METHOD FOR PRODUCING A PART MADE OF A Y/Y' NICKEL-BASED ALLOY BY HOT FORGING

Abstract

The invention relates to a method for producing a part made of a nickel-based alloy with a Y/Y microstructure in which at least one hot-forging step is performed, which method is characterised in that the temperature at which the part is heated in the forging step is maintained within a temperature range lower than the abnormal grain growth temperature range of the alloy, the hot-forging temperature being maintained at a temperature lower than the temperature of the part, the hot-forging temperature being such that the difference compared with the temperature at which the part is heated is less than 250 C. and preferably less than 150 C.

Claims

1. A method for producing a part made of a nickel-based alloy with a / microstructure; the method comprising: a hot-forging step of hot-forging the part; wherein a temperature at which the part is heated in the hot-forging step is maintained within a temperature range lower than an abnormal grain growth temperature range of the nickel-based alloy; and wherein a hot-forging temperature is maintained at a temperature lower than the temperature at which the part is heated in the hot-forging step, and the hot-forging temperature being such that a difference between the hot-forging temperature and the temperature at which the part is heated in the hot-forging step is less than 325 C.

2. The method according to claim 1, wherein the hot-forging temperature is such that the difference between the hot-forging temperature and the temperature at which the part is heated in the hot-forging step is less than 150 C.

3. The method according to claim 1, wherein the nickel-based alloy is of Rene65, AD730 or Udimet720.

4. The method according to claim 3, wherein a blank forging or finishing step is performed at a temperature at which the part is heated equal to or lower than the solvus temperature of the nickel-based alloy minus 80 C. (+/10 C.), the hot-forging temperature being higher than 700 C. (+/10 C.) and less than 900 C. (+/10 C.).

5. The method according to claim 4, wherein the temperature at which the part is heated in the blank forging or finishing step is 1025 C. (+/10 C.) or lower.

6. The method according to claim 5, wherein the temperature at which the part is heated in the blank forging or finishing step is 1000 C. (+/10 C.) or higher.

7. The method according to claim 4, wherein the hot-forging temperature is higher than 800 C.

8. The method according to claim 4, wherein the hot-forging temperature is 850 C. or higher.

9. An aircraft high-pressure turbine disc, low-pressure turbine disc, or high-pressure compressor disc produced using the method according to claim 1.

10. An aircraft turbine engine comprising high-pressure turbine disc, low-pressure turbine disc, or high-pressure compressor disc according to claim 9.

Description

DESCRIPTION OF THE FIGURES

[0035] Other features, purposes and advantages of the invention will emerge from the description which follows, which is purely illustrative and non-limiting, and which must be read in conjunction with the appended drawings in which:

[0036] FIG. 1 is a snapshot of burst grains;

[0037] FIG. 2a illustrates a turbine disc produced using a production method in accordance with the state of the art;

[0038] FIG. 2b illustrates a turbine disc produced according to a production method in accordance with the invention;

[0039] FIG. 3 schematically illustrates an example of a turbojet engine structure.

DETAILED DESCRIPTION OF THE INVENTION

Nickel-Based Superalloys with - Microstructure

[0040] The alloy used for the production of the part is a nickel-based superalloy with - microstructure.

[0041] Nickel-based superalloys are typically composed of a phase (or matrix) of the y-Ni face-centered cubic austenitic type, possibly containing substitution additives in solid solution (Co, Cr, W, Mo, Re), and a phase (or precipitates) of the -Ni.sub.3X type, with X=Al, Ti or Ta. The phase has an ordered L12 structure, derived from the face-centered cubic structure, consistent with the matrix, that is to say having an atomic mesh very close thereto.

[0042] Due to its ordered nature, the phase has the remarkable property of having a mechanical resistance that increases with temperature up to about 800 C. The very strong coherence between the and phases gives nickel-based superalloys very high mechanical resistance when hot, which itself depends on the / ratio and the size of the hardening precipitates.

[0043] The chosen superalloy may be mainly composed of nickel and preferably have a mass fraction of chromium, cobalt, aluminum, titanium, molybdenum, and in particular preferably between 15 and 17% of chromium, between 8 and 15.5% of cobalt, between 1.5 and 4% of aluminum, between 3 and 5.2% of titanium, between 2 and 4% of molybdenum, between 2 and 4.2% of Tungsten.

[0044] The superalloy can also comprise carbon, zirconium, iron, etc.

[0045] Typically, as an example, the production alloy may be AD7300, Rene65.

[0046] An example of mass composition is as follows (AD730): [0047] Cr: 15% to 17%, [0048] Co: 8% to 10%, [0049] Mo: 2.5% to 3.5%, [0050] W: 2.3% to 3.3%, [0051] Nb: 0.8% to 1.4%, [0052] Ti: 3.2% to 3.8%, [0053] Al: 2% to 2.6%, [0054] B: 0.005% to 0.025%, [0055] Zr: 0.01% to 0.05%, [0056] Fe: 3% to 5% [0057] C: 0.005% to 0.02%, [0058] Mn<0.5%,

[0059] Another example of mass composition is still (Rene65) [0060] Cr: 15.5% to 16.5%, [0061] Co: 12.5% to 13.5%, [0062] Al: 1.95% to 2.3%, [0063] Ti: 3.55% to 3.9%, [0064] Mo: 3.8% to 4.2%, [0065] W: 3.8% to 4.2%, [0066] Nb: 0.6% to 0.8%, [0067] B: 0.012% to 0.02%, [0068] Zr: 0.03% to 0.06%, [0069] C: 0.005% to 0.011% [0070] Mn<0.1%, [0071] Fe<1.2% [0072] Ta: traces (1000 ppm max).

[0073] Other compositions are of course possible. The alloy can for example also be Udimet720 whose composition is as follows:

Udimet 720

TABLE-US-00001 Elements % Ni C Cr Co Ti Mo Al W Chemical Mini Base 0.006 16.00 14.00 4.95 2.75 2.45 1.10 composition Maxi 0.012 17.00 15.50 5.20 3.25 2.65 1.40 Elements % Zr B Fe Si Mn Cu P S Mini 0.025 0.010 Maxi 0.050 0.020 0.50 0.35 0.35 0.30 0.010 0.0020 Elements % O2 N2 Pb Ag Bi Chemical Mini composition Maxi 50 100 5 5 0.3 in p.p.m.

Hot-Forging Tools

[0074] Different hot-forging tools can be provided depending on the operations considered: crushing of the billet, stamping of the blank, finish stamping, etc.

[0075] Typically, the hot-forging tool is mounted on a press with press speeds comprised between 0.5 and 20 mm/s and pressures between 2000 and 60000 T.

[0076] A possible press is, for example, a hot die type forging press of the type described in patent application FR2880827.

[0077] A hot heating system maintains the temperature of the hot-forging tool so that its contact surface with the part is permanently above 750 C. Several systems can be provided for this purpose: heating by heating rods immersed in the hot-forging tool, induction heating via a peripheral heating system, heating by peripheral electrical resistors.

Examples of Forging

[0078] Solvus temperatures are as follows: Rene65, or Udimet720 [0079] Udimet720: 1155 C. [0080] AD730: 1110 C. [0081] Rene65: 1105 C.

[0082] In the case of alloys of the Rene65 and AD730 type, in particular (but also in the case of Udimet720), forging can take place under the following conditions:

Blank Forgings and Finishing:

[0083] Heating temperature of the part: between 1000 C. and 1040 C. [0084] Hot-forging temperature: between 750 C. and 900 C. [0085] Maintaining tools at temperature under the press

[0086] Preferably, the temperature at which the part is heated is more particularly comprised between 1000 C. and 1025 C.

[0087] Preferably, the hot-forging temperature is more particularly comprised between 800 C. and 900 C.

[0088] Alternatively, the hot-forging temperature is more particularly comprised between 750 C. and 850 C.

[0089] Other upstream forgings can be carried out under different conditions: [0090] Heating temperature: between 1040 C. and 1060 C. [0091] Temperature of the stamping tool: between 400 C. and 650C. In the case of rolled blanks, this rolling operation is carried out in a conventional manner, the finish forging steps are then carried out under the conditions indicated above.

Examples of Parts

[0092] The production method is used, for example, for the production of an aircraft turbine engine part, in particular a high-pressure turbine or low-pressure turbine part, or else a high-pressure compressor part.

[0093] Different tests were able to be carried out for the production of different types of parts.

Example 1

[0094] In particular, a test campaign was carried out for the production of crowns by circular blank rolling, then low-deformation stamping at a temperature comprised between 1000 C. and 1025 C. with a Rene65 type alloy.

[0095] The crowns obtained do not have any burst grains.

[0096] As illustrated in FIGS. 2a and 2b, significant differences in terms of crack formation were observed depending on the hot-forging temperature at the contact surface with the part (heated flat pile hot-forging tool).

[0097] For a hot-forging temperature of 650 C. (FIG. 2a), deep cracks could be observed (up to 1.5 mm) over a large portion of the circumference.

[0098] For a hot-forging temperature of 750 C. or higher (typically, 850 C. and higher), the crown does not have a crack (FIG. 2b).

Example 2

[0099] Tests were also conducted on reduced-scale slugs heated to between 1000 C. and 1025 C. and forged in two low-deformation operations, with hot tools at contact surface temperatures maintained between 800 C. and 900 C.

[0100] The slugs were found to have no burst grains and also no cracks.

Turbojet Engine

[0101] The dual-flow turbojet engine 1 of FIG. 3 extends along an axis A-A and includes a flow path for a primary flow or primary flow path 2 comprising, from upstream to downstream in the direction of circulation of the gas flow within the turbomachine, a low-pressure compressor 3, a high-pressure compressor 4, a combustion chamber 5, a high-pressure turbine 6 and a low-pressure turbine 7.

[0102] The discs of the low-pressure compressor 3 are for example made of titanium alloy, while all or part of the discs of the high-pressure and low-pressure turbines and the discs of the last stages of the high-pressure compressor can be produced according to a production method of the type described above.