EP3016764A2 - Process for additive manufacturing of parts by melting or sintering particles of powder(s) using a high-energy beam with powders adapted to the targeted process/material pair - Google Patents

Abstract

The invention relates to a process for rapid manufacturing of parts made of a metallic, intermetallic or ceramic material, made of a ceramic matrix composite or made of a metal matrix composite with discontinuous reinforcement, especially with ceramic or intermetallic reinforcement, by melting or sintering particles of powder(s) using a high-energy beam. Characteristically, the powder used is a single powder, the particles of which have a sphericity of between 0.8 and 1.0 and a shape factor of between 1 and √2, each powder particle having a substantially identical mean composition and the particle size distribution of the particles of said powder is narrowed about the mean diameter d₅₀% value so that: (d₉₀% - d₅₀%) / d₅₀% ≤ 0.66 and (d₅₀% - d₁₀%) / d₅₀% ≤ 0.33 with a "span" (d₉₀% - d₁₀%) / d₅₀ % < 1.00. Application to the rapid manufacturing of parts by selective laser melting (SLM) or by selective laser sintering (SLS) or else by direct metal deposition (DMD). Such powders are adapted to the targeted process/material pair.

Description

 Process for the additive manufacturing of parts by melting or frittaae of powder particles) by means of a high energy beam with powders adapted to the process / material pair The present invention relates to the field of manufacturing parts made of metallic material, intermetallic ceramic, Ceramic Matrix Composite (CMC) or Metallic Matrix Composite (CMM) with discontinuous reinforcement, in particular ceramic or intermetallic reinforcement, by melting or sintering powder particles (s) by means of a high beam energy.

 By discontinuous reinforcement is meant reinforcing elements such as short fibers (whiskers or whiskers), particles, in particular monocrystalline particles, and not continuous reinforcing elements of the long fiber type.

 Among these high energy beams, mention may be made in particular, without limitation, the laser beam and the electron beam. Regarding the laser, it can be either pulsed or continuous.

 The invention aims in particular the rapid manufacture of parts by laser projection or by selective melting of powder beds by laser or by selective sintering of powder beds by laser.

 Selective Laser Sintering (SLS) is a process in which one part of the powder is melted while the other part remains solid. This concerns in particular the manufacture of ceramic material parts, CMC and some CMM. For the first two materials (ceramic and CMC), the liquid phase is a minority (most often between 0.5 and 3% vol.) And for CMM this liquid phase is predominant but rarely less than 70% by volume.

 Selective Laser Melting (SLM) refers to a process in which the entirety of the powder is melted and the main characteristics of which are recalled below, with reference to FIG. 1.

For example, using a roller 30 (or any other removing means), a first layer 10 of powder of a material is deposited on a construction support 80 (it can be a massive support , from part of another part or a support grid used to facilitate the construction of certain parts).

 This powder is transferred to the construction support 80 from a feed tank 70 during a forward movement of the roll 30, then it is scraped, and possibly slightly compacted, during one (or more) movement (s) of return of the roll 30. The powder is composed of particles 60. The excess powder is recovered in a recycling bin 40 located adjacent to the building tank 85 in which the construction support 80 moves vertically.

 Also used is a laser beam generator 90, and a driver 50 capable of directing the beam 95 over any region of the building support 80 so as to scan any region of a powder layer. The shaping of the laser beam and the variation of its diameter in the focal plane are done respectively by means of a beam expander or "Beam Expander" 52 and a focusing system 54, the assembly constituting the optical system .

Next, a region of this first powder layer 10 is scanned with a laser beam 95 at a temperature above the melting temperature T _F of this powder.

 The SLM process can use any high energy beam in place of the laser beam 95, as long as this beam is sufficiently energetic to melt the powder particles and a part of the material on which the particles rest (also called diluted zone making integral part of the liquid bath).

This scanning of the beam is carried out for example by a galvanometric head forming part of a control system 50. For example, this control system comprises, in a nonlimiting manner, at least one orientable mirror 55 on which the laser beam 95 is reflected before to reach a powder layer where each point of the surface is always located at the same height relative to the focusing lens, contained in the focusing system 54, the angular position of this mirror being controlled by a galvanometric head so that the laser beam scans at least one region of the first layer of powder, and thus follows a predetermined part profile. To do this, the galvanometric head is controlled according to the information contained in the computer tool database used for computer-aided design and manufacturing of the part to be manufactured.

 Thus, the powder particles 60 of this region of the first layer 10 are melted and form a first integral element 15, integral with the construction support 80. At this stage, it is also possible to scan with the laser beam several regions independent of this first layer to form, after melting and solidification of the material, a plurality of first elements 15 disjoint from each other.

 The support 80 is lowered by a height corresponding to the thickness of the first layer (20 to 100 μΐη and in general from 30 to 50 μηη).

 A second layer 20 of powder is then deposited on the first layer 10 and on this first element in one piece or consolidated 15, and a region of the second layer 20 which is located partially or completely is heated by exposure to the laser beam 95. above this first element in one piece or consolidated in the case illustrated in Figure 1, so that the powder particles of this region of the second layer 20 are melted with at least a part of the element 15 and form a second element in one piece or consolidated 25, all of these two elements 15 and 25 forming, in the case illustrated in Figure 1, a block in one piece.

 It is understood that depending on the profile of the part to be built, and in particular in the case of undercut surface, it is possible that the aforementioned region of the first layer 10 is not, even partially, below the aforementioned region of the second layer 20, so that in this case the first consolidated element 15 and the second consolidated element 25 do not then form a block in one piece.

 This process of building the piece layer by layer is then continued by adding additional layers of powder to the already formed assembly.

The scanning with the laser beam 95 makes it possible to construct each layer by giving it a shape in accordance with the geometry of the part to be produced. The lower layers of the room cool more or less quickly as the upper layers of the room are built. The "laser projection" or "direct deposition" (DMD) deposition process is explained below with reference to FIG. 2.

A first layer 110 of material is formed by spraying powder particles 60, under an inert gas, onto a construction support 180, through a nozzle 190. This nozzle 190 conveys, simultaneously with the projection of particles 60 of powder, a laser beam 195 which originates from a generator 194. The first orifice 191 of the nozzle 190 through which the powder is projected on the construction support 180 is coaxial with the second orifice 192 through which the laser beam 195 is emitted, so that that the powder is projected into the laser beam 195. The term "coaxial nozzle" therefore means a powder beam concentric to the laser beam with the alignment of the Focal Laser point (F _L ) and the Focal Powder point (F _P ) on the axis of symmetry of the nozzle 190 (the Focal Laser point (F _L ) being adjustable relative to the point Focal Powder (F _P )). The powder forms a conical envelope, and the laser beam is conical in shape. The laser beam 195 carries the powder at a temperature higher than its melting temperature T _{F /} so that this powder forms a bath 102 on the surface of the support 180 under the laser beam 195. The bath 102 may also have begun to be formed on the support 180 by melting the region of the support 180 exposed to the laser beam 195, to a certain depth: in this case the powder feeds the bath 102 in which it reaches the fully molten state.

 Alternatively, the position of the nozzle 190 can be adjusted with respect to the position of the laser beam so that the powder does not pass for example enough time in the laser beam 195 or the speed of the powder particles at the nozzle outlet either too large or this laser beam is not sufficiently energetic so that the powder particles are completely melted upstream of the bath, and completely melt after only having reached the bath 102 formed beforehand on the surface of the support 180 by melting the region of this support 180 exposed to the laser beam 195.

The powder may also, upstream of the bath, not be melted by the laser beam 195 or be only partially because the size of certain particles constituting the powder is too great or that their mass flow is too big for them to be completely melted before arriving in the bath.

 Finally, the powder may not be brought to temperature before arriving then cold in the previously formed bath on the surface of the support 180 because the setting of the nozzle 190 relative to the laser beam is such that there is no intersection between the powder beam and the laser beam at the right of the work plane.

 While the assembly formed of the nozzle 190 and the laser beam 195 (or the support 180) moves downstream, the bath 102 is maintained and solidifies step by step to form a first bead of solidified material 105 on the support 180. The process is continued to form another solidified bead on the support 180, this other bead being for example juxtaposed and parallel to the first bead.

 Thus, by moving the assembly formed of the nozzle 190 and the laser beam 195, or the support 180, is deposited on the support 180 a first layer 110 of material which solidifies a first element 115 integrally whose geometry conforms to that defined by the information contained in the database of the computer tool used for computer-aided design and manufacture of the part to be manufactured.

 A second scan of the nozzle 190 is then performed to similarly form a second layer 120 of material on the first previously consolidated member 115. This second layer 120 forms a second consolidated element 125, all of these two elements 115 and 125 forming a block in one piece. The baths 102 formed step by step on the first element 115 during the construction of this second layer 120 generally comprise at least a portion of the first element 115 which has been remelted by exposure to the laser beam 195 (also called diluted zone forming part of integral of the liquid bath), and the particles of the powder feed the baths 102.

 This process of developing the layer-by-layer part is then continued by adding additional layers to the already formed assembly.

The scanning with the laser beam 195 makes it possible to give each layer a shape independent of the adjacent layers. Layers The lower parts of the room cool down more or less quickly as the upper layers of the room are formed.

 Alternatively or cumulatively, one can dissociate the trajectory of the powder from that of the laser beam and create on the one hand a very localized melt in the preceding layers, by action of the laser beam which can be adjusted very precisely with respect to the worktop, and secondly inject by means of a side nozzle of the powder in this melt.

Moreover, the aforementioned techniques by fast manufacturing of parts are not limiting and in particular Selective Laser Sintering (SLS) can be considered here: in this case, all or part of the particles of powder remains at a temperature below the melting temperature T _F of this powder.

 In order to reduce the contamination of the part, for example oxygen, oxide (s) or another pollutant during its manufacture layer by layer as described above, this manufacture must be carried out inter alia in a chamber to degree hygrometry and oxygen content controlled and adapted to the process / material pair.

 By way of example, as can be seen in the micrographs of FIG. 3, an oxide film (s) is formed with a release of hydrogen inside porosities (occluded gas) within a fused aluminum alloy according to the reaction:

2 Al (iiquid) + 3 H2O ( _goes scared) → + 3 H2 (gas),

when using, for example, the selective laser melting process without a drastic control of the dew point of the surrounding atmosphere (in this case the ratio between the partial pressures of H ₂ and H ₂ 0 corresponding to a quantity of water vapour). For example, at a dew point of -50 ° C is associated a water vapor content of 38.8 ppm.

In order to avoid any contamination by the residual oxygen, the chamber is filled with a neutral gas (non-reactive) with respect to the material in question such as nitrogen (N ₂ ), argon (Ar) , carbon monoxide (CO), carbon dioxide (CO2), or helium (He) with or without the addition of a small amount of hydrogen (H ₂ ) known for its reducing power. A mixture of at least two of these gases can also be considered. To prevent the contamination, especially by the oxygen of the surrounding environment, it is customary to put this chamber under pressure.

 Thus, according to the state-of-the-art of the art, selective laser melting or laser projection makes it possible to construct, with good dimensional accuracy, weakly polluted parts whose three-dimensional geometry can be complex but whose mechanical strength is still insufficient for certain applications and therefore requires a better optimization of the process and in particular a better optimization of the constitution of the powders.

 The selective laser melting or the laser projection also uses and preferably a powder composed of particles of spherical morphology, homogeneous composition, clean (ie not contaminated with residual elements from the synthesis of the powder) and fine (the dimension each particle is between 1 and 100 μm and preferably between 1 and 50 μm or even between 1 and 25 μm), which makes it possible to obtain an excellent surface state of the finished part.

 Selective laser melting or laser spraying also reduces manufacturing time, costs and fixed costs, compared to a molded, injected, compacted and sintered, wrought or machined piece.

 However, the parts produced by selective fusion by laser or laser projection have disadvantages.

 The current practice is to use, when possible, a pre-alloyed powder (FIG. 6A) with single-component particles of substantially spherical (or quasi-spherical) shape, dense (absence of intraparticle porosity, that is, ie absence of occluded gas in the particle), uncontaminated and unoxidized at the surface, whose composition is homogeneous, that is to say the same in any elemental volume of the particle, and identical to that referred to for the part resulting from the process of melting powder particles. In this case, the particles are formed of continuous material, of homogeneous composition and are, according to the invention, quasi-spherical and dense. They can be composed of a single chemical element (single-element powder), or of several chemical elements (multi-element powder).

However, one is sometimes forced to use a mixture of several types of powder (s) whose morphology, density (or mass volume, size distribution, composition, chemical homogeneity, surface and volume oxygen contamination, agglomeration state, specific surface area, flowability, in other words constitution or architecture of these powders, as well as their cost, must be adapted to the specificities of these rapid manufacturing processes in order to meet the specifications of manufactured parts.

 The use of a bulk mixture (not agglomerated) of several types of powders of different composition, and in particular powders readily available on the market, makes it possible to obtain rapidly and at a lower cost the desired average composition, either by using powders whose particles are composed of a single chemical element (single-element powder), or by using powders whose particles are composed of several chemical elements (multi-element powder), or by using these two categories of powder.

 However, the use of such a bulk mixture of several types of powder poses a number of problems.

 In particular, the flow or fluidity of such a bulk mixture of powders of different composition proves difficult through the powder dispenser (s) and through the nozzle in the case of the DMD process. Moreover, in the case of the SLM process, it is the homogeneous deposition and spreading of the powder bed that is affected by the use of such a bulk powder mixture.

 In addition, by using a mixture of several types of powders (single-element powder (s) and / or multi-element powder (s)), it is not easy to have a homogeneous fusion of all the particles of these powders. Indeed, the particles of each of these powders have an intrinsic melting temperature so that there is sometimes a significant difference between their melting temperatures.

Therefore, there is a proven risk of not being able to achieve, in the time allowed corresponding to the duration of the laser / material interaction, a melt of homogeneous composition and consistent with that referred in which all particles of the powders in the presence are perfectly dissolved, failing to be able to increase among others the laser power or decrease the speed of sweeping and thus increase the temperature and / or the volume of the bath without jeopardizing its stability and thus the construction stability.

 Depending on the reactivity of these different powders of the mixture, the formation of fragile intermetallics can also occur, often causing breaks in the raw parts of manufacture.

 This situation is illustrated on the micrographs of FIGS. 4A to 4C showing fracture facies of test pieces obtained from a first AISilOMg alloy powder supplemented by a low volume proportion of a second powder consisting of reactive and refractory particles of different compositions (based on iron and chromium for FIG. 4A, nickel, chromium and cobalt for FIG. 4B and based on iron, nickel and chromium for FIG. 4C), carried out under a scanning electron microscope different settings so that one of the two views of each micrograph shows the topography (secondary electron image, denoted by SE) and the other view highlights the differences in chemical composition (electron-retro-scattered image, designated by BSE). The larger particles of the second powder could not be put in solution they formed intermetallic inclusions, causing the rupture of the test pieces.

 The phenomenon described above can be accentuated by a broad particle size distribution of the second powder and by a large average size for the second powder, having the highest melting temperature among the various powders making up the reactive mixture.

 Also, because of similar particle sizes, large average size and very different melting temperatures between the various powders of the mixture considered here as non-reactive but soluble, one can find in the case of these melting processes, non-reactive particles. completely melted and / or dissolved in the supernatant liquid for larger ones on the surface of the bath. It can especially be particles of refractory material such as intermetallics or ceramics.

By way of example illustrating this situation, the micrographs of FIG. 5 relate to the case of a steel part reinforced with particles of titanium carbide in which some of these particles of the most refractory powder of the mixture do not have been completely implemented solution in the liquid bath, and thus concentrated on the surface of the bath, encircling and sometimes trapping even pockets of gas.

 This situation is all the more marked in that the particles, especially refractory particles, have a low density compared to the other powders of the mixture and are in a non-negligible volume proportion. These unmelted, after solidification of the liquid bath, may hinder the adhesion of the next layer or the subsequent layering and even be the cause of manufacturing defects (macroscopic porosity) if the size and the volume fraction of these unfused are important. Indeed, these unmelted are hard inclusions in a ductile matrix and thus contribute to the premature failure of manufactured parts.

 Moreover, the dissolution, sometimes incomplete or delayed over time, of these different types of powders can lead very locally during cooling to chemical segregation phenomena (case of a mixture of non-reactive powders) leading to phases low melting point eutectics and / or unwanted chemical reactions between them (case of a mixture of reactive powders) leading to the presence of hard phases (for example intermetallic phases, such as those of FIGS. 4A, 4B , and 4C) undesired, which leads to obtaining a microstructure of the raw material of manufacture not corresponding to that desired in fine and having mechanical strength properties lower than those desired for the application in question as well as a risk of burning after thermal post-treatment.

 Also, if the various powders of the non-reactive mixture are not sufficiently wettable between them, due inter alia to the total absence of solubility between these powders, the "good material health" of the parts will not be reached.

The object of the present invention is to provide a method of manufacturing a desired composition and microstructure part in a metallic, intermetallic, ceramic, ceramic matrix composite (CMC) or intermittently reinforced metal matrix composite (CMM), by melting powder particles (s) by means of a high energy beam, which overcomes the disadvantages of the prior art. In particular, by this invention, it is intended to obtain a homogeneous composition of the part conforming to the desired composition, the absence of manufacturing defects, a macro- and microstructure (size and morphology of the grains, then morphology, fineness and composition of the phases ) adapted from the raw material (at the end of the melt manufacturing stage), a good dimensional quality (ensured by a perfect bath stability), a minimization of the residual stresses, a total mass yield of the process (fusion + recycling) the greatest possible and an optimal manufacturing speed or optimal manufacturing time, whatever the materials envisaged.

 This goal is achieved thanks to the fact that the powder used is a single powder whose particles have a sphericity between 0.8.

(corresponding to a cube) and 1.0 (corresponding to a sphere) and a form factor between 1 (corresponding to a sphere) and V2 (corresponding to a cube), each particle of powder having a substantially identical average composition and in the particle size distribution of said powder is tightened around the average diameter value d ₅ o% such that: (dg ₀ oa - dso%) / dso _% ≤ 0.66 and (d ₅ o% - dio %) / d ₅ o% ≤ 0.33 with (dgo% - dio%) / d ₅ o% ≤ 1.00.

Preferably, this particle size distribution, defined by the value of "span", (dgo% - dio%) / dso%, must be less than or equal to 0.50 with (dg ₀ % - d ₅₀ %) / d ₅ o% ≤ 0.33 and (d ₅ o% - di ₀ %) / d ₅₀ % ≤ 0.17.

By sphericity is meant the sphericity factor (a dimensionless number) as defined by Wadell as follows: the ratio between the sphere area of the same volume as the particle and the surface of the particle in question (ψ _ν ), Equivalent squared equivalent of the ratio of volume equivalent diameter to surface equivalent diameter.

 Preferably, this sphericity factor is greater than 0.82, advantageously greater than 0.85, and still more preferably greater than 0.90 with an even more advantageous situation when this sphericity factor is greater than 0.95.

Advantageously, all the particles of the single powder used according to the invention have a form factor between 1 (corresponding to a sphere) and V2 (corresponding to a cube). This form factor, which gives a good indication of the slenderness of the particles, is defined as the ratio between maximum Feret diameter (maximum distance between two parallel tangents at opposite sides of the particle) and the minimum Feret diameter (minimum distance between two parallel tangents at opposite sides of the particle).

 Preferably, this form factor is less than 1.3, advantageously less than 1.25, and still more preferably less than 1.15 with an even more advantageous situation when this form factor is less than 1.05.

 In the present text, the term "particle" corresponds to a physical entity isolated from the other physical entities of the powder considered and may correspond to different situations among which those of FIGS. 6A to 61

 Thus, according to the invention, one does not use a mixture in bulk (non-bound powders particles) of two or more different powders.

 Indeed, according to the invention, a single powder is used, the "particles" (which are optionally isolated macro-particles from each other) all have on average the same composition.

 It should therefore be noted that the identical average composition of all the "particles" of the single powder used according to the process of the present invention corresponds to a chemical composition that is close to or identical to that of the material that is intended to be obtained in the part of the additive manufacturing process.

 In this way, by not using a bulk mixture of several powders that is to say by the use of a single powder, it avoids the presence of isolated particles of these different powders of the mixture, whose temperatures are different, or very different, and / or whose average sizes and size distributions may not be equivalent and / or the fineness of each of the powders of the mixture makes it difficult to obtain a homogeneous mixture, and / or or whose density is different or very different, and / or whose volume proportion of one of these different powders is low compared to the others.

For the manufacture of CMM parts from a mixture of powders, it has become clear to the inventors the need to have a single powder having both good flowability (provided by a coarse and spherical powder) and rapid dissolution between elementary particles, for example ceramic and metallic (provided by elementary fine particles and preferably those of the refractory material). However, the use of elementary fine particles for each of the powders of the mixture is difficult because of a pronounced risk of agglomeration during mixing. Indeed, due to the adhesion forces between elementary particles that increase with a decrease in their sizes, these forces can become greater than the force of gravity. Moreover, fine elementary particles promote the concentration of electrostatic charges generating dust explosion. However, the smaller the size of the elementary particles of this mixture, the easier the dissolution and the more the assembly has homogeneous properties. Also, the use of macro-particles consisting of a homogeneous mixture of fine elementary particles bound together by a binder and from different powders is unavoidable.

 According to the invention, therefore, a single powder of suitable composition which forms a pre-alloyed powder taken in the broad sense (single-component powder, (atomized powders, coated powders, kneaded powders, kneaded and milled powders, encrusted powders, ...) or multi-component powder (agglomerated powders, ..)), the "particles" of which have a high degree of sphericity (sphericity greater than 0.7, preferably greater than 0.8 and advantageously greater than 0, 9).

 During the implementation of the synthesis processes of this single powder, we will be vigilant so that the "particles" are free of occluded gas and are uncontaminated in certain chemical elements or at least that these elements are below redhibitory levels for the intended application.

 In some cases, it will be necessary to use the use of an additive manufacturing chamber under a controlled atmosphere (partial pressure of oxygen and water vapor), slight overpressure or preferably slight regulated depression.

When possible, the "particles" of this single powder are mono-components that is to say consist of a single component, namely formed of a continuous material of homogeneous composition (FIG. 6A) or heterogeneous composition, that is to say non-homogeneous, at the scale of the "particle" (FIGS. 6B, 6C, 6D, 6E, 6F, 6G and 6H).

 Preferably, the powder used is obtained by atomization or centrifugation (in particular by rotating electrode) of a parent alloy and its composition is then homogeneous at the particle scale but not necessarily at the scale of the microstructure.

 For example, and preferably if its melting temperature, its chemical composition and its reactivity allow it, the pre-alloyed powder consists of single-component "particles" formed of a continuous material of homogeneous composition at the scale of "Particle", composed of a single chemical element (single-element powder) or most often of several chemical elements (multi-element powders), of spherical or quasi-spherical morphology (FIG. 6A) and used according to the method of The present invention is obtained by gas atomization ("Gas Atomization" in English) or by spinning-type centrifugation ("Rotating Electrode Process" in English) of a mother alloy in rotation and in fusion from which droplets are formed and formed. cool in flight in a chamber under a protective or neutral atmosphere, to form the particles of the powder. Such parent alloy is for example metallic.

 After recovery of solidified droplets at the bottom of these devices, the finest from separator cyclones of the atomizing device, a selective sorting of these droplets is ensured initially by pneumatic vibration assisted sieving for a certain size range in the limit of 30 to 40 pm and in a second time by elutriation (air or gas turbine) for the finest particles in the limit of 1 pm.

 Another case approaching the previous case differs only in the fact that the single-component "particles" of the pre-alloyed single powder (ie, multi-element particles formed of continuous material) exhibit a heterogeneous composition on the the "particle".

These pre-alloyed powders can be produced by different processes or combination of different synthesis processes, in particular processes based on mechanical or thermomechanical treatment in the dry, wet or inert gas (in particular by conventional grinding by means of balls, balls, knives, hammers, discs or rollers, ... or by co-grinding at higher or lower energy and preferably between a ceramic powder and a metal powder using a high energy planetary ball mill (grinding mechanically). synthesis) or for very specific applications by cryogenic grinding, reactive grinding between reactive solid particles or solid particles and reactive gas or by mechanofusion), a chemical or thermo-chemical treatment (in particular by CVD coating "Chemical Vapor Deposition", PECVD or PACVD "Plasma Enhanced (Assisted!) Chemical Vapor Deposition" and OMCVD "Organo-Metallic Chemical Vapor Deposition" in English), or a reactive synthesis (in particular by self-propagating combustion better known under the acronym SHS "Self-propagating High Temperature Synthesis"" in English).

 Remember that unlike the gas atomization and the centrifugation of a metal alloy which give very spherical particles of high chemical purity, the mechanical or thermomechanical grinding or the mechano-synthesis of metal powders preferably introduce impurities from the grinding elements and do not allow rigorous control of the morphology and size of the particles. However, the particle morphology is usually isotropic and fairly spherical.

 We then obtain different types of pre-alloyed powders whose "particles" are mono-components of heterogeneous composition at the scale of the "particle" such as those visible in Figures 6B to 6H.

 According to an advantageous possibility, the powder used is obtained by coating or incrustation.

 FIG. 6B shows such a particle of pre-alloyed powder formed by a mono- or multi-element particle of homogeneous composition coated or coated, the core of which is continuous and made of a first material and whose envelope is continuous, made of a second material of a composition different from the first, and deposited, for example, under vacuum in the chemical vapor phase (CVD deposition) or physically (PVD deposition, "Physical Vapor Deposition") or by a thermo-chemical treatment in beds fluidized dry or wet or by a thermo-mechanical treatment of the mechanofusion type.

Hard particle mechanofusion metal coating will improve the ductility and toughness of high fraction CMM volume of ceramic reinforcements non-oxides (carbides, nitrides, silicides and borides) or intermetallic because for such voluminal fractions the fusion of such a metal coating by means of a high energy beam greatly facilitates its distribution between the ceramic reinforcements which remain strong. Note that the coating of the pre-alloyed particles by these same synthetic processes mentioned above may be of the multilayer type.

 According to another advantageous possibility, the powder used is obtained by grinding / kneading, namely by grinding / mechanical kneading by impact or attrition (frictional wear) or by shearing or compression or a combination of two or more of these efforts. The final average size of the particles depends on the grinding technique used, the characteristics of the grinding elements (type of material, shape, size), the grinding time, the grinding medium (dry grinding with or without controlled atmosphere, in the middle aqueous or non-aqueous, with or without dispersant), the charge ratio (mass of the grinding elements on powder mass) and the speed of rotation of the grinding elements and / or the jar.

FIG. 6C illustrates the case of a particle of pre-alloyed powder obtained by incrustation. In particular, incrustation of fine hard particles of a first powder on the surface of mono- or multi-element ductile particles of homogeneous composition of much larger size from a second pre-alloyed powder. One of the means of achieving this result is the mechano-synthesis ("mechanical alloying" in English) of mixing at high energy in the desired volume proportions a second fine powder of high hardness with a first ductile and coarse powder. This can be ensured by attrition and / or under the impact of balls by means of a planetary mill. The energy released is by an opposite rotation of the grinding vessel (jar) and the support disc under a protective gas. For example, the particle of pre-alloyed powder which is visible in FIG. 6C, consists of a metal alloy core T16AI4V of homogeneous composition, and of an envelope formed of ceramic elementary fine particles (for example TiB ₂ or TiC). ) or non-metallic (for example B for boron) which have encrusted on the surface of T6A4V. FIG. 6D illustrates the case of a particle of pre-alloyed powder of dispersed type whose material is continuous and obtained from the intimate mixing of two or more particles of original powders of different chemical composition, preferably comprising metal alloys. ductile, consisting of multi-elements: for example in Figure 6D, we distinguish the parts, respectively clear and dark, of the two original powders whose particles of homogeneous but different composition have deformed plastically and many times linked together to form the pre-alloyed powder particle of Figure 6D (the particle sizes of the two original powders can be of the same order of magnitude or frankly different).

 FIG. 6E illustrates the case of a particle of pre-alloyed powder of dispersed type but whose material is continuous and obtained from the intimate mixing of two or more particles of original powders of very different size and of different chemical composition, comprising preferably a ductile metal alloy and hard elementary particles, especially oxides (ODS materials "Oxide Dispersion Strengthened" materials): for example, one distinguishes the parts, respectively clear and dark, of the two original powders whose particles are of homogeneous composition but different, the clear particles of the first powder having plastically deformed and having repeatedly bonded with the hard and dark particles of the second powder, to form the pre-alloyed powder particle of Figure 6E.

 In the latter two cases, it is a technique of pre-alloy by grinding and intense mechanical mixing medium or high energy most often requiring the use of a planetary mill.

FIG. 6F illustrates the case of a particle of pre-alloyed powder combining the characteristics of the powder particles of FIGS. 6D and 6E: this particle of pre-alloyed powder is of dispersed type but whose material is continuous and obtained from the intimate mixing of three original powders of different chemical composition, comprising two powders of ductile metal alloys: for example in FIG. 6F, there is a white matrix resulting from one or more large particles, the large dark parts each coming from a single particle of average size, even close to that of the first powder and dark elementary particles of much smaller hard size, including oxides.

 FIG. 6G illustrates the case of a pre-alloyed powder particle combining the characteristics of the powder particles of FIGS. 6B and 6D: a first production step makes it possible to obtain pre-alloyed powder particles such as those in FIG. 6D, namely of dispersed type but whose material is continuous and obtained from the intimate mixing of two or more particles of original powders of different chemical composition, preferably comprising ductile metal alloys, consisting of multi-elements: it is is the heart of the particle of Figure 6G. A second development step makes it possible to form the continuous envelope, made of a second material of different composition from the first material forming the core.

 FIG. 6H illustrates the case of a pre-alloyed powder particle combining the characteristics of the powder particles of FIGS. 6D and 6C: a first production step makes it possible to obtain pre-alloyed powder particles such as those in FIG. 6D, namely of dispersed type but whose material is continuous and obtained from the intimate mixing of two or more particles of original powders of different chemical composition, preferably comprising ductile metal alloys, consisting of multi-elements: it is is the heart of the particle of Figure 6H. A second development step makes it possible to form the discontinuous envelope by inlaying fine hard particles of a second powder on the surface of ductile particles of heterogeneous composition of much larger size resulting from a first pre-alloyed powder, such as those in FIG. 6D.

In the other cases, illustrated in FIGS. 61 and 6J, the "particles" of this single powder are multi-components, namely each formed identically by several components (or elementary particles) of different chemical composition, interconnected by an organic or inorganic binder within a "macroparticle". We are still talking about composite powders. In this case, the particles are formed of discontinuous material, of heterogeneous composition and are, according to the invention, quasi-spherical. The use of a binder in the synthesis of this agglomerated powder confers discontinuous matter character to the agglomerates and justifies the name of multi-component particle powder.

 In some cases, this binder is removed after the agglomeration step by the use of a consolidation step of pyrolyzing or evaporating the binder by bringing the agglomerated powders into temperature.

 Such "particle" type "macro-particle" can be obtained by granulation comprising an agglomeration of components or elementary particles of different sizes, shapes and / or chemical compositions in the presence of moisture followed by drying. The development of particles of "macro-particle" type powders by agglomeration-drying or spray-drying of a slip ("spray-drying" in English) requires, however, to master the following phases:

 the formulation of the slip, in particular the choice of the solvent, the dispersant, the plasticizer and the binder (stability, homogeneity, rheological behavior and sedimentation),

 the spray of the slip and the drying of the droplets (size and distribution of the droplets, speed and drying method): this granulation of the mixture of elementary particles in the form of a suspension makes it possible to transform it by atomization at low temperature (in a stream of air or hot inert gas) in spherical agglomerates of comparable size, often greater than 50μιη and whose flowability is excellent,

 A consolidation step of the granules thus formed (furnace, flame or plasma torch treatment) may sometimes be considered if denser and cohesive agglomerates are desired. Moreover, the binder can cause problems during additive manufacturing from unembedded agglomerated powders, hence the interest of removing this binder. The furnace treatment makes it possible to consolidate the structure of the granules without modifying their characteristics while the oxyacetylene flame treatment leads to partial melting, sintering and spheronization of the granules modifying their morphology.

Also, this unique powder is formed of "macro-particles", also referred to as "agglomerates", "aggregates" or still "granules", and is a powder referred to under the generic name of "engineered owders".

 Different types of composite powders or pre-alloyed powders with multi-component particles are obtained, such as those visible in FIGS. 61 and 61.

According to an advantageous possibility, the powder used is obtained by granulation from a suspension also called slip. The slip is an aqueous or non-aqueous suspension of fine powders consisting of a mixture or not of different elementary particles different in shape, composition and / or size. The solvent should have a low boiling point and low viscosity. It must ensure the dissolution of the binder which may be organic or inorganic, that of the plasticizer and various additions such as deflocculants or dispersants and wetting agents. On the other hand, the solvent must not be soluble or reactive with the elementary particles of the composite powder. Although flammable and toxic, organic solvents are still widely used because of their low viscosity, their low surface tension (γι _ν ) favoring the wetting of the elementary particles, their high vapor pressure leading to a rapid drying of the particles. granules. Nevertheless, aqueous solvents are starting to take precedence over organic solvents for obvious environmental and cost reasons. Water has the major disadvantage of a low rate of evaporation. After evaporation of the solvent, the binder ensures the mechanical cohesion between the elementary particles of the granules, their handling and transport. Generally, a plasticizer which is often a low molecular weight polymer is added to the binder to lower its viscosity and reduce its glass transition temperature (Tg). The addition of plasticizer as its name suggests increases the plasticity of the granules.

"Particles" formed of granulated composite particle macro-particles are visible in FIGS. 61 and 6J, they are granules consisting of components or elementary particles essentially connected to each other by a binder, for example water-soluble polymers such as vinyl polymers, acrylic polymers, polyimines and polyoxides, but also emulsion polymers and polymers of natural origin. In Figure 61, there are two types of elementary particles or elementary components: elementary metal particles ductile clear, of different sizes and fragile elementary components formed of dark short fibers (or "whiskers" in English). Very often, it is ceramic or intermetallic type refractory fibers, acting as reinforcement to increase the mechanical strength of the metal matrix, insofar as the volume fraction of reinforcement is sufficiently large. These fragile and refractory elementary components of ceramic and / or intermetallic type may also be of equiaxed or spherical shape. Moreover, a mixture of metal elementary particles and refractory elementary components of variable form can be considered.

 In FIG. 63, there are several elementary particles or elementary components of the same types, in particular metallic but sometimes also ceramic or intermetallic, of different size, shape and chemical composition, namely in the case represented three metallic elementary particles: small clear elementary particles (eg aluminum), clear elementary particles of larger size (eg titanium) and dark ovoid elementary particles (eg niobium).

For the formation of these composite powders, one generally starts from a homogeneous mixture of several types of particles (several powders mono-element and / or multi-elements, "element" relating to the chemical element) having an average size, a size distribution and morphology suitable for macro-particle synthesis by known mixing and agglomeration techniques, using a binding additive (eg an organic binder) and other additions with or without densification (or consolidation) and spheroidization. It is by these well-known techniques of powder metallurgy to obtain a homogeneous and relatively narrow distribution of the various powders constituting the mixture with the average composition initially aimed at, a low porosity and a spherical morphology of the "particles" formed by these say macro-particles. The examples mentioned in FIGS. 6A to 6J relate to the illustration of the structure or constitution of powder particles falling within the scope of the present invention and are of course not limiting.

These different pre-alloy processes of varying cost and cleanliness are adapted on the one hand to the volume fraction, specific surface, ductility (or hardness), melting temperature, reactivity, absorption of the radiation emitted by the laser, density (density) and the nature of the chemical bonds of the various elementary components of the powder and secondly the chemical composition of the homogeneous liquid obtained by partial or complete melting of said powder (it is recalled that because the powders are sometimes constituted particles whose melting temperatures are very different). Furthermore, according to the invention, the possible size range of the macro-particles of the composite powder (defined by dgo% - dio% or even preferably by di ₀ o% - d ₀ %), referred to the diameter value medium or median (d ₅ o%) is low so as not to have too much size difference between these macro-particles as well as too coarse granules (d ₅₀ % close to 50μπι).

 In general, according to the invention and for any type of powder described in the present application, it is necessary to ensure a relatively narrow particle size distribution of the particles. However, for the composite powder, the granulation process results in the narrowest particle size distribution and the coarsest powder. Also, this agglomerated composite powder is more suitable for the DMD process than for the SLM process. Recall that in practice a better compactness of the powder bed deposited on the production plate is obtained by considering a wide particle size distribution, accessible by atomization.

According to the invention, (d ₉₀ % - d ₅ %) / d ₅ % and (d ₅ % - di ₀ %) / d ₅ % are two terminals, the first of which is less than or equal to 0.66 (66%), or even less than or equal to 0.33 (33%), and preferably less than or equal to 0.17 (17%), and the second is less than or equal to 0.33 (33%), or even less than or equal to 0.17 (17%), and preferably less than or equal to 0.08 (8%).

However, the use of composite powders (also called granules, aggregates or agglomerates) of desired composition having a spherical morphology greatly facilitates their flow through the distributor (s) of powders and through the nozzle in the case of the DMD process as well as their homogeneous spread in a bed of powder on the production plate in the case of the SLM process. The granulation of the homogeneous mixture of elementary particles of different powders, to form the single powder consisting of macro-particles, also facilitates its handling, transport and storage by avoiding the segregation or sedimentation of particles of different sizes and / or masses. of these different powders (the smaller and / or heavier particles tend to flow easily through the interstices of the granular edifice). Granulation techniques are numerous in the science of powder metallurgy and are well known to those skilled in the art.

 The use of a composite powder consisting of macro-particles makes it possible to envisage among the various powders to be mixed a powder composed of refractory particles, preferably fine and in a moderate amount. In this case, the technique of manufacturing this composite powder requires that the mixing of these different powders is homogeneous before it is followed by a suitable granulation technique. In this case, this technique not only makes it possible to avoid, on the one hand, problems of layering and homogeneity of the powder bed in SLM and, on the other hand, problems of flow through the nozzle, but also prevents dispersion (scattering) of these fine particles at the outlet of the DMD nozzle, especially since they are not very dense (low density), thus guaranteeing a repeatable (or reproducible) composition of the liquid bath.

 It is indeed important that the particles of the different powders are mixed homogeneously before the granulation process. Otherwise, it may result in granules or macro-particles of different composition, which affects the composition of the final part which is then heterogeneous. The mixture is even more difficult to homogenize than the volume proportion of one of these powders is low compared to the others (for example additions to the rare earth mixture as deoxidizing elements or surfactant elements to facilitate the wetting between solid and liquid).

Other pre-alloy techniques relating to single-component powders exist such as "Splat Cooling" and "Melt- Spinning "which are, however, techniques much less common in the industry or are specific to a class of materials (especially aluminum alloys in this case).

 Thanks to the invention, the use of such a pre-alloyed powder by these techniques, in the straight line of the atomization, makes it possible in particular to ensure the obtaining of a homogeneous chemical composition in each particle and between all the particles.

 Thus, it is possible to produce a part as close as possible to the dimensions of the final part, and having the properties of resistance, in particular, of mechanical strength, but also of resistance to oxidation or corrosion corresponding to the level expected for the application. to which the piece is intended.

 Therefore, it follows that it is no longer systematically necessary to use subsequent heat treatment homogenization (that is to say, high temperature treatments), which provides a substantial saving and prevents the piece from distorting itself. Also, since the structurally hardened materials are sufficiently quenched as a result of these particle fusion processes by a high energy beam, a precipitation treatment of the low temperature (tempering) hardening phase may suffice.

 The solution according to the invention therefore makes it possible to very substantially reduce the heterogeneity of composition and microstructure of the material forming the part resulting from the additive manufacturing process by melting powder particles by means of a high energy beam.

 The invention will be better understood and its advantages will appear better, on reading the detailed description which follows, of embodiments given by way of non-limiting example. The description refers to the accompanying drawings in which:

 FIGS. 1 and 2, already described, are explanatory diagrams of two additive manufacturing processes by melting of powder particles, known and preferably used in the context of the present invention,

FIG. 3, already described, illustrates the formation of a film of oxide (s) which forms with the presence of occluded gas porosity during the melting of an aluminum alloy in the presence of water vapor, FIGS. 4A, 4B and 4C, already described, are micrographs of fracture facies of specimens exhibiting intermetallic inclusions following the reaction of an aluminum-rich liquid with refractory particles based on iron or nickel which play. the role of complements to obtain the desired composition of the aluminum alloy,

 FIG. 5, already described, corresponds to micrographs representing a steel part reinforced with particles of titanium carbide of lower density, some of which could not be completely dissolved and could not be solidified in the form of primary dendrites, and

 FIGS. 6A to 6J, already described, represent different mono-component pre-alloyed powders (both of homogeneous composition, FIG. 6A, and of heterogeneous composition, FIGS. 6B, 6C, 6D, 6E, 6G, 6G and 6H) or multi -composantes (also called composite powders, Figures 61 to 6J) whose constitution or structure differs according to the methods of synthesis of these pre-alloyed powders.

 In order to overcome some of the disadvantages of additive manufacturing processes of structural materials by melting powder particles, such as for example the evaporation of a highly volatile chemical element of the bath, an inappropriate microstructure of the piece by the size and / or the morphology of the phases and / or grains, a marked anisotropy of the material, the presence of undesirable fragile oxides or precipitates, the presence of defects ..., it should be considered, according to one of the methods of synthesis of granular materials described in the present invention, a mono-component pre-alloyed powder or a multi-component composite powder resulting from mixing and agglomerating powders, of average composition different from that usually accepted for the alloy with which the part is carried out while retaining at best a powder or a mixture of powders of spherical morphology.

 According to a first embodiment of the invention, the powder used has a composition enriched in at least one chemical element of the composition of said material forming the part resulting from said process.

It is a question of adding in the composition of the master alloy of the powder a sufficient quantity of one or more elements entering into the composition of said material forming the final piece, and this for to compensate for a natural loss of a proportion of these elements during the implementation of the additive manufacturing process by melting powder particles by means of a high energy beam. In this case, it is a mono-component pre-alloyed powder of homogeneous composition.

 In this case, it is considered that the average chemical composition of the powder is slightly different from that of the material, in particular of the metal alloy, of the part resulting from the process according to the invention because the loss of a quantity of one or more chemical elements during manufacture, especially by evaporation. This evaporation is all the more favored by the use of an additive manufacturing process under vacuum, in particular by electron beam selective melting (EBM), unlike the SLM process, which The manufacturing enclosure is generally placed in overpressure.

This natural loss can result from the particularly high evaporation of these elements, after the powder particles have been brought to very high temperatures, beyond their melting and / or in a high vacuum (1 CT ⁵ to 10 ⁶ mbar).

 According to this first variant of the first embodiment, said chemical element or one of its oxides is volatile at the implementation temperature by said high energy beam.

 In the case where the content of volatile chemical element which is lost under the effect of a high energy beam remains low, this disadvantage is most often overcome by the use of a pre-alloyed powder monocomponent, homogeneous composition (powder of Figure 6A), enriched with said volatile element. In the case of evaporation of greater magnitude, it is appropriate - if it is not possible to obtain industrially a mono-component pre-alloyed powder of homogeneous composition by the technical limitations known to date - to consider a mono pre-coated powder composition of heterogeneous composition resulting from a coating (powders of FIGS. 6B and 6G) or an encrustation of fine particles of powder (powders of FIGS. 6C and 6H), the composition of which consists of the volatile chemical element.

 For example, said material is a metal alloy which is

Ti6Al4V and said volatile element is aluminum. This alloy TÏ6AI4V or TA6V is composed of titanium, 6% by weight of aluminum and 4% by weight of vanadium.

 An enrichment of the aluminum powder is preferably considered, which is between 0.15 and 3% by weight relative to the composition of the TiAl4V alloy, and preferably between 0.15 and 1.5% by weight.

 According to another example, said material is a metal alloy based on aluminum and lithium (especially alloys with mass composition 2.7% <Cu <4.3% - 0.8% <Li <1.6% - 0.25% <Ag <0.45% - 0.01% <Mn <0.45% - 0.3% <Mg <0.8% - Zn <0.63% - Si <0.12% - Fe <0.15% and the remainder being Al) and said volatile element is lithium, the evaporated amount of which can be from 0.1 to 0.5% by weight.

 According to another example, said material is a metal alloy based on titanium, preferably 6242 (ie Ti-6Al-2Sn-4Zr-2Mo-O, lSi in% by weight), and said volatile element which is enriched is Sn, this enrichment being between 0.15 and 1.5% by weight relative to the composition of the alloy.

 According to another example, said material is an aluminum-based metal alloy, preferably 6061 whose main alloying elements are Mg and Si, and said volatile element which is enriched is Mg and / or Cu , this enrichment being between 0.05 and 0.40% by weight relative to the composition of the alloy for Cu and 0.05 to 1% by mass for Mg.

 According to another example, said material is an intermetallic TiAl type, preferably TiAl 48-2-2 (ie Ti-48Al-2Cr-2Nb atomic%), and said volatile element which is enriched is Al, this enrichment being between 0.15 and 3% by weight relative to the composition of the intermetallic.

According to another example, said material is a nickel-based metal alloy, precipitation hardening type γ'-Ni ₃ (AI, ^~ n) and said volatile element which is enriched is Al, this enrichment being between 0 , 05 and 3% by mass relative to the composition of the alloy.

According to another example, said material is an iron-based metal alloy and more specifically a martensitic stainless steel with a Cu-structured hardening, preferably 17-4PH (Z6CNU 17-04 or X5CrNiCuNbl7-4 or 1.4542) of mass composition C: 0.07% max, Mn: 1.00% max, P: 0.040% max, S: 0.03% max, Si: 1.00% max, Cr: between 15.00 and 17.00%, Ni: between 3.00 and 5.00%, Cu: between 2.8 and 5.00%, Nb + Ta: between 0.15 and 0.45% and the remainder being Fe, and said volatile element which is enriched is Cu this enrichment being between 0.15 and 3% by weight relative to the composition of the alloy.

 According to another example, mention may be made of the 15-5 PH alloy which is a precipitation-hardened martensitic stainless steel (Z7CNU 15-05 or X5Cr1 / CuNbl5-5 or 1.4540) of mass composition C: 0.07% max, Mn: 1.00 % max, P: 0.040% max, S: 0.03% max, Si: 1.00% max, Cr: between 14.00 and 15.50%, Ni: between 3.50 and 5.50%, Cu: between 2.50 and 4.50%, Nb + Ta: between 0.15 and 0.45% and the remainder being Fe. An enrichment in Cu (total quantity between 1500ppm and 2.5%), of this element likely to volatilize under a high energy beam, should be considered in order to maintain the desired volume fraction. of hardening phases which is strongly related to the Cu content. But since the 15-5 PH, obtained by a liquid-phase process, is sensitive to the notch effect following the Cu enrichment of certain grain boundaries forming "gutters" on the surface of the material and of this fact has a high tolerance to defects, it is most often not to readjust the loss of Cu if the precipitation hardening of the piece manufactured by laser is sufficient for the application in question.

 Let us take another example concerning the magnesium alloy RZ5, which is designated according to the French standard AFNOR by GZ4TR and by ZE41 (or Mg-Zn-RE-Zr) according to the ASTM standard. Its mass composition is as follows: Cu: <0.10%, Mn: <0.15%, Ni: <0.01%, Zn: between 3.50 and 5.00%, Zr: between 0.40 and 1.00%, Ce (rare earth): between 0.75 and 1.75% and the rest being Mg.

 To this magnesium alloy RZ5 can be added zinc which is a volatile element whose evaporated amount can be from 0.5 to 2.5% by mass.

According to a second embodiment of the invention, the composition of the powder used has at least one additional chemical element in a reasonable amount (non-zero, in particular greater than 0.001% by mass, ie 10 ppm or 10 mg / kg but less than 0.5% by weight, ie 5000 ppm or 5 g / kg) and able to modify the microstructure of said material of the resulting part of said process with respect to the case where this additional chemical element is absent from the composition of the powder.

 This is done, where possible, by the use of a mono-component pre-alloyed powder of homogeneous composition (powder of FIG. 6A), enriched with said element. Sometimes, it is necessary to consider a mono-component pre-alloyed powder, of heterogeneous composition resulting from a coating (powders of FIGS. 6B and 6G) or of an encrustation of fine particles of powder (powders of FIGS. 6C and 6H), whose composition consists of the said added element. Insofar as the additions are not ductile, compared to the one-component pre-alloyed powder, it will be preferred to knead-grind this mono-component powder with the hard fine particles (powders of FIGS. 6E and 6F), the composition of which is consisting of the said added element.

 Furthermore, it must be taken into account that a too high content of modifying elements reduces the fluidity of the bath and increases the dissolved hydrogen content in the bath accompanied by a gas porosity occluded upon solidification.

 In this case, it is an unnecessary element as an element in the composition of the desired parent alloy, but present only to modify the microstructure of the material and in particular the metal alloy of the final piece in order to fulfill the specifications while overcoming certain specificities of the process, in particular the microstructural anisotropy and the large size of the grains.

 According to a first variant of the second embodiment, said material is a metal alloy and said additional chemical element is able to modify the morphology of the metallurgical phase or phases of said metal alloy.

For example, for the Al-Si hypo-eutectic aluminum alloys it is the additional chemical elements sodium (Na) and / or strontium (Sr) and / or calcium (Ca) and / or antimony (Sb) which have in effect to refine the morphology of the lamellar or fibrous eutectic. Note that this refining effect of the eutectic microstructure which increases the ductility of the alloy is reduced by the addition of the phosphorus element (P) which reacts with the modifying elements, and in particular sodium, to form phosphures. Also, the phosphorus content should be kept low (<15 to 30 ppm). Recall that another way to refine the eutectic microstructure is to use process parameters to generate a high rate of solidification which also already characterizes these rapid manufacturing processes by melting powder particles by means of a beam high energy.

 According to a second variant of the second embodiment, said material is a metal alloy and said additional chemical element is capable of refining the size of the grains of said metal alloy without systematically modifying the morphology of the grains: it is a question of carrying out a refining the grain size by adding inoculant.

For example, it is well known that for aluminum alloys the equiaxed fine grain structure offers the best combination of strength and ductility. The morphology and size of the grains formed after solidification of the bath are determined by the composition of the alloy, the rate of solidification and the small addition of additional chemical elements known as "refiners", in particular titanium and boron in the form of Ti, B or Ti-B salts or Al-Ti, Al-B or Al-Ti-B alloys. These refining chemical elements form, in contact with liquid aluminum, intermetallic compounds with a high melting point which constitute sites of heterogeneous germination of grains and increase the number of grains. Other inoculants such as Nb, Zr and Cu-P (where the phosphorus element acts in particular on Si germination) are also used for the refining of aluminum alloys. The small addition (10 to 5000 ppm) of Ti and / or Zr in the aluminum alloys, leading to the formation of TiAl ₃ and ZrAl ₃ intermetallics, reduces the hot cracking during the solidification of these aluminum alloys by refining their grain.

For example, said parent metal alloy is an aluminum-based alloy of the AISilOMg type close to the 43000 alloy according to the NF EN 1706 standard or is still close to the A360 alloy according to the "Aluminum Association" in the USA. This alloy is composed of aluminum, 9.5% by weight of silicon, 0.5% by weight of magnesium and 1.3% by mass of iron and said element is titanium and / or boron and / or zirconium (preferably 100 to 300 ppm Ti, and / or 20 to 50 ppm B and / or 100 to 500 ppm Zr).

These three elements can be introduced into the parent alloy in the form of an Al-Ti or Al-Zr binary alloy containing from 3 to 10% by mass of Ti or Zr, or else in the form of a ternary alloy Al -Ti-B or Al-Zr-B consisting of the said same Al-Ti or Al-Zr binary alloy with in addition 0.2 to 1% by mass of B. The direct introduction of TiB ₂ or ZrB ₂ particles into the aluminum-rich parent alloy is to be discarded because of its high melting point making it difficult to dissolve, especially since the particles are large. Also by the introduction of these alloys into the aluminum alloy, aluminides (essentially TiAl ₃ or ZrAl ₃ ) and borides (essentially TiB ₂ or ZrB ₂ and sometimes AIB ₂ ) are formed with a size, a morphology and a distribution that go well, to constitute sites of heterogeneous germination of aluminum grains.

 Thus, preferably, titanium and / or boron are two chemical elements which are introduced, alone or together, preferably in the form of binary (Al-Ti) or (Al-B) or ternary (Al-Ti) alloys. -B) with a low melting point, close to that of the aluminum-based alloy.

For other types of alloys other than aluminum alloys, for example, said parent metal alloy is a titanium-based alloy which is TiAl4V or TA6V and said additional chemical element or refining element is boron (10 to 5000 ppm of B) or TiB ₂ type borides (10 to 5000 ppm of TiB ₂ ).

Preferably, these chemical elements (B or TiB ₂ ) are introduced in the form of elementary fine particles by incrustation (discontinuous coating as in the case of FIG. 6C) and / or by kneading (as in the case of FIG. 6E). .

 To the aforementioned magnesium alloy RZ5, either Ca and / or Zr may be added, which, in a small quantity (total of between 10 to 5000 ppm), may have a beneficial effect on the refining of the grain.

According to other examples, for alloys based on Ti, Fe, Al or Ni, the enrichment of additional chemical elements known as "refiners" comprises one or more chemical elements from C, B, N, TiC, TiN, TiB ₂ , Fe ₃ C and FeSi, for a total addition of between 50 and 5000 ppm.

According to a third variant of the second embodiment, said element is able to deoxidize the bath of said metal alloy. For example, said metal alloy is an iron-based alloy which is preferably 16NCD13, 32CDV13 or 15CDV6 and said additional chemical element or deoxidizing element is titanium introduced in the form of TiC and / or TiB ₂ particles ( less than 1% by volume, preferably 50 to 5000 ppm TiC and / or TiB ₂ and preferably 50 to 500 ppm TiC and / or TiB ₂ ).

According to other examples, the addition of rare earths in the synthesis of metal matrix composites (CMM) or oxygen-hungry materials has the effect of limiting the dissolved oxygen in the liquid bath during additive manufacturing. The most common rare earths are Scandium (Se), Neodyne (Nd), Yttrium (Y) and Lanthanum (La). They have the particularity of fixing the dissolved oxygen in the form of oxides, which oxides are chemically stable with respect to the matrix of CMM and oxygen-hungry materials. In order to reduce costs and improve the efficiency of deoxidation of the liquid bath, it is most often necessary to introduce the rare earths in the synthesis of powders in the form of fine hexaborides of the RB type. ₆ (NdBô, YB _6, LaB _6, ScB _6), which are capable of forming borides (refiners) in addition to scavenge dissolved oxygen from the liquid bath by forming oxides.

Thus, preferably, said additional chemical element is added by adding fine particles of TiC, TiB ₂ and / or hexaborides of rare earths for Ti, Fe and Al-based alloys.

 In another example, it can be enriched from 50 to 5000ppm RZ5 magnesium alloy aforementioned rare earth which in addition to act as a deoxidizer bath, can increase the resistance to galvanic corrosion and can reduce the microporosity and cracking on solidification of the liquid bath.

According to a fourth variant of the second embodiment, concerning the particles of a composite powder having reinforcements, preferably discontinuous of slender (fiber) or equiaxed (particles) form, (powder of FIG. 61), said additional chemical element ( surfactant or surfactant) is capable of facilitating the wetting of the reinforcements (discontinuous) by the liquid formed by the melting of a part of the particles of the composite powder by means of a high energy beam: in particular it is is the fusion by the beam of high energy of other metallic elementary particles of the composite powder.

 For example, for SiC-reinforced aluminum-based matrix composites, the dissolved Mg element increases the wetting of SiC by the liquid aluminum while the Cu element decreases it.

 The addition of Si in small quantities (50 to 5000ppm) makes it possible to control the Fe content of the aluminum-rich liquid bath and lowers its melting temperature somewhat, thus improving the wettability of the liquid with respect to the SiC reinforcement.

 With the Cu and Si elements (total amount between 50 and 5000 ppm), the same effect is observed with respect to the wetting of the SiC reinforcements in the magnesium alloys.

 According to a fifth variant of the second embodiment, said element is capable of improving the absorptivity of the radiation provided by the high energy beam so as to facilitate on the one hand the sinter densification if the compactness of the powder bed is sufficiently important (case of the SLS process) or on the other hand the melting of the powders (in the case of the SLM and DMD processes) of the material in question.

For example, said material is a ceramic that is almost transparent to the radiation of the high energy beam, preferably oxides (Al ₂ O ₃ , SiO ₂ , ZrO ₂ , Y ₂ O ₃ , MgO, TiO _2, etc.) or mixtures more oxides (Al ₂ 0 ₃ -Si0 _2, Al ₂ 0 ₃ -Zr0 _2, Zr0 ₂ -Y ₂ 0 _3, Al ₂ 0 ₃ -Si0 ₂ -Y ₂ 0 ₃ ...) some of which may play the role of melting (reducing the solidus temperature of the mixture by the formation of a small amount of low melting point liquid facilitating the densification and consolidation of the material during its additive manufacturing), and the said element is carbon - or any another absorbent element vis-à-vis the wavelength of the laser used - preferably introduced in the form of a continuous coating (50 to 5000 ppm carbon or its derivatives and preferably 100 to 1000 ppm carbon ) of an atomized or centrifuged powder (powder of FIG. 6B) or else agglomerated and then densified (It is a powder c as in Figure 6J, which is further coated after it has been densified by flame or oven to completely remove the binder).

According to a sixth variant of the second embodiment, said element or additional chemical compound is capable of reinforcing the metal alloy from a mechanical point of view for high application. temperature: in particular, said additional chemical compound is used with a sufficiently large volume fraction, between 3 and 30% by volume, and a sufficiently fine size and a sufficiently homogeneous distribution, both close to those of the elementary metal particles of the composite powder presented in Figure 61

 For steels 16NCD13, 32CDV13, 15CDV6 ..., FeAI compounds,

TiC and many others can play the role of reinforcements. The specific strength of these metal matrix composites (CMM) and their temperature resistance are necessarily improved compared to unreinforced materials. However, their ductility is reduced and requires an optimization of the volume fraction of the reinforcements so as to limit this decrease in ductility.

According to another example, titanium alloys such as TA6V may be reinforced by additions of TiB and / or TiC with a volume fraction of these reinforcements, which preferably does not exceed 15% by volume. These additions can be obtained by reacting the titanium alloy with the reinforcement B ₄ C.

The inclusion of SiC reinforcements in 5000 series aluminum alloys and Al ₂ 0 ₃ reinforcements in 6000 series aluminum alloys is envisaged. The introduction of SiC reinforcements into magnesium alloys is also considered.

Claims

1. Process for manufacturing parts made of metallic material, intermetallic material, ceramic material, ceramic matrix composite or metal matrix composite material with discontinuous reinforcement, in particular with ceramic or intermetallic reinforcement, by melting or sintering powder particles (s) by means of of a high energy beam, characterized in that the powder used is a single powder whose particles have a sphericity of between 0.8 and 1.0 and a form factor of between 1 and V2, each particle of powder having a substantially identical average composition and in that the particle size distribution of said powder is narrowed around the average diameter value d ₅ o% such that: (dgo% - d5oo / ₀ ) / d5o% ≤ 0.66 and (d ₅₀ % - dio%) / d ₅₀ % ≤ 0.33 with (d ₉ o% - di ₀ %) / d ₅ o% ≤ 1/00.

 2. Method according to claim 1, characterized in that the composition of the powder used has at least one additional chemical element in non-zero but less than 0.5% by mass, or 5000ppm or 5g / kg and able to modify the microstructure said material of the resulting part of said process with respect to the case where this additional chemical element is absent from the composition of the powder.

 3. Method according to claim 2, characterized in that said material is a metal alloy and in that said additional chemical element is capable of modifying the morphology of the metallurgical phase or phases of said metal alloy.

 4. Method according to claim 2, characterized in that said material is a metal alloy and in that said additional chemical element is able to refine the grain size of said metal alloy.

 5. Method according to claim 4, characterized in that said parent metal alloy is an aluminum-based alloy and in that said additional chemical element is titanium and / or boron and / or zirconium.

6. Method according to claim 4, characterized in that said parent metal alloy is a titanium-based alloy and in that said Additional chemical element is boron or TiB ₂ borides.

7. Method according to claim 4, characterized in that said parent metal alloy is a Ti, Fe, Al or Ni-based alloy, said additional chemical element comprising one or more chemical elements from C, B, N, TiC, TiN, TiB ₂ , Fe ₃ C and FeSi, for a total addition of between 50 and 5000 ppm.

 8. Method according to claim 2, characterized in that said additional chemical element is able to deoxidize the bath of said metal alloy.

9. Process according to the preceding claim, characterized in that said parent metal alloy is an iron-based alloy of the type 16NCD13, 32CDV13 or 15CDV6 and in that said additional chemical element is titanium introduced in the form of TiC particles and / or TiB ₂ .

 10. Method according to claim 2, characterized in that said particles of the powder have reinforcements and in that said additional chemical element is able to facilitate the wetting of the reinforcements by the liquid formed by melting of a part of the particles of the composite powder by means of a high energy beam.

 11. The method of claim 2, characterized in that said additional chemical element is capable of improving the absorptivity of said ceramic material vis-à-vis the radiation emitted by the high energy beam.

 12. The method of claim 2, characterized in that said material is a metal alloy and in that said element or additional chemical compound is capable of reinforcing the mechanical strength of the metal alloy.

13. Method according to any one of claims 1 to 12, characterized in that the particle size distribution, defined by the value of "span", (d ₉₀ % - dio%) / d ₅ o%, must be less than or equal to 0.50 with (d ₉₀ % - d ₅ o%) / d5o% ≤ 0.33 and (d ₅ o% - dio%) / d ₅ o% ≤ 0.17.

14. Method according to any one of claims 1 to 13, characterized in that the powder used is obtained by atomization or centrifugation of a parent alloy.

 15. Process according to any one of Claims 1 to 13, characterized in that the powder used is obtained by coating

(continuous coating) or inlay (discontinuous coating).

 16. Method according to any one of claims 1 to 13, characterized in that the powder used is obtained by grinding / kneading.

 17. Method according to any one of claims 1 to 13, characterized in that the powder used is obtained by granulation from a suspension also called slip.

 18. A method according to any one of claims 1 to 17, characterized in that the powder used has a composition enriched in at least one chemical element of the composition of said material forming the part resulting from said process.

 19. The method of claim 18, characterized in that said chemical element, or one of its oxides, is volatile at the implementation temperature by said high energy beam.

 20. Process according to claim 19, characterized in that said material is the metal alloy T16A4V and in that said volatile chemical element is aluminum.

 21. The method of claim 20, characterized in that said enrichment of the aluminum powder is between 0.15 and 3% by weight relative to the composition of the alloy TÏ6AI4V.

 22. The method of claim 19, characterized in that said material is a metal alloy based on aluminum and lithium and in that said volatile chemical element is lithium.

 23. Method according to any one of claims 1 to 22, characterized in that said high energy beam is a laser beam.

24. The method of claim 23, characterized in that it uses the laser projection technique (Direct Metal Deposition, DMD), fusion selective laser (Selective Laser Melting, SLM) or selective laser sintering (Selective Laser Sintering) of powder beds.