Method for manufacturing micro-parts by micro-machining

Abstract

The invention relates to a method for preparing a ceramic part by micro-machining, comprising, in particular, the preparation of a suspension comprising, in particular, a ceramic powder, a binder and a plasticizer, and a thermocompression step prior to machining of the green ceramic part.

Description

[0001] Micro-machining manufacturing process for micro-parts

[0002] TECHNICAL FIELD OF THE INVENTION

[0003] The present invention belongs to the field of ceramic materials. More particularly, the present invention relates to a method for manufacturing a part by micromachining.

[0004] STATE OF THE ART

[0005] Complex ceramic parts are components typically ranging in size from millimeters to centimeters, possessing complex three-dimensional shapes or architectures. These can be manufactured using technical ceramic materials such as alumina oxide, silicon carbide, or zirconium oxide. Such parts find applications in a wide range of technical fields, including microelectronics, telecommunications and aerospace, optics and photonics, medical imaging, and watchmaking. These parts can exhibit complex shapes incorporating fine geometric features such as grooves, holes, very small channels, precise contours, or other miniature structures, with tight dimensional tolerances and / or sophisticated surface finishes.

[0006] To manufacture such complex ceramic or metallic parts, it is known to use methods such as direct micromachining, laser engraving or 3D lithography (two-photon polymerization). However, these methods have significant limitations.

[0007] Direct micromachining performed after firing can generate internal stresses or cracks, particularly on very high-resolution micro-parts, which is detrimental to the properties of the final part. The three-dimensional geometry of patterns created by direct micromachining is also limited by the size of the available tools (diameter and length). Finally, although micromachining is compatible with a wide variety of materials (e.g., ceramics or metals), these materials can cause varying degrees of wear on the cutting tools, resulting in high maintenance costs for production equipment.

[0008] 3D lithography enables the creation of objects with micron-level precision, but its use remains largely limited to polymer materials. Methods such as laser engraving, micromachining after sintering, and 3D lithography are extremely expensive to implement due to the equipment required (high-power lasers, CNC machining centers, cutting tools, photosensitive resins), as well as the associated safety and control requirements. These methods are also time-consuming, both in optimizing process parameters for a given material (machining strategy, laser power, beam scanning speed in laser engraving, resin selection and light exposure parameters in 3D lithography) and in their execution.

[0009] Document W02002 / 018298A1 discloses aluminum nitride (AIN) preforms obtained from ceramic powders mixed with a thermosetting polyester resin and a solvent to produce a slip, which then undergoes a drying and granulation step. The resulting granules are compacted in a mold. The resulting preform (raw part) can be machined before a sintering step. However, this process is not suitable for manufacturing parts based on oxides (Al₂O₃, ZrCl, MgO, etc.). Furthermore, this process uses thermosetting polyester resins as a binder, which are insoluble in water, require handling under fume hoods, pose a health risk to operators, and impose significant constraints for industrial-scale use.

[0010] Document JP3486666B2 discloses a ceramic processing method. This method involves shaping a green ceramic preform or a calcined ceramic body using a YAG laser under specific frequency conditions (3 to 10 kHz). After initial shaping, the ceramic is fully sintered in a furnace, resulting in a dense and strong final shape. This method is expected to reduce damage and cracking in the workpiece, while increasing the speed and efficiency of the shaping process compared to conventional methods using diamond tools or electrical discharges. However, such laser machining of the raw workpiece does not allow for dimensional tolerances of less than ±20 µm after sintering.Furthermore, such a ceramic preform would not be compatible with machining by mechanical tools, which would allow the part to be structured with lower dimensional tolerances, for example dimensional tolerances of about 10 pm.

[0011] Document JPH0477207A describes an improved cutting method for a green ceramic body, using a thin cemented carbide blade, 0.3 mm thick or less. This reduces the contact area between the blade and the body being cut, minimizing cutting resistance. The cut is performed while the green ceramic body rotates in a cutting box. This process minimizes the consumption of cutting materials, significantly reducing processing costs. The described method, which uses a lathe, is only suitable for machining parts with cylindrical geometry and is therefore not compatible with machining raw parts using a 5-axis machine for manufacturing complex shapes with tight dimensional tolerances.

[0012] Thus, there is a considerable need to develop new processes to produce on a large scale by micromachining ceramic parts or components of complex shapes, with tight dimensional tolerances.

[0013] DESCRIPTION OF THE INVENTION

[0014] In the context described above, the present invention aims to overcome, in whole or in part, the drawbacks of the prior art mentioned above. The inventors have developed a method for preparing a ceramic part by micromachining. The method according to the invention is based in particular on the use of raw ceramic materials, which advantageously exhibit improved mechanical properties, notably improved rigidity and cohesion, compared to conventional cold uniaxial compression processes, thus allowing for easy machining of said raw ceramic material with tight dimensional tolerances and limiting wear on machining tools. The method according to the invention is advantageously easy to implement, quick to execute, and inexpensive, unlike laser engraving processes, for example.

[0015] Thus, the invention relates to a method for preparing a ceramic part by micromachining comprising

[0016] 1) a step of preparing a suspension comprising a first ceramic powder, a binder and a plasticizer,

[0017] 2) a step of preparing a second powder from the suspension prepared in step 1),

[0018] 3a) a heat treatment step of the second powder prepared in step 2), 3b) a compression step of the second powder heat-treated in step 3a), thereby obtaining a raw ceramic part,

[0019] 4) a machining step of said raw ceramic piece obtained in step 3b),

[0020] 5) a sintering step of the raw ceramic part machined in step 4), resulting in a ceramic part. Surprisingly, the raw ceramic part obtained after heat treatment steps 3a) and compression steps 3b) exhibits particularly advantageous mechanical properties, notably cohesion and rigidity, and is thermosetting. The nature of the organic components in the suspension improves the cohesion of the raw ceramic. Heat treatment step 3a) advantageously activates the crosslinking of the organic components present in the second powder, particularly the crosslinking of the binder, substantially improving the rigidity (resistance to fracture, especially in biaxial bending, and the Young's model) of the raw ceramic parts to be machined.Thus, the Young's modulus and biaxial flexural strength of a raw ceramic part obtained after heat treatment step 3a) and step 3b) are increased by 50% to 100% and 50% to 200%, respectively, compared to a raw ceramic part that has been cold-pressed, i.e., without heat treatment. For example, a raw part as prepared in the process according to the invention may have a Young's modulus equal to or greater than 10 GPa, preferably equal to or greater than 14 GPa, and even more preferably equal to or greater than 16 GPa.

[0021] The nature of the organic components in the suspension also allows for the production of raw ceramic parts with both high density and mechanical properties compatible with machining, as well as plasticity that minimizes tool wear. Furthermore, the organic components present in the raw part after compression and heat treatment provide valuable lubrication for the tools during machining, further reducing tool wear.

[0022] According to one embodiment, the suspension prepared in step 1) of the process according to the invention comprises between 10 and 30% by mass of a first ceramic powder, preferably between 15% and 25%, and even more preferably about 20%. Such a mineral content advantageously allows for the production of compact and substantially spherical granules after the step of preparing a second powder from the suspension.

[0023] According to one embodiment, the first ceramic powder used in step 1) of the process according to the invention comprises oxides, for example Al₂O₃, Zr₂O₂, Ti₂O₂, SiO₂, BaO, or SrO; carbides, for example SiC, TiC, WC, TaC, or NbC; nitrides, for example Al₂O₃, TiN, TaN, or NbN; or a mixture comprising these chemical species, for example Al / SiC or Al / WC. The first ceramic powder used in step 1) of the process according to the invention may have a particle size between 0.05 and 5 µm, and preferably between 0.1 and 1 µm. Such a particle size advantageously prevents premature wear of the cutting tools and results in a raw workpiece after machining with a good surface finish, for example, low roughness, a uniform finish, and the absence of structural defects such as microcracks.

[0024] According to a particular embodiment, the suspension prepared in step 1) of the process according to the invention further comprises a dispersant. Advantageously, such a dispersant ensures a repulsion (steric and / or electrostatic) between the ceramic powder particles contained in the suspension, so that said ceramic powder particles are dispersed throughout the suspension.

[0025] According to one embodiment, the binder and plasticizer are present in the suspension prepared in step 1) in a binder / plasticizer volume ratio of between 0.6 and 0.9, preferably 0.8. Such a binder / plasticizer volume ratio makes it possible both to give the raw part good rigidity at the end of the compression and heat treatment step, and to allow good lubrication of the cutting tool during the machining operation, due to the presence of the plasticizer in the formulation of the raw part.

[0026] According to a particular embodiment, the suspension prepared in step 1) of the process according to the invention may further comprise a crosslinking agent or a catalyst. Advantageously, such a crosslinking agent or catalyst accelerates the crosslinking reaction activated by the heat treatment carried out in step 3a) of the process according to the invention. The suspension prepared in step 1) of the process according to the invention may comprise between 0.1% and 10% of a crosslinking agent or catalyst, as a mass percentage relative to the total mass of organic components (binder, plasticizer, and optionally a dispersant). Preferably, a crosslinking agent or catalyst usable in a process according to the invention may be boric acid.

[0027] According to a particular embodiment, the suspension prepared in step 1) of a process according to the invention comprises (as a mass percentage relative to the total mass of the suspension): between 0.01% and 0.2% of dispersant; between 0.5% and 1% of binder;

[0028] - between 0.5% and 1.5% plasticizer.

[0029] According to a particular embodiment, step 1) of preparing a suspension in a process according to the invention comprises successively 1a) mixing the first ceramic powder and the dispersant in a solvent, thereby obtaining a first mixture, 1b) adding the binder and the plasticizer to said first mixture.

[0030] Such a two-step preparation advantageously allows the ceramic powder to be dispersed while avoiding competition and / or adsorption between the dispersant and other components (e.g., binder or plasticizer) on the surface of the ceramic powder particles.

[0031] According to a particular embodiment, the binder used to prepare the suspension in step 1) of the process according to the invention comprises polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), polyethylene glycol (PEG), preferably high molecular weight polyethylene glycol (greater than 1000 Da), for example PEG 6000, acrylic latex, cellulose, polysaccharides, or mixtures thereof. Such binders are advantageously water-soluble and exhibit limited toxicity.

[0032] According to a particular embodiment, the plasticizer used to prepare the suspension in step 1) of the process according to the invention comprises polyethylene glycol, preferably low molecular weight polyethylene glycol (less than 1000 Da), for example PEG 300, phosphonates, polycarboxylates or mixtures thereof.

[0033] When polyethylene glycol is used as a plasticizer or binder in the suspension, the suspension must include at least one other plasticizer or binder besides polyethylene glycol. Alternatively, the suspension prepared in the process according to the invention may include high molecular weight polyethylene glycol, for example PEG 6000, as a binder, and low molecular weight polyethylene glycol, for example PEG 300, as a plasticizer.

[0034] According to a particular embodiment, step 2) of preparing a second powder in the process according to the invention comprises a spray granulation step. Such a spray granulation step can be carried out using a spray gun.

[0035] According to an alternative embodiment, step 2) of preparing a second powder in the process according to the invention includes a cryogenic granulation step. Such a cryogenic granulation step can be carried out using a cryogenic granulator.

[0036] According to one embodiment, step 2) of preparing a second powder further includes a freeze-drying step, preferably following the spray-drying or cryogenic granulation step. Such a freeze-drying step advantageously allows the recovery of a second dry powder composed preferably of homogeneous spherical particles.

[0037] According to one embodiment, step 3a) of heat treatment of the process according to the invention may include heat treatment at a temperature between 40 and 220 °C, for a duration between 2 minutes and 75 minutes.

[0038] According to one embodiment, compression step 3b) of the process according to the invention may include applying a pressure of 20 to 150 MPa to the powder heat-treated in step 3a), for a period of between 2 minutes and 30 minutes.

[0039] According to a particular embodiment, heat treatment steps 3a) and compression steps 3b) are carried out simultaneously in a single thermocompression step. In such an embodiment, the single thermocompression step can be carried out by applying a pressure of 20 to 150 MPa to the second powder prepared in step 2), at a temperature between 40 and 220 °C, for a duration of 2 to 10 minutes.

[0040] The invention also relates to a part that can be obtained by the process according to the invention.

[0041] DETAILED DESCRIPTION OF THE INVENTION

[0042] Definitions:

[0043] For the purposes of this invention, a "part" is any manufactured object that can be obtained by the micromachining preparation process according to the invention. Such a part may be made of ceramic materials. The composition of such a part will depend on the ceramic powder (mineral filler) used to formulate the suspension used in the process according to the invention. A part according to the invention can have a wide variety of shapes depending on the machining step applied to the raw part, its shape and patterns being chosen according to the intended applications of that part.Advantageously, the process according to the invention makes it possible to obtain parts with complex shapes, for example, parts with patterns where the depth-to-width ratio can exceed 3, and / or parts with geometric details on the order of micrometers, for example, crenellated structures or periodic arrays of microcylinders. Also advantageously, the process according to the invention makes it possible to obtain parts with tight dimensional tolerances. A part obtainable by a process according to the invention can find application in a wide variety of fields. By way of example, a part according to the invention is suitable for various industrial applications, for example in the medical, telecommunications, aerospace, defense, watchmaking, photonics, or any other field requiring high-precision parts.

[0044] Dimensional tolerance refers to an acceptable range of variation on a given dimension of a part or a feature of a part. Dimensional tolerance thus defines the limits within which the dimension of the part or a feature of the part may deviate from its nominal (or theoretical) value, while still meeting the part's quality or functionality specifications. A narrow dimensional tolerance implies that the part's manufacturing process exhibits high reproducibility. A narrow dimensional tolerance, as defined in the invention, is a dimensional tolerance less than or equal to 20 µm, preferably less than or equal to 15 µm, and even more preferably less than or equal to 10 µm, 5 µm, 3 µm, 2 µm, or 1 µm.

[0045] For the purposes of this invention, "micromachining" or "machining" refers to a process for treating a raw ceramic part by removing material in order to give it a shape or patterns of precise dimensions, preferably with a tight dimensional tolerance. Such machining or micromachining can be carried out using cutting tools on machine tools, for example by milling, turning, or drilling.

[0046] Method according to the invention:

[0047] A first object of the invention relates to a method for preparing a ceramic part by micromachining comprising

[0048] 1) a step of preparing a suspension comprising a first ceramic powder, a binder and a plasticizer,

[0049] 2) a step of preparing a second powder from the suspension prepared in step 1),

[0050] 3a) a heat treatment step of the second powder prepared in step 2), 3b) a compression step of the powder heat-treated in step 3a), thereby obtaining a raw ceramic part,

[0051] 4) a machining step of said raw ceramic piece obtained in step 3b),

[0052] 5) a sintering step of the raw ceramic piece machined in step 4), resulting in a ceramic piece. Preparation of a suspension:

[0053] The suspension prepared in the process according to the invention advantageously comprises a first ceramic powder.

[0054] The first ceramic powder used to prepare a suspension in a process according to the invention may comprise particles with a size (particle size) between 0.05 µm and 5 µm, preferably between 0.1 µm and 1 µm. A ceramic powder with such a particle size advantageously prevents premature wear of cutting tools and results in a raw workpiece after machining with a good surface finish, for example, low roughness, a uniform finish, and the absence of structural defects such as microcracks.

[0055] The term "ceramic powder" or "first ceramic powder" refers to a powder comprising an inorganic material. Such a ceramic powder may comprise oxides, preferably metal oxides, for example, Al₂O₃, ZrC₂, TiCh, SiC₂, BaO, or SrO; carbides, preferably metal carbides, for example, SiC, TiC, WC, TaC, or NbC; nitrides, preferably metal nitrides, for example, A₂N, TiN, TaN, or NbN; or mixtures comprising these chemical species. When said first ceramic powder comprises a mixture of several chemical species, for example, several powders comprising distinct chemical species, a substep of homogenizing said first ceramic powder may be implemented, for example, using a three-dimensional mixer.

[0056] The suspension prepared in the process according to the invention may comprise between 1% and 50% (powder volume relative to solution volume) of a first ceramic powder. In one embodiment, the suspension prepared in the process according to the invention comprises between 10% and 30% (powder volume relative to solution volume) of a first ceramic powder, preferably between 15% and 25%, and even more preferably about 20%. Such a mineral content advantageously allows for the production of compact and substantially spherical granules after the step of preparing a second powder from the suspension.

[0057] The suspension prepared in the process according to the invention may advantageously include a binder. By "binder" is meant an agent that improves the cohesion of the ceramic powder in the suspension, and thus its stability. Advantageously, such a binder can be removed, for example, during the heat treatment or sintering steps. By way of example, a binder that can be used to prepare a suspension in the process according to the invention may include polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), polyvinyl butyral (PVB), polyethylene glycol (PEG), preferably low molecular weight polyethylene glycol (less than 500 g / mol), acrylic latex, cellulose and its derivatives, or polysaccharides, for example in gel form, or a mixture of these compounds.Preferably, the binder in a suspension prepared according to the invention comprises polyvinyl alcohol (PVA), and even more preferably, consists of polyvinyl alcohol (PVA). Different polyvinyl alcohols (PVA) that can be used in a suspension according to the invention may be PVA 4-88, PVA 18-88, or PVA 40-88 (Sigma Aldrich).

[0058] According to a particular embodiment, the suspension prepared in the process according to the invention comprises between 0.1% and 20% of binder, preferably between 0.5% and 10%, even more preferably between 0.5% and 1% (as a mass percentage relative to the total mass of the first powder).

[0059] The suspension prepared in the process according to the invention advantageously comprises a plasticizer. By "plasticizer" is meant an agent that improves the flexibility and plasticity of the ceramic powder in the suspension. The plasticizer advantageously reduces the viscosity of the suspension, while facilitating the shaping and consolidation of the ceramic powder within the suspension. Advantageously, such a plasticizer can be eliminated, for example, during heat treatment or sintering steps. By way of example, a plasticizer that can be used to prepare a suspension in the process according to the invention may comprise a latex emulsion, polyethylene glycol (PEG), preferably low molecular weight polyethylene glycol (less than 500 g / mol), vitrimers, thermosetting polymers, or mixtures thereof.The term "vitrimers" refers to polymers composed of covalent networks that, at high temperatures, can flow like viscoelastic liquids and, at low temperatures, behave like thermosetting materials. Preferably, the plasticizer used in a suspension prepared in the process according to the invention can be polyethylene glycol (PEG) having a low molecular weight (less than 500 g / mol), preferably polyethylene glycol (PEG) having a molecular weight of approximately 400 g / mol, also known as PEG 400. A molecular weight of approximately 400 g / mol is understood to be a molecular weight between 380 g / mol and 420 g / mol. Alternatively, plasticizers comprising phosphonates, for example, modified phosphonates, and / or polycarboxylates, for example, modified polycarboxylates, can be used to prepare a suspension in a process according to the invention.For example, such plasticizers can be found under the trade names OPTIMA 100, OPTIMA 145, or OPTIMA 206 (CHRYSO).

[0060] According to a particular embodiment, the suspension prepared in the process according to the invention comprises between 0.1% and 10% of plasticizer, preferably between 0.1% and 5%, even more preferably between 0.5% and 1.5% (mass percentage relative to the mass of dry mineral filler).

[0061] The suspension prepared in the process according to the invention may comprise the binder and the plasticizer in a binder / plasticizer volume ratio of between 0.6 and 0.9, for example 0.8.

[0062] According to one embodiment, the binder and plasticizer are present in the suspension prepared in step 1) in a binder / plasticizer volume ratio of between 0.4 and 2, preferably 0.8. Such a binder / plasticizer volume ratio makes it possible both to give the raw part good rigidity at the end of the compression and heat treatment step and to allow good lubrication of the cutting tool in the machining operation, due to the presence of the plasticizer in the formulation of the raw part.

[0063] The suspension prepared in the process according to the invention can be prepared in an aqueous solvent or in an organic solvent, depending on the nature of the binder and plasticizer used.

[0064] The term "aqueous solvent" refers to a solution in which water acts as the primary solvent. Preferably, the aqueous solvent is demineralized water (obtained through permutation or distillation), meaning water free of mineral salts, contaminants, and other impurities. The aqueous solvent can also be tap water or reverse osmosis water, meaning water that has been filtered by a reverse osmosis process using a semi-permeable membrane to remove unwanted ions and molecules.

[0065] An "organic solvent" is defined as a solution in which an organic substance acts as the principal solvent. Preferably, the organic solvent is a hydrocarbon, an alcohol, a ketone, an ether, an ester, an amine, or a mixture thereof. Particularly preferred, the organic solvent is ethanol, methyl ethyl ketone (MEK), or a mixture thereof.

[0066] The suspension prepared in the process according to the invention may further comprise a dispersant. By "dispersant," we mean an agent that improves the homogeneity of the distribution of the first ceramic powder in the suspension. The dispersant advantageously allows for obtaining a stable and homogeneous suspension. A dispersant usable for preparing a suspension in the process according to the invention may comprise a surfactant, a polyelectrolyte, or a complexing agent. By way of example, a dispersant usable for preparing a suspension in the process according to the invention may comprise citric acid, poly(acrylic acid) (PAA), polyacrylates or their derivatives (for example, a solution of sodium poly(acrylate)), lignosulfonate or its derivatives, polyvinylpyrrolidone (PVP). As an example of poly(acrylic acid), polyammonium methacrylate, marketed under the name DARVAN CN (VANDERBILT MINERALS), may be cited.

[0067] According to a particular embodiment, the suspension prepared in the process according to the invention comprises between 0.01% and 5% of dispersant, preferably between 0.01% and 1%, even more preferably between 0.01% and 0.5% (mass percentage relative to the mass of dry mineral filler).

[0068] According to a particular embodiment, the suspension prepared in the process according to the invention may further comprise a lubricant. Such a lubricant advantageously improves the fluidity of the suspension and reduces friction between the particles of the first ceramic powder. Furthermore, such a lubricant advantageously facilitates the machining operation by lubricating the cutting tools, thus limiting their wear. By way of example, a lubricant usable in a suspension according to the invention may be a fatty acid, preferably stearic acid or oleic acid.

[0069] According to a particular embodiment, the suspension prepared in the process according to the invention may further comprise a crosslinking agent or a catalyst. Such a crosslinking agent or catalyst advantageously allows the formation of bonds between the different components of the ceramic material, particularly during the heat treatment step, thereby improving the mechanical properties of the raw part obtained after the heat treatment and compression steps. For example, boric acid is a crosslinking agent that can be used in the process according to the invention.

[0070] According to one embodiment, the suspension prepared in the process according to the invention comprises between 0.01% and 1% of dispersant, preferably between 0.01% and 0.5%, even more preferably between 0.01% and 0.2% (as a mass percentage relative to the total mass of the suspension).

[0071] The preparation step of a suspension in a process according to the invention may successively comprise: a) mixing the first ceramic powder and the dispersant in a solvent, thereby obtaining a first mixture; b) adding the binder and the plasticizer to said first mixture. Thus, in step 1a), the ceramic powder is advantageously dispersed in the solvent by the dispersant, without competing with the other components (for example, the binder or the plasticizer) for adsorption onto the surface of the ceramic powder particles.

[0072] The step of preparing a suspension in a process according to the invention may include at least one substep of homogenizing and / or stirring the suspension, for example, using a rotary agitator or a three-dimensional mixer. Such at least one homogenizing and / or stirring substep may be carried out for a period of between 1 and 72 hours, preferably between 24 and 72 hours, and even more preferably for a period of approximately 48 hours. Attrition beads may also be added to the suspension to facilitate its homogenization.

[0073] Preparation of a second powder from the suspension:

[0074] The step of preparing a second powder in a process according to the invention can be carried out at the end of step 1) of preparing the suspension.

[0075] For the purposes of this invention, "second powder" means a powder obtained from the suspension prepared in step 1) of the process according to the invention, preferably by granulation. Such a second powder is thus distinct from the first ceramic powder used to prepare the suspension in step 1) of the process according to the invention.

[0076] The preparation step of the second powder in a process according to the invention may include a granulation step. For the purposes of this invention, "granulation" means any process for obtaining a second powder from the suspension prepared in step 1) comprising a first ceramic powder, a binder, a plasticizer, and optionally other organic components. During such a granulation step, the particles of the first ceramic powder agglomerate to form larger, preferably substantially spherical, grains. This granulation step affects the final mechanical properties of the ceramic product.

[0077] According to one embodiment, the preparation step of the second powder in a process according to the invention may include a granulation step by atomization. Such an atomization step may be carried out using an atomizer. In an atomizer, the suspension to be atomized is directed into an atomization chamber, where it is sprayed, for example, using a high-pressure nozzle. This step nebulizes the suspension, creating a mist of fine droplets. A stream of hot gas, for example, air or nitrogen, then encounters this nebulized suspension and rapidly evaporates the solvent.The particle size and morphology of the second powder obtained after this atomization step can be adjusted by modifying the step parameters, such as air temperature, flow rate, spray pressure, or atomizer rotation speed (if the step is performed in a rotary atomizer). The second powder can then be collected from the output stream of the atomization chamber, for example, using a cyclone separator or filtration system.

[0078] According to another embodiment, the preparation step of the second powder in a process according to the invention may include a cryogenic granulation step. Such a cryogenic granulation step may be carried out using a cryogenic granulator. The suspension to be cryogenically treated is sprayed in a chamber, for example using a high-pressure nozzle, with an atomizing gas, preferably compressed air. This step nebulizes the suspension, creating a mist of fine droplets. This nebulized suspension then falls into a container containing a cryogenic fluid, for example, liquefied nitrogen or argon. A second powder is thus obtained in the container containing the cryogenic fluid.The particle size of this second powder can advantageously be controlled by modifying the parameters of the step, for example the atomizing gas flow rate, or the suspension flow rate, during its spraying.

[0079] According to a particular embodiment, the preparation step of the second powder in the process according to the invention further comprises a freeze-drying step. Such a freeze-drying step can be carried out after the spray-drying or cryogenic granulation step. This freeze-drying step is particularly useful after the cryogenic granulation step, as it allows for the recovery of a second dry powder, preferably composed of homogeneous spherical particles. Freeze-drying can be carried out using a freeze-dryer comprising a chamber in which the pressure and temperature can be controlled. The powder recovered after the spray-drying or cryogenic granulation step can be placed in the chamber of a freeze-dryer, in which a stable vacuum is created.During freeze-drying, the freeze-dryer chamber can advantageously be maintained at a temperature equal to or lower than -20°C, preferably equal to or lower than -50°C, and even more preferably at a temperature less than or equal to -100°C. According to a particular embodiment, the step of preparing the second powder in the process according to the invention may include:

[0080] A granulation step by atomizing the suspension prepared in step 1) of the process according to the invention, or alternatively

[0081] A cryogenic granulation step of the suspension prepared in step 1) of the process according to the invention, followed by a lyophilization step.

[0082] Heat treatment and compression of the second powder:

[0083] Step 3a) of heat treatment of the second powder prepared in step 2) of the process according to the invention may include heat treatment at a temperature between 40°C and 220°C, preferably between 80°C and 200°C, and even more preferably between 100°C and 180°C. By way of example, such a heat treatment step may be carried out at a temperature of 50°C, 80°C, 100°C, 125°C, 140°C, or 180°C. Such a heat treatment step may be carried out for a duration of between 2 and 75 minutes, preferably between 10 and 65 minutes.

[0084] Such a step 3a) heat treatment can be implemented in any equipment suitable for heating the powder to the temperatures of the heat treatment, for example a furnace.

[0085] Step 3b), compression of the second powder heat-treated in step 3a), may involve applying a pressure of 20 MPa to 150 MPa to said powder. For example, such a compression step may involve applying a pressure of 100 MPa. This compression step may be carried out for a duration of between 2 and 30 minutes, preferably between 5 and 20 minutes. For example, such a compression step may be carried out for 5, 10, or 20 minutes.

[0086] Such a compression step (3b) can be carried out in any equipment capable of applying pressure to the powder, for example, a press. The heat-treated powder can be placed in a mold or die for this compression step.

[0087] Advantageously, a cohesive raw ceramic part is obtained after compression step 3b), for example, in the form of a pellet. Such heat treatment and compression steps advantageously crosslink the binder contained in the powder, thus giving the raw ceramic part cohesive properties compatible with direct machining. Such a raw part advantageously exhibits high stiffness. For example, such a raw part obtained after compression step 3b) may advantageously have a Young's modulus of 10 GPa or greater, preferably 14 GPa or greater, and even more preferably 16 GPa or greater.For the purposes of this invention, "raw part," "unworked part," or "green part" refers to a ceramic part that has undergone a heat treatment step and a compression step, for example, a thermocompression step, during a process according to the invention. Such a raw part is thus in an intermediate form and has not yet undergone a sintering step.

[0088] In one embodiment, heat treatment steps 3a) and compression steps 3b) are carried out simultaneously in a single thermocompression step. Such a single thermocompression step is particularly advantageous as it simplifies and increases the efficiency of the process. In this embodiment, this single thermocompression step can be carried out by applying a pressure of 20 MPa to 150 MPa to the second powder prepared in step 2), at a temperature between 40 and 220°C, preferably between 80°C and 200°C, and even more preferably between 100°C and 180°C. By way of example, such a heat treatment step can be carried out at a temperature of 50°C, 80°C, 100°C, 125°C, 140°C, or 180°C.Such a single thermocompression step can be carried out for a duration of between 2 and 30 minutes, preferably between 5 and 20 minutes. For example, such a single thermocompression step can be carried out for 5, 10, or 20 minutes.

[0089] According to a particular embodiment, the process according to the invention may include a preheating step of the second powder, preceding the single thermocompression step. Such a preheating step of the second powder may include preheating to the temperature of the thermocompression step, that is to say, a temperature between 40°C and 220°C, preferably between 80°C and 200°C, and even more preferably between 100°C and 180°C. Such a preheating step may be carried out for a duration of between 30 and 60 minutes, preferably between 40 and 50 minutes, and even more preferably for a duration of approximately 45 minutes. Advantageously, such a preheating step allows all the particles of the second powder to reach the thermocompression temperature before the start of this thermocompression step.

[0090] Machining of the raw ceramic part:

[0091] Machining step 4) in the process according to the invention is performed on the raw workpiece prepared during heat treatment steps 3a) and compression steps 3b). This machining step can be carried out using various machine tools to produce machined parts of varying complexity. Examples of machine tools that can be used to perform a machining step in a process according to the invention include a CNC lathe, a CNC milling machine, or a 5-axis CNC machining center. A 5-axis CNC machining center advantageously allows the workpiece to be machined on multiple axes, thus offering great flexibility for shaping complex shapes or patterns in a single operation, without having to reposition the workpiece.

[0092] The raw ceramic part prepared during steps 3a) heat treatment and 3b) compression is advantageously easy to machine. While exhibiting cohesion and rigidity compatible with machining, such a raw part displays significantly greater plasticity than a fired part (i.e., one that has undergone a sintering step), which facilitates machining and reduces wear on the cutting tools of machine tools. Furthermore, the various organic compounds present in the raw part, for example, the binder, the plasticizer, and especially the lubricant when present, allow for lubrication of the cutting tools during machining.

[0093] Sintering

[0094] Following the machining stage, the raw machined part undergoes a sintering stage, resulting in the final ceramic part. This sintering stage advantageously allows the ceramic material particles to partially or completely fuse, thereby reducing the part's porosity and increasing its strength and density. This sintering stage can be carried out at a temperature chosen according to the nature of the first ceramic powder used in the process according to the invention, for example, at a temperature between 60% and 80% of the melting point of the first ceramic powder. The conditions of this sintering stage can be adapted according to the nature of the first ceramic powder used, its particle size, its reactivity, any impurities it contains, and the size of the part to be sintered.

[0095] For example, such a sintering step can be carried out at a temperature between 1100°C and 2200°C. A person skilled in the art knows how to choose a temperature and duration for the sintering step that is appropriate for the part being sintered.

[0096] Part that can be obtained by the process according to the invention:

[0097] The invention also relates to a part that can be obtained by a process according to the invention. Such a part may be a ceramic part, comprising, for example, oxides, carbides, nitrides, or a mixture comprising these chemical species. Preferably, such a part exhibits tight dimensional tolerances.

[0098] The embodiments exemplified below are given only as illustrations and do not in any way constitute a limitation of the present invention.

[0099] Example 1: Preparation of an Alumina + 9%TiO2 suspension.

[0100] A suspension with a solids content of 6% (ratio of the volume of the powder mixture to the final volume of the suspension) is prepared by mixing 45.5 g of alumina powder (TAIMEI) with an average particle size of 0.2 µm with 4.5 g of TiCh (SIGMA-ALDRICH) with an average particle size of 1.6 µm (i.e., 9 wt% of TiC>2 relative to the total mass of the alumina-titanium powders) with 197.3 mL of distilled water in a plastic bottle. 0.33% of DARVAN C (VANDERBILT MINERALS) is added to the suspension as a dispersant (as a wt% relative to the total mass of the alumina-titanium powders). Alumina attrition beads with a diameter of 2 mm are added to the suspension until the total mass reaches three times that of the alumina-titanium powders. The mixture is placed in a TURBULA 3D mixer for 3 hours in order to deagglomerate the powder particles using the alumina beads and to obtain a suspension with a homogeneous mixture of precursors.

[0101] Next, a binder-plasticizer mixture comprising 1.89 g of polyvinyl alcohol 18-88 (PVA) (SIGMA-ALDRICH) as the binder and 2.37 g of polyethylene glycol 400 (PEG400) (SIGMA-ALDRICH) as the plasticizer is prepared with a binder-to-plasticizer ratio of 0.8. This binder-plasticizer mixture is then added to the suspension to achieve a binder-plasticizer concentration of 8.87% (as a mass percentage relative to the total mass of the alumina-titanium powders). The resulting suspension is stirred in a roller mixer at a speed of 35 rpm to ensure thorough homogenization and integration of the binder and plasticizer. Stirring is maintained for 48 hours until a free-flowing suspension is obtained. Finally, after the stirring step, the alumina attrition beads are removed from the bottle using a sieve with 400 pm mesh.The following table presents the formulation of an alumina-titanium-based ceramic suspension according to example 1.

[0102] [Table 1]: Formulation of an alumina-titanium ceramic suspension

[0103] Example 2: Preparation of a suspension in pure alumina.

[0104] A suspension with a solids content of 6% (ratio of the volume of the powder mixture to the final volume of the suspension) is prepared by mixing 50 g of alumina powder (TAIMEI) with an average particle size of 0.2 µm with 196.8 mL of distilled water in a plastic bottle. 0.33% of DARVAN C (VANDERBILT MINERALS) is added to the suspension as a dispersant (as a percentage of the total mass of alumina powder). Alumina attrition beads with a diameter of 2 mm are added to the suspension until the total mass reaches three times that of the alumina powder. The mixture is placed in a TURBULA 3D mixer for 3 hours to deagglomerate the powder particles with the alumina beads and obtain a suspension with a homogeneous mixture of the precursors.

[0105] A binder-plasticizer mixture comprising 1.89 g of polyvinyl alcohol 18-88 (PA) (SIGMA-ALDRICH) as the binder and 2.37 g of polyethylene glycol 400 (PEG400) (SIGMA-ALDRICH) as the plasticizer is prepared with a binder-to-plasticizer ratio of 0.8. The binder-plasticizer mixture is added to the solution to achieve an organic content of 8.87% (as a percentage by mass relative to the mass of alumina powder). The resulting suspension is stirred in a roller mixer at a speed of 35 rpm to ensure thorough homogenization and integration of the binder and plasticizer. Stirring is maintained for 48 hours until a free-flowing suspension is obtained. Finally, after the stirring step, the alumina attrition beads are removed from the bottle using a sieve with 400 pm mesh.The following table presents the formulation of an alumina-based ceramic suspension according to example 2.

[0106] [Table 2]: Formulation of an alumina-based ceramic suspension

[0107] Ceramic pieces (pellets) were prepared from the suspensions described in examples 1 and 2, by implementing a process according to the invention.

[0108] Preparation of a powder by cryogenic granulation:

[0109] Before the step of preparing a powder by cryogenic granulation, the suspensions prepared according to examples 1 and 2 are homogenized for 2 minutes using a VIBRA-CELL 75041 ultrasonic probe (BIOBLOCK SCIENTIFIC) and are then left on a rotary shaker for two hours.

[0110] The concentrated suspensions are then granulated using an LS-2 cryogenic granulator (POWDER-PRO), employing a dual-fluid atomizing nozzle with a 1 mm internal diameter tip. The atomizing gas (compressed air) and suspension flow rates can be modulated. During the cryogenic granulation step, the suspensions are atomized at a suspension flow rate of 33 ml / min and a relative compressed air pressure of 0.3 bar. The suspension droplets sprayed by the nozzle are collected in a suitable beaker containing liquid nitrogen and are thus frozen, resulting in solid granules. The granules are then freeze-dried using an ALPHA 2-4 LDPLUS freeze dryer (CHRIST) for 24 hours. During this freeze-drying stage, the granules are arranged in a bed approximately 5 mm thick on stainless steel trays within the chamber of a freeze dryer. A stable vacuum of 10 minutes is maintained.3 A pressure of mbar and a temperature of approximately -100°C are maintained in the chamber. A homogeneous powder of spherical particles is recovered after lyophilization.

[0111] Formatting the lozenges:

[0112] The freeze-dried granules are formed into pellets by thermocompression. A 30 mm diameter tungsten carbide (WC) matrix is ​​placed in a thermocompression press equipped with a 20-tonne vertical press and an induction generator. The matrix is ​​preheated to a temperature chosen for heat treatment: 50°C, 80°C, 100°C, 125°C, 140°C, or 180°C, for 45 minutes. After preheating, 6.31 g of freeze-dried powder are placed on the matrix, and a pressure of 100 MPa is applied by the thermocompression press for 5 minutes. Following this thermocompression step, a cohesive pellet with a diameter of 30 mm and a height of approximately 4 mm is obtained. The impact of thermocompression temperature on the mechanical properties of the raw pellets (Young's modulus and tensile strength) is presented in the following table.

[0113] [Table 3]: Influence of the thermocompression conditions used on the mechanical properties of the raw parts (Pressing time: 5 minutes)

[0114] The process according to the invention thus makes it possible to obtain a raw part with improved mechanical properties, compatible with a subsequent micromachining step. Therefore, the mechanical properties of the raw parts obtained (Young's modulus greater than 10 GPa and tensile strength greater than 10 MPa) are particularly well-suited to machining, or even micromachining, of the part.

Claims

DEMANDS 1. A process for preparing a ceramic part by micromachining comprising: 1) a step of preparing a suspension comprising a first ceramic powder, a binder, a plasticizer and a solvent, 2) a step of preparing a second powder from the suspension prepared in step 1), 3a) a heat treatment step of the second powder prepared in step 2), 3b) a compression step of the powder heat-treated in step 3a), thereby obtaining a raw ceramic part, 4) a machining step of said raw ceramic piece prepared in step 3b), 5) a sintering step of the raw ceramic part machined in step 4), by which the ceramic part is obtained.

2. A process according to claim 1, characterized in that said suspension comprises between 10 and 30% by mass of a first ceramic powder, preferably between 15% and 25%, even more preferably about 20%.

3. A process according to any one of the preceding claims, characterized in that said first ceramic powder comprises oxides, for example Al2O3, ZrC>2, TiC>2, SiC>2, BaO or SrO; carbides, for example SiC, TiC, WC, TaC or NbC; nitrides, for example AlN, TiN, TaN or NbN; or mixtures comprising these chemical species, for example Al / SiC or Al / WC, 4. A method according to any one of the preceding claims, characterized in that said first ceramic powder has a particle size between 0.05 pm and 5 pm, preferably between 0.1 pm and 1 pm.

5. A method according to any one of the preceding claims, characterized in that said suspension prepared in step 1) further comprises a dispersant.

6. A method according to any one of the preceding claims, characterized in that the binder and plasticizer are present in a binder / plasticizer ratio of between 0.6 and 0.9, preferably about 0.

8.

7. A process according to any one of the preceding claims, characterized in that said suspension prepared in step 1) further comprises a crosslinking agent or catalyst, preferably boric acid.

8. A method according to any one of the preceding claims, wherein said suspension comprises between 0.01 and 0.2 mass % of dispersant; between 0.5 and 1 mass % of binder; - between 0.5 and 1.5% mass of plasticizer.

9. A process according to any one of the preceding claims, characterized in that step 1) of preparing a suspension comprises successively: a) mixing the first ceramic powder and the dispersant in a solvent, thereby obtaining a first mixture, b) adding the binder and the plasticizer to said first mixture.

10. A method according to any one of the preceding claims, characterized in that - the binder comprises polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), poly(vinyl butyral) (PVB), polyethylene glycol (PEG), acrylic latex, cellulose, polysaccharides, or mixtures thereof; - the plasticizer includes polyethylene glycol, phosphonates, polycarboxylate or mixtures thereof.

11. A process according to any one of the preceding claims, characterized in that said step 2) of preparing a second powder consists of a step of atomization granulation or cryogenic granulation.

12. Process according to claim 11, characterized in that said process further comprises a freeze-drying step after the spray-drying or cryogenic granulation step.

13. A process according to any one of the preceding claims, characterized in that heat treatment step 3a) comprises heat treatment of the second powder prepared in step 2) at a temperature between 40°C and 220°C, for a period of 2 minutes to 75 minutes, and step 3b) of compression of the powder heat-treated in step 3a) includes the application of a pressure of 20 MPa to 150 MPa on said powder for a period of between 2 minutes and 30 minutes.

14. A method according to any one of the preceding claims, characterized in that the heat treatment steps 3a) and compression steps 3b) are carried out simultaneously in a single thermocompression step.

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