Method for producing a component of gamma—TiAl and component produced therefrom

Abstract

The present invention relates to a method for producing a component of a γ-TiAl alloy, in which, in a first step, a forging blank made of a γ-TiAl alloy is built up from a powder material by an additive method, and subsequently, in a second step, the forging blank is reshaped into a semi-finished product, wherein the degree of reshaping over the entire forging blank is high enough that, in a third step, the structure is recrystallized during a heat treatment. In addition, the invention relates to a component produced therefrom.

Claims

1. A method for producing a component of a γ-TiAl alloy, wherein a forging blank made of the γ-TiAl alloy is built up from powder material in a first step by an additive method, and subsequently the forging blank is reshaped into a semi-finished product in a second step, wherein, in a third step, the forging blank is subjected to heat treatment wherein recrystallization occurs during the heat treatment.

2. The method according to claim 1, wherein the third step of recrystallization occurs simultaneously with the second step, in a form of dynamic recrystallization during a heat reshaping, and/or the third step of recrystallization takes place after the second step of reshaping during a compression by hot isostatic pressing of the semi-finished product, combined with the heat treatment.

3. The method according to claim 1, wherein the additive manufacture takes place by electron beam melting.

4. The method according to claim 1, wherein the reshaping takes place in one step.

5. The method according to claim 1, wherein a form of the additively manufactured forging blank is selected wherein a substantially complete recrystallization of the reshaped semi-finished product occurs.

6. The method according to claim 1, wherein during the additive manufacture, the forging blank is produced with at least two regions of different chemical composition with a continually varying chemical composition over one region of the forging blank.

7. The method according to claim 1, wherein a different chemical composition is produced in the forging blank during the additive manufacture by burning off aluminum at different intensity during a melting of the powder.

8. The method according to claim 1, wherein after the third step of recrystallization, the semi-finished product is quenched from a recrystallization temperature.

9. The method according to claim 1, wherein the semi-finished product is post-processed mechanically, chemically, and/or electrochemically.

10. The method according to claim 1, wherein a blade or a blade segment having a plurality of blades is produced in one piece as the component.

11. The method according to claim 10, wherein regions in the blade root and/or at the blade edges are formed with a higher Al concentration than remaining blade regions.

12. The method according to claim 10, wherein, in a region of the blade root and/or of blade edges, a structure with a higher proportion of γ-TiAl grains is present than in remaining blade regions, wherein a structure having a completely lamellar structure is present in blade regions with higher creep loads than in other regions.

13. The method according to claim 1, wherein the component is formed as a blade or a blade segment of an aircraft engine or a gas turbine, wherein the component is produced from a γ-TiAl alloy, wherein the component does not have undesired textures and segregations.

14. The method according to claim 13, wherein the component has a length of at least 0.3 m.

15. The method according to claim 13, wherein the component has pre-defined regions with different or continuously varying chemical composition and/or pre-defined regions with completely lamellar structure.

Description

BRIEF DESCRIPTION OF THE DRAWING FIGURES

(1) In a purely schematic manner, in the appended drawings,

(2) FIG. 1 shows a γ-TiAl structure;

(3) FIG. 2 shows a duplex structure made of γ-TiAl grains and lamellar grains with alternating laminae of γ-TiAl and α.sub.2-Ti.sub.3Al;

(4) FIG. 3 shows a completely lamellar structure; and

(5) FIG. 4 shows a perspective representation of a rotating blade segment having two rotating blades.

DESCRIPTION OF THE INVENTION

(6) Further advantages, characteristics, and features of the present invention will become apparent in the following detailed description of the embodiment examples. Of course, the invention is not limited to these embodiment examples.

(7) In particular, the present invention can be utilized for producing components of turbomachines, such as stationary gas turbines or aircraft engines. For example, it is possible to produce blades, and in particular rotating blades, as well as blade segments having a plurality of blades, by the method according to the invention. For this purpose, first a forging blank is constructed from powder material by an additive method, such as, for example, selective laser melting or electron beam melting. As powder, γ-TiAl powder is used, which is formed, for example, by an alloy with a chemical composition containing 43.5 at. % aluminum, 4 at. % niobium, and 1 at. % Mo, with the remainder of titanium.

(8) The forging blank produced by the additive method has a form that is already close to the final form of the component to be produced, such as, for example, the blade or the blade segment. Of course, the form is selected such that in a subsequent reshaping step, the degree of reshaping over the entire forging blank is high enough that a recrystallization of the structure can occur.

(9) Correspondingly, after its additive manufacture, by means of drop forging in one single reshaping step, the forging blank is brought to a form that represents a semi-finished product of the component to be produced, which already to a great extent has the final contour of the component and only requires a surface processing or a slight adjustment in form for the final shaping of the component.

(10) After the production of the semi-finished product by reshaping, the thus-produced semi-finished product is subjected to a heat treatment, so that a recrystallization of the structure takes place. Due to the recrystallization, microsegregations that may arise during the additive manufacture, for example, due to the layer-by-layer formation of the forging blank, are completely eliminated, and the structure will be homogenized. The heat treatment can take place in the scope of a hot isostatic pressing (HIP) process, by means of which a compressing of the component can be achieved simultaneously, so that pores that may arise during the additive manufacture can be eliminated. It is also possible, of course, that a dynamic recrystallization already occurs in the reshaping of the forging blank into the semi-finished product during the hot reshaping.

(11) For establishing the desired structure, after the reshaping and/or the recrystallization heat treatment or the hot isostatic pressing, the semi-finished product is cooled in a suitable way, so that a desired structure is established. In particular, the establishing of the lamellar spacings in the lamellar regions of the structure can be influenced by a rapid cooling.

(12) Due to the production method employed, it is possible in a simple way to establish different structures in different regions of the component to be produced, so that the component can have different mechanical properties in different regions, even though it is formed in one piece. Therefore, the different requirements for the component can be fulfilled, in particular for blades or blade segments of turbomachines, by establishing different structures in different regions.

(13) For example, in the production of blades or blade segments, regions in the blade root and at the edges of the blade, which should have a ductility that is as high as possible and a good resistance to fatigue loading, are formed with high aluminum content, so that γ-TiAl structures are established for the most part, as this is shown, for example, in FIG. 1, in which γ-TiAl grains 1 are present exclusively in the structure shown. In contrast, in the blade body, where high creep resistances may be necessary, a fully lamellar-formed structure can be established, as is shown in FIG. 3. FIG. 2 shows a duplex structure with lamellar grains 2 and γ-TiAl grains 1.

(14) Establishing the different structure can be accomplished by varying the aluminum content. The aluminum content can be established during the additive manufacture by vaporizing (burning off) aluminum with varying intensity. During the additive manufacture, if the melt of the powder is brought to a higher temperature and/or kept for a longer time at a higher temperature, then more aluminum can be vaporized and the aluminum content can be varied over the forging blank despite the use of one and the same powder. Correspondingly, the formation of a graded microstructure is also possible by establishing a gradient of aluminum content over the component.

(15) In a perspective representation, FIG. 4 shows an example of a rotating blade segment 3 with two blades 4, which are arranged on an inner shroud with a common root 5. The ends of the blades 4 lying opposite to the root 5 are joined via an outer shroud 6. In such a component, aluminum-rich regions can be formed in the region of the root 5 and in the region of the outer shroud, as well as at the blade edges 7, so that structures with a high proportion of γ-TiAl can be established, whereas in the region of the blade element, a completely lamellar structure can be established by a lower aluminum content. For example, if there is a fracture of a blade element due to an impact of a foreign body in the region of the blade element that has a high creep resistance but a low ductility based on the completely lamellar structure, then, via the inner and outer shrouds 6, which have a higher ductility, the fractured parts of the blade 4 additionally join to the blade segment 3, so that possibly a total failure can be avoided.

(16) Although the present invention has been described in detail on the basis of the embodiment examples, it is obvious to the person skilled in the art that the invention is not limited to these embodiment examples, but rather that modifications are possible in a way such that individual features are omitted or other kinds of combinations of features can be made without departing from the protective scope of the appended claims. In particular, the present disclosure includes in it all combinations of the individual features shown in the different embodiment examples, so that individual features that are described only in conjunction with one embodiment example can also be utilized in other embodiment examples, or combinations of individual features that are not explicitly shown can also be utilized.