US2234969A - Tungsten base contact - Google Patents

Description

Patented Mar. 18, 1941 UNITED STATES PAlENT OFFICE,

TUNGSTEN BASE CONTACT wa're No Drawing. Application February 24, 1939, Serial No. 258,182. Renewed June 14, 1940 6 Claims.

This invention relates to improvements in tungsten base contacts.

An object is to provide a new and superior alloy for electrical contacting purposes.

It is another object of the invention to provide a tungsten base alloy containing compounds of high melting points.

A further object of the invention is to provide a contact material which possesses, in addition to an inherent low average contact resistance, the ability to resist material transfer under heavy electrical loads.

It is a further object of the invention to produce an electrical make-and-break contact which has less tendency for arcing and pitting during operation, than the materials of the prior art.

Other objects of the invention will be apparent.

from the following description, taken in connection with the appended claims.

The present invention comprises the combination 'of elements, methods of manufacture and the product thereof, brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferredembodiment of the invention is described herein, it is contemplated that considerable variation may be made inthe method of procedure and combination of elements, without departing from the spirit of the invention.

According to the present invention, an improved alloy is contemplated, having the following ingredients, present in substantially the ranges of proportions given below:

Metal taken fromthe group consisting of-- Per cent Tungsten, molybdenum and rhenium 90 to 99.8 Boride of boride forming elements of the 4th and 5th group (particularly titanium, zirconium and hafnium and vanadium, columbium and tantalum) .1 to

We have found that special combinations within the composition ranges given above produce highly desirable alloys for, contact applications. The following combinations are given by way of ex- .ample only:

' Per cent Tungsten 97.5 Columbium boride 2.5

Tungsten 95.

Hafnium boride 5 Tungsten-.. 80

Molybdenum Tantalum boride 5 Tungsten 98 Zirconium boride 2 Tungsten 96.5

Titanium boride 3.5

A useful group of compositions is the one in which tungsten makes up 60 to 99.8% of the alloy, the boride of the 4th or 5th group metal amounting to .l to 10% of the composition and the balance of the alloy being made up essentially of molybdenum or rhenium or both.

It has been found that in electrical systems wherein material transfers or build-up is the main factor to be considered, that the application of such combinations as mentioned above in either positive or negative positions, depending upon circuit characteristics, will produce operating characteristics far more satisfactory than was possible with prior art materials. Specifically, combinations based upon the present disclosure operated 100% satisfactory, for periods in excess of 500 hours continuous operation, whereas combinations of prior art produced failures prior to 250 hours under the same condition. The operation was satisfactory. both from the standpoint of build-up and oxidation characteristics.

While the majority of tests to date have been conducted on direct current, at relatively low voltages, indications are that the combinations covered by the present disclosure will operate satisfactorily on both A. C. and D. C. circuits,

at contact burdens of much greater magnitude.

It has also been found possible with these new contact alloy combinations to change the circuit characteristics materially, such as the capacity or inductance in arc quenching circuits, and.

improve the performance still further.

It has been definitely established bya series of tests, that erosion on electric make-and-break contacts is'initially established in the grain boundary material. This condition continues and is especially undesirable where the quantity of grain boundary material is relatively large and susceptible to contamination by oxides of the contact forming elements. In view of the grain size contrast encountered in the material, it has been noted experimentally that entire grain particles can be electrically transferred from one operating member to the other, forming a nucleus for additional metal transfer.

The presence of borides materially assists in reducing the grain boundary erosion through the elimination of oxides and the formation in the grain boundary material and grains of uniformly dispersed borides. This greatly reduces the tendency for electrical displacement of metallic particles in the active operating area.

In many cases a contact of the composition herein disclosed may be used in co-operation with a mating contact of pure tungsten and the advantages of the improved composition be obtained thereby.

In carrying out the invention, the new materials are usually formed from finely divided particles of the various elements and the borides to be incorporated into the ultimate composition, the said composition being subjected to a high pressure after properly mixing, to form an ingot or special shapes may then be sintered and used either in the as sintered condition or as sintered and forged, or after forging, and swaging, they may be rolled or drawn out to a convenient shape, from which the contact parts can be manufactured.

It is understood that the metallic ingredients of the composition can be present originally in the form of oxides or other suitable chemical compounds and can be reduced together to the metallic state. Sinceye'ry high sintering temperatures are necessary, the-different ingredients will difiuse in a very short'z'time into each other, producing combinations having improved physical, chemical and electrical properties.

What is claimed is:

1. An electric contacting element composed of metal or metals taken from the group of tungsten, molybdenum and rhenium, in percentages ranging from 90 to 99.8% and borides of the boride forming metals of the fourth and fifth group of the periodic system in percentages ranging from .1 to 10%. 2. An electrical contacting element composed of 90 to 99.8% tungsten and .1 to 10% of material selected from the group consisting of vanadium, columbium and tantalum boride.

3. An electrical contacting element composed of 90 to 99.8% tungsten, and .1 to 10% of the boride of a metal taken from the group consisting of titanium, zirconium and hafnium.

4. An electrical contacting element composed of metal taken from the group consisting of molybdenum, tungsten and rhenium in percent- I ages ranging from 90 to 99.8%, where the tungsten content is at least 60% or higher, and borides of the boride forming metals of the fourth group of the periodic system, in percentages ranging from .1 to 10%.

5. An electrical contacting element composed of metal taken from the group consisting of molybdenum, tungsten and rhenium, in percent ages ranging from 90 to 99.8%, where the tungsten content is at least 60% or higher, and borides of the boride forming metals of the fifth group of the periodic syste in percentages ranging from .1 to 10%.

6. The combination of two electrical contacting elements working against each other, one of which comprises a material of claim 1 and the other one being substantially pure tungsten.

FRANZ R. HENSEL. KENNETH L. EMMERT.