Metal powder for additive manufacturing

Abstract

The invention relates to a metal powder, the composition of which comprises the following elements, expressed in contents by weight: 12% < = Mo < = 18%, 3% < = P < = 7%, 0.5% < = C < = 3%, 0.5% < = B < = 5%, Si < = 1%, the remainder being Fe and unavoidable impurities resulting from processing, the microstructure of the metal powder comprising at least 95% by weight of an amorphous phase, the remainder consisting of a crystalline phase.

Description

Technical Field

[0001] The present invention relates to metal powders for the manufacture of steel components, in particular for their additive manufacturing. The present invention also relates to a method for manufacturing metal powders. Background Art

[0002] Fe-based bulk metallic glasses (BMGs) have attracted much attention due to their excellent soft magnetic properties, high corrosion resistance, good mechanical properties, high wear resistance, etc. They are particularly used as efficient magnetic medium and high-frequency transformers in the electronics and electrical industries. However, so far, most Fe-based BMGs with good soft magnetic properties can only be produced under very complex process conditions. The liquid composition must be cast between cooling rollers at a high cooling rate to obtain an amorphous material, usually in the form of a thin strip. In addition to the complex process, the production of such thin strips also greatly limits their use. Summary of the Invention

[0003] Therefore, the object of the present invention is to overcome the disadvantages of the prior art by providing Fe-based BMGs that can be easily produced and processed to obtain the final components.

[0004] For this purpose, the first object of the present invention includes a metal powder, expressed in terms of the content by weight, the composition of the metal powder comprising the following elements:

[0005] 12% ≤ Mo ≤ 18%

[0006] 3% ≤ P ≤ 7%

[0007] 0.5% ≤ C ≤ 3%

[0008] 0.5% ≤ B ≤ 5%

[0009] Si ≤ 1%

[0010] The balance is Fe and unavoidable impurities generated by processing, and the microstructure of the metal powder contains at least 95% by weight of an amorphous phase, and the remaining part is composed of a crystalline phase.

[0011] The metal powder according to the present invention may also have the following optional features considered individually or in combination:

[0012] - The Mo content is 13% to 16.5% by weight,

[0013] - The P content is 6% to 7% by weight,

[0014] - The B content is 0.7% to 2% by weight,

[0015] - The Si content is 0.3% to 0.6% by weight,

[0016] - The microstructure of the metal powder contains at least 99 wt% amorphous phase,

[0017] - The average particle size is between 1 μm and 150 μm,

[0018] - The average particle size is between 1 μm and 20 μm,

[0019] - The average particle size is between 20 μm and 63 μm,

[0020] - The average particle size is between 60 μm and 150 μm.

[0021] The second object of the present invention includes a method for manufacturing metal powder for additive manufacturing, the method comprising:

[0022] - a) melting elements and / or metal alloys at a temperature at least 100 °C above the liquidus temperature to obtain a molten composition, which, expressed as a content by weight, contains the following elements:

[0023] 12% ≤ Mo ≤ 18%

[0024] 3% ≤ P ≤ 7%

[0025] 0.5% ≤ C ≤ 3%

[0026] 0.5% ≤ B ≤ 5%

[0027] Si ≤ 1%

[0028] the balance being Fe and inevitable impurities resulting from processing,

[0029] - b) atomizing the molten composition with a gas pressurized to 10 bar to 30 bar through a nozzle.

[0030] The third object of the present invention includes a method for manufacturing a printed component by additive manufacturing, wherein the powder according to the present invention or the powder obtained by the method according to the present invention is printed by laser powder bed fusion.

[0031] The method for manufacturing a printed component may also have the following optional features considered individually or in combination:

[0032] - It further includes a first step of forming a powder layer with a thickness less than 100 μm, and a second step of focusing a laser beam to melt at least a part of the powder layer to form a formed layer in an atmosphere consisting essentially of an inert gas,

[0033] - The laser power is limited to a maximum of 120 W,

[0034] - The scanning speed is 400 mm / second to 750 mm / second,

[0035] - The linear energy density is from 80 J / m to 200 J / m,

[0036] - The hatch spacing is from 40 μm to 100 μm,

[0037] - The volume energy density is from 80 J / mm 3 to 200 J / mm 3 .

[0038] A fourth object of the present invention includes a printed part obtained from the powder according to the present invention or a printed part obtained by the method according to the present invention, wherein the microstructure of the printed part contains at least 75 wt% of an amorphous phase, and the remaining part is composed of a crystalline phase. Detailed Description

[0039] The present invention will be better understood by reading the following description, which is provided solely for purposes of illustration and is in no way intended to be limiting.

[0040] Molybdenum is present in the composition according to the present invention in an amount of 12 wt% to 18 wt%. Molybdenum is an element that promotes the confusion effect to enhance the glass-forming ability of steel. Below 12 wt%, the glass-forming ability is insufficient. Above 18 wt%, molybdenum may segregate during solidification, which will promote the nucleation of a Mo-rich phase that is harmful to the glass-forming ability.

[0041] Preferably, the Mo content is 13 wt% to 16.5 wt% to further improve the glass-forming ability.

[0042] The phosphorus content is 3 wt% to 7 wt%. Phosphorus is another element that promotes the glass-forming ability of steel. Below 3 wt%, the glass-forming ability is insufficient. Above 7 wt%, phosphorus may form a brittle phase and cause thermal cracking, which is harmful to the material integrity. It also increases the crystallinity of the material.

[0043] Preferably, the P content is 6 wt% to 7 wt% to further enhance the glass-forming ability.

[0044] The carbon content is 0.5 wt% to 3 wt%. Carbon is another element that promotes the confusion effect to enhance the glass-forming ability of steel. It has a high negative enthalpy of mixing with Fe, and its atomic radius is 89 pm smaller than that of Fe atoms. However, a high carbon content may lead to the formation of carbides, especially cementite, M6C-carbides, and KSI-carbides (where nucleation will start). This is harmful to the microstructure.

[0045] Preferably, the C content is 1.4 wt% to 2.2 wt% to further improve the glass-forming ability of the steel and delay crystallization.

[0046] The boron content is from 0.5 wt% to 5 wt%. Boron greatly increases the hardness and wear resistance of the material. It is also used for grain refinement and for improving the Glass Forming Ability (GFA) of the steel, and its atomic radius is 69 pm smaller than that of the Fe atom. For these reasons, the B content is at least 0.5 wt%. However, the B content is limited to 5 wt% because beyond this value, the formation of borides is promoted, which causes brittleness of the material.

[0047] Preferably, the B content is from 0.7 wt% to 2 wt% to further avoid brittleness.

[0048] Silicon is present in the composition according to the invention in an amount up to 1 wt%. Si reduces the liquidus temperature, thus minimizing the risk of crystallization at temperatures above the glass transition temperature. It also promotes the disordering effect because it tends to form complex phases at equilibrium. However, above 1 wt%, Si tends to increase the liquidus temperature (which increases the risk of crystallization) and tends to form Si-rich carbides such as (Fe)2(Mo)2(FeMoSi)2(C)1 (where nucleation will start). Preferably, the Si content is from 0.3 wt% to 0.6 wt%.

[0049] The balance consists of iron and unavoidable impurities generated during processing. Nickel, chromium, manganese, titanium, rare earths, sulfur, nitrogen, oxygen, aluminum, vanadium, and copper are the main impurities. They are not deliberately added. They may be present in the ferroalloys and / or pure elements used as raw materials. Nitrogen may also be introduced during atomization. It is preferably controlled to avoid harmfully altering the microstructure and / or avoiding crystallization. Thus, the content of Ni should be limited to 2 wt%, Cr should be limited to 1 wt%, Mn should be limited to 1 wt%, Ti should be limited to 0.5 wt%, rare earths should be limited to 1 wt% and the content of other impurities should be limited to 0.03 wt%.

[0050] The microstructure of the metal powder contains at least 95 wt% of an amorphous phase, and the remainder is composed of a crystalline phase. The crystalline phase can be at least one of the following: austenite, ferrite, cementite, M2B-type boride such as (FeMoMn)2(B)1, M3B2-type boride such as (FeMo)0.4(Fe)0.2(B)0.4, M2P-type phosphide such as (FeMoMn)2(PSi)1, M3P-type phosphide such as (FeMO)3(P)1, M6C-type carbide such as (Fe)2(Mo)2(FeMoSi)2(C)1, and KSI-type carbide such as (FeMo)3(C)1. Preferably, the microstructure contains at least 99 wt% of an amorphous phase, and the remainder is composed of a crystalline phase. More preferably, the microstructure is completely amorphous. The weight fraction of the amorphous phase can be calculated by Rietveld refinement of the powder X-ray diffraction (XRD) measurement results.

[0051] The sphericity or shape factor of the powder is preferably high. The shape factor is defined in ISO 9276-6:2008 as 4πA / P 2 , where A is the measured area covered by the particle projection, and P is the measured perimeter / periphery length of the particle projection. A value of 1.0 represents a perfect sphere. The average shape factor of the powder is preferably at least 0.70 and more preferably at least 0.80. Due to this high shape factor, the metal powder is highly flowable. Thus, it further makes additive manufacturing easier, and the printed parts are denser and harder. The average shape factor can be measured by Dynamic Image Analysis according to ISO 13322-2:2021. It can be measured especially with a Digital Imaging Particle Size and Shape Analyzer such as to measure.

[0052] Preferably, the shape factor of no more than 7% of the particles is lower than 0.65.

[0053] In addition to the shape factor, the aspect ratio can also be used for the classification of powder particles. The aspect ratio is defined in ISO 9276-6:2008 as the ratio between Feret’s minimum length and Feret’s maximum length. It can be measured by Dynamic Image Analysis according to ISO 13322-2:2021. It can be measured especially with a Digital Imaging Particle Size and Shape Analyzer such as to measure. The average aspect ratio should preferably be higher than 0.7, more preferably higher than 0.75.

[0054] The particle size distribution measured by laser diffraction according to ISO13320:2020 preferably meets the following requirements (in μm):

[0055] 5≤D10≤25

[0056] 35≤D50≤85

[0057] 100≤D90≤280

[0058] The powder can be obtained by first mixing and melting pure elements and / or ferroalloys as raw materials. It can also be obtained by using pre-alloyed ingots of the desired composition.

[0059] Pure elements are usually preferred to avoid having too many impurities from ferroalloys, as these impurities may facilitate crystallization. However, in the case of the present invention, it has been observed that impurities from ferroalloys are harmless to achieving the amorphous phase.

[0060] Ferroalloys refer to various ferroalloys having a high proportion of one or more other elements (such as molybdenum, phosphorus, boron, silicon...). The main alloys are FeMo (usually containing 60 wt% to 75 wt% Mo), FeP (usually containing 15 wt% to 30 wt% P), FeB (usually containing 17.5 wt% to 20 wt% B), FeSi (usually containing 15 wt% to 90 wt% Si), FeNi (usually containing 70 wt% to 95 wt% Ni), FeCr (usually containing 50 wt% to 70 wt% Cr), FeMn (usually containing 70 wt% to 80 wt% Mn), FeTi (usually containing 45 wt% to 75 wt% Ti), FeAl (usually containing 40 wt% to 60 wt% Al), FeV (usually containing 35 wt% to 85 wt% V).

[0061] The raw materials can alternatively be added as pure elements (usually with a purity exceeding 99 wt%). The pure elements can in particular be carbon and pure metals, such as iron, molybdenum, boron, silicon, nickel, chromium, manganese, titanium, rare earths, aluminum, vanadium, copper.

[0062] Those skilled in the art know how to mix different ferroalloys and pure elements to achieve the target composition.

[0063] Preferably, the mixture contains FeMo ferroalloy, FeP ferroalloy, FeB ferroalloy, FeSi ferroalloy, graphite and Fe.

[0064] After obtaining a composition by mixing pure elements and / or ferroalloys in appropriate proportions, the composition is heated at a temperature at least 100 °C above its liquidus temperature and held at this temperature to melt all the starting materials and homogenize the melt. Due to this overheating, the reduced viscosity of the molten composition contributes to obtaining powders with high sphericity without satellites and with an appropriate particle size distribution. That is, since the surface tension increases with temperature, it is preferably not to heat the composition at a temperature more than 530 °C above its liquidus temperature.

[0065] Preferably, the composition is heated at a temperature at least 200 °C above its liquidus temperature to promote the formation of highly spherical particles. More preferably, the composition is heated at a temperature 220 °C to 280 °C above its liquidus temperature.

[0066] In a variant of the invention, the composition is heated between 1300 °C and 1600 °C, which represents a good compromise between the reduction in viscosity and the increase in surface tension.

[0067] The molten composition is then atomized into fine metal droplets by forcing the molten metal stream through the orifice of a nozzle under medium pressure and by impinging it with a gas jet (gas atomization) or a water jet (water atomization). In the case of gas atomization, the gas is introduced into the metal stream just before it leaves the nozzle, for generating turbulence when the entrained gas expands (due to heating) and enters a large collection volume (atomization tower). The atomization tower is filled with gas to promote further turbulence of the molten metal jet. The metal droplets cool during their fall through the atomization tower. Gas atomization is preferred as it favors the production of powder particles with high roundness and a small number of satellites.

[0068] The atomizing gas is preferably argon or nitrogen or a mixture thereof. Both of them increase the melt viscosity more slowly than other gases such as helium, which promotes the formation of smaller particle sizes. They also control chemical purity, avoiding undesirable impurities, and play a role in the good morphology of the powder. Since the molar weight of nitrogen is 14.01 g / mol, compared with 39.95 g / mol for argon, finer particles can generally be obtained with argon than with nitrogen. On the other hand, the specific heat capacity of nitrogen is 1.04 J / (g K), compared with 0.52 J / (g K) for argon. Therefore, nitrogen increases the cooling rate of the particles. Argon may be preferred over nitrogen to avoid contamination of the composition by nitrogen.

[0069] The gas pressure directly affects the particle size distribution. Additionally, the higher the pressure, the higher the cooling rate. Therefore, high pressure prevents particle crystallization. Thus, the gas pressure is set to be between 10 bar and 30 bar to optimize the particle size distribution and facilitate the formation of an amorphous phase. Preferably, the gas pressure is set to be between 14 bar and 20 bar to promote the formation of particles whose size is most compatible with the additive manufacturing technique.

[0070] The nozzle diameter has an impact on the flow rate of the molten metal and thus on the particle size distribution and on the cooling rate. The maximum nozzle diameter is limited to 4 mm to limit the increase in the average particle size and the decrease in the cooling rate. The nozzle diameter is preferably between 2 mm and 3 mm to more accurately control the particle size distribution.

[0071] The gas-to-metal ratio, defined as the ratio between the gas flow rate (in Kg / hour) and the metal flow rate (in Kg / hour), is preferably maintained between 1.5 and 7, and more preferably between 3 and 4. It helps to regulate the cooling rate.

[0072] According to a variant of the invention, in the case of hygroscopicity, the metal powder obtained by atomization is dried to further improve its flowability. The drying is preferably carried out in a vacuum chamber at 100 °C.

[0073] The metal powder obtained by atomization can be used as it is, or it can be sieved to retain the particles whose size is better suited to the additive manufacturing technique for later use. For example, in the case of additive manufacturing by powder bed fusion, the range from 20 μm to 63 μm (referred to as fraction F2) is preferred, and the range from 20 μm to 40 μm is even better. In the case of additive manufacturing by laser metal deposition or direct metal deposition, the range from 60 μm to 150 μm (referred to as F3) is preferred, and the range from 40 μm to 125 μm is even better. The fraction F1, which covers particle sizes below 20 μm, can be used, for example, in binder jetting.

[0074] Components made from the metal powder according to the present invention can be obtained by additive manufacturing techniques such as: Laser Powder Bed Fusion (LPBF), Direct Metal Laser Sintering (DMLS), Electron Beam Melting (EBM), Selective Heat Sintering (SHS), Selective Laser Sintering (SLS), Laser Metal Deposition (LMD), Direct Metal Deposition (DMD), Direct Metal Laser Melting (DMLM), Direct Metal Printing (DMP), Laser Cladding (LC), Binder Jetting (BJ). Coatings made from the metal powder according to the present invention can also be obtained by manufacturing techniques such as cold spraying, thermal spraying, High Velocity Oxygen Fuel.

[0075] In particular, the present invention can utilize the LPBF process which is a layer-upon-layer additive manufacturing technique. A thin layer of metal powder is evenly distributed on a substrate platform (usually metal) using a coating mechanism, and this substrate platform is fixed to a indexing table that moves along a vertical axis. This occurs inside a chamber that houses a strictly controlled atmosphere. After each layer has been distributed, the 2D slices of the component geometry are fused by selectively melting the powder. This is achieved using a high-power laser beam (usually a ytterbium fiber laser). The laser energy is strong enough to allow the particles to completely melt (weld) in the form of tracks or stripes. Basically, after completing one track, the process is repeated with the next track, which is separated from the first track by a scan spacing. This process is repeated layer by layer until the component is complete. Overhanging geometries are supported by the unmelted powder from the previous layer. The main process parameters used in LPBF are typically layer thickness, scan spacing, scan speed, and laser power. After completing the process, the remaining powder is sieved for reuse.

[0076] A method for producing an additive manufacturing part by LPBF includes a first step of forming a powder layer with a powder according to the present invention. Preferably, the powder layer is less than 100 μm. Above 100 μm, the laser may not be able to melt the powder in all layer thicknesses, which may result in porosity in the part. Preferably, the layer thickness is maintained at 10 μm to 60 μm to optimize the melting of the powder.

[0077] In a second step, a focused laser beam forms a formed layer by melting at least a portion of the powder layer under the process conditions detailed below.

[0078] In the case of LPBF, the individual layers of the printed part are at least partially melted in an atmosphere consisting essentially of an inert gas.

[0079] The laser power is preferably limited to a maximum of 120 W. Preferably, the laser power is set to be greater than 50 W to facilitate melting in all layer thicknesses. In a preferred embodiment, the laser power is 55 W to 115 W.

[0080] The scan speed is preferably 400 mm / second to 750 mm / second, and more preferably 450 mm / second to 700 mm / second. Below 400 mm / second, the excessive energy provided by the laser may cause keyhole porosity and / or cause spatter, which, if not properly dragged outside the powder bed, will deposit on the powder layer, creating voids in the printed part. Above 750 mm / second, the energy provided by the laser to the powder may not be sufficient to melt the powder in all layer thicknesses.

[0081] The linear energy density (LED) is preferably 80 J / m to 200 J / m. LED is defined as the ratio between the laser power and the scan speed expressed in m / second. Below 80 J / m, the LED may not be sufficient to properly print the part (due to keyholing). Above 200 J / m, the excessive energy provided by the laser may cause spatter, which, if not properly dragged outside the powder bed, will deposit on the powder layer. Such deposits create voids in the printed part.

[0082] The scan spacing is preferably 40 μm to 100 μm. Below 40 μm, the individual points of the printed part may be remelted multiple times, which may cause overheating. Above 100 μm, unmelted powder may be trapped between two tracks. More preferably, the scan spacing is 50 μm to 80 μm.

[0083] The volumetric energy density (VED) is preferably 80 J / mm 3 to 200 J / mm3 The VED is defined as P / (v·h·l t ), where P is the laser power, v is the scanning speed, h is the scanning pitch, and l t is the powder layer thickness. More preferably, the VED is 90 J / mm 3 to 160 J / mm 3 .

[0084] The laser spot size is preferably from 30 μm to 150 μm.

[0085] Components made of the metal powder according to the invention by additive manufacturing techniques have specific features and properties.

[0086] Its microstructure contains at least 75 wt% of an amorphous phase, with the remainder consisting of a crystalline phase. The crystalline phase can be at least one of the following: austenite, ferrite, cementite, M2B-type boride such as (FeMoMn)2(B)1, M3B2-type boride such as (FeMo)0.4(Fe)0.2(B)0.4, M2P-type phosphide such as (FeMoMn)2(PSi)1, M3P-type phosphide such as (FeMO)3(P)1, M6C-type carbide such as (Fe)2(Mo)2(FeMoSi)2(C)1, and KSI-type carbide such as (FeMo)3(C)1. The microstructure preferably contains at least 80 wt%, more preferably at least 95 wt% of the amorphous phase, with the remainder consisting of a crystalline phase.

[0087] The component is very hard, with a Vickers hardness Hv1 greater than 780.

[0088] Embodiment

[0089] The following examples and tests presented hereinafter are essentially non-limiting and must be considered only for illustrative purposes. The following examples and tests will illustrate the advantageous features of the invention, the importance of the parameters selected by the inventors after extensive experimentation, and further determine the properties achievable with the metal powder according to the invention.

[0090] Powder 1:

[0091] First, a metal composition containing 16.11 wt% Mo, 6.23 wt% P, 1.464 wt% C, 0.8 wt% B, 0.47 wt% Si, <0.25 wt% Mn, <0.3 wt% Ti, <0.01 wt% Al, <0.001 wt% Cr, <0.2 wt% V, 0.019 wt% O, 0.0076 wt% S, 5.9 ppm N, and the remainder iron is obtained by mixing and melting the following ferroalloys and pure elements in the following proportions:

[0092] - FeP at 23.83 wt%, containing 73.61 wt% Fe, 25.93 wt% P, 1.55 wt% Si, 1.5 wt% Ti, < 0.7 wt% Mn, < 0.4 wt% Cr, < 0.7 wt% V,

[0093] - FeB at 6.04 wt%, containing 82.33 wt% Fe, 18.16 wt% B, 0.13 wt% Al, 0.007 wt% S, 0.31 wt% C, 0.03 wt% P and 0.54 wt% Si,

[0094] - Molybdenum at 14.49 wt%,

[0095] - Graphite at 2.37 wt%,

[0096] - Iron ingot material at 53.26 wt%, containing 99.79 wt% Fe, 0.005 wt% C, 0.001 wt% Al, 0.15 wt% Mn, 0.002 wt% Si, 0.002 wt% P, 0.002 wt% S.

[0097] The metal composition is heated up to 1315 °C (i.e., 250 °C above the liquidus temperature), and then gas atomized with argon under the following process conditions:

[0098] - Gas pressure: 16 bar

[0099] - Nozzle diameter: 2.5 mm

[0100] - Gas-to-metal ratio: 3.21

[0101] The obtained metal powder is then dried in vacuum at 100 °C for 0.5 to 1 day.

[0102] The powder is then sieved and classified into fractions F1 to F3. Its flowability, sphericity and roundness are evaluated and found to meet the requirements for additive manufacturing applications.

[0103] The metal powder has the following characteristics:

[0104] XRD and electron backscatter diffraction (EBSD) analysis show no evidence of any crystalline phase. Thus, at least 99 wt% of the microstructure is amorphous.

[0105] For fraction F2, The average shape factor measured by dynamic image analysis according to ISO 13322-2:2021 is 0.87.

[0106] The particle size distribution measured by laser diffraction according to ISO13320:2020 presents the following characteristics: D10 = 15.64μm, D50 = 52.06μm and D90 = 137.15μm.

[0107] Due to these characteristics, the obtained metal powder exhibits the following magnetic properties measured by a Vibrating-Sample Magnetometer (VSM): The coercivity Hc measured at room temperature is 8×10 -5 T. The magnetic saturation Ms measured at room temperature is 70.6 Am 2 / Kg. The remanence Mr measured at room temperature is 0.043 Am 2 / Kg.

[0108] Powder 2:

[0109] First, a metal composition containing 14.2 wt% Mo, 6.53 wt% P, 1.94 wt% C, 1.02 wt% B, 0.43 wt% Si, 0.77 wt% Mn, <0.01 wt% Al, 0.11 wt% Cr, 0.09 wt% Ni, <0.1 wt% Cu, 0.019 wt% O, 0.012 wt% S, <20 ppm N, and the balance being iron is obtained by mixing and melting the following ferroalloys and pure elements in the following proportions:

[0110] - 21.41 wt% of FeMo, which contains 32.3 wt% Fe, 0.09 wt% C, 0.45 wt% Cu, 66.86 wt% Mo, 0.04 wt% P, 0.04 wt% S, 0.29 wt% Si,

[0111] - 24.37 wt% of FeP, which contains 73.61 wt% Fe, 25.93 wt% P, 1.55 wt% Si, 1.5 wt% Ti, <0.7 wt% Mn, <0.4 wt% Cr, <0.7 wt% V,

[0112] - 6.17 wt% of FeB, which contains 82.33 wt% Fe, 18.16 wt% B, 0.13 wt% Al, 0.007 wt% S, 0.31 wt% C, 0.03 wt% P, and 0.54 wt% Si,

[0113] - 0.1 wt% of FeSi, which contains 23.51 wt% Fe, 0.82 wt% Al, 0.09 wt% C, 0.018 wt% P, 0.002 wt% S, 75.56 wt% Si,

[0114] - 2.38 wt% of graphite,

[0115] - 45.57 wt% ingot charge, which contains 99.79 wt% Fe, 0.005 wt% C, 0.001 wt% Al, 0.15 wt% Mn, 0.002 wt% Si, 0.002 wt% P, 0.002 wt% S.

[0116] The metal composition is heated up to 1580 °C (i.e., 515 °C above the liquidus temperature), and then gas atomized with argon under the following process conditions:

[0117] - Gas pressure: 16 bar

[0118] - Nozzle diameter: 3 mm

[0119] - Gas-to-metal ratio: 1.79

[0120] Then the obtained metal powder is dried in vacuum at 100 °C for 0.5 to 1 day.

[0121] Then the powder is sieved and classified into fractions F1 to F3. Its flowability, sphericity and roundness are evaluated and found to meet the requirements for additive manufacturing applications.

[0122] The metal powder has the following characteristics:

[0123] XRD and electron backscatter diffraction (EBDS) analyses do not show any evidence of a crystalline phase. Thus, at least 99 wt% of the microstructure is amorphous.

[0124] For fraction F2 The equipment has an average shape factor of 0.71 measured by dynamic image analysis according to ISO 13322-2:2021.

[0125] The particle size distribution measured by laser diffraction according to ISO13320:2020 presents the following characteristics: D10 = 15.7 μm, D50 = 72.1 μm and D90 = 247.2 μm.

[0126] Printing test:

[0127] Then, fraction F2 of powder 1 and powder 2 is used for printing a 1 cm 3 cube by laser powder bed fusion with a layer thickness of 20 μm and a laser spot size of 55 μm.

[0128] The cube was then evaluated and the corresponding results are summarized in Table 1 below. The weight fraction of the amorphous phase was calculated by Rietveld refinement of the powder X-ray diffraction (XRD) measurements using TOPAS software from Bruker. All printed parts according to the present invention have a microstructure comprising an amorphous phase of 80 wt% to 90 wt%, with the balance consisting of a crystalline phase containing austenite. No segregation or thermal cracking was observed.

[0129]

[0130] Table 1

[0131] *According to the present invention

Claims

1. A metal powder, expressed in terms of content by weight, the composition of the metal powder comprising the following elements: 12% ≤ Mo ≤ 18% 3% ≤ P ≤ 7% 0.5% ≤ C ≤ 3% 0.5% ≤ B ≤ 5% Si ≤ 1% The balance is Fe and inevitable impurities generated by processing, and the microstructure of the metal powder comprises at least 95% by weight of an amorphous phase, with the remaining part consisting of a crystalline phase.

2. The metal powder according to claim 1, wherein the Mo content is 13% to 16.5% by weight.

3. The metal powder according to any one of claims 1 or 2, wherein the P content is 6% to 7% by weight.

4. The metal powder according to any one of claims 1 to 3, wherein the B content is 0.7% to 2% by weight.

5. The metal powder according to any one of claims 1 to 4, wherein the Si content is 0.3% to 0.6% by weight.

6. The metal powder according to any one of claims 1 to 5, wherein the microstructure of the metal powder comprises at least 99% by weight of an amorphous phase.

7. The metal powder according to any one of claims 1 to 6, wherein the average particle size is between 1 μm and 150 μm.

8. The metal powder according to claim 7, wherein the average particle size is between 1 μm and 20 μm.

9. The metal powder according to claim 7, wherein the average particle size is between 20 μm and 63 μm.

10. The metal powder according to claim 7, wherein the average particle size is between 60 μm and 150 μm.

11. A method for manufacturing a metal powder for additive manufacturing, comprising: - a) Melting the elements and / or metal alloy at a temperature at least 100 °C above the liquidus temperature to obtain a molten composition which, expressed as contents by weight, comprises the following elements: 12% ≤ Mo ≤ 18% 3％≤P≤7％ 0.5％≤C≤3％ 0.5％≤B≤5％ Si ≤ 1% The balance being Fe and unavoidable impurities resulting from processing, - b) Atomizing the molten composition by means of a gas pressurized to 10 bar to 30 bar through a nozzle.

12. A method for manufacturing a printed part by additive manufacturing, wherein the powder according to any one of claims 1 to 10 or the powder obtained according to claim 11 is printed by laser powder bed fusion.

13. The method according to claim 12, comprising a first step of forming a powder layer having a thickness of less than 100 μm, and a second step of focusing a laser beam to melt at least a portion of the powder layer in an atmosphere consisting essentially of an inert gas to form a formed layer.

14. The method according to any one of claims 12 or 13, wherein: - The laser power is limited to a maximum of 120 W, - The scanning speed is from 400 mm / second to 750 mm / second, - The linear energy density is from 80 J / m to 200 J / m, - The scanning pitch is from 40 μm to 100 μm, - The volume energy density is 80 J / mm 3 to 200 J / mm 3 .

15. A printed part obtained from the powder according to any one of claims 1 to 10 or a printed part obtained by the method according to any one of claims 12 to 14, wherein the microstructure of the printed part comprises at least 75 wt% amorphous phase and the balance is constituted by a crystalline phase.

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