US3496030A - Anti-seizing surfaces - Google Patents

Description

United States Patent Oflice 3,496,030 Patented Feb. 17, 1970 3,496,030 ANTI-SEIZING SURFACES Richard M. Powers, Stormville, N.Y., assignor to the United States of America as represented by the United tates Atomic Energ Commission Drawing. Filed Dec. 13, 1966, Ser. No. 601,823 Int. Cl. C22c 27/00, 21/00; B23d 3/00 U.S. Cl. 148--6.3 3 Claims ABSTRACT OF THE DISCLOSURE A coating and a process for preparing the coating for an alloy of aluminum and a transition metal such as either iron or vanadium in which the aluminum is 1n solid solution. The coating is formed by heating the alloy in an oxidizing atmosphere of helium containing steam.

BACKGROUND OF THE INVENTION Considerable difficulty is often experienced with seizing of rotating pump shafts in bearings or stickmg of valve seats situated in hot alkali metal systems and selfwelding of stainless steel in a hot sodium environment, in particular. For example, in a recent series of tests, balls of chromium stainless steel in contact With each other were tested in flowing sodium at 700 C. with an extrenal load of 11.6 pounds on each ball support point. The balls were thereafter examined and it was found that extensive sintering at the points of contact took place. This demonstrated that stainless steels of the usual type for this purpose are unsuitable in such applications where seizing is to be avoided.

SUMMARY OF THE INVENTION The invention described herein was made in the course of, or under a contract with the US. Atomic Energy Commission.

This invention relates to alloys consisting of sohd solutions of aluminum in certain transition metals that DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides a type of alloy and a bearing construction which avoids the problems mentioned above. In accordance with the principles of this invention, an alloy consisting of a solid solution of aluminum in a transition metal is treated to generate a barrier or surface film which is impervious to and is stable in molten sodium.

A principal requirement of an alloy made in accordance with the principles of this invention is the use of a transition metal with the aluminum in which the aluminum has an appreciable solid solubility. In one embodiment the presence of suflicient aluminum in the alloy is provided to form a barrier layer consisting principally of A1 0 This barrier layer, insoluble in and impervious to the metal matrix and at least partially adherent to the alloy, provides the principal barrier to sintering or adhesion of one loaded unit to another. In an alloy system such as Cr-Al, for example, where a mutual solid solubility exists, a barrier layer of A1 0 must be present to an appreciable extent in the resulting solid solution oxide, Cr O -Al O for the alloy to be useful as a bearing alloy in a hot alkali metal system. In addition, the use of such an alloy, as a barrier layer for separating liquid sodium from its containment, will reduce or eliminate mass transfer between the liquid metal and the container material.

The presence of additional minor elements in the solid solution alloy does not alter the results or contribuate significantly to improvement of the anti-seizing properties of the alloys but may, on the other hand, result in poorer anti-seizing properties or barrier properties for the binary Al-transition metal solid solution.

Examples of alloys prepared in accordance with this invention are as follows:

EXAMPLE 1 The iron-aluminum binary shows extensive solid solubility of aluminum in iron (approximately 50 a/o). In this system, because of embrittling effects of high aluminum additions and the possible formation of Fe Al ordered solid solutions, the anticipated useful high aluminum limit is somewhat lower. By a/o is meant atom percent.

A typical binary alloy near the useful upper aluminum limit was prepared as follows:

High purity Al (20.45 g.) was arc melted 5 times in an inert atmosphere copper cold hearth furnace with 193 grams of high purity iron without measurable weight loss. The resulting alloy corresponded to 17.97 a/o Al and 82.03 a/o Fe. The alloy was then cut into fragments weighing 0.93:.05 g. to yield in. fragments which were then placed into hemispheric cavities in a copper block and melted to yield nearly spherical alloy pellets.

The samples were then removed and heated at 1000 C. in an A1 0 boat for 3 /2 hours under an atmosphere of H +He saturated with water at 0 C. by bubbling through the water and rapidly cooled in dry H +He. This resulted in a relatively adherent film of A1 0 on the balls and a weight gain of .0001 g./ .93 g. sphere or approximately .0001 g./cm. alloy surface as a result of oxidation.

The spheres were tested under 11.6 lbs. load in flowing 700 C. sodium and examination afterwards showed that they did not adhere to each other.

EXAMPLE 2 A second group of Re-Al alloy spheres was prepared and oxidized as in the preceding example except with the composition 10 a/o Ala/o Fe. The resulting spheres were similarly tested under an 11.6 lb. load flowing 700 C. sodium and these spheres also did not stick to each other.

EXAMPLE 3 Another group of Fe-Al alloy spheres was prepared as in the previous example, but were oxidized by pretreating for 8 hours at 1000 C. in an H +'I-Ie atmosphere saturated with water at 0 C. followed by flushing with dry H +He at 1000" C. before rapid cooling to produce a protective film containing A1 0 over the surfaces. Tests showed that the resulting spheres were not sintered together in the sodium alkali environment mentioned previously. However, it is believed that if the protective film were to be removed by abrasion in a hot sodium system, it would take longer to heal by reaction with trace oxygen (i.e. 10 to 500 ppm.) in the sodium than would a 15 or 20 a/o aluminum alloy. It is thought that to obtain the protective coating or barrier layer which is self-healing it is desirable to have an alloy containing aluminum approaching the maximum amount consistent with acceptable mechanical properties for the particular alloy application.

3 j r EXAMPLE; 4 A group of Al-V alloy spheres was prepared as in the preceding examples with the composition of 9.5 a/o Al and 90.5 a/o'V from pure elements by are melting and then oxidized for one hour in an atmosphere of He+H saturated with water 'at C at about 1000? C. and

cooled in dry helium to avoid hydriding of the vanadium, to give a uniformly gray suirface. These spheres were tested in 700 C. sodium as in the preceding examples and it was noted that the spheres did not stick to each other.

The upper limit for aluminum content of these alloys is'taken as the maximum solubility of aluminum in the major element at 600 C. of above. Because of poor workability (brittlenessj of saturated solid solutions of aluminum in these elements, less than the maximum aluminum content is generally desirable.

Representative composition limits for a variety of aluminum alloys which maybe suitable for hot sodium applicatiou's are given in the following table.

System: Atom Percent-Al Al Fe 3-35 Al-V W 3-40 A l-CI 3-15 Al-Ni 3-10 Al-Cu 3-15 Al-Mo G. 2-4

Al-W 2-8 It is thus seen that there has been prepared alloys having the ability of functioning in a hot sodium environment. These alloys may be used to form the articles such as bearings having the anti-seizing surfaces, or the alloys may be used as cladding materials oni other materials on the articles before coating, if desired and feasible for the particular application. a

What I claim is: a e

'1. An article of manufacture having ana-n-ti-seizing surface layer thereon for use in a liquid sodium system, said surface layer comprising an alloy of a solid solution of aluminum in vanadium, the aluminum beingpresent in the range of 3 to aton1 percent, said layer having an in situ oxidized barrier impervious to and stable in liquid sodium, the barrier consisting principally of A1 0 2. A method of preparing an anti-seizing surface layer foraan article of manufacture for usesin molten sodium comprising depositing a surface layer of an alloy of a solid solution of aluminum in vanadium, the aluminum being present in the range of 3 to 40atom percent, upon the article of manufacture, and simultaneously heat treating and oxidizing the surface layer at a temperatureof at least 900 C. whereby an oxidized surface barrier is formed on the surface layer.

7 3. The method of claim 2 in which the heat treatment of the article is conductediin an atmosphere of hydrogen and helium previously saturated with water vapor at 0 C.

. References Cited UNITED STATES PATENT-S in Transactions of American Society for Metals, vol. 46, pp; 1136, 1137 (1954).

ALFRED L. LEAVITT, Primary Examiner W W. E. BALL, Assistant EXaminer US. Cl. X.R.