Method for producing a metal part comprising a luminescent optical marking

Abstract

The present invention relates to a method for producing a metal part from a metal alloy powder, the metal part comprising a luminescent optical marking. This method comprises the following consecutive steps (a) to (c): (a) preparing a first mixture in the form of a powder, the mixture comprising: - at least one first oxide of one or more metals chosen from among Li, K, Mg, Ca, Sr, Ba, Sc, Y, La, Lu, Ti, Zr, Hf, V, Nb, Ta, Zn, Cd, B, Al, Ga, Si and Ge; and - at least one precursor of a luminescent cation added in the form of a second metal oxide; (b) preparing a second mixture comprising the metal alloy powder and the first mixture; and (c) transforming the second mixture via additive manufacturing, thereby forming a luminescent optical marking layer.

Description

[0001]Description Title: Method for manufacturing a metal part comprising a luminescent optical marking TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for manufacturing a metal part, in particular a steel part, comprising a luminescent optical marking. The method according to the invention makes it possible to manufacture metal parts characterized by a luminescent optical marking which is unique, complex, non-reproducible and which, when incorporated into the part, is non-degradable and, therefore, permanent. The metal parts manufactured by the method according to the invention thus have the advantage of being able to be easily identified and traced, whether in the context of procedures for monitoring and controlling the quality of these parts or in the context of the fight against counterfeiting.The present invention finds applications in particular in many industrial sectors and, in particular, in the nuclear, automotive, aeronautics, railway, luxury and food sectors. STATE OF THE ART Traditionally, in industry, the traceability of metal parts is carried out by methods such as labeling, engraving (for example, by micro-percussion) or marking which can be inkjet marking, laser marking or even luminescent marking. Manufacturers thus have the choice of marking their metal parts with a marking that can be read by everyone or with a codified marking, for example with two-dimensional bar codes such as QR codes or Data Matrix codes.However, these different markings all have a certain number of limitations insofar as they are generally made on the surface of metal parts, as in document DE 102014117519 A1 for example. These surface markings can therefore deteriorate over time. In addition, these markings are more or less easily reproducible. Furthermore, the manufacturing processes for marked metal parts implement one or more additional steps necessary to produce such markings.The aim of the present invention is, consequently, to overcome the drawbacks of the methods for manufacturing marked metal parts of the prior art and to propose a method for manufacturing a metal part comprising a particular marking, in this case a luminescent optical marking, this luminescent optical marking being unique, non-reproducible, or even permanent, this method not necessarily requiring the implementation of additional steps to obtain this particular marking. Documents CN 113231649 A, CN 114559046 A, CN 115625345 A, CN 110711862 A, CN 110735065 A and CN 115846927 A describe methods for preparing, by additive manufacturing, materials from powders of metal alloys and metal oxides.STATEMENT OF THE INVENTION The aims stated above and others are achieved by a method of manufacturing a metal part from a metal alloy powder, said metal part comprising a luminescent optical marking.According to the invention, the method comprises the following successive steps (a) to (c): (a) preparing a first mixture in the form of a powder and comprising: - at least one first oxide of one or more metals chosen from Li, K, Mg, Ca, Sr, Ba, Sc, Y, La, Lu, Ti, Zr, Hf, V, Nb, Ta, Zn, Cd, B, Al, Ga, Si and Ge, and - at least one precursor of a luminescent cation, this precursor being introduced in the form of a second metal oxide; (b) preparing a second mixture comprising the metal alloy powder and the first mixture, and (c) transforming the second mixture obtained at the end of step (b) by additive manufacturing, whereby the formation of a luminescent optical marking layer is obtained.The method according to the invention makes it possible to manufacture a metal part comprising a luminescent optical marking which is obtained by implementing a step (c) of transformation, by additive manufacturing, of the second specific mixture formed by a mixture of powders resulting from steps (a) and (b) of the method of the invention. More particularly, during step (c) of the method according to the invention, luminescent precipitates are formed in situ from the first non-luminescent metal oxide(s) and the second metal oxide(s) which form the first mixture, by interaction of these first and second metal oxides with each other and / or with the metal matrix formed from the metal alloy powder.These interactions between the first and second metal oxides and the metal matrix, under these high-temperature processing conditions which are implemented in step (c) of additive manufacturing and which allow the complete fusion of these first and second metal oxides and the metal matrix, generate a multitude of phases formed from the first metal oxide(s) and doped with the luminescent cation(s) present in the second metal oxide(s) which make the corresponding precipitations luminescent. Since the precipitations and their doping by this (these) cation(s) are not controlled, the signals emitted by the luminescent precipitates thus formed in situ are random and non-reproducible.In doing so, the metal part manufactured by the method according to the invention is characterized by a unique, complex and non-reproducible luminescent optical marking (or signature), allowing its identification as well as its traceability. In addition, by incorporating one or more first non-luminescent metal oxides as precursor compounds of these luminescent precipitates, the method according to the invention presents a real economic and environmental interest compared to a method which would use, as starting compounds, luminescent or luminophore compounds; in particular, the steps of synthesis of such luminescent or luminophore compounds are eliminated. Furthermore, the fact of incorporating these first metal oxides, and not luminophore compounds as such, makes it possible to obtain uncontrolled precipitations of luminescent phases and, therefore, numerous random and non-reproducible signals.On the contrary, the incorporation of phosphor compounds as starting materials would greatly reduce the number of random signals. The method according to the invention comprises steps (a) to (c) mentioned above and detailed below. During step (a) of the manufacturing method according to the invention, a first mixture is prepared which is in the form of a powder and which comprises at least one first metal oxide and at least one second metal oxide. The expression "first metal oxide(s)" should be understood to mean that it can be a simple metal oxide, i.e. an oxide of a single metal, or a mixed metal oxide, i.e. an oxide of two or more metals. This first mixture may comprise only one first metal oxide or, on the contrary, may comprise a mixture of two, three, or even more first metal oxides.The metal(s) of the first metal oxide(s) are chosen from Li, K, Mg, Ca, Sr, Ba, Sc, Y, La, Lu, Ti, Zr, Hf, V, Nb, Ta, Zn, Cd, B, Al, Ga, Si and Ge. When the first metal oxide(s) are simple metal oxides, they may in particular be chosen from Li2O, K2O, MgO, CaO, SrO, BaO, Sc2O3, Y2O3, La2O3, Lu2O3, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, ZnO, CdO, B2O3, Al2O3, Ga2O3, SiO2 and GeO2. In an advantageous embodiment of the method according to the invention, the first mixture comprises Y2O3 and Al2O3. When the first metal oxide(s) are mixed metal oxides, they may in particular be chosen from Y3Al5O12, YAlO3, Y4Al2O9, Sr4Al2O7, Sr3Al2O6, SrAl2O4, SrAl4O7 and Sr4Al. 12 O 19. The fact of implementing several of these first metal oxides makes it possible to further complicate the luminescent signal and the generation of random signals of the luminescent optical marking which will be obtained at the end of the manufacturing process according to the invention. Indeed, by multiplying the number of first metal oxides present in the first mixture, the number of precipitated phases which can then be doped by the luminescent cation(s) is multiplied and, therefore, the number of associated thermodynamic systems which will be formed. For example, when the first mixture comprises Al2O3 and Y2O3 as first metal oxides, the Y3Al5O phases 12, YAlO3 and Y4Al2O9 will be formed in situ during step (c) of additive manufacturing. It should be noted that one can choose to form all or part of the phases in situ by introducing the first corresponding precursor metal oxides and / or to introduce all or part of these phases which will have been previously formed (for example by other synthesis techniques such as solid state synthesis), in the form of first metal oxide(s). As examples, one can form the phases Y3Al5O 12, YAlO3 and Y4Al2O9 in situ from the first metal oxides Al2O3 and Y2O3 and / or introducing, into the first mixture, the first metal oxides Y3Al5O12, YAlO3 and Y4Al2O9. When the first mixture comprises SrO, Al2O3 and Y2O3 as first metal oxides, the phases of the Y2O3-Al2O3 system (namely Y3Al5O12, YAlO3 and Y4Al2O9) as well as the phases of the SrO-Al2O3 system (namely Sr4Al2O7, Sr3Al2O6, SrAl2O4, SrAl4O7 and Sr4Al12O19) will be formed in situ during the additive manufacturing step (c). The use of ZrO2, La2O3, Y2O3 and Al2O3 as first metal oxides also allows for the formation of several in situ phases during step (c) of additive manufacturing. Similarly, the first mixture may comprise only one second metal oxide or, on the contrary, may comprise a mixture of two, three, or even more second metal oxides.This or these second metal oxides are these precursor compounds of one or more luminescent cations. During step (c), the luminescent cations, which are well known to those skilled in the art, will dope in situ the precipitated phases formed from the first metal oxide(s) described above. This doping is obtained by substituting the luminescent cation(s) for one or more cations of the phases formed from the metal oxide or the mixture of metal oxides. To be able to substitute itself in the metal oxide or the mixture of metal oxides, the luminescent cation must have an atomic size close to that of the cation(s) it replaces. For example in the case of the phosphor Y3Al5O. 12 :This 3+ , the Ce 3+ has an atomic radius close to Y 3+ and will substitute in the dodecahedral sites of the latter. When we have Cr as dopant 3+ (e.g. Y3Al5O 12 :This 3+ , Cr 3+), the Cr 3+ will substitute on the octahedral sites of Al 3+ due to their close atomic radii. In a particular embodiment of the method according to the invention, the luminescent cation(s) are chosen from In + , Sn 2+ , Pb 2+ , Sb 3+ , Bi 3+ , This 3+ , This 4+ , Pr 3+ , Nd 3+ , Sm 2+ , and To + . Thus, the second metal oxide(s) may in particular be chosen from In2O, PbO, Sb2O3, Bi2O3, Ce2O3, CeO2, Pr2O3, Nd2O3, SmO, Sm2O3, EuO, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, TmO, Tm2O3, YbO, Yb2O3, Ti2O3, VO, V2O3, VO2, Cr2O3, CrO2, MnO, Mn2O3, MnO2, Fe2O3, FeO2, Fe2O5, Co2O3, CoO2, NiO, Cu2O, RuO, Ru2O3, PdO, Ag2O, Ir2O3, PtO and Au2O. It is noteworthy that some of these second metal oxides, such as Eu2O3 which is a precursor of the luminescent cation Eu 3+, may have luminescence properties. In a preferred embodiment, the second metal oxide(s) are chosen from CeO2, Cr2O3 and Eu2O3. In a variant of the method according to the invention, the first mixture comprises: - at least 90% by mass of the first metal oxide(s), and - up to 10% by mass, in particular at least 0.1% by mass and up to 10% by mass, of the second metal oxide(s). Of course, there is nothing to prevent the introduction of less than 0.1% by mass of the second metal oxide(s) into the first mixture. However, the luminescent optical marking could be less easily detectable in the metal part. In an advantageous variant of the method according to the invention, the first mixture comprises: - between 95% by mass and 99.5% by mass of the first metal oxide(s), and - between 0.5% by mass and 5% by mass of the second metal oxide(s).In a preferred variant of the method according to the invention, the first mixture comprises: - between 97% mass and 99% mass of the first metal oxide(s), and - between 1% mass and 3% mass of the second metal oxide(s). It is specified that the expressions "from ... to ...", "ranging from ... to ..." and "between ... and ...", which are used in the present description to define an interval must be understood as defining not only the values ​​of the interval, but also the values ​​of the limits of this interval. In a more particularly preferred embodiment of the method according to the invention, the first mixture comprises Y2O3, Al2O3 and CeO2. In an advantageous variant, this first mixture comprises: - from 30% mass to 85% mass of Y2O3, - from 15% mass to 70% mass of Al2O3, and - from 0.1% mass to 10% mass, advantageously from 0.5% mass to 5% mass and, preferably, from 1% mass to 3% mass of CeO2.During step (a) of the method according to the invention, the first metal oxide(s) and the second metal oxide(s) are ground and / or mixed using any conventional technique making it possible to obtain a first mixture in the form of a powder, this powder preferably being as homogeneous as possible. Among these conventional techniques, mention may in particular be made of grinding techniques, for example using an attritor (or attrition mill), and mixing techniques, in particular using a pestle, a mortar, a mixer or a stirrer such as a Turbula® three-dimensional stirrer. At the end of step (a), a powder of metal oxides is obtained comprising one or more first metal oxides and one or more second metal oxides. The particles forming the powder of the first mixture may be of either irregular or regular shape, for example spherical.In a particular embodiment, the powder of the first mixture is formed from particles having an average particle size of between 1 µm and 5 µm. During step (b) of the manufacturing method according to the invention, a second mixture is prepared which comprises the powder of the metal alloy used to manufacture the metal part, and the first mixture. In a particular embodiment, the second mixture comprises: - from 0.1% mass to 20% mass of the first mixture, and - from 80% mass to 99.9% mass of the metal alloy powder. In an advantageous embodiment, the second mixture comprises: - from 0.5% mass to 15% mass of the first mixture, and - from 85% mass to 99.5% mass of the metal alloy powder. In an advantageous embodiment, the second mixture comprises: - from 1% mass to 10% mass of the first mixture, and - from 90% mass to 99% mass of the metal alloy powder.The metal alloy of the metal alloy powder may be selected from iron alloys, aluminum alloys, titanium alloys, nickel alloys, copper alloys, and steels. According to one variant, the metal alloy forming the metal alloy powder does not comprise any precursor element of luminescent cation(s). According to another variant which is preferred, the metal alloy forming the metal alloy powder comprises one or more precursor elements of luminescent cations. However, and although in this variant the metal alloy contains precursors of luminescent cations which will subsequently serve as luminescent cations in the precipitated phases, the metal alloy powder is not luminescent. In a particular embodiment, the steels are stainless steels, i.e. steels which comprise Cr, an element which, as indicated previously, is a precursor of the luminescent Cr cations.3+ and Cr 4+. In an advantageous embodiment, this steel is an austenitic steel, which can advantageously be chosen from 316L steel, 304L steel and 1.4404 steel. In a particular embodiment, the particles forming the metal alloy powder are spherical in shape. In a particular embodiment, this metal alloy powder is formed from particles having an average particle size of between 15 µm and 106 µm, so as to meet the characteristics of the powders used for implementing step (c) of transformation by additive manufacturing. More particularly, the particles forming this metal alloy powder have an average particle size of between 15 µm and 45 µm when step (c) is carried out by laser melting on a powder bed, and of between 45 µm and 106 µm when step (c) is carried out by laser melting of projected powder.The mixing of the metal alloy powder and the first mixture can be carried out by any conventional powder mixing technique such as those mentioned above (mixer, attritor or agitator). The second mixture obtained at the end of step (b), which is also in the form of a powder, is then subjected to a step (c) of transformation by additive manufacturing. This transformation step (c) is advantageously implemented by an additive manufacturing process which makes it possible to consolidate the material by a laser source or an electron beam.This additive transformation step (c) is typically carried out at temperatures that are greater than or equal to 2000°C, or even much higher than 2000°C to reach temperature values ​​at which the metal oxide phases doped with the luminescent cation(s) have completely melted and will then solidify to form the luminophores which are in the form of luminescent inclusions in the mass of the luminescent optical marking layer thus formed. Examples of luminophore compositions that can be formed in situ during the additive manufacturing transformation step (c) include: Of course, it will be necessary to select the first and second metal oxides present in the first mixture and, where appropriate, the metal alloy present in the second mixture according to the desired phosphor compositions. For example, with the first metal oxides Y2O3 and Al2O3 and the luminescent cations Ce 3+ and Cr 3+ at least one of which is present in the second metal oxide (the other may also be present or be present in the metal alloy), all or part of the phases of the Y2O3-Al2O3 system can be formed in situ with Ce doping 3+ and / or Cr 3+ and in particular the luminophores of the following compositions: Y3Al5O12:Ce 3+ , YAlO3:Ce 3+ , Y4Al2O9:Ce 3+ , ,Y3Al5O12:Cr 3+ , YAlO3:Cr 3+ , Y3Al5O12:Ce 3+ ,Cr 3+ , YAlO3:Ce 3+ ,Cr 3+ , Al2O3:Cr 3+ , and mixtures thereof such as, for example, Y3Al5O12:Ce3+ ,Cr 3+ + Al2O3:Cr 3+ or Y3Al5O 12 :This 3+ ,Cr 3+ + YAlO3:Cr 3+. Step (c) of transformation by additive manufacturing is preferably carried out by laser powder bed fusion (also known by the acronyms L-PBF, SLM and LBM corresponding respectively to the English terminologies Laser Powder Bed Fusion, Selective Laser Melting and Laser Beam Melting) or by laser fusion of projected powder (also known by the acronyms LMD and DED corresponding respectively to the English terminologies Laser Metal Deposition and Directed Energy Deposition), this second process based on the combined use of a power laser and a powder distribution device (typically, a nozzle) coaxial or with lateral injection.When carried out by laser powder bed fusion, step (c) consists of spreading the powder of the second mixture on a manufacturing plate and then passing a laser over the powder thus spread to melt this powder, the molten material then solidifying by cooling, this step (c) being repeated as many times as necessary until the desired layer thickness is obtained. The trajectory of the laser is defined by a digital file. The laser powder bed fusion process depends on several parameters and, in particular, the characteristics of the powder, the nature and power of the laser, the laser scanning speed, the layer thickness and the distance between each manufacturing bead. Those skilled in the art will determine, if necessary, by preliminary tests, these different parameters, depending on the layer and / or the metal part that they wish to obtain.In particular, when the second mixture is formed by a mixture of a 316L steel powder and a first mixture comprising Y2O3, Al2O3 and CeO2, the parameters for forming the luminescent optical marking layer by laser powder bed fusion may be as follows, for a Trumpf TruPrint 1000 machine with an infrared fiber laser doped with ytterbium having a wavelength of 1064 nm and a laser spot of 55 µm: - a laser power ranging from 20 W to 200 W, - a scanning speed ranging from 10 mm / s to 1300 mm / s, - a layer thickness ranging from 10 µm to 100 µm, and - an inter-bead distance ranging from 10 µm to 150 µm.When step (c) is carried out by laser melting of projected powder, the powder of the second mixture, which is transported by a carrier gas such as argon, helium or nitrogen, is melted in whole or in part upon contact with the laser beam, the melting being able to be completed upon contact with the liquid metal bath formed on the substrate (or manufacturing plate) resulting from the laser-material interaction, before solidification of the assembly (molten powder and liquid metal bath resulting from the melting of the lower layers). The movement of the laser, the powder distribution device and the substrate are controlled relative to a digital model defined in the formation of the part to be obtained.Like the laser powder bed fusion process, the projected powder laser fusion process depends on several parameters, including the characteristics of the powder, the nature and power of the laser, the laser scanning speed, the powder flow rate, the desired layer thickness and the distance between each manufacturing bead. Those skilled in the art will determine, if necessary, by prior testing, these various parameters, depending on the layer and / or the metal part that they wish to obtain. In the projected powder laser fusion process, the powder is supplied by powder distributors. Thus, the first mixture comprising the first and second metal oxides is introduced into a first distributor while the metal alloy powder is introduced into a second distributor.The first and second distributors are then activated simultaneously to form the second mixture within the machine's feed pipes. In particular, when the second mixture is formed by a mixture of a 316L steel powder and a first mixture comprising Y2O3, Al2O3 and CeO2, the parameters for forming the luminescent optical marking layer by laser fusion of projected powder may be as follows, for an Optomec machine with an infrared fiber laser and doped with ytterbium having a wavelength of 1064 nm and a laser spot of 1.2 mm for a working distance fixed at 12 mm: - a laser power ranging from 300 W to 1000 W, - a scanning speed ranging from 1 mm / s to 100 mm / s, - a powder flow rate ranging from 0.5 rpm to 20 rpm (rpm corresponding to the rotation speed of the powder distribution motor), - a layer thickness ranging from 0.1 mm to 2 mm, and - an inter-cord distance ranging from 0.1 mm to 2 mm.In a particular embodiment, the thickness of the luminescent optical marking layer obtained at the end of step (c) is at least 30 µm, in particular when step (c) is carried out by laser powder bed fusion. This minimum thickness of at least 30 µm has the advantage of minimizing the influence of inclusions on the mechanical properties of the metal part manufactured by the method according to the invention. Of course, the thickness of the luminescent optical marking layer obtained at the end of step (c) may be greater than these 30 µm and reach 0.1 mm, in particular when step (c) is carried out by laser fusion of projected powder. In a particular embodiment, step (c) is repeated as many times as necessary to give the desired thickness to the luminescent optical marking layer, in particular depending on the specifications and the desired application.At the end of this or these steps (c), a luminescent optical marking layer has been formed which comprises, throughout its thickness, the luminophor compounds which were formed in situ during step (c). In a first variant, it is possible to envisage applying this luminescent optical marking layer manufactured by the method according to the invention to any metal part so as to mark this part in a unique and non-reproducible manner. It should be noted that, in this first variant, preference will be given to a step (c) implemented by laser fusion by powder projection which makes it possible to apply luminescent optical marking layers to any shape of metal part. In a second variant, it is possible to envisage manufacturing a metal part by implementing only steps (a), (b) and (c) of the method, that is to say to manufacture a metal part of which each constituent layer is formed by implementing the necessary number of steps (c).In doing so, a part is obtained comprising a luminescent optical marking which is unique, non-reproducible and produced throughout the mass of the part. In addition, thanks to the formation by additive manufacturing, in particular by laser fusion on a powder bed or by laser fusion by powder projection, of the luminescent optical marking layers, the metal part manufactured according to this second variant of the method can have a complex geometric shape. In a third, more advantageous variant, the method according to the invention further comprises at least one step (i) of transformation of the metal alloy powder by additive manufacturing. As in the second variant, this third variant has the advantage of carrying out the luminescent optical marking of the metal part during the actual manufacturing process of this metal part; there is therefore no additional marking step, unlike the marking methods of the prior art.Furthermore, in this third variant, all the steps of transformation of the second mixture and of the metal alloy powder implemented to manufacture the metal part being carried out by additive manufacturing, in particular by laser fusion on a powder bed or by laser fusion by powder projection, it becomes possible to form a metal part of complex geometry comprising a luminescent optical marking, on the surface and / or located in the mass of the part. This or these steps (i) of transformation of the metal alloy powder by additive manufacturing can be implemented before and / or after step(s) (c). In contrast to the second variant described previously, the metal part manufactured according to this third variant comprises at least one layer of luminescent optical marking and at least one layer of metal alloy devoid of luminescent optical marking.In this third variant, the luminescent optical marking of the metal part may be surface-based or localized in the mass of the part, for example at a chosen thickness. In a preferred embodiment, this or these steps (i) are carried out by laser powder bed fusion or by laser fusion of projected powder of the metal alloy powder. In a preferred embodiment, this or these steps (i) are carried out by laser powder bed fusion of the metal alloy powder. In a preferred embodiment of this third variant, the steps (i) of transforming the metal alloy powder by additive manufacturing are implemented before and after the step(s) (c). Thus, in addition to being unique, non-reproducible and localized in the mass of the metal part, for example at a chosen thickness, the luminescent optical marking of the part is permanent and does not risk being degraded.Other advantages and characteristics of the present invention will appear on reading the following example of at least one particular embodiment of the method according to the invention. It is specified that this example is given only as an illustration of the subject of the invention and in no way constitutes a limitation of this subject. BRIEF DESCRIPTION OF THE FIGURES Figure 1 corresponds to a photograph taken using a scanning electron microscope (SEM) of a section of the metal part obtained from the second mixture A2 and comprising a final layer of luminescent optical marking on which different spots marked 1 to 11 are identified.Figure 2 illustrates the curves translating the evolution of the intensity, noted I and expressed in arbitrary unit (au), as a function of the wavelength, noted λ and expressed in nm, it being specified that the curves i, iii, iv, v, vi, vii, viii and ix correspond respectively to the spots noted 1, 3, 4, 5, 6, 7, 8 and 9 of the metal part of figure 1. DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS 1. Preparation of the first mixtures A1 and B1 The first mixtures of metal oxides, noted A1 and B1, were prepared from the following three metal oxides: - the first metal oxides Al2O3 and Y2O3, and - the second metal oxide CeO2. These first mixtures A1 and B1 were produced by mixing, using a Turbula® three-dimensional agitator, the mass proportions of said metal oxides which are specified in Table 1 below.After this mixing using the agitator, the first mixtures A1 and B1 appear in the form of a powder formed of particles of irregular shape and granulometry (average particle size) between 1 µm and 5 µm. Mixture Y2O3 Al2O3 CeO2 Mass (g) 16.8 12.9 0.4 Mixture A1 % mass 55.8 42.9 1.3 Mass (g) 16.8 11.7 0.8 Mixture B1 % mass 57.4 39.9 2.7 Table 1 2. Preparation of the second mixtures A2 and B2 The second mixtures, denoted A2 and B2, were respectively prepared by mixing the following mass proportions of a 316L stainless steel powder and each of the first mixtures A1 and B1: - 95% mass of 316L stainless steel powder (162 g), and - 5% mass of the first mixture A1 or B1. It is specified that the 316L stainless steel powder is formed of spherical particles with a granulometry (average particle size) of between 15 µm and 45 µm. 3.Fabrication of the metal part In a first step, 434 layers of stainless steel were deposited from the same spherical 316L stainless steel powder used to prepare the second mixtures A2 and B2. Each of these 434 layers was deposited by laser powder bed fusion (L-PBF) using a TruPrint 1000 machine with an infrared fiber laser doped with ytterbium having a wavelength of 1064 nm and a laser spot of 55 µm, the other parameters used being: - laser power: 165 W, - scanning speed: 950 mm / s, - inter-bead distance: 50 µm, and - layer thickness: 30 µm. In a second step, 33 layers of either mixture A2 or mixture B2 were deposited.Each of these 33 layers was deposited by laser powder bed fusion (L-PBF) using a TruPrint 1000 machine with an infrared fiber laser and doped with ytterbium having a wavelength of 1064 nm and a laser spot of 55 µm, the other parameters used being the following: - laser power: 60 W, - scanning speed: 25 mm / s, - inter-bead distance: 50 µm, and - layer thickness: 30 µm. At the end of this second step, a metal part was formed comprising a final layer of 1 mm thickness, which is arranged at the surface of this metal part and which corresponds to the luminescent optical marking of said metal part. This luminescent optical marking as obtained from the A2 mixture corresponds to the zone marked Z and located between the two dotted lines marked on the sectional image of the metal part shown in figure 1.With reference to this same figure 1, the white particles identified by SEM in the final layer of luminescent optical marking correspond to oxide phases precipitated after rapid solidification of the metal part. Due to the complexity of the process (temperature gradient in the molten pool, reflows by adjacent layers, various thermal cycles, etc.), each precipitated particle has its own thermal history. These temperature and thermal conditions result in the precipitation of various heterogeneous phases which will be responsible for the formation of random luminescent optical signals, characteristic of the luminescent optical marking of the metal part. 4. Evaluation by optical spectroscopy Laser spectroscopy tests were carried out using a continuous laser of 405 nm wavelength, 0.7 s acquisition time and 3.2% optical density.The laser beam was focused on the spots identified in Figure 1 by the circles numbered 1, 3, 4, 5, 6, 7, 8 and 9, it being specified that the spots correspond to the oxide precipitations. The emission spectra obtained at the end of these tests were reported in Figure 2. Referring to this Figure 2, it can be seen that fluorescence was generated in situ during the manufacturing process of the metal part, while the three metal oxides Al2O3, Y2O3 and, to a lesser extent, CeO2 present in the mixtures A1 and A2 are not luminescent. Indeed, two luminescent centers were detected: these centers correspond to the Ce ions. 3+ , which emit around 525 nm wavelength (broadband), and Cr ions 3+ , which emit in the wavelength region between 680 nm and 780 nm. These ions Ce 3+ and Cr 3+come from CeO2 and 316L stainless steel powders respectively. The emission of Ce ions 3+ and Cr 3+ depends on the crystalline structure surrounding them and, consequently, on the phase for which they have been substituted. The phases which have precipitated during the manufacturing process of the metal part according to the invention and which have been identified are the following: - the phases formed between the Al2O3 and Y2O3 powders, namely the phases resulting from the Al2O3-Y2O3 phase diagram, and - the luminescent Y3Al5O precipitates 12 doped with Ce 3+ (Y3Al5O 12 :Ce), Y3Al5O 12 doped with Ce 3+ and to the Cr 3+ (Y3Al5O 12 :Ce:Cr), YAlO3doped with Ce 3+ and to the Cr 3+ (YAlO3:Ce:Cr), Al2O3doped with Cr 3+ (Al2O3:Cr) as well as all phase combinations between these precipitates such as, for example, Ce-doped Y3Al5O12 3+ and Cr-doped YAlO3 3+. In the molten bath, the oxides Al2O3, Y2O3 and / or CeO2 interacted with each other and with the metal matrix resulting from the melting of the 316L stainless steel powder. After solidification, various heterogeneous phases precipitated. By substitution, the Ce ions 3+ and Cr 3+ are present in these phases, leading to a multitude of randomly generated luminescent signals.

Claims

Claims 1. Method for manufacturing a metal part from a metal alloy powder, said metal part comprising a luminescent optical marking, this method comprising the following successive steps (a) to (c): (a) the preparation of a first mixture in the form of a powder and comprising: - at least 90% by mass of at least one first oxide of one or more metals chosen from Li, K, Mg, Ca, Sr, Ba, Sc, Y, La, Lu, Ti, Zr, Hf, V, Nb, Ta, Zn, Cd, B, Al, Ga, Si and Ge, and - at least 0.1% by mass of at least one precursor of a luminescent cation, this precursor being introduced in the form of a second metal oxide; (b) preparing a second mixture comprising: - from 0.1% mass to 20% mass of the first mixture, and - from 80% mass to 99.9% mass of the metal alloy powder;and (c) transforming the second mixture obtained at the end of step (b) by additive manufacturing allowing the material to be consolidated by a laser source or an electron beam, whereby the formation of a luminescent optical marking layer is obtained.

2. The method of claim 1, wherein the first metal oxide(s) are chosen from Li2O, K2O, MgO, CaO, SrO, BaO, Sc2O3, Y2O3, La2O3, Lu2O3, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, ZnO, CdO, B2O3, Al2O3, Ga2O3, SiO2, GeO2, Y3Al5O; 12 , YAlO3, Y4Al2O9, Sr4Al2O7, Sr3Al2O6, SrAl2O4, SrAl4O7 and Sr4Al 12 O 19 .

3. Method according to claim 1 or 2, in which the first mixture comprises Y2O3 and Al2O3.

4. Method according to any one of claims 1 to 3, in which the luminescent cation(s) are chosen from In + , Sn 2+ , Pb 2+ , Sb 3+ , Bi 3+ , This 3+ , This 4+ , Pr 3+ , Nd 3+, Sm2+, Sm 3+ , Eu 2+ , Eu 3+ , Gd 3+ , Tb 3+ , Dy 3+ , Your 3+ , Er 3+ , Tm 2+ , Tm 3+ , Yb 2+ , Yb 3+ , Home 3+ , V 2+ , V 3+ , V 4+ , Cr 3+ , Cr 4+ , Mn 2+ , Mn 3+ , Mn 4+ , Fe 3+ , Fe 4+ , Fe 5+ , Co 3+ , Co 4+ , We 2+ , Cu + , Ru 2+ , Ru 3+ , Pd 2+ , Ag + , Ir 3+ , Pt 2+ and Au + .

5. Method according to any one of claims 1 to 4, wherein the second metal oxide(s) are chosen from In2O, PbO, Sb2O3, Bi2O3, Ce2O3, CeO2, Pr2O3, Nd2O3, SmO, Sm2O3, EuO, Eu2O3, Gd2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, TmO, Tm2O3, YbO, Yb2O3, Ti2O3, VO, V2O3, VO2, Cr2O3, CrO2, MnO, Mn2O3, MnO2, Fe2O3, FeO2, Fe2O5, Co2O3, CoO2, NiO, Cu2O, RuO, Ru2O3, PdO, Ag2O, Ir2O3, PtO and Au2O and, preferably, from CeO2, Cr2O3 and Eu2O3.

6. The method of claim 5, wherein the first mixture comprises Y2O3, Al2O3 and CeO2.

7. The method of any one of claims 1 to 6, wherein the metal alloy of the metal alloy powder is selected from iron alloys, aluminum alloys, titanium alloys, nickel alloys, copper alloys and steels, in particular stainless steels. 8.Method according to claim 7, wherein, when the metal alloy is a steel, this steel is an austenitic steel, advantageously chosen from 316L steel, 304L steel and 1.4404 steel.

9. Method according to any one of claims 1 to 8, wherein the first mixture comprises: - between 95% mass and 99.5% mass and, preferably, between 97% mass and 99% mass of the first metal oxide(s), and - up to 10% mass, advantageously between 0.5% mass and 5% mass and, preferably, between 1% mass and 3% mass of the second metal oxide(s).

10. Method according to any one of claims 1 to 9, in which the second mixture comprises: - from 0.5% mass to 15% mass of the first mixture, and - from 85% mass to 99.5% mass of the metal alloy powder. 11.Method according to any one of claims 1 to 10, in which step (c) of transformation by additive manufacturing is carried out by laser fusion on a powder bed or by laser fusion of projected powder.

12. Method according to any one of claims 1 to 11, wherein step (c) is repeated as many times as necessary to give the desired thickness to the luminescent optical marking layer.

13. Method according to any one of claims 1 to 12, further comprising at least one step (i) of transformation of the metal alloy powder by additive manufacturing, this or these steps (i) being able to be implemented before and / or after step(s) (c) and, preferably, before and after step(s) (c).

14. Method according to claim 13, wherein this or these steps (i) are carried out by laser powder bed fusion or by laser fusion of projected powder of the metal alloy powder.

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