Zirconium alloy EBSD electrolytic polishing method

Abstract

The invention discloses a zirconium alloy EBSD electrolytic polishing method. The method comprises the following steps that S1, a zirconium alloy sample to be subjected to EBSD characterization is obtained through cutting; s2, impurities and oxide skin on the surface of the zirconium alloy sample are removed through polishing, so that the surface of the zirconium alloy sample is smooth and bright, and the zirconium alloy sample is blow-dried for use after being cleaned; s3, an electrolytic polishing solution composed of a perchloric acid solution, an ethylene glycol monobutyl ether solution and a methanol solution is prepared; s4, taking the zirconium alloy sample as an anode, and connecting the anode with a power supply anode; stainless steel or other steel sheets are used as cathodes to be connected with the cathode of the power supply; after the electrolytic polishing solution is cooled, the zirconium alloy sample is subjected to electric polishing; and S5, after electric polishing is completed, the zirconium alloy is rapidly cleaned and blow-dried, and the zirconium alloy EBSD sample is obtained. According to the method, the formula and process parameters of the electrolytic polishing solution are optimized, the solution viscosity and the reaction stability are adjusted through ethylene glycol monobutyl ether and methyl alcohol, the electromagnetic stirring technology is combined under the conditions of low acid content and low temperature, and effective removal of the deep deformation stress layer of the zirconium alloy, especially the large-strain zirconium alloy is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of material science testing and characterization, and in particular relates to a zirconium alloy EBSD electrolytic polishing method. Background Art

[0002] Zirconium alloys have a low thermal neutron absorption cross section (0.18×10 -28 pcs / m 2 ), good corrosion resistance, good creep resistance and good comprehensive mechanical properties, and is widely used in aerospace, nuclear reactions, chemical industry and other fields. The crystal structure of zirconium at room temperature is a hexagonal close-packed (HCP) structure with an axial ratio (c / a) of 1.593, which leads to significant differences in the performance of the material in the c-axis and a-axis directions. During the large plastic deformation process of zirconium alloy tubes and plates, a strong texture is easily formed, which significantly affects its physical properties. Therefore, studying the crystal orientation information of zirconium alloys after large strain is of great guiding significance for in-depth understanding of its performance characteristics and optimization of processing technology.

[0003] Electron Backscatter Diffraction (EBSD) is a crystal orientation analysis technique based on a scanning electron microscope. The principle is that the electron beam excites and forms diffraction Kikuchi bands on the inclined sample surface. By analyzing the Kikuchi pattern, the crystal structure, orientation and related information of the sample can be quickly determined. The diffraction of backscattered electrons forms Kikuchi bands, which are captured by the sample chamber fluorescent screen and converted into electronic images by a CCD camera. Compared with X-ray diffraction technology that can only characterize macroscopic textures, EBSD technology has higher resolution and can simultaneously obtain microscopic crystal orientation and grain morphology information. EBSD combines microstructure with crystallographic analysis, and can provide information such as grains, subgrains and phase composition, and intuitively display grain orientation and distribution through pole figures, inverse pole figures and orientation distribution functions.

[0004] However, in the EBSD test, the quality of the zirconium alloy sample directly determines the clarity of the diffraction pattern and the reliability of the test results, so the preparation of the zirconium alloy sample becomes a key step. Since EBSD relies on the diffraction effect of backscattered electrons, if there is residual stress or lattice distortion on the surface of the zirconium alloy sample, the Kikuchi pattern will be blurred and accurate crystallographic analysis cannot be performed. Therefore, EBSD places high demands on the preparation of zirconium alloy samples. It must be ensured that there is no deformation stress on the surface of the sample, and the surface is smooth and defect-free. For those large-strain zirconium alloys with a plastic strain of more than 20% (hereinafter referred to as large-strain zirconium alloys), the difficulty of sample preparation is further increased. This is mainly because the processing process will produce deep residual stress and significant lattice distortion, and the stress layer needs to be completely removed during the sample preparation process. The stress layer that is not completely removed will significantly reduce the clarity of the Kikuchi pattern and affect the resolution and accuracy of EBSD. At the same time, the sample surface must also meet high finish and high uniformity requirements. Although traditional mechanical polishing and vibration polishing can improve the surface finish, it is often difficult to completely eliminate the residual stress layer, and these methods are prone to introduce new surface defects, such as scratches and pits, which will further affect the quality of the diffraction pattern. Although the electrolytic polishing method will not introduce new surface defects, due to the complex texture characteristics and uneven stress distribution of large-strain zirconium alloys, this complexity may lead to uneven dissolution, which in turn affects the surface quality and increases the difficulty of sample preparation. Therefore, the EBSD sample preparation of large-strain zirconium alloys requires a more refined and targeted process design.

[0005] The patent with publication number CN107607383A discloses an electrolytic polishing method for preparing zirconium alloy EBSD samples. Although this method has achieved certain results in the preparation of ordinary zirconium alloy samples, it has significant deficiencies in the preparation of large strain zirconium alloy EBSD samples. The electrolytic polishing liquid formula and process parameters (such as voltage and temperature) are mainly designed for ordinary zirconium alloys, and are not optimized for the removal of deep residual stress layers of large strain zirconium alloys. In addition, the problem of uneven surface dissolution that may occur during the polishing process of complex textured materials leads to insufficient surface treatment or excessive dissolution.

[0006] In view of the above problems, it is urgent to develop an EBSD sample preparation method specifically suitable for zirconium alloys, especially large strain zirconium alloys. This method needs to achieve effective removal of the deep stress layer during the sample preparation process, while ensuring that the sample surface has high finish and uniformity, thereby ensuring the clarity of the Kikuchi pattern and the reliability of the test. This can not only meet the technical requirements of high-resolution EBSD testing, but also provide support for in-depth research on the texture and microstructure of zirconium alloys, especially large strain zirconium alloys. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the present invention provides a zirconium alloy EBSD electrolytic polishing method, which solves the problem that zirconium alloys, especially large strain zirconium alloys, are difficult to remove deep residual stress layers and uneven surface dissolution, and is suitable for EBSD sample preparation of different types of zirconium alloys.

[0008] The technical solution adopted by the present invention to solve the technical problem is: a zirconium alloy EBSD electrolytic polishing method, comprising the following steps:

[0009] S1, zirconium alloy cutting to obtain the zirconium alloy sample that needs EBSD characterization;

[0010] S2, polishing to remove impurities and oxide scale on the surface of the zirconium alloy sample to make its surface smooth and bright, and then cleaning and drying the polished surface of the zirconium alloy sample for standby use;

[0011] S3, preparing an electrolytic polishing solution consisting of a perchloric acid solution, an ethylene glycol monobutyl ether solution and a methanol solution;

[0012] S4, using the zirconium alloy sample as the anode and connected to the positive electrode of the power supply; using stainless steel or other steel sheets as the cathode and connected to the negative electrode of the power supply; after cooling the electrolytic polishing liquid, electropolishing the zirconium alloy sample;

[0013] S5, after the zirconium alloy sample is electro-polished, it is quickly cleaned and blown dry to obtain a zirconium alloy EBSD sample.

[0014] Furthermore, in step S3, the volume percentage of the perchloric acid solution in the electrolytic polishing solution is 5-15%, the volume percentage of the ethylene glycol monobutyl ether solution is 10-30%, and the volume percentage of the methanol solution is 60-80%.

[0015] Furthermore, the concentration of the perchloric acid solution is 70-72%, the concentration of the ethylene glycol monobutyl ether solution is above 99%, and the concentration of the methanol solution is above 99.5%.

[0016] Furthermore, in step S4, the temperature of the electrolytic polishing solution is -40 to -20°C, the polishing voltage is 20V, and the polishing time is 15 to 150s.

[0017] Furthermore, in step S5, the zirconium alloy sample is judged to have completed electropolishing by the fact that a dark grey epidermis falls off on the surface of the EBSD sample analysis area.

[0018] Furthermore, the zirconium alloy sample is a large strain zirconium alloy sample with a plastic strain of more than 20%.

[0019] Furthermore, in step S4, the electrolytic polishing liquid is cooled, and after the temperature stabilizes, the stainless steel sheet or other steel sheet is immersed in the electrolytic polishing liquid, and then the magnet is placed in the electrolytic polishing liquid, and the liquid is continuously stirred using an electromagnetic stirring device, and finally the zirconium alloy sample is immersed in the electrolytic polishing liquid for electrolytic polishing.

[0020] Furthermore, in step S2, the analytical surface of the zirconium alloy EBSD sample is polished in sequence using 240#, 600#, 1200#, 3000# and 5000# sandpapers, and the polishing direction needs to be rotated 90° each time the sandpaper of the next mesh is changed for polishing.

[0021] Furthermore, in step S4, the EBSD analysis surface of the zirconium alloy sample faces the negative electrode stainless steel sheet or other steel sheet.

[0022] Furthermore, in the step S5, the cleaning and drying process uses clean water and ethanol to clean the surface of the zirconium alloy sample in sequence, and then uses cold air from a hair dryer to dry the surface of the zirconium alloy sample along one side.

[0023] The beneficial effect of the present invention is that by optimizing the electrolytic polishing liquid formula and process parameters, using ethylene glycol monobutyl ether and methanol to adjust the solution viscosity and reaction stability, and combining electromagnetic stirring technology under low acid content and low temperature conditions, the deep deformation stress layer of zirconium alloys, especially large strain zirconium alloys with plastic strains of more than 20%, can be effectively removed. This method slows down the rate of reaction between the electrolyte and the surface of the zirconium alloy sample, avoids the problem of excessive dissolution, and significantly improves the surface uniformity and finish. In view of the characteristics of the complex texture of large strain materials, the patent ensures that the reaction rate is controllable and avoids the generation of secondary defects through precise dissolution control and clear polishing completion phenomenon, and finally obtains a clear EBSD Kikuchi pattern and significantly improves the resolution rate (>95%). Compared with traditional methods, this technology has achieved good results in the preparation of EBSD samples of zirconium alloys, especially large strain zirconium alloys with plastic strains of more than 20%. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 The EBSD orientation imaging diagram of the Zr-4 alloy after rolling is prepared by the method of the present invention.

[0026] Figure 3 The present invention is used to prepare a secondary electron image of a Zr-4 alloy after rolling.

[0027] Figure 4 The EBSD orientation imaging diagram of the rolled N36 alloy is prepared by the method of the present invention.

[0028] Figure 5 The present invention is used to prepare a scanning electron microscope secondary electron image of the rolled N36 alloy.

[0029] Figure 6 The EBSD orientation imaging diagram of the rolled Zr-4 alloy is prepared at 20°C using the method of the present invention.

[0030] Figure 7 This is the EBSD orientation imaging image of the Zr-4 alloy after rolling prepared in Example 6. DETAILED DESCRIPTION

[0031] In order to enable those skilled in the art to better understand the solutions of the present invention, the following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0032] The present invention provides a zirconium alloy EBSD electrolytic polishing method, the zirconium alloy may be a common zirconium alloy or a large strain zirconium alloy with a plastic strain of more than 20% (hereinafter referred to as a large strain zirconium alloy), which is not specifically limited. The large strain zirconium alloy is taken as an example for explanation. The method is formed by subjecting the zirconium alloy to large plastic deformation, and comprises the following steps:

[0033] S1, using a wire cutting tool to perform electric spark wire cutting on the Zr-4 zirconium alloy plate after rolling down by 30%, to obtain a large strain Zr-4 sample with a length × width × thickness of 8 mm × 4 mm × 1 mm;

[0034] S2, use 240#, 600#, 1200#, 3000#, and 5000# sandpaper to polish each surface of the large strain Zr-4 sample obtained in S1, ensuring that the direction of each sandpaper polishing is rotated 90°. After polishing, the depth and direction of the scratches are basically consistent, and the polished sample is obtained;

[0035] S3, prepare the electrolytic polishing solution used for sample surface treatment with a volume ratio of: 5-15% perchloric acid solution, 10-20% ethylene glycol monobutyl ether solution and 60-80% methanol solution, and the sum of the volume percentages of the three solutions is 100%;

[0036] Specifically, in this embodiment 1, the volume ratio of the electrolytic polishing solution is: 10% perchloric acid solution, 20% ethylene glycol monobutyl ether solution and 70% methanol solution. The concentration of the perchloric acid solution used is 70-72%, the concentration of the ethylene glycol monobutyl ether solution is more than 99%, and the concentration of the methanol solution is more than 99.5%.

[0037] S4, the large strain Zr-4 sample is used as the anode, connected to the positive electrode of the power supply, which is a constant current stabilized power supply; the stainless steel sheet or other steel sheet is used as the cathode, connected to the negative electrode of the power supply, which is a constant current stabilized power supply. After the voltage is stabilized, the stainless steel sheet or other steel sheet is immersed in the electrolytic polishing liquid for electrolytic polishing. The temperature of the electrolytic polishing liquid is -40 to -20°C. In Example 1, it is specifically -30°C. The polishing voltage of the electrolytic polishing is 20V. The magnetic rotor stirs slowly during the polishing process; the large strain Zr-4 sample is immersed in the electrolytic polishing liquid, the EBSD analysis surface is facing the negative electrode stainless steel sheet or other steel sheet, and the polishing time is 15 to 150s. In this Example 1, the sample is taken out after polishing for about 20s. Specifically, the time node for completing the electropolishing is when most of the dark gray epidermis on the surface of the EBSD sample analysis area falls off.

[0038] S5, the large strain Zr-4 zirconium alloy sample taken out after electro-polishing is quickly cleaned with clean water and ethanol in turn, and finally the surface is blown dry. Specifically, cold air is used to blow dry along one side. After drying, there is no trace of water stains on the surface of the sample, thereby obtaining an EBSD sample with a smooth and bright surface.

[0039] The grain morphology of the highly strained Zr-4 sample prepared by the above method is shown in the EBSD. Figure 2 As shown, the grain orientation distribution and lattice information inside the sample can be clearly seen, with a resolution of 98%.

[0040] Example 2

[0041] The difference between this embodiment and embodiment 1 is that the types of zirconium alloys treated are different. As shown in Table 1, these zirconium alloys are all subjected to a rolling and pressing treatment of 30%. The EBSD sample preparation method described in embodiment 1 is used to prepare samples of the different types of zirconium alloys in the table and analyze their resolution rates. The results are shown in Table 1.

[0042] Table 1

[0043] Zirconium Alloy Model Zr-4 N36 Zirlo Resolution rate (%) 98 97 98

[0044] It can be seen from the results shown in Table 1 that since zirconium accounts for more than 97% of the zirconium alloy, whether it is Zr4 with elemental composition of Zr and Sn, or N36 and Zirlo with elemental composition of Zr, Sn and Nb, the electropolishing effect using the electrolytic polishing liquid of the present invention is very good.

[0045] Example 3

[0046] In this example, only the temperature during electrolytic polishing was changed on the basis of Example 1. The resolution of large strain Zr-4 EBSD sample prepared by the electrolytic polishing liquid described in this example was analyzed. The results are shown in Table 2.

[0047] Table 2

[0048] Electropolishing temperature(℃) -40 -35 -30 -25 -20 0 20 Resolution rate (%) 95 97 98 96 94 76 68

[0049] From the results shown in Table 2, it can be seen that when the ratio of the electrolytic polishing solution remains unchanged, increasing or decreasing the polishing temperature is not conducive to the electrolytic polishing treatment of the large strain Zr-4 surface, especially at 20 ° C, the resolution rate drops to 68%, such as Figure 6 shown.

[0050] Example 4

[0051] In this example, only the degree of plastic deformation of Zr4 is changed on the basis of Example 1. The electrolytic polishing solution described in this example is used to analyze the EBSD resolution of Zr-4 samples with different degrees of deformation. The results are shown in Table 3.

[0052] Table 3

[0053] Dependent variable original 8% compression 14% compression 20% compression Rolling 30% Resolution rate (%) 99 99 99 99 98

[0054] From the results shown in Table 3, it can be seen that the electrolytic polishing liquid has excellent effects on the electrolytic polishing treatment of Zr-4 surfaces with different deformation degrees.

[0055] Example 5

[0056] In this example, only the ratio of the electrolytic polishing solution is changed on the basis of Example 1. The resolution of the large strain Zr-4 EBSD sample prepared by the electrolytic polishing solution described in this example is analyzed, and the results are shown in Table 4.

[0057] Table 4

[0058] Perchloric acid (%) Ethylene glycol monobutyl ether (%) Methanol(%) Resolution 5 20 75 97 10 10 80 97 10 20 70 98 10 30 60 96 15 20 65 94

[0059] From the results shown in Table 4, it can be seen that different ratios of electrolytic polishing liquid have different effects on the electrolytic polishing treatment of large strain Zr-4 surface, among which the best effect is perchloric acid: ethylene glycol monobutyl ether: methanol = 1:2:7.

[0060] Example 6

[0061] In this embodiment, only the electrolytic polishing solution is changed on the basis of embodiment 1. The electrolytic polishing solution is composed of 10% perchloric acid and 90% ethanol. The resolution rate of the large strain Zr-4 EBSD sample prepared by the electrolytic polishing solution of this embodiment is analyzed. The result shows that the resolution rate is only 86%. Figure 7 shown.

[0062] The above specific implementation modes are used to explain the present invention rather than to limit the present invention. Any modification and change made to the present invention within the spirit of the present invention and the protection scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A zirconium alloy EBSD electrolytic polishing method, characterized in that: The following steps are involved: S1, zirconium alloy cutting to obtain the zirconium alloy sample that needs EBSD characterization; S2, polishing to remove impurities and oxide scale on the surface of the zirconium alloy sample to make its surface smooth and bright, and then cleaning and drying the polished surface of the zirconium alloy sample for standby use; S3, preparing an electrolytic polishing solution consisting of a perchloric acid solution, an ethylene glycol monobutyl ether solution and a methanol solution; S4, using the zirconium alloy sample as the anode and connected to the positive electrode of the power supply; using stainless steel or other steel sheets as the cathode and connected to the negative electrode of the power supply; after cooling the electrolytic polishing liquid, electropolishing the zirconium alloy sample; S5, after the zirconium alloy sample is electro-polished, it is quickly cleaned and blown dry to obtain a zirconium alloy EBSD sample.

2. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: In step S3, the volume percentage of the perchloric acid solution in the electrolytic polishing solution is 5-15%, the volume percentage of the ethylene glycol monobutyl ether solution is 10-30%, and the volume percentage of the methanol solution is 60-80%.

3. The zirconium alloy EBSD electrolytic polishing method according to claim 2, characterized in that: The concentration of the perchloric acid solution is 70-72%, the concentration of the ethylene glycol monobutyl ether solution is above 99%, and the concentration of the methanol solution is above 99.5%.

4. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: In step S4, the temperature of the electrolytic polishing solution is -40 to -20°C, the polishing voltage is 20V, and the polishing time is 15 to 150s.

5. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: In step S5, the zirconium alloy sample is judged to have completed electropolishing by the fact that the dark grey epidermis falls off on the surface of the EBSD sample analysis area.

6. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: The zirconium alloy sample is a large strain zirconium alloy sample with a plastic strain of more than 20%.

7. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: In step S4, the electrolytic polishing liquid is cooled, and after the temperature stabilizes, the stainless steel sheet or other steel sheet is immersed in the electrolytic polishing liquid, and then the magnet is placed in the electrolytic polishing liquid, and the liquid is continuously stirred by an electromagnetic stirring device, and finally the zirconium alloy sample is immersed in the electrolytic polishing liquid for electrolytic polishing.

8. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: In step S2, the analytical surface of the zirconium alloy EBSD sample is polished in sequence using 240#, 600#, 1200#, 3000# and 5000# sandpapers, and the polishing direction needs to be rotated 90° each time the sandpaper of the next mesh is changed for polishing.

9. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: In the step S4, the EBSD analysis surface of the zirconium alloy sample faces the negative electrode stainless steel sheet or other steel sheet.

10. The zirconium alloy EBSD electrolytic polishing method according to claim 1, characterized in that: In the step S5, the cleaning and drying process uses clean water and ethanol to clean the surface of the zirconium alloy sample in sequence, and then uses cold air from a hair dryer to dry the surface of the zirconium alloy sample along one side.

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