Method for manufacturing turbomachine components, blank and final component

Abstract

The manufacture of a metal turbomachine part, comprising steps consisting of melting a titanium-aluminium intermetallic compound by plasma torch in a ring mould, extracting therefrom an ingot, as cast, in a state cooled from molten, cutting the ingot into at least one blank with an external shape that is simpler than the more complex one of said part to be manufactured, and machining the blank in order to obtain the part with said more complex external shape.

Claims

1. A method for manufacturing a plurality of elongated metal turbomachine parts, the method comprising: a) completely melting a titanium-aluminium intermetallic alloy, by plasma torch, and keeping it at a homogeneous temperature, then keeping the titanium-aluminium intermetallic alloy molten by plasma torch, in a ring mould, b) extracting from the ring mould an ingot, as cast, in a state cooled from molten, c) cutting the ingot into at least one blank, d) performing at least one of: dl) heat treating the at least one blank to obtain a duplex microstructure consisting of gamma grains and lamellar grains (alpha2/gamma), and d2) heat treating the at least one blank to prepare the at least one blank for a hot isostatic compacting and then carrying out such a hot isostatic compacting, and e) machining the at least one blank in order to obtain, from said at least one blank, said plurality of elongated metal turbomachine parts, wherein the plurality of elongated metal turbomachine parts are disposed parallel with respect to each other.

2. The method of claim 1, wherein said step d) includes performing said steps dl) and d2) so that a TiAl alloy with gamma grains having a composition containing between approximately 47 and 49 percent aluminium (at %) undergoes, at said step d2): said heat treatment by heating to a temperature of approximately 1038 C. to 1149 C., for a period of approximately 5 to 50 hours, then said hot isostatic compacting (HIC) at a temperature of between 1185 C. and 1204 C.

3. The method of claim 2, wherein said hot isostatic compacting of step d2) is followed by another heat treatment at a temperature of between approximately 1018 C. and 1204 C.

4. The method of claim 1, wherein: the cut blank produced in step c) has a given external volume A1, each elongated turbomachine part produced in step e) has a given external volume A2, and A2/A1 is greater than 0.95.

5. The method of claim 1, wherein the at least one cut blank produced at step c) represents more than 95% of at least one of the external volume and the mass of the extracted ingot.

6. The method of claim 1, wherein step b) of obtaining an ingot comprises the obtaining of a cylindrical or polyhedral ingot.

7. The method of claim 1, wherein, at step b), the extracted ingot has a diameter of less than or equal to 200 mm, or a cross section of less than approximately 3210.sup.3 mm.sup.2.

8. The method of claim 1, wherein the titanium-aluminium intermetallic alloy comprises 48% Al 2% Cr 2% Nb (at %).

9. The method of claim 1, wherein: said step d) includes performing said step d1) so that said titanium-aluminium intermetallic alloy has the gamma grains and a composition containing between approximately 47 and 49 percent aluminium (at %), and heat treating the at least one blank includes: - performing a first heat treatment by heating the at least one blank to a temperature of approximately 1038 C. to 1149 C., for a period of approximately 5 to 50 hours, and - performing a second heat treatment by heating the at least one blank to a temperature of between approximately 1018 C. and 1204 C., without hot isostatic compression.

10. The method of claim 1, wherein: the cut blank produced in step c) has a given mass Al, each elongated turbomachine part produced in step e) has a given mass A2, and A2/A1 is greater than 0.95.

11. The method of claim 1, wherein at step a) the titanium-aluminium alloy is completely melted in various vessels and refining hearths above each of which are disposed at least one of multiple plasma torches.

12. The method of claim 1, wherein at step a) a succession of complete meltings of the titanium-aluminium alloy is carried out.

13. The method of claim 1, wherein the at least one blank cut from the ingot at step c) has a length (L2) of less than 300 mm.

14. The method of claim 1, wherein the at least one blank cut from the ingot at step c) has a length (L2) between 220 mm and 240 mm.

15. The method of claim 1, wherein the ingot extracted at step b) has a diameter of less than or equal to 200 mm, or a cross section of less than approximately 3210.sup.3 mm.sup.2 and the at least one blank cut from the ingot at step c) has a length (L2) of less than 300 mm.

16. A method for manufacturing at least one metal turbomachine part, the method comprising: a) completely melting a titanium-aluminium intermetallic alloy, by plasma torch, and keeping it at a homogeneous temperature, then keeping the titanium-aluminium intermetallic alloy molten, by plasma torch, in a ring mould, b) extracting from the ring mould an ingot, as cast, in a state cooled from molten, c) cutting the ingot into at least one blank, d) performing at least one of: dl) heat treating the titanium-aluminium intermetallic alloy to obtain a duplex microstructure consisting of gamma grains and lamellar grains (alpha2/gamma), and d2) heat treating the titanium-aluminium intermetallic alloy to prepare the titanium-aluminium alloy for a hot isostatic compacting and then carrying out such a hot isostatic compacting, and e) machining the at least one blank in order to obtain, from said at least one blank, said at least one metal turbomachine part.

17. The method of claim 16, wherein at step a) the titanium-aluminium alloy is completely melted in various vessels and refining hearths above each of which are disposed at least one of multiple plasma torches.

18. The method of claim 16, wherein at step a) a succession of sftid-complete meltings of the titanium-aluminium alloy is carried out.

19. The method of claim 16, wherein the at least one blank cut from the ingot at step c) has a length (L2) of less than 300 mm.

20. The method of claim 16, wherein the at least one blank cut from the ingot at step c) has a length (L2) between 220 mm and 240 mm.

21. The method of claim 16, wherein the ingot extracted at step b) has a diameter of less than or equal to 200 mm, or a cross section of less than approximately 3210.sup.3 mm.sup.2 and the at least one blank cut from the ingot at step c) has a length (L2) of less than 300 mm.

22. The method of claim 16, wherein: the cut blank produced in step c) has a given external volume A1, each elongated turbomachine part produced in step e) has a given external volume A2, and A2/A1 is greater than 0.95.

23. The method of claim 16, wherein: the cut blank produced in step c) has a given mass Al, each elongated turbomachine part produced in step e) has a given mass A2, and A2/A1 is greater than 0.95.

24. A method for manufacturing at least one metal turbomachine part, comprising steps: a) melting a titanium-aluminium intermetallic alloy and keeping it at a homogeneous temperature by means of multiple plasma torches, then keeping the titanium-aluminium intermetallic alloy molten by plasma torch in a ring mould, b) extracting from the ring mould an ingot, as cast, in a state cooled from molten, c) cutting the ingot into at least one blank having a length of less than 300 mm, d) performing at least one of: dl) heat treating the titanium-aluminium intermetallic alloy to obtain a duplex microstructure consisting of gamma grains and lamellar grains (alpha2/gamma), and d2) heat treating the titanium-aluminium intermetallic alloy to prepare the titanium-aluminium intermetallic alloy for a hot isostatic compacting and then carrying out such a hot isostatic compacting, and e) machining the at least one blank in order to obtain, from said at least one blank, said at least one metal turbomachine part.

Description

(1) Other advantages and features of the invention will also emerge from a reading of the following description given by way of non-limitative example and with reference to the accompanying drawings, where FIGS. 1 and 2 are dimensionally precise and correspond to industrial reality, like dimensioned drawings, and in which:

(2) FIG. 1 shows schematically a PAM fusion furnace from which an ingot is extracted,

(3) FIG. 2 is a schematic view in perspective of a block of material, or blank, issuing from a rough cut of the ingot extracted,

(4) and FIG. 3 is a table that presents and compares these cases of manufacture of a metal part in accordance with those mentioned above, intended for a turbomachine, in particular a movable turbine wheel blade of an aircraft turbojet engine or turboprop engine.

(5) In the left-hand column in FIG. 3, the steps are listed involving remelting, with lost-wax moulding (temporary mould), of a rough ingot issuing from melting (other than PAM), at the initial step.

(6) In the central column the steps also involving remelting are listed, with moulding in a centrifuged mould (permanent mould), of a rough ingot issuing from melting (other than PAM), at the initial step.

(7) And in the right-hand column the steps of the present invention are listed without moulding or necessarily remelting, after a rough ingot issuing from PAM melting has been obtained at the initial step.

(8) Thus: in the lost-wax casting prior art, the following steps are successively carried out: obtaining a rough ingot issuing from melting, and then production of wax models, then assembly of a wax cluster, then moulding of the shell, then firing the shell, then dewaxing of the shell, then remelting of the ingotcasting of the metal, then the mould is broken, then cutting the remelted ingot obtained into blanks, then heat/optionally HIC treatment, then dimensional check and machining; in the centrifugal permanent mould prior art, the following steps are successively carried out: obtaining a rough ingot resulting from melting, then remelting an ingotcasting the metal in a permanent mould, then cutting the remelted ingot obtained into a blank, and then HIC heat treatment and machining; the invention prior art, the following steps are successively carried out:

(9) obtaining a rough ingot resulting from PAM melting, then cutting the remelted ingot obtained into a blank, and then heat treatment/optionally HIC and machining.

(10) The solution in the favoured example in the right-hand column therefore consists of limiting the manufacture of this part to four steps making provision for:

(11) a) initially casting a TiAl intermetallic compound in a ring mould (or PAM furnace), with melting by plasma torch,

(12) b) extracting therefrom an as-cast ingot, in a state cooled from molten,

(13) c) cutting the ingot into at least one blank with a simpler external shape than the more complex one of said part to be manufactured,

(14) d) machining the blank in order to obtain the part with said more complex external shape.

(15) As shown schematically in FIG. 1, the PAM melting 1 is here carried out with a material 3 that is TiAl, in this case 48-2-2 TiAl, therefore comprising 48% AI 2% Cr 2% Nb, at %). This raw material is introduced by means of a wide channel 5 where the material is poured, as shown in FIG. 1. A series of plasma torches 7 melt the metal provided and then keep it molten. There is at least one such torch above each vessel or receptacle 9 and refining hearth 11a and then 11b, with its beam such as 8 directed towards the metal in the vessel or hearth. The circulation (see arrows) of the metal bath is done from vessel to vessel. The flow of the material and the stirring of the liquid make it possible to prevent problems of segregation and the presence of any inclusion of heavy metals (high density inclusionHDI), these problems being well known in the conventional technology of a VAR (vacuum arc remelting) remelting arc furnace. It is thus possible to consider a single melting, whereas by the VAR method two or even three successive meltings (referred to as remeltings) are necessary. The PAM technique also makes it possible to limit the appearance of alpha-phase inclusions (hard phase inclusionHPI).

(16) A last plasma torch 70, placed above a final mould or vessel, keeps the top of the bath arriving from the tanks 11a and then 11b molten therein. This final vessel is in the form a ring mould 13. The ring mould 13 comprises a bottom 13a that is retractable or movable, for example axially, here with controlled vertical movement. The ring mould 13 is cold, typically cooled from outside, for example with water, via cooling means 15. Under its bottom opening 13b and here by lowering of the movable bottom 13a, the bottom of the bath flows, by gravity or other, then sufficiently cold to form an ingot 17, as cast, in this state cooled from molten. The ring mould 13 may be made from copper.

(17) By using the various vessels 9, multiple refining hearths, such as here 11a, 11b, and then the ring mould 13, with plasma torches 7, 70 also multiple and placed above each of these receptacles, the travel of the material will be optimised, so as to completely melt it and to keep it therein at a substantially homogenous temperature. Reducing the number of inclusions or non-molten parts will also be possible by using, as illustrated, a plurality of overflow tanks. To guarantee an even greater quality, it will also be possible to make provision for carrying out successive meltings of the material.

(18) Typically, the ingot 17 obtained will be substantially cylindrical or polyhedral.

(19) In order to assist compliance with the requirements of a bar or ingot 17 intended for direct machining, and therefore with neither any intermediate moulding nor the conventional drawbacks of lost-wax founding (casting) (defects resulting from interactions with the mould, which is typically made from ceramic), or other defects characteristic of producing by casting in centrifugal permanent moulds (central shrinkage and chemical macrosegregation, in particular), it is here proposed to cast ingots of small sizes, in particular such that each ingot 17 extracted has a transverse dimension d (diameter or width for a square cross section) less than or equal to 200 mm, and preferably 120 mm, or, in cross section, less than approximately 3210.sup.3 mm.sup.2 and 1210.sup.3 mm.sup.2 within 5%, respectively.

(20) It is next from such an as-cast ingot that one and preferably a plurality of blanks 21 will be directly cut (by basic tools), each with a simple shape, in particular once again substantially cylindrical or polyhedral and in any case with an external shape simpler than the more complex one of each of said parts to be manufactured, the result of the machining of each blank, such as the two blades 19a, 19b that can be seen by transparency in the blank 21 of FIG. 2, aiming at a maximum use of the material.

(21) This objective and a search for optimisation of the manufacturing processes in particular of turbine blades, with shortening of the cycle times, has moreover led to preferring: that each blank 21 issuing from the ingot 17 should have a length L2 of less than 300 m, preferably between 220 mm and 240 mm, and a cross section S (perpendicular to its length L2) of less than 1210.sup.3 mm.sup.2 within 5% (that is to say 1.2 dm.sup.2), that at step c) all the cut blanks 21 represent more than 95% of the external volume and/or of the mass of the ingot 17 extracted, and/or: that at step c) the cut blank 21; that is to say therefore the block from which the part of step d) (blade such as 19a or 19b) is to be machined, should have a determined external volume and/or mass, referred to as A1, that at this step d) the machined part 19a or 19b should have a given external volume and/or mass, referred to as A2, and that the ratio A2/A1 is greater than 0.95 and less than 1.

(22) From a reading of the above table it will moreover have been clear that, between the step of cutting the ingot into blanks and the machining of each blank, preferably heat treatment (in a single sequence or multiple sequences) of each of these blanks will occur.

(23) As already indicated, one aim will be to thereby assist the achieving of the expected mechanical and microstructure criteria.)

(24) In fact, it is recommended carrying out: a heat treatment so that the material of the blank has a duplex microstructure consisting of gamma grains and lamellar grains (alpha2/gamma), and/or heat treatment for preparation for HIC (hot isostatic compacting) and the HIC (to close the porosities again).

(25) One aim being therefore to obtain a duplex microstructure (intermetallic compound) consisting of gamma grains and lamellar grains (alpha2/gamma), and it is in practice advised to proceed as follows (with values supplied within 5%): a TiAl alloy with gamma grains, in particular the aforementioned one issuing from the PAM furnace 1, typically having a composition containing between approximately 47 and 49 percent aluminium (at %), undergoes heat treatment at a temperature from approximately 1035 C. to approximately 1150 C., for a period of approximately 5 to approximately 50 hours, then it undergoes another heat treatment at a temperature of between approximately 1000 C. and 1220 C.

(26) Between the two steps of this heat treatment, the material will also have been able to undergo hot isostatic compression (HIC) at a temperature of approximately 1200 C., preferably between 1185 C. and 1204 C.