In-situ treatment of powder for additive manufacturing to improve its thermal and / or electrical conductivity

Abstract

The invention relates to an additive manufacturing process by selective melting of metal or ceramic powder comprising the steps of: - Deposition of a layer (C) of powder; - Selective melting of at least one zone of the powder layer, wherein the process comprises, after deposition and prior to selective melting, a coating step in which metal or ceramic powder grains (1) are at least partially coated with a layer of an additive material (2), the metal or ceramic powder grains (1) having a first electrical conductivity, the additive material (2) having a second electrical conductivity greater than or equal to the first conductivity. Figure for the abstract: Fig. 2

Description

Title of the invention: In-situ treatment of powder for additive manufacturing to improve its thermal and / or electrical conductivity FIELD OF INVENTION

[0001] The invention relates to the general technical field of additive manufacturing.

[0002] More particularly, the invention relates to the treatment of metal powders or ceramics for additive manufacturing by melting metal or ceramic powders.

[0003] Metal powders are powders made up of elements from the metal family such as iron, titanium, aluminum, vanadium, chromium, manganese, cobalt, nickel, copper, gold, platinum, etc. The powder can be a single component or in the form of an alloy or even a composite.

[0004] Ceramic powders are powders made up of non-metallic and non-organic materials obtained by the action of high temperatures. It is these high temperatures that induce, at the heart of the raw material, an irreversible transformation which gives the ceramic produced new properties: strength and resistance to wear, heat resistance, insulating properties, etc.

[0005] The invention relates in particular, but not exclusively, to ceramics that can be obtained from metallic elements such as:

[0006] - oxides: aluminium oxide, zirconium oxide; etc;

[0007] - non-oxides: carbides, borides, nitrides, silicon-based ceramics and atoms such as tungsten, magnesium, platinum or titanium, etc;

[0008] - composite ceramics: combination of oxides and non-oxides. STATE OF THE ART

[0009] Classically, a process for manufacturing a part by adding metallic or ceramic powders is carried out by depositing successive layers of powders on a flat support surface, thus forming a powder bed.

[0010] After the deposition of a layer C of powder, a power source performs selective heating of certain areas of the powder bed, so as to cause the powders to melt in the heated areas and thus form a coherent layer of part after cooling.

[0011] The layers of powder are thus successively deposited and selectively solidified so as to form a part by successive layers.

[0012] Conventionally, the power sources used to perform the selective melting of powders can include one or more laser sources, or one or more electron beam or particle beam sources, or a combination of sources using a laser, an electron beam or a particle beam.

[0013] When manufacturing metallic or ceramic parts, the thermal and electrical conductivity and the reflection coefficient of the powders used limit the energy absorption rate of the powders.

[0014] The energy efficiency of the selective fusion operation is therefore greatly reduced.

[0015] Furthermore, during an additive manufacturing process using at least one electron beam, the charging effect can lead to electrostatic charging and electrostatic repulsion of the powder grains, known as "smoke," but also of the electron beam. This phenomenon arises in particular from the low electrical conductivity of the powder.

[0016] The current state of the art consists of preheating the powder (pre-sintering operation) in order to create micro-contacts between the powder grains and to counteract the effect of smoke. This step is energy-intensive and time-consuming.

[0017] It is therefore necessary to improve the energy efficiency of an additive manufacturing operation by melting metal or ceramic powders, using an electron beam. Description of the invention

[0018] One object of the invention is to improve the energy efficiency of such a process.

[0019] Another goal is to reduce the duration of a selective fusion cycle.

[0020] Another goal is to achieve nuances in the powder coating material.

[0021] Another objective is to improve the thermal conductivity between the powder grains, particularly for additive manufacturing processes operating by thermal conductivity such as manufacturing processes using a laser beam alone or in combination with another energy or heat source.

[0022] Another objective is also to improve the electrical conductivity between the powder grains, particularly for additive manufacturing processes operating by electrical conductivity such as manufacturing processes using an electron beam alone or in combination with another source of energy or heat.

[0023] To address these issues, the invention proposes an additive manufacturing process by selective melting of metallic or ceramic powder comprising the following steps:

[0024] - Deposition of a layer of powder;

[0025] - Selective melting of at least one area of ​​the powder layer, in which the The process includes, after deposition and prior to selective melting, a coating step during which grains of metallic or ceramic powder are at least partially covered with a film of a material, different or chemically identical, hereinafter referred to as the addition material, the metallic or ceramic powder grains having a first conductivity, the addition material having a second conductivity at least equivalent to the first.

[0026] The invention may advantageously include the following features, taken alone or in combination:

[0027] - the powder is metallic and comprises a metal or alloy having a electrical conductivity less than 1 Sm', and the addition material comprises a metal or a metal or carbon alloy, or an organometallic, or a carbon-based composite having a conductivity at least equivalent to that of graphite;

[0028] - the powder is metallic and comprises at least one metal or a metal alloy chosen from:

[0029] - precious metals, for example gold, silver, platinum, bronze, copper, zinc, tin,

[0030] - refractories, for example tungsten, tantalum, molybdenum,

[0031] - transition metals, for example titanium, vanadium, iron, cobalt, nickel,

[0032] - rare earths, for example yttrium, lanthanides;

[0033] - the coating step is carried out using a surface treatment device configured to project the addition material by means of a projected plasma according to a predefined pattern, for example substantially linear, the surface treatment device being adapted to be moved over the metal or ceramic powder so as to project the addition material onto the metal or ceramic powder;

[0034] - the surface treatment device includes an electric arc device comprising at least one electrode containing the additive material, the electrode being positioned opposite the powder layer in such a way that additive material is projected towards the powder layer when an electric arc is established between the electrode and the layer;

[0035] - the surface treatment device comprises a phase-coating device steam comprising an electrode having a wall delimiting an internal cavity, and a gaseous precursor injection system configured to inject a precursor gas into the cavity, the wall further having an orifice located opposite the layer, the precursor gas being configured to generate particles of the addition element when excited by the electrode, the particles of the addition element being expelled through the orifice onto the powder layer;

[0036] - the surface treatment device comprises a cathode device magnetron containing the additive material, oriented towards the powder layer, and allowing the additive material to be projected onto the powder by ca- spraying methodical;

[0037] - the surface treatment device comprises a blown wire device, comprising a wire connected to a power source, wherein the wire extends above the powder bed and is made of the addition material, the power source being configured to inject a current into the wire in such a way that the addition material vaporizes and is deposited on the powder layer;

[0038] - the device for superimposing a film of the additive material onto the layer of powder, film having a thickness of less than 50 pm, preferably less than 1 pm, and which for coating processes can still be less than 200 nm, and preferably less than 50 nm.

[0039] - the selective melting step is carried out using a power source comprising a laser source and / or a particle beam source, for example an electron beam;

[0040] - a surface treatment step of metallic or ceramic powders is carried out successively at each stage of laying down a layer of metallic or ceramic powder;

[0041] - the film is deposited by spraying a liquid solution of additive material into a volatile solvent at high temperature;

[0042] - the film is mechanically deposited by covering the powder layer with a film composite comprising a high-temperature volatile matrix and loaded with additive material.

[0043] According to another aspect, the invention provides an additive manufacturing device configured to carry out an additive manufacturing process according to the invention, the additive manufacturing device comprising:

[0044] - a coating element configured to dispose of a layer of powder me flat or ceramic;

[0045] - a surface treatment device configured to perform a process of surface treatment of the metallic or ceramic powder layer according to the invention;

[0046] - a power source configured to perform a selective fusion of at least an area of ​​the powder layer.

[0047] Advantageously, in such an additive manufacturing device, the layering element can be configured to deposit a layer of powder when moved across the surface of a support, and the surface treatment device can be fixed in movement to the layering element, such that when the layering element is moved, the layering element deposits a layer of powder and the surface treatment device simultaneously or with a time lag processes the layer of powder deposited by the layering element. DESCRIPTION OF THE FIGURES

[0048] Other features and advantages of the invention will become apparent from the following description, which is purely illustrative and not limiting, and should be read in conjunction with the accompanying figures in which:

[0049] [fig.l]

[0050] - Fig. 1 is a diagram representing an additive manufacturing device according to the invention;

[0051] [fig.2]

[0052] - [Fig. 2] is a generic diagram representing the implementation of a process of surface treatment according to the invention;

[0053] [fig.3]

[0054] - [Fig. 3] is a diagram representing a variant of an embodiment of a surface treatment device operating preferably at around atmospheric pressure according to the invention;

[0055] [fig.4]

[0056] - [Fig. 4] is a diagram representing a variant of an embodiment of a chemical surface treatment device preferably operating under a "primary" vacuum (1 to 10-3 mbar) according to the invention;

[0057] [fig.5]

[0058] - Fig. 5 represents a variant of an embodiment of a device surface treatment with a magnetron preferably operating under a "secondary" vacuum (10-3 to 10-7 mbar) according to the invention;

[0059] [fig.6]

[0060] - Fig. 6 represents a diagram depicting a variant of an embodiment of a blown wire surface treatment device according to the invention;

[0061] [fig.7]

[0062] - Fig. 7 is a schematic representation of one embodiment of a surface treatment device by spraying according to the invention;

[0063] [fig.8]

[0064] - Fig. 8 is a schematic representation of one embodiment of a surface treatment device with film roller, in particular single-component or composite, according to the invention.

[0065] DESCRIPTION OF ONE OR MORE METHODS OF IMPLEMENTATION AND REALIZATION Generalities

[0066] The figures illustrate an example of an additive manufacturing process by selective melting of metal or ceramic powder comprising the steps of:

[0067] - Deposition of a C layer of metallic or ceramic powder;

[0068] - Selective melting of at least one area of ​​the powder layer, in which the process includes, after deposition and prior to selective melting, a coating step in which metallic or ceramic powder grains 1 are at least partially covered with a film of an additive material 2, the metallic or ceramic powder grains 1 having a first conductivity, the additive material 2 having a second conductivity greater than or at least equal to the first conductivity.

[0069] Such surface treatment makes it possible to increase the energy absorption rate of the powder grains, which makes it possible to heat the metal or ceramic powders 1 more quickly and efficiently. This makes it possible to improve the energy efficiency of the process while making it possible to reduce the duration of a melting cycle of metal or ceramic powder 1 during an additive manufacturing process by selective melting.

[0070] Advantageously, the powder treatment is carried out during an additive manufacturing process comprising at least one step of depositing a layer C of metallic or ceramic powder and at least one step of selectively melting at least one area of ​​the layer C of metallic or ceramic powder 1.

[0071] The manufacturing process thus advantageously includes a step of processing the metal or ceramic powders 1, which can be carried out in one embodiment after the step of depositing the layer C of metal or ceramic powder 1 and prior to the selective melting step.

[0072] This helps to avoid any interruption in the manufacturing process, which helps to reduce the cycle time.

[0073] Advantageously, powder processing is carried out "in situ", i.e. within the additive manufacturing machine, unlike "mass" powder processing methods carried out by installations outside the additive manufacturing machine.

[0074] In a preferred embodiment, a metal or ceramic powder treatment step 1 is carried out before each selective melting step.

[0075] Advantageously, in one embodiment, a surface treatment step is carried out after each step of deposition of a layer C of metallic or ceramic powder 1.

[0076] In one embodiment, the powder 1 is metallic and comprises a metal having an electrical conductivity of less than 1 S m'. A metallic powder may therefore comprise a metal or a metal alloy selected from:

[0077] - precious metals, for example gold, silver, platinum, bronze, copper, zinc, tin, etc.;

[0078] - refractories, for example tungsten, tantalum, molybdenum, etc.;

[0079] - transition metals, for example titanium, vanadium, iron, cobalt, nickel, etc.;

[0080] - rare earths, for example yttrium, lanthanides, etc.

[0081] The addition material 2 may comprise carbon or aluminum or copper, or an alloy comprising one or more of these elements, or others with equivalent properties.

[0082] The addition material 2 can be the same element as the powder material 1, or generally a material with a conductivity greater than or equal to the conductivity of the powder 1 being coated.

[0083] For example, for a copper powder and an additive material containing carbon, the latter is not miscible in the copper. During temperature rise, the carbon diffuses onto the surface of the copper and structures itself, generally in graphitic form (the stable phase of carbon).

[0084] Graphite (or graphene, i.e. a monosheet of graphite) on the surface has a conductivity higher than that of the powder, even for copper powder, and makes it possible to increase the energy absorption on the surface of the copper, but also to improve the conductivity of the copper powder.

[0085] Furthermore, graphite passes directly from the solid phase to the vapor phase (it has no liquid phase at ambient pressure; this is called sublimation) with a boiling point (liquid-vapor transition) much higher (3825°C) than that of copper (2560°C), which, moreover, first passes into the liquid phase at 1083°C. In fact, some of the energy required to melt the metal or ceramic powder, copper for example, can be dissipated by the graphite, thus reducing the cooling time of the liquid bath and reducing the amount of metal evaporated (evaporation also called fume emission).

[0086] Advantageously, carbon can be combined with other elements (such as iron, molybdenum, etc.) preserving the high-temperature evaporation effect, and can also improve the electrical conductivity of the film.

[0087] In another example, tungsten, or any other refractory metal, exhibits behaviors similar to carbon, although it passes through a liquid phase before evaporation. For example, the melting point of tungsten is 3422°C and its boiling point is 5555°C.

[0088] In another example, the presence of aluminum on and between the grains of metallic or ceramic powder, such as copper, significantly reduces the electrical resistance of the grains. Furthermore, the two metals, aluminum and copper, although they have different melting points, have very similar boiling points (2470 °C for Al versus 2560 °C for Cu), thus limiting the vaporization of aluminum before the copper melts.

[0089] In another example, in the event of pollution, aluminum can also absorb traces of oxygen to form alumina. Unlike the metal, the melting point of alumina (2072°C) is higher than that of copper, behaving in a manner similar to refractories.

[0090] In another example, such a process can also make it possible to produce nuances in the material, by forming an alloy between the material of the metal or ceramic powders 1 and the addition material 2 (by controlling the quantity of addition material 2 relative to the material 1), which makes it possible to modify certain physical or physico-chemical properties of the final material constituting the manufactured part, for example the mechanical, electrical, chemical or thermal characteristics of the alloy.

[0091] In another example, this also allows the additive material to be deposited only on the visible part of the powder layer. Visible here is understood as exposed to the radiation from the power source. This significantly limits the contamination that could be generated in the powder layer by the film of the additive material within the powder grain material. This makes it possible to limit the contamination of the powder material 1 by the additive material 2 to 100 ppm (parts per million, in mass proportion equivalent to a proportion of 1 milligram per kilogram), preferably to 1 ppm.

[0092] This same technology can be used to deposit a thin film (~5 nm to 200 nm) of alloying metal 2 on top of the powder grains, a film of the same nature or composition as that constituting the metal powder grains 1, for example to create a thin layer of copper on copper grains, or a layer of aluminum on aluminum powders, etc. This aims to improve the electrical and / or thermal conductivity between the powder grains, without affecting the stoichiometry, in the case of alloys, or the nature of the material, if they are pure.

[0093] Indeed, in the case of microscopic contacts (two spheres in contact share a common surface of less than about 100 nm2, i.e. less than 10 4 pm2), the contact resistance is significant (> 1 MQ).

[0094] If the metallic or ceramic powder grains 1 are coated with a thin surface film of a conductive material 2 (in a particular case, materials 2 and 1 are identical), this coating can considerably increase the contact area between the powder grains (especially if they were not in contact before or if the contact area was nanometric), thereby significantly reducing the electrical and / or thermal contact resistance between the powder grains. Thus, the flow of charge from a power source is greatly improved and the Coulomb repulsion effects are significantly reduced, which is particularly useful when the power source is from a particle beam source, for example an electron beam.

[0095] Since the deposited material is of the same chemical nature, this does not affect the final functionalities of the part obtained by selective melting. Additive manufacturing device

[0096] Such a manufacturing process is implemented using an additive manufacturing device 3 comprising a layering element 4 configured to deposit a layer C of metallic or ceramic powder, a surface treatment device 5 configured to treat the metallic or ceramic powder and a power source 10 configured to perform a selective melting of at least one area of ​​the powder layer C.

[0097] An embodiment of an additive manufacturing device 3 is shown in [fig.1].

[0098] The additive manufacturing apparatus 3 comprises:

[0099] - a support such as a horizontal platform 7 on which are successively placed the different layers of additive manufacturing powder (metal powder, ceramic powder, etc.) allowing the fabrication of a three-dimensional object (Christmas tree-shaped object in the figure),

[0100] - a powder reservoir 9 located above the tray 7,

[0101] - the layering element 4 for spreading the various successive layers of powder (displacement along the double arrow A),

[0102] - the surface treatment device 5 configured to treat powders of fa additive construction,

[0103] - a power source 10 to supply the energy necessary for fusion (total or partial) of thin layers spread,

[0104] - a control unit 11 which controls the various components of Device 3 operates based on pre-stored information (memory M),

[0105] - a mechanism 12 for allowing the support of the tray 7 to be lowered gradually and measurement of layer deposition (displacement along the double arrow B).

[0106] In the example described with reference to [fig.1], assembly 10 comprises two consolidation sources:

[0107] - an electron beam gun 13 and - a laser-type source 14.

[0108] Alternatively, the assembly 10 may comprise only one source, for example a laser, or only one localized energy source under vacuum or at very low pressure (< 0.1 mbar), for example an electron gun.

[0109] As an alternative, the assembly 10 may also include several sources of the same type, such as several electron guns and / or laser sources, or means for obtaining several beams from the same source.

[0110] In the example described in [fig. 1], at least one galvanometric mirror 15 allows the laser beam from the source 14 to be oriented and moved relative to the object 8 according to the information sent by the control unit 11, and deflection and focusing coils 16 and 17 allow the electron beam to be deflected and focused locally on the areas of layers to be sintered or fused.

[0111] Any other diversion system may of course be considered.

[0112] A thermal shield 18 can be interposed between the beam(s) of the assembly 10 and the walls of the enclosure 19 in the case where at least one source is of the electron gun type.

[0113] The components of the device 3 are arranged inside a sealed enclosure 19 that can be connected to at least one vacuum pump 20 which maintains a secondary vacuum (10³ to 10⁷ mbar) inside said enclosure 19 (typically about 10² / 10³ mbar, or even 10⁴ / 10⁶ mbar) in the case where at least one source is of the electron gun type. This makes it possible to limit collisions between the particles emitted by the electron gun and the working atmosphere, thereby improving the energy efficiency of the additive manufacturing process.

[0114] The layering element 4 can advantageously be configured to dispose of a substantially flat layer C of metallic or ceramic powder on the support 7 so as to form a powder bed.

[0115] The coating element 4 can advantageously be configured to inject metallic or ceramic powder according to a pattern, for example substantially linear along a longitudinal axis, and can then be translated in a transverse direction so as to spread the powder deposited linearly as a layer C of powder on the surface of the powder bed. Surface treatment device

[0116] In an embodiment shown in [fig.2], the surface treatment device 5 is configured to project particles of additive material 2 onto the surface of the powder layer C.

[0117] In one embodiment, the surface treatment device 5 projects the addition material 2 in a substantially linear pattern extending in a first direction, and is moved parallel to the powder layer C in a second direction so as to treat the surface of the powder layer C.

[0118] In one embodiment, particularly as shown in [Fig. 1], the surface treatment device 5 is fixed in movement to the layering element 4, both being mounted on the same motor module 21 configured to move them. Thus, the surface treatment device 5 processes the layer C of powder deposited by the layering element 4 in a single step, thereby reducing the cycle time.

[0119] In a first embodiment, the surface treatment device 5 and the layering element 4 can be parallel, so as to promote the compactness of the assembly comprising the surface treatment device 5 and the layering element 4.

[0120] In another embodiment not shown, the surface treatment device 5 can be driven individually and can, for example, be moved so as to treat only those areas of the powder layer C that are likely to be heated to melt and then solidify upon cooling. This saves on additive material 2 and reduces the conductivity improvement operation.

[0121] In one embodiment, as represented in [fig.2], the surface treatment device 5 comprises a generic plasma projection device, configured to project the addition material 2. The arrow indicates the direction of movement above the bed of the powder layer C leading to the creation of a coating on the upper part of the powder grains at the rear of the device 5. This plasma device can be made according to different variants.

[0122] In an embodiment of the surface treatment device 5 as shown in [fig.3], it is possible to use an electric arc, preferably operating at atmospheric pressure, and more generally at high pressure (> 1 mbar).

[0123] In another embodiment of the plasma device as shown in [fig.4], it is possible to use a plasma-assisted vapor phase coating system, which can operate over a wide range of pressures, from atmospheric pressure to "primary" vacuum (1 to 10-3 mbar).

[0124] In another embodiment of the plasma device as shown in [fig.5], it is possible to use a magnetron-type coating system, preferably operating at low pressure or under secondary vacuum (< 0.1 mbar).

[0125] In another embodiment as represented in [fig.6], the surface treatment device 5 comprises a blown wire device.

[0126] Electric arc device

[0127] An electric arc device such as that shown in [Fig. 3] comprises an electrode 501, preferably negatively polarized (and acting, in this case, as the cathode) with respect to the powder layer C, which is generally connected to ground. The electrode 501 may contain or be made of the additive material 2, which is projected towards the powder layer C when one or more electric arcs 201 are established between the electrode 501 and the powder layer C.

[0128] A device not shown in [Fig. 3] allows the distance d between the electrode and the powder layer C to be modified to facilitate the establishment of electric arcs. Furthermore, this system allows the alignment of the electrode 501 in a substantially parallel to the layer of powder.

[0129] A power supply 111 connected to the electrode 502 creates an electric arc between the electrode 501 and the powder layer. The power supply 111 is controlled by a control unit 11. The power supply 111 can be continuous, radio frequency, or pulsed.

[0130] During the establishment of the electric arc, part of the electrode 501 is vaporized and this vapor condenses favorably just below, i.e. on the surface of the powder layer C, thus modifying its surface properties and ensuring the desired surface treatment.

[0131] In another embodiment, not shown, the device for establishing the electric arc may be a set of two electrodes located above the powder layer C, which can be heated to fuse. It may optionally include a system for adjusting the distance between these electrodes, as well as a system for adjusting the distance between the position of the electrodes and the surface of the powder layer C. By modifying these distances, it is easy to control the amount of added material deposited, as well as the surface area on which the film is deposited.

[0132] Vapor phase coating device

[0133] A plasma-assisted vapor-phase coating device as shown in [Fig. 4] comprises an electrode 502 having a wall delimiting an internal cavity forming the reaction chamber, and a gaseous precursor injection system 52 configured to inject precursor gas into the cavity of the electrode 502. The gaseous precursor must contain the dopant element 2 in its composition. For example, to achieve a metallic coating of the powder layer, an organometallic compound must be used. In another example, where the dopant 2 is carbon, the precursor can be a hydrocarbon. More generally, any gas capable of producing a coating that increases photon absorption and improves electrical conductivity can be used as a precursor.

[0134] A power supply 112 connected to the electrode 502 supplies the electrode so as to create a plasma in the cavity of the electrode 502. The power supply 112 is controlled by a control unit 11. The power supply 112 can be continuous, radio frequency or pulsed.

[0135] The plasma thus created decomposes the precursor by the action of free and energetic electrons on the gas and chemically activates it. These species 202 can leave the cavity 502 through one or more orifices 51 formed through the wall of the electrode 502. The orifice 51 is advantageously oriented towards the powder layer C to be treated.

[0136] A device not shown in [fig.4] allows the distance d between the electrode and the powder layer C to be modified. Thus the surface treatment is adjusted below of the slot optimally. The entire powder layer C can be coated by moving the device over the powder layer C, as indicated by the double arrow.

[0137] In an alternative, not shown in [fig.4], the gas containing the precursor can be thermally activated, for example by a heating system, which is controlled by a control unit 11.

[0138] Magnetron device

[0139] A magnetron device such as shown in [fig.5] includes an electrode 503, preferably negatively polarized (and playing, in this case, the role of cathode) and allowing the creation of a plasma.

[0140] An arrangement of magnets 54, disposed at the rear of the electrode 503, generates a magnetic trap 55 which allows the electrons of the plasma to be confined with respect to the other face of the electrode 503. In order to further increase the efficiency of the trap, an alternating arrangement is generally made (north outside and south in the center, or the reverse) to make a closed magnetic track not shown.

[0141] The magnets can be permanent or electromagnets, or a combination of both. This confinement is very effective at low pressure (< 0.1 mbar), making the surface treatment particularly advantageous.

[0142] This type of device is therefore preferentially used in additive manufacturing devices using electron gun sources, which work better at low pressure.

[0143] Depending on the requirements, the electrode 503 can be powered (source 113) by direct current (DC), radio frequency (RF), or high-power pulsed magnetron sputtering (HiPIMS), but generally receives a negative voltage. The source 113 is controlled by a control unit 11.

[0144] The electrode 503 is advantageously made of the addition material 2 used to treat the metal or ceramic powder 1.

[0145] Indeed, under the action of the plasma (in particular the ions), particles 203 from the material of the electrode 503 are atomized and projected at high speed towards the surface of the powder layer C. A protective shield 53 surrounds the rear of the electrode 503 to prevent material loss and to ensure efficient treatment of the layer C.

[0146] This material deposition allows for the surface treatment of metallic or ceramic powders.

[0147] An unrepresented circulation of a cooling fluid (e.g. water, glycol, etc.) is generally provided in the vicinity of the magnets, supplied by an external system.

[0148] In some embodiments, the electrode 503 is a cylindrical roll as in [fig.5], but the electrode 503 can also be flat, in the form of a disc or even rectangular (not shown).

[0149] During operation of the magnetron device with a cylindrical electrode, the electrode 503 is rotated. In this way, the portion of the electrode 503 exposed to the plasma changes regularly, limiting the heating of any particular area, the plasma always being confined to the magnetic trap 55 generated by the arrangement of magnets 54, which has a fixed orientation relative to the magnetron device, specifically towards the powder layer C, as illustrated in [Fig. 5]. When the electrode 503 is rotated, the shield 53 also maintains a fixed orientation relative to the magnetron device.

[0150] In an alternative embodiment not shown, the additive material 2 can be sprayed by ion bombardment alone. A high-energy ion flux (>100 eV) from an ion source (e.g., an ion gun) is directed onto the surface of the additive material 2, inducing its spraying. By appropriately selecting the position and power of the ion source, it is possible to keep the ion source stationary and bombard the doping material 2 while moving it parallel to the powder layer C, thus depositing a surface film on the powder layer C. In this embodiment, the additive material 2 can be a simple plate of material, eliminating the need for an electrode feed.

[0151] Blown wire device

[0152] A blown wire device as shown in [Fig. 6] comprises a wire 504 with a reduced cross-section (diameter < 0.5 mm). The wire 504 consists of the additive material 2 which is projected towards the powder layer C when a very high electric current (> 10 A) passes through it.

[0153] A device not shown allows the distance between the electrode and the C layer to be changed. In addition, this system allows the electrode to be aligned substantially parallel to the powder layer.

[0154] A power supply 114 injects a strong current into the wire 504, which heats up by Joule heating until it is completely vaporized. The power supply 114 is controlled by a control unit 11.

[0155] During the evaporation of wire 504, this vapor condenses favorably just below, i.e., on the surface of layer C, thus modifying the surface properties of layer C and ensuring the desired surface treatment. A screen 182 is placed just above wire 504 to prevent any metallization towards the enclosure 19 or towards the heat shield 18.

[0156] Typical coating deposition rates for the various devices just described are from 0.2 to 2 nm / s, or between 1 and 8 ML / s (single-layers of the English 'MonoLayer' per second, i.e. ML / s). Even taking the lowest deposition speed, it is therefore conceivable to deposit 2 monolayers (round trip), thus significantly modifying the surface state of the powder grains, in particular the contact points between the powder grains by improving their conductivity, but without significantly modifying the stoichiometry of the powder grains.

[0157] The advantages of the treatment obtained are numerous, particularly in the case of metals and alloys, or ceramics. Taking copper as an example of powder, if the additive material is different from the powder, it thus promotes:

[0158] - covering the surface of the powder with a minute amount of material (~2 ML);

[0159] - the reduction of surface reflectivity, allowing better absorption of photons;

[0160] - increasing surface roughness and / or texturization, allowing for better photon trapping during multiple reflections;

[0161] - the improvement of thermal conduction between the powder grains, i.e. the improvement of the thermal conductivity of the powder bed;

[0162] - the improvement of the electrical and / or thermal conductivity of the powder bed;

[0163] - limiting the repulsion (lifting) of powders by the formation of bridges atomic bridges between the powder grains facilitate the flow of charges during selective melting. During powder melting, these bridges should be destroyed by simple local evaporation;

[0164] - increasing the contact area between the grains, making it possible to reduce the hot spots at the contacts between the powders and thus the "aspiration" of the grains joined to the area under the beam;

[0165] - improving control of the quantity of additive material 2 allowing for the creation of nuances for the final part. Thus, depending on the fraction of additive material 2 deposited, the final properties of the part made from powders can be improved, without having to modify the powder manufacturing process.

[0166] Liquid spray coating

[0167] In one embodiment of the surface treatment device 5 shown in [Fig. 7], a liquid solution containing the additive in atomic form or as a nanometric precipitate (submicron size) can be sprayed as microdroplets 204 over the powder bed by a spraying device 301 having one or more nozzles 311 configured to project droplets of this liquid solution onto the powder grains and supplied from the reservoir 400. The liquid solution of the additive can be conveyed from the reservoir 400 to the spraying device 301 by means of a flexible conduit.

[0168] Optionally, the spraying device 301 includes a plurality of micro-nozzles or electro-nozzles configured to control the size of the liquid solution droplets of the adding agent, so as to control the amount deposited on the powder grains.

[0169] In a preferred embodiment, the liquid chosen for the liquid solution of absorbent agent is a high-temperature volatile solvent, for example an organometallic solvent such as Me2S.CuBr (with Me a metal) dissolved in deuterated acetonitrile (CD3CN); or organometallic gold with trimethoxybenzene (TMB) and with silver fluorides; etc.

[0170] In this way, during a selective melting step, only the additive, which significantly modifies the surface conductivity of the powder bed, remains on the surface. The liquid vaporized during the melting of the powder grains can also be vented as fumes, along with the other elements released during the formation of the molten metal bath.

[0171] The assembly can be controlled by the control unit 11 which ensures the control of the various components of the surface treatment device 5.

[0172] Microfilm coating

[0173] In one embodiment of the surface treatment device 5 shown in [Fig. 8], the surface treatment device 5 includes a drive device 601 configured to unwind, onto the surface of the powder layer C, a roll 210 of very thin, single-component or composite film 205. In the case of a composite film, it is formed of a very thin matrix (preferably with a thickness on the order of a micrometer) that is volatile at high temperature and preferably electrically conductive. The polymer used can be a polyester, a thermoplastic polymer, or a resin conventionally used for making matrices of composite materials.

[0174] The composite film 205 may, for example, comprise one or more additive material components such as carbon black, carbon nanotubes, graphene, or conductive nanoparticles, particularly metallic nanoparticles and their alloys. This purely mechanical operation results in the composite film 205 covering the upper surface of the powder bed.

[0175] In one embodiment, the film 205 can be a pure metal, for example aluminum, a few micrometers thick, between 1 and 50 pm, and preferably less than 10 pm. It can also be ultra-thin, with thicknesses less than 1 pm, but greater than 50 nm.

[0176] The choice of aluminum is advantageous because aluminum has a relatively low melting point, good electrical conductivity, a low price, and is non-toxic. During melting, the resulting liquid phase can advantageously Wetting the surrounding powder grains improves electrical conductivity between them. Its easier evaporation leads to its removal in the vapor phase, resulting in a very low, or even nonexistent, residual effect in the final part. Of course, other metals in microfilm form can be used, such as tin, silver, gold, copper, etc.

Claims

Demands

1. A process for additive manufacturing by selective melting of metallic or ceramic powder comprising the steps of: - deposition of a layer (C) of powder, and - selective melting of at least one area of ​​the powder layer, wherein the process comprises, after deposition and prior to selective melting, a coating step in which grains of the powder layer (1) are at least partially covered with a film of an additive material (2), the powder grains (1) having a first electrical conductivity, the additive material (2) having a second electrical conductivity greater than or equal to the first conductivity, the film of additive material having a thickness less than or equal to 1 pm.

2. An additive manufacturing process according to claim 1, wherein the powder (1) is metallic and comprises a metal or alloy having an electrical conductivity of less than 1 Sm', and wherein the additive material (2) comprises a metal or metal or carbon alloy, or an organometallic, or a carbon-based composite having a conductivity at least equivalent to that of graphite.

3. An additive manufacturing process according to any one of claims 1 to 2, wherein the powder (1) is metallic and comprises at least one metal or metal alloy selected from precious metals, refractories, transition metals, and rare earths.

4. An additive manufacturing method according to any one of claims 1 to 3, wherein the coating step is carried out by means of a surface treatment device (5) configured to generate a plasma and project the plasma in a substantially linear pattern, the surface treatment device (5) being adapted to be moved over the metal powder so as to project the plasma onto the metal powder.

5. An additive manufacturing method according to claim 4, wherein the surface treatment device (5) comprises an electric arc device having an electrode (501) having additive material (2), the electrode (501) being positioned opposite the powder layer (C) such that additive material (2) is projected towards the powder layer (C) when an electric arc (201) is established between the electrode (501) and the layer (C).

6. An additive manufacturing method according to claim 4, wherein the surface treatment device (5) comprises a magnetron device (503) positioned opposite the powder layer (C) such that additive material (2) is projected towards the powder layer (C) by spraying.

7. An additive manufacturing method according to claim 4, wherein the surface treatment device (5) comprises a blown wire device, including a wire (504) connected to a power source, wherein the wire (504) extends above the powder bed and consists of the additive material, the power source being configured to inject a current into the wire (504) such that the additive material vaporizes and is deposited onto the powder layer (C).

8. An additive manufacturing method according to any one of the preceding claims, wherein the selective melting step is carried out by means of a power source (10) comprising at least one particle beam source (13), for example an electron beam.

9. An additive manufacturing process according to any one of the preceding claims, wherein a surface treatment step of the metal or ceramic powders is carried out successively at each step of laying a layer (C) of metal powder.

10. An additive manufacturing method according to any one of the preceding claims, wherein the film is deposited by spraying a liquid solution of additive material into a volatile solvent at high temperature.

11. An additive manufacturing process according to any one of the preceding claims, wherein the film is mechanically deposited by covering the layer (C) of powders with a composite film (205) comprising a high-temperature volatile matrix and loaded with additive material.

12. An additive manufacturing process according to any one of claims 1 to 7, 10 and 11 wherein the additive material film has a thickness of less than 200 nm.

13. An additive manufacturing device configured to carry out an additive manufacturing process according to any one of the preceding claims, the additive manufacturing device comprising: - a layering element (4) configured to deposit a substantially flat layer (C) of metal or ceramic powder (1); - a surface treatment device (5) configured to carry out a surface treatment process for the metal powder layer (C). or ceramic; and - a power source (10) configured to perform selective melting of at least one area of ​​the powder layer (C).

14. Additive manufacturing device according to the preceding claim, wherein the layering element (4) is configured to deposit a layer (C) of powder when moved across the surface of a support (7), and wherein the surface treatment device (5) is fixed in movement to the layering element (4), such that during the movement of the layering element (4), the layering element (4) deposits a layer (C) of powder and the surface treatment device (5) processes the layer (C) of powder deposited by the layering element (4).

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