Method for surface treatment of metals or ceramics with a continuous wave laser beam and associated system

Abstract

The invention relates to a method (100) for treating 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 such that a point on the surface of said sample receives a treatment surface energy density (Est) determined such that the material (MM) of the sample at this point reaches a melting temperature,the treatment process being 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 methods for treating the surface of metals or ceramics with a view to improving their physical properties. More particularly, the invention relates to treatment methods using a continuous wave laser. STATE OF THE ART

[0002] Surface treatment methods for metals, alloys or ceramics are known from the state of the art. For example, these treatments seek to improve resistance, or to obtain ductility and a fatigue limit greater than those of the "raw" material (i.e. before treatment).

[0003] These materials are characterized by microstructures, and the aim is to design microstructures that exhibit higher strength, ductility, and fatigue limit than is currently possible, while reducing energy and material consumption.

[0004] The advent of 3D printing of metals, or additive manufacturing, makes it possible to produce parts manufactured with microstructures that exhibit unprecedented strengths 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] At the root of the strength-ductility trade-off lies the hierarchical microstructure resulting from the highly unbalanced processes that occur during the additive manufacturing process. The heat-material interaction induced by the dynamics of the melt pool, rapid solidification and thermal cycling in the solid state result in a microstructure with physical and chemical heterogeneities ranging from a few tens of nanometers to several hundred micrometers. The main contribution to the strength of the material 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 treatment) has a crystallographic grain structure, and in each grain there are a multitude of smaller dislocation structures. A dislocation is a linear-type crystal defect that occurs due to a missing atomic plane. A microsegregation cell has cell walls that have a higher concentration of one or more elements than in the interior of the cell.

[0007] As a general rule, it is known that the smaller (higher) the size (and density) of these micro-segregation cells / dislocation structures, the higher the strength 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 toward equilibrium by minimizing stored energy. However, this process inadvertently results in an increase in cell / structure size and a decrease in density, which inevitably results in a decrease in strength.

[0009] Furthermore, the fatigue response of dense parts (negligible amount of porosities / 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 mainly due to nucleation (if not already present) and propagation of surface cracks.

[0010] The fatigue response of manufactured parts can be improved by post-manufacturing surface treatments, the most common of which are mechanical in nature (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, of the order of 500 pm to a few mm, available industrially. 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 performance 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] An aim of the present invention is to remedy the aforementioned drawbacks by proposing a method for surface treatment of samples made of metallic or ceramic material using a continuous wave laser, allowing the significant and simultaneous improvement of several physical properties of the treated sample. DESCRIPTION OF THE INVENTION

[0014] The subject of the present invention is a method for treating a 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 called a treatment laser beam having a treatment power and a treatment spot on said surface, the treatment spot having a diameter called treatment, said treatment spot moving at a so-called treatment scanning speed on said surface, • the treatment diameter being less than or equal to 100 pm, • the processing power, the processing diameter and the processing scanning speed being determined so that a point on the surface of said sample receives a determined surface energy density of processing so that the material of the sample at this 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 method according to the invention comprises a step of characterizing the sample with a scanning microscope implemented after the treatment step, the characterization taking place without removing the sample from the inert atmosphere or under vacuum.

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

[0018] According to one embodiment, the manufacturing and treatment 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 comprises 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 method of laser melting of a powder bed.

[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 laser energy deposition method.

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

[0023] According to one 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, the manufacturing diameter and the manufacturing scanning speed are determined so 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 depending on 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 treatment beam having a treatment power, • a focusing device configured to focus the treatment laser beam on 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 on said surface of said sample with a treatment scanning speed, • an enclosure configured to provide an inert atmosphere or vacuum around the sample and including a porthole, • the treatment power, the treatment diameter and the treatment scanning speed being determined so that a point on the surface of said sample receives a determined surface energy density of treatment so that the material of the sample at this 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 part configured to interface the housing and the enclosure.

[0027] According to one embodiment of the processing system according to the invention, the latter 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 made of 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 having an adjustable power so as to generate on a given surface a so-called manufacturing power or a so-called processing power, • a device for positioning a metal powder in a suitable manner relative to said laser beam, • a focusing device configured to focus the laser beam on said powder with a manufacturing spot having a manufacturing diameter, and to focus the laser beam on the surface of said sample once manufactured with a treatment spot having a treatment 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 provide an inert atmosphere or vacuum around the sample and including a porthole, • the laser source, the scanning device and the focusing device being configured so that: • during manufacturing, the manufacturing power, the manufacturing diameter and the manufacturing scanning speed are determined so as to cause consolidation of said powder in order to manufacture the sample by additive manufacturing, • during processing, the processing power, the processing diameter and the processing scanning speed are determined so that a point on the surface of said sample receives a determined surface energy density of processing so that the material of the sample at this point reaches a melting temperature.

[0029] According to one embodiment of the additive manufacturing and surface treatment system according to the invention, the latter 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 system for additive manufacturing of a sample and treatment of 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 system for additive manufacturing of a sample and treatment of 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 depending on the metallic or ceramic material.

[0032] The following description presents several exemplary embodiments of the device of the invention; these examples are not limiting of the scope of the invention. These exemplary embodiments present both the essential characteristics of the invention as well as additional characteristics linked to the embodiments considered.

[0033] The invention will be better understood and other characteristics, aims and advantages thereof will appear during the detailed description which follows and with reference to the appended drawings given as non-limiting examples and in which:

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

[0035] [Fig.2] illustrates an image with a transmission electron microscope of the same area of ​​the sample after application of the method according to the invention.

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

[0037] [Fig.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] [Fig.6] illustrates a sample seen in profile before the application of the method according to the invention.

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

[0041] [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 part.

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

[0044] [Fig. 10] illustrates an embodiment of the method 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 in a non-limiting manner 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 thus suitable for all these types of sample.

[0047] The implementation of the method 100 according to the invention is the result of a significant set of observations and experiments. The inventors noted that the state-of-the-art continuous laser-based surface treatments used a spot size on the surface of the sample typically greater than 500 μm, with smaller diameter spots being used only for the additive manufacturing of the samples. The inventors demonstrated that the use of a small diameter spot, less than 100 μm, associated with appropriate scanning parameters, is likely to 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 SAM sample made of metallic or ceramic material (called 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 called the treatment laser beam LBT. The treatment laser beam has a power Pt and a spot ST called the treatment spot on the surface S, the treatment spot ST having a diameter called the treatment diameter DST. The spot ST moves at a scanning speed called the treatment speed vt on 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 μm. 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 achieve the improvement of the material properties. It is appropriate that the power Pt, the DST diameter of the treatment spot ST and the treatment scanning speed vt are determined so that a point on the sample surface receives a surface energy density of treatment Is determined so that the MM material of the sample at this point, illuminated by the moving laser beam, reaches the melting temperature.

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

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

[0053] In other words, the energy Est should 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. In addition, 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 speed, after the material of the sample MM has melted. Indeed, when the treatment spot is wider, it takes longer to release the energy provided by the laser and the cooling speed decreases.

[0055] And it has also been established that the higher the cooling rate, the smaller the dislocation structures that reform. By applying the treatment according to the invention, structures are obtained that are smaller than initially, and denser. In addition, during solidification after fusion, the dendrites that form in the material have microsegregation cells that are smaller than initially.

[0056] Another advantage of the method according to the invention has been revealed: the roughness of the treated surface is reduced, which improves the fatigue response of the material. This is particularly true for metal samples produced by additive manufacturing based on metal powder. These samples have residual powder sintered on the surface after their manufacture, causing an increase in roughness. Due to the melting which takes place on the surface of the sample, the method according to the invention allows the melting and subsequent solidification of these residual powders (see below).

[0057] In order to avoid, during melting, the penetration of unwanted atoms or molecules present in the environment of the sample, the method 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 into the molten material. Indeed, certain atoms or molecules injected into the sample are likely to modify its properties, by degrading them. The method according to the invention is a universal surface treatment method which 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 inert atmosphere the sample is positioned in an enclosure.

[0058] For a certain effectiveness of the treatment according to the invention it is sought that fusion is 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 metal (pure or alloy) or ceramic sample manufactured by other methods.

[0060] In order to illustrate the physical reasoning and the results obtained with the method according to the invention, an E316L sample 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 made using the laser direct energy deposition (LDED) method. The laser used to manufacture 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 surface energy density Esf received by the sample of 10.7 J / mm2 (formula (1)).

[0062] [Fig. 1] illustrates an image obtained with a transmission electron microscope (or TEM) of the surface of an area of ​​the walls of the E316L sample before the 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 the dislocation structures. [Fig. 2] illustrates a TEM image of the same area of ​​the surface after the application of the method according to the invention. It can be seen that the dark areas are denser and smaller in size on the treated sample.

[0063] [Fig. 3] illustrates an energy dispersive X-ray spectroscopy image of an area of ​​the E316L sample before treatment, and [Fig. 4] illustrates a similar image of the same area of ​​the surface, after application of the method according to the invention. The contrast has been amplified to better reveal the light and dark areas. Energy dispersive X-ray spectroscopy makes it possible to identify the areas in which atoms of a specific species, here chromium, are accumulated. The light areas illustrate the aforementioned microsegregation cells. It can be seen that these cells are denser and smaller after treatment. This same effect is obtained for iron, nickel, molybdenum, manganese, silicon, etc., also present in the sample.

[0064] The light areas 11 and 22 visible respectively in Figures 1 and 2 and the dark areas 33 and 44 respectively in Figures 3 and 4 correspond to microsegregation cells seen from above. The cells are formed when the metal liquefied by fusion. They are separated by dislocation structures 12 and 23 in dark respectively in figures 1 and 2, and we also observe chemical segregation between the cells, light zones 34 and 45 respectively in figures 3 and 4 for chromium.

[0065] When the cooling rate increases, the size of the microsegregation cells decreases, and thus with the method according to the invention a very clear reduction in the size of the dislocation structures and the microsegregation cells of the treated sample is obtained. 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 characteristics strengthen the material.

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

[0068] Q = m.AHf

[0069] with Q energy to be supplied to obtain fusion, m mass of the sample and AHf latent heat of fusion. The transition from this volumetric formula to the surface energy Estmin to be supplied for a sample of given shape (surface and thickness) is not easy analytically.

[0070] From a sufficiently small spot size, i.e. less than or equal to 100 pm, the power Pt and the speed vt must be determined so as to obtain melting of the material at least at 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 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. In parentheses is indicated the corresponding surface energy density Est, in J per mm2 . [Fig.5] illustrates a transverse 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 with respect 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 produced by backscattered electron imaging, or BSE (for "back scattered electrons" in English). It is easily identified in [Fig.5] A that the energy is not high enough to cause fusion, the sample is not impacted by the passage of the laser. In [Fig.5] B we see that the laser penetrated the sample in a zone 50, to a maximum depth pmax of approximately 10 pm and caused a local melting inducing a change in the microstructure of the sample. Zone 51 was not impacted by the passage of the beam, zones 50 and 51 being separated by an interface 52 illustrating the boundary between a zone (50) in which the melting temperature was reached and a zone (51) in which the melting did not take place.

[0074] The elementary characteristics are smaller in the zone 50 having been in fusion. In C the laser has penetrated more deeply (pmax of approximately 25 pm depth) and the volume of the zone 50 having entered into fusion is larger. With this experiment it is clearly seen that for this sample of stainless steel an energy Es of 0.4 J / mm2 is insufficient, whereas an energy Es of 1.6 J / mm2 is higher than the energy Estmin allowing a zone on the surface of the sample to exceed the fusion temperature. Thus the energies Es of 1.6 and 8 J / mm2 are compatible with the method according to the invention.

[0075] Consequently, to identify laser parameters suitable for implementing the method according to the invention for obtaining surface melting, it is appropriate to carry out preliminary experimental measurements with a sample of material and shape identical to that which is to be treated, or even with the sample to be treated itself, by varying at least one parameter among (Pt, vt, DST). A variation of the diameter is not necessary if it is also possible to vary Pt and / or vt, provided that it is less than 100 pm. A variation of Pt can be easily obtained because the lasers generally have adjustable power. A variation of vt is also easily accessible because the scanning devices generally have an adjustment of the speed value.The experimental identification of the presence (or not) of a melting on the surface 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 not) of a melting on the surface of the sample can be verified by means of the experiment described above.

[0076] Once a set of values ​​(DST0, Pt0, vt0) has been identified which allows the desired effect to be obtained (surface fusion), 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 a homogeneous treatment over the entire treated surface, 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. Thus, it is ensured that the entire volume of the sample up to pmax has melted, and a treated layer of homogeneous thickness is obtained. For example, with a spot of 60 μm in diameter, the parallel scanning tracks are preferably separated by a maximum distance of 30 μm.

[0078] The E316L sample was characterized in order 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, i.e. a surface treatment energy density:

[0079] Est = 11.7 J / mm2.

[0080] The treatment is carried out under vacuum. The scanning was carried out with 50% overlap.

[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 passage of the laser. An increase of about 9% in the ductility of the sample after treatment was even measured. Both the initial and treated samples fulfill the Considerer criterion, meaning that all microstructures reach their full deformation capacity before failure.

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

[0084] An Ao of 182 MPa was measured before treatment and Ao of 227 MPa after treatment, for a number of failure cycles N = 3,106, i.e. an increase of approximately 25% of the fatigue limit Ao.

[0085] Concerning the roughness, before the treatment a roughness (arithmetic mean height Sa) of 16.6 pm was measured, whereas after the treatment under the aforementioned conditions the roughness is 0.9 pm. The roughness of the treated surface is significantly better after the treatment. This is illustrated by figures 6 and 7 showing the sample seen in profile respectively before and after the aforementioned treatment. The contrast has been reinforced for better visibility. These images are images by secondary electron microscopy (called SE for "secondary electron"). In [Fig. 6] the upper white zones 60 are powder residues appearing during additive manufacturing. It can be seen in [Fig. 7] that the residual powder is compacted (zone 70) because it has fused. In addition the surface of the sample appears well smoothed compared to the surface of the sample in [Fig. 6]. We can see in [Fig.7] zone 71 corresponding 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. We can list in a non-exhaustive manner the elastic limit, the roughness and the fatigue resistance.

[0087] According to one embodiment, the treatment method according to the invention comprises a step of ETAc characterization of the sample with a scanning electron microscope (SEM), implemented at least after the treatment step. The characterization is carried out without removing the sample from the inert atmosphere or under vacuum, that is to say say by keeping the sample in the enclosure in which the treatment is carried out. The method 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, a 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 not yet published to date.

[0088] According to 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 treatment laser beam LBT having on the surface of the sample SAM a treatment power Pt. It also comprises a scanning device DS configured to move the treatment laser beam on the surface S of the sample, with the treatment scanning speed vt. It finally comprises a focusing device DFOC configured to focus (or defocus) the laser beam on the surface S of the sample so that the so-called treatment spot diameter DST is less than 100 pm.

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

[0090] Furthermore, 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 comprises a coupling part PA configured to interface the housing and the enclosure. The laser beam and the various optical elements which make up the focusing device are thus confined and protected.

[0092] [Fig. 9] illustrates an embodiment of the system 80 according to the invention making it possible to also carry out a characterization of the sample, after the treatment and optionally before. The system 80 comprises a device COL configured to generate an electron beam FE and to focus the electron beam on the sample, and at least one detector Det configured to detect electrons from the sample. The device COL and the detector Det are arranged with the enclosure E to form a scanning electron microscope SEM.

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

[0094] The method 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] Metallic additive manufacturing consists of producing parts by successively adding (metallic) material, from a 3D digital file. The material is modeled by consolidating a metallic powder. The metallic material constituting the powder is, for example, chosen from: stainless steels, titanium-based alloys, aluminum-based alloys, nickel-based alloys, etc.

[0096] A first method called metallic additive manufacturing on a powder bed (or MAM-PB for "metallic additive manufacturing - powder bed" in English) is implemented from a powder bed. A powder bed PB is understood to mean a controlled thickness of MP powder having a flat surface. The manufacturing is carried out by spreading thin layers of powder (typically between 10 and 100 μm thick) one above the other, with a step of selective consolidation of the material between each layer deposit. Selective consolidation is carried out for example with one or more laser beams, with an electron beam, by laser sintering or by binder projection. Consolidation is understood to mean making the material rigid by binding 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 manufacture the sample. The LDED method conventionally 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 for treating the surface of this sample, comprising a step ETAf of manufacturing said sample by an additive manufacturing technology, which consolidates a metallic powder. The method also comprises a step ETAt of treatment implementing the method 100 according to the invention described previously.

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

[0100] The method 200 is compatible with the embodiment of the method 100 integrating a step of characterizing the sample manufactured and treated with an electron scanning microscope as described previously. Optionally, the sample is also characterized before treatment.

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

[0102] Thus, the method 200 allows the manufacturing and processing to be carried out with the same laser, without moving the sample. It also allows a reduction in 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 manufacturing laser beam LBM has a manufacturing power Pf, a manufacturing spot SF defined at the moment when the laser meets the powder to consolidate it, the spot SF having a manufacturing diameter DSF. The spot moves on the powder with a manufacturing scanning speed vf. A point on the surface of the powder at the time of consolidation sees a surface density of manufacturing energy 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 manufacturing power Pf, the manufacturing diameter DSF and the manufacturing scanning speed vf are determined so that:

[0108] Esf > x.Est (3)

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

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

[0111] Formula (3) is expressed by:

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

[0113] Carrying out the method with the same spot diameter for manufacturing and processing has the advantage of simplifying the implementation of the method 200 because it is not necessary to modify the optical adjustment between the two steps. In this case, typically with spots between 40 and 90 pm (only possible with the LPBF method) and without modifying the laser power, condition (2) is verified 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 made of material metallic or ceramic MM, and to treat the surface S of the SAM sample, as shown schematically in [Fig. 11].

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

[0116] The system 10 also comprises:

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

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

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

[0120] The laser source LS, the scanning device DS and the focusing device DFOC are further 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 the powder in order to manufacture the sample 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 Is determined so that the material MM of the sample at this point reaches a melting temperature.

[0121] The system 10 thus allows the manufacturing and post-manufacturing processing of the sample with the same laser source, guaranteeing speed and reduction of processing costs.

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

Claims

Claims

1. 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 pm, • 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 treatment surface energy density (Est) determined so that the material (MM) of the sample at this point reaches a melting temperature, • the treatment process being carried out under an inert atmosphere or under vacuum.,

2. Treatment method according to the preceding claim in which 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.

3. Treatment method according to one of the preceding claims comprising a step of characterization (ETAc) of the sample with a scanning microscope implemented after the treatment step, the characterization taking place without removing the sample from the inert atmosphere or under vacuum.

4. Method (200) for manufacturing said sample from metallic or ceramic material and for treating the surface of said sample comprising: • a manufacturing step (ETAf) of said sample by an additive manufacturing technology, • a treatment step (ETAt) according to one of claims 1 or 2.

5. Method (200) of manufacturing and treatment according to the preceding claim further comprising a characterization step according to claim 3.

6. Manufacturing and processing method according to one of claims 4 or 5 in which the additive manufacturing step is carried out with a manufacturing beam (LBM) which is a laser beam.

7. Manufacturing and processing method according to the preceding claim in which the additive manufacturing step is carried out by the laser powder bed fusion (LPBF) method.

8. A manufacturing and processing method according to claim 6 wherein the additive manufacturing step is carried out by the laser direct energy deposition (LDED) method.

9. Manufacturing and processing method according to one of claims 6 to 8 in which 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).

10. A manufacturing and processing method according to the preceding claim wherein the manufacturing laser beam (LBM) has a manufacturing power (Pf) and a manufacturing scanning speed (vf), and wherein the manufacturing power (Pf), the manufacturing diameter (DSF) and the manufacturing scanning speed (vf) are determined such that a manufacturing surface energy density (Esf) is greater than or equal to x times the processing surface energy density (Est), with x < 1 having a positive value and depending on the metallic or ceramic material.

11. Method according to one of claims 6 to 10 in which the manufacturing laser beam (LBM) and the treatment laser beam (LBT) are generated by the same continuous wave laser source.

12. Treatment system (80) configured to treat a surface (S) of a sample (SAM) made of metallic or ceramic material (MM), comprising: • a laser source (LS) configured to generate a continuous wave laser beam called treatment (LBT) having a treatment power (Pt), • a focusing device (DFOC) configured to focus the treatment laser beam on the surface of said sample according to a so-called treatment spot (ST) having a treatment diameter (DST) less than or equal to 100 pm, • a scanning device (DS) configured to move the treatment spot on said surface (S) of said sample with a treatment scanning speed (vt), • an enclosure (E) configured to ensure an inert atmosphere or vacuum around the sample and comprising a window (H), • 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 treatment surface energy density (Est) determined so that the material (MM) of the sample at this point reaches a melting temperature.

13. Processing system (80) according to the preceding claim wherein the laser source, the scanning device and the focusing device are arranged in a housing (BT), the system further comprising a coupling part (PA) configured to interface the housing and the enclosure.

14. Processing system (80) 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).

15. Additive manufacturing and surface treatment system (10) configured to manufacture 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 given surface a so-called manufacturing power (Pf) or a so-called treatment power (Pt), a positioning device (PPD) of a metal powder in a suitable manner relative 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 manufactured with a treatment spot (ST) having a treatment diameter (DST) less than or equal to 100 pm, a scanning device (DS) configured to move the manufacturing spot on said powder to manufacture said sample, with a manufacturing scanning speed (vf), and to move the treatment spot on said surface (S) of said sample,once the sample is manufactured, with a processing scan speed (vt), an enclosure (E) configured to provide an inert atmosphere or vacuum around the sample and including a 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 treatment, the treatment power (Pt), the treatment diameter (DST) and the treatment scanning speed (vt) are determined so that a point on the surface of said sample receives a treatment surface energy density (Est) determined so that the material (MM) of the sample at this point reaches a melting temperature.

16. 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).

17. System for additive manufacturing of a sample and treatment of a surface of said sample according to one of claims 15 or 16 in which the manufacturing diameter (DSF) is greater than or equal to the treatment diameter (DST).

18. System for additive manufacturing of a sample and treatment of a surface of said sample according to the preceding claim in which the laser source, the scanning device and the focusing device are further configured so that a surface energy density of manufacture (Esf) is greater than or equal to x times a surface energy density of treatment (Est), with x < 1 having a positive value and depending on the metallic or ceramic material.

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