WO2021197471A1

WO2021197471A1 - Diamond composite phase material and preparation method therefor

Info

Publication number: WO2021197471A1
Application number: PCT/CN2021/085261
Authority: WO
Inventors: 田永君; 徐波; 周向锋; 胡文涛; 高宇飞; 李子鹤; 应盼; 刘笑笑; 于栋利; 何巨龙; 柳忠元; 聂安民; 王霖; 高国英; 陈俊云; 赵智胜
Original assignee: 燕山大学
Priority date: 2020-04-03
Filing date: 2021-04-02
Publication date: 2021-10-07
Also published as: CN113493202A; CN113493202B

Abstract

Provided are a diamond composite phase material and a preparation method therefor. Onion carbon is used as a raw material, and a novel diamond composite phase bulk material containing multiple types of diamond phases of 3C, 2H, 4H, 6H, 8H, 10H, 9R, 15R and 21R is prepared by means of a high-temperature and high-pressure synthesis method. Two or more types of diamond phases of 2H, 3C, 4H, 6H, 8H, 9R, 10H, 15R and 21R can be found in the crystal grains of the bulk material. Among them, the 3C type diamond has an ultra-fine nano-twin crystal structure with a twin crytal width of 1-15nm. The diamond composite phase bulk material has an internal grain size of 2-80 nm, a Vickers hardness of 150-260 GPa, and a fracture toughness of 12-30 MPa m^1/2. The diamond composite phase bulk material has broad applications in the fields of precision and ultra-precision machining, wire drawing dies, abrasives and special optical components.

Description

Diamond composite material and preparation method thereof

This application claims the priority of Chinese Patent Application No. 202010261332.0 filed on April 3, 2020, which is incorporated herein by reference in its entirety.

Technical field

This application belongs to the field of inorganic materials, and specifically relates to a diamond material and a preparation method thereof.

Background technique

Superhard materials refer to materials with a hardness above 40GPa, which are widely used in tools and wear-resistant materials. In the 1950s, researchers from General Electric Company in the United States successively synthesized synthetic diamond and cubic boron nitride (cBN). Since then, superhard materials represented by diamond and cBN have been widely used in many fields such as machining, geological prospecting, oil drilling, metallurgy, instrumentation, electronics industry, aerospace and so on. Diamond and cBN have strong covalent bonds, resulting in poor sintering properties of their powders, and it is difficult to directly sinter into polycrystalline bulk materials even under high temperature and high pressure conditions. At present, polycrystalline diamond (PCD) and polycrystalline cubic boron nitride (PCBN) materials with metal Co as a bonding agent are commonly used. Although the toughness of the above two materials is improved, the hardness and thermal stability of PCD and PCBN become low due to the presence of the binder.

In 2003, Japanese researcher Tetsuo Irifune et al. used the direct phase change of polycrystalline graphite to synthesize a binder-free superhard nanocrystalline diamond block (NPCD) under the conditions of 12-25GPa and 2300-2500℃ (Reference: " Ultrahard polycrystalline diamond from graphite "Nature 421, P599-600). The grain size in NPCD bulk material is 10-30nm, and its Knoop hardness (Hk) is as high as 120-140GPa. In 2006, German scholar Dubrovinskaia et al. compressed C ₆₀ under the conditions of 20GPa and 2500K to synthesize binder-free superhard polycrystalline diamond nanorods (ADNRs), the diameter of the nanorods is about 20nm (document: "Superior Wear Resistance of Aggregated Diamond Nanorods", Nano Letters 2006, 6, P824-826). The Knoop hardness of ADNRs can reach 105GPa; the fracture toughness reaches 11.1±1.2MPa·m ^1/2 , which is 2-3 times that of single crystal diamond; its wear resistance coefficient is 3 times that of commercial binder-containing polycrystalline diamond (PCD) Times. However, these superhard materials still have disadvantages such as harsh synthesis conditions and poor overall material properties.

With the continuous progress of industrial society, the performance requirements of superhard materials are getting higher and higher, and the existing superhard materials have become more and more difficult to meet the needs of modern processing industries. Therefore, seeking high-performance tool materials with higher hardness, toughness and heat resistance has become an urgent requirement of today's society.

Summary of the invention

The purpose of this application is to provide a new type of superhard material that meets the requirements of modern industry and has better comprehensive performance and a preparation method thereof.

In one aspect, the present application provides a new type of diamond multiphase bulk material, the diamond multiphase bulk material is a 3C type diamond phase with a zinc blende structure and selected from 2H, 4H, 6H, 8H, 9R, 10H, 15R and 21R are composed of one or more other diamond phases, and the prerequisite is that when the diamond multiphase bulk material is composed of two phases, the other phase except the 3C phase is not the 6H phase.

In a preferred embodiment, the diamond multiphase bulk material is composed of a 3C type diamond phase with a zinc blende structure and two or more selected from 2H, 4H, 6H, 8H, 9R, 10H, 15R, 21R It is composed of other diamond phases.

In other preferred embodiments, the diamond complex bulk material is a 3C type diamond phase with a zinc blende structure and one or more selected from 2H, 4H, 8H, 9R, 10H, 15R, 21R It is composed of other diamond phases.

In other preferred embodiments, the diamond complex bulk material is a 3C-type diamond phase with a zinc blende structure and two or more selected from 2H, 4H, 8H, 9R, 10H, 15R, 21R It is composed of other diamond phases.

Preferably, the grain size inside the diamond multiphase bulk material of the present application is 2-80nm, and the crystal grains contain the nano twin structure formed by the 3C diamond, and the twin crystal width is 1-15nm, other diamonds The phase is also embedded in the crystal grains of the bulk material.

The 3C, 2H, 4H, 6H, 8H, 9R, 10H, 15R, 21R and other diamond phases mentioned in this application are well known to those skilled in the art and have the meanings commonly understood by those skilled in the art. The Vickers hardness and fracture toughness described in this application can be measured by conventional methods known in the art. For specific measurement methods, for example, refer to the references cited in the background art section above or the specific embodiments of this application.

Those skilled in the art can understand that "diamond multiphase bulk material is composed of 3C type diamond phase with zinc blende structure and one or more other selected from 2H, 4H, 6H, 8H, 9R, 10H, 15R, 21R The “consisting of diamond phase” does not exclude that there may be a small amount of impurities in the diamond complex bulk material. The impurities may be other diamond phases not specifically mentioned herein or non-diamond components. Generally, the weight percentage or volume percentage of the impurities relative to the diamond multiphase bulk material is less than 5%, preferably less than 3%, more preferably less than 2%, and most preferably less than 1%.

On the other hand, this application also provides a method for preparing the diamond complex bulk material, which includes the following steps:

(1) Use seedless onion carbon as raw material, put it into a mold and pre-compress it into a green body;

(2) Put the prefabricated body into a high-temperature and high-pressure synthesis mold, and perform high-temperature and high-pressure treatment.

Preferably, the preparation method further includes the following steps:

(3) After cooling, the pressure is relieved to obtain the diamond complex bulk material.

In a preferred embodiment, the process parameters of the high temperature and high pressure treatment are: the pressure is in the range of 8-18 GPa, and the temperature is in the range of 1500-2300°C; more preferably, the synthesis pressure is 10-15 GPa, and the synthesis temperature is 1800- 2200°C.

Preferably, the operation sequence of the high-temperature and high-pressure treatment is: firstly increase the pressure, then increase the temperature, and then keep the temperature for 10-60 minutes. Preferably, the pressure increase rate of the temperature and high pressure treatment is 2-4 GPa/h, and the temperature increase rate is 200-300° C./min.

The hardness of single crystal diamond exhibits obvious anisotropy. According to the different crystallographic orientation, the hardness of single crystal diamond is between 60-120GPa, and the fracture toughness is 3-5MPa·m ^1/2 . In addition, single crystal diamond is prone to cleavage along the weakest crystal plane under stress. These characteristics limit the application of single crystal diamond. The diamond complex bulk material of the present application is isotropic, with a Vickers hardness of 150-260 GPa, which can be up to two times that of natural diamond, and a fracture toughness of 12-30 MPa·m ^1/2 , which is the same as natural diamond. 3 to 6 times. These excellent mechanical properties make it widely used in the fields of precision and ultra-precision processing, wire drawing dies, abrasives and special optical components. In addition, due to the diversification of the phase composition types of the diamond multiphase bulk material of the present application, the properties of the diamond can be conveniently adjusted according to actual needs, thereby allowing the provision of materials with better comprehensive performance and broadening its application range.

Hereinafter, each aspect of the present application will be further described in detail with reference to the drawings and specific implementations.

Description of the drawings

In Figure 1, a shows the TEM image of the non-nuclear onion carbon raw material used in the preparation method of the present application; b shows the TEM image of the onion carbon with diamond cores obtained in other documents for comparison.

Fig. 2 is a schematic longitudinal cross-sectional view of a high-temperature and high-pressure assembly used in the preparation method of the present application.

Figure 3 shows the physical photo of the diamond complex bulk material synthesized under high temperature and high pressure conditions of 15 GPa and 1900°C.

Figure 4 shows the X-ray diffraction pattern of the diamond complex bulk material synthesized under high temperature and high pressure conditions of 15 GPa and 1900°C.

Figure 5 shows the high-resolution electron micrograph (HRTEM) and selected area electron diffraction pattern (SAED) of the diamond multiphase bulk material synthesized under the conditions of 15 GPa and 1900° C. under high temperature and high pressure.

Figure 6 shows the size and distribution of crystal grains in the diamond complex bulk material synthesized under high temperature and high pressure conditions of 15 GPa and 1900°C.

In Figure 7, a shows the ideal atomic arrangement of different diamond phases, and b shows the high-resolution electron micrograph of the diamond complex bulk material synthesized under the conditions of 15 GPa and 1900 ℃ high temperature and high pressure, in which different diamonds can be distinguished. Mutually.

Fig. 8 shows the variation of Vickers hardness of diamond multiphase bulk materials synthesized under high temperature and high pressure conditions of 15 GPa and 1900° C. with load.

Figure 9 shows a physical photo of a diamond complex bulk material synthesized under high temperature and high pressure conditions of 10 GPa and 2100°C.

Figure 10 shows the X-ray diffraction pattern of the diamond multiphase bulk material synthesized under the conditions of 10 GPa and 2100°C of high temperature and high pressure.

Figure 11 shows the physical photo of the diamond complex bulk material synthesized under the conditions of 12 GPa and 1800°C of high temperature and high pressure.

Figure 12 shows the X-ray diffraction pattern of the diamond multiphase bulk material synthesized under the conditions of 12 GPa and 1800°C of high temperature and high pressure.

Detailed ways

The inventor of the present application found that: using seedless onion carbon as the starting material, a kind of 3C diamond and 2H, 4H, 6H, 8H, 9R, 10H, 15R, 21R diamond phases were synthesized by high temperature and high pressure. Diamond complex bulk material. In the multiphase material, 3C diamond can form a nano twin structure (twins width is usually 1-15nm), non-3C diamond polytypes such as 2H, 4H, 6H, 8H, 9R, 10H, 15R, 21R diamond, embedded In the crystal grains, the thickness is usually only a few nanometers. Diamond complex bulk is usually colorless and transparent or yellow and transparent or black and opaque. Therefore, this application relates to a diamond multiphase bulk material, which is composed of a 3C type diamond phase with a zinc blende structure and selected from 2H, 4H, 6H, 8H, 9R, 10H, 15R, 21R At least one other diamond phase (preferably at least two other diamond phases, for example, at least three other diamond phases) is composed, but when the diamond multiphase bulk material is composed of two phases, the other diamond phases are not 6H phases.

Onion carbon, also known as shallot carbon, is a nano-spherical carbon with a Russian doll-like structure. The properties, characteristics and preparation methods of the material are known to those skilled in the art. The raw material for the preparation method of the present application is onion carbon without a diamond core in its core, that is, seedless onion carbon. An exemplary TEM image of seedless onion carbon particles is shown in Figure 1a. This kind of seedless onion carbon is prepared by another patented technology of the present inventor (Patent Publication No. CN 103382025B, which is incorporated herein by reference in its entirety). Its particle size is usually in the range of 5-50nm, uniformly distributed, and its core is a chaotic layer structure instead of a diamond core. As a comparison, Figure 1b shows the TEM image of onion carbon with diamond cores obtained by heating nanodiamonds in the previous literature (excerpted from the paper "Carbon onions as nanoscopic pressure cells for diamond formation" by Banhart, F et al., Nature 1996 , 382, P433-435).

According to CN 103382025B, the non-nuclear onion carbon used as the raw material of the preparation method of the present application can be prepared by the following method: adding carbon black to alcohol to form a suspension; and pouring the suspension into a liquid flow pulverizer. The liquid flow pulverizer can make the suspension produce the turbulent flow vibration oscillator caused by the high-speed jet to generate ultrasonic waves and shock waves; after the carbon black suspension is squeezed and deformed many times, the onion-structured nano-spherical carbon can be obtained. The carbon core has no diamond core.

An exemplary specific preparation method of seedless onion carbon includes the following steps:

(1) Using carbon black as a raw material, put carbon black particles with a particle size of 30-100nm into alcohol (analytical purity) to prepare a suspension with a concentration of 1-30wt%;

(2) Pour the suspension into the ultra-micronization device for cyclic treatment, and keep it at a pressure of 100-150MPa and run it for 50-1000 cycles;

(3) Put the product solution in a drying box at 45-60°C for 3-6 hours to dry, and grind the dried product into powder particles and collect them to obtain nano-onion carbon with a particle size of 5-50 nm.

The onion-structured nano-spherical carbon used in the preparation method of this application is a nano-scale carbon material with approximately spherical particles. It is characterized in that each layer of the spherical carbon has a spherical shape, and its particle size is usually 5-50nm. Within the range, the particle size distribution is relatively uniform, and there is no diamond core in the core. As the reaction raw material, it is generally required that its purity is not less than 90%, preferably its purity is not less than 95%. In the preparation method of the present application, the seedless onion carbon powder must be compressed into a preform before the high temperature and high pressure experiment, preferably pre-compressed under an inert gas environment, for example, in a glove box protected by high-purity argon or high-purity nitrogen .

Generally, when high-temperature and high-pressure synthesis is performed, the raw material preform is put into a high-temperature and high-pressure assembly block (also known as a "high-temperature and high-pressure synthesis mold"), and then the high-temperature and high-pressure assembly block containing the raw material preform is placed in the high-temperature and high-pressure synthesis equipment. A schematic diagram of an exemplary high-temperature and high-pressure assembly block is shown in Figure 2. The principle is to use ceramic powder such as MgO to prepare a block with a central hole (octahedron in the T25 system), and put the sample in the central hole The precursor (preform), the heating body and the thermocouple of the temperature measuring element, use the MgO block to pressurize and densify to realize the pressure transmission, sealing and heat insulation during the synthesis process. The high-temperature and high-pressure assembly blocks used in the examples of this application are manufactured by Arizona State University in the United States and purchased from TJ Pegasus, the United States. Two types of high-temperature and high-pressure composite blocks of 10/5 and 8/3 are used in the synthesis.

In the high temperature and high pressure treatment in step (2) of the preparation method of the present application, the pressure range used is usually 8-18 GPa, for example from 8, 9, 10 or 11 GPa to 14, 15, 16, 17 or 18 GPa, preferably 10- 15GPa; the temperature range used is usually 1500-2300℃, for example from 1500℃, 1600℃, 1700℃ or 1800℃ to 1900℃, 2000℃, 2100℃, 2200℃ or 2300℃, the preferred temperature range is 1800-2200 ℃. The operation sequence of the high-temperature and high-pressure treatment is preferably: first increase the pressure, then increase the temperature, and then keep warm. The holding time of the reaction is usually not critical. For example, it can be 1-120 minutes, 2-120 minutes, 10-120 minutes, etc., and can be adjusted according to the temperature and pressure used. The preferred holding time is 10-60 minutes. The pressure increase and temperature increase rate will affect the formation of the diamond complex. The pressure increase rate preferably used is 2-4 GPa/h; the temperature increase rate preferably used is 200-300°C/min.

Equipment for high-temperature and high-pressure synthesis is known, and it is preferable to use a commercial press, such as a T25 press produced by Rockland Research in the United States.

Under the high temperature and high pressure conditions of step (2), the seedless onion carbon will be converted into diamond crystals. As mentioned above, since this application uses seedless onion carbon particles as the raw material, the shell of onion carbon is highly wrinkled and contains a large number of stacking faults. By controlling the high pressure synthesis process (such as pressure increase and heating rate), it can be obtained 2H, 3C, 4H, 6H, 8H, 9R, 10H, 15R, 21R and other types of diamond phases, among which the 3C type diamond phase formed has an ultra-fine twin structure. Under the combined action of multiphase diamond and twin crystal structure, its mechanical properties have been greatly improved.

Example

In order to better understand the present application, the content of the present application will be further elaborated below in conjunction with examples, but the content of the present application is not limited to the following examples.

Raw material preparation

The non-nuclear onion carbon nanoparticles used in this application are prepared according to the preparation method in the Chinese patent with publication number CN 103382025B. A transmission electron microscope (TEM) photo of the obtained onion carbon is shown in Figure 1(a). It can be seen that there is no diamond core in the center, and there are a lot of defects in the carbon layer, such as bending and wrinkles of the carbon layer.

High temperature and high pressure treatment

The onion carbon nano-powder obtained by the above method is pre-pressed into a shape, and then the prefabricated body is placed in a high-temperature and high-pressure assembly, and a T25 press produced by Rockland Research is used for high-temperature and high-pressure treatment to obtain a diamond complex block material.

Structure and performance test

X-ray diffraction pattern: D8 ADVANCE (Bruck, Germany), wavelength 0.154nm (Cu target Kα), scanning speed 0.2 degrees/min.

Transmission electron microscope: Talos F200X (American FEI company), acceleration voltage 200KV; Themis Z (American FEI company), acceleration voltage 300KV.

Micro hardness tester: KB-5BVZ (KB Prüftechnik GmbH, Germany). The Vickers hardness uses a diamond quadrangular pyramid with an angle of 136° as the indentation head, and its value is calculated according to the following formula: H _V =1854.4·P/d ² (where: H _V -Vickers hardness, GPa; P-load, N; d-diagonal length of pit, μm).

Example 1: Preparation of Diamond Multiphase Block 1

(1) Raw material prefabricated body: onion carbon (particle size: 5-50nm) is placed in a glove box protected by high-purity argon and pre-compressed

Cylinder with a length of 3mm.

(2) High-temperature and high-pressure synthesis: Put the above-mentioned pre-compressed block into a hexagonal boron nitride crucible and high-temperature and high-pressure assembly block (as shown in Figure 2), then put it into a T25 press, and increase the pressure to a rate of 3GPa/h 15 GPa, and then heated to 1900°C for 30 minutes at a rate of 200°C/min. After cooling, the pressure was relieved to obtain a diamond complex bulk material. The actual photo is shown in Figure 3.

(3) The structure and properties of the diamond complex bulk material: The X-ray diffraction spectrum (XRD) of the prepared diamond complex bulk material is shown in Figure 4. You can see 3C cubic diamond and 2H, 9R, 15R and other many Diffraction peaks of type diamond. The results of high-resolution electron microscopy are shown in Figure 5 and Figure 7. Various types of diamond phases can be seen in the crystal grains, including 3C, 2H, 9R, 15R and other diamonds. Among them, 3C diamond can form a high-density {111} twin structure with a twin width of 1-15nm; non-3C diamond polytypes, such as 2H, 9R, 15R diamonds, are embedded in the crystal grains, and the thickness is only a few nanometers. It can be seen from the electron microscope Figure 6 that the grain size of the bulk material is 2-80nm. The asymptotic Vickers hardness of the sample measured by the KB-5BVZ microhardness tester is 210±4GPa, as shown in Figure 8; its fracture toughness is 26MPa·m ^1/2 .

Example 2: Preparation of diamond complex bulk material 2

(1) Raw material prefabricated body: onion carbon (particle size: 5-50nm) is placed in a glove box protected by high-purity nitrogen gas to be pre-compressed

A body with a length of 3mm.

(2) High temperature and high pressure synthesis: put the above pre-compressed block into a hexagonal boron nitride crucible, then put it into a high temperature and high pressure assembly block, put the assembly block into a T25 press, and increase the pressure to 10 GPa at a rate of 2 GPa/h Then, the temperature is increased to 2100°C for 20 minutes at a rate of 250°C/min, and the pressure is relieved after cooling to obtain a diamond complex bulk material, as shown in Figure 9.

(3) The structure and properties of the diamond complex bulk material: the X-ray diffraction spectrum of the prepared diamond complex bulk material is shown in Figure 10. Its phase composition includes 3C cubic diamond, which contains a lot of {111} twin structure; it also contains non-3C diamond phases, including 2H, 4H, 10H, 21R diamond, which are embedded in crystal grains. The asymptotic Vickers hardness of the sample measured by the KB-5BVZ microhardness tester is 180±9GPa, and its fracture toughness is 30MPa·m ^1/2 .

Example 3: Preparation of diamond complex bulk material 3

(1) Raw material prefabricated body: onion carbon powder (particle size: 5-50nm) is placed in a glove box protected by high-purity nitrogen gas to be pre-compressed

A body with a length of 3mm.

(2) High-temperature and high-pressure synthesis: Put the above pre-compressed block into a hexagonal boron nitride crucible, then into a high-temperature and high-pressure assembly block, and then load it into a T25 type press, increase the pressure to 12 GPa at a rate of 4 GPa/h, and then The temperature was increased to 1800°C for 60 minutes at a rate of 300°C/min, and the pressure was relieved after cooling to obtain a diamond complex bulk material, as shown in Figure 11.

(3) The structure and properties of the diamond complex bulk material: The X-ray diffraction spectrum (XRD) of the prepared diamond complex bulk material is shown in Figure 12. Its phase composition and microstructure are similar to those of Examples 1 and 2, specifically including 3C cubic diamond, which contains a large number of {111} twin structure, and also contains non-3C type diamond phases, including 9R, 10H, 21R In diamond, these phases are embedded in the crystal grains. The asymptotic Vickers hardness of the sample measured by the KB-5BVZ microhardness tester is 190±4GPa, and its fracture toughness is 18MPa·m ^1/2 .

Example 4: Preparation of Diamond Multiphase Bulk Material 4

A body with a length of 3mm.

(2) High temperature and high pressure synthesis: Put the above pre-compressed block into a hexagonal boron nitride crucible, then put it into a high temperature and high pressure assembly block, and then load it into a T25 type press, and increase the pressure to 18 GPa at a rate of 3 GPa/h, and then The temperature is increased to 2000°C for 60 minutes at a rate of 250°C/min, and the pressure is relieved after cooling to obtain a diamond complex bulk material.

(3) The structure and properties of the diamond complex bulk material: The X-ray diffraction spectrum (XRD) of the prepared diamond complex bulk material is similar to Figure 12, and its phase composition includes 3C-type cubic diamond, which contains a large amount of {111} The twin structure also contains non-3C types of diamond phases, mainly 2H and 8H diamonds, which are embedded in the crystal grains.

The above are only preferred specific implementations of this application, but the protection scope of this application is not limited to this. Any person skilled in the art can easily think of changes or changes within the technical scope disclosed in this application. Replacement shall be covered within the scope of protection of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

The specification of this application lists the optional materials of various components, but those skilled in the art should understand that: the list of the above-mentioned component materials is not restrictive or exhaustive, and various components can be used. The equivalent materials not mentioned in the specification of this application can be replaced, and the purpose of this application can still be achieved. The specific examples mentioned in the specification are only for the purpose of explanation, not for limiting the scope of the application.

In addition, the dosage range of each component in this application includes any combination of any lower limit and any upper limit mentioned in the specification, as well as any combination of the specific content of the component in each specific embodiment as the upper or lower limit. Scope; all these scopes are covered in the scope of this application, just to save space, the combined scopes are not listed one by one in the description. Each feature of this application listed in the specification can be combined with any other feature of this application, and this combination is also within the scope of the disclosure of this application; just to save space, the range of these combinations is not in the specification List one by one.

Claims

A multiphase diamond block material, characterized in that: the multiphase diamond block material is a 3C type diamond phase with a zinc blende structure and one selected from the group consisting of 2H, 4H, 6H, 8H, 9R, 10H, 15R, 21R One or more other diamond phases are formed, and the prerequisite is that when the diamond multiphase bulk material is composed of two phases, the other phase except the 3C phase is not the 6H phase.
The diamond multiphase bulk material of claim 1, wherein the diamond multiphase bulk material is a 3C type diamond phase with a zinc blende structure and is selected from 2H, 4H, 6H, 8H, 9R, 10H, It is composed of two or more other diamond phases of 15R and 21R.
The diamond multiphase bulk material of claim 1 or 2, wherein the grain size inside the diamond multiphase bulk material is 2-80nm, and the crystal grains contain nanometers formed by the 3C diamond. Twin crystal structure, twin crystal width 1-15nm, other diamond phases are also embedded in the crystal grains of the bulk material.
The diamond complex bulk material according to any one of claims 1 to 3, wherein the Vickers hardness of the diamond complex phase bulk material is 150-260 GPa, and the fracture toughness of the diamond complex phase bulk material is 12 -30MPa·m 1/2 .
The diamond multiphase bulk material according to any one of claims 1 to 4, wherein the diamond multiphase bulk material is colorless and transparent, or yellow and transparent, or black and opaque.
A method for preparing the diamond complex bulk material according to any one of claims 1 to 5, comprising the following steps:

(1) Use seedless onion carbon as raw material, put it into a mold and pre-compress it into a green body;

(2) Put the prefabricated body into a high-temperature and high-pressure synthesis mold, and perform high-temperature and high-pressure treatment.
The method for preparing the diamond complex bulk material according to claim 6, further comprising the following steps:

(3) After cooling, the pressure is relieved to obtain the diamond complex bulk material.
The method for preparing the diamond multiphase bulk material according to claim 6 or 7, characterized in that the process parameters of the high temperature and high pressure treatment in step (2) are: the pressure is in the range of 8-18 GPa, preferably in the range of 10-15 GPa ; The temperature is in the range of 1500-2300°C, preferably in the range of 1800-2200°C.
The method for preparing the diamond multiphase bulk material according to claim 6 or 7, characterized in that the high temperature and high pressure treatment in step (2) is to increase the pressure first, then increase the temperature, and then keep the temperature for 10-60 minutes.
The method for preparing diamond multiphase bulk material according to claim 8 or 9, characterized in that: in step (2), the pressure increase rate of the high temperature and high pressure treatment is 2-4 GPa/h, and the temperature rise rate is 200-300°C/min .