EP0064191B1 - Compound material for electrical contacts, and method for its manufacture - Google Patents

Description

The invention relates to a composite material for electrical contacts made of at least two components that are not dissolved in one another, one of the components being a copper alloy to which at least one active component is added, in particular for low-voltage and installation switching devices. The invention further relates to a method for producing this composite material.

Composites for electrical contacts must contain electrically and thermally conductive parts to prevent excessive heating. Your mechanical properties such as B. hardness, strength or elastic behavior are to be optimally adapted to the respective application. In addition, the susceptibility to corrosive media should be low. In general, tarnish and scale layers and thus high contact resistances can only be avoided on relatively noble materials. Furthermore, the composite materials must not stick or weld when switching, and their burn-up and material migration should be low.

Thanks to the excellent physical and chemical properties of these materials, composite materials with silver and its alloys meet these and other requirements for good contact materials to such an extent that these materials have been widely used in low-voltage technology. However, silver is a relatively expensive material, so efforts are being made to replace it with other, less expensive materials. Here copper, its alloys or composite materials with a metallic matrix of these materials are suitable (cf. e.g. BA Keil: "Materials for electrical contacts", Springer-Verlag, Berlin, 1960; or D. Stöckel and others: "Materials for electrical Contacts «, Kontakt & Studium Vol. 43, Expert Verlag, 7031 Grafenau 1 / Württ., 1980). No other contact material achieves the high electrical and thermal conductivity of the copper, combined with favorable mechanical properties, affordable costs and generally good procurement options. Because of its less noble character compared to silver, especially its willingness to oxidize, this material in its pure form, however, often cannot be used to manufacture contact pieces, especially for low-voltage switchgear and installation switching devices such as. B. for contactors, auxiliary contactors, circuit breakers or circuit breakers. Although alloying certain elements to this material, the material properties such. B. improve the oxidation behavior. However, known contacts made of copper alloys or of composite materials with such alloys, inexpensive elements being alloyed with the copper, generally have a relatively high contact resistance after only a few circuits, so that they are usually not suitable for low-voltage switching devices or installation switching devices.

From DE-A-2 813 087 a corresponding contact element made of a composite material is known, the matrix of which consists of a copper alloy, the inclusions of e.g. B. contains tin oxide or graphite. Palladium is intended as the alloying partner for copper.

However, this precious metal, which is to be used, for example, in a proportion by weight of between 8 and 50% of the alloy, is so expensive that a replacement of silver or silver alloys is not an option with the known copper alloy for reasons of cost.

The object of the present invention is to provide a composite material with a copper alloy which, on the one hand, has at least approximately similar contact properties to the known silver-based composite materials used for contacts of low-voltage or installation switching devices and, on the other hand, is less expensive than these known materials. In particular, the composite material should show lower scale rates compared to pure copper composite materials and at the same time have a relatively low contact resistance.

This object is achieved according to the invention for the composite material of the type mentioned at the outset in that the alloy component of the copper is at least one element from the group of antimony, gallium and germanium, the antimony content of the alloy being between 0.01 and 7 atom% or the corresponding gallium content is between 0.5 and 20 atom% or the corresponding germanium content is between 0.5 and 10 atom%.

The copper alloy components mentioned have a finite solubility in solid copper. The component of the composite material which is not dissolved in these copper alloys is generally known materials, the usual mixing ratios of these materials having to be provided with the component of the copper alloy (cf. e.g. the book by D. Stöckel et al., In particular pages 35) and 109 to 113).

The advantages achieved by the invention are to be seen in particular in that, by alloying the elements mentioned with the copper, on the one hand the corrosion resistance of the composite material compared to the pure copper composite material is increased and on the other hand contacts made of composite materials with these copper alloys in switching tests are tolerable for the intended application Show contact resistance. Since the alloys mentioned are generally less expensive than the silver-based materials used in composite materials, they can therefore be used partially serve as a substitute for these silver-based materials.

According to an advantageous development of the composite material according to the invention, its copper alloy can also contain at least one further alloy component. This component is then one or more elements from the group of cadmium, chromium, cobalt, palladium or silicon. The cadmium content is between 0.1 and 2 atom% or the chromium content between 0.01 and 0.8 atom% or the cobalt content between 0.1 and 1.8 atom% or to choose the palladium content between 0.1 and 3 atom% or the silicon content between 0.5 and 10 atom%. However, the proportion of these further components of the alloy should at most be equal to the proportion of antimony or gallium or germanium in the alloy.

To further explain the invention and its developments characterized in the subclaims, reference is made to the table and the diagrams in the drawing, from which properties of composite materials according to the invention can be derived. The diagrams of FIGS. 1 to 4 show frequency curves of contact voltages. 1 to 3 are based on metallic alloys for composite materials according to the invention, while in FIG. 4 exemplary embodiments of such composite materials are assumed.

It is generally known that the properties of contacts made of composite materials are largely determined by the properties of their components which are not soluble in one another. The copper alloy as the first component of the composite materials according to the invention must be corrosion-resistant and lead to a low contact resistance. The second component, also called the active component, is used primarily to increase the wear resistance and to reduce the erosion of the contacts. The behavior of the first component is discussed in more detail below. For this purpose, information about the scale and corrosion behavior of some binary copper alloys to be used for composite materials according to the invention in comparison to pure copper can be found in a table.

Sheets were used to test the corrosion resistance of these materials. These sheets can be produced, for example, by melting the alloys mentioned using chemically pure starting materials under argon as protective gas in a graphite crucible and annealing them at temperatures between 600 ° C. and 950 ° C. to avoid increases. The homogeneous bodies obtained in this way Alloys can be processed into sheet metal using conventional forming processes such as rolling or hammering. The weight increase Δ m of the individual materials, measured in micrograms per square centimeter in the table, can be obtained after oxidation in air after a 24-hour heat treatment at 250 ° C.

The proportions of the respective alloy additions to the copper in atomic% are noted in the table. As can be seen from the table, the reductions to be used for composite materials according to the invention have a significantly lower tendency to scale than pure copper.

On the basis of the curves in the diagram of FIG. 1, the contact resistance of contact pieces which are made from materials according to the invention can be estimated. The predetermined copper alloys contained in these materials largely determine the contact resistance of these materials. The embodiment according to the curves in the diagram of the figure is therefore based on a contactor with contacts which are only made from the pure matrix material from some of the predetermined copper alloys. This diagram shows the contact voltage U _k in millivolts (mV) on the abscissa, while the ordinate shows the cumulative frequency W of the contact voltages measured at the respective contactor contact according to the so-called Weibull statistics. These contact voltages are measured after approximately 2000 switching operations of the contactor under an average load of 45 A at 110 V AC voltage under an ohmic load.

In the area of the diagram denoted by I are the frequency curves of contact voltages on contacts which are produced from copper alloys to be provided for composite materials according to the invention. Three copper alloys are selected as the exemplary embodiment, the proportion of alloy in antimony or gallium or germanium in each case being approximately between 1.75 and 7 atom%. For comparison, a curve labeled 11 is entered in the figure, which indicates the frequency of the contact voltages on contacts made of pure copper. The frequency curve labeled 111 results for contacts made of a common composite material based on silver, here for Sil cadmium oxide with a cadmium oxide content of 15% by volume. It can be seen from the diagram in FIG. 1 that the contact voltages of the alloys to be provided for materials according to the invention correspond at least approximately to the contact voltages of previously used silver-based materials.

In FIG. 2, contact voltages are indicated in a diagram, which are to be measured on contacts made of binary copper-germanium alloys with different germanium concentrations. The germanium concentration in atomic% is plotted on the abscissa and the contact voltage U _k in mV on the ordinate for a frequency of 50%. The exemplary embodiment of the figure is based on contact voltages on contacts at 45 A and 110 V AC under ohmic load after 2000 switching of the contacts. As can be seen from the diagram in this figure, the contact voltages and thus the contact resistances are particularly low, in particular at germanium concentrations between 3 and 7 atom%, preferably around 5 atom%. Part of the germanium can be replaced by cobalt. This fact is surprising insofar as the specific electrical resistance of the alloys does not show a minimum at about 5 atomic percent germanium, but assumes a value of about 18 μΩ · cm. This resistance value is greater than that of an alloy with a lower germanium content than 5 atom%. From this it can be seen that a low contact resistance is also achieved with materials with a relatively high specific resistance if only the external layer resistance is low (cf. the books by A. Keil and D. Stöckel mentioned).

• Cadmium mit einem Gehalt zwischen 0,1 und 2 Atom-% oder Chrom mit einem Gehalt zwischen 0,01 und 0,8 Atom-% oder Kobalt mit einem Gehalt zwischen 0,1 und 1,8 Atom-% oder Palladium mit einem Gehalt zwischen 0,1 und 3 Atom-% oder Silizium mit einem Gehalt zwischen 0,5 und 10 Atom-%. Selbstverständlich kann als dritter Legierungsbestandteil auch ein Element aus der Gruppe Antimon, Gallium, Germanium innerhalb der im Zusammenhang mit den binären Legierungen genannte Grenzen der Legierungsanteile ausgwählt werden. Der in Atom-% angegebene Anteil der zusätzlichen, dritten und/oder vierten Legierungsbestandteile ist dabei i. a. kleiner oder höchstens gleich dem zweiten Legierungsbestandteil an Antimon oder Gallium oder Germanium. Einige Ausführungsbeispiele solcher ternärer, Germanium enthaltender Legierungen, wie sie für Verbundstoffe nach der Erfindung als Matrixmaterial vorgesehen werden können, sind den in dem Diagramm der Fig. 3 wiedergegebenen Kurven zugrundegelegt. Dabei sind die Meßbedingungen wie bei den Ausführungsbeispielen gemäß dem Diagramm der Fig. 1 gewählt. In dem Diagramm der Fig. 3 ist auf der Abszisse die Kontaktspannung U_k in mV angegeben, während auf der Ordinate die kumulative Häufigkeit W der zu messenden Kontaktspannungen aufgetragen ist. Als Kontaktmaterialien sind drei spezielle CuGe_3-xX_x-Legierungen mit x Atom-% als Ausführungsbeispiele ausgewählt, nämlich: CuGe 2,5Co0,5 (Kurve a), CuGe2,5Sb0,5 (Kurve b) und CuGe2,9Cr0,1 (Kurve c). Außerdem sind zum Vergleich das binäre CuGe3,0 (Kurve d) und zusätzlich ein bekannter Verbundwerkstoff auf Silberbasis, nämlich AgCdO (Kurve e) aufgeführt. Aus dem Verlauf der Kurven a bis c in dem Diagramm ist ersichtlich, daß auch Kontakte aus ternären Kupferlegierungen Kontaktwiderstände aufweisen, die ohne weiteres in der Größenordnung von Kontaktmaterialien auf Silberbasis liegen. Einen besonders geringen Kontaktwiderstand haben Legierungen mit Kobalt als drittem Legierungspartner (Kurve a). Aufgrund der geringen Kontaktwiderstände der Kontakte aus den reinen ternären Kupferlegierungen sind entsprechend günstige Kontaktwiderstände von Kontakten aus Verbundmaterialien mit diesen Legierungen zu erwarten. Diese Legeirungen sind deshalb als Matrixmaterial für die Verbundwerkstoffe nach der Erfindung besonders gut geeignet.

In the exemplary embodiments in the table and the two FIGS. 1 and 2, matrix materials for composite materials which consist of a binary copper alloy were assumed. If necessary, further elements can be added to these alloys. so that, for example, ternary or quaternary alloys are then formed. This allows z. B. further improve the corrosion behavior or the contact resistance compared to the binary alloys. The following materials are particularly suitable as such additional alloy components:

• Cadmium containing 0.1 to 2 atomic% or chromium containing 0.01 to 0.8 atomic% or cobalt containing 0.1 to 1.8 atomic% or palladium containing between 0.1 and 3 atom% or silicon with a content between 0.5 and 10 atom%. An element from the group of antimony, gallium and germanium can of course also be selected as the third alloy component within the limits of the alloy proportions mentioned in connection with the binary alloys. The proportion of the additional, third and / or fourth alloy constituents stated in atomic% is generally less than or at most equal to the second alloy constituent of antimony or gallium or germanium. Some exemplary embodiments of such ternary alloys containing germanium, such as can be provided as matrix material for composites according to the invention, are based on the curves shown in the diagram in FIG. 3. The measurement conditions are chosen as in the exemplary embodiments according to the diagram in FIG. 1. 3 shows the contact voltage U _k in mV on the abscissa, while the ordinate plots the cumulative frequency W of the contact voltages to be measured. Three special CuGe _3-x X _x alloys with x atom% are selected as contact materials as exemplary embodiments, namely: CuGe 2.5Co0.5 (curve a), CuGe2.5Sb0.5 (curve b) and CuGe2.9Cr0.1 (Curve c). In addition, the binary CuGe3.0 (curve d) and also a known silver-based composite, namely AgCdO (curve e), are listed for comparison. From the course of the curves a to c in the diagram it can be seen that contacts made of ternary copper alloys also have contact resistances which are in the order of magnitude of contact materials based on silver. Alloys with cobalt as a third alloy partner have a particularly low contact resistance (curve a). Due to the low contact resistance of the contacts made of pure ternary copper alloys, correspondingly favorable contact resistance of contacts made of composite materials with these alloys can be expected. These alloys are therefore particularly well suited as matrix material for the composite materials according to the invention.

The additives mentioned for the binary copper-antimony or copper-gallium alloys also result in similar contact stress ratios, so that these alloys can also be advantageously used for composite materials according to the invention.

With the aforementioned alloys as matrix components, composite materials can be produced in a known manner. As components of the composite materials which are not dissolved in the copper alloys of the matrix, the materials which are generally known in the field of composite materials for electrical contacts from the switching devices mentioned can be provided as active components. These active components are to be introduced into the metallic matrix of the composite material in the usual mixing ratios. For example, in order to increase the welding strength and reduce the burn-up of the composite materials, a predetermined proportion of oxidic substances such as beryllium oxide (BeO), cadmium oxide (CdO), molybdenum oxide (Mo03), lithium oxide (Li ₂ 0), bismuth oxide (Bi ₂ 0 ₃ ), Zinc oxide (ZnO) or tin oxide (Sn0 ₂ ) or carbon or graphite or refractory metals such as. B. molybdenum, tungsten, niobium, tantalum, Va nadium or carbides such as B. tungsten carbide (WC), titanium carbide (TiC) or tungsten titanium carbide [(W, Ti) C] can be provided. The composite materials mentioned according to the invention can, for. B. create on a powder metallurgical basis by single press technology or extrusion. A powder mixture of the individual elements of the alloy and the active component can be assumed here. However, it is also possible to first produce a powder of the alloy and then mix it with the powder of the active component. Composite materials with refractory metals or carbides can also be produced using the known sintering technique.

Some of the composite materials according to the invention composed of the copper alloys and the active components mentioned are based on the diagram in FIG. 4. The following three composite materials were selected as exemplary embodiments: Cu-5 atomic% Ge-5% by volume Mo; Cu-5 atom-Wo Ge-5 vol .-% Zn0 and Cu-1.5 atomic% Ge-5 wt .-% C. When making the contacts of a contactor from these materials was made from a mixture of copper powder , Germanium powder and the powder of the active component. The molybdenum additive and the zinc oxide additive guarantee a high erosion resistance with at the same time favorable welding behavior, while contacts with carbon or graphite additives show particularly high weld strength.

The curves in the diagram can be used to make statements about the contact resistance of contact pieces made from these materials. As in the previous diagrams, the abscissa shows the contact voltage U _k to be measured on the contactor contact in mV, while the ordinate shows the cumulative frequency W of these contact voltages. In the exemplary embodiments of the figure, an average load of the contactor contacts of 45 A at 110 V AC voltage was assumed, the contacts being switched about 2000 times under an ohmic load.

The frequency curves of the contact voltages of contacts made from the aforementioned composite materials according to the invention lie in the region of the diagram of FIG. 4 designated by A. For comparison, a curve labeled B is entered in the diagram, which indicates the frequency of the contact voltages of pure copper contacts. The frequency curve denoted by C results for a common contact material based on silver, here for silver-cadmium oxide with a cadmium oxide content of 15% by volume.

As can be seen from the diagram in FIG. 4, the contact voltages of the materials according to the invention approximately correspond to the contact voltages of previously used silver-based materials. It is therefore possible to replace more expensive silver-based contact materials with the relatively inexpensive pre-bonded materials according to the invention.

Claims (11)

1. A compound material for electrical contacts which consists of at least two components which are mutually insoluble, wherein one of the components is a copper alloy to which at least one active component is added, in particular for low- voltage and wiring switching apparatus, characterised in that the alloying constituent of the copper is at least one element from the group of antimony, gallium and germanium, the antimony content of the alloy being in the range of between 0,01 and 7 atom %, the corresponding gallium content being in the range of between 0,5 and 20 atom %, and the corresponding germanium content being in the range of between 0,5 and 10 atom %.

2. A compound material as claimed in Claim 1, characterised in that the copper alloy comprises at least one further alloy constituent, namely one or more elements from the group of cadmium, chromium, cobalt, palladium and silicon, the respective alloy content of cadmium being in the range between 0,1 and 2 atom %, of chromium between 0,01 and 0,8 atom %, of cobalt between 0,1 and 1,8 atom %, of palladium between 0,1 and 3 atom % and of silicon between 0,5 and 10 atom-%; and wherein the proportion of the further alloy constituent at the most equals the proportion of antimony or gallium or germanium.

3. A compound material having a metallic matrix which consists of a copper.germanium alloy as claimed in Claim 1 or Claim 2, characterised by a germanium content of the alloy of between 3 and 7 atom %.

4. A compound material as claimed in Claim 3, characterised by a germanium content of the alloy of approximately 5 atom %.

5. A compound material as claimed in Claim 3 or Claim 4, characterised in that the germanium content is partially replaced with cobalt.

6. A compound material as claimed in one of Claims 1 zo 5, characterised in that beryllium oxide (BeO), or cadmium oxide (CdO), or molybdenum oxide (Mo03), or lithium oxide (Li₂0), or bismuth oxide (Bi₂0₃), or zinc oxide (ZnO), or tin oxide (Sn0₂), is provided as active component of the compound material, which is insoluble in the copper alloy. ,

7. A compound material as claimed in one of Claims 1 to 5, characterised in that molybdenum, or tungsten, or niobium, or tantalum, or vanadium, is provided as active component of the compound material, which is insoluble in the copper alloy.

8. A compound material as claimed in one of Claims 1 to 5, characterised by carbon, or graphite, as active component of the compound material, which is insoluble in the copper alloy.

9. A compound material as claimed in one of Claims 1 to 5, characterised in that tungsten carbide (WC), or titanium carbide (TiC), or tungsten titanium carbide [(W, Ti)C] is provided as active component of the compound material, which is insoluble in the copper alloy.

10. A process for the production of a compound material as claimed in one of Claims 1 to 9, characterised in that powders of the components are combined by the use of the individual pressing technique, or extrusion.

11. A process for the production of a compound material having high-melting materials as claimed in one of Claims 1 to 9, characterised by a sintering impregnation technique.

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