US 3523354 A
Description (OCR text may contain errors)
Aug." 11, 1970 P. LOEWENSTEIN 3,523,354
METHOD OF PRODUCING LARGE SHAPES Filed April 22. 1968 FIG. 1
INVENTOR. PAUL LOEWEN STEIN BY 0%): M M'PAIZ: W
ATTORNEYS United States Patent O 3,523,354 METHOD OF PRODUCING LARGE SHAPES Paul Loewenstein, Lincoln, Mass., assignor to Whittaker Corporation, Nuclear Metals Division, Concord, Mass. Filed Apr. 22, 1968, Ser. No. 722,988
Int. Cl. B23 17/00 US. Cl. 29-423 13 Claims ABSTRACT OF THE DISCLOSURE A structure of relatively large size having dispersionstrengthened, extensively work-hardened portions distributed throughout its interior is formed from stock of relatively small diameter or thickness which has first been dispersion-strengthened and then extensively cold-worked to enhance its properties. The stock, in the form of rods or sheet, is bundled together into a large body after the working. This body is then extruded or otherwise pressureformed into a monolithic structure of relatively large size having the indivdual rods or sheets metallurgically bonded to each other and incorporated therein such that the workhardened portions are distributed throughout its interior. The resultant structure has a strength comparable to that obtained with structures of smaller thickness or crosssectional area.
BACKGROUND OF THE INVENTION Field of the invention The invention relates to metallurgical operations, particularly strengthening operations. It comprises a novel product consisting of a relatively large monolithic structure having dispersion-strengthened, extensivelyworked portions distributed throughout its interior, the structure being characterized by significantly higher strength (in.
terms of force per unit area) than previously obtainable with dispersion-strengthened materials of comparable large cross section. The invention also comprises a method for forming the novel structure.
Prior art nickel. This material has especially advantageous properties in the temperature rangeof from 1800 F. to 2400 F. which is above the range in which the superalloys are most useful and below the range at which the refractory materials are most useful. Like many other dispersionstrengthened materials, its physical properties (melting temperature, density, and thermal conductivity among others, approximate those of the pure metal,.while its mechanical properties are greatly improved by the dispersion treatment.
Dispersion-strengtheed materials are formed by uniformly dispersing fine particles (termed dispersoids) throughout a matrix of another metal or alloy. These dispersoids are chosen to be non-reactive with the matrix metal. Many different methods are used for achieving a uniform dispersion. One such method involves a mechanical blending of powders of the matrix metal with finelydivided powders of a metal oxide and subsequent treatment by any of the known pressure-forming methods such as by extruding, rolling, and compacting and sintering operations among others. Another method involves the co precipitation of finely-divided oxide powders in a slurry of the matrix material, followed by reduction, compacting, sintering, and then by rolling or extruding. This technique is described in an article by C. I. Bradford published Oct. 31, 1966 in Steel magazine. TD Ni prepared by this "ice method is especially advantageous in providing a generally uniform dispersion of finely-divided particles in the matrix and in providing desirable strength characteristics in the material formed by this process. Further, unlike precipitation-hardened materials which are formed by adding a strengthening agent at an elevated temperature and precipitating it out in the matrix metal in the form of fine particles at a lower temperature which tend to lose their strength at elevated temperatures, dispersion-strengthened materials retain substantial strength at temperatures close to their melting temperature, I utilize this fact to advantage. If the reduction in cross-sectional area of the stockbeing worked is taken as a measure of the amount of working which the stock has undergone, the strength increases, at a gradually decreasing rate, up to a reduction in diameter (for rod stock) or thickness (for flat plate) of about 25:1 or 30:1 for TD Ni; above this range relatively little additional strength is gained by cold-working. As an example of the magnitude of improvement possible, a 7" diameter bar of TD Ni had a .2% yield strength of 17,500 p.s.i. at 2000 F. when reduced to 2" in diameter and achieved a yield strength of 28,000 p.s.i. at the same temperature when reduced to /2" diameter.
From the standpoint of obtaining extended strength at elevated temperatures, therefore, it is desirable to utilize stock which has undergone extensive cold-working. Since such working always reduces the cross-sectional area of the stock, this means that it is desirable to utilize stock of relatively small cross-sectional area as compared to the starting billet from which the stock was formed. When shapes of relatively large size are desired, however, it is necessary to start with a billet of the largest practicable size in order to obtain the full benefits of cold-working and yet end up with stock of the desired size. Unfortunately, there is a practical upper limit to the size of the starting billet which can be handled by most facilities. In
general, this upper limit is of the order of 7" or .so in diameter for rod stock. Thus, when final shapes of the order of several inches in diameter of thickness are to be obtained, billets of practical size cannot be worked to the fullest extent desirable in order to obtain the maximum increase in strength through cold-working since such work-.
ing would reduce their size below the required dimensions.
SUMMARY OF THE INVENTION Accordingly an object of the invention is to provide a monolithic structure of relatively large size formed from.
dispersion-strengthened, extensively work-hardened material.
Another object of the invention is to provide a monolithic structure of relatively large size having a substantial amount of extensively cold-worked material distributed throughout its interior.
A further object of the invention is to provide a relatively large, monolithic, dispersion-strengthened structure formed from a large number of relatively small structures which retains the strength of the small structures.
Yet a further object of the invention is to provide a method of forming a relatively large monolithic structure having dispersion-strengthened, extensively work-hardened portions distributed throughout its interior.
Another object of the invention is to provide a method of work-hardening a metallic structure throughout the interior thereof.
In accordance with the above, I form a monolithic structure of relatively large size having dispersionstrengthened, extensively work-hardened portions distributed throughout its interior by consolidating a' number of segments of relatively thin stock which has first been dispersion-strengthened and then extensively workhardened with consequent reduction in diameter or thick-- ness. The segments, which may take the form of rods or sheet, are bundled together after the initial working and are then extruded or otherwise pressure-formed into a monolithic structure such as a billet or shape of relatively large size. During the pressure-forming, the work-hardened portions are metallurgically bonded to each other throughout the interior of the resultant billet or shape to form a monolithic structure of relatively large size having the dispersion-strengthened, work-hardened portions distributed throughout its interior. The resultant structure retains the advantageous strength characteristics of the individual structures from which it was formed while providing a substantially larger cross-section than any of the starting structures.
The invention accordingly comprises the several steps and the relation of one or more of such steps with re spect to each of the others, and the article possessing the features, properties, and the relation of elements, which are exemplified in the following detailed disclosure, while the scope of the invention will be indicated in the claims.
BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawing, in which:
FIG. 1 is a view in perspective of a relatively small, dispersion-strengthened, work-hardened rod of the type which may advantageously be used to carry out the invention;
FIG. 2 is a side view, partly in section, of an extrusion press suitable for consolidating a number of the rods of FIG. 1 into a monolithic structure;
FIG. 3 is a view in perspective of a typical large-sized bar such as may be formed with the apparatus of FIG. 2;
FIG. 4 is a view in perspective of a thin dispersionstrengthened flat sheet which may also be utilized to carry out the invention; and
FIG. 5 is a view in perspective of the sheet of FIG. 4 wound in a spiral configuration for subsequent consolidation by pressure-forming operations.
SPECIFIC DESCRIPTION OF THE INVENTION FIG. 1 shows a rod of relatively small size which has first been dispersion-strengthened and then extensively cold-worked to enhance its properties. For purposes of illustration, the dispersoids are shown as dots 12 distributed throughout the rod, although it will be understood that these dispersoids will ordinarily be invisible to the eye. The dispersoids may be incorporated in the base material by any of several processes, but are preferably inf:orgorated by means of the process described by Brad- In order to obtain the full benefits of the invention, the rod 10 should be extensively cold-worked prior to consolidation. This will result in a substantial reduction in diameter. For example, starting from an unworked billet of TD Ni roughly 7 inches in diameter, the rod 10 may advantageously be worked until its diameter is reduced to about /2 inch or inch. At this point, the rod will be fully worked and will exhibit its maximum strength properties.
After the rod 10 has been dispersion-strengthened and adequately work-hardened, it must be consolidated with other rods in order to form a billet of the desired larger diameter.
FIG. 2 is a longitudinal view, partly in section, of an extrusion press which is particularly adapted to perform the desired consolidation. As shown therein, a cylindrical extrusion cannister 16 having a nose cone 18 welded onto its forward end is positioned within an extrusion container 20. A ram 22 is moved axially within the container 20 to drive the cannister 16 through an extrusion die 26 mounted in a backer plate 28 screwed into the end walls of the container 20. The ram 22 is driven by suitable driving means such as by an hydraulic actuator (not shown).
The rods 10 are packed into the cannister 16 with their longitudinal axes parallel to each other and aligned with the cannister axis. Preferably, they are tightly packed within the cannister. If desired, the interstices between the rods or between the rods and the cannister walls may be packed wih rods of smaller diameter to form a tighter bundle. Prior to its insertion in the container 20 and after the rods have been tightly packed within it, the cannister 16 is evacuated and sealed off; it is then heated, inserted into the container 20, and extruded through the die 26 by means of the ram 22. This forms a monolithic structure in which the individual rod segments are consolidated by metallurgical bonding to each other. The container walls are then removed from the resultant structure by such techniques as machining or acid etching and the resultant structure is then ready for its ultimate use.
FIG. 3 is a pictorial view of a bar 30 obtained from extrusion of the rods 10 after the cannister material has been removed. The individual rods 10 have been consolidated into a monolithic bar of substantially larger cross-sectional area than any of the individual rods prior to their consolidation, but smaller than the cross-sectional area of the bundle from which the bar 30 was formed. Each individual rod 10 is reduced in cross section by an amount proportional to the reduction ratio; however, the strength of each rod is unimpaired by the extrusion and consolidation and the resultant structure, although of substantially larger size than any of the starting structure, has substantially the same strength characteristics as each of them, assuming that they have been fully worked to bring them up to their full strength capabilities prior to the extrusion. (If they have been less than fully worked, the consolidating extrusion may itself enhance their properties.) For example, with an extrusion press capable of extruding a cannister of up to three feet in diameter at an extrusion ratio (defined as the ratio of the cross-sectional area of the starting billet to the cross-sectional area of the resultant extruded billet) of approximately 2521, consolidated rods of approximately seven inches in diameter can be obtained whose strength is comparable to those found in rods of one-half inch in diameter. Thus, the full benefits of dispersion-strengthening and cold-working can now be obtained in structures of substantially larger crosssectional area than heretofore obtainable.
The particular extrusion parameters such as extrusion temperature, speed, force, reduction ratio, etc., as well as the preliminary procedures utilized to obtain a good extrusion, depend on the particular metals being extruded. The following specific example will illustrate the operation of the invention:
A cold rolled steel extrusion cannister was prepared by heating it to 1800 F. for twenty-four hours in a vacuum of approximately 1 torr. to insure outgassing of undesired components. After the cannister was outgassed, it was cleaned in acetone, etched with diluted nitric acid 10%) and subsequently cleaned in alcohol. A number of TD nickel rods, each 0.135" in diameter, were then packed into the cannister in a close-packed array, the cannister sealed from the atmosphere, evacuated to 10" torr. at 500 F., flushed with H gas to reduce the NiO and then finally sealed off. The cannister was then heated to 1950 F. in an argon atmosphere and was extruded at a ram speed of from sixty to one hundred twenty inches per minute. After the canning material was removed, the resulting bar was 0.750 inch in diameter and had an overall yield strength of approximately 30,000 p.s.i. at 2000" F.
It is, of course, possible to obtain shapes other than solid round billets. For example, one may extrude the rods 10 within the cannister 16 directly into the desired shape such as rotor blades for turbine engines, tubing, or other desired shapes. Other shapes, for example, from flat stock which is dispersion-strengthened and coldworked in the usual manner before processing in accordance with the invention. As was the case with the bar stock, the flat stock should first be cold-worked to a relatively small thickness after the dispersoids have been incorporated into it in order to achieve the full increase in strength obtainable from dispersion-strengthened materials. Such a flat plate is illustrated in FIG. 4 which is a perspective view of a relatively thin plate 32 having dispersoids (again represented by dots) uniformly distributed throughout it. After the flat plate 32 has been suitably work-hardened, it may be stacked with other plates and pressure-formed into a monolithic structure by such means as hot rolling. Alternatively, the plate 32 may be rolled into a spiral in the form of a pack-roll 32', as shown in FIG. 5, and fitted into an extrusion cannister for consolidation into a monolithic structure by extrusion. The resultant billet has the same form as the billet 30 in FIG. 3. As was the case with the processing of the rods 10, the pack'roll 32' may alternatively be extruded directly into the desired end shape, such as turbine blades, tubing, or other desired shapes.
From the above it may be seen that I have provided a monolithic structure having dispersion-strengthened, work-hardened portions distributed throughout its interior. For comparable strength, this structure can have a substantially larger cross-sectional area than the structures from which it is formed. Further, it will be seen that I have provided a simple and effective method of forming such a structure from stock which is either rod-shaped or fiat.
It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the article set forth without departing from the scope of the invention, it is intended that all matter contained in the above description (or shown in the accompanying drawings) shall be interpreted as illustrative and not in a limiting sense.
It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.
1. A method of producing a relatively large monolithic structure having extensively work-hardened portions distributed throughout its interior, comprising the steps of (A) work-hardening a solid preliminary structure formed from a dispersion-strengthened material having a dispersoid distributed throughout the interior thereof by working said structure to a cross section substantially smaller than the cross section of the structure ultimately to be formed;
(B) packing at least one said preliminary structure in a container for further working, portions of structures so packed being disposed adjacent to each other and distributed throughout the interior of said container;
(C) pressure-forming said preliminary structures in said container with a consequent reduction in the cross section of said structures to thereby form a monolithic structure having said preliminary structures integrally bonded therein; and
(D) removing the container from said monolithic structure after pressure forming.
2. The method of claim 1 in which a plurality of preliminary structures are incorporated into said container, each said preliminary structure comprising a flat plate which has been extensively Work-hardened to a relatively small thickness prior to insertion into said container, said plates being stacked with their flat faces in contact with each other in said container.
3. The method of claim 2 in which said pressure-forming operation comprises a rolling operation whereby said flat plates are consolidated into a monolithic structure by means of said rolling.
4. The method of claim 1 in which said preliminary structure comprises a fiat plate which has been extensively work-hardened to a relatively small thickness and formed into a spiral roll before insertion into said container and in which said pressure-forming operation comprises an extrusion operation whereby said spiral roll is consolidated into said monolithic structure by means of said extrusion.
5. The method of claim 4 in which said spiral roll is consolidated by extrusion directly into the form of tubing.
6. The method of claim 1 in which said preliminary structure comprises a rod which has been extensively work-hardened to a relatively small thickness, a plurality of such rods being inserted into said container parallel to each other and in generally closely-packed relation for consolidation by said further working.
7. The method of claim 6 in which said pressure-forming operation comprises an extrusion operation whereby said plurality of rods is consolidated into a monolithic structure by means of said extrusion.
8. The method of claim 6 in which said pressure-forming operation comprises a rolling operation whereby said plurality of rods is consolidated into a monolithic structure by means of said rolling.
9. The method of claim 6 in which said preliminary structures are consolidated by extrusion directly into the form of tubing.
10. The method of claim 1 in which said preliminary structure is formed from TD nickel.
11. A method of producing a monolithic structure of relatively large cross section having dispersionstrengthened, extensively work-hardened portions distributed throughout its interior, the method comprising the steps of (A) dispersion-strengthening and extensively workhardening a plurality of rod segments to a relatively small cross section as compared to their initial cross section;
(B) packing the rod segments in a container in a closely-packed bundle;
(C) pressure-forming said rod segments into a monolithic structure having a cross section larger than any of said rod segments but smaller than said bundle, whereby said segments are integrally bonded therein; and
(D) removing the container from said monolithic structure after pressure forming.
12. The method of claim 11 in which said pressureforrning operation comprises an extrusion process in which said segments are extruded into said monolithic structure.
13. The method of claim 12 in which said segments are formed from TD nickel.
References Cited UNITED STATES PATENTS 67,683 8/1867 Sweet 29-184 2,050,298 8/ 1936 Everett. 2,457,861 1/1949 Brassert 29-4723 X 3,029,496 4/1962 Levi 29419 X 3,371,407 3/1968 Forsyth et a1. 29472.3 X
JOHN P. CAMPBELL, Primary Examiner D. C. REILEY, Assistant Examiner U.S. Cl. X.R.