ODS ALLOY POWDER AND ITS MANUFACTURING METHOD BY PLASMA TREATMENT

Abstract

A method of manufacturing a powder of a reinforced alloy (ODS alloy) whose grains forming the particles of the powder comprise a metal matrix in the volume of which crystallized oxide particles are dispersed, the method comprising the following successive steps: i) providing a mixture of powders to be ground comprising a master alloy intended to form the metal matrix and a complementary powder comprising at least one intermediate compound intended to incorporate atoms intended to form the dispersed oxide particles; ii) grinding the mixture of powders according to a mechanosynthesis method to manufacture a precursor powder; iii) subjecting the precursor powder to a thermal plasma generated by a plasma torch comprising a plasmagenic gas, in order to obtain the reinforced alloy powder.The method of the invention is particularly suitable for the manufacture of an ODS alloy which has compositional and / or microstructural characteristics which are optimized. The invention also relates to the ODS alloy powder obtained by the manufacturing method.

Description

ODS ALLOY POWDER AND ITS MANUFACTURING PROCESS BY PLASMA TREATMENT. DESCRIPTION TECHNICAL FIELD The present invention belongs to the field of oxide dispersion strengthened alloys (known as "ODS" alloys, according to the English acronym for "Oxide Dispersion Strengthened"), the oxides constituting reinforcements of the metallic matrix in which they are dispersed. The invention relates more particularly to a powder of an ODS alloy, as well as its manufacturing process. TECHNICAL BACKGROUND Atomization is the most common process for manufacturing metal powder. It consists of spraying a stream of molten metal exposed to a high-pressure jet of gas or water into fine droplets to obtain the powder. However, atomization is not suitable for the manufacture of an ODS alloy powder; it is often impossible to obtain the raw material essential for atomization, which is a base metal in massive form (such as, for example, in the form of an ingot) which would also contain reinforcements of oxides which are dispersed in a more or less homogeneous way. Indeed, oxide reinforcements do not melt at the same temperature as the base metal. They then agglomerate due to problems with the wettability of the reinforcements in the molten base metal and density differences between the reinforcements and the metal. In practice, the processes of Foundries are therefore not used to form ODS alloys. To form unsalted alloys, the mechanosynthesis manufacturing process is currently preferred. This powder metallurgy process is described, for example, in the document by C. Suryanarayana, "Mechanical alloying and milling," Progress in Materials Science, 2001, 46, 184 [reference 1]. It relies on the high-energy co-milling of a first powder of the base metal (possibly pre-alloyed), previously obtained by atomization and intended to form the metal matrix, with at least one second metal powder intended to form an oxide reinforcement within the metal matrix. During milling, all or part of the constituent atoms of the second metal powder are incorporated into the metal matrix, possibly and most likely in the form of a solid solution. However, at this stage of the mechanosynthesis process, oxides have not yet formed and the corresponding reinforcements have not yet grown within the ground powder particles. Only an additional consolidation step (for example, by hot spinning or hot isostatic pressing) causes the oxide reinforcements to grow within the metal matrix in order to definitively obtain an ODS alloy. However, it is difficult to control the formation of the ODs alloy powder thus obtained, in particular its composition, size, morphology and the distribution of oxide reinforcements within the metallic matrix. DESCRIPTION OF THE INVENTION One of the aims of the invention is therefore to avoid or mitigate one or more of the disadvantages described above, by proposing a new manufacturing process for an ODS alloy powder, more particularly exhibiting optimized conposition and / or microstructure characteristics. The present invention thus relates to a method for manufacturing a powder of a reinforced alloy in which the grains forming the powder particles comprise a metallic matrix in the volume of which crystallized oxide particles are dispersed (Oops alloy), the method comprising the following successive steps: (i) have a mixture of powders to be ground comprising: a metallic mother powder comprising a master alloy intended to form the metallic matrix; a complementary powder comprising at least one intermediate compound intended to incorporate into the metallic matrix, possibly in the form of a solid solution, atoms intended to form the dispersed oxide particles; ii) grind the powder mixture in a gaseous grinding medium according to a mechanosynthesis process to produce a precursor powder comprising a metallic matrix incorporating said atoms, possibly in the form of a solid solution: iii) subject the precursor powder to a thermal plasma generated by a plasma torch comprising a plasma-generating gas, in order to obtain the reinforced alloy powder. According to the manufacturing process of the invention, the combination of a mechanosynthesis grinding step and a plasma treatment step produces an Oops alloy powder comprising crystallized oxide particles as reinforcements to the metallic matrix. Such a result is unexpected for a person skilled in the art for the following reasons: The treatment of a powder with thermal plasma typically causes the powder to melt. A thermal plasma (also called a "hot plasma") is a highly energetic plasma in which electrons and ions influence the plasma's behavior. A thermal plasma is the opposite of a cold plasma, which is less energetic and in which only electrons influence the plasma's behavior. However, as previously stated, a melting process is absolutely not recommended for forming an ODS alloy, which is why mechanosynthesis was developed, as indicated in the article reviewing the state of the art "DJ Lloyd, "Particle reinforced aluminium and magnesium matrix composites"; International materials reviews, 1994, vol. 39, no. 1, pages 1 to 23." [reference 2). This is also why hot isostatic compaction at too high a temperature is generally avoided. Indeed, oxide particles generally melt at a higher temperature than the master alloy intended to form the metal matrix. They therefore tend to agglomerate due to their low wettability in the molten metal and their density, which differs from that of the metal. Under such conditions, it is impossible to obtain a reinforced alloy with oxide reinforcements dispersed throughout the metal matrix. relatively homogeneous, in particular reinforcements of a nanometric size. After mechanosynthesis, the atoms destined to form the oxide particles are distributed within the metallic matrix, possibly and most likely as a solid solution, although this is a subject of debate within the scientific community. It is only during the subsequent consolidation stage that the oxide particles will nucleate and then crystallize. However, this consolidation stage, as currently performed, is not conducive to controlling the characteristics of the resulting reinforcements; in particular, their size, morphology, degree of crystallization, and / or distribution within the metallic matrix. Plasma torches are designed to process and produce a powder with micrometer-sized particles. To obtain a nanopowder, that is, a powder with nanometer-sized particles, the plasma torch must incorporate a quenching ring. Plasma torch processing is very energetic, and without additional equipment such as a quenching ring, those skilled in the art would expect that a plasma torch treatment would not form a nanopowder, nor would it produce nanoprecipitates within a powder particle, as the precipitates would agglomerate there. However, contrary to the prejudice that the use of a plasma treatment step during which the powders are melted would not allow obtaining an oDs alloy powder with optimized characteristics, the inventors have shown that the oxide particles do not coalesce during the plasma treatment step. On the contrary, they remain individualized during their precipitation in two stages: 1) germination, during which metal atoms migrate into the metal matrix and meet to form oxide molecules within the powder particles themselves, then ii) crystallization including the growth of oxide crystals to form oxide particles. Simultaneously, during the plasma treatment stage, the master alloy generally crystallizes in bulk, either partially or completely, to form the metallic matrix. The crystallized oxide reinforcements thus formed are dispersed homogeneously within the partially or completely crystallized metallic matrix. Advantageously, the manufacturing process of the invention therefore makes it possible to manufacture an ODS alloy with very good control of the size and dispersion of the oxide precipitates reinforcing the metallic matrix of the ODS alloy. In the first stage of the invention's manufacturing process, the powder mixture is ground using a mechanosynthesis process. The powder mixture comprises the metallic base powder and the complementary powder. Generally, when the grinding conditions have been adjusted during step ii) of mechanosynthesis, the metallic master powder and the complementary powder mix intimately, such that all the atoms of the intermediate compound which are intended to form the dispersed oxide particles are incorporated, possibly and most likely in the form of a solid solution, into the master alloy which then forms the metallic matrix. Regarding the characteristics of these powders, there is no real limitation to the particle size of the powders composing the powder mixture used in the manufacturing process of the invention. Most often, the particles of the mother powder have a median diameter (dso) between 0 µm and 200 µm, or even between 20 µm and 80 µm, typically between 60 µm and 65 µm. The median diameter (dso) of a powder is the size for which 50% of the particle population composing that powder has a size less than dso. It can be determined by a technique such as the laser diffraction method via a particle size analyzer as described for example in ISO 13320 (2009-12-01 edition). The metallic mother powder includes the master alloy which can be chosen from an iron-based alloy, a nickel-based alloy or an aluminium-based alloy. The iron-based alloy can include by weight 10% to 30% chromium. 10% to 30% aluminum. 8% to 25% chromium and 3% to 8% aluminum. The base iron alloy can be a steel, for example an austenitic, martensitic or ferritic steel, where appropriate respecting the previous weight compositions. The nickel-based alloy can be contained by weight 10% to 40% chromium, such as Inconel® 600 containing 14% to 17% chromium. 10% to 40% chromium, 0.2% to 5% aluminum, 0.3% to 5% titanium, 0% to 5% tungsten, 0% to 2% molybdenum and 0% to 2% tantalum, such as for example Inconel® 625 or 718 containing respectively 20% to 23% or 17% to 21% chromium. 10% to 30% alum. Generally, the nickel base alloy can be an Inconel®. When the master alloy is an iron-based alloy or a nickel-based alloy, the powder mixture may include by weight 0.1% to 2.5% of the complementary powder, or even 0.1% to 0.5% to 8%. The basic aluminium alloy may comprise by weight 0% to 1% iron (or even 0% to 0.5% iron), 0% to .% silicon and 0% to 1% magnesium. Examples include the following weight compositions: the aluminium alloy 1100 comprising 0.95% iron, 0.05% magnesium, 0.2% copper, and 0.1% zinc; 6262 aluminum alloy containing up to 0.7% iron: an aluminium alloy of the 1000 series, such as aluminium alloy 105C containing less than 0.4% iron, less than 0.25% silicon and no magnesium; an aluminium alloy of the 6000 series, such as aluminium alloy 6063 containing less than 0.35% iron, less than 0.6% silicon and less than 0.9% magnesium. Iron is most often an impurity and silicon improves the castability of the alloy. When the master alloy is an aluminum base alloy, the powder mixture may include by weight 0.2% to 5% of the complementary powder. In general, the proportion of the precursor powder that precipitates as oxide particles during step iii) of plasma treatment can be increased thanks to the high yield of the manufacturing process of the invention. This proportion can typically be from 80% (or even 90%) to 100%. When it reaches 100%, all the atoms intended to form the dispersed oxide particles have precipitated as reinforcements in the metal matrix of the ODS alloy. Thus, depending on the complementary proportion, the proportion of atoms intended to form the dispersed oxide particles present in the metal matrix of the ODS alloy is reduced to approximately 8%. Thanks to this property of the manufacturing process of the invention, the proportion of additional powder in the mixture of powders to be ground can be reduced. This promotes, during the plasma treatment stage iii), the formation of smaller oxide particles (for example, in the form of nanoreinforcements) and their homogeneous distribution within the metallic matrix of the ODS alloy. This also reduces the cost of the manufacturing process. This proportion should therefore be 0.1% to 0.3%, or even 0.1% to 0.2% of additional powder in the mixture of powders to be ground. Regarding the complementary powder, its particles generally have a median diameter (dsp) between 0 µm and 80 µm. This median diameter can then be smaller than that of the parent powder, which promotes the incorporation of atoms destined to form the dispersed oxide particles within the master alloy of the metallic parent powder. The intermediate compound intended to incorporate the atoms destined to form the dispersed oxide particles can be chosen from YFes, Y2O3, Fe2zO3, Fe2Ti, FeCrWTi, TiHz, TiO2z, Al2OO:, HfO;, SiOO2, ZrO2, ThO:, MgO or mixtures thereof. The atoms intended to form the dispersed oxide particles can therefore include at least one metallic atom chosen from yttrium, titanium, iron, chromium, tungsten, silicon, zirconium, thorium, magnesium, aluminum or hafnium. Most often, the intermediate compound is a metallic oxide and therefore includes at least one oxygen atom intended to enter into the composition of the oxide particle. When the intermediate compound does not include an oxygen atom, for example in the case of an intermetallic compound (such as Fe:Ti or FeCrWTi) or a hydride (such as TiH), the oxycene is supplied by another intermediate compound of the metal oxide type, possibly supplemented by oxygen present in the master alloy. The mixture of powders to be ground is subjected to step ii) of grinding according to a mechanosynthesis process. This step can be carried out in a crusher chosen for example from a ball mill or an attrition mill. The gaseous medium in grinding is generally an atmosphere of controlled composition. It may include hydrogen, argon, helium, nitrogen, air, or mixtures thereof. The precursor powder obtained at the end of step ii) of grinding is then subjected to step iii) of thermal plasma treatment. The parameters of the plasma torch operated during the plasma treatment of step iii) are those classically used in the field of powder manufacturing, for example in the following studies: Fan, X.; Gitzhofer, F.; Boulos, M., “Statistical Design of Experiments for the Spheroidization of Powdered Alumina by Induction Plasma Processing”, J Therm Spray Tech 1998, 7 (2), 247-253 [reference 3], Jiang, Ye, R.; Ishigaki, T.; Jurewicz, J.; Proulx, P.; Boulos, MI, “In-Flight Spheroidization of Alumina Powders in Ar-H2 and Ar-NZ Induction Plasmas”, Plasma Chem Plasma Process 2004, 24 (4), 555-571 [reference 5]. These studies show that there are no strict operating parameters and that a person skilled in the art can easily adapt them, for example by iteration, according to the quantity of powder to be processed and / or the type of powders they wish to obtain. Indicative operating parameters adapted to the manufacturing process of the invention are nevertheless specified below. The plasma torch used can be an inductively coupled radio frequency plasma torch, a blown arc torch or a transferred arc torch. Radiofrequency plasma operates without electrodes. Energy transfer is achieved through inductive coupling: a magnetic field is applied to the plasma-generating gas circulating inside the induction coil to form the plasma. The power of the plasma torch can range from 20 kW to 80 kW. The thermal plasma used in step iii) of the inversion manufacturing process can be a plasma such as described for example in the document "P. Fauchais, "Thermal plasmas fundamental aspects", Techniques de l'ingénieur, fascicle D2810 V1, 2905)" [reference 6]. The thermal plasma can have a plasma temperature ranging from 200 °C to 12,000 °C, for example, between 700 °C and 4,000 °C to melt aluminum or magnesium, or tungsten, which melts at 3,500 °C. This temperature is generally sufficient to melt the species, particularly those containing a metallic atom, that make up the precursor powder. Thermal plasma can have an electron density between 10⁻¹² m³ and 10⁻¹² m³, or even between 10⁻¹² nm³ and 10⁻¹² m³, particularly for arc plasmas. Ionization energies can range from 0.5 eV to 50 eV. At such temperatures and / or thermal plasma energies, the plasma gas contained in the plasma torch is generally fully ionized. For this reason, the plasma gas can be chosen from argon, helium, nitrogen, or mixtures thereof. It typically constitutes the core gas of the plasma torch, into which it can be introduced at a flow rate of between 10 liters / minute and 40 liters / minute. At the beginning of step iii), the pressure in the reaction chamber of the plasma torch may be low (by example less than 200 Pa) to promote plasma formation by facilitating ionization of the plasma gas. However, during step iii), the pressure in the plasma torch reaction chamber is generally between 25 kPa and 100 kPa. The lower this pressure, the faster the injection flow rate and therefore the faster the flow rate of the scouring powder through the plasma torch. For an inductively coupled radiofrequency plasma torch, the re-acricinal enclosure corresponds to the containment tube. When the precursor powder comes into contact with the plasma, the precipitation reaction (i.e. germination then growth) of the oxide particles is thermally activated and occurs almost instantaneously. The injection rate of the precursor powder into the plasma torch can nevertheless be adapted, particularly according to the composition and / or quantity of powder to be treated. The precursor powder can be injected into the plasma torch at a rate between 10 grams / minute and 45 grams / minute. This precursor powder introduction rate can be set independently of the central gas flow rate, although it can be at least partially increased by increasing the plasma generator and / or sheathing gas flow rates. The injection of the precursor powder into the plasma torch can be carried out by vibration, with a screw conveyor or a rotating disc. An upstream injection (in relation to the plasma gas flow) of the reaction vessel is generally coupled with a rapid powder flow rate, while a downstream injection is coupled with a slower powder flow rate, primarily to optimize the travel time of the precursor powder within the reaction vessel. This is because the upstream portion of the thermal plasma in the plasma torch is at a higher temperature, which may not be optimal. Furthermore, a high powder flow rate prevents the powder from dispersing through recirculation within the plasma. For example, a good compromise may be to adjust the height of the outlet of the injection probe described below so that it opens into the first upstream third of the reaction vessel. To maximize the proportion of intermediate compound that precipitates as oxide particles, it can also be advantageous to combine a moderate plasma torch power with a moderate precursor powder injection rate. Typically, a plasma torch power between 10 kW and 30 kW coupled with a precursor powder flow rate between 10 g / minute and 30 g / minute can improve the proportion of oxide particles that precipitate. The precursor powder and / or plasma-generating gas can be introduced into the plasma torch via an injection probe. The precursor powder can be injected into the plasma torch simultaneously with the plasma gas, for example via the injection probe. The injection probe can be swept on its external surface by a sheathing gas which can help to stabilize the plasma and increase the yield of the manufacturing process of the invention. The sheathing gas can be introduced into the plasma torch at a flow rate between 10 liters / minute and 100 liters / minute. It can be chosen from argon, helium, nitrogen, hydrogen, or mixtures thereof. The sheathing gas can be a mixture of at least one main sheathing gas and at least one supplementary sheathing gas. The main cladding gas (most often argon) can be introduced into the plasma torch at a high flow rate, for example a flow rate between 40 liters / minute and 100 liters / minute. The supplementary packing gas exhibits good thermal conductivity, which improves heat transfer between the plasma gas and the precursor powder. Examples include helium, nitrogen, or preferably hydrogen, due to its reducing properties that limit surface oxidation of the precursor powder particles. The supplementary packing gas can be injected into the plasma torch at a flow rate lower than the main packing gas flow rate (Dprincipal), for example, between 1 and 40 liters per minute. At the end of step iii) of thermal plasma treatment according to the manufacturing process, a powder of a CDS alloy is obtained. The particles of this powder generally have a size close to or identical to that of the precursor powder obtained at the end of step ii) of grinding. Regarding their microstructure, the particles of the ODS alloy powder include oxide particles dispersed and wholly or partially crystallized in the volume of the metallic matrix of the ODS alloy. The oxide particles can be distributed homogeneously throughout the volume rotation of the metal matrix, and not just in a specific area. In particular, they do not preferentially locate at the grain boundaries of an ODS alloy powder particle, which would be detrimental to the mechanical properties of a material obtained from an ODS alloy powder (cracking, lower toughness, etc.). The jisotropic microstructure of the reinforced alloy guarantees, in particular, homogeneous mechanical properties throughout the powder, and therefore in a material possibly manufactured with this powder, regardless of the direction of mechanical stress on this material. The oxide particles may include at least one oxide selected from Y2O3, TiO2, Al2O3, HfO2, SiO2, ZrO2, ThO2, MgO, Al2O3, Y2Ti2O7, Y2TiOs. Generally, when the complementary powder contains only one intermediate compound, typically a metal oxide, it enters directly into the composition of the oxide particle dispersed in the ODS alloy, or even ends up partially in the matrix if part of the complementary powder has not precipitated. When the complementary powder comprises several intermediate compounds, one or more types of chemical combinations between these compounds may occur. produce, which can lead to the formation of mixed oxides. For example, when the complementary powder includes yttrium oxide Y2O3 and titanium hydride TiH;, at least one oxide chosen from Y2Ti2O4, Y2TiOs, YTiO3, YTi2zOs may compose all or part of the oxide particle of the ODS alloy. Most often, when the oxide includes yttrium and / or titanium, it is a pyrochlore structure oxide such as, for example, Y,Ti2,O-. The oxide particles formed in the ODS alloy can have a median diameter (dso) ranging from 1 nm to 500 nm. Preferably, it is between 1 nm and 200 nm, or even between 0 and 150 nm: these are therefore nanoparticles. Ideally, such a result can be obtained by the manufacturing process of the invention without using a quenching ring incorporated into the plasma torch. Most often, all or part of the particles in the reinforced alloy powder are spherical, or at least spheroidal. The average circularity coefficient of the particles in the reinforced alloy powder can thus be between 0.95 and 1, or even between 0.98 and 1. The closer the value of this coefficient for a powder is to 1, the greater the proportion of particles in that powder that have a morphology close to the sphere. As indicated in the publication "G. Mollon "Mechanics of granular materials", INSA Lyon, 2015" (in particular pages 23 and 24) [reference 7] available at the following Internet address: "http: / / guilhem.mollon.free.fr / Telechargements / Mecaniq ue des Materiaux Granulaires.pdf" and in accordance with ISO 9276-6 (2008 edition), the circularity coefficient of a particle is a shape descriptor that can be calculated from the following formula from the radius of the circle totally inscribed in the particle (Rinser) and the radius of the circle that totally circumscribes the particle (Rec:irc), These radii being represented in Figure 6 extracted from reference [7] Circularity = In practice, the average circularity coefficient of a powder can be obtained from photographs of the particle followed by automated digital analysis. Preferably, several photographs of the same particle are taken from different angles. The average circularity for these different angles is then calculated. Once this operation has been performed on several grains, the average of the circularity averaged for each grain across all these grains yields the average circularity coefficient of the powder. From an instrumental point of view, the average circularity coefficient of a powder can be obtained automatically using equipment such as the "CAMSIZER Dynamic Image Analyzer" marketed by HORIBA Scientific. Regarding its composition, the reinforced alloy may also include by weight at least one of the following elements: - from 10 to 5000 ppm of silicon; - 10 to 100 ppm of sulfur - less than 20 ppm of chlorine - 2 to 10 ppm of phosphorus - 0.1 to 10 ppm of boron - from 0.1 to 10 ppm of calcium; less than 0.1 ppn of each of the following elements: lithium, fluorine, heavy metals, Sn, As, Sb. These elements are most often initially contained in the master alloy. Since the chemical composition of the metal master powder is generally not modified during the manufacturing process of the invention, these elements are found unchanged in the metal matrix. Since all or part of the metallic matrix and / or the oxide particles it contains can be crystallized, the reinforced alloy powder can itself be crystallized in whole or in part (preferably totally crystallized). The microstructure of the reinforced alloy powder particles can preferably be single-crystal (all particles have the same crystalline structure), or also polycrystalline (the particles can have different crystalline structures). The high proportion of reinforced alloy powder that is crystallized can be used to advantage in cold spray manufacturing processes. Other microstructure and / or composition characteristics of the reinforced alloy obtained by the manufacturing process of the invention will be specified below. The invention also relates to a reinforced alloy powder obtained or obtainable by the manufacturing process as defined in this description, in particular in one or more of the variants described for this process, such as for example the microstructure and / or composition of the reinforced alloy powder. The invention relates more particularly to a reinforced alloy powder whose grains forming the powder particles comprise a metallic matrix in the volume of which crystallized oxide particles are dispersed. To the inventors' knowledge, an ODS alloy has never been obtained directly in powder form, which has the advantage of providing good control of precipitates, of being able to be used in a cold forming process (for example, of the "cold spray" type) and / or of obtaining via an additive manufacturing process an ODS alloy (for example, an ODS steel) with an improved density. The particles of the reinforced alloy can have an average circularity coefficient which is between 0.95 e- 1. The metallic matrix of the reinforced alloy can be crystallized. Preferably, the oxide particles are distributed homogeneously in the volume of the metallic matrix. The metallic matrix can be composed of an iron-based alloy, a nickel-based alloy, or an aluminum-based alloy. The iron-based alloy can include by weight 10% to 30% chromium. 10% to 30% alum. 8% to 25% chromium and 3% to 8% aluminum. The base iron alloy can be a steel, for example an austenitic, martensitic or ferritic steel, where appropriate respecting the previous weight compositions. The nickel-based alloy can be contained by weight 10% to 40% chromium, such as Inconel® 600 containing 14% to 17% chromium. 10% to 40% chromium, 0.2% to 5% aluminum, 0.3% to 5% titanium, 00% to 5% tungsten, 0% to 2% molybdenum and 00% to 2% tantalum, such as Inconel® 625 or 718 containing 20% ​​to 23% or 17% to 21% chromium respectively. 10% to 30% alum. In general, the nickel base alloy can be an Inconel@. When the metal matrix is ​​composed of an iron-based alloy or a nickel-based alloy, the reinforced alloy may comprise by weight 0.1% to 2.5% of oxvde particles, or even 0.1% to 0.5%. The basic aluminium alloy may comprise by weight from 0% to 1% iron (or even from 0% to 0.5% iron), from 00% to .% silicon and from 00% to 1% magnesium. Examples include the following weight compositions: the aluminium alloy 1100 comprising 0.95% iron, 0.05% magnesium, 0.2% copper, and 0.1% zinc; 6262 aluminum alloy containing up to 0.7% iron: an aluminium alloy of the 1000 series, such as aluminium alloy 105C containing less than 0.4% iron, less than 0.25% silicon and no magnesium; an aluminium alloy of the 6000 series, such as aluminium alloy 6063 containing less than 0.35% iron, less than 0.6% silicon and less than 0.9% magnesium. Iron is most often an impurity and silicon improves the castability of the alloy. When the metal matrix is ​​composed of an aluminum base alloy, the reinforced alloy may comprise by weight 0.2% to 5% of oxide particles. The proportion of oxide particles in the reinforced alloy is such that it can comprise 0.1% to 0.5% oxide particles by weight. If some of the additional powder remains unprecipitated during the manufacturing process of the invention, the reinforced alloy may comprise from 0.1% to 2.5% by weight of an atom of the intermediate compound intended to form the oxide particles, preferably from 0.1% to 1%, or even less than 0.1%. The intermediate compound is then generally located within the metal matrix. This percentage reflects the degree of precipitation of the intermediate compound(s) as oxide particles. It can notably be measured by X-ray microanalysis (for example, EDX analysis using Transmission Electron Microscopy) focused on a volume of the metal matrix that does not contain oxide particles. If it remains in the reinforced alloy, the intermediate compound intended to form the oxide particles can be YFezs, Y2O3, Fe2O3, Fe,Ti, FeCrWTi, TiHz, TiO2, Al2O3, HfO2, SiO2, ZrO2, ThO2, MgO or mixtures thereof. Starting from this composition, the oxide particles can include at least one oxide chosen from Y2O3, TiOz, Al2O3, HfO, SiOz, ZrO2, ThO, MgO, Al2O3, Y, Ti2O7, YaTiOs. Oxide particles can have a median diameter (dso) between: nm and 500 nm, or even between: nn e- 200 nn. The reinforced alloy may further comprise by weight one of the following elements - from 10 to 5000 ppm of silicon; - 10 to 100 ppm of sulfur - less than 20 ppm of chlorine - 2 to 10 ppm of phosphorus - 0.1 to 10 ppm of boron - from 0.1 to 10 ppm of calcium; less than 0.1 ppn of each of the following elements: lithium, fluorine, heavy metals, Sn, As, Sb. These elements are most often found in the metallic matrix. The invention is advantageously complemented by the following features, taken alone or according to any of their technically possible combinations. DETAILED DESCRIPTION OF THE INVENTION In this description of the invention, a verb such as "understand," "incorporate," "include," "contain," and its conjugated forms are open terms and therefore do not exclude the presence of additional element(s) and / or step(s) added to the element(s) and / or initial step(s) stated after these terms. However, these open terms also refer to a particular embodiment in which only the initial element(s) and / or step(s), to the exclusion of any others, are referred to; in which case the open term also refers to the closed term "consist of", "constitute", "compose of" and its conjugated forms. The use of the indefinite article "un" or "une" for an element or a step does not exclude, unless otherwise stated, the presence of a plurality of elements or steps. Any reference sign in parentheses in the claims shall not be interpreted as limiting the scope of the invention. Furthermore, unless otherwise indicated the values ​​at the terminals are included in the ranges of parameters indicated the temperatures indicated are considered for a atmospheric pressure implementation any percentage by weight of a component of the alloy reinforced, master alloy, copper powder mixture relates to the total weight of this alloy or of this blend. In this description, the term "base alloy" refers to any metal used in the composition of the master alloy or any other alloy, or any alloy based on the metal in which the content of the base metal is at least 50% by weight of the alloying metal, particularly more than 90%, or even more than 95%. Examples of base metals include iron, nickel, and aluminum. The base alloy is preferably suitable for use in the nuclear field and / or under irradiation. The expression "according to one or more of the variants described in this description" for a material or element refers in particular to variants concerning the chemical composition and / or proportion of the constituents of that material and any additional chemical species it may contain, and in particular to variants concerning the chemical composition, structure, geometry, spatial arrangement, and / or chemical composition of that element or a constituent sub-element of the element. These variants are, for example, those indicated in the claims. Other objects, features and advantages of the invention will now be specified in the following description of particular embodiments of the invention, given by way of illustration and not limitation, with reference to the attached Figures 11A to 6. BRIEF DESCRIPTION OF THE FIGURES Figures 1A (general view) and 1B (sectional view) represent images obtained by Scanning Electron Microscopy (SEM) of a precursor powder obtained after step ii) of grinding of the manufacturing process of the invention. Figures 2A (general view), 2B and 3A (view of a section) and 3B (zoomed view of a section focusing on the oxide precipitates) represent SEM images of a powder of a forced alloy obtained after step iii) of plasma treatment of the manufacturing process of the invention. Figure 3C is a table showing atomic molar percentages obtained by energy-dispersive X-ray spectroscopy (EDX). "Energy Dispersive X-Ray spectrometry") within the oxide precipitates identified by the numerical indices 1 to 7 in Figure 3B. Figures 4A and 4B represent a bright-field TEM image of a cross-section of an ODS alloy obtained by the manufacturing process of the invention. Figures SA to SD represent a series of images used to analyze an oxide precipitate contained in the matrix of an ODS alloy powder obtained by the manufacturing process of the invention. Figure SA, obtained by bright-field TEM, is centered on the analyzed oxide precipitate. Figures S5B and S5C are TEM diffraction images obtained with the sample holder tilted at an angle of -2° along the X-axis, respectively in their raw form and annotated after analysis to identify the diffraction spots corresponding to the matrix and the oxide precipitate. Figure 5D is the corresponding annotated image obtained with the sample holder tilted at an angle of -20° along the X-axis. Figure 6 is a diagram illustrating the Rinser and Rcire parameters necessary to calculate the circularity of a powder grain from a photograph taken at a given angle. PRESENTATION OF SPECIFIC IMPLEMENTATION METHODS The following particular embodiments relate to the manufacturing process of the invention, as well as the composition and microstructure of the reinforced alloy that it makes possible to obtain. 1. Implementation of the manufacturing process for an alloy reinforced according to the invention. In a ball mill under a hydrogen atmosphere, a metallic master powder composed of an iron-based master alloy (weight composition 14% Cr, .% W, 0.3% Si, 0.3% Mn and 0.2% Ni, 1000 ppm C, and the remainder Fe) is mixed with a complementary powder, comprising by weight relative to the total powder mixture, 0.3% of a titanium hydride (TiH) powder and 0.3% of a yttrium oxide (Y2O3) powder as intermediate compounds intended to form oxide particles. The powder mixture is ground for 176 hours in order to form by mecharosynthesis a precursor powder comprising a metallic matrix composed of the master alloy in which the titanium, yttrium and oxygen atoms have been incorporated. At this stage of the manufacturing process of the invention, no oxide particles in the form of precipitates have yet been formed. The precursor powder is then introduced into an inductively coupled radio frequency plasma torch capable of delivering up to 80 kW of power (PL50 model marketed by the company Tekna). This type of torch is described for example in the document "Kim, KS; Moradian, A.; Mostaghimi, J.; Soucy, G. Modeling of Induction Plasma Process for Fullerene Synthesis Effect of Plasma Gas Composition and Operating Pressure; Plasma Chemistry and Plasma Processing 2010, 30, 91-110". The plasma torch comprises a ceramic containment tube immersed in cooling water circulating at high speed along its outer wall. Cooling the tube is essential for its protection. of the significant heat flux generated by the plasma. Around the containment tube and beyond the cooling channel is the induction coil embedded in the body of the plasma torch and connected to the high-frequency generator. This coil generates the alternating magnetic field that creates the plasma medium. Inside the containment tube, a plasma-generating gas (also called central gas) is continuously injected. To protect the inner wall of the ceramic containment tube, a sheathing gas is introduced in a vortex along the inner wall of the containment tube through an intermediate quartz tube placed inside the containment tube. The precursor powder is injected directly into the center of the plasma discharge via a water-cooled injection probe positioned in the upstream third of the plasma torch's reaction chamber. It is then heated in flight and melted. Since induction plasmas operate without an electrode in contact with the plasma gas, a contamination-free process can be achieved. The precursor powder obtained previously is subjected to a thermal plasma according to the operating conditions indicated in Table 1. The gas flow rates are as follows: - Plasma gas (clamp) :: 30 L / minutes main sheathing gas —(argon) 80 to 100 L / minutes: additional sheathing gas (helium or hydrogen) = from 00 to 30 L / minutes. The proportion by weight of ODS powder according to the invention relative to the total weight of powder mixture treated is indicated in the last column of Table 1. It is estimated as a first approximation by an analysis of the SEM images of the powders obtained at the end of the manufacturing process of the invention. Table 1 Table 1 shows that the proportion of oxide that precipitated is greater for moderate power levels. plasma torch (typically <39 kW) and a moderate injection rate of the precursor powder into the plasma torch (typically <30 g / min). Thus, in tests 4 and 12, an ODS alloy powder with spherical particles and in which 100% of the oxide nanoreinforcements have germinated is obtained with: - a powder flow rate of 12 g / minute - a power output for the plasma torch of 25 kW : a pressure of 6 psi or 41369 Pa in the plasma torch reaction chamber gas flow rates of 30 liters / minutes of argon for the central gas, 100 J liters / minutes of argon for the main sheathing gas and 10 liters / minutes of helium for the supplementary sheathing gas. The comparison of tests 4 and 12 also shows the perfect reproducibility of the manufacturing process of the invention, and therefore the control of the characteristics of the ODS alloy powder which it advantageously allows to be obtained. Typically, to obtain an iron-based ODS alloy powder whose particles are spherical and comprise a specific proportion of oxide nanoreinforcements homogeneously dispersed in the metallic matrix of the ODS alloy, a person skilled in the art can, for example, use the following operating conditions for the plasma torch: for 20% to 30% "by weight of crystallized oxide particles relative to the initial weight of the complementary powder: plasma torch power between 30 kW and 80 kW, precursor powder flow rate between 20 g / min and 45 g / min, a pressure in the reaction vessel of the plasma torch between 5 psi and 14.5 psi (i.e. the atmospheric pressure), Main carriage gas flow rate: between 80 L / min and 100 L / mir, supplementary sheathing gas flow rate: between 10 L / min and 40 L / min. for more than 80% by weight of crystallized oxide particles compared to the initial weight of the complementary powder: plasma torch power between 20 kW and 30 kW, precursor powder flow rate between 10 g / min and 30 g / min, a pressure in the reaction vessel of the Plasma torch: between 4 psi and 8 psi, Main carriage gas flow rate: between 80 L / min and 100 L / mir, complementary duct gas flow rate between 10 L / min and 40 L / min. 2. Composition and microstructure of a reinforced alloy of the invention. The precursor powder and the reinforced alloy powder obtained respectively at the end of the mechanosynthesis step and the oxide precipitation step in the plasma torch according to test no. 4 are characterized by SEM (Figures 1A, 1B, 2A, 2B, 3A and 3B), TEM (Figures 4A and 4B) and EDX (table in Figure 3C). According to these analyses, the precursor powder particles are of variable shape (Figure 1A) and have a chaotic, non-crystalline microstructure containing no oxide particles have germinated to constitute a reinforcement of the master alloy (Figure 1B). In contrast, the combination of steps ii) grinding and iii) plasma treatment according to the manufacturing process of the invention makes it possible to obtain a reinforced ODS-type alloy whose powder particles are essentially spherical and / or spherical (Figures 2A, 2B, and 3A) and consist of grains composed of a crystallized metallic matrix into which crystallized oxide particles are homogeneously incorporated. These oxide particles appear as black dots on the gray background of varying shade that constitutes the metallic matrix of the grains (Figures 2B, 3A, and 3B). The crystallized oxide particles are nanoreinforcements, their median diameter d50 being between 150 nm and 200 nm. Numerous precipitates smaller than 5 nm are also present. EDX analyses were also performed using SEM and TEM electron microscopy. These are summarized in the table in Figure 3C, which shows that the nanoreinforcements present in zones 1 to 5 within the ODS alloy powder particles are rich in titanium, yttrium, and oxygen. Conversely, the corresponding EDX analyses performed in zones 6 and 7 of the metallic matrix show the absence of oxygen, titanium, aluminum, and yttrium in the matrix (molar % < 0.1% within the margin of uncertainty, or even zero when no value is given, as for aluminum and yttrium). These results prove that all the atoms of the complementary powder intended to form the dispersed oxide particles have indeed precipitated as nanoreinforcements within the alloy powder particles. ODS, as also shown in the close-up views of Figures 4A and 4B. Figures SB, 5C, and 5D were obtained by TEM diffraction of the area shown in Figure SA, which is centered on an oxide precipitate of the ODS alloy of the invention. They exhibit superstructure diffraction peaks (i.e., every other spot is brighter) that are characteristic of a pyrochlore-type oxide Y,Ti2O7, commonly obtained in an iron-based ODS alloy. The present invention is in no way limited to the embodiments described and represented, and a person skilled in the art will be able to combine them and, with their general knowledge, make many variations and modifications to them. REFERENCES CITED [1] C. Suryanarayana “Mechanical alloying and milling”, Progress in Materials Science 2001, 46, 1-184. [2] DJ LIoyd; “Particle reinforced aluminum and magnesium matrix composites”; International materials reviews, 1994, vol. 39, No. 1, pages 1 to 23. [3] Fan, X.; Gitzhofer, F.; Boulos, M., “Statistical Design of Experiments for the Spheroidization of Powdered Alumina by Induction Plasma Processing”, J Therm Spray Tech 1998, 7 (2), 247-253. [4] Jiang, X.-L.; Boulos, M., “Plasma Induction Spheroidization of Tungsten and Molybdenum Powders”, Transactions of Nonferrous Metals Society of China 2006, 16 tl), 13-17. [5] Ye, R.; Ishigaki, T.; Jurewicz, J.; Proulx, P.; Boulos, MI, “In-Flight Spheroidization of Alumina Powders in Ar-H2 and Ar-N2 Induction Plasmas”, Plasma Chem Plasma Process 2004, 24 (4), 555-571. [6] P. Fauchais, "Thermal Plasmas: Aspects fundamentals”, Engineering Techniques, booklet D2810 V1, 2005). [7] G. Mollon "Mechanics of granular materials", INSA Lyon, 2015 » (in particular pages 23 and 24 of the version downloaded in April 2018), available at the following Internet address: "http: / / guilhem.mollon.free.fr / Telechargements / Mecanique des Materiaux Granulaires.pdf"

Claims

DEMANDS 1) A process for manufacturing a powder of a reinforced alloy, the grains of which form the powder particles comprise a metallic matrix in the volume of which crystallized oxide particles are dispersed, the process comprising the following successive steps: (i) have a mixture of powders to be ground comprising: a metallic mother powder comprising a master alloy intended to form the matrix metallic a supplementary powder comprising at least an intermediate compound intended to incorporate in the metallic matrix of atoms destined for form the dispersed oxide particles ii) grind the powder mixture in a gaseous grinding medium according to a mechanosynthesis process to produce a precursor powder comprising a metallic matrix incorporating said atoms; iii) subject the precursor powder to a thermal plasma generated by a plasma torch comprising a plasma-generating gas, in order to obtain the reinforced alloy powder. 2) A method for manufacturing a powder according to claim 1, wherein the master alloy is selected from an iron-based alloy, a nickel-based alloy or an aluminium-based alloy. 3) A method for manufacturing a powder according to claim 2, wherein the base iron alloy comprises by weight 10% to 30% of chromium. 4) A method for manufacturing a powder according to claim 2, wherein the base iron alloy comprises by weight 10% to 30% aluminium. 5) A method for manufacturing a powder according to claim 2, wherein the base iron alloy comprises by weight 8% to 25% chromium and 3% to 8% aluminium. 6) A method for manufacturing a powder according to any one of claims 2 to 5, wherein the base iron alloy is a steel. 1) A method for manufacturing a powder according to claim 2, wherein the nickel base alloy comprises by weight 10% to 40% of chromium. 8) A method for manufacturing a powder according to claim 7, wherein the nickel base alloy comprises by weight 10% to 40% chromium, 0.2% to 5% aluminium, 0.3% to 5% titanium, 0% to 5% tungsten, 00% to 2% molybdenum and 0% to 2% tantalum. 9) A method for manufacturing a powder according to claim 2, wherein the nickel base alloy comprises by weight 10% to 30% aluminium. 10) A method for manufacturing a powder according to any one of claims 3 to 9, wherein, where the master alloy is an iron-based alloy or a nickel-based alloy, the powder mixture comprises by weight 0.1 to 2.5% of the complementary powder. 11) A method for manufacturing a powder according to claim 2, wherein the base aluminum alloy comprises by weight 0% to 0.5% iron, 0% to:% silicon and 0% to 1% magnesium. 12) A method for manufacturing a powder according to claim 2 or 11, wherein, when the master alloy is an aluminum base alloy, the powder mixture comprises by weight 0.2% to 5% of the complementary powder. 13) A method for manufacturing a powder according to any one of claims 2 to 12, wherein the powder mixture comprises by weight 0.1% to 0.3% of the complementary powder. 14) A method for manufacturing a powder according to any one of the preceding claims, wherein the intermediate compound for forming the dispersed oxide particles is selected from YFezs, Y2O3, Fe2O3, Fe2Ti, FeCrWTi, TiHz, TiO2, Al2O3, HfO2, SiO2, ZrO, ThO2, MgO or mixtures thereof. 15) A method for manufacturing a powder according to any one of the preceding claims, wherein said atoms intended to form the dispersed oxide particles comprise at least one metal atom selected from yttrium, titanium, iron, chromium, tungsten, silicon, zirconium, thorium, magnesium, aluminum or hafnium. 16) A method for manufacturing a powder according to any one of the preceding claims, wherein the plasma torch is a radiofrequency plasma torch inductive coupling, a blown arc torch or a transferred arc torch. 17) A method for manufacturing a powder according to any one of the preceding claims, wherein the power of the plasma torch is between 20 kW and 80 kW. 18) A method for manufacturing a powder according to any one of the preceding claims, wherein the plasma-forming gas is selected from argon, helium, nitrogen or mixtures thereof. 19) A method for manufacturing a powder according to any one of the preceding claims, wherein the plasma-generating gas is injected into the plasma torch at a flow rate of between 10 liters / minutes and 40 liters / minutes. 20) A method for manufacturing a powder according to any one of the preceding claims, wherein the precursor powder is injected into the plasma torch at a flow rate of between 10 grams / minute and 45 grams / minute. 21) Reinforced alloy powder obtained or capable of being obtained by the manufacturing process as defined in any one of the preceding claims. 22) Reinforced alloy powder whose grains forming the particles of the powder comprise a metallic matrix in the volume of which crystallized oxide particles are dispersed. 23) Reinforced alloy powder according to claim 22, wherein the alloy particles reinforced have an average circularity coefficient which is between 0.95 and 1. 24) Reinforced alloy powder according to claim 22 or 23, wherein the metallic matrix is ​​crystallized. 25) Reinforced alloy powder according to any one of claims 22 to 24, wherein the oxide particles are distributed homogeneously in the volume of the metal matrix. 26) Reinforced alloy powder according to any one of claims 22 to 25, wherein the metal matrix is ​​composed of an iron-based alloy, a nickel-based alloy or an aluminium-based alloy. 27) Reinforced alloy powder according to claim 26, wherein the base iron alloy comprises by weight 10% to 30% chromium. 28) Reinforced alloy powder according to claim 26, wherein the base iron alloy comprises by weight 10% to 30% aluminium. 29) Reinforced alloy powder according to claim 26, in which the base iron alloy comprises by weight 8% to 25% chromium and 3% to 8% aluminium. 3C) Reinforced alloy powder according to any one of claims 26 to 29, wherein the base iron alloy is steel. 31) Reinforced alloy powder according to claim 26, in which the nickel base alloy comprises by weight 10% to 40% chromium. 32) Reinforced alloy powder according to claim 31, in which the nickel base alloy comprises by weight 10% to 40% chromium, 0.2% to 5% aluminium, 0.3% to 5% titanium, 0% to 5% tungsten, 00% to 2% molybdenum and 0% to 2% tantalum. 33) Reinforced alloy powder according to claim 26, wherein the nickel base alloy comprises by weight 10% to 30% aluminium. 34) Reinforced alloy powder according to any one of claims 27 to 33, wherein, where the metal matrix is ​​composed of an iron-based alloy or a nickel-based alloy, the reinforced alloy comprises by weight 0.1% to 2.5% of oxide particles. 35) Reinforced alloy powder according to claim 26, wherein the base aluminium alloy comprises by weight 00% to 0.5% iron, 00% to:% silicon and 0% to 1% magnesium. 36) Reinforced alloy powder according to claim 26 or 35, wherein, when the metal matrix is ​​composed of an aluminium base alloy, the reinforced alloy comprises by weight 0.2% to 5% of oxide particles. 37) Reinforced alloy powder according to any one of the preceding claims 26 to 36, wherein the reinforced alloy comprises by weight 0.1% to 0.5% of oxide particles. 38) Reinforced alloy powder according to any one of claims 22 to 37, wherein the reinforced alloy comprises 0.1% to 2.5% by weight of an atom of the intermediate compound intended to form the oxide particles. 39) Reinforced alloy powder according to claim 38, wherein intermediate compound for forming oxide particles is YFe3, Y2O3, Fe2O3, Fe,Ti, FeCrWTi, TiH, TiO2, Al,O;, HfO;, SiO,, ZrO2, ThO2, MgO or mixtures thereof. 40) Reinforced alloy powder according to any one of claims 22 to 39, wherein the oxide particles comprise at least one oxide selected from Y2O3, TiOz, Al2O3, HfO, SiO2, ZrO2, ThO2, MgO, Al2O3, Y,Ti2O7, Y,TiOs. 41) Reinforced alloy powder according to any one of claims 22 to 40, wherein the oxide particles have a median diameter (dso) between: nm and 500 nm. 42) Reinforced alloy powder according to claim 41, in which the oxide particles have a median diameter (ds) between 1 nm and 200 nn. 43) Reinforced alloy powder according to any one of claims 22 to 42, wherein the reinforced alloy further comprises by weight at least one of the following: - from 10 to 5000 ppm of silicon; - 10 to 100 ppm of sulfur - less than 20 ppm of chlorine - 2 to 10 ppm of phosphorus - 0.1 to 10 ppm of boron; - 0.1 to 10 ppm of calcium; - less than 0.1 ppm of each: elements su var lithium, fluorine, heavy metals, As, Sb.