US2096924A - Composite structural product and method of making the same - Google Patents

Description

Patented Oct. 26, 1937 UNITED STATES PATENT OFFICE COMPOSITE STRUCTURAL PRODUCT AND METHOD OF MAKING THE SAME Paul Schwarzkopf, Reutte, Tyrol, Austria 9 Claims.

This invention relates to a composite structural material and shaped articles made therefrom intended more particularly for electrical purposes without however being limited to such use.

In particular this application forms a continuation in part of my co-pending application, Ser. No. 594,154, filed February 19, 1932 issued as Patent No. 2,030,229, on February 11, 1936.

Numerous composite structural materials, more particularly alloys of the various heavy and light metals, have already been proposed. They have been designed to yield particular strength with a low density or ready shaping capability; they frequently also unite high electrical conductivity with low density and suificient mechanical strength. More particularly importance has been attached to a content of higher melting and hard constituents, such as tungsten, molybdenum, tantalum, whilst the greater shaping capability, more particularly the adaptability for being poured or cast and for being mechanically worked, has been yielded by softer or lower melting metals, such as copper or silver.

This invention relates to a structural material (conglomerate) and shaped articles made therefrom which consists of material taken from each of the following two groups: molybdenum, titanium, vanadium, tungsten, tantalum, as a first group and silver, gold, aluminium, cobalt, chromium, copper, nickel, platinum, tin, zinc, iron, as a second group, such material being obtained in the hot and/or under pressure as a conglomerate, which exhibits, therefore, no chemical combination between the several elements but on the contrary a solid mixture, solid solution or permeation of at least two constituents.

According to the invention, the material of the first group 'is used in a special granular texture.

The preparation of tungsten and molybdenum suitable for the purposes of the invention may be described first.

A known process for obtaining tungsten and molybdenum consists in obtaining from the ore an oxide of the metal in the gaseous or vapour state by sublimation and precipitating the same by condensatiorf. The metal is obtained from, the resulting oxide by reduction. This reduction may be carried out in such a way, e. g. retarded, that as a. result of the reduction and the heat evolution accompanying the same, a metal powder is obtained which is more coarsely granulated than that obtained by the normal method of production. Since the reaction velocity during the reduction depends both on the temperature as well as on the concentration of the reducing agent in the reducing gas mixture, then by adjusting one of these factors, or both factors, the course of the reduction may be retarded as desired and as a result the formation 5 of larger crystals, that is to say the production of a coarsely granulated powder, promoted. If operations are carried out with reducing hydrogen, then steam may, for example, be mixed with the same for this purpose.

Another way of obtaining the special texture of the material of the first group is explained more in detail in my co-pending application Ser. No. 594,154, and consists in sintering or smelting into a coherent body the crystals of which are coarser than the granulation of the starting powder, then hammering the sintered or fused body and commlnuting it until a powder of the desired coarse granule is obtained.

In order to make a conglomerate usable for this invention, the powder is then mixed with the softer or lower melting metal powders and heated, a body may be obtained which, according to the mixing proportions, shows desired physical, electrical and mechanical properties.

The metal of the second group may be present in quantities of 3-6% if it is to act merely as a binder, and in larger quantities, up to about 15% of the body obtained, if it is also decisively 30 to influence other properties of the body, such as its surface quality. For many purposes it will be advantageous to use the lower melting or soft metals in quantities up to -90%.

The following binary compositions are particularly advantageous for use with this invention:

Tungsten-silver; tungsten-chromium; tungsten-copper; tungsten-tin; tungsten-zinc; molybdenum-silver; molybdenum-copper; molybdenumchromium; molybdenum-tin; molybdenumzmc.

The following ternary compositions are particularly advantageous:

Molybdenum-nickel-copper; molybdenum-silver-chromium; molybdenum-chromium-copper; tungsten-nickel-copper; tungsten-silver-copper; tungsten-copper-chromium; tungsten coppertin.

In order to make this conglomerate material the procedure adopted is such that the coarsely granular highermelting metal powder obtained is cast over with the liquid soft metals, or the powders are mixed and heated until at last the soft metal melts, or both these procedures are combined. Whole blocks of any desired shape and size can be obtained in this way which are either homogeneous or which contain the hard metal in larger quantities in some parts and the soft metal in larger quantities in other parts. Such layering may, for example, be produced by mixing the soft and hard metals, causing the soft metals to melt, and then allowing the hot bath to subside, as a result of which a more or less considerable demixing occurs and the heavier metals collect in larger quantities, i. e. concentrate, at desired places.

The material obtained in this way may be mechanically worked; more particularly it may be extended by hammering or rolling and the sheets obtained punched and pressed.

It is a well-known fact that the union of higher melting metals like tungsten and molybdenum with other bodies oifers difllculties. Such bodies of high melting point are frequently chosen since they can be heated to a higher temperature during use, and the union with a support must then be effected with the aid of a hard solder. As a rule when soldering undesirable oxidation apcal pressure.

pears on the tungsten etc. body. For many purposes also tungsten etc. bodies are required having a compact surface (high lustre) which offers resistance to corrosion. Such compact bodies, however, can be produced only by mechanical working, for example, by rolling out tungsten sheets of extraordinary thinness. If now bodies are shaped or cut from such sheets and united with other bodies by means of hard solders, then merely the compact skin is lost by oxidation.

According to the invention sheets of tungsten, molybdenum and so forth are made of the desired thickness, and also sheets of a conglomerate of the kindabove described, e. g. of coppertungsten, and these two sheets are layed one upon the other and united in the hot, advantageouslyinareducing atmosphere and by mechani- The sheets blend together and a unitary sheet is obtained which consists of tungsten on-one side and of copper-tungsten on the other side. However, copper-tungsten is easy to solder. In addition the tungsten on the coppertungsten side can be dissolved out, erg. by etching with potassium nitrite, so that a sheet is obtained which consists of tungsten on one side and to a greater or less extent of pure copper on the other side. The union between these two parts is extraordinarily intimate and they cannot be separated either during subsequent working or during operation. No perceptible electrical transition resistance can be detected and nor is it to be expected since non-conducting oxides are absent.

The procedure may also be such that a sheet of copper-tungsten is laid on' a tungsten sheet of any desired thickness or thinness and on top of the same a sheet of copper is placed, and the three sheets are united to a three-fold sheet in the hot and in a reducing atmosphere and preferably with employment of a suitable pressure. Once again the copper-tungsten is intimately and inseparably united both with the tungsten and with the copper. In this case the chemical treatment of the copper-tungsten for the purpose of dissolving out the tungsten is dispensed with. This latter process is frequently of advantage since pores are formed in the copper owing to the dissolution of the tungsten which are desirable for soldering purposes.

A further method consists in rolling out a block of copper-tungsten prepared as being described above and which consists for the most part of tungsten on the one side and on the other side for the most part or exclusively of copper in the direction of the layers whereby a sheet is obtained which on one side consists for the most part or exclusively of tungsten and on the other side for the most part or exclusively of copper. A tungsten sheet can be united with this sheet on the side consisting for the most part of tungsten in the manner previously described, should the sheet not be forthwith suitable for the purpose in view.

Sheets obtained in this way may be of .any desired thickness or thinness; the thickness of three-fold sheets can always be considerably less than 1 mm. since the individual sheets can be rolled out tothicknesses amounting to a fraction of a millimetre (e. g. mm.).

If electric contacts are stamped out of such a sheet then these can be united with the support, e. g. iron or aluminium spring, by soft soldering, all oxidation and structural change in the Joined part being excluded. Sheets obtained in the said way may also be coated with tin on the copper side, or a sheet of tungsten-copper-tin may be made first of all when the soldering is particularly facilitated and soldering temperatures of 230 C. and less may be employed. 'No oxidation nor impairing of the mirror-smooth highly lustrous rolled surface of the tungsten can take place, which latter surface on account of its great compactness is substantially more resistant to corrosion .and oxidation than the surfaces of known contacts. If, however, as has been frequent hitherto, the contacts must be hardsoldered with nickel or nickel alloys or even welded then oxidation of the tungsten-body is unavoidable, the compact rolled surface disappears and of course the contact surface cannot be produced again even by subsequent rubbing with emery or polishing. It is obvious that by such heat treatment steel springs or special alloys which rust only with difliculty are impaired. In addition the expedient of welding the tungsten contact on to an iron base first of all which in turn is united with the support has, quite apart from its cost, afforded no permanent help.

A further advantage of the invention, how-- ever, consists in'this that contacts can now be made from the thinnest sheet tungsten, which is made of a thinness approaching that of a skin (about mm. thick) and united to the support by means of soft soldering with the aid of the connecting layer. This expedient can be adopted in all cases in which particular heating does not arise during the operation, as, for example, in the case of telephone contacts (more particularly for contact springs in automatic telephony), which must not oxidize and must occupy as little space as possible.

-Double or multi-layered sheet made in the manner described can also be pressed in an astonishing manner in the cold or under conditions of slight heat. Obviously the thin tungsten sheet is made more shapeable (i. e. plastic) owing to its ideal union with the still more ductile coppertungsten sheet. A body made in this way can then be used as such or after removal of the copper by,chemica1 means (dissolution in nitric acid). The tungsten skeleton remaining after dissolution of the copper can then be rubbed down, scraped ofi or ground 01!. In this way it is possible to make even complicated articles of tungsten, molybdenum and so forth, such as, for example, calottes or bodies of revolution, such as hitherto for many purposes (Rontgen electrodes) could be made only at much cost and trouble by difiicult casting operations.

It may be said in general that the invention enables either diificultly melting or hard bodies to be coated, more particularly plated, with low melting or softer bodies to any desired thickness on one or both sides, or vice versa low melting or soft bodies to be coated or plated with higher melting or harder bodies on one or both sides. The union is in every case efiected in the heat with suitable mechanical pressure and absence of oxidizing agents.

The invention is not in any way limited to the procedures set forth in the examples given. It may be used, for example, for loom motor switches which as is well known are subjected to a very great mechanical wear. The contact of such a switch has approximately a double T-cross section and according to the invention is made for the most part from a copper rod which is provided on one side with a layer of copper-tungsten and is then drawn or rolled into the desired section, so that a copper rail is obtained which has one surface of copper-tungsten and from which a contact of the desired length can be cut oil. In a similar way, from round copper rods which are coated completely with a copper-tungsten layer it is possible to draw tubes or wires which consist on the exterior of coppertungsten and in the interior of copper.

Although here conglomerate bodies of any desired shapes, such as wires and sheet, consisting of tungsten and copper have been more particularly described, yet the process may be employed to every other conglomerate body such as has been set forth in the introduction. Thus, for many purposes aluminium bodies with tungsten or molybdenum layers, as well as copper bodies with tungsten layers, are to be recommended.

What I claim is:

1. A composite article consisting of metal taken from a first group, comprising tungsten, molybdenum, tantalum, and at least one metal taken from a second group, comprising silver, gold, aluminum, cobalt, chromium, iron, copper, nickel, platinum, tin, zinc, titanium, said article consisting of at least two parts intimately connected with eachother, one part consisting substantially of coherent metal of the first group, another part consisting of metal of the first and second groups, the metals of both groups present in the body being chosen so that they do not substantially combine or form solid solutions, the metal of the first group consisting of particles being coarser than the original metal powder and forming at least .part of a working or free surface of said article.

2. A composite article as claimed in claim 1, in which at least one metal of the second group forms a solidified melt, and the metal of the second group amounts to between about 3 to 90% of the article.

' 3. A composite article as claimed in claim 1, the part consisting substantially of metals of the first group being thinner than about 1 mm. and forming a sheet, and the second part forming a layer thereon.

4. A composite article as claimed in claim 1, in which both parts form sheets intimately con= nected with each other.

5. A composite article according to claim 1, comprising a. coherent layer consisting substantially of material of the first group, another layer intimately connected with the first one and consisting of metal taken from the first and the second group, and a third layer intimately connected with the second one and consisting substantially of metal taken from the second group.

6. A method of manufacturing a composite article, shaped into a sheet, comprising heating metal powder taken from a first group comprising tungsten, molybdenum, tantalum, to at least sintering temperature, comminuting the coherent solid body so obtained to particles being coarser than the original metal powder, uniting said particles by at least one metal taken from a second group comprising silver, gold, aluminum, cobalt, chromium, iron, copper, nickel, platinum, tin, zinc, titanium, rolling the body so. obtained into a sheet, combining said sheet with another one, consisting substantially of metal taken from the first group and adapted to form at least part of a working or free surface.

7. A- method as claimed in claim 6, supplemented by the steps of adding a further layer, substantially consisting of metal of the second group, and uniting such layer with that consisting of metal of the first and second group in the heat, but below sintering temperature of the metal of the first group.

8. A composite article comprising one part adapted to form a working or free surface, said part consisting substantially of coherent metal taken from a first group comprising tungsten, molybdenum and tantalum, a second part intimately connected with the first one, and consisting of metal of the first and of a second group, comprising silver, gold. aluminum, cobalt, chromium, iron, copper, nickel, platinum, tin, zinc, titanium, and a third part intimately connected with the second one, and consisting substantially of metal of said second group.

9. A composite article according to claim 8,

being formed into a sheet, comprising a sheet consisting substantially of metal taken from the first group, another sheet, intimately connected with the first one and consisting of metal taken