Production method of self-heating monocrystal diamond for ultra-precision machining tool, tool and ultra-precision cutting method

Abstract

The present application relates to the field of diamond for ultra-precision cutting, and particularly relates to a production method of self-heating monocrystal diamond for ultra-precision machining tool, a tool and an ultra-precision cutting method.A production method of self-heating monocrystal diamond for ultra-precision machining tool, comprising the following steps: S1. providing high-quality monocrystal diamond with a crystal orientation inclination angle of 45-55° as a seed crystal; S2. constructing a hydrogen plasma atmosphere with a hydrogen flow rate of 500±10sccm, and inputting carbon source gas, boron source gas, oxygen, nitrogen and argon; S3. continuously depositing on the surface of the seed crystal for at least 300 hours to obtain a deposited monocrystal diamond with a thickness of not less than 1.1mm; and S4. heat treating the synthesized deposited monocrystal diamond in a pure oxygen environment to obtain a monocrystal diamond with a resistivity of 0.8-2.0Ω·m, and capable of self-heating to 200-500℃ under the action of Joule heating effect after inputting a variable current. The present application uses monocrystal diamond self-heating to realize precise spatial limitation, rapid response and fine regulation of the cutting micro-zone thermal field without an external thermal field, and is convenient for realizing ultra-precision cutting machining of hard and brittle material optical-grade surfaces.

Description

Technical Field

[0001] This invention relates to the field of diamond for ultra-precision cutting, and specifically to a method for producing self-heating single-crystal diamond for ultra-precision machining tools, the tool itself, and the ultra-precision cutting method. Background Technology

[0002] In strategic fields such as infrared detection, laser weapons, and advanced semiconductor manufacturing, core high-end optical components are typically made of hard and brittle materials such as silicon nitride, gallium arsenide, and zinc selenide. These brittle materials are characterized by high hardness, high brittleness, and poor toughness at room temperature and pressure, with their critical depth for plastic deformation typically only tens to hundreds of nanometers. During ultra-precision machining, traditional methods can easily lead to brittle spalling, microcrack propagation, and even fracture of the workpiece surface, easily causing defects such as out-of-tolerance machining shape accuracy and surface / subsurface damage.

[0003] To improve the machinability of hard and brittle materials, existing technologies (such as those disclosed in CN111055012A and CN115625565A) generally soften and regulate the cutting area through an external thermal field to promote the brittle-plastic transition and ductility removal. However, the range of the external thermal field is usually on the millimeter scale, which is severely mismatched with the micro-nano-scale cutting micro-areas required for ultra-precision cutting. It is difficult to achieve precise focusing of the thermal field in the cutting micro-area and dynamic control that follows the tool tip trajectory in real time. Moreover, the uneven power density distribution within the area of ​​the external thermal field can produce unexpected additional thermal modification effects on the machined surface / subsurface micro-areas, making it difficult to achieve non-destructive ultra-precision cutting of typical hard and brittle structures and functional device surfaces. Summary of the Invention

[0004] The purpose of this invention is to provide a method for producing self-heating single-crystal diamond for ultra-precision machining tools that can be used in heat-assisted ultra-precision machining and achieve precise spatial confinement, rapid response, and fine control of the thermal field in the cutting micro-area.

[0005] To achieve the above objectives, this invention employs a method for producing self-heating single-crystal diamond for ultra-precision machining tools, synthesized via microwave plasma-assisted chemical vapor deposition, comprising the following steps:

[0006] S1. Provide high-quality single-crystal diamond with a crystal orientation tilt angle of 45-55° as a seed crystal. The surface and subsurface of the seed crystal are free of dislocations, cracks, pits and other defects, and the growth surface does not contain non-diamond carbon structures.

[0007] S2. Construct a hydrogen plasma atmosphere with a hydrogen flow rate of 500±10 sccm by introducing a carbon source gas, a boron source gas, oxygen, nitrogen, and argon. The carbon source gas includes methane with a flow rate of 35-45 sccm, the boron source gas is borane with a flow rate of 3-5 sccm, the oxygen flow rate is 6-8 sccm, the nitrogen flow rate is 0.5±0.05 sccm, and the argon flow rate is 2±0.1 sccm. The purity of all gases is 99.9999%.

[0008] S3. Under the conditions of temperature 590-980℃, pressure 20-22kPa, and microwave power 5-5.5kW, microwave plasma-assisted chemical vapor deposition is used to continuously deposit on the surface of the seed crystal for at least 300 hours to obtain a deposited single crystal diamond with a thickness of not less than 1.1mm.

[0009] S4. The synthesized deposited single-crystal diamond is heat-treated in a pure oxygen environment at a temperature of 700-800℃ for 1-2 hours to obtain a single-crystal diamond with a resistivity of 0.8-2.0Ω·m, which can self-heat to 200-500℃ under the Joule heating effect after a variable current is applied; wherein, after a fixed current is applied to the single-crystal diamond, the self-heating temperature reaches a steady state.

[0010] Pure diamond has a band gap of approximately 5.47 eV and is non-conductive. This invention constructs impurity energy levels in the single-crystal diamond lattice through shallow-level heteroatomic (boron) doping, thereby narrowing the band gap and enabling single-crystal diamond to acquire electrical properties similar to semiconductors or metals. Furthermore, high-concentration doping of shallow-level impurity boron allows the conductivity of single-crystal diamond to approach that of metallic materials. Based on this, when a controllable current is passed into the interior of the high-concentration boron-doped single-crystal diamond, the single-crystal diamond can form a spatially confined, rapidly responding, and precisely controllable thermal field under the Joule heating effect. When used in cutting tools, the single-crystal diamond obtained by the method of this invention can achieve softening and ductility removal in the cutting micro-region during ultra-precision cutting of hard and brittle materials.

[0011] Ultra-precision cutting using single-crystal diamond as a cutting tool, under self-heating conditions, naturally confines the thermal field to a space of tens of nanometers to micrometers at the tool tip. The thermally affected area completely overlaps with the area where the hard and brittle workpiece material is removed, avoiding the thermal influence of the external thermal field on the machined area of ​​the workpiece. This prevents unexpected additional thermal modification of the machined surface / subsurface micro-regions, thus ensuring the surface machining shape accuracy of the workpiece while transforming the brittle fracture mode of the workpiece material into a ductile shear mode, achieving damage-free ultra-precision machining of optical-grade surfaces of hard and brittle materials.

[0012] The boron-doped single-crystal diamond of the present invention is synthesized by microwave plasma-assisted chemical vapor deposition. This method can achieve diamond epitaxial growth at a lower substrate temperature, reduce thermal stress accumulation, and achieve uniform doping of high-concentration boron in the diamond lattice.

[0013] Currently, there are two main methods for synthesizing high-quality diamond single crystals: high-temperature high-pressure (HTHP) and microwave plasma-assisted chemical vapor deposition (MPCVD). However, HTHP cannot achieve high concentrations (e.g., 500-1000 ppm) of boron doping. During HTHP synthesis, boron tends to agglomerate significantly in the interstitial spaces of the diamond lattice, causing severe lattice distortion. In contrast, while boron also tends to agglomerate during MPCVD, the doping uniformity is significantly improved due to the plasma state of the raw material. Furthermore, large-angle seed crystals and high-concentration oxygen etching can be used in MPCVD to suppress boron agglomeration in the diamond lattice.

[0014] In general, a 0° crystal orientation angle is used in the synthesis of pure or low-concentration boron-doped diamond. However, in step S1 of this invention, a single-crystal diamond with a crystal orientation angle of 45-55° is used. The larger crystal orientation angle allows the doped boron impurities to flow uniformly into the crystal lattice along the diamond growth steps, avoiding the segregation of boron impurities in the single-crystal diamond lattice, thereby improving the doping uniformity of boron impurities.

[0015] This invention determines the boron doping concentration through step S2. The boron doping concentration affects resistivity, but the effect is not linear. If the boron doping concentration is too high, the lattice quality of the single-crystal diamond deteriorates, preventing the cutting edge from being ground to the required level when used as a tool. Conversely, if the boron doping concentration is too low, the resistivity becomes too high, making it impossible to heat the single-crystal diamond through current excitation. This results in the single-crystal diamond tool not reaching the self-heating temperature required to soften brittle workpiece materials. If the boron doping concentration is too low, the single-crystal diamond produced by this invention will exhibit thermosensitive characteristics similar to semiconductor materials (material resistance changes with temperature). In this case, applying current will cause self-heating, leading to changes in its own resistance and making it impossible to maintain a constant heating temperature. Only when the boron doping concentration reaches a certain value will the single-crystal diamond exhibit constant electrical conductivity characteristics similar to metals.

[0016] High-purity hydrogen is used as the hydrogen plasma source. During the synthesis process, the hydrogen plasma promotes the activation of the carbon surface of single-crystal diamond and etches the small amount of amorphous carbon generated during the synthesis, thereby improving the purity and crystallinity of the single-crystal diamond. Methane and borane are decomposed into carbon plasma groups and boron plasma groups under microwave irradiation, and deposited on the seed crystal surface under certain temperature and pressure to form boron-doped single-crystal diamond. High-concentration oxygen plasma selectively accelerates the etching of boron clusters and graphite phases, maintaining excellent lattice integrity while ensuring high doping concentration, thus improving the crystal quality of the single-crystal diamond. High-purity nitrogen is used to increase the growth rate of the single-crystal diamond and repair atomic defects such as dislocations in the lattice during growth. High-purity argon is used to stabilize the plasma environment, maintaining pressure and temperature stability within the plasma atmosphere.

[0017] This invention utilizes the settings in step S3 for continuous deposition synthesis, thereby enabling the production method of this invention to obtain single-crystal diamond suitable for ultra-precision machining tools. The continuous deposition synthesis time is directly proportional to the thickness of the obtained boron-doped single-crystal diamond. The minimum thickness requirement for diamond tools is 1 mm. In order to leave sufficient removal allowance for tool grinding, the thickness of the single-crystal diamond before processing is set to at least 1.1 mm, thus requiring at least 300 hours of continuous deposition synthesis.

[0018] The present invention uses the above steps to produce single-crystal diamond with a resistivity of 0.8-2.0 Ω·m. When this single-crystal diamond is used as a cutting tool, this resistivity range ensures that the tool has a sufficiently high electrical conductivity to achieve efficient Joule heat conversion, while maintaining the excellent properties of diamond itself, such as super hardness, wear resistance, and chemical stability. This overcomes the defect of traditional diamond cutting tools being unable to be electrically heated due to their insulation properties.

[0019] Furthermore, by applying different currents to the interior of the single-crystal diamond, it can self-heat to 200-500℃. This allows for selection of different self-heating temperatures for the single-crystal diamond tool based on the material of the workpiece, enabling ultra-precision machining of various workpiece materials. The single-crystal diamond of this invention can self-heat to different temperatures when a larger current (compared to milliamperes) is applied. With increasing current, it can heat to even higher temperatures, maintaining a steady-state, balanced temperature without significant temperature fluctuations. This prevents electrical breakdown due to excessive terminal voltage, thus enabling the single-crystal diamond of this invention for ultra-precision machining. The heating power of the single-crystal diamond of this invention can be precisely adjusted by the current magnitude, with a response speed reaching the millisecond level, achieving real-time matching of thermal field intensity and cutting conditions.

[0020] Preferably, after step S4, the single-crystal diamond is processed to the required size, and an insulating layer is formed on the surface of the single-crystal diamond.

[0021] After the single-crystal diamond obtained by the production method of this invention is cut and ground to the required shape and size of the cutting tool, an insulating layer is formed on its surface. When the single-crystal diamond tool is used for ultra-precision cutting of conductive workpiece materials, the current path can be completely confined inside the single-crystal diamond tool, without electrical conduction between the tool and the workpiece. This ensures the stable and controllable heating behavior of the single-crystal diamond tool, thereby guaranteeing the ultra-precision machining effect.

[0022] Preferably, the variable current has a range of 0.5-2A.

[0023] By using a current of 0.5-2A, the tool can be kept at an operating temperature of 200-500℃, achieving a balance between heating efficiency and the reliability of single-crystal diamond tools. This ensures the ultra-high precision and operational stability of single-crystal diamond tools in ultra-precision machining. Compared to milliampere-level currents, the 0.5-2A current provides more controllable output, while allowing the single-crystal diamond to self-heat to a relatively high temperature (around 650℃) without causing oxidation.

[0024] Preferably, the boron doping concentration of the single-crystal diamond is 500-1000 ppm.

[0025] Preferably, an insulating layer is formed by ion implantation of nitrogen impurities onto the outer surface of a single-crystal diamond. The ion implantation energy is 300 keV and the implantation metering is 10. 15 -10 16 ions / cm², with an implantation depth of 200±20nm.

[0026] Ion implantation is a non-equilibrium process that can embed nitrogen atoms into the near-surface lattice without altering the surface morphology and geometric precision of the diamond matrix, thus maintaining the nanometer-level sharpness and shape accuracy of the cutting edge. The implantation depth is precisely controllable; 300 keV of energy can cause nitrogen ions to form a modified layer of approximately 200 nm in the diamond, a thickness sufficient to block current without significantly affecting the overall mechanical properties of the tool. The implantation metering is 10... 15 -10 16 The ions / cm² ratio ensures that the nitrogen atom concentration reaches the level required to neutralize the hole carriers formed by boron doping, achieving a surface resistivity improvement to a good insulating effect, while avoiding surface amorphization or excessive residual stress due to excessive implantation. Of the 200nm, 100nm represents the maximum wear limit of the diamond tool, and the remaining 100nm represents the minimum insulation thickness, ensuring surface insulation even after the diamond tool reaches its maximum wear limit.

[0027] Preferably, after forming an insulating layer on the surface of the single-crystal diamond, the single-crystal diamond is heat-treated in an inert gas environment at a temperature of 550-700℃ for 0.5-2 hours.

[0028] The above configuration can intensify the dispersion of nitrogen atoms in the single-crystal diamond lattice and their binding with boron atoms.

[0029] Preferably, in or after step S4, an electrode is disposed on the surface of the single crystal diamond, and the electrode is connected to a current-carrying wire, through which the variable current or fixed current is passed.

[0030] By setting electrodes, good ohmic contact between the energized wire and the single-crystal diamond can be ensured. The electrode area should be as large as possible to allow for higher current values ​​and higher excitation temperatures, thus maintaining the tool's self-heating. The electrode position limits the location where current is introduced into the single-crystal diamond, keeping it away from the cutting edge. This ensures the mechanical strength and thermal stability of the electrical connection area, avoiding negative impacts on the cutting edge of the single-crystal diamond tool. Positioning the electrodes away from the cutting edge's working area ensures no interference or damage to the nanoscale sharp cutting edge, while ensuring efficient heat conduction to the tool tip. Specifically, when setting the electrodes and energized wires first, and then the insulation layer, nitrogen impurities at the electrodes should cover the solder on the electrodes and the energized wires. If insulation is performed first, and then the electrodes and wires are set, the surface of the single-crystal diamond at the electrode location can be ground to remove the insulation layer before setting the electrodes.

[0031] Preferably, the electrode is a multilayer electrode; the multilayer electrode includes a Mo layer and an Au layer, and the multilayer electrode is deposited on the single crystal diamond by an electron beam evaporation process.

[0032] The stacked electrode with Mo and Au layers provides better ohmic contact and lower contact resistance with the single-crystal diamond surface. Furthermore, electron beam evaporation, compared to existing processes like vapor deposition and sputtering, enables better adsorption and fixation of the electrode on the single-crystal diamond surface. The Mo layer, as the inner layer in direct contact with the single-crystal diamond, exhibits lower interfacial thermal stress at high temperatures. Mo also possesses excellent wettability on the single-crystal diamond surface at high temperatures, enabling strong chemical adsorption and metallurgical bonding, ensuring reliable electrode adhesion. The Au layer, as the outer layer, has extremely low resistivity and excellent oxidation resistance, effectively reducing the electrode's own resistance, preventing electrode overheating, and protecting the Mo layer from oxidation and corrosion.

[0033] The present invention also employs a cutting tool, wherein the contact portion of the cutting tool with the workpiece comprises single-crystal diamond produced by the above-described production method.

[0034] This invention also employs an ultra-precision cutting method. Using the aforementioned cutting tool, an electric current is passed into the interior of a single-crystal diamond, causing the single-crystal diamond to heat up under the Joule heating effect. Under the self-heating state of the single-crystal diamond, ultra-precision cutting is performed on the workpiece made of hard and brittle materials. The local thermal softening effect of the cutting micro-region increases the critical cutting depth for the brittle-plastic transition of the workpiece material, thereby achieving ductile domain cutting.

[0035] This invention can produce a self-heating single-crystal diamond. When used in cutting tools, the single-crystal diamond heats itself, achieving precise spatial confinement, rapid response, and fine control of the thermal field in the cutting micro-area without the need for an external thermal field. This significantly improves the critical cutting depth for the brittle-plastic transition of hard and brittle workpiece materials, achieving high-quality ductile removal and facilitating ultra-precision cutting of optical-grade surfaces of hard and brittle materials. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the self-heating cutting tool structure in an embodiment of the present invention.

[0037] Figure 2 This is a schematic diagram of the self-heating tool current excitation principle in an embodiment of the present invention.

[0038] Figure 3 This is a schematic diagram of the synthesis process of high-concentration boron-doped single-crystal diamond in an embodiment of the present invention.

[0039] Figure 4 This is a physical image of a high-concentration boron-doped single-crystal diamond used as a tool blank in an embodiment of the present invention.

[0040] Figure 5 This is a physical image of the single-crystal diamond cutting tool and its cutting edge contour in an embodiment of the present invention.

[0041] Figure 6 This is a graph showing the temperature results of a self-heating cutting single-crystal diamond tool measured by an infrared thermal imager in an embodiment of the present invention.

[0042] Figure 7 This is a temperature rise curve diagram corresponding to different currents when a self-heating cutting single-crystal diamond tool is applied to it in an embodiment of the present invention.

[0043] Figure 8 This is a physical image of the cutting platform used in the embodiment of the present invention to cut zinc selenide workpieces with a self-heating single-crystal diamond tool.

[0044] Figure 9 These are experimental results of chip microstructure obtained by using a self-heating single-crystal diamond tool and a non-heating diamond tool during the cutting of zinc selenide workpieces in this embodiment of the invention.

[0045] Figure 10These are the surface contour morphology results obtained by using a self-heating single-crystal diamond tool and a non-heating diamond tool during the cutting of zinc selenide workpieces in this embodiment of the invention.

[0046] Figure 11 This is a diagram showing the main cutting force measured during the cutting of zinc selenide workpieces in this embodiment of the invention, using a self-heating single-crystal diamond tool and a non-heating diamond tool respectively. Detailed Implementation

[0047] The present invention will now be further described with reference to the accompanying drawings and specific embodiments.

[0048] This embodiment discloses a method for producing self-heating single-crystal diamond for ultra-precision machining tools, such as... Figure 3 As shown, the synthesis is carried out using a microwave plasma-assisted chemical vapor deposition process, including the following steps S1-S4.

[0049] S1. Seed crystal pretreatment. High-quality single-crystal diamond with a size of 6×6×0.5mm and a crystal tilt angle of 45-55° is used as seed crystal 9. Compared with the 0° crystal tilt angle seed crystal used in conventional diamond synthesis, high concentration of boron impurities will change the activation kinetics of the carbon plasma atmosphere for diamond growth. In this embodiment, a 50° crystal tilt angle seed crystal is used. The larger tilt angle can induce a significant step flow growth mode, so that the boron doped atoms are arranged in an orderly manner along the growth step front, significantly suppressing the impurity segregation and local stress concentration caused by two-dimensional island nucleation, thereby achieving high-concentration uniform doping of boron atoms in the diamond lattice. Before the synthesis begins, the surface of the seed crystal is etched by a plasma of mixed hydrogen and oxygen to remove contaminants from the growth surface. The high-quality single-crystal diamond is a single-crystal diamond with no microscopic defects such as dislocations, cracks, and pits on the surface / subsurface, and no non-diamond carbon structure on the growth surface.

[0050] S2. A high-purity hydrogen plasma atmosphere 6 (hydrogen flow rate 500 ± 10 sccm) is constructed on a molybdenum growth substrate 10 to allow single-crystal diamond to be deposited and grown in the high-purity hydrogen plasma atmosphere 6, using high-purity hydrogen as the hydrogen plasma source. During the synthesis process, the hydrogen plasma can promote the activation of the carbon surface of the diamond and etch the small amount of amorphous carbon generated during the diamond synthesis process, thereby improving the purity and crystallinity of the single-crystal diamond.

[0051] In the synthesis of this single-crystal diamond, high-purity methane is used as the carbon plasma source, with a methane flow rate of 35-45 sccm, preferably 40 sccm. Borane (B₂H₆) is used as the boron plasma source, with a boron flow rate of 3-5 sccm, preferably 4 sccm. Methane and boronane are decomposed into carbon plasma groups 7 and boron plasma groups 8 under microwave irradiation, and then deposited on the surface of seed crystal 9 under specific temperature and pressure to form boron-doped diamond.

[0052] This embodiment innovatively employs high-purity oxygen, introducing 6-8 sccm of high-purity oxygen (conventional diamond synthesis only uses 0.5-2 sccm of oxygen). Simultaneously, 0.5 sccm of high-purity nitrogen is introduced to increase the growth rate of single-crystal diamond and repair atomic defects such as dislocations in the crystal lattice during growth. 2 sccm of high-purity argon is introduced to stabilize the plasma environment, maintaining pressure and temperature stability within the plasma atmosphere. The purity of the hydrogen, methane, borane, nitrogen, and argon gases mentioned above is all 99.9999% (6N).

[0053] In this embodiment, high-purity oxygen at 7 sccm can be introduced. Under microwave irradiation, the oxygen decomposes into oxygen plasma groups 11. Compared to the low-concentration oxygen plasma growth atmosphere used in the synthesis of pure or low-concentration boron-doped diamond, the high-concentration boron impurities significantly alter the chemical balance of the growth plasma atmosphere during the synthesis of high-concentration boron-doped single-crystal diamond. This causes the nucleation of carbon plasma ions on the seed crystal surface to favor the formation of sp² hybridized graphite phases. Furthermore, the high-concentration boron impurities tend to agglomerate within the diamond lattice, forming clusters and disrupting the diamond lattice structure. The high-concentration oxygen plasma can selectively accelerate the etching of boron clusters and graphite phases, maintaining excellent lattice integrity while ensuring high doping concentration, thereby improving the quality of the diamond crystal.

[0054] S3. In the synthesis of this single-crystal diamond, the temperature range of the molybdenum growth substrate 10 is 590-980℃, preferably 950℃ in this embodiment. The synthesis pressure range is 20-22kPa, preferably 21kPa in this embodiment. The microwave power is set to 5.5kW, and the continuous deposition synthesis time is at least 300 hours to obtain boron-doped single-crystal diamond with a thickness of at least 1.1mm. The continuous deposition synthesis time is directly proportional to the thickness of the obtained boron-doped single-crystal diamond. The minimum thickness requirement for the diamond tool is 1mm. In order to leave sufficient removal allowance for tool grinding, the thickness of the single-crystal diamond before processing is set to be at least 1.1mm, hence the need for at least 300 hours of continuous deposition synthesis.

[0055] S4. The synthesized deposited single-crystal diamond was heat-treated at 750℃ for 1 hour in a pure oxygen environment to promote the dispersion of boron atoms in the diamond lattice, further optimizing its electrical properties and enhancing its conductivity. The final product was a single-crystal diamond with a resistivity of 0.8-2.0 Ω·m, which could self-heat to 200-500℃ under the Joule heating effect after a variable current was applied. The self-heating temperature of this single-crystal diamond reached a steady state after a fixed current was applied. This steady state, rather than a constant value, indicates a small real-time temperature error that does not affect ultra-precision machining.

[0056] After the single-crystal diamond is synthesized, it is laser-cut into tool blanks with dimensions of 2.5×2.5×1.1mm, such as... Figure 4 As shown in the figure. The sample was then placed in a standard solution of nitric acid and sulfuric acid (volume ratio approximately 2:1) and cleaned at 120°C for 4 hours. After acid washing, the sample was ultrasonically cleaned for 15 minutes using an organic solvent (such as acetone or isopropanol). Following this, the sides of the diamond material were cleaned again using argon ion sputtering. During argon ion sputtering, the argon ion flow rate was 20 sccm, the working gas pressure was 1 mTorr, the sputtering voltage was 300 V, the argon ions were sputtered perpendicularly at a 0° incident angle, and the sputtering time was 1 minute. Figure 4 The length of the red line in the diagram indicates that the actual length is 0.5mm, serving as a reference for the actual size; ↓A represents a view perpendicular to the tool surface, and AA represents a view perpendicular to the side of the tool.

[0057] The above operations aim to completely remove amorphous carbon and graphite formed on the diamond surface during the growth process and laser cutting. Since a Mo / Au multilayer electrode needs to be deposited on the side surface of the single-crystal diamond subsequently, and an electrical path needs to be formed between it and a nickel-chromium alloy wire for current input, completely removing the amorphous carbon and graphite from the side surface of the single-crystal diamond effectively ensures the subsequent deposition of a dense Mo / Au multilayer electrode on this surface.

[0058] The aforementioned single-crystal diamond tool blanks are ground on a commercial grinding machine to produce ultra-precision cutting tools with nanoscale defect-free cutting edges. For example... Figure 5 As shown, the tool has a rake angle of 0°, a clearance angle of 7°, and a tip angle of 75°. Atomic force microscopy measurements reveal that the tool possesses a high-quality, defect-free cutting edge with a radius of approximately 35 nm (35 ± 5 nm). In ultra-precision machining, the radius of the cutting edge must be less than half the thickness of the material to be removed from the workpiece surface. Generally, the minimum thickness to be removed in ultra-precision machining is 100 nm; therefore, a cutting edge radius of 35 nm ensures the success of ultra-precision cutting.

[0059] Due to the high conductivity of high-concentration boron-doped single-crystal diamond tools, the outer surface of the diamond tool needs to be insulated to prevent electrical conduction between the workpiece and the tool when cutting various conductive workpieces. In this embodiment, nitrogen impurities are implanted into the outer surface of the tool using ion implantation technology. Based on the hole-electron neutralization effect between boron and nitrogen atoms, the insulation of the boron-doped diamond outer surface is achieved. Specifically, in a high vacuum environment (<10⁻⁶ ppm), the insulation is achieved... -6 Torr employs high-purity nitrogen ions with single-charge N+ or double-charge N2+ as the ion source for ion implantation on the tool surface. The particle implantation energy is 300 keV, and the ion implantation metering is 10. 15 -10 16 ions / cm 2 The implantation angle is 0° and the beam diameter is 0.5 mm to ensure uniform ion distribution over a large area. The ion implantation depth is approximately 200 nm (i.e., 200 ± 20 nm). After the ion implantation process is completed, the tool is placed in an inert gas environment at 600°C for 1 hour for heat treatment to intensify the dispersion of nitrogen atoms and their combination with boron atoms.

[0060] Depend on Figure 1 As shown, the single-crystal diamond tool produced by the method of this embodiment is brazed onto a silicon nitride ceramic tool holder 2. An electrode 3 is deposited on each of the two opposite sides of the single-crystal diamond tool 1, away from the cutting edge. Electrode 3 is a Mo / Au multilayer electrode. A current-carrying wire 4 is brazed to each of the two electrodes 3. The current-carrying wire 4 is a 0.4mm diameter nickel-chromium alloy wire, capable of carrying a current of 2.0 amperes for an extended period in a high-temperature environment up to 800°C. Figure 2 As shown, the energized wire 4 is connected to a commercial DC power supply 5. Before connecting the energized wire 4, electrodes 3 are deposited in an area of ​​approximately 0.8 × 1 mm on two opposing side surfaces of the tool 1, offset from the cutting edge, using an electron beam evaporation process. A 100 nm thick Mo layer is deposited on the tool side surface from electrode 3, and a 150 nm thick Au layer is deposited on top of the Mo layer. The outer surface of the single-crystal diamond tool 1 is provided with nitrogen impurities implanted using ion implantation technology. Based on the hole-electron neutralization effect between boron and nitrogen atoms, an insulating layer is formed to prevent electrical conduction between the single-crystal diamond tool 1 and the workpiece during cutting of conductive workpiece materials.

[0061] This embodiment discloses an ultra-precision cutting method using single-crystal diamond obtained by the above-described production method as a cutting tool. An electric current is passed through the single-crystal diamond cutting tool, causing it to heat up under the Joule heating effect. Under this self-heating state, ultra-precision cutting is performed on workpieces made of hard and brittle materials. The localized thermal softening effect in the cutting micro-region increases the critical depth of cut for the brittle-plastic transition of the workpiece material, achieving ductile-domain cutting.

[0062] The following specific examples demonstrate the thermal assistance capability of the aforementioned high-concentration boron-doped single-crystal diamond tool in the ultra-precision cutting process of hard and brittle workpiece materials.

[0063] Before conducting self-heat-assisted cutting experiments with the cutting tool, it is necessary to test the tool's thermal excitation performance, such as... Figure 6 As shown, the self-heating temperature of the cutting tool was measured using an infrared thermal imager. Figure 7 This is a data curve plotted based on the self-heating temperature values ​​of the tool measured under different current conditions.

[0064] Figure 8 This is a photograph of a typical hard and brittle workpiece material, zinc selenide, being machined using the tool described in this embodiment with ultra-precision cutting.

[0065] Figure 9 The images show the chip morphology of a zinc selenide workpiece during ultra-precision cutting under both with and without heat assistance, captured by a high-speed camera. Cutting parameters were: spindle speed 1000 rpm, feed rate 0.4 mm / min, depth of cut 300 nm. The zinc selenide workpiece diameter was 50 mm. As shown in the figures, with the aid of tool self-heating, the machining mode of the zinc selenide workpiece changed from brittle fracture to ductile removal.

[0066] Figure 10 The surface morphology of zinc selenide workpieces measured by white light interferometer under conditions of machining with and without thermal excitation, and the cutting parameters are as follows: Figure 9 Consistent. As shown in the figure, with the assistance of tool self-heating, the surface quality of zinc selenide machining is significantly improved. Compared with the condition without tool self-heating assistance, the surface roughness Ra is improved from 167nm to 35nm.

[0067] Figure 11 The curves showing the uniaxial main cutting force versus cutting time for zinc selenide workpieces under both with and without thermal excitation conditions, measured using a commercial multidimensional force gauge, are shown. Cutting parameters and... Figure 9 Consistent. By Figure 11 It can be seen that with the assistance of the tool's own heating, the cutting force is significantly reduced and exhibits a more stable fluctuation.

Claims

1. A method for producing self-heating single-crystal diamond for ultra-precision machining tools, characterized by synthesis via microwave plasma-assisted chemical vapor deposition (CVA). Includes the following steps: S1. Provide high-quality single-crystal diamond with a crystal orientation tilt angle of 45-55° as a seed crystal. The surface and subsurface of the seed crystal are free of dislocations, cracks, pits and other defects, and the growth surface does not contain non-diamond carbon structures. S2. Construct a hydrogen plasma atmosphere with a hydrogen flow rate of 500±10 sccm by introducing a carbon source gas, a boron source gas, oxygen, nitrogen, and argon. The carbon source gas includes methane with a flow rate of 35-45 sccm, the boron source gas is borane with a flow rate of 3-5 sccm, the oxygen flow rate is 6-8 sccm, the nitrogen flow rate is 0.5±0.05 sccm, and the argon flow rate is 2±0.1 sccm. The purity of all gases is 99.9999%. S3. Under the conditions of temperature 590-980℃, pressure 20-22kPa, and microwave power 5-5.5kW, microwave plasma-assisted chemical vapor deposition is used to continuously deposit on the surface of the seed crystal for at least 300 hours to obtain a deposited single crystal diamond with a thickness of not less than 1.1mm. S4. The synthesized deposited single-crystal diamond is heat-treated in a pure oxygen environment at a temperature of 700-800℃ for 1-2 hours to obtain a single-crystal diamond with a resistivity of 0.8-2.0Ω·m, which can self-heat to 200-500℃ under the Joule heating effect after a variable current is applied; wherein, after a fixed current is applied to the single-crystal diamond, the self-heating temperature reaches a steady state.

2. The production method according to claim 1, characterized in that: After step S4, the single-crystal diamond is processed to the required size, and an insulating layer is formed on the surface of the single-crystal diamond.

3. The production method according to claim 1, characterized in that: The variable current has a range of 0.5-2A.

4. The production method according to claim 1, characterized in that: The boron doping concentration of the single-crystal diamond is 500-1000 ppm.

5. The production method according to claim 2, characterized in that: The insulating layer is formed by ion implantation of nitrogen impurities on the outer surface of the single crystal diamond, the ion implantation energy being 300 keV, the implantation dose being 10 15 -10 16 ions / cm2, and the implantation depth being 200 ± 20 nm.

6. The production method according to claim 5, characterized in that: After forming an insulating layer on the surface of the single-crystal diamond, the single-crystal diamond is heat-treated in an inert gas environment at a temperature of 550-700℃ for 0.5-2 hours.

7. The production method according to claim 6, characterized in that: After step S4, an electrode is disposed on the surface of the single crystal diamond, and the electrode is connected to a current-carrying wire, through which the variable current or fixed current is passed.

8. The production method according to claim 7, characterized in that: The electrode is a multilayer electrode; the multilayer electrode includes a Mo layer and an Au layer, and the multilayer electrode is deposited on the single crystal diamond by an electron beam evaporation process.

9. A cutting tool, wherein the contact portion of the cutting tool with a workpiece comprises single-crystal diamond produced by the production method of any one of claims 1-8.

10. An ultra-precision cutting method, using the tool described in claim 9, passing an electric current into the interior of the single-crystal diamond, causing the single-crystal diamond to heat up under the Joule heating effect, and performing ultra-precision cutting on a workpiece made of hard and brittle material under the self-heating state of the single-crystal diamond, thereby increasing the critical cutting depth for the brittle-plastic transition of the workpiece material through the local thermal softening effect of the cutting micro-region, and realizing ductile domain cutting.

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