Composite ceramic-metal laminate - with intermediate low modulus, low density material absorbing thermal deformations

Ceramic-metal composite laminate # porous ceramic joints and their manufacturing process.

Right of priority of the patent application in the United States of America No 674,047 of April 5, 1976 on behalf of Arnold R. Erickson, Carlino Panzera and Robert P. Tolokan and the patent application in the United States of America No 677.258. dated April 15, 1976 in the name of Carlino Panzera.

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/ .

The invention relates to laminated or laminated products, hereinafter called laminates, ceramic-metal and more particularly, on the one hand, to a process for producing a laminate of this type which makes it possible to absorb thermal deformations without harmful effects and, on the other hand, the article produced by this process.

A number of methods are known for bonding a metal element to a thin ceramic blade. US Patent No. 2,996,401, for example, describes a process for the manufacture of electronic tubes in which the surface of the ceramic body is metallized by means of refractory metals and the metal member is then brazed to the metal coating. other USA patent No. 3.114.612 describes a ceramic laminate suitable for high temperature applications, in which the ceramic material is coated with a metallic bonding agent and welded to a corrugated sheet of stainless steel.

Although the previously known methods are suitable for the uses for which the products are intended, laminates intended to work at high temperature under oxidizing and mechanical stress conditions such as those encountered in turboshaft engines, must be capable of withstanding significant deformations due, in part, to extreme differences in the thermal expansion values ​​occurring during operation of the turbine and, in part, to, thermal gradients in the transverse direction of the laminate. Previous products tend towards an anisotropic state in their capacity to absorb thermal deformations and there is a need for a fixing process which responds elastically to thermal deformations at relatively low stress levels in all directions .

The direct bond between ceramic materials and metallic materials is currently limited to / materials having small differences in coefficient, / • 6 of thermal expansion (0.9 x 10 cm / cm / ° C) as well as in the geometry of structure (the ceramic material must remain in compression). The differences in coefficient of thermal expansion (a) can be reduced by using a technique in which materials having very close coefficients are arranged next to each other, thus forming a gradient between a ceramic material (a), cermets (a, .... a where the cermets are mixtures c 1 n of powdered metals and ceramic material of variable density, so that with the appropriate thickness, we can have an infinite number of layers each presenting a

I has slightly different) and a metal, which can be written as follows:

at.

at.

at.

CL.

ceramic a

m metal ^atl &lt; ^at2 &lt; °3........&lt;^atm

Unfortunately, this technique is strictly limited to low temperature uses due to the temperature limits imposed by:

1. relatively low resistance to oxidation of alloys with low thermal expansion,

2. the great diversity of expansions, at high temperatures, of metal, cermets and ceramic materials, and

3. the stresses in the ceramic material due to the thermal gradient.

The development of seals placed on a gas path, capable of undergoing abrasion at high temperature, intended for turboshaft engines, required the development of a process for manufacturing a ceramic-metal laminate which is not limited in its applicatins due to differences in expansion rate or non-resistance to oxidation.

In conditions of such a high thermal gradient where the surface of the ceramic withstands temperatures from 537 ° C to 1649 ° C and where there is a temperature gradient along the transverse direction of the ceramic, the hot surface expands stronger than the cooler surface. If this expansion is hampered, as is the case in a ceramic-cermet-metal laminate, excessive stresses occur in the ceramic material and cause damage by thermal cracking. Consequently, this laminate is unacceptable when the thermal gradients exceed 260 to 537 ° C. For example, if the ceramic material is alumina and the metal is a Ni-Al alloy, a temperature gradient of 360 ° C will not be not properly absorbed by the structure.

Consequently, the present invention relates to a laminate comprising a ceramic layer, a metal structure interface, three-dimensional, flexible, elastic and having a low modulus and a low density, this interface being fixed to the ceramic layer, as well as '' a metal member fixed to the low modulus metal structure. The thermal deformations due to the differences in the coefficients of thermal expansion of the metallic member and of the ceramic are absorbed by the interface in low modulus material which has sufficient tensile strength, resistance to oxidation at high temperatures. and elastic flexibility.

The main object of the present invention is to present a ceramic-metal laminate which can be used in applications working at high temperatures, in particular as a joint for turbo-engine blades.

Another object of the present invention is to present a ceramic-metal laminate in which · the thermal deformations due to different values ​​of thermal expansion and contraction of the ceramic and the metal are absorbed by an interface with a low-modulus metallic structure and low density which is interposed between ceramic and metal.

Yet another object of the invention is

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V present a method of bonding ceramic to a fibrous metallic structure with low modulus.

Yet another object is to present a method of bonding the intermediate ceramic-metal composite element to the low fibrous metal structure. module so that the tensile strength of the ceramic is not exceeded at the location of the bond during thermal expansion.

Yet another object is to present a felt metallic mattress made of fibers of a metal with a high melting point as a porous interface, elastic, low modulus.

Yet another object is to present a method for connecting one face of the fibrous metallic mattress to a metallic structure by brazing and the other face of the mattress. (or fabric) with a layer having a ceramic structure.

Another important object of the invention also consists in making a porous ceramic element, felted, made of aluminosilicate, which prevents the devitrification of quartz by the addition of glass with low expansion.

Yet another object of the invention is to present a ceramic-metal laminate, suitable for example as a seal for turbo-engine blades, in which the ceramic layer is porous and is therefore more easily subjected to abrasion than a layer of substantially solid ceramic material.

Yet another object of the invention is a method of manufacturing this porous ceramic material.

Yet another object of the invention is to provide a binding interface between ceramic materials and metals which work cyclically at extreme temperatures (either high or low) relative to ambient temperature and high gradients of / temperature in transverse direction, which is essentially // isotropic with regard to its elasticity and low modulus characteristics.

Yet another object of the invention is to provide a fixing interface between ceramic materials and metals which work with high temperature gradients between them, which has a low thermal conductivity in order to reduce heat losses.

Other details and particularities of the invention will emerge from the description given below, without implied limitation, of several exemplary embodiments of the invention, with reference to the drawings in which:

Figure 1 shows a sectional view of a first embodiment of the invention, which illustrates a ceramic composite laminate-elastic-metal interface.

Figure 2 shows another sectional view of the laminate according to the invention.

Figure 3 shows a sectional view of another embodiment of the invention.

Figure 4 shows a sectional view, on a larger scale, of a detail according to the invention.

Figure 5 shows a sectional view, on a larger scale, of another detail according to the invention.

Figure 6 shows a sectional view of an intermediate product of one of the embodiments of the invention.

FIG. 7 is a jhotomacrography of the first embodiment of a laminate according to the invention, taken with an enlargement of 15 times.

In Figure 1, there is shown a sectional view of a high temperature abrasion seal 100 for a turbo-engine. The ceramic member 1 can be made of a ceramic for high temperatures such as alumina, stabilized cubic zirconia, magnesia, zircon (2r0_.Si0_o), fosterite (2MgO.SiO), mullite, compound / mullite-quartz, aluminum diboride, calcium oxide / Z

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Yttria, glass, silicon carbide, silicon nitride, aluminoborosilicate, etc. , with the desired thickness and degree of porosity, as is necessary for abrasion seals, for high temperatures.

The ceramic member 1 has a very low coefficient of thermal expansion, generally of the order - * 6 -6 of about 1.8 x 10 to 14.4 x 10 cm per cm per ° C. On the other hand, the metal base 3 to which the ceramic member is ultimately connected, has a very high coefficient of thermal expansion, of the order of about 3.6 to 10 - at 6 x 10 cnupar cm per ° C. Used in a turbo-engine where the external surface of the ceramic member 1 is subjected to temperatures close to 982 ° C - 1982 ° C while the free surface of the metal is subjected only to temperatures of several tens to a few hundred degrees C, a direct connection of the two components would result in the immediate rupture of the ceramic due to the difference in the expansion coefficients and the effect of the temperature gradient in the transverse direction of the ceramic. Consequently, according to the present invention and in accordance with a first embodiment of this invention, an elastic interface 2, with low modulus, is fixed both to the ceramic member 1 and to the metal base 3 to absorb the differences. geometric due to variations in thermal expansion of the two materials and to the temperature gradient.

Interface 2 comprises a fibrous fabric or three-dimensional metallic padded structure, flexible, elastic, porous, having a low modulus, a low density and a high melting point, as described in detail in the patents UÎS.A. No. 3,469,297, 3,505,038 or 3,127,668. Typical alloys used to constitute the fibers of this interface are known under the registered trademarks of Hastelloy X, Hoskins 875, Haynes 188, DH 242? f are also suitable for nickel-based superalloys, / 2 / as well as 4 and 5 element alloys, of iron, cobalt, nickel, chromium, aluminum and yttrium (or rare earths). Advantageously, the porous fabric or mattress has a density of approximately 35% although, depending on the particular use which is made of it, the fabric constituting the interface 2 may have any density between 5 and 80%. It will appear that the precise alloy to be used to make the mattress will depend on the temperature, oxidation and stress conditions which occur during end use.

One method of manufacturing the embodiment shown in Figure 1 is to braze a fabric interface 2 to the metal base 3, as shown in 20.

The ceramic layer 1 is formed by spraying, by a plasma jet, the ceramic material on the accessible face of the interface 2, so that the ceramic material penetrates into the surface of the fabric interface 2 by mechanically bonding the ceramic material to the fibers of the interface 2. Then, the additional spraying of ceramic material by the plasma jet gives rise to the desired thickness of the ceramic layer 1. The product thus produced is a ceramic-metal composite element having an elastic interface, so that when the metal member expands, due to thermal expansion, to a greater extent than the ceramic material, the interface can absorb the different amounts of thermal expansion of the two materials. This produces a composite element having a high degree of thermal expansion incompatibility between the ceramic material 1 and the adjacent metal 3, this composite element being able to remain intact for extreme thermal cycles thanks to the capacity of the interface. in metallic fabric 2 to absorb the differential thermal expansion and the resulting thermal deformation. f

FIG. 2 represents an enlarged view / scale of the basic embodiment illustrated in FIG. 1, in this FIG. 2, it is shown that the metallic fibers 4 of the fabric interface 2a penetrate into the surface ceramic up to about 1/4 the thickness of the ceramic material 1a, while the other surface of the interface 2a is soldered at 20a to the metal plate 3a. In this case, the interface 2a in felted metal mattress is embedded in the surface of the ceramic layer la. The ceramic material and the metal alloy must be selected so as to minimize any chemical reaction between the metallic fibers of the interface and the ceramic material, and in the first place to make a mechanical connection between the two. The ceramic-metal interface composite part can be formed by pressing the metal felt interface into a plastic mass of ceramic material, over a distance which is sufficient to ensure a mechanical connection of sufficient strength; this represents another method of joining the ceramic material to the interface. As has been said above, a value of approximately 1/4 of the thickness of the ceramic layer is sufficient to obtain that the interface 2a is embedded therein; however, this value may vary depending on the model. ' After the mattress has been embedded in the plastic ceramic material, the composite element thus formed is dried and fired. As stated above, the fabric or interface can be attached to the metal base first or it can be attached to the metal base after the ceramic element has been attached, as desired.

In another embodiment of the invention, metal wire staples for a U-shaped card, about 0.95 cm, are attached to a fabric base by being stitched through it in a position generally vertical. A muddy ceramic-water mixture of ceramic fibers and / or powders is deposited on the fabric and held in the area of ​​the metal staples. This initial material is then agglomerated in an oven in order to react the ceramic mud and form the desired ceramic material at the same time as it mechanically encapsulates the metal staples. As shown in FIG. 6, the fabric 14a has metal staples 13a which are embedded in the ceramic material 12a, thus producing a ceramic layer - metallic wire 11a. When the ceramic is fired in the oven, the fabric layer 14a disintegrates, leaving the staples 13a in the embedded state in the ceramic 12a. The staples projecting from the layer 13a can be bent flat on the two surfaces for convenience. As with the metallic fibrous fabric interface, the chemical reaction between the metal staples and the ceramic material must be reduced to prevent the stresses resulting from the mismatch of the expansion coefficients (a) from causing cracking. of the material. A chemical reaction between the metal and the composite material would cause a rigid bond between them, which would accentuate the degradation in the ceramic-metal interfacial zone and would reduce the movement of both.

As shown in FIG. 3, this ceramic layer with embedded staples 11a is fixed to a layer of pure ceramic 1b by means of a glass frit 23b by placing the two layers in a kiln. high temperatures for a short time. A metal base 3a is brazed as shown at 20b at a porous fabric interface 2b. The ceramic laminate is then brazed by points at the fabric interface 2b, on the side of the visible staples, at 10b. Since the fibers of the interface 2b do not have a density of 100% and since of course the staples 13a of the ceramic layer do not have a density of 100%, the brazing of the two can be

100 %, but the total metal surface will not be higher than the metal density of the material with the lowest metal density. This type of composite element thus has the same characteristics and advantages as the basic embodiment shown in FIG. 1.

It will be noted that in FIGS. 4 and 5, the geometric connection between the ceramic material 1 and the fibers 4 of the interface 2 or the staples 13a promotes a mechanical connection. This particular characteristic is extremely important for the work of this material.

In addition to the metals listed for the interface, the staples 13a can also be made of materials such as platinum, tungsten, molybdenum and the like, depending on the location. The ceramic materials used in accordance with the present invention are those which are available on the market, known as ceramic materials for high temperatures as well as the unforeseen materials which have been found during the development of the invention and which are described below. -after.

In the use of ceramic materials for high temperature seals and gas turbines, and more particularly when the seals are subjected to abrasion as taught in the prior art, for example in US Patent No. 3,880 .550, a sintered aluminosilicate ceramic product comprising mullite 25 and quartz has very limited possibilities as insulation material for high temperatures (above 1426 °).

Free quartz, present in fibers that can be purchased (known as Fiberfrax and Kaowoôl), becomes brittle since molten quartz devitrifies and converts to cristobalite when subjected to temperatures of 982 ° C and above. It has been found that by using a mixture of aluminosilicate fibers and low-expansion glass fibers or powders, a mixture which is then sintered, a ceramic material can be produced.

able to work at temperatures of the order of

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1204 ° to 1648 ° C (which represents an increase of more than 204 ° C compared to known Fiberfrax materials). During the sintering of the mixture, the glass surrounds the aluminosilicate and at the same time dissolves any free quartz, so that a mixture of mullite and glass results. This new ceramic material has been used as one of the porous materials proposed for the ceramic part of the corrosite material which is the subject of the present invention. Surprisingly, it has been found that this material exhibits excellent characteristics at high temperature. When using a common aluminosilicate, which typically includes 35-55% SiO? and 45-65% of A1₂O₃ at temperatures above 982 ° C, the molten quartz also devitrifies and forms cristobalite which makes the fibers very brittle and weakens the whole product. By adding powder or glass fibers to aluminum silicate, the glass reacts with the quartz to form a new glass which does not devitrify. The¹ aluminosilicate, alumina and zirconia represent 3 types of fiber-making material, corresponding to different temperature ranges which, when applied to this powder or glass fiber technique, give a far better ceramic material.

FIG. 7 shows a base 3 made of a cobalt-based superaxlloy; macro photography is performed with an enlargement of 15 times. The metallic fabric 2 has a density of about 20%, is produced by means of the Hoskins 875 alloy and brazed at the base 3. A ceramic layer has been sprayed on the fabric with a plasma jet. as seen in the macro30 photograph. The ceramic layer 1 was composed of 4% by weight of CaO and 9.6% by weight of zrO ?.

It should be understood that the specific examples of implementation which follow, of ceramic interface-metal composite elements produced according to the present invention, do not / in any way limit the scope of the present invention /?

EXAMPLE I.

According to 1¹ teaching that Içbrevet gives

USA No 3.127.668, a felted fabric made of threads of _3

12.7.10 cm of the metallic alloy FeCrAISi (Hoskins-875) twisted to 1.27 cm was sintered for 15 hours in a -5 vacuum oven at 10 mm Hg and at a temperature of 1190 ° C,

The fabric produced had a density of about 30%. A metal base of a high temperature cobalt based alloy was brazed to the sintered fabric by subjecting the fabric and the metal base to a temperature of 1176 ° C in a vacuum oven for about 10 min. The zirconia was sprayed by a plasma jet on the apparent surface of the fabric, in the open air, and impregnated the fabric on about 25.4.10 cm; surprisingly, the zirconia then expanded to form a layer of zirconia of about 254.10 cm (layers up to 0.63 cm of zirconia were obtained by this process). The composite element formed was subjected to a cyclic heat treatment, during which the zirconia face was subjected to 1593 ° C and the metal base was exposed to air at room temperature, and this during a series of cycles, without any significant separation of the ceramic material from the zirconia and the metal.

EXAMPLE II

In accordance with the teaching given by the patent

USA No 3.127.668, a felted fabric made from -3 threads

9.6.10 cm Hastelloy X metal alloy twisted to

1.27 cm was sintered for 10 hours in a vacuum oven -5 to 10 mm Hg and at a temperature of 1190 ° C. The fabric produced had a density of approximately 20%. A metal base of Hastelloy X alloy was brazed to the sintered fabric by subjecting the fabric and the metal base to 1176 ° C in a vacuum oven for about 10 min. A ceramic composite element, of ceramic material and metal staples for card was prepared, by establishing a bed of metal staples directed upwards, 30.10 cm in diameter.

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having a U shape, 0.95 cm, stitched through a porous fabric base which held the staples in a semi-vertical position. A mud based on water and mineral fibers having diameters ranging from 8 to 80 microns, made of aluminosilicate, was mixed with a glass powder with low expansion (the powder having a fineness allowing it to pass through a sieve to 325 meshes, powders having a diameter up to 44 microns); the slurry had a composition of 50% by weight of aluminum silicate and 50% by weight of glass mixed with 50% by volume of water. The mud was deposited on the fabric over the staples, metallic i

directed upwards, so as to surround them, and held in place by the walls of an external container. This mud-staple composite element was sintered at 1204 or 1260 ° C for 2 hours in an argon purged oven to allow the glass to melt by reacting with the aluminosilicate and at the same time forming a matrix around it. aluminosilicate in order to eliminate any free quartz. The final product is the low expansion ceramic material, impregnated with staples, in which the ceramic material is a combination of mullite and glass (mullite - SA ^ O ^. SSiO ^).

In a muddy felted mixture, aluminosilicate fibers having a diameter of approximately 8 microns, a length of 0.31 cm and representing 98% by weight were mixed with 2% of aluminoborosilicate glass fibers also having a diameter of approximately 8 microns and a length of about 0.31 cm, these fibers being mixed with 450 parts of water for one part of solid material. This mixture was deposited by suction to form a porous ceramic felt which was compressed to a density of about 40%.

The compressed ceramic felt was sintered at 1593 ° C in air for about 4 hours; during this treatment, the glass fibers melted and reacted by binding the free quartz resulting in a combination of mullite plus glass; / the resulting structure had a thickness of approximately /?

0.31 cm and a density of 65%. This ceramic material was fixed to one of the faces of the ceramic composite element staples by means of a glass powder with low expansion such that, in% by weight: 80.5 of SiO ^ ï 12.9 of^Β2θ3 * θ of Na₂0? 2.2 of A1₂O₃; 0.4 K₂0; at the same time, the free surface of the metal fiber fabric was spot-welded using Nicrobraz LM (registered trademark of the Wall Colomony Company) on the other side of the ceramic-staples composite element by placing the elements in a oven for 10 min at 1176 ° C under an argon atmosphere. The composite element finally formed was subjected to a thermal cycle according to which it was heated to 982 ° C and cooled to room temperature. At the end of a period of 30 cycles, the ceramic material had not been cracked and the interface had retained its structural integrity.

EXAMPLE III.

In accordance with the teaching of the USA patent

No 3.127.668, a fabric made of 12.7.10 cm threads.

alloy of PeCrAISi (Hoskins-875) twisted to 1.27 cm was sintered for 9 hours in a vacuum oven at 10 Hg and at a temperature of 1190 ° C. The fabric produced had a density of about 30 30 A high temperature alloy metal base, cobalt based, was brazed to the sintered fabric by subjecting the fabric, the brazing alloy and the metal base to a temperature of 1176 ° C in a vacuum oven for 10 minutes. A mixture of zirconia stabilized with calcium oxide or yttria and graphite powders (70-30% by volume, respectively) was sprayed with a plasma jet on the free surface of the fabric. The pulverized composite element was then subjected to a temperature of 926 ° C for 15 hours, under an air atmosphere. The burnt sample had a ceramic layer which was substantially more porous than that sprayed with zirconia without graphite as described in / Example 1. A second fixed tissue was coated with a plasma jet, first with a layer of zirconia stabilized by means of calcium oxide or pure yttria and then, without interruption, with a mixture of 70% by volume. of zirconia stabilized using calcium oxide or yttria and 30% by volume of graphite. After the graphite burned, it was evident that the layer close to the fabric had a higher density and was # ei&gt; tonsequence, more resistant than the outer layer containing graphite. The density as well as the resistance can be adjusted by dosing the volume fraction of the graphite or of another sacrificed material.

Examples I, II and III correspond to three of the embodiments described. It is understood that those skilled in the art understand that it is possible to modify the composition of the ceramic material, and to substitute different metal alloys both for the base and for the metal interface. It is understood that the invention presents a very effective method for absorbing thermal deformations in a laminated ceramic-metal structure by providing an interface consisting of a metallic fibrous mattress, elastic, with low modulus and low density, this interface being fixed. with metal base and ceramic.

I

The products according to the present invention can find other technically advantageous applications in the shields of gas turbines, the chambers of burners, the end walls of blades, in reactors and magneto-hydrodynamic generators, fusion reactors nuclear, and coatings for pistons and cylinders in diesel and gasoline engines.

It should be understood that the invention is not limited to the embodiments described and that many _zvariants can be made without departing from the scope of this patent.