JPH05170562A - Connection of superplastic ceramic wire - Google Patents

Abstract

PURPOSE:To enable the connection of wires with each other by superposing the end parts of a pair of wires composed of an electrically conductive superplastic ceramic and pressing the superposed part at a specific temperature, thereby increasing the contact area by the deformation of the wires. CONSTITUTION:In the connection of a pair of wires made of an electrically conductive superplastic ceramic material containing at least one kind of ion, conduction electron and hole as a carrier (e.g. zirconia solid solution and alumina incorporated with Y2O3, MgO, CaO, etc.), the end parts of both wires are superposed one upon another and subjected to superplastic processing at a straining rate of 10<-2> to 10<-5>S<-1> while keeping at a temperature between 0.5Tm and 0.8Tm (Tm is melting point) to enable the connection of the wires. Concretely, a sintered ceramic material is heated to a temperature to exhibit superplasticity and subjected to constrictive wire-drawing by extrusion or drawing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of joining ceramic wire rods having electrical conductivity, and more specifically, to a connection by diffusion joining of the wire rods by superplastically deforming a densely sintered ceramic polycrystalline body. Regarding the method.

[0002]

2. Description of the Related Art Oxide ceramics exhibit electric conductivity with ions, conduction electrons and holes as carriers. Materials exhibiting high ionic conductivity include β-alumina structure oxides and fluorite structure oxides such as yttrium-stabilized zirconia. Certain oxides and nonstoichiometric compounds containing transition elements, such as TiO and NiO, have a large electric conductivity due to the movement of conduction electrons and holes. Furthermore, certain perovskite type oxides having a non-stoichiometric composition, such as YBa ₂ Cu ₃ O
In _7-x and _{Sr x La 2-x CuO 4} -y becomes superconducting below a certain critical temperature. These electrically conductive materials are applied to oxygen sensors, solid electrolytes and the like. However, almost no attempts have been made to use ceramics as electrically conductive wires, as with metals. This is because the sintered ceramics are brittle and cannot be plastically processed, and it is extremely difficult to handle them as a wire rod. As a method for producing a wire rod of ceramics exhibiting superconductivity, a metal pipe is filled with powder, drawn, and fired. However, in this method, since firing is performed through the metal coating, it is difficult to densify the ceramic and control the nonstoichiometry, and a large critical current cannot be obtained. In addition, there is a drawback that reproducibility and reliability are poor because the internal ceramics are broken and broken during the winding process.

In addition, even when wires are connected to each other, it is easy to weld and solder with a metal material.
There is a problem that it is difficult to apply to ceramics.

The present invention solves the above-mentioned conventional problems, and an object thereof is to provide a connection method by diffusion bonding similar to that of a metal wire rod by utilizing the superplastic deformation phenomenon of ceramics.

[0005]

The inventors of the present invention have found that a sintered body composed of fine grains of partially stabilized zirconia exhibits superplastic deformation, and that the ceramics after sintering can be processed by superplastic processing. Clarified that it is applicable. Further, the present inventor has continued to research the superplastic deformation mechanism of partially stabilized zirconia, and has found that the superplasticity of oxide ceramics and the superplasticity of metals and alloys are described by the same constitutive equation, Is an equiaxed shape, regardless of the type of interatomic bond,
It is concluded that it is a common property for polycrystalline bodies with fine grains. As a result of research on an ultra-fine crystal grain oxide polycrystal based on this, not only zirconia having a fluorite type crystal structure but also YBa having an alumina or perovskite type crystal structure is obtained.
It was confirmed that even ₂ Cu ₃ O _7-x exhibits a deformation behavior corresponding to superplasticity. Furthermore, if pressure is applied to the superplastic ceramic wire at the temperature and stress at which superplastic deformation occurs, and diffusion bonding is performed, the wires having circular cross sections are deformed to each other, increasing the contact area and obtaining a strong bond. The present invention has been completed and the present invention has been completed.

That is, the present invention relates to ions, conduction electrons,
When two wires of superplastic ceramics having electric conductivity having at least one kind of holes as a carrier are bonded to each other, the ends of the wires are overlapped with each other, and the wire ends of 0.5 Tm to 0.
Hold at a temperature of 8 Tm (Tm is melting point) and pressurize,
The present invention provides a method for joining wire rods, which is characterized by increasing a contact area due to deformation.

Ceramics to which the processing and bonding method of the present invention can be applied are oxide polycrystals having electric conductivity with at least one of ions, conduction electrons and holes as a carrier and exhibiting superplasticity. Is. Among the electrically conductive oxides, those exhibiting high ionic conductivity include Y ₂ O ₃ ,
Examples thereof include zirconia solid solution added with MgO and CaO, and alumina. YBa ₂ that exhibits superconductivity
_{Cu 3 O 7-x, Sr} x La 2-x CuO 4-y can be exemplified. The ceramics having electrical conductivity are not limited to the polycrystals composed of these single compositions, and may be a composite in which other crystals coexist. At this time, the other crystal body does not need to be electrically conductive, but it does not react with the electrically conductive crystal to form a crystal having another composition. As a combination of such crystals, for example, zirconia solid solution and _alumina, there is a YBa ₂ Cu _{3 O 7-x} and BaCuY ₂ O _5. In order for the composite to have electrical conductivity, the content of insulating crystals must be 70% or less.

The oxide polycrystal exhibiting superplasticity in the present invention is composed of equiaxed fine crystal grains having a grain size of 2 μm.
It is preferable not to include the above coarse particles. The smaller the crystal grain size, the easier the superplastic deformation due to the grain boundary slip at high temperature.

In the method of the present invention, the above-mentioned electrically conductive ceramics are superplastically worked at a strain rate of 10 ⁻² to 10 ⁻⁵ S ⁻¹ within a temperature range of 0.5 to 0.8 of the melting point. At temperatures below the melting point of 0.5, diffusion of atoms is slow,
It is not preferable because it breaks before high temperature deformation occurs. At temperatures above the melting point of 0.8, remarkable grain growth occurs and the grains become coarse, so superplasticity due to grain boundary slip does not occur.

Next, the method of manufacturing the wire used in the method of the present invention will be specifically described.

By heating the ceramics sintered in a special shape to a temperature at which superplasticity is generated, and extruding or drawing,
The cross-sectional area is reduced and wire drawing is performed. The extrusion or drawing die itself must be kept at a high temperature, and it is preferable to use a heat-resistant alloy such as a heat-resistant alloy, silicon nitride, or silicon carbide as a raw material.

When bending or coiling a wire obtained by sintering or superplastic working, the wire is heated to a superplastic temperature and the strain applied to the wire by the working is 10 ⁻² to It deforms at a rate of 10 ⁻⁵ S ⁻¹ .

Next, the method for joining the wire rods of the present invention will be specifically described.

FIGS. 1 and 2 are sectional views for explaining the procedure of the method according to the present invention. First, as shown in FIG.
The ends of the two wire rods 1 and 2 are overlapped with each other, and the superplastic temperature is maintained and pressure is applied. As shown in FIG. 2, the wire material is deformed to increase the contact area and is firmly bonded by diffusion bonding. In this way, the connection of the ceramic wire is achieved.

[0015]

EXAMPLES Next, the present invention will be described in more detail by way of examples.

Example YBa ₂ Cu ₃ O _7-x polycrystal (average grain size 0.5 μm)
The wire rod having a diameter of 1 mm of m) was overlapped at 900 ° C., pressed at 5 kg for 5 minutes and held for 30 minutes for diffusion bonding. The critical current after connection is 90% of the critical current of the material.
%Met.

[0017]

As described above, according to the present invention, it is possible to connect wires to each other by superplastic working of electrically conductive ceramics, and particularly in coil forming and wiring for superconducting magnets that operate at liquid nitrogen temperature or higher. Therefore, it is possible to apply and handle a densely sintered ceramic wire rod.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a contact state of wires before joining.

FIG. 2 is a cross-sectional view showing a state where the contact area of the wire rod after joining is enlarged.

[Explanation of symbols]

 1,2 wire rod

Claims (1)

[Claims] 1. When two wire rods of superplastic ceramics having electric conductivity using at least one of ions, conduction electrons and holes as a carrier are bonded to each other, the end portions of the wire rods are overlapped and A method for joining wire rods, which comprises maintaining a temperature of 0.5 Tm to 0.8 Tm (where Tm is a melting point) and applying pressure to increase the contact area due to deformation.