Multilayer diamond phase change strengthening method

Abstract

The invention provides a multi-layer diamond phase change strengthening method, which relates to the technical field of material strengthening, and comprises the following steps: S1, pretreating the surface of a substrate; step S2, sowing of seed crystals; s3, preparing a diamond layer without hole defects; s4, preparing a twin crystal diamond layer with hole defects; s5, preparing a multi-layer diamond; and S6, diamond phase transformation strengthening is conducted. The preparation method is simple in preparation and low in operation difficulty, the strength of the obtained diamond can be further improved, and a CVD diamond film can serve under the harsh working condition.

Description

Technical Field

[0001] The present invention relates to the technical field of diamond material strengthening, and particularly to a multi-layer diamond phase transformation strengthening method. Background Art

[0002] Diamond has a face-centered cubic structure with a lattice constant of The carbon-carbon bond length is only The bond angle is 109°28′, and the carbon atom density is 1.77×10 2 cm- 3 , closely arranged in a tetrahedral structure. Due to its unique carbon atom arrangement, extremely strong covalent bonds are formed in diamond, making diamond have a strong ability to resist damage when subjected to an external force. Therefore, diamond has been widely used in many fields such as industry, medicine, and aerospace due to its extremely high strength. For example, diamond-made indenters are used in various testing devices; diamond tools can efficiently cut and process various materials; using the high strength and sharpness of diamond, precision surgical knives can be manufactured, etc.

[0003] Strength is an important quality index of synthetic diamond, and the level of strength is directly related to the quality of use performance. With the development of science and technology and the progress of humanity, workers in some industries have higher and higher requirements for the strength of diamond. Therefore, a method to improve the strength of diamond needs to be found to meet the strength requirements of diamond in some fields. Summary of the Invention

[0004] The purpose of the present invention is to achieve a multi-layer diamond in-situ phase transformation strengthening method, belonging to the field of material strengthening. The method mainly uses the MPCVD method to deposit multi-layer diamond with alternating growth of non-porous layers and pore twin layers, thereby significantly enhancing the strength of the diamond film. In particular, the microwave plasma chemical vapor deposition method is used to deposit a non-porous diamond layer, and then by destroying the stable growth environment, a large number of twins are introduced into the new diamond layer, making defects similar to pore structures generated around the twins. Finally, heat treatment is used to cause in-situ phase transformation of the diamond at the defect sites to generate low-density sp 2 carbon, and local stress is generated by the accumulation of sp 2 carbon plugs in the pores, thereby obtaining multi-layer diamond with ultra-high strength. Specifically:

[0005] A multi-layer diamond phase transformation strengthening method includes:

[0006] Step S1: First, grind the substrate with diamond micropowder, and then ultrasonically clean the substrate with absolute ethanol and deionized water to remove the micropowder on the substrate surface; through the pretreatment step, the nucleation incubation period of diamond can be effectively shortened and the nucleation density of diamond can be increased;

[0007] Step S2: Regulate the zeta potential of the substrate and prepare a diamond seed crystal suspension that matches the zeta potential of the substrate. Sow the diamond seed crystals on the substrate by ultrasonic waves;

[0008] Step S3: Perform microwave plasma chemical vapor deposition on the substrate sown with diamond seed crystals to prepare a diamond layer without pore defects;

[0009] Step S4: Periodically change the microwave power to prepare a twin diamond layer with pore defects on the diamond layer without pore defects; by periodically changing the microwave power, the deposition and stacking processes of atoms are affected, twins are introduced, and pore-like defects will be generated around the twins, thus preparing a twin diamond layer with pore defects. Except for changing the microwave power, the other operations in Step S4 are the same as those in S3;

[0010] Step S5: Alternately repeat Steps S3 and S4 to obtain a multi-layer diamond in which diamond layers without pore defects and twin diamond layers with pore defects appear alternately;

[0011] Step S6: Heat-treat the multi-layer diamond in a vacuum heating device. The diamond at the pore defects undergoes in-situ phase transformation to generate low-density sp 2 carbon, and the sp 2 carbon plugs the pores through volume expansion, causing local stress in the diamond and strengthening the diamond.

[0012] Optionally, in Step S1, the substrate is selected from Si substrates.

[0013] Optionally, to ensure the seeding effect, Step S2 includes: Immerse the Si substrate and oxygen-terminated diamond seed crystals (i.e., the diamond surface has been specifically treated so that oxygen atoms become the main terminal atoms on the diamond surface. The oxygen termination can increase the nucleation site density and contribute to the growth of diamond) in a solution of polydiallyldimethylammonium chloride for 10 - 50 minutes to make the zeta potential of the substrate 30 - 60 mV and the potential of the seed crystal -30 - -60 mV, and then perform ultrasonic treatment at a power of 80 - 300 W for 10 - 60 min

[0014] Optionally, Step S3 includes: Place the substrate sown with diamond seed crystals in a microwave plasma chemical vapor deposition chamber, introduce hydrogen and slowly increase the microwave power, control the chamber pressure and the substrate temperature, then introduce high-purity oxygen for etching for 10 - 50 min, and the proportion of oxygen in hydrogen is 0.2 - 0.5%; after the etching is completed, introduce methane into the chamber to prepare a diamond layer without pore defects.

[0015] Optionally, in step S3, the process parameters of microwave plasma chemical vapor deposition are set as follows: the total gas flow rate is 200 - 600 sccm (i.e., the total gas flow rate remains within this range throughout the deposition process), the volume ratio of CH4 in the gas is 1% - 5% (the other gas is hydrogen), the gas pressure is 10 - 20 kPa, the deposition temperature is 700 - 900 °C. If the microwave frequency is 915 MHz, the microwave power range is 30 - 80 kW; if the microwave frequency is 2.45 GHz, the microwave power range is 2 - 10 kW.

[0016] Optionally, in step S4, periodically changing the microwave power includes: if the microwave frequency is 915 MHz, the initial microwave power is set within the range of 35 - 60 kW; if the microwave frequency is 2.45 GHz, the initial microwave power is set within the range of 3 - 7.5 kW. Through program setting, the microwave power changes periodically in the range of -30% to +30% per minute in the form of a sine wave (i.e., changes ±30% in the form of a sine wave based on the initial microwave power) for 3 - 300 times. The deposition time is determined according to the thickness to be deposited.

[0017] Optionally, in step S5, the thickness of the diamond layer without pore defects is ≥12 μm, the thickness of the twinned diamond layer with pore defects is ≥10 μm, and the number of alternating layers is ≥1 layer.

[0018] Optionally, in step S6, the multi-layer diamond is placed in a vacuum heating device and heated for 20 - 60 s under the conditions of a pressure of 3 - 7 kPa and a temperature of 1500 - 2000 °C.

[0019] The strengthened multi-layer diamond of the present invention has an ultra-high strength of up to 1.1 GPa. It can be applied to grinding tools and cutting tools. Due to the expanded growth area, it can be widely applied in the industrial processing field, significantly improving the service life of cutting tools, grinding tools, etc., and meeting the precision processing requirements of difficult-to-machine materials.

[0020] The technical solution of the present invention has at least the following beneficial effects compared with the prior art:

[0021] The present invention uses the method of microwave plasma chemical vapor deposition to prepare a diamond layer with high strength, large size and no pore defects. By periodically changing the microwave power and disturbing the equilibrium growth, twin crystals are prepared in the new diamond layer to introduce pore defects, and two types of diamond layers are grown alternately to form multi-layer diamond. This method has low requirements for equipment conditions, is easy to operate, and is conducive to popularization.

[0022] The present invention introduces a phase change through heat treatment to generate low-density sp 2 carbon at twin crystals. Utilizing the characteristic that the density of diamond is greater than that of sp 2 carbon density, the sp 2Carbon generates local stress at the holes in the structure of a wedge through volume expansion to further strengthen diamond. The strength of diamond after in-situ phase transformation is increased from ~700 MPa to ~1.1 GPa compared with that of diamond without in-situ phase transformation, with an increase of ~58%. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a process flow chart of the present invention.

[0025] Figure 2 It is a schematic cross-sectional view of multi-layer diamond of the present invention.

[0026] Wherein: 1 - diamond layer without hole defects; 2 - twin diamond layer with hole defects. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0027] The following describes the technical solutions in the present invention.

[0028] In the embodiments of the present invention, words such as "exemplarily" and "for example" are used to represent examples, illustrations or explanations. Any embodiment or design solution described as "example" in the present invention should not be construed as more preferred or more advantageous than other embodiments or design solutions. Exactly speaking, the use of the word "example" is intended to present concepts in a specific way. In addition, in the embodiments of the present invention, the meaning expressed by "and / or" can be both, or either of the two can be selected.

[0029] In the embodiments of the present invention, sometimes subscripts such as W1 may be miswritten as non-subscript forms such as W1. When the difference is not emphasized, the meanings to be expressed are the same.

[0030] In order to make the technical problems to be solved, technical solutions and advantages of the present invention clearer, the following will be described in detail with reference to the drawings and specific embodiments.

[0031] Embodiment 1

[0032] The 10 mm×10 mm Si substrate was pretreated by grinding with diamond powder and then ultrasonically cleaned with acetone, absolute ethanol, and deionized water. After pretreatment, the substrate and the oxygen-terminated diamond seed crystal were immersed in a solution of poly(diallyldimethylammonium chloride) for 30 min to make the zeta potential of the substrate +50 mV and that of the seed crystal -50 mV. Then, seeding was carried out by ultrasonic treatment at a microwave power of 100 W for 30 min. The seeded substrate was placed in the chamber of an MPCVD apparatus with a microwave frequency of 915 MHz, 500 sccm of hydrogen was introduced, the microwave power was slowly increased to 50 kW, the chamber pressure was controlled at 15 kPa to raise the substrate temperature to 800 °C, and high-purity oxygen was introduced with the proportion of oxygen in hydrogen being 0.2%, and etching was carried out for 30 min. After the etching process ended, the methane flowmeter was opened, methane with a concentration of 3% was introduced into the chamber, and deposition was carried out for 4 h to prepare a diamond layer without pore defects. After the deposition ended, through program setting, the microwave power was periodically changed by 10% in the form of a sine wave per minute, with 150 cycles per minute, and deposition was carried out for 4 h to prepare a twinned diamond layer with pore defects. Taking the pore-free layer and the pore-containing twinned layer as one cycle, after one cycle, two layers of diamond with the alternating growth of diamond without pore defects and twinned diamond with pore defects were deposited. The multilayer diamond was placed in a vacuum heating device, evacuated, and then an inert gas was introduced until the pressure reached 4 kPa, and then the temperature was raised to 1800 °C. After heat treatment for 60 s, it was taken out. At this time, the diamond at the pore defects of the twinned layer underwent in-situ phase transformation to generate low-density sp2 carbon. The sp2 carbon expanded in volume and plugged the pores in the form of a wedge, increasing the local stress of the diamond, thereby enhancing the strength of the diamond. Compared with the diamond without in-situ phase transformation, the strength was increased from 700 MPa to 1.1 GPa, an increase of 58%.

[0033] Example 2

[0034] The 6 mm × 6 mm Si substrate is pretreated by grinding with diamond powder and then ultrasonically cleaned with acetone, absolute ethanol, and deionized water. After pretreatment, the substrate and the oxygen-terminated diamond seed crystal are immersed in a poly(diallyldimethylammonium chloride) solution for 35 min to make the zeta potential of the substrate +55 mV and that of the seed crystal -55 mV. Then, seeding is carried out by ultrasonic treatment at a microwave power of 200 W for 20 min. The seeded substrate is placed in the chamber of an MPCVD device with a microwave frequency of 2.45 GHz, 350 sccm of hydrogen is introduced, the microwave power is slowly increased to 6 kW, the chamber pressure is controlled at 14 kPa to bring the substrate temperature to 850 °C, and high-purity oxygen is introduced with the proportion of oxygen in hydrogen being 0.3%, and etching is carried out for 50 min. After the etching process is completed, the methane flowmeter is opened, methane with a concentration of 2.5% is introduced into the chamber, and deposition is carried out for 5 h to prepare a diamond layer without pore defects. After deposition, through program settings, the microwave power is periodically changed by 20% in the form of a sine wave per minute, with 200 cycles per minute, and deposition is carried out for 5 h to prepare a twinned diamond layer with pore defects. Taking the pore-free layer and the pore-containing twinned layer as one cycle, the cycle is repeated twice to deposit 4 layers of diamond with alternating growth of diamond without pore defects and twinned diamond with pore defects. The multi-layer diamond is placed in a vacuum heating device, the vacuum is pumped, and then an inert gas is introduced until the pressure reaches 5 kPa, and then the temperature is raised to 2000 °C. After heat treatment for 40 s, it is taken out. At this time, the diamond at the pore defects of the twinned layer undergoes in-situ phase transformation to produce low-density sp2 carbon. The sp2 carbon expands in volume and accumulates in the pores in the form of a wedge, increasing the local stress of the diamond, thereby enhancing the strength of the diamond. Compared with the diamond without in-situ phase transformation, the strength is increased by 58.5%.

[0035] As described above, the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention can easily think of changes or substitutions, which should all be covered by the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims described above.

Claims

1. A multi-layer diamond phase change strengthening method, characterized in that: include: Step S1, first grinding the substrate with diamond powder, and then ultrasonically cleaning the substrate with anhydrous ethanol and deionized water to remove the powder on the surface of the substrate; Step S2, regulating the zeta potential of the substrate and preparing a diamond seed crystal suspension that matches the zeta potential of the substrate, and sowing the diamond seed crystals on the substrate by ultrasound; Step S3, performing microwave plasma chemical vapor deposition on the substrate seeded with diamond seed crystals to prepare a diamond layer without hole defects; Step S4, periodically changing the microwave power to prepare a twin diamond layer containing hole defects on a diamond layer without hole defects; Step S5, alternately repeating steps S3 and S4 to obtain a multilayer diamond in which diamond layers without hole defects and twin diamond layers containing hole defects appear alternately; Step S6, placing the multi-layer diamond in a vacuum heating device to perform heat treatment and strengthen the multi-layer diamond.

2. The method according to claim 1, characterized in that In step S1, the substrate is selected from a Si substrate.

3. The method according to claim 1, characterized in that Step S2 includes: soaking the Si substrate and the oxygen-terminated diamond seed crystal in a polydimethyl ammonium chloride solution for 10 to 50 minutes, so that the zeta potential of the substrate is 30 to 60 mV and the potential of the seed crystal is -30 to -60 mV, and then ultrasonicating at a power of 80 to 300 W for 10 to 60 minutes.

4. The method according to claim 1, characterized in that Step S3 includes: placing the substrate seeded with diamond seed crystals in a microwave plasma chemical vapor deposition chamber, introducing hydrogen and slowly increasing the microwave power, controlling the chamber pressure and substrate temperature, and then introducing high-purity oxygen for etching for 10 to 50 minutes, with the proportion of oxygen in hydrogen being 0.2 to 0.5%; after the etching is completed, methane is introduced into the chamber to prepare a diamond layer without hole defects.

5. The method according to claim 4, characterized in that In step S3, the process parameters of microwave plasma chemical vapor deposition are set as follows: the total gas flow rate is 200-600 sccm, the proportion of CH4 in the gas is 1%-5%, the gas pressure is 10-20 kPa, and the deposition temperature is 700-900°C; when the microwave frequency is 915 MHz, the microwave power range is 30-80 kW; when the microwave frequency is 2.45 GHz, the microwave power range is 2-10 kW.

6. The method according to claim 1, characterized in that In step S4, the periodic change of microwave power includes: when the microwave frequency is 915 MHz, the initial microwave power is set in the range of 35 to 60 kW; when the microwave frequency is 2.45 GHz, the initial microwave power is set in the range of 3 to 7.5 kW, so that the microwave power is periodically changed 3 to 300 times per minute in the range of -30% to +30% in the form of a sine wave.

7. The method according to claim 1, characterized in that In step S5, the thickness of the diamond layer without hole defects is ≥12 μm, the thickness of the twin diamond layer with hole defects is ≥10 μm, and the number of alternating layers is ≥1.

8. The method according to claim 1, characterized in that In step S6, the multilayer diamond is placed in a vacuum heating device and heated at a pressure of 3 to 7 kPa and a temperature of 1500 to 2000° C. for 20 to 60 seconds.

9. The multilayer diamond prepared by the method according to any one of claims 1 to 8, characterized in that: The strength of multilayer diamond reaches 1.1GPa.

10. Use of the multilayer diamond according to claim 9 in the fields of abrasive tools, cutting tools and industrial processing.

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