Seal for turbine ring made of ceramic matrix composite material

Abstract

Component in a turbine comprising: - at least one turbine ring made of ceramic composite material with a silicon carbide, SiC, matrix and fibres, said ring comprising a plurality of sector segments (10) arranged circumferentially end to end, each ring sector segment (10) comprising at least one circumferential edge (26, 28) having at least one slot (30a, 30b, 30c) developing circumferentially; - at least one sealing member, a first portion of which is inserted into one of said slots (30a, 30b, 30c) of the edge of a first ring sector segment and a second portion of which is inserted into one of said slots (30a, 30b, 30c) of the edge of a second ring sector segment circumferentially adjacent to said first ring sector segment, said component being characterized in that said sealing member is made of ceramic matrix composite material.

Description

TECHNICAL FIELD

[0001] The present document relates to inter-sector sealing in turbomachines. BACKGROUND

[0002] To reduce fuel consumption and to reduce the carbon impact, one first solution proposed is to reduce the weight of the aircraft. For this purpose, aircraft manufacturers are moving towards the use of composite materials having a lower density than traditional metallic materials.

[0003] A second solution to reduce fuel consumption is to increase the efficiency of turbojet engines, which means increasing the temperature of the combustion gases. However, the metallic materials currently used in turbomachines, and more particularly nickel-based or cobalt-based alloys, have reached their temperature limits, so it is not possible to increase the combustion temperature any further. Indeed, the hot structural parts of turbomachines must have good mechanical properties in difficult environments (extremely high temperatures, high pressures, rich in water vapor and oxidizing atmosphere).

[0004] To provide a solution to the weight and temperature problems, CMC materials can be used. Ceramic matrix composites (CMC) have a density of between 2 and 3, which is lighter than the higher density nickel-based or cobalt-based alloys.

[0005] The highest level CMC used to date is a CMC formed from a matrix of silicon carbide SiC and fibers. Despite being made of fragile materials (matrix, fibers, interface), CMCs are robust materials due to their structure and architecture. Indeed, the interface deposited on the fibers can divert cracks, while the matrix protects the fibers and the interface.

[0006] In turbomachines, it is known to use a matrix and fibers in silicon carbide SiC (referred to later as SiC-based CMC) to manufacture a turbine distributor or a ring surrounding an annular row of movable blades. The distributor comprises an inner annular platform and an outer annular platform connected to each other by radial blades. These platforms form a ring which is only similar to a ring surrounding an annular row of movable blades. These rings are fastened to a metallic casing in a manner well known to those skilled in the art.

[0007] These ring sectors are arranged circumferentially end to end and sealing at their circumferential joints is achieved by sealing means, such as tabs, which can limit the leakage of air between the sectors. Half of these metallic tabs are inserted into the circumferential edge of a first ring sector and the other half is inserted into the circumferential edge of a second ring sector which is circumferentially adjacent to the first ring sector.

[0008] Conventionally, the tabs can be made of nickel or cobalt alloys.

[0009] Many works study the reactivity between SiC and many metals including nickel Ni and cobalt Co. Indeed, nickel Ni and cobalt Co react with silicon to form brittle silicides, which is accompanied by the precipitation of carbon in the form of graphite sheets, thus weakening the system (SiC-based CMC / metal). In the presence of SiC, nickel or cobalt can produce nickel or cobalt silicides, depending on the silicon concentration and the temperature. Since the system must operate at high temperature, this reactivity problem is more important. Indeed, high temperatures promote the growth of the reaction layer, leading to an uncontrolled evolution of chemical species, which is detrimental to the mechanical strength of the system. It is also observed that many cracks can appear at the reaction interface, which tends to weaken the system. Furthermore, under mechanical load, these cracks in the matrix form a special network for the propagation of oxidizing species (O2, H2O) within the material. These oxidizing species diffuse throughout the microcracks and deteriorate them by oxidation / corrosion. This affects the long-term durability of the CMC: these oxidation reactions change the structural properties and significantly reduce their mechanical performance.

[0010] In other words, the metal alloy of the tab reacts with the silicon carbide SiC-based CMC material and produces silicides. These silicides change the chemical properties at the interface of the SiC-based CMC material, leading to the appearance of microcracks through which oxidation molecules such as O2 and H2O can pass and oxidize, i.e. corrode, the SiC-based CMC material. The metal alloy is also known to oxidize. SUMMARY

[0011] To this end, the present document relates to an assembly in a turbine, the assembly comprising:

[0012] - at least one turbine ring made of a ceramic composite material having a matrix and silicon carbide SiC fibers, the ring comprising a plurality of sector segments arranged end to end in a circumferential direction, the ring sector segments comprising at least one circumferential edge having at least one slot developing in a circumferential direction,

[0013] - at least one sealing part having a first portion inserted into one slot of an edge of a first ring sector segment and a second portion inserted into one slot of an edge of a second ring sector segment circumferentially adjacent to the first ring sector segment,

[0014] The assembly is characterized in that the sealing part is made of a composite material having an oxide ceramic matrix.

[0015] Thus, to avoid the formation of these silicides, the sealing part traditionally made of Ni or Co metal of the prior art is replaced by a CMC.

[0016] The sealing part can be made of a ceramic matrix composite material having an oxide matrix and fibers.

[0017] The CMC material with an oxide matrix and fibers, also known as oxide CMC, is stable at high temperatures, which can avoid oxidation / corrosion problems. Moreover, said sealing part made of oxide CMC has the property of being inert with respect to the chemical interaction with silicon carbide SiC at high temperatures, is gas-tight and is mechanically compatible with SiC-based CMC. Finally, the replacement of the metal alloy assembly with a part made of oxide CMC exhibits a net gain in weight thanks to the low density exhibited by this material and therefore a reduction in polluting emissions.

[0018] Said composite material of the sealing part can comprise alumina fibers and a silico-aluminate matrix.

[0019] The sealing part can have a thickness less than 1 mm.

[0020] The oxide CMC is a material that can be made in the form of a plate with a thickness of a few tenths of a millimeter. This smaller thickness makes it more likely to guarantee the sealing of the two ring sectors.

[0021] The sealing part can be a sealing part with a substantially planar shape. It can then be described as a tab.

[0022] This planarity favors the sealing and limits the air leakage by its shape.

[0023] The ring can externally surround an annular row of movable vanes and be carried by an outer casing.

[0024] Said assembly can comprise an annular row of stationary vanes, comprising an inner and an outer annular platform, at least one of said inner and outer annular platforms being formed by said ring.

[0025] The sealing part can be arranged between the two circumferential edges of two adjacent turbine ring sectors, said sealing part being characterized in that it is made of a ceramic matrix composite material.

[0026] The present description and other details, features and advantages of the present text will be better understood when reading the following description, provided as a non-limiting example, while reading the attached drawings. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is a perspective view of a turbine ring.

[0028] Figure 2 is a perspective view of a turbine distributor.

[0029] Figure 3 is a perspective view of a sealing part according to the present invention. DETAILED DESCRIPTION

[0030] Traditionally, in a turbomachine, the moving wheels of the turbine are externally surrounded by a support ring made of a wear-resistant material. The ring is fastened to the outer casing and is formed of a plurality of sector segments arranged end to end circumferentially.

[0031] Figure 1 This ring sector 10 of a turbine of a turbomachine is shown, the ring being made of CMC, CMC having a matrix of silicon carbide SiC and fibers. The ring sector 10 comprises a cylindrical annular wall portion 12, cylindrical in the present case, comprising a radially outer surface 14 from which an upstream AM first radial annular wall 16 and a downstream AV second radial annular wall 18 extend radially outward. The upstream first radial annular wall 16 and the downstream second radial annular wall 18 have apertures 20 intended for fastening the ring sector 10 to the outer casing of the turbine by bolting. The ring sector 10 carries, on a radially inner surface 22 of the cylindrical annular wall portion 12, a layer 24 of wear-resistant material intended to cooperate with the radially outer ends of the blades of the bladed movable wheel.

[0032] Each ring sector 10 has two circumferentially opposite edges 26, 28, facing the circumferential edges of an adjacent ring sector. Each circumferential edge 26, 28 of the ring sector 10 has at least one slot, in the present case three slots 30a, 30b, 30c, which are circumferentially developed in the direction of an adjacent ring sector and face the slots of said adjacent ring sector.

[0033] In a particular embodiment, each circumferential edge 26, 28 comprises a first longitudinal slot 30a extending parallel to the axis of rotation X of the turbomachine.

[0034] The circumferential edges 26, 28 also comprise a second oblique slot 30b and a third oblique slot 30c extending according to a longitudinal component X and a radial component Z. The second slot 30b and the third slot 30c are developed radially inward on the first longitudinal slot 30a and extend radially outward at least partly across the thickness of the upstream radial annular wall 16 and the downstream radial annular wall 18. The second slot 30b and the third slot 30c are radially outwardly separated from each other. Thus, the second slot 30b extends toward the upstream edge 32 of the ring sector 10 and the third slot 30c extends toward the downstream edge 34 of the ring sector 10.

[0035] These first, second and third slots 30a, 30b, 30c are intended to receive sealing members 60, in the present case O-rings, intended to cooperate with the sealing members 70 of the adjacent ring sector 10. Figure 3In the embodiments represented, the sealing members have a substantially planar shape. Such sealing members can be described as tabs. These sealing tabs are thus inserted into the slots 30a, 30b, 30c at the circumferential ends 26, 28 of the ring sectors. The sealing tabs are partially inserted into the slots 30a, 30b, 30c of the circumferential ends 26, 28 of the ring sector 10 and partially into the slots of the circumferential ends of the adjacent ring sector. These sealing tabs guarantee the sealing between two adjacent ring sectors 10.

[0036] Figure 2 An example of a turbine distributor 36 sector is shown. Traditionally, the distributor comprises an annular column of substantially radial vanes 38 connected at their radially inner end by an inner annular platform or inner ring 40 and at their radially outer end by an outer annular platform or outer ring 42. The distributor comprises several sectors 36 assembled to each other circumferentially, each sector 36 comprising several vanes 38 and an inner ring sector 40 or inner platform sector and an outer ring sector 42 or outer platform sector.

[0037] In a similar manner as already described with reference to Figure 1 Each inner ring sector 40 and outer ring sector 42 comprises two circumferential edges 52, 53, 54, 55, each containing at least one slot 56, 58 into which a sealing member, for example a tab 60, is fitted. These tabs 60 are partially inserted into the slots 56, 57, 58, 59 of the circumferential ends of the inner annular platform sector 40 or outer annular platform sector 42 respectively and partially into the slots 56, 58 of the circumferential ends of the inner annular platform sector 40 or outer annular platform sector 42. This also serves to guarantee the sealing between two sectors. The inner annular platform sector 40 and the outer annular platform sector 42 each form a ring.

[0038] As mentioned above, the sealing tabs are generally made of a metallic material, more precisely a nickel-based or cobalt-based alloy, which reacts at high temperature with the CMC material of the ring sector 10, 40, 42. As mentioned above, the use of tabs made of a metallic material causes difficulties in terms of silicide formation and oxidation.

[0039] According to the present text, it is proposed to manufacture the tabs 60 with CMC and more precisely with CMC having a matrix and oxide fibers. Generally, the fibers are made of alumina and the matrix is made of silico-aluminate. The tabs 60 have two circumferential edges 60a, 60b which can be inserted into the slots 30a, 30b, 30c, 56, 58.

[0040] The tabs 60 have a thickness less than 1 mm and have a substantially planar shape. In fact, due to the properties of the oxide CMC, the tabs can be manufactured in the form of plates with a thickness of a few tenths of a millimeter. The total thickness is therefore small, which makes the sealing of the two ring sectors easier. In turn, the planarity can also limit the air leakage.

Claims

1. An assembly in a turbine comprising: - at least one turbine ring made of a ceramic composite material having a matrix and silicon carbide, SiC, fibres, the turbine ring comprising a plurality of ring sectors (10, 36) arranged circumferentially end to end, each ring sector (10, 40, 42) comprising at least one circumferential edge (26, 28, 52, 53, 54, 55) having at least one slot (30a, 30b, 30c, 56, 58) circumferentially developed, - at least one sealing member having a first portion inserted into one of said slots (30a, 30b, 30c, 56, 58) of an edge of a first ring sector and a second portion inserted into one of said slots (30a, 30b, 30c, 56, 58) of an edge of a second ring sector circumferentially adjacent to said first ring sector, the assembly being characterized in that the sealing member is made of a composite material having an oxide ceramic matrix and oxide ceramic fibres, the composite material of the sealing member comprising alumina fibres and a silico-aluminate matrix.

2. The assembly of claim 1, wherein, the sealing member has a thickness less than 1 mm.

3. The assembly of claim 1, wherein, the sealing member is a sealing member having a substantially planar shape.

4. The assembly of claim 1, wherein, the turbine ring externally surrounds an annular row of moving blades and is carried by an external casing.

5. The assembly of any one of claims 1 to 3, wherein, the assembly comprises an annular row of stator blades (38) comprising an inner annular platform (40) and an outer annular platform (42), at least one of the inner annular platform (40) and the outer annular platform (42) being formed by the turbine ring.

Images