EP3962879A1

EP3962879A1 - Part made of silicon-based ceramic or cmc and method for producing such a part

Info

Publication number: EP3962879A1
Application number: EP20731919.5A
Authority: EP
Inventors: Amar Saboundji; Hugues Denis Joubert; Philippe Picot; Luc Patrice BIANCHI
Original assignee: Safran SA
Current assignee: Safran SA
Priority date: 2019-05-03
Filing date: 2020-04-30
Publication date: 2022-03-09
Also published as: WO2020225508A1; FR3095645A1; FR3095645B1; US20220204415A1; CN113784938A

Abstract

The invention relates to a part made of silicon-based ceramic material or silicon-based ceramic matrix composite (CMC) comprising an environmental barrier coating (EBC), the coating (12, 13) comprising a bonding layer (12) arranged on the surface of the ceramic material or ceramic matrix composite (CMC), the bonding layer (12) being topped by one or more layers which together form a multi-functional protective structure (13). The invention is characterised in that the bonding layer (12), at its interface with the multi-functional structure, comprises a layer (12) or sub-layer (12b) made of polycrystalline silicon.

Description

Ceramic part or CMC based on silicon and method of making such a part

GENERAL TECHNICAL FIELD AND PRIOR ART

The present invention relates to parts made of a silicon-based ceramic material or of a silicon-based ceramic matrix composite (CMC) material.

CMC materials are currently widely considered in the aeronautical or space field, in particular for parts of turbomachines which are subjected to high temperatures during operation.

Economic and environmental constraints are indeed pushing engine manufacturers in the aeronautics industry to develop lines of research aimed at reducing noise pollution, fuel consumption, and NOx and C02 emissions.

To meet these requirements and in particular the last two, one solution consists in increasing the temperature of the gases in the combustion chamber of the turbojets. This induces an improvement in engine efficiency (reduction in kerosene consumption) and allows operation with a lean fuel mixture (reduction of NOx). However, the materials used in the combustion chamber must be able to withstand higher temperatures.

Currently, the materials used in aircraft engines for parts subjected to high operating temperatures are superalloys. However, the temperatures reached (around 1,100 ° C) are close to their limit of use.

To significantly increase these operating temperatures (up to 1400 ° C), it has been proposed for several years to use silicon-based ceramics: silicon carbide ceramic SiC or ceramic matrix composites (CMC) of SiC type / SiC.

These materials are indeed promising candidates due to their mechanical and thermal properties and their high temperature stability. Also, in addition to their properties at high temperature, the CMC materials based on silicon carbide have the advantage of having a lower density than the metallic materials for which they are substituted. A large number of studies have focused on the introduction of these materials for extreme applications (high temperature, high pressure, corrosive atmosphere, mechanical stresses).

Under these conditions, a thin layer of silica forms, which limits the diffusion of oxygen to the substrate. However, in the presence of water and from 1200 ° C, a surface recession phenomenon appears following the volatilization of this layer in the form of HxSiyOz species, such as Si (OH) 4 or SiO (OH) 2.This phenomenon leads to a decrease in the net growth rate of the oxide, the thickness of which tends towards a limit value and an accelerated recession of the SiC present in the CMC.

Thus, for prolonged use and / or at higher temperatures the CMC must be protected to avoid evaporation of the protective silica layer. This is particularly the case for CMC materials used in combustion chambers, High Pressure turbines and to a lesser extent engine exhaust components.

Conventionally, CMC materials are protected by layers of environmental barriers (known as EBC or “Environmental Barrier Coatings” according to the English terminology generally used).

Such an EBC coating typically comprises, as illustrated in FIG. 1, a bond layer 2 (“bond coat”) of silicon which covers the layer 1 of CMC to be protected and which is topped with a ceramic structure 3 ( s) multifunctional.

The multifunctional structure 3 is for example made up of:

- one or more layers of mullite (intended to prevent the diffusion of oxygen to layer 2 of silicon),

- one or more layers intended to protect layer 2 from a diffusion of water vapor.

Multilayer environmental barriers of the Si / Mullite / BSAS (barium strontium aluminosilicate) type or even those comprising a silicon bonding layer and a layer of a rare earth silicate (for example Y2SÎ207) are also known, for example. These experimental barriers can be deposited, in a manner known per se, by thermal spraying processes, physical phase deposition (PVD) or by deposits of slurries (for example "dipcoating" or "spray coating" Such structures nevertheless remain subject to deterioration over time due to inhomogeneities in the formation of silica (dashed line 4a and agglomerates 4b in FIG. 1) between the Si layer and the other layers of the EBC coating.

These inhomogeneities in the formation of silica give rise to residual stresses in the EBC coating.

It initiates and propagates cracks in the superimposed layers (cracks 4c in figure 1).

This results in spalling of the ceramic layers, so that the CMC underlayments are exposed to a corrosive environment of water vapor leading to its accelerated recession limiting the life of the CMC.

This leads to the premature degradation of the system by delamination mechanisms.

GENERAL PRESENTATION OF THE INVENTION

A general aim of the invention is to overcome the drawbacks of structures known in the state of the art.

In particular, an object of the invention is to provide an EBC coating structure which allows improved service life.

Thus, the invention provides a part made of silicon-based ceramic or of a silicon-based ceramic matrix composite (CMC) material comprising an environmental protection coating (EBC), said coating comprising a bonding layer deposited on the surface of ceramic or ceramic matrix composite material (CMC), said bonding layer being surmounted by one or more layers together forming a multifunctional protective structure, characterized in that the bonding layer comprises at its interface with the multifunctional structure a polycrystalline silica layer or sublayer.

In particular, the polycrystalline silica layer or sub-layer has grain boundaries doped with Hf and / or HfO 2 and / or phosphorus.

According to one mode of implementation, the part is produced by implementing the following steps:

- deposition of a layer of silicon on the surface of the ceramic or ceramic matrix composite material,

- thermal oxidation,

- introduction of doping agents. As a variant, the production is done by implementing the following steps:

- deposition of a first layer of silicon on the surface of the ceramic or ceramic matrix composite material,

- deposition of a second layer of silicon, said layer being a doped layer,

- thermal oxidation.

The invention also proposes an aeronautical or space device, in particular a turbomachine, comprising at least one part of the type proposed.

PRESENTATION OF FIGURES

Other characteristics and advantages of the invention will emerge from the following description, which is purely illustrative and non-limiting, and should be read with reference to the appended figures in which:

Figure 1, already discussed, illustrates the formation of defects and the degradation of a structure known in the state of the art;

Figure 2 illustrates an example of a part according to the invention;

Figures 3a and 3b illustrate an EBC coated stack according to one embodiment of the invention (Figure 3a);

Figure 4 illustrates a possible embodiment of the invention for producing a stack of the type of that of Figure 3a;

Figures 5 and 6 illustrate another possible implementation mode for the method of the invention.

DESCRIPTION OF ONE OR MORE MODES OF IMPLEMENTATION AND REALIZATION

The part 5 illustrated in Figure 2 by way of example comprises a blade 5a of a high pressure turbine engine turbine rotor and a blade 5b.

Said part 5 is made of a composite material with a CMC ceramic matrix coated with an EBC protective barrier, which is more particularly described below.

It will be noted that the use of CMC ceramics for the blades of high pressure turbines of a turbomachine is particularly advantageous insofar as it makes it possible, if necessary, to eliminate on the blades the holes which are conventionally formed therein for the circulation of cooling air. . Removing these holes further increases engine performance.

As will be understood, the high pressure turbine engine blades of a turbomachine are only an example of application for the proposed EBC structure: this more generally finds application, in particular in space or aeronautics, for any part subjected in operation to high temperatures (above 1100 ° C): combustion chamber of a turbomachine, exhaust component of a engine, etc.

Creation of a CMC structure

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

By CMC material is meant here and throughout the present text composite materials comprising a set of ceramic fibers incorporated in a also ceramic matrix.

The fibers are, for example, carbon (C) and silicon carbide (SiC) fibers.

They can also be fibers of aluminum oxide or alumina (A1203), or mixed crystals of alumina and silicon oxide or silica (SiO2) such as mullite (3A1203, 2S102).

The matrix is made of silicon carbide SiC or any mixture comprising silicon carbide.

SiC-SiC composites with silicon carbide fibers and a silicon carbide matrix are particularly advantageous for aeronautical applications given their high thermal, mechanical and chemical stability and their high strength / weight ratio.

These composites can use pyrocarbon (or PyC) or boron nitride (BN) as the interphase material.

Various techniques can be envisaged for the manufacture of a part made of composite material with a ceramic matrix.

In particular, according to a first technique, the parts made of CMC material can be made from a fiber preform with a woven fiber texture. This fiber preform is consolidated and densified by chemical infiltration in the gas phase (CVI or “Chemical Vapor Infiltration” according to the English terminology).

As a further variant, the preform may be in fiber strata based on silicon carbide, the fibers of said preform being coated by CVI with a layer of boron nitride surmounted by a layer of carbon or carbide, in particular of silicon carbide.

For examples of techniques for manufacturing a CMC SiC / SiC structure, reference may be made, for example, to patents US9440888, or US8846218.

EBC structure - First embodiment

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

The tie layer (layer 12) is polycrystalline silica with doped grain boundaries.

The dopants implanted in the grain boundaries are for example hafnium (Hf) and / or hafnium oxide (HfO 2) and / or phosphorus dopants.

The production of this layer 12 is carried out as follows (Figure 4):

Step 20: deposition of a layer of Si,

Step 21: thermal oxidation,

Step 22: introduction of dopants.

The structure then obtained for the layer 12 is of the type of that illustrated in FIG. 3b: it comprises large grains of SiO 2 (grains 12a) and doped grain boundaries (boundaries 12b). By large grains is meant here whose dimensions are between about ten nm and up to 50 microns.

Such a structure is dense (less than 10% porosity) and polycrystalline. It has great homogeneity (difference in porosity of less than 10%), large particle size and tightness to oxygen and high water vapor.

In particular, the implantation of dopants makes it possible to strengthen the grain boundaries of the SiO2 sublayer and to slow the permeability to oxygen and water vapor in the Si02 layer.

The silica layer is stabilized by blocking the grain boundaries with hafnium and / or hafnium oxide and / or phosphorus.

The growth kinetics of silica are then blocked or at the very least slowed down.

It will also be noted that hafnium oxide provides better results than SiO 2 in terms of water permeability. The deposition of the Si layer (step 20) can be carried out by different techniques: plasma spraying, vapor phase deposition by electron beams, etc. , or any combination of these different techniques.

Such a layer has for example a thickness between 5 and 30 μm

Thermal oxidation (step 21) is carried out in an oven in the presence of oxygen (dry oxidation).

This oxidation is for example carried out under the following conditions: temperature of the heat treatment: 1100 ° C to 1300 ° C; duration: 1 to 50 hours; oxygen rate: 1 l / min at 201 / min

The introduction of dopants (step 22) is then carried out by ion bombardment.

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

The multifunctional structure 13 is produced after the layer 12 has been produced. It comprises several layers of ceramics (YbzSiOs _, BSAS, etc.) intended to ensure that they are chosen and sized to ensure the various seals desired.

EBC structure - Second embodiment

In the embodiment illustrated in FIG. 5, the bonding layer 12 comprises a sub-layer 121 of silicon and a sub-layer 122 of silica with doped joints.

In this second mode of implementation, this layer 12 is obtained as follows (FIG. 6):

Step 30: deposition of a first layer of silicon;

Step 31: deposition of a second layer of silicon, said layer being a doped layer;

Step 32: thermal oxidation.

Thermal oxidation is then followed by the deposition of the other layers of the EBC structure (deposition of the layers of the multifunctional structure).

The deposition of the silicon layer (step 30) is carried out by chemical vapor deposition (CVD) under the following conditions: P = 100-200 mbar; T = 1020-1050 ° C with the gas flow and the following reaction:

3AICI (g) + (2y) Ni + H2 (g) ==> 1 AINiy + AIC13 + HCl

The deposited layer is typically between 10 and 20 μm thick. The doped silicon layer is also deposited by CVD technique (step 31).

This doped layer is typically between 1 and 5 µm thick.

The silicon doping is carried out beforehand by ion implantation. The doping of the second layer of silicon is an Hf and / or phosphorus doping with an atomic mass concentration of between 1 and 2% of Hf and less than 20% for phosphorus.

At the end of the oxidation, there is available for the tie layer 12 an underlayer 121 of silicon and a sub-layer 122 of silica with doped joints.

The sublayer 122 has a polycrystalline structure with large SiO 2 grains and Hf and / or HfO 2 grain boundaries and / or phosphorus.

It has high oxygen and vapor tightness.

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

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

This results in improved service life for the EBC structure.

Claims

1. Part of silicon-based ceramic material or of silicon-based ceramic matrix composite material (CMC) comprising an environmental protection coating (EBC), said coating (12, 13) comprising a bonding layer (12) deposited on the surface of the ceramic or ceramic matrix composite (CMC) material, said bonding layer (12) being surmounted by one or more layers together forming a multifunctional protective structure (13), characterized in that the bonding layer (12) comprises at its interface with the multifunctional structure a layer (12) or sub-layer of polycrystalline silica.

2. Part according to claim 1, characterized in that the polycrystalline silica layer or sublayer has Hf and / or Hf02 and / or Phosphorus doped grain boundaries.

3. A method of making a part according to one of the preceding claims, characterized in that the following steps are implemented:

- deposition of a silicon layer on the surface of the ceramic or ceramic matrix composite material (step 20),

- thermal oxidation (step 21)

- introduction of dopants (step 22).

4. A method of making a part according to one of claims 1 or 2, characterized in that the following steps are implemented:

- deposition of a first layer of silicon (step 30) on the surface of the ceramic or ceramic matrix composite material,

- deposition of a second layer of silicon, said layer being a doped layer (step 31),

- thermal oxidation (step 32).

5. Method according to claim 3 or according to claim 4, characterized in that the thermal oxidation is a dry oxidation in the presence of oxygen.

6. Method according to claim 3 or according to claim 4, characterized in that the dopants are Hf and / or Hf02 and / or phosphorus dopants.

7. Method according to claim 3, characterized in that the step of introducing dopants implements ion implantation.

8. Aeronautical or space device (5) comprising at least one part according to one of claims 1 or 2.

9. Turbomachine (5) comprising at least one part according to one of claims 1 or 2.