US2957232A - Forged powdered metal articles - Google Patents

Description

' Oct. 25, `1960 K. M. BARTLETT 2,957,232

FORCED POWDERED METAL ARTICLES Filed July 29. 1954 2 Sheets-Sheet 1 ./Tz'q 7 39 Il." I

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Oct. 25, 1960 K. M. lsAR'rLra-mF 2,957,232

FORCED POWDERED METAL ARTICLES Filed July 29 1954 2 SheetS-Sheet 2 54 I; F q. f4 .50 l

. 2,957,232 Patented Oct. 25, 1960 ice 2,957,232 n rondan gewonnen 'METAL ARTICLES Kenneth M. Bartlett, Lyndhurst, Ohio, assignor to Thompson Ramo Wooldridge Inc., Cleveland, Ohio, a corporation of ho Filed July 29, 1954, Ser. No. 446,495

1 Claim. (Cl. 29192) This invention relates to a method of producing strong, dense, `creep-resisting powdered metal articles.

Specifically this invention deals. with the production of powdered metal Huid-directing members, lsuch as pop- -pet valves for internal combustion engines and blades or vanes for turbine engines, by closed die forging of powdered metal compacts containing slip-preventing aggregates.

In .accordance with this invention, powdered metals are pressure molded and sintered to form starting slugs or billets. These slugs or billets are then heated and forged in closed type dies to further compact and weld the particles together without melting the particles. The closed die forging is typified by extrusion. The powdered metal mixture preferably contains slip-preventing aggregates such .as refractory metal carbides or intermetallic compounds, which are insoluble in the metals forming the main body of the mixture. These aggregates minimize and control slippage of the constituent main body, particles, thereby decreasing creep under stress, both in the finished product and during the die forging formation `of the product. In the sintering operation or during the hot die forging treatment, some of the constituents of the powdered metal mixture may be oxidized to provide an enhancedk refractory property to the article.

The invention will be hereinafter, specifically described las embodied in fluid directing members .for high temperature usage, such as poppet valves for internal combustion engines and turbine vanes or bucketsfor gas turbine engines and the like, but it should be understoodV that the principles of this invention are generally applicable to the production of strong, dense articles from powdered metals. Therefore, the inventionl is not intended to be limited to the preferred hereinafter described embodiments.

It is then an object of this invention to provide dense, strong, die-forged powdered metal articles.

A lfurther object of the invention is to provide a method of increasing the strength and stress resistance of powdered metal articles.

A still further object of the invention is to provide a method of making fluid directing members of enhanced density and strength from sintered powdered metal compacts by extruding the compacts `at elevated temperatures to weld together and further compact the metal particles and thereafter finish shaping the resulting extruded body into the form of a liuid directing member.

A still further object of the invention is to provide stronger powdered metal articles than have heretofore been produced under known powdered metallurgy techniques.

A specic object of the invention is to provide poppet valves `and turbine blades from sintered powdered inetal compacts by extrusion and coining operations.

A still further and specific object of this invention is to provide strong powdered metal articles having a density of 95% or more.

Other and further objects of the invention will be apparent to those skilled in the art from the following detailed description of the annexed sheets ot' drawings which, by way of preferred examples only, illustrate several embodimentsof the invention.

Figure 1 is a fragmentary elevational view, with parts in vertical cross section, illustrating a pressure molding die and punch assembly for producing a starting slug from powdered metal and illustrating the open position of the assembly;

Figure 2 is a view similar to Figure 1 butillustrating the closed position of the assembly;

Figure 3 is a side elevationalview of a sintered powdered metal slug `or billet forming a starting blank for the process of this invention;

Figure 4 is a fragmentary side elevational view, with parts in vertical cross section, illustrating an extrusion die assembly for extrusion of the slug of Figure 3 and showing the assembly in open position;

Figure 5 is a view similar to Figure 4 but showing the assembly at the completion of the extrusion operation;

Figure 6 isa side elevational view of an extruded headed rod produced in the dies illustrated in Figures 4 and 5;

Figure 7 is a cross sectional View of a coining die assembly for the extruded headed rodof Figure 6 and illustrating the open position of the assembly;

Figure 8 is a view lsimilar to Figure 7 showing the closed position of the assembly;

Figure 9 is a side elevational View of a coined poppet valve blank produced according to this invention;

Figure Al0 is a `side'elevational View of a finished poppet valve produced from thel coined blank of Figure 9;

Figure 11 is a vertical cross sectional view, with parts in elevation, showing a coining die assembly employed in producing la turbine engine blade from an extruded, headed rod similar to the one shown in Figure 6;

Figure l2 is a view similar to Figure 1l illustrating the closed position of" the coining die;

Figure 13 is an elevational view of a turbine engine blade blank produced by coining the headed rod in Figure 6 in the manner shown in Figures lil and l2; and

Figure 14 is an elevational view of a nished turbine bucket produced from the coined blank shown in Figure 13.

As shown on the drawings:

The method' `of the instant invention is applicable to substantially any metal which isV capable of lending itself to working and processing by powdered metallurgical techniques. Since, however, the preferred invention deals with the production of uid directing members, such as poppet valves, turbine bucketsand thelike, the present discussion shall be limited to those metals which are particularly suitable for` these purposes. Such metals are iron and iron base alloys, nickel base alloys and especially nickel-chromium and nickel-cobalt base alloys. Iron-aluminum alloys `containing 'from about 98% to iron and from about 2% to 15% aluminum are useful since some of the aluminum may be converted to the oxide during sintering and hot forging for increasing the refractory properties of the product.

Preferred nickel-base chromium alloys are Inconel alloys as such are disclosed in the Bieber et al. Patent 2,664,354 and T.P.A. alloys containing:

Preferred nickel-cobalt base alloys include alloys containing 35-70% Ni; up to 20% C0, up to 10% W, .0S-1.0% C; bal. Fe with small amounts of Mo; Si; Cr,

etc.A i l In order to decrease and control slippage resulting in tensile strains and creep both during extrusion and in the use ofthe finished product non-slip aggregates are incorporated into the powdered metal mix. The preferred materials for such use as aggregates comprise the socalled hard metals and intermetallic compounds of aluminum.

The hard metals comprise carbides of metals of the 4th, 5th and/or 6th group of the periodic system, particularly titanium carbide and tungsten carbide. In addition to the hard metals, such aggregates also include chromium carbide, and mixtures of chromium carbide with titanium carbide and tungsten carbide; intermetallic compounds of nickel and aluminum and of nickel and boron; and the borides and nitrides of zirconium and titanium.

These insoluble aggregates will decrease slippage of the crystal planes so that molecular continuity will be maintained Vand rupture or slip cracks or pressing cracks will not develop when the compact is extruded. When extruding nickel-base alloys, mass slippage of a part of the compact may sometimes occur during extrusion resulting in cracking or rupturing of the extruded piece. Mass slippage usually results in a complete loss f the article produced. If, however, a hard phase aggregate material, such as for example an insoluble powdered hard metal, is dispersed throughout the matrix of a nickelbase alloy compact, a definite resistance is offered to deformation of the compact during the extrusion step. The resistance to `deformation has been found to be proportional to the logarithm of the average length of a straight path through the continuous (nickel alloy) phase. Therefore, by dispersing an insoluble aggregate material throughout the matrix of the alloy it is possible to interrupt or eliminate straight paths through the continuous phase which otherwise would afford a nucleus for the creation of slippage or cleavage planes. The amount of aggregate admixed with the powdered nickel-base alloy prior to compacting the same varies to some extent depending upon the continuous or alloy phase employed. In general, however, a ratio of from about 0.5% to 25% by volume of aggregate to from about 99.5% to 75% of the alloy gives operable and advantageous results.

The particle size of the powdered metal from which the compact is produced is not critical and can vary within limits. If iron or a ferrous alloy are employed without the use of an aggregate, metal powders ner than about l0() mesh are operable; with particle sizes of from 100 mesh to 325 mesh being preferred.

Where nickel-base alloys are admixed with aggregates prior to compacting the same, the alloy phase of the mixture should have particle sizes about the same as indicated above; and the aggregate preferably has a particle size in the low micron range, for example, from 1/2 to 2O microns and preferably from l to 5 microns.

ln accordance with the instant invention the powdered metals are pressure molded into a suitable slug or billet by means of a suitable compacting die assembly 20. The compacting die assembly includes a die body member 21, having a suitable cylindrical bore or die cavity 22 formed therein, a lower punch member Z3 slidably receivable in the bottom portion of the die cavity 22, and an upper punch member 24 slidably receivable in the top portion of the die cavity 22. The die assembly 20 is preferably of the double action type; that is, both the upper punch member 24 and the lower punch member 23 are capable of exerting pressures upon a powdered metal 25 contained in the die cavity 2.2. In this fashion the molding pressure is maintained at a uniform rate on both sides of the powder thereby producing a slug or billet displaying substantially uniform density throughout. In a single action'prss, such as where only the upper punch member 24 is activated to deliver compacting pressures, uniform densities do not always result, and the resulting slug or billet displays inferior extruding properties.

As seen in Figures l and 2 the `die cavity 22 is tilled flush with the top of the die body member 21 with a suitable powdered metal mixture 25 which, as noted previously, may comprise iron; iron-aluminum alloys; nickel base alloys; etc., and 0.5-25% by volume of a suitable insoluble, slip-preventing aggregate. The powdered metal or mixture 25 is then compressed between the upper punch member 24 actuated downwardly and the lower punch member 23 actuated upwardly in the die cavity 22.

In general, the compacting pressures employed will vary to some extent with the metal being pressure molded. ln general, however, compacting pressures of from about 20 tons per square inch to about 60 tons per square inch are operative and produce slugs or billets which, after being sintered, may be extruded satisfactorily to produce a suitable fluid directing member blank.

After the powdered metal 25 has been pressure molded to form a suitable slug or billet 26 as shown in Fig. 2, the billet or slug 26 is expelled from the die cavity 22. by withdrawing the upper punch member 24 and raising the lower punch member 23. Thereafter the slug 26 is sintered to produce a self-sustaining extrusion slug. The temperature employed in sintering will vary depending upon the metal employed; the length of the heating time; and the size of the slug 26 produced. In general, however, sintering at a range of from about l400 F. to about 2400 F. for from about 1 to 20 hours produces a slug or billet 26 having suitable self-sustaining properties, and which is capable of being extruded. The longer heating times, of course, are employed with the lower sintering temperatures, while the shorter periods are associated with the higher temperatures.

The compact or slug 26 should preferably be sintered in a non-oxidising atmosphere. An atmosphere of this type may be provided by employing cracked or disassociated ammonia; partially combusted hydrocarbon gases; inert gases such as argon or the like; hydrogen; or under vacuum conditions. If the powdered metal employed comprises a high carbon steel, it is important that the sintering atmosphere be non-decarburizing. Likewise, when a nickel-base alloy is employed it is important that a sulphur-free atmosphere be employed, for nickel and sulfur at elevated temperatures are extremely reactive.

The sintered compact slug or billet 26 may be cooled and stored for extrusion at a later time or may be taken directly in its heated condition from the sintering furnace and extruded. The extruding step is carried out in closed extrusion dies to keep the material in `a state of complete compression during extrusion to prevent the formation of excessive tensile forces and stresses. This is best effected by means of the extruding die assembly 27 shown in Figures 4 and 5. As seen therein the slug or billet 26 is placed in an extruding die member 28 having a cylindrical die hole 29 of a larger diameter than the slug 26. The die hole 29 extends to a conical throat 30 which converges to a small diameter cylindrical outlet passage 3.1. An extrusion plunger 32 snugly iitting the hole 29 is pressed on top of the slug 26 to force the slug partially through the extrusion throat 30 to form a headed rod or blank 33 (Fig. 5). The blank or rod 33 has a solid cylindrical elongated rod portion 33a of the same diameter as the outlet passage 31 and a conical head portion 33b conforming with the tapered throat 30. The head 34 has a cylindrical top rim portion 33C of the same diameter as the hole 29. The divergent end of the head is therefore of larger diameter than the original slug 26.

The temperature to which the slug 26 is heated prior to the extrusion step, in general, will vary depending upon the metal employed. Generally, speaking, however, a range of from about 1600" F. to about 2400 F. gives operable results, with a temperature range of from about 1800 to about 2200 F. being preferred. Temperatures of from about 1600 F. to `2000 F. are preferred forV iron and ferrous alloys, while temperatures generally in excess of 2000 giveL the best results with nickel-base alloys.

Preferably the extrusion die Z7 should be lubricated prior to the extrusion step. This may be best effected by means of a mixture of a sulphur-free grease `and graphite, such as tallow and bone black.

The pressures employed during the extrusion operation, again will vary depending upon the metal employed; the size of the slug 26; the temperature to which the slug or billet 2-6 was heated prior to the extrusion; `and the rate at which 4the pressure is applied by the extrusion plunger 32. In general, however, pressures of from about 100 tons per square inch to about 300 tons per square inch denote anoperable range, with pressures of from about 150 tons per square inch to about 200 tons per square inch being preferred.

The pressures and heat created during the extrusion process causes the discrete particles of the powdered metal or powdered metals and aggregate to become more completely welded together in the sintered compact. This further welding together of the individual particles creates what appears to be, in reality, a solid stage diffusion of the constituents in a non-fluid condition. This welding together of the particles produces a headed rod or uid directing member blank 33 having a density of from about 95 to 100% of the theoretical density. The density and other physical properties of the extruded blank 33 are substantially equal to the properties which might be expected in a blank produced from a cast ingot. However, the headed rod or blank 33 has, in addition to densities approaching those of cast rods, the distinct advantages which can be achieved only in articles produced by powdered metallurgical techniques, for example, the controlled proportioning of the constituents in the blank; the working of alloys and metals which are not amenable to conventional casting techniques, to name only a few.

The extruded headed rod or blank 33 may then be formed into various shaped articles. For example, as seen in Figures 7-10, the blank 33 may be coined by means of a suitable coining die 36 to produce a poppet valve blank 37. As seen therein the blank or headed rod 33 is positioned on a lower die member 38 of a coining die assembly 36 beneath an upper die member or punch 39. The upper die member 39 has a cylindrical bore 40 formed therein which terminates downwardly in a flared-out circular recessed portion 41 having the general shape of the valve head to be produced. This is preferably a hot coining operation; the blank 33 being heated to from about 1800 to about 2000 F. prior to the coining operation. The blank 33 is heated and centered on the lower die member 38 directly below the upper die member 39, so that the elongated rod portion of the headed rod 33 is in direct alignment with the cylindrical bore y40. The upper die member 39 is actuated dovwiwardly over Ithe blank 33 and the blank 33 is blocked vdown or coined to form a poppet valve blank 37. The valve blank 37 has an elongated stem portion 43 conforming to the diameter and length of the cylindrical bore 40 and has a flared-out circular head portion 44 conforming 4to the flared circular recess 41 on the die 39. The poppet valve blank 37 is thereafter suitably machined and finished to produce the finished poppet valve V (Fig. 10).

As best seen in Figures 11-14, the headed rod or blank 33 may also be employed advantageously in producing la turbine bucket 45. As seen in Figures 1'1 and 12 the headed rod or blank 33 is coined or blocked down in a suitable coining die assembly 46. 'The die yassembly 46 comprises an upper ydie member 47 and a lower die member 48. The upper and lower die members 47 and `4t;

have diametrically opposed aligned die facesV y49, 49 shaped for forming the root portion 50 and the vane or air foil portion 51 of the turbine bucket 45. A flash gutter portion 52 is provided to receive flash meta-l 53. The headed rod or blank 32 is heated to from about 1800 to `about 2000 F. prior to the coining operation. The turbine bucket blank 54 (Fig. 13) resulting from the coining operation is freed of the flash metal 53 and suitably nished and machined into a turbine bucket having a transverse root section 50 and an upstanding integral vane portion 51.

By means of the instant invention it is now possible to produce articles of intricate shapes from metals which are extremely diicult to handle by conventional techniques. Certain metals or mixtures of metals or alloys cannot be cast adequately due to the extreme activity of such metals at elevated temperatures. Therefore such metals must be worked, if `at all, strictly by powder metallurgical techniques. The flexibility of the type of article which can be produced by powder metallurgical methods, however, is limited. This is due to the inherent difficulty of producing proper dies of intricate or nonsymmetrical shapes. In addition, the compacting of powdered metals in odd shaped or intricate ldies is far from satisfactory, for uneven molding pressures -are created often resulting in defective products. By the instant invention, however, this limitation in producing intricate objects from non-castable metals has been eliminated.

By the instant method it is now possible to produce 'articles from powdered metal having la density substantially equal to of theoretical. Heretofore, powdered metal compacts having a density equal substantially to 100% of theoretical could only be achieved by infiltrating the compact with ya low melting metal, or cold pressing the compact lat extreme pressures often in excess of tons per square inch and/or sintering the compact at extreme temperatures often in excess of 2600" F.

Previous attempts at producing compacts of 100% theoretical density by drop hammer forging sintered compacts in open dies has been generally unsatisfactory. Such methods have inevitably resulted in articles having extreme strains and defects and considerable tensile forces and slippage. In the instant invention, however, none of these defects or limitations are present, due to the fact that the extruding step is carried out entirely under extruding compression in closed dies.

In addition to the above features and advantages another distinct feature of the instant invention lies in the production of an article wherein certain materials and properties can be localized 4and controlled in specific portions of the article. For example, by employing the present invention it is possible to produce a billet or extrusion slug such as 2.6 wherein a certain portion, such as the top, consists primarily of highly refractory metal particles, while the remainder of the slug may consist Iof a non-refractory metal. A headed rod or blank 32 produced therefrom would, then, have refractory metal particles concentrated primarily in the head portion thereof. A poppet valve produced from such a blank or headed rod would have a `stern formed of a standard ferrous alloy while the integral head portion would consist of a highly refractory metal. This structure is advantageous, for the head portion of a poppet valve is the part which is subject to the most extreme temperatures of the exhaust gases. In a similar manner it would be possible to produce turbine buckets or other fluid directing members having specific portions or parts thereof produced from a particular material while the remainder or other portions could be produced from other desirable components.

It will be apparent to those skilled in the art that I have now provided a new and improved method for producing uid directing members from powdered metals. It will also be apparent that the method of the instant um t.

7 invention is applicable to substantially any meta1 which is amenable to working by powdered metallurgical techniques. l

It will be understood that modifications and varia-l tions may be effected without departing from the scope of the novel concepts of the present invention.

I claim as my invention:

A fluid directing member comprising, a shaped body having a matrix formed from 99.5 to 75.0% by Volume of a metal selected from the group consisting essentially of iron-aluminum, nickel-chromium `and nickel-cobalt base alloys, the iron-aluminum alloy containing from about 98 to 85% iron and from about 2 to 15% aluminum, said matrix having uniformly dispersed therethrough 0.5 to 25.0% by volume of an insoluble powdered slippreventing metal aggregate selected from the group consisting essentially of the carbides of titanium, tungsten and chromium and mixtures thereof, borides and nitrides of zirconium and titanium, and intermetallic compounds of nickel and aluminum and of nickel and boron, the

8 shaped body having a density substantially 100% of theoretical.

y.References Cited in the le ofthis patent

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