US 3790303 A
In a gas turbine bucket, having a blade and a root, composed of a eutectic alloy the blade is reinforced by eutectic fibers disposed in grain-orientated form, whilst in the root of the bucket the structure is non-orientated and enjoys a desirably high impact strength and ductility.
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Description (OCR text may contain errors)
United States Patent [1 1 Endres GAS TURBINE BUCKET  Inventor: Wilhelm Endres, Ennetbaden, Switzerland  Assignee: Aktiengesellschaft Brown, Boveri &
Cie, Baden, Switzerland  Filed: Apr. 5, 1972  Appl. No.: 241,165
 Foreign Application Priority Data Apr. 8, 1971 Switzerland 5225/71  US. Cl. 416/241  Int. Cl. Fold 5/28  Field of Search 416/241; 164/60, 122, 125, 164/127  References Cited UNITED STATES PATENTS v 2,422,193 6/1947 Hague 416/241 UX Feb. 5, 1974 3,044,746 7/1962 Stargardter 416/241 3,260,505 7/1966 Ver Snyder... 416/214 X 3,342,455 9/1967 Fleck et al. 416/241 3,494,709 2/1970 Piearcey 416/241 X Primary Examiner-Everette A. Powell, Jr. Attorney, Agent, or Firm-Ralph B. Parker et al.
[5 7] ABSTRACT In a gas turbine bucket, having a blade and a root,
composed of a eutectic alloy the blade is reinforced by eutectic fibers disposed in grain-orientated form, whilst in the root of the bucket the structure is nonorientated and enjoys a desirably high impact strength and ductility.
4 Claims, 2 Drawing Figures 1 GAS TURBINE BUCKET This invention relates to turbine buckets, and is concerned with the development of quite different properties in different parts of the bucket, the chemical composition of the metal in the bucket being the same in both blade and root.
The prior art discloses gas turbine buckets which are reinforced by eutectic fibers, solidified in grainorientated form. They suffer from the disadvantage of having only a low notch impact strength. While a low notch impact strength in the blade of the bucket does not result in any substantial disadvantages, the bucket root itself suffers from the serious disadvantage that it is unable to deform itself sufficiently in the zone at which it is joined to the rotor.
An object of the present invention is to provide a gas turbine bucket, the blade of which is reinforced in known manner by eutectic fibers but having sufficient impact strength in the bucket root.
According to the invention this and other inventive objects are achieved in that in the gas turbine bucket, which is constructed of a eutectic alloy, the crystals embedded in the parent material are formed as fibers disposed longitudinally in parallel to the bucket blade and extending into the bucket root, the bucket root having a non-orientated structure.
The invention will now be explained in greater detail I hereinbelow, and with reference to the accompanying schematic drawing, in which:
FIG. 1 is a gas turbine bucket in section; and
FIG. 2 is an apparatus forproducing a gas turbine bucket of the-kind illustrated in FIG. 1. FIG. 1 shows a gas turbine bucket 1 comprising a bucket blade 2 and a bucket root 3. The gas turbine bucket l is composed 'of a eutectic alloy, the bucket blade having been subjected to grain-oriented solidification. The crystals embedded in the parent material 4 take the form of longitudinally parallel fibers 5 extending from the outer end of the bucket blade 2 through the blade and into the bucket root 3. A gas turbine bucket of this kind is constructed as follows.
A melt of a pseudo binary eutectic alloy Co1 ,,Cr Cr ,Co,C containing in weight percentages, 56.] percent cobalt, 40 percent chromium and 2.4 percent carbon, is cast into a precision mold of corundum. The precision mold 6 is introduced into a graphite succeptor 7 which may be inductively heated by means of a heating spiral 8. To this endthe precision mold 6 is introduced into the graphite succeptor 7 so that the bucket blade 2 and the upper quarter of the bucket root 3 are disposed in the graphite succeptor 7 while the lower part of the bucket root 3 extends from the aforementioned succeptor, as shown in FIG. 2.
The graphite succeptor 7 is heated to a temperature between .1 ,400 and l,600 C. and is maintained at the aforementioned temperature. Since the melting temperature of the alloy is 1,310 C., the melt forming the bucket blade is retained in the superheated, fluid state while the bucket root 3 solidifies. After solidification of the bucket root 3, the graphite succeptor 7 is moved upwardly in the direction of the arrow and axially relative to the precision mold 6, the velocity of the said motion being between 5 and cm/h. Accordingly, the melt solidifies in the upper quarter of the bucket root 3 and then in the bucket blade 2, the solidification front moving from the bucket root 3 to the upper end of the bucket blade 2. The gas turbine blade may be stripped from the mold as soon as the precision mold 6 has been entirely withdrawn from the graphite succeptor 7 and the melt has solidified.
By practicing this technique the blade structure is reinforced by eutectic fibers which are solidified in grain-oriented form, whilst in the root per se of the bucket the structure is non-oriented, as is illustrated in FIG. 1, and has an advantageous ductility at the operating temperature of the turbine bucket.
The method is also suitable for the following alloys:
' Co, ,,Cr TaC CoTaC Ni, ,,Cr -TaC. I claim: 1. Gas turbine bucket formed of a eutectic alloy and having a root and a bIade,-said blade having a crystalline structure oriented in parallel to the longitudinal orientation of the bucket blade whilst in the bucket root the structure is not grain-oriented and is ductile at the operating temperature of the turbine.
2. Gas turbine bucket according to claim 1, in the blade of which crystals embedded in matrix are present as fibers disposed longitudinally in parallel to the blade and extend through the blade and to the root per se.
3. Gas turbine bucket according to claim 1, in which the eutectic alloy is a member of the group of alloys consisting of CoCrC, NbNb C, Ta'Ta C,
Ni-Ni Nb, Ni Ni Ti, NiAlvCr, CoTiC, Ni-TaC,
' the alloy is a CoCrC alloy consisting essentially of 56.1 wt. percent cobalt, 40 wt. percent chromium and 2.4 wt. percent carbon.