Preparation method of polycrystalline diamond composite sheet

Abstract

The present invention relates to a method for preparing a polycrystalline diamond composite sheet. The method comprises the following steps: soaking diamond particles of primary and secondary sizes in strong acid and alkali, and repeatedly washing with pure water; sandblasting a cemented carbide substrate; mixing the primary and secondary diamond particles in a mixer; placing the mixed diamond particles and cemented carbide substrate in a high-temperature resistant metal cup; placing a composite block in the metal cup, and placing the metal cup in a six-sided top press; and performing three-stage high-pressure and two-stage high-temperature sintering. The first stage is high-pressure, cold pressurization to 6.5-8.2 GPa, maintained for 30-60 seconds; the second stage is high-pressure and simultaneous heating, sintering at a pressure of 6-8 GPa, a temperature of 1490-1580°C, maintained for 300-600 seconds; and the third stage is high-pressure and simultaneous heating, pressure of 5.0-6.0 GPa, a temperature of 1150-1250°C, maintained for 150-200 seconds. The pressure and temperature are then reduced to normal pressure and room temperature to obtain a polycrystalline diamond composite sheet blank. After sintering, fine particles are evenly distributed around coarse particles.

Description

Technical Field

[0001] The invention relates to a method for preparing a polycrystalline diamond composite sheet, and belongs to the technical field of superhard material preparation. Background Art

[0002] Currently, polycrystalline diamond compacts (PDCs) consist of a diamond working layer and a cemented carbide substrate. The diamond working layer is formed by sintering countless diamond particles under high temperature and pressure using a metal catalyst, Co. Polycrystalline diamond compacts are used in oil and gas drilling. The dimensions of these compacts are standardized, with diameters and heights (in mm) ranging from Φ13.44*13.2, Φ15.88*13.2, and Φ19.05*13.2, respectively. The diamond working layer thickness ranges from 1.2 to 2.5 mm. Polycrystalline diamond compacts combine the high hardness and wear resistance of diamond with the high impact resistance of cemented carbide. Furthermore, cemented carbide offers excellent weldability, enabling the compacts to be securely welded to the diamond drill bit body. As oil and gas drilling continues to advance deeper into the earth, from the traditional depth of 2,000 to 3,000 meters to 4,000 to 5,000 meters, the geological environment becomes more complex at greater depths, and the hardness, abrasiveness, and impact resistance of the formations become increasingly stringent. These factors place higher demands on the performance of polycrystalline diamond composite sheets. To achieve high performance, the diamond content in the working layer must be increased. Due to the particle shape, the gaps between the diamond particles should be filled with finer diamond particles as much as possible to achieve the highest possible diamond content.

[0003] The addition of fine-grained diamonds brings two unavoidable negative effects to the manufacture of polycrystalline diamond composites. First, during the batching and mixing stage, fine-grained diamonds are difficult to mix evenly with coarse-grained diamonds, and the fine particles easily aggregate into clumps, resulting in unstable performance of the diamond working layer after sintering. Second, the specific surface area of ​​fine-grained diamond particles is much larger than that of coarse particles. The surface area of ​​the particles will absorb impurities such as oxygen and moisture in the air. These impurities will seriously hinder the effectiveness of the catalyst Co, resulting in a poor high-temperature and high-pressure sintering process and a reduced yield rate of the sintering process.

[0004] Therefore, it is necessary to improve the current preparation method of polycrystalline diamond composite sheets, especially to propose new research ideas to overcome the negative effects of fine-grained diamonds. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for preparing a polycrystalline diamond composite sheet. The prepared polycrystalline diamond composite sheet can better meet the needs of oil and gas drilling and is more suitable for drilling tasks in deeper strata.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] The preparation method of polycrystalline diamond composite sheet is characterized by: soaking main-size diamond particles and auxiliary-size diamond particles in strong acid and strong alkali, and then repeatedly washing with pure water to remove impurities; sandblasting the cemented carbide matrix; mixing the treated main-size diamond particles and auxiliary-size diamond particles in a mixer; sequentially placing the mixed diamond particles and cemented carbide matrix into a high-temperature resistant metal cup, and then closing the cup; placing a composite block in the metal cup, and placing it in a six-sided top press; and performing three The process is characterized by two stages of high-pressure and high-temperature sintering. In the first stage, the pressure is increased to 6.5-8.2GPa in a cold state and maintained for 30-60 seconds. In the second stage, high pressure and simultaneous heating are performed, with a sintering pressure of 6-8GPa and a sintering temperature of 1490-1580°C and maintained for 300-600 seconds. In the third stage, high pressure and simultaneous heating are performed, with a pressure of 5.0-6.0GPa and a temperature of 1150-1250°C and maintained for 150-200 seconds. The pressure is then reduced and the temperature is lowered to normal pressure and room temperature to obtain a polycrystalline diamond composite sheet blank.

[0008] Furthermore, in the above-mentioned method for preparing the polycrystalline diamond composite sheet, the surface impurity content of the main-sized diamond particles and the auxiliary-sized diamond particles is less than 70 ppm after being soaked in strong acid and strong base and repeatedly washed with pure water.

[0009] Furthermore, in the above-mentioned method for preparing the polycrystalline diamond composite sheet, the diamond particle mixing ratio is 65-95wt% of the main particle size diamond particles and 5-35wt% of the auxiliary particle size diamond particles.

[0010] Furthermore, in the above-mentioned method for preparing the polycrystalline diamond composite sheet, the main diamond particle size is 8 to 40 μm, and the particle shape is blocky or nearly spherical.

[0011] Furthermore, in the above-mentioned method for preparing a polycrystalline diamond composite sheet, the auxiliary diamond particles have a particle size of 8 to 40 μm and are in the shape of elongated strips or sheets.

[0012] Furthermore, in the above-mentioned method for preparing the polycrystalline diamond composite sheet, the high-temperature resistant metal cup is made of Zr, Mo, Nb or Ta.

[0013] Furthermore, in the above-mentioned method for preparing the polycrystalline diamond composite sheet, the cemented carbide substrate is made of a W-Co alloy, and the Co content is 10-18 wt%.

[0014] Furthermore, in the above-mentioned method for preparing the polycrystalline diamond composite sheet, the primary-sized diamond particles and the secondary-sized diamond particles are put into a mixer and mixed for 4 to 8 hours.

[0015] Compared with the prior art, the present invention has significant advantages and beneficial effects, which are specifically reflected in the following aspects:

[0016] ① Using long strip or flake diamond particles (auxiliary diamond particles) with a particle size basically consistent with that of the main diamond particles as the precursor of the fine diamond particles after sintering. During the mixing stage, since the particle size of the long strip or flake diamond particles (auxiliary diamond particles) is comparable to that of the main diamond particles and the physical size of the two are similar, the mixing device can more easily mix the main diamond particles and the auxiliary diamond particles evenly;

[0017] ② The crushing resistance of long strip or flake diamond particles is lower than that of block or nearly spherical diamond particles. Under the cold high pressure in the first stage, the long strip or flake diamond particles are crushed into fine-grained diamond particles, which are evenly distributed around the block or nearly spherical coarse particles;

[0018] ③ During the sintering process, the pressure used in the first stage of the sintering process is slightly higher than the pressure used in the actual sintering in the second stage. The effect is to crush the long (or flaky) auxiliary diamond particles and fix them around the main diamond particles, so that the main and auxiliary diamond particles in the diamond working layer of the final product are evenly distributed; the positional relationship between the coarse and fine diamond particles is fixed in situ by the huge external pressure, and the uniform distribution of coarse and fine particles is solidified. After sintering, the fine particles are evenly distributed around the coarse particles, and the metal catalyst Co is evenly dispersed in the gaps between the diamond particles, eliminating the agglomeration of fine particles;

[0019] ④ Since the precursor of fine-grained diamond particles is mixed in the form of large particles, under the premise of a certain weight of fine-grained diamond, the specific surface area of ​​the precursor is smaller than the specific surface area of ​​fine-grained diamond particles of the same weight or volume, and the impurities such as oxygen and moisture adhered to it are far less than the impurities adhered to fine-grained diamond, which purifies the sintering environment, is conducive to the smooth progress of high-temperature and high-pressure sintering, improves the sintering quality, and increases the yield rate.

[0020] ⑤ The high pressure and high temperature in the second section are applied simultaneously to complete the sintering of the polycrystalline diamond composite sheet; the high pressure and high temperature in the third section are applied simultaneously to effectively reduce and release the internal stress of the polycrystalline diamond composite sheet, ensuring the final use effect of the composite sheet.

[0021] ⑥ The resulting polycrystalline diamond composite sheet has a highly uniform diamond particle structure, eliminating fine particle agglomeration. This provides high wear resistance and impact strength, resulting in improved performance and a longer service life, making it more suitable for current drilling missions at deeper strata. Furthermore, the yield rate of the composite sheet during the sintering process has increased by 5-10%.

[0022] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or will be understood by practicing the specific embodiments of the present invention. The purposes and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 : Schematic diagram of particle distribution before sintering;

[0025] Figure 2 : Schematic diagram of particle distribution after sintering. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0027] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of the present invention, directional terms and order terms are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0028] The preparation method of the polycrystalline diamond composite sheet of the present invention comprises the following steps: soaking main-size diamond particles and auxiliary-size diamond particles in strong acid and strong alkali, and then repeatedly washing with pure water to remove impurities, wherein the surface impurity content of the main-size diamond particles and the auxiliary-size diamond particles is less than 70 ppm; sandblasting the cemented carbide substrate; mixing the treated main-size diamond particles and auxiliary-size diamond particles in a mixer, wherein the main-size diamond particles account for 65-95 wt% and the auxiliary-size diamond particles account for 5-35 wt%; the main-size diamond particles have a particle size of 8-40 μm and are in a block or nearly spherical shape; the auxiliary-size diamond particles have a particle size of 8-40 μm and are in a strip or sheet shape; mixing in the mixer for 4-8 hours; and sequentially mixing the mixed diamond particles and cemented carbide. The substrate is placed in a high-temperature resistant metal cup. The carbide substrate is made of a W-Co alloy with a Co content of 10-18 wt%. The high-temperature resistant metal cup is made of Zr, Mo, Nb, or Ta. The cup is then covered. The metal cup is placed in the composite block and placed in a six-sided top press. Three high-pressure and two high-temperature sintering steps are performed. The first high-pressure step involves applying pressure to 6.5-8.2 GPa from a cold state for 30-60 seconds without heating. The second high-pressure and simultaneous heating step involves sintering at a pressure of 6-8 GPa and a temperature of 1490-1580°C for 300-600 seconds. The third high-pressure and simultaneous heating step involves applying pressure of 5.0-6.0 GPa and a temperature of 1150-1250°C for 150-200 seconds. The pressure is then reduced and the temperature is lowered to room temperature at ambient pressure to obtain a polycrystalline diamond composite blank. The blank is then processed through mechanical grinding, electrical discharge, and laser processing to meet the technical requirements for commercialization.

[0029] like Figure 2 As shown, the sintered composite sheet consists of a polycrystalline diamond working layer 1 and a cemented carbide substrate 2. The polycrystalline diamond working layer 1 contains primary (coarse) diamond particles 3, secondary (fine) diamond particles 4, and catalyst metal Co 5. The diamond working layer has super wear resistance and certain impact resistance, and the cemented carbide substrate has excellent impact resistance and weldability, making it easy to connect the polycrystalline diamond composite sheet to the drilling body.

[0030] Before high temperature and high pressure sintering, when mixing the ingredients, instead of adding fine diamond particles directly, diamond particles of auxiliary size that are basically the same as the main diamond particles are added. However, the shapes of the main diamond particles and the auxiliary diamond particles are obviously different. The coarse diamond particles serve as the precursor of the fine diamond particles. Figure 1 After mixing and before sintering, it contains main particle size (coarse particles) diamond particles 3 and auxiliary particle size (coarse particles) diamond particles 4. The main particle size diamond particles are block-shaped or nearly spherical, and the auxiliary particle size diamond particles are long strips or sheets, but the particle sizes are basically the same.

[0031] The auxiliary diamond particles are not added to the main diamond particles in their original fine particle state, but are added as precursors of fine diamond particles with a particle size roughly equivalent to that of the main diamond particles but with a significantly different particle shape.

[0032] The pressure used in the first stage of the sintering process is slightly higher than the pressure used in the actual sintering in the second stage. The effect is to crush the long strip (or sheet) of auxiliary diamond particles and fix them around the main diamond particles, so that the main and auxiliary diamond particles in the diamond working layer of the final product are evenly distributed.

[0033] like Figure 2 The microstructure of the prepared polycrystalline diamond composite sheet is shown in FIG. 1 , in which coarse and fine diamonds are evenly distributed, fine diamond particles 4 are evenly distributed around coarse diamond particles 3 , and metal catalyst Co 5 is evenly dispersed in the gaps between diamond particles.

[0034] The specific surface area of ​​diamond particles is greatly affected by their particle size. Usually, the specific surface area of ​​fine particles is much larger than that of coarse particles, and the impurities such as oxygen adsorbed by them are much more than those adsorbed by coarse particles.

[0035] As shown in Table 1, the specific surface area of ​​diamond particles of different particle sizes shows that the finer the particle size, the higher the impurity content. For example, the surface area of ​​the particle size of 1.81um (D50) is 35 times that of 51.9um (D50), and the impurity content is 1.5 times that of 51.9um (D50).

[0036] Table 1

[0037] name 40 / 60 30 / 40 20 / 28 12 / 22 8 / 16 7 / 9 4 / 6 1 / 3 Particle size μm (D50) 51.9 33.55 24.26 16.12 11.2 7.64 4.29 1.81 <![CDATA[Specific surface area cm 2 / cm -3 > 1232.36 1887.95 2616.24 3943.88 5715.88 8571.23 16067.8 43818.5 Impurity content ppm 34.949 37.34 39.445 41.118 42.321 45.125 47.31 47.966

[0038] The long strip (or flake) auxiliary diamond particles are crushed into fine particles, which does not bring extra oxygen and other impurities to the diamond working layer. Relatively speaking, it purifies the sintering environment, improves the high temperature and high pressure sintering conditions, makes the sintering smooth, and increases the sintering yield by 5-10%.

[0039] Example 1

[0040] Coarse block diamond particles with a particle size of 22 μm and long strip diamond particles with a particle size of 22 μm are soaked in strong acid and strong alkali, and then washed multiple times with high-purity water to remove surface impurities from the diamonds, so that the surface impurity content is less than 70 ppm; 80% of the block diamonds and 20% of the long strip diamonds are mixed in a mixer by weight; the cemented carbide substrate is sandblasted; and the mixed diamond particles and cemented carbide substrate are sequentially placed in a high-temperature resistant metal Zr bottom cup, which is then covered.

[0041] The high-temperature resistant Zr cup is placed into the composite block and placed in a six-sided top press for high-temperature and high-pressure sintering. The first high-pressure stage is 7.0GPa, maintained for 30 seconds, crushing the elongated diamond particles and fixing them around the block diamond particles. The second high-pressure and high-temperature stage is 6.8GPa, 1500°C, maintained for 420 seconds, completing the sintering of the polycrystalline diamond composite sheet. The third high-pressure and high-temperature stage is 5.5GPa, 1180°C, maintained for 160 seconds, releasing the huge stress within the polycrystalline diamond composite sheet. Finally, the pressure is reduced and the temperature is lowered to room temperature at normal pressure, and the sintered polycrystalline diamond composite sheet blank is removed. Mechanical grinding, electric spark discharge, laser and other processing techniques are used to complete commercial processing.

[0042] Example 2

[0043] Coarse block diamond particles with a particle size of 35 μm and flake diamond particles with a particle size of 35 μm are soaked in strong acid and strong alkali, and then washed multiple times with high-purity water to remove surface impurities from the diamonds, so that the surface impurity content is less than 70 ppm; 73% of the block diamonds and 27% of the flake diamonds are mixed in a mixer by weight; a cemented carbide substrate is sandblasted; and the mixed diamond particles and cemented carbide substrate are sequentially placed in a base cup made of high-temperature resistant metal Nb, which is then covered.

[0044] The high-temperature-resistant Nb cup is placed into the composite block and placed in a six-sided top press for high-temperature and high-pressure sintering. The first high-pressure stage, at 6.8 GPa, is maintained for 30 seconds, crushing the flake diamond particles and securing them around the block diamond particles. The second high-pressure and high-temperature stage, at 6.6 GPa and 1490°C, is maintained for 380 seconds, completing the sintering of the polycrystalline diamond compact. The third high-pressure and high-temperature stage, at 5.5 GPa and 1200°C, is maintained for 160 seconds, releasing the significant stress within the polycrystalline diamond compact. Finally, the pressure is reduced and the temperature is lowered to room temperature, and the sintered polycrystalline diamond compact blank is removed. Processing techniques such as mechanical grinding, electrical discharge (EDM), and laser processing are used to complete commercial processing.

[0045] Example 3

[0046] Coarse block diamond particles with a particle size of 12 μm and long strip diamond particles with a particle size of 12 μm are soaked in strong acid and strong alkali, then washed multiple times with high-purity water to remove surface impurities from the diamonds, reducing the surface impurity content to less than 70 ppm. 90% of the block diamonds and 10% of the long strip diamonds are mixed in a mixer by weight. The cemented carbide substrate is sandblasted. The mixed diamond particles and cemented carbide substrate are sequentially placed in a high-temperature resistant metal Mo bottom cup, which is then covered.

[0047] The high-temperature resistant metal Mo cup is placed into the synthetic block and placed in a six-sided top press for high-temperature and high-pressure sintering. The first high-pressure stage is 7.5GPa, maintained for 30 seconds, crushing the elongated diamond particles and fixing them around the block diamond particles. The second high-pressure and high-temperature stage is 7.2GPa, 1520℃, maintained for 500 seconds, completing the sintering of the polycrystalline diamond composite sheet. The third high-pressure and high-temperature stage is 5.5GPa, 1200℃, maintained for 170 seconds, releasing the huge stress in the polycrystalline diamond composite sheet. Finally, the pressure is reduced and the temperature is lowered to room temperature at normal pressure, and the sintered polycrystalline diamond composite sheet blank is removed. The commercial processing is completed using mechanical grinding, electric spark, laser and other processing technologies.

[0048] Example 4

[0049] Coarse block diamond particles with a particle size of 8 μm and flake diamond particles with a particle size of 8 μm are soaked in strong acid and strong alkali, then washed multiple times with high-purity water to remove surface impurities from the diamonds, reducing the surface impurity content to less than 70 ppm. 95% of the block diamonds and 5% of the flake diamonds are mixed in a mixer by weight. The cemented carbide substrate is sandblasted. The mixed diamond particles and cemented carbide substrate are sequentially placed in a high-temperature resistant metal Ta bottom cup, which is then covered.

[0050] The high-temperature resistant metal Ta cup is placed into the synthesis block and placed in a six-sided top press for high-temperature and high-pressure sintering. The first high-pressure stage is 8.0GPa, maintained for 30 seconds, crushing the flake diamond particles and fixing them around the block diamond particles. The second high-pressure and high-temperature stage is 7.8GPa, 1550°C, maintained for 560 seconds, completing the sintering of the polycrystalline diamond composite sheet. The third high-pressure and high-temperature stage is 5.5GPa, 1220°C, maintained for 180 seconds, releasing the huge stress within the polycrystalline diamond composite sheet. Finally, the pressure is reduced and the temperature is lowered to room temperature at normal pressure, and the sintered polycrystalline diamond composite sheet blank is removed. Mechanical grinding, electric spark discharge, laser and other processing techniques are used to complete commercial processing.

[0051] Comparative Example

[0052] Coarse block diamond particles with a particle size of 12 μm and block fine diamond particles with a particle size of 4 μm are soaked in strong acid and strong alkali, and then washed multiple times with high-purity water to remove surface impurities from the diamonds, so that the surface impurity content is less than 70 ppm; 90% of the coarse diamond particles with a particle size of 12 μm and 10% of the fine diamond particles with a particle size of 4 μm are mixed in a mixer; the cemented carbide substrate is sandblasted; the mixed diamond particles and cemented carbide substrate are sequentially placed in a high-temperature resistant metal Mo bottom cup, and the cover cup is buckled.

[0053] The high-temperature resistant metal Mo cup is placed into the synthesis block and placed in a six-sided top press for high-temperature and high-pressure sintering. The sintering pressure is 7.2GPa and the sintering temperature is 1520℃. The sintering is maintained for 500 seconds to complete the sintering of the polycrystalline diamond composite sheet. Finally, the pressure is reduced and the temperature is lowered to normal pressure and room temperature, and the sintered polycrystalline diamond composite sheet blank is taken out. The commercial processing is completed using mechanical grinding, electric spark, laser and other processing technologies.

[0054] Performance test and sintering yield:

[0055] The test specimen size of the polycrystalline diamond composite sheet is unified as follows: diameter Φ15.88mm, height 13.2mm, diamond working layer thickness 3.0mm, diamond end chamfer 0.4*45°, carbide end chamfer 0.7*45°.

[0056] Wear resistance testing: A polycrystalline diamond compact was mounted on a toolholder and turned into cylindrical granite of uniform structure and a certain diameter. The cutting speed, crossfeed rate, and cutting depth were kept constant during the test. The cutting edge was photographed and measured after cutting. The polycrystalline diamond compact was weighed before and after cutting, and the wear ratio (Q) was calculated for each cut. Three samples were taken each time, and the volumetric wear ratio (Q) was calculated for each cut, taking the average value.

[0057] Impact resistance test: A polycrystalline diamond compact sample is mounted on an impact rack. A heavy hammer of a certain mass is dropped freely from a height h. The potential energy of the falling hammer creates an impact on the polycrystalline diamond compact. The energy of a single impact is 40J. The cumulative impact energy experienced by the compact is recorded until it breaks. Three to ten samples are collected at a time, and the cumulative impact energy E experienced by each piece is recorded and averaged.

[0058] Sintering yield rate: the number of qualified products in the final inspection (minus the number of defective products caused by commercial processing) divided by the total number of sintering processes.

[0059] The performance of the polycrystalline diamond compacts prepared in Examples 1 to 4 and the comparative example is compared, as shown in Table 2.

[0060] Table 2

[0061] Example 1 Example 2 Example 3 Example 4 Comparative Example Wear-resistant Q / (X104) 642 514 738 770 642 Impact resistance E / J 441 476 431 363 353 Sintering yield% 83 86 82 75 74

[0062] Polycrystalline diamond composite sheets are subject to the challenges of various harsh and complex geological conditions in actual oil and gas drilling applications. The wear resistance and impact resistance of diamond composite sheets largely determine the drilling efficiency. Laboratory test results provide important reference for actual use.

[0063] Experimental tests show that the polycrystalline diamond composite sheet prepared by the present invention has wear resistance and impact resistance improved by more than 15% and 22% respectively compared with the polycrystalline diamond composite sheet prepared by the prior art; the yield rate of the sintering process is improved by 8 percentage points compared with the prior art.

[0064] Long strip or flake diamond particles (auxiliary diamond particles) with a particle size basically consistent with that of the main diamond particles are used as precursors of fine diamond particles after sintering. During the mixing stage, since their particle size is comparable to that of the main diamond particles and the physical sizes of the two are similar, the mixing device can more easily mix the main diamond particles and the auxiliary diamond particles evenly.

[0065] The crushing resistance of long strip or flaky diamond particles is lower than that of massive or nearly spherical diamond particles. Under the cold high pressure in the first stage, the long strip or flaky diamond particles are crushed into fine-grained diamond particles, which are evenly distributed around the massive or nearly spherical coarse particles.

[0066] During the sintering process, the positional relationship between coarse and fine diamond particles is fixed in situ by huge external pressure, and the uniform distribution of coarse and fine particles is solidified. After sintering, the fine particles are evenly distributed around the coarse particles, eliminating the agglomeration of fine particles.

[0067] Since the precursor of fine-grained diamond particles is mixed in the form of large particles, under the premise of a certain weight of fine-grained diamond, the specific surface area of ​​the precursor is smaller than the specific surface area of ​​fine-grained diamond particles of the same weight or volume. The impurities such as oxygen and moisture adhered to it are far less than the impurities adhered to fine-grained diamond, which purifies the sintering environment, is conducive to the smooth progress of high-temperature and high-pressure sintering, improves the sintering quality, and increases the yield rate.

[0068] The high pressure in the second stage is combined with high temperature to complete the sintering of the polycrystalline diamond composite sheet.

[0069] The high pressure in the third section is combined with high temperature to effectively reduce and release the internal stress of the polycrystalline diamond composite sheet, ensuring the final use effect of the composite sheet.

[0070] In summary, in the preparation method of the present invention, fine-grained diamond particles are not added in the mixing process. In the mixing process, coarse diamond particles of the main particle size and diamond particles with a particle size close to the main particle size but with a shape significantly different from the main particle size are added. The latter serve as precursors of the fine-grained diamond particles in the working layer of the final diamond composite sheet. The mixture of the diamond working layer and the cemented carbide substrate are placed in a high-temperature resistant metal cup. There is no fine-grained diamond in the ingredients. After sintering in three stages of high pressure and two stages of high temperature, a polycrystalline diamond composite sheet blank containing fine-grained diamond is obtained. There is no fine particle aggregation, and the coarse and fine diamond particles are evenly distributed. The sintering process is smooth, the yield rate is improved, and the performance of the composite sheet is greatly improved, extending the service life of the polycrystalline diamond composite sheet.

[0071] The resulting polycrystalline diamond compacts have a highly uniform diamond particle structure, eliminating fine particle agglomeration. These compacts boast high wear resistance and impact strength, resulting in improved performance and a longer service life, making them more suitable for drilling deeper into the earth. Furthermore, the yield rate of the compacts' sintering process has increased by 5-10%.

[0072] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Various modifications and variations are readily apparent to those skilled in the art. Any modifications, equivalent substitutions, improvements, and the like made within the spirit and principles of the present invention are intended to be included within the scope of protection of the present invention. It should be noted that similar reference numerals and letters denote similar items in the following figures. Therefore, once an item is defined in one figure, it need not be further defined or explained in subsequent figures.

[0073] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

[0074] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

Claims

1. A method for preparing a polycrystalline diamond compact, characterized in that: The main diamond particles and the auxiliary diamond particles are soaked in strong acid and strong alkali, and then repeatedly washed with pure water to remove impurities. The main diamond particles have a particle size of 8 to 40 μm and a block or nearly spherical particle shape. The auxiliary diamond particles have a particle size of 8 to 40 μm and a long strip or sheet shape. The main diamond particles have a particle size that is substantially the same as the auxiliary diamond particles. The cemented carbide substrate is sandblasted. The treated main diamond particles and auxiliary diamond particles are mixed in a mixer. The mixed diamond particles and cemented carbide matrix are sequentially placed into a high-temperature resistant metal cup, and the cup is covered; the synthetic block is placed in the metal cup and placed in a six-sided top press; three-stage high-pressure and two-stage high-temperature sintering are carried out, in which the first stage is high-pressure, pressurized to 6.5-8.2GPa in a cold state and maintained for 30-60 seconds; the second stage is high-pressure and simultaneous heating, with a sintering pressure of 6-8GPa and a sintering temperature of 1490-1580°C, maintained for 300-600 seconds; the third stage is high-pressure and simultaneous heating, with a pressure of 5.0-6.0GPa and a temperature of 1150-1250°C, maintained for 150-200 seconds; the pressure is then reduced and the temperature is lowered to normal pressure and room temperature to obtain a polycrystalline diamond composite sheet blank.

2. The method for preparing a polycrystalline diamond compact according to claim 1, wherein: After being soaked in strong acid and strong alkali and repeatedly washed with pure water, the surface impurity content of the main-sized diamond particles and the auxiliary-sized diamond particles is less than 70 ppm.

3. The method for preparing a polycrystalline diamond compact according to claim 1, wherein: The mixing ratio of diamond particles is 65-95wt% of main-size diamond particles and 5-35wt% of auxiliary-size diamond particles.

4. The method for preparing a polycrystalline diamond compact according to claim 1, wherein: The high temperature resistant metal cup is made of Zr, Mo, Nb or Ta.

5. The method for preparing a polycrystalline diamond compact according to claim 1, wherein: The cemented carbide substrate is made of W-Co alloy, and the Co content is 10-18wt%.

6. The method for preparing a polycrystalline diamond compact according to claim 1 or 3, wherein: The main-size diamond particles and the auxiliary-size diamond particles are put into a mixer and mixed for 4 to 8 hours.

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