Manufacturing process for metal parts and metal parts obtained using SPS sintering

Abstract

The invention relates to a method for manufacturing a metallurgical part characterized by the following steps: - Using a powder of a metallurgical material having a particle size of less than 400 micrometers, - Reducing the size of the grains and / or crystallites of the powder so as to obtain aggregates with a characteristic size of less than 1000 micrometers, and an average crystallite size of less than 200 nanometers, - Sintering the reduced powder using an SPS sintering process, so that the metallurgical part obtained has a Vickers hardness greater than 320Hv. Abstract figure: Fig. 1

Description

Title of the invention: Method for manufacturing metal parts and metal parts obtained using SPS sintering TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to the manufacture of metal parts by sintering, in particular the manufacture of parts having mechanical properties of particular hardness. STATE OF THE ART

[0002] A metallurgical material such as steel mainly comprises iron and carbon, the carbon being between 0.02% and 2% by mass. In order to increase the hardness of a steel, it is known to increase the carbon content. For example, some steels have carbon concentrations greater than 1.7% (ledeburitic steels). In addition, it is possible to carry out heat treatments, these treatments being mainly surface treatments.

[0003] It is thus desirable to propose a material having a hardness equivalent to or greater than those of the state of the art, and / or a hardness which is homogeneous in volume. Another aim of the invention is to limit the number of operations and / or treatments. THE INVENTION

[0004] To this end, and according to a first aspect, the invention proposes a method for manufacturing a metallurgical part characterized by the following steps:

[0005] - use a powder of a metallurgical material having a particle size in less than 400 pm (micrometers),

[0006] - reducing the size of the grains and / or crystallites of the powder so as to obtain aggregates with a characteristic size of less than 1000 pm (micrometers), and an average crystallite size of less than 200 nm (nanometers),

[0007] - sintering using an SPS sintering process the reduced powder,

[0008] so that the metallurgical part obtained has a Vickers hardness greater than 320Hv.

[0009] The part obtained according to the invention makes it possible to increase the hardness compared to the results of the prior art, while limiting the costs thanks in particular to the reduction in the number of operations and / or post-treatments. In addition, this makes it possible to limit the carbon content compared to the results of the prior art. The metallurgical part obtained is thus intrinsically different compared to the results of the prior art.

[0010] For the above and for the remainder of the description, the following terms are understood to mean:

[0011] - SPS sintering, acronym for “Spark Plasma Sintering”, a sintering process under pressure based on the densification of a powder sample by application of a mechanical stress associated with the passage of a pulsed current to heat the sample; for example, a sintering method related to hot isostatic pressing but using the Joule effect to heat the pre-compacted powder in a hollow cylindrical crucible between two graphite electrodes under an inert atmosphere or under vacuum, the whole being subjected to a pressure of several megapascals under the action of a hydraulic press. A direct or alternating current of several kiloamperes, pulsed or not, is applied between the electrodes with a voltage of a few volts. ;

[0012] - binder, any material making it possible to improve densification and / or the mechanical properties final canics giving mechanical cohesion to the final part, for example cobalt material or another sintering agent;

[0013] - grain size, or granulometry, or grain granulometry, the characterized size by the values dlO, d90, d50 in order to quantify the dispersion of this grain size distribution;

[0014] - crystallite size, or average crystallite size, each grain being able to present crystallites, the size relating to coherent crystallographic domains and which is measured by techniques such as SEM, TEM, etc.;

[0015] - form factor, the ratio between two characteristic lengths, each length extending in a determined direction, said characteristic lengths having a non-zero angle with respect to each other, for example an angle of 90 degrees;

[0016] - atomization or atomizing, in particular concerning a powder, a method of transformation of a metal ingot into spherical powder by melting and projecting the metal drops under a gas flow to make them spherical,

[0017] - spheroidization, or spheroidizing, in particular concerning a powder, a method of transforming an angular ground metal powder by fusion, most often assisted by plasma, to make it spherical;

[0018] - grinding or crushing, in particular concerning a powder, a method of trans forming by mechanical action, for example by beads, so as to reduce the size of the crystallites and / or the size of the grains of a powder;

[0019] - aggregates, the result of a reduction in grain size and / or scree size tallites, for example by grinding, which results in an agglomeration of small grains to form larger agglomerates, but each grain constituting the agglomerates has smaller crystallite sizes;

[0020] - hardness, the resistance of a material to be marked by another, we will use here the Vickers hardness.

[0021] Preferably, the metallurgical part or the metallurgical material comprises at least one metallic element. The part or the material comprises at least 50% in mass of at least one metallic element.

[0022] Preferably, the metallurgical material powder used has a particle size of less than 50 μm (micrometers).

[0023] According to alternative embodiments, the metallurgical material powder used comprises: - at least 98% of a metallic phase, or - at least 95% of a metallic phase, or - at least 85% of a metallic phase, or - at least 80% of a metallic phase, or - at least 75% of a metallic phase.

[0024] In connection with the preceding paragraph, the metallurgical material powder may comprise doping agents making it possible to further increase the final hardness, in order to complete the composition of said powder and respectively: - at most 2% of one or more doping agents, - at most 5% of one or more doping agents, - at most 15% of one or more doping agents, - at most 20% of one or more doping agents, - at most 25% of one or more doping agents.

[0025] By metallic phase is meant a metallurgical or crystallographic phase which is a particular compound combining several chemical elements and having a particular microstructure. An alloy is a combination of mainly metallic elements and optionally, to a lesser extent, ceramic elements. An alloy may comprise one or more metallurgical phases.

[0026] Preferably, the metallic phase is an iron-based alloy, such as steel or cast iron, or an aluminum-based alloy, or a titanium-based alloy, or a nickel-based alloy. The present invention relates to all alloys.

[0027] Preferably, the metallurgical material has a carbon content of less than or equal to 2% by weight relative to the total weight of the metallurgical material. Preferably, the metallurgical material has a carbon content of less than or equal to 2%, preferably less than or equal to 1.75%, preferably less than or equal to 1.5%, preferably less than or equal to 1.25%, preferably less than or equal to 1%, preferably less than or equal to 0.75%, preferably less than or equal to 0.5%.

[0028] Each grain type has a predetermined grain size, a predetermined crystallite size, and a predetermined shape factor.

[0029] Preferably, the powder is reduced, particularly when the powder cannot be used as is, so that: - the aggregates have a characteristic size of less than 200 micrometers, and / or - the average size of the crystallites is less than 100 nanometers.

[0030] According to alternative embodiments which may or may not be combined, the reduction in the size of the grains and / or crystallites of the powder comprises: - a step of atomizing the metallurgical material, and / or - a step of grinding the metallurgical material, so that the powder used has a particle size of less than 1000 micrometers.

[0031] Preferably, the method comprises a step of atomizing the powder used so that the grain size has a size less than or equal to 150 micrometers.

[0032] According to other embodiment variants, which may or may not be combined, the reduction in the size of the grains and / or crystallites of the powder comprises: - a step of atomization of the metallurgical material, and / or - a step of grinding the metallurgical material, so that the size of the agglomerates is less than 1000 micrometers.

[0033] Preferably, and in the case of the combination of the two steps, the atomization step is carried out before the grinding step.

[0034] The predetermined grain microstructure may have the following characteristics: - Particle size distribution: d50 being between 0.1 and 100 pm, - Crystallite size: 20 to 1000 nm, - Form factor: between 1 and 5 (spherical to angular, without being cylindrical).

[0035] One embodiment consists of using a monomodal particle size distribution before grinding of between 0.1 and 100 micrometers (pm).

[0036] According to another embodiment, the powders have a bimodal distribution before grinding with d50 values separated by a decade, typically 0.1pm and Ipm or Ipm and lOpm or even lOpm and lOOpm. This bimodal distribution may be separated by 2 decades, typically 0.1 and lOpm or 1 and lOOpm.

[0037] According to yet another embodiment, the distribution is trimodal with d50s separated by a decade, typically O.lpm, Ipm and lOpm. These examples are obviously non-limiting.

[0038] In one embodiment, the powder is used as is, raw from the supplier. For example, this powder may have a d50 value, in particular a grain diameter of less than 100 micrometers, preferably less than 50 micrometers, preferably less than 15 micrometers.

[0039] In a preferred mode, the powder is ground in order to refine the size of the crystallites (coherent crystallographic domains) which is different from the particle size distribution. metric. Thus, after grinding, there is a reduction in the size of the crystallites, but not necessarily a reduction in the size of the grains.

[0040] Preferably, the size of the crystallites is between 20 and 1000 nanometers (nm). Preferably, the size of the crystallites is between 20 and 100 nm. Finally, preferably, the size of the crystallites is between 20 and 50 nm. In one embodiment, it is possible to combine several crystallite sizes.

[0041] According to one embodiment, the manufacturing method comprises a step of adding at least one doping agent with the metallurgical material, before the sintering step.

[0042] Preferably, the at least one doping agent is or comprises boron nitride BN, titanium carbide TiC, tungsten carbide WC, silicon carbide SiC, niobium carbide NbC, boron carbide B4C, silicon nitride Si3N4, aluminum oxide A12O3, zirconium oxide ZrO2, yttrium oxide Y2O3 or a mixture thereof. Preferably, the at least one doping agent is or comprises the doped variants of the preceding elements.

[0043] According to a particular embodiment, the manufacturing method comprises only a step of atomizing the powder of the metallurgical material, and then the powder obtained, called intermediate powder, can be mixed, or not, with at least one doping agent.

[0044] According to another particular embodiment, the manufacturing method comprises only a step of grinding the powder of the metallurgical material, and then the powder obtained, called intermediate powder, can be mixed, or not, with at least one doping agent.

[0045] According to a first embodiment, the sintering step is carried out until a part of predetermined shape is obtained which is composed or made up of the sintered metallurgical material. Preferably, the part of predetermined shape is composed or made up solely of the sintered metallurgical material, the metallurgical material comprising one or more of the characteristics stated above.

[0046] According to a second embodiment, the sintering step is carried out until a part, called the starting part, is covered with a layer of the sintered metallurgical material so as to obtain a part of predetermined shape.

[0047] For example, the manufacturing method further comprises the following steps: - choose a room, called the starting room, - sinter the reduced powder on the starting part until it covers the said part in order to obtain the metallurgical part.

[0048] According to an alternative embodiment, the starting part is obtained by the sintering step according to the first embodiment.

[0049] Preferably, according to any embodiment, the manufacturing method comprises a step of adding at least one substrate metal powder with the metallurgical material, before the sintering step.

[0050] Preferably, according to any embodiment, the height of each layer of sintered powder as required.

[0051] By substrate metal powder is meant any alloy, thermochemically compatible with the metallurgical powder resulting in high hardness metallic materials. For example, the substrate metal powder is 316L steel or nickel-free stainless steel.

[0052] Preferably, the manufacturing method further comprises a heat treatment step after the sintering step.

[0053] According to a second aspect, the invention provides a metallurgical part obtained according to one or more of the characteristics of the manufacturing method of the first aspect.

[0054] The metallurgical part is, for example, and in a non-limiting manner, a cutting tool for machining or drilling.

[0055] The metallurgical part is obtained by SPS sintering of a powder of a metallurgical material characterized in that the powder has a grain size of less than 1000 micrometers and / or a crystallite size of less than 200 nanometers, so that the metallurgical part obtained has a Vickers hardness greater than 320Hv.

[0056] Description of the figure

[0057] [fig. 1] [fig.l] represents a flowchart presenting the different embodiments of the manufacturing process.

[0058] With reference to [fig. 1], a method of manufacturing a metal part is provided during which:

[0059] - the powder of metallic material “Alloy” can be only atomized or only crushed, see the first two lines,

[0060] - the powder of metallic material “Alloy” can be atomized then ground, see the third line,

[0061] - the powder of metallic material “Alloy” can be atomized and mixed with a addition element or doping agent, see fourth line,

[0062] - the powder of metallic material “Alloy” can be ground and mixed with a addition element or doping agent, see fifth line,

[0063] - the powder of metallic material “Alloy” can be atomized, then ground and mixed with an addition element or doping agent, see sixth line.

[0064] Obtaining this powder, called intermediate alloy powder, is then sintered using the SPS sintering method, see “SPS sintering A”.

[0065] The hardness of the ex nihilo metallurgical part obtained or of the coating of the part metallurgical obtained is: - greater than 200Hv in the case of atomization alone or grinding alone, - greater than 350Hv in the case of atomization then grinding, - greater than 450Hv in other cases.

[0066] According to another embodiment, the intermediate powder can be deposited before or after a metal substrate powder so as to form a superposition of layers. The height of each layer will be adjusted according to the need.

[0067] Then this superposition of layers is sintered using the SPS sintering method, see “SPS sintering B”, making it possible to obtain an ex nihilo metallurgical part.

[0068] According to an alternative embodiment compared to the previous embodiment, it is possible to carry out the previous manufacturing method so as to form a coating, see “SPS C sintering”, on a metallurgical part obtained ex nihilo, after “SPS A sintering”.

[0069] According to another variant, the coating can be applied, see “SPS D sintering”, on a part, called the starting part, for example a steel called 316L.

[0070] The coating may have a thickness greater than or equal to one millimeter.

[0071] The hardness of the parts obtained is thus increased to reach a value between 200 Hv and 1500 Hv with doping agents.

[0072] According to one embodiment, the doping agent is, for example, silicon carbide. The aggregates have, for example, a size of between 100 and 500 micrometers. The grain size is, for example, between 50 and 150 nanometers. This example makes it possible to obtain a part having a hardness approximately equal to 1000 Hv.

Claims

Claims

1. Method for manufacturing a metallurgical part characterized by the following steps: - Using a powder of a metallurgical material having a particle size of less than 400 micrometers, - reducing the size of the grains and / or crystallites of the powder so as to obtain aggregates with a characteristic size of less than 1000 micrometers, and an average crystallite size of less than 200 nanometers, - Sintering the reduced powder using an SPS sintering process, so that the metallurgical part obtained has a Vickers hardness greater than 320Hv.

2. Manufacturing method according to the preceding claim, in which the metallurgical material powder comprises at least 98% of a metallic phase.

3. Manufacturing method according to the preceding claim, in which the metallurgical material powder comprises at least 75% of a metallic phase.

4. A manufacturing method according to claim 2 or 3, wherein the metallic phase is an iron-based alloy, such as steel, or an aluminum-based alloy, or a titanium-based alloy, or a nickel-based alloy.

5. Manufacturing method according to one of the preceding claims, in which the aggregates have a characteristic size of less than 200 micrometers.

6. Manufacturing method according to one of the preceding claims, in which the average size of the crystallites is less than 100 nanometers.

7. Manufacturing method according to one of the preceding claims, in which the reduction of the size of the grains and / or crystallites of the powder comprises a step of atomizing the metallurgical material so that it has a particle size of less than 1000 micrometers.

8. Manufacturing method according to one of the preceding claims, in which the reduction of the size of the grains and / or crystallites of the powder comprises a step of grinding the metallurgical material so that it has a particle size of less than 1000 micrometers.

9. Manufacturing method according to one of the preceding claims, comprising a step of adding at least one doping agent with the metallurgical material, before the sintering stage.

10. A manufacturing method according to the preceding claim, wherein the at least one doping agent is boron nitride, titanium carbide, tungsten carbide, silicon carbide, niobium carbide, boron carbide, silicon boride, aluminum oxide, zirconium oxide, yttrium oxide or a mixture thereof.

11. Manufacturing method according to one of the preceding claims, in which the sintering step is carried out until a part of predetermined shape composed of the sintered metallurgical material is obtained.

12. Manufacturing method according to one of claims 1 to 10, further comprising the following steps: - choosing a part, called the starting part, - sintering the reduced powder on the starting part until said part is covered so as to obtain the metallurgical part.

13. Manufacturing method according to the preceding claim, in which the starting part is obtained by the sintering step according to claim 11

14. 1 1. Manufacturing method according to one of the preceding claims, comprising a step of adding at least one substrate metal powder with the metallurgical material, before the sintering step.

15. Manufacturing method according to one of the preceding claims, comprising a heat treatment step after the sintering step.

16. Metallurgical part characterized in that it is obtained according to one of the preceding claims.

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