Process for manufacturing a metal alloy powder reinforced by dispersion of ceramic nanoparticles by fluidization

Abstract

Method (10) for manufacturing a metal powder of an alloy reinforced by dispersion of ceramic nanoparticles comprising spherical metal particles forming a metal matrix and ceramic nanoparticles distributed in the metal matrix, the method comprising: - introducing a precursor alloy metal powder intended to form the metal matrix into a fluidization chamber of a fluidized bed reactor (E1); - injecting at least one fluidizing gas into the fluidization chamber with a defined injection flow rate so that the powder particles are suspended under the effect of the drag force exerted by the gas in the chamber and individualized (E2, E3);- heat the metal powder particles suspended in the gas stream to a defined heating temperature and for a defined heating time so as to generate the formation of ceramic nanoparticles on the surface of the metal particles and inside the metal particles (E4). Abstract figure: Figure 2;

Description

Title of the invention: Method for manufacturing a metal powder of alloy reinforced by dispersion of ceramic nanoparticles by fluidization Technical field

[0001] The present disclosure relates to the field of alloys reinforced by dispersion of ceramic nanoparticles within the metal matrix.

[0002] The invention relates more particularly to a method for manufacturing a metal powder of reinforced alloy by dispersion of ceramic nanoparticles by gas fluidization, as well as a metal powder of reinforced alloy obtained by such a method. Prior art

[0003] It is known to reinforce a metal matrix by a distribution of nanometric oxides aimed at improving the mechanical properties of the material. This material is used for example in the manufacture of power plant components such as gas burner heads or heat exchangers operating under extreme and fluctuating conditions. It must have good mechanical properties at high temperature, good resistance to corrosion and oxidation.

[0004] The introduction of temperature-stable oxide nanoparticles makes it possible to obtain a specific microstructure, thus giving the material good resistance to fining and resistance to corrosion and oxidation. Indeed, the deformations of a material are governed mainly by the movement of dislocations. The introduction of temperature-stable nano-oxides induces an obstacle effect on the sliding of dislocations.

[0005] In powder metallurgy, the process for obtaining reinforced parts generally takes place in three main stages: a powder manufacturing stage by grinding with oxide, for example yttrium oxide Y2O3, followed by a consolidation stage carried out by isostatic compaction and a sintering stage in order to increase the density of the material. Grinding makes it possible to distribute the oxide particles homogeneously in the metal matrix. The nanometric-sized reinforcements are formed during the grinding and consolidation phases of the ground powder. This production method involves several successive stages to be carried out and requires large masses of powders to obtain parts. In addition, the means of consolidation by compaction do not allow the production of parts with complex geometries, thus limiting the potential applications of alloys reinforced by ceramic dispersion.

[0006] In order to reduce the number of steps and produce parts with complex geometry, the additive manufacturing process is a possible alternative way to produce parts made of alloy reinforced by dispersion of oxides, either by deposition under concentrated energy or by powder bed fusion.

[0007] However, all these manufacturing methods require a prior step of manufacturing oxide dispersion powders.

[0008] Atomization is the most common process for manufacturing such a metal powder. It consists of spraying into fine droplets a stream of molten metal exposed to a jet of gas or a jet of high-pressure water in order to obtain the powder.

[0009] However, atomization is not suitable for the manufacture of a reinforced metal powder with oxide dispersion. Indeed, this process requires the provision of raw material, namely a base metal which must contain oxide reinforcements. In addition, since the oxide reinforcements do not have the same melting temperature as the base metal, they agglomerate in the metal matrix, making it impossible to obtain a homogeneous distribution.

[0010] It is also possible to manufacture metal powder reinforced by dispersion of oxides by mechanosynthesis. This technique is based on the high-energy co-grinding of a first basic metal powder previously obtained by atomization and intended to form the metal matrix with at least one other powder intended to form an oxide reinforcement in the metal matrix. During the grinding, at least part of the oxide powder is incorporated into the metal matrix. However, the use of nano-oxide powders can generate safety and health risks. This process therefore requires the establishment of specific working conditions to take these constraints into account, in particular working for example in a clean room, which increases production costs.Furthermore, such a co-grinding process makes it difficult to control the formation of the reinforced metal powder thus obtained, in particular its composition, size, morphology and the distribution of oxide reinforcements within the metal matrix. In particular, the powders obtained at the end of the co-grinding step have a deformed geometric shape and are no longer spherical, sphericity being the ideal geometry in additive manufacturing.

[0011] In order to make ceramic dispersion powders spherical, it is proposed to subject the co-milled powders to a thermal plasma generated by a plasma torch to obtain the reinforced powder. However, plasma treatment requires very precise operating conditions to obtain powders with a rounded shape. In addition, thermal plasma treatment includes a particle melting phase and a solidification phase, which can also lead to a modification of the microstructure of the metal powders.

[0012] One of the aims of the invention is therefore to propose a new method for manufacturing a metal powder reinforced by dispersion of ceramic nanoparticles, simple to implement, while making it possible to keep the spherical shape of the particles of the metal powder.

[0013] Another aim of the present invention is to propose a method which makes it possible to obtain an optimal distribution of the ceramic nanoparticles in the metal matrix, making it possible to possibly reduce the sliding of the dislocations and to refine the microstructure of the metal matrix. Summary

[0014] The present disclosure improves the situation.

[0015] A method of manufacturing a metal powder of an alloy reinforced by dispersion of ceramic nanoparticles comprising spherical metal particles forming a metal matrix and ceramic nanoparticles distributed in the metal matrix is ​​provided, the method comprising: - introducing a precursor alloy metal powder intended to form the metal matrix into a fluidization chamber of a fluidized bed reactor (El); - injecting at least one fluidization gas into the fluidization chamber with an injection flow rate defined so that the particles of the powder are suspended under the effect of the drag force exerted by the gas in the chamber and individualized (E2, E3); - heating the particles of the metal powder suspended in the gas flow to a heating temperature and for a heating time defined so as to generate the formation of ceramic nanoparticles on the surface of the metal particles and inside the metal particles (E4).

[0016] Advantageously, the ceramic nanoparticles are formed in a homogeneous distribution on the surface of the metal particles.

[0017] Preferably, the heating temperature is lower than the melting temperature of the particles of the alloy powder.

[0018] The features set out in the following paragraphs may, optionally, be implemented independently of one another or in combination with one another.

[0019] The heating step is carried out at a temperature between 400°C and 1300°C, for a duration between 0.5 and 12 hours, preferably between 1 and 4 hours.

[0020] The fluidizing gas is introduced into the chamber at a flow rate of between 0.4 liters / minute and 4.0 liters / minute, preferably between 1 and 1.5 liters / minute.

[0021] The metal alloy powder intended to form the metal matrix is ​​chosen from an iron-based metal alloy powder, an alloy powder based on nickel, a nickel-copper based alloy powder.

[0022] According to one embodiment, the iron-based alloy metal powder is a powder comprising by weight: - 19.0% to 23.5% chromium (Cr); - 4.5% to 5.5% aluminum (Al); - less than 0.7% silicon (Si); - less than 0.4% manganese (Mn); - less than 0.08% by weight of carbon (C).

[0023] The ceramic nanoparticles formed on the surface of the particles of the iron-based metal powder are oxides Fe2O3, a-Al2O3, and the ceramic nanoparticles formed inside the particles of the iron-based metal powder are oxides A12O,

[0024] According to another embodiment, the nickel-based alloy powder is a powder comprising by weight: 26.0% to 30.0% chromium (Cr); - 1.9% to 3.0% of aluminum (Al); - less than 2.5% iron (Fe); - less than 0.6% titanium (Ti).

[0025] The ceramic nanoparticles formed on the surface of the particles of the nickel-based metal powder are NiCr2O4 Cr2O3, A12O3, and the ceramic nanoparticles formed inside the particles of the nickel-based metal powder are A12O3 and / or Cr2O3 or mixtures of the two oxides.

[0026] According to yet another embodiment, the nickel-copper based alloy metal powder is a powder comprising by weight: - 27.8% to 34.2% copper (Cu); - less than 2.5% iron (Fe); - less than 2.1% manganese (Mn); - 1% titanium (Ti).

[0027] The ceramic nanoparticles formed on the surface of the nickel-copper metal powder particles are Ni / Cu / Mn mixed oxides and the ceramic nanoparticles formed inside the nickel-copper metal powder particles are TiN.

[0028] Preferably, the fluidizing gas is chosen from argon, nitrogen or dry air or a mixture of said gases.

[0029] According to another aspect, there is provided a metal powder of alloy reinforced by dispersion of ceramic nanoparticles obtained by the manufacturing method as defined above, comprising a metal matrix formed by metal particles of alloy and ceramic nanoparticles formed on the surface of the metal particles and inside metal particles.

[0030] Advantageously, the reinforced alloy metal particles have an average circularity coefficient which is between 0.9 and 1.

[0031] According to one embodiment, the alloy metal powder forming the metal matrix is ​​an iron-based powder comprising 19%-23.5% by weight of chromium (Cr), 4.5%-5.5% by weight of aluminum (Al), less than 0.7% by weight of silicon (Si), less than 0.4% by weight of manganese (Mn) and less than 0.08% by weight of carbon (C), and the ceramic nanoparticles formed on the surface of the particles of the iron-based metal powder are Fe2O3, a-Al2O3, and the ceramic nanoparticles formed inside the particles of the iron-based metal powder are A12O3.

[0032] According to another embodiment, the alloy metal powder forming the metal matrix is ​​a nickel-based powder comprising, mainly, 26%-30% by weight of chromium (Cr), 1.9%-3.0% by weight of aluminum (Al), less than 2.5% of iron (Fe), less than 0.6% of titanium (Ti), the ceramic nanoparticles formed on the surface of the particles of the nickel-based metal powder are NiCr2O4 Cr2O3, Al2 O3, and the ceramic nanoparticles formed inside the particles of the nickel-based metal powder are Al2O3 and / or Cr2O3 or mixtures of the two oxides.

[0033] According to yet another embodiment, the alloy metal powder forming the metal matrix is ​​a nickel-copper based powder comprising 27.8%-34.2% by weight of copper (Cu), less than 2.5% by weight of iron (Fe), less than 2.1% by weight of manganese, and 1% by weight of titanium (Ti), and the ceramic nanoparticles formed on the surface of the particles of the nickel-copper based metal powder are Ni / Cu / Mn mixed oxides and the ceramic nanoparticles formed inside the particles of the nickel-copper based metal powder are TiN oxides.

[0034] Preferably, the metal particles of the alloy powder have a median diameter of between 3 μm and 50 μm.

[0035] Preferably, the ceramic nanoparticles have a median diameter of between 10 nm and 500 nm. Brief description of the drawings

[0036] Other characteristics, details and advantages will appear on reading the detailed description below and on analyzing the attached drawings, in which: Fig.l

[0037] [Fig.l] [Fig.l] shows a schematic sectional view of a fluidized bed reactor plant used in a method for manufacturing metal particles of reinforced alloy by dispersion of ceramics according to one embodiment. Fig. 2

[0038] [Fig.2] [Fig.2] shows a flowchart illustrating a manufacturing process of metal particles of alloy reinforced by dispersion of ceramics according to one embodiment. Fig. 3

[0039] [Fig.3] [Fig.3] shows a schematic sectional view of the fluidized bed reactor and of the furnace of [Fig.l] in a configuration where the particles are in a fixed regime. Fig. 4

[0040] [Fig.4] [Fig.4] shows a schematic sectional view of the fluidized bed reactor and of the furnace of [Fig.l] in a configuration where the particles are in a fluidized regime. Fig. 5

[0041] [Fig.5] [Fig.5] shows a scanning electron microscopy (SEM) image showing the distribution and spherical morphology of an iron-based alloy metal powder (AM 100) at different magnifications intended to be introduced into the fluidized bed reactor. Fig. 6

[0042] [Fig.6] [Fig.6] shows secondary electron SEM images of the mor Surface physiology of AM100 particles after 4 hours of oxidation in the fluidized bed reactor at 650°C (a, b), 800°C (c, d), 1050°C (e, f). Fig. 7

[0043] [Fig.7] [Fig.7] shows (a) a secondary electron SEM image showing the surface of iron-based alloy metal powder showing the dispersion of Al2O3 oxides on the surface of a particle and (b) a backscattered electron SEM image of a cross-section of an AM100 particle showing the dispersion of Al2O3 oxides inside the particle after subjecting the particles to fluidization in air at 1050°C for 4h. Description of the embodiments

[0044] [Fig.l] schematically illustrates a fluidized bed reactor installation 100 used in a method for manufacturing metal particles of reinforced alloy by dispersion of ceramic nanoparticles according to one embodiment.

[0045] The installation 100 comprises a fluidized bed reactor 101, a differential pressure sensor 106, a furnace 105, a residual particle and gas recovery unit 102, a fluidization gas injection unit 103 and a control and data acquisition unit 104.

[0046] The fluidized bed reactor 101 comprises a fluidization chamber 113, with a vertical axis, having a substantially cylindrical shape. For example, the chamber has an internal diameter of 53.1 mm and a height of 500 mm. The chamber comprises a lower part and an upper part. The lower part comprises a porous metal support 109 on which the metal particles 1 to be fluidized are arranged. The average diameter of the pores is for example 2.5 μm. The diameter of the pores is smaller than the size of the particles of the powder introduced into the column. The metal support also has the function of ensuring a homogeneous distribution of the gas in the column.

[0047] The reactor 101 comprises in its lower part a fluidization gas inlet 107 connected to the gas injection unit 103 via a gas supply circuit 117 and a plenum 112 which is separated from the fluidization chamber by the porous support 109. The gas or gases is / are injected at the gas inlet 107. In the case where there are several gases injected, the gases are mixed homogeneously in the plenum, before being distributed homogeneously towards the porous support 109.

[0048] The reactor 101 comprises in its upper part a gas outlet 108 connected to the gas and fine metal particle recovery unit 102 via a gas outlet circuit.

[0049] The sealing of the chamber 113 is ensured by the presence of elastomer seals at the level of the upper and lower attachment flanges.

[0050] The fluidization chamber 113 is surrounded by an external heating system 105, composed for example of an electric furnace which is made up of two parts surrounding the external wall of the chamber. The temperature of the furnace is adjusted by means of a thermocouple (not shown in the figure). The temperature within the chamber is monitored via a thermocouple placed in the chamber.

[0051] The gas supply unit 103 is configured to inject a fluidizing gas or a mixture of several fluidizing gases according to the need of the process. The gas supply unit further comprises flow meters 111 and valves 114 positioned on the gas supply circuit to control the nature of the fluidizing gas to be injected into the column, the mixture of gases, and the flow rate of the injected gas. In particular, the flow rate of the injected gases is adjusted so that the fluidization speed is sufficient to entrain the particles in a gas flow to form a fluidized bed. The particles are then separated from each other and adopt the behavior of a fluid.

[0052] In [Fig.l], the gas supply unit 103 comprises for example three gas supply sub-units, namely Ar, N2 or air selected as fluidization gas. Each sub-unit comprises a flow meter 111 and two valves 114 positioned respectively upstream and downstream of the gas flow.

[0053] The gas and fine particle recovery unit 102 comprises a cooling system 110, a gas recovery tank 115 and a recovery tank 116 for fine particles carried by the gas flow towards the outlet of the column. The recovered particles are the finest particles, whose size is less than the limit determined by the velocity of the injected fluidizing gas, which are entrained to the top of the chamber and are directed towards the chamber outlet.

[0054] The total pressure drop experienced by the gas, when it passes through the metal support as well as the powder bed, is measured by means of a differential pressure sensor 106. The pressure taps are located under the metal support and at the outlet of the chamber and are connected to the differential sensor.

[0055] The control and data acquisition unit 104 is connected to the gas supply unit 103, the thermocouples (not shown) and the differential pressure sensor 106 to record the signals from the flow meters, the differential pressure sensor and the thermocouples. The control unit is also configured to control them so as to adjust the flow rate of the fluidizing gases, the heating temperature and the heating duration.

[0056] Reference is now made to [Fig.2] which illustrates a method of manufacturing metal particles of alloy reinforced by dispersion of ceramic nanoparticles according to one embodiment.

[0057] With reference to [Fig.2], the method of manufacturing particles of a metal powder of an alloy reinforced by dispersion of ceramic nanoparticles comprises the following steps: - introducing a metal powder of alloy 1 intended to form a metal matrix into the fluidization chamber 113 of the fluidized bed reactor 101; - injecting at least one fluidizing gas into the fluidizing chamber with an injection flow rate defined so as to entrain the particles of the powder in a gas flow and to suspend them under the effect of the drag force exerted by the gas and to separate them from each other; - heating the particles of the metal powder suspended in the gas flow to a heating temperature and for a heating time defined so as to generate the formation of ceramic nanoparticles on the surface of the metal particles and inside the metal particles.

[0058] For the purposes of the present invention, ceramic nanoparticles are materials consisting of ionic or covalent bonds or a mixture of the two in variable proportions.

[0059] Advantageously, the nanoparticles are formed in a homogeneous distribution on the surface of the metal particles.

[0060] According to the manufacturing method of the invention, in the fluidized bed reactor, thanks to the combination of fluidization, the controlled gaseous medium, the nature of the gas and the heating, the injected gas(es) react with the particles of the metal powder to cause a heterogeneous solid-gas reaction, such as oxidation, or nitriding, thus allowing the germination of ceramic nanoparticles not only on the surface of the particles but also inside the particles, while maintaining the sphericity of the powder particles.

[0061] Such a result is unexpected for those skilled in the art. Indeed, generally speaking, the treatment of materials in a fluidized bed is most often used for the coating of particles intended for various uses, sometimes even to coat them via chemical vapor deposition processes. However, all these phenomena give rise to surface reactions, without any approach ever having been developed with a view to generating a dispersion of ceramic nanoparticles, for example oxides or nitrides inside the particles, and in particular creating a dispersion from the surface of the particles to the very center of the particles.

[0062] Advantageously, the manufacturing method of the invention makes it possible to control the size and dispersion of the ceramic nanoparticles germinated in the metal matrix.

[0063] Also advantageously, the manufacturing method of the invention makes it possible to maintain the sphericity of the particles of the metal powder. Unlike the mechanosynthesis method, it is no longer necessary to grind a mixture of powders consisting of a metal powder, intended to form the metal matrix, and a complementary powder, intended to form the oxide particles to achieve the dispersion and incorporation of oxide particles in the metal matrix.

[0064] In a step E1, a metal powder intended to be reinforced is introduced into the fluidized bed reactor. The particles of the metal powder are poured into the chamber and arranged on the porous metal support 109.

[0065] The metal powder is for example obtained beforehand by the atomization technique.

[0066] The particles of the alloy metal powder intended to form the metal matrix have a median diameter of between 3 pm and 50 pm.

[0067] The median diameter of a powder is the size for which 50% of the population of particles making up this powder has a size smaller than the median diameter.

[0068] The measurements were carried out for example with a known CAMSIZER X2 analyzer and a Hall effect flow device.

[0069] The metal alloy powder intended to form the metal matrix may for example be chosen from an iron-based alloy, a nickel-based alloy or a nickel-copper-based alloy.

[0070] The iron-based alloy (AM 100) may comprise by weight: - 19.0% to 23.5% by weight of chromium (Cr); - 4.5% to 5.5% by weight of aluminum (Al); - less than 0.7% by weight of silicon (Si); - less than 0.4% by weight of manganese (Mn); - less than 0.08% by weight of carbon (C).

[0071] The nickel-based alloy (699XA) may comprise by weight: - 26.0% to 30.0% chromium (Cr); - 1.9% to % of aluminum (Al); - less than 2.5% iron (Fe); - less than 0.6% titanium (Ti); - less than 0.50 of niobium, silicon, copper and manganese; - less than 0.10% carbon.

[0072] The nickel-copper based alloy (400) may comprise by weight: - 27.8% to 34.2% copper; - less than 2.5% iron; - less than 2.1% manganese; - less than 0.55 of aluminum and silicon; - less than 0.20% carbon; - the remainder being mainly nickel.

[0073] The metal powder does not contain any ceramic nanoparticles before its introduction into the fluidized bed reactor. In the remainder of the description, this metal powder intended to be reinforced is also called the precursor powder.

[0074] The particles have a circularity coefficient of between 0.9 and 1. The average circularity coefficient of a powder can be obtained automatically using an image analysis device.

[0075] [Fig. 3] shows a schematic sectional view of the fluidized bed reactor of the installation of [Fig. 1]. The metal powder introduced into the fluidization chamber rests on the porous metal support. The particles thus form a fixed bed.

[0076] In a fluidization gas injection step E2, one or more fluidization gases is (are) first continuously injected into the plenum via the gas inlet. The gas then passes through the porous support.

[0077] The fluidizing gas can be injected into the plenum at a flow rate of between 0.40 liters / minute and 4.0 liters / minute, preferably between 1 liter / minute and 1.5 liters / minute. This flow rate is defined according to the diameter of the reactor, the particle charge, i.e. the height in the reactor and the physical characteristics of the powders which are mainly the density, viscosity and morphology of the particles.

[0078] The control of the fluidization of the powder is carried out by pressure regulators and flow meters.

[0079] At very low speed of the fluidizing gas, the particles are in a fixed regime.

[0080] The parameters of the fluidization carried out to put the particles in suspension and separating them from each other can be defined beforehand, for example by iteration, depending on the size of the powder particles, the density of the particles, the quantity of the powder, the density and viscosity of the gas used, and the size of the fluidization chamber.

[0081] Thus, it is possible to establish the minimum fluidization speed according to a known technique of pressure loss between the outlet and the inlet of the gases relative to the speed of the gases.

[0082] As an example, the minimum fluidization velocity Umf is determined experimentally with different fluidization gases, argon, nitrogen and air, for spherical powders made of nickel-based alloy (699XA), having a particle size of 30 μm, at room temperature and under 2 bars of pressure, for different Hq / D ratios, Ho being the height of the powder bed before fluidization and D the diameter of the reactor chamber.

[0083] Table 1 below represents the minimum fluidization speed according to the quantity of powder (spherical particles) of nickel-based alloy, with an average diameter of 30 pm, and the type of fluidization gas used. The result shows that the higher the gas density, the lower the fluidization speed required.

[0084] [Tables 1] Umf±0.5 (L.min ') Air Ar n2 Ho / D 0.55 0.45 0.50 Ho / D 0.65 0.50 0.55 Ho / D 0.75 0.50 0.65

[0085] In a fluidization step E3, after passing the porous support, the thrust force exerted by the gas on the particles is sufficient to compensate for their weight, from a fluid velocity commonly called the minimum fluidization velocity. The particles are individualized and suspended in the fluidization chamber. The particles are suspended in the gas flow and in motion relative to each other. The state of the solid-gas system is comparable to that of a fluid.

[0086] [Fig.4] shows a schematic cross-sectional view of the fluidized bed reactor of [Fig.l] in a situation where the particles are suspended in the chamber, in the gas flow. The particles are separated from each other. The particles are thus individualized and the entire surface of the particle is in contact with the gas, thus allowing an optimal solid-gas reaction.

[0087] In the heating step E4 which is applied when the particles are fluidized, the heating is applied by the vertical furnace which surrounds the external wall of the chamber. The solid-gas medium is heated to a certain temperature and for a certain duration which are defined so as to cause a heterogeneous solid-gas reaction, such as oxidation or nitriding in the metal matrix.

[0088] The heating can be applied with a temperature between 400°C and 1300°C and a duration between 0.5 hours and 12 hours, preferably between 1 hour and 4 hours.

[0089] The temperature inside the fluidization chamber is controlled for example using one or more thermocouples introduced into the chamber in order to be able to control and adjust the temperature so as to promote the oxidation or nitriding reaction in the reactor.

[0090] Such a heated solid-gas medium is particularly interesting for causing and promoting heat exchanges between the gas and the particles and chemical reactions between the particles and the gases. The particles of the alloy metal powder then undergo a modification by the formation of ceramic nanoparticles, for example oxide or nitride nanoparticles.

[0091] The test which will be described in more detail below, carried out with the powder of an iron-based alloy (AM 100), shows for example a dispersion of oxides not only on the surface of the particles but also inside the particles.

[0092] The nature of the ceramic nanoparticles obtained depends on the temperature of the heating applied, the duration of the heating, but also on the size of the particles.

[0093] Advantageously, the manufacturing method of the present invention makes it possible to germinate ceramic nanoparticles on the surface of the particles and inside the particles without deforming the particles of initial spherical shape. Indeed, the manufacturing method of the present invention does not require grinding or compaction of the powder particles.

[0094] At the end of the step of heating the fluidized particles, a metal powder of an alloy reinforced by dispersion of ceramic nanoparticles is obtained. The particles of this reinforced powder have a size and a sphericity close to or identical to that of the precursor powder obtained at the end of the atomization step, before its introduction into the fluidization chamber.

[0095] The metal particles of the reinforced alloy powder have a median diameter of between 3 pm and 50 pm.

[0096] Thanks to the oxidation reaction caused by a combination of fluidization, heating and gaseous media, the particles of the metal powder now comprise nanoparticles dispersed homogeneously not only on the surface of the particles ([Fig.6]) but also inside the particles ([Fig.7]).

[0097] The homogeneous distribution of nanoparticles in the metal matrix ensures homogeneous mechanical properties throughout the powder.

[0098] These ceramic nanoparticles have a median diameter between 10 nm and 500 nm.

[0099] The particles of the reinforced metal powder have a circularity coefficient of between 0.9 and 1. For a powder, the closer the value of this coefficient is to 1, the greater the proportion of particles of this powder which have a morphology close to the sphere.

[0100] The average circularity coefficient of a powder can be obtained automatically using an image analysis device.

[0101] The alloy powder reinforced by dispersion of ceramic nanoparticles obtained by the manufacturing method of the present invention is particularly suitable for use, for example, in additive manufacturing techniques for producing parts of complex shape and geometry. Thanks to the homogeneous dispersion of the ceramic nanopowders, the part obtained has homogeneous mechanical properties, regardless of the direction of mechanical stress on this part.

[0102] As an example, three types of precursor powders are indicated below as well as the nanoparticles formed.

[0103] Typically, when the precursor or initial alloy metal powder is an iron-based powder comprising 19.0% - 23.5% by weight of chromium (Cr), 4.5%-5.5% by weight of aluminum (Al), less than 0.7% by weight of silicon (Si), less than 0.4% by weight of manganese (Mn) and less than 0.08% by weight of carbon (C), the ceramic nanoparticles formed on the surface of the particles of the iron-based metal powder are Fe2O3, A12O3, and the ceramic nanoparticles formed inside the particles of the iron-based metal powder are A12O3

[0104] The test below shows the formation of Fe2O3 nanoparticles at a temperature between 750°C and 800°C, the formation of a-Al2O3 nanoparticles at a temperature between 800°C and 1100°C, after 4 hours in dry air.

[0105] When the alloy metal powder forming the metal matrix is ​​a nickel-based powder mainly comprising 26%-30% by weight of chromium (Cr), 1.9-3.0% by weight of aluminum (Al), the ceramic nanoparticles formed on the surface of the particles of the nickel-based metal powder are NiCr2O4 Cr2O3, Al2 O3, and the ceramic nanoparticles formed inside the particles of the nickel-based metal powder are Cr2O3 1. When the alloy metal powder forming the metal matrix is ​​a nickel-copper based powder mainly comprising 27.8%-34.2% by weight of copper (Cu), less than 2.5% by weight of iron (Fe) and less than 2.1% of manganese, the ceramic nanoparticles formed on the surface of the particles of the nickel-copper based metal powder are Ni / Cu / Mn mixed oxides and the ceramic nanoparticles formed inside particles of the nickel-copper based metal powder are TiN oxides. Examples

[0106] Implementation of the method for manufacturing a reinforced iron-based alloy powder according to the invention

[0107] An iron-based alloy powder comprising 22% by weight of chromium (Cr), 5% by weight of aluminum (Al), 0.5% by weight of silicon (Si), 0.3% by weight of manganese (Mn) and 0.05% by weight of carbon (C) is obtained beforehand by atomization and supplied by the company Kanthal.

[0108] The characteristics of the particles used in the test are shown below in Table 2.

[0109] [Tables2] Sample Diameter (qm) Apparent density (kg.m3) Circularity coefficient D10 D50 D90 AM100 24.0 41.0 55.9 7440 0.91

[0110] [Fig.5] represents a scanning electron microscopy (SEM) image showing the spherical morphology of the initial iron-based alloy powder (AM100) from Table 2, produced by atomization, at different magnifications: 300 pm, 20 pm and 2 pm. The particles of this metal powder have a circularity coefficient of 0.91. According to the analyses, the particles do not contain any ceramic nanoparticles.

[0111] The precursor powder is then introduced into the fluidized bed reactor.

[0112] A dry air flow rate was set at 1.2 L / minute and the pressure drop or differential pressure between the top and bottom of the reactor was measured by a differential pressure gauge with a resolution of 0.1 mbar to control the fluidization step.

[0113] The tests were carried out with a ratio Hq / D = 1, Ho being the height of the powder bed before fluidization and D the diameter of the reactor chamber.

[0114] Heating was applied by heating ramps, followed by cooling, respectively at 10°C / minute and 20°C / minute, for 4 hours, in order to form the ceramic nanoparticles.

[0115] The powders obtained at the end of the manufacturing process were characterized by secondary electron scanning electron microscopy (SEM) and by Raman microscopy.

[0116] Raman spectroscopy analysis showed that the metal powder particles are oxidized after 4 hours in dry air in the bed reactor fluidized for a temperature ranging from 550°C to 1100°C. Fe2O3 nanoparticles and two alumina phases (a-Al2O3 and 0-Al2O3) were identified. Fe2O3 nanoparticles are detected on the particle surface at low temperatures (from 550°C to 750°C). At intermediate temperatures (750°C to 1000°C), a-Al2O3 and 0-Al2O3 nanoparticles begin to germinate. At higher temperatures, above 1000°C, a-Al2O3 nanoparticles are detected on the particle surface.

[0117] [Fig.6] represents secondary electron SEM images showing the surface morphology of AM100 particles of different sizes, after 4 h of oxidation in the fluidized bed reactor at 650°C (a, b), 800°C (c, d), 1050°C (e, f).

[0118] The images show that the combination of fluidization and heating according to the manufacturing method of the invention makes it possible to obtain an alloy powder reinforced by dispersion of ceramic nanoparticles. Advantageously, the powder particles retain their spherical shape. The nanoparticles formed have a median diameter of between 10 nm and 300 nm.

[0119] Image (a) of [Fig.6] shows that the oxide appears to grow from the grain boundaries before propagating towards the grain surface after 4 hours of heating at 650°C in dry air.

[0120] Image (c) of [Fig.6] shows that at 800°C a more compact and dense oxide layer is formed and covers the entire surface of the particle.

[0121] Image (e) of [Fig.6] shows that at 1050°C a layer composed solely of a-Al2O3 is formed on the surface of the particles.

[0122] Comparison between particles of different sizes has shown different growth rates of oxide nanoparticles depending on the particle size. The tests show that the smallest particles, less than 30 pm, are more oxidized than the larger particles, greater than 30 pm, with the same oxidation conditions.

[0123] [Fig.7] shows (a) a secondary electron SEM image of the surface of the iron-based alloy metal powder (AM 100) and (b) a backscattered electron SEM image of a cross-section of an AM 100 particle, showing the presence of a dispersion of A12O3 type oxides inside the particle after subjecting the particles to fluidization in air at 1050°C for 4 h.

[0124] Similar tests were conducted with nickel-based (699XA) and nickel-copper-based (400 + Ti) precursor powders.

[0125] The characteristics of these powders are summarized in Table 3 below.

[0126] [Tables3] Sample s Diameter (qm) Apparent density (kg.m3) Shape D10 D50 D90 699XA 24.2 33.7 45.4 8000 Spherical Alloy 400 28.9 42.3 61.5 8800 Spherical

[0127] The analyses made it possible to identify, for example, the formation of Cr2O3 nanoparticles on the surface of the particles of the nickel-based metal powder and of a-Al2O3 oxides inside the particles, after oxidation at 1100°C for 30 minutes under air in the fluidized bed reactor.

[0128] For the nickel-copper alloy powder (400+Ti), the analyses made it possible to identify the formation of Ni / Cu / Mn nanoparticles on the surface of the powder particles and the formation of TiN ceramic nanoparticles inside the metal powder particles after nitriding at 1100°C for 4 hours under N2. Industrial application

[0129] The method of the present invention can be used to reinforce any type of powder of metallic nature, with spherical geometry, and which can be fluidized, by dispersion of ceramic nanoparticles, such as oxides, nitrides, carbides or any other metal and non-metal combination.

[0130] The powders obtained at the end of the manufacturing process of the present invention are particularly suitable for applications in additive manufacturing, powder metallurgy, to produce parts having high mechanical resistance and resistance to corrosion and oxidation.

[0131] The present disclosure is not limited to the embodiments described above, but it encompasses all the variants that a person skilled in the art may envisage within the framework of the protection sought.

Claims

Claims

1. Method (10) for manufacturing a metal powder of an alloy reinforced by dispersion of ceramic nanoparticles comprising spherical metal particles forming a metal matrix and ceramic nanoparticles distributed in the metal matrix, the method comprising: - introducing a precursor alloy metal powder intended to form the metal matrix into a fluidization chamber of a fluidized bed reactor (El); - injecting at least one fluidization gas into the fluidization chamber with a defined injection flow rate so that the particles of the powder are suspended under the effect of the drag force exerted by the gas in the chamber and individualized (E2, E3);- heating the particles of the metal powder suspended in the gas flow to a heating temperature and for a heating time defined so as to generate the formation of ceramic nanoparticles on the surface of the metal particles and inside the metal particles (E4).;

2. The method of claim 1, wherein the heating temperature is lower than the melting temperature of the alloy powder particles.

3. A method according to claim 1 or 2, wherein the heating step is carried out at a temperature between 400°C and 1300°C, for a period of between 0.5 and 12 hours, preferably between 1 and 4 hours.

4. Method according to one of claims 1 to 3, in which the fluidizing gas is introduced into the chamber at a flow rate of between 0.4 liters / minute and 4.0 liters / minute, preferably between 1 and 1.5 liters / minute.

5. Method according to one of claims 1 to 4, in which the metal alloy powder intended to form the metal matrix is chosen from an iron-based alloy metal powder, a nickel-based alloy powder, a nickel-copper-based alloy powder.

6. A method according to claim 5, wherein the iron-based alloy metal powder is a powder comprising: - 19.0% to 23.5% by weight of chromium (Cr) - 4.5% to 5.5% by weight of aluminum (Al) - less than 0.7% by weight of silicon (Si) - less than 0.4% by weight of manganese (Mn) - less than 0.08% by weight of carbon (C).

7. A method according to claim 5, wherein the nickel-based alloy powder is a powder comprising by weight: - 26.0% to 30.0% chromium (Cr) - 1.9% to 3.0% aluminum (Al) - less than 2.5% iron (Fe) - less than 0.6% titanium (Ti)

8. A method according to claim 5, wherein the nickel-copper based alloy metal powder is a powder comprising by weight: - 27.8% to 34.2% copper (Cu) - less than 2.5% iron (Fe) - less than 2.1% manganese (Mn) - 1% titanium (Ti)

9. Method according to one of claims 1 to 8, in which the fluidizing gas is chosen from argon, nitrogen or dry air or a mixture of said gases.

10. A metal powder of alloy reinforced by dispersion of ceramic nanoparticles obtained by the manufacturing method defined according to any one of claims 1 to 9, comprising a metal matrix formed by metal particles of alloy and ceramic nanoparticles formed on the surface of the metal particles and inside the metal particles.

11. The ceramic nanoparticle dispersion-reinforced alloy metal powder of claim 10, wherein the reinforced alloy metal particles have an average circularity coefficient of 0.9 to 1.

12. The ceramic nanoparticle dispersion-reinforced alloy metal powder according to claim 10 or 11, wherein the alloy metal powder forming the metal matrix is an iron-based powder comprising 19%-23.5% by weight of chromium (Cr), 4.5%-5.5% by weight of aluminum (Al), less than 0.7% by weight of silicon (Si), less than 0.4% by weight of manganese (Mn) and less than 0.08% by weight of carbon (C), and the ceramic nanoparticles formed on the surface of the particles of the iron-based metal powder are Fe2O3, a-Al2O3, and the ceramic nanoparticles formed inside the particles of the iron-based metal powder are A12O

13. 3- Metal powder of alloy reinforced by dispersion of ceramic nanoparticles according to one of claims 10 or 11, wherein the metal powder of alloy forming the metal matrix is a nickel-based powder comprising,, 26%-30% by weight of chromium (Cr), 1.9%-3.0% by weight of aluminum (Al), less than 2.5% of iron (Fe), less than 0.6% of titanium (Ti), the ceramic nanoparticles formed on the surface of the particles of the nickel-based metal powder are NiCr2O4 Cr2O3, A12O3, and the ceramic nanoparticles formed inside the particles of the nickel-based metal powder are A12O3 and / or Cr2O3 or mixtures of the two oxides

14. The ceramic nanoparticle dispersion-reinforced alloy metal powder according to claim 10 or 11, wherein the alloy metal powder forming the metal matrix is a nickel-copper-based powder comprising 27.8%-34.2% by weight of copper (Cu), less than 2.5% by weight of iron (Fe), less than 2.1% by weight of manganese, and 1% by weight of titanium (Ti), and the ceramic nanoparticles formed on the surface of the particles of the nickel-copper-based metal powder are Ni / Cu / Mn mixed oxides and the ceramic nanoparticles formed inside the particles of the nickel-copper-based metal powder are TiN oxides.

15. A ceramic dispersion-reinforced alloy metal powder according to one of claims 10 to 14, wherein the metal particles of the alloy powder have a median diameter of between 3 pm and 50 pm.

16. A ceramic dispersion-reinforced alloy metal powder according to one of claims 14 to 15, wherein the ceramic nanoparticles have a median diameter of between 10 nm and 500 nm.

17. A ceramic nanoparticle dispersion-reinforced alloy metal powder according to one of claims 10 to 16, wherein the ceramic nanoparticles are formed in a homogeneous distribution on the surface of the metal particles.

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