PART MADE OF SILICON-BASED CERAMIC OR CMC AND METHOD FOR PRODUCING SUCH A PART

Abstract

The invention relates to a part made of silicon-based ceramic material or silicon-based ceramic matrix composite (CMC) material comprising an environmental barrier coating (EBC), said coating (12, 13) comprising a bonding layer (12) deposited on the surface of the ceramic material or ceramic matrix composite (CMC), said bonding layer (12) being topped by one or more layers together forming a multifunctional barrier structure (13), characterised in that the bonding layer (12) has at its interface with the multifunctional structure a polycrystalline silica layer (12) or sub-layer (12b).

Claims

1. A part made of silicon-based ceramic material or silicon-based ceramic matrix composite material comprising an environmental barrier coating, the environmental barrier coating comprising a bonding layer deposited on a surface of the silicon-based ceramic material or the ceramic matrix composite material, the bonding layer being topped by one or more layers together forming a multifunctional barrier structure, wherein the bonding layer has a polycrystalline silica layer or sub-layer at an interface with the multifunctional barrier structure.

2. The part of claim 1, wherein the polycrystalline silica layer or sub-layer has grain boundaries doped with Hf and/or HfO.sub.2 and/or phosphorus.

3. A method for producing the part of claim 1, the method comprising: depositing a silicon layer on the surface of the silicon-based ceramic material or silicon-based ceramic matrix composite material; performing thermal oxidation; and introducing dopants.

4. A method for producing the part of claim 1, the method comprising: depositing a first silicon layer on the surface of the silicon-based ceramic material or silicon-based ceramic matrix composite material; depositing a second silicon layer that is a doped layer; and performing thermal oxidation.

5. The method of claim 3, wherein the thermal oxidation is a dry oxidation in presence of oxygen.

6. The method of claim 3, wherein the dopants are Hf and/or HfO.sub.2 and/or phosphorus dopants.

7. The method of claim 3, wherein the introduction of dopants implements ionic implantation.

8. An aeronautic or space device comprising the part of claim 1.

9. A turbomachine comprising the part of claim 1.

10. The method of claim 4, wherein the thermal oxidation is a dry oxidation in presence of oxygen.

11. The method of claim 4, wherein the dopants are Hf and/or HfO2 and/or phosphorus dopants.

Description

PRESENTATION OF THE FIGURES

[0035] Other characteristics and advantages of the invention will appear from the following description, which is purely illustrative and non-limiting and should be read with regard to the attached drawings, in which:

[0036] FIG. 1, already discussed, illustrates the formation of defects and the degradation of a structure known in the state of the art;

[0037] FIG. 2 illustrates an example of the part conforming to the invention;

[0038] FIGS. 3a and 3b illustrate an EBC-coated stack conforming to one embodiment of the invention (FIG. 3a);

[0039] FIG. 4 illustrates a possible embodiment of the invention for producing a stack of the type of FIG. 3a;

[0040] FIGS. 5 and 6 illustrate another possible embodiment for the method of the invention.

DESCRIPTION OF ONE OR MORE EMBODIMENTS

[0041] The part 5 illustrated in FIG. 2 by way of example comprises a turbomachine high pressure turbine rotor blade 5a and a blade root 5b.

[0042] Said part 5 is of a ceramic matrix composite CMC coated with a protection barrier EBC, which is more particularly described below.

[0043] Note that the use of CMC ceramics for turbomachine high-pressure turbine rotor blades is particularly advantageous insofar as it makes it possible, as applicable, to eliminate the holes on the blades that are conventionally provided there for the circulation of cooling air. Eliminating these holes improves engine performance still further.

[0044] As can be understood, the turbomachine high pressure turbine blades are only one example of application for the proposed EBC structure: it can be more generally applied, especially in space or aeronautics, for any part subjected to operating at high temperatures (above 1100° C.): turbomachine combustion chamber, engine exhaust component, etc.

[0045] Producing a CMC Structure

[0046] The materials of the CMC structure of the part 5 are silicon-based ceramics (silicon carbide SiC, for example) or ceramic matrix composites (CMC).

[0047] Here and throughout this text, CMC material means composite materials comprising a set of ceramic fibres incorporated in a matrix that is also ceramic.

[0048] The fibres are, for example carbon (C) and silicon carbide (SiC) fibres.

[0049] They can also be aluminum oxide or alumina (Al.sub.2O.sub.3) fibres, or mixed crystals of alumina and silicon oxide or silica (SiO.sub.2) such as mullite (3Al.sub.2O.sub.3, 2SiO.sub.2).

[0050] The matrix is silicon carbide SiC or any mixture comprising silicon carbide.

[0051] The SiC—SiC composites with silicon carbide fibers in silicon carbide matrix are particularly interesting for aeronautical applications given their high thermal, mechanical and chemical stability and their high strength/weight ratio.

[0052] These compounds can use pyrocarbon (or PyC) or boron nitride (BN) as interphase material.

[0053] Different techniques can be envisaged for the production of a ceramic matrix composite material part.

[0054] Especially, according to a first technique, the CMC material parts can be produced from a fibre preform in woven fibre texture. This fibre preform is consolidated and densified by chemical vapour infiltration (CVI).

[0055] In yet another variant, the preform can be in fibrous layers based on silicon carbide, the fibres of said preform being coated by CVI with a layer of boron nitride topped with a layer of carbon or carbide, in particular of silicon carbide.

[0056] For examples of the techniques for producing a SiC/SiC CMC structure, reference advantageously may be made to U.S. Pat. No. 9,440,888 or 8,846,218, for example.

EBC Structure—First Embodiment

[0057] In the example of FIG. 3a, the CMC layer is referenced by 11 and the multifunctional structure of the EBC coating by 13.

[0058] The bonding layer (layer 12) is of polycrystalline silica with doped grain boundaries.

[0059] The dopants implanted in the grain boundaries are, for example, dopants of hafnium (Hf) and/or hafnium oxide (HfO.sub.2) and/or phosphorus.

[0060] This layer 12 is produced as follows (FIG. 4):

[0061] Step 20: deposition of Si layer,

[0062] Step 21: thermal oxidation,

[0063] Step 22: introduction of dopants.

[0064] The structure then obtained for the layer 12 is of the type illustrated in FIG. 3b: it comprises large SiO.sub.2 grains (grains 12a) and doped grain boundaries (boundaries 12b). Here, large grains means that the dimensions are comprised between around 10 nm and up to 50 microns.

[0065] Such a structure is dense (less than 10% porosity) and polycrystalline. It has a great homogeneity (porosity difference less than 10%), a large grain size and a high oxygen and water vapour tightness.

[0066] Especially, implanting dopants allows reinforcing the grain boundaries of the SiO.sub.2 sub-layer and slowing the permeability to oxygen and water vapour in the SiO.sub.2 layer.

[0067] The silica layer is stabilised by blocking the grain boundaries by hafnium and/or hafnium oxide and/or phosphorus.

[0068] The silica growth kinetics are thus blocked or at least slowed.

[0069] Also note that the hafnium oxide gives better results than SiO.sub.2 in terms of water permeability.

[0070] The Si layer (step 20) can be deposited by different techniques: plasma spraying, electron beam vapour deposition, etc., or any combination of these techniques.

[0071] Such a layer has a thickness comprised between 5 and 30 μm, for example.

[0072] The thermal oxidation (step 21) is conducted in an oven in the presence of oxygen (dry oxidation).

[0073] This oxidation is conducted under the following conditions, for example: heat treatment temperature: 1100° C. to 1300° C.; duration: 1 to 50 hours; oxygen rate: 1 l/min to 20 l/min

[0074] The dopants are then introduced (step 22) by ion bombardment.

[0075] The atomic percentage of dopants in the layer 12 is, for example 1-2% for Hf and less than 20% for phosphorus.

[0076] The multifunctional structure 13 is produced after the production of layer 12. It comprises several layers of ceramics (Yb.sub.2SiO.sub.5, BSAS, etc.) intended to be chosen and dimensioned to ensure the various desired seals.

EBC Structure—Second Embodiment

[0077] In an embodiment illustrated in FIG. 5, the bonding layer 12 comprises a silicon sub-layer 121 and a doped-boundary silica sub-layer 122.

[0078] In this second embodiment, this layer 12 is obtained as follows (FIG. 6):

[0079] Step 30: deposition of a first silicon layer,

[0080] Step 31: deposition of a second silicon layer, said layer being a doped layer,

[0081] Step 32: thermal oxidation,

[0082] The thermal oxidation is then followed by the deposition of other layers of the EBC structure (deposition of the layers of the multifunctional structure).

[0083] The silicon layer is deposited (step 30) by chemical vapour deposition (CVD) under the following conditions: P=100-200 mbar; T=1020-1050° C. with the gas flow and the following reaction:

3AlCl(g)+(2y)Ni+H.sub.2(g)==>1AlNiy+AlCl.sub.3+HCl

[0084] The layer deposited has a thickness typically comprised between 10 and 20 μm.

[0085] The doped silicon layer is also deposited by CVD technique (step 31).

[0086] This doped layer has a thickness typically comprised between 1 and 5 μm.

[0087] The silicon doping is conducted beforehand by ion implantation.

[0088] The doping of the second silicon layer is an Hf and/or phosphorus doping with a concentration by atomic mass between 1 and 2% for Hf and less than 20% for phosphorus.

[0089] After oxidation, the bonding layer 12 is provided with a silicon sub-layer 121 and a doped-boundary silica sub-layer 122.

[0090] The sub-layer 122 has a polycrystalline structure with large SiO.sub.2 grains and Hf and HfO.sub.2 grain boundaries.

[0091] It has a high oxygen and water tightness.

[0092] It ensures a relatively homogeneous thickness at the silica interface between the silicon layer and the multifunctional layer 13.

[0093] The growth of silica is slower than in the prior art.

[0094] This results in an improved service life for the EBC structure.