A nickel-based additive manufactured product

Abstract

An additive manufactured product produced from a Nickel-based super-alloy powder is disclosed. The powder has a size between 15 and 105 µm and comprises at least the following components, by weight: 0,05-0,14% C, 15,0-22,5% Cr, 1.5-2,5% Mo, 3.5-4,6% Al, 9,0-11,0% Co, 0,01-2,2% Ta, 1,5-3,5% Ti, 2,0-4,0% W, the rest being Ni, wherein the additive manufactured product has secondary and tertiary γ' precipitation content up to 35% volume in the grain interior and the presence of M23C6 carbides at grain boundaries as well as the primary γ' precipitation. Additive manufactured turbomachinery components obtained by the super-alloy are also disclosed, the components being able to withstand high temperature and thermo-mechanical stresses.

Description

A NICKEL-BASED ADDITIVE MANUFACTURED PRODUCTDescriptionTECHNICAL FIELD[1] The present disclosure concerns a additive manufactured products produced from a metal alloy,in particular turbomachinery components that are subjected to high temperature and stresses. Exemplary components are statoric and rotoric parts of gas turbines and turboexpanders. Embodiments disclosed herein specifically concern additive manufactured products produced from a Nickel-based super-alloy powder through the so called Direct Metal Laser Melting (DMLM) technology.BACKGROUND ART[2] The components of internal combustion engines, such as the components of a gas turbine (e.g. buckets, nozzles, shrouds, combustion chambers) must be manufactured with metal alloys capable of withstanding extreme operating conditions, in particular very high temperature. This is particularly true for components that are located near the combustors, such as turbine nozzles, statoric shrouds and rotoric buckets. The temperature of the combustion gas at the first stage nozzles can be higher than 1100°C, while in the most downstream turbine stages the temperature can be as high as 700°C. Special high-temperature Nickel-based alloys are used to manufacture both statoric and rotoric components. These alloys are expensive but are required in view of the need to withstand the combined effect of high temperature and high static and dynamic stresses generated during the lifecycles of turbomachinery (e.g. start up, shot down, steady state regime).[3] Manufacturing of such components would take advantage of modern additive manufacturing techniques, such as DMLM (Direct Metal Laser Melting) technology. Additive manufacturing allows complex mechanical components to be manufactured starting from a file containing data on the shape of the final article to be produced, which data are directly used to control an energy source, such as a laser source or an electron beam, to selectively melt thin layers composed of tiny particles. The manufactured components obtained by means of this technology exhibit fine, dense and homogeneous characteristics.[4] However, in this field, Nickel-based super-alloys processed via DMLM can encounter several limitations associated to their mechanical strength and especially to the ductility in temperature combined with their oxidation resistance. Most of the Nickel-based powder super-alloys for additive manufacturing do not contain high levels of Aluminum and Titanium, which contribute to the alloy’s mechanical strength at high temperature and, as far as Aluminum is concerned, at the same time promotes good oxidation resistance at the higher temperatures, since these chemical species tend to limit the printability of the alloy powder leading to manufacts with poor structural integrity.[5] Accordingly, gas turbine components produced from a Nickel-based super-alloy, which shows good properties in terms of mechanical strength at high temperatures, ductility and creep properties would be welcome in the field.SUMMARY[6] In one aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a Nickel-based super-alloy with a good combination of mechanical properties and oxidation resistance.[7] In another aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a Nickel-based super-alloy with a relatively high Aluminum and Titanium content, guaranteeing good printability, i.e. a dense material free of defects (porosity and cracks). The high Aluminum and Titanium content favours and stabilises the formation of γ’ precipitates that contribute to the alloy's mechanical strength at high temperature. At the same time, the high Aluminum content promotes good oxidation resistance due to the surface formation of aluminum oxide (Al2O3) during operation at temperatures over 850°C.[8] A further aspect of the present disclosure is drawn to additive manufactured turbomachine components configured to withstand high temperature, pressure and stresses, composed of the previously identified Nickel-based super-alloys. Examples of components comprise but are not limited to gas turbine nozzles (with or without an internal cooling system), stator / rotor blades and gas turbine shrouds.BRIEF DESCRIPTION OF THE DRAWINGS[9] A more complete appreciation of the disclosed embodiments of the invention and many of the resulting advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig.1 illustrates an image of the microstructure of an additive manufactured product according to example 1 of the present disclosure; andFig.2 and Fig. 3 illustrates an image of the microstructure of an additive manufactured product according to example 2 of the present disclosure.DETAILED DESCRIPTION OF EMBODIMENTS

[10] According to one aspect, the present subject matter is directed to an additive manufactured product produced from a Nickel-based super-alloy, in particular machine components that are subjected to high temperature and stresses, wherein the components made of the identified alloy and processing technology show good properties in terms of mechanical strength at high temperatures, ductility, creep properties.

[11] According to one aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a Nickel-based super-alloy with a high amount of ’ forming elements (such as Aluminum and Titanium), i.e. with a secondary and tertiary γ’ precipitation content up to 35% volume in the grain interior and the presence of M23C6 carbides at grain boundaries as well as the primary γ’ precipitation, in order to increase the precipitation hardening effect, but keeping an appreciable gap between the solidus and ’ solvus temperature (necessary to optimize the size of precipitates via appropriate heat treatments). In particular, Titanium is a stabilizer for the ’ phase. According to most of the weldability charts available in the scientific literature, an alloy with a high amount of Al and Ti would not be printable without defects (e.g. cracks). Differently, the alloy of the present disclosure is strengthened by ’ phases as well as carbides (M23C6) located at grain boundaries.

[12] According to another aspect, the present subject matter is directed to an additive manufactured product produced from a Nickel-based super-alloy wherein the amount of Cr (between 15,4 and 22,4% by weight), Mo (between 0,01 and 2,0% by weight) and W (between 2,1 and 3,9% by weight), together with the greater possible reduction of Nb and Hf is chosen in order to limit the formation of tetragonal closed-packed (TCP) phases. This allows keeping the Co content below 20% by weight without impacting significantly the ’ solvus temperature, but still providing a solid solution hardening effect for the phase (matrix).

[13] According to still another aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a Nickel-based super-alloy wherein the Cr and Mo content were chosen to strengthen the phase (matrix) as well as to promote the formation of limited grain boundary carbides (M23C6), without encouraging the formation of TCP phases (e.g., phase).

[14] According to another aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a Nickel-based super-alloy wherein the Carbon content is constrained in a range chosen in order to allow grain boundary carbides formation without impacting the printability of the alloy. Grain boundary carbides have to some extent a positive effect of creep performance of the alloy. However, an excessive Carbon content leads to hot cracking formation during the printing process. This is due to the preferential segregation of Carbon atoms at grain boundaries during solidification.

[15] According to still another aspect, the present subject matter is directed to an additive manufactured product produced from a Nickel-based super-alloy wherein, in order to counterbalance the relatively low amount of Co and other -strengthening elements, refractory elements such as W were introduced in the alloy. A medium W content was considered to limit the formation of MC carbides during the printing process, thus ensuring a structural integrity of the as-printed microstructure (no cracks) and providing at the same time a solid solution strengthening effect for the phase. The amount, distribution and size of grain boundary carbides (M23C6) was such to avoid cracking while providing a strengthening effect especially for what regard creep properties. Noteworthy, being Co an increasingly expensive material, which extraction is mostly obtained from poor counties where miners usually work in absence of safety precautions, a low content of Co makes the alloy of the present invention socially and economically more sustainable.

[16] According to still another aspect, the present subject matter is directed to an additive manufactured product produced from a Nickel-based super-alloy wherein, in order to ensure a good oxidation resistance at high temperature, considering the relatively low Cr:Ti ratio (due to low Cr content), a relatively high Aluminum content was chosen to promote, beside ’ formation, also a compact Al2O3 protective layer when the alloy is exposed to temperatures as high as 850-900°C.

[17] According to yet another aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a Nickel-based super-alloy wherein the Nb content, despite its strengthening effect of the phase, leading to an increase of the APB theoretically evaluated hence the alloy strength, in our case was kept to a minimum since its presence is related to the formation of , and phases which are known to have negative effects on the mechanical performance of Nickel-based super-alloys.

[18] According to another aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a Nickel-based super-alloy wherein Mn, B, Si are kept to a minimum since their combination can have negative effects on the printability of the alloy (cracks formations during solidification).

[19] Finally, according to another aspect, the subject matter disclosed herein is directed to an additive manufactured product produced from a super-alloy that has the form of a powder with a size between 15 and 105 µm.

[20] Reference now will be made in detail to embodiments of the disclosure, one or more examples of which are illustrated. Each example is provided by way of explanation of the disclosure, not limitation of the disclosure. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure without departing from the scope or spirit of the disclosure. Reference throughout the specification to “one embodiment” or “an embodiment” or “some embodiments” means that the particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrase “in one embodiment” or “in an embodiment” or “in some embodiments” in various places throughout the specification is not necessarily referring to the same embodiment(s). Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

[21] When introducing elements of various embodiments the articles “a”, “an”, “the”, and “said” are intended to mean that there are one or more of the elements. The terms “comprising”, “including”, and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.

[22] In particular, an additive manufactured product produced from a Nickel-based super-alloy for high temperature applications according to the present disclosure comprises the following components, by weight: 0,05-0,14% C,15,0-22,5% Cr,1,5-2,5% Mo,3,5-4,6% Al,9,0-11,0% Co,0,01-2,2% Ta,1,5-3,5% Ti,2,0-4,0% W,the rest being Nickel. Additionally, the super-alloy can comprise up to 0,5% by weight of Fe and up to 0,1% by weight of B. Moreover, due to contamination, the super-alloy can additionally comprise one or more of the following components: P, S, N, O, Si, Cu, Mn, Nb, Hf and Zr. Preferably, the amount of Nb and Hf in the Nickel-based super-alloy is as low as possible. Typically, the amount of contaminants, as a weight percentage is the following: lower than 0,006% P, lower than 0,005% S, lower than 0,05% N, lower than 0,05% O, lower than 0,03% Si, lower than 0,01% Cu, lower than 0,1% Mn, lower than 0,05% Nb, lower than 0,05% Hf and lower than 0,05% Zr.Example 1

[23] A Nickel-based super-alloy for high temperature applications in turbomachinery was obtained, comprising the following components, by weight: 0,14% C, 15,7% Cr, 2,0% Mo, 4,0% Al, 9,6% Co, 0,1% Fe, 0,02% Ta, 1,5% Ti, 0,016% B, 3,9% W, Ni up to balance. An analysis of the super-alloy determined that, due to contamination, it also contained 0,01% Nb, 0,002% P, 0,002% S, 0,01% N, 0,007% O, 0,1% Si, 0,1% Cu, 0,1% Mn, 0,01% Hf, 0,04% Zr. Fig.1 illustrates an image of the microstructure of the super-alloy.

[24] The super-alloy was used for the production of statoric turbomachinery components. The super-alloy, after heat treatment, was subjected to tensile testing (according to ASTM E21-17) and creep testing (according to ASTM E139-11) at a temperature of 871°C. The results are summarized in the following table.Table 1Tensile PropertiesValues at 871°C0,2%YS (MPa)450UTS (MPa)560El. (%)5RoA (%)8The stress rupture life at 871°C and 300 MPa was tested to be of about 5 hours with an elongation to rupture between 1 – 2 %. The observed elongation-to-rupture measured both under tensile testing conditions as well as after stress rupture testing is determined by the higher volume fraction of secondary phases (e.g. carbides, borides and carbo-borides) formed at grain boundaries.Example 2

[25] A Nickel-based super-alloy for high temperature applications in turbomachinery was obtained, comprising the following components, by weight: 0,06% C, 15,7% Cr, 2,0% Mo, 4,4% Al, 9,5% Co, 0,1% Fe, 0,06% Ta, 1,8% Ti, 0,002% B, 3,9% W, Ni up to balance. An analysis of the super-alloy determined that, due to contamination, it also contained 0,01% Nb, 0,003% P, 0,002% S, 0,01% N, 0,01% O, 0,01% Si, 0,1% Cu, 0,01% Mn, 0,01% Hf, 0,01% Zr. Fig. 2 illustrates an image of the microstructure of the super-alloy. A lower secondary phases formation at grain boundaries, with respect to the Example 1, reduced the grain boundary pinning effect, thus allowing a further grain growth during the heat treatment (ASTM 4.5 against ASTM 4 for Example 1).

[26] The super-alloy was used for the production of both statoric and rotoric turbomachinery components. The alloy used to produce the nozzles, after heat treatment, was subjected to tensile testing (according to ASTM E21-17) and creep testing (according to ASTM E139-11) at a temperature of 871°C The results are summarized in the following table.Table 2Tensile PropertiesValues at 871°C0,2%YS (MPa)600UTS (MPa)670El. (%)19RoA (%)17The stress rupture life at 871°C and 300 MPa was tested to be around 33 hours with an elongation to rupture between 5 – 11 %. A significantly increased ductility under tensile testing conditions at high temperature is achieved. Similarly, a significantly higher elongation-to-rupture after stress rupture testing as well as a notably longer creep life under stress rupture test condition is achieved. Such increases are directly attributable to the lower, but still present, secondary phases formation at grain boundaries. In Example 2, a lower formation of carbides (M23C6) at grain boundaries along with precipitation of primary ’ contributed at increasing the creep strength of the alloy without weakening grain boundaries, therefore allowing accommodation of appreciable plastic strain before specimens’ breakage. Also, a lower formation of carbides at grain boundaries allowed for more solute elements (e.g., Cr, Mo, W, Ti, Ni, etc.) to be retained in the grain interior, thus further contributing at the strength of the alloy via both solid solution hardening of the phase and precipitation hardening (tertiary ’ phase formation close to the grain boundary in addition to the secondary ’ phase formed in the grain interior due to high Al and Ti content). An example of the microstructural features (around a grain boundary and in the grain interior) mentioned above is illustrated in Fig. 3, wherein carbides 10, primary ’ phase 11, secondary ’ phase 12 and tertiary ’ phase 13 are shown. These microstructural features lead to manufacture an alloy with tensile properties at 871°C, in particular yield strength and ultimate tensile strength (see table 2), above those of some additively manufactured Nickel-based super-alloys such as EOS NickelAlloy IN939 [https: / / www.eos.info / 03_system-related-assets / material-related-contents / metal-materials-and-examples / metal-material-datasheet / nickelalloy-inconel / material_datasheet_eos_nickelalloy_in939_premium_en_web.pdf] and Pear Micro ABD-850AM [https: / / www.aubertduval.com / wp-media / uploads / 2019 / 09 / ABD-850AM_PearlMicro_AM_V0_GB.pdf].

[27] While the invention has been described in terms of various specific embodiments, it will be apparent to those of ordinary skill in the art that many modifications, changes, and omissions are possible without departing form the spirt and scope of the claims. In addition, unless specified otherwise herein, the order or sequence of any process or method steps may be varied or re-sequenced according to alternative embodiments.

Claims

1. An additive manufactured product produced from a Nickel-based super-alloy powder with a size between 15 and 105 µm, the super-alloy comprising the following components by weight: 0,05-0,14% C,15,0-22,5% Cr,1,5-2,5% Mo,3,5-4,6% Al,9,0-11,0% Co,0,01-2,2% Ta,1,5-3,5% Ti,2,0-4,0% W,Ni up to balance,wherein the additive manufactured product has secondary and tertiary γ’ precipitation content up to 35% volume in the grain interior and the presence of M23C6 carbides at grain boundaries as well as the primary γ’ precipitation.

2. The additive manufactured product of claim 1, further comprising up to 0,2% Fe.

3. The additive manufactured product of claim 1 or 2, further comprising up to 0,1% B.

4. The additive manufactured product of one or more of the preceding claims, further comprising contaminants, including one or more of the following: P, S, N, O, Si, Cu, Mn, Nb, Hf, Zr.

5. The additive manufactured product of claim 4, wherein the amount of Nb is lower than 0,05% by weight.

6. The additive manufactured product of claim 4 or 5, wherein the amount of Hf is lower than 0,05% by weight.

7. The additive manufactured product of one or more of the preceding claims 1-6, wherein the additive manufactured product is a component of a turbo machine.

8. The additive manufactured product of one or more of the preceding claims 1-6, wherein the additive manufactured product is a gas turbine nozzle.

9. The additive manufactured product of one or more of the preceding claims 1-6, wherein the additive manufactured product is a gas turbine stator blade.

10. The additive manufactured product of one or more of the preceding claims 1-6, wherein the additive manufactured product is a gas turbine rotor blade.

11. The additive manufactured product of one or more of the preceding claims 1-6, wherein the additive manufactured product is a gas turbine shroud.

12. A method for the production of an additive manufactured product according to one or more of the preceding claims, the method comprising the step of treating a super-alloy powder with the components of one or more of the preceding claims through Direct Metal Laser Sintering (DMLS) technology. 

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