CN110436928A - High-performance nano twin boron carbide ceramics block materials and preparation method thereof - Google Patents

Abstract

The invention discloses a high-performance nano-twinned boron carbide ceramic block material and a preparation method thereof. The method is as follows: using nano-boron carbide powder as a raw material (1) synthesizing a nano-twinned boron carbide block by a discharge plasma sintering method; ( 2) Synthesize nano-twinned boron carbide bulk material by hot pressing sintering method; (3) Synthesize nano-twinned boron carbide bulk material by high temperature and high pressure, the hardness of the synthesized nano-twinned boron carbide bulk material is 30‑55GPa, fracture The toughness is 4.0-8.0 MPa m ^1/2 , the bending strength is 500-850MPa, the twin width is 1-100nm, the grain size is 10nm-10μm, the density is 95-100%, and it has higher density, The characteristics of specific strength, high hardness and high fracture toughness, as a superhard material, can be used in light armor, bulletproof equipment, cutting tools and drill bits, high temperature resistant structural components, etc., and has broad application prospects.

Description

High-performance nano-twinned boron carbide ceramic bulk material and preparation method thereof

technical field

The invention relates to the technical field of high-performance structural ceramics, in particular to a high-performance nano-twin boron carbide ceramic block material and a preparation method thereof.

Background technique

Boron carbide ceramic is a material with low density (only 2.52g/cm2), high hardness (second only to diamond and cubic boron nitride), high melting point (2450°C), high chemical stability and high neutron absorption cross-section . These excellent properties make boron carbide widely used, such as bulletproof armor, cutting tools, high temperature resistant structural parts, wear resistant parts and neutron absorbers, etc. However, due to the strong covalent bonds between the atoms in the boron carbide crystal, the diffusion coefficient is low, the plasticity is poor, and the grain boundary slip resistance is large during the sintering process, which makes it difficult to sinter a dense boron carbide block and limit its further application.

Usually, in order to increase the density of boron carbide bulk materials and promote sintering densification, sintering aids such as silicon, aluminum, carbon, carbides and borides are introduced. Although these sintering aids can reduce the sintering temperature and promote densification, the introduction of the second phase will cause the density of the product to be greater than the theoretical density of single-phase boron carbide, and sometimes reduce the strength, hardness and thermal stability of the material, which cannot be guaranteed Boron carbide ceramics have the characteristics of light weight, high strength and high hardness. In aerospace, weapon armor and other application fields, the specific strength of boron carbide ceramic materials is the most important indicator, that is to say, the lower the density of the material and the higher the strength/hardness, the higher the specific strength and the better the protection ability. powerful. Therefore, it is of great significance to prepare low-density, high-strength, high-hardness, and binder-free single-phase boron carbide ceramics. It is well known that the morphology, particle size and microstructure of the precursor boron carbide powder will have an important impact on the density and mechanical properties of the boron carbide bulk product. It is generally believed that reducing the size of the boron carbide precursor powder to the nanometer scale will reduce the sintering temperature, which is conducive to sintering densification and obtaining high-performance boron carbide ceramic materials. Recently, Tian Yongjun and others found that nano-twinned diamond and cubic boron nitride bulk materials have extremely high hardness and fracture toughness. The reduction of the microstructure (reduction of grain or twin size) continues to increase. Therefore, it is an effective way to refine the microstructure by introducing high-density twins to improve the properties of materials such as hardness and toughness.

Contents of the invention

The technical problem to be solved in the present invention is to provide a kind of sintering nano-twinned boron carbide ceramics using high-purity nano-boron carbide powder as a precursor to obtain high density, low density, higher hardness, higher strength and higher fracture toughness. A boron carbide ceramic bulk material and a preparation method thereof.

In order to solve the problems of the technologies described above, the technical solution adopted in the present invention is:

A high-performance nano-twinned boron carbide ceramic bulk material and a preparation method thereof, comprising the following steps:

(1) Using nano-boron carbide powder as raw material, put it into a mold and pre-press it on a powder tablet press;

(2) The formed raw materials are sintered and synthesized under certain pressure and temperature by different methods.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling and pressure relief.

Further, the particle size of the nano-boron carbide powder used in the step (1) is 10-1000 nm, and the purity is greater than 90%.

Further, in the step (2), the sintering synthesis method is to put the formed raw material and graphite mold into spark plasma sintering equipment, keep the pressure at 30-100MPa, and keep the temperature at 1600-2100°C for 0-120 minutes .

Further, in the step (2), the sintering synthesis method is to put the formed raw material and graphite mold into a hot-press sintering furnace, and keep it warm for 1-600 minutes at a temperature of 1800-2300°C and a pressure of 20-100MPa .

Further, in the step (2), the sintering synthesis method is to put the pre-pressed raw materials into a high-temperature and high-pressure synthesis mold, keep the pressure at 1-25GPa, and keep the temperature at 1400-2000°C for 0-120 minutes.

Further, a high-performance nano-twinned boron carbide ceramic bulk material was prepared by the above method.

Furthermore, the high-performance nano-twinned boron carbide ceramic bulk material prepared by the above method contains high-density twin structure inside the grain, the twin width is 1-100 nm, and the grain size is 10 nm-10 μm.

Furthermore, the high-performance nano-twinned boron carbide ceramic bulk material prepared by the above method has a rhombohedral B ₄ C crystal structure, a hardness of 30GPa-55GPa, and a fracture toughness of 4.0-8.0 MPa m ^1/2 . The bending strength is 500-850Mpa.

Owing to having adopted above-mentioned technical scheme, the technical progress that the present invention obtains is:

1. The present invention is based on the advantages of small particle size, large surface energy, and high sintering activity based on nano-boron carbide powder. Using nano-boron carbide powder as a precursor effectively improves the problem that boron carbide is difficult to sinter and compact, making it possible to prepare high-density , High-performance boron carbide blocks become possible.

2. According to the Hallpech effect and quantum confinement effect, the present invention significantly improves the hardness, fracture toughness and other properties of boron carbide ceramics by reducing the microstructure: reducing grains or introducing fine twin substructures. On this basis, using nano-boron carbide powder as a precursor, a boron carbide ceramic block with high density, high hardness, high fracture toughness and high strength is obtained.

3. In the present invention, nano-boron carbide powder is used as raw material. The specific surface area of nano-powder is large, and the high surface energy contributes to the sintering and densification of boron carbide ceramics. In order to prepare high-density, high-performance boron carbide Blocks offer new avenues.

4. The preparation method of the present invention is easy to implement, and the equipment used is all general-purpose equipment that can be bought on the market. The equipment model is not unique and can be replaced by the same type. For example, the discharge plasma equipment of the present invention is the 3.20MK-IV type produced by Japan Sinter Land Company; the hot pressing equipment is the ZRY-15 multifunctional high temperature hot pressing sintering furnace manufactured by Jinzhou Boda High Temperature Material Equipment Manufacturing Co., Ltd.; High-temperature and high-pressure sintering equipment CS-1B six-sided top hydraulic press produced by Guiye Heavy Industry and T25 high-temperature and high-pressure synthesis equipment produced by Rockland Research in the United States.

5. The high-performance nano-twinned boron carbide ceramic bulk material prepared in the present invention contains a large number of twin structures inside the grains, and the twin boundaries existing in the boron carbide bulk can inhibit the movement and slip of dislocations. shift, improving its mechanical properties.

6. Compared with the boron carbide bulk material prepared by the prior art, the density, hardness, fracture toughness and strength of the obtained high-performance nano-twinned boron carbide ceramic bulk material are higher than those of the commercial boron carbide bulk material , the hardness is up to 55GPa, the fracture toughness is up to 8.0 MPa m ^1/2 , and the bending strength is up to 850MPa. Nano-twinned boron carbide bulk materials have broad application prospects in bulletproof armor, cutting tools, wear-resistant parts and abrasives.

7. The preparation method of the present invention is simple, the parameters are easy to control, and it is suitable for industrial production.

Description of drawings

The picture of the scanning electron microscope of the nano-boron carbide powder of Fig. 1;

The X-ray diffraction pattern of Fig. 2 nano-boron carbide powder and nano-twinned boron carbide ceramic bulk material;

Figure 3 Transmission electron microscope (a) topography and (b) high-resolution images of nano-twinned boron carbide ceramic bulk materials;

Fig. 4 Vickers indentation diagram of nano-twinned boron carbide ceramic bulk material.

Detailed ways

Below in conjunction with specific embodiment the present invention is described in further detail:

The invention provides a high-performance nano-twinned boron carbide ceramic block material and a preparation method thereof, comprising the following steps:

(1) Using nano boron carbide powder as raw material, putting it into a mold and pre-compressing it on a powder tablet press; the particle size of the nano boron carbide powder used is 10-1000nm, more preferably 10-500nm. As the reaction raw material, its purity is required to be above 90%, preferably the raw material purity is above 95%.

The nano boron carbide powder used in the present invention, the boron carbide powder particles have an irregular spherical structure, and the average particle size is about 100nm, as shown in FIG. 1 .

(2) The formed raw materials are sintered under certain pressure and temperature by different methods

to make. There are three methods:

a. The first method is to put the formed raw material and graphite mold into the spark plasma sintering equipment to keep the pressure at 30-100MPa and the temperature at 1600-2100℃ for 0-120 minutes. The pressure range used is 30-100MPa, for example: 30MPa, 40MPa, 50MPa, 60MPa, 70MPa, 80MPa, 90MPa or 100Mpa; the temperature range used is 1600-2100°C, for example: from 1600°C, 1700°C, 1800°C, 1900°C , 2000°C, 2100°C or 1800-2100°C; the sintering time is 0-120 minutes, for example: 0, 10, 15, 20, 30, 40, 50, 60, 100, 120 minutes. It is not necessary to keep warm, as long as the temperature reaches the preset value.

b. The second method is to put the formed raw material and graphite mold into a hot-press sintering furnace, and keep it warm for 1-600 minutes at a temperature of 1800-2300°C and a pressure of 20-100MPa. The temperature used is 1800-2300°C, for example: from 1800, 1900, 2000 to 2150, 2200, 2250, 2300°C; pressure 20-100MPa, for example: 20, 30, 40, 50, 60 to 80, 100Mpa; holding time 1 - 600 minutes, eg: 1, 30, 50, 70, 90, 100 minutes or 100-200, 200-300, 400-600 minutes.

c. The third method is to put the pre-pressed raw material into a high-temperature and high-pressure synthetic mold, keep the pressure at 1-25GPa, and keep the temperature at 1400-2000°C for 0-120 minutes. The pressure used is 1GPa-25GPa, for example: 1, 5, 10, 15, 20, 25 or 1-10, 10-20, 20-25Gpa; the temperature is 1400-2000°C, for example: 1400, 1500, 1600, 1650, 1750, 1800, 1850, 1900, 1950, 2000°C; holding time 0-120 minutes, for example: 0, 5, 10, 20, 30, 40, 50, 60 minutes or 60-120 minutes. It is not necessary to keep warm, as long as the temperature reaches the preset value.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling and pressure relief.

In the process of step (1) and step (2) from the preparation of the powder to loading into the sintering mold, the raw materials are preferably placed in a vacuum environment or an inert atmosphere, such as an argon glove box.

The high-performance nano-twinned boron carbide ceramic bulk material prepared by the above method contains a high-density twin structure inside the grain, the twin width is 1-100nm, the grain size is 10nm-10μm, and the crystal structure is rhombohedral. B ₄ C, the density is as high as 95%, the hardness is 30GPa-55GPa, the fracture toughness is 4.0-8.0 MPa m ^1/2 , and the bending strength is 500-850Mpa. The grain size is 10nm-10μm, for example: from 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or 110nm to 1μm, 2-10μm; its hardness is 30GPa-55GPa, for example: from 30, 31, 32, 33, 34, 35GPa or 35-45Gpa, 46, 47, 48, 49, 55Gpa; fracture toughness of 4.0-8.0 MPa m ^1/2 , for example: 4.0, 4.5 or 5.0 MPa m ^1/2 to 5-8 MPa m ^1/2 ; the bending strength is 500-850Mpa, for example: 500, 550, 600, 650, 700 or 800 MPa to 850 MPa.

There are a large number of twin structures in the grains of high-performance nano-twinned boron carbide ceramic bulk materials, and the twin grain boundaries existing in boron carbide bulk materials can inhibit the movement and slip of dislocations, thereby improving their mechanical properties; High-performance boron carbide ceramic bulk material with high density, high specific strength, high hardness and high fracture toughness.

Specific examples are as follows:

Example 1:

In this embodiment, spark plasma sintering is used to prepare a high-performance nano-twinned boron carbide ceramic bulk material.

(1) Raw material preparation for spark plasma sintering (SPS): Weigh 2g of nano-boron carbide powder and put it into a Φ15mm graphite mold, and press 2MPa on the powder tablet press for pre-compression molding.

(2) Synthesis of high-performance nano-twinned boron carbide ceramic bulk material by SPS: put the above-mentioned pre-pressed raw materials and graphite mold into the SPS equipment, vacuumize until the vacuum degree is lower than 1e-2Pa, pressurize to 50MPa, and heat up to Heat at 1850°C for 3 minutes.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling under pressure and pressure relief.

The performance of the high-performance nano-twinned boron carbide ceramic bulk material prepared by this embodiment: its density is 2.46g/cm3, and the relative density reaches 98%. Its X-ray diffraction pattern is as shown in Figure 2, and its phase composition is pure Phase B ₄ C has a hardness of 38GPa measured by a hardness tester KB-5 BVZ microscope, a relative density of 98%, a fracture toughness of 6 MPa m ^1/2 , and a bending strength of 780MPa.

As shown in Figure 3, the transmission electron microscope picture of the high-performance nano-twinned boron carbide ceramic bulk material shows that there is a high-density twin structure inside the grain, and the twin width is about 5-15nm.

Example 2:

In this embodiment, spark plasma sintering is used to prepare a high-performance nano-twinned boron carbide ceramic bulk material.

(1) Raw material preparation for spark plasma sintering: Weigh 2.5g of nano-boron carbide powder and put it into a Φ15mm graphite mold, and press 2MPa on the powder tablet press for pre-compression molding.

(2) Synthesis of high-performance nano-twinned boron carbide ceramic bulk materials by SPS: Put the above-mentioned pre-pressed samples and graphite molds into the SPS equipment, evacuate until the vacuum degree is lower than 1e-2Pa, pressurize 100MPa, and heat up to 1600°C, keep warm for 120min.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling under pressure and pressure relief.

The properties of the high-performance nano-twinned boron carbide ceramic bulk material prepared in this embodiment: its density is 2.51g/cm3, the relative density reaches 100%, its composition is pure phase B ₄ C, the grain size is 100nm, the hardness It is 37GPa, its fracture toughness is 5.0 MPa m ^1/2 , and its bending strength is 750MPa.

Example 3:

In this example, high-performance nano-twinned boron carbide ceramic bulk material is prepared by hot pressing and sintering.

(1) Preparation of raw materials for hot pressing sintering: Weigh 2g of nano-boron carbide powder and put it into a Φ15mm graphite mold, pressurize 2MPa on a powder tablet press for pre-compression molding.

(2) Put the pre-pressed raw material and graphite mold into the hot press, evacuate until the vacuum degree is lower than 10Pa, raise the temperature to 2100°C, the heating rate is 5°C/min, pressurize 50Mpa, and keep at 2100°C for 30 minute.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling under pressure and pressure relief.

The properties of the high-performance nano-twinned boron carbide ceramic bulk material prepared in this embodiment: according to the Archimedes drainage method, the relative density is 97.5%, the hardness is 36GPa, and the fracture toughness is 5.4 MPa m ^1/2 , The bending strength is 700MPa.

Example 4:

In this example, high-performance nano-twinned boron carbide ceramic bulk material is prepared by hot pressing and sintering.

(1) Preparation of raw materials for hot pressing sintering: Weigh 2g of nano-boron carbide powder and put it into a Φ15mm graphite mold, pressurize 2MPa on a powder tablet press for pre-compression molding.

(2) Put the pre-pressed raw material and graphite mold into the hot press, evacuate until the vacuum degree is lower than 10Pa, raise the temperature to 2300°C, pressurize to 100Mpa, keep the temperature for 100 minutes, release the pressure and cool down to get high performance Nano-twinned boron carbide ceramic bulk material.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling under pressure and pressure relief.

The performance of the high-performance nano-twinned boron carbide ceramic bulk material prepared in this example: its composition is pure phase B ₄ C, the average grain size is 10 μm, the test shows that its hardness is 38 GPa, and its fracture toughness is 4.5 MPa m ^{1 /2} , the bending strength is 850MPa.

Example 5:

In this embodiment, a high-temperature and high-pressure sintering high-performance nano-twinned boron carbide ceramic block material is used in a six-sided top press.

(1) High-temperature and high-pressure raw material preparation: Press nano-boron carbide powder into a cylindrical block with a diameter of Φ5mm and a height of 8mm.

(2) High-temperature and high-pressure synthesis: Put the above-mentioned pressed raw materials into a hexagonal boron nitride crucible with a diameter of Φ5mm and a height of 8mm, and then put it into a high-temperature and high-pressure synthesis sample device, pressurize to 6GPa first, and then pressurize at 100℃/min Raise the temperature to 1700°C, hold the temperature for 15 minutes, release the pressure and cool down to obtain a high-performance nano-twinned boron carbide ceramic block material.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling under pressure and pressure relief.

The properties of the high-performance nano-twinned boron carbide ceramic bulk material prepared in this example: its X-ray diffraction is shown in Figure 2, its phase composition is pure phase B ₄ C, its hardness is 38GPa, and its fracture toughness is 6.2 MPa m ^1/2 , the relative density is 99%.

Embodiment 6:

In this embodiment, a high-temperature and high-pressure sintering high-performance nano-twinned boron carbide ceramic block material is used in a six-sided top press.

(1) High-temperature and high-pressure raw material preparation: Press nano-boron carbide powder into a cylindrical block with a diameter of Φ5mm and a height of 8mm.

(2) High-temperature and high-pressure synthesis of high-performance nano-twinned boron carbide ceramic block materials: put the above-mentioned pressed raw materials into a hexagonal boron nitride crucible with a diameter of Φ5mm and a height of 8mm, and then put it into a high-temperature and high-pressure synthesis sample device. Pressurize to 1Gpa, then raise the temperature to 2000°C at a rate of 100°C/min, and hold for 0min. The high-performance nano-twinned boron carbide ceramic bulk material is obtained after pressure relief and cooling.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling under pressure and pressure relief.

The performance of the high-performance nano-twinned boron carbide ceramic bulk material prepared in this example: its phase composition is pure phase B ₄ C, the hardness is 38GPa, the fracture toughness is 8.0 MPa m ^1/2 , and the relative density is 99%.

Embodiment 7:

This embodiment uses T25 high temperature and high pressure to synthesize high-performance nano-twinned boron carbide ceramic bulk material.

(1) High-temperature and high-pressure raw material preparation: pre-press nano-boron carbide powder into a block with a diameter of Φ1.5-3mm and a height of 3-5mm.

(2) Preparation of high-performance nano-twinned boron carbide ceramic block materials at high temperature and high pressure: put the above-mentioned pre-pressed block raw materials into a high-temperature and high-pressure synthesis device, and then put them into a T25 pressurization device, slowly pressurize to 25GPa, and raise the temperature 1100-1600°C, heat and hold for 10 minutes, release the pressure and cool down to obtain a high-performance nano-twinned boron carbide ceramic block material.

(3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling under pressure and pressure relief.

The performance of the high-performance nano-twinned boron carbide ceramic bulk material prepared in this embodiment: its relative density is greater than 99% as measured by the Archimedes drainage method, as shown in Figure 4. Its Vickers hardness indentation diagram, its The hardness is 42-55Gpa, and the fracture toughness is 7-8 MPa m ^1/2 .

The analysis of the experimental results shows that high-performance nano-twinned boron carbide ceramic bulk materials can be synthesized at relatively low temperatures by using high-temperature and high-pressure synthesis methods, and the grains do not grow abnormally, resulting in high density, high hardness, high Fracture-tough boron carbide ceramic bulk material.

In summary, the above is a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any replacement or change that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention covers all Within the protection scope of the present invention.

Claims (7)

1. The preparation method of high-performance nano-twinned boron carbide ceramic block material, is characterized in that: comprise the following steps: (1) Using nano-boron carbide powder as raw material, put it into a mold and pre-press it on a powder tablet press; (2) The formed raw materials are sintered and synthesized under certain pressure and temperature by different methods; (3) High-performance nano-twinned boron carbide ceramic bulk material is obtained after cooling and pressure relief. 2. The preparation method of high-performance nano-twinned boron carbide ceramic bulk material according to claim 1, characterized in that: the particle size of the nano-boron carbide powder used in the step (1) is 10-1000nm, the purity Greater than 90%. 3. The method for preparing high-performance nano-twinned boron carbide ceramic bulk material according to claim 1, characterized in that: in the step (2), the sintering synthesis method is to put the formed raw material and graphite mold into In the spark plasma sintering equipment, the pressure is kept at 30-100MPa, and the temperature is kept at 1600-2100°C for 0-120 minutes. 4. The preparation method of high-performance nano-twinned boron carbide ceramic bulk material according to claim 1, characterized in that: in the step (2), the sintering synthesis method is to put the formed raw material and graphite mold into In a hot pressing sintering furnace, the temperature is kept at 1800-2300° C. and the pressure is 20-100 MPa for 1-600 minutes. 5. The method for preparing high-performance nano-twinned boron carbide ceramic bulk material according to claim 1, characterized in that: in the step (2), the sintering synthesis method is to put the pre-pressed raw material into high temperature In the high-pressure synthesis mold, keep the pressure at 1-25GPa, the temperature at 1400-2000°C, and keep warm for 0-120 minutes. 6. A high-performance nano-twinned boron carbide ceramic bulk material, characterized in that: the internal grains of the bulk material contain high-density twinning structures, the twinning width is 1-100nm, and the grain size is 10nm-10μm. 7. The high-performance nano-twinned boron carbide ceramic bulk material according to claim 6, characterized in that: the crystal structure of the bulk material is B ₄ C with a rhombohedral structure, its hardness is 30GPa-55GPa, and its fracture toughness is 4.0 -8.0 MPa m ^1/2 , the bending strength is 500-850MPa.