JP2006185925A - MANUFACTURING METHOD OF NbTi SUPERCONDUCTING MULTI-LAYER PLATE, AND NbTi SUPERCONDUCTING MULTI-LAYER PLATE - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of an NbTi superconducting multi-layer plate, and an NbTi superconducting multi-layer plate having large critical current density which can be manufactured by heat treatment within a short time at low cost. <P>SOLUTION: The NbTi superconducting multi-layer plate is formed by arranging plate-shaped NbTi alloy layers in Cu or Cu alloy base materials through Nb layers. Plate-shaped normal conducting depositions, having a thickness of not more than 1 nm and not less than 100 nm, a distance in a plate thickness direction of not less than 1 nm and not more than 500 nm, and a volume percentage to the total volume of the NbTi alloy layer of not less than 3% and not more than 50%, are deposited in parallel with a plate face in the NbTi layer. On the manufacturing method, the superconducting multi-layer is formed into a plate shape or foil shape by applying cold rolling with a processing percentage of 30 to 98% after hot rolling with a processing percentage of 30 to 98% at 500 to 1,000°C, and repeating a heat treatment with a holding time of 1 to 168 hours at every turn and the cold rolling with a processing percentage of 30 to 98% by six times or less at 300 to 450°C. Afterwards, cold rolling of a 30 to 90% processing percentage is applied after heat treatment with a holding time of 168 to 1,000 hours at 300 to 450°C. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of manufacturing a superconducting multilayer plate mainly used in a magnetic shield in superconducting equipment such as MRI (Magnetic Resonance Medical Imaging), superconducting linear motor car, and the like, and particularly relates to α in NbTi. -It relates to a thermomechanical treatment method in which the Ti precipitate phase is dispersed at a high density and the precipitation form of the normal conductive precipitate.

  About the manufacturing method of the superconducting multilayer board used by MRI, a linear motor car, etc., as shown in patent document 1, the holding time per time is 1 to 168 at a temperature of 300 to 450 ° C. after hot rolling. Super heat conduction in NbTi by repeating heat treatment for a period of time and cold rolling with a processing rate of 30 to 98% per turn alternately, followed by a final heat treatment for 1 to 1000 hours at a temperature of 300 to 450 ° C. There is a method of precipitating α-Ti as a pinning point. This is a method in which dislocations and vacancies as a driving force for precipitation are introduced by cold working and combined with heat treatment to cause sufficient precipitation.

Even in a superconducting multi-core wire, α-Ti is precipitated by a combination of the same processing and heat treatment, and a good critical current density is obtained (Patent Document 2 and Patent Document 3). In contrast to the superconducting multi-layered plate, only the change rate of the plate thickness can be obtained, and therefore, it is necessary to devise the processing and heat treatment method more than in the case of the superconducting multi-core wire.
Japanese Patent Laid-Open No. 3-136400 JP 57-210516 A Japanese Patent Laid-Open No. 7-141937

The material produced by the conventional manufacturing method has a critical current density of 100,000 to 120,000 A / cm ² under a strong magnetic field of 5 Tesla, but the critical current density of a general superconducting multicore wire is the same in a magnetic field environment. About 270,000 A / cm ² (“Metal Society Seminar Text: Nano / Meso-Structure Control and Development of High-Functional Materials” p. 93), the value is about twice that of the superconducting plate. When a superconducting multilayer board is used as a magnetic shield material, the magnitude of the magnetic field that can be magnetically shielded is approximately proportional to the critical current density and the thickness of the magnetic shield material ("The Institute of Electrical Engineers of Japan, Superconducting Engineering, Electrical Society of Japan" p.52). ). Therefore, if the critical current density is low, a large amount of material must be used. Therefore, there is a problem that the material has low shielding performance and poor cost performance for its weight.

In addition, Jc (critical current density) of the conventional method has a problem that it takes a long time for heat treatment to be as small as 100,000 to 120,000 A / cm ² under a magnetic field of 5 Tesla. The fact that the heat treatment time can be reduced when obtaining a Jc equivalent to the Jc of the conventional method is very meaningful from the viewpoint of reducing the manufacturing cost.

The NbTi superconducting multilayer plate is a superconducting plate in which one or more plate-like NbTi layers are present via a Nb layer in a Cu or Cu alloy base material which is a good conductor. The critical current density of such a superconducting plate is determined by normal conducting Ti deposited in the NbTi layer. The Ti precipitates present in the NbTi layer of the conventional NbTi superconducting multilayer plate as shown in JP-A-2-94498 have an ellipsoidal shape having a major axis of 200 nm to 2 μm and a minor axis of about 100 nm to 1 μm. It was. These precipitates are deposited as a result of repeated rolling and heat treatment (Patent Document 1). The normal conducting precipitate in the NbTi layer is kept in a superconducting state by pinning magnetic flux quanta that has entered the superconductor in a regular arrangement (triangular arrangement) in a magnetic field higher than the upper critical magnetic field Hc2. Intermediate state). The lattice spacing of the flux quanta is about 49 nm in a 1 Tesla magnetic field and about 22 nm in a 5 Tesla magnetic field. The size of the normal conducting precipitate that can pin the magnetic flux quantum most efficiently is about the same as the size of the interface of the superconducting normal conducting region in the intermediate state (corresponding to the coherence length; 5.5 nm for NbTi) and the magnetic flux. It is said that it is dispersed to the same degree as the quantum lattice spacing (several tens of nm). From this point of view, the Ti precipitate in the NbTi layer of the conventional NbTi alloy-based superconducting plate has an ellipsoidal shape with a minor axis of 100 to 200 nm and a major axis of 200 nm to 500 nm, and the ideal size of the Ti precipitate. As described above, the critical current density was 10 to 120,000 A / cm ² at 5 Tesla, which was lower than that of a commercially available NbTi alloy superconducting wire (the magnetic field was parallel to the plate). When applied).

  The present invention has been made in view of these problems, and it is possible to optimize the manufacturing method of the superconducting multilayer plate and to manufacture the NbTi superconducting multilayer plate having a large critical current density at a low cost by heat treatment as short as possible. An object of the present invention is to provide a method for producing an NbTi superconducting multilayer plate and an NbTi superconducting multilayer plate.

  In the first invention, at least one NbTi alloy and a high conductivity metal are alternately laminated, a Nb or Ta barrier layer exists between the NbTi alloy and the high conductivity metal, and the NbTi layer includes Further, it is deposited in a plate shape parallel to the plate surface, and the thickness is 1 nm or more and 100 nm or less, the interval in the plate thickness direction is 1 nm or more and 500 nm or less, and the volume fraction with respect to the entire NbTi alloy layer is 3% or more and 50%. A method for producing a superconducting multilayer board in which the following normal conductive precipitates are present, and after hot rolling at a processing rate of 30 to 98% at a temperature of 500 to 1000 ° C., cold rolling at a processing rate of 30 to 98% The sheet is formed by alternately repeating heat treatment with a holding time of 1 to 168 hours at a temperature of 300 to 450 ° C. and cold rolling with a processing rate of 30 to 98% per turn alternately 6 times or less. After forming a foil, 300-4 0 After holding time at a temperature of ℃ was heat-treated at 168 to 1000 hours, a method for performing rolling 30% to 90% of the cold. High conductivity metals refer to copper, aluminum, and the like.

2nd invention is a manufacturing method of the NbTi superconducting multilayer board characterized by performing the heat processing for 1 second-5 hours with the temperature of 300-450 degreeC to 1st invention.
According to a third invention, in a NbTi superconducting multilayer plate in which a plate-like NbTi alloy layer is arranged via a Nb layer in a Cu or Cu alloy substrate, the NbTi layer of the NbTi superconducting multilayer plate is parallel to the plate surface. A normal conducting precipitate having a thickness of 1 nm or more and 100 nm or less, a distance in the thickness direction of 1 nm or more and 500 nm or less, and a volume fraction with respect to the entire NbTi alloy layer of 3% or more and 50% or less. It is a NbTi superconducting multilayer board characterized by existing.

  The superconducting multilayer board manufactured by the manufacturing process of the present invention has a critical current density of up to twice that of the conventional manufacturing process, and the thickness of the board used when shielding the same magnetic field. As a result, the weight of the magnetic shield was reduced and the manufacturing cost was significantly reduced. As can be seen from the comparison of Jc per unit heat treatment time (in 8T), the manufacturing method is more efficient than the conventional technology, and the manufacturing cost can be reduced.

  Further, in the third invention, the plate-like normal conductive precipitates extending thinly in the rolling direction to a thickness comparable to the size of the superconductive / normal conductive interface are arranged at intervals close to the magnetic flux quantum intervals. A large critical current density can be obtained because the flux quantum that has entered in the intermediate state is efficiently captured and pinned with a large force.

  Since the material of the present invention is used in a DC strong magnetic field, it is necessary to be superconductively stable. The reason for using a composite material of a superconducting material and a high conductivity metal as the magnetic shield material is to increase the superconducting stability. The superconducting material has zero electrical resistance in the superconducting state, but if for some reason it partially transitions to normal conduction, it will generate heat because of its large electrical resistance in the normal conduction state, and the normal conducting part will expand and the entire material will A phenomenon occurs in which the superconducting state is broken all at once (quenching phenomenon).

  On the other hand, in a composite material in which a high-conductivity material is adjacent to a superconducting material, even if a partial normal-conducting transition occurs, the current flowing in the superconducting material flows through the high-conducting metal, and once transitions to normal-conducting This part can also return to the superconducting state, and the superconducting state can be kept stable. In order to maintain a superconducting state even in a DC strong magnetic field of 1 Tesla or higher, the superconducting material must be a material having a high critical magnetic field Hc2 (1 Tesla or higher), and workability such as rolling is good. Therefore, an NbTi alloy was selected as the superconducting material. The barrier layer of Nb or Ta is arranged between the NbTi layer and the high conductivity material layer because the high conductivity metal such as copper and Ti in NbTi do not form an intermetallic compound in the hot rolling process in the manufacturing process. It is for doing so.

After hot rolling, 30 to 98% cold rolling is performed, and heat treatment with a holding time of 1 to 168 hours at a temperature of 300 to 450 ° C. and a processing rate of 30 to 98% at one time. The reason why the cold rolling is alternately repeated 6 times or less is to make the NbTi crystal grains fine. When a second type superconductor such as NbTi is placed in a magnetic field, the magnetic field is divided into quantized magnetic flux lines having a magnetic flux quantum φ ₀ and enters the superconductor. When a current is passed through the superconductor in this state, Lorentz force acts on the quantized magnetic flux lines. If the quantized magnetic flux lines move here, an electromotive force is generated, and eventually the superconducting state with zero electric resistance is broken. In the case of NbTi, titanium (α-Ti) precipitates deposited in the alloy prevent the movement of the quantized magnetic flux lines against the Lorentz force. In addition to precipitates such as α-Ti, there are defects, impurities, etc. in the material that play a role in stopping the movement of the quantized magnetic flux lines, and these are collectively called a magnetic flux pinning point. Previous studies by the inventor have shown that α-Ti in NbTi tends to precipitate at the grain boundaries. Therefore, if the crystal grain size of NbTi is reduced, a large amount of precipitates can be obtained, so that the pinning efficiency is good and a large critical current density can be obtained.

  The reason why the lower limit of the heating temperature during hot rolling is 500 ° C. is that if it is less than 500 ° C., NbTi and Nb or Ta are not sufficiently softened and the adhesiveness with copper is insufficient. The reason why the upper limit is set to 1000 ° C. is that when the temperature exceeds 1000 ° C., the melting point of copper is too soft. The reason why the hot rolling processing rate is 30 to 98% is that if it is less than 30%, it is difficult to obtain sufficient adhesion even if the temperature is high, and if it exceeds 98%, the subsequent cold working rate becomes too small. It is.

  The crystal grains become fine by cold rolling after recrystallization. Since a large amount of α-Ti finally precipitates at the grain boundaries, the density of precipitation is greatly improved by refinement of the crystal grains. The reason why the reduction ratio of cold rolling after recrystallization is 30 to 98% is that if it is less than 30%, the amount of lattice defects to be introduced is insufficient and the effect of heat treatment cannot be utilized, and if it exceeds 98% This is because a part or the whole of the material is destroyed and processing defects occur. The reason why the temperature of the subsequent intermediate heat treatment is set to 300 to 450 ° C. is that if it is less than 300 ° C., the precipitation rate of α-Ti at the magnetic flux pinning point is too small and takes too much time. This is because the grain size becomes coarse and hinders the subsequent cold working. The reason why the holding time per heat treatment is 1 to 168 hours is that the amount of precipitation is insufficient if it is less than 1 hour, and if it exceeds 168 hours, the precipitate is coarsened and is used for the subsequent cold working. This is to cause trouble.

  In order to introduce dislocations and vacancies as a driving force for precipitation and to precipitate a sufficient amount of α-Ti, the cold working and the heat treatment are alternately repeated to further increase the effect. The reason why the number of repetitions is set to 6 times or less is that if the number of repetitions exceeds 6 times, a sufficient cold reduction ratio between the heat treatments cannot be obtained and the effect on the precipitation amount is saturated. The reason why the cold work rate between each heat treatment and the final shape is 30 to 98% is the same as in the case of cold rolling after recrystallization. The reason why the final heat treatment is performed with the final plate thickness is to further increase the density of α-Ti precipitated by repeated cold working and heat treatment in the middle. The reason why the temperature range of this heat treatment is set to 300 to 450 ° C. is the same as the case of the heat treatment described above. The reason why the holding time is set to 168 to 1000 hours is that if the retention time is less than 168 hours, the effect of increasing the precipitation amount cannot be obtained, and if it exceeds 1000 hours, the precipitation is saturated.

  The particle diameter of the α-Ti precipitate deposited up to the final heat treatment step of the present invention is approximately several hundred nm. In the present invention, this precipitate is further thinned by rolling and the precipitation interval is reduced, so that the size and distribution of α-Ti pinning points are distributed with a particle size of several tens of nanometers suitable for pinning quantized magnetic flux lines. The interval is several tens of nm. The lower limit of the rolling reduction after the final heat treatment is set to 30% because the effect of downsizing the α-Ti is small if it is less than 30%, and the upper limit is set to 90%. This is because disorder occurs in the layered structure of NbTi. From the viewpoint of downsizing α-Ti to a theoretically optimum size and not disturbing the layered structure, the final cold working rate is preferably in the range of 50 to 75%.

  By such a method, in the NbTi layer of the NbTi superconducting multilayer plate, it is deposited in a plate shape parallel to the plate surface, and the thickness is 1 nm or more and 100 nm or less, the interval in the plate thickness direction is 1 nm or more and 500 nm or less, NbTi A superconducting multilayer board characterized by the presence of normal conductive precipitates having a volume fraction of 3% or more and 50% or less with respect to the entire alloy layer is obtained.

This is described in detail in FIG. FIG. 1 shows the form of the NbTi layer of the NbTi superconducting multilayer board. When normal conducting precipitates 2 having a thickness t exist in the NbTi layer 1 at intervals d,
1 nm ≦ t ≦ 100 nm,
1 nm ≦ d ≦ 500 nm,
When the volume fraction of normal conducting precipitates in the NbTi layer is v,
3% ≦ v ≦ 50%
It is what. Here, the width w and the length L of the normal conductive precipitate are not particularly limited and may be any size.
With this configuration, when the applied magnetic field is in the direction of B or B 'and the current is passed in the direction of I or I', the normal conducting precipitate 2 overcomes the Lorentz force F or F 'and effectively uses the quantum magnetic flux. The critical current density is increased.

  The reason why the thickness of the normal conductive precipitate is set to 1 nm or more is that if it is smaller than this, the size of the region of the NbTi superconductive and normal conductive interface is too small to sufficiently pin the magnetic flux quantum. The reason why the thickness of the conductive precipitate is set to 100 nm or less is that if it is larger than this, it becomes larger than the interval between the magnetic flux quanta, and there are many magnetic flux quanta in the normal conductive precipitate, and sufficient pinning cannot be performed.

  The reason why the interval between the normal conductive precipitates is set to 1 nm or more is that if it is smaller than this, there are many normal conductive precipitates that do not contribute to pinning in the magnetic flux quantum interval, and the cross-sectional area of the NbTi superconductor is mischievous. The reason why the interval between the normal conductive precipitates is set to 500 nm or less is that the number of magnetic flux quanta that are not pinned becomes too large if the distance is further away.

  The reason why the volume fraction in the NbTi layer of the normal conducting precipitate is set to 3% or more is that if it is smaller than this, the magnetic flux quantum cannot be pinned sufficiently, and the reason why it is set to 50% or less is larger than this. This is because it does not make sense even if the superconducting cross-sectional area is reduced and the critical current density is increased.

  When normal conducting precipitates extend long in the direction parallel to the applied magnetic field, many flux quanta are trapped in energetically stable normal conducting precipitates. To pull apart, a large force is required, and the pin is strong. Further, the width W of the normal conductive precipitate is not related to the pinning force regardless of whether it is large or small as long as the direction of the magnetic field and current is the same as in FIG. Therefore, the width and length of the normal conductive precipitate may be arbitrary.

  As described above, the second invention is characterized in that the first invention is subjected to heat treatment at a temperature of 300 to 450 ° C. for a holding time of 1 second to 5 hours. In the first invention, the material is work-hardened in the final cold rolling. In the case of using the NbTi superconducting multilayer board as it is, there is no problem with this. However, in the case where press working is necessary, the material is hard, so it is not convenient. Also, since many dislocations are introduced into the Cu layer portion, the residual resistance ratio is small, and therefore there is a slight problem from the viewpoint of superconducting stability. In order to solve this problem, a heat treatment was performed at a temperature of 300 to 450 ° C. for 1 second to 5 hours after the final cold rolling. The reason why the heat treatment temperature is set to 300 ° C. is that the material is not sufficiently softened at a temperature lower than that, and the temperature of 450 ° C. or lower is set to α− which has been downsized by the final cold rolling at a temperature higher than that. This is because Ti starts to grow. The reason for setting the time to 1 second or longer is that the softening occurs when the temperature reaches the set temperature, and the minimum time is 1 second. The reason for setting the time to 5 hours or less is that if this time is exceeded, α-Ti that has been reduced in size by the final cold rolling will increase in size again.

  As described above, the third invention is a NbTi superconducting multilayer plate in which a plate-like NbTi alloy layer is arranged in a Cu or Cu alloy base material via an Nb layer, and the NbTi superconducting multilayer plate includes a plate in the NbTi layer. Usually deposited in a plate shape parallel to the surface, the thickness is 1 nm or more and 100 nm or less, the interval in the plate thickness direction is 1 nm or more and 500 nm or less, and the volume fraction of the entire NbTi alloy layer is 3% or more and 50% or less. The conductive precipitate is present, but the reason for defining the size and volume fraction of the normal conductive precipitate is as described in the detailed description of the first invention.

  Table 1 shows the results of measurement of critical current density (Jc) of the superconducting multilayer plate manufactured according to the present invention and the superconducting multilayer plate manufactured by the conventional method, and Jc (8T) relative to the total time of intermediate heat treatment and final heat treatment after hot rolling. The ratio of The higher this ratio, the higher Jc can be obtained without the cost of heat treatment. Jc is a value at 5T (Tesla) and a value at 8T (Tesla). The superconducting multilayer plates shown in the examples all have the same multilayer structure. The structure of the superconducting multilayer plate having a total thickness of 1 mm is as follows. The outermost layer is a copper layer of approximately 0.11 mm, and 30 NbTi layers of about 11 μm are stacked alternately with copper layers of the same thickness. Further, an Nb layer of about 1 μm is inserted between the NbTi layer and the copper layer. Superconducting multilayer plates having a total thickness of 0.5, 0.2 and 0.1 mm are 1 mm plates rolled at 50%, 80% and 90% reduction, respectively.

  The critical current density is the current value that can be applied until the voltage between terminals is 1 μV by attaching voltage terminals to a test piece with a width of 0.5 mm with a thickness of 10 mm between the test pieces with the plate thickness kept as the test material. The critical current density (Jc) was obtained by dividing this by the total cross-sectional area of NbTi. The direction of rolling was constant for both hot and cold rolling, and samples for critical current density measurement were taken in a direction perpendicular to the rolling direction. A critical current was measured by passing a current through the sample while immersed in liquid helium. No. of the present invention. 1-No. No. 3 production process and Comparative Example No. 4, no. 5 and no. The manufacturing process of 6 is as follows.

  No. 1 (Invention 1): Hot rolling (holding at 800 ° C. for 1 hour, reduction rate 50%) → cold rolling (reduction rate 50%) → heat treatment (holding 400 ° C. for 2 hours) → cold rolling (reduction rate 50) %) → heat treatment (retained at 380 ° C. for 5 hours) → cold rolling (reduction rate 50%) → heat treatment (retained at 380 ° C. for 5 hours) → cold rolling (reduction rate 80%) → heat treatment (380 ° C. 240 hours) → cold Hot rolling (rolling ratio 50%), final plate thickness 0.5 mm. Total heat treatment time after hot rolling: 252 hours.

  No. 2 (Invention 1): Hot rolling (holding at 550 ° C. for 3 hours, reduction rate 35%) → cold rolling (rolling rate 30%) → heat treatment (holding at 400 ° C. for 3 hours) → cold rolling (reduction rate 50) %) → heat treatment (held at 380 ° C. for 168 hours) → cold rolling (reduction rate of 95%) → heat treatment (340 ° C. for 336 hours) → cold rolling (reduction rate of 80%), final thickness 0.2 mm. Total heat treatment time after hot rolling: 507 hours.

  No. 3 (Invention 1): Hot rolling (holding at 950 ° C. for 1 hour, reduction rate 85%) → cold rolling (rolling rate 30%) → heat treatment (320 ° C. holding for 96 hours) → cold rolling (reduction rate 50) %) → heat treatment (320 ° C. 96 hours) → cold rolling (rolling rate 75%) → heat treatment (400 ° C. 168 hours) → cold rolling (rolling rate 90%), final plate thickness 0.1 mm. Total heat treatment time after hot rolling: 360 hours.

  No. 4 (Comparative Example 1): Hot rolling (holding 800 ° C. for 1 hour, reduction rate 50%) → heat treatment (holding 380 ° C. for 5 hours) → cold rolling (rolling rate 50%) → heat treatment (holding 380 ° C. for 5 hours) ) → Cold rolling (reduction rate 50%) → Heat treatment (holding at 380 ° C. for 5 hours) → Cold rolling (reduction rate 50%) → Heat treatment (holding at 380 ° C. for 5 hours) → Cold rolling (reduction rate 85%) → Heat treatment (350 ° C. 700 hours), final plate thickness 1.0 mm. Total heat treatment time after hot rolling: 720 hours.

  No. 5 (Comparative Example 2): Hot rolling (holding 800 ° C. for 1 hour, reduction rate 50%) → heat treatment (holding 380 ° C. for 5 hours) → cold rolling (rolling rate 50%) → heat treatment (holding 380 ° C. for 5 hours) ) → Cold rolling (reduction rate 50%) → Heat treatment (holding at 380 ° C. for 5 hours) → Cold rolling (reduction rate 50%) / Heat treatment (holding at 380 ° C. for 5 hours) → Cold rolling (reduction rate 85%) → Heat treatment (310 ° C. 400 hours → 360 ° C. 300 hours), final plate thickness 1.0 mm. Total heat treatment time after hot rolling: 720 hours.

  No. 6 (Comparative Example 3): Hot rolling (holding at 800 ° C. for 1 hour, reduction rate 50%) → heat treatment (holding at 380 ° C. for 5 hours) → cold rolling (rolling rate 50%) → heat treatment (holding at 380 ° C. for 5 hours) ) → Cold rolling (reduction rate 50%) → Heat treatment (holding at 380 ° C. for 5 hours) → Cold rolling (reduction rate 50%) → Heat treatment (holding at 380 ° C. for 5 hours) → Cold rolling (reduction rate 85%) → Heat treatment (350 ° C., 1000 hours), final plate thickness 1.0 mm. Total heat treatment time after hot rolling: 1020 hours.

No. of Example 1 The material of the present invention 2 obtained by subjecting the material of No. 2 to a heat treatment at 350 ° C. for 1 hour was designated as No. 2. 7 No. Table 1 shows the critical current density of 7 under 5 Tesla and 8 Tesla. About 3% under 5 Tesla and about 5% under 8 Tesla. However, when the critical current density under 1 Tesla is compared, 2 was 3945 A / mm ² , whereas 7 increased by about 3.5% to 4085 A / mm ² . This is presumably because the superconducting stability was improved due to an increase in the Cu resistance ratio, and the effect was exhibited particularly on the low magnetic field side. No. 2 and No. No. 7 was measured for mechanical elongation in the rolling direction. No. 2 was about 1%, whereas No. 2 7 was approximately 11%. No. for applications where the plate is used without being processed. 2 is sufficient. 7 (Invention 2) is more suitable.

  NbTi / Nb / Cu multilayer with a total thickness of 1 mm and 30 NbTi layers (thickness of about 12 μm) stacked alternately with copper layers (thickness of about 12 μm) via Nb layers (thickness of about 1 μm) A plate was made. The manufacturing process is shown below, following the example of Example 1.

  No. 8 (Invention 3): Hot rolling (reduction rate 60% after holding at 830 ° C. for 2 hours) → cold rolling (reduction rate 50%) → heat treatment (380 ° C. 5 hours) → cold rolling (reduction rate 50%) ) → Heat treatment (380 ° C. for 5 hours) → Cold rolling (50% reduction) → Heat treatment (380 ° C. for 5 hours) → Cold rolling (80% reduction) → Heat treatment (370 ° C. for 500 hours) → Cold rolling ( Reduction ratio 60%) → heat treatment (350 ° C. for 1 hour). The average thickness of normal conducting Ti precipitates in the NbTi layer as viewed from the cross section in the rolling direction of this material is 30 nm, the average interval is 100 nm, and the volume fraction is 10%. A superconducting plate was obtained.

  In addition, as a comparative example, No. 1 was prepared by the following manufacturing process. Nine materials were produced. No. 9 (Comparative Example 4): Hot rolling (holding at 830 ° C. for 2 hours, reduction rate 60%) → cold rolling (reduction rate 50%) → heat treatment (380 ° C. 5 hours) → cold rolling (reduction rate 50%) ) → heat treatment (380 ° C., 5 hours) → cold rolling (rolling rate 50%) → heat treatment (380 ° C., 5 hours) → cold rolling (rolling rate 80%) → heat treatment (370 ° C., 500 hours).

  In the NbTi layer as seen from the cross section in the rolling direction of Comparative Example 4, ellipsoidal normal conducting Ti precipitates having an average major axis of 250 nm and an average minor axis of 150 nm were deposited with an average interval of 250 nm and a volume fraction of 10% (see FIG. 3). No. 8 (Invention 3) and No. 8 Table 2 shows the results of measurement of the critical current density in the width direction of the rolled material of No. 9 (Comparative Example 4).

It is a general view which shows the NbTi alloy layer in the superconducting plate in connection with this invention. It is rolling direction sectional drawing of the NbTi alloy layer in the superconducting plate which shows the Example of this invention. It is sectional drawing of the rolling direction of the NbTi alloy layer in the conventional superconducting plate.

Explanation of symbols

1 NbTi
2 Normal conducting Ti precipitate 3 Grain boundary

Claims (3)

  At least one NbTi alloy and a high conductivity metal are alternately laminated, a Nb or Ta barrier layer exists between the NbTi alloy and the high conductivity metal, and the NbTi layer is parallel to the plate surface. A normal conductive precipitate having a thickness of 1 nm or more and 100 nm or less, a thickness direction interval of 1 nm or more and 500 nm or less, and a volume fraction of 3% or more and 50% or less with respect to the entire NbTi alloy layer. Is a method of manufacturing a superconducting multilayer board, in which hot rolling is performed at a processing rate of 30 to 98% at a temperature of 500 to 1000 ° C, followed by cold rolling at a processing rate of 30 to 98% and 300 to 450 ° C. After the heat treatment with a holding time of 1 to 168 hours at one temperature and the cold rolling with a processing rate of 30 to 98% per turn are repeated alternately 6 times or less to form a plate or foil At a temperature of 300-450 ° C After the lifting time is subjected to a heat treatment of 168 to 1000 hours, and characterized by applying rolling 30% to 90% of the cold method for producing a NbTi superconducting multilayer board.   2. The method for producing a NbTi superconducting multilayer board according to claim 1, wherein after the cold rolling of 30 to 90%, heat treatment is further performed at a temperature of 300 to 450 ° C. for 1 second to 5 hours.   In the NbTi superconducting multilayer plate in which the plate-like NbTi alloy layer is arranged via the Nb layer in the Cu or Cu alloy base material, the NbTi layer of the NbTi superconducting multilayer plate is deposited in a plate shape parallel to the plate surface, And a normal conductive precipitate having a thickness of 1 nm or more and 100 nm or less, an interval in the plate thickness direction of 1 nm or more and 500 nm or less, and a volume fraction of 3% or more and 50% or less with respect to the entire NbTi alloy layer. NbTi superconducting multilayer board.

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