Method of production of composite conductors based on high-temperature superconducting bismuth ceramics in a silver shell

 

(57) Abstract:

The invention relates to high-temperature superconductivity and can be used for single core and multi-core composite conductors based on ceramics (Bi, Pb)(2)Sr(2)Ca(2)Cu(3)O(y) with high superconducting properties. The inventive composite billet is deformed, and then subjected to thermomechanical processing. Up to deformation or between strains produce additional heat treatment of the composite workpiece in a temperature range of 780 - 815oC for at least 10 hours Method improves the superconducting properties of conductors. The critical current density measured at the liquid nitrogen temperature increases, depending on the design Explorer 5 times. table 1.

The invention relates to high-temperature superconductivity and can be used for single core and multi-core composite conductors based on ceramics (Bi, Pb)(2)Sr(2)Ca(2)Cu(3)O(y)-(Bi-2223) high superconducting characteristics.

A method of obtaining stranded composite wires in a silver shell-based ceramics Bi-Pb-Sr-Ca-Cu-O, if W(Ag/Bi-2223/Ag) in a spiral, get a precursor, Packed in a silver shell and distort the obtained composite billet. The resulting conductor thermoablative at a temperature (T) 830oC for 24 h and cooled in the furnace to room temperature.

Closest to the proposed technical solution is the method of getting stranded composite wires in a silver shell-based ceramics Bi-2223, in which a combination of methods "powder in tube" and jelly-roll get a precursor, Packed in a silver shell and deform (extrusion) at 840oC with diameter 8 to 10 mm up to a diameter 2 to 4 mm, the resulting conductor is subjected thermotechnical processing (TMO) at 840oC for the total time 100 300 including the Maximum value of the critical current density at the liquid nitrogen temperature in zero magnetic field (jk(N2,O, T)) conductors obtained by the described method, amounted to 3200 A/cm2[2] the prototype.

The main disadvantage of this method is poor geometry of the ceramic core and the low quality of the boundary ceramic-silver, which affects the formation of phase Bi-2223 and may not provide a high level criticism is based on high-temperature superconducting bismuth ceramics in a silver sheath, including the production of composite workpiece deformation and TMO, before deformation of the composite billet or in the course of this deformation, between stages of deformation, conduct additional heat treatment in the temperature range of 780 815oC for at least 10 h of the Deformation is carried out either by extrusion or forging, or by drawing or rolling, or a combination of these methods.

At the stage of obtaining the composite billet Bi-ceramics/Ag in a silver sheath is sealed precursor. As a precursor use either composite composite billet obtained by combining methods "powder in tube" and jelly-roll (multi-design Explorer) or powder Bi ceramic (single-design Explorer).

At the stage of obtaining the composite billet Bi-ceramic/silver, during manufacture of the precursor and its packaging in a silver shell powder accumulate unevenly distributed voltage. An additional heat treatment in air in the temperature range of 780 - 815oC for at least 10 h prior to deformation (or between strains) contributes to a more uniform relaxation made stresses in powdered acuautla during subsequent heat treatments in the process of the Dura mater. Removing stress leads to improving the geometry of the core and to improve the quality of the surface of the partition ceramics-silver (improves the smoothness of the boundary), which during the subsequent TMO starts the growth of the superconducting phase Bi-2223. In addition, in the process, additional heat treatment is likely the formation of non-superconducting phases required composition is in a liquid state under normal temperature conditions. Their presence allows for subsequent heat treatments, in the process of the Dura mater, to heal the resulting microstructure defects.

Thus, additional heat treatment performs a twofold task: on the one hand, correct defects of the microstructure inherent in the conductor at the initial stages of its manufacture, on the other hand, creates conditions favorable for the subsequent (TMO) directional growth of the superconducting phase Bi-2223 in the volume of the ceramic core, which leads to an increase in the critical current density up to 5 times.

An additional heat treatment in air at a temperature below 780oC does not increase current-carrying capacity of conductors, as at T <780C leads to the formation of non-superconducting F15oC is not advisable, since above this temperature there is a significant growth phase Bi-2223, which is not desirable, as during subsequent deformations included in TMO, narrowing crystal phase Bi-2223 and the appearance of additional cracks.

An additional heat treatment for less than 10 h does not increase current-carrying capacity of conductors due to diffusion limitations of the processes of formation of non-superconducting phases, their fusion and healing of cracks.

The influence of additional heat treatment to increase the current-carrying ability was tested on solid and stranded conductors. Composite conductors of different designs based on high-temperature superconducting ceramics in Bi silver shell received in several stages.

In the case of single core design ceramic powder composition Bi(2-x)Pb(x)Sr(2)Ca(2-y)Cu(3-y)O(z), where 0<x<0,4; 0<y<1, containing phase Bi(2)Pb(0,4)Sr(2)Ca(1)Cu(2)O(z)-Bi-2212 in the amount of 10 to 90% oxides and cuprates individual elements are tightly Packed in a silver sheath. Then, the resulting composite billet deformed by extrusion with a diameter of 10 mm to a diameter of 4 mm at 270 400oC, held for more get out to a thickness of 0.3 to 0.1 mm and subjected to TMO 2 3 intermediate pressovaniya at 820 880oC for the total time 100 300 h

In the case of a multi-strand design ceramic powder composition Bi(2-x)Pb(x)Sr(2)Ca(2-y)Cu(3-y)O(z), where 0<x<0,4; o<y<1, containing phase Bi-2212 in the amount of 10 to 90% of the oxides and the cuprates individual elements are tightly Packed in intermediate silver shell, then the intermediate composite billet was progulivali in the tape. The tape from the ceramic core was clocked on the rod, the obtained precursor was placed in a silver tube and tightly Packed. Composite composite billet was subjected to additional heat treatment in air at 780 and 815oC for 10 and 20 h at each temperature. Next were extrusion with a diameter of 10 mm up to a diameter 2 to 4 mm at a temperature of 320 420oC and thermomechanical processing 2 3 intermediate pressovaniya when 820-880oC for the total time 100 300 h

In the case of a stranded conductor used deformation not only by extrusion, and drawing with a diameter of 10 mm to a diameter of 2.5 to 4 mm (10% deformation per pass), and further heat-treated in air at 780 and 815oC for 10 and 20 h at each temperature was carried out before drawing.

The table shows the critical density that is in the data table shows the introduction of additional heat treatment on the conductors single-core design has allowed to increase Jr(N2) 5 times. The introduction of additional heat treatment on the conductors of multi-conductor constructions allowed to increase Jk(n2200 450 A/cm2. Lower values of Jk(N2) stranded conductors due to complex reasons related to their structural features.

Method of production of composite conductors based on high-temperature superconducting bismuth ceramics in a silver shell from which it receives the composite billet, produce sequential deformation and thermomechanical processing, characterized in that before the deformation or between the stages of the composite billet additionally thermoablative in air in the temperature range of 780 815oWith at least 10 hours

 

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