Small particle functionalized metal powders prepared 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 machinability in additive manufacturing (AM). The present invention comprises bonding primary particles consisting of a metal or a metal alloy to a plurality of secondary particles consisting of a metal, a metal alloy, a ceramic or a polymer by means of a non-thermal plasma treatment. The primary particles have an average diameter greater than that of the secondary particles. Both particles are injected by a non-thermal plasma glow discharge and / or in the afterglow region (downstream region of the plasma discharge), 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 then processed by AM to produce high-quality parts. The functionalized metal powder produced by this plasma treatment improves the machinability of metals by AM. In fact, reducing reflectivity, removing contaminants and oxide layers, enhancing isotropic solidification of molten materials, and reducing sintering temperatures improve the efficiency of powder-based AM processes.

Description

Technical Field

[0001] The present invention relates to a method for providing a non-thermal plasma process to produce metal or metal alloy functionalized powders. The present invention also relates to a method for processing the functionalized powders by a melting or sintering additive manufacturing process.

[0002] More specifically, the present invention relates to plasma treatment of metal powders to improve their processability in additive manufacturing. Background Art

[0003] Additive Manufacturing (AM) is an emerging technology for machining complex components from a wide range of materials. The AM process consists in building three-dimensional objects by stacking layers of material one on top of the other in a defined pattern. Among the main advantages of AM, such as the wide variety of materials that can be used (polymers, ceramics, metals, etc.) and the large number of available machining systems, the ability to design complex components that cannot be machined by conventional manufacturing has attracted particular interest from the industry.

[0004] In this field, three main categories of processes are usually distinguished. First, a bed of material powder is selectively sintered or melted by a laser, such as selective laser sintering (SLS), selective laser melting (SLM); or by an electron beam, such as electron beam melting (EBM). The high-energy beam sinters or melts the powder to produce a first layer. Once the first layer is formed, a new layer of powder is applied to the surface and sintered or melted to add a new layer on top of the previous layer. This operation is repeated until the desired component is produced. Secondly, directed energy deposition (DED) consists in sending a stream of powder or a line of material at the focus of a laser or electron beam. The material melts and is deposited on the surface to build up the component layer by layer. Thirdly, the article is formed by depositing extruded powder or a line of material on a surface. The extrusion nozzle is moving to track the target component.

[0005] Additive manufacturing processes using high-energy beams still face some major challenges, especially when applied to metal or metal alloy powders. In fact, only a few of the more than 5,000 metal or metal alloy powders used in industry can be manufactured today. Several gates must be overcome to provide industry with high-performance metal alloys with high strength, wear resistance or oxidation resistance.

[0006] One challenge is the high reflectivity of metal powders such as aluminum or copper, which makes them difficult to melt or sinter with a laser source. In fact, a major portion of the laser energy can be reflected rather than absorbed to form the material. The process must be performed at a higher power, which reduces its productivity.

[0007] Another challenge with metal powder additive manufacturing is that some alloys such as aluminum will oxidize by the moisture present in the air. This oxide layer prevents the powder from sintering properly during processing. Powders must be carefully stored before use, and systems must be adjusted to avoid this phenomenon which can increase their cost (prize).

[0008] Another challenge is the formation of microstructures with cracks, voids and defects, which are usually encountered when producing metal parts by sintering processes. These defects are attributed to the thermodynamics of the solidification of the molten material. In fact, the sharp temperature gradients used by the laser or electron beam lead to high cooling rates. In the case of certain alloys, this high cooling rate induces anisotropic solidification that produces cracks.

[0009] Finally, an important challenge is to avoid eutectic or peritectic decomposition leading to a multiphase brittle structure. In fact, the high temperatures reached during the sintering of metal alloy powders often lead to such decomposition. The use of sintering aids to reduce the sintering temperature is a strategy often encountered in metallurgy.

[0010] To address these challenges, some compounds are added to the powder. For example, some patents emphasize the use of sintering aids such as ceramic particles (US6814926, US20180161874, US20160175929, US7070734, US10507638 and US5980602A) to strengthen the component structure. Sintering aids act as grain refiners and nucleating agents, reducing the sintering temperature and causing isotropic solidification of the molten material. These particles limit the number of cracks and voids, resulting in a strong microstructure. However, it is sometimes difficult to achieve a uniform dispersion of these additives, and defects still exist in the microstructure when the components are manufactured.

[0011] In fact, intimate mixing of two powders can be obtained by co-grinding under high-energy modification of the powder surface (called mecanosynthesis), as described in US3816080, US3591362 and US4706894. However, the powders obtained do not meet the requirements required for additive manufacturing, because the surface of the powders is not fully restored / functionalized.

[0012] One solution developed is to attach sintering aid particles to metal powder particles to improve sintering aid dispersion. Some patents show that combining smaller particles with metal particle powders increases their ability to be processed by additive manufacturing (US10005127, WO2015036802, WO2015184474, US20080248306, EP1594679, US20170368603, US20150337423, US20160339517, EP3088104 and WO2018046871). Functionalization of metal particle powders solves some of the problems associated with metal additive manufacturing.

[0013] For example, it has been shown that the attachment of small particles to metal powder particles changes the chemical properties and roughness of their surface. The change in surface roughness can be controlled by the distribution of smaller particles present on the powder particles. In addition, it has been shown that particle surface roughness affects reflectivity. Increasing surface roughness leads to reduced reflectivity (WO2015036802).

[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 (US20170368603 and US20150337423).

[0015] Recently, different ways of attaching small particles to larger particles have been developed. Most of them involve chemical reactions (US20100209696), emulsion detonation (US20110183833), laser ablation (US7527824), thermal treatment (US6652967), plasma torch assisted fluidized bed and high energy grinding reactors (WO2018046871), and have been used in various applications as catalysis or as sensors. However, the main disadvantages or limitations of these production routes are their multi-step processes, use of large amounts of solvents, hazardous chemicals, need for high temperatures, and non-continuous processes.

[0016] Plasma treatments have also been considered to form such structured particles. For example, palladium catalysts supported on carbon and aluminum have been obtained by injecting two precursors in a plasma discharge (US5989648). However, most often, such plasma processes are applied to monomer-coated particles by injecting liquid precursors that polymerize in the discharge (US20080248306 and US20080145553). This in-situ polymerization in the discharge to form the structured particles does not allow significant control over the resulting material. Another example is described as injecting primary particles in a plasma discharge so as to decompose and condense on secondary particles. Similar to the previous example, it is difficult to achieve correct control due to the changes in the particle characteristics during the process. Finally, a patent describes the production of functionalized powders by fluidized bed (WO2018046871). The functionalized particles are sprayed onto such powders circulating in a fluidized bed at a controlled temperature. This reaction can be assisted by a plasma torch to promote the diffusion of heteroatoms such as nitrogen, carbon, pores or oxygen. In addition, thermal plasma torches can be used to provide spheroidization of the powder. However, in previous patents, plasma does not allow nucleating agents, sintering aids or small particles to be grafted onto the metal powder. In addition, the process is not continuous, which limits the production rate.

[0017] In summary, the interest in functionalized powders specifically for additive manufacturing is real, and efficient methods of production must be developed. Some of these have been established, however, the need for one-step, solvent-free and hazardous chemical-free synthesis methods as well as better control of particle characteristics are essential to expand the use of these powders in additive manufacturing. Summary of the invention

[0018] The present invention was developed against this background and against the background of limitations and problems associated therewith.

[0019] A need exists for a Flight control system that provides improved processability for non-thermal plasma treated metal and metal alloy powders in additive manufacturing (AM).

[0020] It is therefore a primary object of the present invention to provide a non-thermal plasma process that provides improved reflectivity, sensitivity to oxidation, and the presence of cracks, voids, or defects in structures encountered in metal additive manufacturing that limit its use.

[0021] The object of the present invention relates to the use of non-thermal plasmas by activating the surfaces of the two powders, providing them with sufficient energy to react together by electrostatic reaction. In fact, the powders circulating in a continuous flow through the glow or afterglow plasma are excited, generating positive or negative charges on their surfaces. In this application, the primary particles can be positively or negatively charged, depending on the chemical nature of the powders, while the secondary powders carry an opposite charge, making it possible for them to react with the primary powders and to cover them appropriately.

[0022] To achieve this, a method of the invention is provided for producing a metal or metal alloy functionalized powder by a non-thermal plasma process comprising the features claimed in claim 1, and the invention provides a method for processing the functionalized powder by a melting or sintering additive manufacturing process according to claim 20.

[0023] Advantageous embodiments of the invention are claimed in the dependent claims.

[0024] The present invention discloses a non-thermal plasma treatment of metal and metal alloy powders to improve their processability in additive manufacturing (AM). Such treatments are particularly challenged by high reflectivity, sensitivity to oxidation, and the presence of cracks, voids, or defects in structures encountered in metal additive manufacturing that limit their use.

[0025] In the first aspect, the present method provides a non-thermal plasma process to produce metal or metal alloy powder, the functionalized powder is composed of multiple metal or metal alloy particles, and the primary particles of the defined average diameter are attached to the metal, metal alloy, ceramic or polymer particles of the secondary particles with 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 injected in the same manner as the primary particles.

[0026] In a second aspect, the non-thermal plasma process may include: providing metal or metal alloy primary particles; providing metal, metal alloy, ceramic or polymer secondary particles; providing a carrier gas flow to guide the particles throughout the entire process; providing a non-thermal plasma glow discharge, allowing the particles to be cleaned, activated and react with each other; providing at least two containers arranged after the plasma discharge, the collectors being used to receive the functionalized powder.

[0027] 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 to a non-thermal plasma glow discharge where a reaction occurs. Then, a functionalized powder consisting of the primary particles coated with the plurality of secondary particles is collected.

[0028] In some other embodiments, a plurality of primary particles are injected into a gas stream. A plurality of secondary particles are injected into another gas stream. These carrier gas streams direct both the primary and secondary particles to a non-thermal plasma glow discharge where a reaction occurs. Then, a functionalized powder consisting of the primary particles coated with the plurality of secondary particles is collected.

[0029] In some other embodiments, a plurality of primary particles are injected into a gas stream. The carrier gas stream guides the primary particles to a non-thermal plasma glow discharge to be cleaned and activated. A plurality of secondary particles are injected into another gas stream. The second carrier gas stream guides the secondary particles to a downstream region of the aforementioned non-thermal plasma glow discharge, and the reaction occurs in the afterglow region. Then, a functionalized powder consisting of the primary particles coated with the plurality of secondary particles is collected.

[0030] In some other 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 guides the particles to the afterglow region where the reaction occurs. Then, a functionalized powder consisting of the primary particles coated with the plurality of secondary particles is collected.

[0031] In some other embodiments, a plurality of primary particles are injected into a gas stream. The carrier gas stream guides the primary particles to the afterglow region. A plurality of secondary particles are injected into another gas stream. The second carrier gas stream guides the secondary particles to the afterglow region where the reaction occurs. Then, a functionalized powder consisting of the primary particles coated with the plurality of secondary particles is collected.

[0032] The present invention relates to the generation of a non-thermal plasma glow discharge by an electric field, such as RF, microwave, DC, etc., applied to an incoming gas flow.

[0033] In some embodiments, the electric field is generated by applying tension between two electrodes. The voltage applied between these electrodes can vary between about 10V and 100kV. When using alternating current, the non-thermal plasma glow discharge can be generated by an electric field having a frequency of about 1Hz to about 900MHz. The power applied to generate the non-thermal plasma glow discharge can vary between about 10 to about 10000W.

[0034] 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 a combination thereof. The gas stream may be fixed at about 0.1 to 5000 standard liters per minute. The pressure in the reactor producing the non-thermal plasma glow discharge may be selected between about 0.01 to about 30 atmospheres.

[0035] In a third aspect, the present invention relates to processing the functionalized powders described above by a melt or sintering additive manufacturing process. The additive manufacturing process is improved by such processing and high quality parts are produced. These parts have enhanced properties such as mechanical strength and a microstructure free of cracks, voids and defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Different possible structures of the powder 10 after non-thermal plasma treatment are shown. Figure 1 In A, the secondary particles 2 are distributed on the surface of the primary particles 1 without using organic linkers 3. Figure 1 In B, secondary particles 2 are distributed on the surface of primary particles 1 using organic linkers 3. Figure 1 In C, the surface of primary particle 1 is completely covered by secondary particle 2 to form a particle layer (without organic joints). Figure 1 In D, the surface of the primary particle 1 is completely covered by the secondary particle 2, forming at least two particle layers (without organic linkers).

[0037] Figure 2 One embodiment of the invention 20 is depicted 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.

[0038] Figure 3 An embodiment of the invention 30 is depicted where primary particles 31 and secondary particles 32 are poured into different containers and injected into a non-thermal plasma discharge 33 in two different ways (without mixing) and pass through an afterglow region 34. Once the powder is processed, it is collected in a collector 35.

[0039] Figure 4 An embodiment of the present invention 40 is depicted 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 is processed, it is collected in a collector 45.

[0040] Figure 5 One embodiment of the invention 50 is depicted in which primary and secondary particles are mixed together 51 before being injected directly into an afterglow region 53 produced by a non-thermal plasma glow discharge 52. Once the powder is processed, it is collected in a collector 54.

[0041] Figure 6An embodiment of the invention 60 is depicted, where primary particles 61 and secondary particles 62 are poured into different containers and injected by two different means (without mixing) into an afterglow region 64 produced by a non-thermal plasma discharge 63. Once the powder is processed, it is collected in a collector 65. DETAILED DESCRIPTION

[0042] The present invention discloses a non-thermal plasma treatment of metal and metal alloy powders to improve their processability in additive manufacturing (AM). Such treatments are particularly challenged by high reflectivity, sensitivity to oxidation, and the presence of cracks, voids, or defects in structures encountered in metal additive manufacturing that limit their use.

[0043] According to a first aspect of the invention, the method provides a non-thermal plasma process to produce a metal or metal alloy functionalized powder 10 consisting of a plurality of particles, wherein the primary particles 1 having a defined average diameter are attached to a plurality of metal, metal alloy, ceramic or polymer particles of the secondary particles 2 having 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 organic linkers 3 to enhance the binding ability of the secondary particles on the primary particles. The organic linkers 3 are injected in the same manner as the primary particles 1. In some preferred embodiments, the process is carried out without organic linkers.

[0044] The primary particles 1 of the metal, metal alloy powder may consist of a metal 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 alloying elements from the following list: B, C, N, O, Si, P, S, Ge, As, Se, Sb, Te, At and combinations thereof.

[0045] In some preferred embodiments, the primary particles 1 may be composed of aluminum alloys of the 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, and 9000 series.

[0046] Primary particles 1 can have various sizes and shapes. In some embodiments, primary particles 1 can be spherical, rod-shaped or hollow. These primary particles 1 can have an aspect ratio of 1:1 to 200:1. The aspect ratio defines the ratio between the longest dimension and the shortest dimension. In some other embodiments, primary particles 1 can have an average diameter between 0.01 μm and 1000 μm.

[0047] Primary particles 1 composed of metals and metal alloys can be produced by various synthesis methods, including but not limited to comminution of solid metal parts, laser ablation of metal targets, plasma synthesis, electrodeposition, precipitation of metal salts, reduction of metal oxides, thermal decomposition of metal compounds or gas atomization.

[0048] The secondary particles 2 may be composed of metals, metal alloys, ceramics or polymers. The metal 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 be composed 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 can be selected from the following family list: polyethylene, polypropylene, polystyrene, polyurethane, polybutadiene, polyacrylic acid, polyethylene terephthalate, polyamide, polyimide, polyacrylonitrile, polyethylene, polyester, polyisoprene, polychloroprene, polyacetal, polyaniline, polysiloxane, polyphosphazene, polyacrylate, polymethacrylate, polyacetate, polycarbonate, derivatives of these polymers and their copolymers.

[0049] The secondary particles 2 may have various sizes and shapes. In some embodiments, the secondary particles 2 may be spherical, rod-shaped, 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 between 0.002 μm and 900 μm. However, the secondary particles 2 are always smaller than the primary particles.

[0050] The secondary particles 2 composed of metals and metal alloys can be produced by various synthetic means, including but not limited to comminution of solid metal parts, electrodeposition, precipitation of metal salts, reduction of metal oxides, thermal decomposition of chemicals or gas atomization.

[0051] The secondary particles 2 composed of ceramics can be produced by various synthesis methods, including but not limited to hydrothermal synthesis, sol-gel synthesis, thermal decomposition of chemicals, precipitation synthesis, evaporation condensation or solvent removal methods.

[0052] The secondary particles 2 consisting of polymers can be produced by various synthesis methods, including but not limited to plasma polymerization, spray drying, emulsion synthesis, multiphase polymerization or by conventional wet chemistry.

[0053] The secondary particles 2 may be distributed on the surface of the primary particles 1 ( Figure 1 A and Figure 1 B). In some embodiments, the primary particles 1 may have a surface coverage percentage of 0.1 to 100%. A 100% coverage rate means that the primary particles 1 are coated by a layer of secondary particles 2 ( Figure 1 C). The 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 ( Figure 1 D).

[0054] In some embodiments, a plurality of secondary particles 2 having different compositions may coat the primary particle 1. The plurality of secondary particles 2 may be composed of different metals, metal alloys, ceramics, or polymers.

[0055] 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 can 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 can be selected from the following non-exhaustive list of polymers: polyacrylic acid, polyalkylamine, polyvinylpyrrolidone, polyquaternary ammonium salt, polyglutamic acid, polyaspartic acid, polylysine and copolymers or combinations thereof.

[0056] Additive manufacturing of powders consisting of primary particles 1 coated with a plurality of smaller secondary particles 2 is an appropriate answer to the challenges in this field.

[0057] Firstly, the secondary particles 2 distributed on the surface of the primary particles 1 can change the reflectivity of the powder. In fact, some metals or metal alloys such as aluminum alloys or copper have high reflectivity for a wide range of wavelengths. Highly reflective powders reflect the most important part of the incident laser beam. This reflection hinders the melting of the particles. In order to correctly manufacture the parts, the laser power needs to be increased, and in this way, the process is less efficient. The fact that less reflective particles are distributed on its surface reduces the overall reflectivity and energy absorption of the powder without changing its overall composition and its properties. In addition, the secondary particles 2 form a granular layer on the surface of the primary particles 1, the reflectivity of which is reduced by a greater amount than a smooth layer of the same material. In fact, the rough surface reduces the regular reflectivity of the surface and enhances the absorption of the laser beam by the material.

[0058] Secondly, forming a layer of secondary particles 2 around the primary particles 1 can provide protection from surface oxidation of external moisture. Oxidation of metal powders is an important issue in additive manufacturing processes. In fact, in some cases, the thick oxide layer formed inhibits correct sintering or melting. For example, it is well known that aluminum alloys are highly sensitive to moisture and will immediately form an aluminum oxide passivation layer when exposed to air. The aluminum oxide shell has a high melting point and hinders the growth and diffusion of grains at the boundaries when exposed to a laser beam. The processing of such powders results in fragile or multiphase parts with cracks, voids and defects. The distribution of secondary particles 2 on the primary particles 1 acts as a barrier to prevent air moisture and avoids the formation of an oxide layer. Secondary particles 2 having a similar or lower melting point than the primary particles allow grains to grow and diffuse at the boundaries and thus promote the easy handling and machinability of such powders.

[0059] Again, the secondary particles 2 attached to the primary particles 1 can act as sintering aids and nucleating agents, improving / strengthening the final structure of the sintered part. The sharp temperature gradients used in additive manufacturing to process parts result in high heating and cooling rates. Some metal powders cannot withstand such high cooling rates and cracks will appear in the microstructure during the solidification step. This solidification dynamics is highly anisotropic and produces uneven growth, resulting in the presence of cracks and voids, forming brittle parts. In the present invention, the secondary particles 2 act as sintering aids and nucleating agents that cause the molten material to solidify isotropically. The secondary particles 2 prevent the formation of cracks, voids and defects in the microstructure. In addition, combining the secondary particles 2 with the primary particles 1 ensures uniform distribution of the sintering aid throughout the material, which can sometimes be difficult to achieve.

[0060] Finally, the secondary particles 2 can act as a sintering aid and reduce the sintering temperature of the powder. The high temperatures used to sinter the metal powder in the additive manufacturing process can lead to eutectic or peritectic decomposition and the formation of multiphase structures. Sintering aids are used to reduce the sintering temperature of the material and also to strengthen the component structure. The secondary particles 2 reduce the sintering temperature of the primary particles 1, avoiding decomposition and multiphase structures. In summary, the secondary particles 2 ensure that the overall alloy composition of the produced component is the same as the starting material.

[0061] According to a second aspect of the invention, the non-thermal plasma process may include: providing primary particles of metal or metal alloy; providing secondary particles of metal, metal alloy, ceramic or polymer; providing a carrier gas flow to guide the particles throughout the entire process; providing a non-thermal plasma glow discharge, allowing the particles to be cleaned, activated and react with each other; providing at least two containers arranged after the plasma discharge, and the collector is used to receive the functionalized powder.

[0062] In the next section, technical terms will be introduced and explained in detail to facilitate technical personnel to understand. The following description of the concepts is described for all documents.

[0063] "Non-thermal plasma glow discharge" describes an ionized gas, called plasma, which is produced by applying a strong electric field to the gas. This electric field can be generated using radio frequency, microwaves or direct current. To generate this electric field, a high voltage is applied between two electrodes. The gap between the two electrodes is supplied with a gas, which is ionized under the electric field to produce a plasma, which discharges. The voltage is selected in a range below the formation of an arc to maintain a non-thermal plasma discharge (below 80°C). This plasma consists of high-energy species, such as free electrons, ions, free radicals, excited species and UV rays. The reactive species present in the plasma discharge can be used to etch or activate the surface of the material and can also be used to initiate chemical reactions. Some common uses of non-thermal plasma glow discharge applied to particles are, for example, removal of layers and contaminants by plasma etching, surface activation for consideration of further processing, formation of particles from liquid monomers by homogenous polymerization and growth or functionalization of particles by attaching compounds to the surface.

[0064] The "afterglow zone" describes the area downstream of a non-thermal plasma glow discharge. This specific region consists of reactive species, such as free electrons, ions, free radicals, excited species, and UV rays. These species diffuse or are carried to this specific region by the gas flow from the non-thermal plasma glow discharge. The reactive species present in the plasma discharge can be used to etch or activate the surface of materials, and can also be used to initiate chemical reactions. The most common applications of the afterglow zone are mostly the same as for non-thermal plasma glow discharge. However, the amount of reactive species and their energy in this region is lower, and this region can be considered less reactive. At the same time, the absence of strong electric fields in this region is beneficial for the processing of particles that are sensitive to electric fields, such as some conductive particles. In fact, high electric fields can lead to parasite aggregation or conductive particle deposition.

[0065] "Carrier gas flow" describes a gas flow that is used to guide the particles from their container through different plasma regions and to the collectors. The particles are mixed with the gas flow through the ejector and sent to the different plasma regions. The carrier gas flow passes through the gap between the electrodes. This gas flow also serves as the gas to generate the plasma discharge. Finally, the processed particles are driven to one of the collectors.

[0066] In implementation mode 20 ( Figure 2 ), a plurality of primary particles 1 are mixed with a plurality of secondary particles 2. The particle mixture can be composed of primary and secondary particles in different ratios. The particle ratio can 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 21 is poured into a container before being mixed with a carrier gas stream via a syringe. The carrier gas stream may contain 0.1 ng / cm 3 Up to 2g / cm 3 particles. In certain embodiments, the organic linker 3 can be injected in the same carrier gas stream, if desired. The 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 families of particles are cleaned and activated by the plasma and become reactive, and multiple secondary particles are bonded to the primary particles through this interaction. The carrier gas stream then propagates the particles toward the afterglow region 23, where bonding reactions can still occur. Finally, the functionalized powder 10, consisting of primary particles 1 coated with multiple secondary particles 2, is directed to one of the collectors 24 by a unique carrier gas.

[0068] In another embodiment 30 ( Figure 3 ), a plurality of primary particles are poured into a first container 31 before being mixed with a first carrier gas stream via a syringe. The first carrier gas stream may contain 0.1 ng / cm 3 Up to 2g / cm3 In some embodiments, the organic linker 3 can be injected in the same carrier gas stream if desired. The plurality of secondary particles are poured into a second container 32 before being mixed with a second carrier gas stream via another syringe. The second carrier gas stream can contain 0.1 ng / cm 3 Up to 2g / cm 3 particles. The carrier gas flow directs the primary and secondary particles to a non-thermal plasma glow discharge 33. The carrier gas flow mixture can be composed of from 1% primary carrier gas flow and 99% secondary carrier gas to 99.9% primary carrier gas flow and 0.1% secondary carrier gas. In the plasma discharge, the plasma reactive species interact with the primary and secondary particles. The surfaces of both families of particles are cleaned and activated by the plasma and become reactive, and multiple secondary particles are bonded to the primary particles through this interaction. The carrier gas flow then propagates the particle mixture toward the afterglow region 34 where bonding reactions can still occur. Finally, the powder 10 consisting of primary particles 1 coated with multiple secondary particles 2 is directed to one of the collectors 35 by a unique carrier gas.

[0069] In another embodiment 40 ( Figure 4 ), a plurality of primary particles are poured into a first container 41 before being mixed with a first carrier gas stream via a syringe. The first carrier gas stream may contain 0.1 ng / cm 3 Up to 2g / cm 3 In some embodiments, the organic linker 3 can be injected in the same carrier gas flow if necessary. The first carrier gas flow guides the primary particles to the non-thermal plasma glow discharge 43. In the non-thermal plasma glow discharge, the plasma reactive species interact with the primary particles. Their surfaces are cleaned and activated by the plasma and become reactive. The activated primary particles are then guided by the carrier gas flow to the afterglow region 44. At the same time, a plurality of secondary particles are poured into a second container before being mixed with a second carrier gas flow through another syringe. The second carrier gas flow may contain 0.1 ng / cm 3 Up to 2g / cm 3 The second carrier gas stream directs the secondary particles to the afterglow region 44. The carrier gas stream mixture can be composed 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 afterglow region, the secondary particles interact with the plasma reactive species diffused from the non-thermal plasma glow discharge and the activated primary particles. This interaction causes a plurality of secondary particles to combine with the primary particles. Finally, the powder 10 composed of the primary particles 1 coated with a plurality of secondary particles 2 is directed to one of the collectors by a unique carrier gas.

[0070] In embodiment 50 ( Figure 5), a plurality of primary particles 1 are mixed with a plurality of secondary particles 2. The particle mixture can be composed of primary and secondary particles in different ratios. The particle ratio can be selected from 0.5% secondary particles and 99.5% primary particles to 99% secondary particles and 1% primary particles.

[0071] First, the particle mixture is poured into container 51 before being mixed with a carrier gas stream via a syringe. The carrier gas stream may contain 0.1 ng / cm 3 Up to 2g / cm 3 particles. In certain embodiments, the organic linker 3 can be injected in the same carrier gas stream, if desired. The carrier gas stream directs the particle mixture to the afterglow region 53. In the afterglow region, the plasma reactive species diffused from the non-thermal plasma glow discharge 52 interact with the primary and secondary particles. The surfaces of both families of particles are cleaned and activated by the plasma and become reactive, and a plurality of secondary particles are bonded to the primary particles through this interaction. Finally, a powder 10 consisting of primary particles 1 coated with a plurality of secondary particles 2 is directed to one of the collectors 54 by a unique carrier gas.

[0072] In another embodiment 60 ( Figure 6 ), a plurality of primary particles are poured into a first container 61 before being mixed with a first carrier gas stream via a syringe. The first carrier gas stream may contain 0.1 ng / cm 3 Up to 2g / cm 3 In some embodiments, the organic linker 3 can be injected in the same carrier gas stream if desired. The plurality of secondary particles are poured into a second container 62 before being mixed with a second carrier gas stream via another syringe. The second carrier gas stream may contain 0.1 ng / cm 3 Up to 2g / cm 3 particles. The carrier gas flow directs the primary and secondary particles to the afterglow region 64. The carrier gas flow mixture can be composed of 1% primary carrier gas flow and 99% secondary carrier gas to 99.9% primary carrier gas flow and 0.1% secondary carrier gas. In the afterglow region, plasma reactive species diffused from the non-thermal plasma glow discharge 63 interact with the primary and secondary particles. The surfaces of both particle groups are cleaned and activated by the plasma and become reactive, and multiple secondary particles are combined with the primary particles through this interaction. Finally, the powder 10 composed of primary particles 1 coated with multiple secondary particles 2 is directed to one of the collectors 65 by a unique carrier gas.

[0073] The present invention relates to the generation of a non-thermal plasma glow discharge by an electric field, such as RF, microwave, DC, etc., applied to an incoming gas flow.

[0074] In some embodiments, the electric field is generated by applying tension between two electrodes. The voltage applied between these electrodes can vary between about 10V and 100kV. When using alternating current, the non-thermal plasma glow discharge can be generated by an electric field having a frequency of about 1Hz to about 900MHz. The power applied to generate the non-thermal plasma glow discharge can vary between about 10 to about 10000W.

[0075] In some embodiments, the gas flow injected between the electrodes can be composed of helium, nitrogen, argon, hydrogen, carbon dioxide, carbon monoxide, nitric oxide, nitrous oxide, nitrogen dioxide, krypton, neon, xenon or a combination thereof. The gas flow can be fixed between about 0.1 and 5000 standard liters per minute. The pressure in the reactor producing the non-thermal plasma glow discharge can be selected between about 0.01 and about 30 atmospheres. In a preferred embodiment, the reactor is operated at atmospheric pressure.

[0076] The present invention describes a non-thermal plasma glow discharge process to produce primary particles combined with smaller secondary particles to improve additive manufacturing processability. The present invention has several advantages over the prior art in this field of additive manufacturing.

[0077] First, the present method avoids the use of solvents and hazardous chemicals. In fact, this non-thermal plasma glow discharge process operates using only gases, particles, and in some embodiments, non-toxic organic linkers.

[0078] Secondly, the process avoids a multi-step production consisting of wet chemistry and drying and / or purification steps. In fact, the functionalized powder is produced by injecting particles into a plasma reactor and collecting them at the outlet of this reactor. In addition, contaminants and oxide layers present on the surface of the particles can be removed by the etching power of the plasma discharge. The particles are cleaned, depassivated and bonded together in the same process, resulting in a significant increase in processing time.

[0079] Finally, the present method can be run in a continuous mode, which allows scaling up the technology and meeting industrial demands for metal powders. In practice, multiple collectors are installed at the outlet of the plasma reactor. One of the collectors can receive the functionalized powder while the others are being emptied and cleaned. Once the collector in use is full, the gas flow filled with the functionalized powder can be directed to another collector to receive the particles in a continuous manner.

[0080] According to a third aspect of the invention, the invention relates to processing the functionalized powders described above by a melt or sintering additive manufacturing process. By this treatment, the additive manufacturing process is improved and high-quality parts are produced thereby. These parts have enhanced properties, such as mechanical strength and a microstructure free of cracks, voids and defects.

[0081] In order to form high-quality parts from the above powders, additive manufacturing 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, the sintering process is mainly selected instead of the melting process of the metal alloy because sintering is softer and no alloy decomposition occurs.

[0082] In one embodiment, an additive manufacturing process for functionalized powders includes:

[0083] First, a certain amount of functionalized powder is sintered or melted, which is provided by exposure to a high energy beam, such as a laser or electron beam. This high energy beam melts the powder completely or partially in a desired pattern.

[0084] Next, the molten material solidifies, resulting in a first solid layer forming the desired pattern.

[0085] Again, a new amount of functionalized powder is provided and the first and second steps are repeated until the target part is obtained.

[0086] The functionalized powder can be provided by continuously blowing the powder through a nozzle at the location where the material needs to be deposited, or by filling a powder bed and continuously forming new powder layers after a solid layer is formed.

[0087] Additive manufacturing processes with such functionalized powders produce components with good mechanical resistance and without cracks, voids and defects. The secondary particles act as sintering aids and nucleating agents, avoiding the formation of cracks, voids and defects. In fact, the secondary particles enhance the isotropy of solidification. The absence of oxide layers and contaminants at the surface of the primary particles also plays an important role in machining high-quality components.

[0088] Furthermore, the use of functionalized powders composed of primary particles composed of a metal or metal alloy coated with smaller secondary particles composed of a metal, metal alloy, ceramic or polymer allows the additive manufacturing process to be more efficient in two ways.

[0089] First, the presence of secondary particles on the surface of the primary particles can reduce the reflectivity of the powder. This reduced reflectivity allows the beam energy to be reduced.

[0090] Secondly, the oxide protective layer formed by the secondary particles allows easier handling of the material before processing. Especially for powder bed processes, the bed must be installed in an inert atmosphere.

[0091] In summary, this invention consists of three main aspects. First, the characteristics of the powder produced by this method and its advantages in additive manufacturing processes are described. Second, the non-thermal plasma glow discharge process, its variations and the interest in this technology are provided. Finally, the additive manufacturing process and efficiency gains of this processed powder are explained.

[0092] Although the invention has been described in conjunction with its specific embodiments, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. It is therefore intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims.

Claims

1. A method of providing a non-thermal plasma process to produce a metal or metal alloy functionalized powder consisting of a plurality of particles, the functionalized powder comprising a primary particle attached to a plurality of smaller secondary particles, the secondary particles being distributed on the surface of the primary particle for additive manufacturing applications, the non-thermal plasma process comprising: Providing metal or metal alloy primary particles; Providing metal, metal alloy, ceramic or polymer secondary particles; providing a plurality of carrier gas flows to direct the particles throughout the process; Providing a non-thermal plasma glow discharge and providing a region downstream of the discharge, an afterglow region, which allows particles to be cleaned, activated and react with each other; and providing at least two collectors located after the plasma discharge, the collectors being used to receive the functionalized powder, A plurality of primary particles are injected into a first carrier gas flow of the plurality of carrier gas flows, the first carrier gas flow guides the primary particles to the non-thermal plasma glow discharge to be cleaned and activated, the secondary particles are injected into a second carrier gas flow of the plurality of carrier gas flows, the second carrier gas flow guides the secondary particles to a downstream region of the non-thermal plasma glow discharge, the downstream region of the non-thermal plasma glow discharge being referred to as an afterglow region where the reaction occurs, and then the functionalized powder consisting of primary particles coated with a plurality of secondary particles is collected by at least two provided collectors.

2. The method according to claim 1, wherein the primary particles are aluminum alloys of the 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000 series. 3 . The method according to claim 1 , wherein the primary particles have an average diameter between 0.01 μm and 1000 μm. 4 . The method according to claim 1 , wherein the secondary particles have an average diameter between 0.002 μm and 900 μm, the secondary particles being always smaller than the primary particles.

5. The method of claim 1, comprising generating a non-thermal plasma glow discharge by an electric field applied to an incoming gas flow.

6. The method according to claim 5, wherein the electric field is generated by applying tension between two electrodes, the voltage applied between these electrodes varies between 10 V and 100 kV, and when alternating current is used, the non-thermal plasma glow discharge is generated by an electric field with a frequency of 1 Hz to 900 MHz.

7. The method of claim 5, wherein power is applied to generate the electric field, the electric field generating a non-thermal plasma glow discharge varying from 10 W to 10,000 W.

8. The method of claim 5, wherein the incoming gas stream consists of helium, nitrogen, argon, or a combination thereof.

9. The method of claim 5, wherein the incoming gas flow is fixed between 0.1 and 5000 standard liters per minute.

10. The method of claim 1, wherein the pressure in the reactor producing the non-thermal plasma glow discharge is selected between 0.01 and 30 atmospheres.

11. The method of claim 1 , wherein the functionalized powder is processed by a melting or sintering additive manufacturing process, the method comprising: In a first step, sintering or melting of a certain amount of functionalized powder is provided by exposure to a high energy beam which completely or partially melts said powder in a desired pattern, In a second step, the molten material solidifies, resulting in a first solid layer forming the desired pattern, and In a third step, a new amount of functionalized powder is provided and the first and second steps are repeated until the target component is obtained.

12. The method according to claim 11, wherein the functionalized powder is provided by continuously blowing the powder through a nozzle at the location where the material needs to be deposited, or by filling a powder bed and continuously realizing a new powder layer after the solid layer is formed.

13. The method according to claim 11 results in good mechanical resistance and parts without cracks, voids and defects. The secondary particles acting as sintering aids and nucleating agents avoid the formation of cracks, voids and defects, and the secondary particles enhance the isotropy of the solidification. The absence of oxides and contaminants at the surface of the primary particles also enhances the processing of high-quality parts.

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