KR20220085777A - Printable Powder Material of FeCrAl for Additive Manufacturing and Additive Manufacturing Objects and Their Uses - Google Patents

Abstract

The present disclosure relates to novel printable powder materials and additively manufactured objects and uses thereof for additive manufacturing. The present disclosure also relates to an additive manufacturing process for manufacturing an object.

Description

Printable Powder Material of FeCrAl for Additive Manufacturing and Additive Manufacturing Objects and Their Uses

FIELD OF THE INVENTION The present invention relates to novel printable powder materials and additively manufactured objects and uses thereof for additive manufacturing. The present disclosure also relates to an additive manufacturing process for manufacturing an object.

Additive manufacturing is becoming an increasingly attractive solution for the fabrication of functional prototypes and components of metals, especially those with complex designs.

Ferritic alloys containing aluminum are attractive for use in electrical heating and high temperature applications. However, one of the problems with these alloys is that they are difficult to weld due to their brittleness. In addition, these alloys can also be difficult to machine. Thus, fabricating composite structures from these alloys can be both difficult and complex. The present disclosure aims to solve or at least reduce the above-mentioned problems.

Accordingly, it is an aspect of the present invention to provide a printable ferritic iron-chromium-aluminum (FeCrAl) metal powder composition for use in additive manufacturing. Accordingly, the present disclosure relates to a printable ferritic FeCrAl powder composition, wherein the FeCrAl powder composition comprises:

Cr 9.0 to 25.0;

Al 2.5 to 8.0;

Si ≤ 3.0;

Mo ≤ 4.0;

Ni ≤ 1.0;

Mn ≤ 1.0;

C ≤ 0.1;

O ≤ 0.2,

S ≤ 0.01;

P ≤ 0.01;

N ≤ 0.1;

Ti ≤ 1.7;

Y ≤ 3.0;

Nb ≤ 3.3;

Zr ≤ 3.3;

V ≤ 1.8;

Ta + Hf ≤ 6.5;

La ≤ 1.0;

Ce ≤1.0,

The balance is Fe and unavoidable impurities, and the FeCrAl powder composition has a powder size distribution of 4 to 200 μm, for example 10 to 120 μm.

The powder of the present invention has good flowability, good packing density and good spreadability and thus the printing will be very good. The printable powder composition is also a gas atomized ferritic iron-chromium-aluminum (FeCrAl) powder composition, meaning that the powder is obtained by a gas atomizing process. The printable ferrite FeCrAl powder composition is advantageous for obtaining 3D molded objects that are essentially overall dense, will have good high temperature oxidation properties, and will have good high temperature creep properties. Additionally, the powder may also be sieved to a particular desired particle size distribution.

The present invention also relates to an additively fabricated object comprising alloying elements in the scope as FeCrAl powder as defined above or below and produced from said FeCrAl powder. The 3D shape of an additively fabricated object will depend on the end use. The inventors have surprisingly found that an additive fabricated object made from FeCrAl powder as defined above or below, comprising an alloy consisting of the same elements in the same ranges of powder as defined above or below, has excellent mechanical properties at high temperatures. properties, and more specifically good creep resistance at high temperatures and additionally high oxidation resistance.

The additively fabricated object is particularly useful as an electrical heating element or component in high temperature applications (in applications operating at 400 to 1350° C.) or as a component in electrical heating applications. Objects can also be used to protect another object against high temperature wear and corrosion. Accordingly, the object of the present invention can be used in both electric heating and high temperature applications.

Another aspect of the present disclosure is to provide an additive manufacturing process. Accordingly, the present disclosure relates to an additive manufacturing process for manufacturing an object as defined above or below of a powder as defined above or below, wherein the additive manufacturing process is a powder bed fusion additive manufacturing process or Direct Energy Deposition (DED) is selected.

1 shows the difference in creep properties at 900° C. and 1100° C. and 1200° C. between printed samples and a conventionally prepared alloy.
2 shows the difference in mass gain at 1100° C. between a printed sample and a conventionally prepared alloy.
3 shows a photomicrograph of an object prepared from a powder as defined above or below by using DED.

The present invention relates to a printable ferritic FeCrAl powder composition, wherein the FeCrAl powder composition comprises:

Cr 9.0 to 25.0;

Al 2.5 to 8.0;

Si ≤ 3.0;

Mo ≤ 4.0;

Ni ≤ 1.0;

Mn ≤ 1.0;

C ≤ 0.1;

S ≤ 0.01;

P ≤ 0.01;

N ≤ 0.1;

O ≤ 0.2;

Ti ≤ 1.7;

Y ≤ 3.0;

Nb ≤ 3.3;

Zr ≤ 3.3;

V ≤ 1.8;

Ta + Hf ≤ 6.5;

La <1.0;

Ce <1.0,

the balance being Fe and unavoidable impurities,

The FeCrAl powder composition has a powder size distribution of 4 to 200 μm, for example 10 to 120 μm. It is therefore also an aspect of the present disclosure to provide a printable ferritic FeCrAl powder composition that can be used in an additive manufacturing process to obtain an object superior in composite structure and mechanical properties. The term “printable” means that the powder can be used in at least one additive manufacturing process.

Most of the alloying elements of the powder will be described below. The description lists some of the important properties of the element. However, such a list should not be considered a complete list. Elements may have other properties not listed here.

Chromium (Cr)

Chromium will promote the formation of the Al ₂ O ₃ layer on the alloy, as defined above or below, through the so-called third element effect, ie by the formation of chromium oxide in the transient oxidation step. Chromium must be present in the alloy as specified above or below in an amount of at least 9 wt %. The increased Cr content will provide an increased solid solution hardening effect on the ferrite structure. From about 11 wt % Cr and above, the ferrite structure will become unstable in the temperature range of 300 to 500 °C. Thereafter, the ferrite may be decomposed into one low Cr ferrite phase and one high Cr ferrite phase. When this happens, the material becomes harder and more brittle. This instability increases with increasing Cr, so the maximum Cr is set to 25 wt%. According to one embodiment of the present invention, therefore, the content of Cr is 18 to 24 wt%, for example 19 to 23.5 wt%. According to another embodiment of the present invention, the content of Cr is thus 9 to 11 wt %, and according to still another embodiment, the content of Cr is 9 to 15 wt %.

Aluminum (Al)

Aluminum is an important element in the powder, as defined above and below, because when exposed to oxygen at high temperatures, aluminum forms a dense and thin oxide Al ₂ O ₃ that protects the underlying alloy surface from further oxidation. to be. The amount of aluminum is at least 2.5 to ensure that there is enough aluminum to form the Al ₂ O ₃ layer and to heal the Al ₂ O ₃ layer if damaged. It should be in % by weight. However, aluminum negatively affects the formability of the mules obtained from the powder composition of the present invention, and the amount of aluminum should not exceed 8 wt % in the powder of the present invention as specified above or below. According to one embodiment, Al may be 3 to 7% by weight. According to another embodiment, Al is 3 to 6 wt%, for example 3.5 to 6 wt%, for example 4 to 6 wt%.

Silicon (Si)

In FeCrAl alloys, silicon is often present at levels up to about 0.5 wt %. Thus, according to one embodiment, Si is present at a level of up to 0.5 wt %. However, Si can play an important role to improve oxidation and corrosion resistance. Thus, Si may be present in an amount greater than 0.5 to 3 wt %, for example 1-3 wt %, eg 1 to 2.5 wt %, eg 1.5 to 2.5 wt %. The upper limit of Si is due to the increasing susceptibility to the formation of brittle Cr ₃ Si and σ phases during prolonged exposure. Therefore, the addition of Si should be performed in consideration of the contents of Al and Cr.

Manganese (Mn)

Manganese may be present as an impurity in the powder as defined above or below. Manganese can also negatively affect oxidation lifetimes above 1100°C. Therefore, the maximum content of Mn is at most 1.0 wt%. According to one embodiment, the content of Mn is ≤ 0.5% by weight.

Molybdenum (Mo)

Molybdenum may be an impurity or may be added as an alloying element. When considering Mo as an impurity in the examples, the maximum level is 0.5 wt% or less. In an embodiment, when Mo is regarded as an alloying element and added to provide a solid solution hardening effect, the minimum level is greater than 0.5 wt%, such as greater than 1.0 wt%, such as 1.0 to 4.0 wt%.

carbon (C)

Carbon may be included to increase strength. At too high a level, carbon can cause difficulties in forming the material and negatively affect corrosion resistance. Accordingly, C is limited to ≤ 0.1 wt %, for example ≤ 0.05 wt %. According to one embodiment, the C content is between 0.001 and 0.1 wt %.

Nitrogen (N)

Nitrogen may be included to increase strength. Nitrogen may also be present as an unavoidable impurity resulting from the manufacturing process. At too high a level, nitrogen can cause difficulties in forming the material and negatively affect corrosion resistance. Therefore, N is limited to ≤ 0.1 wt%. According to one embodiment, the N content is 0.001 to 0.1 wt %.

Oxygen (O)

Oxygen may also be present as an impurity resulting from the manufacturing process. Thus, O is limited to ≤ 0.2 wt%, for example ≤ 0.1 wt%.

Reactive Elements (RE)

According to the definitions in this disclosure, the reactive elements are highly reactive with carbon, nitrogen and oxygen. Yttrium (Y), titanium (Ti), zirconium (Zr), niobium (Nb), vanadium (V), hafnium (Hf), tantalum (Ta), lanthanum (La) and cerium (Ce) and these elements have oxidation properties may be added to improve them.

According to the present disclosure, these elements have the following contents in the powder of the present invention and thus an object made from the powder.

Ti ≤ 1.7 wt%;

Y ≤ 3.0 wt %;

Nb ≤ 3.3 wt%;

Zr ≤ 3.3 wt%;

V ≤ 1.8 wt %;

Ta + Hf ≤ 6.5 wt%;

La ≤1.0 wt%;

Ce ≤1.0 wt%.

According to one embodiment, the FeCrAl powder as defined above or below may have these elements in weight (wt%):

Ti ≤ 0.5;

Y ≤ 1.0;

Nb ≤ 0.5;

Zr ≤ 0.5;

V ≤ 0.5;

Ta + Hf ≤ 1.0;

La ≤ 0.5;

Ce ≤ 0.5.

According to one embodiment, the printable FeCrAl powder composition comprises:

Cr 18 to 24;

Al 4 to 6;

Mn ≤0.5;

Si ≤ 0.5 or greater than 0.5 to 3;

Mo ≤ 0.5;

Ti ≤ 0.5;

Y ≤ 1.0;

Nb ≤ 0.5;

Zr ≤ 0.5;

V ≤ 0.5;

Ta + Hf ≤ 1.0;

La ≤ 0.5;

Ce ≤ 0.5.

The balance is Fe and unavoidable impurities, and C is ≤ 0.1% by weight or C is ≤0.05% by weight.

According to another embodiment, the printable FeCrAl powder composition comprises:

Cr 18 to 24;

Al 4 to 6;

Mn ≤0.5;

Si ≤ 0.5 or greater than 0.5 to 3;

Mo 1 to 4;

Ti ≤ 0.5;

Y ≤ 1.0;

Nb ≤ 0.5;

Zr ≤ 0.5;

V ≤ 0.5;

Ta + Hf ≤ 1.0;

La ≤ 0.5;

Ce ≤ 0.5.

The balance is Fe and unavoidable impurities, and C is ≤ 0.1% by weight or C is ≤0.05% by weight.

Iron (Fe) and unavoidable impurities constitute the remainder both in the powder or in the object as specified above or below.

An illustrative, but non-limiting example of unavoidable impurities is a metal that will form low melting phases as these low melting phases affect crack resistance properties.

Therefore, it has been found that by removing certain alloying elements from the FeCrAl powder, it is possible to achieve a product having, but not limited to, excellent high temperature corrosion resistance and creep strength. Examples of such elements are cobalt, copper, zinc and magnesium.

According to embodiments, the powder size distribution may be selected from 4 to 200 μm, 10 to 120 μm, and 10 to 90 μm.

Additive fabricated objects made by using ferritic FeCrAl powder as defined above or below will perform very well at operating temperatures of up to 1350°C. In addition, the subject matter of the present invention will have significant high temperature corrosion resistance and high resistance to oxidation, sulphidization and carburization. Additionally, additively fabricated objects will have significant high temperature creep strength and high dimensional stability and high electrical resistance compared to conventionally manufactured objects.

The additive manufacturing processes described above or below use a computer-aided design of a 3D shaped object to be printed, which is also decomposed into 2D thin slices by using software that will link the generated data to hardware.

According to one embodiment of the present disclosure, a powder sintering additive manufacturing process is used. According to another embodiment, the powder sintering additive manufacturing process is selected from selective laser melting (SLM) or electron beam melting (EBM). A powder bath is used in both of these processes. The powder layer is exposed to an energy source and will thereby melt or at least partially melt. A new powder layer will be provided, which will continue until the desired object is obtained. In SLM, the energy source is one or more laser beams, for example the energy source is a continuous laser beam or a pulsed laser beam, and in EBM the energy source is an electron beam.

SLM is performed in an inert atmosphere such as an argon or nitrogen atmosphere. Also, the process may use a support when needed to reinforce small angles, for example, and the support will then be removed. SLM printing is also performed directly on the loose powder layer.

In EBM, each powder layer can be preheated before being melted locally by an electron beam. The process is carried out in vacuum and at high temperatures. Also, in EBM, each new powder layer is first pre-sintered with an electron beam before the actual printing of the powder layer begins.

According to one embodiment, the powder layer thickness is between 10 and 250 μm. For example, in SLM the layer thickness may be 10-80 μm, and in EBM the layer thickness may be 10-250 μm.

According to a further one embodiment, the power of the energy source in printing is between 80 and 400 W when a laser beam is used and between 300 and 1000 W when an electron beam is used. Optionally more than one laser beam may be used, each beam then having a power stated herein.

According to one embodiment, the energy density for the energy source is in the range of 1 to 6 J/mm ² . Energy density is the energy transferred by the energy source per unit area in the powder layer during printing.

According to one embodiment, the additive manufacturing process used is direct jet deposition (DED). In this type of process, an energy source is used to create a local melt pool. Metal powder is fed into this molten pool as a filler material. The position of the molten pool is constantly shifted so that a three-dimensional body is created by the solidifying material. The energy source may be a laser beam or a plasma arc. According to one embodiment, in the DED, the power of the laser source may be between 50 and 2000 W.

According to one embodiment, the DED process is performed with an inert shielding gas atmosphere that protects the molten pool. According to one embodiment, the material feed angle can be changed depending on what the object of the predetermined shape is.

According to an embodiment, an object manufactured by DED can be stress relieved. The stress relaxation temperature will range from 650 to 1200° C. and will depend on the volume of the object being manufactured. The stress relaxation time will vary from a very short time, such as 15 minutes, to a longer time, such as several hours. According to an embodiment, the pre-oxidation may be performed at the same time as the stress is relieved after printing. The purpose of the pre-oxidation is to form an aluminum oxide surface layer. According to one embodiment, the aluminum oxide layer has a thickness of at least 0.5 μm.

The additive manufactured object obtained from any of the methods/processes mentioned above or below may be post-treated.

Embodiments of the present disclosure will be described in more detail with reference to the following examples. The examples are to be considered as illustrative and non-limiting embodiments.

examples

Example 1

Print by SLM

Three powders (powders 1 to 3) having a chemical composition of wt% according to table 1 were prepared using gas atomization, then powder 1 and powder 3 and powder 4 having a particle size within 10-45 μm , was sieved into suitable fractions so that powder 2 had a particle size within 1 to 45 μm.

Several samples of different powders were printed as follows:

Powders as described above were provided to the SLM machine by adding to the powder delivery system. During the printing process, the powder was provided from the powder delivery system to the machine, and a scraper spread the layer of powder onto a building plate. A laser is then passed over the layer of powder according to the 3D drawing provided, whereby the layer of powder is exposed to the laser beam and thus melted. After the powder layer was melted, a new layer was provided until the desired sample(s) were formed according to the 3D drawing.

The thickness of the powder layers was between 20 and 30 μm. Printing was performed in an inert atmosphere using argon. The scan speed was between 500 and 800 mm/s. The power of the energy source was 80-200 W.

Samples were allowed to cool to room temperature in an inert atmosphere. The printed sample was de-powdered, after which the building plate containing the sample was removed from the machine. The building plate with the samples was heat treated at 650 to 1200° C. for 0.5 to 3 hours. The building plate and samples were then cooled to room temperature and then machined (cut) to remove the samples from the building plate.

Example 2

Printing by DED

Two powders having compositions according to Table 2 were prepared using gas atomization and then sieved into suitable fractions to obtain powders within a particle size of 45 to 90 μm.

Some samples from these powders in the form of cubic blocks were printed as follows:

A laser source was used to create a local melt pool. The powder was fed into the melt pool and solidified rapidly. Powder was added to the pool by using a focused powder stream. The laser traveled along a predesigned path, creating a layer of solidified substrate (X-Y plane). The laser then moved up (Z axis) and started creating a molten pool on the surface of the old substrate, creating a new layer along a specific path. A three-dimensional body was created.

The powder bed height was between 0.3 and 2 mm. Printing was performed with or without an argon atmosphere. Deposition rates ranged from 1000 mm/min to 2500 mm/min. The powder feed was between 4 g/min and 25 g/min. The power of the laser source was 50 to 2000 W.

3 discloses a photomicrograph of the DED printed structure of Powder 5. The structure is very dense and shows no signs of cracking, defects or porosity. A Leica stereo microscope was used.

Example 3 - Testing

1 shows samples containing a FeCrAl (CP 1) alloy prepared conventionally, samples prepared by additive manufacturing by using SLM (SLM 1), and samples prepared by additive manufacturing by using (SLM 2); Provides a comparison of their creep strength.

Conventional samples were prepared by casting and rolling, having a diameter, d ₀ , 4 mm and original gauge length, L ₀ , 20 mm, SS EN ISO 6892-2:2018, "Cylindrical test pieces with threaded gripping ends" was prepared according to

The conventional sample had a composition according to the following specifications.

Additive manufacturing samples were machined to standard SS EN ISO 6892-2:2018 with gripped (turned) ends after printing, diameter, d ₀ 4 mm and original gauge length, L ₀ , 20 mm. The additive manufacturing samples (SLM 1 and SLM 2) had a composition according to the following specifications:

Samples were loaded with a dead load. The creep rate was calculated as the percentage change in the length of the samples over time at constant loading and temperature. Testing of the printed samples was performed at 1100 °C and 1200 °C. Previously prepared samples were tested at 900°C and 1100°C.

The printed material was found to be anisotropic. The creep results shown in Figure 1 are for a stronger orientation of the material when the samples are loaded parallel to the printing direction. Also, as can be seen from FIG. 1, the additively fabricated samples have a much lower creep rate compared to the conventionally fabricated samples. Although the previously prepared samples were tested at lower temperatures, the creep strength of the printed samples was still higher at lower creep rates. In addition, printed samples have a longer time to rupture, which means that these products will last longer.

FIG. 2 shows mass gain curves at 1100° C. versus time for additive fabricated samples made from powder 4 in Table 1 and conventionally made samples having a composition similar to powder 4; The mass gain weight was checked at 100 hour intervals. The mass gain curve shows that the additive fabricated sample has better oxidation properties than the conventional fabricated sample, meaning that it will therefore be superior in high temperature applications and will have a longer lifetime.

Claims (14)

A printable ferrite FeCrAl powder composition comprising:
The FeCrAl powder composition is in wt%,
Cr 9.0 to 25.0;
Al 2.5 to 8.0;
Si ≤ 3.0;
Mo ≤ 4.0;
Ni ≤ 1.0;
Mn ≤ 1.0;
C ≤ 0.1;
S ≤ 0.01;
P ≤ 0.01;
N ≤ 0.1;
O ≤ 0.2;
Ti ≤ 1.7;
Y ≤ 3.0;
Nb ≤ 3.3;
Zr ≤ 3.3;
V ≤ 1.8
Ta + Hf ≤ 6.5
La ≤ 1.0;
Ce ≤1.0,
the balance being Fe and unavoidable impurities,
wherein the FeCrAl powder composition has a powder size distribution of 4 to 200 μm, for example 10 to 120 μm. The method of claim 1,
The content of C is ≤ 0.05% by weight, printable ferritic FeCrAl powder composition. 3. The method of claim 1 or 2,
A printable ferritic FeCrAl powder composition, wherein the content of Mn is ≤ 0.5% by weight. 4. The method according to any one of claims 1 to 3,
A printable ferritic FeCrAl powder composition, wherein the content of Si is less than 0.5% by weight or greater than 0.5 and up to 3.0% by weight. 5. The method according to any one of claims 1 to 4,
A printable ferritic FeCrAl powder composition, wherein the content of Al is 3 to 6% by weight. 6. The method according to any one of claims 1 to 5,
A printable ferrite FeCrAl powder composition, wherein the content of Cr is 9 to 11% by weight or 18 to 24% by weight. 3. The method of claim 1 or 2,
in weight %,
Cr 18 to 24;
Al 4 to 6;
Mn ≤0.5;
Si ≤ 0.5 or greater than 0.5 to 3;
Mo ≤ 0.5;
Ti ≤ 0.5;
Y ≤ 1.0;
Nb ≤ 0.5;
Zr ≤ 0.5;
V ≤ 0.5;
Ta + Hf ≤ 1.0;
La ≤ 0.5;
Ce ≤ 0.5,
A printable ferritic FeCrAl powder composition, the balance being Fe and unavoidable impurities. 3. The method of claim 1 or 2,
in weight %,
Cr 18 to 24;
Al 4 to 6;
Mn ≤0.5;
Si ≤ 0.5 or greater than 0.5 to 3;
Mo 1 to 4;
Ti ≤ 0.5;
Y ≤ 1.0;
Nb ≤ 0.5;
Zr ≤ 0.5;
V ≤ 0.5;
Ta + Hf ≤ 1.0;
La ≤ 0.5;
Ce ≤ 0.5,
A printable ferritic FeCrAl powder composition, the balance being Fe and unavoidable impurities. An additively fabricated object comprising the printable powder composition according to claim 1 . 10. The method of claim 9,
wherein the object is a high temperature resistant heating element or a high temperature resistant component. 10. The method of claim 9,
wherein the object is an electrical heating element or an electrical resistance component. 12. An additive manufacturing process for manufacturing an object according to any one of claims 9 to 11, comprising:
The additive manufacturing process is selected from a powder bed fusion additive manufacturing process or Direct Energy Deposition (DED), and the ferrite FeCrAl powder according to any one of claims 1 to 9 is used. An additive manufacturing process for manufacturing an object. 13. The method of claim 12,
An additive manufacturing process for manufacturing an object, wherein a powder sintering additive manufacturing method is used, wherein the powder sintering additive manufacturing method is SLM or EBM. Use of an additively fabricated object according to any one of claims 9 to 13 as a heating element or as a component in electrical heating or high temperature applications.

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