An ultra-high voltage discharge plasma sintering system

Abstract

This invention relates to the field of high-performance ceramic material preparation technology, specifically an ultra-high pressure discharge plasma sintering system, comprising a six-sided press body, a high-power DC pulse power supply, and a high-pressure synthesis assembly block. The six-sided press body has a frame providing ultra-high pressure and a hydraulic drive system. Its six carbide hammers together form a cubic space for placing the high-pressure synthesis assembly block containing the sample. The two poles of the high-power DC pulse power supply are respectively connected to two upper and lower large pads through two conductive copper strips. The ends of the two large pads are fitted with steel rings, and the ends of the steel rings are embedded with carbide hammers. This ultra-high pressure discharge plasma sintering system achieves rapid and uniform bulk heating of the sample. The synergistic effect of the two systems enables the densification sintering preparation of ultra-hard ceramics at temperatures far lower than those of traditional high-temperature and high-pressure methods in a short time.

Description

Technical Field

[0001] The invention relates to the field of high-performance ceramic material preparation technology, specifically an ultra-high pressure discharge plasma sintering system. Background Technology

[0002] Superhard ceramic materials, such as cubic boron nitride, polycrystalline diamond composites, and certain superhard borides and carbides, possess irreplaceable application value in cutting tools, drilling, and precision machining due to their extremely high hardness, wear resistance, thermal stability, and chemical inertness. However, these materials typically exhibit extremely high covalent bond energies and low grain boundary diffusion coefficients, making their sintering densification extremely difficult.

[0003] Currently, the main technical means for preparing high-density, ultrahard ceramic materials include: 1. High-Temperature and High-Pressure Method: Represented by a six-sided press, this method can provide ultra-high pressures at the GPa level and ultra-high temperatures exceeding 2000 degrees Celsius, making it the mainstream method for synthesizing diamond, cubic boron nitride, and their polycrystalline composites. However, traditional six-sided presses mainly use external heaters (such as graphite tubes) for indirect heating of the sample, which suffers from low heating efficiency, uneven temperature field, and long holding times. Prolonged high-temperature treatment can easily lead to abnormal grain growth, which is not conducive to obtaining an ultrafine grain structure, thus affecting the hardness and toughness of the material.

[0004] 2. Discharge plasma sintering: This technology directly introduces high-frequency pulsed DC current into powder samples, utilizing discharge plasma activation and Joule heating effects to achieve rapid densification of materials at relatively low temperatures and in a very short time (minutes to tens of minutes), effectively suppressing grain growth. However, the pressure of conventional discharge plasma sintering equipment is usually limited to the MPa range. For ultra-hard ceramic materials, such pressure is insufficient to achieve complete densification at temperatures far below their melting points, making it difficult to obtain sintered bodies with densities close to the theoretical density.

[0005] Therefore, those skilled in the art have long desired to develop a novel sintering technology that combines ultra-high pressure capability with the advantages of rapid sintering by discharge plasma, and to develop an ultra-high pressure discharge plasma sintering method to meet the needs of the synthesis and preparation of high-performance ultra-hard ceramic materials. Summary of the Invention

[0006] In view of the problems existing in the prior art, the invention discloses an ultra-high pressure discharge plasma sintering system, the technical solution of which includes a six-sided top press body, a high-power DC pulse power supply and a high-pressure synthesis assembly block; The main body of the six-sided top press has a frame that provides ultra-high pressure and a hydraulic drive system. Its six carbide top hammers together form a cubic space for placing the high-pressure synthesis assembly block that encapsulates the sample. The two poles of the high-power DC pulse power supply are respectively connected to the upper and lower large pads through two conductive copper strips. The ends of the two large pads are fitted with steel rings, and the ends of the steel rings are embedded with hard alloy hammers. Small pads are filled between the hard alloy hammers and the large pads. The small pads are in contact with the large pads and the hard alloy hammers respectively. The high-frequency pulse current of the high-power DC pulse power supply is transmitted to the hard alloy hammers through the conductive copper strips, large pads and small pads. The high-pressure synthesis assembly includes a pressure-transmitting medium. An insulation tube is embedded in the inner wall of the pressure-transmitting medium's cavity. A graphite tube is sleeved inside the insulation tube. Hexagonal boron nitride tubes are connected above and below the graphite tube. The inner and outer diameters of the hexagonal boron nitride tubes are the same as those of the graphite tube. A powder sample is placed in the middle of the graphite tube, and the powder sample is in contact with the inner wall of the graphite tube. Conductive graphite plugs are provided at both ends of the graphite tube. The total height of the sample and the conductive graphite plugs is the same as the total height of the graphite tube and the hexagonal boron nitride tubes. Above the conductive graphite plugs, along the direction away from the sample, a conductive graphite sheet, a conductive molybdenum sheet, and a conductive steel cap are sequentially arranged. A high-frequency pulsed DC is transmitted sequentially through a hard alloy hammer, a conductive steel cap, a conductive molybdenum sheet, a conductive graphite sheet, and a conductive graphite plug to the sample, forming a closed loop.

[0007] As a preferred embodiment of the invention, the high-power DC pulse power supply adopts a DC pulse IGBT power supply.

[0008] As a preferred embodiment of the invention, the sample is in close contact with the graphite tube and the conductive graphite plug to ensure that the Joule heating effect is uniformly applied to the sample.

[0009] As a preferred technical solution of the invention, the heat insulation tube is interference-fitted with the cavity of the pressure transmission medium to achieve stable installation.

[0010] As a preferred embodiment of the invention, the inner wall of the hexagonal boron nitride tube is flush with the inner wall of the graphite tube and contacts the conductive graphite plug.

[0011] Beneficial effects of the invention: 1. Highly efficient synergy between pressure and temperature fields: The ultra-high pressure at the GPa level greatly promotes the plastic flow and rearrangement of powder particles, reducing the temperature required for sintering densification; while the high-frequency pulsed DC power supply generates discharge plasma and Joule heating effect, realizing rapid and uniform bulk heating of the sample. The synergistic effect of the two can achieve complete densification of ultra-hard ceramics within minutes at temperatures far lower than those of traditional high-temperature and high-pressure methods.

[0012] 2. Obtaining an ultrafine grain structure: Due to the low sintering temperature and extremely short time, the coarsening and growth of grains during the sintering process is effectively suppressed, which is conducive to obtaining an ultrafine grain structure at the nanometer or submicron level.

[0013] 3. High energy efficiency and controllable process: The direct heating method of discharge plasma sintering has a much higher thermal efficiency than traditional external indirect heating, with a fast heating rate and low energy consumption. At the same time, through precise programming of pressure and electrical parameters by the control system, complex sintering processes can be realized, which is beneficial for studying sintering mechanisms and optimizing material properties.

[0014] 4. Expanded material preparation capabilities: This invention provides a brand-new technical means for preparing a new generation of ultra-hard, ultra-strong, and ultra-fine grain ceramic materials and their composites, which are not limited to cubic boron nitride and diamond, but can also be used in advanced ceramic systems such as high-entropy borides and carbides that are difficult to sinter. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the cross-sectional structure of the invention.

[0016] In the figure: 1. High-power DC pulse power supply; 2. Conductive copper strip; 3. Large pad; 4. Steel ring; 5. Small pad; 6. Hard alloy top hammer; 7. Conductive steel cap; 8. Conductive molybdenum sheet; 9. Conductive graphite sheet; 10. Conductive graphite plug; 11. Graphite tube; 12. Sample; 13. Pressure transmitting medium; 14. Insulation tube; 15. Hexagonal boron nitride tube. Detailed Implementation

[0017] Example 1 like Figure 1 As shown, the invention discloses an ultra-high pressure discharge plasma sintering system, the technical solution of which includes a six-sided top press body, a high-power DC pulse power supply 1, and a high-pressure synthesis assembly block; The main body of the six-sided top press has a frame that provides ultra-high pressure and a hydraulic drive system. Its six carbide top hammers 6 together form a cubic space for placing the high-pressure synthesis assembly block that wraps the sample. The two poles of the high-power DC pulse power supply 1 are connected to the upper and lower large pads 3 through two conductive copper strips 2 respectively. The ends of the two large pads 3 are fitted with steel rings 4. The ends of the steel rings 4 are embedded with hard alloy hammers 6. Small pads 5 are filled between the hard alloy hammers 6 and the large pads 3. The small pads 5 are in contact with the large pads 3 and the hard alloy hammers 6 respectively. The high-frequency pulse current of the high-power DC pulse power supply 1 is transmitted to the hard alloy hammers 6 through the conductive copper strips 2, the large pads 3 and the small pads 5. The high-pressure synthesis assembly includes a pressure-transmitting medium 13. An insulation tube 14 is embedded in the inner wall of the cavity of the pressure-transmitting medium 13. A graphite tube 11 is sleeved inside the insulation tube 14. Hexagonal boron nitride tubes 15 are connected to both the top and bottom of the graphite tube 11. The inner and outer diameters of the hexagonal boron nitride tubes 15 are the same as those of the graphite tube 11. A powder sample 12 is placed in the middle of the graphite tube 11, and the powder sample 12 is in contact with the inner wall of the graphite tube 11. Conductive graphite plugs 10 are provided at both ends of the graphite tube 11. The total height of the sample 12 and the conductive graphite plugs 10 is the same as the total height of the graphite tube 11 and the hexagonal boron nitride tubes 15. Above the conductive graphite plugs 10, along the direction away from the sample 12, conductive graphite sheets 9, conductive molybdenum sheets 8, and conductive steel caps 7 are sequentially arranged. High-frequency pulsed DC is transmitted to the sample 12 sequentially through a hard alloy hammer 6, a conductive steel cap 7, a conductive molybdenum sheet 8, a conductive graphite sheet 9, and a conductive graphite plug 10, forming a closed loop.

[0018] The working principle of this embodiment: The main body of the six-sided top press uses its frame and hydraulic drive system to synchronously close the six hard alloy top hammers 6, applying GPa-level ultra-high pressure to the high-pressure composite assembly block placed in the cubic space. This pressure is uniformly transmitted to the graphite tube 11, hexagonal boron nitride tube 15 and sample 12 inside through the pressure transmission medium 13 on the outer layer of the assembly block, promoting the plastic flow and rearrangement of the powder sample 12 particles and reducing the sintering densification temperature threshold. After the high-power DC pulse power supply 1 is started, the high-frequency pulse DC output from its two poles passes through two conductive copper strips. 2. The current is conducted to the upper and lower large pads 3 respectively. The steel rings 4 sleeved at the ends of the large pads 3 serve to fix and enhance conductivity. The pulse current is transmitted through the large pads 3 to the small pads 5 between them and the hard alloy top hammer 6. The small pads 5 are in close contact with the large pads 3 and the hard alloy top hammer 6 to ensure low current loss conduction. Then, it is transmitted sequentially through the conductive steel cap 7, conductive molybdenum sheet 8, conductive graphite sheet 9, and conductive graphite plug 10 in the high-voltage composite assembly block to the sample 12, forming a closed loop. The current flows through the sample 12, the conductive graphite plug 10, the graphite tube 11, etc. The electrical components generate Joule heating, and the sample 12 is in close contact with the graphite tube 11 and the conductive graphite plug 10, achieving rapid and uniform bulk heating. Simultaneously, high-frequency pulsed DC current forms discharge plasma between the particles of sample 12, removing impurities from the particle surface and activating atoms, reducing diffusion activation energy. The heat-insulating tube 14, embedded in the pressure-transmitting medium 13 cavity, has an interference fit with the cavity to reduce heat loss and maintain a stable temperature field. The inner wall of the hexagonal boron nitride tube 15 is flush with the inner wall of the graphite tube 11 and contacts the conductive graphite plug 10, ensuring smooth current conduction and pressure transmission. The sample 12 is fully densified at a temperature far lower than that of traditional processes and within a few minutes under the synergistic effect of ultra-high pressure, Joule heating and plasma activation. This effectively suppresses grain coarsening and forms a nano- or submicron-scale ultrafine grain structure. At the same time, the electrical parameters of the high-power DC pulse power supply 1 and the pressure parameters of the six-sided top press can be precisely programmed through the control system to achieve personalized process curves and meet the preparation requirements of different ultrahard ceramic materials and composite materials such as cubic boron nitride, diamond and difficult-to-sinter borides, carbides, and nitrides.

[0019] Example 2 Using commercially available nano-titanium diboride (TiB2) powder as raw material, high-density ultra-hard ceramic bulks were prepared using an ultra-high voltage discharge plasma sintering system. The system's ability to densify difficult-to-sinter high-entropy boride systems was verified, and the correspondence between process parameters and finished product performance was clarified.

[0020] 1. Sample raw material parameters The raw material is commercially available nano titanium diboride (TiB2) powder with a purity of not less than 99.9% and a particle size of 50±10nm.

[0021] 2. Dimensions and material parameters of high-pressure composite assembly blocks Pressure transmission medium: The material is hollow pyrophyllite, with dimensions of 40×40×40mm (cube) and a pore size of 24.1mm. It is required to be free of cracks, have uniform density, and have an interference fit between the cavity and the insulation pipe.

[0022] Insulation pipe: Made of dolomite, with dimensions of 24.1mm inner diameter × 32mm outer diameter × 20mm height, it is interference-fitted with the pyrophyllite pressure transmission medium cavity, and the inner wall is smooth and free of impurities. The insulation pipe is embedded within the pyrophyllite pressure transmission medium.

[0023] Graphite tube: The material is isostatic graphite (purity ≥99%), the dimensions are inner diameter 6mm × outer diameter 24mm × length 12mm, the parallelism of the two end faces is ≤0.02mm, and there are no pore defects.

[0024] Hexagonal boron nitride tube: The material is hot-pressed sintered hexagonal boron nitride (purity ≥99.8%), and the dimensions are 6mm inner diameter × 24mm outer diameter × 4mm length (1 piece each on the top and bottom). The inner and outer diameters are the same as those of the graphite tube, and the inner wall is flush with the inner wall of the graphite tube.

[0025] Conductive graphite plug: made of isostatic graphite, with a diameter of 6mm and a height of 8.5mm (one for the top and one for the bottom), which fits tightly against the inner wall of the graphite tube.

[0026] Conductive graphite sheet: made of isostatic graphite, with dimensions of 24mm in diameter and 1mm in thickness (one piece on the top and one on the bottom).

[0027] Conductive molybdenum sheet: made of industrial pure molybdenum (purity ≥99.9%), with dimensions of 24mm in diameter × 0.5mm in thickness (one piece on the top and one on the bottom), free of oxide scale.

[0028] Conductive steel cap: Made of No. 45 steel, with dolomite embedded inside, measuring 24mm in diameter × 8.5mm in height (one piece on top and one on the bottom), the inner surface is tightly attached to the molybdenum sheet, and has good conductivity.

[0029] 3. Equipment and process parameters The main body of the six-sided top press is model GY460. The experimental setting is a pressing pressure of 5.5 GPa and a holding time of 40 min.

[0030] High-power DC pulse power supply: IGBT type DC pulse power supply, experimental settings: pulse frequency 1kHz, duty cycle 80%, peak current density 80A / cm². 2 The heating rate was 200℃ / min, the sintering temperature was 1500℃, and the holding time was 10min.

[0031] Temperature detection system: Uses type C thermocouples (WRe5-WRe26), with a temperature measurement range of room temperature to 2300℃ and a temperature measurement accuracy of ±5℃.

[0032] 4. Experimental Procedure Sample pretreatment and assembly: Commercially available nano-titanium diboride (TiB2) powder was first cold-pressed at a pressure of 50 MPa into a circular disc with a diameter of 6 mm and a height of 3 mm. The cold-pressed circular sample was then placed inside a graphite tube, with conductive graphite plugs placed at both ends to ensure that the sample was in close contact with the plugs and the inner wall of the graphite tube (total height = graphite tube length + length of upper and lower hexagonal boron nitride tubes = 12 + 4 + 4 = 20 mm).

[0033] Assembly of the assembly block: The assembled graphite tube-hexagonal boron nitride tube assembly is inserted into the pyrophyllite pressure transmission medium cavity with dolomite insulation tube, and conductive graphite sheet, conductive molybdenum sheet and conductive steel cap are assembled in sequence at the upper and lower ends to ensure that there is no gap in contact between the conductive components.

[0034] Equipment debugging and positioning: Place the high-pressure composite assembly block into the cubic space of the six-sided top press (enclosed by six hard alloy top hammers), adjust the position of the top hammers to ensure that the center of the assembly block is aligned with the pressure center of the top hammers; connect the two poles of the high-power DC pulse power supply to the upper and lower large pads through the conductive copper strip, and check the circuit continuity (resistance ≤ 5Ω).

[0035] Sintering process control: Start the six-sided top press and increase the pressure to 5.5 GPa at a rate of 0.4 GPa / min, and hold the pressure for 40 min; after holding the pressure for 5 min, start the DC pulse power supply and increase the temperature to 1500℃ at the set heating rate (200℃ / min), and hold the temperature for 10 min; after the holding temperature is completed, cool down to room temperature at a rate of 200℃ / min; then after the holding pressure is completed, depressurize to atmospheric pressure at a rate of 0.1 GPa / min.

[0036] Sample post-processing: Remove the sintered assembly block and take out the titanium diboride block sample, and then polish its surface.

[0037] 5. Finished Product Performance and Structural Parameters Density: The test result was 99.2%, and the theoretical density of this material is 4.520 g / cm³. 3 The measured density is 4.484 g / cm³. 3 .

[0038] Vickers hardness: The test result was 29.7 ± 0.4 GPa (4.9 N load).

[0039] Phase composition: The test results show that it is a single phase of TiB2 (hexagonal crystal system). P6 / mmm (Space group), no impurities are generated, and the material phases are pure.

[0040] In this embodiment, TiB2 superhard ceramics were successfully prepared using an ultra-high pressure discharge plasma sintering system. Under the synergistic effect of an ultra-high pressure of 5.5 GPa, a low temperature of 1500℃, and a short holding time of 10 min, the finished product achieved a density of 99.2% and a hardness significantly superior to products prepared using traditional processes. This verifies the system's highly efficient densification capability for difficult-to-sinter superhard boride ceramics. Furthermore, the process is controllable and has high energy utilization, meeting the requirements for the preparation of high-performance superhard ceramics.

[0041] Components not described in detail in this article are existing technologies.

[0042] While the specific embodiments of the invention have been described in detail above, the invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the invention. Modifications or variations that do not involve creative effort are still within the protection scope of the invention.

Claims

1. An ultra-high voltage discharge plasma sintering system, characterized in that, It includes a six-sided top press body, a high-power DC pulse power supply (1), and a high-voltage composite assembly block; The main body of the six-sided top press has a frame and hydraulic drive system that provide ultra-high pressure. Its six carbide top hammers (6) together form a cubic space for placing the high-pressure synthesis assembly block that wraps the sample. The two poles of the high-power DC pulse power supply (1) are connected to the upper and lower large pads (3) through two conductive copper strips (2). The ends of the two large pads (3) are fitted with steel rings (4). The ends of the steel rings (4) are embedded with hard alloy hammers (6). Small pads (5) are filled between the hard alloy hammers (6) and the large pads (3). The small pads (5) are in contact with the large pads (3) and the hard alloy hammers (6) respectively. The high-frequency pulse current of the high-power DC pulse power supply (1) is transmitted to the hard alloy hammers (6) through the conductive copper strips (2), the large pads (3) and the small pads (5). The high-pressure composite assembly includes a pressure-transmitting medium (13), with an insulation tube (14) embedded in the inner wall of the cavity of the pressure-transmitting medium (13). A graphite tube (11) is sleeved inside the insulation tube (14). Hexagonal boron nitride tubes (15) are connected to both the top and bottom of the graphite tube (11). The inner and outer diameters of the hexagonal boron nitride tubes (15) are the same as those of the graphite tube (11). A powder sample (12) is placed in the middle of the graphite tube (11), and the powder sample (12) is in contact with the inner wall of the graphite tube (11). Conductive graphite plugs are provided at both ends of the graphite tube (11). The head (10), the total height of the sample (12) and the conductive graphite plug (10) is consistent with the total height of the graphite tube (11) and the two upper and lower hexagonal boron nitride tubes (15). The conductive graphite plug (10) is provided with a conductive graphite sheet (9), a conductive molybdenum sheet (8) and a conductive steel cap (7) in sequence above the sample (12) along the direction away from the sample (12). The high-frequency pulse DC is transmitted to the sample (12) in sequence through the hard alloy top hammer (6), the conductive steel cap (7), the conductive molybdenum sheet (8), the conductive graphite sheet (9) and the conductive graphite plug (10), forming a closed circuit.

2. The ultra-high voltage discharge plasma sintering system according to claim 1, characterized in that: The high-power DC pulse power supply (1) adopts a DC pulse IGBT power supply.

3. The ultra-high voltage discharge plasma sintering system according to claim 1, characterized in that: The sample (12) is in close contact with the graphite tube (11) and the conductive graphite plug (10) to ensure that the Joule heating effect is uniformly applied to the sample (12).

4. The ultra-high voltage discharge plasma sintering system according to claim 1, characterized in that: The insulation tube (14) and the pressure transmission medium (13) are interference-fitted to achieve stable installation.

5. The ultra-high voltage discharge plasma sintering system according to claim 1, characterized in that: The inner wall of the hexagonal boron nitride tube (15) is flush with the inner wall of the graphite tube (11) and is in contact with the conductive graphite plug (10).

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