GB2141368A

GB2141368A - Copper-based reaction solder

Info

Publication number: GB2141368A
Application number: GB08405444A
Authority: GB
Inventors: Peter Listemann; Sigurd Moench
Original assignee: Hilti AG
Current assignee: Hilti AG
Priority date: 1983-06-14
Filing date: 1984-03-01
Publication date: 1984-12-19
Also published as: CH658214A5; DK89584D0; DE3321438C2; GB8405444D0; DE3321438A1; DK89584A; JPS59232691A; GB2141368B

Abstract

A copper-based reaction solder having 0.5 to 20 wt.% cobalt has its constituents, copper and cobalt, present at least partly in heterogeneous phase, for example as a sandwich with copper and cobalt layers, or as a copper foil with a cobalt layer on one surface. Such solders are particularly suitable for soldering hard metal to steel. The solder may contain up to 0.6 wt.% of carbon, possibly as a cobalt-carbon alloy.

Description

SPECIFICATION Copper-based reaction solder The present invention relates to a copper-based reaction solder. Copper solders and copper-alloy solders have been known for a long time as hard solders. Apart from the use of solder material consisting exclusively of copper, also known, for example, are copper-alloy solders which contain from about 40 to about 60 percent by weight of copper, small amounts (for example 0.2 percent by weight) of silicon, the remainder being zinc or possibly additionally nickel. To produce solders, the metal or the alloy is melted; it is cast into moulds and is then converted by customary deformation techniques, such as drawing, pressing or rolling, into wires, profiles or sheets, or is formed into a powder by grinding. Fluxing agents can be added or can be melted on.

Copper and copper-alloy solders are capable of reacting with cast iron, steel, hard metal and so forth that is to be sldered, with the formation of solid solutions and/or stoichiometrically-defined compounds. Solders of this kind are, therefore designated, for short, as "reaction solders". They are used for economical and technical reasons to a large extent more especially for the hard-soldering or brazing of steel, cast iron and hard metals, to a large extent in the construction of machinery parts, apparatus, equipment, tools, electric motors and the like.

Frequently, especially when steel and hard metals are being soldered, the work is effected at relatively high temperatures, for example over 1 100"C, in a vacuum or under protective gas. Understood by "hard metals" are, more especially, tungsten carbide/cobalt alloys, mostly with a slight specific content of carbon, but the binding agent (cobalt) can be replaced also by other metals, for example nickel.

Relevant hereto are, however, also titanium and tantalum carbides, which also mostly contain cobalt and possibly other metals as binding agent.

It has now become apparent that when using the known copper-based solders, for example when soldering steel to hard metal, the results achieved are not fully satisfactory. Thus, for example, disintegration or separation phenomena, along the grain boundary of the steel, have been observed. The result of this is a corresponding reduction in the static strength and, more particularly the dynamic strength. Especially the toughness of the steel is markedly reduced in this region. In the case of hard metal, on the other hand, frequently embrittlement of the edge zone by diffusion, formation of intermetallic phases and the Kirkendall effect along with the formation of a "rotten" or "decaying" zone have been observed.Furthermore, occasionally the formation of an rl -like layer, particularly in the soldering of steel to hard metal, as a result of specific carbon improverishment on the part of the hard metal, has been observed. These aggravating diffusion-occasioned effects lead to intolerably poor results especially in relation to impact stressing.

Surprisingly it has now been found that these disadvantages can be avoided by a copper-based reaction solder which contains 0.5 to 20 percent by weight of cobalt and in which copper and/or cobalt are present at least partly in heterogenous phase.

Preferably these constituents are present completely in heterogenous phase.

Besides the copper, constituting the predominant component, and the indicated amount of cobalt, further customary alloying constituents may be contained in the solder, such as silicon, for example in amounts from 0.1 to 0.4 percent by weight and/or carbon, more especially in an amount up to 0.8 percent by weight (in other words 0 to 0.8 percent by weight).

Furthermore, customary solder constituents, such as fluxing agents, binding agents which are volatile at soldering temperature, for example in the case of powdery solder, powderformlings or layer-shaped structure of the solder, organic compounds which release carbon under soldering conditions, more especially instead of or in addition to an existing carbon component, strength-increasing substances, which may in the appropriate circumstances also participate in the reaction, metals, non-metals, organic substances and similar known 'per se' substances can be added to the solder.

What has proved its worth above all is a reaction solder having 88 to 97 percent by weight of copper, 1 to 12 percent by weight of cobalt, and 0 to 0.6, more especially 0.05 to 0.5 percent by weight of carbon, with a possibly additionally-present remainder constituent of customary solder sonstituents, as set forth at the beginning hereof, can exist and copper and/or cobalt are present at least partly, preferably fully in heterogeneous phase.

What has proved its worth more particularly is a reaction solder which is present in the aforesaid manner in heterogeneous phase and which contains at least 91 percent by weight of copper, 2 to 8 percent by weight of cobalt, and up to 0.4 percent by weight of carbon. In a particularly preferred embodiment, the heterogeneous reaction solder consists of 94 to 97 percent by weight of copper, 3 to 6 percent by weight of cobalt and up to 0.6 percent by weight of carbon. Quite generally it is particularly preferred if the cobalt content lies between 1 percent by weight and the amount by weight of cobalt which is at a maximum soluble at soldering temperature.

The carbon possibly present in the heterogeneous reaction solder in accordance with the invention can be present for example as a mixture constituent, especially in the case of a powdery structure, as, possibly saturated, CoC alloy or as an organic substance which forms a corresponding or appropriate amount of carbon. Such organic carbon compounds which form carbon under decomposition are generally known (see R6mpps Chemie Lexicon, 7th edition, more especially at page 1811).

The constituents of the reaction solder, preferably copper and/or cobalt, can be present, at least partly in a finely-divided, preferably powdery, state. In this respect it can be a matter of powder mixtures, shaped bodies produced for example in a powdermetallurgical way, possibly with a content of further additives, with or without carrier. The heterogeneous reaction solders can be contained for example also in slid or pasty carriers which are preferably inert or else also reactive, for example carbon compounds which form carbon, metals and so forth.

Quite particularly preferred is a multi-layer (for example sandwich-like) structure for the reaction solder, the layers having a different composition, for instance in such a way that copper and cobalt, or at least a part of these, are arranged in different layers.

The arrangement may be such that layers are provided which contain only copper or cobalt, besides other constituents, or layers are provided having mutually different copper cobalt concentrations. Particularly preferred in this respect, are heterogeneous reaction solders which have layers consisting substantially or predominantly of copper or cobalt respectively, more especially if one such copper layer is arranged between two cobalt layers.

Customary soldering aids, such as binding agents, agents which form carbon, and the like can be arranged, for example, between the layers.

Besides the soldering of steel and cast iron, the copper-alloy solders in accordance with the invention have proved their worth more especially for the soldering of steel to hard metals, more especially tungsten carbide cobalt hard metals, which normally contain WC, Co and C in specific proportions. Also the use for the soldering of steel to titanium or tantalum-carbide based hand metals which contain cobalt or other metals, such as nickel as binding agent, is possible. In this respect, particularly when the cobalt layer is arranged on the steel side, a seal-like effect, along with extensive prevention of iron diffusion, occurs.

The invention is illustrated in the following examples: Example 1 In the preparation of a copper-based reaction solder a cobalt layer 8 > in thickness is applied to one side of a copper foil of 0.1 mm thickness, for example galvanically. When this solder is used for the soldering of steel to hard metal, preferably in such a way that the cobalt layer faces the steel, a considerable increase in the impact strength of the soldering is achieved, in comparison with prior known solders.

Example 2 In the preparation of a copper-based reaction solder, a cobalt layer 5 in thickness is applied to a copper foil of 0.15 mm thickness, on both sides of the foil, for example, galvanically. Considerable strength increase is achieved upon the soldering of steel to hard metal using this solder, in comparison with prior known solders.

The invention is not confined to these two examples, of course, and variations may be made thereto within the scope of the following claims. Thus, for instance, the solder of the invention may comprise its copper and cobalt constituents in powder form and contained in a solid, pasty or viscous carrier which so preferably inert.

Claims

1. A copper-based reaction solder characterised in that it comprises 0.5 to 20 percent by weight of cobalt and the constituents, copper and cobalt, are present, at least partly, in heterogeneous phase.

2. A reaction solder as claimed in claim 1 characterised in that it comprises 88 to 97 percent by weight of copper, 1 to 12 percent by weight of cobalt, and 0 to 0,6 (preferably 0.05 to 0.5) percent by weight of carbon, the remainder being customary solder constituents, the copper and the cobalt, at least partly and preferably completely, being present in heterogeneous phase.

3. A reaction solder as claimed in claim 1 or 2 characterised in that it comprises at least 91 percent by weight of copper, 2 to 8 percent by weight of cobalt and up to 0.4 percent by weight of carbon.

4. A reaction solder as claimed in claim 1, 2 or 3 characterised in that it comprises 94 to 97 percent by weight of copper, 3 to 6 percent by weight of cobalt, and up to 0.6 percent by weight of carbon.

5. A reaction solder as claimed in any preceding claim characterised in that the carbon is contained as a mixture constituent, in the form of a cobalt/carbon alloy, preferably up to saturation of the cobalt and/or in the form of a substance which under soldering conditions supplies the appropriate amount of carbon.

6. A reaction solder as claimed in any preceding claim characterised in that the constituents, preferably copper and/or cobalt, are present, at least partly, in a finely-divided, preferably powdery state.

7. A reaction solder as claimed in any preceding claim characterised in that the constituents are contained in a solid or pasty carrier, which is preferably inert.

8. A reaction solder as claimed in any preceding claim, characterised in that it is of multi-layer form and the constituents, copper and cobalt, are arranged at least partly in different layers thereof.

9. A reaction as claimed in claim 8, characterised by a layer consisting, at least quite predominantly, preferably solely of copper and a layer consisting quite predominantly, preferably solely of cobalt and possibly containing small proportions of carbon or by one such copper layer between two such cobalt layers.

10. Use of the reaction solder in accordance with any of the preceding claims for soldering steel to hard metal, more especially tungsten carbide/cobalt hard metal.

11. A reacion solder substantially as hereinbefore described by way of example.