EP4048463A1

EP4048463A1 - Printable powder material of fecral for additive manufacturing and an additive manufactured object and the uses thereof

Info

Publication number: EP4048463A1
Application number: EP20792676.7A
Authority: EP
Inventors: Pengcheng CAO; Mikael KJELLÉN; Saud SALEEM
Original assignee: Kanthal AB
Current assignee: Kanthal AB
Priority date: 2019-10-22
Filing date: 2020-10-22
Publication date: 2022-08-31
Also published as: WO2021078885A1; CN114929920A; JP2022553315A; KR20220085777A

Abstract

The present disclosure relates to a new printable powder material for additive manufacturing and an additive manufactured object and the uses thereof. The present disclosure also relates to an additive manufacturing process for producing the object.

Description

PRINTABLE POWDER MATERIAL OF FECRAL FOR ADDITIVE MANUFACTURING AND AN ADDITIVE MANUFACTURED OBJECT AND THE USES THEREOF

Technical field The present disclosure relates to a new printable powder material for additive manufacturing and an additive manufactured object and the uses thereof. The present disclosure also relates to an additive manufacturing process for producing the object.

Background

Additive manufacturing has become a more and more attractive solution for the manufacturing of metallic functional prototypes and components, especially those with complicated design.

Ferritic alloys containing aluminum are attractive to 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 brittle nature. Furthermore, these alloys may also be difficult to machine. Thus, it may be both difficult and complicated to manufacture complex structures in these alloys. The present disclosure aims at solving or at least reducing the above-mentioned problems.

Summary An aspect of the present disclosure is therefore to provide a printable ferritic iron- chromium-aluminum (FeCrAl) metal powder composition to be used in additive manufacturing. The present disclosure therefore relates to a printable ferritic FeCrAl powder composition, wherein the FeCrAl powder composition consists in weight%:

Cr 9.0 - 25.0; A1 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;

Balance Fe and unavoidable impurities; and wherein the FeCrAl powder composition has a powder size distribution between 4 to 200 pm, such as 10 and 120 pm.

The present powder will have good flowability, good packing density and good spreadability thus it will be excellent to print. The printable powder composition is also a gas atomized ferritic iron-chromium-aluminum (FeCrAl) powder composition meaning that the powder has been obtained by a gas atomizing process. The printable ferritic FeCrAl powder composition is advantageous for obtaining 3D shaped objects which will essentially be fully dense and will have excellent high temperature oxidation properties and will have excellent high temperature creep properties. Additionally, the powder may also be sieved to the specific desired particle size distribution.

The present disclosure also relates to an additive manufactured object comprising the alloying element in the ranges as the FeCrAl powder as defined hereinabove as hereinafter and manufactured from said FeCrAl powder. The 3D shape of the additive manufactured object will depend on the final use. The inventors have surprisingly found that an additive manufactured object manufactured from the FeCrAl powder as defined hereinabove or hereinafter and thereby comprising an alloy consisting the same elements in the same ranges of the powder as defined hereinabove or hereinafter will have excellent mechanical properties in high temperature, more specifically it will have excellent creep resistance at high temperature and additionally high oxidation resistance.

The additive manufactured object is especially useful in as an electrical heating element or a component in high temperature applications (in applications operating between 400 to 1350 °C) or as a component in electrical heating applications. The object may also be used for protecting another object against high temperature wear and corrosion. Hence, the present object may be used in both electrical heating and high temperature applications.

Another aspect of the present disclosure is to provide an additive manufacturing process. Thus, the present disclosure relates to an additive manufacturing process for manufacturing an object as defined hereinabove or hereinafter of the powder as defined hereinabove or hereinafter, wherein the additive manufacturing process is selected from a powder bed fusion additive manufacturing process or from Direct Energy Deposition (DED). Brief description of Figures

Figure 1 shows the difference in creep properties at 900 °C and 1100 °C and

1200 °C between printed samples and a conventional manufactured alloy;

Figure 2 shows the difference in mass gain at 1100 °C between a printed sample and a conventional manufactured alloy. Figure 3 shows a micrograph of an object manufactured from the powder as defined hereinabove or hereinafter by using DED.

Detailed description

The present disclosure relates to a printable ferritic FeCrAl powder composition, wherein the FeCrAl powder composition consists in weight% (wt%):

Cr 9.0 - 25.0;

A1 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;

Balance Fe and unavoidable impurities; and wherein the FeCrAl powder composition has a powder size distribution between 4 to 200 pm, such as 10 to 120 pm. Further, it is accordingly an aspect of the present disclosure to provide a printable ferritic FeCrAl powder composition which may be used in an additive manufacturing process for obtaining an object superior in complex structure and mechanical properties. By the term “printable” is meant 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. In the description some of the important properties of the elements are listed. However, that list should not be consider as a complete list. The elements may have other properties not listed herein.

Chromium (Cr)

Chromium will promote the formation of an AI2O3 layer on the alloy as defined hereinabove or hereinafter through the so-called third element effect, i.e. by formation of chromium oxide in the transient oxidation stage. Chromium shall be present in the alloy as defined hereinabove or hereinafter in an amount of at least 9 wt%. An increased Cr content will provide for an increased solid solutioning hardening effect on the ferritic structure. From around 11 wt% Cr and above, the ferritic structure will become instable in the temperature range 300-500°C. The ferrite may then be decomposed into one low Cr ferrite phase and one high Cr ferrite phase. When this occur, the material becomes harder and more brittle. This instability increases with increasing Cr and therefore, the maximum Cr is set to 25 wt%. According to one embodiment of the present disclosure, the content of Cr is therefore of from 18 to 24 wt%, such as 19 to 23.5 wt%. According to another embodiment of the present disclosure, the content of Cr is therefore of from 9 to 11 wt%, and according to yet another embodiment, the content of Cr is therefore from 9 to 15 wt%.

Aluminum (AO

Aluminum is an important element in the powder as defined hereinabove or hereinafter as aluminum, when exposed to oxygen at high temperature, will form the dense and thin oxide AI2O3, which will protect the underlying alloy surface from further oxidation. The amount of aluminum should be at least 2.5 wt% to ensure that an AI2O3 layer is formed and that sufficient aluminum is present to heal the AI2O3 layer if damaged. However, aluminum has a negative impact on the formability of the object obtained from the present powder composition and the amount of aluminum should not exceed 8 wt% in the present powder as defined hereinabove or hereinafter. According to one embodiment, A1 is between 3 - 7 wt%. According to another embodiment, A1 is between 3 - 6 wt%, such as 3.5 - 6 wt%, such as 4 to 6 wt%.

Silicon (Si)

In FeCrAl alloys, silicon is often present in levels of up to about 0.5 wt%. Thus, according to one embodiment, Si is present in a level up to 0.5 wt%. However, Si may play an important role for improving oxidation and corrosion resistance. Thus, Si may be present above 0.5 to 3 wt%, such as 1 to 3 wt%, such as 1 to 2.5 wt%, such as 1.5 to 2.5 wt%. The upper limit of Si is by the increasing susceptibility to formation of brittle CnSi and s phase during long term exposure. Additions of Si therefore have to be done by taken into consideration the content of A1 and Cr.

Manganese

Manganese may be present as an impurity in the powder as defined hereinabove or hereinafter. Manganese may also have a negative impact on the oxidation life above 1 100 °C. The maximum content of Mn is therefore up to 1.0 wt%. According to one embodiment, the content of Mn is < 0.5 weight%.

Molybdenum (Mo)

Molybdenum may be an impurity or may be added as an alloying element. In the embodiment when Mo is considered to be an impurity, the maximum level is less than or equal to 0.5 wt%. In the embodiment when Mo is considered as an alloying element and added to in order to provide a solid solution hardening effect, the minimum level is more than 0.5 wt%, such as more than 1.0 wt% such as between 1.0 to 4.0 wt%.

Carbon (C)

Carbon may be included to increase strength. At too high levels, carbon may result in difficulties to form the material and have a negative effect on the corrosion resistance. Hence, C is therefore limited to <0.1 wt%, such as <0.05 wt%. According to one embodiment, the C content is from 0.001 to 0.1 wt%.

Nitrogen (N)

Nitrogen may be included to increase strength. Nitrogen may also be present as an unavoidable impurity resulting from the production process. At too high levels, nitrogen may result in difficulties to form the material and may have a negative effect on the corrosion resistance. Hence, N is therefore limited to < 0.1 wt%. According to one embodiment, the N content is from 0.001 to 0.1 wt%.

Oxygen (O)

Oxygen may exist as an impurity resulting from the production process. Hence, O is therefore limited to < 0.2 wt%, such as < 0.1 wt%.

Reactive elements (RE)

Per definition in the present 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 Ce (Cerium) and these elements may be added in order to improve the oxidation properties. According to the present disclosure, these elements have the following content in the present powder and thereby in the object made from the powder Ti <1.7 wt%;

Y <3.0 wt%;

Nb <3.3 wt%;

Zr <3.3wt%;

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 hereinabove or hereinafter may have these elements in the following 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 consists in weight%:

Cr 18-24;

A1 4 to 6;

Mn <0.5;

Si < 0.5 or above 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.

Balance Fe and unavoidable impurities and wherein C is < 0.1 weight% or C is < 0.05 weight%.

According to another embodiment, the printable FeCrAl powder composition consists in weight%:

Cr 18 - 24;

A1 4 to 6;

Mn <0.5;

Si <0.5 or above 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.

Iron (Fe) and unavoidable impurities make up the balance in the powder or the object both as defined hereinabove or hereinafter.

Example but not limiting of unavoidable impurities are metals which will form low melting phases as these low melting phases have shown to have an impact on the crack resistance properties. Thus, it has been found that by eliminating certain alloying elements in a FeCrAl powder, it is possible to achieve a product having but not limiting 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 pm, 10 to 120 pm, 10 to 90 pm.

An additive manufactured object manufactured by using the ferritic FeCrAl powder as defined hereinabove or hereinafter will perform well in operating temperatures up to 1350°C. Furthermore, the present object will have significant high-temperature corrosion resistance and a high resistance against oxidation, sulphidization and carburization. Additionally, the additive manufactured object will have significant high- temperature creep strength and high form stability and high electrical resistivity compared to conventionally manufactured objects.

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

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

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

In EBM, each powder layer may be preheated before they are locally melted by the electron beam. The process is performed in vacuum and high temperatures.

Additionally, in EBM, each new powder layer is first pre-sintered with the electron beam before the actual printing of the powder layer starts.

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

According to yet one embodiment, the power of the energy source when printing is, when laser beam is used between 80 - 400 W, and when electron beam is used 300 - 1000 W. Optionally, more than one laser beam may be used, each beam has then the power mentioned herein.

According to one embodiment, the energy density for the energy source is in the range of 1 - 6 J/mm². The energy density is the energy delivered by the energy source per unit area in the powder layer during printing.

According to an embodiment, the additive manufacturing process used is direct energy deposition (DED). In this type of process, an energy source is used to create a local melt pool. Metal powder is feed into this melt pool as filler material. The position of the melt pool is constantly shifting so that a 3-dimensional body is created by the solidifying material. The energy source may either be laser beam or a plasma arc. According to one embodiment, in DED, the power of the laser source can be between 50 - 2000 W.

According to one embodiment, the DED process is performed with an inert shielding gas atmosphere protecting the melt pool. According to one embodiment, the material feed angle may be altered depending on what is the predetermined shaped object.

According to an embodiment, an object manufactured by DED may be stress-relieved. The stress relieve temperature will range from 650 - 1200 °C and will depend on volume of the manufactured object. The stress relieve time will vary from very short, such as from 15 min, to longer times, such as several hours. According to an embodiment, pre-oxidation may be performed at the same time as the stress relive after printing. The purpose of pre oxidation is to form an aluminium oxide surface layer. According to one embodiment, said aluminium oxide layer has a thickness of at least 0.5 pm. The obtained additive manufactured object, from any of the methods/processes mentioned hereinabove or hereinafter may be post-treated.

Embodiments of the present disclosure will be disclosed in more detail in connection with the following examples. The examples are to be considered as illustrative and not limiting embodiments.

EXAMPLES

Example 1

Printing by SLM

Three powders (Powder 1 to 3) with the chemical composition in wt% according to Table 1 were produced using gas atomization and then sieved to suitable fraction so that Powder 1 and Powder 3 and Power 4 had a particle size within 10 - 45 pm, Powder 2 had a particle size within 1 - 45 pm. .

Table 1 Several samples of the different powders were printed as follows:

The powders as described above were provided to a SLM machine by addition to the powder delivery system. During the printing process, the powder was provided from the powder delivery system in the machine and a scraper spread a layer of powder on the building plate. The laser then passed over the layer of powder according to a provided 3D drawing, whereby the powder layer was exposed to the laser beam and therefore melted. After the layer of powder 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 pm. The printing was performed in an inert atmosphere using argon. The scan speed was between 500 to 800 mm/s. The power of the energy source was between 80 - 200 W. The samples were allowed to cool to room temperature in the inert atmosphere. The printed samples were de-powdered and then the building plate comprising the samples was removed from the machine. The building plate with the samples was heat treated in 650 to 1200 °C for 0.5 to 3 hours. The building plate and the samples were then cooled to room temperature and then machined (cut) in order to remove the samples from the building plate.

Example 2

Printing by DED

Two powders having the compositions according to Table 2 were produced using gas atomization and then sieved to suitable fraction so that powders within particle size of 45-90 pm were obtained .

Table 2

Several 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 feed into the melt pool and was rapidly solidified. The powder was added to the pool by using a focused powder stream. The laser was moved along a pre-designed path, creating a layer of solidified substrate (X-Y plane). The laser was then moved up (Z axis) and started to create melt pool on the surface of the previous substrate, creating a new layer following the specific path. Thus, a 3 -dimensional body was created.

The powder layer height was between 0.3 to 2 mm. The printing was performed with or without using argon atmosphere. The deposition speed was between 1000 mm/min - 2500 mm/min. Powder feed was between 4 g/min to 25 g/min. The power of the laser source was between 50 - 2000 W.

In Figure 3, a micrograph of a DED printed structure of Powder 5 is disclosed. The structure is very dense, not showing any indications of cracking, defects or porosity. A Leica stereo microscope was used.

Example 3 — Testing

Figure 1 presents a comparison of the creep strength of samples containing conventionally produced FeCrAl (CP 1) alloys and samples which have been manufactured by additive manufacturing by using SLM (SLM 1) and samples which has have been manufactured by additive manufacturing by using (SLM 2).

The conventional samples were produced by casting and rolling and-prepared according to S.S. EN ISO 6892-2:2018, “Cylindrical test pieces with threaded gripping ends”, with diameter, do, 4 mm and original gauge length, Lo, 20 mm.

The conventional samples had a composition according to the following specification:

The additive manufacturing samples were, after printing, machined to standard S.S. EN ISO 6892-2:2018, with gripped (turned) ends, diameter, do 4 mm and original gauge length, Lo, 20 mm. The additive manufacturing samples (SLM 1 and SLM2) had a composition according to the following specification:

The samples were loaded with dead load. The creep rate was calculated as percentage change in length of the samples over time at constant loading and temperatures. The testing of the printed samples was performed at 1100 °C and 1200 °C. The conventional produced samples (CP 1) were tested 900 °C and 1100 °C.

The printed material is found to be anisotropic. The creep results shown in Figure 1 are for the stronger direction of the material where samples were loaded parallel to printing direction. Further, as can be seen from Figure 1, the additive manufactured samples have much lower creep rate compared to the conventionally produced sample. Even though the conventionally produced samples were tested at lower temperature, the creep strength of the printed samples was still higher as the creep rate was lower. In addition, the printed samples had a long time to rupture which means that the lifetime of such product will be longer.

Figure 2 shows mass gain curves vs time at 1100 °C for an additive manufactured sample made from Powder 4 of Table 1 and a conventional manufactured sample having a similar composition as Powder 4. The mass gain weight was checked at 100 h intervals. The mass gain curves show that the additive manufactured sample have better oxidation properties than the conventional manufactured sample thus meaning that it will be excellent in high temperature applications and will have a longer service life.

Claims

1. A printable ferritic FeCrAl powder composition, wherein the FeCrAl powder composition consists in weight%

Cr 9.0-25.0;

A1 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;

2. The printable FeCrAl powder composition according to claim 1, wherein the content of C is < 0.05 weight%.

3. The printable FeCrAl powder composition according to claim 1 or claim 2, wherein the content of Mn is < 0.5 weight%.

4. The printable FeCrAl powder composition content according to any one of claims 1 to 3 wherein the content of Si is less than 0.5 wt% or more than 0.5 up to 3.0 weight%.

5. The printable FeCrAl powder composition according to any one of claim 1 to 4, wherein the content of A1 is from 3 to 6 weight%.

6. The printable FeCrAl powder composition according to any one of claim 1 to 5, wherein the content of Cr is from 9 to 11 weight% or 18 to 24 weight%.

7. The printable FeCrAl powder composition according to claim 1 or claim 2, consisting in weight%

Cr 18 - 24; A1 4 to 6;

Mn <0.5;

Si <0.5 or more than 0.5 - 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.

Balance Fe and unavoidable impurities.

8 The printable FeCrAl powder composition according to claim 1 or claim 2, consisting in weight%

Cr 18 - 24;

A1 4 to 6;

Mn <0.5; Si <0.5 or above 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.

Balance Fe and unavoidable impurities.

9. An additive manufactured object comprising the printable powder composition according to any one of claims 1 to 8.

10 The additive manufactured object according to claim 9, wherein the object is a high temperature resistant heating element or a high temperature resistant component.

11 The additive manufactured object according to claim 9, wherein the object is an electrical heating element or electrical resistive component.

12 An additive manufacturing process for manufacturing the object according to any one of claims 9 to 11, wherein the additive manufacturing process is selected from a powder bed fusion additive manufacturing process or Direct Energy Deposition (DED) and wherein the ferritic FeCrAl powder according to any of claims 1 to 9 is used,

13. The additive manufacturing process according to claim 12, wherein a powder bed fusion additive manufacturing method is used and wherein the powder bed fusion additive manufacturing method is SLM or EBM.

14. Use of the additive manufactured object according to any of claims 9 to 13 as a component in electrical heating or high temperature applications or as a heating element.