Fe-cr-al powder for use in additive manufacturing

Abstract

To provide a ferritic Fe-Cr-Al alloy powder having a chemical composition particularly adapted to additive manufacturing providing crack-free objects, and to provide a method for producing three dimensional objects using the powder.SOLUTION: The present disclosure relates to iron-chromium-aluminum (Fe-Cr-Al) powders suitable for additive manufacturing, and additive manufacturing methods. In particular, the TiN inoculant will improve the solidification structure during the additive manufacturing process, which results in an object with improved material quality, in particular an object with a more equiaxed as-solidified grain structure.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to powders suitable for additive manufacturing. More specifically, the present disclosure relates to iron-chromium-aluminum (Fe—Cr—Al) powders having specific chemical compositions for use in additive manufacturing processes. The present disclosure also relates to additive manufacturing processes and methods for producing three-dimensional objects using the Fe—Cr—Al powders. The present disclosure also relates to additively manufactured articles comprising the Fe—Cr—Al powders. [Background technology]

[0002] Additive manufacturing is defined as the process of building an object from a three-dimensional data model by joining material layer by layer. Metal-based additive manufacturing enables the layer-by-layer fabrication of near-net-shape metallic parts with complex geometries that are not limited by the process limitations of traditional manufacturing.

[0003] Objects containing iron-chromium-aluminum (Fe-Cr-Al) powders are attractive for electrothermal and high-temperature applications. However, one of the challenges associated with objects fabricated from these powders using additive manufacturing techniques is their tendency to crack during and after fabrication. In additive manufacturing techniques such as selective laser melting (SLM), electron beam melting (EBM), and directed energy deposition (DED), resolidification is dominated by epitaxial growth of crystals from previously solidified layers. The solidified material is primarily composed of large, columnar grains with significant elongation in the build direction. Such a coarse, elongated structure makes Fe-Cr-Al objects susceptible to cracking at low temperatures. Layer-by-layer melting and solidification methods also create high thermal stresses in the build. As a result, the combination of residual stresses and columnar structures makes the resulting three-dimensional objects prone to cracking during and after fabrication. One reason for this may be that the Fe-Cr-Al powder compositions used in additive manufacturing are based on conventional compositions, i.e., these compositions are still made using conventional manufacturing methods. This may make these compositions unsuitable for epitaxial growth induced by directional temperature gradients during additive manufacturing, which can result in anisotropic structural properties and coarse-textured microstructures with cracking. Thus, it may be difficult and complicated to fabricate complex structures in these Fe-Cr-Al powders.

[0004] Document CN110125383 discloses a ferritic Fe-Cr-Al powder composition containing, by weight, 18-34% Cr, 4-6% Al, Si≦0.5%, Ti≦0.5%, Y≦1%, Zr≦0.5, and the balance Fe. However, although the powder composition is disclosed and it is mentioned that it may be usable in additive manufacturing, no products actually manufactured by additive manufacturing are disclosed.

[0005] In conclusion, there remains a need in the art for ferritic Fe—Cr—Al alloy powders with chemical compositions particularly adapted for additive manufacturing that provide crack-free objects.

[0006] The present disclosure aims to solve or at least reduce the aforementioned problems. Summary of the Invention

[0007] Accordingly, the present disclosure provides ferritic iron-chromium-aluminum (Fe—Cr—Al) powder compositions optimized for additive manufacturing of three-dimensional objects.

[0008] The Fe—Cr—Al powder according to the present disclosure has the following composition (in weight percent): Cr 12.0~25.0, Al 3.50~6.50, Ti 0.20~1.10, N 0.06~0.20, Zr 0.05~0.20, Y 0.02~0.15, C ≦0.050, Si ≦0.50, Hf ≦0.30, Ta ≦ 0.30, Mn ≤ 0.40, Ni ≤ 0.60, O ≦600 ppm, The balance is Fe and unavoidable impurities. It is characterized in that TiN is present as an inoculant.

[0009] In the present disclosure, TiN is present in the Fe—Cr—Al powder as an inoculant. It has been shown that inoculants can provide many benefits during additive manufacturing processes and in the objects produced thereby. In particular, TiN inoculants can introduce grain refinement and, as will be disclosed hereinafter, provide a near-isotropic grain structure.

[0010] The present disclosure further provides a method for producing three-dimensional objects using an additive manufacturing process and the Fe—Cr—Al powder composition as defined above or below. Surprisingly, it has been found that the additive manufacturing process and the use of the disclosed Fe—Cr—Al powder allow for the production of crack-free objects with complex designs and shapes in a cost- and time-efficient manner. In particular, it has been found that the TiN inoculant improves the solidification structure during the additive manufacturing process, resulting in objects with improved material quality, in particular objects with a more equiaxed, as-solidified grain structure.

[0011] The present disclosure further relates to crack-free additively manufactured objects obtained using the Fe-Cr-Al powder as defined above or below and containing the same alloying elements in the same ranges as the powder. Crack-free objects can have complex designs and shapes and perform well in high-temperature applications. Surprisingly, it has been found that TiN inoculant in the Fe-Cr-Al powder can limit cracking behavior during the manufacturing process by promoting nucleation, thereby resulting in the collapse of the columnar structure and providing objects with improved properties. "Crack-free" means that cracks are not visible to the naked eye or under a microscope. [Brief explanation of the drawings]

[0012] [Figure 1a-b] 1 is a SEM micrograph of Fe-Cr-Al powder particles of various compositions. [Figure 1c-d] 1 is a SEM micrograph of Fe-Cr-Al powder particles of various compositions. [Figure 2a-b] 10 is a photograph showing printed cubes composed of various Fe—Cr—Al powder compositions. [Figure 3a-b] EBSD micrographs of printed cubes composed of various Fe-Cr-Al powder compositions. DETAILED DESCRIPTION OF THE INVENTION

[0013] The present disclosure provides a composition having the following composition (in weight percent): Cr 12.0~25.0, Al 3.50~6.50, Ti 0.20~1.10, N 0.06~0.20, Zr 0.05~0.20, Y 0.02~0.15, C ≦0.050, Si ≦0.50, Hf ≦0.30, Ta ≦ 0.30, Mn ≤ 0.40, Ni ≤ 0.60, O ≦600 ppm, The balance is Fe and unavoidable impurities. The present invention relates to an Fe-Cr-Al powder characterized in that TiN is present as an inoculant.

[0014] The alloying elements of the powders according to the present disclosure will now be described in more detail. The terms "weight %" and "wt %" are used synonymously. Also, the list of properties or contributions mentioned for particular elements should not be considered exhaustive.

[0015] Iron (Fe) The primary function of the iron in the Fe-Cr-Al powder is to balance the alloying element composition of the powder composition or body.

[0016] Chromium (Cr) 12.0 to 25.0% by weight Chromium is an important element because it can improve the corrosion resistance of the resulting body and increase its tensile strength and yield strength. Furthermore, chromium facilitates the formation of an Al2O3 layer on the final body through the so-called third element effect, i.e., the formation of chromium oxide during a transient oxidation stage. Too low a chromium content can result in insufficient corrosion resistance. Thus, chromium should be present in an amount of at least 12.0 wt.%, e.g., at least 15.0 wt.%, e.g., at least 20.0 wt.%. Too much chromium can lead to α decomposition to α' and 475°C embrittlement, and can also lead to increased solid solution strengthening effects on the ferritic structure. Thus, the maximum chromium content is set at 25.0 wt.%, e.g., at most 24.0 wt.%, e.g., at most 23.50 wt.%, e.g., at most 23.0 wt.%, e.g., at most 22.50 wt.%, e.g., at most 22.0 wt.%, e.g., at most 21.50 wt.%. According to an embodiment, the chromium content is 12.0-25.0 wt.%, for example 18.00-24.0 wt.%, for example 20.0-23.50 wt.%.

[0017] Aluminum (Al) 3.50 to 6.50% by weight Aluminum is an important element because, when exposed to oxygen at high temperatures, it can form a dense, thin Al2O3 layer on the surface of the manufactured object, protecting the underlying surface from further oxidation. Furthermore, aluminum improves electrical resistance. If the amount of aluminum is too low, it may lose its ability to form the Al2O3 layer, which may reduce electrical resistance. Thus, aluminum should be present in an amount of at least 3.50 wt%, e.g., at least 4.00 wt%, e.g., at least 4.50 wt%, e.g., at least 4.80 wt%. Too high an aluminum content may also cause brittleness at low temperatures and increase the formation of unwanted, brittle aluminides. Thus, the maximum amount of aluminum is set at 6.50 wt%, e.g., at most 6.00 wt%, e.g., at most 5.50 wt%, e.g., at most 5.40 wt%, e.g., at most 5.30 wt%, e.g., at most 5.20 wt%. According to an embodiment of the present disclosure, the aluminum content is 3.50-6.50 wt%, for example, 4.00-5.50 wt%, for example, 4.50-5.50 wt%.

[0018] Titanium (Ti) 0.20 to 1.10 weight percent Titanium is an important element because it can form TiN with nitrogen. According to one embodiment, the ratio in weight % of Ti / N, due to the molar weights of Ti and N, should be at least 3.3, such as at least 4.5.

[0019] Furthermore, titanium can also reduce carbon activity through the formation of TiC, further improving high-temperature creep strength. If the amount of Ti is too low, the powder of the present disclosure will not have enough TiN inoculant for ferrite crystal nucleation during solidification in the additive manufacturing process. Furthermore, if the Ti content is too low, there is a high risk of forming unwanted chromium carbides and / or brittle aluminum nitrides. Therefore, titanium should be present in an amount of at least 0.20 wt%, such as at least 0.25 wt%, e.g., at least 0.30 wt%. On the other hand, if the titanium content is too high, TiO may be formed, which may have a negative effect on the formation of AlO. For these reasons, the maximum Ti content is set to 1.10 wt%, e.g., at most 1.00 wt%, e.g., at most 0.90 wt%, e.g., at most 0.8 wt%. According to an embodiment of the present disclosure, the Ti content is 0.20-0.80 wt%, e.g., 0.20-0.70 wt%, e.g., 0.24-0.60 wt%.

[0020] Nitrogen (N) 0.06 to 0.20% by weight Nitrogen is an important element because it can form TiN particles with titanium. In the present disclosure, TiN is a desirable particle because it can function as an inoculant. According to an embodiment, due to the molar weights of Ti and N, the ratio of Ti / N by weight % should be at least 3.3, for example at least 4.5.

[0021] Nitrogen is also an important element because it can enable the precipitation of other metal nitrides, such as ZrN. ZrN can improve high-temperature creep resistance. However, if the nitrogen content is too low, nitrides can only be formed in small amounts. Therefore, nitrogen should be present in an amount of at least 0.06 wt%, such as at least 0.07 wt%, such as at least 0.08 wt%, such as at least 0.09 wt%. Furthermore, if the nitrogen content is too high relative to the titanium content, there is a risk that AlN may form, which may adversely affect oxidation resistance. For these reasons, the maximum N content is set to 0.20 wt%, such as at most 0.15 wt%, such as at most 0.10 wt%. According to an embodiment of the present disclosure, the N content is 0.060-0.20 wt%, such as at most 0.07-0.15 wt%, such as at most 0.07-0.12 wt%.

[0022] TiN inoculant The Fe-Cr-Al powder, as defined above or below, may have a TiN inoculant uniformly dispersed throughout the powder, which is a desirable inoculant that can introduce both grain refinement and a more isotropic grain structure in additively manufactured parts.

[0023] It has been shown that utilization of the disclosed Fe—Cr—Al powders in additive manufacturing processes can reduce the range of grain boundary alignments, providing manufactured objects with increased crystallographic diversity.

[0024] A further advantage of TiN inoculants is that they can refine the interior of the resulting additively manufactured object, with the resulting grain structure having a significantly reduced average grain size compared to typical conventional additively manufactured materials without these TiN inoculants.

[0025] Another advantage is that the TiN inoculant in the Fe—Cr—Al powder of the present disclosure can control the solidification state during the additive manufacturing process, thereby eliminating the need for time-consuming layer-to-layer conditioning.

[0026] We found that the introduction of TiN inoculant into Fe-Cr-Al powders can refine the solidification structure during additive manufacturing, because TiN inoculant can act as a nucleus for the formation of ferrite crystals, thereby forming a finer grain structure. TiN is thermodynamically stable in liquid alloys and can form prior to ferrite crystals during solidification. This allows it to act as an effective nucleation site for ferrite crystals at the ferrite solidification temperature. Without being bound by any theory, it is believed that the undercooling required for ferrite nucleation on TiN particles is very low due to the good lattice match between the lattice structure of TiN particles and the ferrite crystals, as well as the low interfacial energy. In addition, the good coherence between TiN and ferrite may also reduce stress in the formed object.

[0027] The size and / or size distribution of the TiN inoculants can determine the undercooling for equiaxed growth. For this reason, according to embodiments, the average size of the TiN inoculants is at least 30 nm, such as at least 50 nm, for example at least 100 nm.

[0028] Additionally, the presence of oxides such as corundum in the Fe—Cr—Al powders of the present disclosure during solidification at high cooling rates can be advantageous for the nucleation and growth of TiN inoculants.

[0029] Thus, the uniform and finely dispersed TiN inoculant in the Fe—Cr—Al powder of the present disclosure may provide a more isotropic and refined solidification structure during the layer-by-layer additive manufacturing process with a more random crystallographic orientation, which may provide reduced cracking behavior during and / or after additive manufacturing of the Fe—Cr—Al object. The lower residual stresses and less columnar grained structure formed during additive manufacturing may be more likely to result in crack-free additively manufactured objects.

[0030] Zirconium (Zr) 0.05 to 0.20% by weight Zirconium is an important element in the powder composition of the present invention because it can reduce the activity of C and N by forming ZrC or ZrN precipitates. Zirconium can also improve the high-temperature creep strength of the manufactured object. Too little Zr can increase the risk of unwanted chromium carbide and / or aluminum nitride formation. Therefore, zirconium should be present in an amount of at least 0.05 wt%, such as at least 0.07 wt%, e.g., at least 0.10 wt%. On the other hand, too high a zirconium content can adversely affect the formation of Al2O3. For these reasons, the maximum zirconium content is set at 0.20 wt%, e.g., up to 0.15 wt%. According to an embodiment of the present disclosure, the zirconium content is 0.05-0.20 wt%, e.g., 0.07-0.20 wt%, e.g., 0.070-0.10 wt%.

[0031] Yttrium (Y) 0.02 to 0.15% by weight The addition of yttrium improves the oxidation resistance of the manufactured object. If the amount of yttrium added is too small, it will result in a decrease in oxidation resistance. For this reason, yttrium must be added in an amount of at least 0.02 wt%, for example at least 0.04 wt%, for example 0.05 wt%, for example 0.06 wt%. However, if the amount of yttrium added is too large, it may cause high-temperature embrittlement. As a result, the maximum yttrium content is set to 0.15 wt%, for example 0.10 wt%, for example 0.08 wt%.

[0032] Carbon (C)≦0.050% by weight Carbon is an element that is not intentionally added, but is unavoidable due to powder processing. This element can cause a reduction in hot ductility and the formation of metal carbides. Thus, to limit the presence of too many metal carbide precipitates, the carbon content must be ≦0.050 wt.%, e.g., ≦0.040 wt.%, e.g., ≦0.030 wt.%.

[0033] Silicon (Si)≦0.50% by weight Silicon may be present in concentrations up to 0.50 wt. % to improve electrical resistivity and improve high temperature corrosion resistance, but concentrations above this level can increase hardness and may also cause low temperature cracking.

[0034] Tantalum (Ta)≦0.30% by weight Tantalum can be optionally added, and when added, tantalum can improve high temperature creep strength. Tantalum can also reduce carbon activity by forming TaC precipitates, so the maximum tantalum content is set at 0.30 wt%.

[0035] Hafnium (Hf)≦0.30% by weight Hafnium can be optionally added. The addition of hafnium can improve high-temperature creep strength. However, hafnium can reduce carbon activity by forming HfC precipitates. Therefore, the maximum hafnium content is set to ≦0.30 wt%.

[0036] Manganese (Mn)≦0.40% by weight Manganese may be present as an impurity. Manganese can inhibit the formation of the Al2O3 layer, which has a negative effect on oxidation resistance. Thus, the maximum manganese content is ≦0.40 wt.%, for example ≦0.20 wt.%.

[0037] Nickel (Ni)≦0.60% by weight Nickel may be present as an impurity, but may increase hardness and brittleness at low temperatures, so the maximum nickel content is therefore ≦0.60 wt.%, for example ≦0.5 wt.%.

[0038] Oxygen (O)≦600ppm Oxygen may be present in the form of oxides. The maximum permitted content is ≦600 ppm.

[0039] According to embodiments, the powder may also contain small amounts of one or more of the above impurity elements, such as, but not limited to, magnesium (Mg), cerium (Ce), calcium (Ca), phosphorus (P), tungsten (W), cobalt (Co), sulfur (S), molybdenum (Mo), niobium (Nb), vanadium (V), and copper (Cu), in amounts up to 0.2 wt.%.

[0040] Furthermore, the Fe—Cr—Al powder as defined above or below can include any of the alloying elements referenced herein, within any of the ranges referenced herein. According to one embodiment, the powder of the present disclosure is composed of all of the alloying elements referenced herein, within any of the ranges referenced herein.

[0041] Additionally, the additively manufactured object as defined above or below can comprise or consist of alloying elements of the Fe—Cr—Al powder as defined above or below in this disclosure, within any ranges mentioned herein.

[0042] The Fe—Cr—Al powder as defined above or below can be produced by various methods, including but not limited to: Direct gas atomization method, heating a powder containing a low nitrogen content but containing all alloying elements within the ranges described above or below in a nitrogen-rich atmosphere, i.e., nitriding the powder; a method of mixing a powder containing a low nitrogen content but all alloying elements within the ranges described above or below with a powder containing fine particles of less stable nitrides; A method of mixing fine / small particles of TiN with Fe-Cr-Al powder so that the resulting powder has the same alloy element composition as defined above or below. Examples include:

[0043] According to an embodiment, to be suitable for use in additive manufacturing processes, the Fe—Cr—Al powder particle (average) size is less than 200 μm, such as less than 120 μm, such as less than 100 μm.

[0044] According to an embodiment, the size distribution of the Fe—Cr—Al powder may be selected from 4 to 200 μm, such as 10 to 120 μm, for example 10 to 90 μm.

[0045] The present disclosure also relates to an additive manufacturing process and a method for producing a three-dimensional object using the Fe—Cr—Al powder composition as defined above or below.

[0046] According to an embodiment, the additive manufacturing method is selected from powder bed fusion or directed energy deposition (DED).

[0047] In powder bed fusion manufacturing, layers of powder are selectively melted, for example, using a high-power laser. Due to the small interaction volume and the melt pool, the cooling rate during the process is extremely high. As a result, the microstructure is very different compared to a forged or cast object using the same powder composition.

[0048] During powder bed fusion additive manufacturing processes, TiN inoculants in Fe-Cr-Al powders are present in the melt before solidification and can promote grain refinement by acting as nucleation sites as the melt solidifies. Solidification by growth of crystals nucleated by TiN particles opposes the epitaxial growth of crystals from previously solidified material. Crystals nucleated by TiN inoculants in the undercooled melt can grow as equiaxed grains until they become incorporated by epitaxial solidification fronts or until they join other solidification structures during the additive manufacturing process.

[0049] According to one embodiment, the powder bed fusion manufacturing method is selected from selective laser melting (SLM) or electron beam melting (EBM). In both of these embodiments, a powder bed is used, where the powder is provided in a layer and an energy source is passed over the area of ​​the layer of powder to be melted, causing the powder to melt or at least partially melt as it is irradiated by the energy source. After the desired portion of the powder layer has melted, a new layer is provided, and so on until the desired object is obtained.

[0050] In SLM, the energy source is one or more laser beams, while in EBM, the energy source is an electron beam. SLM is performed in an inert atmosphere, such as an argon or nitrogen atmosphere. Furthermore, the process can utilize a support, if necessary, for example to compensate for small angles, which is subsequently removed. Furthermore, SLM printing is performed directly on a loose powder layer.

[0051] In EBM, each powder layer is preheated before it is locally fused together by an electron beam. -5 It is carried out in a vacuum of 100 bar and at high temperatures. Furthermore, in EBM, each new powder layer is first pre-sintered using an electron beam before the actual printing of the powder layer begins.

[0052] According to one embodiment, the powder layer has a thickness between 10 and 250 μm, for example, in SLM the layer thickness is between 10 and 80 μm, such as between 10 and 45 μm, and in EBM the layer thickness is between 10 and 250 μm.

[0053] According to one embodiment, the additive manufacturing method is directed energy deposition (DED). In this type of method, an energy source is used to generate a localized melt pool. Metal powder is fed into this melt pool as a filler material. The position of the melt pool is constantly changed as a three-dimensional object is generated by the solidified material. The energy source can be either a laser beam or a plasma arc. The heat generated by the source should be sufficient to melt the surface of the substrate, thereby forming a melt pool. By using a focused powder stream, the powder is added to the pool, i.e., melted and bonded by being propelled by a focused energy source. DED methods are typically performed using an inert shielding gas atmosphere to protect the melt pool. The material feed angle can be varied depending on the desired shape of the object.

[0054] Furthermore, due to the additive manufacturing process and the Fe-Cr-Al powder composition as defined above or below, post-processing such as heat treatment or shaping may not be necessary, and deposition rate reductions may be avoided, thereby potentially increasing deposition productivity.

[0055] Additively manufactured articles obtained from Fe—Cr—Al powders as defined above or below can perform well at temperatures reaching 1350°C. Furthermore, the articles of the present disclosure can have exceptionally high-temperature corrosion resistance and resistance to oxidation, sulfidation, and carburization. Furthermore, the additively manufactured articles can have exceptionally high-temperature creep strength, dimensional stability, and high electrical resistance. The additively manufactured articles are particularly useful as electric heating elements or components in high-temperature applications (for applications operating between 400 and 1350°C). The additively manufactured articles are also particularly useful as components in electric heating applications. The articles can also be used to protect other objects from high-temperature wear and corrosion. This allows the articles of the present disclosure to be used in both electric heating and high-temperature applications.

[0056] The present invention is further illustrated by the following non-limiting examples. [Example]

[0057] powder composition Four Fe-Cr-Al powders (see Table 1 for their compositions) were prepared with various titanium and nitrogen contents. Powders 1 and 2 were comparative examples, and Powder 3 * and 4 * is a powder of the present invention. The powder was produced by induction melting followed by gas atomization. A metal melt with a specific composition was injected through a small melt nozzle into an atomic chamber filled with an inert atmosphere. A high-speed gas nozzle system broke the melt stream into very fine droplets, which cooled and then transformed into solidified particles in the air in a fraction of a second. The particles were collected and cooled to room temperature in an inert atmosphere. The powder was sieved to -45 μm. TIFF2026031921000001.tif216170

[0058] The grain refinement effect achieved through the introduction of TiN inoculant is visually noticeable in the solidification microstructure of the as-atomized powder. Qualitatively, monocrystallinity, as opposed to polycrystallinity, can be visually recognized through "grainography" or "electron channeling imaging," as briefly described below. Fe-Cr-Al powder is mixed with conductive Bakelite powder and formed into a solid cylindrical puck. One of the flat surfaces of the puck is comminuted to a sufficient depth and then polished to a very high surface finish. This allows polished portions of several powder particles to be visible on the polished puck surface during analysis by scanning electron microscopy (SEM). The depth to which incident SEM electrons penetrate the crystalline metallic material under study, and therefore the number of backscattered electrons reflected, also depends on the crystal orientation of the crystals under study in the sample. Thus, grains with different crystal orientations relative to the electron incidence direction will result in different amounts of reflected backscattered electrons, ultimately resulting in contrasting grains under study. Consequently, this effect is best discerned by the backscattered electron detector.

[0059] The results of this qualitative analysis, performed on powder particles ranging in size from 1 to 45 μm from four powders, can be seen in Figures 1a-d. The results of this analysis indicate that the powder with a combination of high titanium and high nitrogen content (Powder 4) yielded the highest degree of polycrystallinity and the smallest average grain size. Powder 4's particles also exhibited the highest number of cubic TiN precipitates. The second-highest degree of polycrystallinity was exhibited by the powder with moderate concentrations of titanium and nitrogen (Powder 3). The powder with both low titanium and low nitrogen contents (Powder 2) exhibited the lowest degree of polycrystallinity. Powder 1 exhibited no or only slight refinement. Thus, it can be concluded that to achieve refinement through the incorporation of an inoculant, both the titanium and nitrogen concentrations should be increased simultaneously to obtain a TiN inoculant that promotes ferrite grain nucleation.

[0060] printing Many parts were printed from each of these powders using the same printing parameter settings. Four different powders with the compositions described above were fed into the SLM machine by adding them to the powder delivery system. During the printing process, powder was fed from the powder delivery system within the machine and a scraper was used to spread the layer of powder on the build plate. The laser then printed the provided 20 x 20 x 20 mm 3 The powder layer was melted by irradiating it with a laser beam, which passed through it according to the 3D drawing of a cube of the size of 1. After the powder layer had melted, a new layer was added until the desired sample was formed according to the 3D drawing.

[0061] The thickness of the powder layer was 20 μm. Printing was performed in an inert atmosphere using argon. The scanning speed was 500 mm / s. The power of the energy source was 95 W.

[0062] The samples were allowed to cool to room temperature in an inert atmosphere, and then finished cubes were cut from the build plates without any prior heat treatment.

[0063] evaluation The four printed cubes were visually inspected. No cracks were observed for the cubes containing powders 3 or 4, in contrast to the cubes containing powders 1 or 2. Figure 2a discloses a printed cube containing powder 2 (Object 2) in which cracks are visible (see arrows in Figure 2a), and Figure 2b discloses a printed cube containing powder 4 (Object 4).

[0064] The microstructure was analyzed in the as-printed state. Grain maps determined by electron backscatter diffraction (EBSD) analysis (accelerating voltage 20 kV, sampling size 1 μm, minimum 10 pixels per grain) of polished vertical sections parallel to the build direction of the cubes suggest that the cube containing powder 4 (object 4 in Figure 3b) exhibits significantly smaller grain sizes than the other cubes, such as the cube containing powder 2 (object 2 in Figure 3a). This difference is related to the elevated concentrations of titanium and nitrogen. According to ECD, the 20 largest grains are 164 ± 52 for object 2, compared to 106 ± 21 for object 4. Correspondingly, the grains / mm 2 >100 μm is 397 for object 2 and 1428 for object 4.

[0065] SEM+EBSD analysis performed on Object 4 shows that even with the finer grains, solidification still occurs primarily epitaxially, but there are grain clusters present that represent a coaxial morphology. However, SEM analysis cannot confirm which mechanism is causing the grain refinement for Powder 4 compared to Powder 2. It could be a combination of grain boundary pinning and inoculation, both of which could be correlated to the TiN inoculant in the melt pool.

[0066] SEM+EBSD analysis performed on Object 2 shows columnar grains aligned primarily parallel to the build direction. The microstructure is characterized by coarse columnar grains up to mm in length. Epitaxial columnar grain growth across multiple layers suggests the absence of active inoculants and the impossibility of fine grain formation within the melt pool due to heterogeneous nucleation. The material was found to have a high crack susceptibility, with the majority of cracks observed being transverse.

[0067] Tensile tests performed on the printed objects showed that Object 4 had higher ductility than Object 2, likely due to finer grains.

[0068] Oxidation testing showed similar results for the two bodies. Thus, the TiN inoculant does not have a detrimental effect on the oxidation resistance of Body 4.

[0069] Thus, the very positive effect of TiN inoculant in Fe-Cr-Al powder on grain refinement and crack resistance in the finished part is evident.

Claims

1. The composition below (by weight): Cr 12.00~25.00, Al 3.50-6.50, Ti 0.20-1.10, N 0.06-0.20, Zr 0.05-0.20, Y 0.02~0.15, C ≦0.050, Si≦0.50, Hf≦0.30, Ta ≦ 0.30, Mn≦0.40, Ni≦0.60, O ≦600 ppm, The balance is Fe and unavoidable impurities, An Fe-Cr-Al powder characterized in that TiN is present as an inoculant.

2. 2. The Fe—Cr—Al powder according to claim 1, wherein the Cr content is 18.0 to 24.0 wt.

3. 3. The Fe—Cr—Al powder according to claim 1, wherein the Al content is 4.0 to 6.0 wt %.

4. 4. The Fe—Cr—Al powder according to claim 1, wherein the Ti content is 0.30 to 1.00 wt %.

5. The Fe—Cr—Al powder according to any one of claims 1 to 4, wherein the N content is 0.09 to 0.20 wt %.

6. 6. The Fe—Cr—Al powder according to claim 1, wherein the Zr content is 0.07 to 0.10 wt %.

7. The Fe—Cr—Al powder according to any one of claims 1 to 6, wherein Ti / N≧3.

3.

8. 8. The Fe—Cr—Al powder according to any one of claims 1 to 7, having a powder size of less than 120 μm.

9. A method for producing a three-dimensional object using an additive manufacturing process and the Fe—Cr—Al powder according to any one of claims 1 to 8.

10. 10. The method of claim 9, wherein the additive manufacturing process is selected from powder bed fusion or directed energy deposition (DED).

11. The method of claim 10, wherein the powder bed fusion process is SLM or EBM.

12. 12. An additively manufactured object comprising the powder of any one of claims 1 to 8 or produced by the method of any one of claims 9 to 11.

13. The additive manufactured object according to claim 12, which is a high-heat resistant heating element or a high-heat resistant part.

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