Preparation method of ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material

Abstract

The invention relates to a preparation method of an ultra-hard and high-strength bionic laminated diamond-B4C-SiC / SI3N4-SiC ceramic composite material, comprising the following steps: S1, selecting diamond, boron powder and silicon powder as raw materials for a first layer, and obtaining a ternary mixed powder consisting of B, Si and diamond after ball milling and drying; selecting α-Si3N4 powder, SiC powder, Y2O3 powder and Al2O3 powder as raw materials for a second layer; S2, spreading the B, Si and diamond mixed powder on the bottom of a graphite mold and applying pressure to level it, then spreading α-Si3N4, SiC, Y2O3 and Al2O3 on the surface of the first layer, and applying pressure to form a prefabricated body; S3, filling with argon gas, performing axial pressure, applying pulse current, and sintering; and cooling with the furnace to obtain a desired block sample; S4, removing graphite paper on the sample surface, and performing grinding, polishing, etching and other treatments on the block sample surface. The present invention has high surface hardness and overall high strength, and plays an important role in the field of impact protection; it can be applied to motor bearings in the field of new energy vehicles, with lower density and higher wear resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and more particularly to an ultra-hard and high-strength bionic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material and a preparation method thereof. Background Art

[0002] The demand for wear-resistant materials has become key to ensuring their safe application. Currently, the main high-hardness wear-resistant materials are diamond, and high-strength ceramic materials include silicon nitride. However, how to combine the ultra-hard wear resistance of diamond with the high strength of silicon nitride ceramics remains a problem that needs to be solved.

[0003] Diamond, due to its unique crystal structure, possesses extremely high hardness. Diamond is often added as a functional additive to ceramic or metal matrices to produce diamond composites with excellent overall performance. Currently, lightweight diamond-B4C-SiC composite ceramics, prepared at low temperatures using a diamond-B-Si reactive sintering system, avoid the graphitization of diamond, significantly retaining its intrinsic properties and exhibiting ultra-high hardness. However, the material's strength and toughness need to be improved to meet the high hardness and strength requirements of impact-resistant protective materials.

[0004] Silicon nitride mainly has two crystal forms: α-Si3N4 and β-Si3N4. The mechanical properties (hardness, strength, toughness, etc.) of silicon nitride ceramics are usually affected by the ratio of α-Si3N4 to β-Si3N4. When the content of β-Si3N4 is high, the overall strength of the material is higher. By adjusting the sintering process and the content of additives to promote the transformation of α-Si3N4 to β-Si3N4, high-strength silicon nitride composite materials can be prepared. Shi et al. [1] Studies have shown that as the content of additives increases, the percentage of β-Si3N4 in the prepared Si3N4-Y2O3-Al2O3 composite ceramics will increase accordingly, and its strength can reach up to 1122.4MPa. At present, researchers add diamond as a reinforcing phase directly into the silicon nitride matrix to prepare diamond-silicon nitride based composite materials. However, due to the large contact angle between the diamond particles and the material matrix, the interface bonding force between the diamond and the matrix silicon nitride will be weak during the sintering process of the material, affecting the composite of the material. Wu et al. developed a new composite material with silicon nitride as the matrix and diamond particles (with Ti coating on the surface) as the reinforcing phase. [2] , which greatly improves the hardness and thermal conductivity of the material, but also causes the bending strength to drop sharply to 265.13MPa, failing to fully exert the high-strength properties of silicon nitride ceramics.

[0005] To meet the demands for high-performance, impact-resistant parts and automotive ceramic components, it is necessary to design new sintering systems. By designing the material structure and selecting appropriate sintering processes to control the material composition, we can produce ceramic-based composites that combine high hardness and strength. Currently, in the new energy vehicle sector, ceramic bearings are replacing steel ball bearings. For example, the output shaft of Tesla's motor uses a ceramic bearing with 50 silicon nitride balls. However, its wear resistance needs to be further improved when used under extreme operating conditions. Diamond, as the hardest material, has excellent wear resistance, but direct composite with a ceramic matrix is ​​difficult. Therefore, new structures and sintering methods are needed to meet the application requirements of wear resistance. In recent years, various biomimetic materials, based on the close connection between biological microstructure and properties, have gradually come into the spotlight, greatly improving the performance of these materials. Among them, shell is a rigid biomaterial with both high hardness and high toughness, which is due to the multi-layer structure of the shell nacre layer with alternating soft and hard layers; therefore, by studying the layered structure of the shell, the structure and components of the material are designed, and materials with high hardness and high strength properties are selected, it is expected to prepare ceramic materials with excellent mechanical properties through stacking. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing an ultra-hard and high-strength bionic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material. By studying the layered structure of shells, ultra-hard diamond-B4C-SiC composite ceramics and high-strength Si3N4-SiC composite ceramics are selected respectively, and an active element sintering system is adopted to assemble and prepare a ceramic composite material with a laminated structure, which can improve the comprehensive mechanical properties of the material.

[0007] The technical solution adopted by the present invention to solve the technical problem is to construct a method for preparing an ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material, comprising the following steps:

[0008] S1. Preparation of mixed powder: The raw materials for the first layer are selected from diamond with a purity greater than 98% and an average particle size of 20-30 μm, boron (B) powder with a particle size of 1-3 μm and silicon (Si) powder with a particle size of 1-3 μm. Diamond powder accounts for 35-45 wt% of the total mass of the raw materials, and the mass ratio of boron powder to silicon powder is 1:2-2:1. The raw material powders are weighed and ball-milled to obtain a ternary mixed powder consisting of B, Si and diamond. The raw materials for the second layer are selected from boron (B) powder with a purity greater than 99% and an average particle size of 0.1-2 μm. α-Si3N4 powder with a diameter of 2 to 6.5 μm, SiC powder with a diameter of 2 to 6.5 μm, Y2O3 powder with a diameter of 50 to 500 nm, and Al2O3 powder with a diameter of 10 to 200 nm are weighed in a ratio of 50 to 80 wt% α-Si3N4, 15 to 40 wt% SiC, and 5 to 25 wt% Y2O3-Al2O3, wherein the mass ratio of Y2O3 to Al2O3 is fixed at 3:2, and after ball milling and drying, a mixed powder consisting of α-Si3N4, SiC, Y2O3, and Al2O3 is obtained;

[0009] S2. Preparation of green body: Spread the mixed powder of B, Si and diamond on the bottom of the graphite mold and apply pressure to make it flat, then spread α-Si3N4, SiC, Y2O3 and Al2O3 on the surface of the first layer and apply pressure to form a prefabricated green body;

[0010] S3. Rapid densification sintering of the green body: The green body is placed in a spark plasma sintering device, with graphite paper separating the inner wall of the graphite mold, the pressure head, and the powder. Argon is filled in a high vacuum state, axial pressure is applied, and a pulse current is applied. A "two-step method" of in-situ reaction sintering is adopted. Finally, the green body is cooled in the furnace to obtain the desired block sample.

[0011] S4. Subsequent processing of the sample: removing the graphite paper on the sample surface, grinding, polishing, etching and other treatments on the surface of the bulk sample to obtain a diamond-B4C-SiC / Si3N4-SiC ceramic composite material.

[0012] According to the above scheme, in step S1, the first layer of raw materials is ball-milled for 8 hours, and the grinding balls are made of SiC; the second layer of raw materials is ball-milled for 24 hours, and the grinding balls are made of agate; the equipment used for ball milling both layers of raw materials is a drum ball mill, and the ball-to-material ratio is 5:1.

[0013] According to the above scheme, in step S1, the drying temperature of the two layers of slurry is 70-80°C, the drying time is 24-48 hours, and the drying equipment is a blast drying oven or a vacuum drying oven.

[0014] According to the above scheme, in step S1, after drying, the first layer of raw materials are granulated through a 100-mesh sieve, and the second layer of raw materials are granulated through a 200-mesh sieve.

[0015] According to the above scheme, in step S2, when the mixed powder is loaded into the graphite mold for compaction to prepare the green body, after loading the mixed powder of B, Si and diamond, a pressing head with a slightly smaller diameter is used to compact the first layer of powder, and then Si3N4, SiC, Y2O3 and Al2O3 are spread flat on the first layer of powder to prepare a laminated green body with different components.

[0016] According to the above scheme, in step S3, the "two-step" in-situ reaction sintering is specifically as follows: in the front stage of sintering, the temperature is raised to 1600-1700°C at a rate of 100-200°C / min, and then a cooling process of 5-15 minutes is carried out, from 1600-1700°C to 1550-1500°C; the cooling process is a uniform cooling process to the stage of 1550-1500°C, after which the sample is cooled with the furnace.

[0017] According to the above solution, in step S3, the vacuum degree under the high vacuum state is less than 100 Pa, and the axial pressure applied is 50-100 MPa.

[0018] According to the above scheme, in step S4, the etching method is etching in molten NaOH at 380° C. for 20 to 120 seconds.

[0019] The present invention also provides a B4C-SiC / Si3N4-SiC powder obtained by a preparation method of a hard and high-strength bionic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material.

[0020] According to the above solution, the hardness of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material is 40.5 GPa and the strength is 562 MPa.

[0021] The method for preparing the ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material of the present invention has the following beneficial effects:

[0022] 1. The diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared by the present invention has an ultra-high surface hardness. By controlling the sintering temperature, the graphitization of diamond in the diamond-B4C-SiC material is effectively avoided, and a large amount of diamond is evenly dispersed in the matrix, thus achieving ultra-high hardness.

[0023] 2. The Si3N4-SiC ceramic composite material prepared by the present invention has high strength characteristics. By adjusting the sintering temperature, rod-shaped β-Si3N4 grains are obtained in the Si3N4-SiC layer to improve the bending strength. At the same time, the sintering aid added to the Si3N4-SiC layer can reduce the grain boundary phase and further promote the transformation of granular Si3N4 (α-Si3N4) to rod-shaped Si3N4 (β-Si3N4). When the material is subjected to external force and the cracks extend to these rod-shaped particles, the fracture energy can be reduced by crack deflection, bridging, pull-out, etc., thereby improving the fracture toughness and strength;

[0024] 3. By studying the layered structure of the nacre layer, the present invention designs a stacking system, which stacks and sinters diamond composite ceramics with silicon nitride-based ceramics. Compared with the existing sintering method of directly dispersing diamond into the silicon nitride matrix, this double-layer system avoids the problems of loose bonding between diamond and matrix and a significant decrease in bending strength during sintering. The prepared diamond-B4C-SiC / Si3N4-SiC ceramic composite material combines the advantages of single-layer materials and achieves excellent performance of high surface hardness and overall high strength.

[0025] 4. The diamond-B4C-SiC / Si3N4-SiC ceramic composite prepared by this invention has layers containing the same SiC component, forming chemical bonds that serve as a "bridge" connecting the laminated ceramic matrix. This chemical bond has lower interfacial energy than a mechanical bond, resulting in higher bond strength, making the contact between the laminates tighter and more secure.

[0026] 5. The present invention affects the sintering process of the material by changing the current pattern in the external field assisted sintering, thereby achieving the control of the material phase, microstructure and performance. By utilizing the spark plasma sintering technology, the graphitization transformation of diamond can be avoided at low temperature while the silicon nitride is sintered densely by adding a sintering aid, thereby promoting the transformation of α-Si3N4 to β-Si3N4 and improving the comprehensive performance of the material. The results of the embodiment show that the density of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material provided by the present invention is about 98%, the bending strength is as high as 562MPa, and the Vickers hardness is as high as 40.5GPa. In addition, the spark plasma sintering technology described in the present invention has a short sintering time, saves energy, is green and environmentally friendly, and is conducive to mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below with reference to the accompanying drawings and embodiments, in which:

[0028] Figure 1 The XRD spectra of the diamond-B4C-SiC / Si3N4-SiC ceramic composite materials prepared in Examples 1, 2, and 3 of the present invention are shown in FIG.

[0029] a is the XRD spectrum of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared in Example 1,

[0030] b is the XRD spectrum of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared in Example 2;

[0031] Figure 2 The SEM image of the interface of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared in Example 1 of the present invention and the SEM image of the Si3N4-SiC layer after etching;

[0032] Figure 3 This is a SEM image of the interface of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared in Example 2 of the present invention;

[0033] Figure 4 The SEM image of the interface of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared in Example 3 of the present invention and the SEM image of the Si3N4-SiC layer after etching;

[0034] Figure 5 This is an SEM image of the interface of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared in Comparative Example 1 of the present invention;

[0035] Figure 6 These are the interface SEM images of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared in Comparative Example 2 of the present invention and the SEM image of the Si3N4-SiC layer after etching. DETAILED DESCRIPTION

[0036] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are now described in detail with reference to the accompanying drawings.

[0037] Example 1

[0038] like Figure 1-2 As shown, the present invention provides a method for preparing an ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material, comprising the following steps:

[0039] (1) Preparation of mixed powder: The raw materials for the first layer are selected from diamond with a purity greater than 98% and an average particle size of 20 μm, B powder with a purity of 1 μm, and Si powder with a purity of 1 μm. The diamond powder accounts for 45 wt% of the total mass of the raw materials, and the mass ratio of B powder to Si powder is 1:2. The powders are weighed and ball-milled to obtain a ternary mixed powder consisting of B, Si, and diamond. The raw materials for the second layer are selected from α-Si3N4 powder with a purity greater than 99% and an average particle size of 0.1 μm, SiC powder with a purity of 2 μm, Y2O3 powder with a purity of 50 nm, and Al2O3 powder with a purity of 10 nm. The raw materials are weighed according to the mass percentage of 80% α-Si3N4, 15% SiC, 3% Y2O3, and 2% Al2O3. The raw materials are ball-milled to obtain a mixed powder consisting of α-Si3N4, SiC, Y2O3, and Al2O3.

[0040] (2) Preparation of the green body: First, the mixed powder of B, Si and diamond is spread on the bottom of the graphite mold and a certain pressure is applied to make it flat. Then, α-Si3N4, SiC, Y2O3 and Al2O3 are spread on the first layer and a certain pressure is applied to form a prefabricated green body;

[0041] (3) Rapid densification sintering of the green body: The green body is placed in a spark plasma sintering device. The inner wall of the graphite mold, the pressure head, and the powder are separated by graphite paper. Argon gas is injected under high vacuum (vacuum degree <100Pa), axial pressure is applied to 50MPa, pulse current is applied, and the temperature is raised to 1600℃ at a rate of 100℃ / min. Then, the temperature is lowered from 1600℃ to 1500℃ for 5min. Finally, the green body is cooled in the furnace to obtain the desired block sample.

[0042] (4) Subsequent processing of the sample: The graphite paper on the sample surface was removed, and the surface of the bulk sample was ground, polished, etched, and other treatments to obtain a diamond-B4C-SiC / Si3N4-SiC ceramic composite material.

[0043] XRD detection showed that there was a small amount of Si residue in the diamond-B4C-SiC layer, but no graphite was found. Part of the α-Si3N4 component in the Si3N4-SiC layer was transformed into β-Si3N4 (see Appendix Figure 1 Spectrum line a); The SEM image shows that the two layers are tightly bonded at the interface, where the diamonds in the diamond-B4C-SiC layer are evenly distributed in the ceramic matrix. After etching, it can be seen that the Si3N4-SiC layer exhibits a coexistence structure of equiaxed fine grains (α-Si3N4) and rod-shaped grains (β-Si3N4), where large-sized rod-shaped grains are embedded in the fine equiaxed grains to form an interwoven network structure (see Appendix Figure 2 The density of the prepared diamond-B4C-SiC / Si3N4-SiC ceramic composite material is 2.96g / cm 3(Archimedes drainage method), hardness is 38.3GPa (indentation method), and flexural strength is 430MPa (three-point bending method).

[0044] Example 2:

[0045] like Figure 1 and Figure 3 As shown, the present invention provides a method for preparing an ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material, comprising the following steps:

[0046] (1) Preparation of mixed powder: The first layer of raw materials is selected from diamond with a purity greater than 98% and an average particle size of 25 μm, B powder of 2 μm and Si powder of 2 μm, with the diamond powder accounting for 40 wt% of the total mass of the raw materials and the mass ratio of B powder to Si powder being 1:1. After ball milling and drying, a ternary mixed powder consisting of B, Si and diamond is obtained; the second layer of raw materials is selected from α-Si3N4 powder with a purity greater than 99% and an average particle size of 1 μm, SiC powder of 4 μm, Y2O3 powder of 300 nm and Al2O3 powder of 100 nm. The raw materials are weighed according to the mass percentage of 45% α-Si3N4, 40% SiC, 9% Y2O3 and 6% Al2O3. After ball milling and drying, a mixed powder consisting of α-Si3N4, SiC, Y2O3 and Al2O3 is obtained;

[0047] (2) Preparation of the green body: First, the mixed powder of B, Si and diamond is spread on the bottom of the graphite mold and a certain pressure is applied to make it flat. Then, α-Si3N4, SiC, Y2O3 and Al2O3 are spread on the first layer and a certain pressure is applied to form a prefabricated green body;

[0048] (3) Rapid densification sintering of the green body: The green body was placed in a spark plasma sintering device. The inner wall of the graphite mold, the pressure head, and the powder were separated by graphite paper. Argon gas was injected under high vacuum (vacuum degree <100Pa), and axial pressure of 75MPa was applied. A pulse current was applied and the temperature was raised to 1625℃ at a rate of 150℃ / min. The temperature was then cooled from 1625℃ to 1525℃ over a 10-min cooling process. The sample was then cooled in the furnace.

[0049] (4) Subsequent processing of the sample: The graphite paper on the sample surface was removed, and the surface of the bulk sample was ground, polished, etched, and other treatments to obtain a diamond-B4C-SiC / Si3N4-SiC ceramic composite material.

[0050] XRD detection showed that there was a small amount of Si residue in the diamond-B4C-SiC layer, but no graphite was found. Part of the α-Si3N4 component in the Si3N4-SiC layer was transformed into β-Si3N4 (see Appendix Figure 1Spectrum b); The SEM image shows that the two layers are tightly bonded at the interface, where the diamonds in the diamond-B4C-SiC layer are evenly distributed in the ceramic matrix, and the Si3N4-SiC layer shows a structure in which α-Si3N4 grains and β-Si3N4 grains coexist (see Appendix Figure 3 The density of the obtained diamond-B4C-SiC / Si3N4-SiC ceramic composite material is 2.95g / cm 3 (Archimedes drainage method), hardness is 39.7GPa (indentation method), and flexural strength is 482Mpa (three-point bending method).

[0051] Example 3

[0052] like Figure 1 and Figure 4 As shown, the present invention provides a method for preparing an ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material, comprising the following steps:

[0053] (1) Preparation of mixed powder: The raw materials for the first layer are selected from diamond with a purity greater than 98% and an average particle size of 30 μm, B powder of 3 μm and Si powder of 3 μm, with the diamond powder accounting for 35 wt% of the total mass of the raw materials and the mass ratio of B powder to Si powder being 2:1. The raw material powders are weighed and ball-milled to obtain a ternary mixed powder consisting of B, Si and diamond; the raw materials for the second layer are selected from α-Si3N4 powder with a purity greater than 99% and an average particle size of 2 μm, SiC powder of 6.5 μm, Y2O3 powder of 500 nm and Al2O3 powder of 200 nm, respectively. The raw materials are weighed according to the mass percentage of 50% α-Si3N4, 25% SiC, 15% Y2O3 and 10% Al2O3, and ball-milled to obtain a mixed powder consisting of α-Si3N4, SiC, Y2O3 and Al2O3;

[0054] (2) Preparation of the green body: First, the mixed powder of B, Si and diamond is spread on the bottom of the graphite mold and a certain pressure is applied to make it flat. Then, α-Si3N4, SiC, Y2O3 and Al2O3 are spread on the first layer and a certain pressure is applied to form a prefabricated green body;

[0055] (3) Rapid densification sintering of the green body: The green body was placed in a spark plasma sintering device. Graphite paper was used to separate the inner wall of the graphite mold, the pressure head, and the powder. Argon gas was injected under high vacuum (vacuum degree <100 Pa), and axial pressure of 100 MPa was applied. A pulse current was applied, and the temperature was raised to 1600°C at a rate of 200°C / min. The temperature was then lowered from 1600°C to 1550°C over a period of 15 minutes. The sample was then cooled in the furnace.

[0056] (4) Subsequent processing of the sample: The graphite paper on the sample surface was removed, and the surface of the bulk sample was ground, polished, etched, and other treatments to obtain a diamond-B4C-SiC / Si3N4-SiC ceramic composite material.

[0057] XRD detection showed that there was a small amount of Si residue in the diamond-B4C-SiC layer, but no graphite was found. Part of the α-Si3N4 component in the Si3N4-SiC layer was transformed into β-Si3N4 (see Appendix Figure 1 Spectrum line c); The SEM image shows that the two layers are tightly bonded at the interface, where the diamonds in the diamond-B4C-SiC layer are evenly distributed in the ceramic matrix. After etching, the Si3N4-SiC layer shows a structure in which α-Si3N4 grains and β-Si3N4 grains coexist (see Appendix Figure 4 The density of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared by the present invention is 3.02g / cm 3 (Archimedes drainage method), hardness is 40.5GPa (indentation method), and bending strength is 562MPa (three-point bending method).

[0058] Comparative Example 1

[0059] like Figure 1 and Figure 5 As shown, the present invention provides a method for preparing an ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material, comprising the following steps:

[0060] (1) Preparation of mixed powder: The raw materials for the first layer are selected from diamond with a purity greater than 98% and an average particle size of 30 μm, B powder of 3 μm and Si powder of 3 μm, with the diamond powder accounting for 35 wt% of the total mass of the raw materials and the mass ratio of B powder to Si powder being 2:1. The raw material powders are weighed and ball-milled to obtain a ternary mixed powder consisting of B, Si and diamond; the raw materials for the second layer are selected from α-Si3N4 powder with a purity greater than 99% and an average particle size of 2 μm, SiC powder of 6.5 μm, Y2O3 powder of 500 nm and Al2O3 powder of 200 nm, respectively. The raw materials are weighed according to the mass percentage of 50% α-Si3N4, 25% SiC, 15% Y2O3 and 10% Al2O3, and ball-milled to obtain a mixed powder consisting of α-Si3N4, SiC, Y2O3 and Al2O3;

[0061] (2) Preparation of the green body: First, the mixed powder of B, Si and diamond is spread on the bottom of the graphite mold and a certain pressure is applied to make it flat. Then, α-Si3N4, SiC, Y2O3 and Al2O3 are spread on the first layer and a certain pressure is applied to form a prefabricated green body;

[0062] (3) Rapid densification sintering of the green body: The green body was placed in a spark plasma sintering device. Graphite paper was used to separate the inner wall of the graphite mold, the pressure head, and the powder. Argon gas was injected under high vacuum (vacuum degree <100 Pa), and axial pressure of 100 MPa was applied. A pulse current was applied, and the temperature was raised to 1700°C at a rate of 200°C / min. The temperature was then lowered from 1700°C to 1550°C over a period of 15 minutes. The sample was then cooled in the furnace.

[0063] (4) Subsequent processing of the sample: The graphite paper on the sample surface was removed, and the surface of the bulk sample was ground, polished, etched, and other treatments to obtain a diamond-B4C-SiC / Si3N4-SiC ceramic composite material.

[0064] The diamond-B4C-SiC layer was detected by XRD and the diamond diffraction peak disappeared and the graphite peak appeared (see Appendix Figure 1 (a) Spectrum line d), the α-Si3N4 part of the Si3N4-SiC layer is completely transformed into β-Si3N4 (see Appendix Figure 1 (b) Spectrum line d); The cross-sectional SEM image shows that the two layers are tightly bonded at the interface, where all the diamond in the diamond-B4C-SiC layer is converted into graphite. After etching, many rod-shaped β-Si3N4 grains can be seen in the Si3N4-SiC layer (see Appendix Figure 5 The density of the diamond-B4C-SiC / Si3N4-SiC ceramic composite material prepared by the present invention is 2.79g / cm 3 (Archimedes drainage method), hardness is 25.5GPa (indentation method), bending strength is 503MPa (three-point bending method).

[0065] Comparative Example 2

[0066] like Figure 1 and Figure 6 As shown, this comparative example provides a method for preparing a Si3N4-SiC single-layer ceramic composite material, comprising the following steps:

[0067] (1) Preparation of mixed powder: The raw material powders were selected from α-Si3N4 powder with a purity greater than 99% and an average particle size of 1 μm, SiC powder of 4 μm, Y2O3 powder of 300 nm, and Al2O3 powder of 100 nm. The raw materials were weighed according to the mass percentage of 45% α-Si3N4, 40% SiC, 9% Y2O3, and 6% Al2O3, and the mixed powder was obtained after ball milling and drying.

[0068] (2) Preparation of green body: α-Si3N4, SiC, Y2O3 and Al2O3 are spread flat on the bottom of the graphite mold and a certain pressure is applied to make it flat, and a certain pressure is applied to form a prefabricated green body;

[0069] (3) Rapid densification sintering of the green body: The green body was placed in a spark plasma sintering device. The inner wall of the graphite mold, the pressure head, and the powder were separated by graphite paper. Argon gas was injected under high vacuum (vacuum degree <100Pa), and axial pressure of 75MPa was applied. A pulse current was applied and the temperature was raised to 1625℃ at a rate of 150℃ / min. The temperature was then cooled from 1625℃ to 1525℃ over a 10-min cooling process. The sample was then cooled in the furnace.

[0070] (4) Subsequent processing of the sample: The graphite paper on the sample surface was removed, and the surface of the bulk sample was subjected to grinding, polishing, etching, and other treatments to obtain a Si3N4-SiC single-layer ceramic composite material.

[0071] XRD was used to detect that the Si3N4-SiC single layer ceramic contained α-Si3N4, SiC and β-Si3N4 (see Appendix Figure 1 (b) Spectrum e); Through the SEM image, it can be seen that the α-Si3N4 grains are partially transformed into β-Si3N4 grains (see Appendix Figure 6 The density of the obtained Si3N4-SiC single-layer ceramic composite material is 3.20g / cm 3 (Archimedes drainage method), hardness is 18.82GPa (indentation method), and flexural strength is 642Mpa (three-point bending method).

[0072] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the present invention and the claims, all of which are protected by the present invention.

Claims

1. A method for preparing an ultra-hard and high-strength biomimetic laminated diamond-B4C-SiC / Si3N4-SiC ceramic composite material, characterized in that: The following steps are involved: S1. Preparation of mixed powder: The first layer of raw materials is selected from diamond with a purity greater than 98% and an average particle size of 30 μm, boron powder of 3 μm, and silicon powder of 3 μm, respectively. The diamond powder accounts for 35wt% of the total mass of the raw materials, and the mass ratio of boron powder to silicon powder is 2:

1. The raw material powders are weighed, ball-milled and dried to obtain a ternary mixed powder consisting of B, Si, and diamond; The second layer of raw materials is selected from α-Si3N4 powder with a purity greater than 99% and an average particle size of 2μm, SiC powder of 6.5μm, Y2O3 powder of 500nm and Al2O3 powder of 200nm. The raw materials are weighed according to the mass percentage of 50% α-Si3N4, 25% SiC, 15% Y2O3 and 10% Al2O3. After ball milling and drying, a mixed powder consisting of α-Si3N4, SiC, Y2O3 and Al2O3 is obtained; S2. Preparation of green body: Spread the mixed powder of B, Si and diamond on the bottom of the graphite mold and apply pressure to make it flat, then spread α-Si3N4, SiC, Y2O3 and Al2O3 on the surface of the first layer and apply pressure to form a prefabricated green body; S3. Rapid densification sintering of the green body: The green body was placed in a spark plasma sintering device, with graphite paper separating the inner wall of the graphite mold, the pressure head, and the powder. Argon was filled in a vacuum state of <100 Pa, and an axial pressure of 100 MPa was applied. A pulse current was applied, and the temperature was raised to 1600°C at a rate of 200°C / min. The temperature was then lowered from 1600°C to 1550°C over a period of 15 minutes, and the sample was then cooled in the furnace. S4. Subsequent processing of the sample: removing the graphite paper on the sample surface, grinding, polishing and etching the surface of the bulk sample to obtain a diamond-B4C-SiC / Si3N4-SiC ceramic composite material.

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