EP3109337B1 - Method for the preparation of tial forged components - Google Patents

Description

FIELD OF THE INVENTION

The invention relates to a method for producing forged components from TiAl alloys for turbomachines, such as stationary gas turbines or aircraft engines.

STATE OF THE ART

Components made of TiAl materials, which comprise titanium and aluminum as their main components, are very interesting for applications in which components have to be moved quickly, for example as blades of turbomachinery, since they have high strength at a low specific weight. However, such materials are difficult to process, since to achieve the desired property profile of the components, the materials must have a defined microstructure with a specific microstructure.

However, when casting TiAl materials, segregation and aluminum segregation can occur, resulting in an inhomogeneous microstructure. In addition, coarse structures can form, which adversely affect the mechanical properties.

From the DE 100 24 343 A1 It is known to produce a cylindrical semifinished product from a TiAl melt by centrifugal casting. A centrifugal casting apparatus for producing rings of a titanium alloy is known from US2004 / 0040690A1 known

DISCLOSURE OF THE INVENTION OBJECT OF THE INVENTION

Accordingly, it is an object of the present invention to provide a method for the production of TiAl components, which enables an efficient production of components made of TiAl alloys with a defined property profile and a desired microstructure, in particular forged TiAl components being provided for use in turbomachines should.

TECHNICAL SOLUTION

The above object is achieved by a method having the features of claim 1. Advantageous embodiments are the subject of the dependent claims.

The invention proposes to produce TiAl components from TiAl materials by forging, using as semifinished product for forging a TiAl cast semi-finished product which is produced by horizontal centrifugal casting. It has been shown that TiAl cast semi-finished products produced by horizontal centrifugal casting can advantageously be used for further processing by forging in order to provide TiAl components with a particularly advantageous property profile for use in turbomachines in a simple and efficient manner.

The horizontal centrifugal casting, which is to be used according to the present invention for the production of TiAl - cast semi-finished products for the subsequent forging, is characterized in that a mold, in which the melt of the material to be cast is filled and provides the corresponding shapes for the semi-finished products is rotated about a horizontal axis. Horizontal here means that the axis is aligned transversely, in particular perpendicular to the direction of gravity, with deviations by a few degrees in the context of technical implementation accuracy are allowed, ie, for example, deviations of up to +/- 10 °, preferably +/- 5 °. By means of horizontal centrifugal casting, high cooling rates can be achieved at high rotational speeds of the mold, so that segregations in the TiAl alloy can be avoided and a fine microstructure can be produced. In addition, material-saving semi-finished products can be produced with large wall thicknesses or semi-finished products in the form of cylinders and cones.

In the present invention, TiAl alloy is understood to mean a material comprising as its main components titanium and aluminum, so that they form the largest alloy constituents. In particular, it is understood as meaning materials which have intermetallic phases, such as α ₂ -Ti ₃ Al and γ-TiAl, and preferably also as constituents, which account for the largest part of a component made from such a material in terms of volume.

In particular, the TiAl alloy can be a so-called TNM alloy, which contains niobium and molybdenum as further constituents, since such alloys have particularly good mechanical properties for use in turbomachines. In particular, it can be a TNM alloy having the composition 43.5% by weight of aluminum, 4% by weight of niobium, 1% by weight of molybdenum and 0.1% by weight of boron and the remainder titanium and unavoidable impurities and / or alloy constituents with fractions of in each case <0.5% by weight up to a total amount of ≦ 5% by weight, in particular ≦ 2% by weight. The aluminum content of such an alloy may be in the range from 40 to 50% by weight, in particular 42 to 45% by weight, while the niobium content may be in the range from 2 to 6% by weight and in particular 3 to 5% by weight. Again, the molybdenum content may range from 0.5 to 2 weight percent, while boron may range from 0.05 weight percent to 0.15 weight percent.

The TiAl cast semi-finished product produced by horizontal centrifugal casting has the shape of a ring, since this form is a favorable starting material for the subsequent forging process.

The TiAl cast semi-finished product can be cast by centrifugal casting so that the corresponding shapes, namely rings, are produced as separate cast semi-finished products. Moreover, it is also possible to produce the desired semi-finished TiAl castings from a single casting or several castings by cutting, in particular cutting or machining. For example, it is possible to produce a cylindrical tube by horizontal centrifugal casting and then to divide this by mechanical separation processes, such as cutting, sawing, milling or the like into corresponding ring pieces and to use these ring pieces as TiAl - cast semi-finished products for subsequent forging.

By means of the horizontal centrifugal casting process, semi-finished TiAl castings in the form of rings with a length of 5 to 300 cm and / or wall thicknesses of 4 to 30 cm and / or internal diameters of 10 to 100 cm can be poured off as individual castings.

Due to the rapid cooling, which is possible by means of the centrifugal casting process, the cast semi-finished product can be produced with a microstructure which has colonies of .alpha.-titanium and .gamma.-TiAl in a .beta.-titanium matrix, where .beta -TiAl excretions may be present. The γ-TiAl precipitates in the β-titanium matrix can be lenticular and / or the colonies of α-titanium and γ-TiAl can have an elongated shape. Further, the γ-TiAl may be provided in the colonies in the form of fine fins.

The phase composition of the TiAl cast semi-finished product may already be close to the equilibrium phase composition at room temperature and may vary only up to 10% by volume, and more preferably up to 8% by volume, from the equilibrium composition at room temperature. This means that the cast semi-finished product has phases other than on the order of up to 10% by volume and up to 8% by volume, respectively, than should be the case for the equilibrium composition at room temperature.

After the TiAl cast semi - finished product has been produced by forging and optionally with at least one heat treatment, it is manufactured into a TiAl component or TiAl semifinished product which can only be produced by slight reworking into the desired TiAl component Post-processing, in particular the corresponding surface processing or deburring or Entkanten may include.

A TiAl cast semi-finished product in the form of a ring is forged to form an annular disk, from which corresponding blades for turbomachines are cut out.

To ensure that the TiAl melt is heated at a sufficiently high temperature, i. in an overheated state can be introduced into the mold, it is also proposed to provide an inductively heatable feeder in the apparatus for horizontal centrifugal casting, by means of which the melt is introduced into the mold. For inductive heating, the feeder can be surrounded by at least one coil.

The feeder may be embodied as an open-topped trough, which may be cooled by a fluid, such as water, and which may preferably be formed from copper, niobium or molybdenum materials. Copper, niobium or molybdenum materials are understood to mean those materials which contain copper, niobium or molybdenum as the main constituent.

The mold may be formed of a steel and / or copper and / or niobium material to allow rapid heat dissipation. Copper and niobium materials are in turn understood to mean materials which contain copper or niobium as the main constituent. To improve heat dissipation from the mold, the mold may also include suitable cooling channels for fluids such as water and the like.

BRIEF DESCRIPTION OF THE FIGURES

Fig. 1

eine Darstellung des horizontalen Schleudergussverfahrens zur Herstellung von kegelförmigen oder zylinderförmigen TiAl - Gusshalbzeugen,

Fig. 2

eine Schnittdarstellung einer Kokille nach dem Schleuderguss,

Fig. 3

eine perspektivische Darstellung der Kokille aus den Figuren 1 und 2,

Fig. 4

eine weitere Darstellung einer Schleudergussvorrichtung zur Durchführung eines Schleudergussverfahrens gemäß einer zweiten Ausführungsform der Erfindung,

Fig. 5

eine Schnittdarstellung der Kokille aus Figur 4 nach Beendigung des Schleudergusses,

Fig. 6

eine perspektivische Darstellung der Kokille aus den Figuren 4 und 5,

Fig. 7

eine Darstellung des Ablaufs des Schleudergussverfahrens in den Teilbildern a) bis e) bei der Ausführungsform, die in den Figuren 4 bis 6 dargestellt ist,

Fig. 8

eine schematische Darstellung des Gefüges eines TiAl - Gusshalbzeugs nach dem Schleuderguss und in

Fig. 9

eine Darstellung eines Schmiedeschritts zur Umformung eines Rings zu einer Scheibe.

The accompanying drawings show in a purely schematic manner in FIG

Fig. 1

a representation of the horizontal centrifugal casting process for the production of conical or cylindrical TiAl cast semi-finished products,

Fig. 2

a sectional view of a mold after centrifugal casting,

Fig. 3

a perspective view of the mold from the FIGS. 1 and 2 .

Fig. 4

a further illustration of a centrifugal casting apparatus for carrying out a centrifugal casting process according to a second embodiment of the invention,

Fig. 5

a sectional view of the mold FIG. 4 after completion of centrifugal casting,

Fig. 6

a perspective view of the mold from the FIGS. 4 and 5 .

Fig. 7

a representation of the process of the centrifugal casting process in the sub-images a) to e) in the embodiment shown in the FIGS. 4 to 6 is shown

Fig. 8

a schematic representation of the structure of a TiAl - cast semi-finished product after centrifugal casting and in

Fig. 9

an illustration of a forging step for forming a ring to a disc.

EMBODIMENTS

Further advantages, characteristics and features of the present invention will become apparent in the following detailed description of exemplary embodiments, wherein the invention is not limited to the corresponding embodiments.

The FIG. 1 shows a schematic sectional view of an apparatus and a method for centrifugal casting of semi-finished TiAl castings, from which subsequently by forming by forging TiAl - components are produced, which can be used in particular in turbomachines, such as aircraft engines.

The apparatus comprises a mold 1 having a plurality of molds 3, 3 'into which the casting material is filled. In the mold 1 of the embodiment, which in FIG. 1 is shown, it is in the forms 3, 3 'to molds for the production of cones and Cylinders, which are arranged along the longitudinal axis 2 of the mold 1 and along the peripheral wall of the mold 1 spaced from each other.

The mold 1 is in centrifugal casting, with which the molds 3, 3 'of the mold 1 are filled with appropriate molten liquid, rotated about the Kokillenlängsachse 2, so that the casting material, for. in the form of a TiAl alloy, which is molten introduced into the mold 1, by which centrifugal force is forced into the molds 3, 3 '.

The molten TiAl alloy 9 is provided from a crucible 6, which can be heated by a heater 7, wherein the molten TiAl alloy is introduced into the mold 1 via a feeder 5.

Again FIG. 1 can be seen, the feeder 5 is moved in the mold 1 along the longitudinal axis 2, so that successively arranged along the longitudinal axis 2 spaced molds 3, 3 'can be filled.

In order to ensure the fastest possible solidification of the TiAl alloy in the mold 1 or in the molds 3, 3 ', cooling channels 4 are provided in the mold 1 through which cooling liquid, such as water, can flow.

To ensure that the molten TiAl alloy 9 can be introduced in a molten, overheated state into the mold 1 or the molds 3, 3 ', the feeder 5 is provided with an induction heater 8, wherein a coil is provided for the induction heater 8 is, which is arranged around an upwardly open channel of the feeder 5. Through the coil 8, the molten TiAl alloy 9 can be held inductively at temperature on its way via the feeder 5 to the molds 3, 3 '.

The FIG. 2 shows the mold 1 after the horizontal centrifugal casting, wherein all molds 3, 3 'are filled with the cast TiAl material and the TiAl cast semi-finished products in the form of cones 10 and cylinders 11 can be removed, wherein the mold 1, as later in In another embodiment, can be decomposed into corresponding items to remove the TiAl - cast semi-finished products.

The FIG. 3 shows the mold 1 in a perspective view, in which case the individual forms 3, 3 'and their spaced arrangement in the circumferential direction and longitudinal direction of the cylindrical mold 1 can be clearly seen. In addition one recognizes in the FIG. 3 in that a plurality of cooling channels 4 are arranged side by side in the peripheral wall of the mold 1 and run in the longitudinal direction of the mold 1.

The FIGS. 4 to 7 show a further exemplary embodiment of the method according to the invention and the device not according to the invention for the production of centrifugally cast TiAl cast semi-finished products as a precursor for the production of forged TiAl components. The second embodiment differs from the previous embodiment only in that differently shaped TiAl cast semi-finished products 12 are formed and, correspondingly, the mold 1 has other shapes 3 "Instead of the cones and cylinders as used in the exemplary embodiment of FIGS FIGS. 1 to 3 are made according to the embodiment of the FIG. 4 a plurality of rings or tubes 12 (see FIG. 5 ), wherein the corresponding molds 3 "are formed by circumferential indentations in the mold wall 1. Moreover, the method or device differs according to FIG FIG. 4 not further compared to the embodiment of FIG. 1 so that the same components are given the same reference numerals and a repeated description of these identical components is omitted.

The FIG. 7 illustrates in a compilation in the diagrams a) to e) the sequence of the inventive method with respect to the centrifugal casting for the production of semi-finished Ti-Al casting as a precursor for the forging of TiAl - components from the TiAl - cast semi-finished products.

The partial images a) to d) correspond to the representations of FIGS. 4 to 6 , in the partial image a) the beginning of the centrifugal casting is shown, in which the feeder 5, the first row of molds 3 "filled with the casting material, while in the partial image b) the feeder 5 has already been moved along the longitudinal axis 2 of the mold 1 and fill the third row of molds 3 "with molten TiAl alloy.

The drawing e) of the FIG. 7 shows how the mold 1 is constructed of several parts, namely different ring segments 13 to 15, which are disassembled for removing the finished TiAl - cast semi-finished products in the form of rings 12. The mold 1 is in the illustrated embodiment of the invention FIG. 7 e) each of an end plate 13 and a plurality of annular mold segments 14 and separating segments 15, which are arranged alternately side by side so as to form the molds 3 " FIG. 7 e) five forms are provided for the formation of rings 12, wherein the mold 1 with more ring segments 14, 15 may be formed longer to form more rings 12.

The FIG. 8 schematically shows a micrograph to illustrate the microstructure of a TiAl - cast semi-finished product after centrifugal casting. In FIG. 8 is shown that the microstructure off a plurality of colonies 16 of α - titanium and γ - TiAl, wherein the γ - TiAl is in the form of lamellae 18 in the colonies 16. The colonies 16 are elongated and embedded in a β-titanium matrix 17, which additionally has lenticular γ-TiAl precipitates 19. The structure has no globular γ - TiAl grains and gives the material a tensile strength of 650 to 800 MPa with a total elongation of 0.2 to 0.9%. The microstructure is already very close to the equilibrium phase composition at room temperature, with the deviation from the equilibrium phase composition at room temperature only up to 10% by volume, preferably up to 8% by volume of the microstructure.

The TiAl cast semi - finished products produced by horizontal centrifugal casting are outstandingly suitable for further processing into TiAl forged components, as described in US Pat FIG. 9 is shown. According to the FIG. 9 For example, the TiAl cast semi-finished products are produced in the form of rings 12, as described, for example, in accordance with the method FIG. 7 in a forge with corresponding forging tools 20, 21 to a TiAl forging component in the form of an annular disc 22 (see drawing b) FIG. 9 ), from which according to the illustration in FIG. 9c) corresponding TiAl - components 23, such as blades or the like can be separated out, as indicated by the dashed lines in FIG. 9c) is indicated.

Although the present invention has been described in detail with reference to the embodiments, it will be understood by those skilled in the art that the invention is not limited to these embodiments, but rather modifications are possible in the manner that individual features omitted or other combinations of features can be realized as long as the scope of protection of the appended claims is not abandoned. The present disclosure includes all combinations of the subject features.

LIST OF REFERENCE NUMBERS

1

mold

2

Kokillenlängsachse

3, 3 ', 3 "

shape

4

cooling channel

5

Speiser

6

melting pot

7

heater

8th

induction coil

9

melt

10

cone

11

cylinder

12

ring

13

endplate

14

mold segment

15

separating segment

16

colony

17

matrix

18

lamella

19

lenticular excretion

20

forging tool

21

forging tool

22

disc

23

component

Claims (8)

1. Method for producing forged components from TiAl alloys, namely blades (23) for turbomachinery, in which method a melt (9) of a TiAl alloy is provided which is cast in a horizontal centrifugal casting process such that at least one TiAl cast semi-finished product (10, 11, 12) is produced, the TiAl cast semi-finished product being shaped to form a TiAl forged part (22) by means of forging, characterized in that the TiAl cast semi-finished product is in the shape of a ring (12) and is forged to form an annular disc (22) from which blades (23) for turbomachinery are separated.
2. Method according to claim 1, characterized in that the TiAl cast semi-finished product is produced by separating, in particular cutting or machining a casting.
3. Method according to claim 1, characterized in that the TiAl alloy is cast in a mold (1) to form a plurality of separate TiAl cast semi-finished products.
4. Method according to any of the preceding claims, characterized in that the TiAl alloy is cast to form a TiAl cast semi-finished product in the form of rings (12) having a length of 5 to 300 cm and/or wall thicknesses of 4 to 30 cm and/or internal diameters of 10 to 100 cm.
5. Method according to any of the preceding claims, characterized in that the TiAl alloy is a TNM alloy comprising components of niobium and molybdenum.
6. Method according to any of the preceding claims, characterized in that the TiAl cast semi-finished product has a microstructure formed by colonies (16) of α - Ti and γ - TiAl that are embedded in β - Ti.
7. Method according to any of the preceding claims, characterized in that the phase composition of the TiAl cast semi-finished product differs from the equilibrium phase composition at room temperature by up to 10 vol.%, in particular by up to 8 vol.%.
8. Method according to any of the preceding claims, characterized in that the TiAl cast semi-finished product is subjected to a plurality of shaping steps by means of forging and/or at least one heat treatment.

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