BACKGROUND OF THE INVENTION

1. Field of the Invention

The present description discloses an electrically conductive tip member and a method for producing the same.

2. Description of the Related Art

Known conventional electrically conductive tip members used as welding electrodes are used to hold workpieces such as steel or aluminum alloy bodies and cause a large current to flow through the pressed workpieces in a short time in a pressured state to thereby melt and weld their contact interface. For example, in previously proposed welding electrodes, a heat transfer interference portion having lower thermal conductivity than its surrounding area is disposed in a central region of a holding surface of each of the facing electrodes (see, for example, PTL 1). In a previously proposed resistance welding electrode, a tip electrode formed of steel composed mainly of tungsten is embedded in a forward end of a shank (see, for example, PTL 2). It is stated that, with this welding electrode, high-tension coated steel sheets can be resistance-welded.

CITATION LIST

Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. 2009-220168

PTL 2: Japanese Unexamined Patent Application Publication No. 2007-260686

SUMMARY OF THE INVENTION

In each of the tip electrodes described in PTL 1 and PTL 2, the electrode body is formed of Cu or a Cu alloy, and the central region is formed of tungsten. Since different metals with different sintering temperatures are used, many steps are necessary to produce the electrode in some cases. Moreover, since each of these tip electrodes is formed using different metals, an interface may be formed between these metals. This has led to the desire for a novel electrically conductive tip member that can be produced using a simple production process and has no interface between its components.

The invention disclosed in the present description has been made in view of the foregoing circumstances, and it is a principal object to provide a novel electrically conductive tip member having higher electrical conductivity and higher strength and a method for producing the electrically conductive tip member.

Extensive studies have been conducted to achieve the principal object, and the present inventors have found that, when a composite member is used which includes metallic copper used as a current-carrying member and a strong structural body containing a Cu—Zr-based compound and disposed on the inner circumferential side of the current-carrying member, a novel electrically conductive tip member having higher electrical conductivity and higher strength and a method for producing the electrically conductive tip member can be provided.

Accordingly, an electrically conductive tip member disclosed in the present description includes:

an inner periphery portion including a Cu matrix phase and a second phase that is dispersed in the Cu matrix phase and contains a Cu—Zr-based compound, the inner periphery portion having an alloy composition of Cu-xZr (where x is the atomic percentage of Zr and satisfies 0.5≤x≤16.7); and

an outer periphery portion that is present on an outer circumferential side of the inner periphery portion, made of a metal containing Cu, and has higher electrical conductivity than the inner periphery portion.

An electrically conductive tip member production method disclosed in the present description is a method for producing an electrically conductive tip member including an inner periphery portion and an outer periphery portion that is present on an outer circumferential side of the inner periphery portion and has higher electrical conductivity than the inner periphery portion,

the method including a sintering step of: disposing a raw material of the outer periphery portion, the raw material containing Cu and having higher electrical conductivity than the inner periphery portion; disposing a raw material powder for the inner periphery portion on an inner circumferential side of the raw material of the outer periphery portion, the raw material powder having an alloy composition of Cu-xZr (where x is the atomic percentage of Zr and satisfies 0.5≤x≤16.7) obtained using a powder containing Cu and a Cu—Zr master alloy or a powder containing Cu and ZrH2; pressurizing and holding the raw material powder in a prescribed pressure range at a prescribed temperature lower than a eutectic point temperature; and subjecting the raw material powder to spark plasma sintering.

The electrically conductive tip member and the method for producing the same disclosed in the present description can provide a novel product having higher electrical conductivity and also higher strength. The reason for this may be as follows. For example, in this electrically conductive tip member, the outer periphery portion is formed of the metal containing Cu and having high electrical conductivity, and the inner periphery portion is formed of a high-strength material including the Cu matrix phase and the second phase containing the Cu—Zr-based compound. It is therefore inferred that the outer side provides the high electrical conductivity and the inner side provides the high strength and high hardness. Since the outer periphery portion and the inner periphery portion are formed of similar Cu-based materials, an unwanted interface, for example, is unlikely to be formed therebetween, so that problems are less likely to occur than in an electrically conductive tip member having an interface. Generally, in methods for producing such electrically conductive tip members, some metal element powders are highly reactive. For example, Zr powder is highly reactive with oxygen, so that extreme care is required when it is used as a raw material powder in air. However, Cu—Zr master alloy powder (e.g., a Cu-50 mass % Zr master alloy) and ZrH2powder are relatively stable and can be handled with ease even in air. An inner periphery portion containing the Cu—Zr-based compound can be produced using relatively simple treatment in which any of these raw material powders is subjected to spark plasma sintering. Moreover, since the outer periphery portion and the inner periphery portion are formed of the Cu-based materials, their sintering temperatures do not differ significantly. This is advantageous in that the objective product can be obtained by one spark plasma sintering (SPS) operation.

