Functionalized metal powders with small particles produced by non-thermal plasma glow discharge for additive manufacturing applications

Abstract

The present invention discloses a non-thermal plasma treatment of metal powders to improve their processability by additive manufacturing (AM). The non-thermal plasma treatment combines primary particles composed of a metal or metal alloy into multiple secondary particles composed of a metal, metal alloy, ceramic, or polymer. The primary particles have a larger average diameter than the secondary particles. Both particles are injected through a non-thermal plasma glow discharge and / or into its afterglow region (the region downstream of the plasma discharge), where their surfaces are cleaned by removing contaminants and / or oxide layers and activated to react with each other. The functionalized metal powder is then collected and subsequently processed by AM to obtain high-quality parts. The functionalized metal powder produced by this plasma treatment improves the processability of metals by AM. Indeed, the efficiency of powder-based AM processes is improved by reducing reflectivity, removing contaminants and oxide layers, enhancing isotropic solidification of the molten material, and lowering sintering temperatures.

Description

[Technical field]

[0001] The present invention relates to a method for providing a non-thermal plasma process for producing metal or metal alloy functionalized powders. The present invention also relates to such a method for processing functionalized powders by melting or sintering AM processes.

[0002] More particularly, the present invention relates to plasma treatment of metal powders to improve their processability by additive manufacturing. [Background technology]

[0003] Additive manufacturing (AM) is an emerging technology for fabricating complex parts in a wide range of materials. The AM process consists in building three-dimensional objects by depositing layers of material one on top of the other in a defined pattern. Among the main advantages of AM, the ability to design complex parts that cannot be fabricated by traditional manufacturing, such as the wide panel of available materials (polymers, ceramics, metals, etc.) and the large number of available processing systems, has attracted particular interest from the industrial sector.

[0004] In this field, three main categories of processes are generally distinguished. First, there are methods that involve the selective sintering or melting of a powder bed of material by a laser, e.g. selective laser sintering (SLS), selective laser melting (SLM); or by an electron beam, e.g. electron beam melting (EBM). A high-energy beam sinters or melts the powder to produce the first layer. Once the first layer is formed, a new layer of powder is applied to the surface and sintering or melting is carried out to add a new layer on top of the previous one. The operation is repeated until the desired part is produced. Secondly, directed energy deposition (DED) consists in sending a powder stream or a wire of material to the focus of a laser or an electron beam. The material melts and is deposited on the surface, building up the part layer by layer. Thirdly, the article is formed by depositing an extruded powder or a wire of material on a surface. The extrusion nozzle is moving to trace the target part.

[0005] AM processes using high-energy beams still present some major challenges, especially when applied to metal or metal alloy powders. In fact, of the more than 5000 metal or metal alloy powders used in industry, only a few can be produced today. To provide the industry with high-performance metal alloys with high strength, wear resistance or oxidation resistance, several gates need to be overcome.

[0006] One challenge is the high reflectivity of metal powders such as aluminum or copper, which make them difficult to melt or sinter with a laser source. In fact, a large part of the laser energy may be reflected instead of being absorbed to form the material. The process must be carried out at higher powers, thus reducing its productivity.

[0007] Another challenge in metal powder AM is that some alloys, such as aluminum, undergo oxidation due to the moisture present in the air. This oxide layer prevents the powder from sintering correctly during the process. Powders must be stored carefully before being used and systems must be adapted to avoid this phenomenon, which can lead to an increase in their yield.

[0008] Yet another challenge is the formation of microstructures with cracks, voids and defects that are commonly found when metal parts are manufactured by sintering processes. These defects result from the thermodynamics of solidification of the molten material. In fact, the steep temperature gradients used by lasers or electron beams result in high cooling rates that induce anisotropic solidification that generates cracks in the case of some alloys.

[0009] Finally, a key challenge is to avoid eutectic or peritectic decomposition, which would result in a multiphase brittle structure. Indeed, the high temperatures reached by metal alloy powders during sintering often cause such decomposition. Reducing the sintering temperature by using sintering aids is a strategy often found in metallurgy.

[0010] To address these challenges, some compounds have been added to the powder. For example, several patents highlight the use of sintering aids, such as ceramic particles, to strengthen the part structure (US Pat. No. 5,393,633; US Pat. No. 5,493,363; US Pat. No. 5,493,627; and US Pat. No. 5,523,133). Sintering aids act as grain refiners and nucleating agents, lowering the sintering temperature and resulting in isotropic solidification of the molten material. These particles limit the amount of cracks and voids, allowing a strong microstructure to form. However, uniform dispersion of these aids is sometimes very difficult to achieve, and defects still exist in the microstructure when the part is manufactured.

[0011] Indeed, it is possible to obtain a powder surface modification by thoroughly mixing two powders by co-grinding under high energy (known as mechanosynthesis), as described in US Pat. No. 5,399,623, US Pat. No. 5,433,663 and US Pat. No. 5,433,663. However, the powder obtained does not reach the necessary requirements for additive manufacturing, since the surface of the powder is not fully restored / functionalized.

[0012] One solution that has been developed is to attach sintering aid particles to the metal powder particles to improve sintering aid dispersion. Several patents have shown that by attaching smaller particles to the metal particle powder, the ability to be processed by AM is increased (US Pat. No. 5,393,633; US Pat. No. 5,493,521; US ​​Pat. No. 5,593,633; US Pat. No. 5,693,717; US Pat. No. 5,793,816; US Pat. No. 5,893,103; US Pat. No. 5,893,116; US Pat. No. 5,970,363; and US Pat. No. 5,970,363). Functionalization of metal particle powders addresses several issues with metal AM.

[0013] For example, the attachment of small particles to metal powder particles has been shown to change their surface chemistry and their roughness. The change in surface roughness can be controlled by the distribution of smaller particles present on the powder particles. Furthermore, particle surface roughness has been shown to affect reflectivity: increasing surface roughness decreases reflectivity (Patent Document 11).

[0014] Another example is that functionalization provides an additional layer of protection against metal oxidation, improving the ease of handling of the powder and reducing the risk of defective parts due to partial oxidation of the powder (Patent Documents 15 and 16).

[0015] In recent years, various methods have been developed to attach small particles to larger particles. Most of them include chemical reactions (Patent Document 20), emulsion explosion (Patent Document 21), laser ablation (Patent Document 22), heat treatment (Patent Document 23), fluidized beds assisted by plasma torches and high-energy milling reactors (Patent Document 19), and are used for various applications as catalysts or sensors. However, the main drawbacks or limitations of these manufacturing routes are their multi-step processes, the use of large amounts of solvents, harmful chemicals, the high temperatures required, and the non-continuous processes.

[0016] Plasma treatments to form such structured particles have also been considered. For example, supported palladium catalysts on carbon and aluminum have been obtained by injecting both precursors in a plasma discharge (Patent Document 24). Nevertheless, in most cases, such plasma processes are applied to monomer-coated particles by injection of liquid precursors that polymerize during the discharge (Patent Document 13 and Patent Document 25). This in-situ polymerization during the discharge to form structured particles does not allow significant control over the material produced. Another example is described as the injection of primary particles in a plasma discharge to decompose and condense on secondary particles. As in the previous example, it is difficult to achieve correct control, since the particle properties are modified during the process. Finally, one patent describes that functionalized powders have been produced by a fluidized bed (Patent Document 19). Functionalized particles are sprayed onto such powders circulating in a fluidized bed under controlled temperature. Such reactions can be assisted by a plasma torch to promote the diffusion of heteroatoms such as nitrogen, carbon, bore or oxygen. In addition, a high-temperature plasma torch can be used to provide spheroidization of the powder. However, in the previous patent, the plasma does not allow for the grafting of nucleating agents, sintering aids or small particles onto the metal powder, and furthermore, the process limits the production rate discontinuously.

[0017] In conclusion, the interest in functionalized powders specifically for AM is real and there is a need to develop effective fabrication methods. Although some of them have already been constructed, the need for one-step, solvent-free and hazardous chemical-free synthesis methods, as well as better control of particle features, is crucial to extend the use of these types of powders in AM. [Prior art documents] [Patent documents]

[0018] [Patent Document 1] US6814926 [Patent Document 2] US20180161874 [Patent Document 3] US20160175929

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[0019] It is against this background, and the limitations and problems associated therewith, that the present invention has been developed.

[0020] There is a need for a flight control system that provides improved processability for additive manufacturing (AM) non-thermal plasma processing of metal and metal alloy powders.

[0021] Therefore, the primary objective of the present invention is that a non-thermal plasma treatment provides improvements in reflectivity, sensitivity to oxidation and the presence of cracks, voids or defects in structures found in metal AM that limit its use.

[0022] The object of the invention concerns the use of non-thermal plasmas by activating the surfaces of both powders, providing them with enough energy to react with each other by electrostatic reactions. Indeed, the powders circulating in a continuous flow through the glow or afterglow plasma are excited and form positive or negative charges on their surfaces. In such applications, the primary particles can be positively or negatively charged depending on the chemical nature of the powder, and the secondary powders are of the opposite charge, giving them a probability of reacting with the primary powders and coating them appropriately.

[0023] To achieve this, the method of the invention providing a non-thermal plasma process for producing metal or metal alloy functionalized powders comprises the features as set forth in claim 1, and the invention provides a method for processing functionalized powders by melting or sintering AM processes as set forth in claim 20.

[0024] Advantageous embodiments of the invention are set forth in the dependent claims.

[0025] The present invention discloses non-thermal plasma treatment of metal, metal alloy powders to improve their processability by additive manufacturing (AM), which faces challenges that limit its use, particularly high reflectivity, sensitivity to oxidation, and the presence of cracks, voids or defects within the structure found in metal AM.

[0026] In a first aspect, the method provides a non-thermal plasma process for producing metal or metal alloy powders, the functionalized powder being composed of a plurality of metal or metal alloy particles, the primary particles of a defined average diameter being attached to the secondary particles, which are a plurality of metal, metal alloy, ceramic or polymer particles of a smaller defined average diameter. The secondary particles are distributed on the surface of the primary particles. In some cases, the binding ability of the secondary particles on the primary particles can be enhanced by an organic linker. The organic linker is infused in the same manner as the primary particles.

[0027] In a second aspect, the non-thermal plasma process includes the steps of providing metal or metal alloy primary particles; providing metal, metal alloy, ceramic or polymer secondary particles; providing a carrier gas stream to guide the particles through the process; providing a non-thermal plasma glow discharge that allows the particles to be cleaned, activated and react with each other; and providing said collectors, at least two containers for receiving functionalized powders, positioned after the plasma discharge.

[0028] In some embodiments, a plurality of primary particles are mixed with a plurality of secondary particles. The particle mixture is injected into a gas stream. The carrier gas stream directs the particles toward a non-thermal plasma glow discharge where the reaction occurs. A functionalized powder, comprised of primary particles coated with a plurality of secondary particles, is then collected.

[0029] In some other embodiments, the primary particles are injected into a gas stream and the secondary particles are injected into another gas stream. These carrier gas streams guide both the primary and secondary particles towards a non-thermal plasma glow discharge where the reaction occurs. The functionalized powder, comprised of primary particles coated with secondary particles, is then collected.

[0030] In some other embodiments, a plurality of primary particles are injected into a gas stream, which directs the primary particles toward a non-thermal plasma glow discharge for cleaning and activation. A plurality of secondary particles are injected into another gas stream, which directs the secondary particles toward the afterglow region, the region downstream of the non-thermal plasma glow discharge where reactions occur. A functionalized powder, comprised of primary particles coated with a plurality of secondary particles, is then collected.

[0031] In some other embodiments, the primary particles are mixed with secondary particles. The particle mixture is injected into a gas stream. The carrier gas stream directs the particles toward the afterglow region where the reaction occurs. The functionalized powder, comprised of primary particles coated with secondary particles, is then collected.

[0032] In some other embodiments, a plurality of primary particles are injected into a gas stream, which carrier gas stream directs the primary particles toward an afterglow region. A plurality of secondary particles are injected into another gas stream, which second carrier gas stream directs the secondary particles toward an afterglow region where a reaction occurs. A functionalized powder, comprised of primary particles coated with a plurality of secondary particles, is then collected.

[0033] The present invention involves the creation of a non-thermal plasma glow discharge by an electric field, such as RF, microwave, or DC, applied to an incoming gas stream.

[0034] In some embodiments, the electric field is generated by applying a voltage between two electrodes. The voltage applied between these electrodes can vary between about 10V and 100kV. If an alternating current is used, the non-thermal plasma glow discharge can be generated by an electric field with a frequency between about 1Hz and about 900MHz. The power applied to generate the non-thermal plasma glow discharge can vary from about 10W to about 10000W.

[0035] In some embodiments, the gas stream may be composed of helium, nitrogen, argon, hydrogen, carbon dioxide, carbon monoxide, nitric oxide, nitrous oxide, nitrogen dioxide, krypton, neon, xenon, or combinations thereof. The gas stream may be fixed at between about 0.1 and 5000 standard liters per minute. The pressure within the reactor at which the non-thermal plasma glow discharge is generated may be selected between about 0.01 and about 30 atmospheres.

[0036] In a third aspect, the invention involves the processing of the functionalized powders described above by a melting or sintering AM process. The AM processing is improved by this treatment to produce high quality parts. These parts have improved properties such as mechanical strength and microstructure free of cracks, voids and defects. [Brief description of the drawings]

[0037] [Figure 1] 1A and 1B show different possible structures of powder 10 after non-thermal plasma treatment. In FIG. 1A, secondary particles 2 are distributed on the surface of primary particles 1 without the use of organic linkers 3. In FIG. 1B, secondary particles 2 are distributed on the surface of primary particles 1 with organic linkers 3. In FIG. 1C, the surface of primary particles 1 is completely covered by secondary particles 2, forming a layer of particles (without organic linkers). In FIG. 1D, the surface of primary particles 1 is completely covered by secondary particles 2, forming at least two layers of particles (without organic linkers). [Diagram 2]FIG. 1 illustrates one embodiment of the present invention 20 in which primary and secondary particles are mixed together (21) before being injected into a non-thermal plasma glow discharge 22 and passing through an afterglow region 23. Once the powder is processed, it is collected in a collector 24. [Diagram 3] FIG. 1 illustrates one embodiment of the present invention 30 in which primary particles 31 and secondary particles 32 are injected into different containers and injected by two different techniques into a non-thermal plasma discharge 33 (without being mixed) and passing through an afterglow region 34. Once the powder is processed, it is collected in a collector 35. [Figure 4] FIG. 4 illustrates an embodiment 40 of the present invention in which primary particles 41 are injected into a non-thermal plasma discharge 43. Secondary particles 42 are injected into an afterglow region 44. The primary and secondary particles then react in the afterglow region. Once the powder has been processed it is collected in a collector 45. [Diagram 5] FIG. 1 illustrates one embodiment of the present invention 50 in which primary and secondary particles are mixed together (51) before being injected directly into the afterglow region 53 created by the non-thermal plasma glow discharge 52. Once the powder is processed, it is collected in a collector 54. [Figure 6] FIG. 6 illustrates an embodiment 60 of the present invention in which primary particles 61 and secondary particles 62 are injected into different containers and are injected by two different techniques (without mixing) into an afterglow region 64 generated by a non-thermal plasma discharge 63. Once the powder has been processed, it is collected in a collector 65. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0038] The present invention discloses non-thermal plasma treatment of metal, metal alloy powders to improve their processability by additive manufacturing (AM), which faces challenges that limit its use, particularly high reflectivity, sensitivity to oxidation, and the presence of cracks, voids or defects within the structure found in metal AM.

[0039] According to a first aspect of the invention, the method provides a non-thermal plasma process for producing a metal or metal alloy functionalized powder 10 consisting of a plurality of particles, said primary particles 1 of a defined average diameter being attached to said secondary particles 2, which are a plurality of metal, metal alloy, ceramic or polymer particles of a smaller defined average diameter. The secondary particles 2 are distributed on the surface of the primary particles 1. In some embodiments, the primary particles are coated with an organic linker 3 to enhance the binding ability of the secondary particles on the primary particles. The organic linker 3 is infused in the same way as the primary particles 1. In some preferred embodiments, the process is carried out without an organic linker.

[0040] The primary particles 1 of the metal, metal alloy powder may be composed of metals from the following list: Li, Be, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Cs, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi, PO and combinations thereof. The primary particles 1 may also contain alloying non-metallic elements from the following list: B, C, N, O, Si, P, S, Ge, As, Se, Sb, Te, At and combinations thereof.

[0041] In some preferred embodiments, the primary particles 1 may be composed of 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 series aluminum alloys.

[0042] The primary particles 1 may be of various sizes and shapes. In some embodiments, the primary particles 1 may be spherical, rod-like, or hollow. These primary particles 1 may have an aspect ratio of 1:1 to 200:1. The aspect ratio defines the ratio of the longest dimension to the shortest dimension. In some other embodiments, the primary particles 1 may have an average diameter of 0.01 μm to 1000 μm.

[0043] Primary particles 1 composed of metals and metal alloys can be produced from a variety of synthesis methods including, but not limited to, milling of solid metal parts, laser ablation of metal targets, plasma synthesis, electrodeposition, precipitation of metal salts, reduction of metal oxides, pyrolysis or gas atomization of metal compounds.

[0044] The secondary particles 2 may be composed of metals, metal alloys, ceramics or polymers. The metals may be selected from the following list: Li, Be, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Cs, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi, Po and combinations thereof. The metal secondary particles 2 may contain non-metallic elements from the following list: B, C, N, O, Si, P, S, Ge, As, Se, Sb, Te, At and combinations thereof. The ceramic secondary particles 2 may consist of carbides, nitrides, hydrides, oxides or borides of metals from the following list: Li, Be, Na, Mg, Al, K, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, In, Sn, Cs, Ba, Hf, Ta, W, Re, Os, Ir, Pt, Au, Tl, Pb, Bi, PO and combinations thereof. The polymer secondary particles 2 may be selected from the list of the following families: polyethylene, polypropylene, polystyrene, polyurethane, polybutadiene, polyacrylic acid, polyethylene terephthalate, polyamide, polyimide, polyacrylonitrile, polyvinyl, polyester, polyisoprene, polychloroprene, polyacetal, polyaniline, polysiloxane, polyphosphazene, polyacrylate, polymethacrylate, polyacetate, polycarbonate, derivatives of these polymers and copolymers therefrom.

[0045] The secondary particles 2 may be of various sizes and shapes. In some embodiments, the secondary particles 2 may be spherical, rod-like, or hollow. These secondary particles 2 may have an aspect ratio of 1:1 to 200:1. In some other embodiments, the secondary particles 2 may have an average diameter of 0.002 μm to 900 μm. However, the secondary particles 2 are always smaller than the primary particles.

[0046] Secondary particles 2 composed of metals and metal alloys may be produced from a variety of synthesis methods including, but not limited to, milling of solid metal parts, electrodeposition, precipitation of metal salts, reduction of metal oxides, pyrolysis or gas atomization of chemicals.

[0047] The secondary particles 2 composed of ceramic can be produced from a variety of synthesis methods, including, but not limited to, hydrothermal synthesis, sol-gel synthesis, thermal decomposition of chemicals, precipitation synthesis, evaporation condensation or solvent removal methods.

[0048] Secondary particles 2 composed of polymers can be produced from a variety of synthetic methods including, but not limited to, plasma polymerization, spray drying, emulsion synthesis, heterophase polymerization, or by conventional wet chemistry.

[0049] The secondary particles 2 may be distributed on the surface of the primary particles 1 (FIGS. 1A and 1B). In some embodiments, the primary particles 1 may have a surface coverage of 0.1 to 100%. A coverage of 100% represents that the primary particles 1 are coated with a layer of secondary particles 2 (FIG. 1C). This layer may have a thickness of about 0.002 μm to about 900 μm. The primary particles 1 may be coated with 1 to 100 layers of secondary particles 2 (FIG. 1D).

[0050] In some embodiments, multiple secondary particles 2 having different compositions may coat the primary particles 1. The multiple secondary particles 2 may be composed of different metals, metal alloys, ceramics, or polymers.

[0051] In some embodiments, organic linkers 3 can be used to enhance the attachment of secondary particles 2 to primary particles 1. These organic linkers 3 located on the surface of primary particles 1 may contain alcohol, aldehyde, amine, epoxy, ketone, carboxylic acid, thiol or silane functional groups. These organic linkers 3 may be selected from the following non-exhaustive list of organic compounds: glycerol, heparin, maleic anhydride, chondroitin sulfate, heparin, sodium citrate, mannan sulfate, dextran sulfate, 1-carrageenan. These organic linkers 3 may be selected from the following non-exhaustive list of polymers: polyacrylic acid, polyalkylamines, polyvinylpyrrolidone, polyquaternary ammonium salts, polyglutamic acid, polyaspartic acid, polylysine and copolymers or combinations thereof.

[0052] The AM processing of powders consisting of primary particles 1 coated by multiple smaller secondary particles 2 is a suitable answer to the challenges in this field.

[0053] Firstly, the secondary particles 2 distributed on the surface of the primary particles 1 can change the reflectivity of the powder. Indeed, some metals or metal alloys, such as aluminum alloys or copper, have a high reflectivity for a wide range of wavelengths. Highly reflective powders reflect the most important part of the incident laser beam. This reflection prevents the particles from melting. To accurately manufacture the part, the laser power must be increased and thus the process is less efficient. The fact that fewer reflective particles are distributed on the surface reduces the overall reflectivity and energy absorption of the powder, without changing its bulk composition and its properties. In addition, the secondary particles 2 form a granular layer on the surface of the primary particles 1 that reduces the reflectivity more than a smooth layer of the same material. In fact, a rough surface reduces the regular reflectivity of the surface and increases the absorption of the laser beam by the material.

[0054] Secondly, the formation of a layer of secondary particles 2 surrounding the primary particles 1 can provide protection against surface oxidation due to external moisture. Oxidation of metal powders is a significant problem in AM processes. In fact, the thick oxide layer formed can inhibit correct sintering or melting in some cases. For example, aluminum alloys are well known to be very sensitive to moisture and an alumina passivation layer forms as soon as they are exposed to air. The alumina shell has a high melting point and prevents grain growth and diffusion at the boundaries when exposed to the laser beam. Processing of such powders results in brittle or multiphase parts with the presence of cracks, voids and defects. The distribution of secondary particles 2 on the primary particles 1 acts as a barrier against moisture in the air and avoids the formation of an oxide layer. The secondary particles 2, which have a melting point similar to or lower than the primary particles, allow grain growth and diffusion at the boundaries, thus facilitating the easy handling and processability of such powders.

[0055] Third, the secondary particles 2 attached to the primary particles 1 can act as sintering aids and nucleating agents that improve / strengthen the final structure of the sintered part. The steep temperature gradients used to process parts by AM result in high heating and cooling rates. Some metal powders cannot withstand this high cooling rate and cracks appear in the microstructure during the solidification step. This solidification dynamics is highly anisotropic, resulting in uneven growth that leads to the presence of cracks and voids that form brittle parts. In the present invention, the secondary particles 2 act as sintering aids and nucleating agents, resulting in an isotropic solidification of the molten material. The secondary particles 2 prevent the formation of cracks, voids and defects in the microstructure. Furthermore, by bonding the secondary particles 2 to the primary particles 1, a uniform distribution of the sintering aids is ensured throughout the material, which may be difficult to reach.

[0056] Finally, the secondary particles 2 act as sintering aids and can reduce the sintering temperature of the powder. The high temperatures used in the AM process to sinter metal powders can result in eutectic or peritectic decomposition and the formation of multi-phase structures. Sintering aids are used not only to reduce the sintering temperature of the material but also to strengthen the part structure. The secondary particles 2 reduce the sintering temperature of the primary particles 1 and avoid decomposition and multi-phase structures. In conclusion, the secondary particles 2 ensure that the alloy bulk composition of the manufactured part is the same as the starting material.

[0057] According to a second aspect of the invention, the non-thermal plasma process comprises the steps of providing metal or metal alloy primary particles; providing metal, metal alloy, ceramic or polymer secondary particles; providing a carrier gas stream to guide the particles through the process; providing a non-thermal plasma glow discharge that allows the particles to be cleaned, activated and react with each other; and providing said collectors, at least two containers for receiving functionalized powders, positioned after the plasma discharge.

[0058] In the following sections, technical terms are introduced and elaborated to facilitate understanding by those skilled in the art. The following conceptual explanations are explained throughout the document.

[0059] "Non-thermal plasma glow discharge" refers to said plasma, which is an ionized gas produced by applying a strong electric field to a gas. This electric field can be produced using radio frequency, microwave or direct current. To produce this electric field, a high voltage is applied between two electrodes. The gap between both electrodes is supplied with a gas, which is ionized under the electric field to produce a plasma, which is said plasma discharge. The voltage is selected in a range lower than the formation of an electric arc in order to maintain a non-thermal plasma discharge (below 80°C). This plasma is composed of high-energy species such as free electrons, ions, radicals, excited species and ultraviolet light. Reactive species present in the plasma discharge can be used to etch or activate material surfaces, but also to initiate chemical reactions. Some common applications of non-thermal plasma glow discharge applied to particles are, for example, the removal of layers and contaminants by plasma etching, surface activation with a view to further processing, particle formation from liquid monomers by uniform polymerization and growth, or functionalization of particles by attaching compounds to their surfaces.

[0060] The "afterglow region" refers to the zone downstream of a non-thermal plasma glow discharge. This particular region is composed of reactive species such as free electrons, ions, radicals, excited species and ultraviolet light. These species diffuse or are brought by the gas stream from the non-thermal plasma glow discharge to this particular region. The reactive species present in the plasma discharge can be used to initiate chemical reactions as well as to etch or activate material surfaces. The most common applications of the afterglow region are almost the same as those of the non-thermal plasma glow discharge. However, the amount of reactive species and their energy are lower in this region, and this zone can be considered less reactive. At the same time, the absence of strong electric fields in this region facilitates the processing of particles sensitive to electric fields, such as some conductive particles. In fact, high electric fields can lead to parasitic agglomeration or deposition of conductive particles.

[0061] "Carrier gas stream" refers to the gas stream used to guide the particles from their container through the different plasma regions towards the collector. The particles are mixed with the gas stream by the injector and delivered towards the different plasma regions. The carrier gas stream passes through the gap between the electrodes. This gas stream also serves as the gas for generating the plasma discharge. Finally, the treated particles are propelled into one of the collectors.

[0062] In embodiment 20 (FIG. 2), a plurality of primary particles 1 are mixed with a plurality of secondary particles 2. The mixture of particles may be composed of different ratios of primary particles and secondary particles. The particle ratios may be selected from 0.5% secondary particles and 99.5% primary particles to 99% secondary particles and 1% primary particles.

[0063] First, the particle mixture 21 is injected into the vessel before being mixed with a carrier gas stream by an injector. The gas carrier stream has a concentration of 0.1 ng / cm 3 ~2g / cm 3 In certain embodiments, the organic linker 3 may be injected in the same carrier gas stream if desired. This carrier gas stream directs the particle mixture to a non-thermal plasma glow discharge 22. In the plasma discharge, plasma reactive species interact with the primary and secondary particles. The surfaces of both particle families are cleaned and activated by the plasma to become reactive, and such interactions result in multiple secondary particles bonding to the primary particles. The carrier gas stream then propagates the particles towards the afterglow region 23, where the bonding reaction can still occur. Finally, the functionalized powder 10, consisting of primary particles 1 coated with multiple secondary particles 2, is directed by a specific carrier gas to one of the collectors 24.

[0064] In another embodiment 30 (FIG. 3), a plurality of primary particles are injected into a first container 31 before being mixed with a first carrier gas stream by an injector. The first gas carrier stream has a concentration of 0.1 ng / cm 3~2g / cm 3 In certain embodiments, the organic linker 3 may be injected into the same carrier gas stream, if desired. The secondary particles are injected into a second container 32 before being mixed with a second carrier gas stream by a separate injector. The second gas carrier stream may contain particles of 0.1 ng / cm. 3 ~2g / cm 3 The carrier gas stream guides the primary and secondary particles towards the non-thermal plasma glow discharge 33. The carrier gas stream mixture may consist of 1% primary carrier gas stream and 99% secondary carrier gas to 99.9% primary carrier gas stream and 0.1% secondary carrier gas. In the plasma discharge, plasma reactive species interact with the primary and secondary particles. The surfaces of both particle families are cleaned and activated by the plasma to become reactive, and such interactions result in multiple secondary particles bonding to the primary particles. The carrier gas stream then propagates the particle mixture towards the afterglow region 34, where the bonding reaction can still occur. Finally, the powder 10, consisting of primary particles 1 coated with multiple secondary particles 2, is guided by a specific carrier gas to one of the collectors 35.

[0065] In another embodiment 40 (FIG. 4), a plurality of primary particles are injected into a first container 41 before being mixed with a first carrier gas stream by an injector. The first gas carrier stream has a concentration of 0.1 ng / cm 3 ~2g / cm 3In certain embodiments, the organic linker 3 may be injected into the same carrier gas stream, if desired. This first carrier gas stream directs the primary particles to a non-thermal plasma glow discharge 43, where plasma reactive species interact with the primary particles. Their surfaces are cleaned and activated by the plasma, making them reactive. The activated primary particles are then directed by the carrier gas stream towards the afterglow region 44. At the same time, a number of secondary particles are injected into a second vessel before being mixed with a second carrier gas stream by another injector. The second carrier stream of gas has a concentration of 0.1 ng / cm 3 ~2g / cm 3 This second carrier gas stream directs the secondary particles towards the afterglow region 44. The carrier gas stream mixture may consist of 1% of the primary carrier gas stream and 99% of the secondary carrier gas to 99.9% of the primary carrier gas stream and 0.1% of the secondary carrier gas. In the afterglow region, the secondary particles interact with the plasma reactive species and activated primary particles diffusing from the non-thermal plasma glow discharge. This interaction causes multiple secondary particles to bond to the primary particles. Finally, the powder 10, which consists of the primary particles 1 coated with multiple secondary particles 2, is directed by the specific carrier gas to one of the collectors.

[0066] In embodiment 50 (FIG. 5), a plurality of primary particles 1 are mixed with a plurality of secondary particles 2. The mixture of particles may be composed of different ratios of primary particles and secondary particles. The particle ratios may be selected from 0.5% secondary particles and 99.5% primary particles to 99% secondary particles and 1% primary particles.

[0067] First, the particle mixture is injected into a vessel 51 before being mixed with a carrier gas stream by an injector. The gas carrier stream has a concentration of 0.1 ng / cm 3 ~2g / cm 3In a particular embodiment, the organic linker 3 may be injected in the same carrier gas stream if desired. This carrier gas stream directs the particle mixture towards the afterglow region 53, where the plasma reactive species diffused from the non-thermal plasma glow discharge 52 interact with the primary and secondary particles. The surfaces of both particle families are cleaned and activated by the plasma to become reactive, and this interaction causes multiple secondary particles to bond to the primary particles. Finally, the powder 10, consisting of the primary particles 1 coated with multiple secondary particles 2, is directed by a specific carrier gas to one of the collectors 54.

[0068] In another embodiment 60 (FIG. 6), a plurality of primary particles are injected into a first container 61 before being mixed with a first carrier gas stream by an injector. The first gas carrier stream has a concentration of 0.1 ng / cm 3 ~2g / cm 3 In certain embodiments, the organic linker 3 may be injected into the same carrier gas stream, if desired. The secondary particles are injected into the second container 62 before being mixed with a second carrier gas stream by a separate injector. The second gas carrier stream may contain particles of 0.1 ng / cm. 3 ~2g / cm 3 The powder may contain particles of 1000 to 150 ...

[0069] The present invention involves the creation of a non-thermal plasma glow discharge by an electric field, such as RF, microwave, or DC, applied to an incoming gas stream.

[0070] In some embodiments, the electric field is generated by applying a voltage between two electrodes. The voltage applied between these electrodes can vary between about 10V and 100kV. If an alternating current is used, the non-thermal plasma glow discharge can be generated by an electric field with a frequency between about 1Hz and about 900MHz. The power applied to generate the non-thermal plasma glow discharge can vary from about 10W to about 10000W.

[0071] In some embodiments, the gas stream injected between the electrodes may consist of helium, nitrogen, argon, hydrogen, carbon dioxide, carbon monoxide, nitric oxide, nitrous oxide, nitrogen dioxide, krypton, neon, xenon, or combinations thereof. The gas flow may be fixed between about 0.1 and 5000 standard liters per minute. The pressure in the reactor at which the non-thermal plasma glow discharge is generated may be selected between about 0.01 and about 30 atmospheres. In a preferred embodiment, the reactor is operated at atmospheric pressure.

[0072] The present invention describes a non-thermal plasma glow discharge process to produce primary particles that are combined with smaller secondary particles to enhance AM processability. The present invention has several advantages compared to the state of the art in this AM field.

[0073] First, the process avoids the use of solvents and harmful chemicals: in fact, this non-thermal plasma glow discharge process operates only with gases, particles, and, in some embodiments, non-toxic organic linkers.

[0074] Secondly, the process avoids a multi-stage production consisting of wet chemistry and drying and / or purification steps. In fact, the functionalized powders are produced by injecting the particles into a plasma reactor and collecting them at the outlet of this plasma reactor. Furthermore, the etching capacity of the plasma discharge can remove the contaminants and oxide layers present on the particle surface. The particles are cleaned, depassivated and bonded together in the same process, resulting in an important gain in process time.

[0075] Finally, the process can be operated in a continuous mode, which makes it possible to scale up the technology and meet the industrial demand for metal powders. Indeed, several collectors are implemented at the outlet of the plasma reactor. One of the collectors can receive the functionalized powder when the other one is emptied and cleaned. When the collector used is full, the gas stream loaded with functionalized powder may be directed to another collector to continuously receive the particles.

[0076] According to a third aspect of the invention, the invention comprises the processing of the functionalized powders described above by a melting or sintering AM process. The AM processing is improved by this treatment and high quality parts are produced therefrom. These parts have improved properties such as mechanical strength and microstructure free of cracks, voids and defects.

[0077] To form high quality parts from the above mentioned powders, AM processes such as selective laser sintering (SLS), selective laser melting (SLM), electron beam melting (EBM) or directed energy deposition (DED) can be used. In a preferred embodiment, sintering processes are primarily chosen over melting processes of metal alloys because sintering is gentler and no alloy decomposition occurs.

[0078] In one embodiment, the AM process of the functionalized powder comprises: First, there is the sintering or melting of a quantity of functionalized powder provided by exposure to a high energy beam, such as a laser or electron beam, which melts all or part of the powder in a desired pattern.

[0079] Second, the molten material solidifies to form a first solid layer in the desired pattern.

[0080] Third, a new amount of functionalized powder is provided and the first and second steps are repeated until the target component is achieved.

[0081] The functionalized powder can be provided by continuously blowing the powder through a nozzle into the spot where the material has to be deposited, or by filling a powder bed and continuously running a new layer of powder after a solid layer has formed.

[0082] The AM processing of such functionalized powders results in parts with good mechanical resistance and without cracks, voids and defects. The secondary particles are acting as sintering aids and nucleating agents that avoid the formation of cracks, voids and defects. In fact, the secondary particles increase the isotropy of the solidification. The absence of oxide layers and contaminants on the primary particle surface also plays an important role in the processing of high-quality parts.

[0083] Furthermore, the use of functionalized powders, composed of primary particles made of metals or metal alloys coated with smaller secondary particles composed of metals, metal alloys, ceramics or polymers, makes it possible to make the AM process more efficient in two ways.

[0084] First, the secondary particles present on the surface of the primary particles can reduce the reflectivity of the powder. This reduced reflectivity allows the beam energy to be reduced.

[0085] Secondly, the protective layer against oxidation formed by the secondary particles allows easier handling of the material before processing. Especially in the case of powder bed processes, the bed needs to be installed in an inert atmosphere.

[0086] In conclusion, the present invention consists of three main aspects. Firstly, the properties of the powders produced by this method and their advantages for AM processes are described. Secondly, the non-thermal plasma glow discharge process, its variants and the benefits of this technology are presented. Finally, the AM process and increased efficiency of such treated powders are described.

[0087] While the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications, and variations that fall within the scope of the appended claims.

Claims

1. 1. A method for providing a non-thermal plasma process for producing a metal or metal alloy functionalized powder comprised of a plurality of solid particles, comprising: a plurality of primary solid particles attached to a plurality of secondary solid particles, the secondary solid particles being smaller than the primary solid particles, the secondary solid particles being distributed on a surface of the primary solid particles for additive manufacturing applications, the non-thermal plasma process comprising: Providing metal or metal alloy primary solid particles; Providing metal, metal alloy, ceramic or polymer secondary solid particles; providing a carrier gas stream to guide the solid particles through the non-thermal plasma process; providing a non-thermal plasma glow discharge; generating an afterglow plasma downstream of the non-thermal plasma glow discharge, the afterglow plasma cleaning, activating and reacting the solid particles with each other; providing at least two solid particle collection units for receiving the metal or metal alloy functionalized powder, the solid particle collection units being positioned after the non-thermal plasma glow discharge; wherein a ratio of the average diameter of the primary solid particles to the average diameter of the secondary solid particles is greater than 1 and less than 500,000.

2. 2. The method of claim 1, wherein a plurality of primary solid particles are mixed with a plurality of secondary solid particles, the plurality of primary solid particles are mixed with the plurality of secondary solid particles to form a solid particle mixture, the solid particle mixture is injected into a gas stream, which carrier gas stream directs the solid particles towards the non-thermal plasma glow discharge where the reaction occurs, and then the metal or metal alloy functionalized powder comprised of primary solid particles coated with a plurality of secondary solid particles is collected.

3. 2. The method of claim 1, wherein a plurality of primary solid particles are injected into said carrier gas stream, referred to as a first carrier gas stream, and a plurality of secondary solid particles are injected into another carrier gas stream, referred to as a second carrier gas stream, said second carrier gas stream being different from said first carrier gas stream, said first carrier gas stream and said second carrier gas stream directing both primary and secondary solid particles towards said non-thermal plasma glow discharge where said reaction occurs, and then said metal or metal alloy functionalized powder comprised of said primary solid particles coated with said plurality of secondary solid particles is collected.

4. 2. The method of claim 1, wherein a plurality of primary solid particles are injected into a carrier gas stream, referred to as a first carrier gas stream, which directs the primary solid particles towards the non-thermal plasma glow discharge for cleaning and activation, a plurality of secondary solid particles are injected into another carrier gas stream, referred to as a second carrier gas stream, which directs the secondary solid particles towards the afterglow plasma where the reaction occurs, and then the metal or metal alloy functionalized powder comprised of primary solid particles coated with a plurality of secondary solid particles is collected.

5. 2. The method of claim 1, wherein the plurality of primary solid particles are mixed with the plurality of secondary solid particles, the plurality of primary solid particles are mixed with the plurality of secondary solid particles to define a solid particle mixture, the solid particle mixture is injected into the carrier gas stream, the carrier gas stream directs the solid particles towards the afterglow plasma where the reaction occurs, and then the metal or metal alloy functionalized powder comprised of the primary solid particles coated with the plurality of secondary solid particles is collected.

6. 2. The method of claim 1, wherein the plurality of primary solid particles are injected into a carrier gas stream, referred to as a first carrier gas stream, which directs the primary solid particles toward an afterglow plasma, the plurality of secondary solid particles are injected into another carrier gas stream, referred to as a second carrier gas stream, which directs the secondary solid particles toward the afterglow plasma where the reaction occurs, and then the metal or metal alloy functionalized powder comprised of primary solid particles coated with a plurality of secondary solid particles is collected.

7. The method of claim 1 , wherein the primary solid particles are composed of the metal or metal alloy.

8. 2. The method of claim 1, wherein the primary solid particles are a 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 series aluminum alloy.

9. The method of claim 1, wherein the primary solid particles have an average diameter of from 0.01 μm to 1000 μm.

10. The method of claim 1 , wherein the secondary solid particles are comprised of a metal, a metal alloy, a ceramic, or a polymer.

11. 2. The method of claim 1, wherein the secondary solid particles have an average diameter between 0.002 μm and 900 μm, and the secondary solid particles are always smaller than the primary solid particles.

12. The method of claim 1 , wherein an organic linker is used to enhance the attachment of the secondary solid particles to the primary solid particles.

13. The method of claim 1 , wherein the step of providing a non-thermal plasma glow discharge is performed by an electric field including RF, microwave, or DC, the electric field being applied to an incoming gas flow.

14. 14. The method of claim 13, wherein the electric field is generated by applying a voltage between two electrodes, the voltage applied between the two electrodes varying between about 10 V and 100 kV, and when an alternating current is used, the non-thermal plasma glow discharge is generated by an electric field with a frequency between about 1 Hz and about 900 MHz.

15. 14. The method of claim 13, wherein a power ranging from about 10 W to about 10,000 W is applied to generate the electric field that generates a non-thermal plasma glow discharge.

16. 14. The method of claim 13, wherein the input gas stream is comprised of helium, nitrogen, argon, hydrogen, carbon dioxide, carbon monoxide, nitric oxide, nitrous oxide, nitrogen dioxide, krypton, neon, xenon, or combinations thereof.

17. The method of claim 13, wherein the inlet gas flow is fixed between about 0.1 and 5000 standard liters per minute.

18. 10. The method of claim 1, wherein the pressure in a reactor used in the non-thermal plasma process in which the non-thermal plasma glow discharge is generated is selected between about 0.01 and about 30 atmospheres.

19. The metal or metal alloy functionalized powder is processed by a melting or sintering AM process, the method comprising: In a first step, sintering or melting of a quantity of metal powder is provided by exposure to a high energy beam, including a laser or electron beam, which melts all or part of the powder in a desired pattern; In a second step, the molten material is solidified to form a first solid layer in a desired pattern; In a third step, a new amount of metal powder is provided and the first and second steps are repeated until the target part is achieved. The method of claim 1 , comprising:

20. 20. The method of claim 19, wherein the metal or metal alloy functionalized powder is provided by continuously blowing powder through a nozzle into the spot where the material has to be deposited or by filling a powder bed and continuously running a new powder layer after a solid layer has been formed.

21. 20. The method of claim 19, resulting in good mechanical resistance and parts free of cracks, voids and defects, said secondary solid particles acting as sintering aids and nucleating agents to avoid the formation of cracks, voids and defects, said secondary solid particles enhance the isotropy of solidification, and the lack of oxides and contaminants on the surface of the primary solid particles also enhances the fabrication of high quality parts.

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