Patent Application
20150197860
1. Field of the Invention
The invention relates to ceramic materials and more particularly to a process of producing a ceramic matrix composite (CMC) having increased fracture toughness, increased heat-resistance, increased electrical conduction, and increased thermal conduction.
2. Description of Related Art
Materials technology is advancing rapidly in recent years. The traditional structure provided by the application of metals to replace ceramics has been an increasing tendency. Ceramic materials have the following characteristics superior to metals: High elasticity coefficient/weight ratio, high hardness, high compression strength/weight ratio, high/low thermal conductivity, low thermal expansion coefficient, high melting point, and good corrosion/oxidation resistance. These characteristics of the ceramic materials make these materials gradually favored by the industry. Ceramic materials are widely employed in special optical, electrical, thermal and mechanical fields, and many different kinds of ceramic products are developed for producing consumer products.
For example, ceramic knives are made of zirconium dioxide and have properties similar to natural diamonds. The blade can be extremely sharp, hard, and abrasion resistant. Further, the blade surface is dense and is not subject to contamination by food juice. Furthermore, it is easy to clean, which can reduce the growth of microorganisms, and is extremely light. Thus, ceramic knives have become a good house helper.
Electrical conduction of ceramic materials is activated by heating or other methods to generate free electrons In addition, an electric field is applied to the ceramic material. As an end, the electrical conduction is generated. A typical ceramic material having electrical conduction is SiC which has a maximum operating temperature of 1,450 degrees Celsius. Similarly, MoSi2 has a maximum operating temperature of 1,650 degrees Celsius. Novel ceramic materials having electrical conduction include zirconium dioxide having a maximum operating temperature of 2,000 degrees Celsius, and thorium oxide having a maximum operating temperature up to 2,500 degrees Celsius.
An ion-conducting ceramic material is a molten electrolytic solution or electrolyte having high ion conductivity similar to the solid ceramic material. β alumina ceramic material is a typical cationic conductor. It mainly relies on the migration of sodium ions for being conductive. Zirconium dioxide based ceramic material is an anionic conductive material and relies mainly on migration of oxygen anions for being conductive. Ion-conducting ceramic materials can also be used to produce a number of novel solid-state batteries such as sodium-sulfur batteries. It may be applied to electric power supply (e.g., battery) for automobile in the future. As described above, ceramic products not only change the traditional manufacturing processes but also deeply affect our daily lives.
While ceramic materials have become the darling of materials, it has inherent shortcomings such as excessive brittleness. Particularly, they tend to fracture when tensile stress is concentrated on a portion thereof. As a result, it leads to failure. Fracture toughness of typical ceramic materials is shown in
Bonding of ceramic materials is either covalent or ionic. Covalent bonding between atoms is formed by shared and overlapping valence electrons. Ionic bonding is formed by transferring electron(s) from a cation to an anion. Thus, the covalent electron cloud in a covalent bonded ceramic material does not form a bond due to atoms displacement from each other in response to an applied force. Similarly, breaking the ionic bonding between an ionic ceramic material will result in all adjacent atoms becoming either all cations or anions and generate a repulsive force to cause rupture. Consequently, ceramic materials are brittle in nature.
Regarding metals and polymeric materials, use of these materials does not cause fracture or breakage as long as the applied force is lower than the ultimate tensile strengths of the materials. Further, even these materials are overloaded beyond their yield strengths, significant plastic deformation usually occur prior to the final failure and serve as a warning. Because ceramic materials are brittle and have poor toughness, they are subject to sudden failure. Therefore, industrial applications of ceramic materials are significantly limited. Consequently, it is desired to develop a tough ceramic matrix composite maintaining the attractive characteristics but without the disadvantages of conventional ceramic materials.
It is therefore one object of the invention to provide a process of producing a ceramic matrix composite (CMC) comprising the steps of preparing a ceramic material having a plurality of pores as a CMC substrate; heating a metal material to be molten wherein the metal material has a melting point lower than the CMC substrate and has a high activity to react with the component of the CMC substrate; adding the CMC substrate to the molten metal material so that the molten metal material enters the pores of the CMC substrate to occur chemical reactions; removing the CMC substrate filled with the molten metal material; and cooling the removed CMC substrate filled with the molten metal material to form a CMC having a plurality of metal grains.
The above and other objects, features and advantages of the invention will become apparent from the following detailed description taken with the accompanying drawings.
Referring to
In step 10, a porous ceramic material is prepared as a CMC substrate.
In step 20, a metal material is heated to be molten.
In step 30, the CMC substrate is added to the molten metal material so that the molten metal material may enter pores of the CMC substrate to occur chemical reactions.
In step 40, the CMC substrate filled with molten metal material is removed and cooled to form a CMC having a plurality of metal grains.
Referring to
The CMC having the CMC substrate 1 of the invention can be subject to heat treatment to form as a thermal conductive but electrically non-conductive ceramic composite.
The CMC having the CMC substrate 1 of the invention can be subject to heat treatment so that the metal such as aluminum can be oxidized to form as a corrosion proof ceramic composite.
The CMC having the CMC substrate 1 of the invention can be subject to a step of removing portions of the metal grains 2 in the pores by heating to a molten state or by etching with chemicals such as acids so as to form as a ceramic composite having metal residues 3 which are left in the pores near the surface of the CMC. The ceramic composite has the effect of absorbing lubricant and thus can be made into ball bearings or self-lubricating bearings.
In brief, the CMC of the invention of the composite ceramic substrate is produced by filling the molten metal material into the pores of the CMC substrate 1, and causing chemical reactions to occur by replacing the lattice arrangement of ceramic material. As a result, the CMC of the invention has the benefits of significantly increased fracture toughness, heat-resistance, electrical conduction, and thermal conduction.
In
While the invention has been described in terms of preferred embodiments, those skilled in the art will recognize that the invention can be practiced with modifications within the spirit and scope of the appended claims.
