Powder manufacturing process

Abstract

Title of the invention: Powder manufacturing process. The invention relates to a process for manufacturing (100) powder from a first material and a second material (1a, 1b) comprising: a step of melting the first and second materials by means of an electric arc (314), a step of spraying the molten first and second materials to form droplets (2), a step of cooling the droplets with a carrier gas (11) to form solid particles, a step of separating the solid particles from the carrier gas and collecting the solid particles to form the powder (5, 6), the electric current applied to form the electric arc being a short-circuit current. Abstract figure: Fig. 1

Description

Title of the invention: Powder manufacturing process

[0001] The present invention relates to a powder manufacturing process, and more particularly to a powder manufacturing process intended for an additive manufacturing process.

[0002] Prior art processes for manufacturing powder are known, for example, the EIGA process (an acronym for Electrode Induction Melting Gas Atomization). This process melts the material of a slowly rotating metal rod using a high-frequency induction coil. A liquid stream is then formed and flows through an atomizing nozzle. The stream is then broken up and solidified by a high-speed pulsed gas stream from the atomizing nozzle to form fine powder particles. These prior art processes make it possible to obtain spherical metallic powders while limiting contamination of the material composing the resulting powders. However, these processes, like the EIGA process, consume a great deal of energy and are not easy to implement. Furthermore, the particle size distribution of the resulting powders is not easily controlled.

[0003] We also know from application EP4221916A1, a process for manufacturing metal powders from a first material and a second material, the manufacturing process comprising in particular a step of melting the materials, by means of an electric arc, a step of spraying the molten materials so as to form droplets, a step of cooling the droplets by means of a carrier gas so as to form solid particles and a step of separating the solid particles from the carrier gas and collecting the solid particles so as to form the powder.

[0004] This disclosed process does not allow for a satisfactory particle size distribution, that is, a particle size distribution that is sufficiently controlled. The powder thus produced requires additional separation steps, and the process becomes costly to implement in order to obtain a controlled particle size distribution, that is, one suitable for the intended use of the powder by a user.

[0005] The present invention aims to effectively remedy the drawbacks of the prior art by proposing an improved powder manufacturing process that makes it possible to obtain a powder with a better controlled particle size while obtaining a material quality that conforms in terms of material composition.

[0006] The invention relates to a method for manufacturing powder from a first material and a second material, comprising: - a step of melting the first and second materials, by means of an electric arc formed by the application of an electric current between said first and second materials; - a step of spraying the first and second molten materials so as to form droplets; - a step of cooling the droplets using a carrier gas in order to form solid particles; - a step of separating the solid particles from the carrier gas and collecting the solid particles in order to form the powder; said manufacturing process being characterized in that said applied electric current is a short-circuit current.

[0007] According to one embodiment, the short-circuit electric current has a first voltage between 10 V and 30 V, preferably between 11 V and 20 V, preferably still between 14 V and 19 V.

[0008] According to one embodiment, the short circuit has a frequency between 40 and 200 Hz.

[0009] According to one embodiment, the melting and spraying steps are carried out under neutral gas, for example under argon, at a pressure between 4 and 12 bar, preferably between 6 and 10 bar.

[0010] According to one embodiment, the applied electric current has an intensity between 50 and 400 A, preferably between 150 and 250 A, and even more preferably between 180 and 220 A.

[0011] According to one embodiment, the first and second materials are distributed at a distribution rate and the current intensity is determined as a function of said distribution rate of said first and second materials.

[0012] According to one embodiment, the first and second materials are distributed at a speed of between 5 and 10 m / min.

[0013] According to one embodiment, the melting and spraying steps are repeated at least once and said applied electric current has a second voltage different from said first voltage of said applied current.

[0014] According to one embodiment, the manufacturing process includes an additional step of analyzing the powder to determine the density of said powder and / or the oxygen content of said powder and / or the particle size of said powder.

[0015] According to one embodiment, the manufacturing process includes a step of enriching the droplets and / or particles with an active substance, implemented during the cooling step, the enrichment step being preceded by a step of ionizing the active substance.

[0016] According to one embodiment, the enrichment step is carried out during the spraying and cooling steps.

[0017] According to one embodiment, the cooling step is carried out using a cooling gas.

[0018] According to one embodiment, the active substance comprises: - at least one neutral gas; and - at least one active compound comprising at least one of the following atoms: oxygen, nitrogen, carbon or hydrogen; each active compound being in gaseous, liquid or solid phase, the content of each active compound being between 5 ppm and 20000 ppm.

[0019] The invention will be better understood upon reading the following description and examining the accompanying figures. These figures are given only to illustrate, but in no way limit, the invention.

[0020] [Fig. 1] is a schematic representation of a prior art device implementing the invention.

[0021] [Fig.2] is a schematic representation of the powder manufacturing process according to the invention.

[0022] [Fig.3] is a schematic representation of the voltage and current values ​​during the manufacturing process of an embodiment of the invention.

[0023] [Fig.4] is a schematic representation of a distribution device for the process of the invention.

[0024] [Fig. 1] presents a manufacturing device 200 configured to implement the manufacturing process 100 according to the invention. This manufacturing device 200 comprises at least: a spraying means 300; an atomization chamber 400; a first collection means 500; and an exhaust means 600. This manufacturing device 200 may also comprise additional elements, not shown, such as: a gas / particle separation system; and a second collection means.

[0025] With reference to [Fig.2], the manufacturing process 100 comprises at least the following steps: a melting step 110 of two materials la, 1b by means of an electric arc 314; a spraying step 120 of each material la, 1b so as to form droplets 2; a cooling step 130 of the droplets 2, by means of a carrier gas 11, so as to form solid particles 3; and a separation step of the particles 3 from the carrier gas 11 and collection step 140 of the solid particles 3 so as to form a first and a second powder 5, 6.

[0026] Each material la, 1b is an electrical conductor. It can, for example, be a pure metal such as titanium or aluminum, or an alloy such as a titanium-based alloy, an aluminum-based alloy, a nickel-based alloy, or a nickel-based alloy. of copper or an iron-based alloy. The materials 1a, 1b may be of the same type or even identical. The choice of composition for each material 1a, 1b partly determines the composition of the resulting powders 5, 6. In one embodiment, said first or second material is a Ti6Al4V alloy. These materials 1a, 1b are supplied respectively in the form of conductive wires 312a, 312b and distributed to the spraying means 300 shown in [Fig. 1], and more specifically into the chamber 311 by a wire-feeding system, not shown, for example at a predefined speed. In one embodiment, the diameter of the wires 312a, 312b is between 0.8 and 2 mm, preferably between 1.2 and 2 mm. Thus, the wires are easily handled.

[0027] During the melting step 110, this spraying means 300 is configured to perform the melting step 110 of each material la, 1b by means of an electric arc 314. The spraying means 300 includes an electric arc source 310, also called a wire arc torch. The wire arc torch 310 is configured to generate an electric arc 314. The electric arc 314 can be created from the carrier gas 11, such as argon, nitrogen, or helium, or a mixture of these gases. The wire arc torch 310 includes a chamber 311, filled with the carrier gas 11, in which the electric arc 314 is generated. The pressure of the carrier gas 11 in the chamber 311 can be greater than or equal to atmospheric pressure. The arc-wire torch 310 is configured to generate the electric arc 314 between the first material 1a and the second material 1b.The arc-wire torch comprises two conductive wires 312a, 312b, arranged on either side of the enclosure 311, separated from each other and configured to initiate and maintain the electric arc 314 by means of the electric current. During operation, the distance between the two conductive wires 312a, 312b is preferably kept less than 5 mm and depends on the energy delivered. When the arc-wire torch 310 is in operation, the electric arc 314 is located near the two opposite ends 313a, 313b of the two wires 312a, 312b. The carrier gas 11 is introduced in a jet into the enclosure 311 through an inlet 313. The jet of carrier gas 11 is configured to strike the ends 313a, 313b of the two wires 312a, 312b. In one embodiment, the spraying means 300 includes several arc-wire torches 310 allowing the quantity of powder generated by the manufacturing device 200 to be increased.During this melting step 110, the operating regime of the arc-wire torch 310 is chosen such that the temperature of the plasma at the level of the electric arc 314 is greater than the melting temperature of each material la, 1b. Thus, in operation, said plasma melts the ends 313a, 313b of the two wires 312a, 312b.

[0028] The spraying step 120 is also carried out with the spraying means 300. The spraying step 120 of each material la, 1b from the ends 313a, 313b liquefied, allows the formation of droplets 2. During this spraying step 120, the jet of carrier gas 11 is directed directly onto the liquefied ends 313a, 313b of the wires 312a, 312b so as to spray the molten ends 313a, 313b and create the droplets 2. In order to maintain a fixed spacing between the ends 313a and 313b despite the spraying of material, the wires 312a, 312b are always introduced into the enclosure 311 by a winding system, not shown, at a predefined speed.

[0029] [Fig. [1] schematically presents the atomization chamber 400 and the exhaust means 600, configured to carry out the cooling step 130 of the droplets 2, by means of the carrier gas 11, so as to form the solid particles 3. In one embodiment, in order to accelerate the cooling 130, a cooling gas 12 can be injected into the atomization chamber 400. The cooling gas 12 in contact with the carrier gas forms a gas mixture 13. Thus, during the cooling step 130, the droplets 2, in contact with the gas mixture 13, establish a heat transfer with the gas mixture 13. Preferably, the temperature of the injected cooling gas 12 is chosen such that it is lower than the lowest of the solidification temperatures of the materials la, 1b or of the alloys formed by the materials la, 1b within the droplets 2. The cooling mixture 12 is, for example, injected at room temperature.Thus, the expanded carrier gas 11 and the cold cooling gas 12 create a heat transfer from the droplets 2 to the gas mixture 13, cooling the droplets 2. When the temperature of the droplets 2 is lower than the solidification temperature of the droplets 2, the droplets 2 solidify to form the solid particles 3. The cooling step 130 allows the droplets 2 to spheroidize, that is, they adopt a spherical shape thanks to the surface tension at the surface of the molten droplets 2 and the interaction with the gas mixture 13. Thus, upon solidification, the droplets 2 form particles 3 whose sphericity is greater than 0.9 and as close as possible to 1.

[0030] The manufacturing process 100 may also include an enrichment step 160 of the droplets 2 and / or particles 3. The enrichment 160 is carried out by means of an active substance 16. The enrichment 160 is at least implemented during the cooling step 130. However, the enrichment 160 may also begin during the spraying 120 and continue during the cooling 130. By "enrichment", we mean a metallurgical treatment of the materials 1a, 1b and the alloys formed within the droplets 2 by means of an active substance 16 so as to impart particular physico-chemical characteristics to the resulting particles 3.

[0031] The active substance 16 used in the enrichment step 160 comprises: at least one neutral gas, advantageously of the same composition as the carrier gas 11; and at least one active compound comprising at least one of the following atoms: oxygen, nitrogen, carbon, or hydrogen. Each active compound may be in the gaseous, liquid, or solid phase, for example, present as droplets or suspended particles. The concentration of each active compound within the active substance 16 is between 5 ppm and 20,000 ppm and preferably between 5 ppm and 1,000 ppm. It may, for example, be carbon monoxide or hydrogen. The active compound of the active substance 16 may be a hydrocarbon, such as methane, rich in carbon and hydrogen. In the case where the active substance 16 comprises carbon monoxide or methane, the enrichment 160 corresponds to a carburization of the materials 1a, 1b.If the active substance 16 contains nitrogen, the enrichment 160 corresponds to nitriding. If the active substance 16 contains oxygen or hydrogen, the enrichment 160 corresponds to oxidation or, conversely, reduction of the materials la, 1b. The active substance 16 can react with the materials la, 1b whether they are in the form of droplets 2 or solid particles 3. The active substance 16 is preferably injected into the device 200, at the atomization chamber 400. Thus, the active substance 16 reacts with the particles 3. Advantageously, the active substance 16 is involved in the spraying step 120. In this way, the active substance 16 reacts with the droplets 2. Alternatively, the active substance 16 is also injected at the spraying means 300.The partial pressures of the neutral gas and each active compound of the active substance 16 are controlled within the device 200 throughout the process 100 so that the concentration of each active compound remains between 5 ppm and 20,000 ppm, and preferably between 5 ppm and 1,000 ppm. The chemical reactions occurring between the active substance 16 and the surface of the droplets 2 and particles 3 optimize the exchange surface area. In this way, the enrichment step 160 is carried out efficiently. Thus, the enrichment step 160 allows control of the final chemical composition of the resulting particles 3.

[0032] Then, there is a step of separating the solid particles and collecting 140 of the solid particles 3 so as to form the powder 5, 6. This step is first carried out by means of the first collection means 500 which is connected to the atomization chamber 400. With reference to [Fig. 1], the first collection means 500 comprises a main pot 520 configured to receive a first part of the solid particles 3 thus forming the powder 5. Then a gas / particle separation system, not shown, is configured to separate the second part of the particles 3 from the gas mixture 13. This second part of particles is mainly made up of the lightest particles. The gas / particle separation system can, for example, be a means of filtration, a decanter or even a cyclone.

[0033] In [Fig. 2], the schematically presented manufacturing process 100 comprises several combinable steps, shown in dashed lines, which will now be described. An ionization step 150 can be combined with the enrichment step 160 to improve the kinetics of the chemical reactions taking place between the droplets 2, the particles 3, and the active substance 16. The ionization step 150 precedes the enrichment step 160, in which case the enrichment step can begin during the spraying 120. In this step, the active substance 16 can be introduced into the chamber 311 of the spraying means 300 so as to be ionized by the electric arc 314. The electric arc 314 ionizes each component of the active substance 16 so as to create reactive free ions. The highly energetic reactive free ions improve the reaction kinetics during the enrichment step 160.The enrichment reactions therefore reach equilibrium before the droplets 2 solidify. Thus, the chemical composition of the resulting particles 3 is controlled and reproducible. The concentration of reactive free ions is highest within chamber 311. Outside the chamber, the concentration of reactive free ions decreases due to recombination reactions. Advantageously, the reactive free ions follow the trajectory of the droplets 2 in the atomization chamber 400 in order to increase the duration of the enrichment step 160.

[0034] Following the collection step 140, the passivation step 170 of the surface of the particles 3 can be carried out, for example, when the first and second powders 5, 6 are made from flammable materials, i.e., materials with a high affinity for oxygen. This is the case, for example, with powders 5, 6 made from titanium, titanium alloys, or aluminum. The passivation step 170 is carried out using the passivation gas 14. The passivation gas 14 may, for example, comprise a noble gas and an active gas such as oxygen, the active gas preferably having a concentration between 20 ppm and 2%. The passivation step 170 is systematically carried out on both powders 5, 6. In the following example, we present the implementation of the passivation step 170 on the first powder 5 in the first collection means 500. The passivation step 170 is transposable to the gas / particle separation system.

[0035] In order to obtain a first and second powder 5, 6 with specific particle size distribution characteristics, an additional sieving step 180 can be performed on the first and second powders 5, 6. Sieving 180 allows, for example, the removal of particle aggregates 3 or particles exceeding a size limit from the powders 5, 6. The particle size distribution can be characterized by three specific diameters denoted D10, D50, and D90. 10% of the particles 3 have a diameter less than D10, 50% of the particles 3 have a diameter less than D50 and 90% of the particles 3 have a diameter less than D90. Sieving 180 can for example be carried out in order to adjust the distribution of powders 5, 6, in particular the diameter D50, corresponding to the median of the distribution.

[0036] In order to ensure that the chemical composition of the powders 5, 6 is reproducible, the manufacturing device 200 can undergo an additional inerting step 101. The inerting step 101 is carried out by means of an inerting gas and compression and expansion cycles, in order to purge the air contained in the device 200 until the oxygen content is less than 100 ppm, preferably less than 10 ppm, before starting the melting step 110. The inerting gas can, for example, comprise a neutral gas or a mixture of neutral gases.

[0037] Typically, in this process, the transfer method used is a sputtering transfer method. A continuous electric arc 314 is thus obtained by means of a direct electric current during the melting and sputtering stages. Furthermore, a sustained length of electric arc 314 is obtained as long as the material filament 1b is distributed. However, the yields obtained by this powder manufacturing process are not sufficiently satisfactory, as the particle size distribution is not adequately controlled. This can result in an excessive quantity of fine particles, i.e., powders with a size of less than 1 micron. Moreover, the inventors have observed that this process induces a significant temperature rise, and therefore the powder tends to oxidize. In addition, the powder sometimes sinters.

[0038] The inventors thus sought to avoid these drawbacks. They reduced the voltage of the applied electric current, while maintaining a constant material supply, to reduce the length of the electric arc 314 and obtain powders 5, 6 with a larger diameter. The transfer regime was then changed to a short-circuit transfer regime. In this short-circuit regime, the inventors observed a considerable improvement in the control of the particle size distribution of the powders 5, 6. In this transfer regime, the applied electric current is no longer a direct current, but a short-circuit current. Thus, during the melting step, the heat of the electric arc 314 melts the ends of the wires 313a, 313b until a droplet 2 is formed, and the two wires 312a, 312b are then connected. A liquid bridge is also formed between the two wires 312a, 312b and the droplet 2.It is at this moment that a short circuit is created, the voltage of the applied electric current then being equal to 0 V. Referring to [Fig. 3], the applied electric current is regulated by an increase in the intensity of the applied current. At this instant, the increase in intensity, induced by the short circuit, generates electromagnetic fields which, with the effect of the surface voltage, will break the liquid bridge between the wires 312a. 312b and droplet 2. Breaking of the bridge results in the projection of droplets 2 during the spraying step, these droplets 2 subsequently forming the powder 5, 6. Depending on the rate of intensity increase, the formation of large droplets 2 is avoided. Thus, the particle size distribution of the powders 5, 6 is better controlled. The powders 5, 6 produced contain, in particular, fewer fine particles than powders 5, 6 produced using a spray transfer method. Furthermore, the powder is less contaminated, and the resulting composition is also better controlled. Indeed, the oxidation of the powder is less significant, and therefore the composition is better controlled. Then, after the spraying of droplet 2, the voltage is restored, which again creates an electric arc 314, and the melting and spraying cycle is initiated anew.

[0039] In one embodiment, the voltage applied between the two conducting wires 312a, 312b can be between 10 V and 30 V, preferably between 11 V and 20 V, and even more preferably between 14 V and 19 V. The length of the electric arc 314 induced by the application of the electric current to the two materials 1a and 1b is shorter than that for a spray transfer regime. These ranges of values ​​make it possible to guarantee a controlled particle size distribution, that is to say, a particle size distribution desired by the user of the process. Indeed, if the voltage is too low, the metal droplet 2 can no longer detach and the conducting wires 312a, 312b risk becoming bonded. In this case, there is no short circuit. If the voltage is much too low, the electric arc 314 is not created and the wires 312a, 312b unwind without creating drops.Conversely, if the tension is too high, the particle size distribution and composition of the powder will be unsatisfactory. Indeed, the powder particle size may be too heterogeneous and / or contain excessively fine powder particles, for example, particles less than 1 micron in diameter. Furthermore, the quality of the powder can be affected; with high tension, condensation can occur, generating nanoparticles that are ejected. The inventors observed, using a scanning electron microscope, that agglomerates of nanoparticles resulting from these ejections attach to the surface of larger particles. These nanoparticles or ejections increase the surface area for interaction of the produced particles, and their ejection thus contributes to an increase in the oxygen content of the powder produced.The powder to be manufactured is, for example, a Ti6A14V powder, and materials 1a and 1b are Ti6A14V titanium alloys. In one embodiment of the Ti6A14V powder, the voltage is between 15 and 19 V, preferably 16 V. It has been found that this process makes it possible to obtain powders conforming to the specifications defined in ASTM F3001-14 and ASTM F2924-14.

[0040] In one embodiment, the short-circuit frequency is between 40 and 200 Hz. Furthermore, if the applied voltage is increased, the short-circuit frequency can be reduced. These frequency values ​​improve the quality of the powder 5, 6 produced. The powder to be manufactured is, for example, a Ti6A14V powder, and materials 1a and 1b are Ti6A14V titanium alloys. It has been found that this process makes it possible to obtain powders conforming to the specifications defined in ASTM F3001-14 and ASTM F2924-14. Moreover, the particle size distribution is better controlled.

[0041] In one embodiment, the melting and spraying steps are carried out under a neutral gas, for example argon, at a pressure P between 4 and 12 bar. By decreasing the pressure P, the diameter of the droplets 2 formed increases. Preferably, in one embodiment, the pressure P is between 6 and 10 bar. This pressure range P makes it possible, in particular, to obtain a particle size distribution suitable for manufacturing processes using appropriate metal powders, such as laser powder bed fusion and electron beam fusion.

[0042] In one embodiment, the electric current applied between the two conducting wires 312a, 312b has a current intensity between 50 and 400 A, preferably between 150 and 250 A, and even more preferably between 180 and 220 A.

[0043] In one embodiment, the first and second materials la, 1b are distributed at a distribution rate and said current intensity is determined as a function of said distribution rate of said first and second materials la, 1b. Thus the productivity of the manufacturing process can be adjusted.

[0044] In one embodiment, the first and second materials are distributed at a speed of between 5 and 10 m / min. This reduces the mechanical stresses induced in the wire. Furthermore, if the speed is too high, the wire 312a, 312b would not have time to melt, and if the speed is too low, the electric arc 314 is interrupted.

[0045] In one embodiment, when said first voltage is equal to 0, the current intensity increases between 100% and 150% during said spraying step.

[0046] In one embodiment, the melting and spraying steps are repeated at least once, and the applied electric current has a second voltage different from the first voltage. Thus, the particle size of the powder produced is perfectly controlled.

[0047] In one embodiment, the manufacturing process 100 includes an additional step of analyzing the powder to determine its density and / or oxygen content and / or particle size. The process parameters can thus be adjusted based on the powder analysis.

[0048] We will now describe a result obtained by the process according to the invention. In one example, the material 1a, 1b used is a titanium alloy Ti6A14V. The operating regime used is a short-circuit regime. The applied electric current voltage is set at 16 V. The target current intensity is set at 200 A and the pressure P at 8 bar. The diameter of the wire used is 1.6 mm. The process made it possible to obtain a powder 5, 6 conforming to the composition specifications of ASTM F3001-14 and ASTM F2924-14, as well as to the bulk density specifications defined by ASTM-B-212 and the flowability specifications defined by ASTM-B-213. The process of the invention makes it possible to obtain a better controlled particle size distribution of the powders. Thus, at least 75% of the powder particles have a size less than 150 microns.Furthermore, at least 50% of the powder particles are between 20 and 100 microns in size, which is the size range of powders commonly used in additive manufacturing processes employing metal powders. More specifically, over 20% of the powder particles (5, 6) are between 20 and 63 microns in size. This size is suitable for the laser powder bed fusion process. Over 25% of the powder particles (5, 6) are between 63 and 100 microns in size. This size is suitable for the electron beam fusion process.

[0049] In one embodiment, the process of the invention includes an additional distribution step. With reference to [Fig. 1] and [Fig. 4], before the melting step, the wires 312a, 312b, stored as wire spools, are each distributed upstream of the manufacturing device 200 by a wire-feeding means 1000, for example, rollers. The wires 312a, 312b are each distributed in a distribution direction, i.e., from the spool towards the electric arc 314. These wire-feeding means 1000 are located downstream of the spools in the distribution direction. The wire-feeding means 1000 allow the wires 312a, 312b to be pushed towards the manufacturing device 200.

[0050] Then, as close as possible to the electric arc 314, at least one additional feeding means 2000 is added to the device for each wire 312a, 312b distributed. The additional feeding means 2000 allows the wire 312a, 312b to be stabilized by pulling and then pushing it towards the electric arc 314, for example by means of rollers.

[0051] The unwinding means 1000 and the additional means 2000 together form a push-pull unwinder, or push-pull system. The wires 312a, 312b are thus pushed a distance D in the distribution direction. This distance D is the length measured between the unwinding means 1000 and the additional unwinding means 2000. Then the wires 312a, 312b are pulled from the additional unwinding means 2000 towards the electric arc 314 in the distribution direction over this same distance D. Then the wires 312a, 312b are pushed from the additional unwinding means 2000 towards the electric arc 314, up to the ends of the wires 313a, 313b. The means The 1000 unwinding unit and the additional 2000 unit are synchronous, meaning they distribute the wire at the same speed. This push-pull unwinder reduces oxygen absorption of the powder produced by process 100.

[0052] In one embodiment, said first wire 312a and said second wire 312b each have an end 313a, 313b which is melted during the melting step. Said first wire 312a and said second wire 312b are each pushed a distance L, each distance L being equal to the length measured between said additional means 2000 and said respective ends 313a, 313b of the wires 312a, 312b. Thus, there is less mechanical stress on the wire 312a, 312b. Thus, the oxygen content in the powders 5, 6 produced is lower than the oxygen content obtained without the process of the invention.

[0053] In one embodiment, said first wire 312a and said second wire 312b are pulled over a distance L equal to at least 1% of the distance D, preferably equal to at least 10% of the distance D. Thus, the tension of the wires 312a, 312b is well controlled. Furthermore, the oxygen content in the powders 5, 6 produced is lower than the oxygen content obtained without the process of the invention.

[0054] For example, the length of the wire between the unwinding system and the electric arc 314 is 3 meters. The additional unwinding means is located at a distance of between 20 and 50 cm from the ends 313a, 313b. A person skilled in the art will readily adjust these distances based on the teachings of the invention to obtain the desired effect, namely an oxygen content in the powders 5, 6 produced that is lower than the oxygen content obtained without the process of the invention.

[0055] In one embodiment, the wires 312a, 312b are pushed through sheaths. The sheaths are located after the wire-feeding means 1000 in the distribution direction. The sheaths guide the wires 312a and 312b and minimize their bending. This guidance through the sheaths prevents deformation of the wires 312a, 312b and thus limits stress in the material 1a, 1b. In one embodiment, the sheaths are located between the wire-feeding means 1000 and the additional means 2000, thereby reducing friction within the sheaths. The wire distribution is also better regulated.

[0056] In one embodiment, the wire unwinding speed is between 5 and 10 m / min.

[0057] In one embodiment, an additional straightening step allows the wires 312a, 312b to be straightened by means of a wire straightener. Thus, the wires 312a, 312b are perfectly straight, without deformation. The mechanical stresses in the sheaths are reduced. Furthermore, distribution is facilitated. Thus, the electric arc 314 is well controlled, without interruption. In addition, the quality of the powder in terms of composition is improved. is also better controlled. The particle size and sphericity of powders 5, 6 are better controlled.

Claims

Demands

1. A method for manufacturing (100) powder (5, 6) from a first material (la) and a second material (1b), comprising: - a step of melting (110) the first and second materials (la, 1b) by means of an electric arc (314) formed by the application of an electric current between said first and second materials (la, 1b); - a step of spraying (120) the molten first and second materials (la, 1b) so as to form droplets (2); - a step of cooling (130) the droplets (2) by means of a carrier gas (11) so as to form solid particles (3); - a step of separating the solid particles from the carrier gas (11) and collecting (140) the solid particles (3) so as to form the powder (5, 6);said manufacturing process (100) being characterized in that during said melting step a liquid bridge is formed between said first and second material (la, 1b) generating an increase in the intensity of the applied electric current and a drop in the voltage of the electric current to 0 V so that said applied electric current is a short-circuit current.;

2. Manufacturing method (100) according to claim 1, characterized in that said short-circuit electric current has a first voltage between 10 V and 30 V, preferably between 11 V and 20 V, preferably still between 14 V and 19 V.

3. A manufacturing method (100) according to any one of the preceding claims, characterized in that the short circuit has a frequency between 40 and 200 Hz.

4. A manufacturing process (100) according to any one of the preceding claims, characterized in that said melting and spraying steps are carried out under inert gas, for example under argon, at a pressure (P) between 4 and 12 bar, preferably between 6 and 10 bar.

5. A manufacturing method (100) according to any one of the preceding claims, characterized in that said applied electric current has an intensity between 50 and 400 A, preferably between 150 and 250 A, more preferably between 180 and 220 A.

6. Manufacturing method (100) according to claim 5, characterized in that said first and second materials (la, 1b) are distributed at a distribution rate and said current intensity is determined as a function of said distribution rate of said first and second materials (la, 1b).

7. A manufacturing method according to any one of the preceding claims, characterized in that said first and second material are distributed at a speed between 5 and 10 m / min.

8. A manufacturing method (100) according to any one of claims 2 to 8, characterized in that said melting and spraying steps are repeated at least once and said applied electric current has a second voltage different from said first voltage of said applied current.

9. A manufacturing process (100) according to any one of the preceding claims, characterized in that it comprises an additional step of analyzing the powder to determine the density of said powder and / or the oxygen content of said powder and / or the particle size of said powder.

10. A manufacturing process (100) according to any one of the preceding claims, characterized in that it comprises an enrichment step (160) of the droplets (2) and / or particles (3) by means of an active substance (16), carried out during the cooling step (130), the enrichment step (160) being preceded by an ionization step (150) of the active substance (16).

11. A manufacturing process (100) according to any one of the preceding claims, wherein the enrichment step (160) is carried out during the spraying and cooling steps (120, 130).

12. A manufacturing method (100) according to any one of the preceding claims, wherein, in addition to the carrier gas (11), the cooling step (130) is carried out by means of a cooling gas (12).

13. A manufacturing process (100) according to any one of claims 10 to 12, wherein the active substance (16) comprises: - at least one neutral gas; and - at least one active compound comprising at least one of the following atoms: oxygen, nitrogen, carbon, or hydrogen; each compound active being in gaseous, liquid or solid phase, the content of each active compound being between 5 ppm and 20000 ppm.

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