US20070237939A1

US20070237939A1 - Ceramic reinforcement material

Info

Publication number: US20070237939A1
Application number: US11/394,759
Authority: US
Inventors: Wei-Hsing Tuan; Ya-Jen Yu; Hsiu-Ching Hsu; Yu-Jung Huang
Original assignee: National Taiwan University NTU
Current assignee: National Taiwan University NTU
Priority date: 2006-03-31
Filing date: 2006-03-31
Publication date: 2007-10-11

Abstract

The present invention provides a ceramic reinforcement material with a weak interface. The reinforcement material of the present invention contains several ceramic layers, wherein those ceramic layers can be a ceramic layer, a metal layer or a polymer layer. The present invention utilizes the bonding weakness of a middle layer or in between a middle layer and the ceramic layer to create a weak interface in the ceramic reinforcement material. The reinforcement with the weak interface can be added into other materials to improve their toughness.

Description

BACKGROUND OF THE INVENTION

1. Field of Invention
The present invention relates generally to a ceramic reinforcement material comprising a weak interface. More particularly, the present invention relates to a weak interface or a weak interface material of mechanic weakness covered with reinforcement material.
2. Description of the related Art
The toughness of the ceramic material is normally very low, and its utilization is not popular in the industries. The main focus of the ceramic industry is always on how to improve the toughness of the ceramic material.
In order to improve the toughness of the ceramic material, the most common method is to add reinforcement material into the ceramic material. The ceramic reinforcement material can be whisker, ceramic fiber, ceramic particulates or ceramic platelet. Those reinforcement materials are very fine and dense material that comprise high degree of strength and hardness. For example, the silicon carbide platelet, which is a single crystal platelet has high degree of strength and hardness. The silicon carbide platelet can be added to other brittle materials to improve the toughness of the brittle materials.
Although, the ceramic material requires having good mechanical properties, its interface contacting with the brittle matrix must be weak. FIG. 1 is a diagram of showing a crack that has spread in a brittle matrix and is deflected by a weak interface of a reinforcement material. The crack is formed in the brittle matrix, it spreads rapidly throughout the brittle matrix. Thus, the main purpose of the weak interface is to prevent the crack from directing on the same plane such that the crack can be deflected by the weak interface. The weak interface can stop the crack spreading throughout the brittle matrix, the toughness of the brittle matrix is increased using this process.
However, the existing property of the weak interface also restricts the utilization of the ceramic material. The conventional ceramic reinforcement, either in the particulate form or in the platelet form, are dense, hard and strong. Although the strength of the ceramic reinforcement is preferably to be high but the interface between the reinforcement material and the ceramic material is required to be weak. Therefore, in order to fabricate a weak interface, the utilization of reinforcement materials is restricted. Any reinforcement material that would react or sinter with the matrix cannot be used. The silicon carbide platelet, for example, is not suitable for using in the glass matrix as a result of a melting reaction between the silicon carbide and the glass. Thus, silicon carbide platelet cannot be used as a reinforcement material in most glasses. Any slight chemical reaction will result in the toughness being decreased drastically.
The current limitations of the ceramic material in the market are such, the cost of the ceramic material is very high, the addition of the ceramic reinforcement material, the cost of fabrication is also increased, and the reinforcement materials are very limited, only few reinforcement materials are available. Thus, the reinforcement materials, such as silicon carbide and aluminum oxide, are common materials used in current markets. But those materials still would have some reaction with the ceramic materials.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a ceramic reinforcement material with a weak interface. The weak interface of the ceramic reinforcement material can deflect a crack spread in the matrix, and it also can be added to a brittle matrix in order to improve toughness of the matrix.
It is another object of the present invention to provide a ceramic reinforcement material that its function is not affected by its formation of a strong interface with a brittle matrix. The utilization of the ceramic reinforcement material of the present invention can be utilized in various areas without limiting by its fabricating process or the materials used. Thus, the manufacturing costs can be reduced.
The ceramic reinforcement material of the present invention comprises a first reinforcement material and a weak interface. The first reinforcement material can be a ceramic material, an external surface of the first reinforcement material can be in contact with the matrix. The weak interface, wherein the strength of the weak interface is lower than the first reinforcement material, can be chosen either from a second reinforcement material covered under the first reinforcement material or a defected region existed inside the first reinforcement material.
The second material is made of a combination of a ceramic material, a metal material or a polymer material. The weak interface is formed from the second reinforcement material, and it can deflect a crack formed and spread in the matrix. A connecting surface of the weak interface is formed by adhering the first reinforcement and the second reinforcement in order to deflect a crack formed in a brittle matrix.
The present invention provides a technique of using the natural materials such as fish scales as a reinforcement material which can be used to increase the toughness of the ceramic material although the reinforcement may react with the matrix. Both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a further understanding of the present invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. In the drawings,
FIG. 1 is a diagram of showing a crack spreading in a brittle matrix is deflected by a weak interface of a reinforcement material;
FIG. 2 is a graphic diagram of showing a relation between strain and stress of two pieces glasses after adhesion;
FIG. 3 is a cross-sectional view of the two adhered glasses via a scanning electronic microscope (SEM), wherein the arrow indicates an adhering part of the glasses;
FIG. 4 shows a graphic diagram of strain versus stress of a sample tested by a universal testing machine;
FIG. 5 shows a cross-sectional view of a compound material through the SEM, wherein the teeth-shaped portion of the diagram represents back part of the fish scale;
FIG. 6 is a cross-sectional view of a deflection of the crack by adding reinforcement material to increase the toughness of hydroxyapatite materials;
FIG. 7 is a diagram of a plurality of cracks occurring in various directions inside the multilayer ceramic capacitor green body;
FIG. 8 illustrates another kind of ceramic reinforcement materials with a weak interface in accordance with another preferred example of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides a reinforcement material comprising a weak interface. A second reinforcement material can be made of a ceramic material, a metal material or a polymer material. The weak interface can be formed either from the second reinforcement material or from a connecting interface between a first reinforcement material and the second reinforcement material. The weak interface can also deflect a crack formed and spread in the matrix. The present invention provides a reinforcement material comprising a multi-layers structure that is stacked alternatively with the first reinforcement material and the second reinforcement material. The following preferred examples illustrating the advantages of the reinforcement material with weak interface of the present invention.
The first preferred example of the present invention, two pieces of glasses are pressured by a dead load, and are heated up with a rate of one degree Celsius per minute until four hundreds degrees Celsius. The glasses are kept at the temperature of four hundreds degree Celsius for five hours. The glasses are then heated up from four hundreds degree Celsius to seven hundreds fifty degree Celsius. Those glasses are kept in seven hundreds fifty degree Celsius for one hour, and are cooled down slowly to the room temperature. A testing device is used to test those glasses so that a graphic diagram of strain versus stress is shown on FIG. 2. FIG. 3 is a diagram of cross-sectional view of a crack tested by a scanning electron microscope (SEM), indicating that two pieces of glass plates which are adhered together after the heat treatment. The figure indicates that the crack can penetrate through the glass sample. The diagram of strain versus stress in FIG. 2 shows the fracture behavior of the glasses after adhesion.
A second preferred example of the present invention provides a layer-shaped structure of ceramic material with a weak interface producing reinforcement effect.
A plurality of fish scales are arranged evenly in between the two glasses of the first preferred example. The fish scales are one type of ceramic materials comprising a layer-shaped structure. The ceramic layer comprises materials rich in hydroxyapatite. A middle layer comprises protein material, wherein the strength of the protein of the middle layer is weaker than the strength of the ceramic layer. The middle layer can be formed as a ceramic material with a weak interface. A sample of the glasses sandwiched the fish scales is heated up according to the conditions and the temperature of the first preferred example. When the sample is heated at a temperature of 400 degree Celsius for five hours, the organic substance such as, protein produced from the fish scales is completely burn off. The ceramic layer with the weak interface of the hydroxyapatite becomes weaker due to the lost of the protein. FIG. 4 shows a graphic diagram of strain versus stress of the sample tested by a universal testing machine. In FIG. 4, the deviation of the curve indicates that the crack reaches the weak interface to prevent the crack from spreading further. Once the stain is increased to a certain value, the crack will continuously spread. The area located below the stain v stress curve of FIG. 4 is 1.3 times of the area located below the stain v stress curve of FIG. 2. In other words, once the ceramic reinforcement material is added to the sample, the fracture energy of the glasses is increased to 1.3 times.
FIG. 5 shows a cross-sectional view of a compound material, wherein the teeth-shaped portion of the diagram represents back part of the fish scale. The crack is penetrated directly through the glass matrix from above as a result of the back part of the fish scale is adhered partially to the glasses. But, the crack is deflected away when the crack reaches a position of the protein located below the fish scales, the crack would then deflect into the weak interface within the fish scales and then deflect again into the glasses. Due to the addition of the reinforcement material in the sample, the weak interface inside the reinforcement material increases the toughness of the glasses even though the interface of the reinforcement material is adhered to the glasses.
A preferred third example of the present invention provides another fracture demonstration. The powers of Ca(OH)₂and CaHPO₄are mixed together with a ball mill method and with proportional amount. The mixture is then heated up at a temperature of 1200 degrees Celsius for 2 hours so that hydroxyapatite materials of Ca₁₀(PO₄)₆(OH)₂can be obtained. The hydroxyapatite is then ball milled to fine power. The mixed power is formed through a steel mold into three rectangular bars with 3.0×4.0×40 mm. The bars are then heated at a temperature of 1300 degrees Celsius for one hour. The bars are cut with a diamond saw and tested by using the single edge notched beamed (SENB) method to measure the toughness, wherein the toughness of the bars is approximately 1.8±0.02 MPa.mm^1/2.
A fourth preferred example of the present invention provides another kind of ceramic reinforcement material with a weak interface. The hydroxyapatite is fabricated in accordance with the other three preferred examples, 3 wt % of fish scales is added to the hydroxyapatite which is ball milled to form three rectangular bars. The bars are then heated up at 1300 degrees Celsius in order to obtain a toughness of 2.1±0.2 MPa.mm^1/2. The preferred examples of the present invention provide a method of adding reinforcement material to increase the toughness of hydroxyapatite so that the deflection of the crack shown in FIG. 6 is a proof of increasing toughness.
A fifth preferred example of the present invention
The power is mixed with suitable amount of harden acrylic resin into a rectangular mold to from a rectangular bar with 5.0×6.0×50 mm. The rectangular bar is rested for couple hours, and once it is harden, a crack is fabricated. The SENB method is used to measure the toughness, a toughness of 2.3 MPa.mm^1/2is obtained.
Another kind of ceramic reinforcement material with a weak interface in accordance with a sixth preferred example of the present invention. A plurality of multilayer ceramic capacitor (MLCC) green bodies with the dimensions of 3.5×1.75×1.7 mm are added into the mixture mentioned in fifth preferred example. The multilayer ceramic capacitor is a type of electronic device with a structure of packed layers. The multilayer ceramic capacitor comprises several layers of ceramic dielectric layers. The metal electrode layers are located in between every two ceramic dielectric layers. The multilayer ceramic capacitor utilized in the present invention is a green body, which is only processed through the formation of its shape. The green body is not being de-bindered or sintered so that it can be treated as the reinforcement described in the present invention due to the interfaces between the ceramic dielectric layers and the metal electrode layers are very weak. Once the green body is added, the acrylic sample of the packed capacitor is harden, the SENB method is used to test its toughness, a reading of 2.7 MPa.mm^1/2is obtained. The toughness is higher than those structure without reinforcement material. FIG. 7 is a diagram of a plurality of cracks occurring in various directions inside the multilayer ceramic capacitor green body, wherein a plurality of deviations of the cracks are occurred in the reinforcement materials.
The above-mentioned preferred examples of the present invention, when reinforcement material with a weak interface is added to a brittle material, it helps to improve the toughness of the brittle material. Thus, the reinforcement material with weak interface can be utilized in various brittle materials to improve the toughness without any interference to the fabricating process. The reinforcement material with a weak interface of the present invention has more advantage than the prior art.
FIG. 8 illustrates another kind of ceramic reinforcement materials with a weak interface in accordance with another preferred example of the present invention. The reinforcement material is added to a matrix as shown in FIG. 8, wherein the ceramic material (the first reinforcement material) covers partially the weak interface with weaker mechanic property (the second reinforcement material) to form a multi-layers structure that is stacked alternatively. The weak interface with weaker mechanic property comprises ceramic materials, metal materials or polymer materials. FIG. 8 shows that the ceramic material (the second reinforcement material) is a defected region formed from a porous layer, a dislocating layer or a grain boundary layer.
According to the U.S. market, the reports of the American Ceramic Society Bulletin in August 2003 show that in 2002 alone, the advanced ceramic market is US$ 1450 million. Although, the structural ceramic is only about 4.5% of the whole advanced ceramic market (approximate US$ 65 million), but it is the fastest growing portion of the market. It grows with a rate of 9.6% per annul, it is estimated that the structural ceramic will reach US$103 million in year 2007. The current major obstacle in the ceramic industrial is the low toughness of the ceramic property. If the toughness could be improved, the growth of the ceramic market would be increased. The present invention provides a new concept of improving the toughness of the ceramic property by providing a ceramic reinforcement materials with a weak interface. From the above-mentioned preferred examples, it is clear that the ceramic reinforcement materials of the present invention can improve the toughness of the ceramic property drastically such that it also can be added in any type of material to form various compounds. The commercial value of the ceramic reinforcement material of the present invention is therefore increased.
The forgoing is considered illustrative of the principles of the invention. As variations and related embodiments may occur to those skilled in the art, it is to be appreciated the invention, and all suitable modifications and equivalents, are only to be limited by the scope of the claims following hereinafter.

Claims

1. A ceramic reinforcement material with a weak interface, capable of adding into a matrix in order to improve the toughness of the matrix, comprising

a first reinforcement material, wherein the first reinforcement material is a ceramic material;

a weak interface, wherein strength of the weak interface is lower than that of the first reinforcement material, the weak interface can be either a second reinforcement material covered under the first reinforcement material or a defected region existed inside the first reinforcement material.

2. The ceramic reinforcement material of claim 1, wherein the second material is made of a combination of a ceramic material, a metal material or a polymer material.

3. The ceramic reinforcement material of claim 1, wherein the weak interface is formed with the second reinforcement material and can deflect a crack formed and spread in the matrix.

4. The ceramic reinforcement material of claim 1, wherein the weak interface is formed between the first reinforcement material and the second reinforcement material so that the weak interface can deflect a crack formed and spread in the matrix.

5. The ceramic reinforcement material of claim 1, wherein the first reinforcement material and the second reinforcement material are stacked alternatively to form a multi-layer structure.

6. The ceramic reinforcement material of claim 1, wherein the defected region can be a porous layer or a defected layer within the first reinforcement material, or a grain boundary between crystalline grains.

7. The ceramic reinforcement material of claim 1, wherein a plurality of defected regions are formed in the first reinforcement material.

8. The ceramic reinforcement material of claim 1, wherein the defected region and the first reinforcement material are stacked alternatively to form a multi-layer structure.