METHOD FOR PRODUCING A PREFORM FROM AN ALPHA+GAMMA TITANIUM ALUMINIDE ALLOY FOR PRODUCING A COMPONENT WITH HIGH LOAD-BEARING CAPACITY FOR PISTON ENGINES AND GAS TURBINES, IN PARTICULAR AIRCRAFT ENGINES

Abstract

A method for producing a preform from an + titanium aluminide alloy for producing a component with high load-bearing capacity for piston engines and gas turbines, in particular aircraft engines, by forging a blank, wherein the blank held in a manipulator and moved by the manipulator is subjected to merely partial forming by open-die forging by an open-die forging tool.

Claims

1. A method for producing a preform from an + titanium aluminide alloy for producing a component with high load-bearing capacity for piston engines and gas turbines, in particular aircraft engines, by forging a blank, wherein the blank held in a manipulator and moved by means of the manipulator is subjected to merely partial forming by open-die forging by means of an open-die forging tool.

2. The method according to claim 1, wherein the open-die forging is effected in the phase region.

3. The method according to claim 1, wherein the blank has a temperature in the range of 1070-1300 C. during the open-die forging.

4. The method according to claim 1, wherein an open-die forging tool made from a ceramic material is used.

5. The method according to claim 4, wherein an open-die forging tool made from a fiber-reinforced ceramic material is used.

6. The method according to claim 1, wherein open-die forging tools made from molybdenum are used and the open-die forging is effected under a protective gas atmosphere or under reduced pressure.

7. The method according to claim 1, wherein the blank and the open-die forging tool are heated during the open-die forging by means of a radiative heating unit, or in that the blank is heated by means of electrical current flowing through the blank.

8. The method according to claim 1, wherein the blank, before being introduced into the open-die forging tool, is heated by means of a heating unit, especially a radiative heater, or by means of electrical current flowing through the blank or by inductive means.

9. The method according to claim 1, wherein the blank is worked by the open-die forging in such a way that the longitudinal expansion is greater than the lateral expansion.

10. The method according to claim 1, wherein the longitudinal expansion achieved by the open-die forging is between 50%-100%.

11. The method according to claim 1, wherein the blank is worked by open-die forging only in a middle region, so as to leave a first free end section and a second end section, held in the manipulator, of another geometry or another diameter than the open-die-forged region.

12. The method according to claim 11, wherein, during the open-die forging operation, the first free end section is also formed by the open-die forging, but to a lesser degree than the middle region.

13. The method according to claim 1, wherein the blank is moved by means of the manipulator through the open-die forging tool in such a way that the die blocks over-forge a section forged in a preceding stroke, preferably by half.

14. The method according to claim 1, wherein the blank is rotated about its longitudinal axis by means of the manipulator.

15. The method according to claim 1, wherein an open-die forging tool having die blocks having a flat forging surface is used.

16. The method according to claim 1, wherein an open-die forging tool having die blocks having a concave-rounded forging surface is used.

17. The method according to claim 1, wherein an open-die forging tool having die blocks having a three-dimensionally twisted forging surface is used.

18. The method according to claim 1, wherein the alloy used is a TiAl alloy of the following composition (in atom %): 40%-48% Al, 2%-8% Nb, 0.1%-9% of at least one element that stabilizes the phase, selected from Mo, V, Ta, Cr, Mn, Ni, Cu, Fe, Si, 0%-0.5% B, and a residue of Ti and melting-related impurities.

19. The method according to claim 18, wherein the element present in the alloy that stabilizes the phase is Mo, V or Ta only or a mixture thereof.

20. The method according to claim 18, wherein the content of the element that stabilizes the phase is 0.1%-2%.

21. The method according to claim 20, wherein the content of the element that stabilizes the phase is 0.8%-1.2%.

22. The method according to claim 18, wherein a TiAl alloy of the following composition is used: 41%-47% Al, 1.5%-7% Nb, 0.2%-8% of at least one element that stabilizes the phase, selected from Mo, V, Ta, Cr, Mn, Ni, Cu, Fe, Si, 0%-0.3% B, and a residue of Ti and melting-related impurities.

23. The method according to claim 18, wherein a TiAl alloy of the following composition is used: 42%-46% Al, 2%-6.5% Nb, 0.4%-5% of at least one element that stabilizes the phase, selected from Mo, V, Ta, Cr, Mn, Ni, Cu, Fe, Si, 0%-0.2% B, and a residue of Ti and melting-related impurities.

24. The method according to claim 18, wherein an alloy of the following composition is used: 42.8%-44.2% Al, 3.7%-4.3% Nb, 0.8%-1.2% Mo, 0.07%-0.13% B, and a residue of Ti and melting-related impurities.

25. A preform produced by a method according to claim 1.

26. A method for producing a component with high load-bearing capacity from an + titanium aluminide alloy for piston engines and gas turbines, in particular aircraft engines, wherein a preform produced by the method according to claim 1 is formed in a one-stage forming step to a defined shape, with isothermal forming of the preform in the phase region with a logarithmic forming rate of 0.01-0.5 1/s.

27. The method according to claim 26, wherein the forming temperature in the phase region is 1070-1250 C.

28. The method according to claim 26, wherein forming is accomplished using tools made from a material of high heat resistance.

29. The method according to claim 28, wherein tools made from an Mo alloy are used.

30. The method according to claim 28, wherein the tools are protected by an inert atmosphere during the forming operation, or in that reduced pressure is employed.

31. The method according to claim 26, wherein the tools used for forming are actively heated.

32. The method according to claim 31, wherein the tools are inductively heated.

33. The method according to claim 26, wherein the preform is heated prior to the forming in an oven, by inductive means or by resistance heating.

34. The method according to claim 26, wherein forming is followed by a heat treatment of the formed component.

35. The method according to claim 34, wherein the heat treatment comprises recrystallization annealing at a temperature of 1230-1270 C.

36. The method according to claim 35, wherein the hold time during the recrystallization annealing is 50-100 min.

37. The method according to claim 36, wherein the recrystallization annealing is followed by cooling of the component down to a temperature of 900-950 C. within 120 s or less.

38. The method according to claim 37, wherein the component (13) is then cooled down to room temperature and then heated to a stabilization and relaxation temperature of 850-950 C., or in that the component, without prior cooling, is kept at a stabilization and relaxation temperature of 850-950 C.

39. The method according to claim 38, wherein the hold time at the stabilization and relaxation temperature is 300-360 min.

40. The method according to claim 38, wherein the component is then cooled down to a temperature below 300 C. at a cooling rate of 0.5-2 K/min.

41. The method according to claim 40, wherein the cooling rate is 1.5 K/min.

42. A component made from an + titanium aluminide alloy, especially for a piston engine, an aircraft engine or a gas turbine, produced by the method according to claim 26.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0061] In the drawing:

[0062] FIG. 1 a schematic diagram for illustration of the method of the invention for production of a preform and of the method of the invention for production of a finished component, and

[0063] FIG. 2 a schematic diagram of the blank before and in the course of open-die forging, of the preform and of the ready-forged component.

DETAILED DESCRIPTION OF THE INVENTION

[0064] FIG. 1 shows a flow diagram for illustration of the method of the invention for preform production and for finished component production. What is shown is a blank 1 in cylindrical form. This consists of an + titanium aluminide alloy of a composition as specified above. More particularly, the TiAl alloy contains an element that stabilizes the phase, preferably Mo, V or Ta, since the subsequent forming operations are effected in the phase region of the TiAl alloy.

[0065] The blank 1 is (see step a)) fixed in a program-controlled manipulator 2 or robot. In step a), it is first sent to a first heating unit 3, which may be an infrared radiator, an oven or an electrical heater. In this heating unit 3, the blank 1 is heated up to a temperature in the range of 1070-1330 C., i.e., therefore, a temperature at which a phase forms in the alloy structure.

[0066] On attainment of this temperature (see step b)), the blank 1 is moved by means of the manipulator 2 into an open-die forging apparatus 4 arranged adjacent to the heating unit 3. This open-die forging apparatus 4 has a forging tool 5 comprising a moving die block 6 and a fixed die block 7. The die blocks 6, 7 are preferably made from a ceramic, especially fiber-reinforced, material, such that open-die forging is possible under air. The open-die forging apparatus 4 is designed, for example, for a forging force of 10 t.

[0067] The open-die forging apparatus 4 has a dedicated heating unit 8, preferably an infrared radiator, by means of which it is possible to heat the blank 1 present between the die blocks 6, 7 and also the die blocks 6, 7 themselves during the forging operation, such that, in particular, the blank is kept at the appropriate forging temperature.

[0068] During the forging operation, the blank 1, as shown by the horizontal double-headed arrow, is moved in intermittent steps through the forging tool 5. At the same time, the die block 6 is raised in individual strokes and lowered onto the blank 1 for forging, and the blank is formed between the die blocks 6, 7. Between every two strokes, the blank 1 is moved by an increment by means of the manipulator 2. The movement is effected, for example, by half the width of the die blocks 6, 7 that have been designed with the same width, such that, with each stroke, the blank 1 is over-forged once again within half the region forged beforehand.

[0069] By means of the manipulator 2, the blank 1 is moved at least once in a direction through the open-die forging apparatus 4. If required, it is moved in the opposite direction for performance of a further forging cycle. During this movement, the blank 1 can also, if required, be rotated about its longitudinal axis in order to forge a twist or curves, etc.

[0070] The die blocks 6, 7 used may have a flat forging surface or a three-dimensionally shaped forging surface, for example concave-shaped forging surfaces or three-dimensionally twisted forging surfaces, in order to forge controlled geometries.

[0071] Step c) shows, for illustrative purposes, the situation during the forging operation. The blank 1 is accommodated between the two die blocks 6, 7, with the die blocks shown in the closed setting for illustrative purposes. It is clear that the blank 1 is being subjected to only partial forming, meaning that a first free end section 9 and a second end section 10, held in the manipulator 2, i.e. the manipulator jaws, is at rest, with the open-die-forged region 11 extending between them. These end sections 9, 10 serve to form the shroud band and the foot of a blade to be produced later, which is still to be discussed hereinafter.

[0072] Following on from step c), in enlarged form for illustrative purposes, the ready-forged blank, i.e. the open-die-forged preform 12, is shown. What are shown are the two end sections 9, 10 and the flat-forged middle region 11, from which, in the subsequent second forming step, the blade region is formed. This region 11 has already been altered in terms of its mechanical properties by the open-die forging; because of the multiple forging, it has a very fine microstructure, and any pores are inevitably closed. This is appropriate for the mechanical properties and also for the forming operation for production of the finished component.

[0073] This preform 12 is then processed further in a second isothermal forming step for production of a finished component 13 in the form of a turbine blade. This is shown in step d), where the preform 12optionally having been heated once again beforehand to the forging temperature in a heating unit (not shown)is introduced into a shaping second forging apparatus 19 having an upper part 14 and a lower part 15. An isothermal forging operation takes place here, in which the upper and lower parts 14, 15 are heated. The forging temperature here too is between 1070-1250; the forming is effected in the phase region.

[0074] However, the forming is effected here in an isothermal manner at a very slow forming rate; the logarithmic forming rate is in the range of 0.01-0.5 1/s. What effectively takes place is thus extrusion. The tools or molded parts 14, 15 used here are made from an Mo alloy, which is the reason why the forming is effected in a protective gas atmosphere. The forming tools are actively heated, preferably by inductive means.

[0075] The finished component is shown in step e), this being a purely schematic diagram. The component 13 is a turbine blade having a shroud band 16 and a foot 17, as is sufficiently well known. The middle region 18, i.e. the actual blade region, is correspondingly curved or twisted in a manner known per se.

[0076] The secondary forming operation shown in step d) is then followed by a heat treatment of the formed component 13, for example a recrystallization annealing at a temperature of 1230-1270, with a hold time between 50-100 min, after which the component is cooled down relatively quickly to a temperature in the range of 900-950. This is followed by a stabilization and relaxation annealing operation at a temperature in the range of 850-950, for which it is possible either to heat the component once again or for the prior cooling to already take place to this temperature range. The hold time here is about 300-360 min, after which the component is finally cooled to a temperature below 300 C. at a cooling rate in the range of 0.5-2 K/m in.

[0077] FIG. 2 shows, in an enlarged schematic diagram, the blank, the preform and the ready-forged component. Part a) of the figure shows the cylindrical blank directly after introduction into the open-die forging apparatus; the two die blocks begin the forming work.

[0078] Part b) of the figure shows the already partly formed blank. As shown, the ratio of die width (viewed in longitudinal direction of the blank) to the blank width is chosen such that there is primarily longitudinal expansion and only insignificant lateral expansion.

[0079] Part c) of the figure shows the ready-open-die-forged preform 12 with the end sections 9, 10 and the formed region 11. The preform is clearly much longer than the blank in the starting state.

[0080] This preform is then forged in the second forging apparatus 19 to near net shape in an isothermal manner by extrusion. What is shown is the turbine blade is forged from the region 11 with the blade and the shroud band 16 and the foot 17, both of which have been forged from the end sections 9, 10. Only at the edges are there burrs that still have to be removed.

[0081] While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.