An extremely hard and highly tough nanocrystalline diamond composite material and a preparation method thereof

Abstract

The present invention provides an extremely hard and highly tough nanocrystalline diamond composite material and a preparation method thereof. It belongs to the field of preparation of highly tough and extremely hard materials. The extremely hard and highly tough nanocrystalline diamond composite material is composed of cubic diamond and cubic carbon. The molar percentage of the cubic diamond is 70-90%, and the molar percentage of the cubic carbon is 10-30%. The preparation method of the extremely hard and highly tough nanocrystalline diamond composite material of the present invention specifically comprises the following steps: using graphene as a raw material, pre-pressing the graphene into a cylinder in a mold, and subjecting the pre-pressed sample to a high-temperature and high-pressure synthesis reaction. After the high-temperature and high-pressure synthesis reaction, cooling and pressure relief are carried out to obtain the extremely hard and highly tough nanocrystalline diamond composite material. Compared with the prior art, the extremely hard and highly tough nanocrystalline diamond composite material of the present invention has two phases of cubic diamond + cubic carbon. Compared with single-crystal diamond, the toughness is increased by 1-2 times while maintaining comparable hardness.

Description

Technical Field

[0001] The present invention belongs to the field of preparation of high-toughness extremely hard materials, and particularly relates to an extremely hard and high-toughness nanocrystalline diamond composite material and a preparation method thereof. Background Art

[0002] Diamond is widely used in grinding abrasives and cutting tools due to its extremely high hardness (80 - 120 GPa). However, the poor fracture toughness of diamond (4 - 6 MPa·m 0.5 ) leads to the phenomenon of "tool chipping" easily occurring during the cutting process, seriously reducing its cutting efficiency and service life. Therefore, how to improve the toughness of diamond products is a huge technical problem.

[0003] One method is to prepare nanocrystalline diamond (NPD) through the high-temperature and high-pressure phase transformation of graphite without a catalyst. Its hardness value HV≥120 GPa is higher than that of traditional single-crystal diamond, and NPD is isotropic. At the same time, the fracture toughness is increased by about twice compared with single crystal (K IC ≈8 MPa·m 0.5 ). However, due to the inherent brittleness of diamond, the fracture toughness of NPD is still low and difficult to reach the large-scale industrial application level.

[0004] Another commonly used method is to prepare diamond composite materials. For example, by adding metal binders such as Ni, Co, Fe, etc. to diamond and sintering at P = 5 - 6 GPa, T = 1300 - 1700 °C to prepare PCD. Although this method enhances the toughness of diamond products to a certain extent, it significantly reduces the hardness (HV≈40 GPa). In addition, a large amount of heat is generated by friction when PCD is used, increasing the tool temperature. And due to the large difference in the thermal expansion coefficients between the binder and diamond, the bonding is damaged at high temperatures, resulting in easy detachment at high temperatures. Therefore, the wear resistance and thermal stability of PCD are poor. Selecting high-temperature resistant ceramics such as B4C or c-BN with higher hardness as the binder for sintering improves the hardness of the sintered product compared with that sintered with metal binders, but the hardness is still lower than that of single crystal (HV < 80 GPa), and the sintering pressure is severe (P≥12 GPa).

[0005] In summary, selecting a second phase with properties close to those of diamond such as hardness, thermal expansion coefficient, and elastic modulus, and compounding it with cubic diamond to prepare a diamond composite material can effectively overcome the problems existing in PCD. For example, the composite material of cubic diamond and hexagonal diamond has significantly improved toughness compared with single crystal, and at the same time, the hardness is comparable to that of single-crystal diamond. Therefore, exploring new diamond composite materials is beneficial to solving the technical problem of poor diamond toughness and has broad application prospects in fine machining such as industrial precision cutting. Summary of the Invention

[0006] To solve the above-mentioned existing technical problems, the present invention provides an extremely hard and highly tough nanocrystalline diamond composite material and a preparation method thereof, preparing an extremely hard and highly tough nanocrystalline diamond composite material (cubic diamond + cubic carbon), which has a toughness increased by 1-2 times compared with single-crystal diamond while maintaining comparable hardness.

[0007] The present invention provides an extremely hard and highly tough nanocrystalline diamond composite material, which is composed of cubic-phase diamond and cubic carbon. The molar percentage of the cubic-phase diamond is 70-90%, and the molar percentage of cubic carbon is 10-30%.

[0008] Compared with the prior art, this patent firstly prepares a diamond composite material containing cubic carbon, and the prepared diamond composite material has a hardness greater than 120 GPa and an average toughness reaching 12.5 MPa·m 0.5 , which is about 2-3 times that of single crystal.

[0009] In some embodiments, the Vickers hardness of the extremely hard and highly tough nanocrystalline diamond composite material is 120-150 GPa, and the fracture toughness is 12-15 MPa·m 0.5

[0010] The second object of the present invention is to provide a preparation method of an extremely hard and highly tough nanocrystalline diamond composite material. The preparation method specifically includes the following steps: using graphene as a raw material, pre-pressing the graphene into a cylinder in a mold, and performing a high-temperature and high-pressure synthesis reaction on the pre-pressed sample. After the high-temperature and high-pressure synthesis reaction, cooling and pressure relief are carried out to obtain the extremely hard and highly tough nanocrystalline diamond composite material.

[0011] In some embodiments, the graphene is flaky graphene.

[0012] In some embodiments, the high-temperature and high-pressure synthesis reaction is carried out in a Kawai large-volume multi-stage anvil device.

[0013] In some embodiments, the parameters of the Kawai large-volume multi-stage anvil device are as follows: wrapped with hexagonal boron nitride, heated by a rhenium tube, and synchronously measured with a tungsten-rhenium thermocouple.

[0014] In some embodiments, the parameters of the high-temperature and high-pressure synthesis reaction are as follows: the synthesis pressure is 22 GPa, the temperature is 1800-2000 °C, and the reaction time is 30 min.

[0015] The present invention adopts the above narrow range of synthesis parameters. The experimental results show that pressure has an obvious influence on the phase composition of the synthesized material, temperature has a great influence on the ratio of the two phases in the diamond composite material, and the composite phase has a significant influence on hardness and toughness.

[0016] Compared with the prior art, the present invention preferably uses few-layer graphene as the raw material. By utilizing its extremely thin graphite layers and high-concentration defects, the temperature and pressure conditions are precisely controlled, and cubic carbon and cubic diamond composites are synthesized for the first time within a very narrow temperature and pressure range. This composite material has a fracture toughness nearly three times that of single-crystal diamond and comparable hardness. The method of this patent overcomes the technical problem of the contradiction between hardness and toughness in superhard materials, and greatly promotes the preparation of extremely hard and tough diamond-related materials.

[0017] In some embodiments, the specific steps of cooling and depressurizing are as follows: cooling to room temperature at a cooling rate of 100 °C / min, and then depressurizing. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 X-ray diffraction pattern of the cubic diamond prepared in Example 1 of the present invention.

[0019] Figure 2 X-ray diffraction pattern of the cubic diamond prepared in Example 2 of the present invention.

[0020] Figure 3 X-ray diffraction pattern of the graphite and cubic diamond prepared in Example 3 of the present invention.

[0021] Figure 4 X-ray diffraction pattern of the cubic diamond and cubic carbon composite material prepared in Example 4 of the present invention.

[0022] Figure 5 X-ray diffraction pattern of the cubic diamond and cubic carbon composite material prepared in Example 5 of the present invention.

[0023] Figure 6 Indentation diagram of the cubic diamond and cubic carbon composite material prepared in Example 5 of the present invention.

[0024] Figure 7 X-ray diffraction pattern of the cubic diamond prepared in Example 6 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] To make the above objects, features, and advantages of the present invention more obvious and understandable, the specific embodiments of the present invention are described in detail below. It should be noted that the following embodiments are only used to illustrate the implementation methods and typical parameters of the present invention, and are not used to limit the parameter range described in the present invention. Reasonable variations derived therefrom are still within the protection scope of the claims of the present invention.

[0026] It should be noted that the endpoints and any values within the ranges disclosed in this document are not limited to the exact ranges or values. These ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed in this document.

[0027] Unless otherwise defined, all terms, symbols, and other scientific terms used in this document are intended to have the same meaning as commonly understood by those skilled in the art to which this invention pertains. In some cases, for the purpose of clarification or facilitating citation, terms with conventional understood meanings are defined in this document, and such definitions in this document should not be construed as indicating a significant difference from the conventional understanding in the art. The technical methods described or cited in this document are generally well understood by those skilled in the art and are adopted by conventional methods. Unless otherwise stated, the use of commercially available kits, reagents, and instruments follows the protocols and parameters provided by the manufacturers.

[0028] The technical effects of the present invention are described below in conjunction with specific embodiments.

[0029] Example 1

[0030] This example provides a material prepared by the following method: Using lamellar graphene as the raw material, it is pressed into a cylindrical shape (diameter 2 mm, height 1 mm) with a tungsten carbide mold, wrapped with hexagonal boron nitride, heated with a rhenium tube, and the temperature is measured synchronously with a tungsten-rhenium thermocouple. Using a Kawai-type large-volume multi-stage anvil experimental device, a diamond composite material is prepared at a pressure P = 15 GPa and a temperature T = 2000 °C. The holding time range is 30 min, and it is slowly cooled to room temperature at a rate of 100 °C / min, and then the pressure is released.

[0031] Figure 1 is the X-ray diffraction pattern of the cubic diamond prepared in this example; from Figure 1 it can be seen that the main component of the material prepared in this example is cubic diamond. Using a Vickers hardness tester to test the hardness of the sample, the test results show that: the hardness of the material prepared in this example is HV = 122.4 ± 5.8 GPa, (F = 19.6 N), and the fracture toughness is K IC = 7.6 ± 2.8 MPa·m 0.5 .

[0032] Example 2

[0033] This example provides a material, which is prepared by the following method: Using lamellar graphene as the raw material, it is pressed into a cylindrical shape (diameter 2 mm, height 1 mm) with a tungsten carbide mold, wrapped with hexagonal boron nitride, heated with a rhenium tube, and the temperature is measured synchronously with a tungsten-rhenium thermocouple. Using a Kawai-type large-volume multi-stage anvil experimental device, a diamond composite material is prepared at a pressure P = 20 GPa and a temperature T = 2000 °C. The holding time range is 30 min, and it is slowly cooled to room temperature at a rate of 100 °C / min, and then the pressure is released.

[0034] Figure 2 The X-ray diffraction pattern of the cubic diamond prepared in the example; from Figure 2 It can be seen that the main component of the material prepared in this example is lonsdaleite. Using a Vickers hardness tester to measure, the hardness of the material prepared in this example is HV = 123.1 ± 5.5 GPa, (F = 19.6 N), and the fracture toughness is K IC = 8.0 ± 1.5 MPa·m 0.5 .

[0035] Example 3

[0036] This example provides a material, which is prepared by the following method: Using lamellar graphene as the raw material, it is pressed into a cylindrical shape (diameter 2 mm, height 1 mm) with a tungsten carbide mold, wrapped with hexagonal boron nitride, heated with a rhenium tube, and the temperature is measured synchronously with a tungsten-rhenium thermocouple. Using a Kawai-type large-volume multi-stage anvil experimental device, a diamond composite material is prepared at a pressure P = 22 GPa and a temperature T = 1600 °C. The holding time range is 30 min, and it is slowly cooled to room temperature at a rate of 100 °C / min, and then the pressure is released.

[0037] Figure 3 The X-ray diffraction pattern of the graphite and cubic diamond prepared in this example, from Figure 3 It can be seen that the main components of the material prepared in this example are graphite and lonsdaleite.

[0038] Example 4

[0039] This example provides a material, which is prepared by the following method: Using lamellar graphene as the raw material, it is pressed into a cylindrical shape (diameter 2 mm, height 1 mm) with a tungsten carbide mold, wrapped with hexagonal boron nitride, heated with a rhenium tube, and the temperature is measured synchronously with a tungsten-rhenium thermocouple. Using a Kawai-type large-volume multi-stage anvil experimental device, a diamond composite material is prepared at a pressure P = 22 GPa and a temperature T = 1800 °C. The holding time range is 30 min, and it is slowly cooled to room temperature at a rate of 100 °C / min, and then the pressure is released.

[0040] Figure 4 The X-ray diffraction pattern of the cubic diamond and cubic carbon composite material prepared in this example; fromFigure 4 It can be seen that new phases appear in the sample prepared in this example, and the main components are a composite phase of cubic diamond and cubic carbon. Using a Vickers hardness tester for measurement, the hardness of the material prepared in this example is HV = 132.9 ± 9.3 GPa, (F = 19.6 N), and the fracture toughness is K IC = 9.8 ± 3.4 MPa·m 0.5 .

[0041] Example 5

[0042] This example provides a material prepared by the following method: Using layered graphene as the raw material, it is pressed into a cylindrical shape (diameter 2 mm, height 1 mm) using a tungsten carbide mold, wrapped with hexagonal boron nitride, heated with a rhenium tube, and the temperature is measured synchronously with a tungsten-rhenium thermocouple. Using a Kawai-type large-volume multi-stage anvil experimental device, diamond composites are prepared at a pressure P = 22 GPa and a temperature T = 2000 °C, the holding time range is 30 min, and it is slowly cooled to room temperature at a rate of 100 °C / min, and then the pressure is released.

[0043] Figure 5 is the X-ray diffraction pattern of the cubic diamond and cubic carbon composite material prepared in this example; Figure 6 is the indentation pattern of the cubic diamond and cubic carbon composite material prepared in this example; From Figure 5 it can be seen that the main components of the sample prepared in this example are a composite phase of cubic diamond and cubic carbon, and from Figure 4 and Figure 5 it can be seen that as the temperature increases, the content of cubic carbon increases; Using a Vickers hardness tester for measurement, the hardness of the material prepared in this example is HV = 128.4 ± 5.3 GPa, (F = 19.6 N), and the fracture toughness is K IC = 12.5 ± 2.1 MPa·m 0.5 , which is about twice that of single-crystal diamond. The indentation pattern is shown in Figure 6 .

[0044] Example 6

[0045] This example provides a material prepared by the following method: Using layered graphene as the raw material, it is pressed into a cylindrical shape (diameter 2 mm, height 1 mm) using a tungsten carbide mold, wrapped with hexagonal boron nitride, heated with a rhenium tube, and the temperature is measured synchronously with a tungsten-rhenium thermocouple. Using a Kawai-type large-volume multi-stage anvil experimental device, diamond composites are prepared at a pressure P = 22 GPa and a temperature T = 2200 °C, the holding time range is 30 min, and it is slowly cooled to room temperature at a rate of 100 °C / min, and then the pressure is released.

[0046] Figure 7 is the X-ray diffraction pattern of the cubic diamond prepared in this example; FromFigure 7 It can be seen that as the temperature continues to increase, the cubic carbon disappears, and the main component of the sample is cubic diamond. The hardness is HV = 130.4 ± 10.0 GPa, (F = 19.6 N), and the fracture toughness is K IC = 8.5 ± 2.5 MPa·m 0.5 .

[0047] It can be seen from Examples 1-4 that when the synthesis pressure is less than 22 GPa, the second-phase cubic carbon does not appear. Even when the pressure reaches 22 GPa and the temperature is less than 1800 °C, no cubic carbon is formed. And it can be seen from Examples 4-6 that in the range of pressure P = 22 GPa and temperature T = 1800-2000 °C, a diamond composite material with two phases of cubic diamond and cubic carbon is synthesized, and the content of cubic carbon first increases and then decreases with the increase of temperature. When the temperature T > 2000, the cubic carbon disappears, and the synthesized sample is a single phase of cubic diamond. Moreover, compared with the single phase, the fracture toughness of this diamond composite material is increased by 150% under the condition of basically the same hardness.

[0048] In summary, in the preparation process of the extremely hard and high-toughness nanocrystalline diamond composite material prepared by the preparation method of the present invention, the pressure has an obvious influence on the phase composition of the synthesized material, the temperature has a great influence on the proportion of the two phases in the diamond composite material, and the composite phase has a significant influence on the hardness and toughness.

[0049] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A superhard and high-toughness nanocrystalline diamond composite material, characterized in that, The extremely hard and high-toughness nanocrystalline diamond composite material is composed of cubic-phase diamond and cubic carbon. The molar percentage of the cubic-phase diamond is 70-90%, and the molar percentage of the cubic carbon is 10-30%. The preparation method of the extremely hard and high-toughness nanocrystalline diamond composite material specifically includes the following steps: Using graphene as a raw material, pre-pressing the graphene into a cylinder in a mold, and performing a high-temperature and high-pressure synthesis reaction on the pre-pressed sample. After the high-temperature and high-pressure synthesis reaction, cooling and depressurization are carried out to obtain the extremely hard and high-toughness nanocrystalline diamond composite material. The graphene is lamellar graphene. The parameters of the high-temperature and high-pressure synthesis reaction are as follows: The synthesis pressure is 22 GPa, the temperature is 1800-2000 °C, and the reaction time is 30 min.

2. The extremely hard and highly tough nanocrystalline diamond composite material according to claim 1, characterized in that, The Vickers hardness of the ultra-hard and high-toughness nanocrystalline diamond composite material is 120 - 150 GPa, and the fracture toughness is 12 - 15 MPa·m 0.5 .

3. The extremely hard and highly tough nanocrystalline diamond composite material according to claim 1, characterized in that, The high-temperature and high-pressure synthesis reaction is carried out in a Kawai large-volume multi-anvil device.

4. The extremely hard and highly tough nanocrystalline diamond composite material according to claim 3, characterized in that, The parameters of the Kawai large-volume multi-anvil device are as follows: Wrapped with hexagonal boron nitride, heated by a rhenium tube, and synchronously measured with a tungsten-rhenium thermocouple.

5. The extremely hard and highly tough nanocrystalline diamond composite material according to claim 1, wherein The specific steps of the cooling and depressurization are as follows: Cooling to room temperature at a cooling rate of 100 °C / min, and then depressurizing.

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