EP0634497B1 - Composite material with intermetallic matrix of the A1Ni-type reinforced by silicon carbide particles - Google Patents

Description

The present invention relates to a material composite comprising a compound matrix AlNi type intermetallic, reinforced by silicon carbide particles SiC, which is intended for medium or high temperature applications, for example 600 to 1200 ° C, possibly in an atmosphere oxidizing.

Materials based on intermetallic compounds such as AlNi are currently the subject of a major research and development effort in all highly industrialized countries. In the areas of aeronautics and aerospace, where there is a high demand for materials with specific mechanical properties, resistance to creep and resistance to oxidation higher than those of the metal alloys currently used, these intermetallic compounds exhibit great interest.

Indeed, intermetallic compounds AlNi type nickel aluminide have low density (5.9) relative to that (9) of the superalloys nickel based, and they have excellent strength to high temperature oxidation. Also, we already have them used as a protective coating, in particular on nickel-based superalloys. However, until now they could not be directly employed as hot structural elements because their properties mechanical hot are too poor. Furthermore, at low temperature, they lack ductility and have a low toughness.

Also, research has been undertaken to improve the properties of these intermetallic compounds and it has thus been envisaged to use them in the form of composite materials reinforced with fibers or particles. Composite materials of this type reinforced with tungsten fibers, alumina fibers, TiB ₂ particles or aluminum nitride particles are described by K. Vedula in Intermetallic Compounds: Structure and Mechanical Properties. Proc. 6th, Jap Inst. of Metal Int. Nice. Sendai (Japan), June 1991, pages 901-925, and by RJ Arsenault in Advanced Structural Inorganic Composites P. Vincenzini (Editor) Elsevier Science Publishers BV, 1991.

However, materials reinforced with TiB ₂ or Al ₂ O _3, which have a markedly improved resistance to hot creep, have a lower resistance to oxidation than that of the intermetallic compound AlNi. In the case of TiB ₂ reinforcement, this reduction in oxidation resistance is due to the presence of TiB ₂ particles which oxidize faster than the intermetallic compound AlNi; in the case of Al ₂ O ₃ reinforcement, this reduction in oxidation resistance is due to the fact that oxygen can migrate within the composite material by the microcracks which exist at the matrix-particle interface of Al ₂ O ₃ due to the weak interfacial bond.

Also, to increase the creep resistance to hot of an AlNi type intermetallic compound without alter its excellent natural resistance to oxidation, it is best to strengthen it with particles or weakly oxidizable fibers, also forming with the matrix a very strong interfacial bond. Such a bond could be obtained with a chemical reinforcement reactive towards the matrix, but in the latter case the chemical interaction between the matrix and the reinforcement can continue throughout the time when the material is used at high temperature, which will lead to a regular decrease in its properties until the reinforcement is completely destroyed.

As a result, the use of chemically reactive reinforcements with an AlNi matrix as indicated by Vedula who notes on the page 920 of the aforementioned document that it does not currently exist no reinforcing fiber having all the properties required for a NiAl matrix.

The document "Fabrication and Mechanical Properties of Cf / NiAl and SiCw / NiAl Composites ", (Nishiyama et al), 6TH CONF. PROC. JP-US COMPOSITE MATERIAL 1993, pages 417 to 424 discloses the realization of a composite material comprising a matrix of the AlNi type and a reinforcement formed of silicon carbide particles SiC scattered throughout the matrix.

The object of the present invention is precisely use as reinforcement in a matrix intermetallic AlNi type of a compound, carbide silicon, which although reactive with the matrix, can be stabilized in it thanks to a contribution of silicon and lead to a composite material satisfactory.

According to the invention, the composite material comprises a matrix consisting mainly of a compound AlNi type intermetallic comprising 43 to 63% nickel and containing in solid solution from 1.5 to 30% in silicon atoms, and a reinforcement formed of silicon carbide particles SiC dispersed in this matrix, said composite material comprising from 10 to 60% by volume of SiC particles.

Indeed, it has been discovered according to the invention, that the decomposition of silicon carbide by reaction chemical with the intermetallic compound AlNi had not take place when a sufficient quantity of silicon was in solid solution in the compound AlNi intermetallic.

Decomposition of silicon carbide SiC occurs from about 700 ° C by chemical reaction with the intermetallic compound AlNi, which releases aluminum carbide Al ₄ C ₃ or carbon, while silicon passes into solid solution in the intermetallic compound.

However, we have found that, surprisingly, this decomposition of the silicon carbide was totally stopped as soon as a sufficient quantity of silicon had been dissolved in the compound matrix AlNi intermetallic.

Generally, this amount of silicon is 2 at 11% in atoms for materials having to resist temperatures of 1000 ° C.

Therefore, a material associating particles silicon carbide SiC and a matrix AlNi type intermetallic solution solid a sufficient quantity of silicon, constitutes a system in thermodynamic equilibrium which does not evolve more, by chemical reaction matrix / reinforcement of SiC, when worn at high temperature. In addition, a limited chemical reaction between the matrix and the silicon carbide reinforcement creates a strong interfacial bond between the reinforcement and the matrix, which is advantageous for obtaining a high oxidation resistance of the material.

Finally, since silicon carbide has high mechanical characteristics and very good resistance to oxidation up to around 1400 ° C., the composite material comprising a reinforcement of silicon carbide exhibits both chemical stability and good behavior hot creep of AlNi / TiB ₂ composites, while retaining the excellent oxidation resistance of unreinforced AlNi type intermetallic compounds.

According to the invention, the carbide particles of silicon used as reinforcement in the composite material can be in different forms. For example, may be grains with an angular outline, monocrystalline wafers and / or whiskers. Through elsewhere, the silicon carbide may be under different crystalline forms, for example under forms corresponding to alpha-hexagonal varieties and / or beta-cubics.

Preferably, the carbide particles of silicon have an average length, following their longer large dimension, from 1 to 100 µm, because with these dimensions optimal particle efficiency in as reinforcement.

The composite material of the invention can understand more or less significant amounts of particle reinforcement. As in any material composite with particulate reinforcement, we are interested in increase the breaking strength, the modulus elasticity and high creep resistance temperature, use a large amount of reinforcing particles, especially as the density of the silicon carbide being less than that of the matrix (3.2 and 5.9 respectively), the material will be the lighter the quantity of particles will be bigger. However, when the proportion of reinforcement becomes important, the particles tend to enter contact between them and to form porous aggregates, which constitute weak points from which cracks may appear and then spread. he there is therefore a threshold not to be exceeded.

However, when you want resistance very high hot creep, with high contents in SiC particles, we have on the contrary an interest in this that all SiC particles are in contact direct, which requires developing the material at a temperature high enough to allow welding-diffusion of the particles between them, but leads to a behavior of the brittle type material.

Generally, the composite material comprises of 10 60% by volume of SiC particles.

The SiC particle content is also chosen according to the geometrical characteristics (average size, shape, etc.) of the SiC particles and grains of the matrix to get the best results. In the case where the SiC particles have a average length, according to their largest dimension, from 5 to 50 µm, we generally prefer to use 10 to 30% by volume of SiC particles to obtain a good compromise between toughness, breaking strength and resistance to creep at high temperature.

The AlNi type intermetallic compound used as a matrix in the composite material of the invention is an intermetallic aluminum compound and nickel mainly consisting of a phase having the B2 structure (CsCl type) characteristic of compound AlNi, which contains in solution a quantity suitable silicon. The matrix can also include common impurities such as alumina and / or iron, in small proportions, for example of 0.5 to 2% by volume for alumina and 0.5 to 2% by volume weight for iron, dissolved or in the form of microprecipitates. The phase with structure B2 of AlNi compound is characterized by a domain of existence relatively large in the AlNi binary system, since this domain extends for example from 43 to 63% in nickel atoms at 1000 ° C. This phase can dissolve, in the form of a solid solution, an amount of silicon which depends on the temperature and the atomic ratio between aluminum and nickel.

According to the invention, any Al-Ni-Si ternary alloy of composition located inside the domain of existence of this phase of structure B2 can be suitable as a matrix provided that this alloy contains the minimum silicon content required for the intermetallic compound be in equilibrium thermodynamics with silicon carbide at the desired temperature, so that the interface reinforcement matrix no longer evolves by chemical reaction to high temperature.

This minimum content depends on the content of nickel of the matrix and the temperature. So she is 1.5% in the case of a matrix containing 43% in nickel atom at a temperature of 1000 ° C.

Preferably, according to the invention, the compound intermetallic AlNi constituting the matrix comprises of 50 to 63% in atoms of nickel to avoid that, in the case of a limited reaction between the matrix and the silicon carbide, we have a carbide deposit of aluminum at the matrix-particle interface of silicon.

The composite material of the invention can be prepared by conventional metallurgy processes for powders or foundries. Since the reinforcement and the matrix constituting the composite material are very refractory compounds, since the points of fusion of silicon carbide SiC and aluminide of nickel AlNi are respectively around 2550 and 1650 ° C, these processes will preferably be classic solid phase processes in metallurgy of powders such as hot compression, uniaxial or isostatic, or the hot extrusion of mixtures of SiC and AlNi powders. We can however also prepare materials by techniques of very high temperature foundry (over 1700 ° C) and projection by means of a plasma, or by a process mixed combining high casting techniques temperature and metallurgy techniques of powders like Martin's XD brand process Marietta.

On the other hand, the preparation processes making call for reactive sintering from powders aluminum and nickel are excluded because degradation reinforcing particles by chemical reaction with these elements during sintering would be way too much important.

Whatever process is used, it is important to choose conditions allowing to obtain a material with minimum porosity, in which the grains or matrix crystals are intimately welded with a uniform dispersion of particles of SiC in the intermetallic matrix.

According to the invention, the silicon which must be included in the intermetallic compound matrix can be added, at least in part, before manufacture composite material, or be obtained only by partial decomposition of carbide particles from silicon during material development composite.

In both cases, the material can be prepared composite of the invention by subjecting it to a hot densification in solid phase a mixture of powder of an AlNi intermetallic compound containing or not silicon and SiC particles.

We can also prepare the composite material of the invention by dispersing particles of SiC in an AlNi matrix containing or not containing silicon, at a temperature such that the matrix is in the liquid state and that the SiC particles remain in the solid state.

According to a first mode of development of materials composites of the invention, these are prepared from of an AlNi intermetallic compound to which has been added silicon.

In this case the amount of silicon added can be less, equal or greater than the content required in silicon to reach equilibrium thermodynamics between matrix and SiC particles.

When this quantity is equal to or greater than the content corresponding to the thermodynamic equilibrium matrix / particles, at the production temperature, obtains a material characterized by a bond weak at the matrix / particle interface because the chemical compatibility between matrix and particles of SiC is ensured at all stages of the development of the material, so there is no reaction between the matrix and the SiC particles.

On the other hand, when the quantity of silicon added to the intermetallic compound AlNi is lower to that which corresponds to thermodynamic equilibrium matrix / particles, at the processing temperature of material, we get a solution additional silicon in the matrix (Al-Ni-Si) by partial decomposition of the SiC particles, at the processing temperature, to reach equilibrium thermodynamics at this temperature.

In this case, provided you use a matrix containing more nickel than aluminum, we can obtain, at the SiC matrix / particle interface, a two-phase transition zone consisting of a dispersion of free carbon in the matrix.

Indeed, the SiC decomposition reaction gives silicon which diffuses very quickly in the intermetallic compound while carbon remains at near the particle / matrix interface in the form of submicron precipitates.

These precipitates form with the matrix a zone of biphasic interfacial transition particularly favorable, establishing a strong interfacial bond between the particles and the matrix.

Indeed, this interfacial zone has an average coefficient of expansion between that of the particles (4 to 5.10 ^-6 K ^-1 ) and that of the matrix (13 to 15.10 ^-6 K ^-1 ), and therefore it can gradually absorb some of the static mechanical stresses generated in thermal cycling, the submicron carbon precipitates acting as dislocation traps.

Thus, as in most solid-solid reactions, the SiC decomposition reaction is not accompanied by the formation of a continuous layer of a brittle compound at the interface, which is particularly favorable for obtaining high mechanical properties with regard to the composite material. On the other hand, if one used in the intermetallic compound AlNi, a quantity of aluminum higher than the quantity of nickel, aluminum carbide (Al ₄ C ₃ ) is would form at the matrix / particle interface, which is unfavorable for the composite material, due, on the one hand, to the low stability of this carbide in a humid atmosphere, and, on the other hand, to the lower resistance to cracking of matrices poor in nickel.

According to a second mode of development of materials composites of the invention, these are prepared from of an AlNi intermetallic compound without addition of silicon.

In this case, the required silicon content comes only from the decomposition reaction of the silicon carbide during material development composite.

As before, it is beneficial to use a intermetallic compound comprising at least 50% nickel atoms to create around the particles of SiC a two-phase transition zone consisting of a dispersion of free carbon in the matrix.

In this case, the amount of silicon dissolved in the matrix of intermetallic compound depends on the composition of the starting intermetallic compound and the processing temperature, because it corresponds to thermodynamic equilibrium between the matrix and the SiC particles at this temperature.

• 2,5% en atomes lorsque le composé AlNi contient 50% en atomes de Ni,
• 7% en atomes lorsque le composé AlNi contient 53% en atomes de Ni,
• 11% en atomes lorsque le composé AlNi contient 56% en atomes de Ni.

So, at 1000 ° C, this amount of silicon is

• 2.5% by atoms when the compound AlNi contains 50% by atoms of Ni,
• 7 atomic% when the compound AlNi contains 53 atomic% of Ni,
• 11 atomic% when the compound AlNi contains 56 atomic% of Ni.

Consequently, according to the invention, by playing on the Ni / Al ratio, on the quantity of silicon possibly added before preparation and on the volume fraction of SiC particles, we can modulate at will the degree of interaction matrix / particles and therefore the bond strength interfacial in the resulting material.

In addition, by choosing a silicon content high and / or a processing temperature higher than the temperature of use of the composite material, we obtains a material which will retain its properties mechanical during its aging in service at high temperature because, once the elaboration stage finished and the matrix saturated with silicon, the whole matrix-particles of SiC-transition zone interfacial forms a system in equilibrium thermodynamic.

The SiC particles used for the preparation composite materials of the invention can be grains with an angular outline obtained by grinding industrially produced silicon carbide blocks and composed of crystals of the alpha hexagonal variety (more precisely a mixture of polytypes derived from this variety), almost monocrystalline wafers alpha-hexagonal or beta-cubic varieties, obtained by crystal growth techniques or whiskers of silicon carbide obtained by processes classics.

The intermetallic compound AlNi containing or not silicon, used as the starting material for this elaboration, is also obtained by processes classics such as reactive sintering, "O-spray" foundry, plasma projection. Generally, it is used under the powder form with a particle size of 5 to 50 μm.

When using densification techniques hot in solid phase to develop the material, we achieves this densification using the switchgear and the temperature and pressure usually used to manufacture materials of this type. The same is true when produces the material using foundry techniques, or projection by means of a plasma, or by the process mixed XD by Martin Marietta.

Other features and benefits of the invention will appear better on reading the following examples given of course as illustrative and not limiting.

Example 1.

• Al = 50% en atomes
• Ni = 50% en atomes.

In this example, the second mode of preparation of the composite materials of the invention is used, starting from particles of silicon carbide having an average size of 5 to 45 μm, and a powder of single-phase intermetallic compound AlNi having a particle size of 5. at 50 μm and the following composition:

• Al = 50 atomic%
• Ni = 50 atomic%.

A mixture of powders comprising 20% in particle volume of silicon carbide by grinding mechanical in a carbide ball mortar tungsten. The mixture thus obtained is then subjected to densification by hot compression under vacuum of 10Pa, in a cell made up of a matrix cylindrical and two graphite pistons. After application of a pressure of 100 MPa for 2 hours at 1150 ° C, a disc of composite material is obtained with a total porosity of less than 1%.

Metallographic examination of this disc reveals that hot compression allowed welding by solid phase diffusion of compound grains intermetallic between them. The carbide particles of silicon appear uniformly dispersed in the intermetallic compound matrix and a two-phase zone containing the precipitates of submicron carbon is observed around each particle of silicon carbide. The thickness of this two-phase area is around 1.2 µm, which corresponds to decomposition by chemical reaction about 14% of the carbide initially introduced. We also finds uniformly distributed silicon in solid solution in the matrix.

• Al = 47,7%
• Ni = 47,9%
• Si = 4,4%.

The composition in% atoms of this matrix is then:

• Al = 47.7%
• Ni = 47.9%
• If = 4.4%.

With this matrix composition, the particles silicon carbide can no longer react with the matrix as long as the temperature remains below 1150 ° C, which corresponds to an upper limit of use of the material. So we got, after a transient reaction which allowed the establishment of a strong interfacial bond, matrix / particles, a composite disc, in which the interface has become chemically stable.

Example 2.

• Al = 40% en atomes
• Ni = 53% en atomes
• Si = 7% en atomes.

In this example, the first mode of preparation of the composite materials of the invention is used, starting from a powder of silicon carbide identical to that used in Example 1 and a powder of intermetallic compound AlNi containing silicon in solid solution having the following composition:

• Al = 40 atomic%
• Ni = 53 atomic%
• Si = 7 atomic%.

A mixture of the two powders is prepared comprising 30% by volume of SiC particles and are formed at from this mixture a composite disc by hot compression under the same conditions as those of Example 1.

• Al = 38,5% en atomes
• Ni = 50,5% en atomes
• Si = 11% en atomes.

A disc is thus obtained having a residual porosity of less than 2%. In this case, the thickness of the two-phase matrix / carbon zone surrounding each particle of silicon carbide is of the order of 0.7 μm, which corresponds to the decomposition by chemical reaction of approximately 8% of the carbide. initially introduced silicon. During this reaction, the intermetallic matrix is enriched in silicon and its final composition is as follows:

• Al = 38.5 atomic%
• Ni = 50.5 atomic%
• Si = 11 atomic%.

This material is chemically inert at 1150 ° C.

Example 3.

In this example, we use the second mode of preparation of the composite materials of the invention in starting from particles of silicon carbide from 1 to 2µm of average diameter and of a powder of compound AlNi (50% in Al atoms and 50% in Ni atoms) having a average particle size from 1 to 2µm.

We prepare from powder and particles a mixture comprising 50% by volume of particles of SiC. After prolonged mechanical mixing of the mixture in presence of liquid ethyl alcohol, mixture and we introduce it into the cell graphite piston compression used in Example 1. After drying by vacuum evaporation at ambient temperature, the temperature is gradually increased mixing at a temperature of 1450 ° C, under pressure of 100MPa, and it is maintained at this temperature and at this pressure for 30min. In order to avoid too much strong titration by aluminum evaporation, we realize compression under an argon atmosphere.

• Al = 41% en atomes
• Ni = 50% en atomes
• Si = 9% en atomes.

A composite disc is thus obtained having a residual porosity of less than 3% and a density of the order of 4.6. About 8% of the initially introduced silicon carbide was decomposed by reaction with the matrix during processing. The two-phase matrix / carbon zone surrounding each particle of silicon carbide has a thickness of between 0 and 0.3 μm and the final composition of the matrix is as follows:

• Al = 41 atomic%
• Ni = 50 atomic%
• Si = 9 atomic%.

Despite the argon atmosphere, there is a loss aluminum.

Example 4.

• Al : 48% en atomes,
• Ni : 48% en atomes,
• Si : 4% en atomes.

In this example, the first method of preparing the composite materials of the invention is used, starting with SiC whiskers and a powder of AlNi intermetallic compound containing silicon in solution having a particle size of 2 to 5 μm, and having the composition next :

• Al: 48% by atoms,
• Ni: 48% by atoms,
• If: 4 atomic%.

Silicon carbide whiskers are beta-cubic variety and their extreme dimension is 0.2 to 5µm. The whiskers are mixed with the powder of intermetallic compound so as to obtain a fraction volume in whiskers of 15%. After mechanical mixing in the presence of a pasty organic binder, the cold mixing in the form of a ribbon, then cut a disc in this ribbon and we put it in the cell of graphite compression. We then heat slowly the assembly under primary vacuum until evaporation complete with the organic binder, then bring the mixture to 1150 ° C for 2h, under a pressure of 100MPa.

A composite disc is thus obtained having a residual porosity less than 1.5% in which the silicon carbide whiskers are preferably aligned parallel to the direction extrusion.

No chemical reaction occurred during hot compression at the matrix / whiskers interface because the amount of silicon initially present in the powder of intermetallic compound was sufficient to ensure the chemical inertness of the system reinforcement / matrix up to 1150 ° C.

Example 5.

In this example, we use the second mode of manufacture of the composite materials of the invention in starting from particles of silicon carbide and a AlNi intermetallic compound powder (50 atomic% of Al and 50 atomic% of Ni), having a particle size from 5 to 10µm. The silicon carbide particles have also an average dimension of 5 to 10µm and we prepares from these particles a mixture comprising 15% by volume of particles. After homogenization of the mixture, it is injected into the flame of an arc plasma torch whose power has been set in such a way that the grains of compound intermetallic are melted but not the particles of SiC.

By projection on the surface of a part in cast iron, a good adhesion coating of 150µm of average thickness with great hardness, excellent abrasion resistance and protecting the underlying piece of oxidation.

• Al : 41% en atomes
• Ni : 50% en atomes
• Si : 9% en atomes.

The final composition of the matrix is as follows:

• Al: 41 atomic%
• Ni: 50% by atoms
• If: 9% by atoms.

Claims (11)

1. Composite material comprising a matrix mainly constituted by an intermetallic compound of the AlNi type containing 43 to 63 atom % silicon, and a reinforcement formed from silicon carbide (SiC) particles dispersed in said matrix, said composite material containing 10 to 60 vol.% of SiC particles.
2. Material according to claim 1, characterized in that the SiC particles are in the form of grains, monocrystalline platelets and/or whiskers.
3. Material according to either of the claims 1 and 2, characterized in that the silicon carbide is in crystalline form corresponding to the alpha-hexagonal and/or beta-cubic types.
4. Material according to any one of the claims 1 to 3, characterized in that the SiC particles have an average size, in accordance with their largest dimension of 1 to 100 µm.
5. Composite material according to any one of the claims 1 to 4, characterized in that the mean dimension of the SiC particles is 5 to 50 µm and that the composite material contains 10 to 30 vol.% SiC particles.
6. Composite material according to any one of the claims 1 to 5, characterized in that the AlNi-type intermetallic compound constituting the matrix comprises 50 to 63 atom % nickel and in that it is largely constituted by a phase having the B2 structure.
7. Composite material according to any one of the claims 1 to 6, characterized in that the SiC particles are surrounded, at the matrix-particle interface, by a two-phase transition zone constituted a free carbon dispersion in the matrix.
8. Composite material according to any one of the claims 1 to 7, characterized in that the matrix also comprises 0.5 to 2 vol.% alumina and/or iron.
9. Composite material according to any one of the claims 1 to 8, characterized in that the AlNi-type intermetallic compound contains 2 to 11 atom % silicon.
10. Process for the production of a composite material according to any one of the claims 1 to 9, characterized in that a mixture of a powder of an AlNi intermetallic compound and SiC particles is subject to hot densification in the solid phase.
11. Process for the production of a composite material according to any one of the claims 1 to 9, characterized in that it consists of dispersing SiC particles into an AlNi matrix, which may or may not contain silicon, at a temperature such that the matrix is in the liquid state and that the SiC particles remain in the solid state.