CN110436928B

CN110436928B - High-performance nano twin crystal boron carbide ceramic block material and preparation method thereof

Info

Publication number: CN110436928B
Application number: CN201910790880.XA
Authority: CN
Inventors: 赵智胜; 李鹏辉; 马梦冬; 何巨龙; 于栋利; 田永君; 徐波; 柳忠元
Original assignee: Yanshan University
Current assignee: Yanshan University
Priority date: 2019-08-26
Filing date: 2019-08-26
Publication date: 2021-11-23
Anticipated expiration: 2039-08-26
Also published as: CN110436928A

Abstract

The invention discloses a high-performance nanometer twin crystal boron carbide ceramic block material and a preparation method thereof, wherein the method comprises the following steps: synthesizing a nanometer twin crystal boron carbide block by taking nanometer boron carbide powder as a raw material (1) through a spark plasma sintering method; (2) synthesizing a nanometer twin crystal boron carbide block material by a hot-pressing sintering method; (3) synthesizing a nanometer twin crystal boron carbide block material at high temperature and high pressure, wherein the hardness of the synthesized nanometer twin crystal boron carbide block material is 30-55GPa, and the fracture toughness is 4.0-8.0MPa m^1/2The material has bending strength of 500-850MPa, twin crystal width of 1-100nm, grain size of 10nm-10 microns and compactness of 95-100%, has higher compactness, specific strength, high hardness and high fracture toughness, can be used as a superhard material, can be applied to light armor, bulletproof equipment, cutting tools, drill bits, high-temperature resistant structural parts and the like, and has wide application prospect.

Description

High-performance nano twin crystal boron carbide ceramic block 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 crystal boron carbide ceramic block material and a preparation method thereof.

Background

Boron carbide ceramic is a material with low density (density of only 2.52g/cm 2), high hardness (next to diamond and cubic boron nitride), high melting point (2450 ℃), high chemical stability and high neutron absorption cross section. These excellent properties have led to the widespread use of boron carbide, such as ballistic armor, cutting tools, high temperature resistant structural components, wear resistant components, neutron absorbers, and the like. However, because of strong covalent bonds among atoms in the boron carbide crystal, the boron carbide crystal has low diffusion coefficient, poor plasticity and large grain boundary sliding resistance in the sintering process, so that a compact boron carbide block is difficult to sinter, thereby limiting the further application of the boron carbide crystal.

Generally, in order to increase the compactness of the boron carbide bulk material and promote sintering densification, sintering aids such as: silicon, aluminum, carbon, carbides and borides, and the like. Although these sintering aids can lower the sintering temperature and promote densification, the introduction of the second phase may result in a product with a density greater than the theoretical density of single-phase boron carbide, and sometimes may also reduce the strength, hardness and thermal stability of the material, and thus cannot ensure that the boron carbide ceramic has the characteristics of light weight, high strength and high hardness. In the application fields of aerospace, weapon armor and the like, the specific strength of the boron carbide ceramic material is the most important index, namely the lower the density of the material is, the higher the strength/hardness is, the higher the specific strength can be, and the stronger the protection capability can be. Therefore, the preparation of the single-phase boron carbide ceramic with low density, high strength, high hardness and no adhesive has great significance. As is well known, the shape, the grain size and the microstructure of the precursor boron carbide powder can have important influence on the compactness and the mechanical property of a boron carbide bulk product. Generally, the reduction of the size of the boron carbide precursor powder to the nanometer scale is thought to reduce the sintering temperature, which is beneficial to sintering densification and obtain the high-performance boron carbide ceramic material. Recently, Tian Yongjun et al found that nano twin diamond and cubic boron nitride bulk possess extremely high hardness and fracture toughness, and the hardness of covalent materials is continuously increased with the reduction of microstructure (reduction of crystal grains or twin crystal size) according to the combined action of Hall Peltier effect and quantum confinement effect. Therefore, it is an effective way to improve the hardness, toughness and other properties of the material by introducing high-density twin crystals to refine the structure.

Disclosure of Invention

The technical problem to be solved by the invention is to provide a boron carbide ceramic block material which is prepared by sintering nano twin crystal boron carbide ceramic by using high-purity nano boron carbide powder as a precursor, and has high density, low density, higher hardness, higher strength and higher fracture toughness, and a preparation method thereof.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

the high-performance nanometer twin crystal boron carbide ceramic block material and the preparation method thereof comprise the following steps:

(1) putting nano boron carbide powder serving as a raw material into a die, and performing pre-pressing forming on a powder tablet press;

(2) sintering and synthesizing the molded raw materials by adopting different methods under certain pressure and temperature.

(3) Cooling and releasing pressure to obtain the high-performance nanometer twin crystal boron carbide ceramic block material.

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

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

Further, in the step (2), the sintering synthesis method is to put the molded raw material and the graphite mold into a hot-pressing sintering furnace, and to preserve heat for 1-600 minutes at the temperature of 1800-.

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

Further, the high-performance nano twin crystal boron carbide ceramic block material is prepared by the method.

Furthermore, the high-performance nanometer twin crystal boron carbide ceramic block material prepared by the method has the advantages that the crystal grains contain high-density twin crystal structures, the twin crystal width is 1-100nm, and the grain size is 10nm-10 mu m.

Furthermore, the high-performance nanometer twin crystal boron carbide ceramic block prepared by the methodMaterial, crystal structure is rhombohedral structure B₄C, the hardness is 30GPa-55GPa, and the fracture toughness is 4.0-8.0MPa m^1/2The bending strength is 500-850 MPa.

Due to the adoption of the technical scheme, the invention has the technical progress that:

1. the invention is based on the advantages of small particle size, large surface energy, high sintering activity and the like of the nano boron carbide powder, and the nano boron carbide powder is used as a precursor, so that the problem that boron carbide is difficult to sinter and compact is effectively solved, and the preparation of boron carbide blocks with high density and high performance is possible.

2. The invention is based on the Hall-Peltier effect and the quantum confinement effect, by reducing the microstructure: the crystal grains are reduced or fine twin crystal sub-structures are introduced, and the properties of the boron carbide ceramic such as hardness, fracture toughness and the like are obviously improved. On the basis, the nanometer boron carbide powder is used as a precursor, so that the boron carbide ceramic block with high density, high hardness, high fracture toughness and high strength is obtained.

3. In the invention, the nanometer boron carbide powder is used as a raw material, the specific surface area of the nanometer powder is large, the surface energy is high, the sintering and densification of boron carbide ceramic are facilitated, and a new way is provided for preparing the boron carbide block material with high density and high performance.

4. The preparation method is easy to implement, all the used equipment is universal equipment and can be purchased from the market, the equipment model is not unique, and the equipment model can be replaced by the same type. For example, the discharge plasma device of the present invention is of type 3.20MK-IV, manufactured by Sinter Land, Japan; the hot-pressing equipment is a ZRY-15 type multifunctional high-temperature hot-pressing sintering furnace manufactured by Boda high-temperature material equipment manufacturing company Limited in Jinzhou; a CS-1B type cubic hydraulic press produced by the heavy industry of smelting and sintering equipment with high temperature and high pressure and T25 type high temperature and high pressure synthesis equipment produced by Rockland Research of America.

5. The high-performance nano twin crystal boron carbide ceramic block material prepared by the invention contains a large amount of twin crystal structures in crystal grains, and the twin crystal boundary in the boron carbide block material can inhibit the movement and slippage of dislocation, thereby improving the mechanical performance of the boron carbide ceramic block material.

6. Compared with the boron carbide block material prepared by the prior art, the density, hardness, fracture toughness and strength of the obtained high-performance nanometer twin crystal boron carbide ceramic block material are higher than those of the commercial boron carbide block material, the hardness can reach 55GPa, and the fracture toughness can reach 8.0MPa m^1/2The bending strength can reach 850 MPa. The nanometer twin crystal boron carbide block material has wide application prospect in the aspects of bulletproof armor, cutting tools, wear-resistant parts, abrasive tools and the like.

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

Drawings

FIG. 1 is a scanning electron microscope image of nanometer boron carbide powder;

FIG. 2 is an X-ray diffraction diagram of nano boron carbide powder and nano twin boron carbide ceramic bulk material;

FIG. 3 is a transmission electron microscope (a) morphology diagram and (b) high resolution diagram of the nanometer twin crystal boron carbide ceramic block material;

FIG. 4 is a Vickers indentation diagram of a nano twin boron carbide ceramic bulk material.

Detailed Description

The present invention will be described in further detail with reference to specific examples below:

the invention provides a high-performance nanometer twin crystal boron carbide ceramic block material and a preparation method thereof, wherein the preparation method comprises the following steps:

(1) putting nano boron carbide powder serving as a raw material into a die, and performing pre-pressing forming on a powder tablet press; the particle size of the nano boron carbide powder is 10-1000nm, and more preferably 10-500 nm. The purity of the reaction raw material is required to be 90% or more, and preferably 95% or more.

In the nano boron carbide powder used in the invention, the particles of the boron carbide powder are of an irregular spherical structure, and the average particle size is about 100nm, as shown in figure 1.

(2) Sintering the formed raw materials by different methods under certain pressure and temperature

And (4) obtaining. There are three methods:

a. the first method is to put the molded raw material and the graphite mold into a spark plasma sintering device 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 100 MPa; the temperature range used is 1600-: from 1600 ℃, 1700 ℃, 1800 ℃, 1900 ℃, 2000 ℃, 2100 ℃ or 1800-; the sintering time is 0 to 120 minutes, for example: 0. 10, 15, 20, 30, 40, 50, 60, 100, 120 minutes. The temperature can be kept without heat preservation and can reach the preset value.

b. The second method is to put the molded raw material and the graphite mold into a hot-pressing sintering furnace, and keep the temperature for 1-600 minutes under the conditions of temperature of 1800 plus materials and 2300 ℃ and pressure of 20-100 MPa. The temperature used is 1800-: from 1800, 1900, 2000 to 2150, 2200, 2250, 2300 ℃; pressure 20-100MPa, for example: 20. 30, 40, 50, 60 to 80, 100 Mpa; incubation times of 1 to 600 minutes, for example: 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 high-pressure synthesis mould, keep the pressure at 1-25GPa and keep the temperature at 1400-2000 ℃ for 0-120 minutes. The pressures used are from 1GPa to 25GPa, for example: 1.5, 10, 15, 20, 25 or 1-10, 10-20, 20-25 Gpa; temperature 1400-: 1400. 1500, 1600, 1650, 1750, 1800, 1850, 1900, 1950, 2000 ℃; incubation times of 0 to 120 minutes, for example: 0. 5, 10, 20, 30, 40, 50, 60 minutes, or 60-120 minutes. The temperature can be kept without heat preservation and can reach the preset value.

In the process of preparing the powder in the step (1) and the step (2) before the powder is loaded 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 nanometer twin crystal boron carbide ceramic block material prepared by the method has high-density twin crystal tissue in crystal grains and twin crystal width1-100nm, grain size of 10nm-10 μm, and crystal structure of rhombohedral structure B₄C, the density is up to more than 95 percent, the hardness is 30GPa-55GPa, and the fracture toughness is 4.0-8.0MPa m^1/2The bending strength is 500-850 MPa. The grain size is 10nm to 10 μm, for example: from 10, 20, 30, 40, 50, 60, 70, 80, 90, 100 or 110nm to 1 μm, 2-10 μm; the hardness is 30GPa to 55GPa, for example: from 30, 31, 32, 33, 34, 35GPa or 35-45Gpa, 46, 47, 48, 49, 55 Gpa; the fracture toughness is 4.0-8.0MPa m^1/2For example: 4.0, 4.5 or 5.0 MPa m^1/2To 5-8 MPa m^1/2(ii) a The bending strength is 500-850MPa, such as: 500. 550, 600, 650, 700 or 800 MPa to 850 MPa.

The interior of the crystal grain of the high-performance nanometer twin crystal boron carbide ceramic block material contains a large number of twin crystal structures, and the twin crystal boundary in the boron carbide block material can inhibit the movement and slippage of dislocation, so that the mechanical performance of the boron carbide ceramic block material is improved; the high-performance boron carbide ceramic block material has high density, high specific strength, high hardness and high fracture toughness.

The specific embodiment is as follows:

example 1:

in the embodiment, the high-performance nanometer twin crystal boron carbide ceramic block material is prepared by adopting spark plasma sintering.

(1) Preparation of discharge plasma sintering (SPS) raw material: weighing 2g of nano boron carbide powder, putting the nano boron carbide powder into a graphite die with the diameter of 15mm, and pressurizing the nano boron carbide powder on a powder tablet press for prepressing and forming under 2 MPa.

(2) Synthesizing a high-performance nano twin crystal boron carbide ceramic block material by SPS: putting the pre-pressed and molded raw materials and the graphite mold into SPS equipment, vacuumizing until the vacuum degree is lower than 1e-2Pa, pressurizing at 50MPa, and heating to 1850 ℃ for 3 minutes.

(3) Cooling, releasing pressure and cooling to obtain the high-performance nano twin crystal boron carbide ceramic block material.

The high-performance nano twin crystal boron carbide ceramic block material prepared by the embodiment has the following properties: the density is 2.46g/cm3, the relative density reaches 98%, the X-ray diffraction pattern is shown in figure 2, and the phase composition is pure phase B₄C, the hardness is 38GPa, the relative density reaches 98 percent and the fracture toughness is 6 MPa m as measured by a hardness meter KB-5 BVZ microscope^1/2The flexural strength was 780 MPa.

As shown in FIG. 3, it can be seen from the transmission electron microscope picture of the high-performance nano twin boron carbide ceramic bulk material that a high-density twin structure is contained in the crystal grains, and the twin width is about 5-15 nm.

Example 2:

(1) Preparing a discharge plasma sintering raw material: weighing 2.5g of nano boron carbide powder, putting the nano boron carbide powder into a graphite die with the diameter of 15mm, and pressurizing the nano boron carbide powder on a powder tablet press for prepressing and forming under 2 MPa.

(2) Synthesizing a high-performance nano twin crystal boron carbide ceramic block material by SPS: and putting the pre-pressed and molded sample and the graphite mold into SPS equipment, vacuumizing until the vacuum degree is lower than 1e-2Pa, pressurizing to 100MPa, heating to 1600 ℃, and preserving the temperature for 120 min.

The high-performance nano twin crystal boron carbide ceramic block material prepared by the embodiment has the following properties: the density is 2.51g/cm3, the relative density reaches 100 percent, and the composition is pure phase B₄C, the grain size is 100nm, the hardness is 37GPa, and the fracture toughness is 5.0 MPa m^1/2The flexural strength was 750 MPa.

Example 3:

in the embodiment, the high-performance nano twin crystal boron carbide ceramic block material is prepared by hot-pressing sintering.

(1) Preparing hot-pressing sintering raw materials: weighing 2g of nano boron carbide powder, putting the nano boron carbide powder into a graphite die with the diameter of 15mm, and pressurizing the nano boron carbide powder on a powder tablet press for prepressing and forming under 2 MPa.

(2) Putting the pre-pressed raw materials and the graphite mould into a hot press, vacuumizing until the vacuum degree is lower than 10Pa, heating to 2100 ℃, heating at the rate of 5 ℃/min, pressurizing at 50Mpa, and keeping the temperature at 2100 ℃ for 30 minutes.

The high-performance nano twin crystal boron carbide ceramic block material prepared by the embodiment has the following properties: the relative density of the alloy is 97.5 percent, the hardness is 36GPa, and the fracture toughness is 5.4 MPa m measured according to an Archimedes drainage method^1/2The flexural strength was 700 MPa.

Example 4:

(2) And putting the pre-pressed raw materials and the graphite mould into a hot press, vacuumizing until the vacuum degree is lower than 10Pa, heating to 2300 ℃, pressurizing to 100Mpa, preserving the heat for 100 minutes, and releasing the pressure, cooling and cooling to obtain the high-performance nano twin crystal boron carbide ceramic block material.

The high-performance nano twin crystal boron carbide ceramic block material prepared by the embodiment has the following properties: the composition of which is pure phase B₄C, the average grain size is 10 mu m, and the test shows that the hardness is 38GPa and the fracture toughness is 4.5 MPa m^1/2The flexural strength was 850 MPa.

Example 5:

in the embodiment, a cubic press is adopted to sinter the high-performance nano twin crystal boron carbide ceramic block material at high temperature and high pressure.

(1) Preparing high-temperature and high-pressure raw materials: pressing the nanometer boron carbide powder into a cylindrical block with the diameter phi of 5mm and the height of 8 mm.

(2) High-temperature high-pressure synthesis: and putting the pressed raw materials into a hexagonal boron nitride crucible with the diameter phi of 5mm and the height of 8mm, then putting the crucible into a device for synthesizing a sample at high temperature and high pressure, firstly pressurizing to 6GPa, then heating to 1700 ℃ at the speed of 100 ℃/min, preserving heat for 15min, and releasing pressure, cooling and cooling to obtain the high-performance nano twin crystal boron carbide ceramic block material.

The high-performance nano twin crystal boron carbide ceramic block material prepared by the embodiment has the following properties: its X-ray diffraction is shown in FIG. 2, and its phase composition is pure phase B₄C, hardness of 38GPa and fracture toughness of 6.2 MPa m^1/2The relative density was 99%.

Example 6:

(2) Synthesizing a high-performance nano twin crystal boron carbide ceramic block material at high temperature and high pressure: the pressed raw materials are put into a hexagonal boron nitride crucible with the diameter phi of 5mm and the height of 8mm, then put into a device for synthesizing a sample at high temperature and high pressure, firstly pressurized to 1Gpa, then heated to 2000 ℃ at the speed of 100 ℃/min, and kept warm for 0 min. And (4) relieving the pressure, reducing the temperature and cooling to obtain the high-performance nano twin crystal boron carbide ceramic block material.

The high-performance nano twin crystal boron carbide ceramic block material prepared by the embodiment has the following properties: the phase composition of the mixed solution is pure phase B₄C, hardness of 38GPa and fracture toughness of 8.0MPa m^1/2The relative density was 99%.

Example 7:

in the embodiment, T25 is adopted to synthesize the high-performance nano twin crystal boron carbide ceramic block material at high temperature and high pressure.

(1) Preparing high-temperature and high-pressure raw materials: pre-pressing the nanometer boron carbide powder into a block with the diameter phi of 1.5-3mm and the height of 3-5 mm.

(2) Preparing a high-performance nano twin crystal boron carbide ceramic block material at high temperature and high pressure: and putting the pre-pressed block raw material into a high-temperature high-pressure synthesis device, then putting the pre-pressed block raw material into a T25 pressure device, slowly pressurizing to 25GPa, heating to 1100 ℃ and 1600 ℃, heating and preserving heat for 10 minutes, and relieving pressure, cooling and cooling to obtain the high-performance nano twin crystal boron carbide ceramic block material.

The high-performance nano twin crystal boron carbide ceramic block material prepared by the embodiment has the following properties: the relative density is greater than 99% as measured by Archimedes drainage method, and its Vickers hardness indentation pattern is shown in FIG. 4, its hardness is 42-55GPa, and its fracture toughness is 7-8 MPa m^1/2。

The analysis of experimental results shows that the high-temperature and high-pressure synthesis method can be used for synthesizing the high-performance nano twin crystal boron carbide ceramic block material at relatively low temperature, and the abnormal growth of crystal grains is not generated, so that the boron carbide ceramic block material with high density, high hardness and high fracture toughness is obtained.

In summary, the present invention is described in the embodiments, but the scope of the present invention is not limited thereto, and any alternatives or variations that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims

1. The preparation method of the high-performance nanometer twin crystal boron carbide ceramic block material is characterized by comprising the following steps of: the crystal grains in the high-performance nanometer twin crystal boron carbide ceramic block material contain a high-density twin crystal structure, the twin crystal width is 1-100nm, the grain diameter is 10nm-10 mu m, and the crystal structure of the block material is B with a rhombohedral structure₄C, the hardness of the alloy is 30GPa-55GPa, and the fracture toughness of the alloy is 4.0-8.0MPam^1/2The bending strength is 500-850 MPa;

and the preparation method comprises the following steps:

(1) putting nano boron carbide powder serving as a raw material into a die, and performing pre-pressing forming on a powder tablet press; the used nanometer boron carbide powder is of an irregular spherical structure, and the particle size is 10-500 nm;

(2) placing the molded raw materials into a discharge plasma sintering device or a hot-pressing sintering device for sintering, or sintering at high temperature and high pressure;

the sintering synthesis method comprises the steps of putting the molded raw materials and the graphite mold into a discharge plasma sintering device, keeping the pressure at 60-100MPa and keeping the temperature at 1600-2100 ℃ for 0-120 minutes;

the sintering synthesis method comprises the steps of putting the molded raw materials and a graphite mold into a hot-pressing sintering furnace, and preserving heat for 1-600 minutes under the conditions that the temperature is 1800 plus materials and 2300 ℃ and the pressure is 60-100 MPa;

the high-temperature high-pressure sintering is adopted, namely, the pre-pressed and molded raw materials are put into a high-temperature high-pressure synthesis mould, the pressure is kept between 1 and 25GPa, the temperature is kept between 1400 ℃ and 2000 ℃, and the temperature is kept for 0 to 120 minutes;

2. The preparation method of the high-performance nano twin crystal boron carbide ceramic block material according to claim 1, characterized by comprising the following steps: the purity of the nano boron carbide powder used in the step (1) is more than 90%.