Manufacturing method of gamma / gamma' nickel-based alloy parts by hot forging

Abstract

The present invention relates to a method for the manufacture of a part made of a nickel-based alloy with a Y / Y' microstructure, in which at least one hot forging step is performed, characterized in that the temperature to which the part is heated in the forging step is maintained within a temperature range that is 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 difference of the hot forging temperature compared to the temperature to which the part is heated being less than 250°C, preferably less than 150°C.

Description

[Technical field]

[0001] The present invention relates to the field of manufacturing gamma / gamma prime alloy parts by means of hot forging tools.

[0002] The invention finds advantageous application in the field of aeronautics, in particular for the manufacture of turboshaft engine parts, such as high-pressure or low-pressure turbine disks or high-pressure compressor disks. [Background technology]

[0003] New nickel-based alloys with a gamma / gamma prime microstructure (such as Aubert & Duval's AD730® or Rene 65, selected by Safran Aircraft Engines for some of its engines) are traditionally used in aircraft components that are subject to extreme stresses during service.

[0004] Such alloys are selected, for example, by turboshaft manufacturers as components of the high or low pressure turbine disks or for the high pressure compressor disks of the latest generation aircraft engines.

[0005] More generally, these may be any turboshaft engine part for which it is desirable to increase its resistance to operating temperatures and mechanical stresses at those temperatures.

[0006] The forging method for these parts is a series of hot deformation steps (milling of billet, blank stamping, finish stamping, etc.) and heat treatment. Hot deformation is generally carried out in a hydraulic press using conventional hot forging tools heated up to 650℃ / 680℃.

[0007] These alloys have a very narrow range of forgeable temperatures due to the high content of the hardening phase γ'. During the pressing process, the parts are heated to temperatures of 1040°C-1070°C, and the surface temperature of the parts exceeds 800°C throughout the entire forging.

[0008] When manufacturing components using these alloys, two major problems must be overcome.

[0009] Cooling during travel between the furnace and press during the forging operation, or during contact with the cooler hot forging tool during forging, can cause cracks to appear on the surface which must be removed in a finishing operation after forging.

[0010] Furthermore, these alloys are sensitive to abnormal grain growth phenomena, which appear under very specific forging conditions and which lead to very significant localized coarsening of the grains, which must be avoided at all costs and which cause the components to be rejected, since their mechanical properties in these areas, in particular their fatigue resistance, are prohibitive with respect to the required specifications.

[0011] Various research efforts have been carried out on these subjects, and the treatment of these problems generally results in significant limitations on forging conditions.

[0012] Typically, this process allows for minimal deformation throughout the part during the forging operation.

[0013] Also, the proposed solutions usually require a larger material loading weight, on the one hand due to the anticipated material loss during finishing operations intended to eliminate forging cracks, and on the other hand to be able to comply with the minimum deformation criterion by avoiding the phenomenon of abnormal grain growth by adding material in certain areas.

[0014] As a result, additional machining operations are carried out before the heat treatment operation. Since the unmachined forged parts have a much larger mass, there is a risk that the heat treatment will not produce the required mechanical properties. Indeed, in these γ / γ' alloys, the static mechanical properties are highly dependent on the cooling rate during heat treatment. As the mass increases, this rate decreases and therefore the mechanical properties decrease.

[0015] Removal of cracks on raw forged parts, either by finish machining or machining before heat treatment, always involves certain checks to ensure complete removal of the crack. In fact, if residual surface cracks are present before heat treatment, they may propagate within the part during quenching. These additional checks incur additional costs. Summary of the Invention [Problem to be solved by the invention]

[0016] The aim of the present invention is to propose a technique for manufacturing γ / γ' alloy parts using hot press tools, which makes it possible to overcome the problems of abnormal grain growth and cracks, without the drawbacks of the complexity and weight of the solutions proposed so far.

[0017] In particular, one object of the invention is to propose a press forging technique that makes it possible to obtain parts without abnormal grain growth zones and with very few cracks, while reducing the amount of material and optimizing the weight of the part.

[0018] The present invention proposes to carry out the forging by designing a new forging range, which is at a lower temperature compared to the current ranges.

[0019] In fact, the inventors have discovered that it is possible to eliminate the phenomenon of abnormal grain growth on this type of alloy by carrying out the forging at a lower temperature, which makes it possible to get out of the abnormal growth range and therefore no longer runs the risk of degrading the microstructure of the part during forging. [Means for solving the problem]

[0020] To this end, according to one aspect, the invention proposes a method for the manufacture of a part made of a nickel-based alloy with a γ / γ' microstructure, in which at least one hot forging step is carried out, characterized in that the temperature to which the part is heated is maintained within a temperature range that is lower than the abnormal grain growth temperature range of the alloy, and that the hot forging tool is maintained at a temperature lower than the temperature of the part, the difference between this temperature and the temperature to which the part is heated being less than 325°C, preferably less than 250°C and more preferably less than 150°C.

[0021] By abnormal grain growth temperature of an alloy is meant herein and throughout the text the temperature at which small deformations in the conventional range of forging speeds do not produce abnormal grain growth, i.e., a burst grain size at least twice as large as the nominal grain size. In this regard, reference may be made to the article by Marie Agathe Charpagne.

[0022] "Evolutions de microstructure au cours du forgeage de l'alliage Rene65" -PSL Research University-Mines Paris Tech-https: / / pastel.archives-ouvertes.fr / tel-01764932

[0023] A snapshot of a burst crystal particle in a matrix of fine particles is shown in Figure 1. This snapshot is taken from the above paper (p. 151). The burst crystal particle corresponds to the white area in the center.

[0024] Therefore, the parts are forged at low temperatures to avoid entering the region of abnormal grain growth which degrades the microstructure.

[0025] This change in heating temperature is further accompanied by a change in the forging tool temperature, with the hot tool temperature (higher) reducing heat loss during tool / part contact, allowing the part to remain within its forgeability range and not crack.

[0026] The alloy is Udimet 720 TM may be also possible.

[0027] In a preferred embodiment, the alloy is of the Rene65 or AD730(R) type.

[0028] At least one blank forging or finishing step is carried out at a temperature in which the part is heated to the solvus temperature γ' of the alloy minus 80°C (+ / - 10°C) or less, in particular to 80°C or less, and the hot forging temperature is higher than 700°C, preferably higher than 750°C and less than 900°C, or even 850°C.

[0029] In a preferred embodiment, the difference compared to the heating temperature of the part is less than 150°C.

[0030] The heating temperature may advantageously be between 1000°C and 1025°C.

[0031] For example, the heating temperature of the part is not higher than 1025°C (especially Udimet720 when the alloy is Rene65 or AD730(R) whose solvus temperatures γ' are 1105°C and 1110°C, respectively). TM The solvus temperature γ' of is 1155°C.

[0032] The invention further relates to an aircraft turbine engine part manufactured using the proposed manufacturing method, in particular a high pressure turbine disk part, a low pressure turbine disk or a high pressure compressor disk.

[0033] The invention also relates to an aircraft turbine engine including such a component.

[0034] Other characteristics, objects and advantages of the invention will become apparent from the following description, which is purely illustrative and non-limiting and which must be read in conjunction with the accompanying drawings, in which: [Brief description of the drawings]

[0035] [Figure 1]A snapshot of a burst crystal particle. [Figure 2a] 1 shows a turbine disk manufactured using state of the art manufacturing methods. [Figure 2b] 1 shows a turbine disk manufactured according to the manufacturing method according to the present invention. [Diagram 3] 1 illustrates a schematic diagram of an example turbojet engine configuration; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0036] Nickel-based superalloy with γ-γ' microstructure The alloy used to manufacture the component is a nickel-based superalloy having a γ-γ' microstructure.

[0037] Nickel-based superalloys are usually composed of a γ-Ni face-centered cubic austenite type γ phase (or matrix) possibly containing substitutional additives in solid solution α (Co, Cr, W, Mo, Re) and a γ'-Ni3X type γ' phase (or precipitates) with X=Al, Ti or Ta. The γ' phase has a regular L12 structure, derived from the face-centered cubic structure, which coincides with the matrix, i.e. it has an atomic mesh very close to that of the matrix.

[0038] Due to its ordered nature, the γ' phase has the remarkable property of increasing mechanical resistance at temperatures up to about 800° C. The very strong coherence between the γ and γ' phases gives nickel-base superalloys very high mechanical resistance at high temperatures, which itself depends on the γ / γ' ratio and the size of the hardening precipitates.

[0039] The selected superalloy may be composed primarily of nickel, preferably with mass fractions of chromium, cobalt, aluminum, titanium and molybdenum, and particularly preferably with mass fractions of 15-17% chromium, 8-15.5% cobalt, 1.5-4% aluminum, 3-5.2% titanium, 2-4% molybdenum and 2-4.2% tungsten.

[0040] Superalloys can also contain carbon, zirconium, iron, and the like.

[0041] Typically, the alloys produced may be AD730(R), Rene65, by way of example only.

[0042] An example of mass composition is as follows (AD730(R)). Cr: 15%~17% Cobalt: 8% to 10% Mo: 2.5% to 3.5% W: 2.3%~3.3% Nb: 0.8% to 1.4% Ti: 3.2%~3.8% Al: 2% to 2.6% B: 0.005%~0.025% Zr: 0.01% to 0.05% Fe: 3% to 5% C: 0.005%~0.02% Mn<0.5%

[0043] Another example of mass composition is as follows (Rene65): Cr: 15.5%~16.5% Cobalt: 12.5% ​​to 13.5% Al: 1.95%~2.3% Ti: 3.55%~3.9% Mo: 3.8%~4.2% W: 3.8%~4.2% Nb: 0.6% to 0.8% B: 0.012%~0.02% Zr: 0.03% to 0.06% C: 0.005% to 0.011% Mn<0.1% Fe<1.2% Ta: Trace (max 1000ppm)

[0044] Other compositions are of course possible. The alloy is e.g. Udimet 720 TM and the composition is as follows:

[0045] UDIMET 720

[0046] [Table 1]

[0047] Hot forging tools Depending on the operation considered, i.e. billet grinding, blank stamping, finish stamping, etc., different hot forging tools may be provided.

[0048] Typically, the hot forging tool is mounted on a press with a press speed between 0.5mm / s and 20mm / s, and a pressure between 2000T and 60000T.

[0049] A possible press is, for example, a hot die forging press of the type described in patent FR 2 880 827.

[0050] The hot heating system maintains the temperature of the hot forging tool so that its contact surface with the part is permanently above 750° C. For this purpose, several systems may be provided: heating by heating rods immersed in the hot forging tool, induction heating via a peripheral heating system, heating by peripheral electrical resistors.

[0051] Forging examples The solvus temperature γ' is as follows: Rene65 or Udimet720 TM ·Udimet720 TM : 1155℃ AD730(R): 1110℃ ·Rene65: 1105℃

[0052] Especially for Rene65 and AD730(R) type alloys (but not Udimet720 TM (also in the case of ), forging can be carried out under the following conditions: Blank forging and finishing: Parts heating temperature: 1000℃~1040℃ Hot forging temperature: 750℃~900℃ · Maintains tool temperature under press

[0053] Preferably, the temperature to which the part is heated is more particularly between 1000°C and 1025°C.

[0054] Preferably, the hot forging temperature is more particularly between 800°C and 900°C.

[0055] Alternatively, the hot forging temperature is more particularly between 750°C and 850°C.

[0056] Other upstream forgings may be performed under different conditions as follows: ·Heating temperature: 1040℃~1060℃ · Temperature of stamping tool: 400℃~650℃. In the case of rolled blanks, this rolling operation is carried out in the conventional manner, and then the finish forging process is carried out under the above conditions.

[0057] Parts Examples The manufacturing method is used, for example, in the manufacture of aircraft turbine engine parts, in particular high-pressure or low-pressure turbine parts or high-pressure compressor parts.

[0058] Different tests can be performed on different types of parts produced. EXAMPLES

[0059] Example 1 In particular, a test campaign was carried out on the manufacture of crowns by circular blank rolling followed by low deformation stamping at temperatures between 1000°C and 1025°C using a Rene 65 type alloy.

[0060] The resulting crown is free of burst grains.

[0061] Significant differences were observed in terms of crack formation depending on the hot forging temperature at the contact surface with the part (heated flat pile hot forging tool), as shown in Figures 2a and 2b.

[0062] At a hot forging temperature of 650 °C (Fig. 2a), deep cracks (up to 1.5 mm) were observed over most of the circumference.

[0063] At hot forging temperatures above 750°C (typically above 850°C), there are no cracks in the crown (Figure 2b).

[0064] Example 2 Tests were also carried out on reduced-scale slugs that were heated to 1000°C–1025°C and forged in two low deformation operations using hot tools maintained at contact surface temperatures of 800°C–900°C. The slag was found to be free of burst grains and free of cracks.

[0065] Turbojet engine The dual flow turbojet engine 1 of FIG. 3 extends along an axis AA and includes a flow path for a primary flow, or primary flow path 2, and includes, from upstream to downstream in the direction of circulation of 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.

[0066] The disks of the low pressure compressor 3 are for example made of a titanium alloy, but all or part of the disks of the high and low pressure turbines and the disks of the last stage of the high pressure compressor may be manufactured according to a manufacturing method of the type described above.

Claims

1. A method for manufacturing a part made of a nickel-based alloy having a γ / γ' microstructure, comprising at least one hot forging step, characterized in that the temperature at which the part is heated during the forging step is maintained at a temperature lower than the abnormal grain growth temperature range of the alloy, the hot forging temperature is maintained at a temperature lower than the temperature of the part, and the difference between the hot forging temperature and the temperature at which the part is heated is less than 325°C.

2. The method according to claim 1, characterized in that the hot forging temperature is maintained at a temperature less than 150°C below the temperature at which the part is heated.

3. The alloy is Rene65, AD730(R) or Udimet720 ＴＭ The method according to claim 1, characterized in that it is of a certain type.

4. The method according to claim 3, characterized in that at least one blank forging or finishing step is performed at a temperature at which the part is heated to below the alloy's sorbus temperature γ' minus 80°C (+ / - 10°C), and the hot forging temperature is higher than 700°C (+ / - 10°C) and lower than 900°C (+ / - 10°C).

5. The method according to claim 4, characterized in that the heating temperature of the component is 1025°C (+ / - 10°C) or less.

6. The method according to claim 5, characterized in that the heating temperature of the component is 1000°C (+ / - 10°C) or higher.

7. The method according to claim 4, characterized in that the hot forging temperature is higher than 800°C.

8. The method according to claim 7, characterized in that the hot forging temperature is 850°C or higher.

9. An aircraft turbine engine component, particularly a high-pressure turbine disk, a low-pressure turbine disk, or a high-pressure compressor disk, characterized by being manufactured using the manufacturing method described in any one of claims 1 to 5.

10. An aircraft turbine engine characterized by including the component described in claim 9.

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