CN114763306A

CN114763306A - Layered boron nitride grain boundary phase toughened zinc blende boron nitride ceramic and preparation method thereof

Info

Publication number: CN114763306A
Application number: CN202110056514.9A
Authority: CN
Inventors: 赵智胜; 孙磊; 罗坤; 陈俊云; 刘兵; 何巨龙; 于栋利; 柳忠元; 胡文涛; 徐波; 田永君
Original assignee: Yanshan University
Current assignee: Yanshan University
Priority date: 2021-01-15
Filing date: 2021-01-15
Publication date: 2022-07-19

Abstract

The invention discloses a laminar boron nitride grain boundary phase toughened zinc blende boron nitride ceramic and a preparation method thereof. The ceramic body comprises two typical textures: one is that when the layered BN grain boundary phase is distributed around the zinc blende boron nitride crystal grains, the hardness of the material reaches 20-40 GPa, and the fracture toughness reaches 6-9 MPa.m^1/2(ii) a The other is that when the layered BN grain boundary phase only exists at the intersection (triangular zone) of boron nitride grain boundaries of zincblende, the hardness of the material reaches more than 40GPa, and the fracture toughness is more than 9 MPa.m^1/2. The invention also discloses a process for preparing the layered Boron Nitride (BN) grain boundary phase toughened sphalerite boron nitride ceramic body. The process comprises sintering one or more phase structure BN powder raw materials under non-pressure or high temperature and high pressure, forming in situ zinc blende boron nitride as main phase and layered BN as crystal boundaryA phase ceramic body.

Description

Layered boron nitride grain boundary phase toughened zinc blende boron nitride ceramic and preparation method thereof

Technical Field

The invention belongs to the field of inorganic non-metallic materials, and relates to boron nitride ceramic and a preparation method thereof.

Background

It is well known that zincblende boron nitride (cBN) is a superhard material having hardness second only to diamond. Furthermore, zincblende boron nitride has some superior properties not comparable to diamond, such as higher thermal stability and chemical inertness to iron group metals and their alloys. Therefore, the sphalerite boron nitride as an engineering material is widely applied to the processing industry of ferrous metals and alloy materials thereof. Meanwhile, the material is applied to a series of high-tech fields by virtue of excellent thermal, electrical, optical, acoustic and other properties, and becomes a functional material with development prospect.

The sphalerite boron nitride single crystal has limited synthesis size, a dissociation plane and low fracture toughness (2.8 MPa-m)¹ ^/2) Severely limiting its application in industry. Therefore, the development of isotropic, high-hardness, high-toughness polycrystalline zinc blende boron nitride (PcBN) blocks has become a major research goal in science and industry.

Suitable binders are almost always necessary to obtain isotropic PcBN ceramics. Currently, the common binders for PcBN synthesis are mainly classified into three major categories: 1) ceramic binder, mainly nitride, carbide, silicide, etc.; 2) a metallic binder composed of a metal or alloy (e.g., aluminum, titanium, cobalt, nickel, etc.); 3) the metal ceramic adhesive consists of ceramic and metal or metal alloy in certain proportion. Upon sintering, a grain boundary phase is typically created in association with the binder, and the sphalerite boron nitride grains are embedded in a matrix of the grain boundary phase, thereby forming a dense, isotropic ceramic body. Disadvantageously, the existence of such grain boundary phase greatly affects the direct bonding between boron and nitrogen atoms, thereby seriously reducing the properties of hardness, thermal stability, wear resistance and the like of the sample. Moreover, the binder in the PcBN is one of the potential pollution sources in the processing process, and can cause certain pollution to the workpiece in the use process of grinding, cutting and the like, thereby seriously affecting the performance of the workpiece.

Therefore, there is a great need for new boron nitride materials with isotropy and methods of making them that are environmentally friendly.

Disclosure of Invention

It is an object of the present invention to provide an isotropic zincblende boron nitride ceramic material having both high hardness and high toughness.

It is another object of the present invention to provide a method for manufacturing an isotropic boron nitride ceramic material which avoids the use of environmentally unfriendly binders and the like.

Therefore, the technical solution of the first aspect of the present invention is a sphalerite boron nitride ceramic material, which is composed of sphalerite boron nitride crystal grains as a main phase and a layered boron nitride grain boundary phase distributed around the sphalerite boron nitride crystal grains, wherein the sphalerite boron nitride crystal grains have sp phase³A hybrid structure, the layered boron nitride grain boundary phase has sp²Hybrid structures. At present, no related patent and literature reports that the lamellar boron nitride grain boundary phase toughened zinc blende boron nitride ceramics exist.

Because the zinc blende boron nitride main phase and the layered BN grain boundary phase are in a symbiotic relationship, the obtained zinc blende boron nitride ceramic body is not only an all-BN material (the whole material is directly bonded by boron and nitrogen), but also can improve the fracture toughness of the zinc blende boron nitride ceramic body on the premise of ensuring that the hardness, the thermal stability, the wear resistance and the like are not reduced, and solves the very key problem in the PcBN field at present; in addition, no patent literature or non-patent literature reports on the material exist.

Considering sp²The layered BN of the structure may be with sp³The zinc blende boron nitride phase of the structure is converted with each other under a certain temperature and pressure condition, which is similar to the conversion process between graphite and diamond; therefore, the zinc blende boron nitride ceramic material of the invention can utilize the structure phase change mechanism of BN material per se to sp²Hybridized boron nitride or sp³The hybridized boron nitride is used as a raw material for preparation.

Therefore, the second aspect of the present invention provides a method for preparing a sphalerite boron nitride ceramic material, which comprises the following steps:

(1) providing pure boron nitride powder raw material or block raw material;

(2) purifying the pure boron nitride powder or block raw material by heating under vacuum;

(3) and (3) carrying out high-temperature sintering treatment on the purified boron nitride block raw material, or prefabricating the purified boron nitride powder raw material into a blank and then carrying out high-temperature sintering treatment on the prefabricated blank, thereby forming the zinc blende boron nitride ceramic material, wherein the high-temperature sintering treatment is preferably carried out under high pressure.

The method can obtain the authigenic layered BN grain boundary phase toughened zincblende boron nitride ceramic material which contains zincblende boron nitride tissues as a main phase and further contains a layered BN grain boundary phase distributed in a grain boundary, namely the zincblende boron nitride ceramic material according to the first aspect of the invention. The preparation method is environment-friendly because no additional binder is used, and the obtained material is an all-BN material, so that the problem of workpiece pollution in the further processing process of the material is avoided, and the high hardness, the high thermal stability, the high wear resistance and the high fracture toughness of the material are ensured.

Detailed Description

The technical scheme of the first aspect of the invention is that the zincblende boron nitride ceramic material is composed of zincblende boron nitride grains as a main phase and nitrogen distributed in the zincblendeA layered boron nitride grain boundary phase around boron nitride grains, wherein the zincblende boron nitride grains have sp³Hybrid structure, layered boron nitride grain boundary phase having sp²Hybrid structures. Such zincblende boron nitride may also be referred to as "lamellar boron nitride grain boundary phase toughened zincblende boron nitride".

In the present application, unless otherwise indicated or defined, all terms should be interpreted as having meanings commonly understood by those skilled in the art. For clarity, the following terms should be construed and understood in accordance with the definitions set forth herein.

For the purposes of the present invention, an "all-BN material" or an "all-boron nitride material" means that the chemical composition contains only B and N, and no other chemical elements. It will be understood by those skilled in the art that "all-BN material" does not exclude unavoidable trace impurities present in the feedstock itself or inadvertently introduced during processing. By "all-BN material" for the purposes of the present invention is meant that the mass of the B and N elements represents at least 97%, preferably at least 98%, more preferably at least 99%, most preferably at least 99.9% or close to 100% of the total mass of the material.

"Layered BN" or "Layered boron nitride" ("Layered-BN") refers to graphitic sp-like materials with ordered or disordered material microstructures (structures observed by transmission electron microscopy)²A hybrid BN structure. As will be understood by those skilled in the art, a "layered BN" is composed primarily of sp²Structural carbon, but it is not excluded that it contains small amounts (e.g. less than 10%, 5%, 3%, 2%, 1%, 0.5%, 0.3%, etc.) of sp as an impurity³BN or even other elements.

In the present application, "toughening" is generally understood to mean that the fracture toughness of the toughened material is at least 6MPa · m^1/2. The zincblende boron nitride ceramic material of the present application "consists of zincblende boron nitride grains as a main phase and a layered boron nitride grain boundary phase distributed around the zincblende boron nitride grains" in terms of its microstructure. Those skilled in the art will appreciate that there are a variety of techniques for obtaining microstructural information about a material. For example, when the grain size of the zincblende boron nitride grains is 1 μm andin the above process, whether a layered boron nitride grain boundary phase exists between the sphalerite boron nitride grains can be visually judged through XRD and/or SEM images of the polished material sample surface. When the grain size of the zincblende boron nitride grains is below 1 μm, the SAED (selected area electron diffraction) and HRTEM (high resolution transmission electron microscope) of a TEM electron microscope can be generally used to detect whether a lamellar boron nitride grain boundary phase exists between the zincblende boron nitride grains in a sample of the material. For accurate characterization, for TEM detection, it is preferable to analyze the material internal sample; in addition, to avoid interference from small amounts of contaminants that may be present in the sample, multiple (e.g., more than 3) sample points may be randomly taken for analysis.

The zinc blende boron nitride ceramic material takes zinc blende boron nitride as a main phase and layered boron nitride as a grain boundary phase. Specifically, the sphalerite boron nitride major phase is present in an amount of at least 50% by volume, such as at least 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, etc., but generally no more than 99%; the volume content of the lamellar boron nitride grain boundary phase is at most 50%, such as at most 45%, 40%, 35%, 30%, 25%, 20%, 15%, 10%, 5%, 4%, 3%, 2%, etc., but generally not less than 1%. The volume content of the major phase and the grain boundary phase can be determined by one skilled in the art according to conventional techniques, for example, multiple regions of the material can be observed by microscopic imaging techniques (such as SEM or TEM, etc.), the volume ratio of the two phases can be estimated according to the area ratio of the two phases in the microscopic image of the material of each region, and the average value of the multiple regions can be calculated to determine the volume ratio of the two phases.

In the zincblende boron nitride ceramic material of the present invention, the size (average particle diameter) of the zincblende boron nitride crystal grains as the main phase is generally between 0.1 μm and 20 μm; for example, the grain size may be greater than 0.2 μm, greater than 0.3 μm, greater than 0.4 μm, greater than 0.5 μm, greater than 0.8 μm, greater than 1.0 μm, greater than 1.5 μm, greater than 2.0 μm, greater than 2.5 μm, greater than 3.0 μm, and the grain size may be less than 18 μm, less than 15 μm, less than 12 μm, less than 10 μm, less than 8 μm, less than 6 μm, less than 5 μm. Preferably, the size of the zincblende boron nitride grains as the main phase is between 0.2 μm and 10 μm. The size of the boron nitride grains of zincblende as the main phase can be determined by one skilled in the art according to conventional techniques, for example, by observing multiple regions of the material by microscopic imaging techniques (such as SEM or TEM, etc.), then determining the average grain size of the grains according to microscopic images of the material of each region, and finally calculating the average value of the multiple regions to determine the total average grain size of the grains.

The inventive zincblende boron nitride ceramic material may be in the form of a bulk material or may also be pulverized into a particulate or powder form, preferably used in the form of a bulk material (or sintered body). By "bulk" material is understood herein to mean that the volume of an individual mass of material present independently is at least 1mm³E.g. at least 5mm³At least 10mm³At least 20mm³At least 50mm³At least 100mm³At least 200mm³At least 500mm³At least 1000mm³(ii) a The upper limit of the volume of the block material is not particularly limited and may be selected as appropriate according to the actual needs and the processing capacity of the equipment, and may be, for example, up to 1000cm³。

It will be appreciated by those skilled in the art that the sphalerite boron nitride ceramic material of the present application "consisting of sphalerite boron nitride grains as the main phase and a lamellar boron nitride grain boundary phase distributed around the sphalerite boron nitride grains" is not to be understood as an absolute limitation, i.e. that in addition to the sphalerite boron nitride as the main phase and the lamellar boron nitride grain boundary phase, there may be small amounts of other phase structured boron nitride or other components that are inevitably formed during the manufacturing process, which are typically present in a volume content of up to 5%, such as less than 3%, 2%, 1%, 0.5% or 0.3%, etc.

The application mainly obtains the blende boron nitride ceramic material (in the form of a sintered body) toughened by the layered boron nitride grain boundary phase with two structures.

A layered boron nitride grain boundary phase toughened zincblende boron nitride ceramic body comprising: a. a main boron nitride phase of zincblende with a volume content of 50% or more (preferably 50-98%), b. a lamellar BN grain boundary phaseIs dispersed (i.e., substantially uniformly distributed) around the zincblende boron nitride grains at a volume content of 50% or less (preferably 2% to 50%). Such boron nitride grain boundary phase toughened zincblende boron nitride ceramic bodies typically have a vickers hardness of greater than 20GPa, 6MPa · m^1/2Fracture toughness of (3).

Another layered boron nitride grain boundary phase toughened zincblende boron nitride ceramic body comprises: a. a main sphalerite boron nitride phase having a volume content of at least 90% (preferably 90% to 99%), b. a lamellar BN grain boundary phase distributed at the sphalerite boron nitride grain boundary junctions (triangles) having a volume content of at most 10% (preferably 1% to 10%). Such boron nitride grain boundary phase toughened zincblende boron nitride ceramic bodies generally have a vickers hardness of greater than 40GPa, greater than 9 MPa-m^1/2The fracture toughness of (2).

The second aspect of the invention provides a preparation method for preparing the sphalerite boron nitride ceramic material, which comprises the following steps:

(1) providing pure boron nitride powder raw material or block raw material;

In some embodiments, step (1) is to purify the BN powder or powders to remove impurities that may be present, in order to obtain a pure BN powder. In the present application, "BN powder" refers to nanometer, submicron, or micron sized BN. In the present application, "pure BN powder" is understood to mean a purity of at least 90%, preferably at least 95%, more preferably at least 97%, most preferably at least 98% or at least 99%. In order to obtain the "pure BN powder", the raw BN powder material may be subjected to a purification treatment. The purification treatment may be, for example: treating BN powder with nanometer, submicron or micron size with nitric acid, hydrofluoric acid, hydrochloric acid or sulfuric acid, and treating at 20-500 deg.C (such as 50 deg.C, 70 deg.C, 90 deg.C, 100 deg.C, 150 deg.C, 200 deg.C, 250 deg.C, 300 deg.C, 350 deg.C, 400 deg.C, 450 deg.C) to dissolve impurities in BN powder; or treated with other methods. Alternatively, the BN powder after acid treatment may be washed with deionized water to wash the acid solution, filtered, separated, dried, and the like. In some embodiments, the higher purity BN feedstock may not need to be purified and utilized directly.

In some embodiments, step (1) is a purification of the BN block feedstock to remove impurities that may be contained, in order to obtain a pure BN block. In the present application, "pure BN mass" is understood to mean a purity of at least 90%, preferably at least 95%, more preferably at least 97%, most preferably at least 98% or at least 99%. In order to obtain the "pure BN block", the raw crude BN block material may be subjected to a purification treatment. The purification treatment may be, for example: treating the block by using nitric acid, hydrofluoric acid, hydrochloric acid or sulfuric acid, and dissolving impurities in the BN block at the temperature of 20-500 ℃; or treated with other methods. Alternatively, the acid-treated BN mass may be washed with deionized water to wash the acid solution, filtered, separated, dried, etc. In some embodiments, the higher purity BN feedstock may not need to be purified and utilized directly.

The BN powder or block used in step (1) may be various types of NB, for example, may be selected from sp²Hybridized boron nitride and/or sp³Hybrid boron nitride material, said sp²The hybridized boron nitride material comprises BN with different phase structures such as hexagonal boron nitride (hBN), pyrolytic hexagonal boron nitride (pBN), spherical boron nitride (oBN) and Boron Nitride Nanotubes (BNNTs)³The hybrid boron nitride material comprises BN with different phase structures such as sphalerite boron nitride (sphalerite boron nitride) and wurtzite boron nitride (wBN). As the BN powder, one NB raw material may be used, or a mixture of plural NB raw materials may be used. The size of the BN powder can be nano-scale, submicron-scale or micron-scale. For NB blocks, then, typically, a single block is used, which may be a single crystal form of NB, orAlternatively, NB polycrystalline or mixed crystals mixed with different crystal forms may be used.

The vacuum purification treatment in the step (2) is mainly used for purifying the surface of BN powder or block material so as to remove oxygen, nitrogen and water vapor impurities adsorbed on the surface. For example, the specific operating conditions of step (2) may be: under vacuum degree of 4X10^-3～4×10^-5Pa, and the temperature is 800-1600 ℃ for 10-500 min. The degree of vacuum may be, for example, 5 × 10^-5Pa、8×10^-5Pa、1×10^-4Pa、4×10^-4Pa、8×10^-4Pa、1×10^-3Pa、2×10^-3Pa, etc., the temperature can be 850 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃, etc., and the treatment time can be 15min, 20min, 35min, 45min, 60min, 120min, 180min, 300min, 360min, 420min, etc., for example.

If the raw material is a BN block, the sintering treatment of step (3) may be directly performed after purification. If the raw material is BN powder, the purified BN powder needs to be pre-pressed into a blank body and then sintered. The blank may be any shape as desired, such as a cylinder, a square, a sphere, etc. The pre-pressing in step (3) may be carried out on a conventional embryo press or hydraulic press, and is usually carried out at room temperature, and may be carried out in air or an inert atmosphere as required. The pressing pressure is not critical as long as the compact of the green body is ensured, and may be, for example, 0 to 60MPa, such as 0.2MPa, 0.3MPa, 0.5MPa, 1MPa, 2MPa, 5MPa, 10MPa, 20MPa, 30MPa, 40MPa, 50MPa, or the like. For example, one exemplary operational step may be: and (3) putting the BN powder raw material into a blank pressing machine to be prefabricated into a BN column, and pressing the BN column into a relatively compact blank block on a common hydraulic press at room temperature under 0.1-60 MPa.

In step (3), the purified NB bulk or the purified BN powder preform is subjected to sintering treatment. The sintering treatment may be carried out in a non-pressure or pressure-bearing sintering apparatus such as a muffle furnace, a tube furnace, a hot-pressing furnace, a pulse discharge plasma sintering furnace, or a high-temperature and high-pressure apparatus. The sintering temperature is usually in the range of 800-3000 ℃, for example 850 ℃, 900 ℃, 1000 ℃, 1100 ℃, 1200 ℃, 1300 ℃, 1400 ℃, 1500 ℃, 1600 ℃, 1700 ℃, 1800 ℃, 1900 ℃, 2000 ℃, 2100 ℃, 2200 ℃, 2300 ℃, 2400 ℃, 2500 ℃, 2600 ℃, 2700 ℃, 2800 ℃, 2900 ℃ and other temperatures. The sintering pressure is usually 0 to 30GPa, for example, 0.001GPa, 0.01GPa, 0.05GPa, 0.1GPa, 0.2GPa, 0.3GPa, 0.5GPa, 1GPa, 2GPa, 5GPa, 10GPa, 12GPa, 15GPa, 18GPa, 20GPa, 25GP and the like. Pressureless sintering processes are best performed in an inert atmosphere, whereas pressurized sintering processes require components that flow better under high pressure to provide a uniform pressure and temperature environment. The sintering time may be 1-600 min, for example, 5min, 10min, 15min, 20min, 35min, 45min, 60min, 120min, 180min, 300min, 360min, 420min, 480min, 540min, etc.

Compared with the prior art, the invention has the following advantages: compared with pure phase PcBN and PcBN ceramic containing a binder in the prior art, the zinc blende boron nitride ceramic body has obviously higher fracture toughness and hardness. Advantageously, the toughened grain boundary phase layered BN of the zincblende boron nitride ceramic bodies of the present invention is autogenous and therefore more strongly bonded to the main phase. And the sphalerite boron nitride ceramic body is a full BN material, and can solve the problem of workpiece pollution caused by external additives in commercial PcBN. The room temperature hardness and compressive strength of the zincblende boron nitride ceramics of the present invention are not much reduced at high temperatures (e.g., 1000 c) or higher. The ceramic body is then suitable for high temperature applications. The invention also provides a novel method for preparing the layered BN grain boundary phase toughened novel sphalerite boron nitride ceramic by taking BN with different phase structures as raw materials. The method aims to produce the layered BN grain boundary phase toughened novel zinc blende boron nitride ceramic with more excellent mechanical properties by a low-cost investment and an industrialized method, and the prepared layered BN grain boundary phase toughened novel zinc blende boron nitride ceramic is a full BN material and has excellent properties of higher density, hardness, fracture toughness and the like than commercially prepared PcBN.

Drawings

FIG. 1 is an HAADF electron micrograph of a sample obtained in example 1 of the present invention;

FIG. 2 is a SAED electron micrograph of a sample obtained in example 1 of the present invention;

FIG. 3 is a schematic view of the microstructure of the sample obtained in examples 1 and 2 of the present invention;

FIG. 4 is a photo of a cracked Vickers indentation optical film under a 3kg load of a sample obtained in example 2 of the present invention;

FIG. 5 is an HAADF electron micrograph of a sample obtained in example 3 of the present invention;

FIG. 6 is a SAED electron micrograph of a sample obtained in example 3 of the present invention;

FIG. 7 is a schematic view of the microstructure of the sample obtained in examples 3, 4 and 5 of the present invention.

Examples

The embodiments described below are some, but not all embodiments of the invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the invention as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without departing from the inventive concept, are within the scope of the present invention.

For the sake of brevity, some of the materials, equipment, and process steps conventionally employed in the art are not specifically identified in the examples. All the processing methods and analytical testing procedures (and the relevant parameters) not specifically mentioned in the examples were carried out as commonly employed by those skilled in the art; materials and equipment from specific sources are not noted to be laboratory-routine.

Apparatus and material analysis detection method

The high temperature and high pressure apparatus used in each example was a cubic press CS-1B (national Guilin Metallurgical machinery headquarters), a Kawai model T25 hydraulic press (Rockland, USA).

The used pulse discharge plasma sintering furnace was a SPS-3.20MK-IV type discharge plasma sintering system (Nippon Sumitomo Stone coal mining Co., Ltd.)

The main analytical detection methods and instruments used in the examples were as follows:

SAED, HAADF test: for SAED, HAADF analysis, TEM samples (4X 8X 0.1 μm) were prepared using Focused Ion Beam (FIB) and tested using a scanning transmission electron microscope (Sammer Feishell science, USA) with an acceleration voltage of 300kV using Sammer Fetalos F200X.

The Vickers hardness detection method comprises the following steps: and (3) carrying out microhardness test on the sample by adopting a German KB-5-BVZ type microhardness tester, wherein the test parameters are loading for 30s and pressure maintaining for 30 s. The indenter is pressed into the sample under test by applying a load, leaving a trace of plastic deformation on the sample surface after the load is removed. The Vickers hardness is achieved by using a diamond pyramid pressure head with an included angle of 136 degrees between opposite surfaces, the diamond pyramid pressure head is vertically pressed into the surface of a material under the action of a certain pressure and is kept for a certain time, and diamond-shaped indentations generated by plastic deformation are reserved on the surface of a sample. The area of the indentation is calculated according to the diagonal length of the indentation left after unloading. The applied load divided by the area of the indentation is the hardness measured by the indentation method. The calculation formula of vickers hardness is: h_v＝1854.4F/L²Wherein F is the loaded load size and the unit is N; l is the average diagonal length of the indentation and is expressed in μm.

The fracture toughness detection method comprises the following steps: fracture toughness is the ability of a material to resist crack propagation, and can quantitatively characterize the toughness difference of the material. The samples were tested for fracture toughness using a KB-5-BVZ microhardness tester from Germany, by applying a sufficiently large load to produce substantially uniform cracks at the four apex angles of the indentation in the surface of the sample. Its value K_ICIt can be calculated from the applied load F and the radial propagation length C of the pre-crack generated at the four vertices of the indentation under this load. K_ICThe calculation formula of (a) is as follows: k_IC＝7.42×10-2F/C^1.5(2 is more than or equal to C/A is less than or equal to 6), wherein F is the size of the loaded load and the unit is N; c is the average length of the radial crack measured from the center of the indentation and a is half the average diagonal length L of the indentation in μm.

Example 1

Commercial hBN powder with the average grain diameter of about 100nm to 200nm is added into a purifying kettle in nitric acid with the concentration of 25 percent and the weight ratio of the nitric acid to the hBN powder of 2: 1, stirred and heated to 70 ℃ in water bath, treated for 72 hours,after the powder is settled, pouring out the liquid, washing the powder to be neutral by using deionized water, then washing the powder by using methanol, repeating the acid dissolution and impurity removal for 4 times, and drying the hBN powder; then putting the hBN powder at the vacuum degree of 4x10^-4Pa, the temperature is 1000 ℃, and the treatment is carried out for 3h to remove oxygen, nitrogen and water vapor impurities adsorbed on the surface of hBN; the surface of a wrapping material tantalum foil is ground, polished, deoiled, ultrasonically cleaned and infrared dried, then, purified hBN powder is placed into a wrapping material, the wrapping material tantalum foil is pre-pressed into a compact block with the diameter and the height of 1mm under the pressure of 10MPa, the pressed compact block is placed on a high-temperature high-pressure device, the sintering is carried out for 15min under the pressure of 15GPa and the temperature of 1900 ℃, the pressure is reduced and the temperature is reduced to the room temperature at normal pressure, then a sample is placed into mixed acid of 20ml of 30% hydrofluoric acid and 20ml of 40% nitric acid to remove the wrapping material tantalum, and the sample is ground to be bright by using a grinding disc.

The HAADF electron microscope picture, the SAED electron microscope picture and the schematic structural diagram of the sample are respectively shown in figures 1-3, the situation that the layered BN grain boundary phase in the sample only exists at the intersection of the zinc blende boron nitride grain boundaries can be visually seen, and the grain diameter of the zinc blende boron nitride grains is 500 nm. Vickers hardness test shows that the hardness of the material is 50GPa, and the fracture toughness reaches 11 MPa.m^1/2。

Example 2

Commercially available pyrolytic hexagonal boron nitride (pBN) was ground into a cylinder of 5mm in diameter and height, and the pBN cylinder was evacuated at 4X10^-3Pa at the temperature of 800 ℃, treating for 5h, and removing oxygen, nitrogen and water vapor impurities adsorbed on the surface of the pBN; grinding, polishing, deoiling, ultrasonic cleaning and infrared drying are carried out on the surface of the wrapping material tantalum foil; then, the purified pBN cylinder is placed in a package, the pBN cylinder is placed on a high-temperature high-pressure device, sintering is carried out for 30min at the pressure of 8GPa and the temperature of 1700 ℃, the pressure is reduced and the temperature is reduced to the room temperature of normal pressure, the sample is placed in a mixed acid of 20ml of 30% hydrofluoric acid and 20ml of 40% nitric acid to remove the tantalum serving as a packaging material, and the sample is polished to be bright by using a grinding plate.

The HAADF electron microscope photograph, SAED electron microscope photograph and the schematic structural diagram of the sample are respectively similar to those shown in FIGS. 1-3 of example 1, and it can be seen that the lamellar BN grain boundary phase only exists at the intersection of the zinc blende boron nitride grain boundaries. FIG. 4 is a graph of Vickers under a 3kg loadThe Vickers hardness test shows that the hardness of the material is 44GPa, and the fracture toughness reaches 9.5 MPa.m^1/2。

Example 3

Commercially purchasing zinc blende boron nitride powder with the average particle size of about 80 mu m, adding 15% sulfuric acid and the zinc blende boron nitride powder in a weight ratio of 2: 1 into a purification kettle, stirring and heating in a water bath to 70 ℃, treating for 72 hours, pouring out liquid after the powder is settled, washing with deionized water to be neutral, repeating the acid dissolution and impurity removal for 3 times, and drying the zinc blende boron nitride powder; then zinc blende boron nitride powder is processed at the vacuum degree of 4x10^-3Pa, the temperature is 1500 ℃, the treatment is carried out for 0.5h, and oxygen, nitrogen and water vapor impurities adsorbed on the surface of the zinc blende boron nitride are removed; polishing, deoiling, ultrasonically cleaning and infrared drying the surface of a wrapping material tantalum foil, then prepressing the purified sphalerite boron nitride powder under the pressure of 60MPa into compact briquettes with the diameter of 200mm and the height of 200mm, placing the pressed briquettes into an atmosphere box furnace, sintering for 20min at the temperature of 1200 ℃ in the atmosphere of ammonia gas, cooling to room temperature, then placing a sample into mixed acid of 20ml of 30% hydrofluoric acid and 20ml of 40% nitric acid to remove the tantalum wrapping material, and grinding the sample to be bright by using a grinding disc.

The HAADF electron microscope picture, the SAED electron microscope picture and the schematic structural diagram of the sample are respectively shown in figures 5-7, the layered BN grain boundary phase in the sample can be visually seen to exist at the grain boundary junction and also be dispersedly distributed around the zinc blende boron nitride grains, the grain diameter of the zinc blende boron nitride grains is 60 mu m, the Vickers hardness test shows that the material hardness is 28GPa, and the fracture toughness is 6.5 MPa.m^1/2。

Example 4

Adding zincblende boron nitride powder with the average particle size of about 5 microns into 38% hydrochloric acid, wherein the weight ratio of the hydrochloric acid to the zincblende boron nitride powder is 2: 1, adding the zincblende boron nitride powder into a purification kettle, stirring and heating the zincblende boron nitride powder in a water bath to 70 ℃, treating the zincblende boron nitride powder for 72 hours, pouring out liquid after the powder is settled, washing the powder to be neutral by using deionized water, and drying the zincblende boron nitride powder after repeating the acid dissolution and impurity removal for 5 times; then zinc flashThe vacuum degree of the ore boron nitride powder is 4x10^-5Pa, the temperature is 1200 ℃, and the treatment is carried out for 2h to remove oxygen, nitrogen and water vapor impurities adsorbed on the surface of the zinc blende boron nitride; then, prepressing the purified zinc blende boron nitride powder into compact blocks with the diameter of 20mm and the height of 10mm under the pressure of 10MPa, placing the pressed green bodies on a pulse discharge plasma sintering furnace, sintering for 10min under the conditions of the pressure of 70MPa and the temperature of 1700 ℃, reducing the pressure and the temperature to the room temperature at normal pressure, and grinding the samples to be bright by using a grinding disc.

The HAADF electron microscope picture, the SAED electron microscope picture and the schematic structural diagram of the sample are respectively similar to those shown in the figures 5-7 of the embodiment 3, the layered BN grain boundary phase in the sample can be visually seen to exist at the grain boundary intersection and also be dispersedly distributed around the zinc blende boron nitride grains, and the Vickers hardness test shows that the material hardness is 22GPa, and the fracture toughness reaches 6 MPa.m^1/2。

Example 5

The raw material was commercially available BNNTs (boron nitride nanotubes) powder having an average particle size of about 5 μm, treated with hydrofluoric acid having a concentration of 40%. Adding hydrofluoric acid and BNNTs powder into a purification kettle at a weight ratio of 2: 1, stirring and heating to 70 ℃ in a water bath, treating for 72 hours, pouring out liquid after the powder is settled, washing with deionized water to be neutral, then placing the BNNTs powder into sulfuric acid with the concentration of 25%, adding the sulfuric acid and BNNTs powder at a weight ratio of 2: 1 into the purification kettle, stirring and heating to 70 ℃ in the water bath, treating for 72 hours, pouring out liquid after the powder is settled, washing with deionized water to be neutral, repeating the above steps of acid dissolution and impurity removal for 6 times, and drying the BNNTs powder; then BNNTs powder is treated at the vacuum degree of 4x10^-3Pa, the temperature is 1500 ℃, the treatment is carried out for 0.5h, and oxygen, nitrogen and water vapor impurities adsorbed on the surface of BNNTs are removed; then, prepressing the purified BNNTs powder into a compact briquette with the diameter and the height of 2mm under the pressure of 5MPa, placing the pressed briquette on a high-temperature high-pressure device, sintering for 5min under the pressure of 25GPa and the temperature of 800 ℃, reducing the pressure and the temperature to the room temperature of normal pressure, removing a wrapping material from a sample, and grinding the sample to be bright by using a grinding disc.

HAADF and SAED electron micrographs of samplesThe sheet and the tissue structure schematic diagrams are respectively similar to those shown in figures 5-7 of the embodiment 3, the lamellar BN grain boundary phase in the sample can be visually seen to exist at the grain boundary intersection and also be dispersedly distributed around the zinc blende boron nitride grains, the Vickers hardness test shows that the material hardness is 39GP, and the fracture toughness reaches 8.5 MPa.m^1/2。

The preparation process parameters and material property test results of the above examples are also shown in table 1 below.

TABLE 1 preparation method and performance comparison table of zincblende boron nitride ceramics of examples 1-5 layers

Claims

1. The sphalerite boron nitride ceramic material consists of sphalerite boron nitride crystal grains as a main phase and a layered boron nitride grain boundary phase which is dispersedly distributed around the sphalerite boron nitride crystal grains, wherein the sphalerite boron nitride crystal grains have sp³Hybrid structure, layered boron nitride grain boundary phase having sp²Hybrid structures.

2. The zincblende boron nitride ceramic material of claim 1, wherein the volume content of the zincblende boron nitride grains is 50% to 99% (preferably 70% to 96% or 80% to 95%), and the volume content of the layered boron nitride grain boundaries is 1% to 50% (preferably 4% to 30% or 5% to 20%).

3. The zincblende boron nitride ceramic material according to claim 1 or 2, having a vickers hardness of more than 20GPa and a fracture toughness of more than 6 MPa-m^1/2。

4. The zincblende boron nitride ceramic material of claim 1 or 2, wherein the volume content of the zincblende boron nitride main phase is 50% to 98%, the volume content of the lamellar carbon grain boundary phase is 2% to 50%, and the lamellar boron nitride grain boundary phase is substantially uniformly distributed around the zincblende boron nitride grainsThe Vickers hardness of the alloy is more than 20GPa, the fracture toughness is more than 6 MPa.m^1/2。

5. The zincblende boron nitride ceramic material of claim 1 or 2, wherein the volume content of the zincblende boron nitride main phase is at least 90%, the volume content of the lamellar boron nitride grain boundary phase is at most 10%, and the lamellar boron nitride grain boundary phase is only distributed at the zinc blende boron nitride grain boundary junction, has the Vickers hardness of more than 40GPa and the fracture toughness of more than 9 MPa-m^1/2。

6. The zincblende boron nitride ceramic material of claim 1 or 2, in the form of a bulk material.

7. A method for preparing the zincblende boron nitride ceramic material of any one of claims 1 to 6, comprising the steps of:

(1) providing pure boron nitride powder raw material or block raw material;

8. The method for preparing a sphalerite boron nitride ceramic material according to claim 7, wherein the boron nitride raw material in the step (1) is: sp²Hybrid boron nitride materials including hexagonal boron nitride (hBN), pyrolytic hexagonal boron nitride (pBN), spherical boron nitride (oBN), and Boron Nitride Nanotubes (BNNTs); and/or sp³Hybrid boron nitride materials including sphalerite boron nitride and wurtzite boron nitride (wBN), optionally the BN starting material is a powder with a grain size of nanometer, submicron or micrometer.

9. The method for preparing a zincblende boron nitride ceramic material according to claim 8, wherein the operation of step (2) is: at vacuum degree of 4X10^-3～4x10^-5Pa and the temperature is 800-1600 ℃, and the purification treatment is carried out for 10-500 min.

10. The method for preparing zincblende boron nitride ceramic material according to any one of claims 7 to 9, wherein the high-temperature sintering treatment conditions of step (3) are: sintering for 1-600 min in a sintering device selected from a muffle furnace, a tubular furnace, a hot pressing furnace, a pulse discharge plasma sintering furnace and a high-temperature high-pressure device at the temperature of 800-3000 ℃ and under the pressure of 0-30 GPa.