Method and device for characterizing a metallic powder

Abstract

The invention relates to a device for characterizing a powder, comprising: - a powder container configured to hold a representative powder sample of powder remaining after an additive manufacturing operation by a powder bed fusion process; - an eddy current transmitter / receiver configured to emit electromagnetic signals in a predefined range of operating frequencies near the surface of the powder sample contained in said container; and - a data acquisition and control system configured to measure, for each operating frequency, impedance values ​​across a receiving coil of the eddy current transmitter / receiver; and to evaluate the quality of the remaining powder based on the impedance values ​​measured for the powder sample. Figure 3

Description

Title of the invention: Method and device for characterizing a metallic powder. Field of the invention

[0001] The present invention relates to the field of metal powder characterization, and is more particularly concerned with the control by eddy currents of the quality of a residual austenitic steel powder after an additive manufacturing operation. State of the art

[0002] The term Additive Manufacturing (AM) refers, according to standard NF E 67-001, to "all processes that allow the layer-by-layer fabrication of a physical object from a digital object by adding material." This term encompasses dozens of manufacturing technology names, classified into seven process categories according to standard NF ISO 17296-2 June 2015.

[0003] Powder bed fusion (PBF) processes, where the powder is melted and locally resolidified, have the common feature of carrying out a partial or total melting of a powder, generally from metallic, ceramic or plastic materials.

[0004] PBF processes differ according to the nature of the energy source used to produce the fusion, which can be, for example, a laser (the process is then called L-PBF for "Laser-Power Bed Fusion") or an electron beam (the process is then called EB-PBF for "Electron Beam-Power Bed Fusion").

[0005] In additive manufacturing of metal parts, particularly by PBF, L-PBF, EB-PBF processes, the quantity of powder used in the manufacture of a part rarely exceeds 30% of the total volume of powder used for the complete manufacturing process.

[0006] In some cases, to avoid any risk on a subsequent operation, the unfused and recovered powder is either discarded directly or subjected to a lengthy recycling process (melting + atomization) in order to use only new powder and ensure the quality of future manufactured parts. This leads to an increase in the cost of the part.

[0007] In view of the quantity of powder remaining after a part manufacturing operation, it is therefore advantageous, at least for cost reasons, to be able to reuse the remaining metal powder in future manufacturing.

[0008] However, reuse of the powder is only possible for residual powder whose quality is effectively controlled. Indeed, during the process of During manufacturing, part of the powder was exposed to high temperatures, and this may have changed the properties of the powder.

[0009] In particular, in L-PBF manufacturing, some particles in the vicinity of solidified cords can be carried along by the gas flow and melt under the effect of the laser (these are hot ejecta).

[0010] In the case of austenitic steel powders (which are a specific type of stainless steel alloy containing austenite), depending on their cooling kinetics, these particles can resolidify as ferrite. And due to their magnetic properties, ferritic particles pose a problem in controlling powder spreading for additive manufacturing operations.

[0011] Therefore, direct reuse of such used powder could have the adverse effects of degrading the properties of a part manufactured with it.

[0012] According to the ASTM F3184 standard (“Standard Specification for Additive Manufacturing Stainless Steel Alloy (UNS S31603) with Powder Bed Fusion”), the reuse of powder is permitted for an unlimited number of times, provided that the quality of the final part manufactured remains constant.

[0013] Also, it is essential to control the quality of residual powder after use in additive manufacturing, with a view to reusing all or part of the remaining powder for a new part manufacturing.

[0014] An article by T. Delacroix, et al., “Influence of powder recycling on 316L stainless steel feedstocks and printed parts in laser powder bed fusion” (Addit. Manuf. 2021, 50, 102553), investigates the presence of ferrite in different types of powders: virgin powder or powder recycled up to 15 times. The reference method for accurately characterizing the presence of ferrite is electron backscatter diffraction (EBSD).

[0015] This method can provide very precise information on the composition of the powder and the crystalline orientation of the particles. However, it requires specific sample preparation and significant time for measurements and analyses. Furthermore, it can only process very limited quantities of material and is therefore not suitable for an industrial environment.

[0016] On a slightly larger scale, X-ray Diffraction (XRD) allows quantification of the observed phases with less need for sample preparation, but the quantities of material investigated remain limited, and the XRD technique is not suitable for an industrial environment either.

[0017] There is therefore a need for a suitable solution to characterize a residual metal powder after a part manufacturing operation in additive manufacturing, and in particular to determine the presence of ferrite particles in such a powder.

[0018] The present invention meets this need. Summary of the invention

[0019] An object of the present invention relates to a method and a device for characterizing a metallic powder.

[0020] An object of the present invention is to remedy the aforementioned drawbacks of known approaches, by proposing a method, and an associated device, for determining the presence of ferrite particles in a residual metal powder after an additive manufacturing operation according to a powder bed fusion process.

[0021] The general principle of the invention consists of controlling, by eddy current measurements, the appearance of ferritic particles in a stainless steel powder recovered after an additive manufacturing operation according to a powder bed fusion process.

[0022] The device of the invention combines the use of a container for receiving the powder to be characterized, a container having a volume determined according to the characteristics of the additive manufacturing application, with the use of an eddy current measurement sensor.

[0023] Advantageously, the container is designed to take measurements on a sufficiently representative sample of powder, allowing the quality of the recovered powder to be assessed.

[0024] Advantageously, the eddy current sensor according to the invention is optimized to be sensitive to changes in the electromagnetic properties of a powder in the presence of ferrite particles.

[0025] The invention will find advantageous applications in many technical fields such as the aeronautical, space, automotive or nuclear industries, to name only these examples.

[0026] To obtain the desired results, a device for characterizing a powder is proposed. The device comprises:

[0027] - a powder container configured to hold a powder sample representative of a powder remaining after an additive manufacturing operation by a powder bed fusion process;

[0028] - an eddy current transmitter / receiver device configured to transmit at near the surface of the powder sample contained in said container electromagnetic signals within a predefined range of operating frequencies; and

[0029] - an acquisition and control system configured for:

[0030] - measure, for each operating frequency, impedance values ​​across the terminals of a receiving coil of the eddy current transmitter / receiver device; and

[0031] - evaluate the quality of the remaining powder, based on the impedance values measured for the powder sample.

[0032] According to alternative or combined embodiments:

[0033] - The powder container comprises a main body including at least one powder receiving chamber, and a support block allowing the powder to be pressed down, the powder receiving chamber being sized to receive a sample of powder representative of the powder remaining after manufacture.

[0034] - The powder container includes an air venting device configured for suck out the air from the powder container.

[0035] - The container is made of a range of non-metallic materials, including including Delrin (polyoxymethylene POM), plexiglass (polymethyl methacrylate), acrylic (polyacrylonitrile PAN), Mylar (PET polyester film), rubber.

[0036] - The eddy current transmitter / receiver device comprises a sensor composed of a coil (which can be the same for the excitation and reception functions) without amplification in absolute mode, the diameter of the coil being sized according to the dimensions of the powder container.

[0037] - The eddy current transmitter / receiver device comprises a sensor composed of a coil (which can be the same for the excitation and reception functions) whose number of layers and number of turns is predefined to ensure that the resonant frequency of the coil is higher than the range of working frequencies of the sensor.

[0038] - The acquisition and control system includes an impedance meter for measuring impedance values.

[0039] The invention also relates to a method for characterizing a powder, the method being carried out on a sample of residual powder contained in a powder container calibrated in its dimensions to contain said sample and comprising a top cover consisting of a coating film and a sealing lid. The method comprises steps consisting of:

[0040] - activate by means of an eddy current sensor CF, the emission of signals electromagnetic fields within a predefined range of working frequencies, in the vicinity of the surface of a powder sample contained in a powder container of the device, the powder sample being representative of a powder remaining after an additive manufacturing operation by a powder bed fusion process;

[0041] - measure, for each operating frequency, the impedance across the terminals of the coil CF sensor reception; and

[0042] - evaluate the quality of the remaining powder, based on the impedance values measured for the powder sample.

[0043] According to alternative or combined embodiments:

[0044] - The CF sensor activation step is performed within a frequency range of operating range between 2 MHz and 10 MHz.

[0045] - The CF sensor activation step is performed within a frequency range of operating between 4 MHz and 5 MHz.

[0046] - The step of evaluating the quality of the remaining powder includes a step consisting of to compare impedance measurements to predefined impedance values, and to quantify the presence of ferrite particles in the powder sample based on deviations between measured values ​​and predefined values.

[0047] - The step of evaluating the quality of the remaining powder includes a step consisting of to define an acceptable ratio of ferrite particles present in the powder sample to preserve the remaining powder for future additive or non-additive manufacturing.

[0048] - The characterization of a powder consists of determining the presence of particles of ferrite in a sample of type 316L austenitic powder. Description of the figures

[0049] Various aspects and advantages of the invention will become apparent in support of the description of a preferred but non-limiting embodiment of the invention, with reference to the figures below:

[0050] Fig. 1 is a schematic representation of a powder container for carrying out the measurements according to the principles of the invention in one embodiment.

[0051] Fig. 2 is an exploded view of the powder container of Fig. 1.

[0052] Figure 3 is a schematic representation of the device for characterizing a powder according to an embodiment of the invention.

[0053] Figure 4 illustrates the general steps of the process for determining the presence of ferrite particles in a powder according to the invention.

[0054] Figures [Fig. 5a] and [Fig. 5b] respectively illustrate comparative measurements of the reactance and resistance of a new powder and a recycled powder. Detailed description of the invention

[0055] Fig. 1 schematically illustrates an embodiment of a container according to the invention, intended to receive a sample of powder, in order to carry out characterization measurements of the powder according to the principles of the invention.

[0056] The container 100 is made so as to carry out measurements on a mass of powder representative of the powder existing at the end of an additive manufacturing operation (this powder is also referred to as residual powder).

[0057] The container 100 is mainly composed of two parts: a main body 102 comprising at least one powder holding chamber, and a support block 104 allowing the powder to be pressed down. The powder is pressed down onto the upper part of the container (which houses an eddy current sensor) to prevent air from getting between the sensor and the powder and thus avoid distorting the measurement result.

[0058] The container 100 is further equipped with an air evacuation device 106.

[0059] Other components enabling the assembly of the structure and its operation are described in detail with reference to [Fig.2].

[0060] Advantageously, a container is developed and dimensioned for a given application. In particular, the diameter of the powder holding chamber is calculated to accommodate a mass of powder representative of the powder recovered after an additive manufacturing operation.

[0061] The volume of powder required for measurements according to the principles of the invention is typically on the order of one hundred grams. By way of non-limiting example, for a powder mass between 50 and 250 grams, the diameter of the container chamber can be adjusted between 30 and 75 millimeters. Those skilled in the art can adapt container sizes to other powder volumes while maintaining the measurement principles of the invention.

[0062] Fig. 2 is an exploded view of the container of Fig. 1 in one embodiment.

[0063] The container 200 is composed of a main body 202 which is preferably made of a transparent material in order to visualize the powder.

[0064] In a particular embodiment, the main body is made of plexiglass.

[0065] The main body 202 rests on a support block 204. In one embodiment, the main body is screwed onto the support block using a set of screws 206. In a particular embodiment, four stainless steel screws, of type M10 x 35mm, allow the two blocks to be sealed together.

[0066] The main body 202 includes a movable internal piston 208, with O-rings 210 for sealing (two in [Fig. 2]), to allow adjustment of the volume of powder 212 inside the container. The powder volume is adjusted using the support block 204 with the screws 206 at the rear of the container.

[0067] In a particular embodiment, the piston is a piston made of Delrin acetal homopolymer (Polyoxymethylene POM), the O-rings are made of rubber.

[0068] The powder 212 is blocked in the receiving chamber by a paper filter 214 which serves as a retaining surround.

[0069] The container 200 further includes a cover to enclose the powder in the container, via a top cover (216, 218) adapted to the sizes of the probes that will be used for the measurements.

[0070] In one embodiment, the cover is composed of a covering film 216 and a sealing cover 218, all sealed to the main body 202 by a set of screws 220.

[0071] In a particular embodiment, the covering film is a plastic film with a thickness between 50 µm and 200 µm.

[0072] In a particular embodiment, the sealing cover 218 is made of Delrin acetal homopolymer.

[0073] In a particular embodiment, the sealing cover 218 is sealed to the main body by a set of eight M6 x 12mm type screws made of polytetrafluoroethylene (PTFE).

[0074] An air exhaust device 222 is provided at the level of the chamber containing the powder, in order to draw out the air and prevent a reaction of the powder with the air. This ensures that the measurements on the powder are carried out without the influence of air.

[0075] In one embodiment, the air evacuation device is a tube attached to the main body 202 and in which a syringe (not shown) is placed in order to aspirate the air.

[0076] In a particular embodiment, the tube is made of acrylic.

[0077] A person skilled in the art may derive other specific embodiments from the general principles described. In particular, containers of different sizes may be designed, bearing in mind the principle that the materials used should not influence the measurements.

[0078] Thus, preferably, the powder containers and their components can be made from a range of non-metallic materials: Delrin (polyoxymethylene POM), plexiglas (polymethyl methacrylate), acrylic (polyacrylonitrile PAN), Mylar (PET polyester film), and rubber.

[0079] Fig. 3 is a schematic representation of the powder characterization device of the invention in one embodiment.

[0080] Generally, the powder characterization device 300 of the invention is a simple and compact device. It consists of a powder container 302 calibrated to hold a powder sample whose volume is representative of powder recovered after an additive manufacturing operation.

[0081] The powder characterization device also includes an Eddy Current (EC) transmitter / receiver device comprising an eddy current sensor 304 optimized for the study of powder.

[0082] The characterization device further includes an acquisition and control system 306 coupled to the eddy current transmitter / receiver device, configured to determine impedance values ​​from the signals received during CF control, and to determine the presence or absence of ferrite particles in the powder sample as a function of the measured impedance values.

[0083] Due to its compact size, the measuring device of the invention can be used in the vicinity of an additive manufacturing machine or a powder recycling station.

[0084] Advantageously, due to its simplicity of design and use, the measuring device of the invention allows the detection of the presence of ferrite in a volume of residual austenitic powders, without the need for specific preparation of the sample to be characterized.

[0085] Another advantage of the device of the invention lies in the speed of the characterization of the powder, obtained by taking measurements by eddy currents on the surface of the powder contained in the container, and by the immediate analysis of the measured impedance.

[0086] The Eddy Current (EC) technique is based on the detection of an electrical signal emitted by an electrically conductive material subjected to a time-varying electromagnetic field.

[0087] An eddy current sensor includes a control head which generally includes at least one transmitting circuit powered by alternating current and enabling the generation of a local electromagnetic field, and at least one receiver sensitive to this electromagnetic field.

[0088] The electromagnetic receiver often consists of a receiving coil (or possibly several connected together, for example in a differential configuration) across whose terminals an electromotive force of the same frequency as that of the alternating supply current is induced. The receiver can also be a Hall effect sensor or a magnetoresistive (MR) sensor. This latter family of sensors includes, in particular, anisotropic magnetoresistive (AMR) sensors, giant magnetoresistive (GMR) sensors, tunnel magnetoresistive (TMR) sensors, and giant magnetoimpedance (GMI) sensors.

[0089] According to AFNOR standard NF EN 1330-5, Oct. 1998, an eddy current transducer is a physical device comprising excitation elements and receiving elements. In the following description, the term CF sensor refers to such an eddy current transducer.

[0090] The arrangement and geometric shape of transmitting or receiving elements (transmitting / receiving (T / R) elements) represent a "pattern". A pattern may consist of elements with separate transmitting and receiving functions, elements combining T / R functions, or elements having a transmitting function for several receivers.

[0091] According to different embodiments of the invention, the excitation and reception functions can be performed in a differentiated manner in separate E / R mode, or be performed in combined E / R mode, in order to measure the impedance response of the coil.

[0092] When the control head of an eddy current sensor is positioned in the vicinity of a structure to be inspected or is moved across the surface of such a structure, The transmitter circuit is supplied with a sinusoidal signal. An electromagnetic field of the same frequency is emitted into the structure to be inspected. This results, across the terminals of the receiving coil, in an induced electromotive force arising, on the one hand, from the coupling between the transmitter circuit and the receiving coil and, on the other hand, from the magnetic field radiated by the currents induced in the structure (eddy currents).

[0093] In applications for detecting defects in structures, the flow of induced currents is altered in the presence of inhomogeneity in the inspected material. The magnetic field receiver measures the magnetic field resulting from this change in the path of the induced currents.

[0094] In the context of the invention for the detection of ferrite particles, the circulation of induced currents is modified according to the impedance of the material being inspected.

[0095] In CF, the sensitivity of the measurement (or, in other words, the signal-to-noise ratio) is all the better when the distance between the transmitting and receiving elements of the CF inspection head and the material to be inspected is small. Furthermore, during the movement of the inspection head over the material, this distance (called the air gap) must be as constant as possible to avoid bias in the measurements.

[0096] Since the CF sensor is a device quite sensitive to the air gap, the inventors recommend working in contact with the surface of the powder, i.e. the head of the sensor comes into contact with the surface of the powder through the covering film 216.

[0097] To design the sensor, i.e. to design the coil, the principle is firstly to optimize the diameter of the coil according to the dimensions of the container and to set a range of working frequencies adapted to the material to be inspected.

[0098] In a second step, the number of layers and the number of turns must be optimized to ensure that the resonant frequency of the coil is higher than the working frequency.

[0099] The CF sensor of the invention is thus optimized for the detection of the ferritic phase in the metal powder.

[0100] Indeed, it is necessary to use higher working frequencies on the powder than the working frequencies usually known on solid materials, because the electrical conductivity of powders is lower than for solid materials.

[0101] Specifically in the context of the invention, which is centered on the detection of ferrite in austenitic materials, the working frequency range is within a range between 2 MHz and 10 MHz.

[0102] In a particular implementation, the operating frequencies are taken from a range between 3 MHz and 7 MHz.

[0103] In another embodiment, the operating frequencies are taken from a range between 4 MHz and 5 MHz.

[0104] The inventors have determined that the ratio of the external diameter of the coil to the diameter of the container must be between 0.2 and 0.35, in order to carry out global measurements on the surface of the container while avoiding edge effects.

[0105] In one embodiment, the excitation frequency of the coil is chosen to be at least 1 MHz higher than the upper limit of the operating frequency range, and preferably 2 MHz higher.

[0106] In a particular embodiment, the sensor consists of a coil without amplification in absolute mode (i.e., transmission / reception are combined). The diameter of the powder container is 45 mm, and the outer diameter of the coil is 12 mm. The resonant frequency of the coil is 7.2 MHz, and impedance measurements to assess the presence of ferrite are taken in a frequency range from 4 MHz to 5 MHz.

[0107] Figure 4 illustrates the general steps of the process for characterizing a powder according to the invention.

[0108] The process is notably applied to the determination of the presence of ferrite particles in a residual powder, in particular an austenitic powder of type 316L.

[0109] Indeed, such a powder, after an additive manufacturing operation using a powder bed fusion (PBF, L-PBF, EB-PBF) process, may contain particles that are resolidified as ferrite. These ferritic particles can alter the powder's spreading quality before fusion, which can lead to the formation of defects, particularly at the beginning of manufacturing. It is therefore important to control the appearance of ferrite in the residual powder.

[0110] The general principle of the process of the invention 400 consists of quantifying the presence of ferrite particles in a powder sample representative of residual powder remaining after an additive manufacturing operation according to a powder bed fusion process. The determination of the proportion of ferrite particles is based on the value of the complex impedance across the receiving coil of a CF sensor operating in transmit / receive mode (combined or separate transmit / receive), within a range of operating frequencies optimized for the powder being measured.

[0111] Indeed, in the presence of ferrite particles in the powder, the values ​​of the conductivity and permeability of the powder are modified, which will lead to a modification of the impedance (resistance and reactance), and which makes it possible to reveal the presence of ferrite.

[0112] The process of the invention is operated on a device having the general characteristics of the device described with reference to [Fig. 3], and having characteristics specifics determined according to the context of the additive manufacturing for which the powder control is done.

[0113] Thus, the device on which the process of the invention is implemented comprises a powder container whose powder receiving chamber has been previously dimensioned and a CF sensor whose working frequencies have been predefined.

[0114] A sample of powder is placed in the receiving chamber, the powder is compacted towards the lid and any air that may be contained in the chamber is aspirated. The device is prepared.

[0115] In a first step 402, the method enables the CF sensor to emit electromagnetic measurement signals within a predefined operating frequency range. The predefined frequency range is optimized for the type of powder contained in the container and takes into account the requirement not to be too close to the resonant frequency of the CF sensor coil.

[0116] The CF sensor head is placed in close proximity, through the covering film 216, to the surface of the powder contained in the container, for the entire duration of a measurement sequence (a few seconds to record about one hundred points). The information collected comes from a subsurface volume of the powder sample.

[0117] The coating film serves a safety function because the powdered material is potentially hazardous in itself. Such coating films have well-known characteristics. Furthermore, the presence of this film also affects the powder, as it helps to make its surface more even.

[0118] In a subsequent step 404, the method allows the impedance across the receiving coil (electromagnetic force) to be measured using an impedance meter, for each frequency in the predefined frequency range, according to defined measurement steps.

[0119] Then the process in a subsequent step 406, allows the quality of the remaining powder to be evaluated, based on the impedance values ​​measured for the powder sample.

[0120] Indeed, in the presence of a ferrite-free powder, for example new, with conductivity values ​​ol and permeability pl, the impedance of the powder, denoted ZipOUdre,cMJ4, can be formulated according to the following equation:

[0121] ZipOudre,Chpi — R|,(>n(||L. O,p |+J Xpoiidi^.Op |.

[0122] where RpOUdre represents the real part and jXpoudre the imaginary part of the impedance ZlpOudre,(hPl*

[0123] In the presence of ferrite particles, the conductivity and permeability values ​​of the powder are modified. They are denoted as o2 and p2 respectively. The impedance of the powder with ferrite is then formulated according to the following equation:

[0124] Z2 powder,P- Rpowder,^2»^2+j^powder,^42*

[0125] Depending on the amount of ferrite present in the measured sample, the impedance values ​​Zi and Z2 may be consistent or different.

[0126] In one embodiment, step 406 of evaluating the quality of the remaining powder, includes a step of comparing the impedance measurements to predefined impedance values, and of quantifying the presence of ferrite particles in the powder sample, based on deviations between the measured values ​​and the predefined values.

[0127] In one embodiment, step 406 of evaluating the quality of the remaining powder, includes a step of defining an acceptable ratio of ferrite particles present in the powder sample to preserve the remaining powder for future additive or non-additive manufacturing.

[0128] Figures 5a and 5b respectively illustrate comparative measurements of the reactance and resistance of new 316L steel powder (solid lines) and 316L steel powder recycled 15 times (dashed lines), measured in a frequency range of 4.5 MHz to 5 MHz in 5 kHz measurement steps. The dashed curves illustrate that the recycled steel powder contains ferrite particles, and the reactance and resistance values ​​differ from the respective values ​​for the new powder.

[0129] Thus, the process of the invention implemented on the device described, makes it possible to determine, from measurements of impedance values ​​for a sample of powder representative of a residual powder, whether the powder can be reused for a future additive manufacturing operation or not.

[0130] The impedance values ​​measured on the sample are compared to impedance values ​​of ferrite-free powder, for example, new or non-recycled powder. In case of non-compliance between the values, and depending on a level of ferrite particle contamination that can be predefined as an acceptable threshold, the powder from which the sample is extracted can be used or reused for a subsequent additive manufacturing operation.

Claims

Demands

1. A device (300) for characterizing residual powder remaining after an additive manufacturing operation by a powder bed fusion process, the device comprising: - a powder container (302) for receiving a sample of said residual powder, the container being calibrated in its dimensions to contain said sample and comprising a top cover consisting of a covering film and a sealing cover; - an eddy current transmitter / receiver apparatus (304), having a coil whose diameter is dimensioned according to the dimensions of the powder container, and configured to emit electromagnetic signals on the surface of the powder sample through the covering film, in a predefined range of operating frequencies;and - an acquisition and control system (306), configured to: - measure, for each operating frequency, impedance values ​​across a receiving coil of the eddy current transmitter / receiver device; and - evaluate the quality of the remaining powder based on the impedance values ​​measured for the powder sample.

2. The device according to claim 1 in which the powder container comprises a main body (102) including at least one powder receiving chamber, and a support block (104) allowing the powder to be pressed, the powder receiving chamber being dimensioned to receive a sample of powder representative of the remaining powder.

3. The device according to claim 1 or 2 wherein the powder container comprises an air evacuation device (106, 222) configured to draw the air contained in the powder container.

4. The device according to any one of the preceding claims wherein the container is made of a range of non-metallic materials, including in particular Delrin (polyoxymethylene POM), plexiglas (polymethyl methacrylate), acrylic (polyacrylonitrile PAN), Mylar (PET polyester film), rubber.

5. The device according to any one of the preceding claims, wherein the eddy current transmitter / receiver apparatus includes a sensor consisting of a coil without amplification in absolute mode, the diameter of the coil being sized according to the dimensions of the powder container.

6. The device according to any one of the preceding claims wherein the eddy current transmitter / receiver apparatus comprises a sensor consisting of a coil whose number of layers and number of turns is predefined to ensure that the resonant frequency of the coil is higher than the operating frequency range of the sensor.

7. The device according to any one of the preceding claims in which the acquisition and control system includes an impedance meter for measuring impedance values.

8. A method (400) for characterizing residual powder remaining after an additive manufacturing operation by a powder bed fusion process, the method being carried out for a sample of said residual powder contained in a powder container calibrated in its dimensions to contain said sample and comprising a top cover composed of a covering film and a sealing cover, and comprising steps of: - (402) activating by means of an eddy current sensor CF having a coil whose diameter is dimensioned according to the dimensions of the powder container, the emission of electromagnetic signals, in a range of predefined working frequencies, on the surface of said powder sample through the covering film; - (404) measuring, for each working frequency, the impedance across the terminals of the receiving coil of the sensor CF;and - (406) evaluate the quality of the remaining powder, based on the impedance values ​​measured for the powder sample.;

9. A method according to the preceding claim in which the CF sensor activation step is carried out in a range of working frequencies between 2 MHz and 10 MHz.

10. Method according to claim 8 wherein the CF sensor activation step is carried out in a range of working frequencies between 4 MHz and 5 MHz.

11. A method according to any one of claims 8 to 10, wherein step 406, of evaluating the quality of the remaining powder, comprises a step of comparing the impedance measurements to predefined impedance values, and of quantifying the presence of particles of ferrite in the powder sample, depending on the differences between the measured values ​​and the predefined values.

12. A method according to any one of claims 8 to 11 wherein step 406 of evaluating the quality of the remaining powder includes a step of defining an acceptable ratio of ferrite particles present in the powder sample to preserve the remaining powder for further additive or non-additive manufacturing.

13. A method according to any one of claims 8 to 11 wherein the characterization of a powder consists of characterizing a sample of austenitic powder of type 316L.

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