CN114783681B - Preparation method of ultra-low-loss NbTi superconducting wire - Google Patents
Preparation method of ultra-low-loss NbTi superconducting wire Download PDFInfo
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Abstract
The invention belongs to the technical field of superconducting wire preparation processes, and relates to a preparation method of an ultra-low loss NbTi superconducting wire. The multi-core secondary composite rod is prepared by 3D printing of the porous copper tube, the 10 ten thousand-core high-critical-current-density and ultralow-loss NbTi superconducting wire is successfully prepared by three times of tube penetration and combination of multiple aging heat treatments, the traditional hot extrusion process is omitted in the preparation of the primary single-core fine wire and the secondary composite rod, and the problems of high wire loss of the superfine core wire, poor deformation of the core wire, low yield and the like are thoroughly solved.
Description
Technical Field
The invention belongs to the technical field of superconducting wire preparation processes, relates to an NbTi superconducting wire, and particularly relates to a preparation method of an ultra-low loss NbTi superconducting wire.
Background
With the continuous start of the overall planning, conceptual design, construction and upgrading of large-scale scientific devices at home and abroad, the devices comprise an international thermonuclear fusion experimental reactor (ITER), a Large Hadron Collider (LHC), a heavy ion accelerator project (HIAF), a ring-shaped positive and negative electron collider (CEPC) and the like which are continuously concerned by top physicists in the world, and one of key materials used in the large-scale scientific devices is a superconducting wire. It is known in the art that a superconducting wire has a zero resistance characteristic at a low temperature, and due to the characteristic of the self-meissner, a large amount of magnetic field can be generated in a low-temperature environment, and the ultrahigh magnetic field strength and the ultrafast change rate of the magnetic field strength can accelerate charged particles and deflect the moving particles. In order to generate high magnetic field strength and high magnetic field change rate, the superconducting wire used is required to have both ultra-high critical current density and ultra-low loss. The internationally recognized low-temperature superconducting wire at present also belongs to an NbTi superconducting wire with the highest cost performance, and the excellent processing performance of the low-temperature superconducting wire enables a magnet or a stranded cable to be wound more conveniently and can be prepared into superconducting magnets in various shapes.
The existing special fast pulse superconducting magnet requires that an NbTi wire has ultralow loss, so that the NbTi wire is required to be made of a high-resistance copper alloy material instead of copper in the preparation process, and the resistivity of a matrix is increased; the conventional low-loss wire rod is usually made of CuNi or CuMn alloy, the higher the Ni content and the Mn content in the alloy are, the larger the matrix resistance is, but the hardness of the corresponding wire rod can be greatly increased, so that the fine-drawn wire rod is frequently broken, and therefore, in order to introduce a matrix material with higher resistance and ensure the stable processing process of the superfine core wire rod, the conventional mode is inevitably unavailable. Meanwhile, in order to reduce the loss of the NbTi wire rod, the core number of the wire rod needs to be increased, and the loss is lower as the core number is larger and the core wire is thinner, so the invention prepares the NbTi superconducting wire rod with ultralow loss based on the two aspects.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide a preparation method of an ultra-low loss NbTi superconducting wire, which ensures that the ultra-fine core wire has excellent processing performance and has ultra-low loss.
In order to achieve the purpose, the invention provides the following technical scheme:
the preparation method of the ultra-low loss NbTi superconducting wire specifically comprises the following steps:
step 1), preparing an NbTi/Cu single core rod;
step 2), stretching the NbTi/Cu single-core rod into a fine wire, electroplating Ni to obtain the NbTi/Cu single-core fine wire with the surface uniformly plated with Ni, and cutting the fine wire to length;
step 3), preparing a porous copper pipe by using high-purity copper powder in a 3D printing mode;
step 4), inserting the NbTi/Cu single-core thin wire with the surface uniformly plated with Ni in the step 2) into the porous copper pipe in the step 3), and obtaining an NbTi/Cu secondary composite rod through drawing, sizing cutting and straightening treatment;
step 5), tightly arranging the cleaned NbTi/Cu secondary composite rods in a copper pipe, and combining multiple aging heat treatments in the cold drawing process to obtain a tertiary composite wire;
and 6) carrying out vacuum low-temperature annealing treatment on the tertiary composite wire to fully diffuse Ni and Cu in the matrix to form a Cu-Ni solid solution, and finally obtaining the NbTi superconducting wire with ultralow loss.
Further, the step 1) specifically comprises:
firstly, placing a cleaned NbTi rod at the center of a casting mould prepared in advance;
heating and insulating the casting mould at the heating temperature of 100-200 ℃ for 30-90 min;
then slowly pouring molten copper into the mold, wherein the casting temperature is 1100-1200 ℃, and the casting speed is 150-250 mm/min;
finally obtaining the NbTi/Cu single core rod by cooling and demoulding, coolingThe water flow is 0.5-1.5 m 3 And h, the outer diameter of the NbTi/Cu single core rod is not more than phi 100 mm.
Further, in the step 2), when the size of the NbTi/Cu single core rod is phi 70 mm-phi 100mm, the NbTi/Cu single core rod is drawn by a roller die, and the processing rate of each pass is not more than 5%; when the size of the NbTi/Cu single core rod is smaller than phi 70mm, cold drawing is carried out by adopting a conventional die, the processing rate of each pass is not more than 15%, and the processing rate of each pass of peeling is not more than 3%; the size of the finally formed NbTi/Cu single-core thin wire is phi 1 mm-phi 3mm, and the thickness of the Ni coating is 5-10 mu m.
Further, in the step 3), the outer diameter of the porous copper pipe is not more than 100mm, the surface roughness Ra of the porous copper pipe is less than 3.2 microns, the total bending degree of the porous copper pipe is not more than 1mm/1000mm, the number of pores of the porous copper pipe is 1000-4000, and the size of the pores is 1-2 mm.
Further, in the step 4), when the size of the NbTi/Cu secondary composite rod is phi 70 mm-phi 100mm, a roller die is adopted for drawing, and the processing rate of each pass is not more than 5%; when the size of the NbTi/Cu secondary composite rod is smaller than phi 70mm, cold drawing is carried out by adopting a conventional die, the processing rate of each pass is not more than 15%, the die selects a small-angle die, and the total bending degree of each NbTi/Cu secondary composite rod is not more than 1mm/1000mm in the straightening process.
Further, in the step 5), the final size of the three-time composite wire is phi 0.8mm, the processing rate of each pass of cold drawing of the die is not more than 20%, the aging heat treatment temperature is 350-450 ℃, the times are 3-5, and the heat treatment time is 20-40 h each time.
Further, in the step 6), the vacuum degree of vacuum annealing of the three times of composite wires is less than 1 multiplied by 10 -3 Pa, the annealing temperature is 700-800 ℃, and the annealing time is 3-5 h.
Compared with the prior art, the technical scheme provided by the invention has the following beneficial effects: preparing an NbTi/Cu single-core rod by adopting a casting method, cold-drawing the NbTi/Cu single-core rod into a fine wire, uniformly plating nickel on the surface of the fine wire, and finally carrying out annealing heat treatment to improve the resistivity of a wire substrate; the resistivity of the matrix is regulated and controlled by adjusting the thickness of the nickel coating, so that the superfine core wire rod is ensured to have excellent processing performance and ultralow loss. Meanwhile, an NbTi/Cu secondary composite rod is prepared on the basis of 3D printing of a porous copper tube, a 10-ten-thousand-core high-critical-current-density and ultralow-loss NbTi superconducting wire is successfully prepared by three times of tube penetration and combination of multiple aging heat treatments, the traditional hot extrusion process is replaced by a preparation process of a primary single-core fine wire and a secondary composite rod, and the problems of high loss of the superfine core wire and the wire, poor deformation of the core wire, low yield and the like are thoroughly solved.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.
In order to more clearly illustrate the embodiments or technical solutions in the prior art of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious for those skilled in the art to obtain other drawings without inventive labor.
FIG. 1 is a flow chart of a method for preparing an ultra-low loss NbTi superconducting wire rod provided by the invention;
fig. 2 is a design diagram of a 3169 hole copper pipe structure provided in embodiment 1 of the present invention;
FIG. 3 is a structural design diagram of a NbTi/Cu triple composite wire (121 core) provided in example 1 of the present invention;
fig. 4 is a design diagram of a 1141 hole copper pipe structure provided in embodiment 2 of the present invention;
FIG. 5 is a structural design diagram of a NbTi/Cu triple composite wire (114 core) provided in example 2 of the present invention;
FIG. 6 is a structural design diagram of an NbTi/Cu triple composite wire (85 core) provided in example 3 of the present invention;
FIG. 7 is a structural design diagram of a NbTi/Cu triple composite wire (78 core) provided in example 4 of the present invention;
FIG. 8 is a structural design diagram of a NbTi/Cu triple composite wire (37 core) provided in example 5 of the present invention.
Detailed Description
Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of methods consistent with certain aspects of the invention, as detailed in the appended claims.
In order to make those skilled in the art better understand the technical solution of the present invention, the following detailed description of the present invention is provided with reference to the accompanying drawings and examples.
The invention relates to a preparation method of an ultra-low loss NbTi superconducting wire, which is shown in figure 1 and is implemented according to the following steps:
step 1, placing a cleaned NbTi rod in the center of a casting mold prepared in advance, starting heating the mold and preserving heat for a period of time, then slowly pouring molten copper into the mold, and finally obtaining an NbTi/Cu single core rod through cooling and demolding;
wherein the chemical composition of copper in the NbTi/Cu single core rod is limited in the range of oxygen-free copper, the heating temperature of a die is 100-200 ℃, the heat preservation time is 30-90 min, the casting temperature is 1100-1200 ℃, the casting speed is 150-250 mm/min, and the cooling water flow of the die is 0.5-1.5 m 3 H, the maximum size of the outer diameter of the cast single core rod does not exceed phi 100 mm;
step 2, drawing the NbTi/Cu single-core rod through a multi-pass roller die, peeling and cold drawing of a die, finally drawing the NbTi/Cu single-core rod into a thin wire, then electroplating Ni to obtain the NbTi/Cu single-core thin wire with the surface uniformly plated with Ni, and finally cutting the thin wire to a fixed length;
wherein when the size of the NbTi/Cu single-core rod is phi 70 mm-phi 100mm, the rolling die is adopted for drawing, and the processing rate of each pass is not more than 5%; when the size of the NbTi/Cu single-core rod is smaller than phi 70mm, cold drawing is carried out by adopting a conventional die, the processing rate of each pass is not more than 15%, the processing rate of each pass of peeling is not more than 3%, the size of the final single-core thin wire is phi 1 mm-phi 3mm, and the thickness of a Ni coating is 5-10 mu m;
step 3, preparing the porous copper pipe by using the prepared high-purity copper powder in a 3D printing mode, wherein the size and the number of holes in the copper pipe can be flexibly adjusted;
the chemical components of the high-purity copper powder are limited in an analytical purity range, the chemical components of the porous copper pipe are limited in an oxygen-free copper range, the maximum size of the outer diameter of the porous copper pipe is not more than 100mm, the surface roughness Ra of the porous copper pipe is less than 3.2 mu m, the total bending degree of the porous copper pipe is not more than 1mm/1000mm, the number of pores of the porous copper pipe is 1000-4000, and the size of the pores is 1-2 mm;
step 4, inserting the cleaned NbTi/Cu single-core thin rods with uniformly plated Ni on the surface into the prepared porous copper pipe in order, then adopting a roller die to draw the nickel-plated single-core thin rods and the porous copper pipe to be tightly combined, and finally adopting a multi-pass die to carry out cold drawing, cut to length and straighten to obtain NbTi/Cu secondary composite rods with different specifications and lengths;
wherein when the size of the NbTi/Cu secondary composite rod is phi 70 mm-phi 100mm, the NbTi/Cu secondary composite rod is drawn by a roller die, and the processing rate of each pass is not more than 5%; when the size of the NbTi/Cu secondary composite rod is smaller than phi 70mm, cold drawing is carried out by adopting a conventional die, the processing rate of each pass is not more than 15%, the die selects a small-angle 6-degree die, and the total bending degree of each NbTi/Cu secondary composite rod is not more than 1mm/1000mm in the straightening process;
step 5, closely arranging the cleaned and sized NbTi/Cu secondary composite rods in the copper pipe again, adopting a multi-pass die to carry out cold drawing to enable the rods to be closely combined to obtain a third composite wire, combining the cold drawing process of the third composite wire with multiple aging heat treatments to enable NbTi to separate out a large amount of alpha-Ti, and improving the magnetic flux pinning performance of the wire;
wherein the final size of the tertiary composite line is phi 0.8mm, the processing rate of each pass of cold drawing of the die is not more than 20%, the temperature of aging heat treatment is 350-450 ℃, the times are 3-5, and the time of each heat treatment is 20-40 h;
step 6, winding the tertiary composite wire on a stainless steel wire wheel for vacuum low-temperature annealing, so that Ni and Cu in the matrix are fully diffused to form a Cu-Ni solid solution, and finally obtaining the NbTi superconducting wire with ultralow loss;
wherein the vacuum degree of the three times of composite wire vacuum annealing is less than 1 multiplied by 10 -3 Pa, the annealing temperature is 700-800 ℃, and the annealing time is 3-5 h.
Example 1
The embodiment provides a preparation method of an ultra-low loss NbTi superconducting wire, which is implemented according to the following steps:
step 1, heating a die with the outer diameter of phi 101mm to 150 ℃, preserving heat for 1h, then placing an NbTi rod with the diameter of phi 78mm at the central position of the die, then pouring molten copper into the die, wherein the casting temperature is 1150 ℃, the casting speed is 250mm/min, and the flow of cooling water of the die is 1m 3 Finally, obtaining the NbTi/Cu single core rod through demoulding;
step 2, drawing the single-core rod with the diameter phi of 100mm to phi of 70mm by using a roller die, wherein the processing rate of each pass is not more than 5%, then drawing to phi of 0.985mm by using a conventional peeling die and a drawing die, wherein the thickness of the electroplated Ni is 5 mu m, and finally cutting the Ni-plated single-core thin wire with the diameter phi of 1.0mm to 2000mm in length in a fixed length manner;
step 3, inserting the single-core thin wires into the porous copper pipe in order, wherein the outer diameter of the copper pipe is phi 100mm, the number of holes is 3169, then adopting a roller die to draw and stretch the copper pipe to phi 70mm, then adopting a conventional die to cold-draw to phi 4.45mm, the processing rate of each pass of the roller die drawing is not more than 5%, the processing rate of each pass of the conventional die cold-drawing is not more than 15%, selecting a die with a small angle of 6 degrees, and finally cutting and straightening to obtain a secondary composite rod;
step 4, arranging 121 secondary composite rods in a copper pipe with phi 66mm in outer diameter and 5.5mm in wall thickness in a neat and close manner, cold-drawing the assembled tertiary composite wire by using a conventional die, wherein the processing rate of each pass is not more than 20%, carrying out aging heat treatment on different specifications in the cold-drawing process to separate a large amount of alpha-Ti out of NbTi, wherein the total times of the aging heat treatment are 5 times, the heat treatment temperature is 380 ℃ each time, the heat treatment time is 40h each time, and finally drawing to obtain a phi 0.8mm NbTi/Cu tertiary composite wire;
step 5, rewinding the three-time composite wire to a stainless steel wire wheel for vacuum annealing, wherein the annealing vacuum degree is less than 1 multiplied by 10 - 3 Pa, the annealing temperature is 700 ℃, the annealing time is 4h, and finally the NbTi/Cu superconducting wire with ultra-low loss is obtained, wherein the structural diagram of 3169 porous copper tubes is shown in figure 2, and the structural design diagram of a 121-core three-time composite wire is shown in figure 3.
The NbTi superconducting wire with low loss prepared by the preparation method provided by the embodiment is uniformly plated with Ni on the surface of a single-core thin wire, the resistivity of a matrix is improved through final vacuum annealing, the core number of the wire is increased through three-time compounding, the diameter of a core wire is reduced, the loss of the wire is reduced in all aspects, the core number of the finally prepared three-time composite wire is 383449 cores, the diameter of the core wire is about 750nm, and the critical current density is up to 3280A/mm 2 (4T, 4.22K), and the loss of the wire rod in unit volume is 12.3mJ/cm 3 。
Example 2
The embodiment provides another preparation method of an ultra-low loss NbTi superconducting wire, which is implemented according to the following steps:
step 1, heating a die with the outer diameter of phi 76mm to 100 ℃, preserving heat for 1h, then placing an NbTi rod with the diameter of phi 58mm at the central position of the die, then pouring molten copper into the die, wherein the casting temperature is 1150 ℃, the casting speed is 150mm/min, and the flow rate of cooling water of the die is 0.5m 3 H, finally obtaining the NbTi/Cu single core rod through demoulding;
step 2, drawing the single-core rod with the diameter phi of 75mm to phi 1.990mm by adopting a conventional peeling die and a drawing die, electroplating Ni with the thickness of 10 mu m, and finally cutting the Ni-plated single-core thin wire with the diameter phi of 2.0mm to 2000mm in length in a fixed length mode;
step 3, inserting the single-core thin wires into the porous copper pipe in order, wherein the outer diameter of the copper pipe is phi 100mm, the number of holes is 1141, drawing the copper pipe to phi 70mm by adopting a roller die, then cold-drawing the copper pipe to phi 4.45mm by adopting a conventional die, wherein the processing rate of each pass of the roller die drawing is not more than 5 percent, the processing rate of each pass of the conventional die cold-drawing is not more than 15 percent, the die selects a die with a small angle of 6 degrees, and finally, a secondary composite rod is obtained by cutting and straightening;
step 4, arranging 114 secondary composite rods and 7 copper rods in a copper pipe with phi 66mm in outer diameter and 5.5mm in wall thickness in a neat and close manner, cold-drawing the assembled tertiary composite wire by adopting a conventional die, wherein the processing rate of each pass is not more than 20%, carrying out aging heat treatment on different specifications in the cold-drawing process to separate out a large amount of alpha-Ti from NbTi, wherein the total times of the aging heat treatment are 4 times, the heat treatment temperature of each time is 400 ℃, the heat treatment time of each time is 30 hours, and finally stretching to obtain a phi 0.8mm NbTi/Cu tertiary composite wire;
step 5, rewinding the three-time composite wire to a stainless steel wire wheel for vacuum annealing, wherein the annealing vacuum degree is less than 1 multiplied by 10 - 3 Pa, the annealing temperature is 750 ℃, the annealing time is 5h, and finally the NbTi/Cu superconducting wire with ultra-low loss is obtained, wherein the structural diagram of 1141 porous copper tubes is shown in figure 4, and the structural design diagram of a 114-core three-time composite wire is shown in figure 5.
The NbTi superconducting wire with low loss prepared by the preparation method provided by the embodiment is uniformly plated with Ni on the surface of a single-core thin wire, the resistivity of a matrix is improved through final vacuum annealing, the core number of the wire is increased through three times of compounding, the diameter of a core wire is reduced, the loss of the wire is reduced in all aspects, the number of the cores of the three times of compounding finally prepared is 130074 cores, the diameter of the core wire is about 1.3 mu m, and the critical current density is as high as 3190A/mm 2 (4T, 4.22K) and a loss per unit volume of 15.7mJ/cm 3 。
Example 3
The embodiment provides a preparation method of an ultra-low loss NbTi superconducting wire, which is implemented according to the following steps:
step 1, heating a die with the outer diameter of phi 101mm to 150 ℃, preserving heat for 1h, then placing an NbTi rod with the diameter of phi 78mm at the central position of the die, then pouring molten copper into the die, wherein the casting temperature is 1150 ℃, the casting speed is 250mm/min, and the flow of cooling water of the die is 1m 3 Finally, obtaining the NbTi/Cu single core rod through demoulding;
step 2, drawing the single-core rod with the diameter phi of 100mm to phi of 70mm by adopting a roller die, wherein the processing rate of each pass is not more than 5%, then drawing to phi of 0.985mm by adopting a conventional peeling die and a drawing die, wherein the thickness of the electroplated Ni is 5 mu m, and finally cutting the Ni-plated single-core thin wire with the diameter phi of 1.0mm to 2000mm in length in a fixed length manner;
step 3, inserting the single-core thin wires into the porous copper pipe in order, wherein the outer diameter of the copper pipe is phi 100mm, the number of holes is 3169, drawing the copper pipe to phi 70mm by adopting a roller die, then cold-drawing the copper pipe to phi 4.45mm by adopting a conventional die, wherein the machining rate of each pass of the roller die drawing is not more than 5 percent, the machining rate of each pass of the conventional die cold-drawing is not more than 15 percent, the die selects a small-angle 6-degree die, and finally, cutting and straightening are carried out to obtain a secondary composite rod;
step 4, arranging 85 secondary composite rods in a copper pipe with phi 52mm in outer diameter and 3mm in wall thickness in a neat and close manner, cold-drawing the assembled tertiary composite wire by using a conventional die, wherein the processing rate of each pass is not more than 20%, carrying out aging heat treatment on different specifications in the cold-drawing process to separate a large amount of alpha-Ti out of NbTi, the total times of the aging heat treatment are 3 times, the heat treatment temperature is 450 ℃ each time, the heat treatment time is 20h each time, and finally stretching to obtain a phi 0.8mm NbTi/Cu tertiary composite wire;
step 5, rewinding the three-time composite wire to a stainless steel wire wheel for vacuum annealing, wherein the annealing vacuum degree is less than 1 multiplied by 10 - 3 Pa, the annealing temperature is 750 ℃, the annealing time is 4h, and finally the NbTi/Cu superconducting wire with ultralow loss is obtained, wherein the structural diagram of 3169 porous copper tubes is shown in figure 2, and the structural design diagram of a 85-core three-time composite wire is shown in figure 6.
The low-loss NbTi superconducting wire prepared by the preparation method provided by the embodiment is uniformly plated with Ni on the surface of a single-core thin wire, the resistivity of a matrix is improved through final vacuum annealing, the core number of the wire is increased through three times of compounding, the diameter of a core wire is reduced, the loss of the wire is reduced in all aspects, the number of the cores of the three times of compounding wires finally prepared is 269365, the diameter of the core wire is about 950nm, and the critical current density is up to 3270A/mm 2 (4T, 4.22K), and the loss of the wire rod in unit volume is 13.3mJ/cm 3 。
Example 4
The embodiment provides another preparation method of an ultra-low loss NbTi superconducting wire, which is implemented according to the following steps:
step 1, heating a die with the outer diameter of phi 76mm to 100 ℃, preserving heat for 1h, then placing an NbTi rod with the diameter of phi 58mm at the central position of the die, then pouring molten copper into the die, wherein the casting temperature is 1150 ℃, the casting speed is 150mm/min, and the flow rate of cooling water of the die is 0.5m 3 Finally, obtaining the NbTi/Cu single core rod through demoulding;
step 2, drawing the single-core rod with the diameter phi of 75mm to phi of 1.990mm by adopting a conventional skinning die and a drawing die, electroplating Ni with the thickness of 10 mu m, and finally cutting the Ni-plated single-core fine wire with the diameter phi of 2.0mm to 2000mm in length;
step 3, inserting the single-core thin wires into a porous copper pipe in order, wherein the outer diameter of the copper pipe is phi 100mm, the number of holes is 1141, drawing the copper pipe to phi 70mm by adopting a roller die, then cold-drawing the copper pipe to phi 4.45mm by adopting a conventional die, wherein the machining rate of each pass of the roller die drawing is not more than 5 percent, the machining rate of each pass of the conventional die cold-drawing is not more than 15 percent, the die selects a small-angle 6-degree die, and finally, cutting and straightening are carried out to obtain a secondary composite rod;
step 4, densely arranging 78 secondary composite rods and 7 copper rods in a copper pipe with phi 52mm in outer diameter and 3mm in wall thickness, cold-drawing the assembled tertiary composite wire by using a conventional die, wherein the processing rate of each pass does not exceed 20%, performing aging heat treatment on different specifications in the cold-drawing process to separate out a large amount of alpha-Ti from NbTi, wherein the total times of the aging heat treatment are 4 times, the heat treatment temperature is 400 ℃ each time, the heat treatment time is 30 hours each time, and finally stretching to obtain a phi 0.8mm NbTi/Cu tertiary composite wire;
step 5, rewinding the three-time composite wire to a stainless steel wire wheel for vacuum annealing, wherein the annealing vacuum degree is less than 1 multiplied by 10 - 3 Pa, the annealing temperature is 750 ℃, the annealing time is 5h, and finally the NbTi/Cu superconducting wire with ultra-low loss is obtained, wherein the structural diagram of 1141 porous copper tubes is shown in figure 4, and the structural design diagram of 78-core three-time composite wire is shown in figure 7.
The low-loss NbTi superconducting wire prepared by the preparation method provided by the embodiment is uniformly plated with Ni on the surface of a single-core thin wire, the resistivity of a matrix is improved through final vacuum annealing, the core number of the wire is increased through three times of compounding, the diameter of a core wire is reduced, the loss of the wire is reduced in all aspects, the number of the cores of the three-time compounded wire finally prepared is 88998, the diameter of the core wire is about 1.6 mu m, and the critical current density is up to 3266A/mm 2 (4T, 4.22K) and a loss per unit volume of 17.7mJ/cm 3 。
Example 5
The embodiment provides another preparation method of an ultra-low loss NbTi superconducting wire, which is implemented according to the following steps:
step 1, heating a die with the outer diameter of phi 101mm to 150 ℃, preserving heat for 1h, then placing an NbTi rod with the diameter of phi 78mm at the central position of the die, then pouring molten copper into the die, wherein the casting temperature is 1150 ℃, the casting speed is 250mm/min, and the flow of cooling water of the die is 1m 3 Finally, obtaining the NbTi/Cu single core rod through demoulding;
step 2, drawing the single-core rod with the diameter phi of 100mm to phi of 70mm by using a roller die, wherein the processing rate of each pass is not more than 5%, then drawing to phi of 0.985mm by using a conventional peeling die and a drawing die, wherein the thickness of the electroplated Ni is 5 mu m, and finally cutting the Ni-plated single-core thin wire with the diameter phi of 1.0mm to 2000mm in length in a fixed length manner;
step 3, inserting the single-core thin wires into the porous copper pipe in order, wherein the outer diameter of the copper pipe is phi 100mm, the number of holes is 3169, drawing the copper pipe to phi 70mm by adopting a roller die, then cold-drawing the copper pipe to phi 5.0mm by adopting a conventional die, wherein the machining rate of each pass of the roller die drawing is not more than 5 percent, the machining rate of each pass of the conventional die cold-drawing is not more than 15 percent, the die selects a small-angle 6-degree die, and finally, cutting and straightening are carried out to obtain a secondary composite rod;
step 4, arranging the 37 secondary composite rods in a copper pipe with phi 44mm of outer diameter and 4mm of wall thickness in a neat and close manner again, cold-drawing the assembled tertiary composite wire by adopting a conventional die, wherein the processing rate of each pass does not exceed 20%, carrying out aging heat treatment on different specifications in the cold-drawing process to separate out a large amount of alpha-Ti from NbTi, wherein the total times of the aging heat treatment are 4, the heat treatment temperature is 400 ℃ each time, the heat treatment time is 40h each time, and finally stretching to obtain the NbTi/Cu tertiary composite wire with phi 0.8 mm;
step 5, rewinding the three-time composite wire to a stainless steel wire wheel for vacuum annealing, wherein the annealing vacuum degree is less than 1 multiplied by 10 - 3 Pa, the annealing temperature is 800 ℃, the annealing time is 5h, and finally the NbTi/Cu superconducting wire with ultra-low loss is obtained, wherein the structural diagram of 3169 porous copper tubes is shown in figure 2, and the structural design diagram of a 37-core triple composite wire is shown in figure 8.
The low-loss NbTi superconducting wire prepared by the preparation method provided by the embodiment is uniformly plated with Ni on the surface of a single-core thin wire, and is finally subjected to vacuum annealingThe resistivity of the matrix is improved by fire, the number of the cores of the wire rods is increased by three times of compounding, the diameter of the core wire is reduced, the loss of the wire rods is reduced comprehensively, the number of the cores of the finally prepared three times of compounding wires is 117253, the diameter of the core wire is about 1.4 mu m, and the critical current density is as high as 3268A/mm 2 (5T, 4.22K) and a loss per unit volume of 16.4mJ/cm 3 。
From the above data, the wire losses of examples 1 to 5 were 12.3, 15.7, 13.3, 17.7, and 16.4mJ/cm, respectively 3 The AC loss of the conventional commercial NbTi/Cu superconducting wire for MRI is as high as 700-800 mJ/cm 3 The surface of the single-core thin wire is uniformly plated with Ni, the resistivity of a matrix is improved through final vacuum annealing heat treatment, and meanwhile, the diameter of a wire core wire is reduced through the core thinning of the tube-penetrating three-time composite wire core wire, so that the ultra-low-loss NbTi superconducting wire is obtained.
The invention discloses a preparation method of an NbTi superconducting wire with ultralow loss, which is characterized in that a casting method is adopted to prepare an NbTi/Cu single core rod, the surface of the single core rod is uniformly plated with Ni after being cold-drawn into a thin wire, the resistivity of a wire substrate is improved through final annealing heat treatment, and the resistivity of the substrate is regulated and controlled by adjusting the thickness of a Ni plating layer, so that the superfine core wire not only has excellent processing performance, but also has ultralow loss. The multi-core secondary composite rod is prepared by 3D printing of the porous copper tube, the 10 ten thousand-core high-critical-current-density and ultralow-loss NbTi superconducting wire is successfully prepared by three times of tube penetration and combination of multiple aging heat treatment, the traditional hot extrusion process is omitted in the preparation of the primary single-core fine wire and the secondary composite rod, and the problems of high wire loss of the superfine core wire, poor deformation of the core wire, low yield and the like are thoroughly solved.
The foregoing are merely exemplary embodiments of the present invention, which enable those skilled in the art to understand or practice the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention.
It is to be understood that the present invention is not limited to what has been described above, and that various modifications and changes may be made without departing from the scope thereof. The scope of the invention is limited only by the appended claims.
Claims (7)
1. A preparation method of an ultra-low loss NbTi superconducting wire is characterized by comprising the following steps:
step 1), preparing an NbTi/Cu single core rod;
step 2), stretching the NbTi/Cu single-core rod into a thin wire, electroplating Ni to obtain an NbTi/Cu single-core thin wire with the surface uniformly plated with Ni, and cutting the thin wire into a fixed length;
step 3), preparing a porous copper pipe by using high-purity copper powder in a 3D printing mode;
step 4), inserting the NbTi/Cu single-core thin wire with the surface uniformly plated with Ni in the step 2) into the porous copper pipe in the step 3), and obtaining an NbTi/Cu secondary composite rod through drawing, sizing cutting and straightening treatment;
step 5), tightly arranging the cleaned NbTi/Cu secondary composite rods in a copper pipe, and combining multiple aging heat treatments in the cold drawing process to obtain a tertiary composite wire;
and 6) carrying out vacuum low-temperature annealing treatment on the tertiary composite wire to fully diffuse Ni and Cu in the matrix to form a Cu-Ni solid solution, and finally obtaining the NbTi superconducting wire with ultralow loss.
2. The method for preparing the ultra-low loss NbTi superconducting wire rod according to claim 1, wherein the step 1) is specifically as follows:
firstly, placing a cleaned NbTi rod at the center of a casting mould prepared in advance;
heating and insulating the casting mould at the heating temperature of 100-200 ℃ for 30-90 min;
then slowly pouring molten copper into the mold, wherein the casting temperature is 1100-1200 ℃, and the casting speed is 150-250 mm/min;
finally obtaining the NbTi/Cu single core rod in a cooling and demoulding way, wherein the flow of cooling water is 0.5-1.5 m 3 And h, the outer diameter of the NbTi/Cu single core rod is not more than phi 100 mm.
3. The preparation method of the ultra-low loss NbTi superconducting wire rod as claimed in claim 1, wherein in the step 2), when the size of the NbTi/Cu single core rod is phi 70 mm-phi 100mm, the rolling die drawing is adopted, and the processing rate of each pass is not more than 5%; when the size of the NbTi/Cu single core rod is smaller than phi 70mm, cold drawing is carried out by adopting a conventional die, the processing rate of each pass is not more than 15%, and the processing rate of each pass of peeling is not more than 3%; the size of the finally formed NbTi/Cu single-core thin wire is phi 1 mm-phi 3mm, and the thickness of the Ni coating is 5-10 mu m.
4. The preparation method of the ultra-low loss NbTi superconducting wire rod as claimed in claim 1, wherein in the step 3), the outer diameter of the porous copper pipe is not more than 100mm, the surface roughness Ra of the porous copper pipe is less than 3.2 μm, the total bending degree of the porous copper pipe is not more than 1mm/1000mm, the number of pores of the porous copper pipe is 1000-4000, and the size of the pores is 1-2 mm.
5. The preparation method of the ultra-low loss NbTi superconducting wire rod as claimed in claim 1, wherein in the step 4), when the size of the NbTi/Cu secondary composite rod is phi 70 mm-phi 100mm, the rolling die drawing is adopted, and the processing rate of each pass is not more than 5%; when the size of the NbTi/Cu secondary composite rod is smaller than phi 70mm, cold drawing is carried out by adopting a conventional die, the processing rate of each pass is not more than 15%, and the total bending degree of each NbTi/Cu secondary composite rod is not more than 1mm/1000mm in the straightening process.
6. The preparation method of the ultra-low loss NbTi superconducting wire rod as claimed in claim 1, wherein in the step 5), the final size of the three-time composite wire is phi 0.8mm, the processing rate of each pass of cold drawing of the die is not more than 20%, the aging heat treatment temperature is 350-450 ℃, the times are 3-5, and the time of each heat treatment is 20-40 h.
7. The method for preparing an ultra-low loss NbTi superconducting wire as claimed in claim 1, wherein in step 6), the vacuum degree of vacuum annealing of the tertiary composite wire is less than 1 x 10 -3 Pa, annealing temperature of 700And annealing at 800 ℃ for 3-5 h.
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| CN115954157B (en) * | 2023-03-14 | 2023-06-20 | 西部超导材料科技股份有限公司 | Preparation method of multi-core NbTi superconducting wire |
| CN116487110B (en) * | 2023-06-21 | 2023-09-01 | 西安聚能超导线材科技有限公司 | NbTi superconducting switch wire with high nickel content and preparation method thereof |
| CN116580894B (en) * | 2023-07-13 | 2023-10-13 | 西安聚能超导线材科技有限公司 | Preparation method of superfine NbTi filaments |
| CN117476286B (en) * | 2023-12-27 | 2024-04-02 | 西安聚能超导线材科技有限公司 | Preparation method of NbTi superconducting wire with high critical current density |
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