A method for corona discharge ion wind assisted chemical mechanical polishing processing of ceramics

Abstract

The application discloses a kind of corona discharge ion wind auxiliary chemical mechanical polishing processing method for ceramic, comprising the following steps: step S1, ceramic workpiece is immersed in alkaline abrasive liquid;Step S2, ion wind is released using ion wind generating device, ceramic workpiece is in ion wind covered area, ion wind generating device is installed in the spindle support of grinding machine tool, ion wind generating device moves together with spindle, so that ion wind released by ion wind generating device is aligned with the processing area of ceramic workpiece in real time;Step S3, active oxygen free radicals contained in ion wind dissolve into alkaline abrasive liquid, and continuously occur chemical reaction with ceramic workpiece surface in processing process and produce soft layer, under the stable state of ion wind, ceramic workpiece surface is polished.The application provides a kind of corona discharge ion wind auxiliary chemical mechanical polishing processing method for ceramic, improves material removal efficiency, while improving surface quality and inhibiting surface damage, and regulates wettability.

Description

Technical Field

[0001] This invention relates to the field of polishing technology, and more specifically, to a corona discharge ion wind-assisted chemical mechanical polishing method for ceramics. Background Technology

[0002] Silicon nitride ceramics, as a typical hard and brittle material, have always faced a key bottleneck in efficient and low-damage precision machining, hindering their widespread application in related industries. In traditional machining processes, the material surface is prone to microcracks, pits, and other damage layers due to brittle fracture, severely impacting the fatigue strength, corrosion resistance, and other service performance of parts. Currently, chemical mechanical polishing (CMP) can be used for such hard and brittle materials. Its core mechanism lies in the chemical reaction between the abrasive slurry and the workpiece surface to generate a softer modified layer, thereby changing the material removal method from brittle fracture to plastic removal, thus suppressing surface damage and obtaining a high-quality surface. However, existing CMP processes have the following shortcomings: First, the ability of simple chemical action to modify the surface of inert ceramic materials such as silicon nitride is limited, resulting in a slow and thin modified softened layer formation, making it difficult to further improve material removal efficiency and surface integrity. Second, this process struggles to effectively control the wettability of the processed surface, limiting its application in specific fields such as biomedicine and microfluidics. Therefore, how to develop a new processing method that can achieve efficient and low-loss processing of silicon nitride ceramics by enhancing the modification and softening effect, and simultaneously control its surface wettability to meet diverse application needs, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a corona discharge ion wind-assisted chemical mechanical polishing method for ceramics, which improves material removal efficiency, improves surface quality, inhibits surface damage, and regulates wettability.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: a corona discharge ion wind-assisted chemical mechanical grinding and polishing method for ceramics, comprising the following steps: Step S1, immersing the ceramic workpiece in an alkaline abrasive solution; Step S2, releasing ion wind using an ion wind generator, with the ceramic workpiece positioned within the ion wind coverage area, the ion wind generator mounted on the spindle support of the grinding machine tool, the ion wind generator moving together with the spindle so that the ion wind released by the ion wind generator is aligned with the processing area of ​​the ceramic workpiece in real time; Step S3, the active oxygen free radicals contained in the ion wind dissolve in the alkaline abrasive solution and continuously react chemically with the surface of the ceramic workpiece during the processing to produce a soft layer, and grinding and polishing the surface of the ceramic workpiece under a stable ion wind condition.

[0005] Furthermore, the pH value of alkaline abrasive slurry is 9-12.

[0006] Furthermore, the ceramic workpiece is made of silicon nitride ceramic, and the ion wind contains active oxygen free radicals •O. + Alkaline abrasive slurries contain hydroxide ions (OH-). - The reaction equation with the ceramic workpiece is: O 2 +strong electric field→2•O + +2e - Si3N4+6•O + →3SiO2 + 2N2↑, SiO2 + 2OH - →SiO3 2- +H2O.

[0007] Furthermore, the grinding rod passes through the ion wind generator, and the top of the grinding rod is mounted on the spindle of the machining center. The grinding rod can rotate along its own axis. The grinding rod is made of an insulating rigid material. The ion wind generator includes a top cover, a base plate, electrode needles, and a flow guide shroud. The top cover, base plate, and flow guide shroud are all made of insulating material. The electrode needles are located on the radial outer side of the grinding rod, and there is a gap between the electrode needles and the grinding rod. Multiple electrode needles are evenly distributed along the circumference of the grinding rod. The flow guide shroud is located below the electrode needles, and the bottom of the flow guide shroud has an opening. When the electrode needles are energized, they release ion wind.

[0008] Furthermore, the grinding rod is made of alumina ceramic.

[0009] Furthermore, the inner wall of the fairing is conical, with its smaller end facing downwards.

[0010] Furthermore, the electrode needle is connected to the positive terminal of an external power supply, and the negative terminal of the power supply is grounded. The power supply is a DC high-voltage power supply with a voltage of 5kV to 20kV.

[0011] Furthermore, an ammeter is used, with its negative terminal grounded and its positive terminal connected to the outer sidewall of the abrasive slurry tank used to hold the alkaline abrasive slurry.

[0012] Furthermore, an electrostatic tester is used, with the test head of the electrostatic tester facing the bottom of the grinding rod.

[0013] Furthermore, a pH meter was used, with the test head of the pH meter immersed in an alkaline abrasive solution.

[0014] In summary, the present invention has the following beneficial effects:

[0015] 1. The role of the ion wind generated by corona discharge is twofold. First, the active oxygen free radicals contained in the corona discharge ion wind react with the workpiece surface to form a soft layer, which can reduce grinding resistance and energy consumption, thereby improving material removal efficiency, surface quality, and inhibiting subsurface damage. Second, the positive charge contained in the ion wind can attach to the abrasive particles in the abrasive slurry, making them carry the same charge. The electrostatic repulsion between particles can achieve uniform dispersion of abrasive particles, effectively avoiding agglomeration and thus reducing the generation of surface defects such as large scratches and large pits.

[0016] 2. In this invention, the grinding and polishing process and the corona discharge ion wind generator are integrated into the same equipment, which can simultaneously complete material removal, surface quality improvement and surface wettability control in a designated area (partial or overall of the workpiece), significantly shortening the production process and improving processing efficiency.

[0017] 3. During the ion wind assisted processing generated by corona discharge, on the one hand, the active free radicals in the ion wind that have not participated in the chemical reaction will quickly recombine with gas molecules and become deactivated after processing, causing the pH value of the abrasive slurry to automatically return to its initial level after processing, greatly reducing chemical corrosion to equipment and the environment. On the other hand, the corona discharge system adopts a unipolar open circuit design, with an operating current of only microamps, and no harmful substances are left or released during the processing, combining high operational safety with environmental friendliness. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the structure of an embodiment;

[0019] Figure 2 A surface view of the workpiece;

[0020] Figure 3 This is another surface view of the workpiece;

[0021] Figure 4 This is a contact angle detection diagram for a workpiece;

[0022] Figure 5 This is another contact angle detection diagram for the workpiece.

[0023] Reference numerals in the attached drawings: 1. Top cover; 2. Substrate; 21. Electrode needle; 3. Flow guide; 31. Opening; 4. Grinding rod; 41. Grinding pad; 5. Workpiece; 6. Power supply; 61. Ammeter; 7. Abrasive slurry tank; 71. Fixture; 8. Electrostatic tester; 9. pH tester. Detailed Implementation

[0024] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] like Figure 1 As shown in the figure, this embodiment discloses a corona discharge ion wind assisted chemical mechanical grinding and polishing method for ceramics, which is used to polish and grind workpiece 5. Workpiece 5 is a ceramic workpiece, and its specific material is silicon nitride ceramic.

[0026] The processing method includes the following steps:

[0027] Step S1: Immerse the workpiece 5 in an alkaline abrasive solution. Specifically, the alkaline abrasive solution is placed in the abrasive solution tank 7. The pH value of the alkaline abrasive solution is 9-12. Within this pH range, subsequent processing of the workpiece 5 under the ion wind environment generated by corona discharge achieves a high-efficiency and low-loss processing effect. This effect is not achieved by using acidic abrasive solutions or alkaline abrasive solutions with unsuitable pH values. Specifically, the alkaline diamond abrasive solution is prepared by mixing 10wt% of 0.5μm diamond abrasive particles, 15% of 28μm diamond abrasive particles, and 5% of 60μm diamond abrasive particles with a diluent, and adding alkaline solutions such as NaOH to adjust the pH value to 9-12.

[0028] An abrasive slurry tank 7 is installed on the machine tool worktable, and a fixture 71 is installed inside the abrasive slurry tank 7 for clamping the workpiece 5. In another embodiment, the workpiece 5 can be coated with alkaline abrasive slurry by spraying it onto its surface, and the alkaline abrasive slurry is continuously replenished to the machined surface during the machining process of the workpiece 5.

[0029] Step S2: An ion wind generator is used to release ion wind. The workpiece 5 is located within the ion wind coverage area. The ion wind generator is mounted on the spindle support of the grinding equipment and moves together with the spindle to ensure that the ion wind released by the generator is aligned with the processing area of ​​the workpiece 5 in real time. This allows the reactive oxygen free radicals contained in the ion wind to react more precisely with the surface of the workpiece 5 in real time. The positively charged particles contained in the ion wind dissolve in the alkaline abrasive liquid and adhere to the surface of the workpiece 5. By changing the surface energy of the workpiece 5, the wettability of the workpiece 5 surface can be controlled.

[0030] Specifically, the ion wind generator includes a top cover 1 and a base plate 2. Both the top cover 1 and the base plate 2 are made of insulating materials, preferably polylactic acid. The top cover 1 is fixedly connected to the machine tool spindle support, but does not rotate with the machine tool spindle. The base plate 2 is fixedly mounted on the top cover 1, and electrode needles 21 are mounted on the base plate 2. The electrode needles 21 are fixedly inserted into the base plate 2, with the bottom tip of the electrode needles 21 located below the base plate 2. The bottom (tip) of the electrode needles 21 is the core area of ​​corona discharge. After the electrode needles 21 are energized, they ionize the air under a high-voltage electric field to generate ion wind (containing active oxygen free radicals and positively charged ions). Under the action of the electric field force, the ion wind automatically diffuses to the surface of the workpiece 5 below. Its flow field distribution is guided and constrained by the flow guide structure, and its flow velocity mainly depends on the power supply voltage.

[0031] The bottom tip of the electrode needle 21 extends 5mm-10mm beyond the substrate 2, which can generate a better ion wind effect and protect the equipment. If the extension length is too small (<5mm), the air ionization area is small, resulting in insufficient ion wind generation, reducing the efficiency of the chemical reaction, and the surface of the substrate 2 may be burned by occasional electric sparks; if the extension length is too large (>10mm), it creates structural redundancy, increases the size of the ion wind generator, and the electrode needle is prone to bending and deformation.

[0032] Electrode needles 21 are located radially outside the grinding rod 4, with a gap between them. Multiple electrode needles 21 are evenly distributed along the circumference of the grinding rod 4. The electrode needles 21 are made of tungsten steel, with a conical tip pointing downwards. Tungsten steel possesses high strength, high hardness, high temperature resistance, and excellent conductivity, and can withstand high-voltage electric fields, reducing tip wear or melting. Preferably, in this embodiment, there are 10 electrode needles 21. The needle shank diameter is 0.5 mm, the total length is 20 mm, the tip length is 7 mm, the tip radius is 0.01 mm, the tip cone angle is 5°, and the radius of the circumferential array of electrode needles is 17 mm. This ensures an appropriate gap between adjacent electrode needles; too small a gap can easily generate electric sparks and burn the equipment.

[0033] According to the principle of corona discharge, the smaller the radius of curvature and the narrower the cone angle at the tip of a conductor, the higher the local electric field strength. A needle tip radius of 0.01mm (minimal radius of curvature) combined with a 5° narrow cone angle allows a large amount of charge generated by a high-voltage electric field (5kV-20kV) to quickly converge at the tip, forming a strong local electric field. This field can efficiently ionize surrounding air molecules (mainly oxygen) at room temperature and pressure, rapidly generating a large number of positively charged reactive oxygen free radicals, significantly improving corona discharge efficiency and avoiding problems such as insufficient ionization and low ion wind generation due to electric field dispersion.

[0034] The combination of a 5° narrow cone angle and a 0.01mm tip radius allows for precise control of the electric field concentration range, confining the discharge process to a localized area around the tip and creating a gentle corona discharge (microampere level). If the cone angle is too large (e.g., >10°) or the tip radius is too large (e.g., >0.05mm), the electric field will be dispersed over a larger area of ​​the tip, increasing the ionization threshold of the air and reducing the efficiency of ion wind generation.

[0035] The positive terminal of power supply 6 is connected to the end of electrode needle 21 (i.e., the tip of electrode needle 21). Power supply 6 is a DC high-voltage power supply, and its negative terminal is grounded. The voltage of power supply 6 ranges from 5kV to 20kV to ensure a suitable flow rate for the generated ion wind. Furthermore, power supply 6 forms an open-loop circuit, not a closed-loop circuit; only in the open-loop circuit state can corona discharge be generated and ion wind produced. In addition, the open-loop circuit of the high-voltage power supply provides better safety for equipment and personnel, greatly reducing the occurrence of electric shock accidents.

[0036] The ion wind generator includes a flow guide shroud 3, which is made of environmentally friendly insulating material (such as polylactic acid). The flow guide shroud 3 is located below the electrode needle 21. The inner side of the flow guide shroud 3 is a conical surface with the smaller end facing down. The bottom of the flow guide shroud 3 has an opening 31. When the electrode needle 21 is energized, it generates corona discharge and forms an ion wind inside the flow guide shroud 3. The inner conical surface and the opening 31 are used together to regulate the ion wind flow field, prevent its diffusion, and focus it on the processing area to ensure that there is a high density of active oxygen free radicals in the local space, so as to ensure the chemical reaction rate.

[0037] When using the ion wind generator, after the electrode needle 21 is connected to the positive terminal of the power supply 6, the corona discharge effect is maintained for more than 10 minutes to allow the ion wind release to stabilize before proceeding with subsequent grinding operations. This state is the stable state of the ion wind.

[0038] The grinding rod 4 passes through the ion wind generator and the two are coaxial. The top of the grinding rod 4 is mounted on the spindle of the machining center. Driven by the spindle, the grinding rod 4 can rotate along its own axis to grind the workpiece 5 located below the grinding rod 4.

[0039] A grinding pad 41 is installed at the bottom of the grinding rod 4. The grinding rod 4 is made of a material with good insulation and high rigidity to withstand a certain degree of impact and loading force during processing, while avoiding conductivity and improving safety. Alumina ceramic is preferred here. The grinding pad 41 can be made of polyurethane, felt, diamond film, sandpaper, or a fixed abrasive disc. The distance between the bottom of the grinding pad 41 and the bottom of the electrode needle 21 is 10mm-50mm. During grinding, the grinding pad 41 rotates at high speed (3000rpm-24000rpm) with the grinding rod 4. The 10mm-50mm distance allows sufficient space for corona discharge and ion wind flow, ensuring efficient and stable ion wind output while avoiding the generation of electric sparks and ensuring long-term safe operation of the device. The ion wind (containing reactive oxygen free radicals) released by electrode needle 21 needs to be transported from the needle tip to the surface of workpiece 5 to participate in the chemical reaction with silicon nitride ceramic in the abrasive slurry (generating a soft SiO2 layer; if the alkaline abrasive slurry contains NaOH, the substance generated on the surface of silicon nitride ceramic is sodium silicate Na2SiO3, which is also easily soluble in water, forming a gel-like soft substance). If the spacing is too large, the voltage threshold of ionized air will be greatly increased, making it difficult to generate corona discharge efficiently. Furthermore, the ion wind will diffuse and be lost during transport, and the concentration of reactive oxygen free radicals will decrease significantly, ultimately resulting in insufficient formation of the soft layer, thus reducing material removal efficiency and failing to suppress surface microcracks. If the spacing is too small, it will easily cause electric sparks due to the splashing of the abrasive slurry, burning the equipment and workpiece. A spacing of 10mm-50mm allows the ion wind, under the converging effect of the guide shroud 3, to accurately cover the grinding and polishing area with a suitable concentration, ensuring a sufficient and uniform chemical reaction and guaranteeing the safe, stable, and long-term operation of the device.

[0040] In step S3, the grinding rod 4 starts to rotate, and the spindle is controlled to move along a predetermined trajectory. At the same time, the ion wind generator moves synchronously to grind and polish the designated area on the surface of the workpiece 5 (i.e., the area directly opposite the ion wind). The coverage area of ​​the ion wind can be precisely positioned on the designated area on the surface of the workpiece 5 (i.e., a local area) or can completely cover the surface of the workpiece 5 (i.e., the whole surface).

[0041] Specifically, ion wind contains reactive oxygen free radicals •O + Alkaline abrasive slurries contain hydroxide ions (OH-). - The specific reaction equation with the ceramic workpiece is: O2 + strong electric field → 2•O + +2e - Si3N4+6•O + →3SiO2 + 2N2↑, SiO2 + 2OH - →SiO3 2- +H2O.

[0042] In this step, an ammeter 61 (microamplitude) is used. The negative terminal of the ammeter 61 is grounded, and the positive terminal is connected to the outer sidewall of the abrasive slurry tank 7 to monitor the current during the processing. An electrostatic tester 8 is used, with its test head facing the bottom of the grinding rod 4, to monitor the electrostatic potential and charge on the workpiece surface. When the current reaches 8 μA or higher and the electrostatic potential reaches 5 kV or higher, it is determined that ion wind has effectively occurred, so as to monitor the ion wind status during the grinding process.

[0043] A pH meter 9 is used, fixed to the machine tool table. The test head of the pH meter 9 is immersed in the alkaline abrasive slurry to monitor the pH value of the abrasive slurry during processing, thereby indirectly monitoring the generation of chemical reactions. When the pH value drops by more than 1 compared to the initial value, the process can reflect and determine the effective enhancement of the chemical reaction by the ion wind.

[0044] Initially, the pH value begins to decrease as ion wind occurs and reactive oxygen species are injected. After about 10 minutes, the consumption and injection of reactive oxygen species reach equilibrium, and the pH value also reaches a stable state, decreasing by 1 to 2 compared to the initial value.

[0045] During processing, the hydroxide ions in the alkaline abrasive slurry are consumed as they participate in the reaction, but the amount is very small. Only appropriate replenishment of the abrasive slurry is needed to maintain the pH value. The pH meter 9 can be used to replenish the slurry as needed to maintain the pH value.

[0046] like Figure 2 As shown, under a voltage of 6kV, after the above operating steps, the surface roughness of workpiece 5 can reach Sa12.063nm; Figure 3 As shown, under conventional polishing conditions, the surface roughness of workpiece 5 is Sa 23.830 nm. Figure 4 As shown, under a voltage of 6kV, the initial contact angle between the workpiece 5 obtained through the above operating steps and the artificial simulated body fluid can reach 64.8°; while as Figure 5 As shown, the initial contact angle of workpiece 5 obtained under normal conditions was 91.7°. The release of charged ion wind through corona discharge imparted good hydrophilicity to the material surface. Scanning electron microscopy revealed the formation of micro- and nano-scale grooves and pits on the material surface. The morphology of these grooves and pits, along with the hydrophilicity to simulated body fluids, were obtained. When used in orthopedic implants, this material helps promote osteoblast adhesion and growth, thereby accelerating bone integration and healing. These results indicate that using corona discharge ion wind for polishing helps reduce roughness, improve surface quality, and enhance surface hydrophilicity.

[0047] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for corona discharge ion wind-assisted chemical mechanical polishing of ceramics, characterized in that, Includes the following steps: Step S1: Immerse the ceramic workpiece in the alkaline abrasive solution; Step S2: Use an ion wind generator to release ion wind. The ceramic workpiece is in the ion wind coverage area. The ion wind generator is installed on the spindle support of the grinding machine tool. The ion wind generator moves together with the spindle so that the ion wind released by the ion wind generator is aligned with the processing area of ​​the ceramic workpiece in real time. Step S3: The active oxygen free radicals contained in the ion wind dissolve into the alkaline abrasive liquid and continuously react with the surface of the ceramic workpiece during the processing to produce a soft layer. Under the stable state of the ion wind, the surface of the ceramic workpiece is ground and polished.

2. The method for corona discharge ion wind assisted chemical mechanical polishing of ceramics according to claim 1, characterized in that, The pH value of the alkaline abrasive slurry is 9-12.

3. The method for corona discharge ion wind assisted chemical mechanical grinding and polishing of ceramics according to claim 1, characterized in that, The ceramic workpiece is made of silicon nitride ceramic, and the ion wind contains active oxygen free radicals •O. + Alkaline abrasive slurries contain hydroxide ions (OH-). - The reaction equation with the ceramic workpiece is: O 2 +strong electric field→2•O + +2e - Si3N4+6•O + →3SiO2 + 2N2↑, SiO2 + 2OH - →SiO3 2- +H2O.

4. The method for corona discharge ion wind assisted chemical mechanical polishing of ceramics according to claim 1, characterized in that, A grinding rod (4) for grinding ceramic workpieces passes through the ion wind generating device. The top of the grinding rod (4) is mounted on the spindle of the machining center. The grinding rod (4) can rotate along its own axis. The grinding rod (4) is made of insulating rigid material. The ion wind generating device includes a top cover (1), a base plate (2), an electrode needle (21), and a flow guide (3). The top cover (1), the base plate (2), and the flow guide (3) are all made of insulating material. The electrode needle (21) is located on the radial outer side of the grinding rod (4). There is a gap between the electrode needle (21) and the grinding rod (4). Multiple electrode needles (21) are evenly distributed along the circumference of the grinding rod (4). The flow guide (3) is located below the electrode needle (21). The bottom of the flow guide (3) is provided with an opening (31). The electrode needle (21) releases ion wind after being energized.

5. The method for corona discharge ion wind assisted chemical mechanical polishing of ceramics according to claim 4, characterized in that, The grinding rod (4) is made of alumina ceramic.

6. The method for corona discharge ion wind assisted chemical mechanical grinding and polishing of ceramics according to claim 4, characterized in that, The inner wall of the flow guide (3) is a cone, and its smaller end faces downward.

7. The method for corona discharge ion wind assisted chemical mechanical polishing of ceramics according to claim 4, characterized in that, The electrode needle (21) is connected to the positive terminal of the external power supply (6), the negative terminal of the power supply (6) is grounded, and the power supply (6) is a DC high voltage power supply with a voltage of 5kV to 20kV.

8. The method for corona discharge ion wind assisted chemical mechanical polishing of ceramics according to claim 1, characterized in that, An ammeter (61) is used, with its negative terminal grounded and its positive terminal connected to the outer sidewall of the abrasive slurry tank (7) used to hold the alkaline abrasive slurry.

9. The method for corona discharge ion wind assisted chemical mechanical grinding and polishing of ceramics according to claim 4, characterized in that, Using an electrostatic tester (8), the test head of the electrostatic tester (8) is facing the bottom end of the grinding rod (4).

10. The method for corona discharge ion wind assisted chemical mechanical polishing of ceramics according to claim 1, characterized in that, Using a pH meter (9), the test head of the pH meter (9) is immersed in the alkaline abrasive liquid.

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