Diamond compact and preparation method thereof

Abstract

The invention belongs to the technical field of synthesis of superhard material compacts, and particularly relates to a diamond compact and a preparation method thereof. Powder raw materials are mixed to obtain mixed micro powder, and the powder raw materials comprise, by mass, 92%-98.5% of diamond micro powder, 1%-5% of nanoscale cobalt powder and 0.5%-3% of nanoscale niobium powder; and the mixed micro powder is sequentially subjected to reduction treatment, spreading, hard alloy covering, pressing, high-temperature purification shaping and high-temperature and high-pressure synthesis, and the diamond compact is obtained. According to the preparation method provided by the invention, the yield of the diamond compacts can be remarkably improved, the finished diamond compacts are prevented from cracking, and the obtained finished diamond compacts are complete in appearance and free of cracks. Moreover, the preparation method provided by the invention is simple to operate and high in practicability, and has wide application value.

Description

Technical Field

[0001] This invention belongs to the field of superhard material composite sheet synthesis technology, specifically relating to a diamond composite sheet and its preparation method. Background Technology

[0002] Diamond composite sheets belong to the category of superhard material composite sheets. They are superhard materials polymerized with diamond as the main component on the surface of a cemented carbide substrate. Characterized by high hardness and excellent wear resistance, they are widely used in industries such as oil drilling, geological exploration, coalfield drilling bits, and machining tools. Superhard material composite sheets are widely used in tool manufacturing, especially in cutting processes. With the continuous development of the machining industry, the application range of superhard material composite sheets in the tool industry is expanding, including commonly used machine tool turning tools, machining drills, and milling cutters and profile milling cutters for edge machining. Due to the increasing precision requirements of machining, the demands on superhard material tools are also rising. Generally, the finer the diamond grain size in the superhard material composite sheet, the lower the surface roughness of the workpiece machined as a tool material, better meeting the goal of cutting instead of grinding in the machining of non-ferrous metals or inorganic materials. This saves time and labor costs in the machining industry, reducing the demands for high precision and efficiency. However, the synthesis of submicron and nanodiamond composite sheets often faces the problem of difficult molding, and the molding process is prone to cracking, resulting in a low yield. Summary of the Invention

[0003] The purpose of this invention is to provide a diamond composite sheet and its preparation method. The preparation method provided by this invention can significantly improve the yield of diamond composite sheets, avoid cracking of the finished diamond composite sheets, and the resulting finished diamond composite sheets have a complete appearance and are free of cracks.

[0004] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing diamond composite sheets, comprising the following steps: The powder raw materials are mixed to obtain mixed micro powder, wherein the powder raw materials include the following components in terms of mass content: 92-98.5% diamond micro powder, 1-5% nano-cobalt powder, and 0.5-3% nano-niobium powder; The mixed micro powder is subjected to reduction treatment in a reducing atmosphere to obtain reduced mixed micro powder; The reduced mixed micro powder is spread out and covered with hard alloy to obtain a pre-assembled composite sheet; The pre-assembled composite sheet is pressed to obtain a compacted composite sheet; The compacted composite sheet is subjected to high-temperature purification and shaping to obtain a purified and shaped composite sheet. The high-temperature purification and shaping is carried out under vacuum conditions, and the temperature of the high-temperature purification and shaping is ≥600℃. The purified and shaped composite sheet is subjected to high temperature and high pressure synthesis to obtain the diamond composite sheet. The high temperature and high pressure synthesis temperature is ≥1550℃ and the pressure is ≥5GPa.

[0005] Preferably, the diamond micro powder has a particle size of 100~1000nm; the nano-cobalt powder has a particle size ≤300nm; and the nano-niobium powder has a particle size ≤500nm.

[0006] Preferably, the mixing is ball milling, and the conditions for ball milling include: a ball-to-material ratio of 5 to 15:1; a ball milling time of 3 to 8 hours; and an organic solvent as the ball milling medium. The ball milling yields wet abrasive. The mixture further includes drying and sieving the wet abrasive in sequence, wherein the drying temperature is 70 to 90°C; and the mesh size of the sieve used for sieving is 100 to 120 mesh.

[0007] Preferably, the reducing atmosphere is hydrogen gas with a pressure of 0.02~0.1MPa; the reduction treatment temperature is 350~950℃ and the time is 0.5~3h.

[0008] Preferably, the preparation method of the pre-loaded composite sheet includes: spreading the reduced mixed micro powder evenly in a niobium cup; then covering it with a cemented carbide, and finally using a molybdenum cup as a lid; the diameter of the niobium cup is ≥30mm, and the mass of the reduced mixed micro powder spread in the niobium cup is 3~5mg / mm². 2 .

[0009] Preferably, the thickness of the cemented carbide is 2-4 mm; the grade of the cemented carbide is YG16.

[0010] Preferably, the pressing pressure is 3~5t.

[0011] Preferably, the vacuum degree of the high-temperature purification and shaping is 10. -4 ~10 -2 Pa; temperature is 600~1100℃, and the heat preservation and pressure holding time is 1~3h.

[0012] Preferably, the high-temperature and high-pressure synthesis pressure is 5~6.5GPa; the temperature is 1550~1750℃; and the heat preservation and pressure holding time is 12~25min.

[0013] The present invention provides a diamond composite sheet prepared by the preparation method described in the above technical solution.

[0014] This invention provides a method for preparing a diamond composite sheet, comprising the following steps: mixing powder raw materials to obtain mixed micro powder, wherein the powder raw materials include the following components in terms of mass content: 92-98.5% diamond micro powder, 1-5% nano-cobalt powder, and 0.5-3% nano-niobium powder; reducing the mixed micro powder in a reducing atmosphere to obtain reduced mixed micro powder; spreading the reduced mixed micro powder and covering it with cemented carbide to obtain a pre-assembled composite sheet; pressing the pre-assembled composite sheet to obtain a compacted composite sheet; subjecting the compacted composite sheet to high-temperature purification and shaping to obtain a purified and shaped composite sheet, wherein the high-temperature purification and shaping is performed under vacuum conditions at a temperature ≥600℃; and subjecting the purified and shaped composite sheet to high-temperature and high-pressure synthesis to obtain the diamond composite sheet, wherein the high-temperature and high-pressure synthesis temperature is ≥1550℃ and the pressure is ≥5GPa. The preparation method provided by this invention uses nano-sized niobium powder as a toughening raw material. By compounding diamond micro powder, nano-sized cobalt powder, and nano-sized niobium powder, and controlling the mass ratio of the three raw materials, the toughness of the material during the molding process is improved, effectively avoiding cracking during molding. The toughening principle of this invention is as follows: The high-temperature and high-pressure method for synthesizing diamond polycrystals involves connecting diamond particles through D-D bonds, but this requires very high pressure and temperature. The addition of cobalt lowers the synthesis temperature and pressure, allowing polycrystals to form at around 1550℃ and 5GPa. However, cobalt is easily oxidized by oxygen in the air, and even reduction with hydrogen in a reducing atmosphere cannot completely solve this problem. At the same time, residual air remains during the high-temperature setting process, affecting the catalytic performance of the cobalt catalyst. This invention adds niobium powder dispersed in the mixed micro powder, which can adsorb excess gas, especially oxygen, at high temperatures, thereby effectively protecting the catalytic effect of cobalt and generating more D-D bonds between diamond polycrystals. At the same time, the presence of niobium also acts as a stress buffer, thereby enhancing toughness. Meanwhile, by controlling the temperature and pressure parameters of the high-temperature purification and shaping process and the high-temperature and high-pressure synthesis process, this invention can further enhance the interaction between the three raw materials, optimize the hardness and toughness of the materials, improve the yield of diamond composite sheets, avoid cracking of the finished diamond composite sheets, and obtain diamond composite sheets with a complete appearance and no cracks. Moreover, the preparation method provided by this invention is simple to operate, highly practical, and has wide application value.

[0015] Furthermore, in this invention, the diamond micropowder has a particle size of 100~1000 nm. The preparation method provided by this invention is applicable to the preparation of submicron or nanodiamond composite sheets, and can significantly improve the toughness of submicron or nanodiamond composite sheets, making them less prone to cracking. Attached Figure Description

[0016] Figure 1 Ultrasonic scanning of the sample surface spectrum in Example 1; Figure 2This is an optical photograph of the sample from Example 1. Detailed Implementation

[0017] This invention provides a method for preparing diamond composite sheets, comprising the following steps: The powder raw materials are mixed to obtain mixed micro powder, wherein the powder raw materials include the following components in terms of mass content: 92-98.5% diamond micro powder, 1-5% nano-cobalt powder, and 0.5-3% nano-niobium powder; The mixed micro powder is subjected to reduction treatment in a reducing atmosphere to obtain reduced mixed micro powder; The reduced mixed micro powder is spread out and covered with hard alloy to obtain a pre-assembled composite sheet; The pre-assembled composite sheet is pressed to obtain a compacted composite sheet; The compacted composite sheet is subjected to high-temperature purification and shaping to obtain a purified and shaped composite sheet. The high-temperature purification and shaping is carried out under vacuum conditions, and the temperature of the high-temperature purification and shaping is ≥600℃. The purified and shaped composite sheet is subjected to high temperature and high pressure synthesis to obtain the diamond composite sheet. The high temperature and high pressure synthesis temperature is ≥1550℃ and the pressure is ≥5GPa.

[0018] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0019] The present invention mixes powder raw materials to obtain mixed micro powder, wherein the powder raw materials include the following components in terms of mass content: 92-98.5% diamond micro powder, 1-5% nano-cobalt powder and 0.5-3% nano-niobium powder.

[0020] In this invention, the particle size of the diamond micron powder is preferably 100-1000 nm, more preferably 200-900 nm, and in the embodiments it can be 850 nm, 500 nm or 250 nm. The particle size of the nano-cobalt powder is preferably ≤300 nm, more preferably 50-300 nm, and even more preferably 100-250 nm, and in the embodiments it can be 200 nm. The particle size of the nano-niobium powder is preferably ≤500 nm, more preferably 50-500 nm, and even more preferably 100-400 nm, and in the embodiments it can be 200 nm.

[0021] In this invention, the powder raw material preferably comprises 92-97% diamond micro powder by weight percentage, and in the embodiments, it can be 95%, 96%, or 92%. The powder raw material preferably comprises 2-5% nano-cobalt powder by weight percentage, and in the embodiments, it can be 5%, 3%, or 3.5%. The powder raw material preferably comprises 1-3% nano-niobium powder by weight percentage, and in the embodiments, it can be 3%, 1%, or 1.5%.

[0022] In this invention, the mixing is preferably ball milling. The grinding balls used in the ball milling can be stainless steel balls, and the diameter of the grinding balls can be 2-10 mm. The ball milling conditions preferably include a ball-to-material ratio of 5-15:1, which can be 10:1 in the examples. The ball-to-material ratio in this invention refers to the mass ratio of the grinding balls used in the ball milling to the powder raw material. The ball milling time is preferably 3-8 hours, which can be 3 hours, 4 hours, or 5 hours in the examples. The ball milling speed is preferably 100-160 r / min. The ball milling medium is preferably an organic solvent, which can be ethanol. This invention does not have special requirements for the amount of ball milling medium used, as long as the ball milling mixing proceeds smoothly.

[0023] In this invention, the ball milling process yields wet abrasive balls. Preferably, the invention further includes sequentially drying and sieving the wet abrasive balls. The drying process can be oven drying. The drying temperature is preferably 70-90°C, and in this embodiment, it can be 80°C. The mesh size of the sieve used for sieving can be 100-120 mesh, and in this embodiment, it can be 100 mesh or 120 mesh.

[0024] After obtaining the mixed micropowder, the present invention performs a reduction treatment on the mixed micropowder in a reducing atmosphere to obtain reduced mixed micropowder. By performing the reduction treatment in a reducing atmosphere, the present invention can solve the problem of nano-sized cobalt powder generating cobalt oxide in an oxygen-rich environment, leading to catalytic inactivation.

[0025] In this invention, the reducing atmosphere is preferably hydrogen. The hydrogen pressure is preferably 0.02~0.1 MPa, more preferably 0.03~0.09 MPa, and in the embodiments, it can be 0.08 MPa or 0.05 MPa. The reduction treatment temperature is preferably 350~950℃, more preferably 400~800℃, and in the embodiments, it can be 500℃ or 600℃. The reduction treatment time is preferably 0.5~3 h, more preferably 1~2 h, and in the embodiments, it can be 1 h or 1.5 h.

[0026] After obtaining the reduced mixed micro powder, the present invention spreads the reduced mixed micro powder evenly and covers it with cemented carbide to obtain a pre-assembled composite sheet.

[0027] In this invention, the preferred method for preparing the pre-assembled composite sheet includes: spreading the reduced mixed micro powder evenly in a niobium cup; then covering it with a cemented carbide, and finally using a molybdenum cup as a lid. The diameter of the niobium cup is preferably ≥30mm, and in this embodiment, it can be 35mm. The mass of the reduced mixed micro powder spread in the niobium cup is preferably 3~5mg / mm³. 2 More preferably, it is 3.5~4 mg / mm 2 In the examples, the concentration can be 3.5 mg / mm. 2 .

[0028] In this invention, the thickness of the cemented carbide is preferably 2-4 mm, and in the embodiments it can be 3 mm or 4 mm. The grade of the cemented carbide can be YG16. The molybdenum cup serves as the lid of the niobium cup and is adapted to the size of the niobium cup.

[0029] After obtaining the pre-assembled composite sheet, the present invention presses the pre-assembled composite sheet to obtain a compacted composite sheet. In the present invention, the pressing is performed using a hydraulic press. The pressing pressure is preferably 3~5t, and in the embodiments it can be 4t or 5t. The pressing time is preferably 5~10s.

[0030] After obtaining the compacted composite sheet, the present invention further purifies and shapes the compacted composite sheet at high temperature to obtain a purified and shaped composite sheet. The high-temperature purification and shaping is carried out under vacuum conditions, and the temperature of the high-temperature purification and shaping is ≥600℃. In the present invention, during the high-temperature purification and shaping process, the waste gas adsorbed by the diamond micropowder under vacuum and high temperature is released, and at the same time, the metal powder (i.e., nano-cobalt powder and nano-niobium powder) also adheres to the diamond micropowder, providing a cleaner environment for subsequent high-temperature and high-pressure synthesis.

[0031] In this invention, the vacuum degree of the high-temperature purification and shaping is preferably 10. -4 ~10 -2 Pa, in the embodiment, can be 10. - 4 Pa. The preferred temperature for high-temperature purification and setting is 600~1100℃, more preferably 650~1000℃, and even more preferably 700~800℃, which can be 700℃ in the embodiment. The preferred heat preservation and pressure holding time for high-temperature purification and setting is 1~3h, more preferably 1~2h, which can be 1.5h in the embodiment.

[0032] After obtaining the purified and shaped composite sheet, the present invention performs high-temperature and high-pressure synthesis on the purified and shaped composite sheet to obtain the diamond composite sheet. The high-temperature and high-pressure synthesis temperature is ≥1550℃ and the pressure is ≥5GPa. In the present invention, the high-temperature and high-pressure synthesis preferably includes: applying pressure to the purified and shaped composite sheet using high-pressure equipment, and then heating it. Before the temperature of the high-temperature and high-pressure synthesis is reached, graphitization will occur on the surface of the diamond microparticles under the catalytic action of nano-cobalt powder. When the high-temperature and high-pressure synthesis temperature is reached, new diamonds continue to form under the catalytic action of the nano-cobalt powder. During the high-temperature and high-pressure synthesis process, the new diamonds will link the original diamonds together to form diamond polycrystals. At the same time, the catalyst (nano-cobalt powder) and metallic niobium (nano-niobium powder) are squeezed between the diamond particles. The high-temperature and high-pressure conditions during the high-temperature and high-pressure synthesis process also cause the cemented carbide to bond with the diamond polycrystals. Finally, a diamond composite sheet is obtained.

[0033] In this invention, the high-temperature, high-pressure synthesis is carried out in a six-sided top press. The high-temperature, high-pressure synthesis is conducted with the assistance of carbonate tubes and pyrophyllite blocks.

[0034] In this invention, the pressure of the high-temperature and high-pressure synthesis is preferably 5~6.5 GPa, and in the embodiment it can be 5.5 GPa. The temperature of the high-temperature and high-pressure synthesis is preferably 1550~1750℃, and in the embodiment it can be 1600℃. The holding time of the high-temperature and high-pressure synthesis is preferably 12~25 min, and in the embodiment it can be 15 min.

[0035] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0036] Example 1 (1) 92g of diamond micro powder with a particle size of 850nm, 5g of cobalt powder with a particle size of 200nm, and 3g of niobium powder with a particle size of 200nm were ball-milled in a stainless steel container with 75mL of ethanol and 1000g of stainless steel balls (8mm in diameter) for 3 hours at a speed of 160r / min. The mixture was dried at 80℃ and sieved through a 120-mesh sieve to obtain a diamond micro powder mixed with (cobalt powder) and toughening agent (niobium powder), i.e., mixed micro powder.

[0037] (2) The mixed micro powder obtained in step (1) is reduced in hydrogen at 600℃ for 1 h at a hydrogen pressure of 0.05 MPa to obtain the reduced mixed micro powder.

[0038] (3) Take 3.5g of the reduced mixed micro powder obtained in step (2), spread it evenly into a niobium cup with a diameter of 35mm, and cover it with a 4mm thick hard alloy (grade YG16). Match a molybdenum cup suitable for the niobium cup as a lid to obtain a pre-assembled composite sheet.

[0039] (4) The pre-assembled composite sheet obtained in step (3) is compacted using a hydraulic press with a pressure of 5 tons and a time of 10 seconds to obtain a compacted composite sheet.

[0040] (5) The compacted composite sheet obtained in step (4) is subjected to high-temperature purification and shaping, and then subjected to 10°C. -4 The purified and shaped composite sheet was obtained by holding it at 700℃ for 1.5 hours in a vacuum furnace with a vacuum degree of Pa.

[0041] (6) The purified and shaped composite sheet obtained in step (5) is matched with a suitable traditional carbon salt tube and pyrophyllite block, and then subjected to high temperature and high pressure synthesis in a six-sided top press. The high temperature and high pressure synthesis pressure is 5.5 GPa, the temperature is 1600℃, and the heat and pressure holding time is 15 min to obtain an 850nm diamond composite sheet. Figure 1Ultrasonic scanning of the sample surface spectrum in Example 1; Figure 2 This is an optical photograph of the sample from Example 1. According to... Figure 1 and Figure 2 As can be seen, the composite sheet prepared in Example 1 has a complete appearance and no cracks.

[0042] (7) The 850nm diamond composite sheet obtained in step (6) was tested with an industry-standard silicon carbide grinding wheel, and the wear ratio was found to be 2.16×10. 4 .

[0043] Example 2 (1) 96g of diamond micro powder with a particle size of 500nm, 3g of cobalt powder with a particle size of 200nm, and 1g of niobium powder with a particle size of 200nm were ball-milled in a stainless steel container with 75mL of ethanol and 1000g of stainless steel balls (8mm in diameter) for 3 hours at a speed of 160r / min. The mixture was dried at 80℃ and sieved through a 120-mesh sieve to obtain a diamond micro powder mixed with cobalt powder and toughening agent (niobium powder), i.e., mixed micro powder.

[0044] (2) The mixed micro powder obtained in step (1) is reduced in hydrogen at 600℃ for 1 h at a hydrogen pressure of 0.08 MPa to obtain the reduced mixed micro powder.

[0045] (3) Take 3.5g of the reduced mixed micro powder obtained in step (2), spread it evenly into a niobium cup with a diameter of 35mm, and cover it with a 4mm thick hard alloy (grade YG16). Match a molybdenum cup suitable for the niobium cup as a lid to obtain a pre-assembled composite sheet.

[0046] (4) The pre-assembled composite sheet obtained in step (3) is compacted with a hydraulic press at a pressure of 5 tons for 10 seconds to obtain a compacted composite sheet.

[0047] (5) The compacted composite sheet obtained in step (4) is subjected to high-temperature purification and shaping, and then subjected to 10°C. -4 The purified and shaped composite sheet was obtained by holding it at 700℃ for 1.5 hours in a vacuum furnace with a vacuum degree of Pa.

[0048] (6) The purified and shaped composite sheet obtained in step (5) is matched with a suitable traditional carbon salt tube and pyrophyllite block, and then subjected to high temperature and high pressure synthesis in a six-sided top press. The high temperature and high pressure synthesis pressure is 5.5 GPa, the temperature is 1600℃, and the heat and pressure holding time is 15 min to obtain a 500nm diamond composite sheet. The obtained composite sheet has a complete appearance and no cracks.

[0049] (7) The 500nm diamond composite sheet obtained in step (6) was tested with an industry-standard silicon carbide grinding wheel, and the wear ratio was found to be 1.98×10. 4 .

[0050] Example 3 (1) 95g of diamond powder with a particle size of 250nm, 3.5g of cobalt powder with a particle size of 200nm, and 1.5g of niobium powder with a particle size of 200nm were ball-milled in a stainless steel container with 75mL of ethanol and 1000g of stainless steel balls (8mm in diameter) for 3 hours at a speed of 160r / min. The mixture was dried at 80℃ and sieved through a 120-mesh sieve to obtain diamond powder mixed with catalyst (cobalt powder) and toughening agent (niobium powder), i.e., mixed powder.

[0051] (2) The mixed micro powder obtained in step (1) is reduced in hydrogen at 600℃ for 1 h at a hydrogen pressure of 0.08 MPa to obtain the reduced mixed micro powder.

[0052] (3) Take 3.5g of the reduced mixed micro powder obtained in step (2), spread it evenly into a niobium cup with a diameter of 35mm, and cover it with a 4mm thick hard alloy (grade YG16). Match a molybdenum cup suitable for the niobium cup as a lid to obtain a pre-assembled composite sheet.

[0053] (4) The pre-assembled composite sheet obtained in step (3) is compacted with a hydraulic press at a pressure of 5 tons for 10 seconds to obtain a compacted composite sheet.

[0054] (5) The compacted composite sheet obtained in step (4) is subjected to high-temperature purification and shaping, and then subjected to 10°C. -4 The purified and shaped composite sheet was obtained by holding it at 700℃ for 1.5 hours in a vacuum furnace with a vacuum degree of Pa.

[0055] (6) The purified and shaped composite sheet obtained in step (5) is matched with a suitable traditional carbon salt tube and pyrophyllite block, and then subjected to high temperature and high pressure synthesis in a six-sided top press. The high temperature and high pressure synthesis pressure is 5.5 GPa, the temperature is 1600℃, and the heat and pressure holding time is 15 min to obtain a 250nm diamond composite sheet. The obtained composite sheet has a complete appearance and no cracks.

[0056] (7) The 250nm diamond composite sheet obtained in step (6) was tested with an industry-standard silicon carbide grinding wheel, and the wear ratio was found to be 1.73×10. 4 .

[0057] Comparative Example 1 (1) 92g of diamond powder with a particle size of 850nm, 8g of cobalt powder with a particle size of 200nm, and 0g of niobium powder with a particle size of 200nm were ball-milled in a stainless steel container with 75mL of ethanol and 1000g of stainless steel balls (8mm in diameter) for 3 hours at a speed of 160r / min. The mixture was dried at 80℃ and sieved through a 120-mesh sieve to obtain diamond powder mixed with cobalt powder, i.e., mixed powder.

[0058] (2) The mixed micro powder obtained in step (1) is reduced in hydrogen at 600℃ for 1 h at a hydrogen pressure of 0.05 MPa to obtain the reduced mixed micro powder.

[0059] (3) Take 3.5g of the reduced mixed micro powder obtained in step (2), spread it evenly into a niobium cup with a diameter of 35mm, and cover it with a 4mm thick hard alloy (grade YG16). Match a molybdenum cup suitable for the niobium cup as a lid to obtain a pre-assembled composite sheet.

[0060] (4) The pre-assembled composite sheet obtained in step (3) is compacted with a hydraulic press at a pressure of 5 tons for 10 seconds to obtain a compacted composite sheet.

[0061] (5) The compacted composite sheet obtained in step (4) is subjected to high-temperature purification and shaping, and then subjected to 10°C. -4 The purified and shaped composite sheet was obtained by holding it at 700℃ for 1.5 hours in a vacuum furnace with a vacuum degree of Pa.

[0062] (6) The purified and shaped composite sheet obtained in step (5) is matched with a suitable traditional carbon salt tube and pyrophyllite block, and synthesized in a six-sided top press under high temperature and high pressure. The high temperature and high pressure synthesis pressure is 5.5 GPa, the temperature is 1600℃, and the heat and pressure holding time is 15 min to obtain an 850nm diamond composite sheet. The diamond layer of the obtained composite sheet has fracture-like cracks.

[0063] (7) The 850nm diamond composite sheet obtained in step (6) was tested with an industry-standard silicon carbide grinding wheel, and the wear ratio was found to be 1.72×10. 4 .

[0064] Comparative Example 2 (1) 96g of diamond powder with a particle size of 500nm, 4g of cobalt powder with a particle size of 200nm, and 0g of niobium powder with a particle size of 200nm were ball-milled in a stainless steel container with 75mL of ethanol and 1000g of stainless steel balls (8mm in diameter) for 3 hours at a speed of 160r / min. The mixture was dried at 80℃ and sieved through a 120-mesh sieve to obtain diamond powder mixed with the catalyst (cobalt powder), i.e., mixed powder.

[0065] (2) The mixed micro powder obtained in step (1) is reduced in hydrogen at 600℃ for 1 h at a hydrogen pressure of 0.08 MPa to obtain the reduced mixed micro powder.

[0066] (3) Take 3.5g of the reduced mixed micro powder obtained in step (2), spread it evenly into a niobium cup with a diameter of 35mm, and cover it with a 4mm thick hard alloy (grade YG16). Match a molybdenum cup suitable for the niobium cup as a lid to obtain a pre-assembled composite sheet.

[0067] (4) The pre-assembled composite sheet obtained in step (3) is compacted with a hydraulic press at a pressure of 5 tons for 10 seconds to obtain a compacted composite sheet.

[0068] (5) The compacted composite sheet obtained in step (4) is subjected to high-temperature purification and shaping, and then subjected to 10°C. -4 The purified and shaped composite sheet was obtained by holding it at 700℃ for 1.5 hours in a vacuum furnace with a vacuum degree of Pa.

[0069] (6) The purified and shaped composite sheet obtained in step (5) is matched with a suitable traditional carbon salt tube and pyrophyllite block, and then subjected to high temperature and high pressure synthesis in a six-sided top press. The high temperature and high pressure synthesis pressure is 5.5 GPa, the temperature is 1600℃, and the heat and pressure holding time is 15 min to obtain a 500nm diamond composite sheet. The diamond layer of the obtained composite sheet has radioactive cracks.

[0070] (7) The 500nm diamond composite sheet obtained in step (6) was tested with an industry-standard silicon carbide grinding wheel, and the wear ratio was found to be 1.65×10. 4 .

[0071] Comparative Example 3 (1) 95g of diamond powder with a particle size of 250nm, 5g of cobalt powder with a particle size of 200nm, and 0g of niobium powder with a particle size of 200nm were ball-milled in a stainless steel container with 75mL of ethanol and 1000g of stainless steel balls (8mm in diameter) for 3 hours at a speed of 160r / min. The mixture was dried at 80℃ and sieved through a 120-mesh sieve to obtain diamond powder mixed with the catalyst (cobalt powder), i.e., mixed powder.

[0072] (2) The mixed micro powder obtained in step (1) is reduced in hydrogen at 600℃ for 1 h at a hydrogen pressure of 0.08 MPa to obtain the reduced mixed micro powder.

[0073] (3) Take 3.5g of the reduced mixed micro powder obtained in step (2), spread it evenly into a niobium cup with a diameter of 35mm, and cover it with a 4mm thick hard alloy (grade YG16). Match a molybdenum cup suitable for the niobium cup as a lid to obtain a pre-assembled composite sheet.

[0074] (4) The pre-assembled composite sheet obtained in step (3) is compacted with a hydraulic press at a pressure of 5 tons for 10 seconds to obtain a compacted composite sheet.

[0075] (5) The compacted composite sheet obtained in step (4) is subjected to high-temperature purification and shaping, and then subjected to 10°C. -4 The purified and shaped composite sheet was obtained by holding it at 700℃ for 1.5 hours in a vacuum furnace with a vacuum degree of Pa.

[0076] (6) The purified and shaped composite sheet obtained in step (5) is matched with a suitable traditional carbon salt tube and pyrophyllite block, and synthesized in a six-sided top press under high temperature and high pressure. The high temperature and high pressure synthesis pressure is 5.5 GPa, the temperature is 1600℃, and the heat and pressure holding time is 15 min to obtain a 250nm diamond composite sheet. The appearance of the obtained composite sheet is free of cracks.

[0077] (7) The 250nm diamond composite sheet obtained in step (6) was tested with an industry-standard silicon carbide grinding wheel, and the wear ratio was found to be 1.32×10. 4 .

[0078] Comparative Example 4 (1) 96g of diamond micropowder with a particle size of 500nm, 3g of cobalt powder with a particle size of 200nm, and 1g of niobium powder with a particle size of 200nm were ball-milled in a stainless steel container with 75mL of ethanol and 1000g of stainless steel balls (8mm in diameter) for 3 hours at a speed of 160r / min. The mixture was dried at 80℃ and sieved through a 120-mesh sieve to obtain diamond micropowder mixed with catalyst (cobalt powder) and toughening agent (niobium powder), i.e., mixed micropowder.

[0079] (2) Take 3.5g of the mixed micro powder obtained in step (1), spread it evenly into a niobium cup with a diameter of 35mm, and cover it with a 4mm thick hard alloy (grade YG16). Match a suitable molybdenum cup as a lid to obtain a pre-assembled composite sheet.

[0080] (3) The pre-assembled composite sheet obtained in step (2) is compacted with a hydraulic press at a pressure of 5 tons for 10 seconds to obtain a compacted composite sheet.

[0081] (4) The compacted composite sheet obtained in step (3) is subjected to high-temperature purification and shaping, and then subjected to 10°C. -4 The purified and shaped composite sheet was obtained by holding it at 700℃ for 1.5 hours in a vacuum furnace with a vacuum degree of Pa.

[0082] (5) The purified and shaped composite sheet obtained in step (4) is matched with a suitable traditional carbon salt tube and pyrophyllite block, and then subjected to high temperature and high pressure synthesis in a six-sided top press. The high temperature and high pressure synthesis pressure is 5.5 GPa, the temperature is 1600℃, and the heat and pressure holding time is 15 min to obtain a 500nm diamond composite sheet.

[0083] (6) The 500nm diamond composite sample obtained in step (5) was a fragmented material. Wear ratio test could not be performed.

[0084] As can be seen from the above embodiments, the preparation method provided by the present invention uses nano-sized niobium powder as a toughening raw material. By compounding diamond micro powder, nano-sized cobalt powder, and nano-sized niobium powder, and controlling the mass ratio of the three raw materials, the toughness of the material during the molding process is improved, effectively avoiding cracking during molding. Simultaneously, by controlling the temperature and pressure parameters of the high-temperature purification and shaping process and the high-temperature and high-pressure synthesis process, the present invention can further enhance the interaction between the three raw materials. This optimizes the hardness and toughness of the material, improves the yield of diamond composite sheets, avoids cracking of the finished diamond composite sheets, and results in a complete diamond composite sheet with no cracks. Moreover, the preparation method provided by the present invention is simple to operate, highly practical, and has wide application value.

[0085] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a diamond composite sheet, characterized in that, Includes the following steps: The powder raw materials are mixed to obtain mixed micro powder, wherein the powder raw materials include the following components in terms of mass content: 92-98.5% diamond micro powder, 1-5% nano-cobalt powder, and 0.5-3% nano-niobium powder; The mixed micro powder is subjected to reduction treatment in a reducing atmosphere to obtain reduced mixed micro powder; The reduced mixed micro powder is spread out and covered with hard alloy to obtain a pre-assembled composite sheet; The pre-assembled composite sheet is pressed to obtain a compacted composite sheet; The compacted composite sheet is subjected to high-temperature purification and shaping to obtain a purified and shaped composite sheet. The high-temperature purification and shaping is carried out under vacuum conditions, and the temperature of the high-temperature purification and shaping is ≥600℃. The purified and shaped composite sheet is subjected to high temperature and high pressure synthesis to obtain the diamond composite sheet. The high temperature and high pressure synthesis temperature is ≥1550℃ and the pressure is ≥5GPa.

2. The preparation method according to claim 1, characterized in that, The diamond micro powder has a particle size of 100~1000nm; the nano-cobalt powder has a particle size ≤300nm; and the nano-niobium powder has a particle size ≤500nm.

3. The preparation method according to claim 1 or 2, characterized in that, The mixing is ball milling, and the conditions for ball milling include: a ball-to-material ratio of 5 to 15:1; a ball milling time of 3 to 8 hours; and an organic solvent as the ball milling medium. The ball milling yields wet abrasive. The mixture also includes drying and sieving the wet abrasive in sequence, with the drying temperature being 70 to 90°C and the sieve used for sieving having a mesh size of 100 to 120 mesh.

4. The preparation method according to claim 1, characterized in that, The reducing atmosphere is hydrogen gas, and the hydrogen gas pressure is 0.02~0.1MPa; the reduction treatment temperature is 350~950℃, and the time is 0.5~3h.

5. The preparation method according to claim 1, characterized in that, The preparation method of the pre-assembled composite sheet includes: spreading the reduced mixed micro powder evenly in a niobium cup; then covering it with a cemented carbide, and finally using a molybdenum cup as a lid; the diameter of the niobium cup is ≥30mm, and the mass of the reduced mixed micro powder spread evenly in the niobium cup is 3~5mg / mm. 2 .

6. The preparation method according to claim 1 or 5, characterized in that, The thickness of the cemented carbide is 2~4mm; the grade of the cemented carbide is YG16.

7. The preparation method according to claim 1, characterized in that, The pressing pressure is 3~5t.

8. The preparation method according to claim 1, characterized in that, The vacuum degree of the high-temperature purification and shaping is 10. -4 ~10 -2 Pa; temperature is 600~1100℃, and the heat preservation and pressure holding time is 1~3h.

9. The preparation method according to claim 1, characterized in that, The high-temperature and high-pressure synthesis process involves a pressure of 5~6.5 GPa, a temperature of 1550~1750℃, and a holding time of 12~25 min.

10. The diamond composite sheet prepared by the preparation method according to any one of claims 1 to 9.

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