US2036497A - Nickel alloy of low gas content - Google Patents

Description

Patented Apr. 7, 1936 PATENT OFFICE NICKEL ALLOY F Donald W. Randolph,

LOW GAS CONTENT Flint, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware No Drawing. Application April 17, 1935, Serial No. 16.752

1 Claim.

This is a continuation in part of my prior application S. N. 713,520, filed March 1, 1934.

This invention has to do with a new alloy and method of making same. The alloy disclosed in 5 this application was developed especially for use for the electrodes of spark plugs. In this service resistance to corrosion is of great importance. Because of superior resistance to corrosion at high temperatures and other properties, alloys having a nickel base have been preferred for this use. In an effort to improve this type of alloy I made and tested great numbers of nickel alloys of different compositions and have made many alloys of the same composition by different metal lurgical procedure. As a result of this work I came to the conclusion that gas content may be a determining factor with respect to resistance to corrosion. To test this hypothesis nickel alloys were made up under vacuum so as to reduce the gas content to a minimum, and it was found that this procedure did improve the corrosion resisting properties of the alloys. Subsequently this study was extended to the degassing of elements entering the alloys, and to the use in the alloys of materials which combine with gas and so remove it. I

As a result of this investigation I have devised a method of making alloys of reduced gas content together with apparatus in which to make them, the method and apparatus being the subject of my copending application S. N. 746,153,

filed September 29, 1934. Briefly, the method consists in melting the metals under vacuum and pouring them into the mold under an inert atmosphere to prevent oxidation. I have also discovered that the gas content may be so reduced by proper selection of ingredients with or without vacuum melting that the resulting alloy will,

when used as a spark plug electrode, not only resist corrosion to many times the extent of previously known alloys, but in addition will resist scaling to a far greater degree than any nickel alloy of which I have knowledge.

This substantially non-scaling, non-oxidizable material is of comparatively low cost, and consequently may find'wide use where these properties are of importance. The material possesses substantially the color and luster of silver, and is, therefore, well adapted for ornamentation.

An alloy heretofore used extensively for spark plug electrodes consists chiefly of nickel and chromium with small additions of manganese and barium and a trace of magnesium to facilitate drawing. This alloy is described and claimed in 6 my prior Patent No. 1,978,295. cranted October 9.

1934. A preliminary study was made of each of these ingredients to determine, if possible, which introduced most of the gas content into the melt. This study developed the fact that nickel and manganese contained the greatest amount of absorbed gases, chiefly C0, C02 and nitrogen. Of the two, manganese had the greatest afiinity for gases, the amount of absorbed gas being often ten or twelve times the volume of the material. As a consequence it was found desirable to eliminate manganese from-the alloys, its functions in the melt being accomplished by other ingredients. I employed the vacuum furnace described and claimed in my said copending application S. N. 746,153 in producing alloys low in gas content. Working with the alloy above mentioned the best procedure was found to be melting the nickel and chromium together in vacuum. The time required to out-gas a ten pound melt was found to be from 6 to 8 hours. The vacuum treatment was then discontinued and barium was added to the melt at atmospheric pressure in accordance with the process described and claimed in my prior Patent No. 1,919,479., granted July 25, 1933. Briefly, the barium metal was coated with pyroxylin lacquer, wrapped in nickel foil, and immersed beneath the surface of the melt. The alloy so treated was found to have improved resistance to corrosion. It will be noted that both manganese andmagnesium were dispensed with, their functions being performed in large part by the barium addition.

Improved alloys were made under vacuum in the manner described having compositions falling within the following range:

Per cent Chromium 2 to 15 Nickel 98 to Barium .02 to .06

This range of ingredients should not be regarded as an absolute limiting range, but is simply that within which these studies were made. It is obvious that equally good results may be expected with higher barium contents.

In my prior application S. N. 667,502, filed April 22, 1933 and subsequently refiled under S. N. 740,537 on August 18, 1934 there are disclosed alloys of nickel, barium and copper, and of nickel, barium, copper and chromium, and with these alloys also I have found it desirable to employ the vacuum melting process just described for the removal. of gas, thereby obtaining alloys free of blow holes and with increased resistance to corrosion.

The vacuum process of making the alloys possesses the disadvantage of added cost and complication. Consequently, an effort was made to accomplis'h the same results by the addition to the melt of suitable ingredients to combine with the gases. In this study additions were made both to melts of nickel alone, and to melts of nickel and chromium. A large number of tests were made with many silicon,aluminum,strontium,calcium and lithium. When these ingredients were added alone, while some improvement was observed in reduction of gas, it was not marked. This series of tests was followed by the addition of several ingredients, for example, aluminum or lithium, in combination with barium or silicon. Promising results were obtained by the simultaneous addition of aluminum and barium. Subsequently, a series of alloys of aluminum and barium was made up, and these were added to the melt. It was found that very good results were obtained by the use of aluminum-barium alloys containing from to of barium. Less than this amount of barium produced but slight improvement, while more than.

this amount produced an explosive mixture that could not be worked.

It was found that temperature at which the aluminum-barium alloy is added is an important factor, the optimum temperature range being between 2800 and 2900" F. Temperatures below 2800 are not high enough to promote the necessary reaction with the gases present, and temperatures above 2900fcause the reaction to proceed with such violence that the metals become badly overheated with loss in constituents due to vaporization.

It has been found desirable to subJect the alloy to vigorous-stirring following the addition of the barium-aluminum alloy. This may be done by employing an impeller of carborundum or other refractory material driven by means of an electric motor.

By this means I have superior corrosion resisting properties.

produced alloys of very The range of ingredients within which I have had the most success is as follows:

Aluminum 2 to 6 Chromium .5 to 10 Barium I .02 to .1

Balance nickel different additions including barium,-

The very low gas content the metal is used for devices inclosed in vacuum as little or no gas is given off during necessary Per cent 10% chromium, .02% to .1%

To the above elements I have added on occasion small amounts of magnesium to facilitate drawing, and sometimes small amounts of silicon. But these ingredients do not substantially affect the properties of the material. V

While alloys of the above compositionand of low gas content can be produced by simply melting the ingredients together and casting in the usual way, I have found that by employing the vacuum method above described, alloys may be obtained which are even freer from gas. Whether this will be desirable in commercial production will, of course, depend upon the requirements that the material must meet, and upon the cost of production.

The new nickel alloys herein disclosed diflfer from those formerly made principally in the fact that they contain very little gas. This gas may exist in large number of different forms, either as oxides, nitrides, or other compounds, on as occluded or dissolved gases in the metal. As an example an alloy of nickel with 4% chromium produced by the usual commercial process is found to contain from 2 to 5 cubic centimeters of gas per gram. The same alloy with manganese eliminated and with the addition of barium and aluminum will be found to contain less than .05 cubic centimeters of gas per gram. While the exact eifect of these gases on the properties of the metal is not well understood, the elimination of gas results in the production of an alloy having very great resistance to intercrystalline corrosion. A marked reduction in the rate of grain growth was also noted.

The new alloys have proven to be remarkably resistant to oxidation, and to maintain a clean bright surface when heated in an oxidizing atmosphere to temperatures as high as 1,000" C. Measurements in vacuum show that gas freed nickelgreatly reduced rates of evaporation when heated. is also of advantage if heating of electron I cla m: An alloy containing 2 to 6% emitters or similar parts.

aluminum, .5 to barium, and the balance nickel.

DONALD W. RANDOLPH.

chromium-barium or nickel-barium alloys have