Method for manufacturing a metal part comprising a luminescent optical marking

Abstract

The present invention relates to a method for manufacturing a metal part from a metal alloy powder, said metal part comprising a luminescent optical marking. This method comprises the following successive steps (a) to (c): (a) the preparation of a first mixture in powder form comprising: - at least one first oxide of one or more metals selected 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 introduced in the form of a second metal oxide; (b) the preparation of a second mixture comprising the metal alloy powder and the first mixture; and (c) the transformation of the second mixture by additive manufacturing, thereby obtaining the formation of a luminescent optical marking layer. No figure.

Description

Title of the invention: Method for manufacturing a metal part comprising luminescent optical marking TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method of manufacturing a metal part, in particular a steel part, comprising luminescent optical marking.

[0002] 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.

[0003] 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.

[0004] The present invention finds applications in particular in numerous industrial sectors and, in particular, in the nuclear, automobile, aeronautical, railway, luxury and food sectors. STATE OF THE ART

[0005] 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.

[0006] Manufacturers therefore 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.

[0007] These different markings, however, all have a certain number of limitations insofar as they are generally made on the surface of the metal parts, as in document DE 10 2014 117 519 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.

[0008] The aim of the present invention is, therefore, 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 marking by particular, in this case a luminescent optical marking, this luminescent optical marking being unique, non-reproducible, or even permanent, this process not necessarily requiring the implementation of additional steps to obtain this particular marking. Statement of the invention

[0009] The above-mentioned aims 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.

[0010] According to the invention, the method comprises the following successive steps (a) to (c):

[0011] (a) preparing a first mixture in the form of a powder and including:

[0012] - 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

[0013] - at least one precursor of a luminescent cation, this precursor being introduced under the form of a second metal oxide;

[0014] (b) preparing a second mixture comprising the metal alloy powder and the first mixture, and

[0015] (c) the transformation of the second mixture obtained at the end of step (b) by manufacturing additive, whereby the formation of a luminescent optical marking layer is obtained.

[0016] 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.

[0017] 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 oxide(s) 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 transformation 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. The precipitations and their doping by this (these) cation(s) not being 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 process 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.

[0018] Furthermore, 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.

[0019] Furthermore, the fact of incorporating these first metal oxides, and not luminophoric 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 luminophoric compounds as starting products would greatly reduce the number of random signals.

[0020] The method according to the invention comprises steps (a) to (c) mentioned above and detailed below.

[0021] During step (a) of the manufacturing process 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.

[0022] By the expression "first metal oxide(s)", it should be understood that it can be a simple metal oxide, that is to say an oxide of a single metal, as well as a mixed metal oxide, that is to say an oxide of two or more metals.

[0023] 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.

[0024] 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.

[0025] In an advantageous embodiment of the method according to the invention, the first mixture comprises Y2O3 and A12O3.

[0026] When the first metal oxide(s) are mixed metal oxides, they may in particular be chosen from Y3A150i2, YA1O3, Y4A12O9, Sr4Al2O7, Sr3Al2 O6, SrAl2O4, SrAl4O7 and Sr4Ali20i9.

[0027] 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.

[0028] For example, when the first mixture comprises A12O3 and Y2O3 as first metal oxides, the phases Y3A150i2, YA1O3 and Y4A12O9 will be formed in situ during step (c) of additive manufacturing.

[0029] It will be noted that one can choose to form all or part of the phases in situ by introducing the corresponding first 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 Y3A150i2, YA1O3 and Y4A12O9 in situ from the first metal oxides Al2 O3 and Y2O3 and / or introduce, into the first mixture, the first metal oxides Y3A150i2, YA1O3 and Y4A12O9.

[0030] When the first mixture comprises SrO, A12O3 and Y2O3 as first metal oxides, the phases of the Y2O3-A12O3 system (namely Y3A150i2, YA1O3 and Y4 A12O9) as well as the phases of the SrO-Al2O3 system (namely Sr4Al2O7, Sr3Al2O6, SrAl2O 4, SrAl4O7 and Sr4Ali20i9) will be formed in situ during the additive manufacturing step (c).

[0031] The use of ZrO2, La2O3, Y2O3 and A12O3 as first metal oxides also makes it possible to form several phases in situ during step (c) of additive manufacturing.

[0032] In the same way, 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.

[0033] This or these second metal oxides are these precursor compounds of one or more luminescent cations.

[0034] 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.

[0035] This doping is obtained by the substitution of 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 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 Y3Al50i2:Ce3+, the Ce3+ has an atomic radius close to Y3+ and will substitute in the dodecahedral sites of the latter. When the dopant is Cr3+ (e.g. Y3Al50i2:Ce3+, Cr3+), the Cr3+ will substitute in the octahedral sites of Al3+ due to their close atomic radii.

[0036] In a particular embodiment of the method according to the invention, the luminescent cation(s) are chosen from In+, Sn2+, Pb2+, Sb3+, Bi3+, Ce3+, Ce4+, Pr3+, Nd3+, Sm2+, Sm3+, Eu2+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er3+, Tm2+, Tm3+, Yb2+, Yb3+, Ti3+, V2+, V3+, V4+, Cr3+, CL+, Mn2+, Mn3+, Mn4+, Fe3+, Fe4+, Fe5+, Co3+, Co4+, Ni2+, Cu+, Ru2+, Ru3+, Pd2+, Ag+, Ir3+, Pt2+ and Au+.

[0037] 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.

[0038] It should be noted that some of these second metal oxides, such as Eu2O3 which is a precursor of the luminescent cation Eu3+, can exhibit luminescence properties.

[0039] In a preferred embodiment, the second metal oxide(s) are selected from CeO2, Cr2O3 and Eu2O3.

[0040] In a variant of the process according to the invention, the first mixture comprises:

[0041] - at least 90% mass, advantageously between 95% mass and 99.99% mass and, preferably entially, between 97% mass and 99.9% mass of the first metal oxide(s), and

[0042] - up to 10% mass, advantageously between 0.01% mass to 5% mass and, preferably initially, between 0.1% mass and 3% mass of the second metal oxide(s).

[0043] 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.

[0044] In a more particularly preferred embodiment of the method according to the invention, the first mixture comprises Y2O3, Al2O3 and CeO2.

[0045] In an advantageous variant, this first mixture comprises:

[0046] - from 30% mass to 85% mass of Y2O3,

[0047] - from 15% mass to 70% mass of A12O3, and

[0048] - up to 10% mass, advantageously between 0.01% mass to 5% mass and, preferably initially, between 0.1% mass and 3% mass of CeO2.

[0049] During step (a) of the process according to the invention, the first metal oxide(s) and the second metal oxide(s) are ground and / or mixed by means of any conventional technique for obtaining 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 an agitator such as a Turbula® three-dimensional agitator.

[0050] At the end of step (a), a metal oxide powder is obtained comprising one or more first metal oxides and one or more second metal oxides.

[0051] The particles forming the powder of the first mixture can be of irregular or regular shape, for example spherical.

[0052] 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.

[0053] 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.

[0054] In a particular embodiment, the second mixture comprises:

[0055] - from 1% mass to 20% mass of the first mixture, and

[0056] - from 80% mass to 99% mass of the metal alloy powder.

[0057] The metal alloy of the metal alloy powder may be selected from iron alloys, aluminum alloys, titanium alloys, nickel alloys, copper alloys and steels.

[0058] According to one variant, the metal alloy forming the metal alloy powder does not comprise any precursor element of luminescent cation(s).

[0059] According to another preferred variant, 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.

[0060] In a particular embodiment, the steels are stainless steels, that is to say steels which comprise Cr, an element which, as indicated previously, is a precursor of the luminescent cations Cr3+ and Cr4*.

[0061] In an advantageous embodiment, this steel is an austenitic steel, which can advantageously be chosen from 316L steel, 304L steel and 1.4404 steel.

[0062] In a particular embodiment, the particles forming the metal alloy powder are spherical in shape.

[0063] In a particular embodiment, this metal alloy powder is formed from particles having an average particle size of between 15 μm and 106 pm, so as to meet the characteristics of the powders used for the implementation of step (c) of transformation by additive manufacturing.

[0064] More particularly, the particles forming this metal alloy powder have an average particle size of between 15 pm and 45 pm when step (c) is carried out by laser fusion on a powder bed, and of between 45 pm and 106 pm when step (c) is carried out by laser fusion of projected powder.

[0065] 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 previously (mixer, attritor or agitator).

[0066] 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.

[0067] This transformation step (c) is advantageously implemented by an additive manufacturing process which makes it possible to consolidate the material using a laser source or an electron beam.

[0068] This additive transformation step (c) is typically carried out at temperatures which are greater than or equal to 2000°C, or even much greater 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.

[0069] As examples of phosphor compositions which can be formed in situ during step (c) of transformation by additive manufacturing, mention may in particular be made of: Y3Al5O12:Ce3+, YA103:Ce3+, Y3A15O12:Eu3+, YA103:Eu3+, Y4A12O9:Eu3+, YA103:Sm3+, YA103:Tb3+, Al2O3:Cr3+, Y2O3:Eu3+, LiA102:Fe3+, LiA102:Mn2+, LaA103:Eu3+, LaA103:Sm3+, MgAl2O4:Mn2+, MgGa2O4:Mn2+, CaAl2O4:Mn2+, CaAl2O4:Eu2+, ZnAl2O4:Mn2+, ZnGa2O4:Mn2+, CaGa2O4:Mn2+, CaGa4O:Mn2+, SrAl2O4:Eu2+, BaAl2O4:Eu2+, CaAI4O7:Pb2+,Mn2+, LiAl5O8:Fe3+, LiAl5O8:Mn2+, KAInO17:Ti+, KGanO17:Mn2+, BaMgAl10O17:Ce3+, BaMgAl10O17:Eu2+, BaMgAl10O17:Eu2+,Mn2+, Ca0.5Ba0.5Al12O19:Ce3+,Mn2+, SrAl12 O19:Eu2+,Mn2+, SrGa12O19:Mn2+ and SrAl12O19:Ce3+,Mn2+.

[0070] 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 depending on the desired luminophore compositions.

[0071] For example, with the first metal oxides Y2O3 and A12O3 and the luminescent cations Ce3+ and Cr3+, 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), it is possible forming in situ all or part of the phases of the Y2O3-A12O3 system with doping in Ce3+ and / or Cr3+ and in particular the luminophores of the following compositions: Y3Al50i2:Ce3+, YA103:Ce3+, Y4Al2O9:Ce3+, Y3Al5O12:Cr3+, YA103:Cr3+, Y3Al5O12:Ce3+,Cr3+, YA103:Ce3+ ,Cr3+, Al2O3:Cr3+, and mixtures thereof such as, for example, Y3Al50i2:Ce3+,Cr3+ + Al2O3:Cr3+ or Y3Al50i2:Ce3+,Cr3+ + YA103:Cr3+.

[0072] 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 method being based on the combined use of a power laser and a powder distribution device (typically, a nozzle) coaxial or with lateral injection.

[0073] 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.

[0074] The powder bed 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 layer thickness and the distance between each manufacturing bead. Those skilled in the art will determine, if necessary, by prior tests, these different parameters, depending on the layer and / or the metal part that they wish to obtain.

[0075] In particular, when the second mixture is formed by a mixture of a 316L steel powder and a first mixture comprising Y2O3, A12O3 and CeO2, the parameters for forming the luminescent optical marking layer by laser fusion on a powder bed 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 pm:

[0076] - a laser power ranging from 20 W to 200 W,

[0077] - a scanning speed ranging from 10 mm / s to 1300 mm / s,

[0078] - a layer thickness ranging from 10 pm to 100 pm, and

[0079] - an inter-cord distance ranging from 10 pm to 150 pm.

[0080] When step (c) is carried out by laser fusion 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 whole (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 in relation to a digital model defined in the formation of the part to be obtained.

[0081] Like the powder bed laser fusion process, the projected powder laser 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 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 tests, these different parameters, depending on the layer and / or the metal part that they wish to obtain.

[0082] In the laser melting process of projected powder, the powder supply is carried out 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 feed pipes of the machine.

[0083] In particular, when the second mixture is formed by a mixture of a 316L steel powder and a first mixture comprising Y2O3, A12O3 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:

[0084] - a laser power ranging from 300 W to 1000 W,

[0085] - a scanning speed ranging from 1 mm / s to 100 mm / s,

[0086] - a powder flow rate ranging from 0.5 rpm to 20 rpm (rpm corresponding to the speed rotation of the powder distribution motor,

[0087] - a layer thickness ranging from 0.1 mm to 2 mm, and

[0088] - an inter-cord distance ranging from 0.1 mm to 2 mm.

[0089] 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 fusion on a powder bed.

[0090] 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.

[0091] 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.

[0092] 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.

[0093] 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).

[0094] 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.

[0095] It should be noted that, in this first variant, a step (c) implemented by laser fusion by powder projection will be preferred, which makes it possible to apply layers of luminescent optical marking to any shape of metal part.

[0096] 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 manufacturing 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.

[0097] 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.

[0098] 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 processes of the prior art.

[0099] 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.

[0100] 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).

[0101] In contrast to the second variant described above, 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.

[0102] In this third variant, the luminescent optical marking of the metal part can be surface-based or located in the mass of the part, for example at a chosen thickness.

[0103] In a preferred embodiment, this or these steps (i) are carried out by laser fusion on a powder bed or by laser fusion of projected powder of the metal alloy powder.

[0104] In a preferred embodiment, this or these steps (i) are carried out by laser powder bed fusion of the metal alloy powder.

[0105] In a preferred embodiment of this third variant, steps (i) of transforming the metal alloy powder by additive manufacturing are implemented before and after step(s) (c).

[0106] Thus, in addition to being unique, non-reproducible and located 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.

[0107] 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.

[0108] It is specified that this example is given only as an illustration of the subject of the invention and does not constitute in any way a limitation of this subject. BRIEF DESCRIPTION OF THE FIGURES

[0109] [Fig.l] 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.

[0110] [Fig.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 X 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 [Fig.l]. DETAILED DESCRIPTION OF THE INVENTION

[0111] 1. Preparation of the first mixtures Al and B1

[0112] The first mixtures of metal oxides, denoted Al and Bl, were prepared from of the following three metal oxides:

[0113] - the first metal oxides A12O3 and Y2O3, and

[0114] - the second metal oxide CeO2.

[0115] These first mixtures Al and B1 were produced by mixing, using a Turbula® three-dimensional stirrer, the mass proportions of said metal oxides which are specified in Table 1 below.

[0116] At the end of this mixing using the stirrer, the first mixtures Al and B1 appear in the form of a powder formed of particles of irregular shape and granulometry (average particle size) between 1 pm and 5 pm.

[0117] [Tableauxl] Mixture y2o3 A12O3 CeO2 Mixture Al Mass (g) 16.8 12.9 0.4% mass 55.8 42.9 1.3 Mixture B1 Mass (g) 16.8 11.7 0.8% mass 57.4 39.9 2.7

[0118] 2. Preparation of the second mixtures A2 and B2

[0119] 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 Al and B1:

[0120] - 95% mass of 316L stainless steel powder (162 g), and

[0121] - 5% mass of the first mixture Al or Bl.

[0122] It is specified that the 316L stainless steel powder is formed of spherical particles and having a granulometry (average particle size) of between 15 pm and 45 pm.

[0123] 3. Manufacturing of the metal part

[0124] 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 pm, the other parameters used being the following:

[0125] - laser power: 165 W,

[0126] - scanning speed: 950 mm / s,

[0127] - inter-cord distance: 50 pm, and

[0128] - layer thickness: 30 pm.

[0129] In a second step, 33 layers were deposited, consisting of either mixture A2, or mixture B2. Each of these 33 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 pm, the other parameters used being the following:

[0130] - laser power: 60 W,

[0131] - scanning speed: 25 mm / s,

[0132] - inter-cord distance: 50 pm, and

[0133] - layer thickness: 30 pm.

[0134] At the end of this second step, a metal part has been formed comprising a final layer 1 mm thick, which is arranged at the surface of this metal part and which corresponds to the luminescent optical marking of said metal part.

[0135] This luminescent optical marking as obtained from the mixture A2 corresponds to the zone noted Z and located between the two dotted lines marked on the sectional image of the metal part shown in [Fig.l].

[0136] With reference to this same [Fig.l], 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.

[0137] 4. Evaluation by optical spectroscopy

[0138] Laser spectroscopy tests were carried out using a continuous laser of 405 nm wavelength, 0.7 s acquisition time and 3.2% optical density.

[0139] The laser beam was focused on the spots identified, in [Fig.l], by the circles numbered 1, 3, 4, 5, 6, 7, 8 and 9, it being specified that the spots correspond to the oxide precipitations.

[0140] The emission spectra obtained at the end of these tests were reported in [Fig.2]. Referring to this [Fig.2], it can be seen that fluorescence was generated in situ during the manufacturing process of the metal part, whereas the three metal oxides A12O3, Y2O3 and, to a lesser extent, CeO2 present in the Al and A2 mixtures are not luminescent.

[0141] Indeed, two luminescent centers were detected: these centers correspond to the Ce3+ ions, which emit at around 525 nm wavelength (broad band), and to the Cr3+ ions, which emit in the wavelength zone which is between 680 nm and 780 nm.

[0142] These Ce3+ and Cr3+ ions come from CeO2 and 316L stainless steel powders respectively.

[0143] The emission of Ce3+ and Cr3+ ions depends on the crystal structure surrounding them and, consequently, on the phase to which they have substituted themselves.

[0144] The phases which precipitated during the manufacturing process of the metal part according to the invention and which were identified are the following:

[0145] - the phases formed between the Al2O3 and Y2O3 powders, namely the re phases results of the Al2O3-Y2O3 phase diagram, and

[0146] - the luminescent precipitates Y3A150i2 doped with Ce3+ (Y3Al50i2:Ce), Y3A150i2 doped with Ce3+ and Cr3+ doped YA103 (YA103:Ce:Cr), Cr3+ doped A12O3 (Al2O3:Cr) as well as all phase combinations between these precipitates such as, for example, Ce3+ doped Y3A150i2 and Cr3+ doped YA103.

[0147] In the molten bath, the oxides A12O3, Y2O3 and / or CeO2 interacted with each other and with the metal matrix originating from the melting of the 316L stainless steel powder. After solidification, various heterogeneous phases precipitated. By substitution, the ions Ce3+ and Cr3+ are present in these phases, which leads to a multitude of randomly generated luminescent signals.

Claims

Claims

1. A method of 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) 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.

2. The method of claim 1, wherein the first metal oxide(s) is / are selected from Li2O, K2O, MgO, CaO, SrO, BaO, Sc2O3, Y2O3, La2O3, Lu2O3, TiO2, ZrO2, HfO2, V2O5, Nb2O5, Ta2O5, ZnO, CdO, B2O3, A12O3, Ga2O3, SiO2, GeO2, Y3A150i2, YA103, Y4A12O9, Sr4Al2O7, Sr3Al2O6, SrAl2O4, SrAl4O7 and Sr4Ali20i9.

3. A method according to claim 1 or 2, wherein the first mixture comprises Y2O3 and A12O3.

4. A method according to any one of claims 1 to 3, wherein the luminescent cation(s) are selected from In+, Sn2+, Pb2+, Sb3+, Bi3+, Ce3+, Ce4+, Pr3+, Nd3+, Sm2+, Sm3+, Eu2+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, Er 3+, Tm2+, Tm3+, Yb2+, Yb3+, Ti3+, V2+, V3+, V4+, Cr3+, Cr44, Mn2+, Mn3+, Mn 4+, Fe3+, Fe4+, Fe5+, Co3+, Co4+, Ni2+, Cu+, Ru2+, Ru3+, Pd2+, Ag+, Ir3+, Pt2+ and Au+.

5. A method according to any one of claims 1 to 4, wherein the second metal oxide(s) are selected 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, among CeO2, Cr2O3 and Eu2O3.

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

7. A method according to 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. 8. Method according to claim 7, in which, 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, in which the first mixture comprises: - at least 90% by mass, advantageously between 95% by mass to 99.99% by mass and, preferably, between 97% by mass and 99.9% by mass of the first metal oxide(s), and - up to 10% by mass, advantageously between 0.01% by mass to 5% by mass and, preferably, between 0.1% by mass and 3% by mass of the second metal oxide(s).

10. A method according to any one of claims 1 to 9, wherein the second mixture comprises: - from 1% mass to 20% mass of the first mixture, and - from 80% mass to 99% mass of the metal alloy powder.

11. A method according to any one of claims 1 to 10, wherein 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. A 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. A method according to claim 13, wherein said step(s) (i) are carried out by laser powder bed fusion or by laser powder fusion of the metal alloy powder.

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