JPH05319937A - Functionally gradient material - Google Patents

Abstract

PURPOSE:To obtain a functionally gradient material resistant to warpage and bending and having improved oxidation resistance and strength at high temperature by using a surface layer having excellent oxidation resistance at high temperature and an inside layer having excellent strength at high temperature and interposing an intermediate layer having compositions continuously varying from that of the surface layer to the inside layer. CONSTITUTION:The functionally gradient material is composed of a composite material having plural compositions. The surface layer 1 is made of MgO or Al2O3 and the inside layer 2 is made of a sialon ceramic material. The intermediate layer 3 between the surface layer 1 and the inside layer 2 has stepwise or continuously varying composition. The composition of the intermediate layer 3 gradually varies from that of the surface layer 1 (Al2O3 or MgO) to the inside layer 2 (sialon ceramic).

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a functionally graded material suitable for high temperature materials.

[0002]

2. Description of the Related Art At present, in the field of ceramics, as functional requirements for materials become stricter, development of composite functional materials having various properties is under way. The composite functional material is a material in which excellent ceramic materials are singly stacked in layers to form a composite, and the advantages of each material are combined to improve the characteristics as a whole.

In order to produce this composite functional material, the pressing method is mainly adopted from the economical point of view. This method is a method in which different ceramic powders are sequentially supplied into the die and each powder is pressed by a punch to form a layered compact.

By the way, one of the ceramics of the composite functional material is one used under high temperature conditions, and non-oxide ceramics such as SiC and Si ₃ N ₄ are used as the high temperature material. The pressing method is also used when producing the composite functional material for high temperatures.

[0005]

However, the composite functional material using non-oxide ceramics such as SiC and Si ₃ N ₄ used as a high temperature material has a problem that it is oxidized at a temperature of about 1500 ° C. Therefore 1500 ° C
It was difficult to use at the above temperature.

Further, when the composite functional material for high temperature material manufactured by using the pressing method is used at high temperature, thermal stress is generated due to the difference in thermal expansion coefficient between the combined material layers. Depending on the situation, problems such as warping and bending may occur between the layers. It is possible to use oxide-based ceramics as the high temperature material, but this material has a problem in that it has low strength at high temperatures and is not suitable for high temperature materials.

The present invention has been made based on the above circumstances, and has excellent oxidation resistance at high temperatures, and warpage at high temperatures,
An object of the present invention is to provide a functionally graded material that can suppress the occurrence of defects such as bending and is suitable for high temperature materials.

[0008]

The functionally graded material of the first invention of the present application is a composite material composed of two or more kinds of compositions, the surface layer of which is MgO and the inside of which is sialon-based ceramics. It is characterized in that the composition between the layer and the sialon-based ceramic layer sequentially changes.

The functionally gradient material of the second invention of the present application is a composite material composed of two or more kinds of compositions, the surface layer of which is Al ₂
O ₃ and the inside are sialon-based ceramics, and the composition between the Al ₂ O ₃ layer and the sialon-based ceramics layer is sequentially changed.

The sialon ceramics used in the functionally graded materials of the first and second inventions are:
Si ₃ N ₄ —Al ₂ O ₃ —AlN—SiO ₂ system, which has excellent heat resistance and corrosion resistance.

The sialon-based ceramics of the inner layer in the functionally graded materials of the first and second inventions need only have a constituent phase satisfying the sialon composition, and it is not necessary that all the phases are sialon. That is, the inner layer of the material may include a grain boundary phase such as a glass phase.

The concentrations of MgO and Al ₂ O ₃ in the functionally graded materials of the first and second inventions are 100% in the surface layer 1 and 2 in the inner layer 2 as shown in FIGS. 1 and 2.
Is 0% in the sialon-based ceramics layer, and changes in steps or continuously in the intermediate layer 3 between the surface layer 1 and the inner layer 2. However, when the sialon-based ceramic in the inner layer contains Al ₂ O ₃ as an auxiliary agent, the concentration of Al ₂ O _{3 in} the sialon-based ceramic in the inner layer does not become 0%.

MgO and Al ₂ employed as the surface layer in the functionally graded materials of the first and second inventions
O ₃ is an oxide-based ceramic and therefore has excellent resistance to oxidation at high temperatures. Moreover, the sialon-based ceramics adopted as the inner layer is a material having excellent strength at high temperatures. Therefore, this functionally graded material can suppress the oxidation at a high temperature of 1500 ° C. or higher, which has been difficult to achieve in the past, and the
It can be used under temperature conditions above ℃.

Further, in this functionally graded material, a layer in which the composition of sialon-based ceramics, which is an oxide-based ceramics, is continuously or stepwise changed is formed as an intermediate layer between the surface layer and the inner layer. Has been done. For this reason,
When this material is used at a high temperature, the generation of thermal stress due to the difference in the coefficient of thermal expansion between the surface layer and the inner layer is mitigated, and the defects such as warpage and bending in the material can be suppressed. Therefore, it is possible to remove the obstacle at high temperature and adopt an economical pressing method to form the molded body.

[0015]

EXAMPLES Examples of the present invention will be described below. Example 1 Al ₂ O ₃ and AlN were added to silicon nitride powder so as to form sialon after firing, to prepare a powder for the inner layer.

Next, 10 parts by weight, 20 parts by weight, 40 parts by weight, 60 parts by weight of MgO powder are added to the powder for the inner layer, respectively.
It was added so as to be 80 parts by weight to prepare 5 kinds of intermediate powders. After adding 5 parts by weight of binder to each powder, first, 2 g of MgO powder was put into a mold of 50 mm length × 50 mm width, and subsequently, 2 g of MgO 80 parts by weight powder and MgO 60 were added.
2 parts by weight of powder, and 2 parts each of the remaining 40 parts by weight powder, 20 parts by weight powder, and 10 parts by weight powder were also added. Finally, 13 g of Si ₃ N ₄ compounded powder was added for the inner layer.

A pressing method is applied to the powder thus obtained and a molding pressure of 1000 kg is applied to the powder, which is 50 mm in length and 5 in width.
A plate-shaped molded body having a thickness of 0 mm × 5 mm and a weight of 25 g was formed. This molded body was degreased in a nitrogen gas atmosphere and then sintered in a nitrogen gas at 5 atm under conditions of 1775 ° C. for 4 hours to obtain a sintered body.

The composition of the cross section of the thus obtained sintered body was analyzed, and it was found that MgO was 100% in the surface layer.
It was found that MgO decreased almost continuously from the surface layer to the intermediate layer, and sialon was generated in the inner layer.

Three-point bending strength at a temperature of 1300 ° C. and oxidation resistance at a temperature of 1700 ° C. were examined for each of the sintered bodies. As a result, the three-point bending strength at 1300 ° C was 42 Kgf / mm ² That is, the good result that the structure by the oxidation test at 1700 ° C. did not change was obtained. Example 2

In place of MgO in Example 1, Al ₂ O
₃ was added, and the obtained sintered body was examined for three-point bending strength at 1300 ° C. and oxidation resistance at 1600 ° C., respectively. As a result, the three-point bending strength at 1300 ° C was 42 Kgf / mm ² That is, the good result that the structure after the oxidation test at 1700 ° C. did not change was obtained. Comparative example

Only the powder used for the inner layer in Examples 1 and 2 was used, and Example 1 was applied to the obtained sintered body.
Molding, sintering and testing were performed in the same manner as in. As a result, 1
3-point bending strength at 300 ° C is 42 Kgf / mm ² However, in the oxidation test at 1700 ° C., the tissue was considerably eroded.

[0022]

As described above, the functionally graded materials of the first and second inventions are excellent in oxidation resistance and strength at high temperature, and the concentration of the oxide as the inner layer is graded. It is possible to suppress the occurrence of defects such as warpage and bending due to the difference in thermal expansion coefficient, and it is suitable as a ceramic for high-temperature materials, and it can be manufactured by adopting an economical pressing method.

[Brief description of drawings]

FIG. 1A is a diagram showing a configuration of a functionally gradient material according to the first and second inventions. FIG. 6B is a diagram showing the concentration distribution of oxide in the functionally gradient material.

FIG. 2A is a diagram showing a configuration of a functionally gradient material of the first and second inventions. FIG. 6B is a diagram showing the concentration distribution of oxide in the functionally gradient material.

[Explanation of symbols]

 1 ... surface layer, 2 ... internal layer, 3 ... intermediate layer.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication C04B 35/04 Z 8924-4G 35/10 Z 8924-4G

Claims (2)

[Claims] 1. A composite material composed of two or more compositions,
A functionally graded material characterized in that its surface layer is MgO and its inside is sialon-based ceramic, and the composition between these MgO layer and sialon-based ceramic layer changes sequentially. 2. A composite material composed of two or more compositions,
A functionally graded material characterized in that its surface layer is Al ₂ O ₃ and its inside is sialon-based ceramics, and the composition between these Al ₂ O ₃ layer and sialon-based ceramics layer changes sequentially.