Surface treatment process for metals or ceramics using a continuous wave laser beam and associated system

Abstract

The invention relates to a method for treating (100) a surface (S) of a sample (SAM) made of metallic or ceramic material (MM), comprising a treatment step (ETAt) consisting of scanning said surface (S) to be treated with a continuous wave laser beam called the treatment laser beam (LBT) having a treatment power (Pt) and a treatment spot (ST) on said surface, the treatment spot having a diameter (DST) called the treatment diameter, said treatment spot moving at a scanning speed (vt) called the treatment speed on said surface, the treatment diameter (DST) being less than or equal to 100 µm, the treatment power (Pt), the treatment diameter (DST) and the treatment scanning speed (vt) being determined so that a point on the surface of said sample receives a determined surface energy density (Est) such that the material (MM) of the sample at that point reaches a melting temperature,The treatment process is carried out under an inert atmosphere or under vacuum. No figure.

Description

Title of the invention: Method for surface treatment of metals or ceramics with a continuous wave laser beam and associated system. FIELD OF THE INVENTION

[0001] The present invention relates to the field of surface treatment processes for metals or ceramics in order to improve their physical properties. More particularly, the invention relates to treatment processes using a continuous wave laser. STATE OF THE ART

[0002] Surface treatment processes for metals, alloys or ceramics are known from the prior art. For example, these treatments aim to improve resistance, or to obtain ductility and fatigue limits superior to those of the "as-is" material (i.e., before treatment).

[0003] These materials are characterized by microstructures, and we seek to design microstructures which exhibit strength, ductility and fatigue limit superior to what is currently possible, while reducing energy and material consumption.

[0004] The advent of 3D metal printing, or additive manufacturing, makes it possible to produce parts made with microstructures that exhibit unprecedented strength compared to their conventionally manufactured counterparts. However, this increase in strength is often accompanied by a decrease in ductility and a poorer response to fatigue.

[0005] The strength-ductility trade-off originates from the hierarchical microstructure resulting from the highly unbalanced processes that occur during the additive manufacturing process. The heat-matter interaction induced by the dynamics of the melt pool, rapid solidification, and thermal cycling in the solid state leads to a microstructure exhibiting physical and chemical heterogeneities ranging from a few tens of nanometers to several hundred micrometers. The main contribution to the material's strength comes from the smallest of these features, which, in stainless steels, are precipitates, microsegregation cells, and dislocation structures.

[0006] The "raw" or initial material (before processing) has a crystallographic grain structure, and within each grain there are a multitude of smaller dislocation structures. A dislocation is a linear crystal defect that occurs due to a missing atomic plane. A microsegregation cell exhibits cell walls that have a higher concentration of one or more elements than inside the cell.

[0007] As a general rule, it is known that the smaller (and higher) the size (and density) of these microsegregation cells / dislocation structures, the higher the resistance and the lower the ductility.

[0008] Annealing is a commonly used approach to improve ductility. It is an isothermal heat treatment that evolves the metastable microstructure towards equilibrium by minimizing stored energy. However, this process unintentionally leads to an increase in cell / structure size and a decrease in their density, which inevitably results in a decrease in strength.

[0009] Furthermore, the fatigue response of dense parts (negligible porosity / voids) is highly dependent on their surface roughness. During additive manufacturing, unmelted powder particles sinter on the surface and become the main contributors to the surface roughness of the manufactured parts. Under fatigue loading, failure is primarily due to nucleation (if not already present) and the propagation of surface cracks.

[0010] The fatigue response of manufactured parts can be improved by post-fabrication surface treatments, the most common of which are mechanical in nature (pre-stress shot peening, polishing, etc.), which reduce surface roughness and induce compressive stresses in the plane of the surface.

[0011] Laser-based treatments are also used, with lasers having large spot diameters, on the order of 500 pm to a few mm, which are industrially available. For example, the publication by B. Wang et al., "Effects of quench-tempering and laser hardening treatment on wear resistance of gray cast iron" (JMR&t 2020, 9(4) 8163-8171), describes the application of a laser treatment with a 2 mm spot to improve the wear resistance of gray cast iron.

[0012] Thus, the effectiveness of these various post-manufacturing treatments may prove insufficient, or only improve one physical property while degrading another.

[0013] One object of the present invention is to remedy the aforementioned drawbacks by proposing a surface treatment method for samples made of metallic or ceramic material using a continuous wave laser, allowing the notable and simultaneous improvement of several physical properties of the treated sample. DESCRIPTION OF THE INVENTION

[0014] The present invention relates to a method for treating the surface of a sample made of metallic or ceramic material, comprising a treatment step consisting of scanning said surface to be treated with a continuous wave laser beam, referred to as the treatment laser beam, having a treatment power and a treatment spot on said surface, the treatment spot having a diameter referred to as treatment, said treatment spot moving at a scanning speed called the treatment speed over said surface, • the treatment diameter being less than or equal to 100 pm, • the processing power, the processing diameter and the processing scan speed being determined such that a point on the surface of said sample receives a determined surface energy density of processing such that the sample material at that point reaches a melting temperature, • the treatment process being carried out under an inert atmosphere or under vacuum.

[0015] According to one embodiment, the scanning is configured so that there is an overlap of at least 50% between the two treatment spots associated with two adjacent scanning trajectories.

[0016] According to one embodiment, the process according to the invention includes a step of characterizing the sample with a scanning microscope implemented after the processing step, the characterization being carried out without removing the sample from the inert atmosphere or under vacuum.

[0017] According to another aspect, the invention relates to a method for manufacturing said sample in metallic or ceramic material and for treating the surface of said sample comprising: • a manufacturing step of said sample using additive manufacturing technology, • a processing step according to the processing method according to an aspect of the invention.

[0018] According to one embodiment, the manufacturing and processing method according to the invention further comprises a characterization step.

[0019] According to one embodiment of the manufacturing and processing method according to the invention, this includes an additive manufacturing step carried out with a manufacturing beam which is a laser beam.

[0020] According to one embodiment of the manufacturing and processing method according to the invention, the additive manufacturing step is carried out by the laser powder bed fusion method.

[0021] According to another embodiment of the manufacturing and processing method according to the invention, the additive manufacturing step is carried out by the direct energy deposition method using laser.

[0022] According to an embodiment of the manufacturing and processing method according to the invention, the manufacturing laser beam presents a manufacturing spot having a manufacturing diameter, the manufacturing diameter being greater than or equal to the processing diameter.

[0023] According to an embodiment of the manufacturing and processing method according to the invention, the manufacturing laser beam has a manufacturing power and a manufacturing scanning speed, and the manufacturing power, manufacturing diameter and manufacturing scanning speed are determined such that a manufacturing surface energy density is greater than or equal to x times the processing surface energy density, with x < 1 having a positive value and a function of the metallic or ceramic material.

[0024] According to one embodiment of the manufacturing and processing method according to the invention, the manufacturing laser beam and the processing laser beam are generated by the same continuous wave laser source.

[0025] According to another aspect, the invention relates to a treatment system configured to treat a surface of a sample made of metallic or ceramic material, comprising: • a laser source configured to generate a continuous wave laser beam, known as a processing beam, exhibiting a processing power, • a focusing device configured to focus the laser treatment beam onto the surface of said sample according to a so-called treatment spot having a treatment diameter less than or equal to 100 pm, • a scanning device configured to move the treatment spot over said surface of said sample with a treatment scanning speed, • an enclosure configured to ensure an inert atmosphere or vacuum around the sample and including a viewing window, • the processing power, the processing diameter and the processing scan speed being determined so that a point on the surface of said sample receives a determined surface energy density of processing so that the sample material at that point reaches a melting temperature.

[0026] According to one embodiment of the processing system according to the invention, the laser source, the scanning device and the focusing device are arranged in a housing, the system further comprising a coupling piece configured to interface the housing and the enclosure.

[0027] According to one embodiment of the processing system according to the invention, it further comprises: - a device configured to generate an electron beam and to focus the electron beam onto the sample, - at least one detector configured to detect electrons from the sample, - the device for generating the electron beam and the detector being arranged with the enclosure to form a scanning electron microscope.

[0028] According to a final aspect, the invention relates to an additive manufacturing and surface treatment system configured to manufacture a sample in metallic or ceramic material and to treat a surface of said sample, said system comprising: • a laser source configured to generate a continuous wave laser beam with adjustable power to generate, over a given surface, a so-called manufacturing power or a so-called processing power, • a device for positioning a metallic powder in a manner suitable for the laser beam, • a focusing device configured to focus the laser beam onto said powder with a manufacturing spot having a manufacturing diameter, and to focus the laser beam onto the surface of said sample once manufactured with a processing spot having a processing diameter less than or equal to 100 pm, • a scanning device configured to move the manufacturing spot over said powder to manufacture said sample, with a manufacturing scanning speed, and to move the processing spot over said surface of said sample, once the sample has been manufactured, with a processing scanning speed, • an enclosure configured to ensure an inert atmosphere or vacuum around the sample and including a viewing window, • the laser source, the scanning device and the focusing device being configured such that: • During manufacturing, the manufacturing power, manufacturing diameter, and manufacturing scanning speed are determined in such a way as to cause consolidation of said powder in order to manufacture the sample by additive manufacturing, • During processing, the processing power, processing diameter and processing scan speed are determined so that a point on the surface of said sample receives a determined surface energy density of processing so that the sample material at that point reaches a melting temperature.

[0029] According to one embodiment of the additive manufacturing and surface treatment system according to the invention, it further comprises: - a device configured to generate an electron beam and to focus the electron beam onto the sample, - at least one detector configured to detect electrons from the sample, - the device for generating the electron beam and the detector being arranged with the enclosure to form a scanning electron microscope.

[0030] According to an embodiment of the additive manufacturing system of a sample and of treating a surface of said sample according to the invention, the manufacturing diameter is greater than or equal to the treatment diameter.

[0031] According to an embodiment of the additive manufacturing system for a sample and for treating a surface of said sample according to the invention, the laser source, the scanning device and the focusing device are further configured so that a surface energy density of manufacturing is greater than or equal to x times a surface energy density of treatment, with x < 1 having a positive value and a function of the metallic or ceramic material.

[0032] The following description presents several embodiments of the device of the invention; these examples are not limiting to the scope of the invention. These embodiments illustrate both the essential features of the invention and additional features related to the embodiments considered.

[0033] The invention will be better understood and other features, objectives and advantages thereof will become apparent from the following detailed description and with reference to the accompanying drawings given by way of non-limiting examples and on which:

[0034] Fig. 1 illustrates a transmission electron microscope image of the surface of an area of ​​the sample walls before treatment according to the invention.

[0035] Figure 2 illustrates a transmission electron microscope image of the same area of ​​the sample after application of the process according to the invention.

[0036] Figure 3 illustrates an energy-dispersive X-ray spectroscopy image of an area of ​​the sample before treatment according to the invention.

[0037] Figure 4 illustrates an energy-dispersive X-ray spectroscopy image of the same area of ​​the sample, after application of the method according to the invention.

[0038] Fig. 5 illustrates a cross-sectional profile image of a track followed by the laser beam on a wall of a sample for three different energies A: 0.4 J / mm2; B: 1.6 J / mm2; C: 8 J / mm2.

[0039] Figure 6 illustrates a sample seen in profile before the application of the process according to the invention.

[0040] Fig. 7 illustrates the same sample as that of Fig. 6 seen in profile after application of the process according to the invention.

[0041] The [Fig.8] a system according to the invention for implementing the method according to the invention.

[0042] Fig. 8bis illustrates an embodiment of the system according to the invention comprising a coupling piece.

[0043] Figure 9 illustrates an embodiment of the system according to the invention incorporating a scanning electron microscope.

[0044] Fig. 10 illustrates an embodiment of the process of manufacturing a sample and treating the surface of the sample according to another aspect of the invention.

[0045] Fig. 11 illustrates an additive manufacturing and surface treatment system, configured to manufacture a sample and to treat the surface of the sample, according to another aspect of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0046] The examples cited later in the description relate, without limitation, to stainless steels, but the considerations and results obtained can be extrapolated to any type of metal (including alloys) or ceramic sample. The method according to the invention is therefore applicable to all such types of samples.

[0047] The implementation of the method 100 according to the invention resulted from a significant body of observations and experiments. The inventors noted that state-of-the-art continuous wave laser surface treatments typically used a spot size on the sample surface greater than 500 pm, with smaller diameter spots being used only for additive manufacturing of samples. The inventors demonstrated that the use of a small diameter spot, less than 100 pm, combined with appropriate scanning parameters, can profoundly modify the dislocation structures and microsegregation cells of the material, this modification inducing an improvement in certain properties of the irradiated (treated) material.

[0048] Thus, the method 100 for treating the surface S of a sample SAM made of metallic or ceramic material (referred to as MM) according to the invention comprises a treatment step ETAt consisting of scanning the surface S to be treated with a continuous wave laser beam, referred to as the LBT treatment laser beam. The treatment laser beam has a power Pt and a spot ST, referred to as the treatment spot, on the surface S, the treatment spot ST having a diameter referred to as the treatment diameter DST. The spot ST moves at a scanning speed referred to as the treatment speed vt over the surface.

[0049] Metallic material means a pure metallic material (a single compound) or an alloy.

[0050] The diameter of DST is less than or equal to 100 pm. In order to modify the dislocation structures appropriately, the use of a small diameter as claimed is not sufficient, and the inventors have established an additional condition to be verified to obtain the improvement of the material properties. It is necessary that the power Pt, the diameter DST of the treatment spot ST, and the treatment scanning speed vt be determined so that a point on the sample surface receives a treatment surface energy density Est determined such that the material MM of the sample at that point, illuminated by the moving laser beam, reaches the melting temperature.

[0051] The formula relating the different variables of the laser beam is:

[0052] Est = Pt / (vt.DST) (1)

[0053] In other words, it is necessary that the energy Est be greater than or equal to a minimum surface energy density Estmin for which a point on the surface reaches the melting temperature.

[0054] This condition Est > Estmin ensures that the surface of the material melts. Furthermore, the inventors have established that the small diameter, less than 100 pm, of the treatment spot ST associated with the melting of the material ensures a very strong thermal gradient, which induces a high cooling rate after the sample material MM has melted. Indeed, when the treatment spot is larger, it takes longer to dissipate the energy supplied by the laser, and the cooling rate decreases.

[0055] It has also been established that the higher the cooling rate, the smaller the dislocation structures that reform. Applying the treatment according to the invention results in structures that are smaller than initially formed and denser. Furthermore, during solidification after melting, the dendrites that form in the material exhibit microsegregation cells that are smaller than initially formed.

[0056] Another advantage of the process according to the invention has been discovered: the roughness of the treated surface is reduced, which improves the material's fatigue response. This is particularly true for metallic samples produced by additive manufacturing using metal powder. After their manufacture, these samples exhibit residual sintered powder on the surface, causing an increase in roughness. Due to the melting that occurs on the sample surface, the process according to the invention allows for the melting and subsequent solidification of this residual powder (see below).

[0057] In order to prevent the penetration of unwanted atoms or molecules present in the sample's environment during melting, the process according to the invention is carried out under an inert atmosphere or under vacuum. In an inert atmosphere, the pressure should not be too high so as to ensure that the molecules of the inert gas do not penetrate the molten material. Indeed, certain atoms or molecules Injected substances into the sample can alter its properties by degrading them. The process according to the invention is a universal surface treatment process that does not modify the chemical composition of the sample material, but modifies its microstructures in the vicinity of the treated surface. To carry out the process under vacuum or an inert atmosphere, the sample is positioned in a chamber.

[0058] For a certain effectiveness of the treatment according to the invention it is sought that the fusion be achieved over at least a few microns of depth of the sample.

[0059] These physical considerations apply to samples produced by additive manufacturing, but also to any other type of sample in metal (pure or alloy) or ceramic manufactured by other methods.

[0060] To illustrate the physical reasoning and the results obtained with the process according to the invention, a sample E316L is considered, having thin walls of 316L stainless steel manufactured by an additive manufacturing process. These walls are arranged on a substrate also made of hot-rolled 316L stainless steel.

[0061] The walls were produced using the laser direct energy deposition (LDED) method. The laser used to fabricate the sample walls using the LDED method is a 250 W laser with a scanning speed of 33 mm / s and a spot size on the powder surface of 0.7 mm. These parameters result in a manufacturing surface energy density Esf received by the sample of 10.7 J / mm² (formula (1)).

[0062] Figure 1 illustrates a transmission electron microscope (TEM) image of a surface area of ​​the walls of sample E316L before treatment according to the invention, the contrast of which has been amplified to clearly show the light and dark areas. The dark areas correspond to dislocation structures. Figure 2 illustrates a TEM image of the same surface area after application of the process according to the invention. It can be seen that the dark areas are denser and smaller in size on the treated sample.

[0063] Figure [Fig. 3] illustrates an energy-dispersive X-ray spectroscopy image Figure 4 shows an image of an area of ​​sample E316L before treatment (energy-dispersive X-ray spectroscopy), and Figure 4 illustrates a similar image of the same area of ​​the surface after application of the process according to the invention. The contrast has been amplified to better highlight the light and dark areas. Energy-dispersive X-ray spectroscopy makes it possible to identify areas where atoms of a specific element, in this case chromium, are accumulated. The light areas illustrate the aforementioned microsegregation cells. These cells are denser and smaller after treatment. The same effect is obtained for iron, nickel, molybdenum, manganese, silicon, etc., which are also present in the sample.

[0064] The light areas 11 and 22 visible in Figures 1 and 2 respectively, and the dark areas 33 and 44 visible in Figures 3 and 4 respectively, correspond to microsegregation cells viewed from above. The cells form during the return to the solid state of the liquefied metal by melting. They are separated by the dislocation structures 12 and 23 shown in dark areas in Figures 1 and 2 respectively, and chemical segregation is also observed between the cells, light areas 34 and 45 respectively in Figures 3 and 4 for chromium.

[0065] As the cooling rate increases, the size of the microsegregation cells decreases, and the process according to the invention thus results in a very significant reduction in the size of the dislocation structures and microsegregation cells of the treated sample. Dislocations and microsegregations occur at the interface between two growing microsegregation cells during solidification.

[0066] As stated above, it is well accepted that smaller (a few tens of nanometers) and denser features strengthen the material.

[0067] The minimum energy Estmin from which the surface of the material to be treated melts cannot be calculated in an obvious way. A known formula is as follows:

[0068] Q = m.AHf

[0069] with Q the energy required to achieve fusion, m the mass of the sample, and AHf the latent heat of fusion. Converting this volumetric formula to the surface energy Estmin required for a sample of a given shape (surface area and thickness) is not straightforward analytically.

[0070] Starting from a sufficiently small spot size, i.e., less than or equal to 100 pm, the power Pt and the velocity vt must be determined in such a way as to obtain melting of the material at least on the surface. This determination can be carried out experimentally, for example as described below.

[0071] Different laser treatments were performed on the E316L sample with a constant Pt power, a beam diameter of 60 pm on the surface and a variable scanning speed:

[0072] Pt = 24 W, vt = 50 (8), 100 (4), 250 (1.6), 500 (0.8) and 1000 (0.4) mm / s. The corresponding surface energy density Est, in J per mm², is indicated in parentheses. [Fig. 5] illustrates a cross-sectional profile image of a track followed by the laser beam on a wall of the sample illuminated by the laser beam (z-axis in depth relative to the surface S of the sample, scanning speed vt perpendicular to the plane of the figure) for the three energies A: 0.4 J / mm²; B: 1.6 J / mm²; C: 8 J / mm², obtained by scanning with the three corresponding speeds vt.

[0073] The images were obtained by backscattered electron imaging, or BSE. It is readily apparent in [Fig. 5] A that the energy is insufficient to induce melting; the sample is not impacted by the laser beam. In [Fig. 5] B, it can be seen that the laser penetrated the sample in zone 50, to a maximum depth pmax of approximately 10 pm, and caused local melting, resulting in a change in the sample's microstructure. Zone 51 was not impacted by the beam; zones 50 and 51 are separated by an interface 52, illustrating the boundary between zone (50), where the melting temperature was reached, and zone (51), where melting did not occur.

[0074] The elementary features are smaller in the melted zone 50. In C, the laser penetrated deeper (pmax approximately 25 pm deep) and the volume of the melted zone 50 is greater. This experiment clearly shows that for this stainless steel sample, an energy Es of 0.4 J / mm² is insufficient, while an energy Es of 1.6 J / mm² is greater than the minimum energy Estmin, allowing a surface area of ​​the sample to exceed the melting temperature. Thus, the energies Es of 1.6 and 8 J / mm² are compatible with the process according to the invention.

[0075] Therefore, to identify laser parameters suitable for implementing the process according to the invention for achieving surface fusion, preliminary experimental measurements should be carried out with a sample of material and shape identical to that to be treated, or even with the sample to be treated itself, by varying at least one parameter among (Pt, vt, DST). A variation in diameter is not necessary if it is also possible to vary Pt and / or vt, provided that the latter is less than 100 pm. A variation in Pt can be easily obtained because lasers generally have adjustable power. A variation in vt is also easily accessible because scanning devices generally have a speed setting.The experimental identification of the presence (or absence) of surface melting of the sample can be carried out, for example, by BSE imaging, as illustrated in [Fig. 5]. Thus, the result consisting of the presence (or absence) of surface melting of the sample is verifiable by means of the experimentation described above.

[0076] Once a set of values ​​(DST0, Pt0, vt0) has been identified allowing the desired effect (surface fusion) to be obtained, the treatment by scanning the spot on the surface of the sample to be treated is implemented.

[0077] According to one embodiment, and in order to obtain homogeneous treatment over the entire treated surface, the scanning is configured so that there is an overlap of The difference in thickness between the two treatment spots associated with two adjacent scanning paths is less than 50%. This ensures that the entire sample volume up to pmax is melted, resulting in a treated layer of uniform thickness. For example, with a 60 pm diameter spot, parallel scanning paths are preferably separated by a maximum of 30 pm.

[0078] Sample E316L was characterized to measure the performance gain provided by the treatment according to the invention. The treatment according to the invention was carried out under the following conditions: Pt = 70 W, DST = 60 pm and vt = 100 mm / s, resulting in a surface energy density of treatment:

[0079] Est = 11.7 J / mm2.

[0080] The treatment is carried out under vacuum. The scan was performed with 50% coverage.

[0081] Tensile tests indicate an average yield strength of 360 MPa without treatment and 1157 MPa in the treated area.

[0082] Ductility is not affected by the laser treatment. In fact, an increase of approximately 9% in the sample's ductility was measured after treatment. Both the initial and treated samples meet the Considère criterion, meaning that all microstructures reach their full deformation capacity before fracture.

[0083] Fatigue resistance (uniaxial fatigue at constant amplitude) was measured (Ao) on about thirty samples before and after treatment (same conditions as before with Es = 11.7 J / mm2), with the same measurement conditions.

[0084] An Ao of 182 MPa was measured before treatment and an Ao of 227 MPa after treatment, for a number of failure cycles N = 3106, representing an increase of approximately 25% in the fatigue limit Ao.

[0085] Regarding roughness, before treatment a roughness (arithmetic mean height Sa) of 16.6 pm was measured, while after treatment under the aforementioned conditions the roughness is 0.9 pm. The roughness of the treated surface is significantly better after treatment. This is illustrated by Figures 6 and 7 showing the sample viewed in profile before and after the aforementioned treatment, respectively. The contrast has been enhanced for better visibility. These images are secondary electron microscopy (SE) images. In [Fig. 6], the upper white areas 60 are powder residues that appeared during additive manufacturing. In [Fig. 7], the residual powder is compacted (area 70) because it has fused. Furthermore, the surface of the sample appears much smoother compared to the surface of the sample in [Fig. 6]. [Fig. 7] shows...7] Zone 71 corresponds to the area of ​​the surface treated by the laser.

[0086] Thus, it appears that several physical properties of the MM material are improved by the treatment. These include, but are not limited to, the yield strength, roughness, and fatigue resistance.

[0087] According to one embodiment, the treatment process according to the invention comprises a characterization step ETAc of the sample using a scanning electron microscope (SEM), carried out at least after the treatment step. The characterization is performed without removing the sample from the inert atmosphere or vacuum, that is, by keeping the sample within the chamber in which the treatment is performed. The process according to the invention thus makes it possible to treat according to the invention and to characterize a sample of material in the same instrument comprising the laser and the SEM. According to a variant, characterization of the sample is also carried out before the treatment, in order to be able to compare the sample before and after treatment. Such an instrument is described in patent application FR 2213567, which has not yet been published.

[0088] In another aspect, the invention relates to a system 80 for implementing the method according to the invention, illustrated in [Fig. 8]. The system 80 comprises a laser source LS configured to generate the laser treatment beam LBT presenting a treatment power Pt on the surface of the sample SAM. It also comprises a scanning device DS configured to move the laser treatment beam over the surface S of the sample, with a treatment scanning speed vt. Finally, it comprises a focusing device DFOC configured to focus (or defocus) the laser beam on the surface S of the sample so that the diameter of the so-called treatment spot DST is less than 100 pm.

[0089] The system 80 also includes an enclosure E in which the sample is placed, configured to ensure an inert atmosphere or vacuum around the sample. The enclosure includes a window H to allow the laser beam to enter the enclosure. The sample to be treated SAM is placed on a support Sup.

[0090] In addition, the laser source LS, the scanning device DS and the focusing device DFOC are configured so that the parameters (Pt, vt, DST) satisfy the aforementioned condition, i.e. generate a surface energy density sufficient for the material MM of the sample to reach, at a point on the surface illuminated by the moving laser beam, the melting temperature.

[0091] According to an embodiment illustrated in [Fig. 8bis], the laser source, the scanning device, and the focusing device are arranged in a BT housing, and the system further includes a PA coupling piece configured to interface the housing and the enclosure. The laser beam and the various optical elements that make up the focusing device are thus confined and protected.

[0092] Figure 9 illustrates an embodiment of the system 80 according to the invention, which also allows for characterization of the sample after treatment and optionally before. The system 80 comprises a COL device configured to generate an FE electron beam and to focus the electron beam onto the sample, and at least one Det detector configured to detect electrons emitted from the sample. The COL device and the Det detector are arranged with the enclosure E to form a scanning electron microscope (SEM).

[0093] As explained above, the process according to the invention applies to any type of sample made of metal (pure or alloys) or ceramic.

[0094] The process according to the invention is particularly well suited to materials (metallic or ceramic) produced by additive manufacturing (or 3D printing) from a powder (metallic or ceramic).

[0095] Metal additive manufacturing consists of producing parts by successively adding (metallic) material, starting from a 3D digital file. The material is shaped by consolidating a metal powder. The metallic material constituting the powder is chosen, for example, from: stainless steels, titanium-based alloys, aluminum-based alloys, nickel-based alloys....

[0096] A first method, called metallic additive manufacturing on a powder bed (or MAM-PB), is implemented using a powder bed. A powder bed (PB) is defined as a controlled thickness of powder (MP) with a flat surface. Manufacturing is carried out by spreading thin layers of powder (typically between 10 and 100 µm thick) one on top of the other, with a selective consolidation step of the material between each layer deposition. Selective consolidation is performed, for example, with one or more laser beams, with an electron beam, by laser sintering, or by binder spraying. Consolidation refers to the process of making the material rigid by bonding the powder particles together.

[0097] A second method, called LDED (mentioned above), consists of generating a jet of powder directly melted by the laser to fabricate the sample. The LDED method typically uses spot diameters between 200 pm and 1 mm.

[0098] According to another aspect, the invention relates to a method 200 for manufacturing a metallic SAM sample and treating the surface of this sample, comprising a manufacturing step ETAf of said sample by an additive manufacturing technology, which consolidates a metal powder. The method also includes a treatment step ETAt implementing the method 100 according to the invention described above.

[0099] According to one embodiment, the additive manufacturing step ETAf of process 200 is carried out with an LBM manufacturing beam which is a laser beam, as illustrated in [Fig. 10].

[0100] Process 200 is compatible with the embodiment of process 100 incorporating a step of characterizing the sample produced and treated by scanning electron microscopy as described above. Optionally, the sample is also characterized before treatment.

[0101] According to one embodiment, the manufacturing and processing steps are carried out respectively with manufacturing laser beams (LBM) and processing laser beams (LBT) generated by the same continuous wave laser source. This is possible because the continuous power required for each step is of the same order of magnitude, and the spot size and / or scanning speed can be adapted for each step with the beam deflection device and, where applicable, the beam focusing device.

[0102] Thus, process 200 allows for both manufacturing and treatment using the same laser, without moving the sample. It also reduces the cost of surface treatment, which uses the same laser.

[0103] According to one embodiment, the additive manufacturing step is carried out by the laser powder bed fusion (LPBF) method. According to another embodiment, the additive manufacturing step is carried out by the laser direct energy deposition (LDED) method.

[0104] The LBM manufacturing laser beam has a manufacturing power Pf, and a manufacturing spot SF is defined at the moment the laser encounters the powder to consolidate it. The SF spot has a manufacturing diameter DSF. The spot moves across the powder with a manufacturing scan velocity vf. A point on the powder surface at the moment of consolidation experiences a manufacturing energy density Esf.

[0105] According to one embodiment, in order to obtain a more efficient surface treatment of the sample, the manufacturing diameter DSF is greater than or equal to the treatment diameter DST.

[0106] DSF > DST (2)

[0107] According to one embodiment, in addition to condition (2), the fabrication power Pf, the fabrication diameter DSF and the fabrication scanning speed vf are determined such that:

[0108] Esf > x.Est (3)

[0109] with x < 1 having a positive value and a function of the material composing the sample.

[0110] Such conditions allow for a refinement of the microstructures, which leads to the improvement of the mechanical properties of the material.

[0111] Formula (3) is expressed as:

[0112] Pf / (vf.DSF) > x.Pt / (vt.DST)

[0113] Performing the process with the same spot diameter for manufacturing and processing has the advantage of simplifying the implementation of process 200 because it is not necessary to change the optical settings between the two steps. In this case, typically with spots between 40 and 90 pm (only possible with the LPBF method) and without changing the laser power, condition (2) is satisfied by adapting the scanning speeds.

[0114] According to another aspect the invention relates to an additive manufacturing and surface treatment system 10, configured to manufacture a SAM sample in metallic or ceramic MM material, and to treat the surface S of the SAM sample, as schematically shown in [Fig. 11].

[0115] The system comprises a laser source LS configured to generate a continuous wave laser beam with adjustable power to generate, on a given surface, a so-called manufacturing power Pf or a so-called processing power Pt. It also comprises a device for positioning a metal powder PPD in a manner adapted to the laser beam. This could be, for example, a nozzle and associated elements for implementing the LDED method, or a set of trays with a device for implementing the LPBF method.

[0116] System 10 also includes:

[0117] a DFOC focusing device configured to focus the laser beam onto the powder according to a manufacturing spot SF having a manufacturing diameter DSF, and to focus the laser beam onto the surface S of the sample once manufactured according to a processing spot having a processing diameter DST less than or equal to 100 pm,

[0118] a scanning device DS configured to move the manufacturing spot SF over the powder to manufacture the sample, with a manufacturing scanning speed vf, and to move the processing spot ST over the surface S of the sample, once the sample has been manufactured, with a processing scanning speed vt.

[0119] Finally, the system 10 includes an enclosure E configured to ensure an inert atmosphere or vacuum around the sample during processing. According to one embodiment, the sample is moved into the enclosure after fabrication, which takes place outside the enclosure. According to another embodiment illustrated in [Fig. 11], fabrication also takes place within the enclosure E.

[0120] The laser source LS, the scanning device DS and the focusing device DFOC are further configured such that: • During manufacturing, the manufacturing power Pf, the manufacturing diameter DSF, and the manufacturing scan speed vf are determined. in order to induce consolidation of the powder so that the sample can be manufactured by additive manufacturing, • During processing, the processing power Pt, the processing diameter DST and the processing scan speed vt are determined so that a point on the sample surface receives a processing surface energy density Est determined so that the material MM of the sample at that point reaches a melting temperature.

[0121] System 10 thus enables the manufacture and post-manufacturing treatment of the sample with the same laser source, guaranteeing speed and reduced processing costs.

[0122] According to an embodiment not shown, the system 10 comprises a COL device and a Det detector as described above.

Claims

Demands

1. A method for manufacturing a sample (SAM) of metallic or ceramic material (MM) and for treating (100) a surface (S) of said sample, comprising: • a manufacturing step (ETAf) of said sample by an additive manufacturing technology, carried out with a continuous wave manufacturing laser beam (LBM), • a treatment step (ETAt) consisting of scanning said surface (S) to be treated with a continuous wave laser beam called the processing laser beam (LBT) having a processing power (Pt) and a processing spot (ST) on said surface, the processing spot having a diameter (DST) called the processing diameter, said processing spot moving at a scanning speed (vt) called the processing speed on said surface, - the processing diameter (DST) being less than or equal to 100 pm, - the processing power (Pt),the processing diameter (DST) and the processing scan speed (vt) being determined such that a point on the surface of said sample receives a surface energy density (Est) determined such that the material (MM) of the sample at that point reaches a melting temperature, • the manufacturing step and the processing step being carried out under an inert atmosphere or under vacuum in the same enclosure, • the manufacturing laser beam (LBM) and the processing laser beam (LBT) being generated by the same continuous wave laser source.

2. A manufacturing and processing method according to the preceding claim, wherein, during the processing step, the scanning is configured so that there is an overlap of at least 50% between the two processing spots associated with two adjacent scanning trajectories.

3. A manufacturing and processing method according to any one of the preceding claims comprising a characterization step (ETAc) of the sample with a scanning microscope implemented after the processing step, the characterization being carried out without removing the sample from the inert atmosphere or under vacuum.

4. A manufacturing and processing method according to any one of the preceding claims, wherein the additive manufacturing step is carried out by the laser powder bed fusion (LPBF) method.

5. A manufacturing and processing method according to any one of claims 1 to 3 wherein the additive manufacturing step is carried out by the laser direct energy deposition (LDED) method.

6. A manufacturing and processing method according to any one of the preceding claims wherein the manufacturing laser beam (LBM) has a manufacturing spot (SF) having a manufacturing diameter (DSF), the manufacturing diameter (DSF) being greater than or equal to the processing diameter (DST).

7. Additive manufacturing and surface treatment system (10) configured to fabricate a sample (SAM) of metallic or ceramic material (MM) and to treat a surface of said sample, said system comprising: - a laser source (LS) configured to generate a continuous wave laser beam having an adjustable power so as to generate on a determined surface a so-called manufacturing power (Pf) or a so-called processing power (Pt), - a positioning device (PPD) of a metallic powder adapted with respect to said laser beam, - a focusing device (DFOC) configured to focus the laser beam on said powder with a manufacturing spot (SF) having a manufacturing diameter (DSF), and to focus the laser beam on the surface of said sample once fabricated with a processing spot (ST) having a processing diameter (DST) less than or equal to 100 pm,- a scanning device (DS) configured to move the manufacturing spot over said powder to manufacture said sample, with a manufacturing scanning speed (vf), and to move the processing spot over said surface (S) of said sample, once the sample has been manufactured, with a processing scanning speed (vt), - an enclosure (E) configured to ensure an inert atmosphere or vacuum around the sample and including a viewing window (H), - the laser source (LS), the scanning device (DS) and the focusing device (DFOC) being configured so that: • during manufacturing, the manufacturing power (Pf), the manufacturing diameter (DSF) and the manufacturing scanning speed (vf) are determined so as to cause consolidation of said powder in order to manufacture the sample by additive manufacturing, • during processing, the processing power (Pt), the processing diameter (DST) and the processing scanning speed (vt) are determined so that a point on the surface of said sample receives a determined surface energy density (Est) such that the material (MM) of the sample at that point reaches a melting temperature.

8. Additive manufacturing and surface treatment system (10) according to the preceding claim further comprising: -a device (COL) configured to generate an electron beam (FE) and to focus the electron beam on the sample, -at least one detector (Det) configured to detect electrons from the sample, -the device for generating the electron beam and the detector being arranged with the enclosure to form a scanning electron microscope (SEM).

9. Additive manufacturing and processing system according to any one of claims 7 or 8 wherein the manufacturing diameter (DSF) is greater than or equal to the processing diameter (DST).

10. A manufacturing and processing system according to any one of claims 7 to 9 wherein the laser source, scanning device and focusing device are arranged in a housing (BT), the system further comprising a coupling piece (PA) configured to interface the housing and the enclosure.

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