A wurtzite boron nitride / diamond composite material and a preparation method and application thereof

Abstract

The application provides a wurtzite boron nitride / diamond composite material and a preparation method and application thereof. The composite material is composed of two phases of wurtzite boron nitride and diamond, and has a stacked sandwich microstructure, which comprises at least one first wurtzite boron nitride layer composed of wurtzite boron nitride, at least one second wurtzite boron nitride layer composed of wurtzite boron nitride, and a diamond layer composed of diamond and sandwiched between the first wurtzite boron nitride layer and the second wurtzite boron nitride layer. The wurtzite boron nitride is a metastable phase stably existing under normal pressure, and the Vickers hardness of the composite material is greater than 50 GPa. The novel wurtzite boron nitride / diamond composite material has high hardness, high toughness and high thermal stability, and the preparation method has low starting material price and simple preparation process.

Description

Technical Field

[0001] This invention belongs to the field of superhard composite materials technology, specifically relating to a high-performance wurtzite boron nitride / diamond composite material, its preparation method, and its application. Background Technology

[0002] With the increasing demands on material performance from high-end manufacturing, precision machining, and applications in extreme environments, the development of novel superhard composite materials that combine ultra-high hardness, good toughness, and high thermal stability has become an important research direction. Boron, carbon, and nitrogen, three light elements, have small atomic radii and readily form strong covalent bonds in dense three-dimensional network structures; their composite materials are an important type of superhard material system.

[0003] In existing technologies, research on superhard materials based on the boron-carbon-nitrogen system mainly focuses on thermodynamically stable phases such as cubic boron nitride and diamond, and their composite materials. For example, Chinese patent application CN104759240A discloses a diamond-cubic boron nitride superhard tool material, a tool, and a method for its preparation. The superhard tool material prepared by this document, a composite of diamond and zincblende-structured cubic boron nitride (cBN), has a hardness close to that of natural diamond single crystals and better thermal stability than diamond, exhibiting both high thermal stability and high hardness. However, its microstructure is a random distribution of two phases, used only to achieve the high hardness required for the tool, without considering how to further improve the material's comprehensive mechanical properties, especially its toughness.

[0004] Therefore, the performance optimization space for the thermodynamically stable phases of boron-carbon-nitrogen superhard materials and their composites has approached saturation. The synergistic improvement of hardness and fracture toughness is nearing a bottleneck, failing to achieve a comprehensive synergistic improvement in hardness, toughness, and thermal stability, making it difficult to meet the higher performance requirements of superhard materials in high-end manufacturing and extreme environment applications. Furthermore, the cubic boron nitride used in CN104759240A is expensive, and its preparation method requires complex pretreatment and molding of the raw materials, resulting in a complex manufacturing process.

[0005] In recent years, the development of high-pressure synthesis technology has made it possible to retain metastable phase materials under ambient pressure. Wurtzite-structured boron nitride (wBN), as a type of metastable superhard material, has a single-phase Vickers hardness of about 45 GPa, and has the potential to serve as a matrix for high-performance composite materials.

[0006] However, current research on wurtzite-structured boron nitride mainly focuses on the synthesis and basic performance characterization of single-phase materials under high pressure, and systematic research on its use as a matrix for composite materials has not yet been carried out. This is mainly because single-phase materials of wurtzite-structured boron nitride are thermodynamically unstable under normal pressure and easily transform into soft, graphitic hexagonal boron nitride (hBN). Furthermore, the controllable preparation of high-purity, large-size bulk materials is difficult, which severely restricts its engineering applications.

[0007] In summary, existing boron-carbon-nitrogen superhard composite material systems have two major problems: on the one hand, the performance optimization space of traditional composite materials represented by cBN / diamond is approaching saturation, making it difficult to improve their toughness to meet high-end demands; on the other hand, although wBN can be synthesized under high pressure, its application research in composite materials is insufficient, especially lacking technical solutions that can effectively combine wBN with superhard carbon phases such as diamond, stably retain the wurtzite structure under normal pressure, and simultaneously achieve a synergistic improvement in hardness and toughness.

[0008] Therefore, there is an urgent need for a new type of superhard composite material and its preparation method to achieve stable composite with diamond while maintaining the metastable phase structure of wBN, thus breaking through the technical bottleneck of existing superhard materials in terms of comprehensive mechanical properties and structural stability. Summary of the Invention

[0009] In view of the shortcomings of existing technologies, such as high raw material prices and insufficient overall product performance, the purpose of this invention is to provide a novel superhard boron carbon nitride composite material with high hardness, high toughness and high thermal stability, as well as a preparation method with low starting material prices and simple preparation process.

[0010] To achieve the above objectives, the present invention provides a novel ultrahard boron carbon nitride composite material having a sandwich microstructure composed of a metastable wurtzite boron nitride phase that exists under normal pressure and diamond.

[0011] The term "metastable phase" used in this invention refers to a phase that, under specific conditions (such as room temperature and pressure), is not in its lowest energy or most stable state (i.e., a thermodynamically stable phase), but temporarily maintains a specific state without transforming into its most stable state due to some energy barrier or obstacle. The key technical contribution of this invention lies in its unique preparation process, which forms a sandwich composite microstructure unit with wBN and diamond, successfully preserving the metastable structure of wBN under normal pressure. This allows for the utilization of wBN's high hardness and potential toughness to create a new material with excellent performance. This composite material achieves a synergistic improvement in hardness and toughness while maintaining high thermal stability, synthesizing a wBN / diamond bulk material, effectively solving the technical problem of the current boron-carbon-nitrogen superhard material system's single form and difficulty in synergistically improving hardness and toughness. The preparation method of this invention uses inexpensive and readily available hexagonal boron nitride and graphite as starting materials. Through the simultaneous phase transformation of the two under high temperature and high pressure conditions, a novel boron-carbon-nitrogen ternary superhard composite material in which wBN and diamond coexist is formed. This provides a new technical path for the development of next-generation superhard composite materials.

[0012] The stacked sandwich microstructure described in this invention refers to a randomly stacked sandwich microstructure, that is, a composite morphology formed by the random stacking of multiple sandwich structural units in space. When forming a macroscopic bulk, the spatial orientation, relative position, and stacking order of the multiple sandwich structural units are all randomly distributed. The microstructure of this invention has the dual characteristics of "order within units and disorder between units." This unique structure distinguishes itself from both regularly layered bulk materials with a single orientation and ordinary disordered polycrystalline composite materials with completely random mixing of two-phase crystal structures.

[0013] The above-mentioned objective of this invention is achieved through the following technical solution:

[0014] In a first aspect, the present invention provides a wurtzite boron nitride / diamond composite material, the composite material being composed of two phases, wurtzite boron nitride and diamond, and having a stacked sandwich microstructure, the sandwich microstructure comprising: at least one first wurtzite boron nitride layer composed of wurtzite boron nitride; at least one second wurtzite boron nitride layer composed of wurtzite boron nitride; and a diamond layer composed of diamond sandwiched between the first wurtzite boron nitride layer and the second wurtzite boron nitride layer, wherein the wurtzite boron nitride is a metastable phase that exists stably under normal pressure, and the Vickers hardness of the composite material is greater than 50 GPa.

[0015] The wurtzite boron nitride / diamond composite material according to the present invention exhibits no cracking under a 1 kg load and / or an initial oxidation temperature ≥ 650 °C.

[0016] Preferably, the initial oxidation temperature of the composite material is 650-700℃.

[0017] According to the wurtzite boron nitride / diamond composite material of the present invention, the thickness of the first wurtzite boron nitride layer is 20-200 nm, the thickness of the second wurtzite boron nitride layer is 20-200 nm, and the thickness of the diamond layer is 20-200 nm.

[0018] According to the wurtzite boron nitride / diamond composite material of the present invention, the elemental molar ratio B:N:C of the wurtzite boron nitride / diamond composite material is 7:7:3.

[0019] In a second aspect, the present invention provides a method for preparing a wurtzite boron nitride / diamond composite material according to the first aspect of the present invention, characterized in that it includes: subjecting hexagonal boron nitride powder and graphite powder to high-temperature and high-pressure treatment in a press at a pressure of 10-20 GPa and a temperature of 1000-1800°C, wherein the pressure holding time is 60-180 minutes and the temperature holding time is 10-120 minutes, thereby obtaining the wurtzite boron nitride / diamond composite material.

[0020] According to the preparation method of the present invention, the hexagonal boron nitride powder is a lamellar hexagonal boron nitride powder with a particle size of 1-30 µm, and the graphite powder is a lamellar hexagonal graphite powder with a particle size of 1-30 µm.

[0021] This invention uses lamellar hexagonal boron nitride and lamellar graphite powder as raw materials. By pressing and sintering them at a pressure of 10-20 GPa and a temperature of 1000-1800℃, they can be transformed in situ into a wurtzite boron nitride / diamond / wurtzite boron nitride sandwich structure. Unintentionally, this invention, by applying a pressure of 10-20 GPa at high temperature, utilizes this high-temperature, high-pressure environment to eliminate microscopic porosity and induce covalent bonding between layers, resulting in high-strength covalent bond interfaces. It is this bonding that enables crucial structural locking. After depressurization, the high-modulus diamond layer in the middle effectively constrains the metastable wurtzite boron nitride on both sides through interfacial bonding, inhibiting its reversion to the hexagonal phase and allowing it to remain stably trapped under normal pressure. Therefore, the metastable wurtzite boron nitride phase, after depressurization, can be supported and locked by the sandwiched diamond layer, thus remaining stable under normal pressure and no longer transforming back into the hexagonal phase.

[0022] Unwilling to be bound by any theory, it is believed that due to the random orientation of the sandwich structure units, the problem of excessive differences in mechanical properties in different directions of regular laminated materials is avoided, so that the macroscopic block exhibits uniform hardness and toughness in all directions; random stacking causes cracks to continuously encounter unit interfaces with different orientations during the propagation process, forcing them to deflect, bifurcate or passivate, thereby significantly improving the fracture toughness of the composite material; disordered stacking structure helps to dissipate and disperse the thermal residual stress generated during the preparation process, reducing the risk of macroscopic cracking.

[0023] In a preferred embodiment of the present invention, the high-temperature and high-pressure treatment may include: increasing the pressure to 10-20 GPa at a rate of 0.5-3 bar / min and holding the pressure for 60-180 minutes; during the pressure holding process, increasing the temperature to 1000-1800°C at a rate of 50-100 watts / min and holding the temperature for 10-120 minutes after reaching the target temperature.

[0024] According to the preparation method of the present invention, it may further include: before the high temperature and high pressure treatment, mixing the hexagonal boron nitride powder and graphite powder in a ball mill at a molar ratio of 7:3; then, encapsulating the mixed hexagonal boron nitride powder and graphite powder in a metal capsule, and placing the capsule in the press.

[0025] According to the preparation method of the present invention, it may further include: after the high temperature and high pressure treatment, cooling the product treated by the high temperature and high pressure to room temperature and depressurizing it to normal pressure, removing the capsule, and obtaining the wurtzite boron nitride / diamond composite material.

[0026] According to the preparation method of the present invention, the metal capsule is a gold capsule or a platinum capsule.

[0027] According to the preparation method of the present invention, the metal capsule is cup-shaped.

[0028] According to the preparation method of the present invention, the metal capsule has a wall thickness of 5-12 µm, a diameter of 2-4 mm, and a height of 1-3 mm.

[0029] According to the preparation method of the present invention, the press includes a tungsten carbide secondary hammer and uses magnesium oxide as the pressure transmission medium; wherein the truncated side length of the secondary hammer is 4-8 mm and the side length of the magnesium oxide is 10-14 mm.

[0030] According to the preparation method of the present invention, the step of placing the capsule in the press includes: placing the capsule in a hollow insulating container made of hexagonal boron nitride, the container being covered with a tubular heating element made of rhenium sheets, and having a zirconium dioxide heat-insulating shell disposed on the outside.

[0031] According to the preparation method of the present invention, the step of cooling to room temperature and depressurizing to atmospheric pressure includes: immediately quenching the temperature to room temperature after the high temperature and high pressure treatment is completed, and then reducing the pressure to atmospheric pressure at a rate of 0.1-0.5 bar / min.

[0032] Thirdly, the present invention provides an application of a wurtzite boron nitride / diamond composite material according to the first aspect of the present invention in precision machining tools, petroleum and geological exploration equipment, high-temperature electronic devices and industrial wear-resistant parts.

[0033] As used in this application, the term "10-4 assembly" refers to an assembly setup for a Walker type 6-8 press where the truncated side length of the tungsten carbide secondary hammer is 4 mm and the side length of the magnesium oxide pressure transmission medium is 10 mm.

[0034] Compared with the prior art, the present invention has the following significant advantages:

[0035] The preparation method of this invention significantly reduces raw material costs and greatly improves raw material availability. This invention selects hexagonal boron nitride powder and graphite powder as starting materials, both of which are widely available and inexpensive conventional industrial raw materials. This eliminates the need for expensive cubic boron nitride and diamond powders used in existing technologies, thus achieving a significant reduction in preparation costs from the raw material end and providing an economic foundation for large-scale production.

[0036] The preparation method of this invention is simple, efficient, and suitable for industrial production. This invention employs a one-step synthesis process under high temperature and high pressure conditions to successfully prepare a ternary superhard composite material with metastable wurtzite boron nitride as the matrix and diamond in situ. The process steps are concise, requiring no complex raw material pretreatment, and are easy to operate and control, significantly reducing the complexity of the production process and operating costs, thus meeting the needs of large-scale industrial production.

[0037] This invention achieves stable preservation of metastable phase structures under ambient pressure, expanding the composition of material systems. For the first time, this invention achieves the controllable preparation of a boron-carbon-nitrogen ternary composite system based on metastable wurtzite boron nitride, successfully preserving the metastable structure of wurtzite boron nitride under ambient pressure. This breakthrough overcomes the limitation of traditional boron-carbon-nitrogen superhard materials being developed only around thermodynamically stable phases, enriching and expanding the compositional forms of boron-carbon-nitrogen superhard materials.

[0038] The novel wurtzite boron nitride / diamond composite material of the present invention has a unique sandwich microstructure, which effectively coordinates the stress transfer between the hard phase and the matrix, and provides a guarantee for the improvement of the material's comprehensive mechanical properties from the structural level.

[0039] This invention achieves a breakthrough improvement in the comprehensive mechanical properties of a novel wurtzite boron nitride / diamond composite material, synergistically enhancing both hardness and toughness. By leveraging the synergistic strengthening effect of the wurtzite boron nitride and diamond phases, this invention effectively solves the technical bottleneck of traditional superhard materials, which struggle to simultaneously achieve both hardness and fracture toughness. It provides a practical technical path for developing next-generation high-performance superhard materials, with potential applications in superhard cutting tools, wear-resistant coatings, and high-temperature electronic devices. Under a kilogram load, the composite material exhibits a Vickers hardness of 60 GPa, 15 GPa higher than single-phase wurtzite boron nitride (approximately 45 GPa), and no obvious cracks were observed around the indentation, indicating that it possesses both ultra-high hardness and good fracture toughness. Furthermore, the material has an initial oxidation temperature as high as 677.5 degrees Celsius, demonstrating excellent thermal stability and the potential to operate in high-temperature and extreme environments, expanding its application scenarios. Attached Figure Description

[0040] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0041] Figure 1 These are scanning electron microscopy and energy dispersive spectroscopy images of the uniformly mixed powder of hexagonal boron nitride and graphite obtained after mixing in Examples 1-3.

[0042] Figure 2 These are scanning electron microscopy and energy dispersive spectroscopy images of the wurtzite boron nitride / diamond composite material prepared in Example 1.

[0043] Figure 3 These are X-ray diffraction comparison images of the wurtzite boron nitride / diamond composite materials synthesized in Examples 1-3 and the initial hexagonal boron nitride / graphite powder mixture.

[0044] Figure 4 The diagram shows the hardness-load relationship of the wurtzite boron nitride / diamond composite material synthesized in Example 1 and its indentation diagram under a 1 kg load.

[0045] Figure 5 These are images obtained from simultaneous thermal analysis of the wurtzite boron nitride / diamond composite material synthesized in Example 1.

[0046] Figure 6 This is an energy dispersive spectrum image of the sandwich-layer microstructure of the wurtzite boron nitride / diamond bulk material synthesized in Example 1. Detailed Implementation

[0047] The present invention will be further described in detail below with reference to specific embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0048] For those skilled in the art, any equivalent modifications and substitutions to the embodiments described below are also within the scope of this invention. Therefore, all equivalent transformations and modifications made without departing from the spirit and scope of this invention should be included within its scope.

[0049] Specific conditions not specified in the embodiments are performed under conventional conditions or conditions recommended by the manufacturer. All reagents or instruments without a specified manufacturer are commercially available, conventional products. Numerous specific details are provided in the following detailed embodiments to better illustrate the invention. Those skilled in the art should understand that the invention can be practiced without certain specific details. In other embodiments, methods, means, equipment, and steps well known to those skilled in the art are not described in detail in order to highlight the spirit of the invention.

[0050] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. Unless otherwise specified, all units used in this specification are International Standard Units (SI), and numerical values ​​and ranges appearing in this invention should be understood to include systematic errors unavoidable in industrial production.

[0051] The high-temperature and high-pressure treatments involved in the following embodiments were all completed in a Walker 6-8 press (Walker Technology Co., Ltd.).

[0052] Example 1

[0053] Hexagonal boron nitride powder (particle size 1-30 µm, Nanjing Muko Nanotechnology Co., Ltd.) and graphite powder (particle size 1-30 µm, Nanjing Muko Nanotechnology Co., Ltd.) were mixed in a ball mill at a molar ratio of 7:3 for 24 hours to obtain a homogeneous mixed powder. The homogeneous mixed powder was then packed into cup-shaped gold capsules with a thickness of 10 µm, a diameter of 2.3 mm, and a height of 2.0 mm, and sealed.

[0054] The sealed gold capsules were placed in a 10-4 assembly for high-temperature and high-pressure synthesis. The synthesis pressure was 18 GPa, the synthesis temperature was 1500℃, the holding time was 120 min, the holding time was 10 min, the pressurization rate was 1 bar / min, and the heating rate was 50 watts / min.

[0055] The product obtained after high-temperature and high-pressure synthesis was immediately quenched to room temperature after heat treatment, and then unloaded to atmospheric pressure at a rate of 0.5 bar / min. The X-ray diffraction results of the prepared wurtzite boron nitride / diamond bulk composite material are as follows: Figure 3 As shown.

[0056] Example 2

[0057] Hexagonal boron nitride powder and graphite powder were mixed according to the method in Example 1, and the resulting uniformly mixed powder was sealed.

[0058] The sealed gold capsules were placed in a 10-4 assembly for high-temperature and high-pressure synthesis. The synthesis pressure was 16 GPa, the synthesis temperature was 1600℃, the holding time was 120 min, the holding time was 60 min, the pressure increase rate was 1 bar / min, and the heating rate was 50 watts / min.

[0059] The product obtained after high-temperature and high-pressure synthesis was immediately quenched to room temperature after heat treatment, and then unloaded to atmospheric pressure at a rate of 0.5 bar / min. The X-ray diffraction results of the prepared wurtzite boron nitride / diamond bulk composite material are as follows: Figure 3 As shown.

[0060] Example 3

[0061] Hexagonal boron nitride powder and graphite powder were mixed according to the method in Example 1, and the resulting uniformly mixed powder was sealed.

[0062] The sealed gold capsules were placed in a 10-4 assembly for high-temperature and high-pressure synthesis. The synthesis pressure was 14 GPa, the synthesis temperature was 1800℃, the holding time was 120 min, the holding time was 30 min, the pressure increase rate was 1 bar / min, and the heating rate was 50 watts / min.

[0063] The product obtained after high-temperature and high-pressure synthesis was immediately quenched to room temperature after heat treatment, and then unloaded to atmospheric pressure at a rate of 0.5 bar / min. The X-ray diffraction results of the prepared wurtzite boron nitride / diamond bulk composite material are as follows: Figure 3 As shown.

[0064] Figure 1 These are scanning electron microscopy (SEM) images and energy-dispersive X-ray spectroscopy (EDS) images of the uniformly mixed powder of hexagonal boron nitride and graphite obtained after mixing in Examples 1-3 above. Figure 1 As can be seen, carbon, boron, and nitrogen elements are continuously and uniformly dispersed throughout the observation area, with no obvious enrichment or blank areas. This indicates that the hexagonal boron nitride and graphite powders achieve uniform dispersion at both the macroscopic and microscopic scales after mixing, without significant segregation or phase separation. This provides a uniform precursor basis for subsequent in-situ phase transformation and composite reaction under high temperature and pressure, ensuring the uniformity of the composite material's composition and properties.

[0065] Figure 2 These are scanning electron microscopy and energy-dispersive spectroscopy images of the wurtzite boron nitride / diamond composite material prepared in Example 1. From... Figure 2 It can be seen that the wurtzite boron nitride / diamond composite material exhibits a dense and uniform microstructure with no obvious pores or cracks. Carbon, boron, and nitrogen elements are continuously and uniformly dispersed throughout the observation area, without obvious enrichment or agglomeration regions. The distributions of boron and nitrogen (corresponding to the wurtzite boron nitride phase) and carbon (corresponding to the diamond phase) highly overlap, with stable signal intensity and no local concentration or absence, confirming that the wurtzite boron nitride and diamond phases achieve uniform microscale composite formation in the composite material without significant phase separation. This indicates that hexagonal boron nitride and graphite precursors were successfully converted in situ into wurtzite boron nitride and diamond after high-temperature and high-pressure treatment, and the two phases are uniformly dispersed in the matrix, forming a stable wurtzite boron nitride / diamond composite structure.

[0066] Figure 6 This is an energy dispersive spectral image of the sandwich-layer microstructure of the wurtzite boron nitride / diamond bulk material synthesized in Example 1. From... Figure 6 It can be seen that boron nitride and diamond are composed of alternating layers in a sandwich structure, which is beneficial for improving the material's hardness and toughness. Meanwhile, from... Figure 6As can be seen, carbon, boron, and nitrogen elements are uniformly distributed within the layers, with clear and sharp interlayer interfaces and no obvious elemental interdiffusion or impurity segregation. This confirms that the diamond phase and wurtzite boron nitride phase achieve a tightly bonded, ordered layered stack at the nanoscale, with high interfacial bonding strength and no macroscopic defects. This regular sandwich-like layered structure not only achieves a precise arrangement of the hard and tough phases but also effectively inhibits crack propagation through numerous interfaces, providing crucial structural support for the material to possess both high hardness and high toughness.

[0067] Figure 3 These are X-ray diffraction comparison images of the wurtzite boron nitride / diamond composite materials synthesized in Examples 1-3 and the initial hexagonal boron nitride / graphite powder mixture. Figure 3 The X-ray diffraction patterns show that, in Examples 1-3 of this application, under the synthesis conditions of pressures of 18, 16 and 14 GPa, temperatures of 1500, 1600 and 1800 °C, and holding times of 10, 60 and 30 minutes, hexagonal boron nitride powder and graphite powder with an initial particle size distribution of 1-30 µm can be completely converted into wurtzite boron nitride / diamond composite material without any remaining graphite or hexagonal boron nitride phase.

[0068] Figure 4 This is a hardness-load relationship diagram of the wurtzite boron nitride / diamond composite material synthesized in Example 1, and its indentation diagram under a 1 kg load. The diagram shows that the wurtzite boron nitride / diamond composite material prepared according to this invention has a Vickers hardness as high as 60 ± 2.3 GPa, and no cracks were observed under a 1 kg load, demonstrating its good fracture toughness. Under such high loads, pure diamond or pure cubic boron nitride often produces cracks extending from the four corners of the indentation. The absence of cracks indicates that the composite material of this invention has high resistance to crack propagation, suggesting that the wurtzite boron nitride / diamond interface may act as a "pinning" or "deflecting" mechanism for cracks, absorbing fracture energy and thus preventing brittle fracture.

[0069] Figure 5 These are simultaneous thermal analysis images of the wurtzite boron nitride / diamond composite material synthesized in Example 1. From Figure 5 As can be seen from the data, the wurtzite boron nitride / diamond composite material prepared in this invention has an initial oxidation temperature of 677.5℃, exhibiting excellent thermal stability. This high thermal stability is attributed to the fact that both wurtzite boron nitride and diamond are strongly covalent compounds. The oxidation resistance temperature of 677.5℃ means that this material is sufficient to cover the high-speed dry cutting conditions of most iron-based alloys (such as cast iron and hardened steel). During cutting, this initial oxidation temperature, combined with coolant application, fully meets the requirements of high-performance cutting.

[0070] Therefore, the wurtzite boron nitride / diamond composite material of this invention uses inexpensive and readily available raw materials, has a simple preparation process, and possesses a sandwich-like microstructure. This structure and composition endow it with high hardness (60 GPa), excellent fracture toughness (no cracking under 1 kg load), and outstanding thermal stability (initial oxidation temperature of 677.5℃). This combination of properties makes it show great application potential in the field of work-hardening steel, heat-resistant alloys, and other difficult-to-machine materials.

[0071] As can be seen from the above embodiments, the present invention differs significantly in structure from existing cubic boron-carbon-nitrogen composite materials. The wurtzite boron nitride / diamond composite material of the present invention is a boron-carbon-nitrogen composite material with metastable boron nitride as the matrix. Its microstructure exhibits a unique sandwich-like layered structure, resulting in excellent combined properties of hardness, toughness, and thermal stability. Furthermore, the present invention provides a novel, feasible, and industrially promising method for preparing wurtzite boron nitride / diamond composite materials, offering a new approach to designing multi-component superhard materials.

[0072] While various aspects and embodiments of the invention have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The aspects and embodiments disclosed herein are for illustrative purposes only and not for limiting purposes. The scope and spirit of the invention are determined solely by the appended claims.

Claims

1. A wurtzite boron nitride / diamond composite material, characterized in that, The composite material consists of two phases: wurtzite boron nitride and diamond, and has a randomly stacked sandwich microstructure, the sandwich microstructure comprising: At least one first wurtzite boron nitride layer composed of wurtzite boron nitride; At least one second wurtzite boron nitride layer composed of wurtzite boron nitride; and A diamond layer composed of diamond is sandwiched between the first wurtzite boron nitride layer and the second wurtzite boron nitride layer. The wurtzite boron nitride is a metastable phase that exists stably under normal pressure, and the composite material has a Vickers hardness greater than 50 GPa.

2. The wurtzite boron nitride / diamond composite material according to claim 1, which exhibits no cracking under a 1 kg load and / or an initial oxidation temperature ≥ 650 °C.

3. The wurtzite boron nitride / diamond composite material according to claim 1 or 2, wherein: The elemental molar ratio of the wurtzite boron nitride / diamond composite material is 7:7:3 (B:N:C).

4. The method for preparing the wurtzite boron nitride / diamond composite material according to any one of claims 1 to 3, characterized in that, include: The uniformly mixed powder of hexagonal boron nitride powder and graphite powder is subjected to high-temperature and high-pressure treatment in a press at a pressure of 10-20 GPa and a temperature of 1000-1800℃, wherein the pressure holding time is 60-180 minutes and the temperature holding time is 10-120 minutes, thereby obtaining the wurtzite boron nitride / diamond composite material.

5. The preparation method according to claim 4, wherein, The hexagonal boron nitride powder is a lamellar hexagonal boron nitride powder with a particle size of 1-30 µm, and the graphite powder is a lamellar hexagonal graphite powder with a particle size of 1-30 µm.

6. The preparation method according to claim 4 or 5, wherein, The high-temperature and high-pressure treatment includes: Increase the pressure to 10-20 GPa at a rate of 0.5-3 bar / min, and maintain the pressure for 60-180 minutes; During the pressure holding process, the temperature is increased to 1000-1800℃ at a rate of 50-100 watts / minute, and then held at the target temperature for 10-120 minutes.

7. The preparation method according to claim 4 or 5, further comprising: Before the high temperature and high pressure treatment, the hexagonal boron nitride powder and graphite powder were mixed in a ball mill at a molar ratio of 7:3; Then, the mixed hexagonal boron nitride powder and graphite powder are encapsulated in a metal capsule, and the capsule is placed in the press. and / or After the high temperature and high pressure treatment, the product treated with high temperature and high pressure is cooled to room temperature and depressurized to normal pressure, and the capsule is removed to obtain the wurtzite boron nitride / diamond composite material.

8. The preparation method according to claim 7, wherein: The metal capsule is a gold capsule or a platinum capsule; The metal capsule is cup-shaped; The metal capsule has a wall thickness of 5-12 µm, a diameter of 2-4 mm, and a height of 1-3 mm; and / or The press includes a tungsten carbide secondary hammer and uses magnesium oxide as the pressure transmission medium; wherein the truncated side length of the secondary hammer is 4-8 mm and the side length of the magnesium oxide is 10-14 mm.

9. The preparation method according to claim 7, wherein: The step of placing the capsule in the press includes: placing the capsule in a hollow, insulated container made of hexagonal boron nitride, the container being externally covered with a tubular heating element made of rhenium sheets, and externally provided with a zirconium dioxide insulating shell; and / or The steps of cooling to room temperature and depressurizing to atmospheric pressure include: immediately quenching the temperature to room temperature after the high temperature and high pressure treatment is completed, and then reducing the pressure to atmospheric pressure at a rate of 0.1-0.5 bar / minute.

10. The application of the wurtzite boron nitride / diamond composite material according to any one of claims 1 to 3 in precision machining tools, petroleum and geological exploration equipment, high-temperature electronic devices and industrial wear-resistant parts.

Images