FR3088017A1 - METHOD FOR MANUFACTURING A PART BY DENSIFICATION UNDER LOAD - Google Patents

Abstract

The invention relates to a method of manufacturing a part (lb) in a densification device under load which comprises the following steps: a) there is: - a preform of the part to be manufactured which comprises a core in a 1st pulverulent material surrounded by a layer of solid and porous or dense material or which is completely made of a solid and porous material, and - of a 2nd pulverulent material; b) a deformable coating is applied to the preform; c) the coated preform and the 2nd powdery material are placed in the compression enclosure so that the preform is surrounded by the 2nd powdery material; d) the contents of the compression enclosure are subjected to heating and a compression force is applied so that the preform sintered so as to obtain a part densified by sintering (lb).

Description

The field of the invention is that of the manufacture of parts, in particular mechanical parts, of complex shapes, by a densification technique under load of materials either partly powdery and partly solid and porous or dense, or completely solid and porous .

The invention thus relates to a method of manufacturing a part in a densification apparatus under load.

In the context of the present invention, the term "densification technique under load" means any sintering technique under load or creep aimed at consolidating a defined volume of metallic powders, ceramics, or organic materials (for example polymers) , by heating the latter and applying a uniaxial, multiaxial or isostatic pressure.

Many densification techniques under load of pulverulent or solid and porous materials are known and implemented daily in the industry. Among these techniques, we can cite:

forging, hot pressing (known under the English name "Hot Pressing"), hot isostatic pressing (known under the English name "Hot Isostatic Pressing"), assisted sintering in the field, also known as English acronym "FAST" for "Field Assisted Sintering Technology").

By "assisted sintering under field" means assisted sintering under electric field or magnetic field. Assisted sintering under an electric field is also known under the name of "flash sintering" and under the English acronyms "SPS" for "Spark Plasma Sintering" and "EGAS" for "Electric Current Assisted Sintering".

The SPS is known to subject a cylindrical volume of compressed powders to a pulsating current making it possible to significantly increase the kinetics of densification of these powders, and thus to obtain mechanical parts whose fine microstructures are preserved. However, the densification methods implemented by the SPS have the drawback of causing densification inhomogeneities in the case of parts of complex shapes having significant differences in thickness.

The production of parts of complex shapes by the conventional SPS process is therefore made difficult taking into account the complex geometry of the parts to be manufactured which results in differences in thickness and involves variations in shrinkage.

It should be noted that these densification heterogeneity problems relate exclusively to the sintering of parts of complex shape. Indeed, in the context of volumes to be densified in a simple form, that is to say having a constant thickness, the withdrawal distances are everywhere the same and thus make it possible to obtain a homogeneous densification of the part. There is therefore no reason to draw inspiration from documents relating to the sintering of non-complex shaped parts to solve the observed problems of densification heterogeneity.

There is thus a real need to overcome the heterogeneity of densification of complex parts manufactured by known techniques of densification under load.

The international application WO 2017/077028 A1 proposes a solution which attempts to overcome these difficulties of the heterogeneity of densification of complex parts manufactured by known techniques of densification under load. This solution consists in the implementation in a densification device under load in a compression direction of an assembly which comprises:

a volume to be densified of a pulverulent and / or porous composition and which, depending on the direction of compression, has variations in thickness, a counterform of pulverulent and / or porous composition, a deformable interfacial layer which is interposed between the volume to densify and counterform.

In this assembly, the geometric characteristics of the counterform will give the geometric shape to the complex part which is obtained from the volume to be densified.

During densification under load, the interfacial and deformable layer follows the withdrawal of the volume to be densified and, as a result, distributes the stresses transmitted by the counterform and the tool evenly over the volume being densified. The part thus obtained has a shrinking homothety over its entire surface in contact with the interfacial layer. In addition, the faults and fractures that can be generated within the counterform during the densification process are completely or partially blocked by the deformable interfacial layer and do not propagate in the volume being densified. The part thus obtained also has a preserved microstructure.

However, the assembly as described in international application WO 2017/077028 A1 has limits because the geometric shape of the densified part is dependent on the geometric characteristics of the counterform. However, certain very complex forms of the counter-form cannot, or even be difficult, to be implemented. The shape restrictions of the counterform thus generate shape restrictions of the part obtained with the assembly which is the subject of international application WO 2017/077028 A1. In other words, it is not possible to '' get all the pieces you want with very complex shapes.

This is why the inventors of the present invention have sought to overcome this drawback linked to the limitations of the complexity of the shape of the counterform of the assembly described in application WO 2017/077028 A1, by proposing a new manufacturing process. of parts in a densification apparatus under load which overcomes this counterform and thus makes it possible to obtain parts having any complexity of desired shape.

The subject of the invention is a method of manufacturing a part in a densification apparatus under load in at least one direction of compression which is equipped with a compression enclosure, said method comprises at least the following steps:

a) we have:

a preform of the workpiece which:

i. comprises a core made of a ^1st powder material surrounded by at least one layer of solid and porous material or at least one layer of dense material, or ii. is completely made of a porous solid material, and a ^2nd powder material;

b) at least one deformable covering of a material which does not interact chemically with the ^2nd powder material and the solid material and porous or dense of the preform is applied to the preform;

c) providing the coated preform and the ^2nd pulverulent material into the compression chamber such that the coated preform is surrounded by the ^2nd powder material;

d) the contents of the compression enclosure are subjected to heating and at least one compression force is applied in the at least one compression direction so that the preform sintered in said at least one compression direction so as to obtain a densified part by sintering.

The densification device under load can be a device chosen from forging, hot pressing, hot isostatic pressing and assisted sintering under field devices. These devices are perfectly known to a person skilled in the art, who therefore masters their operation.

The preform of the part to be manufactured may have been obtained using one of the techniques chosen from:

selective laser sintering (known by the acronym "SLS" for "Selective Laser Sintering"), selective laser fusion (known by the acronym "SLM" for "Selective Laser Melting"), modeling by deposition of wire, fusion by electron beam, stereolithography, additive manufacturing by jet of binders, machining, taken alone or in combination of these. These techniques are perfectly within the reach of those skilled in the art.

With the manufacturing process, the preform can have any shape, including a complex shape. By "complex shape" is meant that the preform has variations in thickness of continuous segments of its volume, within the framework of a projection in the direction of compression. It is advisable to distinguish the thickness of a form and its height, the latter being able to designate discontinuous segments of a volume, according to this same projection. For example, a volume in the form of a double cone of revolution, when considered along its axis of revolution, has a constant height but a variable thickness.

The preform manufacturing techniques which have been listed above are suitable for obtaining such complex shapes.

This is why the manufacturing method according to the invention has the advantage of being perfectly suited for the manufacture of parts, and more particularly of parts of complex shape.

In one embodiment of the invention, the preform comprises a core made of a ^1st pulverulent material which is surrounded by at least one layer of dense material.

In the context of the invention, the term "dense material" means a material which does not have porosity. Such a material is thus gas tight.

In this embodiment, the thickness of the layer of dense material can be between 10 μm and 1 mm, preferably between 200 μιτι and 500 μm.

In embodiments of the invention, the preform comprises a solid and porous material which can:

either be an outer layer of the preform when the latter also comprises a heart in a l ^ist powder material or constitute the entire preform.

When the preform comprises a core of a ^1st powder material surrounded by a layer of a solid and porous material, the porosity of this solid material can be closed or open. If the porosity is open, the size of the pores of this solid and porous material is preferably less than the size of the grains of the ^1st powder material forming the heart of the preform. This prevents grains of this ^1st powder material from leaving the layer of solid and porous material with open porosity.

The thickness of the layer of solid and porous material can be between 10 μιτι and 1 mm, preferably between 200 μιτι and 500 μιτι.

The material of the pulverulent core may be identical to or different from that of the layer of solid and porous or dense material.

The preform may include one or more layers of solid and porous or dense material. When the preform comprises several layers (for example superimposed on each other) of solid and porous or dense material, these different layers can be made of identical or different materials. These materials are described below in the description of the materials of the preform.

The preform may include one or more layers of solid and porous and / or dense materials which may be the same or different from each other.

The materials of the preform, of the 2 ^nd powder material, as well as of the coating, are chosen in an appropriate manner so that they do not degrade during step d) of the manufacturing process.

The materials of the preform and the ^2nd powder material may be selected from metals, ceramics and organic materials.

The preform material and / or the ^2nd powder material may be at least one organic material which is synthetic or natural. For example, it may be lignocellulosic material, keratin or even a polymer.

The preform material and / or the ^2nd powder material may be an organic material which is at least one polymer selected from poly-methacrylate methyl (PMMA), polyvinylchloride (PVC), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), polyamide (PA), polycarbonate (PC), polyetheretherketone (PEEK) and polyimide (PI).

The preform material and / or the ^2nd powder material may be at least one ceramic:

based on oxides, in particular chosen from zirconia, alumina, magnesia, zinc oxide, spinels, titanium oxides, barium or strontium titanates, silicas and silicates (for example cordierites and mullites);

non-oxidized, for example chosen from carbides, borides, nitrides and fluorides.

The preform material and / or the ^2nd powder material may be at least one metal. It can be a precious metal chosen by silver, gold and platinum, as well as their associated alloys. It can also be:

super alloys based on nickel or cobalt, nickel alloys, for example nickel alloys of the Iconel 718, 316L stainless steel, FeNi, NiTi type, titanium alloys, and in particular the alloy TÎ-6AI- 4V (commonly called hereinafter “titanium alloy TA6V”), aluminum alloys (for example 5086, 6061, 7075, MCrAI, FeCrAI, FeAI, TiAl, MgAI), or manganese alloys (by example MgSiSn, MgBz).

The materials of the preform and the ^2nd powder material may be the same or different.

The choices of the materials constituting the preform and the 2 ^nd pulverulent material, are oriented taking into consideration the rules of densification of these materials, in order to obtain at the end of the process according to the invention a part having a homogeneity of desired densification .

These densification rules are based in particular on the fact that during densification under load in step d) of the method according to the invention:

if the material of the ^2nd powder material densifies faster than that of the preform, the material of the ^2nd powder material will stop the densification of the preform before it will present the densification desired sintering, which may result by density heterogeneities within the part obtained at the end of the process.

if the material constituting the preform densifies more rapidly than that of the ^2nd material powder, after step d) of the process according to the invention, the piece has the desired densification by sintering.

The rules for densification of materials are within the reach of those skilled in the art who will be able to choose the appropriate materials to obtain, at the end of the process, a part of the desired shape.

In one embodiment of the invention, the preform material and the ^2nd powder material have similar densification curves. This has the advantage of facilitating the prediction of withdrawals of material from the preform which are generated during step d) of the method according to the invention. To do this, it can be materials of the same type: metal / metal or ceramic / ceramic or organic material / organic material (for example polymer / polymer).

For example, the preform may be comprised of zirconia powder and the ^2nd powder material may consist of alumina powder. The coupling of these two materials finds its basis in their sintering behavior (temperature and densification curve) which is relatively similar. The zirconia powder of the preform densifies slightly faster than the alumina powder, and thus makes it possible to obtain a completely densified part by sintering during the process according to the invention.

In one embodiment of the invention, the materials of the preform and the ^2nd powder material are of identical chemical composition and microstructure. This has the advantage of facilitating the prediction of withdrawals of material from the preform which are generated during step d) of the method according to the invention.

In another embodiment of the invention, the preform material and the ^2nd powder material have a chemical composition and / or a different microstructure.

Implementation of material chemical composition and / or different microstructure broadens the possibilities of choice of materials of the preform and the ^2nd powder material. It is thus possible to implement, for the formation of the preform, a material with advanced and therefore costly technical properties, while selecting for the constitution of the ^2nd material powder, a lower cost material.

The deformable coating applied in step b) is selected such that it shows no chemical interaction with either the 2 ^nd or powder material with the solid or dense porous material and the preform. Indeed, in the event of chemical interaction, this would hamper the recovery of the densified part by sintering at the end of the process according to the invention.

This deformable coating creates a separation between the ^2nd powder material and the solid, porous or dense material of the preform. This makes it possible to avoid any chemical interaction between these two materials which would also be likely to hinder, or even prevent, the recovery of the densified part by sintering after densification under load.

In addition, the separation created by the deformable coating also proves advantageous when the ^2nd powder sintered material during step d) of the manufacturing process according to the invention. In the absence of this deformable coating, it would then be difficult, if not impossible, to recover within the compression enclosure the part densified by sintering after densification under load.

In addition, during the densification under load of step d), the deformable coating deforms and follows the withdrawal of the sintered preform. The deformation of the coating on the preform makes it possible to distribute therein homogeneously all the stresses transmitted by the 2 ^nd pulverulent material during step d). The part densified by sintering obtained at the end of step d) exhibits a shrinking homothety over its entire surface in contact with the coating which has been deformed.

The coating can comprise at least one of the materials chosen from boron nitride and graphite, taken alone or as a mixture of these. Preferably, the coating is made of boron nitride.

The coating can have a thickness of between 20 nm and 2 mm, preferably between 1 μιτι and 100 μιτι.

The coating may be applied to the preform by spraying a powder (for example a powder of boron nitride or graphite) or by applying a flexible sheet (for example a sheet of graphite, in particular a sheet of graphite sold by MERSEN under the trade name PAPYEX®).

In one embodiment of the invention, the preform is made into a solid and porous material consisting of a titanium alloy TA6V, the ^2nd powder material is alumina and the coating material is boron nitride.

At the end of step c) of the process according to the invention, the coated preform is surrounded by the ^2nd powder material. In other words, the coated preform is buried within the ^2nd pulverulent material into the compression chamber. In the context of the invention, it is meant by the fact that "the coated preform is surrounded by the 2 ^nd powder material" that the entire surface or even a part of the surface of the coated preform is in contact with the 2 ^nd powder material .

During step d), the temperature within the compression enclosure can be between 50 ° C and 2000 ° C, preferably between 800 ° C and 950 ° C. It will depend on the nature of the materials of the preform and the ^2nd powder material. For example, when it is an organic material, the temperature within the compression enclosure is advantageously between 50 ° C and 500 ° C. In the case of ceramic, depending on its refractory nature, the temperature within the compression enclosure can reach up to 2000 ° C.

The temperature in the compression chamber is appropriately selected such that the materials of the preform, the ^2nd powder material and the coating do not degrade during step d). The choice of temperature within the compression enclosure is perfectly within the reach of those skilled in the art.

During step d), at least one compression force is applied which can be between 10 kN and 200 kN, preferably between 80 kN and 120 kN. The compressive force is appropriately selected such that the materials of the preform, of the ^2nd material powder and the coating do not degrade during step d). The choice of compression force is perfectly within the reach of those skilled in the art.

The direction of compression can be uniaxial, multiaxial or isostatic.

In the case of uniaxial compression, a preform and a ^2nd pulverulent material near the densification properties, stretching height (h) is related to the initial and final relative density of the component (d, , df) and at the desired final height (hf), by the following equation:

h, = hf. df / d.

This so-called “preform” equation makes it possible to better define the deformations of the preform and of the deformable coating.

The withdrawal distances and the deformations induced on the volume of a given preform following the implementation of step d) of the method according to the invention can be predicted using simulation software, for example COMSOL multiphysics® simulation software developed by COMSOL.

The prediction of these data as to the withdrawal distances and the deformations of the preform are perfectly within the reach of the skilled person who will thus be able to determine before the implementation of the method according to the invention, the characteristics of the preform (to know both its geometrical form and or material (s) constituting it) and the ^2nd material powder, and the parameters of temperature and the compression force to be applied depending on the desired shape of the densified part by sintering obtained with said process.

At the end of step d), the part is at least partly densified by sintering, preferably on its external part. In one embodiment of the invention, the part is completely densified by sintering.

The part obtained at the end of step d) preferably has a relative density greater than or equal to 95%, more preferably greater than or equal to 99%. By "relative density" is meant the density of the part obtained with the method according to the invention relative to the estimated density of this same part when it is dense. With the method according to the invention, it is sought that the parts obtained are as dense as possible, namely that they have a relative density which tends towards the value of 100%.

After step d) of the method according to the invention, the densified part is extracted from the compression enclosure by sintering. To do this, it may be necessary to fracture the ^2nd material was powdered before step d) of the process and that is compacted or sintered during the densification step under load.

Thanks to the deformable coating, the cracks liable to be generated during this fracturing are stopped at the level of the coating and therefore do not damage the part densified by sintering. The latter remains intact and can then be removed from the coating.

In one embodiment of the invention, the preform comprises at least one protuberance. This protuberance can help facilitate the extraction of the part densified by sintering obtained with the method according to the invention from the compression enclosure.

The part can be a part chosen from turbocharger turbines, turbine engine turbine blades, watch bodies, bearing balls and seals.

The invention will be better understood using the detailed description of an exemplary embodiment of a blade obtained with the manufacturing process according to the invention.

DESCRIPTION OF THE FIGURES

FIG. 1 is a photograph of the preform of a blade before carrying out step d) of the method according to the invention.

FIG. 2 is a photograph of the dawn at the end of the process according to the invention.

EXPERIMENTAL PART :

A vane 1b was produced according to the manufacturing method according to the invention in the following manner:

The material of the preform 1a was a powder of a TA6V titanium alloy which had the following size distribution:

- 10: 18 pm;

d50: 31.6 µm;

d90: 43.5 pm.

A dawn preform 1a was obtained by the selective laser melting technique in an apparatus marketed by the company 3D SYSTEMS under the trade name ProX® DMP 200.

The parameters of this additive manufacturing were as follows:

scanning speed: 1800 mm / s;

laser power: 300 W;

the spacing: 85 µm;

the thickness of the powder bed: 60 μm.

The dawn preform 1a thus obtained at the end of the additive manufacturing had a pulverulent core which was surrounded by a dense layer with a thickness of 200 μm. The dimensions of the dawn preform la were as follows:

a height h of 43.10 mm;

a width I of 21.50 mm; a length L of 31.70 mm.

The preform 1a was then coated with a layer of boron nitride by spraying. Boron nitride does not chemically react either with the titanium alloy TA6V or with the alumina powder in which the preform 1a was then buried within the graphite compression enclosure of an assisted sintering densification apparatus under electric field which is marketed by the company Sumitomo Coal Mining Co., Ltd under the trade name Dr. SINTER 2080.

The preform 1a was subjected to an assisted sintering cycle under an electric field in the direction of its width "I". The cycle presented the following parameters:

the initial temperature of the compression chamber was 20 ° C and it was increased for 18 minutes by 48.9 ° C / minute until the temperature of 900 ° C was reached. The temperature was maintained for 10 minutes at 900 ° C;

the compression force applied was 6 kN during the first 14 minutes of the cycle, then it was increased for 4 minutes by 23.15 kN / minute until it reached 98.6 kN. The compressive force was maintained at 98.6 kN for 10 minutes.

During assisted sintering under an electric field, the preform sintered it so that:

its height increased from "ha": 43.10 mm to "hb": 43.60 mm;

its width has decreased from "la": 21.50 mm to "Ib": 14.85 mm; its length has decreased from "La": 31.70 mm to "Lb": 31.50 mm.

Thus, during assisted sintering under an electric field, only the width "I" of the preform has varied. This was the direction in which the compressive force was applied. The variations in height "h" and in length "L" of the preform detailed above are negligible.

There was thus obtained a blade densified by sintering lb. More precisely, the blade 1b thus obtained was completely densified by sintering.

Then, the densified dawn lb was unchecked from the boron nitride coating.

This blade 1b had perfect homogeneity in TA6V titanium alloy. Indeed, its relative density was greater than 99%. By "relative density" is meant the density of the part obtained with the method according to the invention relative to the estimated density of this same part when it is dense. In addition, the blade 1b had a homogeneous microstructure and a surface roughness on the order of 6 μm.

The photograph in FIG. 1 shows the preform 1a before step d) of the method according to the invention. The photograph in FIG. 2 shows the blade 1b obtained at the end of the manufacturing process according to the invention. There is a marked reduction in the width between the preform of the blade 1a and the blade 1b obtained at the end of the manufacturing process according to the invention.

Claims (13)

1. A method of manufacturing a part (lb) in a densification apparatus under load in at least one compression direction which is equipped with a compression enclosure, characterized in that said method comprises at least the following steps: a) we have: a preform (la) of the workpiece which: i. comprises a core made of a ^1st powder material surrounded by at least one layer of solid and porous material or at least one layer of dense material, or ii. is completely made of a porous solid material, and a ^2nd powder material; b) applying to the preform (Ia) at least one deformable covering of a material which does not interact chemically with the ^2nd powder material and the solid material and porous or dense preform (Ia); c) placing the preform (Ia) and the ^2nd coated material powder in the compression chamber so that the preform (Ia) coated or surrounded by the ^2nd powder material; d) the contents of the compression enclosure are subjected to heating and at least one compression force is applied in the at least one compression direction so that the preform (la) sintered in said at least one compression direction so as to obtain a part densified by sintering (lb). 2. Manufacturing method according to claim 1, characterized in that the preform (la) was obtained from one of the techniques chosen from selective laser sintering, selective laser fusion, wire deposition modeling , electron beam fusion, stereolithography, additive manufacturing by jet of binders, and machining. 3. The manufacturing method according to any one of claims 1 to 2, characterized in that the material of the preform (Ia) and the ^2nd powder material are selected from metals, ceramics and organic materials. 4. The manufacturing method according to claim 3, characterized in that the preform material (la) and / or the ^2nd pulverulent material is an organic material which is at least one polymer selected from poly methyl methacrylate (PMMA ), polyvinyl chloride (PVC), polypropylene (PP), polyethylene terephthalate (PET), polystyrene (PS), polyamide (PA), polycarbonate (PC), polyetheretherketone (PEEK) and polyimide ( PI). 5. The manufacturing method according to claim 3, characterized in that the preform material (la) and / or the ^2nd powder material is at least one ceramic selected from zirconia, alumina, magnesia, oxide zinc, spinels, titanium oxides, barium or strontium titanates, silicas, silicates, carbides, borides, nitrides and fluorides. 6. The manufacturing method according to claim 3, characterized in that the preform material (la) and / or the ^2nd powder material is at least one metal selected from silver, gold, platinum, alloys nickel, titanium alloys, aluminum alloys and manganese alloys. 7. The manufacturing method according to any one of claims 1 to 6, characterized in that the coating comprises at least one of the materials chosen from boron nitride and graphite, taken alone or as a mixture thereof. 8. The manufacturing method according to any one of claims 1 to 7, characterized in that the coating has a thickness between 20 nm and 2 mm. 9. The manufacturing method according to any one of claims 1 to 8, characterized in that the coating is applied to the preform (la) by spraying a powder or by applying a flexible sheet. 10. The manufacturing method according to any one of claims 1 to 9, characterized in that during step d), the temperature within the compression enclosure is between 50 ° C and 2000 ° C. 11. The manufacturing method according to any one of claims 1 to 10, characterized in that during step d), at least one compression force between 10 kN and 200 kN is applied. 12. The manufacturing method according to any one of claims 1 to 11, characterized in that the compression direction is uniaxial, multiaxial or isostatic. 5 13. Part (lb) manufactured according to the manufacturing method according to any one of claims 1 to 12, characterized in that the part (lb) is a part chosen from turbocharger turbines, the blades of turbojet turbines, watch body, bearing balls and seals.