JP2966989B2 - Silicon carbide ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon carbide ceramic, and more particularly to a silicon carbide ceramic capable of significantly improving toughness and strength.

[0002]

2. Description of the Related Art In general, when comparing ceramics and metal materials, both the toughness and strength of ceramics are low, and the strength distribution is unevenly distributed in a ceramic molded body, so that stress concentration easily occurs. Tend.
For this reason, it is very difficult to use the ceramic molded body as a member having a complicated shape with a high load, and it has not been put to practical use.

[0003] Therefore, in order to put a ceramic molded body into practical use in various shapes in a wide range of applications, it is necessary to reduce brittleness, improve toughness and strength, and make the strength distribution in the ceramic molded body uniform. It is desired to avoid concentration of stress.

[0004] In response to the above demand, ceramics whose crystal lattices are compounded by whiskers and ceramics whose crystal lattices are compounded by new matrix composites have been adopted.

[0005] As an example, Japanese Patent Application No. Hei 3-60557 filed by the present applicant discloses a "ceramic molded article and a method for producing a ceramic molded article" in which a crystal is grown by firing or heat treatment to obtain a single crystal of extremely high purity. Using the basic constituent particles obtained by depositing three types of hexagonal columnar whiskers of different sizes, fill the gaps between the large diameter whiskers with medium and large diameter whiskers, and further fill the remaining gaps with the small diameter whiskers. By doing so, the ratio of the gaps between the basic constituent particles is greatly reduced. Therefore, in the ceramic molded body, the ratio of the sintering aid, which is significantly inferior in toughness and strength to the hexagonal columnar whisker basic constituent particles to fill the gap, can be reduced, so that the toughness and strength are reduced. And the strength distribution is made uniform to avoid concentration of stress.

[0006] Further, Japanese Patent Application Laid-Open No.
Japanese Patent Application Laid-Open No. 192448 discloses a "ceramic sintered body and a method for producing the same", wherein a formed body is formed from ceramic powder, metal powder or a mixed powder thereof, and then the formed body is pre-baked. By impregnating the metal salt or the metal complex, and further performing the main firing, the pores formed in the calcined body are sufficiently impregnated with the metal salt or the metal complex, and high quality with excellent toughness and strength. A ceramic sintered body capable of obtaining a ceramic sintered body and a method for manufacturing the same have been disclosed.

[0007]

By the way, ceramics obtained by sintering using a starting material mainly composed of silicon carbide (SiC) have a problem in that, in the production thereof, silicon carbide (SiC), which is the main component, is flame-retardant. In order to promote the growth of crystal grains because of its sintering property, and to grow the crystal grains at a relatively low temperature, boron carbide (B ₄ C) and carbon (C) are used as sintering aids.
After the addition of the powdery raw materials such as these, sintering is performed at a sintering temperature significantly exceeding 2000 ° C. in an atmosphere in which water (H ₂ O) and hydrogen (H ₂ ) are present.

At this time, due to the presence of added boron (B), hydrogen (H ₂ ), and water (H ₂ O), the crystal grains constituting the obtained ceramic have a flaky, scaly, or plate-like shape. The tensile strength of such flaky, scaly, and plate-like crystal grains is such that hexagonal column-shaped crystal grains are 2,000 kgf / mm ^2.
On the other hand, for example, in the case of a plate,
There is an upper limit of about kgf / mm ² , and the crystal strength is markedly inferior.

Further, the added boron (B), hydrogen (H ₂ ), and water (H ₂ O) cause crystal cracking 2 (see FIG. 3) and precipitation of foreign matter 4 (see FIG. 3), which are factors that greatly influence the strength. 4
(See FIG. 5) and the formation of spheres 6 (see FIG. 5).

[0010] From the above factors, the ceramic obtained by firing using a starting material composed mainly of silicon carbide (SiC), the flexural strength at room temperature is the upper limit 50 kgf / mm ² degree, the fracture toughness value In general, K _IC 3.5MPa
There is an upper limit at about m1 ^{/ 2} . This value is about 1/2 of the silicon nitride-based material currently on the market, which is almost the same as that of the aluminum oxide-based material.

That is, ceramics obtained by firing using a starting material containing silicon carbide (SiC) as a main component have sufficient toughness and strength necessary for practical use in various shapes in a wide range of applications. It is hard to say that it has been obtained.

Accordingly, it is an object of the present invention to provide a silicon carbide-based ceramic having significantly improved toughness and strength so that it can be put to practical use in various shapes in a wide range of applications.

[0013]

In order to solve the above-mentioned problems, the present invention provides a silicon carbide as a main component and a periodic table VII.
A crystal grain growth material containing at least one or more of the group consisting of iron, nickel, and cobalt which are metal elements belonging to Group I, and a crystal grain containing at least one or more of a group consisting of manganese and chromium Forming a starting material containing a growth promoting material and a crystal grain growth controlling material containing at least one selected from the group consisting of aluminum oxide and yttrium oxide, which are oxides of metal elements belonging to Group III of the periodic table. A silicon carbide-based ceramic having crystal grains obtained by growing the silicon carbide into columnar crystals or hexagonal columnar crystals by firing, wherein the composition of the crystal grain growth material is 0% based on the total weight of the starting material. 0.01% by weight or more and 3.5% by weight or less, and the composition of the crystal grain growth promoting material is 0.1% by weight or more and 1.5% by weight or less based on the total weight of the starting materials. And wherein the adjusted.

[0014]

DETAILED DESCRIPTION OF THE STRUCTURE In the silicon carbide-based ceramics according to the present invention, crystal grains of silicon carbide (SiC), which is a main component of the ceramic, are formed into flakes, scales, and the like having low crystal strength.
Alternatively, instead of plate-like crystal grains, hexagonal columnar crystals 10 (see FIG. 2) having high crystal strength or crystal grains of columnar crystals are grown.

Therefore, instead of boron (B), which is a sintering aid for inducing the precipitation and growth of flaky, scaly or plate-like crystal grains, as a reaction catalyst for sintering flame-retardant silicon carbide, Periodic Table VII to induce precipitation and growth of hexagonal columnar crystals
Iron (Fe), nickel (N
i), a reaction system using cobalt (Co) as a reaction catalyst is formed.

That is, silicon carbide (Si) as a main component
C) a crystal growth material containing at least one member selected from the group consisting of iron (Fe), nickel (Ni) and cobalt (Co) which are metal elements belonging to Group VIII of the periodic table; A crystal grain growth controlling material containing at least one member selected from the group consisting of aluminum oxide (Al ₂ O ₃ ) and yttrium oxide (Y ₂ O ₃ ), which are oxides of metal elements belonging to the group _III; In the periodic table, a crystal grain growth promoting material containing at least one or more of a group consisting of manganese (Mn) and chromium (Cr), which are elements belonging to an adjacent group of the crystal grain growing material, is added. A substance is formed.

The above-mentioned crystal grain growth material, as an oxide, a soluble salt, or a simple metal, has a composition range of 0.01% by weight or more and 3.5% by weight or less based on the total weight of the starting materials.
More preferably, it is added in a composition range of 0.05% by weight to 2.3% by weight. The reason for limiting to this composition range is that if it is less than 0.01% by weight, a substantial effect of growing crystal grains cannot be obtained, and if it exceeds 3.5% by weight, segregation and reduction in sintered density occur. This is because the strength at high temperatures is significantly reduced.

Further, for the purpose of shortening the sintering time and promoting the growth of crystal grains, a crystal grain growth promoting material having a composition range of 0.1% by weight to 1.5% by weight is added. The reason for limiting to this composition range is that if it is less than 0.1% by weight, a substantial effect cannot be obtained, and if it exceeds 1.5% by weight, there is a tendency that plate-like crystal grains grow during sintering. , Toughness and strength.

Incidentally, iron (Fe), nickel (Ni), cobalt (Co), manganese (Mn) and chromium (Cr) constituting the crystal grain growth material and the crystal grain growth promoting material are as follows:
At the time of sintering, it is taken into a grain boundary glass layer formed by aluminum oxide (Al ₂ O ₃ ) and yttrium oxide (Y ₂ O ₃ ) described later. At the same time, the crystal grain growth material and the crystal grain growth promoting material play a role as a transfer carrier for carbon (C) and nitrogen (N), so that carbon (C) transferred into the grain boundary glass layer. And nitrogen (N)
In addition to promoting grain boundary crystallization by heat treatment after sintering, the grain growth material and the grain growth promoting material taken into the grain boundary glass are precipitated in the grain boundary as a metal that has passed through the intermetallic compound, and Improve the strength of.

The crystal grain growth controlling material made of aluminum oxide (Al ₂ O ₃ ) and yttrium oxide (Y ₂ O ₃ ) has an excessive grain growth material and a crystal growth promoting material at a grain boundary during firing. At the same time, a grain boundary glass layer is formed to suppress the growth of crystal grains.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the silicon carbide-based ceramics according to the present invention will now be described in detail with reference to the accompanying drawings.

First, as a main component, the average particle diameter is 0.6 μm.
m, specific surface area 12 m ² / g, silicon carbide (SiC) having a SiC purity of 98% (free carbon 1.0%), and a periodic table VIII.
(Fe), nickel (N
i), a crystal grain growth material containing at least one or more of the group consisting of cobalt (Co);
n), at least one of the group consisting of chromium (Cr)
Grain growth-promoting material containing more than one kind, and Periodic Table III
Using a crystal grain growth controlling material containing at least one kind selected from the group consisting of aluminum oxide (Al ₂ O ₃ ) and yttrium oxide (Y ₂ O ₃ ), which are oxides of metal elements belonging to group _III , Ten kinds of starting materials were formed according to the composition shown in one experimental example 1 to 10.

Next, the starting material is replaced with argon (Ar)
Atmospheric pressure sintering was performed at a sintering temperature of 1900 ° C. to 2000 ° C. in an atmosphere where nitrogen and nitrogen (N ₂ ) were present, to thereby obtain test materials 1 to 10.

Also, using the same raw materials as in the above-mentioned experimental examples 1 to 10, seven kinds of starting materials were formed in accordance with the composition shown in comparative examples 1 to 7 in Table 2. Sintering was performed in the same manner, and comparative samples 1 to 7
I got

Further, as Comparative Example 8 in Table 3, Experimental Example 1
The same silicon carbide (SiC) as that used in Experimental Example 10 and Comparative Examples 1 to 7 was used as a main component, and 96.0% by weight based on the total weight of the starting materials, and boron carbide (B ₄ C) was used. 0
% By weight of carbon (C) and 1% by weight of carbon (C), and then the starting material is constantly subjected to a sintering temperature of 2100 ° C. in an atmosphere in which argon (Ar) and nitrogen (N ₂ ) are present. Pressure sintering was performed to obtain comparative test material 8. The comparative test material 8 is a silicon carbide-based ceramic according to the prior art.

The specimens 1 to 10 of the experimental examples 1 to 10 and the comparative specimens 1 to 8 of the comparative examples 1 to 8 obtained as described above were subjected to a three-point bending strength test and a fracture toughness test by a chevron notch method. Was carried out.

Table 4 shows test materials 1 to 1 of Experimental Examples 1 to 10.
Table 5 shows the test results of Comparative Test Materials 1 to 7 of Comparative Examples 1 to 7, and Table 6 shows the test results of Comparative Test Material 8 of Comparative Example 8.

As can be easily understood from the above test results, the bending strength of Examples 1 to 10 was 70 kg / mm ^2.
From 121 kg / mm ² , and a fracture toughness value from 7.1 MPam ^1/2 to 9.6 MPam ^1/2 . Therefore, the bending strength and the fracture toughness value are about 1.5 to 2.5 times and the fracture toughness value about 2 to 3 times the values of Comparative Example 8 showing the general upper limits of the bending strength and the fracture toughness value in the prior art. A numerical improvement of about twice was achieved.

Therefore, it can be determined that the toughness and the strength have been improved.

When Comparative Examples 1 to 7 are compared with Comparative Example 8 according to the prior art, it cannot be determined that both the bending strength and the fracture toughness have achieved numerical improvements.

On the other hand, in Comparative Examples 1 to 7, which deviate from the composition range limited in numerical values in the present embodiment, the average bending strength is 3
3.1 kg / mm ² , average fracture toughness is 8.7 MPa
Showed ^1/2 . In Examples 1 to 10, the average bending strength was 98.8 kg / mm ² and the average fracture toughness value was 8.7 MPa.
m ^1/2 , so that Examples 1 to 10 and Comparative Examples 1 to 7
And a numerical difference of about 3 times in average bending strength and about 2.5 times in average fracture toughness.

Therefore, it is understood that the limitation of the composition range of the components in the present embodiment is appropriate.

FIG. 1 is a schematic diagram of grain boundary etching of a fractured surface of the silicon carbide-based ceramics 20 of the present embodiment. The silicon carbide-based ceramic 20 is composed of hexagonal columnar crystals having three sizes. The first hexagonal columnar crystals 22
Diameter is about 4μm to 5μm, length is 12μm to 15μ
The second hexagonal columnar crystal 24 has an aspect ratio of about 4 to 8 in a shape having a diameter of about 1 μm to 2 μm and a length of about 6 μm to 8 μm. Have. The third hexagonal columnar crystal 26 has a diameter of about 0.3 μm to 0.5 μm and a length of 4 μm 12 μm.
It has an aspect ratio of 4 to 12 with a shape of about m.

As is well known, these hexagonal columnar crystals are generally made of a single crystal, and have extremely high crystallinity, so that the grain boundaries are strengthened.

The silicon carbide ceramic 20 is
The space between the large-diameter first hexagonal columnar crystals 22 is filled with the second hexagonal columnar crystal 24 having an intermediate diameter, and the gap is filled with the small-diameter third hexagonal columnar crystal 26. Can be reduced, and brittleness due to brittleness between grain boundaries, that is, gaps can be reduced. Therefore, the silicon carbide-based ceramic 2 shown in FIG.
In the fracture surface of 0, it was observed that the intragranular fracture and the intergranular fracture occurred simultaneously because the grain boundary was strengthened.

[0036]

[Table 1]

[0037]

[Table 2]

[0038]

[Table 3]

[0039]

[Table 4]

[0040]

[Table 5]

[0041]

[Table 6]

[0042]

As described above, in the silicon carbide-based ceramics according to the present invention, the crystal grains of silicon carbide (SiC), which is the main component of the ceramic, are formed into flakes, scales, or plate-like crystals having low crystal strength. By arranging hexagonal columnar crystals or columnar crystal grains with high crystal strength instead of grains,
It has the effect of significantly improving toughness and strength.

Accordingly, the silicon carbide ceramics can be put to practical use in various shapes in a wide range of applications.

[Brief description of the drawings]

FIG. 1 is an enlarged schematic view showing a fracture surface of a silicon carbide-based ceramic according to the present invention.

FIG. 2 is an explanatory diagram showing hexagonal columnar crystals constituting the silicon carbide-based ceramic according to the present invention.

FIG. 3 is an explanatory view showing crystal cracks of crystal grains constituting a ceramic according to a conventional technique.

FIG. 4 is an explanatory view showing foreign matter precipitation of crystal grains constituting a ceramic according to a conventional technique.

FIG. 5 is an explanatory view showing generation of spheres of crystal grains constituting a ceramic according to a conventional technique.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Hexagonal columnar crystal 20 ... Silicon carbide type ceramics 22 ... 1st hexagonal columnar crystal 24 ... 2nd hexagonal columnar crystal 26 ... 3rd hexagonal columnar crystal

Claims (1)

(57) [Claims] 1. A silicon carbide as a main component and a periodic table VIII
A grain growth material containing at least one member selected from the group consisting of iron, nickel, and cobalt which are metal elements belonging to the group III, and a grain growth material containing at least one member selected from the group consisting of manganese and chromium Forming a starting material containing: an accelerator; and a crystal grain growth controlling material containing at least one member selected from the group consisting of aluminum oxide and yttrium oxide, which are oxides of metal elements belonging to Group III of the periodic table. A silicon carbide-based ceramic having crystal grains in which the silicon carbide is grown into hexagonal columnar crystals or columnar crystals by firing the starting material, wherein the composition of the crystal grain growing material is based on the total weight of the starting material. 0.01% by weight or more and 3.5% by weight or less, and the composition of the crystal grain growth promoting material is 0.1% by weight or more and 1% by weight based on the total weight of the starting materials. 5 wt% or less, silicon carbide based ceramics, characterized in that the adjustment.