US3243289A - Cobalt base alloys containing molybdenum - Google Patents

Description

March 29,

Filed sept.

YIELD STRENGTH KS I I I (/o RA) DUCTILITY 1966 J. J. RAUSCH ETAL 3,243,289

COBALT BASE ALLOYS CONTAINING MQLYBDENUM 24, 1963 2 Sheets-Sheet 1 ROOM TEMPERATURE o l l I l I ROOM TEMPERATURE O l l l l l l l 5 IO 15 2O 25 3O SOLUTE ADDITION (WEIGHT PERCENT) TE NSILE PROPERTIES OF COBALT ALLOYED WITH MOLYBDENUM FIG.

INVENTORS JOHN J. RAUSGH JOSEPH a. McANDREW BY ATTORNEY WIQ March 29, 1966 J, uscH ETAL 3,243,289

COBALT BASE ALLOYS CONTAINING MOLYBDENUM Filed Sept. 24, 1963 2 Sheets-Sheet 2 YIELD STRENGTH, PSI

REDUCTION IN AREA ALLOY ADDITION (WEIGHT PERCENT) THE EFFECT OF TERNARY ADDITION ELEMENTS ON THE I700F TENSILE PROPERTIES OF THE BASE GOM- POSITION= Go-l5Mo.

United States Patent 3,243,289 COBALT BASE ALLOYS CONTAINING MOLYBDENUM John J. Rausch, Evanston, IlL, and Joseph B. McAndrew,

Pittsburgh, Pa., assignors, by mesne assignments, to

the United States of America as represented by the Secretary of the Navy Filed Sept. 24, 1963, Ser. No. 311,265 7 Claims. (Cl. 75-170) The present invention relates to improved cobalt alloys and to methods of making the same. More particularly, the present invention relates to cobalt base alloys having improved physical and metallurgical properties.

The present commercial cobalt alloys do not provide the strength capabilities under extreme conditions of high temperature and in a highly oxidative environment as required in the neoteric nuclear, missile and space technologies. It is necessary under these conditions to provide an alloy having high-temperature oxidation resistance, high-temperature strength and workability.

Accordingly, features and objects of this invention include the provision of new composition with optimum strength and acceptable oxidation resistance at high temperatures.

Another object of the present invention is to provide an alloy of cobalt that is strong and ductile while retaining sufiicient forgeability to be usefully workable.

A further object of the present invention is to provide an oxidation resistant alloy of cobalt that embodies the aforementioned properties.

A further object of the present invention is to provide a novel, wrought cobalt base alloy that is superior in properties to those presently used for high temperature application.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying tables and graphs wherein:

FIG. 1 is a graphical presentation of the eifect of molybdenum addition on the properties of the wrought cobalt base;

FIG. 2 is a graphical presentation of the effect of ternary addition elements on the 1700 F. tensile properties of the base composition CO-lSMO alloy.

The alloy which satisfies the objects of the present invention in its broadest aspects consists essentially of from 1 to 15 weight percent molybdenum with the balance essentially all cobalt. The significance of molybdenum as a cobalt strengthener may be seen in FIG. 1. Primary solid solubility in this system under the condition of heat treatment and testing was limited to 9 weight percent molybdenum. The strength at 1700 F. of the more highly alloyed material is, therefore, derived from both solution and precipitation hardening. The ductility of the alloy, which may also be seen in FIG. 1, was considered to be an important indicator of the fabricability of the material.

Although the foregoing alloys satisfy all of the objects set forth above, it was determined that by the addition of a third element to the binary alloy composition, elevated temperature strength, forgeability and oxidation resistance could be improved. The effect of ternary additions on the 1700 F. tensile properties of the base composition cobalt-15 weight percent molybdenum is shown in FIG. 2. The ternary addition of tantalum had the most significant beneficial effect upon the yield strength of the resulting alloy. The ternary addition of beryllium is particularly advantageous in achieving a ductile alloy. Ternary additions of 5 weight percent columbium or 8 3,243,289 Patented Mar. 29, 1966 ice weight percent aluminum to the base composition cobalt- 15 weight percent molybdenum resulted in small yet nevertheless beneficial increases in both yield strength and ductility.

The oxidation resistance of the cobalt-molybdenum base alloys is improved by the ternary addition of silicon or beryllium. The alloys of cobalt-10 weight percent molybdenum-5 weight percent silicon, and cobalt-15 weight percent molybdenum-5 weight percent silicon are exceptionally oxidation resistant at 1700 F. The addition of up to 8 percent aluminum to cobalt-l5 weight per cent molybdenum decreases the scaling rate of the alloy.

In the preparation of the cobalt base alloys, two grades of cobalt were employed, typical analyses of which are given below:

Rondell v Electrolytic Elements Cobalt Cobalt (Percent) (Percent) 99. 29 99. 6 0. 28 01 20 0. 03 0. O5 nil 0. 01 0. 04 0. 05 0. 02 0. ()3 Trace 0. 04 0. 01 Sulphur 0.01 0. 01

Electrolytic cobalt was found to be the more favorable base metal since this material is forgeable without the use of modifiers or special melting techniques. The alloys of the instant invention and the elements therein were, in general, of equivalent or better purity than the electrolytic cobalt with the exception that beryllium has a nominal purity of 96 to 99%. The molybdenum, tantalum, columbium, and aluminum used were in the form of high purity sheet.

Alloys were prepared as ZSO-gram, pancake-shaped ingots approximately /2" 3" in diameter. There were arc-melted using a water-cooled tungsten-tipped electrode and a water-cooled, copper crucible in an argon atmosphere. The ingots were then hammer-forged to /2 in diameter rods from which test specimens were prepared.

Tensile tests were performed at room temperature and at 1700 F. at a strain rate of approximately 0.12 in./in./ minute. Before testing, all specimens were sealed in evacuated bulbs, treated at 1700 F. for 24 hours and air cooled.

Oxidation tests were performed on cylindrical specimens contained in small individual porcelain crucibles. Weight gain data were recorded and after oxidation the specimens were de-scaled mechanically and electrolytically and reweighed. The data included in FIGS. 1 and 2 disclosed the particularly advantageous high temperature yield strength properties of the ternary alloy cobalt-15 molybdenum-3 tantalum. The data also shows the overall strength improvement in a cobalt-molybdenum base alloy of the ternary addition of up to 8 percent tantalum. The structure of the 3 percent tantalum alloy after heat treatment at 1700 F. for 24 hours was found to contain a fine general precipitate of intermetallic compound. Cobalt-molybdenum-tantalum alloys having a greater percentage of tantalum when heat treated were found to contain more precipitate in a coarser aggregation. As may be seen in the graph of FIG. 2, these alloys were of considerably lower strength and greater ductility than the cobalt-15 molybdenum-3 tantalum.

In the present invention and claims, the phrase up to shall be construed to include zero as the lower limit of the percentage range of optional elements recited.

It will be apparent that new and useful alloys having desirable characteristics and properties have been disclosed. Itv isv therefore desired to further describe the invention as set forth in the appended claims What is claimed is: v 1. A forgeable high-strength alloy consisting essentially of from about 1 to 15 weight percent molybdenum, the

balance being essentially cobalt. v 2. A foregable oxidation resistant alloy consisting of from about 1 to 15 weight percent molybdenum, the

balance being essentially cobalt and beryllium.

3. A forgeable high-strength alloy consisting essentially of from about 1 to 15 weight percent molybdenum,

3 weight percent tantalum,

the balance being cobalt.

4. A forgeable high-strength alloy consisting essentially of from about 1 to 15 weight percent molybdenum,

up to about 8 weight percent tantalum,

the balance being essentially cobalt.

5. A forgeable oxidation resistant alloy consisting essentially of from about 1 to weight percent molybdenum,

up to 5 weight percent silicon,

the balance being essentially cobalt.

6. A forgeable oxidation resistant alloy consisting essentially of about 1 to 15 weight percent molybdenum,

up to about 8 weight percent aluminum,

the balance being essentially cobalt.

7. A forgeable high-strength alloy consisting essentially of about 1 to 15 weight percent molybdenum,

up to about 5 weight percent columbium,

the balance being essentially cobalt.

15 References Cited by the Examiner UNITED STATES PATENTS 1,588,518 6/1926 Brace 75-171 1,949,313 2/1934 Koster 75170 2,250,850 7/1941 Adamoli --170 2,981,620 4/1961 Brown et al. 75170 DAVID L. RECK, Primary Examiner. WINSTON A. DOUGLAS, Examiner. C. M. SCHUTZMAN, R. O. DEAN, Assistant Examiners.

Claims (1)

1. A TORGEABLE HIGH-STRENGTH ALLOY CONSISTING ESSENTIALLY OF FROM ABOUT 1 TO 15 WEIGHT PERCENT MOLYBDENUM, THE BALANCE BEING ESSENTIALLY COBALT.

Images