CN111196730B - High-thermal-conductivity silicon nitride ceramic material and preparation method thereof - Google Patents

High-thermal-conductivity silicon nitride ceramic material and preparation method thereof Download PDF

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CN111196730B
CN111196730B CN201911142254.6A CN201911142254A CN111196730B CN 111196730 B CN111196730 B CN 111196730B CN 201911142254 A CN201911142254 A CN 201911142254A CN 111196730 B CN111196730 B CN 111196730B
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silicon nitride
ceramic material
sintering
nitride ceramic
mpa
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CN111196730A (en
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曾宇平
王为得
左开慧
夏咏锋
姚冬旭
尹金伟
梁汉琴
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Shanghai Institute of Ceramics of CAS
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Abstract

The invention relates to a high thermal conductivityThe silicon nitride ceramic material comprises raw material components of alpha-Si3N4And a sintering aid; the sintering aid is metal hydride and alkaline earth metal oxide, and the total content is 2-12 mol%; the metal hydride is ZrH2(ii) a The alkaline earth metal oxide is preferably at least one of MgO, CaO and BaO.

Description

High-thermal-conductivity silicon nitride ceramic material and preparation method thereof
Technical Field
The invention relates to a silicon nitride ceramic material with high thermal conductivity and a preparation method thereof, in particular to a silicon nitride ceramic material prepared from metal hydride ZrH2And metal oxide as a sintering aid and producing Si with high thermal conductivity by gas pressure sintering3N4A method for preparing ceramic material belongs to the field of inorganic non-metallic material.
Background
With the development of electronic devices toward miniaturization, integration and high power density, heat dissipation is one of the bottlenecks in the development of electronic devices. In integrated circuits, the performance of ceramic substrates is critical to solving heat dissipation problems. Meanwhile, the ceramic substrate must have good mechanical properties to withstand the cyclic thermal stress. Silicon nitride (Si)3N4) As a structural ceramic, it is attracting attention for its excellent mechanical properties, good tribological and wear properties, excellent thermal shock resistance and relatively high electrical resistivity. Haggerty et al (J.Haggerty and A.Lightfoot Opportunities for enhancing the thermal compositions of SiC and Si3N4 ceramics through improved processing, p.475487 in Proceedings of the 19th annular Conference on Composites, Advanced Ceramics, Materials, and Structures-A: Ceramic Engineering and Science Proceedings, Volume 16, Issue 4.) predict β -Si3N4The theoretical thermal conductivity can reach 200-320 Wm-1K-1This discovery has made silicon nitride ceramics a promising candidate material for heat sink substrates in high-density high-power semiconductor devices.
For ideal beta-Si3N4For single crystals, no scattering factors such as impurities, grain boundaries and defects exist, the phonon free path is the largest, and the thermal conductivity of the single crystals is optimal. However, when silicon nitride is actually produced, addition of metal oxides such as MgO, Y is usually employed2O3、ZrO2、Al2O3And the like as a sintering aid to obtain dense silicon nitride ceramics by liquid phase sintering. alpha-Si3N4Formation of beta-Si by a dissolution precipitation process in a liquid phase3N4And the crystal grain growth and densification are realized through a liquid phase, and the liquid phase is remained in a sintering body as an intercrystalline phase with low thermal conductivity during cooling. Thus, liquid phase sintering of the resulting beta-Si3N4The ceramic consists of crystal grains and a small amount of intercrystalline phases, and phonons are scattered by various defects in the intercrystalline phases and the crystal grains, so that beta-Si is generated3N4Is much lower than the theoretical value.
Among the many defects, lattice oxygen is the most negative factor affecting the thermal conductivity of silicon nitride, and grain boundary phase content and distribution are affected by the second factor. Researchers at home and abroad improve the thermal conductivity of the silicon nitride ceramic material by promoting the growth of crystal grains and purifying crystal lattices by means of improving the sintering temperature, prolonging the heat preservation time and the like so as to reduce the crystal lattice defects. However, this method is relatively expensive and not suitable for the popularization and application of silicon nitride. On the other hand, the oxygen content in the silicon nitride lattice is closely related to the composition of the liquid phase during sintering, and if the oxygen content in the liquid phase is low during dissolution and precipitation, the solid dissolution of oxygen into β -Si is inhibited3N4A crystal lattice. Thus, researchers also often substitute oxides with non-oxides, such as MgSiN2Instead of MgO, YF is used3、Y2Si4N6C, etc. instead of Y2O3Using ZrSi2Substituted for ZrO2To regulate the liquid phase composition and reduce the oxygen content in the liquid phase to reduce beta-Si3N4The oxygen content in the crystal lattice further improves the thermal conductivity.
Disclosure of Invention
The invention aims to provide a brand new method for preparing a silicon nitride ceramic material with high thermal conductivity, which uses metal hydride ZrH for the first time2And alkaline earth metal oxide is used as a sintering aid, and the solid solution of oxygen into the silicon nitride crystal lattice is prevented by regulating and controlling the composition of a liquid phase, so that the defects in the silicon nitride crystal lattice are reduced, the scattering of phonons is reduced, and the thermal conductivity is further improved.
In one aspect, the invention provides a silicon nitride ceramic material, wherein the raw material composition of the silicon nitride ceramic material comprises alpha-Si3N4And a sintering aid; the sintering aid is metal hydride and alkaline earth metal oxide, and the total content is 2-12 mol%; the metal hydride is ZrH2The alkaline earth metal oxide is preferably at least one of MgO, CaO and BaO. Wherein a metal hydride ZrH is used2The sintering aid is used, so that the amount of oxygen introduced by the sintering aid can be reduced, the oxygen concentration in a liquid phase is reduced, oxygen is prevented from being dissolved into a silicon nitride crystal lattice in a solid solution mode, crystal defects are reduced, and phonon scattering is reduced; in addition, a metal hydride ZrH is used2As a sintering aid, the content of the amorphous phase with low thermal conductivity in the obtained silicon nitride ceramic is reduced, and the thermal conductivity is improved. Moreover, zirconium hydride can decompose simple substance Zr along with the temperature rise, and the essence is to utilize the simple substance Zr and SiO on the surface of the raw material powder2Redox removal of SiO2。
Preferably, the total content of the sintering aid is 5-10 mol%.
Preferably, the molar ratio of the metal hydride to the alkaline earth metal oxide is 1:10 to 10:1, preferably 1:5 to 5: 1.
Preferably, the thermal conductivity of the silicon nitride ceramic material is 61.25-115.18W/(m.K), the bending strength is 475-759 MPa, and the fracture toughness is 5.38-7.95 MPa.m1/2。
In another aspect, the present invention provides a method for preparing the silicon nitride ceramic material, including:
(1) weighing alpha-Si according to the raw material composition of the silicon nitride ceramic material3N4Mixing the powder and the sintering aid to obtain mixed powder;
(2) and pressing and molding the obtained mixed powder, performing pre-sintering treatment at 600-1600 ℃, and performing sintering treatment at 1780-1950 ℃ to obtain the silicon nitride ceramic material.
In the invention, metal hydride ZrH is selected2And alkaline earth metal oxide as a sintering aid to prepare a high thermal conductivity silicon nitride ceramic. Wherein the metal hydride ZrH2As an oxygen-free auxiliary agent, the introduction of oxygen can be reduced, so that the content of the low-thermal-conductivity intergranular phase in the silicon nitride sintered body is reduced, and the improvement of the thermal conductivity is facilitated. On the other hand, added metal hydride ZrH2Can be decomposed into simple substances of Zr and H in the process of pre-sintering treatment2，H2The presence of (b) reduces the partial pressure of oxygen in the furnace (formula 1: ZrH)2→Zr+H2(g) ). Further, the simple substance Zr and SiO on the surface of the silicon nitride powder2The reaction is carried out at a lower temperature during the presintering treatment to lead SiO2Reduction to SiO (g) or Si to thereby form SiO2Removal with simultaneous reaction to form ZrO2(formula 2: Zr + SiO)2→ZrO2+ SiO (g); and formula 3: zr + SiO2→ZrO2+ Si). And, H2As a strong reducing agent, the oxygen content is clearly reduced. Generated ZrO2And alkaline earth metal oxides can form low oxygen eutectic phases (exemplified by MgO, ZrO) at lower temperatures2+MgO+SiO2+α-Si3N4→β-Si3N4+ Zr-Si-Mg-O-N (liquid phase)), the low oxygen content in the liquid phase can prevent oxygen from being dissolved into the silicon nitride crystal lattice, reduce the number of defects in the crystal lattice, reduce phonon scattering, and the generated liquid phase promotes the crystal grain growth through a dissolution-precipitation mechanism, thereby being beneficial to improving the thermal conductivity.
Preferably, the mixing mode is that after wet ball milling is carried out by adopting a vacuum ball milling tank, rotary evaporation drying is carried outOr vacuum drying to obtain mixed powder; the ball milling atmosphere in the vacuum ball milling tank is vacuum atmosphere, inert atmosphere or nitrogen atmosphere. The mixing mode is adopted for preventing the metal hydride ZrH in the ball milling process or the drying process2Oxidation of (2).
Preferably, the compression molding mode is dry compression molding or/and isostatic pressing treatment, and preferably the dry compression molding is firstly carried out and then the isostatic pressing treatment is carried out; the pressure of the dry pressing is 10-50 MPa, and the pressure of the isostatic pressing is 100-300 MPa. Wherein the isostatic pressing may be cold isostatic pressing.
Preferably, the atmosphere of the pre-sintering treatment is a vacuum atmosphere, a nitrogen atmosphere or an inert atmosphere, and the inert atmosphere is an argon atmosphere; the time of the pre-sintering treatment is 1-8 hours.
Preferably, the sintering treatment mode is air pressure sintering, hot pressing sintering, spark plasma sintering, hot isostatic pressing sintering or pressureless sintering; the time of the sintering treatment is more than or equal to 2 hours; preferably, the atmosphere of the air pressure sintering is nitrogen, and the air pressure is more than or equal to 1 MPa. Wherein, the high nitrogen pressure during the air pressure sintering can avoid the decomposition of silicon nitride at high temperature (above 1780 ℃), improve the sintering activity and be beneficial to densification and grain growth.
Preferably, the temperature rise rate of the sintering treatment is 1-15 ℃/min.
Preferably, after the sintering treatment is completed, the mixture is cooled to 800-1200 ℃ at a cooling rate of less than or equal to 20 ℃/min (preferably to 1000 ℃) and then cooled to room temperature along with the furnace.
Has the advantages that:
in the present invention, a metal hydride ZrH is used2As sintering aid, metal hydride ZrH2As an oxygen-free auxiliary agent, the introduction of oxygen is reduced, the content of a glass phase in a final sintered body can be reduced, the volume fraction of the low-thermal-conductivity glass phase in the sintered body is reduced, and the thermal conductivity is improved;
in the present invention, the metal hydride ZrH is added2Can be decomposed into simple substances of Zr and H in the pretreatment process2，H2The presence of (b) reduces the partial pressure of oxygen within the furnace; in addition, the simple substances Zr and alpha-Si3N4SiO on the surface of powder2React to form ZrO2ZrO produced2And the silicon nitride and the auxiliary sintering aid alkaline earth metal oxide form a eutectic liquid phase, and the sintering of the silicon nitride is promoted through a dissolution and precipitation mechanism. This reaction promotes SiO2To block oxygen with SiO2Form of (b) solid solution into beta-Si3N4The medium crystal lattice reduces defects in the silicon nitride crystal lattice, thereby improving the thermal conductivity;
in the invention, the thermal conductivity of the obtained silicon nitride ceramic material is above 115.18W/(m.K), the bending strength can reach 759MPa, the fracture toughness can be improved, and can reach 7.95 MPa.m1/2Can meet the application requirements of the silicon nitride ceramics in the field of high-density and high-power semiconductor devices.
Drawings
FIG. 1 is a cross-sectional micro-topography of the silicon nitride ceramic material prepared in example 4;
FIG. 2 is a cross-sectional micro-topography of the silicon nitride ceramic material prepared in example 5.
Detailed Description
The present invention is further illustrated by the following examples, which are to be understood as merely illustrative and not restrictive.
In this disclosure, a metal hydride ZrH is first used2And alkaline earth metal oxide as sintering aid to prepare high heat conductivity silicon nitride ceramic. Wherein the metal hydride ZrH2As an oxygen-free auxiliary agent, Zr element can be introduced under the premise of not introducing oxygen, so that the content of the low-thermal-conductivity intergranular phase in the silicon nitride sintered body can be reduced, and the thermal conductivity can be improved. On the other hand, added metal hydride ZrH2Can be decomposed into simple substances Zr and H in the pretreatment process2，H2The presence of (b) reduces the partial pressure of oxygen within the furnace; in addition, the simple substance Zr and SiO on the surface of the silicon nitride powder2The reaction is carried out at a lower temperature during the presintering treatment to lead SiO2Reduction to SiO (g) or Si to thereby form SiO2Removal with simultaneous reaction to form ZrO2. Generated ZrO2And the alkaline earth metal oxide can form a eutectic liquid phase with low oxygen content at a lower temperature, the low oxygen content in the liquid phase can prevent oxygen from being dissolved into a silicon nitride crystal lattice in a solid way, the number of defects in the crystal lattice is reduced, phonon scattering is reduced, and the generated liquid phase promotes the growth of crystal grains through a dissolution-precipitation mechanism, so that the heat conductivity is favorably improved. Wherein the alkaline earth metal oxide is at least one selected from BaO, MgO, CaO, etc.
The method for producing the silicon nitride ceramic material will be described as an example when the alkaline earth metal oxide is MgO.
alpha-Si is mixed3N4And uniformly mixing the powder and the sintering aid to obtain mixed powder. Wherein the sintering aid comprises metal hydride ZrH2And MgO. During pre-sintering treatment, ZrH2Firstly, the decomposition is carried out to generate simple substances Zr and H2Simple substance Zr and alpha-Si3N4SiO on the surface of powder2React to form ZrO2ZrO produced2And forming a low-viscosity liquid phase with MgO in the subsequent temperature rise process to promote the sintering of the silicon nitride. Metal hydride ZrH2The molar ratio of MgO to MgO may be (1:10) to (10:1), preferably (1:5) to (5: 1). When the metal hydride ZrH2And MgO in a molar ratio of (1:5) to (5:1), the amount of the catalyst is maximized in comparison with the amount of alpha-Si3N4SiO on the surface of powder2Reaction takes place and the metal hydride ZrH2With SiO2ZrO formed by reaction2Forming eutectic liquid phase with MgO in subsequent temperature raising process, and promoting beta-Si by dissolution and precipitation mechanism3N4And (4) growing crystal grains.
In alternative embodiments, α -Si3N4The particle size of the powder can be 0.1-2 μm, and the oxygen content is less than 2 wt%; metal hydride ZrH2The particle size of the particles is 0.1-20.0 μm; the particle size of the MgO powder may be 10nm to 5 μm.
In an alternative embodiment, α -Si3N4The proportion of the powder and the sintering aid is 88mol percent to 12mol percent to 98mol percent to 2mol percent, preferably 90mol percent to 10mol percent to 95mol percent to 5mol percent, and the sum of the proportion of the components is 100 percent. The addition amount of the sintering aid is too small to be completely removedα-Si3N4SiO on the surface of powder2And a sufficient amount of low viscosity liquid phase cannot be formed, the sample is difficult to densify; too much addition of the sintering aid increases the content of low thermal conductivity grain boundary phase, and affects the thermal conductivity.
In an alternative embodiment, α -Si is added3N4The powder and the sintering aid are ball-milled by a vacuum ball-milling tank wet method, and the atmosphere in the ball-milling tank can be vacuum or filled with Ar and N2And drying the obtained slurry by rotary evaporation or vacuum drying, and screening to obtain mixed powder. As an example of ball milling mixing, include: alpha-Si is mixed3N4The powder and the sintering aid are mixed, and the uniformly mixed powder is obtained through the processes of ball milling, drying and sieving. Ball milling material mixing adopts a wet ball milling process in a vacuum ball milling tank, and the atmosphere in the ball milling tank can be vacuum or filled with Ar and N2. Wet ball milling uses alcohol as a solvent, and comprises the following materials: the solvent ratio can be (1:1) - (3:1), material: the ball ratio can be (1:1) - (5:1), the ball milling revolution is 200-500 rpm, and the ball milling time is 4-20 h. Drying by rotary evaporation drying or vacuum drying, wherein the whole drying process can be carried out in vacuum, Ar or N2And the like in a protective atmosphere. Wherein the drying temperature can be 50-120 ℃, and the drying time can be 8-24 h. The number of the sieved meshes can be 60-300 meshes.
And pressing and molding the mixed powder to obtain a blank. The press forming may include: and sequentially carrying out dry pressing and isostatic pressing. Wherein, the pressure of dry pressing molding is 10-50 MPa, and the pressure of isostatic pressing treatment is 100-300 MPa. In a preferred embodiment, the isostatic pressing is a cold isostatic pressing.
And placing the blank body in an inert atmosphere, a nitrogen atmosphere or a vacuum environment, and performing pre-sintering treatment at the temperature of 600-1600 ℃ for 1-8 hours. Wherein the temperature of the pre-sintering treatment is preferably 1000-1500 ℃, and more preferably 1000-1400 ℃. The high presintering treatment temperature can accelerate the ZrH of the metal hydride2And alpha-Si3N4SiO on the surface of powder2The reaction rate and the heat preservation time are preferably 2-8h, and the metal hydride ZrH can be ensured by prolonging the heat preservation time2And alpha-Si3N4SiO on the surface of powder2The reaction was complete. The pre-sintering treatment may be performed in a vacuum atmosphere or under Ar.
And sintering the pre-sintered body at 1780-1950 deg.c to obtain high heat conductivity silicon nitride ceramic. The time of the air pressure sintering is at least 2 hours. Wherein, the atmosphere of the pressure sintering can be nitrogen atmosphere. High nitrogen pressure ensures that the silicon nitride does not decompose above 1780 ℃. The silicon nitride has higher sintering activity at 1780 ℃ and is beneficial to the growth and development of crystal grains. The preferred pressure sintering temperature is 1850-1900 ℃ for 2-12 hours. The pressure sintering can be carried out under a pressurized inert atmosphere, and the pressurized pressure can be 1-10 MPa. As an example of the gas pressure sintering, the process conditions include: with N2Heating to 1780-1950 ℃ at a speed of 1-15 ℃/min under the condition of 1-10 MPa of air pressure in a sintering atmosphere, and preserving the temperature for more than 2 hours. The preferable heating rate can be 3-10 ℃/min.
Preferably, after the air pressure sintering is finished, the silicon nitride ceramic is further cooled to room temperature at a specific cooling rate, and the high-thermal-conductivity silicon nitride ceramic is obtained. For example, after sintering, the mixture can be cooled to 1000-1400 ℃ (preferably 1200 ℃) at a cooling rate of 1-15 ℃/min, and then cooled to room temperature along with the furnace.
According to the sintering mechanism of silicon nitride ceramics and literature reports, the thermal conductivity can be further improved by adopting the methods of increasing the pressure and the sintering temperature, prolonging the heat preservation time and slowing down the cooling rate, and obviously, the invention is not limited to the pressure and the sintering temperature range, the heat preservation time and the cooling rate. Also, the present invention should not be limited to the gas pressure sintering, and the desired effects can be obtained by a widely used method of pressureless sintering, hot press sintering, hot isostatic pressing sintering, or thermal treatment after spark plasma sintering.
In the present invention, the bulk density of the sample is measured by the Ahimedes method; si3N4The thermal conductivity of the ceramic material is calculated by the following formula: k is Cpρ · α; wherein ρ is the bulk density of the sample and has a unit of g cm-3α isThermal diffusion coefficient in cm2·s-1C, measured using Netzsch LFA 467pThe heat capacity of the silicon nitride ceramic material is very small with the change of the composition and the microstructure, and can be regarded as a constant, and 0.68J (g.K) is adopted in the invention-1. The thermal conductivity of the obtained silicon nitride ceramic material can be 61.25-115.18W/(m.K).
In the present invention, Si was measured by a three-point bending method using an Instron-5566 Universal Material testing machine3N4The bending strength of the ceramic material is 30mm in span and 0.5mm min in loading rate-1Each data point was tested on 6 bars and then averaged.
The bending strength of the obtained silicon nitride ceramic material can be 475-759 MPa.
In the present invention, the fracture toughness was measured by a single edge notched beam method (SENB), the sample was machined to a size of 3.0 × 6.0 × 30.0mm, the notch width was about 0.25mm, the notch depth was about 3mm, and the fracture toughness of the sample was measured by a three-point bending method on a universal material testing machine. The test span was 24.0mm, the loading rate was 0.05mm/min, 6 specimens were selected for each sample and measured for mean and standard deviation.
The fracture toughness of the obtained silicon nitride ceramic material can be 5.38-7.95 MPa.m1/2。
It should be noted that although the above-described process for preparing a silicon nitride ceramic material is described using MgO as an example, other alkaline earth metal oxides such as BaO, CaO, and the like are also applicable to the above-described process.
The present invention will be described in detail by way of examples. It is also to be understood that the following examples are illustrative of the present invention and are not to be construed as limiting the scope of the invention, and that certain insubstantial modifications and adaptations of the invention by those skilled in the art may be made in light of the above teachings. The specific process parameters and the like of the following examples are also only one example of suitable ranges, i.e., those skilled in the art can select the appropriate ranges through the description herein, and are not limited to the specific values exemplified below.
Example 1
With 0.5 mol% ZrH2And 1.5 mol% MgO as sintering aid, and 98 mol% alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 250 MPa; putting the obtained blank into a BN crucible, preserving heat for 4h at 300 ℃ in Ar atmosphere, heating to 600 ℃ and preserving heat for 4h for pretreatment; then sintering the pre-sintered blank at 1800 ℃ of air pressure, wherein the heating rate is 10 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in the example 1 has a thermal conductivity of 66.3W/(m.K), a three-point bending strength of 759 + -42 MPa, and a fracture toughness of 7.35 + -0.24 MPa.m1/2。
Example 2
With 0.5 mol% ZrH2And 1.5 mol% of MgO as a sintering aid, and 98 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 250 MPa; putting the obtained blank into a BN crucible, preserving heat for 4 hours at 500 ℃ in Ar atmosphere, heating to 1000 ℃ and preserving heat for 4 hours for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the heating rate is 10 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in example 2 has a thermal conductivity of 105.08W/(m.K), a three-point bending strength of 539 + -20 MPa, and a fracture toughness of 6.75 + -0.24 MPa.m1/2。
Example 3
With 2.5 mol% ZrH2And 1.5 mol% MgO as sintering aid, and 96 mol% alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry-pressing under 30MPa, and then under 300MPaCarrying out cold isostatic pressing treatment; putting the obtained blank into a BN crucible, preserving heat for 4h at 400 ℃ under vacuum, heating to 1400 ℃ and preserving heat for 6h for pretreatment; then sintering the pre-sintered blank body at 1850 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1000 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in the embodiment 3 has a thermal conductivity of 78.90W/(m.K), a three-point bending strength of 621 + -14 MPa, and a fracture toughness of 7.72 + -0.23 MPa.m1/2。
Example 4
With 2mol% of ZrH2And 2mol% of MgO as a sintering aid, and 96 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 4 hours at 600 ℃ in a vacuum environment, heating to 1300 ℃ and preserving heat for 8 hours for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 2MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 5 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in example 4 has a thermal conductivity of 115.18W/(m.K), a three-point bending strength of 547 + -26 MPa, and a fracture toughness of 7.95 + -27 MPa.m1/2. The cross-sectional micro-morphology of the silicon nitride ceramic material prepared by the embodiment is shown in fig. 1, the micro-morphology shows bimodal distribution of large grains dispersed in a small grain matrix, wherein the large grains have larger size and higher long diameter ratio, which is very beneficial to the improvement of thermal conductivity.
Example 5
With 3 mol% ZrH2And 2mol% of MgO as a sintering aid, and 95 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; will be provided withPutting the obtained blank into a BN crucible, preserving heat for 2h at 500 ℃ in a vacuum environment, heating to 1300 ℃ and preserving heat for 4h for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the heating rate is 10 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1000 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in example 5 had a thermal conductivity of 110.30W/(m.K), a three-point bending strength of 564. + -. 26MPa, and a fracture toughness of 7.72. + -. 0.15 MPa.m1/2. The cross-section micro-topography of the silicon nitride ceramic material prepared by the embodiment is shown in fig. 2, large grains are sufficiently grown, the length can reach more than 50 microns, the combination part of the grains is cleaner, and the intercrystalline phase with low thermal conductivity is less.
Example 6
With 3 mol% ZrH2And 2mol% of MgO as a sintering aid, and 95 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 450 ℃ under Ar, then heating to 1500 ℃ and preserving heat for 2h for pretreatment; then sintering the pre-sintered blank body at 1850 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 2 h; after sintering, cooling to 1200 ℃ at the cooling rate of 5 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in example 5 has a thermal conductivity of 82.21W/(m.K), a three-point bending strength of 621 + -14 MPa, and a fracture toughness of 7.66 + -0.35 MPa.m1/2。
Example 7
With 4 mol% ZrH2And 3 mol% of MgO as a sintering aid, and 93 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 20MPa, and then carrying out cold isostatic pressing treatment under the pressure of 280 MPa; putting the obtained blank into a BN crucible, keeping the temperature at 300 ℃ for 2h under Ar, and heating to 10 DEG CPreserving heat for 6 hours at 00 ℃ for pretreatment; then sintering the pre-sintered blank at 1800 ℃ of air pressure, wherein the heating rate is 10 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 15 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in example 7 had a thermal conductivity of 73.60W/(m.K), a three-point bending strength of 707. + -.18 MPa, and a fracture toughness of 6.66. + -. 0.09 MPa.m1/2。
Example 8
With 5 mol% ZrH2And 5 mol% of MgO as a sintering aid, and 90 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 40MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 400 ℃ under Ar, then heating to 1100 ℃ and preserving heat for 2h for pretreatment; then sintering the pre-sintered blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 3MPa, and the heat preservation time is 4 h; after sintering, cooling to 1100 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in this example 8 has a thermal conductivity of 103.23W/(m.K), a three-point bending strength of 575. + -. 46MPa, and a fracture toughness of 6.18. + -. 0.18 MPa.m1/2。
Example 9
With 7 mol% ZrH2And 3 mol% of MgO as a sintering aid, and 90 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 600 ℃ under Ar, then heating to 1400 ℃, preserving heat for 2h and carrying out pretreatment; then sintering the pre-sintered blank at 1850 ℃ under the air pressure, wherein the heating rate is 3 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in example 9 had a thermal conductivity of 82.56W/(m.K), a three-point bending strength of 561. + -. 40MPa, and a fracture toughness of 6.71. + -. 0.17 MPa. m1/2。
Example 10
With 9 mol% ZrH2And 2mol% of MgO as a sintering aid, and 89 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 250 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 500 ℃ under Ar, then heating to 1100 ℃ and preserving heat for 6h for pretreatment; then sintering the pre-sintered blank at 1950 ℃ under the pressure of 5 ℃/min with the temperature rise rate of N2The pressure is 2MPa, and the heat preservation time is 4 h; after sintering, cooling to 1200 ℃ at the cooling rate of 15 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in this example 10 had a thermal conductivity of 107.85W/(m.K), a three-point bending strength of 475. + -. 19MPa, and a fracture toughness of 5.38. + -. 0.32 MPa. m1/2。
Example 11
With 1 mol% ZrH2And 10mol% of MgO as a sintering aid, and 89 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 40MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; putting the obtained blank into a BN crucible, preserving heat for 2h at 500 ℃ in Ar atmosphere, heating to 1400 ℃, preserving heat for 2h, and carrying out pretreatment; then sintering the pre-sintered blank at 1800 ℃ of air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 2MPa, and the heat preservation time is 2 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared in this example 11 had a thermal conductivity of 61.25W/(m.K), a three-point bending strength of 736. + -. 24MPa, and a fracture toughness of 5.38. + -. 0.31 MPa.m1/2。
Example 12
A silicon nitride ceramic material was prepared according to the process flow of example 5, with the only difference that: the alkaline earth metal oxide is CaO.
The silicon nitride ceramic material obtained in example 12 had a thermal conductivity of 106.2W/(mK), a three-point bending strength of 634. + -. 12MPa, and a fracture toughness of 8.01. + -. 0.13 MPa. m1/2。
Example 13
A silicon nitride ceramic material was prepared according to the process flow of example 8, with the only difference that: the alkaline earth metal oxide is BaO.
The silicon nitride ceramic material prepared in example 13 had a thermal conductivity of 99.3W/(mK), a three-point bending strength of 602. + -. 23MPa, and a fracture toughness of 6.81. + -. 0.42 MPa. m1/2。
Comparative example 1
With 3 mol% of ZrO2And 2mol% of MgO as a sintering aid, and 95 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; sintering the obtained blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared by the comparative example 1 has a thermal conductivity of 89.2W/(m.K), a three-point bending strength of 529 + -2 MPa, and a fracture toughness of 7.34 + -0.27 MPa.m1/2。
Comparative example 2
5mol percent of MgO is used as a sintering aid, and 95mol percent of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; sintering the obtained blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
Of the silicon nitride ceramic material prepared by the present comparative example 2The thermal conductivity is 56.10W/(m.K), the three-point bending strength is 426 +/-22 MPa, and the fracture toughness is 4.89 +/-0.35 MPa.m1/2。
Comparative example 3
With 5 mol% ZrH2As a sintering aid, 95 mol% of alpha-Si3N4Ball-milling and mixing the powder, drying and sieving to obtain uniformly mixed powder; then dry pressing and forming under the pressure of 30MPa, and then carrying out cold isostatic pressing treatment under the pressure of 300 MPa; preserving heat for 2h at 500 ℃ in Ar atmosphere, heating to 1300 ℃ and preserving heat for 8h for pretreatment; sintering the obtained blank at 1900 ℃ under the air pressure, wherein the heating rate is 5 ℃/min, N2The pressure is 1MPa, and the heat preservation time is 12 h; after sintering, cooling to 1200 ℃ at the cooling rate of 10 ℃/min, and then cooling to room temperature along with the furnace.
The silicon nitride ceramic material prepared by the present comparative example 3 had a thermal conductivity of 45.70W/(m.K), a three-point bending strength of 389. + -. 18MPa, and a fracture toughness of 5. + -. 0.18 MPa. m1/2。
Comparative example 4
A silicon nitride ceramic material was prepared according to the process flow of example 5, with the only difference that: no sintering aid was added.
The silicon nitride ceramic material obtained in this comparative example 4 had a thermal conductivity of 30.2W/(m.K), a three-point bending strength of 203. + -. 52MPa, and a fracture toughness of 4.02. + -. 0.11 MPa.m1/2。
Table 1 shows the raw material compositions and performance parameters of the silicon nitride ceramic materials prepared in examples 1 to 13 of the present invention and comparative examples 1 to 4:
Figure BDA0002281264260000111
Figure BDA0002281264260000121
. Comparing comparative example 1, example 3 and example 4, the same or similar processes are used for the three, and it can be found that ZrH is used2Example 3 and when zirconia was substituted as the sintering aid4, the thermal conductivity of the material obtained in the step (4) is obviously improved.
Finally, it must be said here that: the above embodiments are only used for further detailed description of the technical solutions of the present invention, and should not be understood as limiting the scope of the present invention, and the insubstantial modifications and adaptations made by those skilled in the art according to the above descriptions of the present invention are within the scope of the present invention.

Claims (9)

1. The silicon nitride ceramic material is characterized by comprising the raw material composition of alpha-Si3N4And a sintering aid; the sintering aid is metal hydride and alkaline earth metal oxide, and the total content is 2-12 mol%; the metal hydride is ZrH2(ii) a The alkaline earth metal oxide is at least one of MgO, CaO and BaO; the molar ratio of the metal hydride to the alkaline earth metal oxide is 1: 10-10: 1;
the preparation method of the silicon nitride ceramic material comprises the following steps:
(1) weighing alpha-Si according to the raw material composition of the silicon nitride ceramic material3N4Mixing the powder and the sintering aid to obtain mixed powder;
(2) after the obtained mixed powder is pressed and formed, presintering treatment is carried out at 600-1600 ℃, and then sintering treatment is carried out at 1780-1950 ℃ to obtain the silicon nitride ceramic material; the sintering treatment mode is air pressure sintering, the atmosphere of the air pressure sintering is nitrogen, and the air pressure is more than or equal to 1 MPa;
the silicon nitride ceramic material has the thermal conductivity of 61.25-115.18W/(m.K), the bending strength of 475-759 MPa, and the fracture toughness of 5.38-7.95 MPa.m1/2。
2. The silicon nitride ceramic material of claim 1, wherein the total content of the sintering aid is 5 to 10 mol%.
3. The silicon nitride ceramic material of claim 1, wherein the molar ratio of the metal hydride to the alkaline earth metal oxide is 1:5 to 5: 1.
4. The silicon nitride ceramic material of claim 1, wherein the mixing is performed by wet ball milling in a vacuum ball milling tank, and then rotary evaporation drying or vacuum drying is performed to obtain mixed powder; the ball milling atmosphere in the vacuum ball milling tank is vacuum atmosphere, inert atmosphere or nitrogen atmosphere.
5. The silicon nitride ceramic material according to claim 1, wherein the press forming is dry press forming or/and isostatic pressing; the pressure of the dry pressing is 10-50 MPa, and the pressure of the isostatic pressing is 100-300 MPa.
6. The silicon nitride ceramic material according to claim 1, wherein the atmosphere of the pre-sintering treatment is a vacuum atmosphere, a nitrogen atmosphere, or an inert atmosphere, and the inert atmosphere is an argon atmosphere; the time of the pre-sintering treatment is 1-8 hours.
7. Silicon nitride ceramic material according to any of claims 1-6, characterized in that the sintering process is carried out for a time of not less than 2 hours.
8. The silicon nitride ceramic material according to any one of claims 1 to 6, wherein the temperature increase rate of the sintering treatment is 1 to 15 ℃/min.
9. The silicon nitride ceramic material according to any one of claims 1 to 6, wherein after the sintering treatment is completed, the ceramic material is cooled to 800 to 1200 ℃ at a cooling rate of 20 ℃/min or less, and then is furnace-cooled to room temperature.
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