Process and apparatus for producing forged TiAl components

Abstract

An apparatus and a process for producing forged components composed of TiAl alloys, wherein a melt of a TiAl alloy is provided and is cast by horizontal centrifugal casting so as to produce at least one semifinished TiAl cast part and the semifinished TiAl cast part is converted by forging into a forged TiAl part.

Claims

1. A process for producing a forged component of a TiAl alloy, wherein the process comprises casting a melt of the TiAl alloy by horizontal centrifugal casting to produce at least one semifinished TiAl cast part and forging the at least one semifinished TiAl cast part into a forged TiAl part.

2. The process of claim 1, wherein the at least one semifinished TiAl cast part is in the form of a cylinder, a cone or a ring.

3. The process of claim 1, wherein the at least one semifinished TiAl cast part is produced by parting.

4. The process of claim 3, wherein the at least one semifinished TiAl cast part is produced by dividing or machining of a cast piece.

5. The process of claim 1, wherein the TiAl alloy is cast in a permanent mold to afford a plurality of separated semifinished TiAl cast parts.

6. The process of claim 1, wherein the TiAl alloy is cast to afford a semifinished TiAl cast part in the form of a ring or tube having a length of from 5 to 300 cm and/or a wall thickness of from 4 to 30 cm and/or an internal diameter of from 10 to 100 cm.

7. The process of claim 1, wherein the TiAl alloy is a TNM alloy comprising niobium and molybdenum constituents.

8. The process of claim 7, wherein the TiAl alloy comprises, based on a total weight of the alloy, from 40 to 50% by weight aluminum, from 2 to 6% by weight niobium, from 0.5 to 2% by weight molybdenum, from 0.05% by weight to 0.15% by weight boron, balance Ti and unavoidable impurities and/or alloy constituents in proportions of in each case less than 0.5% by weight up to a total proportion of not more than 5% by weight.

9. The process of claim 8, wherein the TiAl alloy comprises, in percent by weight based on a total weight of the alloy, Al43.5, Nb4, Mo1, B0.1.

10. The process of claim 1, wherein the semifinished TiAl cast part has a microstructure formed by colonies of -Ti and -TiAl which are embedded in -Ti.

11. The process of claim 1, wherein a phase composition of the at least one semifinished TiAl cast part deviates from an equilibrium phase composition at room temperature by up to 10% by volume.

12. The process of claim 1, wherein a phase composition of the at least one semifinished TiAl cast part deviates from an equilibrium phase composition at room temperature by up to 8% by volume.

13. The process of claim 1, wherein the at least one semifinished TiAl cast part is subjected to a plurality of forming steps by forging and/or at least one heat treatment.

14. The process of claim 1, wherein the at least one semifinished TiAl cast part in the form of a ring is forged into an annular disk from which rotor blades for a turbomachine may be cut.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings show, in a purely schematic way,

(2) FIG. 1 a depiction of the horizontal centrifugal casting process for producing cone-shaped or cylindrical semifinished TiAl cast parts,

(3) FIG. 2 a sectional view of a permanent mold after centrifugal casting,

(4) FIG. 3 a perspective view of the permanent mold of FIGS. 1 and 2,

(5) FIG. 4 a further depiction of a centrifugal casting apparatus for carrying out a centrifugal casting process as per a second embodiment of the invention,

(6) FIG. 5 a sectional view of the permanent mold of FIG. 4 after completion of centrifugal casting,

(7) FIG. 6 a perspective view of the permanent mold of FIGS. 4 and 5,

(8) FIG. 7 a depiction of the course of the centrifugal casting process in subfigures a) to e) in the embodiment depicted in FIGS. 4 to 6,

(9) FIG. 8 a schematic depiction of the microstructure of a semifinished TiAl cast part after centrifugal casting and

(10) FIG. 9 a depiction of a forging step for converting a ring into a disk.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(11) The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description in combination with the drawings making apparent to those of skill in the art how the several forms of the present invention may be embodied in practice.

(12) FIG. 1 shows, in a schematic sectional view, an apparatus and a process for the centrifugal casting of semifinished TiAl cast parts according to the present invention, which parts can subsequently be converted by forming by forging into TiAl components which can, in particular, be used in turbomachines such as aircraft engines.

(13) The apparatus comprises a permanent mold 1 which has a plurality of molds 3, 3 into which the material to be cast is introduced. In the permanent mold 1 of the embodiment depicted in FIG. 1, the molds 3, 3 are molds for producing cones and cylinders, which are arranged at a distance from one another along the longitudinal axis 2 of the permanent mold 1 and along the circumferential wall of the permanent mold 1.

(14) During centrifugal molding by means of which the molds 3, 3 of the permanent mold 1 are filled with the appropriate melt, the permanent mold 1 is rotated about the permanent mold longitudinal axis 2 so that the material to be cast, e.g. in the form of a TiAl alloy, which is introduced in molten form into the permanent mold 1 is pushed by centrifugal force into the molds 3, 3.

(15) The molten TiAl alloy 9 is provided from a melting crucible 6 which can be heated by a heating device 7, with the molten TiAl alloy being introduced via a feeder 5 into the permanent mold 1.

(16) As can be seen from FIG. 1, the feeder 5 is moved along the longitudinal axis 2 of the permanent mold 1, so that the molds 3, 3 arranged at a distance from one another along the longitudinal axis 2 can be filled successively.

(17) To ensure very rapid solidification of the TiAl alloy in the permanent mold 1 or in the molds 3, 3, cooling channels 4 through which cooling liquid, for example water, can flow are provided in the permanent mold 1.

(18) To ensure that the molten TiAl alloy 9 can be introduced in a molten, superheated state into the permanent mold 1 and the molds 3, 3, the feeder 5 is provided with induction heating 8, with a coil arranged around a channel of the feeder 5, said channel being open in the upward direction, being provided for induction heating 8. The coil 8 enables the molten TiAl alloy 9 to be inductively maintained at temperature during its passage through the feeder 5 to the molds 3, 3.

(19) FIG. 2 shows the permanent mold 1 after horizontal centrifugal casting, with all molds 3, 3 being filled with the cast TiAl material and the semifinished TiAl cast parts being able to be taken out in the form of cones 10 and cylinders 11 and the permanent mold 1, which is shown later in another working example, being able to be disassembled into corresponding individual parts in order to be able to take out the semifinished TiAl cast parts.

(20) FIG. 3 shows the permanent mold 1 in a perspective view in which the individual molds 3, 3 and their spaced arrangement in the circumferential direction and longitudinal direction of the cylindrical permanent mold 1 can clearly be seen. In addition, it can be seen in FIG. 3 that a plurality of cooling channels 4 are arranged next to one another in the circumferential wall of the permanent mold 1 and run in the longitudinal direction of the permanent mold 1.

(21) FIGS. 4 to 7 show a further working example of the process according to the invention and the apparatus for producing centrifugally cast semifinished TiAl cast parts as precursors for the production of forged TiAl components. The second embodiment differs from the previous embodiment only in that differently shaped semifinished TiAl cast parts 12 are formed and the permanent mold 1 correspondingly has different molds 3. Instead of the cones and cylinders as are produced in the working example of FIGS. 1 to 3, a plurality of rings or tubes 12 (see FIG. 5) are formed in the working example of FIG. 4, with the corresponding molds 3 being formed by circumferential depressions in the permanent mold wall 1. Otherwise, the process and the apparatus of FIG. 4 do not differ further from the embodiment of FIG. 1, so that the identical components are provided with identical reference numerals and a repeated description of these identical components will be dispensed with.

(22) FIG. 7 shows, in a juxtaposition in subfigures a) to e), the course of the process of the invention in respect of centrifugal casting to produce semifinished TiAl cast parts as precursors for the forging of TiAl components from the semifinished TiAl cast parts.

(23) The subfigures a) to d) correspond to the depictions in FIGS. 4 to 6, with the commencement of centrifugal casting in which the feeder 5 fills the first row of the molds 3 with the material to be cast being shown in subfigure a), while in subfigure b), the feeder 5 has already been moved along the longitudinal axis 2 of the permanent mold 1 and fills the third row of molds 3 with molten TiAl alloy.

(24) Subfigure e) of FIG. 7 shows how the permanent mold 1 is made up of a plurality of parts, namely various ring segments 13 to 15 which are taken apart in order to take out the solidified semifinished TiAl cast parts in the form of rings 12. In the working example shown in FIG. 7e), each permanent mold 1 consists of an end plate 13 and a plurality of ring-shaped mold segments 14 and separator segments 15 which are arranged alternately next to one another so as to form the molds 3. In the working example shown in FIG. 7e), five molds for forming rings 12 are provided, although the permanent mold 1 can also be made longer with a larger number of ring segments 14, 15 in order to form a greater number of rings 12.

(25) FIG. 8 schematically shows a polished section to depict the microstructure of a semifinished TiAl cast part after centrifugal casting. It can be seen in FIG. 8 that the microstructure is formed by a plurality of colonies 16 of -titanium and -TiAl, with the -TiAl being present in the form of lamellae 18 in the colonies 16. The colonies 16 have an elongated shape and are embedded in a -titanium matrix 17 which additionally has lens-shaped -TiAl precipitates 19. The microstructure does not have any globular -TiAl grains and gives the material a tensile strength of from 650 to 800 MPa at a total elongation of from 0.2 to 0.9%. The microstructure is very close to the equilibrium phase composition at room temperature, with the deviation from the equilibrium phase composition at room temperature being only up to 10% by volume, preferably up to 8% by volume, of the microstructure.

(26) The semifinished TiAl cast parts produced by horizontal centrifugal casting are highly suitable for further processing to give forged TiAl components, as is shown in FIG. 9. In FIG. 9, the semifinished TiAl cast parts in the form of rings 12, as have been produced, for example, by the process shown in FIG. 7, are converted in a forge by means of appropriate forging tools 20, 21 into a forged TiAl component in the form of an annular disk 22 (see subfigure b) of FIG. 9) from which corresponding TiAl components 23 such as rotor blades or the like can be cut as per the depiction in FIG. 9c), as is indicated by the broken lines in FIG. 9c).

(27) Although the present invention has been described in detail for the working examples, it will be obvious to a person skilled in the art that the invention is not restricted to these working examples, but that modifications arrived at by leaving out individual features or by means of other combinations of features can be realized, as long as these do not go outside the scope of protection of the accompanying claims. The present disclosure encompasses all combinations of the present individual features.

LIST OF REFERENCE NUMERALS

(28) 1 Permanent mold 2 Longitudinal axis of permanent mold 3, 3, 3 Mold 4 Cooling channel 5 Feeder 6 Melting crucible 7 Heating device 8 Induction coil 9 Melt 10 Cone 11 Cylinder 12 Ring 13 End plate 14 Mold segment 15 Separator segment 16 Colony 17 Matrix 18 Lamellae 19 Lens-shaped precipitate 20 Forging tool 21 Forging tool 22 Disk 23 Component