阅读说明：本技术 一种氮化硅基复相导电陶瓷的制备方法 (Preparation method of silicon nitride-based complex phase conductive ceramic ) 是由 张伟儒 张晶 孙峰 董廷霞 李泽坤 李洪浩 徐金梦 荆赫 吕沛远 于 2021-02-02 设计创作，主要内容包括：本发明提供了一种氮化硅基复相导电陶瓷的制备方法,本发明以氮化硅为基体,同时添加导电相以及烧结助剂,采用两步微波烧结法,制备的氮化硅基复相导电陶瓷晶粒细小且均匀、致密度高,且强度、硬度等力学性能也得到了显著提升。本发明采用的两步微波烧结法,可抑制晶界迁移,并利用晶界扩散使坯体达到致密化；因此,该方法既可以抑制烧结后期晶粒的生长,同时又不会影响致密化的进行。实施例的结果显示,本发明提供的氮化硅基复相导电陶瓷的相对密度大于99％,维氏硬度大于15GPa,断裂韧性大于6MPa·m～(1/2),抗弯强度大于900MPa,电阻率小于1Ω·cm。(The invention provides a preparation method of silicon nitride-based complex phase conductive ceramic, which takes silicon nitride as a substrate, simultaneously adds a conductive phase and a sintering aid, adopts a two-step microwave sintering method, and has the advantages of fine and uniform crystal grains, high density, obviously improved mechanical properties such as strength, hardness and the like. The two-step microwave sintering method adopted by the invention can inhibit the migration of crystal boundary and utilize the diffusion of the crystal boundary to densify the blank; therefore, the method can inhibit the growth of crystal grains in the later sintering period, and simultaneously cannot influence the densification. The results of the examples show that the relative density of the silicon nitride-based complex phase conductive ceramic provided by the invention is more than 99 percent, the Vickers hardness is more than 15GPa, and the fracture toughness is more than 6 MPa.m 1/2 The bending strength is more than 900MPa, and the resistivity is less than 1 omega cm.)

1. A method for preparing silicon nitride-based complex phase conductive ceramic comprises the following steps:

(1) mixing silicon nitride, a conductive phase and a sintering aid, and then forming to obtain a blank; the sintering aid comprises rare earth oxide and metal oxide, and the metal oxide comprises aluminum oxide or magnesium oxide;

(2) and (2) sequentially carrying out high-temperature microwave sintering and low-temperature microwave sintering on the blank obtained in the step (1) to obtain the silicon nitride-based complex phase conductive ceramic.

2. The preparation method according to claim 1, wherein the mass content of the silicon nitride in the blank in the step (1) is 40-60%, the mass content of the conductive phase is 30-50%, the mass content of the metal oxide is 1-5%, and the mass content of the rare earth oxide is 2-10%.

3. A method according to claim 1 or 2, wherein said electrically conductive phase comprises TiN, TiC, TiCN, TiB₂、ZrN、ZrC、ZrB₂Or MoSi₂。

4. The production method according to claim 1 or 2, wherein the rare earth oxide comprises yttrium oxide, lanthanum oxide, or cerium oxide.

5. The method according to claim 1 or 2, wherein β -Si in the silicon nitride is present₃N₄The mass content of the silicon nitride is more than or equal to 85 percent, and the average grain diameter D50 of the silicon nitride is less than or equal to 1.0 mu m.

6. The preparation method according to claim 1, wherein the raw material of the green body in the step (1) further comprises a microwave absorbent; the microwave absorber comprises silicon carbide or zirconium oxide.

7. The preparation method according to claim 1, wherein the forming manner in the step (1) comprises one or more of dry pressing, cold isostatic pressing, injection molding, pouring and grouting.

8. The preparation method according to claim 1, wherein the temperature of the high-temperature microwave sintering in the step (2) is 1500-1700 ℃, and the heat preservation time of the high-temperature microwave sintering is 0-30 min; the temperature of the low-temperature microwave sintering is 1400-1600 ℃, and the heat preservation time of the low-temperature microwave sintering is 10-120 mim; the temperature difference between the high-temperature microwave sintering and the low-temperature microwave sintering is 50-150 ℃.

9. The preparation method according to claim 1 or 8, wherein the temperature rise rate of the high-temperature microwave sintering in the step (2) is 2-30 ℃/min, and the temperature fall rate of the high-temperature microwave sintering after the temperature reduction to the temperature of the low-temperature microwave sintering is 30-80 ℃/min.

10. The method according to claim 1 or 8, wherein the high-temperature microwave sintering and the low-temperature microwave sintering in the step (2) are both performed in a nitrogen atmosphere, and the flow rate of the nitrogen is independently 0.5 to 5L/min.

Technical Field

The invention relates to the technical field of conductive ceramics, in particular to a preparation method of silicon nitride-based complex phase conductive ceramics.

Background

The silicon nitride ceramic has excellent comprehensive mechanical properties, particularly has the advantages of high strength, high hardness, high toughness and good wear resistance, has higher chemical stability and thermal shock resistance, is an ideal engineering ceramic material, and is widely applied to the fields of machinery, chemical industry, aerospace, national defense and military industry and the like. However, since silicon nitride ceramics have electrical insulation properties, they can be machined only with conventional diamond tools, which has low machining efficiency and high cost, and cannot be used to machine parts having complicated shapes, thus severely limiting the application of silicon nitride ceramics.

By introducing titanium-based compounds (TiN, TiC, TiCN, TiB) into silicon nitride ceramics₂) Zirconium-based compound (ZrN, ZrC, ZrB)₂) Or MoSi₂The equal conductive phase can improve the conductivity of the silicon nitride ceramics, and further can adopt electric spark machining, thereby improving the machining efficiency and solving the problem that the parts with complicated shapes can not be machined. However, the addition of the conductive phase can hinder the sintering densification of the silicon nitride, so that when the complex phase conductive ceramic is prepared, hot-pressing sintering or high-temperature (1800 ℃ or more) air pressure sintering is needed to realize the densification, and the adoption of the sintering method can cause the reduction of mechanical properties such as the hardness, the strength and the like of the silicon nitride ceramic.

Therefore, in order to realize the rapid processing of silicon nitride ceramic parts with complex shapes, it is necessary to provide a method capable of realizing the densification of silicon nitride-based complex phase ceramics and simultaneously ensuring the mechanical properties of silicon nitride ceramics.

Disclosure of Invention

The invention aims to provide a preparation method of silicon nitride-based complex phase conductive ceramic, which can inhibit crystal boundary migration and densify a blank by utilizing crystal boundary diffusion, thereby improving the mechanical properties of the silicon nitride-based complex phase conductive ceramic, such as strength, hardness and the like.

In order to achieve the above purpose, the invention provides the following technical scheme:

the invention provides a preparation method of silicon nitride-based complex phase conductive ceramic, which comprises the following steps:

(1) mixing silicon nitride, a conductive phase and a sintering aid, and then forming to obtain a blank; the sintering aid comprises rare earth oxide and metal oxide, and the metal oxide comprises aluminum oxide or magnesium oxide;

(2) and (2) sequentially carrying out high-temperature microwave sintering and low-temperature microwave sintering on the blank obtained in the step (1) to obtain the silicon nitride-based complex phase conductive ceramic.

Preferably, the mass content of silicon nitride in the blank in the step (1) is 40-60%, the mass content of the conductive phase is 30-50%, the mass content of the metal oxide is 1-5%, and the mass content of the rare earth oxide is 2-10%.

Preferably, the conductive phase comprises TiN, TiC, TiCN, TiB₂、ZrN、ZrC、ZrB₂Or MoSi₂。

Preferably, the rare earth oxide comprises yttrium oxide, lanthanum oxide or cerium oxide.

Preferably, the silicon nitride contains beta-Si₃N₄The mass content of the silicon nitride is more than or equal to 85 percent, and the average grain diameter D50 of the silicon nitride is less than or equal to 1.0 mu m.

Preferably, the raw materials of the blank in the step (1) further comprise a microwave absorbent; the microwave absorber comprises silicon carbide or zirconium oxide.

Preferably, the forming mode in the step (1) comprises one or more of dry pressing, cold isostatic pressing, injection molding, pouring and grouting.

Preferably, the temperature of the high-temperature microwave sintering in the step (2) is 1500-1700 ℃, and the heat preservation time of the high-temperature microwave sintering is 0-30 min; the temperature of the low-temperature microwave sintering is 1400-1600 ℃, and the heat preservation time of the low-temperature microwave sintering is 10-120 mim; the temperature difference between the high-temperature microwave sintering and the low-temperature microwave sintering is 50-150 ℃.

Preferably, the heating rate of the high-temperature microwave sintering in the step (2) is 2-30 ℃/min, and the cooling rate of the high-temperature microwave sintering after cooling to the low-temperature microwave sintering temperature is 30-80 ℃/min.

Preferably, the high-temperature microwave sintering and the low-temperature microwave sintering in the step (2) are both carried out in a nitrogen atmosphere, and the flow rate of the nitrogen is 0.5-5L/min independently.

The invention provides a preparation method of silicon nitride-based complex phase conductive ceramic, which comprises the following steps: mixing silicon nitride, a conductive phase and a sintering aid, and then forming to obtain a blank; sequentially carrying out high-temperature microwave sintering and low-temperature microwave sintering on the green body to obtain the silicon nitride-based complex-phase conductive ceramic; the sintering aid comprises rare earth oxide and metal oxide, and the metal oxide comprises aluminum oxide or magnesium oxide. According to the invention, silicon nitride is used as a matrix, the conductive phase and the sintering aid are added at the same time, and a two-step microwave sintering method is adopted, so that the prepared silicon nitride-based complex phase conductive ceramic has fine and uniform crystal grains, high density and remarkably improved mechanical properties such as strength and hardness. According to the invention, the conductive phase is added to form a continuous conductive network in the silicon nitride substrate, so that the conductivity of the silicon nitride-based ceramic is improved, and the conductive phase has stronger microwave absorption capacity than the silicon nitride substrate, can promote microwave sintering, and is beneficial to reducing the microwave sintering temperature of the silicon nitride-based complex phase conductive ceramic; by adding the sintering aid, the sintering densification is facilitated to be promoted. The two-step microwave sintering method adopted by the invention can inhibit the migration of crystal boundary and utilize the diffusion of the crystal boundary to densify the blank; therefore, the method can inhibit the growth of crystal grains in the later sintering period, and simultaneously cannot influence the densification. The results of the examples show that the relative density of the silicon nitride-based complex phase conductive ceramic provided by the invention is more than 99 percent, the Vickers hardness is more than 15GPa, and the fracture toughness is more than 6 MPa.m^1/2The bending strength is more than 900MPa, and the resistivity is less than 1 omega cm.

Drawings

FIG. 1 is a schematic view of the microstructure of silicon nitride-based complex phase conductive ceramics prepared in examples 1 to 4 of the present invention and comparative examples 1 to 4;

FIG. 2 is a schematic view of a microwave sintering furnace employed in the present invention;

the method comprises the following steps of 1-alumina fiber hearth, 2-temperature measuring device, 3-crucible, 4-silicon carbide and 5-to-be-sintered blank.

Detailed Description

The invention provides a preparation method of silicon nitride-based complex phase conductive ceramic, which comprises the following steps:

(1) mixing silicon nitride, a conductive phase and a sintering aid, and then forming to obtain a blank; the sintering aid comprises rare earth oxide and metal oxide, and the metal oxide comprises aluminum oxide or magnesium oxide;

(2) and (2) sequentially carrying out high-temperature microwave sintering and low-temperature microwave sintering on the blank obtained in the step (1) to obtain the silicon nitride-based complex phase conductive ceramic.

According to the invention, a blank is obtained by mixing silicon nitride, a conductive phase and a sintering aid and then molding.

In the invention, the mass content of the silicon nitride in the blank is preferably 40-60%, and more preferably 45-55%. In the present invention, the silicon nitride contains beta-Si₃N₄The mass content of (B) is preferably not less than 85%, more preferably not less than 95%. The invention preferably adds beta-Si in the silicon nitride₃N₄The mass content of (a) is controlled within the above range, which is advantageous for forming uniform and fine equiaxed grains in the sintered silicon nitride. In the present invention, the average particle diameter D50 of the silicon nitride is preferably not more than 1.0. mu.m. In the present invention, it is preferable to control the average particle size of the silicon nitride within the above range, and it is possible to prevent the sintering densification from being inhibited and the sintering temperature from being increased when the average particle size of the silicon nitride is too large. The source of the silicon nitride is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.

In the invention, the mass content of the conductive phase in the blank is preferably 30-50%, more preferably 30-45%. In the present invention, the conductive phase preferably comprises TiN, TiC, TiCN, TiB₂、ZrN、ZrC、ZrB₂Or MoSi₂More preferably TiN, TiC, ZrC or MoSi₂. The conductive phase is added to form a continuous conductive network in the silicon nitride substrate, so that the conductivity of the silicon nitride-based complex phase conductive ceramic is improved, and the conductive phase has stronger microwave absorption capacity than the silicon nitride substrate, can promote microwave sintering and is beneficial to reducing the microwave sintering temperature of the silicon nitride-based complex phase conductive ceramic. The source of the conductive phase is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.

In the present invention, the sintering aid includes a rare earth oxide and a metal oxide. In the invention, the addition of the sintering aid is beneficial to promoting sintering densification.

In the invention, the mass content of the metal oxide in the blank is preferably 1-5%, and more preferably 3-5%. In the present invention, the metal oxide includes alumina or magnesia, preferably alumina. The source of the alumina or magnesia is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.

In the invention, the mass content of the rare earth oxide in the blank is preferably 2-10%, more preferably 3-8%, and most preferably 4-6%. In the present invention, the rare earth oxide preferably includes yttrium oxide, lanthanum oxide, or cerium oxide. The source of the rare earth oxide is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.

In the present invention, the raw material of the green body preferably further includes a microwave absorbent. In the present invention, the microwave absorber preferably includes silicon carbide or zirconium oxide. In the invention, the mass content of the microwave absorbent in the blank body is preferably 1-10%, and more preferably 1-5%. In the invention, the silicon carbide or zirconia has high dielectric loss and extremely strong microwave absorption capacity, can further enhance the microwave absorption capacity of the silicon nitride-based complex phase conductive ceramic, and reduces the sintering temperature. The source of the microwave absorbent is not particularly limited in the present invention, and commercially available products known to those skilled in the art may be used.

In the present invention, the purity of the conductive phase, sintering aid and microwave absorber is preferably independently not less than 98%.

In the present invention, the conductive phase, the sintering aid and the microwave absorber preferably have an average particle diameter D50 of not more than 2.0. mu.m, independently. In the present invention, the average particle diameters of the conductive phase, the sintering aid and the microwave absorbent are preferably controlled within the above ranges, which is advantageous for promoting sintering densification and further reducing the sintering temperature.

In the invention, the forming mode preferably comprises one or more of dry pressing, cold isostatic pressing, injection molding, injection setting and grouting. In the present invention, the molding preferably includes: the raw materials are uniformly mixed, then dry pressing molding is carried out, and then cold isostatic pressing treatment is carried out to obtain a blank. In the invention, the pressure of the dry pressing is preferably 10-25 MPa. In the present invention, the size of the product obtained by the dry press molding is preferably 45X 8 mm. In the present invention, the pressure of the cold isostatic pressing treatment is preferably 200 to 300 MPa.

After a blank is obtained, the invention sequentially carries out high-temperature microwave sintering and low-temperature microwave sintering on the blank to obtain the silicon nitride-based complex phase conductive ceramic. The silicon nitride-based complex phase conductive ceramic is prepared by adopting a two-step microwave sintering method, so that the crystal boundary migration can be inhibited, and the blank body can be densified by utilizing the crystal boundary diffusion; therefore, the method can inhibit the growth of crystal grains in the later sintering period, and simultaneously cannot influence the densification.

In the present invention, the apparatus for high-temperature microwave sintering and low-temperature microwave sintering is preferably a microwave sintering furnace. In the present invention, the microwave sintering furnace is preferably as shown in fig. 2, and the microwave sintering furnace preferably comprises an alumina fiber hearth, a temperature measuring device, a crucible and silicon carbide. In the invention, the alumina fiber hearth is used for heat insulation; the temperature measuring device is used for observing the sintering temperature; the crucible is used for placing a green body to be sintered, and the material of the crucible is preferably boron nitride; the silicon carbide is used for auxiliary heating.

In the invention, the temperature of the high-temperature microwave sintering is preferably 1500-1700 ℃. In the invention, the heat preservation time of the high-temperature microwave sintering is preferably 0-30 min, and more preferably 0-15 min.

In the invention, the temperature of the low-temperature microwave sintering is preferably 1400-1600 ℃. In the invention, the heat preservation time of the low-temperature microwave sintering is preferably 10-120 mim, and more preferably 20-80 min.

In the invention, the temperature difference between the high-temperature microwave sintering and the low-temperature microwave sintering is preferably 50-150 ℃.

In the invention, the heating rate of the high-temperature microwave sintering is preferably 2-30 ℃/min. In the invention, the cooling rate of cooling to the temperature of low-temperature microwave sintering after high-temperature microwave sintering is preferably 30-80 ℃/min.

According to the method, the temperature is preferably increased to 1500-1700 ℃ higher for sintering the blank, the temperature is kept for 0-10 min, then the temperature is rapidly reduced to 1400-1600 ℃ relatively lower, and the temperature is kept for 10-120 min, so that the grain boundary migration is inhibited, and the blank is densified by using grain boundary diffusion. Therefore, the method can inhibit the growth of crystal grains at the later sintering stage, and simultaneously the densification is not influenced, and the prepared silicon nitride-based complex phase conductive ceramic has fine and uniform crystal grains, high density and obviously improved mechanical properties such as strength, hardness and the like.

In the present invention, the microwave frequency of the high temperature microwave sintering and the low temperature microwave sintering is preferably 2.45 GHz.

In the present invention, the high-temperature microwave sintering and the low-temperature microwave sintering are preferably both performed in a nitrogen atmosphere. In the invention, the flow rate of the nitrogen is preferably 0.5-5L/min independently.

According to the invention, silicon nitride is used as a matrix, the conductive phase and the sintering aid are added at the same time, and a two-step microwave sintering method is adopted, so that the prepared silicon nitride-based complex phase conductive ceramic has fine and uniform crystal grains, high density and remarkably improved mechanical properties such as strength and hardness.

The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. It is to be understood that the described embodiments are merely exemplary of the invention, and not restrictive of the full scope of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Example 1

Raw materials:

silicon nitride (beta-Si)₃N₄The mass content is more than or equal to 95 percent, and the average grain diameter D50 is 0.5 mu m): the content of the active carbon is 53 percent,

titanium nitride (purity not less than 99%, average particle diameter D50 of 0.1 μm): 35 percent of the total weight of the mixture,

alumina (purity is more than or equal to 99%, and average particle size D50 is 0.5 μm): 3 percent of the total weight of the mixture,

yttrium oxide (purity is more than or equal to 99%, and average particle size D50 is 0.2 μm): 6 percent of the total weight of the mixture,

silicon carbide (purity is more than or equal to 98.5%, and average grain diameter D50 is 0.5 μm): 3 percent.

The raw materials are uniformly mixed and then are subjected to dry pressing forming, the size of the obtained product is 45 x 8mm, the pressure of the dry pressing forming is 20MPa, then cold isostatic pressing treatment is carried out, and the pressure of the cold isostatic pressing treatment is 300MPa, so that a blank is obtained. And putting the blank into a furnace chamber of a microwave sintering furnace, vacuumizing until the vacuum degree in the furnace is less than 100Pa, introducing nitrogen to enable the pressure in the furnace to reach 0.1MPa, repeatedly washing the furnace twice, starting to heat up in a flowing nitrogen atmosphere of 0.1MPa, wherein the nitrogen flow is 1L/min, firstly heating up to 1600 ℃ at the speed of 15 ℃/min, preserving the heat for 5min, then cooling to 1550 ℃ at the speed of 50 ℃/min, preserving the heat for 30mm, and then naturally cooling to room temperature to obtain the silicon nitride-based multiphase conductive ceramic.

Example 2

Raw materials:

silicon nitride (beta-Si)₃N₄The mass content is more than or equal to 95 percent, and the average grain diameter D50 is 0.5 mu m): 50 percent of the total weight of the mixture is,

titanium nitride (purity not less than 99%, average particle diameter D50 of 0.1 μm): 40 percent of the total weight of the mixture,

alumina (purity is more than or equal to 99%, and average particle size D50 is 0.5 μm): 3 percent of the total weight of the mixture,

yttrium oxide (purity is more than or equal to 99%, and average particle size D50 is 0.2 μm): 5 percent of the total weight of the mixture,

silicon carbide (purity is more than or equal to 98.5%, and average grain diameter D50 is 0.5 μm): 2 percent.

The raw materials are uniformly mixed and then are subjected to dry pressing forming, the size of the obtained product is 45 x 8mm, the pressure of the dry pressing forming is 20MPa, then cold isostatic pressing treatment is carried out, and the pressure of the cold isostatic pressing treatment is 300MPa, so that a blank is obtained. And putting the blank into a furnace chamber of a microwave sintering furnace, vacuumizing until the vacuum degree in the furnace is less than 100Pa, introducing nitrogen to enable the pressure in the furnace to reach 0.1MPa, repeatedly washing the furnace twice, starting to heat up in a flowing nitrogen atmosphere of 0.1MPa, wherein the nitrogen flow is 1L/min, firstly heating up to 1650 ℃ at the speed of 15 ℃/min, preserving heat for 0min, then cooling to 1550 ℃ at the speed of 50 ℃/min, preserving heat for 40 mm, and then naturally cooling to room temperature to obtain the silicon nitride-based multiphase conductive ceramic.

Example 3

Raw materials:

silicon nitride (beta-Si)₃N₄The mass content is more than or equal to 95 percent, and the average grain diameter D50 is 0.5 mu m): the content of the active carbon is 48%,

titanium nitride (purity not less than 99%, average particle diameter D50 of 0.1 μm): 45 percent of the total weight of the mixture,

alumina (purity is more than or equal to 99%, and average particle size D50 is 0.5 μm): 3 percent of the total weight of the mixture,

yttrium oxide (purity is more than or equal to 99%, and average particle size D50 is 0.2 μm): 4 percent.

The raw materials are uniformly mixed and then are subjected to dry pressing forming, the size of the obtained product is 45 x 8mm, the pressure of the dry pressing forming is 20MPa, then cold isostatic pressing treatment is carried out, and the pressure of the cold isostatic pressing treatment is 300MPa, so that a blank is obtained. And putting the blank into a furnace chamber of a microwave sintering furnace, vacuumizing until the vacuum degree in the furnace is less than 100Pa, introducing nitrogen to enable the pressure in the furnace to reach 0.1MPa, repeatedly washing the furnace twice, starting to heat up in a flowing nitrogen atmosphere of 0.1MPa, wherein the nitrogen flow is 1L/min, firstly heating up to 1650 ℃ at the speed of 15 ℃/min, preserving the heat for 5min, then cooling to 1600 ℃ at the speed of 50 ℃/min, preserving the heat for 30mm, and then naturally cooling to room temperature to obtain the silicon nitride-based multiphase conductive ceramic.

Example 4

Raw materials:

silicon nitride (beta-Si)₃N₄The mass content is more than or equal to 95 percent, and the average grain diameter D50 is 0.5 mu m): 50 percent of the total weight of the mixture is,

titanium nitride (purity not less than 99%, average particle diameter D50 of 0.1 μm): 40 percent of the total weight of the mixture,

magnesium oxide (purity is more than or equal to 98%, and average particle size D50 is 0.2 μm): 3 percent of the total weight of the mixture,

yttrium oxide (purity is more than or equal to 99%, and average particle size D50 is 0.2 μm): 5 percent of the total weight of the mixture,

zirconium oxide (purity not less than 99%, average particle diameter D50 is 0.5 μm): 2 percent.

The raw materials are uniformly mixed and then are subjected to dry pressing forming, the size of the obtained product is 45 x 8mm, the pressure of the dry pressing forming is 20MPa, then cold isostatic pressing treatment is carried out, and the pressure of the cold isostatic pressing treatment is 300MPa, so that a blank is obtained. And putting the blank into a furnace chamber of a microwave sintering furnace, vacuumizing until the vacuum degree in the furnace is less than 100Pa, introducing nitrogen to enable the pressure in the furnace to reach 0.1MPa, repeatedly washing the furnace twice, starting to heat up in a flowing nitrogen atmosphere of 0.1MPa, wherein the nitrogen flow is 1L/min, firstly heating up to 1600 ℃ at the speed of 15 ℃/min, preserving the heat for 3min, then cooling to 1550 ℃ at the speed of 50 ℃/min, preserving the heat for 30mm, and then naturally cooling to room temperature to obtain the silicon nitride-based multiphase conductive ceramic.

Comparative example 1

The same raw material composition and molding process as in example 1 were used to obtain a green body.

And (3) carrying out air pressure sintering on the obtained blank, wherein the sintering temperature is 1750 ℃, the nitrogen pressure is 9.8MPa, keeping the temperature for 3h, and then naturally cooling to room temperature to obtain the silicon nitride-based complex phase conductive ceramic.

Comparative example 2

The same raw material composition and molding process as in example 2 were used to obtain a green body.

And (3) carrying out air pressure sintering on the obtained blank, wherein the sintering temperature is 1800 ℃, the nitrogen pressure is 9.8MPa, keeping the temperature for 3h, and then naturally cooling to room temperature to obtain the silicon nitride-based complex phase conductive ceramic.

Comparative example 3

The same raw material composition and molding process as in example 3 were used to obtain a green body.

And (3) carrying out air pressure sintering on the obtained blank, wherein the sintering temperature is 1850 ℃, the nitrogen pressure is 9.8MPa, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain the silicon nitride-based complex phase conductive ceramic.

Comparative example 4

The same raw material composition and molding process as in example 4 were used to obtain a green body.

And (3) carrying out air pressure sintering on the obtained blank, wherein the sintering temperature is 1780 ℃, the nitrogen pressure is 9.8MPa, keeping the temperature for 2 hours, and then naturally cooling to room temperature to obtain the silicon nitride-based complex phase conductive ceramic.

Performance testing

The density of the silicon nitride-based complex phase conductive ceramics prepared in examples 1 to 4 and comparative examples 1 to 4 was measured by an archimedes drainage method, and the relative density was calculated, and the results are shown in table 1.

The vickers hardness and the fracture toughness of the silicon nitride-based complex phase conductive ceramics prepared in the examples 1 to 4 and the comparative examples 1 to 4 were measured by an indentation method, the applied load was 196N, and the test results are shown in table 1.

The bending strength of the silicon nitride-based complex phase conductive ceramics prepared in the examples 1-4 and the comparative examples 1-4 is tested by adopting a method for testing the bending strength in the standard GB/T6569-2006, wherein the specification of a test sample is 40 multiplied by 3 multiplied by 4mm, the bending strength at three points is tested, the span is 30mm, and the test results are shown in Table 1.

The microstructure of the silicon nitride-based complex phase conductive ceramics prepared in examples 1 to 4 and comparative examples 1 to 4 was observed by a scanning electron microscope, as shown in fig. 1, and the measurement of the grain size was completed on a randomly taken SEM photograph, the number of grains counted for each sample was not less than 500, and the test results are shown in table 1.

TABLE 1 Properties of silicon nitride-based composite conductive ceramics prepared in examples 1 to 4 and comparative examples 1 to 4

The preparation method provided by the invention can realize the densification of the silicon nitride-based complex phase conductive ceramic and simultaneously improve the mechanical properties of the ceramic, such as strength, hardness and the like. In addition, the relative density of the silicon nitride-based complex phase conductive ceramic prepared by the invention is more than 99 percent, the Vickers hardness is more than 15GPa, and the fracture toughness is more than 6 MPa.m^1/2The bending strength is more than 900MPa, and the resistivity is less than 1 omega cm.

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.