A method of metallographic etching of wrought superalloy fastener

Abstract

The application discloses a kind of high temperature alloy fastener metallographic corrosion methods of deformation, comprising the following steps: first, to be tested sample is cut and metallographic inlay, and is carried out rough grinding and fine grinding;Second, the sample in step one is carried out rough polishing and fine polishing;Third, 10g-20g white crystalline powder state superior pure citric acid and 80ml-90ml deionized water are mixed sufficiently after obtaining 10-20% citric acid aqueous solution etchant;Fourth, the sample is placed in metallographic etchant and carries out electrochemical corrosion, to be tested sample as anode, austenitic stainless steel plate as cathode, working voltage is 5V-15V, current is 0.5A-1.3A, temperature is 20℃-30℃, corrosion time is 60s-200s, with anhydrous ethanol cleaning and blow dry, obtain metallographic sample;Fifth, metallographic sample is placed under optical microscope and scanning electron microscope and carries out observation and analysis, judges its grain size grade.The application is quick, efficient, accurate, safe and reliable, suitable for the popularization and use of high temperature alloy fastener metallographic corrosion.

Description

Technical Field

[0001] This invention belongs to the field of metallographic analysis technology, and specifically relates to a metallographic corrosion method for deformed high-temperature alloy fasteners. Background Technology

[0002] Wrought superalloys possess excellent mechanical, oxidation-resistant, and corrosion-resistant properties at high temperatures, and are used in aerospace vehicles, rocket engines, nuclear reactors, and the chemical industry. Based on matrix composition, they are mainly classified into nickel-based superalloys, iron-based superalloys, and cobalt-based superalloys. GH738 is a nickel-based superalloy that hardens through precipitation of the γ′ phase. Carbides mainly segregate at grain boundaries, forming discontinuous carbide particles that prevent grain boundary sliding and crack formation, thus benefiting aging time and ductility. Energy dispersive spectroscopy (EDS) analysis shows two types of carbides: MC-type Ti-rich carbides and M23C6-type Cr-rich carbides. MC-type carbides are mainly distributed within the grains, while M23C6-type carbides are secondary carbides precipitated during aging, mainly distributed in irregular blocky forms at grain boundaries. GH2132 is a Fe-25Ni-15Cr based superalloy. It contains a uniformly dispersed Ni3(Ti,Al) type γ′ phase, as well as TiN and TiC, in a spherical matrix. Trace amounts of M3B2 are present at the grain boundaries, and small amounts of η and L phases may be present near the grain boundaries. GH159 is a novel high-strength multiphase cobalt-based superalloy. It utilizes cold deformation to first induce a cross-network distribution of lamellar ε phase in a face-centered cubic matrix to prevent long-range dislocation movement and thus strengthen the alloy. Further strengthening is achieved through failure treatment, which precipitates a dispersed Ni3X phase. During cold deformation, some of the γ phase undergoes a martensitic transformation into a stable ε phase. The resulting ε phase is lamellar and exhibits a cross-network distribution within the face-centered cubic γ phase grains.

[0003] Currently, wrought superalloys are developing towards higher temperature resistance, precision forming, and lower cost. Through continuous exploration of potential and the adoption of new technologies and processes, the quality and performance of wrought superalloy materials are being improved. The display and measurement of steel grain size is of great significance for judging material quality, verifying the correctness of heat treatment processes, determining grain inheritance, studying the relationship between grain size and properties, and exploring the relationship between mixed grains and flaw detection defects. Therefore, grain size inspection can be used as the first important indicator for aging analysis and material quality assessment. Grain boundaries are weak points in alloys under high temperature and long-term stress. To improve the grain boundary condition, trace amounts of elements such as boron, magnesium, cobalt, and rare earth elements adsorbed at grain boundaries are added to the alloy, causing localized alloying, improving purity, slowing grain boundary diffusion, and strengthening the grain boundaries. There are various methods for grain size display, among which the direct grain boundary display method is relatively accurate. It eliminates the interference of external factors and truly reflects the grain size. However, for the display of grain size of high-temperature alloys, due to factors such as corrosion method and the use of etchant, the grain size often shows twinned grains, which often confuses researchers and makes it difficult to judge when performing failure analysis.

[0004] The commonly used corrosive agent formula is: concentrated hydrochloric acid: water: hydrogen peroxide = 50:50:2. There are also patented formulas: Formula 1: concentrated nitric acid: concentrated hydrochloric acid: distilled water = 1:1:2; Formula 2: copper chloride: concentrated hydrochloric acid: anhydrous ethanol: deionized water = 3-4g: 40-50ml: 40-50ml: 0-50ml; Formula 3: a mixed solution of electrolytic sulfuric acid and phosphoric acid, etc. However, the concentrated hydrochloric acid, concentrated nitric acid, sulfuric acid, and phosphoric acid used in the above corrosive agents are strong acids, which can easily cause harm to the environment and laboratory personnel. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned shortcomings and provide a metallographic etchant and etching method for deformed high-temperature alloy fasteners that is quick to operate, efficient, accurate, safe, reliable, economical and of high quality.

[0006] The objective of this invention and the solution to its main technical problem are achieved by the following technical solution: The present invention provides a metallographic corrosion method for deformed high-temperature alloy fasteners, comprising the following steps: First, the test sample is cut and metallographically inlaid, and then coarsely ground with 120# and 600# sandpaper using an automatic polishing machine, and finely ground with 1500# and 2500# sandpaper. Second, the sample obtained in step one is rough polished with 2.5μm diamond polishing agent using an automatic polishing machine, and then fine polished with 0.3μm diamond polishing agent. Third, prepare the metallographic etchant: weigh 10g-20g of white crystalline powder of superior pure citric acid and place it in a beaker. Add 80ml-90ml of deionized water to the beaker and stir until fully dissolved to obtain a 10-20% citric acid aqueous solution. Fourth, the finely polished sample is placed in a metallographic etchant for electrochemical corrosion. The sample to be tested is used as the anode, and the austenitic stainless steel plate is used as the cathode. The working voltage is 5V-15V, the current is 0.5A-1.3A, the temperature is 20℃-30℃, and the corrosion time is 60s-200s. Then, it is cleaned with anhydrous ethanol and dried to obtain the metallographic sample. Fifth, the metallographic sample is observed and analyzed under an optical microscope and a scanning electron microscope to determine its grain size grade.

[0007] The above-mentioned method for metallographic corrosion of deformed high-temperature alloy fasteners includes the following steps: In step one, rough grinding is performed using 120# sandpaper. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and grinding time 180s. For rough grinding, 600# sandpaper is used. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and grinding time 180s. For fine grinding with 1500# sandpaper, the automatic grinding and polishing machine's parameters are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s; for fine grinding with 2500# sandpaper, the automatic grinding and polishing machine's parameters are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 120s.

[0008] The above-mentioned metallographic corrosion method for deformed high-temperature alloy fasteners includes the following steps: In step two, a 2.5μm diamond polishing agent is used for rough polishing. The parameters of the automatic polishing machine are set as follows: pressure applied by the pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and grinding time 100s. A 0.3μm diamond polishing agent is used for fine polishing. The parameters of the automatic polishing machine are set as follows: pressure applied by the pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and grinding time 100s. Deionized water is used as cooling water during both rough and fine polishing processes to prevent impurities in tap water from adhering to the surface to be inspected.

[0009] This invention has significant advantages and beneficial effects compared with existing technologies. As can be seen from the above technical solution, in the metallographic corrosion method for deformed high-temperature alloy fasteners of this invention, a 10-20% citric acid aqueous solution is prepared as the metallographic etchant, which reduces acidity and improves safety while balancing corrosion rate and effect. The finely polished sample is placed in the metallographic etchant for electrochemical corrosion, with the test sample as the anode and the austenitic stainless steel plate as the cathode. The working voltage is 5V-15V, the current is 0.5A-1.3A, the temperature is 20℃-30℃, and the corrosion time is 60s-200s, with a controllable process. The etchant of this invention is simple to prepare, the raw materials are readily available, the requirements for the experimental environment are not high, and the cost is low, making it universally applicable. Furthermore, the etchant is non-flammable and non-explosive, making its use relatively safe. The method for preparing deformed high-temperature alloy metallographic specimens according to the present invention can produce specimens with clear grain boundaries, bright crystal surfaces, obvious microstructure, and no obvious through-scratches on the surface, making it suitable for widespread use in the corrosion prevention of nickel-based high-temperature alloys, iron-based high-temperature alloys, cobalt-based high-temperature alloys, etc. Attached Figure Description

[0010] Figure 1(a) is an optical metallographic image of nickel-based superalloy GH738 using Example 1; Figure 1(b) is a scanning electron microscope image of nickel-based superalloy GH738 using Example 1; Figure 2(a) is an optical metallographic image of the iron-based high-temperature alloy GH2132 using Example 1; Figure 2(b) is a scanning electron microscope image of the iron-based superalloy GH2132 using Example 1; Figure 3(a) is an optical metallographic image of cobalt-based superalloy GH159 using Example 1; Figure 3(b) is a scanning electron microscope image of cobalt-based superalloy GH159 using Example 1; Figure 4(a) is an optical metallographic image of nickel-based superalloy GH738 using Example 2; Figure 4(b) is a scanning electron microscope image of nickel-based superalloy GH738 using Example 2; Figure 5(a) shows the optical metallographic image of the iron-based high-temperature alloy GH2132 in Example 2; Figure 5(b) is a scanning electron microscope image of the iron-based superalloy GH2132 using Example 2; Figure 6(a) is an optical metallographic image of cobalt-based superalloy GH159 using Example 2; Figure 6(b) is a scanning electron microscope image of cobalt-based superalloy GH159 using Example 2; Figure 7(a) shows the optical metallographic image of the nickel-based superalloy GH738 as a comparative example; Figure 7(b) shows a comparative scanning electron microscope image of nickel-based superalloy GH738; Figure 8(a) shows the optical metallographic image of the iron-based high-temperature alloy GH2132 as a comparative example; Figure 8(b) shows a comparative scanning electron microscope image of the iron-based superalloy GH2132; Figure 9(a) shows the optical metallographic image of cobalt-based superalloy GH159 as a comparative example; Figure 9(b) shows a comparative scanning electron microscope image of cobalt-based superalloy GH159; Figure 10 The image is a scanning electron microscope image obtained using the conventional method in Example 4; Figure 11 The image shown is a scanning electron microscope image of the present invention using Example 4. Detailed Implementation

[0011] The following, in conjunction with the accompanying drawings and preferred embodiments, details the specific implementation, structure, features, and effects of a metallographic corrosion method for deformed high-temperature alloy fasteners proposed according to the present invention.

[0012] Example 1: A method for metallographic corrosion of deformed high-temperature alloy fasteners includes the following steps: First, the test samples of nickel-based superalloy GH738, iron-based superalloy GH2132, and cobalt-based superalloy GH159 were cut and metallographically inlaid, and then coarsely ground with 120# and 600# sandpaper using an automatic polishing machine, and finely ground with 1500# and 2500# sandpaper. Second, the sample obtained in step one is rough polished with 2.5μm diamond polishing agent using an automatic polishing machine, and then fine polished with 0.3μm diamond polishing agent. Third, prepare the metallographic etchant: weigh 20g of white crystalline powder of superior pure citric acid and place it in a beaker. Measure 80ml of deionized water and add it to the beaker. Stir until fully dissolved to obtain an aqueous solution of citric acid. Fourth, the finely polished sample was placed in a metallographic etchant for electrochemical corrosion. The sample to be tested was used as the anode, and the austenitic stainless steel plate was used as the cathode. The working voltage was 15V, the current was 1.3A, the temperature was 20℃, and the corrosion time was 130s. Then, it was cleaned with anhydrous ethanol and dried to obtain the metallographic sample. Fifth, the grain boundaries, grain boundary carbides, and intragranular carbides were observed and analyzed using optical microscopes and scanning electron microscopes, as shown in Figures 1(a), 1(b), 2(a), 2(b), 3(a), and 3(b). Compared with the comparative example, it can be seen that the grain boundaries of the three materials are clearer, and many carbide corrosion pits left at the grain boundaries are more obvious, indicating a better corrosion effect.

[0013] In step one, use 120# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 180s. Then use 600# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s. For fine grinding using 1500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s; For fine grinding using 2500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 120s.

[0014] In step two, a 2.5μm diamond polishing agent is used for rough polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. A 0.3μm diamond polishing agent is used for fine polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. Deionized water is used as cooling water during both rough and fine polishing processes to prevent impurities in tap water from adhering to the surface to be tested.

[0015] Example 2: A method for metallographic corrosion of deformed high-temperature alloy fasteners includes the following steps: First, the test samples of nickel-based superalloy GH738, iron-based superalloy GH2132, and cobalt-based superalloy GH159 were cut and metallographically inlaid, and then coarsely ground with 120# and 600# sandpaper using an automatic polishing machine, and finely ground with 1500# and 2500# sandpaper. Second, the sample obtained in step one is rough polished with 2.5μm diamond polishing agent using an automatic polishing machine, and then fine polished with 0.3μm diamond polishing agent. Third, prepare the metallographic etchant: weigh 10g of white crystalline powder of superior pure citric acid and place it in a beaker. Measure 90ml of deionized water and add it to the beaker. Stir until fully dissolved to obtain an aqueous solution of citric acid. Fourth, the finely polished sample was placed in a metallographic etchant for electrochemical corrosion. The sample to be tested was used as the anode, and the austenitic stainless steel plate was used as the cathode. The working voltage was 5V, the current was 0.9A, the temperature was 25℃, and the corrosion time was 60s. Then, it was cleaned with anhydrous ethanol and dried to obtain the metallographic sample. Fifth, the grain boundaries, grain boundary carbides, and intragranular carbides were observed and analyzed using optical microscopes and scanning electron microscopes, as shown in Figures 4(a), 4(b), 5(a), 5(b), 6(a), and 6(b). Compared with the comparative examples, it can be seen that the grain boundaries of the three materials are clear after corrosion, and many carbide corrosion pits are left at the grain boundaries.

[0016] In step one, use 120# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 180s. Then use 600# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s. For fine grinding using 1500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s; For fine grinding using 2500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 120s.

[0017] In step two, a 2.5μm diamond polishing agent is used for rough polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. A 0.3μm diamond polishing agent is used for fine polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. Deionized water is used as cooling water during both rough and fine polishing processes to prevent impurities in tap water from adhering to the surface to be tested.

[0018] Example 3: A method for metallographic corrosion of deformed high-temperature alloy fasteners includes the following steps: First, the test samples of nickel-based superalloy GH738, iron-based superalloy GH2132, and cobalt-based superalloy GH159 were cut and metallographically inlaid, and then coarsely ground with 120# and 600# sandpaper using an automatic polishing machine, and finely ground with 1500# and 2500# sandpaper. Second, the sample obtained in step one is rough polished with 2.5μm diamond polishing agent using an automatic polishing machine, and then fine polished with 0.3μm diamond polishing agent. Third, prepare the metallographic etchant: weigh 15g of white crystalline powder of superior pure citric acid and place it in a beaker. Measure 85ml of deionized water and add it to the beaker. Stir until fully dissolved to obtain an aqueous solution of citric acid. Fourth, the finely polished sample was placed in a metallographic etchant for electrochemical corrosion. The sample to be tested was used as the anode, and the austenitic stainless steel plate was used as the cathode. The working voltage was 10V, the current was 0.5A, the temperature was 30℃, and the corrosion time was 200s. Then, it was cleaned with anhydrous ethanol and dried to obtain the metallographic sample. Fifth, the grain boundaries, grain boundary carbides, and intragranular carbides were observed and analyzed using optical microscopes and scanning electron microscopes.

[0019] In step one, use 120# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 180s. Then use 600# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s. For fine grinding using 1500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s; For fine grinding using 2500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 120s.

[0020] In step two, a 2.5μm diamond polishing agent is used for rough polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. A 0.3μm diamond polishing agent is used for fine polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. Deionized water is used as cooling water during both rough and fine polishing processes to prevent impurities in tap water from adhering to the surface to be tested.

[0021] Comparative example: A traditional metallographic etchant is used, which consists of the following components: concentrated hydrochloric acid: water: hydrogen peroxide = 50:50:2.

[0022] Using traditional etchants, GH738, GH2132, and GH159 samples were prepared respectively. The metallographic images of the obtained GH738, GH2132, and GH159 samples are shown in Figures 7(a), 7(b), 8(a), 8(b), 9(a), and 9(b). It can be seen that grain boundary carbides still exist.

[0023] Example 4: To better explain the present invention, GH738 material was subjected to solution treatment at 1000℃, stabilization at 900℃ for 100 min, and aging at 760℃ for 16 h. After metallographic sample preparation, the etching of traditional etchant and electrolytic etching with the etchant of the present invention were compared. The grain boundary carbides and intragranular carbides were observed and analyzed by scanning electron microscopy.

[0024] Traditional metallographic etchants consist of the following components: concentrated hydrochloric acid: water: hydrogen peroxide = 50:50:2. Figure 10 The composition of the metallographic etchant for deformed high-temperature alloys in this embodiment is as follows: 20g citric acid, 80ml deionized water, etc. Figure 11 .

[0025] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments without departing from the technical essence of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for metallographic corrosion of deformed high-temperature alloy fasteners, comprising the following steps: First, the test sample is cut and metallographically inlaid, and then coarsely ground with 120# and 600# sandpaper using an automatic polishing machine, and finely ground with 1500# and 2500# sandpaper. Second, the sample obtained in step one is rough polished with 2.5μm diamond polishing agent using an automatic polishing machine, and then fine polished with 0.3μm diamond polishing agent. Third, prepare the metallographic etchant: weigh 10g-20g of white crystalline powder of superior pure citric acid and place it in a beaker. Add 80ml-90ml of deionized water to the beaker and stir until fully dissolved to obtain a 10-20% citric acid aqueous solution. Fourth, the finely polished sample is placed in a metallographic etchant for electrochemical corrosion. The sample to be tested is used as the anode, and the austenitic stainless steel plate is used as the cathode. The working voltage is 5V-15V, the current is 0.5A-1.3A, the temperature is 20℃-30℃, and the corrosion time is 60s-200s. Then, it is cleaned with anhydrous ethanol and dried to obtain the metallographic sample. Fifth, the metallographic sample is observed and analyzed under an optical microscope and a scanning electron microscope to determine its grain size grade.

2. The metallographic corrosion method for deformed high-temperature alloy fasteners as described in claim 1, characterized in that: In step one, use 120# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 180s. Then use 600# sandpaper for rough grinding. The parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s. For fine grinding using 1500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 150s; For fine grinding using 2500# sandpaper, the parameters of the automatic grinding and polishing machine are set as follows: pressure head 20N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, grinding time 120s.

3. The metallographic corrosion method for deformed high-temperature alloy fasteners as described in claim 1, characterized in that: In step two, a 2.5μm diamond polishing agent is used for rough polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. A 0.3μm diamond polishing agent is used for fine polishing. The parameters of the automatic polishing machine are set as follows: pressure head 18N, center pressure 90N, grinding head speed 50RPM, grinding disc speed 300RPM, grinding disc rotation direction reversed, and polishing time 100s. Deionized water is used as cooling water during both rough and fine polishing processes to prevent impurities in tap water from adhering to the surface to be tested.

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