A high-density fine-grain bulk catalyst for high-quality diamond single crystal growth and a method of preparing the same

Abstract

The application discloses a high-density fine-grain bulk catalyst for high-quality diamond single crystal growth and a preparation method thereof. The method uses high-purity Fe, Co and Ti particles as raw materials, increases the Co element content to more than 35%, improves the carbon atom and the structural adaptability of the catalyst, prepares a catalyst alloy ingot through vacuum induction melting, uses a box-type resistance heat treatment furnace, and performs high-temperature diffusion annealing-high-temperature quenching-low-temperature tempering-homogenization annealing cycle treatment, refines the ingot grains, controls the microstructure of the alloy ingot, and obtains a high-Co-content iron-based alloy catalyst with refined grains, high density and no defects. In terms of synthesis performance, long-time synthesis verification based on the catalyst system shows that the catalyst has good synthesis stability, and the stable operation time is more than 144 hours. The synthesis results show that the synthesis quality of a single block is much better than that of a conventional catalyst.

Description

Technical Field

[0001] This invention belongs to the field of functional metallic materials, specifically relating to a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth and its preparation method. Background Technology

[0002] As a key medium in the high-temperature, high-pressure (HPHT) synthesis of diamond, the catalyst's core function is to effectively reduce the temperature and pressure required during diamond synthesis, providing the necessary thermodynamic conditions for the efficient synthesis of high-quality large diamond single crystals. Based on the solvent theory of catalyst action, under the extreme high-temperature and high-pressure synthesis environment, carbon atoms in the graphite source gradually dissolve in the solvent system formed by the catalyst, forming a stable carbon-catalyst dissolution system. Subsequently, driven by the temperature gradient, the carbon atoms dissolved in the catalyst diffuse directionally to the seed crystal surface, precipitating as diamond crystals, ultimately completing the entire growth process of the diamond crystal (Sang Weidong. Research on the Synthesis of Colorless Large-Size Diamond Single Crystals by High-Temperature and High-Pressure Static Catalyst Method [D]. Henan University of Technology, 2024. DOI:10.27791 / d.cnki.ghegy.2024.000297.). The microstructure and comprehensive physicochemical properties of the catalyst play a crucial role in regulating the dissolution efficiency, diffusion rate, and deposition and crystallization process of carbon in the catalyst. Its performance directly determines the growth rate of diamond crystals, the regularity of crystal morphology, the purity level of crystals, and the content and distribution of internal defects.

[0003] Currently, in the HPHT synthesis process, powder catalysts have become the mainstream catalyst type for the synthesis of abrasive-grade and small-sized (1-3ct) diamonds due to their ease of preparation and doping. For example, CN121225585A discloses a pre-fabricated catalyst layer for the synthesis of colorless diamonds, which is prepared by mixing and pressing Fe, Ni, Co, and Ti powders and then sintering them under high temperature and pressure to form a catalyst core column for the rapid synthesis of colorless single-crystal diamonds. However, the powder catalyst operation process is prone to contamination and uneven mixing, resulting in more impurities and poor color in the diamonds. At the same time, the low molding density makes it prone to deformation under high pressure, making it difficult to stabilize the internal temperature and pressure fields. In severe cases of deformation, internal instability may occur, leading to significant economic losses such as "explosion". With the rapid advancement of diamond functionalization, the demand for high-quality, large-size diamond single crystals is becoming increasingly urgent. The synthesis process of this type of diamond requires sufficient crystal growth space and a highly stable and uniform temperature and pressure field. This places higher demands on the density, microstructure control, and synthesis performance of the catalyst. In terms of density, high-density bulk catalysts exhibit less deformation during synthesis, thus ensuring the stability of the temperature and pressure fields during the synthesis process. In terms of microstructure control, the grain boundary density of the catalyst has a significant impact on the diffusion and transport rate of carbon atoms (SANGJUN CHA, PAK MC, KIM KI, et al. Recrystallization Characteristics of CatalyticAlloy and Graphite in Diamond Synthesis[J]. Journal of Superhard Materials,2021, 43(5): 336-343.). The low grain boundary density of coarse-grained structures inhibits the movement of carbon atoms, thereby affecting the synthesis quality. While this approach can improve crystal quality, it also reduces production efficiency and increases the difficulty of receiving carbon sources in the early stages of synthesis, significantly increasing the risk of overheating of the seed crystals and thus experimental failure. Therefore, appropriate fine-grained structures are needed to control the early growth of crystals during the synthesis process. Regarding synthesis performance, for the synthesis of high-quality colorless single-crystal diamond, iron-based catalyst systems with high crystal quality have become the mainstream choice. Simultaneously, the proportions of elements such as Co and Ti, which significantly improve crystal quality, are also increased. For example, invention CN114908414A discloses a synthesis process for colorless single-crystal diamond catalysts, in which the Co content of the catalyst reaches 24%. However, on the other hand, the increased content of elements such as Co and Ti has a significant negative impact on the toughness of iron-based catalysts, thereby significantly deteriorating the processing performance of the catalysts and making it difficult to control the microstructure through mechanical stress implantation. Therefore, based on the synthesis requirements of high-quality type IIa diamond, it is urgent to design a high-Co iron-based catalyst preparation process that combines high density and controllable microstructure. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a preparation process for high-quality, fine-grained bulk alloy catalysts by redesigning the composition of iron-based catalysts and combining it with a cyclic heat treatment process. By increasing the Co content to over 35%, the structural compatibility between carbon atoms and the catalyst is improved, promoting perpendicular bonding between carbon atoms and the catalyst. Combined with trace amounts of Ti to assist in impurity removal, the synthesis performance of the catalyst is improved. The innovative cyclic heat treatment process solves the problems of high brittleness and difficulty in microstructure control caused by increased Co content in iron-based catalysts. Utilizing the solid-state phase transformation principle of iron-based alloys, multi-stage heat treatment effectively refines the catalyst grains to below 150 μm, achieving synergistic optimization of high density (over 99.9%), effective grain structure control, and high synthesis quality. Based on this catalyst, long-term synthesis experiments have verified the synthesis of single-piece, high-mass, and high-precision-grain ratio colorless diamond.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing high-density fine-grained bulk catalysts for high-quality diamond single crystal growth is disclosed. The method uses high-purity Fe, Co, and Ti particles as raw materials, prepares catalyst alloy ingots through vacuum induction melting, and uses a box-type resistance furnace to refine the ingot grains and control the microstructure of the alloy ingot through a cycle of high-temperature diffusion annealing, high-temperature quenching, low-temperature tempering, and homogenization annealing.

[0006] The specific steps are as follows: (1) Place Fe particles and Co particles in the crucible of the vacuum induction melting furnace, and Ti particles in the feeding hopper. Place the crucible inside the induction coil, close the furnace door, start the vacuum pump, open the low vacuum valve to evacuate the furnace to a vacuum level of 5 Pa or higher, close the low vacuum valve, open the high vacuum valve, and evacuate the furnace to a vacuum level of 8 × 10⁻⁶ Pa. -3 Above Pa, turn on the induction coil power supply and increase the power to 13~17kw to start melting. After the furnace temperature rises to the preset 1650~1750℃, observe the raw material in the crucible through the observation window. When it is completely melted into a liquid state, turn on the mechanical stirrer and the feeding switch of the feeding hopper to add Ti particles into the crucible. Increase the power to 23~27kw to stir and melt. After melting for 10~20 minutes, tilt the crucible and pour the alloy melt into the mold in the vacuum induction melting furnace. Open the furnace door and take out the mold. After cooling in the air, the alloy ingot is obtained. The alloy ingot contains 35~50wt% Co, 1.5~5wt% Ti, and the balance is Fe. (2) Cut the alloy ingot into a cylindrical sample, raise the temperature of the heat treatment furnace to 650±10℃, place the cylindrical sample in the heat treatment furnace and keep it at the temperature for 0.5~2h, then raise the furnace temperature to 1100~1150℃ and keep it at the temperature for 2~6h. After the temperature is maintained, the sample is cooled to 750~850℃ with the furnace, the furnace door is opened and the sample is taken out and air-cooled to room temperature. (3) Raise the temperature of the heat treatment furnace to 650±10℃, place the sample from step (2) in the heat treatment furnace, keep it at the temperature for 0.5~2.5h, then raise the furnace temperature to 1000~1100℃, keep it at the temperature for 1~3h, cool it to room temperature with oil, take out the sample and ultrasonically clean the surface impurities for later use, raise the temperature of the heat treatment furnace to 680~720℃, place the quenched sample in the heat treatment furnace and keep it at the temperature for 1~3h, take out the sample and air cool it to room temperature; repeat the above steps 1~2 times, then replace the quenching medium with water and repeat the above steps 1~2 times again. (4) Raise the temperature of the heat treatment furnace to 800~950℃, place the sample in the heat treatment furnace, keep it warm for 0.5~2h, cool it down to 700~750℃ with the furnace, take out the sample and air cool it to room temperature, and you will get the sample.

[0007] Furthermore, in step (1), the crucible material is MgO, and the purity of Fe, Co, and Ti particles is ≥99.99%, and the mold is an H13 cast steel mold.

[0008] Further, in step (1), the stirring rate is 50~80r / min, the power is increased to 13~17kw at a rate of 1.5~2kw / min, and the power is increased to 23~27kw at a rate of 2~4kw / min.

[0009] Furthermore, in step (2), the cylindrical sample has a diameter of 50~80mm and a height of 100~160mm.

[0010] Furthermore, in step (2), the heating rate of the heat treatment furnace is 10~20℃ / min; the cooling rate of the heat treatment furnace is 5~10℃ / min.

[0011] Furthermore, in step (3), the oil cooling medium is a rapid quenching oil (such as UHB, UHG, UHA, etc.), and the kinematic viscosity of the quenching oil is required to be 30~34 mm. 2 / s, flash point ≥200℃, cooling time ≤5s for 800-400℃.

[0012] Further, in step (3), impurities are cleaned with acetone at an ultrasonic frequency of 100~160kHz.

[0013] Furthermore, in step (4), the cooling rate of the heat treatment furnace is 1~5℃ / min. Furthermore, the heat treatment furnaces in steps (2), (3), and (4) are all box-type resistance furnaces.

[0014] The power supply output voltage of the smelting furnace is 375V, and the maximum output power is 60kW.

[0015] In the processing method described in this invention, the acetone used for cleaning impurities is of analytical grade.

[0016] The above-described preparation method yields a high-density, fine-grained bulk catalyst for the growth of high-quality diamond single crystals.

[0017] Quality Inspection and Performance Verification: After heat treatment, the surface oxide layer of the catalyst is removed, and thin sample sheets are cut using wire electrical discharge machining. The density is determined using Archimedes' water displacement method or the airtightness is tested using a helium leak detection method to verify the sample density. After grinding and polishing, the sample surface is scanned using an electron backscatter diffraction probe of a scanning electron microscope to detect the grain size.

[0018] After heat treatment, the surface oxide layer of the catalyst was removed, and it was cut into circular samples with a diameter of 50-60 mm and a height of 8-10 mm by wire electrical discharge machining. Carbon source graphite powder was then pressed into circular samples with a diameter of 50-60 mm and a height of 8-10 mm. These two materials were combined to form a synthesis core, and a high-temperature, high-pressure synthesis experiment was conducted using a six-sided press. The experimental pressure was 4.5-6.5 GPa, the experimental temperature was 1300-1450℃, and the experimental duration was 120-240 h to verify the catalyst synthesis effect.

[0019] The present invention has the following beneficial effects: In the processing method described in this invention, the grain refinement of high-Co alloy catalysts is successfully achieved without the use of machining through alloy composition redesign and cyclic gradient heat treatment. This solves the problems of high difficulty and poor quality in microstructure control of low-plasticity iron-based alloys, and achieves synergistic optimization of high quality, high density, and effective microstructure control of alloy catalysts.

[0020] Regarding composition control, this invention, based on the principle of structural transformation, increases the Co content in the catalyst, utilizing its strong bonding ability with single atoms in the graphite layer to optimize the catalyst's synthesis performance. Simultaneously, Ti, with its excellent nitrogen removal effect, is used for synergistic doping to improve crystal purity. Regarding microstructure control, this invention, based on the principle of solid-state phase transformation, utilizes the volume difference between α-Fe and γ-Fe to implant stress during the phase transformation process, thereby providing impetus for crystal breakage and recrystallization nucleation during cooling. Based on this, multiple quenching processes with progressively increasing cooling rates are performed, causing repeated grain breakage and recombination, gradually refining the average grain size. Furthermore, considering the low plasticity of iron-cobalt based alloys, diffusion annealing is used before cyclic heat treatment to eliminate ingot composition and microstructure segregation, thus preventing stress concentration caused by the decomposition of some coarse grains during subsequent quenching and tempering. Simultaneously, quenching oil is used to control the cooling rate at approximately 80℃ / s to avoid thermal stress caused by excessively rapid cooling, thereby suppressing the formation of microcracks. After completing cyclic heat treatment, homogenization annealing eliminates residual stress within the alloy, allowing for appropriate grain growth and improving the uniformity of grain size distribution. In summary, through alloy composition redesign and cyclic gradient heat treatment, a high-Co content iron-based alloy catalyst with refined grains, high density, and no defects is obtained without using deformation processes such as forging and rolling to achieve stress implantation.

[0021] Regarding synthesis performance, long-term synthesis verification based on this catalyst system demonstrates its excellent synthesis stability, with a stable operating time exceeding 144 hours. The synthesis results show that the quality of a single catalyst is significantly superior to that of conventional catalysts. Attached Figure Description

[0022] Figure 1 This is an EBSD scan of the microstructure after grain refinement through cyclic heat treatment in Example 1; Figure 2 The image shows a crystal obtained by synthesis using a catalyst in Example 1. Detailed Implementation

[0023] The present invention will be further illustrated below with specific examples. These embodiments should be understood as illustrative only and not as limiting the scope of protection of the present invention. After reading the description of the present invention, those skilled in the art can make various alterations or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

[0024] The heat treatment furnaces used in the following examples are all box-type resistance furnaces. Example 1

[0025] This invention provides a method for preparing a high-density, fine-grained bulk catalyst for high-quality diamond single crystal growth, the specific steps of which are as follows: (1) Alloy ingot smelting Fe and Co raw material particles are placed in the MgO crucible of the vacuum induction melting furnace, and Ti particles are placed in the secondary feeding hopper. The crucible is then placed inside the induction coil, the furnace door is closed, and the vacuum pump is started. The low vacuum valve is opened to evacuate the furnace to 5 Pa, the low vacuum valve is closed, and the high vacuum valve is opened to evacuate the furnace to 8 × 10⁻⁶ Pa. -3 Pa. Turn on the induction coil power and increase the power to 15 kW at a rate of 1.5 kW / min to begin alloy melting. After the furnace temperature reaches the preset 1700°C, observe the raw material in the crucible through the observation window. Once it has completely melted into a liquid state, turn on the mechanical stirrer and secondary feeding hopper, add Ti particles into the crucible, and increase the power to 25 kW at a rate of 3 kW / min while stirring and melting at a stirring speed of 50 r / min. After melting for 15 minutes, tilt the crucible using the external linkage handle to pour the molten alloy into the H13 casting steel mold in the vacuum induction melting furnace. Open the furnace door, remove the mold, and cool it in the air to obtain the alloy ingot.

[0026] The purity of Fe, Co, and Ti raw material particles is 99.99%.

[0027] The alloy ingot is composed of Fe. 58.5 Co 40 Ti 1.5 .

[0028] The power supply output voltage of the smelting furnace is 375V, and the maximum output power is 60kW.

[0029] (2) Pre-annealing The alloy ingot was cut into cylindrical samples with a diameter of 60 mm and a height of 120 mm using wire EDM. The temperature of the heat treatment furnace was raised to 650℃, and the cylindrical sample was placed in the heat treatment furnace and held for 2 hours. Then, the furnace temperature was raised to 1120℃ and held for 4 hours. After the holding period, the sample was cooled to 800℃ with the furnace. The furnace door was opened, the sample was removed, and air-cooled to room temperature.

[0030] The heating rate of the heat treatment furnace is 10℃ / min, and the cooling rate is 5℃ / min.

[0031] (3) High-temperature quenching + low-temperature tempering The heat treatment furnace temperature was raised to 650℃, and the alloy sample that had completed the pre-annealing stage was placed in the furnace and held for 2 hours. The furnace temperature was then raised to 1020℃ and held for 2 hours, followed by oil cooling to room temperature. The sample was removed and ultrasonically cleaned at 150 kHz using acetone as the cleaning agent to remove surface impurities. The furnace temperature was then raised to 700℃, and the quenched sample was placed in the heat treatment furnace and held for 3 hours. The sample was then air-cooled to room temperature. This process was repeated twice, and then the quenching medium was replaced with water, and the process was repeated once more.

[0032] The oil cooling medium is UHG rapid bright quenching oil, and the required kinematic viscosity is 30~34 mm. 2 / s, flash point ≥200℃, cooling time ≤5s for 800-400℃.

[0033] The acetone used for cleaning impurities was of analytical grade.

[0034] (4) Homogenization annealing The temperature of the heat treatment furnace is raised to 850℃, the sample is placed in the heat treatment furnace and kept at that temperature for 2 hours. The temperature is then cooled to 750℃ with the furnace. The sample is then removed and air-cooled to room temperature to obtain the catalyst.

[0035] The cooling temperature of the heat treatment furnace is 1℃ / min.

[0036] (5) Quality inspection and performance verification After heat treatment, the surface oxide layer of the catalyst was removed, and thin sample sheets were cut using wire electrical discharge machining. The density of the sample was determined to be 8.154 g / cm³ using the Archimedes' displacement method. 3 The density is ≥99.9% (or the airtightness is tested by helium leak detection, and the leakage rate of the tested sample is ≤10%). -10 Pa·m 3 / s), meeting high density requirements. After grinding and polishing, the sample surface is scanned using an electron backscatter diffraction probe of a scanning electron microscope to detect the grain size of the sample, such as Figure 1 As shown, from Figure 1 It can be seen that after heat treatment, the alloy microstructure has a uniform equiaxed crystal structure, and the average grain size is 104.4 μm, which is less than 120 μm, thus meeting the fine grain index.

[0037] The heat-treated catalyst had its surface oxide layer removed and was cut into circular samples with a diameter of 60 mm and a height of 9 mm using wire EDM. Carbon source graphite powder was pressed into circular samples with a diameter of 60 mm and a height of 8 mm. These two materials were combined to form a synthesis core, which was then subjected to a high-temperature, high-pressure synthesis experiment using a six-sided press. The experimental pressure was 5.5 GPa, the experimental temperature was 1400℃, and the experimental duration was 144 h to verify the catalyst synthesis effect. The synthesis results are as follows: Figure 2 As shown, the mass of a single synthesized piece exceeded 120 ct. The image reveals that most crystals are completely transparent or contain only trace inclusions. Only about 10% of the crystal samples exhibit obvious black inclusion defects. Grade A material accounts for 18%, and Grade B material accounts for over 69%, with the proportion of superior crystals far exceeding the 80% of conventional catalysts. Example 2

[0038] This invention provides a method for preparing a high-density, fine-grained bulk catalyst for high-quality diamond single crystal growth, the specific steps of which are as follows: (1) Alloy ingot smelting Fe and Co raw material particles are placed in the MgO crucible of the vacuum induction melting furnace, and Ti particles are placed in the secondary feeding hopper. The crucible is then placed inside the induction coil, the furnace door is closed, and the vacuum pump is started. The low vacuum valve is opened to evacuate the furnace to 5 Pa, the low vacuum valve is closed, and the high vacuum valve is opened to evacuate the furnace to 8 × 10⁻⁶ Pa. -3 Pa. Turn on the induction coil power and increase the power to 15 kW at a rate of 2 kW / min to begin alloy melting. After the furnace temperature reaches the preset 1700℃, observe the raw material in the crucible through the observation window. Once it has completely melted into a liquid state, turn on the mechanical stirring and secondary feeding switch, add Ti particles into the crucible, and increase the power to 25 kW at a rate of 4 kW / min while stirring and melting at a stirring speed of 80 r / min. After melting for 20 minutes, tilt the crucible using the external linkage handle to pour the molten alloy into the H13 casting steel mold in the vacuum induction melting furnace. Open the furnace door, remove the mold, and cool it in the air to obtain the alloy ingot.

[0039] The purity of Fe, Co, and Ti raw material particles is 99.99%.

[0040] The alloy ingot is composed of Fe. 47 Co 50 Ti3.

[0041] The power supply output voltage of the smelting furnace is 375V, and the maximum output power is 60kW.

[0042] (2) Pre-annealing The alloy ingot was cut into cylindrical samples with a diameter of 55 mm and a height of 130 mm using wire EDM. The temperature of the heat treatment furnace was raised to 650℃, and the cylindrical sample was placed in the furnace and held for 1 hour. Then, the furnace temperature was raised to 1120℃ and held for 2 hours. After the holding period, the sample was cooled with the furnace to 800℃. The furnace door was opened, the sample was removed, and air-cooled to room temperature.

[0043] The heating rate of the heat treatment furnace is 10℃ / min, and the cooling rate is 5℃ / min.

[0044] (3) High-temperature quenching + low-temperature tempering The heat treatment furnace temperature was raised to 650℃, and the sample that had completed the pre-annealing stage was placed in the furnace and held for 1.5 hours. The furnace temperature was then raised to 1080℃ and held for 1.56 hours, followed by oil cooling to room temperature. The sample was removed and ultrasonically cleaned at 150 kHz using acetone as the cleaning agent to remove surface impurities. The furnace temperature was then raised to 700℃, and the quenched sample was placed in the heat treatment furnace and held for 1.5 hours. The sample was then air-cooled to room temperature. This process was repeated once, and then the quenching medium was replaced with water, and the process was repeated once more.

[0045] The oil cooling medium is UHG rapid bright quenching oil, and the required kinematic viscosity is 30~34 mm. 2 / s, flash point ≥200℃, cooling time ≤5s for 800-400℃.

[0046] The acetone used for cleaning impurities was of analytical grade.

[0047] (4) Homogenization annealing The temperature of the heat treatment furnace is raised to 800℃, the sample is placed in the heat treatment furnace and kept at that temperature for 1 hour. The temperature is then cooled to 750℃ with the furnace. The sample is then removed and air-cooled to room temperature to obtain the catalyst.

[0048] The cooling temperature of the heat treatment furnace is 5℃ / min.

[0049] (5) Quality inspection and performance verification After heat treatment, the surface oxide layer of the catalyst was removed, and thin sample sheets were cut using wire electrical discharge machining. The density was determined using Archimedes' water displacement method or the airtightness was tested using a helium leak detection method to verify the sample density. After polishing, the sample surface was scanned using an electron backscatter diffraction probe of a scanning electron microscope to detect the grain size. The results showed that the grain size was comparable to that of Example 1.

[0050] The heat-treated catalyst had its surface oxide layer removed and was cut into circular samples with a diameter of 60 mm and a height of 8 mm using wire EDM. Carbon source graphite powder was then pressed into circular samples with a diameter of 60 mm and a height of 8 mm. These two materials were combined to form a synthesis core, which was then subjected to a high-temperature, high-pressure synthesis experiment using a six-sided press. The experimental pressure was 5.5 GPa, the experimental temperature was 1300–1450 °C, and the experimental duration was 240 h to verify the catalyst synthesis effect. The synthesis effect was comparable to that of Example 1.

[0051] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-density, fine-grained bulk catalyst for high-quality diamond single crystal growth, characterized in that, The steps are as follows: (1) Place Fe particles and Co particles in the crucible of the vacuum induction melting furnace, and Ti particles in the feeding hopper. Place the crucible inside the induction coil, close the furnace door, start the vacuum pump, open the low vacuum valve to evacuate the furnace to a vacuum level of 5 Pa or higher, close the low vacuum valve, open the high vacuum valve, and evacuate the furnace to a vacuum level of 8 × 10⁻⁶ Pa. -3 Above Pa, turn on the induction coil power supply and increase the power to 13~17kw to start melting. After the furnace temperature rises to the preset 1650~1750℃, observe the raw material in the crucible through the observation window. When it is completely melted into a liquid state, turn on the mechanical stirrer and the feeding switch of the feeding hopper to add Ti particles into the crucible. Increase the power to 23~27kw to stir and melt. After melting for 10~20 minutes, tilt the crucible and pour the alloy melt into the mold in the vacuum induction melting furnace. Open the furnace door and take out the mold. After cooling in the air, the alloy ingot is obtained. The alloy ingot contains 35~50wt% Co, 1.5~5wt% Ti, and the balance is Fe. (2) Cut the alloy ingot into a cylindrical sample, raise the temperature of the heat treatment furnace to 650±10℃, place the cylindrical sample in the heat treatment furnace and keep it at the temperature for 0.5~2h, then raise the furnace temperature to 1100~1150℃ and keep it at the temperature for 2~6h. After the temperature is maintained, the sample is cooled to 750~850℃ with the furnace, the furnace door is opened and the sample is taken out and air-cooled to room temperature. (3) Raise the temperature of the heat treatment furnace to 650±10℃, place the sample from step (2) in the heat treatment furnace, keep it at the temperature for 0.5~2.5h, then raise the furnace temperature to 1000~1100℃, keep it at the temperature for 1~3h, cool it to room temperature with oil, take out the sample and ultrasonically clean the surface impurities for later use, raise the temperature of the heat treatment furnace to 680~720℃, place the quenched sample in the heat treatment furnace and keep it at the temperature for 1~3h, take out the sample and air cool it to room temperature; repeat the above steps 1~2 times, then replace the quenching medium with water and repeat the above steps 1~2 times again. (4) Raise the temperature of the heat treatment furnace to 800~950℃, place the sample in the heat treatment furnace, keep it warm for 0.5~2h, cool it down to 700~750℃ with the furnace, take out the sample and air cool it to room temperature, and you will get the sample.

2. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, In step (1), the crucible is made of MgO, and the purity of Fe, Co and Ti particles is ≥99.99%. The mold is an H13 casting steel mold.

3. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, In step (1), the stirring rate is 50~80r / min, the power is increased to 13~17kw at a rate of 1.5~2kw / min, and the power is increased to 23~27kw at a rate of 2~4kw / min.

4. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, In step (2), the cylindrical sample has a diameter of 50~80mm and a height of 100~160mm.

5. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, In step (2), the heating rate of the heat treatment furnace is 10~20℃ / min; the cooling rate of the heat treatment furnace is 5~10℃ / min.

6. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, In step (3), the oil cooling medium is rapid quenching oil, and the kinematic viscosity of the quenching oil is required to be 30~34 mm. 2 / s, flash point ≥200℃, cooling time ≤5s for 800-400℃.

7. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, In step (3), impurities are cleaned with acetone at an ultrasonic frequency of 100~160kHz.

8. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, In step (4), the cooling rate of the heat treatment furnace is 1~5℃ / min.

9. The method for preparing a high-density fine-grained bulk catalyst for high-quality diamond single crystal growth according to claim 1, characterized in that, The heat treatment furnaces in steps (2), (3), and (4) are all box-type resistance furnaces.

10. A high-density fine-grained bulk catalyst for high-quality diamond single crystal growth prepared by the preparation method according to any one of claims 1 to 9.

Images