EP3389903B1 - Method of making an abradable coating having variable densities - Google Patents

Description

FIELD OF THE INVENTION

This disclosure relates to a process for manufacturing an abradable coating with variable density.

Such an abradable coating, not forming part of the invention, can in particular be used to equip a rotating machine ring in order to seal the machine at the top of the rotating blades for example. Such an abradable coating is very particularly suitable for equipping turbine rings in the aeronautical field, and very particularly in aircraft turbojet engines.

STATE OF THE PRIOR ART

In many rotating machines, it is now known to provide the ring of the stator with abradable tracks facing the top of the blades of the rotor. Such tracks are produced using so-called “abradable” materials which, when they come into contact with the rotating blades, wear out more easily than the latter. This ensures a minimum clearance between the rotor and the stator, improving the performance of the rotating machine, without risking damage to the blades in the event of friction of the latter on the stator. On the contrary, such friction abrads the abradable track, which makes it possible to automatically adjust the diameter of the ring of the stator as close as possible to the rotor. Thus, such abradable tracks are often implemented in the compressors of turbomachines.

On the other hand, their use is much rarer in the turbines of such turbomachines, and especially in high-pressure turbines in which extreme physico-chemical conditions prevail.

Indeed, the burnt gases from the combustion chamber emerge in the high pressure turbine at very high temperature and pressure levels, which causes the premature erosion of the conventional abradable tracks.

Therefore, in order to protect the turbine ring, it is often preferred to provide the latter with a coating of the thermal barrier type whose materials and high density, too high for the coating is effectively abradable, protect the ring against erosion and corrosion.

However, it is naturally understood that in such a case the integrity of the blades is no longer ensured in the event of contact with the stator, which requires providing a greater clearance between the rotor and the stator and therefore increases the leakage rate. at the tip of the blades and thus reduces the performance of the turbine.

We also know the documents US 2014/0263579 , FR 2 996 475 and WO 2014/053754 which describe other methods of making an abradable coating.

There is therefore a real need for a method of manufacturing an abradable coating as well as such an abradable coating which is devoid, at least in part, of the drawbacks inherent in the aforementioned known configurations.

PRESENTATION OF THE INVENTION

This presentation relates to a process for manufacturing an abradable coating with variable density, comprising the following steps: providing a substrate comprising a first portion and a second portion; depositing a first precursor material on the first portion of the substrate; compression of the first precursor material between the substrate and a first support surface; sintering of the first precursor material thus compressed to obtain a first portion of abradable coating, facing the first portion of the substrate, having a first density; depositing a second precursor material on the second portion of the substrate; compression of the second precursor material between the substrate and a second support surface; sintering of the second precursor material thus compressed to obtain a second portion of abradable coating, facing the second portion of the substrate, having a second density distinct from the first.

This process makes it possible to obtain a coating with variable density. Indeed, several parameters can be set differently for each portion of the substrate so as to obtain abradable coating portions having different properties. First of all, it is possible to choose different precursor materials. In particular, the size of the particles constituting the precursor material or the initial porosity rate of the precursor material make it possible to influence the final porosity rate of the abradable coating and therefore its density.

It is also possible to deposit a greater or lesser quantity of precursor material before the compression step, that is to say to deposit a layer of precursor material of greater or lesser thickness. This quantity of material will thus influence the final density of the abradable coating.

It is also possible to compress the precursor materials more or less strongly during the compression steps so as to pack them more or less before sintering: this reduces their porosity rate to a greater or lesser extent, which influences the rate. final porosity and therefore the final density of each part of the abradable coating.

It is also possible to act on the temperature and/or the duration of the sintering steps in order to influence the microstructure of the abradable coating and in particular on its final porosity rate and on its density.

In the present description, the term "porosity rate" means the ratio between the volume of the interstitial spaces separating the grains of the material considered and the overall volume of said material. In addition, it goes without saying within the meaning of the present disclosure that the first and second portions of the substrate, like the first and second portions of the abradable coating, have a significant size in order to fulfill the functions for which they are intended. Thus, as can be seen in the figures, each portion of the substrate, and therefore each abradable coating part, has a width greater than 2 mm, preferably greater than 5 mm, and therefore an even greater length.

Therefore, thanks to this process, it is possible to locally adjust the degree of porosity and therefore the density of the coating in order to satisfy various local requirements or constraints. For example, it is possible to provide the areas of the coating sensitive to erosion with a high density and provide the areas of the coating intended to come into contact with a moving body with a lower density, reinforcing the easily abradable character of these areas. In addition, it is also possible to arrange the first part of the coating, benefiting from a high density, so as to mask and therefore protect the second part of the coating, the density of which is lower.

In certain embodiments, the steps of deposition, compression and sintering of the second precursor material take place after the steps of deposition, compression and sintering of the first material precursor. By thus separating these steps, it is possible to individualize the deposition, compression and sintering parameters for each portion of coating and therefore to easily obtain different properties for each part of the abradable coating.

In certain embodiments, the steps of compression and sintering of the first precursor material are carried out within a first mold; the steps of compression and sintering of the second precursor material are carried out within a second mold; and the second mold is separate from the first mold.

In some embodiments, the first and second mold are one and the same single mold.

In certain embodiments, the first mold comprises the first bearing surface as well as at least one protective wall provided so as to flank the first precursor material at the interface between the first and the second portion of the substrate during the stages of compression and sintering of the first precursor material. This protective wall makes it possible to prevent pieces of the first precursor material from moving and becoming fixed on the second portion of the substrate.

In certain embodiments, the second mold comprises a movable part extending opposite the second portion of the substrate and including the second bearing surface, and a stationary part extending opposite of, preferably against, the first portion of the substrate. This immobile portion makes it possible to protect the first part of abradable coating which is completed. Thus, preferably, only the portion of the mold which faces the second portion of the substrate is mobile.

In some embodiments, the steps of depositing the first and second precursor materials take place simultaneously or successively, the steps of compressing the first and second precursor materials take place simultaneously, and the steps of sintering the first and second precursor materials take place simultaneously . The total duration of the process is therefore reduced. It is also possible to use only one mold. In such a case, the difference in final density can be obtained, for example, thanks to different precursor materials, different thicknesses of layers of precursor material, or differential compression. Such differential compression can be obtained, for example, using a mold having bearing surfaces extending at different levels, or using a mold having several independent moving parts.

In some embodiments, the first portion of the substrate is located at a first level, and the second portion of the substrate is located at a second level different from the first level. Thanks to this difference in level between the first portion and the second portion of the substrate, the reduction in the volume available during the compression step is all the greater the closer the substrate was to the support surface in the initial state: assuming for example that the second level is deeper than the first level, the part of the precursor material located above the first portion of the substrate is thus more compressed than the part of the precursor material located above the second portion of the substrate. A greater pressure therefore prevails in this part of the precursor material, which leads to a greater density of the material after sintering. Conversely, in the second part of the precursor material, the compression being less significant, the reduction in the level of porosity in the material and therefore its densification are less significant.

In certain embodiments, the second portion of the substrate is obtained by machining at least one groove in a blank of the substrate. Such a two-level substrate is thus easy to manufacture since it suffices to manufacture a regular blank then to machine a groove in this blank only at the desired locations.

In certain embodiments, the first portion of the substrate is obtained by adding at least one wall to a blank of the substrate. This method is particularly suitable for repairing an existing part that is not thick enough to machine a groove.

In certain embodiments, the wall is manufactured directly on the blank of the substrate by sintering, in particular by a sintering method of the “Spark Plasma Sintering” (SPS) type.

In some embodiments, the wall is manufactured independently and attached by welding or brazing. It can in particular be attached by a welding method of the “Tungsten Inert Gas” (TIG) type.

In certain embodiments, the first and second bearing surfaces are continuous, one in the extension of the other. It is understood here that the support surfaces do not include any discontinuity such as a step or another sudden change in level within them or at their interface.

In certain embodiments, the support surfaces are rectilinear at least along a direction transverse to the first and second portions of the substrate. There is thus a cutting plane crossing both the first and the second portion of the substrate in which the support surfaces are rectilinear.

In certain embodiments, at least one bearing surface, preferably each bearing surface, takes the form of a cylinder sector, preferably of a cylinder sector of revolution.

In certain embodiments, at least one bearing surface, preferably each bearing surface, is a surface of a form mold.

In certain embodiments, the first part of the abradable coating has a final porosity rate of less than 15%, preferably less than 5%. The first part of the coating thus has a sufficiently low level of porosity, and therefore a sufficiently high density, to resist erosion.

In certain embodiments, the second part of the abradable coating has a final porosity rate greater than 20%, preferably greater than 30%. The second part of the coating thus has a sufficiently high degree of porosity, and therefore a sufficiently low density, to exhibit an easily abradable behavior.

In certain embodiments, the first part of the abradable coating undergoes a densification of at least 80%, preferably of at least 100%, during the compression and sintering step. In this presentation, the term "densification" means the increase in the density of the material making up the abradable coating between the initial state at the time of the step of depositing the precursor material and the final state obtained after the compression steps. and sintering. In other words, it is the difference between the final density and the initial density reported on the initial density.

In certain embodiments, the second part of the abradable coating undergoes a densification of at most 70%, preferably of at most 50%, and preferentially of at most 10% during the compression and sintering step. .

In certain embodiments, the method further comprises, before the step of depositing the precursor material on one of the portions of the substrate, preferably on the second portion of the substrate, a step of forming by sintering a heel layer , whose porosity rate is less than 15% and preferably less than 5%, on the considered portion of the substrate. This heel layer makes it possible to retain a highly densified layer under the second part, which is not very densified, of the abradable coating. Thus, the substrate remains protected in the event of radial displacement of the body circulating opposite the coating greater than the maximum displacement envisaged. This notably protects the substrate in the event of significant unbalance of the moving body, for example.

In certain embodiments, this step of forming a heel layer by sintering is carried out in the second mold or in a mold identical to the second mold.

In certain embodiments, the method further comprises, after the step of sintering one of the precursor materials, a step of forming by sintering a surface layer, the final porosity rate of which is less than 15% and preferably less than 5%, on at least one of the parts of the abradable coating, preferably on its second part. This layer makes it possible to provide the coating with a low surface roughness. It can also be formed over the entire surface of the abradable coating.

In certain embodiments, this step of forming a surface layer by sintering is carried out in the second mold or in a mold identical to the second mold.

In certain embodiments, the thickness of the surface layer is between 0.05 and 0.10 mm.

In certain embodiments, at least one precursor material, preferably each precursor material, is a metal or ceramic powder.

In some embodiments, the first and second precursor materials are different. In other embodiments, they are identical.

In certain embodiments, the first precursor material is a powder whose particle size is less than 20 μm.

In certain embodiments, the second precursor material is a powder whose particle size is greater than 45 μm.

In certain embodiments, the second precursor material is a powder whose particle size is less than 100 μm.

In some embodiments, the substrate is a ring sector. It may in particular be a turbine ring sector which will be mounted on the stator of the turbine.

In some embodiments, the first portion of the substrate extends along the second portion of the substrate.

In some embodiments, the substrate has a longitudinal channel flanked by two longitudinal shoulders, the shoulders forming part of the first portion of the substrate and the bottom of the channel forming part of the second portion of the substrate. At the end of the process, a sparse strip, therefore easily abradable, is thus obtained in the zone likely to come into contact with the blades of a rotor, for example, and two strips of denser coating on either side of the abradable strip making it possible to protect the latter from erosion caused by the axial circulation of an air stream for example.

This presentation also relates to an abradable track with variable density, not forming part of the invention, comprising a first part comprising a sintered material having a first density, and a second part, contiguous to the first part, comprising a sintered material having a second density distinct from the first density. As explained above, this makes it possible to protect the zones most sensitive to erosion while providing an easily abradable layer in the zones intended to come into contact with the mobile body.

In certain embodiments, the thickness of the first part of the abradable track is less than the thickness of the second part.

In certain embodiments, the materials of the first and second parts of the abradable track are different. In other embodiments, they are identical.

In certain embodiments, the abradable track is obtained using a manufacturing method according to any one of the preceding embodiments.

This presentation also relates to a turbine or compressor ring, not forming part of the invention, comprising an abradable track according to any one of the preceding embodiments.

This presentation also relates to a turbomachine, not forming part of the invention, comprising an abradable track or a turbine or compressor ring according to one of the preceding embodiments.

The aforementioned characteristics and advantages, as well as others, will become apparent on reading the following detailed description of exemplary embodiments of the device and of the proposed method. This detailed description refers to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are schematic and are primarily intended to illustrate the principles of the invention.

• La FIG 1 est un plan en coupe d'une turbomachine selon l'invention.
• La FIG 2 est une vue partielle en perspective d'un exemple d'anneau de stator selon l'invention.
• Les FIG 3A à 3G illustrent plusieurs étapes successives d'un exemple de procédé selon l'invention.
• Les FIG 4A à 4E illustrent plusieurs étapes successives d'un exemple de procédé selon l'invention.
• Les FIG 5A à 5E illustrent plusieurs étapes successives d'un exemple de procédé selon l'invention.

In these drawings, from one figure (FIG) to another, identical elements (or parts of elements) are identified by the same reference signs. In addition, elements (or parts of elements) belonging to different embodiments but having a similar function are marked in the figures by numerical references incremented by 100, 200, etc.

• The FIG 1 is a sectional plan of a turbine engine according to the invention.
• The FIG 2 is a partial perspective view of an example of a stator ring according to the invention.
• The FIG 3A to 3G illustrate several successive steps of an example of a process according to the invention.
• The FIGS 4A to 4E illustrate several successive steps of an example of a process according to the invention.
• The FIGS 5A to 5E illustrate several successive steps of an example of a process according to the invention.

DETAILED DESCRIPTION OF EXAMPLE(S) OF IMPLEMENTATION

In order to make the invention more concrete, examples of abradable processes and tracks are described in detail below, with reference to the appended drawings. It is recalled that the invention is not limited to these examples.

The FIG 1 shows, in section along a vertical plane passing through its main axis A, a turbofan engine 1 according to the invention. It comprises, from upstream to downstream according to the circulation of the air flow, a fan 2, a low pressure compressor 3, a high pressure compressor 4, a combustion chamber 5, a high pressure turbine 6, and a low pressure turbine 7.

The high pressure turbine 6 comprises a plurality of blades 6a rotating with the rotor and rectifiers 6b mounted on the stator. The stator of the turbine 6 comprises a plurality of stator rings 10 arranged opposite the moving blades 6a of the turbine 6. As can be seen on the FIG 2 , each stator ring 10 is divided into several sectors 11 each provided with an abradable track 20 on which the moving blades 6a rub in the event of radial excursion of the rotor.

An exemplary embodiment of such an abradable track 20 will be described with reference to the FIG 3A to 3G . In FIG 3A , a blank 30 is first provided. In this case, it is a ring sector obtained by a conventional method. Its 30s surface is regular, rectilinear in the axial section plane of the FIG 3A , and in an arc of a circle in a radial cutting plane.

As depicted in the FIG 3B , a groove 31 is then machined longitudinally, that is to say circumferentially, on the surface of the blank 30 so as to form a channel: a substrate 32 is thus obtained having two shoulders 33 framing the groove 31 upstream and downstream respectively. In the present description, this groove 31 has a depth of 5 mm. However, the production of such a groove is optional: other embodiments of the method can in fact be applied to a regular substrate having no difference in level.

The two shoulders together form a first portion 33 of substrate; the portion of the substrate 32 located at the bottom of the groove 31 forms a second portion 34 of the substrate.

As depicted in the FIG 3C , the substrate 32 thus formed is then placed in the cavity 42 of a first shaped mold 40. This first shaped mold 40 comprises a main part 41, comprising the cavity 42 whose axial dimensions correspond to that of the substrate 32, and a cover part 43 (visible on the 3D FIG ).

A first precursor material 35a, in this case a metal powder, is then deposited on the shoulders 33, that is to say the first portion of the substrate 32, while leaving the groove 31, and therefore the second portion 34 of the substrate, free from powder. On this occasion, a removable masking block can be placed in the groove 31 in order to prevent the powder of the first precursor material 35a from being deposited on the second portion 34.

The powder 35a then forms a continuous layer of constant thickness above the shoulders 33 of the substrate 32. In the present example, the powder is an alumina powder with a particle size centered around 5 μm; this layer has a thickness of 10 mm_ and an initial porosity rate of about 30%.

As depicted in the 3D FIG , the mold 40 is then closed by attaching its cover part 43 to its main part 41. This cover part 43 comprises a central protective block 44 and two support surfaces 45 extending on either side of the block protection 44.

These bearing surfaces 45, rectilinear in the axial plane of the 3D FIG and in an arc of a circle in a radial plane, then apply against the upper surface of each layer of powder of the first precursor material 35a. The protection block 44 is inserted for its part between the layers of powder 35a and penetrates into the groove 31 so as to block it: the layers of powder of the first precursor material 35a are thus enclosed in the space defined by the first portion 33 of the substrate, the walls of the cavity 42 of the main part 41 of the mold 40, the bearing surfaces 45 of the cover 43 of the mold 40 and the side walls 44a of the protection block 44 of the cover 41 of the mold 40.

A stress is then exerted on the cover 43 of the mold 40 to press on the powder layers 35a and compress the latter between the substrate 32 and the bearing surfaces 45 of the cover 43 of the mold 40. The powder layer 35a is thus compressed until his thickness is reduced to 2 mm. In this example, the front surface 44b of the protective block 44 of the cover 43 of the mold 40 then bears against the second portion 34 of the substrate.

During this compression step, the powder particles of the first precursor material 35a are packed against each other and therefore fill certain voids initially present between the particles, the air thus expelled being evacuated from the mold 40. The rate of The porosity of the powder therefore decreases during this compression step and the density of the powder increases.

Once such a compressed state has been obtained, the layer of powder 35a thus compressed is sintered using a conventional method so as to obtain a first part 36a of coating 36 surmounting the first portion 33 of the substrate 32 and having a thickness of 2 mm and a porosity rate of 6%.

The substrate 32 is then transferred into a second shaped mold 50 comprising a main part 51, comprising a cavity 52 whose axial dimensions correspond to that of the substrate 32, and a cover part 53 (visible on the FIG 3F ) comprising two fixed parts 54, that is to say immobile, and a mobile part 55.

As shown in the FIG 3E , a second precursor material 35b, in this case a metallic powder, is then deposited in the groove 31, that is to say on the second portion 34 of the substrate 32, while leaving the first coating part 36a free of powder. On this occasion, removable masking blocks can be placed on these parts 36a of the coating in order to prevent the powder of the second precursor material 35b from being deposited there.

The powder 35b then forms a continuous layer of constant thickness above the second portion 34 of the substrate 32. In the present example, the powder is an alumina powder with a particle size centered around 100 μm; this layer has a thickness of 12 mm and an initial porosity rate of about 70%.

On this occasion, it is noted that it is possible to obtain a higher initial porosity rate by adding to this powder a pore-forming agent which will be eliminated later during the process, during a pyrolysis step for example.

As depicted in the FIG 3F , the mold 50 is then closed by attaching its cover part 53 to its main part 51. The fixed parts 54 of the cover are provided to cover and bear against the first part 36a of the abradable coating obtained previously. The movable part 55 of the cover has for its part a frontal support surface 55a, rectilinear in the axial plane of the FIG 3F and in an arc of a circle in a radial plane, provided opposite the second portion 34 of the substrate 32 such that it then bears against the upper surface of the layer of powder of the second precursor material 35b. This layer of powder of the second precursor material 35b is enclosed in the space defined by the groove 31 of the substrate, the sides of the first coating part 36a, the side surfaces of the fixed parts 54 of the cover 53 of the mold 50 and the surface of support 55a of the movable part 55 of the cover 53 of the mold 50.

A stress is then exerted on the mobile part 55 of the lid 53 of the mold 50 to press on the powder layer 35b and compress the latter between the substrate 32 and the bearing surface 55a of the lid 53 of the mold 50. The powder layer 35b is thus compressed until its thickness is reduced to 7 mm. In this example, the surface level of the layer of powder 35b is then flush with the surface level of the first coating part 36a.

During this compression step, the particles of powder of the second precursor material 35b are packed against each other and therefore fill certain voids present initially between the particles, the air thus expelled being evacuated from the mold 50. The rate of The porosity of the powder therefore decreases during this compression step and the density of the powder increases, but nevertheless to a lesser extent than in the case of the first precursor material 35a.

Once such a compressed state has been obtained, the powder layer 35b thus compressed is sintered using a conventional method. At the end of this sintering step, the abradable track 20 of the FIG 3G in which the substrate 32 is covered with a coating 36 comprising a first part 36a surmounting the shoulders 33, having a thickness of 2 mm and a porosity rate of 6%, and a second part 36b surmounting the second substrate portion 34 having a thickness of 7 mm and a porosity rate of 40.6%.

Naturally, the depth of the groove 31 (which may optionally be zero), the materials 35a, 35b used, the initial thickness of the layers of powder 35a, 35b, and the amplitude of the compressions carried out can be freely adjusted to achieve the densities and desired coating thicknesses.

In a second example, shown in FIGS 4A to 4E , the method comprises additional steps, taking place after the production of the first coating part 136a and before the production of the second coating part 136b, aimed at forming a heel layer 137 of high density, having for example a porosity rate of the order of 6%, on the second portion 134 of the substrate and under the second coating part 136b.

The method begins in the same way as the previous embodiment with the production of a first high-density covering part 136a. These steps will therefore not be described again.

At the end of these steps, as shown in FIG 4A , the substrate 132 is transferred into a mold 150 similar to the second mold 50 of the first embodiment.

A third precursor material 135c is then deposited in the groove 131, that is to say on the second portion 34 of the substrate 32, so as to form a continuous layer of constant thickness above the second portion 34 of the substrate 32. In the present example, the third precursor material 135c is identical to the first precursor material used to produce the first coating part 136a; in addition, this layer has a thickness of 10 mm and an initial porosity rate of approximately 30%.

As depicted in the FIG 4B , the mold 150 is then closed and a stress is then exerted on the mobile part 155 of the lid 153 of the mold 50 to compress the layer of powder 135c between the substrate 32 and the bearing surface of the lid 153 of the mold 150 until its thickness is reduced to 2 mm. Once such a compressed state has been obtained, the powder layer 135c thus compressed is sintered using a conventional method.

At the end of this sintering step, a heel layer 137 is then obtained covering the second portion 134 of the substrate 132, having a thickness of 2 mm and a porosity rate of 6%.

As depicted in FIG 4C and 4D , the rest of the process is then analogous to the first embodiment except that the second precursor material 135b is deposited on the heel layer 137.

At the end of the process, the abradable track 120 of the FIG 4E in which the second part of the lower density coating 136b covers the heel layer 137, the latter protecting the substrate 132 in the event of radial displacement of the body circulating facing the upper coating at the maximum displacement envisaged, in the event of significant unbalance of the moving body by example.

In a third example, compatible with the first and second examples and illustrated in FIGS 5A to 5E , the method comprises additional steps, taking place just after the production of the second part of coating 236b, aimed at forming a surface layer 238 of high density, having for example a porosity rate of 15%, on the second part of covering 236b and/or the first covering part 236a.

The method begins in the same way as the first embodiment with the production of a first high density coating part 236a and a second low density coating part 236b. These steps will therefore not be described again.

It should however be noted on the FIGS 5A and 5B that the thicknesses of the layer of second precursor material 235b in its initial state and its compressed state are possibly adapted, that is to say reduced, so as to leave sufficient space on the surface of the second coating part 236b to receive the surface layer 238 when it is desired that the latter is flush with the first coating part 236a.

At the end of these steps, as shown in FIG 5C , a fourth precursor material 235d, is deposited on the second coating part 236b thus produced, so as to form a continuous layer of constant thickness. In the present example, the fourth precursor material 235d is identical to the second precursor material used to produce the second coating part 236b; besides, this layer has a thickness of 0.6 mm and an initial porosity rate of about 70%.

As depicted in the FIG 5D , the mold 250 is then closed and a stress is then exerted on the movable part 255 of the lid 253 of the mold 250 to compress the layer of powder 235d between the second coating part 236b and the bearing surface of the lid 153 of the mold 150 until its thickness is reduced to 0.10 mm. Once such a compressed state has been obtained, the powder layer 235d thus compressed is sintered using a conventional method.

At the end of the process, the abradable track 220 of the FIG 5E wherein the second part of the lower density coating 236b is covered by a surface layer 238, flush with the first part of the coating 236b, having a thickness of 0.10 mm and a porosity rate of 11.9%. This surface layer 238 has a lower surface roughness than the second part of the coating 236b and therefore offers a gain in aerodynamic friction.

The embodiments or exemplary embodiments described in this presentation are given for illustrative and non-limiting purposes, a person skilled in the art can easily, in view of this presentation, modify these embodiments or exemplary embodiments, or consider others, while remaining within the scope of the invention.

Moreover, the different characteristics of these embodiments or examples of embodiment can be used alone or be combined with one another. When they are combined, these characteristics can be as described above or differently, the invention not being limited to the specific combinations described in the present description.

Claims (8)

1. A fabrication method for fabricating an abradable coating of varying density, the method comprising the following steps:

   providing a substrate (32) having a first portion (33) and a second portion (34);

   depositing a first precursor material (35a) on the first portion (33) of the substrate (32);

   compressing the first precursor material (35a) between the substrate (32) and a first bearing surface (45) ;

   sintering the first precursor material (35a) as compressed in this way in order to obtain a first abradable coating portion (36a) on the first portion (33) of the substrate (32), and possessing a first density;

   depositing a second precursor material (35b) on the second portion (34) of the substrate (32);

   compressing the second precursor material (35b) between the substrate (32) and a second bearing surface (55a); and

   sintering the second precursor material (35b) as compressed in this way in order to obtain a second abradable coating portion (36b) on the second portion (33) of the substrate (32), and possessing a second density distinct from the first.
2. A method according to claim 1, wherein the steps of compressing and sintering the first precursor material (35a) are performed within a first mold (40); and
   wherein the first mold includes the first bearing surface (45) together with at least one protection wall (44a) provided so as to lie beside the first precursor material (35a) at the interface between the first and second portions (33, 34) of the substrate during the steps of compressing and sintering the first precursor material (35a).
3. A method according to claim 1 or claim 2, wherein the steps of compressing and sintering the second precursor material (35b) are performed within a second mold (50); and
   wherein the second mold (50) includes a movable portion (55) extending facing the second portion (34) of the substrate (32) and including the second bearing surface (55a), and a stationary portion (54) extending facing the first portion of the substrate.
4. A method according to any one of claims 1 to 3, wherein the first portion of the abradable coating (36a) possesses final porosity of less than 15%, preferably less than 5%.
5. A method according to any one of claims 1 to 4, wherein the second portion of the abradable coating (36b) possesses final porosity greater than 20%, preferably greater than 30%.
6. A method according to any one of claims 1 to 5, further comprising, prior to the step of depositing the precursor material on one of the portions of the substrate, preferably on the second portion (134) of the substrate (132), a step of forming a backing layer (137) by sintering on the portion under consideration of the substrate, the backing layer having final porosity of less than 15%, and preferably less than 5%.
7. A method according to any one of claims 1 to 6, further comprising, after the step of sintering one of the precursor materials, a step of forming a surface layer (238) by sintering on at least one of the portions of the abradable coating, preferably on its second portion (236b), the surface layer having final porosity of less than 15%, and preferably less than 5%.
8. A method according to any one of claims 1 to 7, wherein the substrate is a ring sector (11).

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