Method for producing long composite conductors around high-temperature superconducting compounds

FIELD: electrical engineering; producing long conductors around superconducting compounds.

SUBSTANCE: proposed method includes formation of single-core billet by filling silver sheath with bismuth ceramic powder; deformation of this single-core billet to desired size by no-heating drawing at deformation degree per pass of 0.5 - 20%; cutting of deformed billet into measured parts; assembly of single-core billet by disposing desired quantity of measured parts of deformed single-core billet in silver sheath of multicore billet; extrusion of multicore billet at temperature ranging between 100 and 200 °C and at drawing coefficient of 4 to 30; air rolling without heating at deformation degree per pass of 1 - 50%; thermomechanical treatment including several heat-treatment stages at temperature of 830 - 860 °C for time sufficient to obtain phase of desired composition and structure in ceramic core with intermediate deformations between heat-treatment stages at deformation degree per pass of 5 - 30 %.

EFFECT: enhanced critical current density due to sequential packing of ceramic core; facilitated manufacture.

1 cl, 1 ex

 

The invention relates to the technical field of superconductivity, in particular to a technology for long composite stranded wire-based high-temperature superconducting (HTS) of compounds designed to create electrical products.

It is known that the stranded wire-based HTSC compounds produced by the method of "powder-in-tube, including the filling of ceramic powder in a metal sheath, the deformation obtained monolignol billet to the desired size, cut-to-length parts, the Assembly of the multi-core preform by placing in a metal shell of the required quantity of these dimensional parts, the deformation of the multi-strand billet and heat treated in several stages with intermediate strain between them (thermomechanical processing) /1/. In the case of filling in a metal shell, such as ceramic powders, the deformation is carried out to obtain the desired wire size and maximum possible compaction of the core before thermomechanical treatment (TMT), which is carried out with the aim of forming a ceramic core superconducting phase of the desired composition and structure. When using ceramic powders deformation is performed by drawing and rolling, which do not allow to achieve the required density ceramic watch is Russian to the core.

Also known methods for producing wire-based HTSC compounds by the method of "powder in tube" on the basis of metal powders, however, when using metal powders to obtain a wire with a critical current density higher than 500 A/cm2difficult /2/.

Closest to the proposed technical solution is the method of getting stranded conductor /3/ prototype, including the production of monolignol blanks by filling metal powder in a silver sheath, the extrusion obtained monolignol billet to the required size at 300-600°and the magnitude of the coefficient hoods up to 800, cutting the deformed billet-to-length parts, the Assembly of the multi-core preform by placing in a silver sheath stranded procurement quantity required dimensional parts deformed monolignol billet, extrusion of multi-strand billet 300-600°and the magnitude of the coefficient hoods up to 800, rolling at 300-600° in a controlled atmosphere (argon), oxidation, thermo-mechanical processing.

In the deformation process extrusion is possible with the currently used main methods of deformation (drawing, rolling, extrusion) sealing the core of mono - and multi-core billet, however, in the case of metal powders of th the deformation spend oxidation (translated metals in oxides), in which there is a softening of the core, and TMO (superconducting phase of the desired composition and structure form already in ceramic consisting of oxides of the core).

This method has a number of disadvantages:

the use of metal powders requires before TMO operations oxidation of these powders, and this greatly complicates the process introduces an additional operation in a controlled atmosphere - oxidation of core by oxygen diffusing through the Explorer shell, which results in the softening of hearts); in addition, the likely difficulties in obtaining the core of stoichiometric superconducting compound, and if TMO is more difficult to obtain the desired structure of the core, which leads to a significant reduction of the critical current density;

- carrying out the extrusion at high temperatures (300-600° (C) with a high elongation ratio up to 800 complicates the process; extrusion can be carried out in vertical and horizontal arrangement of the workpiece and the wire, in both cases, when the extrusion billets of large diameter with high elongation ratio is necessary to provide the snap-in to receive wires with high velocities, which are determined by the speeds of the press equipment;

- p is Vvedenie warm rolling at high temperatures (300-600° (C) in a controlled atmosphere (argon) also complicates the process and reduces its security.

An object of the invention is to increase the critical current density due to sequential (from operation to operation) seal ceramic core and the simplification of the method.

The problem is solved in that in the method prototype, including the filling of powder in a silver shell monolignol workpiece deformation obtained monolignol billet to the desired size, cut, deformed billet-to-length part, Assembly, multi-strand billet, by placing the required number of measuring parts deformed monolignol workpiece in a silver sheath multi-core billet, extrusion, rolling and TMO, features: shell monolignol billet sleep powder bismuth ceramics deform Manoilo the workpiece by drawing at room temperature, i.e. without heating, with the degree of deformation per pass of 0.5-20%, the extrusion of multi-strand billet is carried out at a temperature in the range of 100-200°and with the size of the drawing ratio of from 4 to 30, the rolling is carried out at room temperature in air with a degree of deformation per pass 1-50%, followed by thermomechanical processing, which includes several stages of heat treatment at a temperature of 830-860°With,in the course of time, providing the formation in the ceramic core superconducting phase of the desired composition and structure, with the intermediate deformations between stages of heat treatment on the degree of deformation per pass 5-30%.

During the above operations is consistent seal stranded long wire, which ensures an increase of the critical current.

Backfilling of the ceramic powder in the shell allows you to get at the core of the wire close to the superconducting chemical composition of the material already at the initial stage of obtaining wire. In the process of deformation and heat treatments gradual compaction of the ceramic core. In the case of metal powders in the core are going through similar processes, however, when oxidation is carried out with the aim of obtaining the core wire material close to the superconducting chemical composition, there is a significant softening of the core (obvious with the passage of oxygen into the core through the shell of the wire thickness of 0.4-0.5 mm). After oxidation seal already ceramic core occurs only when TMO, which includes, as a rule, only a few (2-3 and up to a maximum of 4) intermediate deformations, which is insufficient for the required sealing of the ceramic core, and the expansion of the number of intermediate deformations at TMO is impractical due to disruption of the structure, the texture of the ceramic core and the geometry of the wire. This is one of the main reasons small critical currents of the wires on the basis of metal powders.

The deformation obtained in the previous step monolignol blank by drawing at room temperature with the degree of deformation per pass of 0.5-20% provides reception moneilema wire densified ceramic core of the desired shape and size, which greatly simplifies the process, making it more stable (no significant temperature gradient) and safe.

The deformation of the multi-billet extrusion at a temperature of 100-200°and the magnitude of the coefficient extraction 4-30 greatly simplifies the process, making it stable (significantly decreases the temperature gradient), safe and provides a multi-strand long wire with a ceramic core, similar in chemical composition to the superconducting material of the desired shape and size. In addition, when the deformation of multi-billet extrusion also there is a further compaction of the ceramic core.

When reducing the size of the drawing ratio from 800 to 4-30 sharply reduced the likelihood of the geometry lived, which is beneficial later on the increase of the critical current.

Rolling without heating Vozduha when the degree of deformation per pass 1-50% provides the receive wire of the desired shape and size, mainly in thickness, with the required geometry of the core and greatly simplifies the process compared to rolling at a temperature of 300-600°in a controlled atmosphere. In addition, when rolling is further seal the core.

TMO, including several stages of heat treatment at a temperature of 830-860°With intermediate strain between them with a degree of deformation per pass 5-30%, provides a further seal the core and forming in her superconducting phase of the desired composition and structure, which allows to obtain a superconducting wire with high current-carrying characteristics.

When deformation monolignol workpiece drawing with the degree of deformation per pass less than 0.5% is a violation of the geometric dimensions of the wire, you receive the wave-like along the length of the wire, and when drawn with a degree of deformation per pass more than 20% is a violation of the integrity of the shell, which is manifested in the formation of small cracks and their growth until the complete destruction of the membrane, which leads to rupture of the wire.

Carrying out the extrusion at a temperature below 100°when receiving wire from monolignol and multi-strand billet silver shells leads to cracking of the workpiece until the integrity of the ceramic lived due to the reduction of the plasticity of the material on the shell.

With increasing temperature extrusion above 200°when receiving wire from monolignol and multi-strand billet silver shells is a violation of the geometry of the ceramic lived due to the reduction of the strength characteristics of the material of the shell is thinning ceramic lived in some places along the length of the veins and thickening ceramic lived in other places along the length of the veins.

Carrying out the extrusion at the size of the drawing ratio is less than 4 was not feasible due to the need to increase cycles of extrusion and, therefore, increase the total time warp strands billet to the desired size. Carrying out the extrusion at the magnitude of the coefficient hoods over 30 leads to a violation of the geometry of the ceramic lived-related difference in the mechanical properties of the extrudable material, which has a significant influence on the deformation of materials at high degrees of deformation.

Conducting rolling with heating, i.e. at a temperature above room temperature is impractical because the strain exposed material with a ceramic core, which is at this stage in the form of powder (in the prototype - core metal). In addition, on the one hand, when used degrees of deformation per pass (1-50%) there is no need to deformation by heating to policedepartment rolled materials (as in method-prototype), on the other hand, the temperature rise of the rolling can lead to increased plasticity only shell and the violation of the geometry of the ceramic lived due to the reduction of the strength characteristics of the material of the shell, this can lead to thinning ceramic lived in some places along the length of the veins and thickening of the ceramic lived in other places along the length of the veins that always leads to a decrease of the critical current.

When rolling with the degree of deformation per pass to less than 1% is a violation of the geometric dimensions of the wire, you receive the wave-like along the length of the wire, and when rolling with the degree of deformation per pass more than 50% rupture of membranes: from small cracks to its complete destruction, which leads to rupture of the wire.

Holding TMO at temperatures below 830°and above 860°and the degree of deformation per pass to less than 5% and more than 30% is not possible to form a ceramic core superconducting phase of the desired composition and structure, in particular when the degree of deformation per pass to less than 5% at the intermediate deformation does not occur laying of the crystallites in the desired direction - the direction of primary current flow, and when the degree of deformation per pass more than 30% violation occurs geometry of the ceramic core. With decreasing temperature TMO below 830°With no formation from above the conductive phase in the ceramic core. With increasing temperature TMO above 860°With the formation of a large number of the liquid phase, which follows from the shell (for example, through the pores and cracks), which leads to disruption of the integrity of the shell, the violation of the stoichiometry of the ceramic core and a sharp deterioration of the critical characteristics of the superconductor.

The conduct of these operations in the described sequence and when these regimes have led to a new technical result is to increase the critical current density due to a consistent seal ceramic core and the simplification of the method.

The example implementation. Metallic silver capsules (tube length 1000 mm, diameter 10 mm, wall thickness 1 mm shell morozilnik blanks) was filled with powder of bismuth ceramics from the calculation of the final fill factor moneilema wires 25%. Next, the resulting monosilane billet deformed by drawing at room temperature with the degree of deformation per pass 10%, after which he formed a multi-core preform by placing in silver shells stranded blanks dimensional parts deformed morozilnik blanks. As shells stranded blanks used silver tube (with a diameter of 10 mm and a diameter of 16 mm with a wall thickness of 1 mm, a length of 100 and 50 mm for the NGOs). Wrapped multi-strand billet with a diameter of 16 mm was placed 217 dimensional parts deformed morozilnik blanks in a silver shell with a diameter of 0.82 mm, in silver sheath stranded billets with a diameter of 10 mm were placed in each of the 7 dimensional parts deformed morozilnik blanks in a silver sheath diameter of 2.6 mm, Then all received multi-strand billet was subjected to extrusion with the value of the coefficient of the hood 7 and 25 at temperatures of 100 and 200°C. Then all obtained after extrusion materials rolled without heating the air with the degree of deformation per pass 15%. Then all the wires held TMO in two stages at temperatures of 830°and 840°C for a total time of 200 hours with intermediate rolling with a degree of deformation per pass 12% to the final thickness of the wires on the basis of Bi-2223:0,2-0,3 mm

The critical current in the wires was measured by standard four-point method on the criterion of 1 μv/see

All obtained by the proposed method the wires, the magnitude of the critical current density critical current is related to the square of the superconducting core) not less than 9.5 times higher than the best wires obtained with the use of metal powder and at least 5% higher than on the wires, obtained on the basis of ceramic powders without the use of extrusi is, what characterizes the advantage of the proposed method.

Sources of information

1. P.Haldar, L.Motovidlo. Processing High Critical Current Density of Bi-2223 Wires and Tapes. The Journal of The Minerals and Materials Society (JOM), Vol.44, No.10, October 1992, p.54-58.

2. W.Gao, S.-C.Li et al. Synthesis of Bi-Pb-Sr-Ca-Cu Oxide/Silver Superconducting microcomposites by Oxidation of Metallic Precursors, Physica C 161 (1989), 71-75.

3. C.L.H.Thieme, D.Daly et.al. High Strain Warm Extrusion and Warm Rolling of Multiflamentary Bi-2223 Metallic Precursor Wire. Advances in Cryogenic Engineering(Materials), Vol.44 Edited by Balachandran et al., Plenum Press, New York, 1998, pp.533-540 - prototype.

The method of obtaining long-length composite wires on the basis of high-temperature superconducting compounds, including the formation of monolignol blanks by filling the powder in a silver sheath, the deformation obtained monolignol billet to the desired size, cut, deformed billet-to-length parts, the Assembly of the multi-core preform by placing the desired number of measuring parts deformed monolignol workpiece in a silver sheath multi-core billet, extrusion, rolling and thermomechanical processing, characterized in that the shell monolignol billet sleep powder bismuth ceramics, deformation monolignol procurement spend by drawing without heating with the degree of deformation per pass of 0.5-20%, the extrusion of multi-strand billet is carried out at a temperature in the range 100-200°and the value of the coefficient in the grave from 4 to 30, rolling is conducted without heating the air with the degree of deformation per pass 1-50%, thermomechanical processing, which includes several stages of heat treatment carried out at a temperature 830-860°over time, ensuring the formation of a ceramic core phase of the desired composition and structure, with the intermediate deformations between stages of heat treatment on the degree of deformation per pass 5-30%.



 

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