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CN-122000767-A - Superconductive material joint based on nanocrystalline copper bonding and preparation method thereof

CN122000767ACN 122000767 ACN122000767 ACN 122000767ACN-122000767-A

Abstract

The invention relates to the field of superconducting material preparation, in particular to a superconducting material joint based on nanocrystalline copper bonding and a preparation method thereof, comprising the following steps of mechanically polishing the surface to be bonded of a strip material; electroplating a nanocrystalline copper layer on the surface to be bonded, electrochemically polishing the nanocrystalline copper layer, butting and attaching the nanocrystalline copper layers of the two strips, and bonding by pressurizing and heating to obtain the joint. After the nanocrystalline copper layer is introduced into the surface, the bonding pressure and the bonding temperature can be reduced to (50 MPa,140 ℃), the interface crystal grains are smaller, even if defects exist at the bonding contact surface, the defects gradually heal under the drive of the crystal boundary, and the interface resistance is reduced.

Inventors

  • SU XIYANG
  • ZHANG XINGYI
  • FENG XIANPING
  • PENG GANGQIANG

Assignees

  • 兰州大学
  • 香港城市大学

Dates

Publication Date
20260508
Application Date
20260410

Claims (8)

  1. 1. The preparation method of the superconducting material joint based on nanocrystalline copper bonding is characterized by comprising the following steps of: mechanically polishing the surface of the tape to be bonded; electroplating a nanocrystalline copper layer on the surface to be bonded; Electrochemically polishing the nanocrystalline copper layer; And (5) abutting and jointing the nanocrystalline copper layers of the two strips, and pressurizing and heating for bonding to obtain the joint.
  2. 2. The method for preparing a superconducting material joint based on nanocrystalline copper bonding according to claim 1, wherein the thickness of the nanocrystalline copper layer is 0.1-3 μm.
  3. 3. The method for preparing a superconducting material joint based on nanocrystalline copper bonding according to claim 1, wherein after mechanically polishing the surface to be bonded of the tape, the surface roughness of the surface to be bonded is lower than 100 nm.
  4. 4. The method for preparing a superconducting material joint based on nanocrystalline copper bonding according to claim 1, wherein after electrochemical polishing of the nanocrystalline copper layer, the surface roughness of the nanocrystalline copper layer is lower than 10 nm.
  5. 5. The method for preparing a superconducting material joint based on nanocrystalline copper bonding according to claim 1, wherein the pressure is 10-70Mpa, the temperature is 80-180 ℃ and the bonding time is 0.1-5min during the bonding under the condition of pressurizing and heating.
  6. 6. The method for preparing a superconducting material joint based on nanocrystalline copper bonding according to claim 1, wherein the strip is a copper-coated flat superconducting strip and comprises a copper layer, a hastelloy layer, a buffer layer, a rare earth barium copper oxygen layer, a silver layer and a copper layer which are connected in sequence.
  7. 7. The method for preparing a superconducting material joint based on nanocrystalline copper bonding according to claim 6, wherein the surface to be bonded is a copper layer close to one side of a silver layer.
  8. 8. A superconducting material joint based on nanocrystalline copper bonding, characterized by being produced by the production method according to any one of claims 1 to 7.

Description

Superconductive material joint based on nanocrystalline copper bonding and preparation method thereof Technical Field The invention relates to the field of superconducting material preparation, in particular to a superconducting material joint based on nanocrystalline copper bonding and a preparation method thereof. Background Since the first observation of the superconducting phenomenon that mercury resistance drops suddenly to zero at liquid helium temperature was taught by the university Onnes of leiton, the state of condensation physical and material science was extremely active in the front field of superconducting research, and hundreds of superconducting materials were discovered successively, but only NbTi, nb 3Sn、MgB2, bi-based, yttrium-based and other superconducting materials have application values in practical engineering application. Compared with other practical superconducting materials, the second-generation high-temperature superconducting Rare Earth Barium Copper Oxide (REBCO) strip has the excellent properties of high critical temperature, high critical current density, strong current carrying capacity under high field and the like, and is widely applied to advanced scientific equipment such as superconducting current limiters, high-field superconducting magnets, superconducting energy storages, high-energy particle accelerators, thermonuclear fusion stacks and the like and large-scale scientific devices. However, the continuous preparation length of the existing uniform REBCO superconducting material is less than 1 km, and the requirement of a large superconducting device is tens of km or even hundreds of km. Therefore, REBCO tapes must be connected by a large number of joints to meet the requirements of large superconducting devices. Meanwhile, in the process of transmitting current to the superconducting material from a current source, joints are also arranged at the connecting positions of the normally-conductive material and the superconducting material. In the current-carrying operation process of the equipment, the joule heat (the only heat source) caused by the resistance at the joint position not only remarkably increases the refrigeration load of a low-temperature system, but also is more likely to cause local overheating, so that the superconducting state is unstable and even is quenched, and the reliability and the operation efficiency of the device are seriously threatened. Therefore, achieving very low joint resistance is critical to control thermal loading and to promote system stability, especially under high current carrying conditions. The existing joints are divided into superconducting joints, silver diffusion joints and welding joints according to the welding process. The superconducting joint is directly sintered and connected by superconducting materials, then a metal protective layer is added on the outer side, the method can lead to the degradation of more than 10% of critical current and the connection time is more than 10h, the silver diffusion joint is welded by the superconducting materials only comprising silver layers, and the characteristic resistivity (R sj, resistance multiplied by contact area) is more than 10 n Ω & cm 2, but a large number of defect holes exist at the connection position. The joint manufactured by the two methods has lower joint resistance, but also has lower strength, and cannot realize industrial application. The solder joint is formed by welding an outer copper layer of REBCO strips by using low-resistance solder, wherein the solder joint is usually formed by using low-melting-point low-resistance solder as solder, and then performing pressure heat treatment to obtain the low joint resistance (R sj >26 n omega cm < 2 >). The method is easy and convenient to operate and has high joint strength, so that the method is widely used in industry all the time. However, the introduction of the soldering tin layer not only additionally introduces the resistance of the soldering tin layer, but also introduces the interface resistance between the soldering tin and the copper layer, and under the condition of long-time high current carrying, the electromigration phenomenon exists between the soldering tin layer and the copper layer, so that the interface resistance is increased, and the quench risk of superconducting equipment is increased. Therefore, in order to ensure long-term stable operation of the device, it is necessary to remove the solder layer, and to realize direct connection of the copper layer and the copper layer. However, the conventional copper bonding method has the defects of high required pressure, high temperature, long time and the like, and is not beneficial to direct engineering application. Therefore, it is necessary to search for a joint preparation process with a simpler manufacturing method, low resistance, high mechanical strength and good stability, and promote the engineering application of superconducting materials