Patent Application
20220205066
The invention relates to a nickel base alloy for powder.
WO 2015/110668 A2 discloses a method for the manufacture of iron-base powders, which are atomized by means of a centrifuge, with the following method steps:
DE 10 2015 016 729 A discloses a method for the manufacture of metallic semi-finished products from an alloy having more than 50% nickel, containing the following process steps:
It is generally known that Ni and Ni—Co alloys are used in order to fabricate structural parts having special properties in terms of corrosion resistance and good mechanical properties, such as strength, high-temperature strength and fracture toughness.
The task underlying the invention is to provide, for the additive fabrication of components, a powder that has the advantageous properties of the Ni and Ni—Co alloys and can be manufactured inexpensively. Moreover, the powder described above may be used for the manufacture of the structural parts by means of hot isostatic pressing (HIP) or conventional sintering and extrusion-pressing processes. Moreover, the method combination of additive fabrication and subsequent HIP treatment is possible. For this purpose it is possible to apply the post processing steps described below for HIP structural parts for the generative fabrication. In this regard, it is important to meet the special requirements applicable to distribution of the particle size, particle shape and pourability of the powder.
Furthermore, it is intended to propose a method for the manufacture of such a powder.
This task is accomplished by a nickel-base alloy for powder, wherein the contents (in wt %) are defined as follows:
and manufacturing-related impurities.
wherein:
Ni+Fe+Co 56-80%
Nb+Ta 6.0%.
Advantageous further developments of the powder alloy according to the invention can be inferred from the associated dependent claims.
Advantageously, the powder alloy according to the invention is intended to have the following composition (in wt %):
and manufacturing-related impurities.
wherein:
Ni+Fe+Co 57-77%.
Furthermore, the possibility exists of composing the powder alloy for specific application situations as follows:
and manufacturing-related impurities.
wherein:
Ni+Fe+Co 59-72%.
This task is also accomplished by a method for the manufacture of a powder from a nickel-base alloy according to the invention in which
Advantageous further developments of the method according to the invention can be inferred from the associated dependent claims according to the method.
The following initial fabrication steps are conceivable:
After the alternative initial fabrication steps, the following further processing steps may take place:
The powder according to the invention is preferably produced in a vacuum inert gas atomization system (VIGA). In this system, the alloy is melted in a vacuum induction melting furnace (VIM), directed into a casting gate that leads to a gas nozzle, in which the molten metal is atomized to metal particles with inert gas under high pressure of 5 to 100 bar. The melt is heated in the melting crucible to 5 to 400° C. above the melting point. The metal flow rate during atomization amounts to 0.5 to 80 kg/min and the gas flow rate is 2 to 150 m3/min. Due to the rapid cooling, the metal particles solidify in the form of balls (spherical particles). The inert gas used for the atomization may contain 0.01 to 100% nitrogen if necessary. The gas phase is then separated from the powder in a cyclone, and then the powder is packaged.
Alternatively, the powder according to the invention may be manufactured via the so-called EIGA method instead of via VIGA. For this purpose, a prefabricated alloy ingot in the form of a rotating electrode is melted contactlessly in an induction coil. The melt drips from the electrode directly into the gas stream of a gas nozzle.
The alloy ingot for EIGA may in turn be manufactured by the VIM, ESR, VAR, VOD or VLF melting method and combinations thereof and optionally subjected to hot-forming processes such as forging and rolling. A cleaning of the surface of the ingot by a treatment such as grinding or/and scalping prior to the use in the EIGA method is of advantage.
The inert gas for the powder manufacture may optionally be argon or a mixture of argon with 0.01 to 100% nitrogen. Possible limits of the nitrogen content may be:
0.01 to 80%
0.01 to 50%
0.01 to 30%
0.01 to 20%
0.01 to 10%
0.01 to 10%
0.1 to 5%
0.5 to 10%
1 to 5%
2 to 3%
Alternatively, the inert gas may optionally be helium.
The inert gas may preferably have a purity of at least 99.996 vol %. In particular, the nitrogen content should be from 0.0 to 10 ppmv, the oxygen content from 0.0 to 4 ppmv and have an H2O content of 5 ppmv.
In particular, the inert gas may preferably have a purity of at least 99.999 vol %. In particular, the nitrogen content should be from 0.0 to 5 ppmv, the oxygen content from 0.0 to 2 ppmv and have an H2O content of 3 ppmv.
The dew point in the system lies in the range of −10 to −120° C. It preferably lies in the range of −30 to −100° C.
The pressure during powder atomization may preferably be 10 to 80 bar.
The structural parts and components or layers on structural parts and components manufactured by means of additive fabrication are built up from layer thicknesses of 5 to 500 μm and directly after manufacture have a textured microstructure with grains elongated in structure direction and having a mean grain size of 2 μm to 1000 μm. The preferred range lies between 5 μm and 500 μm.
The structural parts and components or layers on structural parts and components manufactured by means of additive fabrication may optionally be subjected to a solution annealing in the temperature range of 700° C. to 1250° C. for 0.1 minutes to 70 hours, if necessary under shield gas, such as argon or hydrogen, for example, followed by a cooling in air, in the agitated annealing atmosphere or in the water bath. Thereafter the surface may optionally be cleaned or machined by pickling, blasting, grinding, turning, peeling, milling. Optionally, such a machining may already take place partly or completely even before the annealing.
The structural parts and components or layers on structural parts and components manufactured by means of additive fabrication may optionally be subjected to a homogenization, stress-relief, solution and/or precipitation-hardening annealing. The heat treatments may take place if necessary under shield gas, such as argon or hydrogen, for example, followed by a cooling in the furnace, if necessary under shield gas, in air, in the agitated annealing atmosphere or in the water bath.
The structural parts and components or layers on structural parts and components manufactured by means of additive fabrication have after an annealing a mean grain size of 2 μm to 2000 μm. The preferred range lies between 20 μm and 500 μm.
The structural parts and components or layers on structural parts and components manufactured from the powder generated according to the invention by means of additive fabrication are intended to be used preferably in areas in which the material is also used as wrought or cast alloy with related analysis.
Under additive fabrication, terms such as generative fabrication, rapid technology, rapid tooling, rapid prototyping or the like are also understood.
In general, the following are distinguished here:
3D printing with powders,
Selective laser sintering and
Selective laser melting
Laser deposit welding
Selective electron beam welding.
The abbreviations used here are defined as follows:
VIM Vacuum Induction Melting
VIGA Vacuum Inert Gas Atomization system
VAR Vacuum Arc Remelting
VOD Vacuum Oxygen Decaburization
VLF Vacuum Ladle Furnace
EIGA Electrode Induction Melting Gas Atomization
Advantageous further developments of the method according to the invention can be inferred from the dependent claims.
The range of values for the particle size of the powder lies between 5 and 250 μm, wherein preferred ranges lie between 5 and 150 μm or 10 and 150 μm.
The powder has gas inclusions of 0.0 to 4% pore area (pores >1 μm) in relation to the total area of evaluated objects, wherein preferred ranges are
0.0 to 2%
0.0 to 0.5%
0.0 to 0.2%
0.0 to 0.1%
0.0 to 0.05%
The powder has a bulk density of 2 up to the density of the alloy, which is approximately 8 g/cm3, wherein preferred ranges may have the following values.
4-5 g/cm3
2-8 g/cm3
2-7 g/cm3
3-6 g/cm3
The quantity of the gas inclusions of the powder permits a low residual porosity of the manufactured parts.
Compared with the prior art, the centrifugation method is omitted, and hereby the operating time of the system is optimized. The subsequent refining processes optimize the quality of the powder for the additive fabrication.
It may be of advantage if the ingot is subjected, prior to the dissection, to a machining of the surface (e.g. by brushing, grinding, pickling, cutting, scalping, etc.). In the process, defects may be removed that cannot be eliminated by the further remelting and that may cause impairment for subsequent applications.
The method according to the invention can be applied to any Ni-base or Ni—Co-base alloy.
In the following, an alloy composition is presented that may be produced as powder by means of the method parameters according to the invention. All values are in wt %:
and manufacturing-related impurities.
Beyond this, the following elements may be present (values in wt %):
Nb+Ta max. 6%
Advantageously, the following elements may be adjusted as shown below (values in wt %):
For improvement of the mechanical properties, the elements boron and carbon may also be adjusted as follows:
In this connection, it is further advantageous when the sum of C+B lies between 0.1875 and 0.530%, between 0.156 and 0.625%, in particular lies in the range of 0.16 and 0.6%, especially in the range of 0.1875 and 0.530%, and the ratio of C/B lies between 12 and 18.
In the following, an example of a powder from an Ni alloy on the basis of alloy 718 is presented (values in wt %):
Alternatively, this alloy may also have higher Ni contents (values in wt %).
Further restrictions are conceivable such as below (values in wt %):
As well as, optionally if necessary (values in wt %):
Optionally, the oxygen content of the generated alloy may lie at 0.00001-0.1%, at 0.0001-0.1%, at 0.001-0.1%, at 0.001-0.0020 or at 0.0015-0.002%.
Optionally, the oxygen content may also be adjusted as follows:
The nitrogen must be smaller than or equal to 0.100%, in order to ensure the manufacturability and usability of the alloy. Too high nitrogen content leads to the formation of nitrides, which negatively influence the properties of the alloy. A too low nitrogen content increases the costs. The nitrogen content is therefore 0.00001%. The following restrictions of the nitrogen content are conceivable:
Both in the powder and in fabricated components (3D printed samples), the particle sizes both of nitrides and of carbides and/or carbonitrides is very low (approximately <8 μm). In some cases, the above-mentioned particles may not be present or may be visible only after heat treatment. Small particle sizes of N-containing precipitates have positive effect on high-temperature properties and resistance to alternating loads (low-cycle Fatigue—LCF), since N-containing precipitates act as crack-initiation sites in conventionally manufactured alloys.
The argon content must be smaller than or equal to 0.08%, in order to ensure the manufacturability and usability of the alloy. Argon cannot be dissolved in the y-matrix, and so it may negatively influence the mechanical properties of the structural part, since argon inclusions may act as crack-initiation sites. A too low argon content increases the costs. The argon content is therefore ≥0.0000001% (≥1 ppb). The following restrictions of the argon content are conceivable, wherein the argon contents from the powder manufacture as well as from the structural part manufacture are included:
The method according to the invention is intended to be usable preferably for the following alloys:
As examples, Table 1 shows ranges of analysis of the aforementioned alloys.
Powders with a particle size from 5 μm to 250 μm are obtained.
A too small particle size below 5 μm impairs the flow behavior and is therefore to be avoided; a too large particle size above 250 μm impairs the behavior during additive fabrication.
A too low bulk density of 2 g/cm2 impairs the behavior during additive fabrication. The greatest possible bulk density of approximately 8 g/cm3 is imposed by the density of the alloy.
The oxygen content must be smaller than or equal to 0.100%, in order to ensure the manufacturability and usability of the alloy. A too low oxygen content increases the costs. The oxygen content is therefore 0.0001%. The powders manufactured according to this method may be used in the additive fabrication for construction of components that have the properties of the underlying alloys.
Moreover, the powder described above may also be used for the manufacture of the structural parts by means of hot isostatic pressing (HIP) or conventional sintering and extrusion-pressing processes. Moreover, the method combination of additive fabrication and subsequent HIP treatment is possible. For this purpose it is possible to apply the post processing steps described below for HIP structural parts for the generative fabrication.
The powders fabricated according to this method and also components fabricated from this powder (3D printed samples) are free of nitrides and also of carbides and/or carbonitrides. Should nitrides and also of carbides nevertheless be present, these have a particle size in the diameter of <100 nm especially <50 nm.
After a heat treatment of components fabricated from this powder (3D printed samples) for homogenization, diffusion annealing above 900° C., especially above 1000° C., ideally above 1100° C. for more than 1 hour, nitrides and also of carbides and/or carbonitrides may appear in the fabricated components (3D printed samples). These have a particle size in the diameter of <8 μm, or respectively <5 μm, ideally <1 μm, especially <500 nm. By way of example, the method according to the invention is explained as follows:
Melts in the following were generated with the method according to the invention and fabricated as powder (values in wt %):
Chemical compositions of the powder manufactured with the method according to the invention are indicated in Table 2.
Both powder and also in fabricated components (3D printed samples) were free of nitrides and also of carbides.
After an annealing at a temperature of 1100° C. for 1 hour followed by a quenching in water, particles such as nitrides and also carbides and/or carbonitrides were present in fabricated components (3D printed samples). These had a particle size in the diameter of smaller than <1 μm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 118 219.0 | Jul 2019 | DE | national |
| 10 2020 116 858.6 | Jun 2020 | DE | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2020/100574 | 7/1/2020 | WO | 00 |
