A method of toughening CVD diamond

Abstract

The application discloses a kind of CVD diamond toughening methods, comprising: taking CVD diamond sample, the CVD diamond sample is CVD single crystal diamond or CVD polycrystalline diamond;The CVD diamond sample is pretreated, including using coating material to coat the diamond sample, and the diamond sample after coating is pre-pressed;The diamond sample after pretreatment is treated at high temperature and high pressure, so that trace graphite phase carbon in the diamond sample after pretreatment is converted into diamond phase, and microdefects are repaired.Cleaning is carried out to the CVD diamond sample after high temperature and high pressure treatment, and the coating material is removed, to obtain the diamond with enhanced toughness.The application effectively coats CVD diamond, and then controls the temperature rising rate and pressure rising rate and holding time in the high temperature and high pressure treatment process, to realize effective control of microstructure under the premise of maintaining high hardness of CVD diamond, and significantly improve the fracture toughness.

Description

Technical Field

[0001] This invention relates to the field of synthetic diamond preparation technology, specifically a toughening method for CVD diamond. Background Technology

[0002] Diamond, due to its extremely high hardness, excellent thermal conductivity, superior wear resistance, and good chemical stability, has great application potential in many high-end fields such as cutting tools, molds, drill probes, optical windows, and heat dissipation devices. Especially in fields such as high-speed cutting, metal processing, oil drilling, precision molds, and wear-resistant parts, the use of diamond materials can greatly improve the performance and lifespan of devices.

[0003] CVD diamond has become a research hotspot in recent years because it can produce large-area, thin-film, or bulk diamonds at relatively low cost. However, while CVD diamond has made significant progress in hardness and size, its structural integrity is weakened by defects and impurities such as pores, grain boundaries, residual stress, non-diamond carbon phases (e.g., sp2-bonded carbon, graphitized carbon, amorphous carbon), nitrogen and hydrogen impurities introduced by the reaction gas environment, and cracks. These defects and impurities significantly reduce its mechanical properties, such as fracture toughness. Under extreme conditions such as thermal shock and high-speed cutting, it is prone to crack propagation and fracture, leading to chipping of cutting tools and thus limiting its practical application in high-load scenarios. Summary of the Invention

[0004] To address the existing problems, this invention provides a toughening method for CVD diamond to solve the aforementioned issues.

[0005] A method for toughening CVD diamond, comprising: Take a CVD diamond sample, wherein the CVD diamond sample is CVD single crystal diamond or CVD polycrystalline diamond; The CVD diamond sample is pretreated by coating the diamond sample with a coating material and pre-pressing the coated diamond sample. The pretreated diamond sample was subjected to high temperature and high pressure treatment, which transformed the trace amount of graphite carbon in the pretreated diamond sample into diamond phase, thus repairing the micro-defects. The high-temperature and high-pressure treatment includes: increasing the pressure to a first target pressure at a constant pressurization rate, then increasing the temperature to a first target temperature at a constant heating rate, maintaining the first target pressure and first target temperature for 5-15 minutes, then increasing the pressure to a second target pressure at the same pressurization rate, then increasing the temperature to a second target temperature at the same heating rate, and then holding the temperature. After the holding period, the pressure is reduced to room temperature and atmospheric pressure at a constant cooling and depressurization rate. The CVD diamond sample after high temperature and high pressure treatment is cleaned to remove the coating material, and then treated with liquid nitrogen to room temperature to obtain diamond with enhanced toughness.

[0006] In one possible implementation, the coating material is sodium chloride, and the coating method is as follows: after dehydrating and grinding sodium chloride powder, it is pre-pressed into a dense cylinder to wrap the CVD diamond sample; wherein, the dehydration temperature of sodium chloride powder is 100-150℃, and the dehydration time is 1-3 hours.

[0007] In one possible implementation, the first target temperature is 800-1000°C and the first target pressure is 3-5 GPa.

[0008] In one possible implementation, the second target pressure is 6-10 GPa, the second target temperature is 1500-1800℃, and the holding time is 10-30 minutes.

[0009] In one possible implementation, the high-temperature and high-pressure treatment has a pressurization rate of 3-5 GPa / h, a heating rate of 90-100℃ / min, a cooling rate of 90-100℃ / min, and a depressurization rate of 3-6 GPa / h.

[0010] CVD diamond samples prepared by CVD exhibit a film-like structure. The core function of coating this film-like CVD diamond with sodium chloride is to pre-press the diamond sample into a dense cylinder after encapsulating it with finely powdered sodium chloride. This provides the diamond with a stress environment as close as possible to hydrostatic pressure within the high-pressure chamber. Sodium chloride can uniformly transmit pressure to a certain extent at 5-10 GPa, both filling the voids around the sample and acting as a buffer and isolation mechanism. This results in a more uniform pressure distribution on the diamond sample, preventing the induction of new thermal and shear stresses that could lead to new cracks during pressurization, heating, depressurization, and cooling processes.

[0011] In one possible implementation, the cleaning of the CVD diamond sample after high temperature and high pressure treatment includes: mixing sulfuric acid and nitric acid in a volume ratio of 2:1 to 4:1 to obtain a mixed acid, and using the mixed acid for cleaning.

[0012] The cleaning temperature is 150-250°C, and the cleaning time is 1-5 hours.

[0013] Sodium chloride first ionizes into Na in mixed acid. + and Cl -In the presence of high-temperature concentrated sulfuric acid, solid sodium chloride may react with liquid H2SO4 to produce soluble NaHSO4 (or Na2SO4), releasing HCl gas. This causes the sodium chloride originally coating the diamond to be converted into a series of soluble salts remaining in the acid solution. Subsequently, an ultrasonic cleaning step with deionized water is used to remove the residual Na... + Cl - And completely wash away the sulfates.

[0014] In one possible implementation, the CVD diamond sample, after being cleaned with mixed acid, is then ultrasonically cleaned with alcohol and deionized water in sequence to remove impurities.

[0015] In one possible implementation, after pre-pressing the coated diamond sample, the process further includes: The pre-compressed cylindrical sample, insulating material, heating material, heat insulation material, and pressure transmission medium are assembled sequentially from the inside to the outside to form an assembly, which is then subjected to high-temperature and high-pressure treatment.

[0016] In this invention, effectively controlling the rate of heating and pressurization and the rate of cooling and pressurization, as well as controlling the holding time, is the key to obtaining high-quality diamonds.

[0017] If the temperature rises too quickly, the temperature difference between the inside and outside of the sample, as well as between the sample and NaCl and the mold, will be very large. Under high pressure environments of 5-10 GPa, thermal stress and non-hydrostatic shear stress can easily induce new cracks in the brittle CVD diamond sample. If the temperature rises too slowly, the sample will remain in the intermediate temperature region (where diffusion begins to be active but has not yet fully entered the target temperature region) for too long, which may result in some slow rearrangements that are detrimental to the structure, without fully utilizing the high temperature and high pressure conditions of the diamond stability region for defect repair. A shorter holding time is sufficient for sp 2 →sp 3 The transformation and healing process of pores and microcracks are basically complete. Under high pressure, the grain boundaries undergo favorable densification and structural rearrangement. At this point, the grains have not yet shown significant coarsening, thus maintaining both high hardness and high toughness. If the holding time is extended further, the originally beneficial repair process approaches saturation. The extra time begins to promote grain growth, grain boundary migration, and possible impurity segregation. As a result, the beneficial aspects no longer increase significantly, and instead, coarsening and local grain boundary weakening are more likely to occur, manifesting as a slight decrease in hardness and a cessation or even a slight decrease in toughness. Too rapid a cooling and depressurization rate can also lead to crack formation, while too slow a cooling and depressurization rate can cause grain growth, which is detrimental to improving the toughness of diamond.

[0018] In this invention, a stepped heating method and liquid nitrogen are used to perform cold treatment on the product after cleaning with mixed acid, which further effectively improves the toughness of the prepared diamond. Before reaching the second target temperature (final temperature), a stress relaxation stage is set at a relatively low temperature (e.g., 800-1000℃) and medium pressure (3-5GPa). During the deposition and growth of CVD diamond, a large amount of initial residual tensile stress is accumulated inside. If the temperature is directly raised to the phase transition region above 1500℃, the lattice distortion will be released too quickly, which can easily induce the propagation of microcracks. The stepped stress relaxation platform allows the diamond to release internal stress gradually before large-scale rearrangement of grain boundaries. The subsequent cold treatment utilizes the volume shrinkage effect of the material at extremely low temperatures to introduce beneficial residual compressive stress into the diamond surface. This residual compressive stress can effectively offset the external tensile stress generated by the cutting tool under impact during actual service, thereby directly improving the fracture resistance of the material.

[0019] Compared with the prior art, the present invention has the following advantages: After effectively coating CVD diamond, a staged heating and pressurization process was adopted, followed by liquid nitrogen cooling after acid cleaning. This process effectively controlled the microstructure of CVD diamond while maintaining its high hardness, thus significantly improving its fracture toughness. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the assembly of the present invention; Figure 2 This is a SEM image of the CVD diamond before processing in Example 1 of the present invention; Figure 3 This is a SEM image of the CVD diamond after processing in Example 1 of the present invention. Detailed Implementation

[0021] The embodiments of this disclosure will now be described in detail with reference to the accompanying drawings.

[0022] The following specific examples illustrate the implementation of this disclosure. Those skilled in the art can easily understand other advantages and effects of this disclosure from the content disclosed in this specification. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. This disclosure can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of this disclosure. It should be noted that, in the absence of conflict, the following embodiments and features in the embodiments can be combined with each other. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure.

[0023] In this invention, the CVD diamond sample is selected from single-crystal or polycrystalline diamond materials prepared by standardized CVD process (CVD polycrystalline diamond prepared by DC arc jet method and hot wire method, and CVD single-crystal diamond prepared by microwave plasma chemical vapor deposition).

[0024] After double-sided mechanical polishing of the CVD diamond film, a smooth diamond film is obtained. This film is then laser-processed into cylindrical shapes of varying sizes for high-temperature, high-pressure (HTHP) treatment. Before treatment, ultrasonic cleaning (e.g., deionized water + acid washing) and drying are performed to ensure a clean sample surface and reduce impurities that could affect the HTHP effect. Sodium chloride powder is used as the coating material for the diamond film to provide a hydrostatic environment. The sodium chloride powder is first placed in a muffle furnace at 120°C. 0 The sample is treated with C for 2 hours to remove internal moisture, then ground into a fine powder with uniform particles. A diamond film and sodium chloride powder (or other materials, provided they are thermally stable at 5-10 GPa and 1500-1800 ℃, chemically inert to diamond, have a certain degree of plasticity under high pressure, and are easy to clean subsequently, can be used as a pressure-transmitting coating medium, such as certain oxides or boron nitride powder) are loaded into a tungsten carbide mold and pre-pressed on a jack to obtain a dense cylinder with a sodium chloride-coated diamond film. The cylindrical sample, insulating material, heating material, thermal insulation material, and pressure-transmitting medium are then assembled sequentially to form an assembly (e.g., ...). Figure 1 (As shown).

[0025] Among them, the pressure transmission medium is magnesium oxide, the heat insulation material is zirconium oxide, the heating material is Ta, and the insulation material is hBN.

[0026] Unlike the direct preparation of diamond from high-purity graphite, the high-temperature, high-pressure (HPHT) method used in this invention significantly reduces the temperature and pressure, with a temperature range of 1500-1800℃ and a pressure range of 5-10 GPa. In contrast, the direct preparation of diamond from high-purity graphite requires a pressure range of 15-25 GPa and a temperature range of 2300-2500℃ to complete the conversion of graphite to diamond. These conditions are significantly more demanding and energy-intensive than those required by this invention.

[0027] The following describes the diamonds obtained under different treatment conditions, using sodium chloride as the coating material and the same pretreatment process. Example 1

[0028] CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 4 GPa and a temperature of 900℃ for 10 minutes, followed by a pressure of 8 GPa and a temperature of 1600℃ for 10 minutes. The heating rate was 96℃ / min, the pressure increase rate was 4 GPa / h, the cooling rate was 92℃ / min, and the pressure decrease rate was 4 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 2:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 150℃ for 1 hour. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 2

[0029] CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 4 GPa and a temperature of 800℃ for 15 minutes, followed by a pressure of 8 GPa and a temperature of 1600℃ for 20 minutes. The heating rate was 90℃ / min, the pressure increase rate was 3 GPa / h, the cooling rate was 90℃ / min, and the pressure decrease rate was 3 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 4:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 250℃ for 5 hours. Liquid nitrogen was then added to cool the diamond to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 3

[0030] CVD single-crystal diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 3 GPa and a temperature of 800°C for 5 minutes, followed by a pressure of 5 GPa and a temperature of 1500°C for 20 minutes. The heating rate was 100°C / min, the pressure increase rate was 5 GPa / h, the cooling rate was 100°C / min, and the pressure decrease rate was 5 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200°C for 3 hours. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 4

[0031] CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 5 GPa and a temperature of 1000℃ for 10 minutes, followed by a pressure of 10 GPa and a temperature of 1600℃ for 10 minutes. The heating rate was 100℃ / min, the pressure increase rate was 5 GPa / h, the cooling rate was 100℃ / min, and the pressure decrease rate was 5 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200℃ for 3 hours. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 5

[0032] CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 5 GPa and a temperature of 950°C for 15 minutes, followed by a pressure of 10 GPa and a temperature of 1800°C for 15 minutes. The heating rate was 90°C / min, the pressure increase rate was 3 GPa / h, the cooling rate was 90°C / min, and the pressure decrease rate was 3 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200°C for 3 hours. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 6

[0033] CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 3 GPa and a temperature of 800°C for 5 minutes, followed by a pressure of 5 GPa and a temperature of 1700°C for 30 minutes. The heating rate was 95°C / min, the pressure increase rate was 4 GPa / h, the cooling rate was 90°C / min, and the pressure decrease rate was 4 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200°C for 3 hours. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 7

[0034] CVD single-crystal diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 4 GPa and a temperature of 950°C for 10 minutes, followed by a pressure of 8 GPa and a temperature of 1600°C for 10 minutes. The heating rate was 95°C / min, the pressure increase rate was 5 GPa / h, the cooling rate was 100°C / min, and the pressure decrease rate was 4 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200°C for 3 hours. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 8

[0035] CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 4 GPa and a temperature of 900℃ for 5 minutes, followed by a pressure of 8 GPa and a temperature of 1800℃ for 20 minutes. The heating rate was 100℃ / min, the pressure increase rate was 4 GPa / h, the cooling rate was 95℃ / min, and the pressure decrease rate was 5 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200℃ for 3 hours. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained. Example 9

[0036] CVD single-crystal diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then subjected to a pressure of 4 GPa and a temperature of 850°C for 15 minutes, followed by a pressure of 8 GPa and a temperature of 1500°C for 30 minutes. The heating rate was 90°C / min, the pressure increase rate was 3 GPa / h, the cooling rate was 100°C / min, and the pressure decrease rate was 5 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had been cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200°C for 3 hours. Liquid nitrogen was then added to cool it to room temperature. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained.

[0037] Comparative Example 1 CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then held at 1400℃ for 30 minutes at a pressure of 5 GPa. The heating rate was 90℃ / min, the pressure increase rate was 3 GPa / h, the cooling rate was 100℃ / min, and the pressure decrease rate was 5 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200℃ for 3 hours. After removing impurities, the diamond was ultrasonically cleaned sequentially with alcohol and deionized water to obtain the treated diamond.

[0038] Comparative Example 2 CVD polycrystalline diamond was pretreated according to the aforementioned pretreatment process to obtain an assembly. The assembly was then held at 200°C for 30 minutes at a pressure of 15 GPa. The heating rate was 90°C / min, the pressure increase rate was 3 GPa / h, the cooling rate was 100°C / min, and the pressure decrease rate was 5 GPa / h. A mixed acid was prepared by mixing sulfuric acid and nitric acid at a volume ratio of 3:1. This mixed acid was used to clean the diamond, which had cooled to room temperature and atmospheric pressure, at a cleaning temperature of 200°C for 3 hours. After removing impurities by ultrasonic cleaning with alcohol and deionized water, toughened diamond was obtained.

[0039] The Vickers hardness and fracture toughness of each embodiment and comparative example were tested using a FutureTech FV-700 Vickers hardness tester. The specific results are shown in Table 1. Table 1 As shown in the table, only by controlling appropriate temperature, pressure, heating rate, cooling rate, pressurization rate, and depressurization rate can the fracture toughness of diamond be significantly increased without a significant change in hardness. Comparative Examples 1 and 2 failed to achieve the toughening effect because the temperature, pressure, heating rate, cooling rate, pressurization rate, or depressurization rate exceeded the specified range. This invention achieves the toughening effect by effectively controlling six parameters—temperature, pressure, heating rate, cooling rate, pressurization rate, and depressurization rate—to process CVD diamond under high temperature and high pressure. Without controlling any one of these parameters, significant toughening cannot be achieved.

[0040] The following is a comparison of the SEM image before processing in Example 1 ( Figure 2 ) and the processed SEM image ( Figure 3 The processing effect of the present invention will be explained below. Figure 2 It can be seen that before processing, the grain boundaries were clear, the intergranular bonding was not tight, many pores existed, and the grain size was approximately 500-600 nm. From Figure 3As can be seen, after treatment, the grain boundaries are blurred, the grains are tightly bonded, there are almost no pores, and the grain size is approximately 300-400 nm. Therefore, the treatment method of this invention reduces the voids between grains, thereby improving the toughness of diamond.

[0041] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for toughening CVD diamond, characterized in that, include: Take a CVD diamond sample, wherein the CVD diamond sample is CVD single crystal diamond or CVD polycrystalline diamond; The CVD diamond sample is pretreated by coating the diamond sample with a coating material and pre-pressing the coated diamond sample. The pretreated diamond sample was subjected to high temperature and high pressure treatment, which transformed the trace amount of graphite carbon in the pretreated diamond sample into diamond phase, thus repairing the micro-defects. The high-temperature and high-pressure treatment includes: increasing the pressure to a first target pressure at a constant pressurization rate, then increasing the temperature to a first target temperature at a constant heating rate, maintaining the first target pressure and temperature for 5-15 minutes, then increasing the pressure to a second target pressure at the same pressurization rate, then increasing the temperature to a second target temperature at the same heating rate, and holding the temperature. After the holding period, the pressure is reduced to room temperature and atmospheric pressure at a constant cooling and depressurization rate. The CVD diamond sample after high temperature and high pressure treatment is cleaned to remove the coating material, and then treated with liquid nitrogen to room temperature to obtain diamond with enhanced toughness.

2. The toughening method for CVD diamond according to claim 1, characterized in that, The coating material is sodium chloride, and the coating method is as follows: after dehydrating and grinding sodium chloride powder, it is pre-pressed into a dense cylinder to wrap the CVD diamond sample. The dehydration temperature of sodium chloride powder is 100-150°C, and the dehydration time is 1-3 hours.

3. The toughening method for CVD diamond according to claim 1, characterized in that, The first target temperature is 800-1000℃, and the first target pressure is 3-5GPa.

4. The toughening method for CVD diamond according to claim 1, characterized in that, The second target pressure is 6-10 GPa, the second target temperature is 1500-1800°C, and the holding time is 10-30 minutes.

5. The toughening method for CVD diamond according to claim 1, characterized in that, The pressure increase rate of the high-temperature and high-pressure treatment is 3-5 GPa / h, the heating rate is 90-100°C / min, the cooling rate is 90-100°C / min, and the pressure decrease rate is 3-5 GPa / h.

6. The toughening method for CVD diamond according to claim 1, characterized in that, The cleaning of the CVD diamond sample after high-temperature and high-pressure treatment includes: mixing sulfuric acid and nitric acid at a volume ratio of 2:1 to 4:1 to obtain a mixed acid, and using the mixed acid for cleaning. The cleaning temperature is 150-250°C, and the cleaning time is 1-5 hours.

7. The toughening method for CVD diamond according to claim 6, characterized in that, The CVD diamond samples after being cleaned with mixed acid were then ultrasonically cleaned with alcohol and deionized water in sequence to remove impurities.

8. The toughening method for CVD diamond according to claim 1, characterized in that, After pre-pressing the coated diamond sample, the process also includes: The pre-compressed cylindrical sample, insulating material, heating material, heat insulation material, and pressure transmission medium are assembled sequentially from the inside out to form an assembly, which is then subjected to high-temperature and high-pressure treatment.

Images