CA1117147A - Porous ceramic seals - Google Patents
Porous ceramic sealsInfo
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- CA1117147A CA1117147A CA000375153A CA375153A CA1117147A CA 1117147 A CA1117147 A CA 1117147A CA 000375153 A CA000375153 A CA 000375153A CA 375153 A CA375153 A CA 375153A CA 1117147 A CA1117147 A CA 1117147A
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Abstract
POROUS CERAMIC SEALS
ABSTRACT OF THE DISCLOSURE
A ceramic-metal composite laminate capable of exposure to high temperature differentials without damage, consisting of an inner ceramic layer, an outer metal layer and an inter-mediate interface layer of a low modulus metallic low density structure having a high melting point. The ceramic layer is secured to the low modulus structure directly or through an intermediate ceramic-metal composite, and the outer metal layer is brazed to the intermediate low modulus layer. Thermal strains caused by a temperature differential between the inner and outer layers are taken up without harmful effect by the intermediate low modulus layer.
ABSTRACT OF THE DISCLOSURE
A ceramic-metal composite laminate capable of exposure to high temperature differentials without damage, consisting of an inner ceramic layer, an outer metal layer and an inter-mediate interface layer of a low modulus metallic low density structure having a high melting point. The ceramic layer is secured to the low modulus structure directly or through an intermediate ceramic-metal composite, and the outer metal layer is brazed to the intermediate low modulus layer. Thermal strains caused by a temperature differential between the inner and outer layers are taken up without harmful effect by the intermediate low modulus layer.
Description
Thls applic~tion i5 c~ clivi~ion Oe Canadian Serial No. 272,409, fiLe~l Febru~ry 23, 1977.
Field of the Invention This inven-tion relates to eer~nic-metal laminates, and more par-ticu~arly, to the method for making a laminate o~ this type which enable~ thermal strains to be taken up without harmful effect.~3 and to the artiele produced by the method. ~his application is related ~n disclosed subject matter to applicant's co-pending applieation Serial No. 271,228 filed February 7, 1977.
Description of Prior Art A number of methods are known in the prior art for joining a metal member to a ceramic section. For example, U. S. Patent 2,996,401 shows a method for use 15 in electron tube manufacture where the surface o the ceramic body is metallized with refractory metals and the metal member is then brazed to the metallized coating.
Another example, U.S. Patent 3,114,612, shows a ceramic laminate useful for high tem~erature ap~lications where the ceramic is coated with a metallic bonding medium and welded to a corrugated stainless steel sheet.
While these prior art methods are satisfactory in uses for which they were designed, in high temperature operation under oxidizing conditions and mechanical stress, such as encountered in gas turbine engines, the required laminates must have the ability to withstand the substantial strains due, in part, to extreme differences in amounts of thermal expansion which are created during turblne's operation and in part due ~o the thermal gradients across them~
The prior art items tend to be anisotropic in their ability l-o ah sorb thermal strains~and there is a need for an attachment method that will respond to thermal strains elastically at moderately low stress levels in all directions.
4'-~.
~I~IAI~Y 01' TI~T, IN~ ;N'I'ION
Direct joining of ceramic rnaterials to metallic materials is presently limited to materials llaving small differences in coefficient of thermal expansion (0.5 x 10-6 in/in/~) and in the gcometry of the structure (the ceramic material must remain in com~ression). Dif~erences in co-efficient of thermal expansion (~) can be minimized by using a technique l~here materials witll closely matched ~ 's are provided adjaccnt to eacll other forming a gradient of ceramic (~c)~ cermets (d~ n, wllerein the cermets are mixtures of powdered metals and ceramics vary-ing in density such that Witll suficient thickness there can be an infinite number of layers, each having a slightly different ~) and metal depicted thusly:
lS ~c ¦ 1 ¦ 2 ~ 3 ¦ m ceramic I I I metal 1 ~ 2 ~ 3 < m Unfortunately, this technique is severely limited to low temperature use because of the te~ )erature limits im-posed by: (1) relatively low oxidation resistance of lowtllermal expansion alloys, (2) wide diversities of expansions at elevated temperatures of the metal, cermets and ceramic materials, and (3) stresses in the ceramic caused by thermal gradient.
The (levelopmellt of hlgh tem~erature abradable gas path seals for use in turbine engines has necessitated the development of a metllod for making a ceramic-metal laminate which is not limite~ by ~ifferences in expansion rates or lack of oxidation resistance.
~ 2 --In s-lch high -thermal yradient conditions where the surface of the ceramic experiences temperatures of 1000F to 3000F and there Ls a temperature yradient across ~he ceramic, the hot surface e~pands greater than the cooler surface. Lf this expansion is constrained as in the ceramic-cermet-metal laminate excessive stresses are built up in the ceraJniC material causing failure by thermally cracking. Thus, this laminate is not acceptable where thermal gradients in e~cess of 500F to 1000F occur. For example, when the ceramic is alumina and the metal is a Ni-Al alloy, then a temperature gradient of 500~F
in such a structure would not perform properly.
Accordingly, the present invention comprises a ceramic layer; a three dimensional, flexible, resilient, low modulus, low density, metallic structural interface secured to the ceramic layer; and a metal member fastened to the low modulus metallic structure. Thermal strains caused by differences in the coefficients of thermal expansion of the metal member and ceramic are absorbed by the low modulus material interface which has sufficient tensile strength, resistance to oxidation at high temperatures and resilient flexibility.
The principal object of this invention is to provide a ceramic-metal lamlnate which can be used in high temperature applications, especially seals for blades in gas turbine engines.
That object is attained by the invention which con-templàtes a ceramic mixture of mullite fibers and a low expansion reactive glass, the mixture consisting of from 70 to 99% by volume of mullite fibers and from 1 to 30% by volume of glass, and the mixture being such that upon heating, the glass reacts and bonds with thè mullite fibers a-t a temperature below the decomposition temperature of the fibers.
t~q Another object o this inventi.on :Ls to provide ceramic-rnetal laminate, such as the seals for blades in a gas turbine engine, wherein -the ceramic layer is porous, thereby abrading easier than substantially solid ceramic material.
In a further embodiment, the invention contempla-tes a ceramic mixture which comprises fibers of an aluminosilicate containing (by weigh-t) 35 - 55~ SiO2 and 45 - 65~ A1203, and particles or fibers of a low expansion glass. The fibers and particles have a maximum size of 80 microns, and the mixture being such that, when it is sintered, free quartz is released and the glass forms a matrix around the free quartz and the aluminosilicate fibers.
Those objects are also attained by the invention which contemplates a ceramic material made of a particle mixture of a first material having a composition of 35 - 55% SiO2 +
45 - 65~ A1203 and up to 2~ a second material having a composi-tion of borosilicate glass, with each of the particles of the~
components having a size range up to 80 microns, wherein upon sintering the first and second component materials, free quartz is released and the material forms a structure having muilite fibers surrounded by a matrix of said glass containing dissolved quartz. Those ceramic materials, formed by sintering a mixture of a'luminosi'l'icate and glass to cause the glass to react and bond with the aluminosilicate at a temperature below the decomposition temperature of the aluminosillcate, are usable in a high temperature range from about 1800F to 3000F dependin~
upon th^ eresion and loading envi:onments.
Yet another o~ect of -this invention is a method for making SUCil a ceramic-metal compos:ite which comprises the steps of providing a metal plate and a metal pad having a densi-ty of ranying from 5 to 80%, bonding the pad to the metal plate, ancl plasma spraying on ~he exposed surface of the metal pad a mixture of iner-t ceramic material and a sacrificial material where the volume fraction o the sacriflcial material is increased from zero percent to sixty percent at convenient intervals to effect strength and porosity required. Tlle inert ceramic material is selected from one or more of the following: stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicon nitride, alumina, mullite, borides, silicides, and cermets. The sacrificial material is removed by a chemical reaction such as oxidation or leaching.
The sacrificial material is selected from one or more of the following: graphite, plastic, aluminum, copper and sawdust.
~l~1.1 71L~7 Yet another object of this invention is to provide an attachment interface between ceramics and metals operating cyclically to extreme temperatures (either high or low) ~rom ambient wi-th high temperature yra~ients across them which is essentially isotropic with regard to its resiliency and low modulus charac-teristics.
Yet ano-ther object of this invention is to provide an a-ttachment interface between ceramics and metals operating with high ternperature gradients between them that has a low thermal conductivity -to minimize heat losses.
The invention also contempla-tes a method of making a three layer ceramic-metal composite which comprises the steps of providing a resilient metallic layer with a densi-ty range of from about 5 to 80~ having two surfaces, and also providing an inert ceramic layer having a controlled porosity and a con-trolled strength by plasma spraying on one of the surfaces of the layer a mixture of a ceramic material and a sacri~icial material where the volume fraction of the sacrificial material is increased from zero~percent to sixty percent at convenient intervals to effect strength and porosity required. The inert ceramic layer is selected from one or more of the following:
stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicon nitride, alumina, mullite, borides, silicides, and cermets. The sacrificial material is removed by a chemical reaction such as oxidation or leaching. A plate of metal is ~also provided, and the exposed surface of the low modulus layer without the ceramic material is bonded to the metal plate to form a composite.
Further objects will become apparent from the following detailed description of the invention.
-~6---~ ID 4508-T
BRIl.I DlS(RIr'r_ N or T~IE DR~WINCS
Flgure 1 is a sectional view of the primary embodiment of this inventioll depictin~ the ccramic-resilient interface-metal composite.
Figure 2 ls anothcr sectional view of the invention.
Figure 3 is a sectiolla] view of anothcr em-bodiment of the inventioll.
Figure 4 is an enlarged sectional view of a facet of tlle invention.
Figure 5 is an enlarged sectional view of an-otller facet of the invention.
Figure 6 is a sectional view of an intermediate product of one of the embodiments of the invention.
Figure 7 is a photo-macrograph of the primary embodiment at a lSX magnification.
DESCRIPTION OF THE INVENTION
In the embodiment shown in Figure 1, a cross section view of an abradable high temperature seal 100 for a gas turbine enginc is shown. Cerami~c member 1 may be made of high temperature ceramics such as alumina, stabilized cubic zirconi magnesia, zircon (ZrO2 SiO2) fosterite (2MgO-SiO2), mullite, mullite ~ quartz, aluminum di-boride, calcia, yttria, glass, silicon carbide, silicon nitride, alumino-borosilicate, etc., -25 that have any desired thickness and degree o porositY such as needed for high temperature abradable seals.
-~ 1) 4508-T
Thc CCl'alll:iC rncml)cr l has a very low coefficient of therlnal eXpallSiOIl generally in the range o~ about lx10-6 to 8xlO G inclles per .inch per cle~ree F. Conversely, the metal basc 3, that the ceramic member 1 is ultimately joined to, has a s very high coefficient of thermal~expansion in the range of about 2x1~-6 to 20xlO G inch per inch per degree F. In the environment of a gas turbine engine, where the outer sur-~ace of the ceramic member 1 is subjected to temperatllres in the neighborlloo~l of 1800-3600~, while the exl)osed surfaco of the metial is subjected -to a tem~crature rangc of only several hull~red deFrees I., a dircc~. joining of the two would cause immediate rupture of the ceramic due to the difference .in coefficients of e~pansion and to the effect of the temperature gradient through the thickness of the ceramic.
Thus, in this invention and the primary embodiment of this `inven tion, a resilient, low modulus, elastic interface 2 is secured t~
both the ceramic member 1 and the metal base 3 absorbing geometriC
differences caused by the variations in thermal expansion of the -two materials and by the temperature gradient.
20 The interface Z comprises a tllree dimensional, flexible, resilient, low modulus, low density, porous, hi~h melting point metallic fiber web or mat structure such as described in detail in U. S. Patent No. 3,46'~,297; 3,505,038;
or 3,127,668. Typical alloys used for the fibers of this interface are sold under the trademarks of Hastelloy X, Hoskins 875, Haynes 188, DH Z42, as well as the nickel base super alloys and the quadrinary and quintinary alloys of iron, cobalt, nickel, chromium, aluminum and yttrium (or 7~7 the rarc earths). Dcsiralily, the porous wcb or mat structure has a clerlsity of approximatcly 35%, although depending upon the particular a[~plication the web corn prising the interf~lce 2 can have a density varying any-where frorn 5 to 80%. It will be apparent tha~ the exactalloy employed in m~lkin~ the mat will be dictated by the temperatureJ oxidat:ion, and strcss conditions to bo en-countered in thc u~timate use.
One Inetllc)d o~ maki.ng the em~odirnent shown in Figure 1 is to~raze a web interface 2 to the metal base 3 as shown at 20. The ceramic layer 1 is formed by plasma spraying the ceramic material onto the exposed face of the interface 2 wherein the ceramic material im-pregnates into the surface of the web interface 2 bonding the ceramic mechanically to the fibers of the intcrface 2.
Subsequently, additional plasma spraying o-f the ceramic will provide the desired thickness of the ceramic layer 1.
The product thus produced is a ceramic-metal composite having a resilient interface so ~hat when the metallic member expands due to thermal expansion a much greater ~; amount than the expansion of the ceramic material, the interface can absorb the different amounts of thermal expansions of the two materials. I`hus, a composite is : provided where there i:s a high degree of thermal expan-sion mismatched between the ceramic 1 and the adjoining metal 3, blt able to remaln in~act over extreme thermal cy~lings , :' , ~ 7~7 rl~ ~508-1 because of the ability of the metal web irlterface 2 to ab-sorb thc differenti.ll cxpansion and the resulting thermal strain In ligurc Z, tllele is an enlarged view of the basic embodimellt as shol~n in ~igure 1, wherein the metal S fibers 4 of thc wel) interface 2a are shown to protrude into the ceramic surface up to approximatcly 1/4 the thick-ness of the ceramic material la whlle the other surface of the interface 2a is brazed at 20a to the metal plate 3a. Here, the ceramic layer la has embedded into its surface the metal felte~ mat interface 2a. The ceramic and metal alloy must be so selected so as to minimize the chemical reaction between the metal fibers of the in-terface and the ceramic thereby providing primarily mechanical bonding between the two. The ceramic-metal interface compositc portion may be formed by pressing the metal felt interface into a plastic mass o the ceramic material for a distance sufficient to insure a mechanical bond of sufficient strength; this being another method of joining the ceramic and the interface. As men-tioned above, about 1/4 of the thickness of the ceramiclayer la would be sufficient to have the interface 2a em-bedded therein; however, this can be varied as may be re-quired by the design. After the mat is embedded into the plastic ceramlc, the thus formed composite Z5 is dried and fired. As =entioned earlier, the web .
interface can be attachecl to the metal base first or may be attached to the me~al base after the ceramic has been joined to the interface, as desired.
In another embodiment of the invention, ap-proxirnately 3/8ths of an inch U-shaped card wire staples are secured to a fabric base and forced therethrough in a generally upright position. A ceramic-water slurring mixture of ceramic fibers and/or powders is deposited on the fabric and confined within the area of the metal 1~ staples. This initial material is then sintered in a furnace in order to react~the ceramic slurry to form the desired ceramic material and at the same time mechanically incapsulate the wire staples. As shown in Figure 6, the fabric 14a has wire staples 13a which are imbedded in the ceramic material 12a thereby defining a ceramic-wire layer lla. ~Yhen the ceramic is fired in the furnace, the fabric layer 14a disintegrates, leaving the staples 13a imbedded in the ceramic 12a. The protruding staples of the layer 13a may,be bent flat on both surfaces for con~enience. As with the metal fiber web interface material, chemical reaction between the wire staples and the ceramic material must be minimized, otherwise stresses resulting from the mismatch of the coefficients of expansion [~ 's) would cause cracking of the material. Chemi cal reaction between the metal and the composite would resul ~ f~7 ID 4508-T
in a strong bon(l bet~Yeell ~hem which would promo-te degrada-tion in the ceramic arld metal interacial area and minimize movement of the two.
As seen in Figure 3, this ceramic layer with S staples lla therein is secured to a purely ceramic layer lb by glass fri~ 23b by placing tlle tlYO in a furnace at elevated temperatures for a short period o~ time.
metal base 3b is brazed as shown at 20b to a porous web interface 2b. The ceramic laminate with th~ exposed staples is then spot bra~ed to the web interface 2b at lOb.
Since the fibers of the interface 2b arc not 100~ dense, and since obviously the staples 13a of thc ceramic layer are not 100% dense, the brazing of thc two may be 100%, but the total area of the metal will not be greater than the metal density of the smallest metal material. This type of composite also exhibits the same characteristics and desirability as the basic embodiment shown in Figure 1.
It should be noted that in Figures 4 and 5 the geometric bond between the ceramic 1 and the fibers 4 of ~ 20 the interface 2 or the staples 13a promote a mechanical ; bond. This particular characteristic is extremely im-portant for the operation of this material.
Besides being made from the metals listed for ; ~ the interface, the staple 13a may also be made from .~
~ ~ 8~-~6 ID ~508-T
mateILals su~ lS I~La(illulll, tullgxten, molybdenum and the like cleperlding upon ~he envilonment. Ihe cerarnic materials used in this invention are those commercially found avail-able as higil tealperatUrC ceramics as well as the unexpected materials found by me and described hereinafter.
In the use of ceramic materials for high tem-perature seals and gas turbines, and especially where the seals are abraded such as taug}lt by the prior art, for example in U. S. Patent No. 3,880,550) a sintered product of an alumino silicate ceramic consisting of mullite plus quartz as a high temperature material and insulation (above 2600F) is very limited. The free quartz present in the available fibers (known by the trade marks of Fiberfrax and Kaowool) becomes brittle because the fused quartz devitrifies and converts to cristobalite when exposed to temperatures of 1800F and over. It has been found that by using a mixture of alumino-silicate fibers and low expansion glass fibers or powders, which is subsequently sintered, a ceramic material may be formed to operate at temperatures in the range of 2200-3000F (an increase of well over 400F for known Fiberfrax).
In sintering the mixture, the glass surrounds the alumino-silicate and at the same time ~lissolves any free quartz and results in a mixture of mullite and glass. This new ceramic has been employed as one of the porous materials , , ~.
.
, ~ 7 ID ~5~)8-l' usecl for the ceralllic portion of the composite material taught herein. Quite surl)risingly, this rnaterial was found to exhibit excellent high temperature characteristics. In using a standar~
alumino-silicate, typically 35-55~ SiO2 and 45-65~ A12O3 at temperatures above 1800F ti~e fused quart2 also devi-trifies and forllls cristobalite which severly imbrittles the fibers and weakens the general product. By the addition of fibrous or powdered glass to the aluminum silicate the glass reacts with the quart~ to orm a new glass that will not devitrify.
Three types of fiber forming materials hclving different temperature ranges that, when subject to this glass powder-fiber technique, produce a much better ceramic are alumino-silicate, alumina, and zirconia.
The cobalt-base super alloy base 3 is shown in Figure 7; a macrophotograph at 15X. The metal web 2 is about 20% dense, made from Hoskins 875 alloy and brazed to the base 3. A ceramic layer 1 was plasma sprayed on the web and embedded therein as may be seen in the macro-photograph. The ceramic layer 1 was composed of CaO, 4% by weight and ZrO2 - 96% by weight.
The following specific embodiments of the ceramic-interface-metal composites made in accordance with this invention should not be construed in any way to limit the scope contemplated by this invention.
According to ~he teachings of U. S. Patent No.
3,127,668 a felt web made from one-half inch kinked 5 mil ~ 17~7 ID 4508~
wire of FeCIAlSi (lloskins^875) rnetal al]oy was sintered for 15 hOUl`S in a ~lrnace vacuurn of 10-5 torr and at a tcmperature of 2175l;. The web produced had an approx-imate 30~ density, A metal base of a high temperature cobalt base alloy was brazecl to the sintered web by exposing the web an, the base metal to 2150F in a vacuum furnace for about 10 minutes. The zirconia, in atrnosphere, was plazma sprayed onto the exposed web surface impregnating the web at least 10 mils, and qui~e surl)rising]y, the zirconia was then -10 built up to forrll a zirconia layer of about 100 mils (layers of as much as ]/4 inch zirconia have been achieved by me by this method). The formed composite was thermally cycled wllerein the zirconia face was subjected to 2900F and the metal base was exposed to air at ambient temperature over a series of cycles without any appreciable separation of the ceramic zirconia from the metal.
EXAMPLE II
According to the teachin~s of U. S. Patent No.
3,127,668 a felt web made from one-half inch kinked 4 mil wire of Hastelloy X metal alloy was sintered for 10 hours in a furnace vacuum of 10-5 torr and at a tem-perature of 2175F. The web produced had an approximate 20% density. ~ metal base of Hastelloy X alloy was brazed to the sintered web by exposing the web and the base metal to 2150 in a ~acuum furnace for about 10 minutes. A
ceramic composite of ceramic ma~erial and staple card wires was prepared by providing a bed of upstanding 12 mil thick staple wires having a 3/8 inch U-shape projecting through 1'71~7 a pO2'0US fabric ba.se thlt llolcls the staples in a semi-upright position. ~ a~er based slurry forlned o alumino-silicate minercll fil)ers having cliameters ranging from 8 microns to 80 microlls were mixed with a low expansion glass S powder (the powder ~laving a size wherc it will pass throu~h a 325 mesh screen the powciers having a diarneter up to 44 micons); the slurry having a composition of 50% aluminum silicate and 50% glass by weight mixed with 50% by volume water. The slurry was deposited on tlle fabric over and surrounding the upright metal staples and hel~ in place by an extermal hol~ling container. This slurry-staple composite was sintered at 2200F for 2 hours in a furnace pur~cd with argon to permit the gl~ss to melt reacting with the alumino-silicate and at the same time form a matrix around the alumino-silicate to eliminate any free quartz -- the final product is the staple impregnated low expansion ceramic wherein the ceramic is mullite and glass combination (mullite -3A1203- 2sio2) -In a felted slurry mixture, alumino-sllicate fibers having a ~iameter of approximately 8 microns and a length of 1/8 of an inch and constituting 98~o by weight were combined with 2% alumino~borosilicate glass fibers also having a dlameter of approximately 8 microns and a length of about 1/8 of an inch, and mixed together with 450 parts of water to one part of solid. This mixture was suctioned deposited to form a porous ceramic felt that was compressed to about 40% density. The densified ceramic -16- ~
Eelt was sintered a~ 2900F in an air atmosphere for ahouk 4 hours wherein the glass fiber melted and reacted tying up the free quartz resultinq in a combination of mullite plus glass; the resulting structure being about 1/8 of an inch thick and 65% dense. This ceramic material was at-tached to one side of the stap]e ceramic composite by a low expansion glass powder such as, in wt. percent, 80.5 i 12 9 s O - 3.~ Na2O - 2-2 ~123 0. 2 the same time the free surface of the metal fiber web was spot brazed using Nicrobraz LM (trademark of Wall Colomony Company) to the other side of the staple-ceramic composite by placing in a Eurnace for 10 minutes at 2150F in an argon atmosphere. The finally formed composite was thermally cycled to 1800~F and cooled to ambient. At the end of a 30 15 cycle period the ceramic had not cracked and the interface had maintained its structural integrity.
Another low expansion glass powder which can be used is a composition such as (in weight percent) 67.0 SiO2 -27.4 BaO - 5.6 A12O3.
AMPLE III
:
According to the teachinqs of U. S. Patent No.
3,127,668, a web made from one half inch kinked 5 mil wire of FeCrAlSi (Hoskins-~75) metal alloy was sintered 9 hours in a furnace vacuum of 10 5 torr and at a temperature of 2175F. The web produced had an approximate density of 30%.
A metal base of high temperature cobalt base alloy was brazed to the sintered web by exposing the web, braze alloy, and base metal to 2150F in a vacuum furnace for 10 minutes. A
mixture of calcia stabilized zirconia and graphite powders (70 - 30 by volume, respectively) WclS plasma sprayed onto the exposed web surace. The sprayed composite was sub-sequently exposed to 1700F for 15 hrs in air. The burned-off sample had a ceramic layer which was noticeably more porous than graph:ite--free zirconia sprayed as described as example I. A second attached web was plasma sprayed coated with a layer of pure calcia stabilized zirconia and without stopping was then coated with a mixture of 70 vol. percent calcia stabilized zirconia and 30 vol. percent graphite.
After the graphi-te was burned off, it was obvious that the layer near the web was of higher density and, therefore, stronger than the outer layer which contained -the graphite.
Density, as well as streng-th, can be controlled by controlling the volume fraction of graphite or other sacrificial material.
The ceramic layer may be formed with a variable density and applied such as by plasma spxaying. During application the ceramic material contains both permanent and sacrificial material with the sacrificial material varying in amount from 0% to 60~. The inert ceramic material may be selected from one or more of the following materials: stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicon nitride, alumina, mullite, borides, silicides, and cermets, etc., but no-t limited thereto.
The sacrificial materlal may be selected from one or more of the following materials: graphite, plastic, aluminum, copper, and sawdust, etc., but not limited thereto. When this variable density ceramic is used as an abradable seal for turbine blades (in a gas turbine engine) it has been found that the lower density material will abrade easier than the higher density materials but still maintain the desired structural characteristics in the high temperature environment.
Examplcs I, II, and :CII correspond to three of the embodiments described herein. It is contemplated that those skilled in the art will thoroughly understand that it is possible to change the composition of the ceramic material, substitute differen-t metal alloys for both the metallic base and metal interface. It will be recognized that the inven-tion provides a very ef~ective method of ab~orbing thermal strains in a ceramic-metal laminate composition structure by providing a low modulous resilient, low density metal fiber mat inter~ace joined to the metal base and the ceramic.
Other technically significant applications of the embodiments of this invention can include gas turbine shrouds, burner cans, vane end walls, magnetohydrodynamic generators, nuclear fusion reactors, and coatings for pistons and cylinders in diesel and gasoline engines.
Although specific embodiments of the invention have been described many modifications and changes may be made to the materials, configurations and methods of making the ceramic-metal composite without departing from the spirit ~20 and the scope of the invention as defined in the appended ~ claims.
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Field of the Invention This inven-tion relates to eer~nic-metal laminates, and more par-ticu~arly, to the method for making a laminate o~ this type which enable~ thermal strains to be taken up without harmful effect.~3 and to the artiele produced by the method. ~his application is related ~n disclosed subject matter to applicant's co-pending applieation Serial No. 271,228 filed February 7, 1977.
Description of Prior Art A number of methods are known in the prior art for joining a metal member to a ceramic section. For example, U. S. Patent 2,996,401 shows a method for use 15 in electron tube manufacture where the surface o the ceramic body is metallized with refractory metals and the metal member is then brazed to the metallized coating.
Another example, U.S. Patent 3,114,612, shows a ceramic laminate useful for high tem~erature ap~lications where the ceramic is coated with a metallic bonding medium and welded to a corrugated stainless steel sheet.
While these prior art methods are satisfactory in uses for which they were designed, in high temperature operation under oxidizing conditions and mechanical stress, such as encountered in gas turbine engines, the required laminates must have the ability to withstand the substantial strains due, in part, to extreme differences in amounts of thermal expansion which are created during turblne's operation and in part due ~o the thermal gradients across them~
The prior art items tend to be anisotropic in their ability l-o ah sorb thermal strains~and there is a need for an attachment method that will respond to thermal strains elastically at moderately low stress levels in all directions.
4'-~.
~I~IAI~Y 01' TI~T, IN~ ;N'I'ION
Direct joining of ceramic rnaterials to metallic materials is presently limited to materials llaving small differences in coefficient of thermal expansion (0.5 x 10-6 in/in/~) and in the gcometry of the structure (the ceramic material must remain in com~ression). Dif~erences in co-efficient of thermal expansion (~) can be minimized by using a technique l~here materials witll closely matched ~ 's are provided adjaccnt to eacll other forming a gradient of ceramic (~c)~ cermets (d~ n, wllerein the cermets are mixtures of powdered metals and ceramics vary-ing in density such that Witll suficient thickness there can be an infinite number of layers, each having a slightly different ~) and metal depicted thusly:
lS ~c ¦ 1 ¦ 2 ~ 3 ¦ m ceramic I I I metal 1 ~ 2 ~ 3 < m Unfortunately, this technique is severely limited to low temperature use because of the te~ )erature limits im-posed by: (1) relatively low oxidation resistance of lowtllermal expansion alloys, (2) wide diversities of expansions at elevated temperatures of the metal, cermets and ceramic materials, and (3) stresses in the ceramic caused by thermal gradient.
The (levelopmellt of hlgh tem~erature abradable gas path seals for use in turbine engines has necessitated the development of a metllod for making a ceramic-metal laminate which is not limite~ by ~ifferences in expansion rates or lack of oxidation resistance.
~ 2 --In s-lch high -thermal yradient conditions where the surface of the ceramic experiences temperatures of 1000F to 3000F and there Ls a temperature yradient across ~he ceramic, the hot surface e~pands greater than the cooler surface. Lf this expansion is constrained as in the ceramic-cermet-metal laminate excessive stresses are built up in the ceraJniC material causing failure by thermally cracking. Thus, this laminate is not acceptable where thermal gradients in e~cess of 500F to 1000F occur. For example, when the ceramic is alumina and the metal is a Ni-Al alloy, then a temperature gradient of 500~F
in such a structure would not perform properly.
Accordingly, the present invention comprises a ceramic layer; a three dimensional, flexible, resilient, low modulus, low density, metallic structural interface secured to the ceramic layer; and a metal member fastened to the low modulus metallic structure. Thermal strains caused by differences in the coefficients of thermal expansion of the metal member and ceramic are absorbed by the low modulus material interface which has sufficient tensile strength, resistance to oxidation at high temperatures and resilient flexibility.
The principal object of this invention is to provide a ceramic-metal lamlnate which can be used in high temperature applications, especially seals for blades in gas turbine engines.
That object is attained by the invention which con-templàtes a ceramic mixture of mullite fibers and a low expansion reactive glass, the mixture consisting of from 70 to 99% by volume of mullite fibers and from 1 to 30% by volume of glass, and the mixture being such that upon heating, the glass reacts and bonds with thè mullite fibers a-t a temperature below the decomposition temperature of the fibers.
t~q Another object o this inventi.on :Ls to provide ceramic-rnetal laminate, such as the seals for blades in a gas turbine engine, wherein -the ceramic layer is porous, thereby abrading easier than substantially solid ceramic material.
In a further embodiment, the invention contempla-tes a ceramic mixture which comprises fibers of an aluminosilicate containing (by weigh-t) 35 - 55~ SiO2 and 45 - 65~ A1203, and particles or fibers of a low expansion glass. The fibers and particles have a maximum size of 80 microns, and the mixture being such that, when it is sintered, free quartz is released and the glass forms a matrix around the free quartz and the aluminosilicate fibers.
Those objects are also attained by the invention which contemplates a ceramic material made of a particle mixture of a first material having a composition of 35 - 55% SiO2 +
45 - 65~ A1203 and up to 2~ a second material having a composi-tion of borosilicate glass, with each of the particles of the~
components having a size range up to 80 microns, wherein upon sintering the first and second component materials, free quartz is released and the material forms a structure having muilite fibers surrounded by a matrix of said glass containing dissolved quartz. Those ceramic materials, formed by sintering a mixture of a'luminosi'l'icate and glass to cause the glass to react and bond with the aluminosilicate at a temperature below the decomposition temperature of the aluminosillcate, are usable in a high temperature range from about 1800F to 3000F dependin~
upon th^ eresion and loading envi:onments.
Yet another o~ect of -this invention is a method for making SUCil a ceramic-metal compos:ite which comprises the steps of providing a metal plate and a metal pad having a densi-ty of ranying from 5 to 80%, bonding the pad to the metal plate, ancl plasma spraying on ~he exposed surface of the metal pad a mixture of iner-t ceramic material and a sacrificial material where the volume fraction o the sacriflcial material is increased from zero percent to sixty percent at convenient intervals to effect strength and porosity required. Tlle inert ceramic material is selected from one or more of the following: stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicon nitride, alumina, mullite, borides, silicides, and cermets. The sacrificial material is removed by a chemical reaction such as oxidation or leaching.
The sacrificial material is selected from one or more of the following: graphite, plastic, aluminum, copper and sawdust.
~l~1.1 71L~7 Yet another object of this invention is to provide an attachment interface between ceramics and metals operating cyclically to extreme temperatures (either high or low) ~rom ambient wi-th high temperature yra~ients across them which is essentially isotropic with regard to its resiliency and low modulus charac-teristics.
Yet ano-ther object of this invention is to provide an a-ttachment interface between ceramics and metals operating with high ternperature gradients between them that has a low thermal conductivity -to minimize heat losses.
The invention also contempla-tes a method of making a three layer ceramic-metal composite which comprises the steps of providing a resilient metallic layer with a densi-ty range of from about 5 to 80~ having two surfaces, and also providing an inert ceramic layer having a controlled porosity and a con-trolled strength by plasma spraying on one of the surfaces of the layer a mixture of a ceramic material and a sacri~icial material where the volume fraction of the sacrificial material is increased from zero~percent to sixty percent at convenient intervals to effect strength and porosity required. The inert ceramic layer is selected from one or more of the following:
stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicon nitride, alumina, mullite, borides, silicides, and cermets. The sacrificial material is removed by a chemical reaction such as oxidation or leaching. A plate of metal is ~also provided, and the exposed surface of the low modulus layer without the ceramic material is bonded to the metal plate to form a composite.
Further objects will become apparent from the following detailed description of the invention.
-~6---~ ID 4508-T
BRIl.I DlS(RIr'r_ N or T~IE DR~WINCS
Flgure 1 is a sectional view of the primary embodiment of this inventioll depictin~ the ccramic-resilient interface-metal composite.
Figure 2 ls anothcr sectional view of the invention.
Figure 3 is a sectiolla] view of anothcr em-bodiment of the inventioll.
Figure 4 is an enlarged sectional view of a facet of tlle invention.
Figure 5 is an enlarged sectional view of an-otller facet of the invention.
Figure 6 is a sectional view of an intermediate product of one of the embodiments of the invention.
Figure 7 is a photo-macrograph of the primary embodiment at a lSX magnification.
DESCRIPTION OF THE INVENTION
In the embodiment shown in Figure 1, a cross section view of an abradable high temperature seal 100 for a gas turbine enginc is shown. Cerami~c member 1 may be made of high temperature ceramics such as alumina, stabilized cubic zirconi magnesia, zircon (ZrO2 SiO2) fosterite (2MgO-SiO2), mullite, mullite ~ quartz, aluminum di-boride, calcia, yttria, glass, silicon carbide, silicon nitride, alumino-borosilicate, etc., -25 that have any desired thickness and degree o porositY such as needed for high temperature abradable seals.
-~ 1) 4508-T
Thc CCl'alll:iC rncml)cr l has a very low coefficient of therlnal eXpallSiOIl generally in the range o~ about lx10-6 to 8xlO G inclles per .inch per cle~ree F. Conversely, the metal basc 3, that the ceramic member 1 is ultimately joined to, has a s very high coefficient of thermal~expansion in the range of about 2x1~-6 to 20xlO G inch per inch per degree F. In the environment of a gas turbine engine, where the outer sur-~ace of the ceramic member 1 is subjected to temperatllres in the neighborlloo~l of 1800-3600~, while the exl)osed surfaco of the metial is subjected -to a tem~crature rangc of only several hull~red deFrees I., a dircc~. joining of the two would cause immediate rupture of the ceramic due to the difference .in coefficients of e~pansion and to the effect of the temperature gradient through the thickness of the ceramic.
Thus, in this invention and the primary embodiment of this `inven tion, a resilient, low modulus, elastic interface 2 is secured t~
both the ceramic member 1 and the metal base 3 absorbing geometriC
differences caused by the variations in thermal expansion of the -two materials and by the temperature gradient.
20 The interface Z comprises a tllree dimensional, flexible, resilient, low modulus, low density, porous, hi~h melting point metallic fiber web or mat structure such as described in detail in U. S. Patent No. 3,46'~,297; 3,505,038;
or 3,127,668. Typical alloys used for the fibers of this interface are sold under the trademarks of Hastelloy X, Hoskins 875, Haynes 188, DH Z42, as well as the nickel base super alloys and the quadrinary and quintinary alloys of iron, cobalt, nickel, chromium, aluminum and yttrium (or 7~7 the rarc earths). Dcsiralily, the porous wcb or mat structure has a clerlsity of approximatcly 35%, although depending upon the particular a[~plication the web corn prising the interf~lce 2 can have a density varying any-where frorn 5 to 80%. It will be apparent tha~ the exactalloy employed in m~lkin~ the mat will be dictated by the temperatureJ oxidat:ion, and strcss conditions to bo en-countered in thc u~timate use.
One Inetllc)d o~ maki.ng the em~odirnent shown in Figure 1 is to~raze a web interface 2 to the metal base 3 as shown at 20. The ceramic layer 1 is formed by plasma spraying the ceramic material onto the exposed face of the interface 2 wherein the ceramic material im-pregnates into the surface of the web interface 2 bonding the ceramic mechanically to the fibers of the intcrface 2.
Subsequently, additional plasma spraying o-f the ceramic will provide the desired thickness of the ceramic layer 1.
The product thus produced is a ceramic-metal composite having a resilient interface so ~hat when the metallic member expands due to thermal expansion a much greater ~; amount than the expansion of the ceramic material, the interface can absorb the different amounts of thermal expansions of the two materials. I`hus, a composite is : provided where there i:s a high degree of thermal expan-sion mismatched between the ceramic 1 and the adjoining metal 3, blt able to remaln in~act over extreme thermal cy~lings , :' , ~ 7~7 rl~ ~508-1 because of the ability of the metal web irlterface 2 to ab-sorb thc differenti.ll cxpansion and the resulting thermal strain In ligurc Z, tllele is an enlarged view of the basic embodimellt as shol~n in ~igure 1, wherein the metal S fibers 4 of thc wel) interface 2a are shown to protrude into the ceramic surface up to approximatcly 1/4 the thick-ness of the ceramic material la whlle the other surface of the interface 2a is brazed at 20a to the metal plate 3a. Here, the ceramic layer la has embedded into its surface the metal felte~ mat interface 2a. The ceramic and metal alloy must be so selected so as to minimize the chemical reaction between the metal fibers of the in-terface and the ceramic thereby providing primarily mechanical bonding between the two. The ceramic-metal interface compositc portion may be formed by pressing the metal felt interface into a plastic mass o the ceramic material for a distance sufficient to insure a mechanical bond of sufficient strength; this being another method of joining the ceramic and the interface. As men-tioned above, about 1/4 of the thickness of the ceramiclayer la would be sufficient to have the interface 2a em-bedded therein; however, this can be varied as may be re-quired by the design. After the mat is embedded into the plastic ceramlc, the thus formed composite Z5 is dried and fired. As =entioned earlier, the web .
interface can be attachecl to the metal base first or may be attached to the me~al base after the ceramic has been joined to the interface, as desired.
In another embodiment of the invention, ap-proxirnately 3/8ths of an inch U-shaped card wire staples are secured to a fabric base and forced therethrough in a generally upright position. A ceramic-water slurring mixture of ceramic fibers and/or powders is deposited on the fabric and confined within the area of the metal 1~ staples. This initial material is then sintered in a furnace in order to react~the ceramic slurry to form the desired ceramic material and at the same time mechanically incapsulate the wire staples. As shown in Figure 6, the fabric 14a has wire staples 13a which are imbedded in the ceramic material 12a thereby defining a ceramic-wire layer lla. ~Yhen the ceramic is fired in the furnace, the fabric layer 14a disintegrates, leaving the staples 13a imbedded in the ceramic 12a. The protruding staples of the layer 13a may,be bent flat on both surfaces for con~enience. As with the metal fiber web interface material, chemical reaction between the wire staples and the ceramic material must be minimized, otherwise stresses resulting from the mismatch of the coefficients of expansion [~ 's) would cause cracking of the material. Chemi cal reaction between the metal and the composite would resul ~ f~7 ID 4508-T
in a strong bon(l bet~Yeell ~hem which would promo-te degrada-tion in the ceramic arld metal interacial area and minimize movement of the two.
As seen in Figure 3, this ceramic layer with S staples lla therein is secured to a purely ceramic layer lb by glass fri~ 23b by placing tlle tlYO in a furnace at elevated temperatures for a short period o~ time.
metal base 3b is brazed as shown at 20b to a porous web interface 2b. The ceramic laminate with th~ exposed staples is then spot bra~ed to the web interface 2b at lOb.
Since the fibers of the interface 2b arc not 100~ dense, and since obviously the staples 13a of thc ceramic layer are not 100% dense, the brazing of thc two may be 100%, but the total area of the metal will not be greater than the metal density of the smallest metal material. This type of composite also exhibits the same characteristics and desirability as the basic embodiment shown in Figure 1.
It should be noted that in Figures 4 and 5 the geometric bond between the ceramic 1 and the fibers 4 of ~ 20 the interface 2 or the staples 13a promote a mechanical ; bond. This particular characteristic is extremely im-portant for the operation of this material.
Besides being made from the metals listed for ; ~ the interface, the staple 13a may also be made from .~
~ ~ 8~-~6 ID ~508-T
mateILals su~ lS I~La(illulll, tullgxten, molybdenum and the like cleperlding upon ~he envilonment. Ihe cerarnic materials used in this invention are those commercially found avail-able as higil tealperatUrC ceramics as well as the unexpected materials found by me and described hereinafter.
In the use of ceramic materials for high tem-perature seals and gas turbines, and especially where the seals are abraded such as taug}lt by the prior art, for example in U. S. Patent No. 3,880,550) a sintered product of an alumino silicate ceramic consisting of mullite plus quartz as a high temperature material and insulation (above 2600F) is very limited. The free quartz present in the available fibers (known by the trade marks of Fiberfrax and Kaowool) becomes brittle because the fused quartz devitrifies and converts to cristobalite when exposed to temperatures of 1800F and over. It has been found that by using a mixture of alumino-silicate fibers and low expansion glass fibers or powders, which is subsequently sintered, a ceramic material may be formed to operate at temperatures in the range of 2200-3000F (an increase of well over 400F for known Fiberfrax).
In sintering the mixture, the glass surrounds the alumino-silicate and at the same time ~lissolves any free quartz and results in a mixture of mullite and glass. This new ceramic has been employed as one of the porous materials , , ~.
.
, ~ 7 ID ~5~)8-l' usecl for the ceralllic portion of the composite material taught herein. Quite surl)risingly, this rnaterial was found to exhibit excellent high temperature characteristics. In using a standar~
alumino-silicate, typically 35-55~ SiO2 and 45-65~ A12O3 at temperatures above 1800F ti~e fused quart2 also devi-trifies and forllls cristobalite which severly imbrittles the fibers and weakens the general product. By the addition of fibrous or powdered glass to the aluminum silicate the glass reacts with the quart~ to orm a new glass that will not devitrify.
Three types of fiber forming materials hclving different temperature ranges that, when subject to this glass powder-fiber technique, produce a much better ceramic are alumino-silicate, alumina, and zirconia.
The cobalt-base super alloy base 3 is shown in Figure 7; a macrophotograph at 15X. The metal web 2 is about 20% dense, made from Hoskins 875 alloy and brazed to the base 3. A ceramic layer 1 was plasma sprayed on the web and embedded therein as may be seen in the macro-photograph. The ceramic layer 1 was composed of CaO, 4% by weight and ZrO2 - 96% by weight.
The following specific embodiments of the ceramic-interface-metal composites made in accordance with this invention should not be construed in any way to limit the scope contemplated by this invention.
According to ~he teachings of U. S. Patent No.
3,127,668 a felt web made from one-half inch kinked 5 mil ~ 17~7 ID 4508~
wire of FeCIAlSi (lloskins^875) rnetal al]oy was sintered for 15 hOUl`S in a ~lrnace vacuurn of 10-5 torr and at a tcmperature of 2175l;. The web produced had an approx-imate 30~ density, A metal base of a high temperature cobalt base alloy was brazecl to the sintered web by exposing the web an, the base metal to 2150F in a vacuum furnace for about 10 minutes. The zirconia, in atrnosphere, was plazma sprayed onto the exposed web surface impregnating the web at least 10 mils, and qui~e surl)rising]y, the zirconia was then -10 built up to forrll a zirconia layer of about 100 mils (layers of as much as ]/4 inch zirconia have been achieved by me by this method). The formed composite was thermally cycled wllerein the zirconia face was subjected to 2900F and the metal base was exposed to air at ambient temperature over a series of cycles without any appreciable separation of the ceramic zirconia from the metal.
EXAMPLE II
According to the teachin~s of U. S. Patent No.
3,127,668 a felt web made from one-half inch kinked 4 mil wire of Hastelloy X metal alloy was sintered for 10 hours in a furnace vacuum of 10-5 torr and at a tem-perature of 2175F. The web produced had an approximate 20% density. ~ metal base of Hastelloy X alloy was brazed to the sintered web by exposing the web and the base metal to 2150 in a ~acuum furnace for about 10 minutes. A
ceramic composite of ceramic ma~erial and staple card wires was prepared by providing a bed of upstanding 12 mil thick staple wires having a 3/8 inch U-shape projecting through 1'71~7 a pO2'0US fabric ba.se thlt llolcls the staples in a semi-upright position. ~ a~er based slurry forlned o alumino-silicate minercll fil)ers having cliameters ranging from 8 microns to 80 microlls were mixed with a low expansion glass S powder (the powder ~laving a size wherc it will pass throu~h a 325 mesh screen the powciers having a diarneter up to 44 micons); the slurry having a composition of 50% aluminum silicate and 50% glass by weight mixed with 50% by volume water. The slurry was deposited on tlle fabric over and surrounding the upright metal staples and hel~ in place by an extermal hol~ling container. This slurry-staple composite was sintered at 2200F for 2 hours in a furnace pur~cd with argon to permit the gl~ss to melt reacting with the alumino-silicate and at the same time form a matrix around the alumino-silicate to eliminate any free quartz -- the final product is the staple impregnated low expansion ceramic wherein the ceramic is mullite and glass combination (mullite -3A1203- 2sio2) -In a felted slurry mixture, alumino-sllicate fibers having a ~iameter of approximately 8 microns and a length of 1/8 of an inch and constituting 98~o by weight were combined with 2% alumino~borosilicate glass fibers also having a dlameter of approximately 8 microns and a length of about 1/8 of an inch, and mixed together with 450 parts of water to one part of solid. This mixture was suctioned deposited to form a porous ceramic felt that was compressed to about 40% density. The densified ceramic -16- ~
Eelt was sintered a~ 2900F in an air atmosphere for ahouk 4 hours wherein the glass fiber melted and reacted tying up the free quartz resultinq in a combination of mullite plus glass; the resulting structure being about 1/8 of an inch thick and 65% dense. This ceramic material was at-tached to one side of the stap]e ceramic composite by a low expansion glass powder such as, in wt. percent, 80.5 i 12 9 s O - 3.~ Na2O - 2-2 ~123 0. 2 the same time the free surface of the metal fiber web was spot brazed using Nicrobraz LM (trademark of Wall Colomony Company) to the other side of the staple-ceramic composite by placing in a Eurnace for 10 minutes at 2150F in an argon atmosphere. The finally formed composite was thermally cycled to 1800~F and cooled to ambient. At the end of a 30 15 cycle period the ceramic had not cracked and the interface had maintained its structural integrity.
Another low expansion glass powder which can be used is a composition such as (in weight percent) 67.0 SiO2 -27.4 BaO - 5.6 A12O3.
AMPLE III
:
According to the teachinqs of U. S. Patent No.
3,127,668, a web made from one half inch kinked 5 mil wire of FeCrAlSi (Hoskins-~75) metal alloy was sintered 9 hours in a furnace vacuum of 10 5 torr and at a temperature of 2175F. The web produced had an approximate density of 30%.
A metal base of high temperature cobalt base alloy was brazed to the sintered web by exposing the web, braze alloy, and base metal to 2150F in a vacuum furnace for 10 minutes. A
mixture of calcia stabilized zirconia and graphite powders (70 - 30 by volume, respectively) WclS plasma sprayed onto the exposed web surace. The sprayed composite was sub-sequently exposed to 1700F for 15 hrs in air. The burned-off sample had a ceramic layer which was noticeably more porous than graph:ite--free zirconia sprayed as described as example I. A second attached web was plasma sprayed coated with a layer of pure calcia stabilized zirconia and without stopping was then coated with a mixture of 70 vol. percent calcia stabilized zirconia and 30 vol. percent graphite.
After the graphi-te was burned off, it was obvious that the layer near the web was of higher density and, therefore, stronger than the outer layer which contained -the graphite.
Density, as well as streng-th, can be controlled by controlling the volume fraction of graphite or other sacrificial material.
The ceramic layer may be formed with a variable density and applied such as by plasma spxaying. During application the ceramic material contains both permanent and sacrificial material with the sacrificial material varying in amount from 0% to 60~. The inert ceramic material may be selected from one or more of the following materials: stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicon nitride, alumina, mullite, borides, silicides, and cermets, etc., but no-t limited thereto.
The sacrificial materlal may be selected from one or more of the following materials: graphite, plastic, aluminum, copper, and sawdust, etc., but not limited thereto. When this variable density ceramic is used as an abradable seal for turbine blades (in a gas turbine engine) it has been found that the lower density material will abrade easier than the higher density materials but still maintain the desired structural characteristics in the high temperature environment.
Examplcs I, II, and :CII correspond to three of the embodiments described herein. It is contemplated that those skilled in the art will thoroughly understand that it is possible to change the composition of the ceramic material, substitute differen-t metal alloys for both the metallic base and metal interface. It will be recognized that the inven-tion provides a very ef~ective method of ab~orbing thermal strains in a ceramic-metal laminate composition structure by providing a low modulous resilient, low density metal fiber mat inter~ace joined to the metal base and the ceramic.
Other technically significant applications of the embodiments of this invention can include gas turbine shrouds, burner cans, vane end walls, magnetohydrodynamic generators, nuclear fusion reactors, and coatings for pistons and cylinders in diesel and gasoline engines.
Although specific embodiments of the invention have been described many modifications and changes may be made to the materials, configurations and methods of making the ceramic-metal composite without departing from the spirit ~20 and the scope of the invention as defined in the appended ~ claims.
:: ~
~ ' ' ~ .
:
.
~ .
Claims (10)
1. A ceramic mixture of mullite fibers and a low expansion reactive glass, the mixture consisting of from 70 to 99% by volume of mullite fibers and from 1 to 30% by volume of glass, the mixture being such that upon heating the glass reacts and bonds with the mullite fibers at a temperature below the decomposition temperature of the fibers.
2. A ceramic mixture which comprises fibers of an aluminosilicate containing (by weight) 35 - 55% SiO2 and 45 - 65% A12O3, and particles or fibers of a low expansion glass, the fibers and particles having a maximum size of 80 microns, the mixture being such that, when it is sintered, free quartz is released and the glass forms a matrix around the free quartz and the aluminosilicate fibers.
3. A ceramic material made of a particle mixture of a first material having a composition of 35 - 55% SiO2 + 45 - 65 A12O3 and up to 2% a second material having a composition of borosilicate glass, each of the particles of the components having a size range up to 80 microns, wherein upon sintering the first and second component materials, free quartz is released and the material forms a structure having mullite fibers surrounded by a matrix of said glass containing dissolved quartz.
4. A ceramic material formed by sintering a mixture as claimed in Claim 2 to cause the glass to react and bond with the aluminosilicate at a temperature below the decomposition temperature of the aluminosilicate, the material being usable in a high temperature range from about 1800°F to 3000°F depending upon the erosion and loading environments.
5. A ceramic material formed by sintering a mixture as claimed in Claim 3 to cause the glass to react and bond with the mullite fibers at a temperature below the decomposition temperature of the mullite fibers, the Material being usable in a high temperature range from about 1800°F to 3000°F depending upon the erosion and loading environments.
6. A mixture according to Claim 1 wherein the low expansion glass is a borosilicate glass.
7. A mixture according to Claim 2 wherein the low expansion glass is a borosilicate glass.
8. A mixture according to Claim 1, Claim 2 or Claim 4 wherein the glass has a weight percent composition selected from the group of compositions:
80.5% SiO2, 12.9% B2O3, 3-8% Na2O
2.2% A12O3, 0.4% K2O;
and 67.0 SiO2, 27.4% BaO, 5.6% A12O3.
80.5% SiO2, 12.9% B2O3, 3-8% Na2O
2.2% A12O3, 0.4% K2O;
and 67.0 SiO2, 27.4% BaO, 5.6% A12O3.
9. A material according to Claim 3 or Claim 5 wherein the borosilicate glass has a weight composition of:
80.5% SiO2, 12.9% B2O3, 3.8% Na2O
2.2% A12O3, 0.4% K2O
80.5% SiO2, 12.9% B2O3, 3.8% Na2O
2.2% A12O3, 0.4% K2O
10. A material according to Claim 6 or Claim 7 wherein the borosilicate glass has a weight composition of:
80.5% SiO2, 12.9% B2O3, 3-8% Na2O
2.2% A12O3, 0.4% K2O
80.5% SiO2, 12.9% B2O3, 3-8% Na2O
2.2% A12O3, 0.4% K2O
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000375153A CA1117147A (en) | 1976-04-15 | 1981-04-09 | Porous ceramic seals |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US677,258 | 1976-04-15 | ||
| US05/677,258 US4075364A (en) | 1976-04-15 | 1976-04-15 | Porous ceramic seals and method of making same |
| CA000375153A CA1117147A (en) | 1976-04-15 | 1981-04-09 | Porous ceramic seals |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1117147A true CA1117147A (en) | 1982-01-26 |
Family
ID=25669299
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000375153A Expired CA1117147A (en) | 1976-04-15 | 1981-04-09 | Porous ceramic seals |
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| CA (1) | CA1117147A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2326608A2 (en) * | 2008-09-18 | 2011-06-01 | Fuelcell Energy, Inc. | Fibrous ceramic material and method for making the same |
| CN109875123A (en) * | 2019-02-27 | 2019-06-14 | 深圳市合元科技有限公司 | Electronic smoke atomizer, electronic cigarette, atomizing component and preparation method thereof |
-
1981
- 1981-04-09 CA CA000375153A patent/CA1117147A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP2326608A2 (en) * | 2008-09-18 | 2011-06-01 | Fuelcell Energy, Inc. | Fibrous ceramic material and method for making the same |
| CN109875123A (en) * | 2019-02-27 | 2019-06-14 | 深圳市合元科技有限公司 | Electronic smoke atomizer, electronic cigarette, atomizing component and preparation method thereof |
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