FR3071867A1 - AUBE CERAMIC MATRIX COMPOSITE AND PROCESS FOR PRODUCING SUCH A BLADE - Google Patents

Abstract

The invention relates to a blade (14), in particular for a turbomachine, comprising a body (21) made of ceramic matrix composite material, comprising a hollow internal zone (25) extending along the axis (Y) of the vane (14), the inner surface of the body (21) having a coating (26) capable of forming a thermal barrier, and a method for producing such a dawn

Description

COMPOSITE BLADE WITH CERAMIC MATRIX AND METHOD FOR MANUFACTURING SUCH A BLADE

The present invention relates to a blade, in particular for a turbomachine, as well as to a method for manufacturing such a blade.

The blade according to the invention is in particular intended to equip a turbine stator, in particular a low pressure turbine of a turbomachine.

A turbine conventionally comprises several successive stages, each stage comprising a moving blade wheel belonging to a rotor and a distributor comprising fixed blades belonging to a stator. The fixed vanes are held by an inner ring and an outer ring so as to form the distributor.

The fixed blades are generally hollow and metallic. Each blade has holes opening into the hollow inner zone and onto the outer surface of the blade, that is to say at the level of the lower surface, of the upper surface, of the leading edge and / or the trailing edge.

Fresh air from the low pressure compressor of the turbomachine is brought into the hollow area of each blade before being discharged into the turbine stream, through the bores.

This air makes it possible in particular to cool the stationary blades.

In fact, in operation, the fixed blades are subjected to temperatures of the order of 1200 ° C. for example, that is to say to temperatures higher than the melting temperature of the material used for their production.

The flow required to cool the stationary blades is relatively high, which penalizes the performance of the turbomachine.

The object of the invention is in particular to provide a simple, effective and economical solution to this problem.

To this end, it offers a blade, in particular for a turbomachine, comprising a profiled body of composite material with ceramic matrix, comprising a hollow internal zone extending along the axis of the blade, the internal surface of the body comprising a coating. able to form a thermal barrier.

The use of a ceramic matrix composite (or CMC) material can withstand high operating temperatures.

However, such a material has a relatively low elongation at break (of the order of 0.05%). It is therefore advisable to avoid the phenomena of differential expansion, due in particular to high temperature gradients.

The coating forming a thermal barrier makes it possible to limit such gradients within the ceramic matrix composite material and therefore to avoid any deterioration or breakage of the blade.

The coating may comprise at least a first layer of a first material applied to the internal surface of the body, capable of forming an undercoat, and a second layer of a second material applied to the first layer.

The use of an undercoat facilitates the adhesion of the second layer on the body.

The first layer may be a silicon-based sublayer, for example made of pure silicon.

The first layer can be deposited by thermal spraying (plasma, by spraying by Supersonic Flame or HVOF ("High Velocity Oxy-Fuel") or by arc), by liquid way (liquid siliciding) or by electrodeposition.

The first layer may have a thickness of between 20 and 300 μm, preferably of the order of 50 μm.

The presence of the sub-layer makes it possible to avoid any delamination phenomenon at operating temperatures within the primary vein, which can reach 1200 ° C. for example at the level of the low pressure turbine.

The second layer can be made from yttrium disilicate or ytterbium silicate.

The second layer can have a thickness of between 500 and 800 μm.

The aforementioned materials of the first layer and of the second layer make it possible to obtain satisfactory results in terms of thermal protection. They also make it possible to avoid oxidation of the body, such oxidation causing premature degradation of said body.

The body can be made from silicon carbide fibers incorporated in a matrix based on silicon carbide.

The invention also relates to a turbine for a turbomachine comprising at least one blade of the aforementioned type.

The invention also relates to a process for manufacturing a blade of the aforementioned type, characterized in that it comprises the steps consisting in:

(a) producing a core, for example a metallic or graphite core, preferably of porous graphite, (b) covering the core with at least one coating layer intended to form a coating of the thermal barrier type, (c) covering the core and the coating of a ceramic matrix composite material forming the body, and (d) removing the core.

The core covering can be implemented easily since it consists in covering an external surface of the core. By comparison, it is less easy to cover the inner surface of a hollow part.

Step (b) can include at least the sub-steps:

(b1) cover the core with a layer of a material based on yttrium disilicate or ytterbium silicate intended to form the second layer, (b2) cover the above-mentioned layer with another layer of a material to silicon base, for example in pure silicon, intended to form the first layer or sublayer.

During sub-step (b1), the layer can be deposited by plasma spraying, for example by plasma spraying at atmospheric pressure.

The vacuum plasma projection process is also known by the acronym APS for Atmospheric Plasma Spraying in English.

During sub-step (b2), the layer can be deposited by plasma spraying, for example by vacuum plasma spraying.

The vacuum plasma spraying process is also known by the acronym VPS for Vaccum Plasma Spraying in English.

In step (d), the nucleus can be removed by chemical attack, by fusion or by oxidation in air.

Step (c) can include at least the sub-steps:

(c1) draping the core and the coating with a layer of reinforcing fibers, for example fibers based on silicon carbide, (c2) impregnating the fiber layer with a ceramic matrix, for example a matrix with silicon carbide base.

Step (c2) can be carried out in a mold, for example at a temperature between 700 and 1000 ° C and for example for a period between 2 hours and 50 hours. The matrix may have a gaseous and / or liquid form.

Step (c1) can be carried out by applying a ply on each side of the assembly formed by the core and the coating, the plies meeting at a leading edge and a trailing edge .

During step (c), part of the composite material is in excess, this excess part then being removed, for example by machining.

The core can be removed by fusion, for example at a temperature between 1000 ° C and 1400 ° C, for example for a period between a few minutes and several hours. Using a drain during this step can speed up material removal.

As a variant, the coating may be deposited by electrophoresis or by dip coating on the internal surface of the body of the blade.

In this case, it is not necessary to provide for the formation of a core, the body being directly immersed in a bath for example.

The invention will be better understood and other details, characteristics and advantages of the invention will appear on reading the following description given by way of nonlimiting example with reference to the appended drawings in which:

- Figure 1 a simplified sectional view of a turbomachine,

FIG. 2 is a sectional view of part of the low pressure turbine of the turbomachine according to the invention,

FIG. 3 is a perspective view of the core,

FIG. 4 is a perspective view of the core covered with the second layer,

FIG. 5 is a perspective view of the core covered with the second layer and with the first layer,

FIG. 6 is a perspective view of the core covered with the second layer, the first layer and a ceramic matrix composite material,

FIG. 7 is a perspective view of the core, of said second and first layers, and of the body,

FIG. 8 is a detailed view of FIG. 6,

- Figure 9 is a perspective view of the dawn.

FIG. 1 represents a turbomachine 1 with double flow and with double body. The axis of the turbomachine is referenced X. In what follows, the terms axial and radial are defined relative to the axis X.

The turbomachine 1 comprises, from upstream to downstream in the direction of flow of the gases within the turbomachine 1, 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 air from blower 2 is divided into a primary flow A flowing in a primary vein 8, and a secondary flow B flowing in a secondary vein 9.

The low pressure compressor 3, the high pressure compressor 4, the combustion chamber 5, the high pressure turbine 6 and the low pressure turbine 7 are formed in the primary stream 8.

The high pressure turbine 6 and the high pressure compressor 4 are coupled in rotation via a first shaft 10 so as to form a high pressure body.

The low pressure turbine 7, the low pressure compressor 3 and the blower 2 are coupled in rotation by means of a second shaft (not shown) so as to form a low pressure body.

FIG. 2 represents a part of the low pressure turbine 7 of the turbomachine 1. The low pressure turbine 7 comprises several successive stages 11, each stage 11 comprising a movable vane wheel belonging to a rotor 12 and a distributor 13 comprising fixed vanes 14 belonging to a stator. The fixed vanes 14 are held by an inner ring 15 and an outer ring 16 so as to form the distributor 13.

As indicated above, the rotor 12 of the low pressure turbine 7 is coupled in rotation to the low pressure compressor 3. The stator is fixed to a casing 17 (FIG. 1) of the turbomachine 1.

In the following description, we will focus more specifically on the process for manufacturing the stationary vanes 14 of the distributor 13.

Figures 3 to 9 illustrate different successive stages of an embodiment of such a method.

First, a metallic core 18 is produced, for example made of silicon, or of graphite, for example of porous graphite. The core 18 has a profiled shape and extends along a Y axis.

The core 18 is then covered with a layer 19 of a material based on yttrium disilicate or ytterbium silicate.

This layer 19 is for example deposited by plasma spraying, for example by plasma spraying at atmospheric pressure.

The atmospheric pressure plasma projection process is also known by the acronym APS for Atmospheric Plasma Spraying in English.

The deposition by atmospheric thermal spraying is generally preferred to the deposition of a cement, because the cement tends to crack at high temperatures. Indeed, deposits made by atmospheric thermal spraying are more cohesive and tenacious. Thermal spraying is a group of surface coating processes in which fine particles of the material to be deposited are deposited in a molten or semi-molten state on a substrate.

Thermal plasma spraying consists in introducing into a very energetic jet (a plasma jet) the material to be deposited in pulverulent form (that is to say in the form of particles, here a few tens of microns in diameter way). The particles are then melted by the jet and simultaneously accelerated towards the core 18 to be coated. Thus these particles are crushed on the surface of the core 18 in the form of drops, which solidify very quickly after their impact by conduction of their heat by forming lamellae on the surface of the core 18. The stacking of these lamellae perpendicular to the surface of the nucleus gradually leads to the formation of the deposit. The projection is carried out at atmospheric pressure in air.

For example, it is possible to use yttrium disilicate powder with a particle size of between 5 and 25 microns, which is projected by means of a plasma torch with a plasma mixture (gas intended to facilitate plasma deposition) argon and hydrogen at 15 to 20% by volume of hydrogen and a power of 40 to 45 kW, on the surface to be coated previously preheated to 750 ° C. The yttrium disilicate underlayment can be between 500 and 800 microns thick.

The growth speed of layer 19 is of the order of 100 microns per minute, for example.

FIG. 3 represents the core 18 coated with the layer 19.

The core 18 is then covered with another layer 20, made of a material based on silicon, for example in pure silicon.

This layer 20 is for example deposited by plasma spraying, for example by vacuum plasma spraying. The vacuum plasma spraying process is also known by the acronym VPS for Vaccum Plasma Spraying in English.

The vacuum plasma spraying technique is a blown arc plasma torch spraying technique, which is practiced in an enclosure filled with argon at low pressure, that is to say at pressure lower than pressure atmospheric. This technique consists, as before, in introducing into a jet of energetic plasma the material to be deposited in powder form. The coating growth rate is of the order of 100 microns per minute.

For example, silicon powder with a particle size between 5 and 25 microns can be used, which is projected into an enclosure where a pressure of 120 millibars prevails, by means of a plasma torch with a plasma-generating mixture (gas intended to facilitate plasma deposition) argon and hydrogen at 15 to 20% by volume of hydrogen and a power of 40 to 45 kW, on the surface to be coated previously preheated to 750 C. The silicon bonding undercoat can be between 50 and 70 microns thick.

FIG. 5 represents the core 18 coated with layers 19 and 20.

The core 18 thus coated is then covered with a ceramic matrix composite material (CMC) intended to form the body 21 of a fixed vane 14.

For this, the core 18 covered with the two aforementioned layers 19, 20 is draped with fibers in the form of a mat or a sheet, the assembly then being placed in a mold in which a ceramic matrix is added in gaseous and / or liquid state. The assembly is then heated in the mold to a temperature between 700 ° C and 1000 ° C, for example for a period between 2 hours and 50 hours, so as to consolidate the assembly and obtain a preform , as shown in Figure 5.

The fibers are for example made from silicon carbide (SiC), the matrix being based on silicon carbide.

During this consolidation, the layers 19, 20 previously deposited on the core adhere to the ceramic matrix composite material.

As illustrated in FIG. 6, the preform obtained comprises excess parts 22, these parts 22 then being machined at an edge intended to form the leading edge 23 of the fixed blade 14, and at the level an edge intended to form the trailing edge 24 of the fixed vane 14, as illustrated in FIG. 6.

The core 18 is then removed, as illustrated in FIG. 8. This removal can be obtained by chemical attack, by fusion or by oxidation in air.

In the case of fusion, the assembly can be heated to a temperature between 1000 ° C and 1400 ° C, for example for a period of between a few minutes and several hours, so as to remove the core 18.

In the case of a graphite core, the temperature can be lower and between 400 and 800 ° C, for example, the heating time can be between 1 hour and 100 hours for example.

After removing the core 18, a blade 14 5 is obtained comprising a body 21 of composite material with a ceramic matrix, comprising a hollow internal zone 25 extending along the axis Y of the blade 14, the surface of which internal is covered with layer 20, forming a sublayer, and with layer 19, intended to be in contact with a gas flow.

In use, cold air from the low pressure compressor passes through the hollow zone 25, for example radially from the outside to the inside, to cool the internal hub of the low pressure turbine 7 for example. This cooling air has for example a temperature between 400 ° C and 600 ° C, for example of the order of 500 ° C.

The body 21 being made of CMC, it is able to withstand high temperatures, so that it is not necessary to provide holes in the body 21 in order to cool it.

The layers 19, 20 form a coating 26 defining a thermal barrier. This thermal barrier prevents significant heating of the cooling air when it passes through the hollow internal zone 25 of the blade 14. Furthermore, this thermal barrier limits the thermal gradients within the body 21 of the blade in CMC , so as to limit the phenomena of differential expansions and avoid any premature degradation of the blade 14.

The coating 26 also forms a so-called environmental barrier preventing corrosion and oxidation, and therefore premature degradation, of the body 21 in CMC.

Other manufacturing processes can be used to make the blade 14.

Thus, as a variant, the layers 19, 20 can be deposited by electrophoresis or by dip coating (dip coating) on the internal surface of the body 21 of the blade 14.

In this case, it is not necessary to provide for the formation of a core 18, the body 21 being directly immersed in a bath for example.

Claims (13)

1. Dawn (14), in particular for a turbomachine (1), comprising a body (21) profiled in composite material with ceramic matrix, comprising a hollow internal zone (25) extending along the axis (Y) of the blade (14), the internal surface of the body (21) comprising a coating (26) capable of forming a thermal barrier. 2. Dawn (14) according to claim 1, in which the coating (26) comprises at least a first layer (20) of a first material applied to the internal surface of the body (21), capable of forming an undercoat , and a second layer (19) of a second material applied to the first layer (20). 3. Dawn (14) according to claim 2, in which the first layer (20) is a silicon-based sublayer, for example made of pure silicon. 4. Dawn (14) according to claim 2, wherein the first layer (20) has a thickness between 20 and 300 pm, preferably of the order of 50 pm. 5. Dawn (14) according to one of claims 2 to 4, in which the second layer (19) is made based on yttrium disilicate or ytterbium silicate. 6. Dawn (20) according to one of claims 2 to 5, wherein the second layer (19) has a thickness between 500 and 800 pm. 7. Dawn (14) according to one of claims 1 to 6, in which the body (21) is made from silicon carbide fibers incorporated in a matrix based on silicon carbide. 8. Turbine (6, 7) for a turbomachine (1) comprising at least one blade (14) according to one of claims 1 to 7. 9. Method for manufacturing a blade (14) according to one of claims 1 to 7, characterized in that it comprises the steps consisting in: (a) producing a core (18), for example a metallic or graphite core, preferably of porous graphite, (b) covering the core (18) with at least one coating layer (26) intended to form a coating (26) barrier type 5 thermal, (c) cover the core (20) and the coating (26) with a ceramic matrix composite material forming the body (21), and (d) remove the core (18). 10. The method of claim 9, wherein the step 10 (b) includes at least the sub-steps: (b1) cover the core (18) with a layer of a material based on yttrium disilicate or ytterbium silicate, intended to form the second layer (19), (b2) cover the layer (19) mentioned above from another layer of a silicon-based material, for example pure silicon, intended to form the first layer (20) or sublayer. 11. The method of claim 10, wherein during the sub-step (b1), the layer (19) is deposited by plasma spraying, for example by plasma spraying at atmospheric pressure. 20 12. The method of claim 10 or 11, wherein during the sub-step (b2), the layer (20) is deposited by plasma spraying, for example by vacuum plasma spraying. 13. Method according to one of claims 9 to 12, wherein, in step (d), the core (18) is removed by chemical attack, by fusion 25 or by oxidation in air.