density and performance of the sintered blank and can not fully exert the advantage of improving the material performance, thereby providing the silicon nitride ceramic and the preparation method thereof.
Therefore, the invention adopts the following technical scheme:
a preparation method of silicon nitride ceramics comprises the following steps:
s1: preparing slurry;
s2: granulating the slurry, and then pressing the slurry into a silicon nitride ceramic ball biscuit;
s3: cold isostatic pressing after removing the adhesive from the ceramic ball biscuit;
s4: semi-firing the ceramic ball biscuit after cold isostatic pressing to obtain a semi-fired blank;
s5: re-sintering the semi-sintered blank to obtain a sintered blank;
s6: processing the sintered blank to obtain the silicon nitride ceramic;
in the step S4, the density of the semi-burned blank is 2.6-2.9 g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The density is 80% -90%.
Further, the method comprises the steps of,
the semi-firing includes: firstly, heating from room temperature to 1300 ℃ at a heating rate of 8-15 ℃/min, and carrying out nitrogen pressure of 0.4-2.0 MPa; then heating from 1300 ℃ to 1400-1600 ℃ at a speed of 4-10 ℃/min, preserving heat for 4-10 hours, and keeping nitrogen pressure at 1.0-10.0 MPa; then cooling from 1400-1600 ℃ to 1100 ℃ at a cooling rate of 6-12 ℃/min, and the nitrogen pressure is 0.4-2.0 MPa; and finally, naturally cooling.
The method comprises the steps of semi-sintering, namely uniformly placing ceramic ball biscuit after cold isostatic pressing in a graphite crucible scattered with boron nitride powder, wherein the particle size of the boron nitride powder is 120 meshes.
The step S4 and the step S5 also comprise the step of grinding the semi-burned silicon nitride ceramic ball blank according to the design drawing size of the semi-burned blank;
when the machining allowance is more than 300 mu m, adopting a diamond grinding wheel with 80-120 meshes to machine, wherein the feeding amount is 10-20 mu m/time;
when the machining allowance is less than or equal to 300 mu m, a diamond grinding plate with 120-180 meshes is adopted for machining, the rotating speed of a main shaft is 80-120 r/min, and the axial pressure is 8-12 kN. According to the size of the ball, the processing time of the semi-burned blank is generally 180-600 min.
In step S1, the raw material slurry includes, in parts by mass:
0.5-3 parts of magnesium oxide;
0.5-3 parts of yttrium oxide;
0.5-3 parts of lanthanum oxide;
0.5-3 parts of titanium carbide;
88-98 parts of silicon nitride;
80-120 parts of absolute ethyl alcohol;
180-220 parts of silicon nitride grinding balls;
4-6 parts of a binder; wherein the binder comprises one or more of PVP, PVB and HPC.
The preparation method of the slurry comprises the steps of taking magnesium oxide, yttrium oxide, lanthanum oxide, titanium carbide and silicon nitride as powder materials, taking absolute ethyl alcohol as a dispersion medium, taking silicon nitride grinding balls as a grinding medium, ball-milling and mixing for 18-36 h, wherein the rotating speed is 1200-1500 r/min during mixing; and adding a binder, and circularly stirring for 2-6 hours to obtain the slurry, wherein the rotating speed is 1300-1800 r/min during the circular stirring.
In the step S2, the granulation is that the slurry is subjected to centrifugal spray drying to prepare granulation powder, wherein a centrifugal atomizer is 80-120 Hz, the temperature of an air inlet is 180-220 ℃, the temperature of an air outlet is 80-100 ℃, and the bulk density of the granulation powder is 0.88-0.92 g/m 3 ；
The diameter of the pressed silicon nitride ceramic ball biscuit is 10-150 mm, and the forming pressure is 10-40 MPa.
In the step S3, the glue is discharged by heating to 380-480 ℃ at a heating rate of 6-15 ℃/min, preserving heat for 8-16 h, and then naturally cooling;
the cold isostatic pressing condition is that the pressure is 120MPa and the pressure maintaining time is 120s.
Sintering, namely heating to 1750-1850 ℃ at a heating rate of 5-10 ℃, and then preserving heat for 1-2 hours, wherein the nitrogen pressure is 120-220 MPa; and then cooling to 1400 ℃ at a speed of 5-10 ℃/min, and naturally cooling after the nitrogen pressure is 50-150 MPa.
The processing includes fine grinding processing and lapping processing;
when the machining allowance is more than or equal to 20 mu m, adopting a structural plate for fine grinding, wherein the granularity of a grinding medium is 180-280 meshes, the rotating speed of a main shaft is 20-80 r/min, and the axial pressurization is 3-15 kN;
when the machining allowance is smaller than 20 mu m, adopting a structural plate for lapping, wherein the granularity of a grinding medium is 320-400 meshes, the rotating speed of a main shaft is 20-80 r/min, and the axial pressurization is 0.5-5 kN.
The invention also provides silicon nitride ceramics, which are prepared by the preparation method, have the diameter of 11.112-50.8 mm, the Vickers hardness (HV 10) of 1400-1700HV, and the fracture toughness (MPa.m) 1/2 ) The precision grade is G3-G20, the crushing load ratio is 40% -80%, and the bending strength is 900-1000 MPa.
The technical scheme of the invention has the following advantages:
(1) According to the invention, the semi-sintering process and the semi-sintering blank re-sintering process are combined on the premise of ensuring the high performance of the silicon nitride ceramic, so that the atmosphere sintering temperature and the heat preservation time are reduced, the processing efficiency of the silicon nitride ceramic is obviously improved, the preparation cost is reduced, and compared with the sintering and HIP processes, the semi-sintering and HIP processes are more obvious in improving the performance of the silicon nitride ceramic, and a feasible scheme is provided for low-cost and mass preparation of the high-performance silicon nitride ceramic.
(2) The method can control the development of the silicon nitride crystal form into uniform short column-shaped grains with low length-diameter ratio by controlling a specific semi-sintering process, and the integral densification degree of the silicon nitride is 80% -90%. Inhibiting the development of alpha-phase crystal grains of silicon nitride to make the crystal grains develop into short columns with fine crystal grains and small length-diameter ratio; meanwhile, the beta phase is controlled to develop into needle shape, so that the effect of 'toughness but not strong' of the semi-sintered blank of silicon nitride is realized, the toughness inhibits the generation of processing defects in the high-speed cutting processing process of the semi-sintered blank, the processing efficiency of the semi-sintered blank can be obviously improved due to low hardness, the semi-sintering process can ensure the processing efficiency, meanwhile, the effect of few processing defects is also achieved, a foundation is provided for improving the performance of a product after re-sintering, the crystal form development of the re-sintered product is ensured by uniform and fine short column-shaped crystal grains, the product performance is superior to that of the product of the traditional sintering process, and the performance stability of the finished product ball is better.
The temperature rise in the stage can ensure that the generation and viscosity of the liquid phase are controlled on the premise of lower content of sintering auxiliary agent, so that the defect of the large pore inside the sintered body is fully eliminated, and the content of the glass phase in the ceramic can be effectively reduced due to the low content of the sintering auxiliary agent.
(3) The invention adds the operation of grinding the near-net-size of the semi-burned blank between the semi-burned process and the semi-burned blank re-sintering process, greatly shortens the machining time of the silicon nitride ceramic, has high machining efficiency of the semi-burned blank, obviously improves the integral machining efficiency of the silicon nitride ceramic by adopting a near-net-size machining mode, obviously shortens the machining period and reduces the machining cost.
(4) The silicon nitride ceramic prepared by the preparation method has excellent strength, short processing time, low cost and wide application range, and is convenient for large-scale production; compared with the traditional sintering mode of silicon nitride ceramics, the preparation method has higher adaptation degree and universality.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
FIG. 1 is a scanning electron microscope image of the silicon nitride ceramic balls obtained in example 1;
fig. 2 is a scanning electron microscope image of the silicon nitride ceramic balls obtained in comparative example 1.
Detailed Description
The following examples are provided for a better understanding of the present invention and are not limited to the preferred embodiments described herein, but are not intended to limit the scope of the invention, any product which is the same or similar to the present invention, whether in light of the present teachings or in combination with other prior art features, falls within the scope of the present invention.
The specific experimental procedures or conditions are not noted in the examples and may be followed by the operations or conditions of conventional experimental procedures described in the literature in this field.
Example 1
The embodiment provides a silicon nitride ceramic, which is prepared by the following steps:
(1) 1kg of magnesium oxide, 1kg of yttrium oxide, 1kg of lanthanum oxide, 1kg of titanium carbide and 96kg of silicon nitride are taken as powder materials, 100kg of absolute ethyl alcohol is taken as a dispersion medium, 220kg of silicon nitride grinding balls are taken as a grinding medium, and the powder materials are put into a roller mill with a silicon nitride ceramic lining for ball milling and mixing, the mixing time is 24 hours, and the rotating speed is 1500r/min during mixing to obtain mixed slurry;
(2) Pouring the mixed slurry into a circulating stirring mill, adding 5kg of binder PVB (polyvinyl butyral) Ding Quanzhi, and carrying out circulating stirring for 4 hours at a rotating speed of 1500r/min to obtain slurry containing the binder;
(3) Preparing granulating powder from slurry containing binder by adopting a centrifugal spray drying mode; the frequency of the centrifugal atomizer is 80Hz, the temperature of the air inlet is 220 ℃, the temperature of the air outlet is 110 ℃, the prepared granulating powder is in the shape of apples with concave two ends, and the stacking density is 0.91g/m 3 ；
(4) Pressing the granulating powder into 47.625mm silicon nitride ceramic ball biscuit by adopting a dry pressing forming mode, wherein the forming pressure is 30MPa;
(5) Placing the ceramic ball biscuit into a hot blast stove for glue discharging, wherein the glue discharging temperature is 470 ℃, the heating rate is 8 ℃/min, the heat preservation is carried out for 12 hours, then the ceramic ball biscuit is naturally cooled, and the ceramic ball biscuit is taken out when the temperature is reduced to below 60 ℃ to obtain the silicon nitride ceramic ball biscuit after glue discharging;
(6) Cold isostatic pressing is carried out on the silicon nitride ceramic ball biscuit after the glue discharge, the cold isostatic pressure is 120MPa, and the pressure maintaining time is 120s;
(7) Uniformly placing the cold and equal silicon nitride ceramic ball biscuit in a graphite crucible scattered with boron nitride powder, sieving the boron nitride powder with a grain size of 120 meshes, placing the graphite crucible in an atmosphere pressure sintering furnace for semi-sintering, and adopting nitrogen pressurization protection in a semi-sintering process, wherein the specific process is as follows: heating from room temperature to 1300 ℃ at a heating rate of 8 ℃ and nitrogen pressure of 1.6MPa; raising the temperature from 1300 ℃ to 1520 ℃ at a temperature raising rate of 5 ℃ and the nitrogen pressure of 6.2MPa; after 8h of heat preservation at 1520 DEG CThe temperature is reduced to 1100 ℃ at a cooling rate of 8 ℃/min, and the nitrogen pressure is 1.4MPa; when the temperature is reduced to 1100 ℃, natural cooling is adopted under normal pressure, and when the temperature is reduced to below 60 ℃, a furnace door is opened, thus obtaining a semi-burned silicon nitride ceramic ball blank, wherein the ball density of the semi-burned blank is 2.72g/m 3 The density is 84%;
(8) Grinding the semi-burned silicon nitride ceramic ball blank according to the size of a design drawing, clamping the semi-burned silicon nitride ceramic ball blank on a machine tool by adopting a tool, machining by adopting an 80-mesh diamond grinding wheel when the machining allowance is more than 300 mu m, and machining by adopting a 120-mesh diamond grinding plate when the feeding amount is 20 mu m/time and the machining allowance is less than or equal to 300 mu m, wherein the rotating speed of a main shaft is 120r/min, the axial pressurization is 12kN, and the machining precision of the semi-burned blank is +/-15 mu m;
(9) Re-sintering the ground semi-sintered silicon nitride ceramic ball blank, heating to a sintering temperature of 1780 ℃ at a heating rate of 6 ℃/min under the condition of nitrogen pressure of 200MPa, and preserving heat for 1.5h; then under the condition of 100MPa of nitrogen pressure, the temperature is reduced from 1780 ℃ to 1400 ℃ at a temperature reduction rate of 5 ℃/min, the normal pressure natural temperature reduction is adopted after 1400 ℃, and the furnace door is opened when the temperature is lower than 60 ℃, thus obtaining the densified sintered silicon nitride ceramic ball blank with the density of 3.254g/cm 3 The machining allowance is 246 mu m, and the diameter variation is 0.03mm at the maximum value;
(10) Placing the densified sintered blank on a vertical ball grinder for fine grinding and lapping, adopting a structural plate for fine grinding when the machining allowance is more than or equal to 20 mu m, wherein the granularity of a grinding medium is 180 meshes, the rotating speed of a main shaft is 40r/min, and the axial pressure is 10kN; when the machining allowance is less than 20 mu m, adopting a structural plate for lapping, wherein the granularity of a grinding medium is 340 meshes, the rotating speed of a main shaft is 40r/min, and the axial pressure is 5kN;
(11) The scanning electron microscope picture of the silicon nitride ceramic ball prepared by the method is shown in figure 1, the Vickers hardness (HV 10) is 1540HV, and the fracture toughness (MPa.m) 1/2 ) The bending strength is 960MPa, the processing precision is 47.625mm diameter silicon nitride ceramic ball with G20 grade specified in GB/T308.2-2010, the fatigue test is 220h, the crushing load ratio is 46%, and the preparation processing period is 25d.
Example 2
The embodiment provides a silicon nitride ceramic, which is prepared by the following steps:
(1) 2kg of magnesium oxide, 2.5kg of yttrium oxide, 1.5kg of lanthanum oxide, 2kg of titanium carbide and 92kg of silicon nitride are taken as powder materials, 100kg of absolute ethyl alcohol is taken as a dispersion medium, 220kg of silicon nitride grinding balls are taken as a grinding medium, and the powder materials are put into a roller mill with a silicon nitride ceramic lining for ball milling and mixing, the mixing time is 24 hours, and the rotating speed is 1500r/min during mixing to obtain mixed slurry;
(2) Pouring the mixed slurry into a circulating stirring mill, adding 5kg of binder PVB, and carrying out circulating stirring for 4 hours at a rotating speed of 1500r/min to obtain slurry containing the binder;
(3) Preparing granulating powder from slurry containing binder by adopting a centrifugal spray drying mode; the frequency of the centrifugal atomizer is 100Hz, the temperature of the air inlet is 220 ℃, the temperature of the air outlet is 110 ℃, the prepared granulating powder is in the shape of apples with concave two ends, and the stacking density is 0.89g/m 3 ；
(4) Pressing the granulating powder into 11.112mm silicon nitride ceramic ball biscuit by adopting a dry pressing forming mode, and forming the granulating powder at the pressure of 20MPa;
(5) Placing the ceramic ball biscuit into a hot blast stove for glue discharging, wherein the glue discharging temperature is 420 ℃, the heating rate is 12 ℃/min, the heat preservation is carried out for 8 hours, then the ceramic ball biscuit is naturally cooled, and the ceramic ball biscuit is taken out when the temperature is reduced to below 60 ℃ to obtain a silicon nitride ceramic ball biscuit after glue discharging;
(6) Cold isostatic pressing is carried out on the silicon nitride ceramic ball biscuit after the glue discharge, the cold isostatic pressure is 120MPa, and the pressure maintaining time is 120s;
(7) Uniformly placing the cold and equal silicon nitride ceramic ball biscuit in a graphite crucible scattered with boron nitride powder, sieving the boron nitride powder with a grain size of 120 meshes, placing the graphite crucible in an atmosphere pressure sintering furnace for semi-sintering, and adopting nitrogen pressurization protection in a semi-sintering process, wherein the specific process is as follows: heating from room temperature to 1300 ℃ at a heating rate of 12 ℃ and nitrogen pressure of 0.8MPa; raising the temperature from 1300 ℃ to 1480 ℃ at a temperature raising rate of 8 ℃ and nitrogen pressure of 4.2MPa; after heat preservation at 1480 ℃ for 6 hours, the temperature is reduced to 1100 ℃ at a cooling rate of 12 ℃/min, and the nitrogen pressure is 1.4MPa; when the temperature is highCooling to 1100 deg.c with normal pressure, and opening the furnace to obtain semi-burnt silicon nitride ceramic ball blank with ball density of 2.76g/m 3 The density is 85%;
(8) Grinding the semi-burned silicon nitride ceramic ball blank according to the size of a design drawing, clamping the semi-burned silicon nitride ceramic ball blank on a machine tool by adopting a tool, machining by adopting a 120-mesh diamond grinding wheel when the machining allowance is more than 300 mu m, and machining by adopting a 180-mesh diamond grinding plate when the feeding amount is 10 mu m/time and the machining allowance is less than or equal to 300 mu m, wherein the rotating speed of a main shaft is 80r/min, the axial pressurization is 8kN, and the machining precision of the semi-burned blank is +/-15 mu m;
(9) Re-sintering the ground semi-sintered silicon nitride ceramic ball blank, heating to a sintering temperature of 1780 ℃ at a heating rate of 6 ℃/min under the condition of nitrogen pressure of 200MPa, and preserving heat for 1.5h; then under the condition of 100MPa of nitrogen pressure, the temperature is reduced from 1780 ℃ to 1400 ℃ at a temperature reduction rate of 5 ℃/min, the normal pressure natural temperature reduction is adopted after 1400 ℃, and the furnace door is opened when the temperature is lower than 60 ℃, thus obtaining the densified sintered silicon nitride ceramic ball blank with the density of 3.260g/cm 3 The machining allowance is 102 mu m, and the diameter variation is 0.008mm at the maximum value;
(10) Placing the densified sintered blank on a vertical ball grinder for fine grinding and lapping, and adopting a structural plate for fine grinding when the machining allowance is more than or equal to 20 mu m, wherein the granularity of a grinding medium is 260 meshes, the rotating speed of a main shaft is 40r/min, and the axial pressure is 6kN; when the machining allowance is less than 20 mu m, adopting a structural plate for lapping, wherein the granularity of a grinding medium is 380 meshes, the rotating speed of a main shaft is 25r/min, and the axial pressure is 1kN;
(11) The silicon nitride ceramic ball prepared by the method has the Vickers hardness (HV 10) of 1510HV and fracture toughness (MPa.m) 1/2 ) The bending strength was 900MPa and the processing precision was 11.112mm diameter silicon nitride ceramic balls of grade G10 specified in GB/T308.2-2010 with a crushing load ratio of 67%, and the preparation process period was 20d.
Example 3
The embodiment provides a silicon nitride ceramic, which is prepared by the following steps:
(1) 1kg of magnesium oxide, 1.5kg of yttrium oxide, 1.5kg of lanthanum oxide, 2kg of titanium carbide and 94kg of silicon nitride are taken as powder materials, 100kg of absolute ethyl alcohol is taken as a dispersion medium, 220kg of silicon nitride grinding balls are taken as a grinding medium, and the powder materials are put into a roller mill with a silicon nitride ceramic lining for ball milling and mixing, the mixing time is 24 hours, and the rotating speed is 1500r/min during mixing to obtain mixed slurry;
(2) Pouring the mixed slurry into a circulating stirring mill, adding 5kg of binder PVB, and carrying out circulating stirring for 4 hours at a rotating speed of 1500r/min to obtain slurry containing the binder;
(3) Preparing granulating powder from slurry containing binder by adopting a centrifugal spray drying mode; the frequency of the centrifugal atomizer is 90Hz, the temperature of the air inlet is 210 ℃, the temperature of the air outlet is 105 ℃, the prepared granulating powder is in the shape of apples with concave two ends, and the stacking density is 0.90g/m 3 ；
(4) Pressing the granulating powder into 36.512mm silicon nitride ceramic ball biscuit by adopting a dry pressing forming mode, wherein the forming pressure is 25MPa;
(5) Placing the ceramic ball biscuit into a hot blast stove for glue discharging, wherein the glue discharging temperature is 450 ℃, the heating rate is 10 ℃/min, the heat preservation is carried out for 10 hours, then the ceramic ball biscuit is naturally cooled, and the ceramic ball biscuit is taken out when the temperature is reduced to below 60 ℃ to obtain a silicon nitride ceramic ball biscuit after glue discharging;
(6) Cold isostatic pressing is carried out on the silicon nitride ceramic ball biscuit after the glue discharge, the cold isostatic pressure is 120MPa, and the pressure maintaining time is 120s;
(7) Uniformly placing the cold and equal silicon nitride ceramic ball biscuit in a graphite crucible scattered with boron nitride powder, sieving the boron nitride powder with a grain size of 120 meshes, placing the graphite crucible in an atmosphere pressure sintering furnace for semi-sintering, and adopting nitrogen pressurization protection in a semi-sintering process, wherein the specific process is as follows: heating from room temperature to 1300 ℃ at a heating rate of 10 ℃ and nitrogen pressure of 1.2MPa; heating from 1300 ℃ to 1480 ℃ at a heating rate of 6 ℃ and nitrogen pressure of 5.5MPa; after the heat preservation at 1480 ℃ for 8 hours, the temperature is reduced to 1100 ℃ at a temperature reduction rate of 10 ℃/min, and the nitrogen pressure is 1.0MPa; when the temperature is reduced to 1100 ℃, natural cooling is adopted under normal pressure, and when the temperature is reduced to below 60 ℃, a furnace door is opened, thus obtaining a semi-burned silicon nitride ceramic ball blankThe density of the semi-burned blank ball is 2.78g/m 3 The density is 85%;
(8) Grinding the semi-burned silicon nitride ceramic ball blank according to the size of a design drawing, clamping the semi-burned silicon nitride ceramic ball blank on a machine tool by adopting a tool, machining by adopting a 100-mesh diamond grinding wheel when the machining allowance is more than 300 mu m, and machining by adopting a 160-mesh diamond grinding plate when the feeding amount is 15 mu m/time and the machining allowance is less than or equal to 300 mu m, wherein the rotating speed of a main shaft is 100r/min, the axial pressurization is 10kN, and the machining precision of the semi-burned blank is +/-15 mu m;
(9) Re-sintering the ground semi-sintered silicon nitride ceramic ball blank, heating to a sintering temperature of 1780 ℃ at a heating rate of 6 ℃/min under the condition of nitrogen pressure of 200MPa, and preserving heat for 1.5h; then under the condition of 100MPa of nitrogen pressure, the temperature is reduced from 1780 ℃ to 1400 ℃ at a temperature reduction rate of 5 ℃/min, the normal pressure natural temperature reduction is adopted after 1400 ℃, and the furnace door is opened when the temperature is lower than 60 ℃, thus obtaining the densified sintered silicon nitride ceramic ball blank with the density of 3.256g/cm 3 The machining allowance is 182 mu m, and the maximum value of the diameter variation is 0.022mm;
(10) Placing the densified sintered blank on a vertical ball grinder for fine grinding and lapping, and adopting a structural plate for fine grinding when the machining allowance is more than or equal to 20 mu m, wherein the granularity of a grinding medium is 220 meshes, the rotating speed of a main shaft is 40r/min, and the axial pressure is 8kN; when the machining allowance is less than 20 mu m, adopting a structural plate for lapping, wherein the granularity of a grinding medium is 360 meshes, the rotating speed of a main shaft is 25r/min, and the axial pressurization is 3kN;
(11) The silicon nitride ceramic ball prepared by the method has the Vickers hardness (HV 10) of 1535HV and fracture toughness (MPa.m) 1/2 ) The bending strength was 920MPa and the processing precision was 36.512mm diameter and 54% crushing load ratio of the G20 grade silicon nitride ceramic balls specified in GB/T308.2-2010, respectively, to prepare a 22d processing cycle.
Comparative example 1
The difference between this comparative example and example 1 is that the cold-and-equal silicon nitride ceramic pellet obtained in step (6) of example 1 is put into an atmosphere pressure sintering furnace to be subjected to air pressure sintering at 1780 ℃ for 4 hours under nitrogen pressure of 10MPa, and then the ceramic pellet blank is obtained by performing post-treatment by adopting the hot isostatic pressing process of step (9) of example 1, and the silicon nitride ceramic pellet with the diameter of 47.625mm is obtained after processing, and a scanning electron microscope picture of the silicon nitride ceramic pellet is shown in fig. 2.
As can be seen by comparing fig. 1 and fig. 2, compared with the GPS fired sample in comparative example 1, the sample fired by the semi-firing process in example 1 has fine grains, incomplete development, mostly short rods with larger length-diameter ratio, lower hardness and certain toughness; by controlling the semi-sintering process, the development of silicon nitride crystal grains can be effectively controlled, and the crystal grain development is more uniform, so that the semi-sintered blank has higher toughness (more than 6.0) and lower strength (1100 HV), and is only about 73% of the hardness of the sintered body, thereby being beneficial to cutting the sintered body. And preparing a blank conforming to the semi-sintering process through controlling the semi-sintering process.
Comparative example 2
The difference between this comparative example and example 2 is that the cold-and-equal silicon nitride ceramic pellet obtained in step (6) of example 2 is put into an atmosphere pressure sintering furnace to be subjected to air pressure sintering at 1780 ℃ for 4 hours under nitrogen pressure of 10MPa, and then the ceramic pellet blank is obtained by performing post-treatment by adopting the hot isostatic pressing process of step (9) of example 2, and the silicon nitride ceramic pellet with the diameter of 11.112mm is obtained after processing.
Comparative example 3
The difference between this comparative example and example 3 is that the cold-and-equal silicon nitride ceramic pellet obtained in step (6) of example 3 is put into an atmosphere pressure sintering furnace to be subjected to air pressure sintering at 1780 ℃ for 4 hours under nitrogen pressure of 10MPa, and then the ceramic pellet blank is obtained by performing post-treatment by adopting the hot isostatic pressing process of step (9) of example 3, and the silicon nitride ceramic pellet with the diameter of 36.512mm is obtained after processing.
Comparative example 4
The difference between the comparative example and the example 1 is that the specific process of semi-burning in the step (7) is changed, the temperature is raised to 1520 ℃ at the heating rate of 8 ℃/min, the heat is preserved for 8 hours, and the nitrogen pressure is 6.2MPa; then the temperature is reduced to 1100 ℃ at a cooling rate of 8 ℃/min, and the nitrogen pressure is 1.4MPa; when the temperature is reducedNaturally cooling to 1100 deg.c with normal pressure, and opening the furnace to obtain silicon nitride ceramic blank with density of 2.56g/m 3 The density is 79%.
Comparative example 5
The difference between the comparative example and the example 1 is that the specific process of semi-burning in the step (7) is changed, firstly, the temperature is increased to 1300 ℃ from normal temperature at the heating rate of 8 ℃/min, and the nitrogen pressure is 1.6MPa; then heating to 1520 ℃ at a heating rate of 5 ℃/min, wherein the heating rate is 5 ℃/min, and the nitrogen pressure is 6.2MPa; preserving heat at 1520 deg.C for 8 hr, naturally cooling under normal pressure, and opening furnace door when temperature is reduced below 60 deg.C to obtain silicon nitride ceramic blank with density of 2.62g/m 3 The density is 81%.
Comparative example 6
The difference between the comparative example and the example 1 is that the specific process of semi-burning in the step (7) is changed, the temperature is raised to 1520 ℃ at the heating rate of 8 ℃/min, the heat is preserved for 8 hours, and the nitrogen pressure is 6.2MPa; then adopting normal pressure natural cooling to cool, when the temperature is reduced to below 60 ℃, opening a furnace door to obtain a silicon nitride ceramic blank with the density of 2.46g/m 3 The density is 76%.
Test example 1
Performing performance tests on the semi-burned silicon nitride ceramic ball blank obtained in the step (7) in the examples 1-3 and the silicon nitride ceramic ball blank obtained after the air pressure sintering in the comparative examples 1-3, and testing the toughness and hardness of the semi-burned silicon nitride ceramic ball blank, wherein the requirements in GB/T23806 and GB/T16534 are adopted, and the specific requirements are shown in the following table 1:
table 1 toughness and hardness of intermediate blanks
As can be seen from the table, the semi-burned silicon nitride ceramic ball blank obtained in the embodiment of the application has obviously lower hardness than that of the comparative example, and is convenient to process. Meanwhile, the toughness is lower than that of the comparative example, and the sintering temperature of the semi-sintering process is low, so that the densification sintering temperature is not reached yet, and the processing performance of the semi-sintered blank is not affected. From the subsequent test example 2, it is understood that the later performance of the silicon nitride ceramic is determined by the final sintering temperature and sintering schedule, and the semi-sintered silicon nitride ceramic ball blank obtained in the example is fully sintered after that, thereby improving the toughness and hardness thereof.
Test example 2
The silicon nitride ceramic blanks prepared in examples 1-3 and comparative examples 1-6 were tested, density was measured by an archimedes drainage method, vickers hardness of the sample block was measured by a method specified in GB/T16534-2009, fracture toughness was measured by an indentation method, and flexural resistance of the sample block was measured by a method specified in GB/T6569; the rolling bearing ball part 2 is adopted in GB/T308.1-2013: the method specified in the ceramic ball is used for testing the precision grade, and a testing machine is used for testing the crushing load ratio.
TABLE 2 silicon nitride ceramic blank test results
| Density g/cm3 | Vickers hardness/HV | Fracture toughness/(MPa.m1/2) | Flexural Strength/MPa | Precision grade | Preparation processing time/day | Crush load ratio | |
| Example 1 | 3.254 | 1540 | 7.2 | 960 | G20 | 25 | 46% |
| Comparative example 1 | 3.252 | 1480 | 6.9 | 890 | G20 | 45 | 31% |
| Example 2 | 3.260 | 1510 | 6.8 | 900 | G10 | 20 | 67% |
| Comparative example 2 | 3.261 | 1460 | 6.8 | 850 | G10 | 35 | 50% |
| Example 3 | 3.256 | 1535 | 7.1 | 920 | G20 | 22 | 54% |
| Comparative example 3 | 3.255 | 1490 | 6.9 | 880 | G20 | 40 | 41% |
| Comparative example 4 | 3.252 | 1485 | 6.8 | 895 | G20 | 30 | 39% |
| Comparative example 5 | 3.249 | 1450 | 6.6 | 870 | G20 | 25 | 34% |
| Comparative example 6 | 3.245 | 1445 | 6.6 | 860 | G20 | 30 | 35% |
As can be seen from the data in the table, the Vickers hardness, fracture toughness/bending strength and crushing load ratio of the silicon nitride ceramic balls prepared by semi-firing and re-sintering in the examples of the invention are superior to those of the silicon nitride ceramic balls obtained in the comparative examples, and the preparation period is shorter.
As can be seen from the comparison of test example 2 and test example 1, the hardness and toughness of examples 1 to 3 in test example 1 are lower than those of comparative examples 1 to 3, because of the artificial control by the semi-firing process; however, in test example 2, the physical properties of the article after hot isostatic pressing were higher in the examples than in the comparative examples. The semi-sintering process adopted by the embodiment of the application is actually optimizing the sintering system, the key temperature node for crystal form conversion is controlled through the semi-sintering process, the conversion rate of silicon nitride can be effectively improved, meanwhile, the crystal form is ensured to develop into a short columnar crystal form, through channels are formed in the crystal form, pressure and heat can be fully conducted into the silicon nitride ceramic during re-sintering due to the existence of the channels, on one hand, the silicon nitride crystal is fully developed, on the other hand, the uniformity of the silicon nitride ceramic is improved, the density of a final product is higher, and meanwhile, the physical property of the final product is excellent. The semi-sintering process can not only effectively improve the processing efficiency of the silicon nitride ceramic, but also fully exert the advantages of the re-sintering process, so that the final performance of the product is improved. In comparison, the GPS sintering process is adopted in comparative examples 1-3, and then the hot isostatic pressing sintering is carried out, so that the improvement effect of heat and the like on the material is not as obvious as the improvement effect of the performance of the sintered product after semi-sintering. In addition, the final properties of the products are also affected by adopting different semi-burning processes, and the properties of the final products of comparative examples 4 to 6 are inferior to those of example 1.
It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations or modifications of the above teachings will be apparent to those of ordinary skill in the art. It is not necessary here nor is it exhaustive of all embodiments. While still being apparent from variations or modifications that may be made by those skilled in the art are within the scope of the invention.
Claims (7)
1. The preparation method of the silicon nitride ceramic is characterized by comprising the following steps:
s1: preparing slurry;
s2: granulating the slurry, and then pressing the slurry into a silicon nitride ceramic ball biscuit;
s3: cold isostatic pressing after removing the adhesive from the ceramic ball biscuit;
s4: semi-firing the ceramic ball biscuit after cold isostatic pressing to obtain a semi-fired blank;
s5: re-sintering the semi-sintered blank to obtain a sintered blank;
s6: processing the sintered blank to obtain the silicon nitride ceramic;
in the step S4, the density of the semi-burned blank is 2.6-2.9 g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the The density is 80% -90%;
the semi-firing includes: firstly, heating from room temperature to 1300 ℃ at a heating rate of 8-15 ℃/min, and carrying out nitrogen pressure of 0.4-2.0 MPa; then heating from 1300 ℃ to 1400-1600 ℃ at a speed of 4-10 ℃/min, preserving heat for 4-10 hours, and keeping nitrogen pressure at 1.0-10.0 MPa; then cooling from 1400-1600 ℃ to 1100 ℃ at a cooling rate of 6-12 ℃/min, and the nitrogen pressure is 0.4-2.0 MPa; finally, naturally cooling;
the step S4 and the step S5 also comprise the step of grinding the semi-burned silicon nitride ceramic ball blank according to the design drawing size of the semi-burned blank;
when the machining allowance is more than 300 mu m, adopting a diamond grinding wheel with 80-120 meshes to machine, wherein the feeding amount is 10-20 mu m/time;
when the machining allowance is less than or equal to 300 mu m, machining by adopting a diamond grinding plate with 120-180 meshes, wherein the rotating speed of a main shaft is 80-120 r/min, and axially pressurizing by 8-12 kN;
the processing in step S6 includes fine grinding processing and lapping processing;
when the machining allowance is more than or equal to 20 mu m, adopting a structural plate for fine grinding, wherein the granularity of a grinding medium is 180-280 meshes, the rotating speed of a main shaft is 20-80 r/min, and the axial pressurization is 3-15 kN;
when the machining allowance is smaller than 20 mu m, adopting a structural plate for lapping, wherein the granularity of a grinding medium is 320-400 meshes, the rotating speed of a main shaft is 20-80 r/min, and the axial pressurization is 0.5-5 kN.
2. The method according to claim 1, wherein,
in step S1, the raw material slurry includes, in parts by mass:
0.5-3 parts of magnesium oxide;
0.5-3 parts of yttrium oxide;
0.5-3 parts of lanthanum oxide;
0.5-3 parts of titanium carbide;
88-98 parts of silicon nitride;
80-120 parts of absolute ethyl alcohol;
180-220 parts of silicon nitride grinding balls;
4-6 parts of a binder.
3. The method according to claim 2, wherein,
the preparation method of the slurry comprises the steps of taking magnesium oxide, yttrium oxide, lanthanum oxide, titanium carbide and silicon nitride as powder materials, taking absolute ethyl alcohol as a dispersion medium, taking silicon nitride grinding balls as a grinding medium, ball-milling and mixing for 18-36 h, wherein the rotating speed is 1200-1500 r/min during mixing; and adding a binder, and circularly stirring for 2-6 hours to obtain the slurry, wherein the rotating speed is 1300-1800 r/min during the circular stirring.
4. A process according to claim 3, wherein,
in the step S2, the granulating step is to prepare granulated powder from slurry by adopting a centrifugal spray drying mode, wherein a centrifugal atomizer is 80-120 Hz, the temperature of an air inlet is 180-220 ℃, the temperature of an air outlet is 80-100 ℃, and the bulk density of the granulated powder is 0.88-0.92g/m 3 ；
The diameter of the pressed silicon nitride ceramic ball biscuit is 10-150 mm, and the forming pressure is 10-40 MPa.
5. The method according to claim 4, wherein,
in the step S3, the glue is discharged by heating to 380-480 ℃ at a heating rate of 6-15 ℃/min, preserving heat for 8-16 h, and then naturally cooling;
the cold isostatic pressing condition is that the pressure is 120MPa and the pressure maintaining time is 120s.
6. The method according to claim 5, wherein the step of re-sintering is performed by heating to 1750 to 1850 ℃ at a heating rate of 5 to 10 ℃ and then maintaining the temperature for 1 to 2 hours at a nitrogen pressure of 120 to 220mpa; and then cooling to 1400 ℃ at a speed of 5-10 ℃/min, and naturally cooling after the nitrogen pressure is 50-150 MPa.
7. A silicon nitride ceramic produced by the production method according to any one of claims 1 to 6.
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