Compositions: ceramic – Ceramic compositions – Carbide or oxycarbide containing
Patent
1985-03-25
1987-11-10
Bell, Mark L.
Compositions: ceramic
Ceramic compositions
Carbide or oxycarbide containing
501 91, 501 92, 501 97, 501 98, C04B 3556, C04B 3558
Patent
active
047057610
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
Technical Field
This invention relates to a ceramic structure having a thermal shock resistance, and more particularly to a ceramic structure having a thermal shock resistance which can be appropriately used for turbine blades and the like.
Background Art
The service temperature of a heat engine tends to become higher and higher to further improve the engine efficiency, and constituent members of the heat engine must have higher temperature characteristics. A turbo charger for automobiles, for example, must withstand the use at an exhaust gas temperature ranging from 1,100.degree. to 1,200.degree. C. In a high-temperature gas turbine, the service temperature of from about 1,300.degree. to about 1,500.degree. C. is planned as the gas temperature. To accomplish these objects, ceramic materials, such as silicon carbide, silicon nitride, sialon and the like, which have a high-temperature strength superior to that of metallic materials have been developed. Though these ceramics have sufficient high-temperature characteristics such as high heat resistance and high strength at high temperature, they are so brittle that once cracking takes place, it readily grows to cause the ceramic materials to be easily broken and lack reliability. Moreover, the strength is likely to vary due to internal defects of sinters or their surface defects and, therefore, strength design of the ceramic materials as a structural material is extremely difficult.
On the contrary, tool materials such as sinters mainly comprising cermet, boron carbide, boron nitride or the like, i.e. so-called "high tenacity materials", are so tough that cracking is difficult to grow even when it takes place. However, these materials have disadvantages in that their properties change and mechanical strength drops remarkably when they are exposed to a high temperature in an oxidizing atmosphere.
In order to eliminate these disadvantages, a method has been proposed, for example, wherein fibers having a high heat resistance and a high strength at high temperature, such as silicon carbide, is mixed into a heat-resistant material such as silicon nitride, and the mixture is sintered.
However, versatility and reliability of such a material as a structural material are not yet sufficiently high for the following reasons. mutually and are difficult to disperse, so that a uniform sinter can not be obtained easily. such as a hot press process must be employed in order to obtain a compact sinter devoid of any cracks, and this results in still another problem that the mass-productivity is low and the application of this method to articles having complicated shapes is difficult. during the molding and sintering processes, so that the mechanical properties of the resulting sinter will have anisotropy. This makes it difficult to use the sinter as a general structural material.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a structure having a thermal shock resistance which is suitable for use as high-temperature members such as a turbo charger or a gas turbine and in which a structural ceramic member having high reliability and versatility is employed.
The present invention is characterized in that a portion exposed to a heat cycle with the highest service temperature of at least 1,100.degree. C. is composed of ceramics having the following features: dispersed in the body; highest service temperature and breaking tenacity of at least 10 MN/m.sup.3/2 in terms of K.sub.1c ; and/or therein are entrapped inside the particles and are bent or branched.
The present invention can be typically applied to structures such as turbines or turbo chargers, rotary members (rotary structural members) and/or those structures which are exposed to combustion gas, explosion gas, and the like.
The requirement of the item (2) described above, i.e., breaking tenacity of at least 10 MN/m.sup.3/2, is based upon the tolerance of strength design of the rotary structures. Si.sub.3 N.sub.4 ceramics that have been known to this date have breaking tenac
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Bell Mark L.
Hitachi , Ltd.
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