This application is a National Stage of Application No. PCT/FR2017/051,475 filed Jun. 9, 2017, claiming priority based on French Patent Application No. 1655343 filed Jun. 10, 2016, the disclosures of each of which are incorporated by reference herein in their entireties.
The present invention concerns a process for manufacturing hafnium-containing nickel-based superalloys.
Nickel-based superalloys are already known in the state of the art.
The term “superalloys” refers to complex alloys which, at high temperature and pressure, exhibit very good resistance to oxidation, corrosion, creep and cyclic stresses (notably mechanical or thermal). A particular application of these superalloys is in the manufacture of parts used in aeronautics, such as turbine blades.
Superalloys can be hardened by a so-called “solutioning” treatment. Such treatment consists in heating the alloy to an appropriate high temperature, below the eutectic temperature, and maintaining this temperature long enough to homogenize the elemental concentrations of its constituents and control the size of the intermetallic precipitates. This optimizes the microstructural properties of the material.
In order to further improve the oxidation resistance of nickel-based superalloys, hafnium is deliberately added thereto. However, the presence of hafnium in the superalloy makes the complete or almost complete solutioning of the eutectics more difficult and leads to burn defects.
The objective of the invention is therefore to overcome the above-mentioned disadvantages of the state of the art and to propose a process for manufacturing a hafnium-containing nickel-based superalloy which produces a superalloy that retains the beneficial role of hafnium in improving oxidation and corrosion resistance but without having the disadvantages of difficult solutioning.
To that end, the invention concerns a process for manufacturing a hafnium-containing nickel-based single-crystal superalloy part.
In accordance with the invention, this process includes the following successive steps consisting in:
By virtue of these features of the invention, the superalloy obtained has improved mechanical properties thanks to an almost complete or improved solutioning of the eutectics while maintaining good resistance to oxidation and corrosion. The use of a layer of pure hafnium further enhances this oxidation resistance.
According to other advantageous and non-limiting features of the invention, taken alone or in combination:
The process in accordance with the invention consists, first, in manufacturing a nickel-based, non-hafnium-doped, single-crystal superalloy. “Non-hafnium-doped” means hafnium-free.
Table 1 below gives several preferential exemplary superalloys useful in the process in accordance with the invention. They are identified by the letters A to F. Other non-hafnium-doped nickel-based single-crystal superalloys may also be used.
The term “remainder” corresponds, for each superalloy, to the residual mass percentage to reach 100% with the various other components mentioned.
A part with a desired shape is then formed from such a superalloy, for example by casting or additive manufacturing.
Preferably, the resulting part is then subjected to a solutioning treatment, as described above in the introduction.
Preferably, this treatment consists of a first step of temperature increase until reaching a temperature of about 1100° C. for a period comprised between a few minutes and 4 hours, followed by a second step of temperature increase until reaching a temperature of about 1200° C. for a period comprised between a few minutes and 4 hours, and finally a third step of temperature increase until reaching a temperature of about 1300° C. for a period comprised between a few minutes and 4 hours.
A layer of hafnium, i.e. either a layer of pure hafnium (100 atomic % hafnium) or a layer containing at least 99.99 atomic % hafnium, is then deposited on the part thus manufactured. This layer is preferably nanocrystalline or microcrystalline. Preferably, this layer has a thickness comprised between 50 nm and 800 nm, more preferably comprised between 50 nm and 300 nm.
The deposition of this layer of hafnium can be carried out by physical vapour deposition (PVD), preferably by cathode sputtering. This allows good control of the deposited thickness.
Mention may also be made of the use of electron beam physical vapour deposition (EBPVD), evaporation, pulsed laser ablation or cathode sputtering. The latter technique has the advantage of allowing the formation of dense films of nanometric or micrometric thickness and having superior adhesion to the preceding layer than that obtained with other deposition techniques.
PVD is carried out inside an enclosure containing the part and one or more targets corresponding to the material(s) to be deposited, here notably hafnium. Under the application of a potential difference between the reactor walls and the target(s), a plasma is formed whose positive species are attracted to the cathode (target) and collide therewith. The atoms of the target(s) are sputtered and then condense on said part.
Preferably, the deposition conditions are as follows:
Ion bombardment is carried out for 10 to 30 minutes between −200V and 500V.
Deposition of the layer of hafnium can also be carried out by chemical vapour deposition (CVD).
Examples of chemical vapour deposition (CVD) techniques include:
Said part is then subjected to a hafnium diffusion treatment, so as to form, on the surface of said part, an interdiffusion layer in which hafnium is present.
Preferably, the diffusion treatment is carried out by placing the part coated with the layer of hafnium inside an enclosure, bringing it under vacuum or introducing within it an atmosphere containing a mixture of 95% by volume argon and 5% by volume helium, and then carrying out the heat treatment described below.
Preferably, this heat treatment comprises a phase of temperature increase until a temperature comprised between 500° C. and 1200° C. is reached, a phase of maintaining this temperature stage for a period of 1 hour to 4 hours and a cooling phase which consists in reducing the temperature inside the enclosure until it returns to room temperature.
The process in accordance with the invention has many advantages, which are listed below.
During the first step of the process, the production of a non-hafnium-doped nickel-based single-crystal superalloy and its use for manufacturing a part do not present difficulties.
In contrast, in the state of the art (hafnium-doped superalloy), the shaping of the part, notably by casting, resulted, during its solidification, in hafnium losses that differed according to the part's geometry or solidification time. Similarly, this part was at risk of oxidizing (formation of hafnium oxide). This is not the case with the process of the invention since there is no hafnium at this stage.
During the solutioning step, the homogenization of the part's components and the re-solutioning of the superalloy are optimal.
During chemical attacks carried out as part of the non-destructive testing of parts, there is no preferential attack of residual eutectics.
Finally, the subsequent deposition of the layer of hafnium and its diffusion result in the formation of a more robust part, with better mechanical strength via almost complete or improved solutioning of the eutectics and better resistance to oxidation and corrosion.
Number | Date | Country | Kind |
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1655343 | Jun 2016 | FR | national |
Filing Document | Filing Date | Country | Kind |
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PCT/FR2017/051475 | 6/9/2017 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2017/212195 | 12/14/2017 | WO | A |
Number | Name | Date | Kind |
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6419763 | Konter | Jul 2002 | B1 |
Number | Date | Country |
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0 718 420 | Jun 1996 | EP |
0 821 078 | Jan 1998 | EP |
1 010 774 | Jun 2000 | EP |
1 036 850 | Sep 2000 | EP |
1 447 457 | Aug 2004 | EP |
2 239 351 | Oct 2010 | EP |
Entry |
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International Search Report for PCT/FR2017/051475 dated Aug. 8, 2017 [PCT/ISA/210]. |
Preliminary Search Report for FR 1655343 dated Mar. 30, 2017. |
Number | Date | Country | |
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20190153591 A1 | May 2019 | US |