Production process for TiAl components

Abstract

The present invention relates to a process for producing a component, in particular a component for a turbomachine, composed of a TiAl alloy, which comprises the following: introduction of a powder of the TiAl alloy into the capsule whose shape corresponds to the shape of the component to be produced and closing of the capsule, hot isostatic pressing of the capsule together with the powder, heat treatment of the hot isostatically pressed capsule, removal of the capsule, post-working of the contour of the component by removal of material.

Claims

1. A process for producing a component of a TiAl alloy, wherein the process comprises: introduction of a powder of the TiAl alloy into a capsule whose shape corresponds to a shape of the component to be produced and closing of the capsule, hot isostatic pressing of the capsule together with the powder, heat treatment of the hot isostatically pressed capsule, removal of the capsule, post-working of a contour of the component by removal of material.

2. The process of claim 1, wherein the powder has been produced by a process which comprises at least one of the following: pressing of starting materials or melting of prealloys which consist of or comprise components to be alloyed, melting of the alloy by one or more of single or multiple plasma arc melting (PAM), vacuum arc remelting (VAR), vacuum induction melting (VIM), atomization of the alloy to produce the powder from a melt bath or with the aid of a cast ingot, classification of powder fractions and selection of one or more powder fractions having average or maximum particle diameters or maximum dimensions smaller than or equal to 150 m, and purification of the powder in a plasma purification process.

3. The process of claim 1, wherein the capsule is formed of titanium or a Ti alloy.

4. The process of claim 1, wherein the capsule is formed by at least two shaped parts.

5. The process of claim 1, wherein the capsule is overdimensioned relative to the component to be produced.

6. The process of claim 1, wherein the introduction of the powder is carried out under protective gas or under reduced pressure.

7. The process of claim 1, wherein the powder before introduction into the capsule or a filled but not yet closed capsule is subjected to a heat treatment under reduced pressure.

8. The process of claim 7, wherein cooling after the heat treatment is carried out at a cooling rate of from 25 C./min to 35 C./min down to a temperature of 120 C. or less.

9. The process of claim 1, wherein a packing density of the powder in the capsule is increased by mechanical excitation before or after closing of the capsule.

10. The process of claim 1, wherein the hot isostatic pressing is carried out in a temperature range of from 1100 C. to 1400 C. at a pressure of from 100 to 250 MPa for from 2 to 6 hours.

11. The process of claim 1, wherein the heat treatment of the hot isostatically pressed capsule comprises at least two of the following: a solution heat treatment at a temperature of up to 1400 C. for from 15 to 45 minutes, a high-temperature heat treatment at a temperature of from 1100 C. to 1300 C. for from 15 to 120 minutes and an aging heat treatment at a temperature of from 850 C. to 1100 C. for from 6 to 100 hours.

12. The process of claim 11, wherein the heat treatment of the hot isostatically pressed capsules comprises at least: a solution heat treatment at a temperature of up to 1400 C. for from 15 to 45 minutes, followed by a high-temperature heat treatment at a temperature of from 1100 C. to 1300 C. for from 15 to 120 minutes.

13. The process of claim 11, wherein the heat treatment of the hot isostatically pressed capsule comprises at least: a high-temperature heat treatment at a temperature of from 1100 C. to 1300 C. for from 15 to 120 minutes, followed by an aging heat treatment at a temperature of from 850 C. to 1100 C. for from 6 to 100 hours.

14. The process of claim 11, wherein the heat treatment of the hot isostatically pressed capsule comprises, in the following order: a solution heat treatment at a temperature of up to 1400 C. for from 15 to 45 minutes, a high-temperature heat treatment at a temperature of from 1100 C. to 1300 C. for from 15 to 120 minutes and an aging heat treatment at a temperature of from 850 C. to 1100 C. for from 6 to 100 hours.

15. The process of claim 1, wherein a net-shape component or near-net-shape component is produced by the hot isostatic pressing.

16. The process of claim 1, wherein the removal of the capsule is effected by at least one of chemical pickling, electrochemical treatment, mechanical working.

17. The process of claim 1, wherein the post-working of the contour is carried out by cutting machining and/or by electrochemical treatment.

18. The process of claim 1, wherein the process further comprises providing the component with one or more functional layers after the post-working of the contour of the component.

19. The process of claim 1, wherein the alloy comprises Ti and Al as main constituents together with one or more of up to 3 at. % W, from 0.2 to 0.35 at. % Si, up to 0.6 at. % C, up to 6 at. % Zr, up to 0.5 at. % Y, up to 0.3 at. % Hf, up to 0.5 at. % Er, up to 0.5 at. % Gd, up to 0.2 at. % B, from 4 to 25 at. % Nb, from 1 to 10 at. % Mo, from 0.1 to 10 at. % Co, from 0.5 to 3 at. % Cr, from 0.5 to 10 at. % V.

Description

WORKING EXAMPLE

(1) 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 making apparent to those of skill in the art how the several forms of the present invention may be embodied in practice.

(2) In a working example, a turbine blade of an aircraft engine composed of a highly alloyed TiAl alloy is made by the process of the invention, with a pressed body composed of powders of the individual elements to be alloyed and/or master alloys firstly being pressed in a first step. In addition, the pressed body can contain titanium sponge (process step I).

(3) The pressed body is subsequently (process step II) melted by means of a single plasma arc melting process so as to give an alloy melt. This is firstly cast and subsequently melted a second time in a third process step (process step III) for powder production in order to be able to carry out gas atomization from the melt bath. The gas atomization from the melt bath can be effected by VIGA or PIGA processes, with preferably spherical powder particles being produced by the gas atomization.

(4) In a fourth process step (process step IV), the particle size fractions desired for further processing, for example particle size fractions having maximum or average diameters of the particles in the range from 15 to 150 m or preferably from 45 to 125 m, are selected from the powder produced. In the case of the working example chosen, the particle size is maintained at 125 m in order to achieve a fine-grained microstructure.

(5) In a fifth process step (process step V), the selected powder fraction is introduced into a plasma so that purification of the powder particles and formation of spherical powder particles is effected by the plasma. For example, the occupation of the powder surface by oxygen is reduced and the surface shape is brought close to a spherical shape by the plasma.

(6) The powder which has been purified in this way is introduced under protective gas, for example helium or argon, into titanium capsules (process step VI) which have, for example, a wall thickness of from 1 to 2 mm and are formed by, for example, two deep-drawn titanium sheets so as to correspond to the shape of the component to be produced. The titanium material used for the capsules can be titanium grade I material.

(7) Before the capsule is closed by welding the capsule parts together in the ninth process step, a further purification of the material is carried out in a seventh process step (process step VII) by baking the capsule which has been filled with powder but not yet been closed at temperatures of up to 450 C. under vacuum conditions at a pressure of 10.sup.3 mbar, in particular 10.sup.5 mbar, in order to volatilize further impurities by evaporation. In this way, the oxygen content can be set to, for example, 600 ppm. From the baking temperature, the capsule which continues to be maintained under reduced pressure can be cooled to 120 C. or 100 C., with a cooling rate of 30 C./min being able to be selected (process step VIII).

(8) In the ninth process step (process step IX), the capsule is closed by welding so that the capsule together with the powder enclosed therein can be hot isostatically pressed at a pressure in the range from 100 to 240 MPa and a temperature in the range from 1150 C. to 1400 C. for a time of from 2 to 6 hours in the tenth process step (process step X).

(9) The hot isostatic pressing (process step X) is followed as eleventh process step (process step XI) by a multistage heat treatment by means of which the microstructure of the component can be adjusted. A solution heat treatment at 1400 C. or just below for a time of from 15 to 45 minutes is firstly carried out. A high-temperature heat treatment at from 1100 C. to 1300 C. is then carried out and, finally, an aging heat treatment at from 850 C. to 1100 C. for a time of from 6 to 100 hours is then carried out. The component is then finished in respect of the microstructure of the material and it is then merely necessary to carry out final work in respect of shaping of the component.

(10) For this purpose, the capsule is removed by corroding away the outer layer and/or electrochemical treatment, blasting with particles, in particular polymer particles, and/or by mechanical working such as milling, grinding or the like in a twelfth process step (process step XII).

(11) In a thirteenth process step (process step XIII), the excess material is then removed from the component by mechanical working, in particular cutting machining, for example by milling, grinding, polishing and the like. As an alternative, the removal of material can also be effected by electrochemical treatment so as to set the final dimensions.

(12) The microstructure which has been set in the component can be checked by X-ray diffraction and other nondestructive test methods. Furthermore, required layers such as corrosion protection layers, oxidation protection layers, wear protection layers and the like can be deposited on the component.

(13) Although the present invention has been described in detail with the aid of the working example, the invention is not restricted to this working example but instead it is possible to carry out modifications by leaving out individual features or implementing other combinations or features, as long as the scope of protection of the accompanying claims is not left. The present invention includes all combinations of the individual features presented.

(14) Although the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the particulars disclosed herein; rather, the present invention extends to all functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.