US 2581252 A
Abstract available in
Claims available in
Description (OCR text may contain errors)
1952 c. G. GOETZEL ETAL POWDER METALLURGY ARTICLE Filed Dec. 31,
IN VEN T 0R5 60467366 By 0114 4 El, J I,
Patented Jan. 1, 1 952 2,581,252 POWDER METALLURGY ARTICLES Claus G. Goetzel, Yonkers, and John L. Ellis, New York, N. Y., assignors to Sintercast Corporation of America, New York, N. Y., a corporation of New York Application December 31, 1947, Serial No. 795,102
Claims. '(CI. 75-22) The invention relates to a turbine blade for use at elevated temperatures, which is composed of substances having difierent melting points, and particularly to a sintered skeleton of a relatively skeleton because the particles of the powdered material will not be distributed evenly within the mold, or distributed in the mold in the desired pattern. In prior impregnation processes, sizing high melting point formed with interconnecting 5 and machining frequently have been necessary pores substantially throughout its entirety, the following the impregnation step. One reason is pores being permeated with an infiltrant metal, the uneven distribution of the second metal on the exeterior faces of the turbine blade having the surface of the skeleton, which is caused by a coating thereon of the infiltrant metal. uncontrollable adherence of the second metal Heat resistant metallic articles such as blades, to the surface of the skeleton, and non-uniformity buckets, valves and the like for jet engines, thereof. rockets, or gas turbines and the like are not satis- One of the objects of the invention is to profactory when made by conventional casting or vide a shaped article having improved physical forging methods. One of the reasons is that characteristics, including high hot tensile the temperature at which the article is formed is strength, high hot fatigue strength, high resistnear that of the operating temperature of the eleance to creep at elevated temperatures, and espement in service and it thus is apparent that the cially high corrosion resistance under conditions element would not be strong and stable in its of operation. dimensions under operating conditions. Another The shaped article of the present invention difiiculty is that the materials which maintain comprises a continuous skeleton of high melting their strength at elevated temperatures under point made from powdered materials suitably protective atmospheric conditions are subject to sintered, the skeleton structure having intercomcorrosion under the conditions of operation of municating pores substantially throughout its enelements such as gas turbine blades, and this tirety. The pores of the skeleton are permeated tends to impair rapidly their strength. throughout by a network of an infiltrant metallic Powder metallurgy methods must be used in material, and a layer of corrosion resistant meorder to meet the high temperature requirements tallic material is formed on the faces of the in articllels in 1the fiel gls1 mentioned as wlell asdin article, said layer being integtrally merged, fused, many 0 er p aces. e previous y use pow er or joined to the metallic ma erial net work permetallurgy processes employing simple pressing meating the pores of the skeleton. The layer of 3nd gintering opteragions lwltlttl inixturdes 0ft p0 W- metal is formed of suificient thickness to suitably e e 1811 S ave 1ml 3 1011s 1 0 protect the article from corrosion. herent po os ty o the article a d fi e grain Size The skeleton is selected from materials so as and weak grain boundar es of the resulting structo have high hot tensile strength, high hot fatigue ture, all of which contribute to unfavorable hot strength, and high resistance to creep at elevated tensi e t e gt hot t e Strength, d temperatures. The infiltrant metallic material is slstance o Creep at elevated tempfiraturesselected to have the desired corrosion resistance In pr v sly u p d r m l r y hand to impart the desired physical properties to mques 1I1V1Vmg1mpTegPat1n a formed the skeleton. Preferably the layer of corrosion pact f sieletoni t g f g fresistant material is the same as that of the in- 01 1'8 IaC QTY 1113. ella. In 2. ere Olm 1S metallic material usually shaped by compression in a mold and The article can be formed eflicaciously by perzfi isg j gfi ggg igg fg 2315 353 2; forming the impregnation step with the skeleton and sintered, a second or auxiliary lower melting g i figi igi fii 223 533? i gi gi fi g metal is brought into Contact with the skeleton m kel t 1 t in a suitable ceramic or metallic vessel and heat e on m P fS a f or Que applied so as to Hquefy the second metal, and condition. The infiltrant nietal wfll completely cause the Second or auxiliary metal to be drawn fi ll the moldso that the art cle will be accurately into the Skeleton by capillary action In such a sized, and will form a continuous layer over the process, the infiltrant metallic material will not faces of article; skeleton can be completely cover the exterior face of the body. ranged in C ju W he mold so th t In the forming of the skeleton, diflicult probthere is sufficient clearance to form the desired lems arise when the shape is complex and irthickness of the coating layer. The thickness of regular, due to lack of uniformity in the pressed this layer of the infiltrant material is increased at the base of the turbine blade for the shaped wheel engagingportions thereof.
The harder and more abrasive types of skeleton materials are diflicult to machine and this difliculty normally remains after the pores have been filled with the infiltrated material. It is desirable, therefore, to provide a layer of a skeletonfree infiltrant portion at places where the article is to be machined. This can be accomplished by placing the skeleton in a mold having an increased clearance between the mold walls and the skeleton at areas where there is to be skeletoniree infiltrant metal. The skeleton is impregnated while in said mold, preferably in a pressure differential apparatus, so that the infiltrant completely fills the mold, thus leaving skeletonfree infiltrant metal of the desired thickness in selected areas.
The refractory materials as employed in this invention have a low coefiicient of expansion, usually in the order of /3 to /2 of that of steel, or other metal alloys conventionally used in the construction of'components of engines, turbines, and the like. This would result in difficulties if plain refractory compounds were used as structural materials for such elements as turbine blades, buckets, valves and the like.
In the present invention, the skeleton can be made of a refractory material having the low coefficient of expansion and the desired strength characteristics at elevated temperatures. The infiltrant material can be selected having a sufficiently high coefficient of expansion, so that the correct dimensional relationship can be maintained with a supporting part for the composite article at all service temperatures. The thickness of the infiltrant outside layer is increased, as required, at the point of joinder of the blade with the element to which it is to be attached, thus maintaining a fit without regard to temperature of operation.
The difierence in coefficients of expansion of the skeleton materials and the infiltrant materials will result in other advantages, such as strengthening of the composite structure, as will be explained hereafter.
These and other features, advantages, and objects of the invention will become apparent from the following description and drawings.
In the drawings:
Fig. 1 shows a side view of one form of a turbine blade of the present invention.
Fig. 2 shows a front view of the blade of Fig. 1.
Fig. 3 shows an enlarged representation of a section of the composite body at the point where the blade body joins the base thereof.
The invention will now be described in con junction with a turbine blade, such as is generally used in gas turbines.
The blade may have a tip or blade portion H] and a base portion H which is machined to fit accurately into a suitably shaped notch or aperture in the turbine wheel.
It is desirable that the materials and dimensions of the base portion relative to the turbine wheel be chosen so that the blade will remain tightly held under the elevated temperature conditions of operation.
In formation of the blade, the skeleton or high refractory phase dimensions or outline are diagrammatically indicated by the inner dashed lines l2 (Figs. 1, 2). The mold used during impregnation is arranged so that the infiltrant metal or corrosion resistant phase will fill the the mold and form the outside of the tip portion of the blade and will reach the dashed lines l3 of the base ll. Thus there will be an excess of the infiltrant metal at 14 which can be machined to the desired base shape [5. Such a formation of the composite article with a thickened infiltrant metal'portion may be termed undercasting. As previously mentioned, the layer of infiltrant metallic material can be increased as desired at other points such as where erosion takes place on the blade.
In Fig. 3, the skeleton or high refractory phase is indicated at IS, the particles thereof being formed together with intercommunicating pores therebetween, said phase being continuous.
As an example, the skeleton material may be tungsten, molybdenum, titanium, tantalum, columbium, chromium, zirconium, or their alloys with each other, or with iron, nickel, cobalt, or
their compounds of metalloidal character with carbon, boron, silicon, nitrogen, etc. Some examples of the aforementioned compounds of metalloidal character are tungsten carbide (WC), titanium carbide ('IiC), molybdenum carbide (MOzC), tantalum carbide (TaC), columbium carbide (CbC), chromium carbide (ClsCz), zirconium carbide (ZrC), vanadium carbide (VC), tungsten boride (W132), titanium boride (TiBz), molybdenum boride (MOB), tantalum boride (TaB), columbium boride (CbB), chromium boride (CrB), zirconium boride (Z1'3B4), vanadium boride (VBz), thorium boride (ThBs); also stable refractory materials or compounds such as beryllium oxide, magnesium oxide, aluminum oxide, zirconium oxide, silicon carbide, and boron carbide can be used, these being stable at elevated temperatures.
' A typical composition of a homogeneous skeleton material as employed by this invention consists of by weight of tungsten carbide (WC), 25% titanium carbide (TiC) and 5% cobalt (C0),
the tungsten carbide (WC) and titanium carbide.v
(TiC) components being combined as a solid solution. Another typical composition of a homogeneous skeleton material as employed by this invention consists of i5% by weight of tungsten carbide (WC), 25% titanium carbide (TiC), 25% chromium carbide (CrsCz) and 5% cobalt (Co), the tungsten carbide (WC) and titanium carbide (TiC) and chromium car-bide (CrsCz) components again being combined as a solid solution.
The infiltrant metallic material or corrosion resistant phase network is indicated at H! (Fig. 3), as entirely permeating all of the intercommunicating pores at the skeleton, thus forming a network as equally continuous as the skeleton. At 20 is seen the excess infiltrant metal of sufiicient thickness to allow for machining and at 2! is indicated the layer of corrosion resistant metal on the exterior faces of the article integrally merged, fused or joined with the infiltrant metal network permeating the pores of the skeleton. The representation in Fig. 3 corresponds to a single plane as is normally obtained in 1netallo-- graphic procedures, the infiltrant metal being a continuous network throughout the pores of the skeleton, this necessarily resulting from the manner in which the infiltrant metal fills the pores of the skeleton. Depending upon the alloyability between skeleton and infiltrant materials, there may be formed an interphase along the boundaries of the same where they are in contact with each other. This interphase may materially contribute to the strength of the composite structure.
Again merely by way of example, the impregnating material may be iron, nickel, cobalt, chro mium and their alloys with each other, or their alloys with the previously mentioned refractory metals, or metal compounds as minor constituents. It is to be understood that the appropriate infiltrant having a dissimilar lower melting point relative to the skeleton can be used, and that the word metal in the claim is to be construed to include the aforementioned. A typical composition of impregnating material employed successfully by this invention comprises an alloy containing 69% by Weight of cobalt, 25% chromium and 6% molybdenum. Another example is a material containing 50% by weight of cobalt, 29% chromium, 15% nickel and 6% molybdenum. Still another example is one containing 52% by weight of cobalt, 28% chromium, 11% nickel, and 9% tungsten. Another example contains 60% by Weight of nickel, 16% molybdenum, 14% chromium, tungsten and 5% iron, while still another contains 60% by weight of chromium, 25% molybdenum and 15% iron.
As mentioned previously, the coeiiicient of expansion of the infiltrant phase is usually much higher than that of the skeleton phase. Consequently, because the infiltrant phase is carried out at a much higher temperature than the operating temperature of the article, there will be a shrinkage of the infiltrant phase relative to the refractory phase. The relationship of the coefiicients will be such as to create internal stress conditions in the article, so that better elevated temperature strength and creep resistance will be obtained.
It is apparent that details of construction can be varied without departing from the spirit of the invention except as defined in the appended claims.
1. A composite material shaped turbine blade having a base portion engageable with a turbine wheel for use at elevated temperatures in corrosive atmospheres, said blade being composed of substances of different melting points and having a sintered porous skeleton of higher melting point normally corrodible at the temperatures of operation and formed with intercommunicating pores substantially throughout its entirety, the pores thereof being permeated with an infiltrant metal having corrosion resistant properties under the conditions of operation and a substantially continuous controlled layer of said infiltrant metal of predetermined thickness on the exterior faces of said blade to protect the same, said layer being integrally fused with the metal permeating said pores, the layer being thickened at the base portion of the blade for the shaped wheel engaging portions thereof.
2. In a composite material shaped turbine blade according to claim .1, the sintered porous skeleton consisting of titanium carbide.
3. In a composite material shaped turbine blade accoridng to claim 1, the sintered porous skeleton consisting of tungsten carbide.
4. In a composite material shaped turbine blade according to claim 1, the sintered porous skeleton consisting of 70 weight per cent tungsten carbide, 25 weight per cent titanium carbide and 5 Weight per cent cobalt.
5. In a composite material according to claim 1, ton consisting of bide, 25 weight Weight per cent per cent cobalt.
shaped turbine blade the sintered porous skeleweight per cent tungsten carper cent titanium carbide, 25 chromium carbide and 5 weight CLAUS G. GOETZEL. JOHN L. ELLIS.
REFERENCES CITED The following references are of record in the file of this patent:
UNITED STATES PATENTS Number Name Date 2,192,792 Kurtz Mar. 5, 1940 2,198,240 Boegehold Apr. 23, 1940 2,239,800 Vogt et al Apr. 29, 1941 2,381,459 Merrick Aug. 7, 1945 2,422,439 Schwarzkopf June 17, 1947 2,456,779 Goetzel Dec. 21, 1948