Multi-material powder with composite particles for additive synthesis

Abstract

The present invention relates to a multi-material powder with composite particles for additive synthesis, comprising carrier particles having a median particle size distribution d50 of 1 μm to 100 μm and functionalized particles having a median particle size distribution d50 that is 10 to 1000 times lower than that of the carrier particles. According to the present invention, the carrier particles and the functionalized particles form composite particles having a core-shell structure, each composite particle having a core formed by the carrier particles and a shell formed by the functionalized particles covering 10% to 100% of the surface of the carrier particles and consisting of at least one surface layer.

Description

[0001] This application is a divisional application of Chinese Patent Application No. 2017800547566, titled "Multi-material Powder with Composite Particles for Additive Synthesis", which is the Chinese national phase entry of the PCT international patent application PCT / FR2017 / 052396 with a filing date of September 8, 2017. Technical Field

[0002] The present invention relates to the manufacture of multi-material powders for use in different fields (such as metallurgy, plastic processing, etc.) and for application in additive synthesis techniques and spray surface treatment techniques. Background Art

[0003] For the purposes of the present invention, the term additive synthesis technique refers to any technique by which a three-dimensional object can be obtained through the consolidation of a powder. Specifically, non-limiting examples that can be mentioned are: 3D printing techniques (such as SLM, SLS, etc.), injection molding techniques (such as PIM, MIM), powder spraying techniques (such as cold spraying, D-gun, etc.), and conventional compaction / sintering techniques.

[0004] Currently, there exist mixtures of powders of different natures or alloy powders as multi-material powders. In the case of mixtures of powders of different natures, the components are more or less homogeneously dispersed depending on the manufacturing method, while in alloy powders, the various elements constituting the alloy powder are all in the form of solid solutions and / or defined compounds. The methods for synthesizing these powders are relatively well-known.

[0005] In particular, techniques for spraying molten metals can obtain dense powders with a spherical morphology. However, the materials obtained by this technique are pure elements or single-phase alloys of mixable elements, such as, for example, certain steels, alloys of nickel, aluminum, or titanium. Currently, these powders constitute the majority of the supply for additive manufacturing applications.

[0006] Co-grinding (mechanical synthesis) techniques can be used to manufacture multi-material powders by closely mixing powders of different natures at high energy with the aid of grinding beads, as described in US Patents US 3,816,080, US 3,591,362, and US 4,706,894. By this method, composite particles with a wide composition range can be obtained. However, the morphology and / or particle size distribution of the powders obtained by this embodiment are not favorable for their application in additive manufacturing. In addition, the particles obtained by this technique are composed of various components that are more or less homogeneously dispersed and do not have a functionalized core structure on the surface.

[0007] The spray-drying technique can also be used to manufacture multi-functional powders by spraying and drying a suspension composed of powder, solvent, and organic binder, as described in U.S. Patents US 5,122,182, US 3,617,358, and US 4,915,733. Composite particles are obtained from the agglomerates through the organic binder that acts as a binder for the elemental powder present in the suspension. The particles obtained by this embodiment have a spherical morphology. However, the intragranular porosity of the particles and the presence of the organic binder make such particles unsuitable for additive manufacturing. For this embodiment, a step of debinding and densifying the particles based on an increase in particle temperature by means of various techniques can be added after the spray / drying operation. Then, sufficiently dense and spherical composite particles can be obtained, which can be used in spray surface treatment methods or additive synthesis manufacturing methods. However, the particles obtained thereby are agglomerates formed from various components that are non-uniformly dispersed and do not have a functionalized core structure on the surface.

[0008] In addition, dry deposition techniques, such as chemical vapor deposition (commonly named by the acronym CVD) or physical vapor deposition (commonly named by the acronym PVD), can also be used on a granular matrix for synthesizing multi-material powders. These techniques are then usually combined with methods that can implement a device (such as a fluidized bed, a rotating reaction chamber, or a vibrating plate) that puts the granular matrix in motion, as specifically taught in U.S. Patent US 7,632,355. Deposits can be obtained on the particle surface by these methods. The PVD technique is highly limited because it cannot process fine particles (particles with a diameter less than 100 μm). The PVD technique is also highly limited in terms of the functionalization rate for these reasonable processing times. If toxicity and the cost of the precursors used are considered, in most cases, the CVD technique has no technical or economic advantages.

[0009] Finally, multi-material particles can be manufactured by surface-treating carrier particles through wet chemical deposition as mentioned in U.S. Patents US 6,732,345, US 5,064,463, and US 4,309457. In this case, deposits can be obtained on the particle surface. However, these embodiments generate a large amount of environmentally harmful emissions and require the use of expensive and dangerous chemical reagents, which greatly complicates the process development of these synthesis paths. These techniques can link different materials at the particle scale.

[0010] However, powders in which different materials are linked at the particle scale may be required to enable and facilitate the manufacture of various alloys, pseudoalloys, composites, and cermets. Summary of the Invention

[0011] To this end, the applicant has invented a method for obtaining a microstructure in strata by functionalizing the surface of particles or carrier particles with additive elements in granular form to obtain composite particles.

[0012] The advantages of being able to have such composite particles are manifold:

[0013] - Facilitating its implementation by avoiding the simple mixing of the carrier element and the additive element (instead of functionalizing the carrier element with the additive element), which simple mixing usually causes problems of homogeneity and segregation during storage and use because the composition is obtained at the particle scale;

[0014] Significantly improving the homogeneity of the material and the reproducibility of the method for forming these powders;

[0015] Blocking intragranular pores and obtaining a specific advantageous microstructure of the material made from these functionalized particles;

[0016] For example, functionalizing carrier particles with a high melting point with functionalized particles having a low melting point facilitates the sintering process and diffusion kinetics in the liquid phase. This embodiment is particularly suitable for the manufacture of cermets.

[0017] Facilitating the deformation process in the solid phase to increase the density of the coatings produced by spraying: The case of cold spraying can be particularly mentioned, where brittle carrier particles are functionalized with ductile carrier particles, and the ductile carrier particles provide the plastic deformation required to obtain a dense and adherent deposit.

[0018] More specifically, the object of the present invention thus lies in a multi-material powder comprising carrier particles having a median particle size distribution d50 of 1 μm to 100 μm and functionalized particles having a median particle size distribution d50 that is 10 to 1000 times lower than that of the carrier particles.

[0019] The powder is characterized in that the carrier particles and the functionalized particles form composite particles having a core-shell structure, and each composite particle has:

[0020] A core formed by the carrier particles, and

[0021] A shell covering 10% to 100% of the surface of the carrier particles and consisting of the functionalized particles of at least one surface layer.

[0022] The advantages provided by the shell consisting of the functionalized particles of at least one surface layer are specifically as follows:

[0023] - On the one hand, the specific surface area of the composite particles thus formed increases, thus inducing better reactivity during the sintering process;

[0024] – On the other hand, the increase in the apparent density and the tapped density of the powder layer is beneficial to the rapid densification during the particle fusion in additive manufacturing.

[0025] In the present invention, assuming that the multi-material powder according to the present invention has a quantity distribution, the claimed particle size distribution range corresponds to a given interval d10 - d90.

[0026] For the present invention, the term median particle size distribution d50 (or median diameter d50) means that 50% of the particles are below this size.

[0027] Advantageously, the functionalized particles have a median particle size distribution d50 greater than or equal to 100 nm, so that the shell has a thickness greater than or equal to 100 nm. The size of the functionalized particles can particularly limit the health and safety issues related to their toxicity during the use of nanoparticles.

[0028] Preferably, the proportion of the carrier particles covered by the functionalized layer is from 0.8 to 1, preferably from 0.9 to 1.

[0029] For the present invention, for a multi-material powder sample, the term proportion of the covered carrier particles means the ratio of the number of functionalized particles to the number of total particles. This ratio is determined by analyzing a plurality of images of the multi-material particles taken by a microscope.

[0030] The advantage provided by a proportion of the covered carrier particles greater than 0.9 is related to the uniformity of the microstructure at the particle scale. This ensures that the carrier particles are indeed all functionalized in the same way. This feature directly affects the absence of microstructural defects in the material obtained from the powder, and thus also has a direct impact on its properties; this also provides a strict guarantee for the reproducibility of its characteristics.

[0031] Preferably, the total roughness Rt of the surface of the functionalized layer at the particle scale is less than 10 μm, preferably from 0.1 μm to 5 μm.

[0032] A rough surface generally includes surface asperities called "peaks" and cavities called "depressions".

[0033] For the present invention, the term total roughness Rt refers to the maximum drop between the top surface of the highest point of the peak and the bottom of the lowest depression.

[0034] The total roughness of the functionalized layer at the particle scale is determined by analyzing a cross-sectional view of the particles taken by a microscope.

[0035] The advantages provided by a total roughness of the functionalized layer at the particle scale of less than 10 μm are related to the flow characteristics of the carrier particles, which may deteriorate after the functionalization treatment. In fact, an excessive total roughness at the particle scale leads to a decrease in the flowability of the powder and makes it difficult to apply it in additive synthesis and thermal spraying technologies where the flow characteristics of the powder are a basic parameter. On the other hand, for a given particle size distribution and morphology of the carrier particles, a total roughness close to zero is not ideal if the reduction in specific surface area related to the total roughness is taken into account.

[0036] Advantageously, the median particle size distribution d50 of the carrier particles is from 1 μm to 45 μm, and these values can respectively correspond to a preferably 1 μm d10 size and a 45 μm d90 size.

[0037] Preferably, the median particle size distribution d50 of the carrier particles can be from 10 μm to 45 μm, corresponding to a specific particle size distribution that is particularly suitable for the additive synthesis method.

[0038] The composite particles can have an irregular morphology with a shape factor greater than 1, or a substantially spherical morphology with a shape factor close to 1.

[0039] For the purposes of the present invention, the term shape factor refers to the ratio of the size of the largest dimension axis, called the major axis, of the particle to the size of the smallest dimension axis, called the minor axis. Preferably, the composite particles according to the present invention have a substantially spherical morphology.

[0040] As regards the carrier particles that can be used in the framework of the present invention, mention may be specifically made of metal particles, ceramic particles or organic particles.

[0041] As regards the functionalized particles that can be used in the framework of the present invention, mention may be specifically made of ceramic particles, and / or metal particles, and / or organic particles, and / or particles comprising at least one element selected from the group consisting of boron, carbon, oxygen and / or nitrogen.

[0042] As regards the composite particles according to the present invention, mention may be specifically made of:

[0043] Ceramic particles functionalized with metals for manufacturing cermets, such as WC / Co, WC / Cu, WC / NiCr, TiC / Ni, B4C / Al, Fe x N y / Ni, Feα(N) / Ni, etc.;

[0044] Metal particles functionalized with ceramics for manufacturing ceramic matrix composites (CMCs), such as Ti / ZrB2, Ti / TiC, Ti / SiC, Ti / ZrB2 / SiC, Al / SiC, Fe / SiC, TA6V / ZrO2, Al6061 / TiC / WC, etc.;

[0045] Metal-functionalized metal particles for manufacturing alloys, intermetallic compounds, and pseudoalloys, such as W / Cu, W / Ni, Ti / Al, Ti / Al / C, Al / Cu, Al / Zn, Cu / Ni, Ti / AgCu, Ti / Mo, Mg / TiNi, Al / TiNi, A16061 / TiNi / SiC, etc.;

[0046] Ceramic-functionalized ceramic particles, such as ZrB2 / SiC, Al2O3 / SiO2, Si3N4 / SiC, etc.;

[0047] Metal-functionalized organic particles for manufacturing functionalized composites, such as PA / Ag, PEKK / Ag, PTFE / Ag, PE / Ni, etc.; and

[0048] Metal particles or ceramic particles functionalized with organic materials, such as Fe3O4 / PA, C / PEKK, Cu / PE, etc.

[0049] Another object of the present invention is to use the multi-material powder according to the present invention as a material that can be used in sintering forming techniques such as additive synthesis and / or spraying surface treatments such as flame spraying, HVOF, plasma spraying, or cold spraying.

[0050] Another object of the present invention is a method for manufacturing the powder according to the present invention (first embodiment), comprising:

[0051] Introducing carrier particles into a circulating fluidized bed reactor to stir the carrier particles through a pneumatic device and / or a hydraulic device or a mechanical device, and using a heating resistor to increase the temperature of the carrier particles;

[0052] Manufacturing a suspension of functionalized particles in a mixture of an organic solvent and an organic binder;

[0053] Then, in the reactor, grafting the functionalized particles onto the surface of the carrier particles by spraying the suspension onto the solid-fluidized carrier particles;

[0054] Performing heat treatment on the functionalized particles by heating and maintaining the temperature in the fluidized bed reactor.

[0055] For the purpose of obtaining composite particles that form the powder according to the present invention, the carrier particles and the functionalized particles implemented in the method according to the present invention are as defined above.

[0056] For the purposes of the present invention, the term circulating fluidized bed refers to a fluidized bed reactor provided with a system that can capture particles on its upper part on the one hand and reintroduce these particles into its lower part on the other hand. This reactor can operate in a two-phase (solid / gas) or three-phase (solid / gas / liquid) mode. In addition, it can be advantageously assisted by a cold plasma torch under atmospheric pressure in order to promote, for example, the diffusion treatment of heteroatoms such as nitrogen, carbon, boron, and oxygen.

[0057] Another object of the present invention is also a method for manufacturing the powder according to the present invention (second embodiment), wherein a high-energy mechanical reactor specifically designed to graft functionalized particles onto the surface of carrier particles is used as the reactor.

[0058] In this embodiment, the method is as follows:

[0059] Introduce the carrier particles and the functionalized particles into the reactor;

[0060] In the reactor, graft the functionalized particles onto the carrier particles by mechanical action at a temperature of 0 °C to +150 °C, preferably at a temperature of 10 °C to 80 °C.

[0061] For the purpose of obtaining composite particles forming the powder according to the present invention, the carrier particles and the functionalized particles implemented in the method according to the present invention are also as defined above.

[0062] Advantageously, the method according to the present invention may further include, after the grafting step, a step of heat-treating and / or surface-treating the composite particles using a circulating fluidized bed as defined above.

[0063] Advantageously, the method according to the present invention may further include, in the case where the composite particles do not have a spherical morphology, a step of spheroidizing the particles using a thermal plasma fluidized bed. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Other features and advantages of the present invention will become more apparent when reading the following description given for information purposes and in a non-limiting manner with reference to the accompanying drawings, in which:

[0065] Figure 1 A block diagram showing a device (fluidized bed reactor) for implementing the first embodiment of the method according to the present invention;

[0066] Figure 2 A block diagram showing a cross-section of a device (grinding device) for implementing the first embodiment of the method according to the present invention;

[0067] Figures 3A to 6B A photograph of the composite particles according to the present invention taken with a scanning electron microscope (SEM), wherein Figure 4BShow Cu-Ni powder analysis - 15 keV (5);

[0068] Figure 7A and Figure 7B are microphotographs showing cross-sections of composite iron-copper materials manufactured by compaction / sintering from a conventional mixture of iron and copper ( Figure 7A ) and from iron powder functionalized with copper ( Figure 7B );

[0069] Figures 3A to 7B Commented on in the examples hereinafter;

[0070] Figure 1 and Figure 2 The same elements shown in are identified by the same numeral labels. Detailed description

[0071] Figure 1 A block diagram of an apparatus (fluidized bed reactor) for implementing a first embodiment of the method according to the invention is shown. It consists of the following elements:

[0072] Tube 1 for filling the reactor,

[0073] Tube 2 for emptying the reactor,

[0074] Cylindrical reaction chamber 3,

[0075] Cyclone separator 4,

[0076] Porous plate 5,

[0077] Tube 6 for supplying fluidizing gas,

[0078] Nozzle 7,

[0079] Four cold plasma torches 8,

[0080] Tube 9 for circulating the powder,

[0081] Tube 10 for discharging gas,

[0082] Hot plasma torch 11,

[0083] Plasma gas supplier 12,

[0084] Powder supplier 13,

[0085] Heating resistor 14,

[0086] Powder layer 15.

[0087] Figure 2 A cross-sectional block diagram of an apparatus (mechanical device) for implementing a second embodiment of the method according to the invention is shown. It consists of the following elements:

[0088] Cylindrical cavity 3,

[0089] The rotor 16, which consists of:

[0090] The shaft 161,

[0091] The compression part 162, and

[0092] The fixed shaft 163,

[0093] The mixture 17 of carrier powder and functionalized powder,

[0094] The double-layer shell 18 for cooling water circulation,

[0095] The pipe 19 for cooling water inlet and outlet,

[0096] The pipe 20 for loading or unloading powder.

[0097] The present invention is also shown in more detail in the following examples. Unless otherwise mentioned, all percentages and shares in these examples are expressed in weight fractions.

[0098] Examples

[0099] Example 1

[0100] The tungsten carbide powder with a particle size distribution d50 of 10 μm was functionalized with cobalt powder having a particle size distribution d50 of 0.9 μm.

[0101] Operate according to the second embodiment.

[0102] Powders with a weight ratio of 80% WC and 20% Co were introduced into a high-energy mechanical device. The circulating water cooling system enables the reaction cavity to be maintained at 20 °C. The cavity was purged with argon for operation under an inert atmosphere. The end of the compression part was adjusted so that the distance from the cavity wall was 1 mm to 3 mm. The cavity wall was set to rotate at a speed of 4000 rpm to 6000 rpm for a reaction time of 30 min to 60 min. The measured temperature inside the cavity was 50 °C to 80 °C. The resulting composite powder, as Figure 3A shown, consists of tungsten carbide particles whose surfaces are functionalized with cobalt particles, and the cobalt particles cover more than 90% of the surface of the carrier particles.

[0103] Example 2

[0104] Using the same operating parameters as in Example 1, copper powder with a particle size distribution d50 of 0.9 μm was used to functionalize the same tungsten carbide powder as in Example 1.

[0105] The resulting composite powder, as Figure 4AAs shown, it consists of tungsten carbide particles functionalized with copper particles on the surface, and the copper particles cover more than 60% of the surface of the carrier particles.

[0106] Example 3

[0107] Functionalize aluminum powder with a particle size distribution d50 of 40 μm using silicon carbide powder with a particle size distribution d50 of 3.5 μm.

[0108] Operate according to the same operating parameters as in Example 1.

[0109] Introduce a powder with a weight ratio of 85% aluminum and 15% SiC into a high-energy mechanical device.

[0110] The composite powder thus obtained consists of Figure 3B (Cross-sectional view) As shown, it consists of aluminum particles functionalized with SiC particles on the surface (forming a layer greater than 1 μm).

[0111] Example 4

[0112] According to the first embodiment of the method of the present invention, cobalt alloy powder (stellite) with a particle size distribution concentrated at 50 μm is introduced into a circulating fluidized bed.

[0113] The powder is fluidized with nitrogen gas at a gas flow rate of 1000 l / h to 1500 l / h. The powder is heated to a temperature of 150 °C to 200 °C. An aqueous suspension of nickel powder with a particle size distribution concentrated at 2 μm, which is added as an organic binder in polyvinyl alcohol, is introduced into the cavity of the fluidized bed by spraying using a nozzle. Nitrogen gas with a gas pressure of 3 bar to 8 bar and a flow rate of 300 l / h to 700 l / h is used as the spraying gas. The suspension is pumped at a flow rate of 0.8 l / h to 1.2 l / h. After the spraying operation is completed, the powder is heated to a temperature of 250 °C to 350 °C, which corresponds to the first level of debinding.

[0114] Then, the powder undergoes a diffusion heat treatment at a temperature of 500 °C to 700 °C. Finally, the powder is cooled and conditioned.

[0115] The cobalt alloy powder functionalized with a nickel layer with a thickness greater than 2 μm as obtained as Figure 5A (Cross-sectional view) shown.

[0116] Example 5

[0117] According to the same embodiment as in Example 4 (the first embodiment of the method of the present invention), functionalize the same cobalt alloy powder with copper using copper powder with a particle size distribution concentrated at 5 μm.

[0118] In this case, a suspension of copper powder in an organic solvent is produced by using polyvinyl acetate as an organic binder. During the spraying operation, the cobalt alloy powder is maintained in a fluidized state at a temperature of 80 to 150 °C. Subsequently, the functionalized powder is subjected to the same heat treatment as described above.

[0119] Thereby, cobalt powder functionalized with a copper layer having a thickness greater than 1 μm, as shown in Figure 5B (cross-sectional view), is obtained.

[0120] Example 6

[0121] According to the same embodiment as in Example 4 (the first embodiment of the method according to the present invention) and the same operating parameters, copper spherical powder with a nickel functionalized particle size distribution concentrated at 40 μm (d50), where nickel covers the surface of more than 95% of the carrier particles, such as Figure 4B shown.

[0122] Example 7

[0123] Polyamide powder (PA) with a particle size distribution d50 of 60 μm is functionalized with silver powder having a particle size distribution d50 of 2 μm.

[0124] The operation is carried out according to the second embodiment of the method according to the present invention.

[0125] Powder with a weight ratio of 93% PA and 7% silver is introduced into a high-energy mechanical device.

[0126] The circulating water cooling system allows the cooling of the reaction chamber. The end of the compression part is adjusted so that the distance from the chamber wall is 1 μm to 3 μm. The chamber wall is set to rotate at a speed of 3000 rpm to 5000 rpm for a grinding time of 10 min to 30 min. The measured temperature inside the chamber is 20 °C to 50 °C.

[0127] The resulting composite powder, as shown in Figure 6A and Figure 6B is composed of polyamide particles functionalized with silver particles on the surface, and the silver particles cover the surface of more than 10% of the carrier particles.

[0128] Example 8

[0129] Figure 7A and Figure 7B are micrographs taken with an optical microscope showing cross-sections of composite iron-copper materials manufactured by compaction / sintering of, on the one hand, a conventional mixture of iron and copper (as shown in Figure 7A ) and, on the other hand, iron powder functionalized with copper (as shown in Figure 7B ).

[0130] The powder is pre-compressed in a matrix under a uniaxial pressure of 700 MPa. Subsequently, the obtained sheet is sintered at 1120 °C in a controlled atmosphere.

[0131] Specifically, Figure 7A shows the microstructure of a material obtained from a conventional mixture of these iron powders (d50 = 50 μm) and copper powders (d50 = 5 μm).

[0132] Figure 7B shows the microstructure of the same material obtained from copper-functionalized iron powders according to an embodiment of the method of the present invention identical to Example 5.

[0133] A significant difference between the two microstructures can be visually observed:

[0134] – In the case of the microstructure obtained from the powder mixture (as Figure 7A shown), a heterogeneous distribution of the components can be seen, while

[0135] – In the case of the microstructure obtained from the functionalized powder (as Figure 7B shown), a special microstructure formed by an iron matrix interconnected by homogeneously dispersed copper particles can be observed.

Claims

1. A multi-material powder for additive synthesis and / or spray surface treatment, comprising carrier particles and functionalized particles having a median particle size distribution d50 that is 10 times lower than that of the carrier particles, The powder is characterized in that the carrier particles and the functionalized particles form composite particles having a core-shell structure, each of the composite particles having: A core formed by the carrier particles, and A shell that covers 10% to 100% of the surface of the carrier particles and is formed by at least one surface layer of the functionalized particles; Wherein, The total roughness Rt of the surface of the functionalized layer at the particle scale is from 0.1 µm to 5 µm, and the total roughness Rt represents the maximum drop between the top surface of the highest peak of the surface and the bottom of the lowest depression of the surface; wherein, the median particle size distribution d50 of the carrier particles is from 10 µm to 45 µm; wherein, the proportion of the carrier particles covered by the functionalized layer is from 0.9 to 1, and the proportion of the carrier particles covered by the functionalized layer represents the ratio of the number of functionalized particles to the total number of particles; wherein, the composite particles have a spherical morphology; wherein, the carrier particles are metal particles, and the metal particles are selected from Cu or Al particles; wherein, the functionalized particles have a median particle size distribution d50 greater than or equal to 100 nm.

2. The powder according to claim 1, wherein, The functionalized particles are ceramic particles, and / or metal particles, and / or particles comprising at least one element selected from the group consisting of boron, carbon, oxygen and / or nitrogen.

3. Use of the powder as defined in claim 1 or 2 as a material for additive synthesis and / or spray surface treatment.

4. A method for manufacturing the powder according to claim 1 or 2, wherein A high-energy mechanical reactor is used as the reactor; The carrier particles and the functionalized particles are introduced into the reactor; In the reactor, the functionalized particles are grafted onto the carrier particles by mechanical action at a temperature of 0 °C to 150 °C.

5. The method according to claim 4, wherein, The temperature at which the grafting is carried out is from 10 °C to 80 °C.

6. The method according to claim 4 or 5 further comprises a step of heat treating and / or surface treating the composite particles using a circulating fluidized bed after the grafting step.

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