Laser remelting treatment method for NbTi rod

Abstract

The invention discloses a laser remelting treatment method for an NbTi rod, and relates to the technical field of superconducting wire processing, and the laser remelting treatment method comprises the following steps: sampling on the NbTi rod, carrying out a laser remelting pre-experiment on an NbTi sample piece to obtain experiment results corresponding to different laser remelting process parameters, and selecting the optimal laser remelting process parameter according to the experiment results; carrying out laser remelting on the surface of the whole NbTi rod by adopting the optimal laser remelting process parameters; and the NbTi rod subjected to laser remelting is subjected to acid pickling. According to the NbTi / Cu composite wire, laser remelting is conducted on the surface of the whole NbTi rod, a large number of nanoscale grains and precipitated phases are introduced into the microstructure of the NbTi rod, more pinning centers can be formed during subsequent machining of the NbTi / Cu composite wire, the critical current density is improved, and meanwhile the NbTi / Cu composite wire has the advantages of being low in cost and short in period.

Description

Technical Field

[0001] The present application relates to the technical field of superconducting wire processing, and in particular to a laser remelting method for NbTi rods. Background Art

[0002] NbTi alloy is currently the most widely used superconducting material in the field of superconductivity, especially in the form of NbTi / Cu composite wires processed into magnets, which are used in fields such as magnetic resonance imaging. The source of NbTi alloy is mainly obtained by vacuum consumable arc furnace melting and high-temperature homogenization treatment of Nb ingots (melting point 2410℃) and high-purity sponge Ti (melting point 1687℃). In order to improve its superconducting performance and uniformity of organization, it is often necessary to forge the NbTi ingots to make the interior of the alloy equiaxed crystals. However, the surface of the forged NbTi rods will have periodically changing "wood grain", which is mainly related to the segregation of Nb. Improving superconducting performance by increasing the purity of raw materials will lead to increased costs, while the space for improving superconducting performance by regulating the heat treatment process is limited, and the processing cycle is long. Therefore, it is necessary to study the processing method of NbTi rods to improve their performance.

[0003] In the prior art, Chinese patent CN117680590A discloses a NbTi material for superconducting wire and a preparation method thereof, the method comprising: smelting, forging and forming NbTi ingots to obtain NbTi material; after smelting the NbTi ingots, before forging, performing at least one aging heat treatment; during forging, performing 1 to 3 aging heat treatments; after forging, performing 1 to 3 aging heat treatments.

[0004] However, the above-mentioned prior art has not studied or solved the problem of periodically changing "wood grain" on the surface of the forged NbTi rod, and the critical current density of the subsequent processing into NbTi / Cu composite wire is low; at the same time, the above-mentioned prior art uses a heat treatment process to improve the superconducting performance, and the processing cycle is long; in addition, if the superconducting performance is improved by increasing the purity of the raw materials, the cost is high. Summary of the invention

[0005] The present application provides a laser remelting method for NbTi rods, which is used to solve the problems in the existing superconducting wire processing technology, that is, the critical current density of the forged NbTi rods subsequently processed into NbTi / Cu composite wires is low, the processing cycle of the heat treatment process to improve the superconducting performance is long, and the cost of improving the superconducting performance by increasing the purity of the raw materials is high.

[0006] On the one hand, the present application provides a laser remelting method for NbTi rods, comprising the following steps: Step 1: Take samples from NbTi rods, perform laser remelting preliminary experiments on NbTi sample sheets, obtain experimental results corresponding to different laser remelting process parameters, and select optimal laser remelting process parameters according to the experimental results.

[0007] Step 2: laser remelting the entire surface of the NbTi rod using the optimal laser remelting process parameters.

[0008] Step 3: pickling the laser remelted NbTi rod.

[0009] In a possible implementation, in step 1, the sampling position on the NbTi rod is the middle of the ingot of the NbTi rod.

[0010] In a possible implementation, in step 1, the laser remelting process parameters include: laser power and scanning speed.

[0011] The laser power ranges from 2000 to 8000 W, and the scanning speed ranges from 200 to 1000 mm / s.

[0012] In a possible implementation, in step 2, before laser remelting the entire surface of the NbTi rod, Ar gas is introduced into the laser remelting chamber, and then vacuum is evacuated. When the vacuum degree of the processing chamber reaches 5×10 -4 MPa, the surface of the entire NbTi rod is laser remelted using the optimal laser remelting process parameters.

[0013] In a possible implementation, in step 2, laser remelting is performed on the surface of the entire NbTi rod using a zigzag scanning path with an overlap rate of 50%.

[0014] In a possible implementation, in step three, the pickling is performed using 60% by volume nitric acid, and the pickling time is 30-60 minutes.

[0015] In a possible implementation, step 3 further includes: Step 4: Perform ultrasonic testing and infrared flaw detection on the pickled NbTi rod. If defects are detected on the surface or inside of the NbTi rod, return to step 2 for a cycle, otherwise the process ends.

[0016] A laser remelting method for NbTi rods in this application has the following advantages: By laser remelting the entire surface of the NbTi rod, a large number of nano-scale grains and precipitated phases are introduced into the microstructure of the NbTi rod, which can form more pinning centers in the subsequent processing of NbTi / Cu composite wires, improve the critical current density, and have the advantages of low cost and short cycle.

[0017] By conducting a laser remelting preliminary experiment on the NbTi sample, the optimal laser remelting process parameters matching the NbTi rod can be obtained, thereby improving the reliability of laser remelting.

[0018] By acid washing the laser remelted NbTi rod, the adverse effect of oxidation on the superconducting properties caused by the possible presence of oxidation on the surface of the NbTi rod during the laser remelting process is reduced, and the surface defects of the NbTi rod are removed.

[0019] It is proposed that before laser remelting the entire surface of the NbTi rod, Ar gas is first introduced into the laser remelting processing chamber, and then vacuum is evacuated to avoid the introduction of elements such as H and O during the laser remelting process, thereby improving the laser remelting quality.

[0020] The proposed laser remelting of the entire surface of the NbTi rod adopts a zigzag scanning path, which improves the laser remelting uniformity.

[0021] By controlling the pickling time, washing away the remelted layer is avoided.

[0022] By performing ultrasonic testing and infrared flaw detection on the pickled NbTi rods, it is ensured that the NbTi rods have high surface quality and internal quality, and finally NbTi rods with good surface quality and excellent superconducting properties are obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A schematic flow chart of a laser remelting method for NbTi rods provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] Embodiment 1: like Figure 1 As shown, the embodiment of the present application provides a laser remelting method for NbTi rods, comprising the following steps: Step 1: Take samples from NbTi rods, perform laser remelting preliminary experiments on NbTi sample sheets, obtain experimental results corresponding to different laser remelting process parameters, and select optimal laser remelting process parameters according to the experimental results.

[0027] Step 2: laser remelting the entire surface of the NbTi rod using the optimal laser remelting process parameters.

[0028] Step 3: pickling the laser remelted NbTi rod.

[0029] Exemplarily, in step 1, the sampling position on the NbTi rod is the middle of the ingot of the NbTi rod.

[0030] Specifically, in this embodiment, in step 1, a sample is taken from the middle of an ingot of a batch of NbTi rods that have been smelted and forged, and the sampling size is 100 mm×50 mm×10 mm.

[0031] Exemplarily, in step one, the laser remelting process parameters include: laser power and scanning speed.

[0032] The laser power ranges from 2000 to 8000 W, and the scanning speed ranges from 200 to 1000 mm / s.

[0033] Specifically, in this embodiment, in step 1, the laser power is set to 4000W, 5000W, 6000W, 7000W, and 8000W, the scanning speed is set to 200mm / s, 300mm / s, 400mm / s, 500mm / s, and 600mm / s, and the spot diameter is 1mm. According to the laser energy density formula, E v =P / (V×D). Among them, E v is the laser energy density, in J·mm -2 ; P is the laser power, unit is W; V is the scanning speed, unit is mm / s; D is the spot diameter, unit is mm.

[0034] In this embodiment, by designing orthogonal experiments, experimental results of 25 cases of 5 laser powers and 5 scanning speeds were obtained, namely, the depth, width and surface quality of 25 remelted layers on the NbTi sample. Among them, the laser power of 8000W and the scanning speed of 200mm / s correspond to the deepest depth, the widest width and the best surface quality of the remelted layer, so the laser power of 8000W and the scanning speed of 200mm / s were selected as the optimal laser remelting process parameters of this embodiment.

[0035] For example, in step 2, before laser remelting the entire surface of the NbTi rod, Ar gas is introduced into the laser remelting chamber, and then vacuum is evacuated. When the vacuum degree of the processing chamber reaches 5×10 -4 MPa, the surface of the entire NbTi rod is laser remelted using the optimal laser remelting process parameters.

[0036] Specifically, in this embodiment, in step 2, the time for introducing Ar gas is 2 hours.

[0037] Exemplarily, in step 2, laser remelting of the entire surface of the NbTi rod is performed using a zigzag scanning path with an overlap rate of 50%.

[0038] Exemplarily, in step three, the pickling uses 60% by volume nitric acid, and the pickling time is 30-60 minutes.

[0039] Specifically, in this embodiment, in step three, the laser remelted NbTi rod is completely immersed in 60% by volume nitric acid, and the pickling time is 30 minutes.

[0040] Exemplarily, step three further includes: Step 4: Perform ultrasonic testing and infrared flaw detection on the pickled NbTi rod. If defects are detected on the surface or inside of the NbTi rod, return to step 2 for a cycle, otherwise the process ends.

[0041] Specifically, in this embodiment, in step 4, ultrasonic testing and infrared flaw detection are performed on the NbTi rod after pickling, and there are no defects on the surface and inside of the NbTi rod, so that a NbTi rod with good surface quality and excellent superconducting performance is obtained.

[0042] Embodiment 2: Specifically, in this embodiment, in step 1, a sample is taken from the middle of a batch of NbTi rods that has been smelted and forged and is different from that in embodiment 1, and the sampling size is 200 mm×50 mm×10 mm.

[0043] Specifically, in this embodiment, in step 1, the laser power is set to 7 types, namely 2000W, 3000W, 4000W, 5000W, 6000W, 7000W, and 8000W, the scanning speed is set to 5 types, namely 200mm / s, 300mm / s, 400mm / s, 500mm / s, and 600mm / s, and the spot diameter is 1mm. According to the laser energy density formula, E v =P / (V×D). Among them, E v is the laser energy density, in J·mm -2; P is the laser power, unit is W; V is the scanning speed, unit is mm / s; D is the spot diameter, unit is mm.

[0044] In this embodiment, by designing orthogonal experiments, experimental results of 35 cases of 7 laser powers and 5 scanning speeds were obtained, namely, the depth, width and surface quality of 35 remelting layers on NbTi samples. The remelting layer corresponding to the laser power of 8000W and the scanning speed of 200mm / s has the deepest depth and the widest width, but there is yellow and gray oxidation on the surface, so the laser power of 7000W and the scanning speed of 200mm / s with relatively better surface quality are selected as the optimal laser remelting process parameters of this embodiment.

[0045] Specifically, in this embodiment, in step 2, the time for introducing Ar gas is 2 hours.

[0046] Specifically, in this embodiment, in step three, the laser remelted NbTi rod is completely immersed in 60% by volume nitric acid, and the pickling time is 45 minutes.

[0047] The other steps and parameters of Example 2 are the same as those of Example 1.

[0048] Specifically, in this embodiment, in step 4, ultrasonic testing and infrared flaw detection are performed on the NbTi rod after pickling, and there are no defects on the surface and inside of the NbTi rod, so that a NbTi rod with good surface quality and excellent superconducting performance is obtained.

[0049] Embodiment 3: Specifically, in this embodiment, in step 1, a sample is taken from the middle of a batch of NbTi rods that has been smelted and forged and is different from that in Embodiment 1 and Embodiment 2, and the sampling size is 300 mm×50 mm×10 mm.

[0050] Specifically, in this embodiment, in step 1, the laser power is set to 2000W, 3000W, 4000W, 5000W, 6000W, 7000W, and 8000W, and the scanning speed is set to 400mm / s, 500mm / s, 600mm / s, 700mm / s, 800mm / s, 900mm / s, and 1000mm / s, and the spot diameter is 1mm. According to the laser energy density formula, E v =P / (V×D). Among them, E v is the laser energy density, in J·mm -2 ; P is the laser power, unit is W; V is the scanning speed, unit is mm / s; D is the spot diameter, unit is mm.

[0051] In this embodiment, by designing orthogonal experiments, experimental results of 49 cases of 7 laser powers and 7 scanning speeds were obtained, namely, the depth, width and surface quality of 49 remelted layers on NbTi samples. Among them, the remelted layer corresponding to the laser power of 8000W and the scanning speed of 400mm / s has the deepest depth, the widest width and the best surface quality, so the laser power of 8000W and the scanning speed of 400mm / s are selected as the optimal laser remelting process parameters of this embodiment.

[0052] Specifically, in this embodiment, in step 2, the time for introducing Ar gas is 2 hours.

[0053] Specifically, in this embodiment, in step three, the laser remelted NbTi rod is completely immersed in 60% by volume nitric acid, and the pickling time is 60 minutes.

[0054] The other steps and parameters of Example 3 are the same as those of Example 1.

[0055] Specifically, in this embodiment, in step 4, ultrasonic testing and infrared flaw detection are performed on the NbTi rod after pickling, and there are no defects on the surface and inside of the NbTi rod, so that a NbTi rod with good surface quality and excellent superconducting performance is obtained.

[0056] The embodiment of the present application introduces a large number of nano-scale grains and precipitated phases into the microstructure of the NbTi rod by laser remelting the entire surface of the NbTi rod, which can form more pinning centers during the subsequent processing of the NbTi / Cu composite wire, thereby improving the critical current density and having the advantages of low cost and short cycle.

[0057] By conducting a laser remelting preliminary experiment on the NbTi sample, the optimal laser remelting process parameters matching the NbTi rod can be obtained, thereby improving the reliability of laser remelting.

[0058] By acid washing the laser remelted NbTi rod, the adverse effect of oxidation on the superconducting properties caused by the possible presence of oxidation on the surface of the NbTi rod during the laser remelting process is reduced, and the surface defects of the NbTi rod are removed.

[0059] It is proposed that before laser remelting the entire surface of the NbTi rod, Ar gas is first introduced into the laser remelting processing chamber, and then vacuum is evacuated to avoid the introduction of elements such as H and O during the laser remelting process, thereby improving the laser remelting quality.

[0060] The proposed laser remelting of the entire surface of the NbTi rod adopts a zigzag scanning path, which improves the laser remelting uniformity.

[0061] By controlling the pickling time, washing away the remelted layer is avoided.

[0062] By performing ultrasonic testing and infrared flaw detection on the pickled NbTi rods, it is ensured that the NbTi rods have high surface quality and internal quality, and finally NbTi rods with good surface quality and excellent superconducting properties are obtained.

[0063] Although the preferred embodiments of the present application have been described, those skilled in the art may make other changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application.

[0064] Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A laser remelting method for NbTi rods, characterized in that: The following steps are involved: Step 1: sampling from a NbTi rod, performing a laser remelting preliminary experiment on the NbTi sample sheet, obtaining experimental results corresponding to different laser remelting process parameters, and selecting the best laser remelting process parameters according to the experimental results; Step 2, laser remelting the entire surface of the NbTi rod using the optimal laser remelting process parameters; Step 3: pickling the laser remelted NbTi rod.

2. The laser remelting method of NbTi rod according to claim 1, characterized in that: In step 1, the sampling position on the NbTi rod is the middle of the ingot of the NbTi rod.

3. The laser remelting method of NbTi rod according to claim 1, characterized in that: In step 1, the laser remelting process parameters include: laser power and scanning speed; The laser power ranges from 2000 to 8000 W, and the scanning speed ranges from 200 to 1000 mm / s.

4. The laser remelting method of NbTi rod according to claim 1, characterized in that: In step 2, before laser remelting the entire surface of the NbTi rod, Ar gas is introduced into the laser remelting chamber, and then vacuum is evacuated. When the vacuum degree of the processing chamber reaches 5×10 -4 MPa, the surface of the entire NbTi rod is laser remelted using the optimal laser remelting process parameters.

5. The laser remelting method of NbTi rod according to claim 1, characterized in that: In step 2, the entire surface of the NbTi rod is laser remelted using a zigzag scanning path with an overlap rate of 50%.

6. The laser remelting method of NbTi rod according to claim 1, characterized in that: In step three, the pickling is performed using 60% by volume nitric acid, and the pickling time is 30-60 minutes.

7. The laser remelting method of NbTi rod according to claim 1, characterized in that: After step 3, it also includes: Step 4: Perform ultrasonic testing and infrared flaw detection on the pickled NbTi rod. If defects are detected on the surface or inside of the NbTi rod, return to step 2 for a cycle, otherwise the process ends.

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