A device and method for removing residual stress on the surface of titanium or zirconium alloy plate in a large area

Abstract

The present invention discloses a device for removing residual stress on the surface of titanium or zirconium alloy plates over a large area, comprising an electrolytic cell, a pair of 304L cathode plates and titanium or zirconium alloy plates are also installed in the electrolytic cell, and are respectively connected to the negative and positive electrodes of a DC power supply through wires; the removal method comprises: 1. selecting a pair of 304L cathode plates according to the surface area of ​​the titanium or zirconium alloy plates to be processed and respectively connecting them to the positive and negative electrodes of the DC power supply; 2. loading a mixed electrolyte into the electrolytic cell and cooling it with liquid nitrogen, and then setting parameters to electropolish the titanium or zirconium alloy plates and remove the surface residual stress. The device of the present invention, by setting a double cathode plate, can quickly and effectively remove the residual stress on the surface of the titanium or zirconium alloy plates over a large area while electropolishing the titanium or zirconium alloy plates, thereby improving the surface finish and plastic deformation capacity of the titanium or zirconium alloy plates. The method of the present invention is simple and efficient, and is suitable for the field of nuclear metal material processing.

Description

Technical Field

[0001] The invention relates to the technical field of plate materials, and in particular to a device and method for removing residual stress on the surface of a titanium or zirconium alloy plate material over a large area. Background Art

[0002] Metal workpieces will generate residual stress during the process of hot and cold processing. Nuclear titanium or zirconium alloys undergo multiple cold processing, and there is high residual stress on the surface. Workpieces with high residual stress values ​​will affect their service life, such as reducing the strength and fatigue limit of components, and will cause stress corrosion and brittle fracture in a corrosive environment. Therefore, it is necessary to reduce and eliminate the residual stress of workpieces, especially for materials used in aviation, aerospace, shipbuilding, ocean, nuclear industry and other fields. Failure caused by residual stress will cause greater losses and cannot be ignored.

[0003] Residual stress is an unstable stress state. When a workpiece is subjected to external force, the applied stress interacts with the residual stress, causing some local areas of the workpiece to undergo plastic deformation and the stress in the cross section to be redistributed. When the external force is removed, the entire component will deform, affecting the accuracy of the component. In addition, in the nuclear industry, when workpieces are exposed to corrosive media during service, residual stress may cause sudden stress corrosion cracking of the workpiece. Especially for titanium or zirconium alloys used in the nuclear industry, there is currently no convenient device or method to eliminate surface residual stress, so people have been studying effective devices and methods to eliminate these effects. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a device for removing residual stress on the surface of titanium or zirconium alloy plates over a large area in view of the shortcomings of the above-mentioned prior art. The device is provided with a double cathode plate, and while electrolytically polishing the titanium or zirconium alloy plates, it can quickly and effectively remove the residual stress on the surface of the titanium or zirconium alloy plates over a large area, thereby improving the surface finish and plastic deformation capacity of the titanium or zirconium alloy plates, and solving the problem of the lack of a convenient device for eliminating surface residual stress in titanium or zirconium alloys used in the nuclear industry.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is: a device for removing residual stress on the surface of a titanium or zirconium alloy plate over a large area, characterized in that it includes an electrolytic cell for containing a mixed electrolyte, the electrolytic cell is also equipped with a pair of 304L cathode plates and a titanium or zirconium alloy plate, and the titanium or zirconium alloy plate is located between the pair of 304L cathode plates, the pair of 304L cathode plates are connected to the negative electrode of a DC power supply through a wire, and the titanium or zirconium alloy plate is connected to the positive electrode of the DC power supply through a wire.

[0006] At the same time, the present invention also discloses a method for removing residual stress on the surface of titanium or zirconium alloy plates over a large area by using the above-mentioned device, characterized in that the method comprises the following steps: Step 1: According to the surface area of ​​the titanium or zirconium alloy plate to be processed, a pair of 304L cathode plates of corresponding size are selected, and then the titanium or zirconium alloy plate is connected to the positive electrode of the DC power supply through a wire, and the pair of 304L cathode plates is connected to the negative electrode of the DC power supply through a wire, and the titanium or zirconium alloy plate is located between the pair of 304L cathode plates; Step 2: Load the mixed electrolyte into the electrolytic cell, use liquid nitrogen to cool the mixed electrolyte, then set the power and voltage parameters, electropolish the titanium or zirconium alloy plate, and remove the surface residual stress at the same time.

[0007] The present invention can accurately remove tiny unevenness and irregular areas on the metal surface by arranging a double cathode plate to electropolish the titanium or zirconium alloy plate. Since there is usually a large local stress in these tiny irregular areas, during the electropolishing process of the present invention, the metal ions passing through the surface metal layer are dissolved and carried away, thereby reducing the stress concentration caused by surface unevenness. At the same time, during the electropolishing process, the metal atoms are rearranged and migrated on the surface, which can effectively reduce the residual stress caused by the processing process (such as cutting, welding, etc.), so that while the titanium or zirconium alloy plate is electropolished, the residual stress on the surface of the titanium or zirconium alloy plate is quickly and effectively removed over a large area, thereby improving the surface finish and plastic deformation ability of the titanium or zirconium alloy plate.

[0008] The above method is characterized in that the titanium or zirconium alloy plate in step 1 is selected from titanium, α, α+β, β-type titanium alloys, and zirconium, Zr-Nb, Zr-Sn, and Zr-Sn-Nb alloys.

[0009] The above method is characterized in that the surface area ratio of the titanium or zirconium alloy plate to be treated and the opposite surface of a pair of 304L cathode plates in step 1 is 1:1.5 to 1:5. By controlling the surface area ratio of the titanium or zirconium alloy plate to be treated and the opposite surface of the cathode plate, the surface of the treated object is covered by the cathode plate, ensuring that all areas of the surface of the treated object can be uniformly ion exchanged, while avoiding excessive current density on the surface of the treated object due to too large a surface area ratio, which causes corrosion and fails to achieve a polishing effect.

[0010] The above method is characterized in that the titanium or zirconium alloy plate in step 1 is placed in parallel with a pair of 304L cathode plates, that is, the two side surfaces of the titanium or zirconium alloy plate are respectively facing the surface of a 304L cathode plate, and the spacing between the titanium or zirconium alloy plate and the pair of 304L cathode plates is 1 cm to 5 cm. By controlling the placement position and spacing between the titanium or zirconium alloy plate and the pair of cathode plates, the technical effects of polishing and removing surface residual stress are simultaneously ensured, and the obstruction of the discharge of dissolved ions caused by too close distance, resulting in the accumulation of metal ions on the surface of the titanium or zirconium alloy plate and affecting the polishing effect, and the instability of ion exchange between the electrode plates caused by too far distance, making the power set per unit area unstable during treatment and affecting the treatment effect.

[0011] The above method is characterized in that the components of the mixed electrolyte in step 2 are methanol: n-butanol: perchloric acid = 6-8: 3-5: 1-1.5 by volume. Titanium and zirconium are elements of the same group, have similar physical and chemical properties, and have the same corresponding mixed electrolyte components. Exclusive selectivity of different alloys for the mixed electrolyte components can be achieved by simply adjusting the composition ratio.

[0012] The above method is characterized in that the mixed electrolyte is cooled to -25°C~-50°C by liquid nitrogen in step 2, and the power set is 50W~100W and the voltage is 25V~80V according to the unit surface area of ​​the titanium or zirconium alloy plate. By controlling the cooling temperature, the temperature of the mixed electrolyte is prevented from rising during electrolytic polishing and removing surface residual stress, which leads to a decrease in its stability and even destroys its formula composition, resulting in a decrease in polishing quality. The choice of voltage during electrolytic polishing directly affects the current density, and then affects the polishing effect. The increase in voltage will cause the current density to rise, but this relationship is not linear. There is a critical point. After exceeding the critical point, the current density will drop sharply. Therefore, the present invention accurately controls the power and voltage, and then controls the current density to ensure a better polishing effect.

[0013] The above method is characterized in that the duration of the electrolytic polishing in step 2 is 60s to 300s. By controlling the duration of the electrolytic polishing, the effects of electrolytic polishing and removing the residual pressure on the surface of the plate can be simultaneously ensured, so as to avoid the inability to completely remove the scratches, spots and other impurities on the surface due to the polishing time being too short, thereby failing to effectively reduce the surface residual stress, and to avoid the generation of new residual stress due to excessive friction due to the polishing time being too long, and even causing surface defects, thereby affecting the polishing quality.

[0014] Compared with the prior art, the present invention has the following advantages: 1. A pair of 304L cathode plates are arranged in the device of the present invention, and the titanium or zirconium alloy plate is placed between the pair of 304L cathode plates. Through the double cathode plate arrangement, while electrolytic polishing the titanium or zirconium alloy plate, the residual stress on the surface of the titanium or zirconium alloy plate is removed quickly and effectively over a large area, thereby improving the surface finish and plastic deformation capacity of the titanium or zirconium alloy plate.

[0015] 2. In the device of the present invention, the synergistic effect of the double cathode plates is used to achieve simultaneous polishing of both surfaces of the titanium or zirconium alloy plate, which greatly improves the polishing efficiency. The device is simple and easy to implement.

[0016] 3. The method of the present invention achieves large-area removal of residual stress on the surface of titanium or zirconium alloy plates and ensures the surface smoothness of the plates by controlling key parameters such as the surface area ratio of the double cathode plates and the titanium or zirconium alloy plates, the electrolyte temperature, the voltage and power of the electrolytic polishing.

[0017] 4. The method of the present invention is simple and efficient, and can improve the surface finish and plastic deformation capacity of titanium or zirconium alloy plates, providing ideas for removing surface residual stress and improving plastic deformation capacity of nuclear metal materials.

[0018] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The present invention is a schematic structural diagram of a device for removing residual stress on the surface of a titanium or zirconium alloy plate over a large area.

[0020] Figure 2 The metallographic microscope images of the titanium alloy plate before and after electrolytic polishing in Example 2 of the present invention.

[0021] Figure 3 The scanning electron microscope images of the zirconium alloy plate before and after electrolytic polishing in Example 3 of the present invention are shown.

[0022] Figure 4 This is a graph showing the results of the Ehrlich cupping test of the titanium plate before and after electrolytic polishing in Example 4 of the present invention.

[0023] Description of Reference Numerals DETAILED DESCRIPTION

[0024] The device of the present invention is described in detail through Example 1.

[0025] Example 1 like Figure 1As shown, the device for removing residual stress on the surface of a titanium or zirconium alloy plate over a large area in this embodiment includes an electrolytic cell 1 for containing a mixed electrolyte, wherein the electrolytic cell 1 is further provided with a pair of 304L cathode plates 2 and a titanium or zirconium alloy plate 3, and the titanium or zirconium alloy plate 3 is located between the pair of 304L cathode plates 2, and the pair of 304L cathode plates 2 is connected to the negative electrode of a DC power supply 4 through a wire, and the titanium or zirconium alloy plate 3 is connected to the positive electrode of the DC power supply 4 through a wire.

[0026] The method of the present invention is described in detail through Examples 2 to 4.

[0027] Example 2 This embodiment includes the following steps: Step 1: Smelt, forge and roll a titanium alloy to obtain a plate with a thickness of 0.5 cm, and the titanium alloy is composed of the following elements in mass percentage: Ta 5%, the balance Ti and inevitable impurities, and cut a block with a size of length × width × thickness of 200 mm × 100 mm × 0.5 mm as the titanium alloy plate 3; According to the surface area of ​​the side of the titanium alloy plate 3 to be processed, 200 cm 2 , select the matching size length × width × thickness of 350mm × 280mm × 3mm, and the surface area of ​​the side is 980cm 2 A pair of 304L cathode plates 2 are provided, and then the titanium alloy plate 3 is connected to the positive electrode of the DC power supply 4 through a wire, and the pair of 304L cathode plates 2 are connected to the negative electrode of the DC power supply 4 through a wire, and the titanium alloy plate 3 is located between the pair of 304L cathode plates 2 and placed in parallel, that is, the two side surfaces of the titanium alloy plate 3 are respectively opposite to the surface of a 304L cathode plate 2, and the distance between the titanium alloy plate 3 and the pair of 304L cathode plates 2 is 4.5 cm; Step 2: A mixed electrolyte with a volume ratio of methanol: n-butanol: perchloric acid = 8:5:1.5 is loaded into the electrolytic cell 1 and the titanium alloy plate 3 is immersed, and the mixed electrolyte is cooled to -50°C using liquid nitrogen, and then the power is set to 50W~100W, the voltage is 80V, and the current is 2.5A according to the unit surface area of ​​the titanium alloy plate 3, and the titanium alloy plate 3 is electropolished for 60s to remove the surface residual stress.

[0028] Figure 2Figure 2 is a metallographic microscope image of the titanium alloy plate before and after electropolishing in this embodiment, wherein Figure (a) is a metallographic microscope image of the titanium alloy plate before electropolishing. From Figure (a), it can be seen that there are obvious rolling streamline marks on the surface of the titanium alloy plate, which is relatively rough; Figure (b) is a metallographic microscope image of the titanium alloy plate after electropolishing. From Figure (b), it can be seen that the original deformation marks of the titanium alloy plate are removed after electropolishing, and the surface shows the grain structure of the titanium alloy itself, and the surface is relatively flat, smooth and beautiful.

[0029] The titanium alloy plate 3 of the present embodiment may also be replaced by other alloy plates selected from titanium, α, α+β, β-type titanium alloys, and zirconium, Zr-Nb, Zr-Sn, and Zr-Sn-Nb alloys.

[0030] Example 3 This embodiment includes the following steps: Step 1: The zirconium alloy is smelted, forged and rolled to obtain a plate with a thickness of 0.5 cm, and the zirconium alloy is composed of the following elements in mass percentage: Sn 2%, the balance Zr and inevitable impurities, and a block with a size of length×width×thickness of 180 mm×150 mm×0.25 mm is cut as the zirconium alloy plate 3; According to the surface area of ​​the side of the zirconium alloy plate 3 to be processed, 270 cm 2 , select the matching size length × width × thickness of 250mm × 200mm × 3mm, and the surface area of ​​the side is 500cm 2 A pair of 304L cathode plates 2 are provided, and then the zirconium alloy plate 3 is connected to the positive electrode of the DC power supply 4 through a wire, and the pair of 304L cathode plates 2 is connected to the negative electrode of the DC power supply 4 through a wire, and the zirconium alloy plate 3 is located between the pair of 304L cathode plates 2 and placed in parallel, that is, the two side surfaces of the zirconium alloy plate 3 are respectively opposite to the surface of a 304L cathode plate 2, and the distance between the zirconium alloy plate 3 and the pair of 304L cathode plates 2 is 2.5 cm; Step 2: A mixed electrolyte with a volume ratio of methanol: n-butanol: perchloric acid = 6:3:1 is loaded into the electrolytic cell 1 and the zirconium alloy plate 3 is immersed, and the mixed electrolyte is cooled to -25°C using liquid nitrogen, and then the power is set to 50W~100W, the voltage is 25V, and the current is 1.5A according to the unit surface area of ​​the zirconium alloy plate 3, and the zirconium alloy plate 3 is electropolished for 300s to remove the surface residual stress.

[0031] Figure 33 are scanning electron microscope images of the zirconium alloy plate before and after electrolytic polishing in this embodiment, wherein Figure (a) is a metallographic microscope image of the zirconium alloy plate before electrolytic polishing. From Figure (a), it can be seen that there are traces of processing streamlines on the surface of the zirconium alloy plate, which is relatively rough; Figure (b) is a metallographic microscope image of the zirconium alloy plate after electrolytic polishing. From Figure (b), it can be seen that the original processing traces of the zirconium alloy plate are removed after electrolytic polishing, and the surface is relatively flat, smooth and beautiful.

[0032] Example 4 This embodiment includes the following steps: Step 1: Cut a titanium block with a size of 200 mm in length × 100 mm in width × 0.3 mm in thickness as the titanium plate 3; According to the surface area of ​​the titanium plate 3 placed on the side of the treatment object 200cm 2 , select the matching size length × width × thickness of 250mm × 150mm × 3mm, and the surface area of ​​the side to be placed is 375cm 2 A pair of 304L cathode plates 2 are provided, and then the titanium plate 3 is connected to the positive electrode of the DC power supply 4 through a wire, and the pair of 304L cathode plates 2 are connected to the negative electrode of the DC power supply 4 through a wire, and the titanium plate 3 is located between the pair of 304L cathode plates 2 and placed in parallel, that is, the two side surfaces of the titanium plate 3 are respectively opposite to the surface of a 304L cathode plate 2, and the distance between the titanium plate 3 and the pair of 304L cathode plates 2 is 1.5 cm; Step 2: A mixed electrolyte with a volume ratio of methanol: n-butanol: perchloric acid = 6:3:1 is loaded into the electrolytic cell 1 and the titanium plate 3 is immersed, and the mixed electrolyte is cooled to -30°C using liquid nitrogen, and then the power is set to 50W~100W, the voltage is 50V, and the current is 1.7A according to the unit surface area of ​​the titanium plate 3, and the titanium plate 3 is electrolytically polished for 200s to remove the surface residual stress.

[0033] In order to compare the plastic deformation ability of the plate before and after electrolytic polishing, the pure titanium plate was tested by the Ehrlich cupping test. In this test, a ball-head punch was used to push the metal sheet, which was pressed by the die and the blank holder, into the die to form a hemispherical bulge until a crack appeared on the top of the bulge. During the test, a 90mm×90mm sample was cut and placed between the die and the blank holder to be pressed to death (the blank holder force was 10kN), and the punch pressing depth value / mm when the specimen just broke was measured, which is the cupping value. The cupping value can be used as an indicator of the material's bulging forming performance. The larger the cupping value, the better the bulging forming performance and the stronger the plastic deformation ability of the material.

[0034] Figure 4 The results of the Eschrich cupping test of the titanium plate before and after electrolytic polishing in this embodiment are shown in FIG. Figure 4It can be seen that the bulging forming performance and plastic deformation ability of titanium sheet can be improved after electrolytic polishing.

[0035] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent change made to the above embodiment according to the technical essence of the invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A device for removing residual stress on the surface of titanium or zirconium alloy plates over a large area, characterized in that: The invention comprises an electrolytic cell (1) for containing a mixed electrolyte, wherein the electrolytic cell (1) is further provided with a pair of 304L cathode plates (2) and a titanium or zirconium alloy plate (3), wherein the titanium or zirconium alloy plate (3) is located between the pair of 304L cathode plates (2), the pair of 304L cathode plates (2) are connected to the negative electrode of a direct current power source (4) via a wire, and the titanium or zirconium alloy plate (3) is connected to the positive electrode of the direct current power source (4) via a wire.

2. A method for removing residual stress on the surface of titanium or zirconium alloy plates over a large area using the device according to claim 1, characterized in that: The method comprises the following steps: Step 1: According to the surface area of ​​the titanium or zirconium alloy plate (3) to be treated, a pair of 304L cathode plates (2) of matching sizes are selected, and then the titanium or zirconium alloy plate (3) is connected to the positive electrode of a DC power source (4) through a wire, and the pair of 304L cathode plates (2) is connected to the negative electrode of the DC power source (4) through a wire, and the titanium or zirconium alloy plate (3) is located between the pair of 304L cathode plates (2); Step 2: Place the mixed electrolyte into the electrolytic cell (1), cool the mixed electrolyte using liquid nitrogen, then set the power and voltage parameters to electropolish the titanium or zirconium alloy plate (3) and remove the surface residual stress.

3. The method according to claim 2, characterized in that The titanium or zirconium alloy plate (3) in step 1 is selected from titanium, α, α+β, β-type titanium alloys, and zirconium, Zr-Nb, Zr-Sn, and Zr-Sn-Nb alloys.

4. The method according to claim 2, characterized in that: In step 1, the ratio of the surface areas of the titanium or zirconium alloy plate (3) to the opposing surfaces of the pair of 304L cathode plates (2) is 1:1.5 to 1:

5.

5. The method according to claim 2, characterized in that: In step 1, the titanium or zirconium alloy plate (3) is placed in parallel with a pair of 304L cathode plates (2), that is, the two side surfaces of the titanium or zirconium alloy plate (3) are respectively opposite to the surface of a 304L cathode plate (2), and the distance between the titanium or zirconium alloy plate (3) and the pair of 304L cathode plates (2) is 1 cm to 5 cm.

6. The method according to claim 2, characterized in that The components of the mixed electrolyte in step 2 are methanol: n-butanol: perchloric acid = 6~8: 3~5: 1~1.5 by volume.

7. The method according to claim 2, characterized in that In step 2, liquid nitrogen is used to cool the mixed electrolyte to -25°C to -50°C. The power is set to 50W to 100W and the voltage is set to 25V to 80V based on the unit surface area of ​​the titanium or zirconium alloy plate (3).

8. The method according to claim 2, characterized in that: The duration of the electrolytic polishing in step 2 is 60s to 300s.

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