In situ processing of powders for additive manufacturing

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 reflectivity, the additive material (2) having a second reflectivity lower than the first reflectivity. Figure for the abstract: Fig. 2

Description

Title of the invention: IN SITU treatment of powders for additive manufacturing FIELD OF THE 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 fusion of 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 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 which induce, at the heart of the raw material, an irreversible transformation which gives the ceramic produced new properties: solidity and resistance to wear, heat resistance, insulating properties, etc.

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

[0006] - oxides: aluminum oxide, zirconium oxide; etc.;

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

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

[0009] Conventionally, a method of 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 carries out selective heating of certain zones of the powder bed, so as to cause the fusion of the powders in the heated zones and thus form a coherent part layer after cooling.

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

[0012] Conventionally, the power sources used to carry out the selective melting of powders may comprise one or more laser sources, or one or more electron or particle beam sources, or a combination of sources. using a laser, electron beam or particle beam.

[0013] When producing metal 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 melting operation is therefore greatly reduced.

[0015] In certain particular cases, for example when using metal powders with high reflectivity during additive manufacturing, such as copper or aluminum, the majority of the laser light, particularly in infrared (IR), is reflected (up to 99%), greatly reducing the efficiency of this type of process, thereby greatly increasing the duration of such processes.

[0016] Reflectivity is conventionally understood to mean the proportion of electromagnetic energy reflected at the surface of a material compared to the total energy of the electromagnetic signal reaching the material. In other words, the electromagnetic energy returns to the medium from which the incident electromagnetic beam originates, after interaction with the surface.

[0017] Estimation methods known in the literature make it possible to determine the reflectivity of certain alloys. The reflectivity of a surface can vary depending on the wavelength of the radiation. This quantity is generally expressed in decibels (for high frequencies) or percentage (for infrared, visible, or even ultraviolet light).

[0018] When a wave reflects on a more or less reflective material, a part of the ground is returned towards the transmitter and a part continues in the material. The part of the wave which continues its propagation in the material can be absorbed by the material, or else come out on the other side, after having crossed it. The reflection coefficient R c is the ratio of the amplitudes between the reflected ground Ar and the incident ground Ai: Rc = ArIAi

[0019] Depending on the Fresnel coefficients, this value can be a complex number.

[0020] Reflectivity RefeA. the reflected energy relative to the incident energy. Since the energy is proportional to the square of the wave amplitude, it turns out to be the following ratio: Ref= Ar2 / A;2 =RC2

[0021] Reflectivity is therefore the reflection coefficient squared, always positive and a real number.

[0022] Additive manufacturing processes therefore suffer from limited energy efficiency, particularly in the case of additive manufacturing from metal or ceramic powders fused using laser beam sources. Statement of the invention

[0023] One aim of the invention is to improve the energy efficiency of such a process.

[0024] Another goal is to reduce the duration of a selective fusion cycle.

[0025] Another aim is to achieve nuances in the material of the powder layer.

[0026] Another aim is to improve the thermal conductivity between the powder grains, in particular for additive manufacturing processes operating by thermal conductivity such as manufacturing processes using a laser beam alone or in combination with another source of energy or heat.

[0027] Another aim is also to improve the electrical conductivity between the powder grains, in particular 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.

[0028] In order to address these issues, the invention proposes an additive manufacturing process by selective melting of metal or ceramic powder comprising the steps of:

[0029] - Deposition of a layer of powder;

[0030] - Selective melting of at least one area of ​​the powder layer, wherein the process comprises, at the end of the deposition and prior to the selective melting, a coating step during which grains of metallic or ceramic powder are at least partially covered with a film of an addition material, the grains of metallic or ceramic powder having a first reflectivity, the addition material having a second reflectivity lower than the first reflectivity.

[0031] The invention may advantageously include the following characteristics, taken alone or in combination:

[0032] - the powder is metallic and comprises a metal or an alloy having a re flectivity greater than 90%;

[0033] - the addition material comprises at least one material from carbon, tungsten or molybdenum, or a mixture thereof;

[0034] - the powder is metallic and comprises at least one metal or an alloy of metals chosen from copper, aluminum, gold, silver and platinum;

[0035] - the coating step is carried out by means of a surface treatment device configured to generate a plasma and project the plasma in a substantially linear pattern, the surface treatment device being adapted to be moved above the metal or ceramic powder so as to project the plasma onto the metal or ceramic powder.

[0036] - the surface treatment device comprises an electric arc device comprising an electrode comprising addition material, the electrode being positioned opposite the powder layer in such a way that addition material is projected towards the powder layer when an electric arc is established between the electrode and the layer ;

[0037] - the surface treatment device comprises a phase coating device vapor comprising an electrode comprising 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 addition element when it is excited by the electrode, the particles of addition element being expelled through the orifice onto the layer of powder;

[0038] - the surface treatment device comprises a magnetron device;

[0039] - 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 additive material, the power source being configured to inject a current into the wire such that the additive material vaporizes and deposits on the powder layer;

[0040] - the layer of addition material has a thickness of less than 100 nm;

[0041] - the selective fusion step is carried out by means of a power source comprising at least one laser source;

[0042] - a step of surface treatment of the metallic or ceramic powders is carried out successively at each stage of arrangement of a layer of metallic or ceramic powder;

[0043] - the powder layer is covered with a film of additive material containing one or several components among carbon black, carbon nanotubes and graphene;

[0044] - the film is deposited by spraying a liquid solution of additive material into a volatile solvent at high temperature;

[0045] - the film is deposited mechanically by covering the layer (C) of powders with a composite film comprising a high-temperature volatile matrix loaded with additive material.

[0046] According to another aspect, the invention proposes an additive manufacturing device configured to carry out an additive manufacturing method according to the invention, the additive manufacturing device comprising:

[0047] - a layering element configured to arrange a layer of powder me substantially flat metal or ceramic;

[0048] - a surface treatment device configured to carry out a surface treatment process surface treatment of the layer of metallic or ceramic powder according to the invention;

[0049] - a power source configured to perform selective fusion of at least an area of ​​the powder layer.

[0050] Advantageously, in such an additive manufacturing device, the layering element can be configured to deposit a layer of powder when it is moved on the surface of a support, and the surface treatment device can be integral in movement with the layering element, such that during the movement of the layering element, the layering element deposits a layer of powder and the surface treatment device simultaneously or with a time lag treats the layer of powder deposited by the layering element. DESCRIPTION OF THE FIGURES

[0051] Other characteristics and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and must be read in conjunction with the appended figures in which:

[0052] [fig.l]

[0053] - [fig.l] is a diagram representing an additive manufacturing device according to the invention;

[0054] [fig.2]

[0055] - [fig.2] is a generic diagram representing the implementation of a method of surface treatment according to the invention;

[0056] [fig.3]

[0057] - [fig.3] is a diagram representing a variant of an embodiment surface treatment device preferably operating at around atmospheric pressure according to the invention;

[0058] [fig.4]

[0059] - [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;

[0060] [fig.5]

[0061] - [fig.5] represents a variant of an embodiment of a device of magnetron surface treatment preferably operating at low pressure according to the invention;

[0062] [fig.6]

[0063] - [fig.6] represents a diagram representing a variant of an embodiment of a blown wire surface treatment device according to the invention;

[0064] [fig.7]

[0065] - [fig.7] is a schematic representation of an embodiment of a surface treatment device by spraying according to the invention;

[0066] [fig.8]

[0067] - [fig.8] is a schematic representation of an embodiment of a surface treatment device with composite film roll according to the invention.

[0068] DESCRIPTION OF ONE OR MORE METHODS OF IMPLEMENTATION AND REALIZATION General information

[0069] The figures illustrate an example of an additive manufacturing process by selective melting of metal or ceramic powder comprising the steps of:

[0070] - Deposition of a layer C of metallic or ceramic powder;

[0071] - Selective melting of at least one area of ​​the powder layer, wherein the process comprises, at the end of the deposition and prior to the selective melting, a coating step during which grains of metallic or ceramic powder 1 are at least partially covered with a film of an addition material 2, the grains of metallic or ceramic powder 1 having a first reflectivity, the addition material 2 having a second reflectivity lower than the first reflectivity.

[0072] Such a 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 more 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 a selective melting additive manufacturing process.

[0073] Advantageously, the treatment of the powders is carried out “in situ”, that is to say within the additive manufacturing machine unlike the “mass” powder treatment processes carried out by different installations outside the additive manufacturing machine.

[0074] Advantageously, the in situ treatment of the powders 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 selective melting of at least one zone of the layer C of metallic or ceramic powder 1.

[0075] The manufacturing method thus advantageously comprises a step of in situ treatment of the metallic or ceramic powders 1, which can be carried out in one embodiment after the step of depositing the layer C of metallic or ceramic powder 1 and prior to the selective melting step.

[0076] This helps avoid any disruption to the manufacturing process, thereby reducing cycle time.

[0077] In a preferred embodiment, a step of treating the metal or ceramic powders 1 is carried out before each selective melting step.

[0078] Advantageously, in one embodiment, a surface treatment step is carried out after each step of depositing a layer C of metallic or ceramic powder 1.

[0079] In one embodiment, the powder 1 is metallic and comprises a metal having a reflectivity greater than 90%, or optionally greater than 95%. The metallic powder may therefore comprise copper, gold, silver, platinum or a mixture of one or more of these metals, and the addition material 2 may comprise carbon or aluminum or tungsten, or an alloy comprising one or more of these elements, or others with equivalent properties.

[0080] The addition material may comprise one or a combination of elements from Zinc, Silver, Copper, Chromium, Nickel, Aluminum, Niobium, Zirconium, Tungsten, Titanium, Carbon and Tantalum.

[0081] Preferably, the addition material 2 comprises at least one material from carbon, tungsten or molybdenum, or a mixture thereof. These refractory materials have a very high melting point and will therefore store heat and restore it to the copper by conduction, thus promoting the melting of the copper. Their interest also lies in their low thermal conductivity, and the high melting point. In fact, they will absorb a lot of energy before passing into the liquid phase or being evaporated and thus the energy transfer time between these materials and the powder grains will heat by conduction, which is not the case if the laser is sent directly onto the powder.

[0082] For example, carbon is not miscible in copper. When the temperature rises, the carbon diffuses to the surface of the copper and structures itself, generally in graphitic form (stable phase of carbon).

[0083] Graphite (or graphene, i.e. a single sheet of graphite) on the surface has a lower reflectivity than copper and makes it possible to increase the energy absorption on the surface of the copper.

[0084] Furthermore, if carbon is present on the surface of the copper in the form of one or a few monolayers (graphene), then the fraction of the incident Fonde electromagnetic radiation that is not reflected propagates and can pass unhindered through the graphene to join the copper below.

[0085] If the carbon is deposited deep in the material (for example by ion implantation), then it rises to the surface with the increase in temperature, including after the establishment of a molten pool. It is thus possible to bring to the surface, after melting layer by layer, a fraction of the carbon present on the surface of the previous layer, and in fact contain (or even control) the level of carbon present in the copper for the final part.

[0086] In addition, graphite passes directly from the solid phase into the vapor phase (it does not have a 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, part of the energy required to melt the copper can be removed by the graphite, thus reducing the cooling time of the liquid bath and reducing the amount of copper evaporated (evaporation also called fume emission).

[0087] Advantageously, carbon can be combined with other elements (such as iron, molybdenum, etc.).

[0088] In another example, tungsten or any other refractory metal exhibits behaviors close to carbon, although they pass through a liquid phase before evaporation. For example, the melting temperature of tungsten is 3422°C and the boiling temperature is 5555°C.

[0089] In another example, the presence of aluminum on the copper grains and between these grains makes it possible to significantly reduce the reflectivity of the grains. Indeed, aluminum has a melting temperature of only 660°C. Since the reflection of the liquid aluminum bath is much lower (77%) than that of the same solid metal (95%, for a wavelength of 1 pm), the electromagnetic energy is favorably absorbed by the liquid aluminum and transmitted to the copper powder below. Moreover, conveniently, the two metals, aluminum and copper, although they have different melting temperatures, they have very close boiling points (2470°C for Al against 2560°C for Cu), limiting the vaporization of the aluminum before the melting of the copper.

[0090] In another example, in the case of pollution, aluminum can also capture traces of oxygen to form alumina. Unlike metal, the melting temperature of alumina (2072°C) is higher than that of copper. Alumina has a lower reflectivity than copper and absorbs photons better, and will also use some of the heat to evaporate.

[0091] Such a method can also make it possible to produce nuances in the material, by forming an alloy between the material of the metallic or ceramic powders 1 and the doping material 2, which makes it possible to modify certain physical properties of the final material constituting the manufactured part, for example the mechanical, chemical or thermal characteristics of the alloy.

[0092] This also makes it possible to deposit the addition material only on the visible part of the powder layer. Visible is understood here as exposed to the radiation of the power source. This greatly limits the pollution that could be generated in the powder layer by the addition of addition material in the material of the powder grains. This makes it possible to limit the pollution to 100 ppm, preferably to 100 ppm. Additive manufacturing device

[0093] Such a manufacturing method is implemented using an additive manufacturing apparatus 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 carry out selective melting of at least one area of ​​the layer C of powder.

[0094] An embodiment of an additive manufacturing apparatus 3 is shown in [fig.l].

[0095] The additive manufacturing apparatus 3 comprises:

[0096] - a support such as a horizontal plate 7 on which are successively deposited the different layers of additive manufacturing powder (metal powder, ceramic powder, etc.) allowing the production of a three-dimensional object (fir tree-shaped object in the figure),

[0097] - a powder reservoir 9 located above the tray 7,

[0098] - the layering element 4 for spreading the different successive layers of powder (movement according to the double arrow A),

[0099] - the surface treatment device 5 configured to treat the powders of fa additive building,

[0100] - a power source 10 to provide the energy necessary for fusion (total or partial) thin layers spread,

[0101] - a control unit 11 which ensures the control of the different components of device 3 based on pre-stored information (memory M),

[0102] - a mechanism 12 to allow the support of the tray 7 to be lowered as and when measurement of the deposition of the layers (displacement according to the double arrow B).

[0103] In the example described with reference to [fig.l], the assembly 10 comprises two consolidation sources:

[0104] - an electron beam gun 13 and

[0105] - a laser type source 14.

[0106] Alternatively, the assembly 10 may comprise only one source, of the laser type for example, or only one source of energy located under vacuum or at very low pressure (< 0.1 mbar), for example an electron gun.

[0107] Still as a variant, the assembly 10 can also comprise several sources of the same type, such as for example several electron guns and / or laser sources, or means making it possible to obtain several beams from the same source.

[0108] In the example described in [fig.l], at least one galvanometric mirror 15 makes it possible to orient and move the laser beam coming from the source 14 relative to the object 8 according to the information sent by the control unit 11, and deflection and focusing coils 16 and 17 make it possible to deflect and focus the electron beam locally on the zones of layers to be sintered or fused.

[0109] Any other diversion system can of course be considered.

[0110] In another example not illustrated, the assembly 10 comprises several laser-type sources 14 and the displacement of the different laser beams is obtained by moving the different laser-type sources 14 above the layer C of powder to be fused.

[0111] A heat shield 18 may 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.

[0112] The components of the apparatus 3 are arranged inside a sealed enclosure 19 which can be connected to at least one vacuum pump 20 which maintains a secondary vacuum inside said enclosure 19 (typically approximately 102 / 103 mbar, or even 10 4 / 106 mbar) in the case where at least one source is of the electron gun type.

[0113] The layering element 4 can advantageously be configured to arrange a layer C of substantially flat metal or ceramic powder on the support 7 so as to form a powder bed.

[0114] The layering element 4 may advantageously be configured to inject metallic or ceramic powder in a substantially linear pattern along a longitudinal axis, and may then be translated in a transverse direction so as to spread the deposited powder linearly in the form of a layer C of powder on the surface of the powder bed. Surface treatment device

[0115] In an embodiment shown in [fig.2], the surface treatment device 5 is configured to project particles of addition material 2 onto the surface of the layer C of powder.

[0116] 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 layer C of powder in a second direction so as to treat the surface of the layer C of powder.

[0117] In one embodiment, notably represented in [fig.l], the surface treatment device 5 is integral in movement with the layering element 4, both being mounted on the same motor module 21 configured to move them. Thus, the surface treatment device 5 treats the layer C of powder deposited by the layering element 4 during the same step, which makes it possible to shorten the cycle time.

[0118] In a first embodiment, the surface treatment device 5 and the layering element 4 may be parallel, so as to promote the compactness of the assembly comprising the surface treatment device 5 and the layering element 4.

[0119] In another embodiment not shown, the surface treatment device 5 can be driven individually, and can for example be moved from so as to only treat the areas of the powder C layer that are likely to be heated to melt and then solidify upon cooling. This saves on additive material.

[0120] In one embodiment, as shown in [fig.2], the surface treatment device 5 comprises a 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 at the rear of the device 5. This plasma device can be produced according to different variants.

[0121] In one 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).

[0122] 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).

[0123] 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).

[0124] In another embodiment as shown in [fig.6], the surface treatment device 5 comprises a blown wire device.

[0125] Electric arc device

[0126] An electric arc device as shown in [fig.3] comprises an electrode 501, preferably negatively polarized (and playing, in this case, the role of cathode) with respect to the powder layer C, generally connected to ground. The electrode 501 is made of the addition 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.

[0127] A device not shown in [fig.3] makes it possible to modify the distance d between the electrode and the layer C of powder to facilitate the establishment of electric arcs. In addition, this system allows the alignment of the electrode 501 in a manner substantially parallel to the layer of powder.

[0128] A power supply 111 connected to the electrode 502 makes it possible to create 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, radiofrequency or pulsed.

[0129] When establishing the electric arc, a part of the electrode 501 is vaporized and this vapor condenses favorably just below, i.e. on the surface of the layer C of powder, thus modifying its surface properties and ensuring the desired surface treatment.

[0130] Vapor phase coating device

[0131] 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 addition element 2 in its composition. For example, to produce a metallic coating of the powder layer, it is preferable to use an organometallic. In another example, where the addition element 2 would be carbon, the precursor may be a hydrocarbon. More generally, any gas capable of producing a coating increasing the absorption of photons and improving the electrical conductivity may be used as a precursor.

[0132] A power supply 112 connected to the electrode 502 powers 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, radiofrequency or pulsed.

[0133] 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 made through the wall of the electrode 502. The orifice 51 is advantageously oriented towards the layer of powder C to be treated.

[0134] A device not shown in [fig.4] makes it possible to modify the distance d between the electrode and the powder layer C. Thus the surface treatment is adjusted below the slot in an optimal manner. The entire powder layer C can be coated by moving the device above the powder layer C, as indicated by the double arrow.

[0135] In a variant, not shown in [fig.4], the gas containing the precursor can be thermally activated, by a heating system for example, which is controlled by a control unit 11.

[0136] Magnetron device

[0137] A magnetron device such as shown in [fig.5] comprises an electrode 503, preferably negatively polarized (and playing, in this case, the role of cathode).

[0138] An arrangement of magnets 54, arranged at the rear of the electrode 503, generates a magnetic trap 55 which allows the confinement of the electrons of the plasma opposite the other face of the electrode 503. In order to further increase the effectiveness of the trap, an alternating arrangement is generally made (north outside and south in the center, or the opposite) to make a closed magnetic track not shown.

[0139] The magnets can be permanent or electromagnets, or even a com combination of the two. This confinement is very effective at low pressure (< 0.1 mbar) making the surface treatment particularly advantageous.

[0140] Depending on the needs, the electrode 503 can be powered (source 113) with direct current (DC), Radio Frequency (RF) or high power pulse mode (HiPIMS - High Power Impulse Magnetron Sputtering), but generally receiving a negative voltage. The source 113 is controlled by a control unit 11.

[0141] The electrode 503 is advantageously made from the addition material 2 used to treat the metal or ceramic powder 1.

[0142] Indeed, under the action of the plasma (in particular of the ions), particles 203 coming from the material of the electrode 503 are pulverized and are projected with high speed towards the surface of the layer C of powders. A protection 53 surrounds the rear of the electrode 503 in order to avoid losses of material and to make the treatment efficient towards the layer C.

[0143] This deposition of material makes it possible to carry out the surface treatment of metallic or ceramic powders.

[0144] A circulation, not shown, of a cooling fluid (for example water, glycol, etc.) is provided near the magnets, supplied by an external system.

[0145] In certain embodiments, the electrode 503 is a cylindrical roller as in [fig.5], but the electrode 503 can also be flat, in the form of a disc or even rectangular (not shown).

[0146] During operation of the magnetron device, the electrode 503 is rotated. In this way, the portion of the electrode 503 that is exposed to the plasma changes regularly, limiting the heating of a 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, in particular towards the powder layer C, as illustrated in [fig.5]. In the case where the electrode 503 is rotated, the protection 53 also maintains a fixed orientation relative to the magnetron device.

[0147] In a variant not shown, the doping material 2 can be sputtered by ion bombardment only. Thus, a flow of high-energy ions (>100 eV) from an ion source (ion gun, for example) is sent towards the surface of the doping material 2 and induces its sputtering. By suitably choosing the position and power of the ion source, it is possible to keep the ion source fixed and to bombard the doping material 2 while moving it parallel to the powder layer C, thus making it possible to deposit a surface film on the powder layer C. In this variant, the doping material 2 can be a simple plate of material, which makes it possible to dispense with an electrode power supply.

[0148] Blown wire device

[0149] A blown wire device as shown in [fig.6] comprises a wire 504 of reduced section (diameter < 0.5 mm). The wire 504 is made of the addition material 2 which is projected towards the powder layer C when a very strong electric current (> 10 A) passes through it.

[0150] A device not shown makes it possible to modify the distance between the electrode and the layer C. In addition, this system allows the electrode to be aligned substantially parallel to the powder layer.

[0151] A power supply 114 injects a strong current into the wire 504 which heats by Joule effect until it is completely vaporized. The power supply 114 is controlled by a control unit 11.

[0152] During the evaporation of the wire 504 this vapor condenses favorably just below, i.e. on the surface of the layer C, thus modifying the surface properties of the layer C and ensuring the desired surface treatment. A screen 182 is placed just above the wire 504 to prevent any metallization towards the enclosure 19 or towards the heat shield 18.

[0153] Typical coating deposition rates for the various devices just described are 0.2 to 2 nm / s, or between 1 and 8 ML / s (monolayers per second, or ML / s). Even using the lowest deposition rate, it is therefore possible to deposit 2 monolayers (back and forth), and therefore to significantly modify the surface state of the powder grains without significantly modifying the stoichiometry of the powder grains.

[0154] The advantages of the treatment obtained are multiple, particularly in the case of copper if the addition material is different from the powder, thus promoting:

[0155] - covering the surface of the powder with a tiny amount of material (~2 ML);

[0156] - the reduction of surface reflectivity, allowing better absorption of photons;

[0157] - increasing the roughness and / or surface texturing, allowing better trapping of photons during multiple reflections;

[0158] - the improvement of thermal conduction between the powder grains, i.e. improving the thermal conductivity of the powder bed;

[0159] - improving the electrical conductivity of the powder bed;

[0160] - limiting the repulsion (lifting) of powders by the formation of bridges atomic bridges between the powder grains, facilitating the flow of charges during selective melting. During powder melting these bridges should be destroyed by simple local evaporation;

[0161] - increasing the contact surface 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 zone under the beam;

[0162] - improving the control of the amount of material of addition material 2 allowing the creation of nuances for the final part. Thus, depending on the fraction of addition material 2 added, the final properties of the part made from the powders can be improved, without having to modify the powder manufacturing process.

[0163] Liquid spray coating

[0164] In one embodiment of the surface treatment device 5 shown in [fig.7], a liquid solution of absorbent agent containing a nanometric precipitate (of sub-micron size) with high laser absorption can be sprayed in the form of microdroplets 204 above the powder bed, by a spraying device 301 comprising one or more nozzles 311 configured to project droplets of liquid solution of absorbent agent onto the powder grains and supplied from the reservoir 400. The liquid solution of absorbent agent can be conveyed from the reservoir 400 to the spraying device 301 by means of a flexible conduit.

[0165] Preferably, the liquid solution is oxygen-free, and the precipitate contains one or more of carbon black, carbon nanotubes, and graphene, thereby forming the addition material.

[0166] Optionally, the spraying device 301 comprises a plurality of micro-nozzles or electro-nozzles configured to control the size of the drops of liquid solution of absorbent agent, so as to control the quantity deposited on the powder grains.

[0167] 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.

[0168] In this way, during a selective melting step, only the absorbing agent remains on the surface of the powder bed, which significantly modifies the absorption of the laser radiation. The liquid vaporized during the melting of the powder grains can also be evacuated in the form of fumes, along with the other elements released during the formation of the liquid metal bath.

[0169] The assembly can be controlled by the control unit 11 which controls the various components of the surface treatment device 5.

[0170] Composite film coating

[0171] In one embodiment of the surface treatment device 5 shown in [fig.8], the surface treatment device 5 comprises a drive device 601 configured to unroll, on the surface of the layer C of powders, a roll 210 of composite film 205 formed from a very fine matrix (preferably having a thickness of the order of a micrometer) and volatile at high temperature and preferentially loaded with absorbent material relative to the laser wavelength, for example a polymer film, which in turn can be loaded with conductive additions. The polymer used can be a polyester, a thermoplastic polymer or a resin conventionally used for the production of composite material matrices.

[0172] The composite film 205 may for example comprise one or more components from carbon black, carbon nanotubes, and graphene, thus forming the addition material. This purely mechanical operation leads to the covering of the upper surface of the powder bed by the composite film 205.

Claims

Claims

1. Additive manufacturing method by selective melting of metal or ceramic powder comprising the steps of: - depositing a layer (C) of powder, and - selective melting of at least one zone of the layer of powder, in which the method comprises, at the end of the deposition and prior to the selective melting, a coating step during which grains of the layer of metal or ceramic powder (1) are at least partially covered with a film of an addition material (2), the grains of metal or ceramic powder (1) having a first reflectivity, the addition material (2) having a second reflectivity lower than the first reflectivity, the film of addition material having a thickness of less than 100 nm.

2. The additive manufacturing method of claim 1, wherein the powder is metallic and comprises a metal or alloy having a reflectivity greater than 90%.

3. An additive manufacturing method according to claim 1 or 2, wherein the addition material (2) comprises at least one of carbon, tungsten or molybdenum, or a mixture thereof.

4. Additive manufacturing method according to one of claims 1 to 3, in which the powder is metallic and comprises at least one metal or metal alloy chosen from copper, aluminum, gold, silver and platinum.

5. Additive manufacturing method according to one of claims 1 to 4, 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 above the metal or ceramic powder so as to project the plasma onto the metal or ceramic powder.

6. Additive manufacturing method according to claim 5, wherein the surface treatment device (5) comprises an electric arc device comprising an electrode (501) comprising addition material (2), the electrode (501) being positioned opposite the powder layer (C) in such a way that addition material (2) is projected towards the powder layer (C) when an electric arc (201) is established between the electrode (501) and the layer (C).

7. Additive manufacturing method according to claim 5, wherein the surface treatment device (5) comprises a vapor-phase coating device comprising an electrode (502) comprising a wall delimiting an internal cavity, and a gaseous precursor injection system (52) configured to inject a precursor gas into the cavity, the wall further having an orifice (51) located opposite the layer (C), the precursor gas being configured to generate particles of addition element when it is excited by the electrode (502), the particles of addition element being expelled through the orifice (51) onto the powder layer (C).

8. An additive manufacturing method according to claim 5, wherein the surface treatment device (5) comprises a magnetron device (503).

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

10. Additive manufacturing method according to one of claims 1 to 9, in which the selective melting step is carried out by means of a power source (10) comprising at least one laser source (14).

11. Additive manufacturing method according to one of claims 1 to 10, in which a step of surface treatment of the metal or ceramic powders is carried out successively at each step of arrangement of a layer (C) of metal or ceramic powder.

12. An additive manufacturing method according to one of claims 1 to 4, wherein the powder layer (C) is covered with a film of additive material containing one or more components from carbon black, carbon nanotubes and graphene.

13. The additive manufacturing method of claim 12, wherein the film is deposited by spraying a liquid solution of additive material into a volatile solvent at high temperature.

14. Additive manufacturing method according to claim 12, in which 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 addition material.

15. Additive manufacturing device configured to carry out an additive manufacturing method according to one of claims 1 to 14, the additive manufacturing device comprising: - a layering element (4) configured to arrange a layer (C) of metal or ceramic powder (1) substantially planar; - a surface treatment device (5) configured to carry out a surface treatment method of the layer (C) of metal or ceramic powder; - a power source (10) configured to carry out selective melting of at least one zone of the layer (C) of powders.

16. Additive manufacturing device according to claim 15, wherein the layering element (4) is configured to deposit a layer (C) of powder when it is moved on the surface of a support (7), and wherein the surface treatment device (5) is integral in movement with 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) treats the layer (C) of powder deposited by the layering element (4).

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