GB1576481A

GB1576481A - Ceramic materials

Info

Publication number: GB1576481A
Application number: GB769177A
Authority: GB
Original assignee: Brunswick Corp
Current assignee: Brunswick Corp
Priority date: 1976-04-15
Filing date: 1977-02-23
Publication date: 1980-10-08
Also published as: JPS54108816A; CA1103279A; AU2414577A; AU519251B2; AU2156983A

Description

(54) CERAMIC MATERIALS (71) We, BRUNSWICK CORPORATION, a corporation organized under the laws of the State of Delaware, United States of America, of One Brunswick Plaza, Skokie, Illinois 60076, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to certain ceramic mixtures and to ceramic materials made by heating the mixtures, which materials are useful inter alia in the ceramic metal laminates as described in our copending patent application no. 5441/77. (Serial No. 1575443) In the use of ceramic materials for high temperature seals and gas turbines, and especially where the seals are abraded in use (see, for example, U.S. Patent No. 3,880,550), a sintered product of an aluminosilicate ceramic consisting of mullite plus quartz as a high temperature material and insulation (above 2600"F) is very limited. The free quartz present in the available fibers (known by the trade names of Fiberfrax and Kaowool) becomes brittle because the fused quartz devitrifies and converts to cristobalite when exposed to temperatures of 1800"F and over.

We have now found that by using a mixture of aluminosilicate 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 2200-3000"F (an increase of well over 400"F for known Fiberfrax). In sintering the mixture, the glass surrounds the aluminosilicate and at the same time dissolves any free quartz and results in a mixture of aluminosilicate and glass.

According to the present invention, there is provided a ceramic mixture which comprises fibers of an aluminosilicate containing (by weight) 35-50% SiO2 and 45 - 65% Awl203, and particles of 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.

The invention also provides 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.

The invention further includes ceramic materials obtained by sintering the above ceramic mixtures.

The ceramic materials of the invention (formed by sintering the mixtures) surprisingly exhibit excellent high temperature characteristics. In the prior art, when a standard aluminosilicate, typically 35-55% SiO2 and 45-65% A1203, is used alone at temperatures above 1800 F, the fused quartz devitrifies and forms cristobalite which severely embrittles the fibers and weakens the general product. By the addition of fibrous or powdered glass to the aluminum silicate (in accordance with the present invention), the glass reacts with the quartz to form a new glass that will not devitrify.

Various methods of making ceramic metal laminates, and the laminates so made, are described and claimed in our copending application no. 5441/77 (Serial No. 1575443) (to which reference should be made for further details) and the ceramic mixtures of the present invention, and the ceramic materials made therefrom, are useful in the methods of our said copending application. Our said copending application describes and claims (i) a method of bonding a ceramic member to a metallic member, the two said members having different coefficients of thermal expansion, which comprises rigidly fastening to a surface of the metallic member a low modulus, flexible, low density metallic structure in the form of a layer covering said surface, and securing the said metallic structure to a ceramic member; the arrangement being such that upon changes in temperature, the difference in expansion or contraction between the metallic member and the ceramic member is taken up by deformation of the said metallic structure whereby the metallic member and the ceramic member are not subjected to undue strain; (ii) a method of bonding a metallic member to a ceramic member which comprises: a) bonding a ceramic member to the ceramic face of a ceramic-metal composite, the ceramic-metal composite having a predominantly ceramic face and metal elements projecting from the opposite surface; b) brazing one surface of a metal fiber mat to the metallic member so that said one surface of the mat is rigidly fastened to the metallic member; and c) spot brazing the other surface of the mat to the metallic elements on the ceramic-metal composite; (iii) a method of making a ceramic-metal composite comprising the steps of: a) providing high temperature resistant alloy metal plate and a low modulus low density metal pad; b) bonding the pad to the metal plate; and c) plasma spraying a coating of ceramic material onto the pad, the ceramic being one or more of stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicone nitride, alumina, mullite, borides, silicides, glass-ceramic, or cermets; (iv) a method of making a ceramic-metal composite comprising the steps of: a) providing a low modulus, low density, flexible metal pad having two surfaces; b) plasma spraying on one surface of the pad a ceramic material, the material being one or more of stabilized zirconia, calcia, magnesia, yttria, glass, silicon carbide, silicon nitride, alumina, mullite, borides, silicides, glass ceramics, or cermets; and c) bonding to the other surface of the pad a plate of high temperature resistant alloy metal to form the composite; (v) a laminated composite comprising: a) a high temperature resistant ceramic layer having inner and outer faces; b) metallic elements rigidly secured to the inner face of the ceramic layer; c) a low modulus, low density, flexible metallic layer having inner and outer faces, fastened at its inner face to the metallic elements; and d) a metallic member layer fastened to the outer face of the low modulus layer; (vi) a laminated structure comprising a fired high temperature ceramic layer having inner and outer faces, a ceramic-metal composite layer having a ceramic outer face and metallic elements projecting from the inner face, the inner face of the ceramic layer being bonded to the outer face of the ceramic-metal composite layer, a layer consisting of a mat of high melting metal fibers, said mat having a low modulus and having inner and outer faces, said mat being brazed at its outer face to the metallic elements on the inner face of the ceramic-metal composite layer, said mat being brazed on its inner face over the entire surface thereof to a metallic member structure; (vii) a laminated structure comprising a fired high temperature ceramic member, said ceramic member having embedded in one face thereof a sufficient thickness of a low modulus metal fiber mat to form a strong mechanical bond, and a metallic structure rigidly fastened to the metal fiber mat; (viii) a laminate composite structure comprising: a) a ceramic layer having a thermal coefficient of expansion ranging from 1x10-6 to 8x10-6 in/in/ F; b) a high temperature corrosion resistant metallic base having a thermal coefficient of expansion ranging from 2x10-6 x 20x10-6 in/in F; c) a resilient metal interface secured to both the ceramic layer and the metallic base to provide movement therebetween without damaging the layer or the base.

The following Examples illustrate the use of the ceramic mixtures and materials of the present invention in a method of our said copending application for making ceramic metal laminates.

EXAMPLE I According to the teachings of U. S. Patent No. 3,127,668 a felt web made from one-half inch kinked 4 mil wire of Hastelloy X (Hastelloy is a trade mark) metal alloy was sintered for 10 hours in a furnace vacuum of 10-5 torr and at a temperature of 2175"F. The web produced had an approximate 20% density. A metal base of "Hastelloy X" alloy was brazed to the sintered web by exposing the web and the base metal to 21500 in a vacuum furnace for about 10 minutes. A ceramic composite of ceramic material 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 a porous fabric base that holds the staples in a semi-upright position. A water based slurry formed of aluminosilicate mineral fibers having diameters ranging from 8 microns to 80 microns were mixed with a low expansion glass powder (the powder having a size where it will pass through a 325 U.S. standard mesh screen, the powders having a diameter 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 mixture of aluminosilicate fibers and glass powder is a ceramic mixture of the present invention. The slurry was deposited on the fabric over and surrounding the upright metal staples and held in place by an external holding container. This slurry-staple composite was sintered at 2200"F for 2 hours in a furnace purged with argon to permit the glass to melt and react with the aluminosilicate, and at the same time form a matrix around the aluminosilicate to eliminate any free quartz. The final product is the staple impregnated low expansion ceramic wherein the ceramic is mullite and glass combination (mullite - 3Al203 2SiO2).

EXAMPLE II In a felted slurry mixture, aluminosilicate fibers, having a diameter of approximately 8 microns and a length of 1/8 of an inch and constituting 98% by weight, were combined with 2% alumino-borosilicate glass fibers, also having a diameter 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 solids (the solids constituting a ceramic mixture of the invention). The mixture of solids and water was suction deposited to form a porous ceramic felt that was compressed to about 40% density. The densified ceramic felt was sintered at 29000F in an air atmosphere for about 4 hours. The glass fiber melted and reacted, tying up the free quartz and resulting in a combination of mullite and glass, the resulting structure being about 1/8 of an inch thick and 65 % dense. This ceramic material was attached to one side of the staple ceramic composite by a low expansion glass powder such as, in wt. percent, 80.5 SiO2 - 12.9 B203 - 3.8 Na2O - 2.2 Al203 - 0.4 K20 and at 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 furnace for 10 minutes at 21500F in an argon atmosphere. The finally formed composite was thermally cycled to 18000F and cooled to ambient. At the end of a 30 cycle period the ceramic had not cracked and the interface had maintained its structural integrity.

Claims

Another low expansion reactive glass which can be used has a weight percent composition of: 67.0% SiO2, 27.4% BaO, 5.6% Al203 WHAT WE CLAIM IS:

1. A ceramic mixture which comprises fibers of an aluminosilicate containing (by weight) 35 - 50% SiO2 and 45 - 65 % Awl203, 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 alumino-silicate fibers.

2. A mixture according to claim 1 wherein the low expansion glass is a borosilicate glass.

3. 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.

4. A mixture according to claim 3 wherein the glass has a weight percent composition of:

80.5% SiO2, 12.9% B203, 3.8% Na20

2.2% Awl203, 0.4% K20 or

67.0% SiO2, 27.4% BaO, 5.6% At203.

5. A ceramic mixture as claimed in claim 1 or 3 substantially as herein described in Example I or II.

6. A ceramic material formed by sintering a mixture as claimed in claim 1 or 2.

7. A ceramic material formed by heating a mixture as claimed in claim 3 or 4 to cause the glass to react and bond with the mullite fibers at a temperature below the decomposition temperature of the fibers.

8. A ceramic material as claimed in claim 6 or 7 substantially as herein described in Example I or II.