JPH02164779A - Ceramic composite material and its production - Google Patents

Abstract

PURPOSE:To improve the strength and toughness of the ceramic composite material by dispersing the SiC fine particles having a specified diameter and the SiC whiskers having a specified diameter in the crystal grains of an MgO matrix having specified size. CONSTITUTION:The SiC fine particles having <=1.0mu diameter and the SiC whiskers having <=3mu diameter are dispersed in the crystal grains of the MgO matrix having 0.5-100mu size to obtain the ceramic composite material. The material is produced by mixing the MgO pulverized to <=5mu particle diameter, the SiC pulverized to <=1.0mu particle diameter, and the SiC whiskers having <=3mu diameter, and calcining the mixture. Since the SiC fine particles are dispersed in the crystal grains of MgO, residual stress is produced due to a difference in the thermal expansion between both materials, hence the cracking of MgO is prevented, and the high-temp. strength is improved. In addition, the drawing effect of the SiC whiskers is simultaneously generated, and high toughness is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a ceramic material with a special structure and a method for producing the same. Furthermore, in detail, it has a special structure, high strength,
This article relates to a heat-resistant, high-performance composite ceramic material and its manufacturing method.

[Prior Art] Although MgO has excellent heat resistance, corrosion resistance, and electrical insulation, it has poor high-temperature strength, fracture toughness, and thermal shock resistance, and is insufficient in terms of strength to be used as a structural material. .

Generally, fine particles (SiC, 5IjN4, etc.) are dispersed as a second phase in a material matrix (e.g. in alumina particles) and sintered to significantly improve physical properties, especially high strength. There are many reports in the literature that it is possible to obtain the following. Among them, MgO
The -3iC system has been reported in the Daiku Shiki report, and it has been reported that its strength is significantly increased and that it is possible to improve the MgO properties. In this report, it was concluded that the increase in strength of MgO due to SiC compounding is due to the obstruction of crack growth caused by crack defraction caused by the uneven distribution of SiC particles at MgO grain boundaries. ing.

In addition, in ceramic sintered bodies such as alumina, a matrix is formed of anisotropic particles, so
It is well known that distortion occurs at grain boundaries due to the difference in thermal expansion between adjacent grains, and for this reason, the grain boundaries become a source of fracture, resulting in a decrease in strength. In addition, there are many ceramic composites in which whiskers are dispersed in order to achieve high strength, but in most cases, the purpose is to obtain high toughness due to the pull-out effect of the whiskers.
Have difficulty. As described above, by dispersing particles or whiskers in the ceramic matrix, the propagation of cracks is inhibited, and therefore, it is expected that toughness will be improved. According to this idea, there is no change in the grain boundary defects that are the source of fractures, and the defects remain as they are, so no significant improvement in strength could be expected.

[Problems to be Solved by the Invention] In order to eliminate the above-mentioned drawbacks, the present invention provides a ceramic composite with high strength and high toughness as a structural ceramic material in which SIC fine particles are composited in an MgO matrix. The purpose is to Therefore, an object of the present invention is to provide a ceramic composite in which the characteristics of MgO are improved. Furthermore, in ordinary fire-resistant, heat-resistant materials, and electronic ceramic materials, thermal shock resistance can be obtained without growing crystals to a large size, and
The object is to provide a material with significantly improved fracture properties during use.

[Means for solving the problems] The present invention provides SiC with a particle size of 1.0 μm or less in an MgO matrix having crystal grains of 0.5 μm to 1100 μm.
This is a ceramic composite material characterized by dispersing fine particles and SICIC rice skulls with a diameter of 3 μm or less. The manufacturing method involves finely pulverizing M to a particle size of 5 μm or less.
This is done by mixing gO, SiC finely pulverized to a particle size of 1°0 Bm or less, and SiC whiskers having a diameter of 3 ttm or less, and firing the mixture.

[Function] The ceramic composite according to the present invention has Mg0t=
In the crystals of the lamic composite material itself, S
The aim is to strengthen and improve the characteristics of a ceramic body by performing so-called nano-order composites in which iC fine particles are dispersed.

That is, by dispersing S%C fine particles by 1 degree in each MgO crystal grain, it is possible to generate residual stress due to the difference in thermal expansion coefficients of MgO and 5iCO. The idea is to use this residual stress to generate a compressive stress field at the grain boundaries of adjacent grains, and to prevent the propagation of cracks by pinning or defraction at the tips of cracks that are about to propagate. .

Such a mechanism will be discussed in further detail with reference to FIG. As for IZg, the ceramic composite of the present invention has a structure in which fine particles of SiC are dispersed within each grain of an MgO matrix, as shown in the schematic diagram of FIG. By dispersing the fine particles, residual stress due to the difference in thermal expansion coefficient between MgO and SiC is avoided. This stress causes a compressive stress field to be generated at the grain boundaries of adjacent MgO particles, and by pinning (or diffraction) the tip of a crack that is about to propagate by 4 degrees to that stress field, crack propagation is prevented. be.

In other words, this stress suppresses slippage and cavitation at MgO grain boundaries, which are major causes of low high-temperature strength of MgO, and thus improves high-temperature strength. Furthermore, the dispersed SiC particles inhibit dislocation movement in MgO at high temperatures, and also suppress high-temperature deformation of MgO itself. Therefore, high strength and high toughness can be obtained. Furthermore, in order to further increase the toughness of the present composite, when SiC whiskers are added, the external stress field simultaneously causes a pull-out effect of the whiskers, so that even greater toughness can be obtained. Naturally, crack propagation due to crack diffraction is prevented, and high strength and toughness can be obtained.

In the present invention, using MgO5 dispersed particles, SiC fine particles and SiC whiskers as a matrix,
This is a feature. The MgO matrix particle size is 0.5 μm to 1100 μm, the SiC fine particles have a particle size of 1.011 m or less, and the SiC whiskers have a diameter of 3 μm.
In the following, SiC filter particles Si in the MgO matrix
It has a structure in which C whiskers are dispersed. The raw materials include MgO finely ground to a particle size of 5 μm or less and
．． SiC finely ground to a particle size of 3μm or less and a diameter of 3μm
The above-mentioned ceramic composite material is manufactured by mixing and firing SiC whiskers having a diameter of less than m.

The MgO matrix particle size in the ceramic composite is
The reason why the diameter is set to 0.5 μm to 100 μm is that this is the range where the strength of the sintered body is maximized, and the reason why the particle size of the SiC fine particles is set to 1.0 μm or less is because the optimum size is incorporated into the MgO matrix crystal grains. This is because the particle size range is .

The reason why the MgO used as the raw material is finely pulverized to a particle size of 511 m or less is because it is easy to sinter, and the reason why the raw material SiC is pulverized to a particle size of 1.0 μm or less. If the thickness exceeds 1.0 μm, microcracks will occur, and SiC in the matrix grains.
and that microcracks do not occur even if the residual stress exceeds a certain limit. The main reason for using SiC whiskers is to improve the toughness in terms of crack growth prevention 1F due to the pull-out effect of the whiskers.

The matrix MgO according to the present invention needs to be sintered densely in the sintering process, and the dispersed phase of SiC
It is necessary that the particles be uniformly dispersed.

This dispersed phase needs to have a lower coefficient of thermal expansion than the matrix, and further needs to maintain higher strength and hardness than the matrix at high temperatures. In addition, the SiC whiskers must be incorporated into the matrix particles during the sintering process.
Must be uniformly dispersed in the matrix.

For this purpose, the sintering temperature must be made sufficiently high; a sintering temperature of 1300°C is also possible, but in consideration of reheating shrinkage, etc., it is desirable to sinter at a temperature of 1400°C or higher.

The ceramic composite obtained by the present invention is particularly suitable as a heat-resistant material and as a refractory material having corrosion resistance, high hot strength, thermal shock resistance, and high toughness.

Next, the results of manufacturing the ceramic composite of the present invention and measuring its obtained properties will be explained.
The present invention is not limited to the following examples.

[Example] [Irukashidadama LII] The matrix includes MgO #1 o o manufactured by Ube Co., Ltd.
o (v average particle size 0.1μ, purity 99.99%),
As the SiC to be added, 5jC manufactured by IBIDEN Co., Ltd.
(β-Random Ultra Fine) and SiC whiskers (SCW) manufactured by Tateho Chemical Co., Ltd., the SIC particles were fixed at 10% by volume with respect to the matrix material, and the SiC whiskers were fixed at 5 to 30% by volume. They were added and mixed in proportion.

Ethyl alcohol was added as a dispersion medium to this mixed powder, wet-mixed, and pulverized and mixed in an alumina ball mill for 12 hours. After sufficiently drying this, dry mixing was performed for 24 hours in an alumina ball mill, and the sample was ground and used.

[Sintering Treatment] For the sintering treatment, an induction heating hot press device (manufactured by Fuji Denpa Kogyo) was used. Approximately 32 g of the AICIC rice powder prepared as described above was filled into a lead die (inner diameter 55 mm), and a 10 M
After pre-compression to Pa, sintering treatment was performed. At this time, in order to prevent the filled sample from coming into direct contact with the inner wall of the die and the pressing area of the punch rod and reacting, these areas were coated with BN powder, and this -L was further coated with graphite foil (
The sample was filled into the sample. The hot pressing conditions were such that the temperature was raised to the sintering temperature and then held for 1 hour, the pressing pressure was 30 MPa, and argon gas was used as the atmospheric gas. The obtained sintered body had a size of about 5041111×4.

[Ku Ka and To 1] Both surfaces of the obtained sintered body were ground with a diamond wheel to a roughness of #1000, and this was cut into a rectangular parallelepiped with a diamond cutter. The sample is JIS R
In accordance with the 1601 regulations, the length of the 3x4 pustules was approximately 36 cm, which was the size of the 3-point bending test piece.

[Honey U constant] Density was measured in a toluene solution using the Archimedes method. The samples were measured using three or more of the above bending test pieces.

[1 payment mass production fi1 bending strength is determined by 3-point bending test method at a loading rate of 0.5■
The strength was measured at room temperature and a high temperature oxidizing atmosphere (up to 1400°C) at a span length of 30cm/min. However, the high temperature strength was measured only on some test pieces. The tensile surface of the test piece was polished to a mirror finish using diamond paste (3μ), and the cut and 7-edge portions were chamfered at an angle of 45° to a width of approximately 0.1, and the measurements were taken.

[Measurement of Vickers hardness and fracture toughness] Vickers hardness and fracture toughness were measured using a microphone [1 pin force-force hardness meter]. Fracture toughness was measured by the 1M method under a load of 1 kg and a holding time of 10 seconds.

[Relationship between amount of added SiC and density] Density measurements revealed that the matrix MgO was made dense by producing a composite with the above structure. That is, FIG. 2 shows the relationship between sintering temperature and SiC
Si showing the change in relative density with respect to whisker addition amount
The amount of C particles added is constant at 10% by volume.

From the results of X-ray diffraction, no mutual reaction between MgO/SiC was observed at sintering temperatures up to 1900''C, but the theoretical density at this time was MgO-3,58
g/as", S i C-3, 21170m",
Calculated by mixing each in a simple ratio, 10
The relative density was determined by setting it to 0%.

MgO without SiC addition has a relative density of 100% at a sintering temperature of 1300° C. or higher. However, as the amount of SiC added increased, the sintering of the matrix was significantly suppressed.
Densification of MgO requires high sintering temperatures.

The relative density of the sintered body fired at 1900° C. with an added amount of SiC whiskers up to 20% by volume was almost 100%. Si
When the amount of C whisker added exceeds 20% by volume, the relative density becomes 97% or less, making it difficult to achieve densification. This is because the inclusion of SiC whiskers inhibits the densification of the matrix MgO by sintering, that is, the S
It is thought that the presence of iC whiskers suppressed the densification and sintering between the zero particles in M, and as a result, the reduction of voids during sintering was insufficient, and residual pores remained in these areas. It is thought that increasing the amount of SiC whiskers added increases the number of voids.

[1 Buddhist Emperor 2 Five Cliffs 1] Figure 3 shows the relationship between the three-point bending strength and the SiC whisker addition temperature. From this measured value, 1300
℃ sintered body, maximum value 430MPa, average 300MPa
The strength was about a. On the other hand, when SiC whiskers are added from 5% to 30% by volume, approximately 600 to 70%
A -F direction of strength was observed up to 50 MPm. Observation of the fracture surfaces of these samples revealed that they were very complex, indicating that the high strength of MgO was due to crack defraction caused by the addition of SIC whiskers.
It is thought that the toughness has been improved.

In sintered bodies with insufficient w1 density (relative density of 95% or less), a significant decrease in strength was observed compared to those with a density of around 100. These often collapsed during sample processing 41. This is thought to be due to insufficient sintering and the residual pores that are present become a source of matrix destruction.

[Effect of SiC whisker addition on hardness and fracture toughness] Figures 4 and 5 are graphs showing the relationship between the amount of SiC whisker added and Vickers hardness and fracture toughness.

This is about 2
A significant improvement in hardness was observed, with double hardness: approximately 10 GPa. When the amount added was further increased, the hardness tended to increase monotonically. When the amount of SiC whiskers added was up to 30% by volume, the hardness improved to about 12 GPa.

A similar trend was observed for fracture toughness.

Therefore, as the SiC whisker addition value increases, the toughness improves, and when the SiC whisker addition amount is 30% by volume,
4. Approximately 2.5 times that of MgO alone (1300°C sintered body).
The toughness value increased to 8 MPa·ll1/fi. S
When no iC particles or whiskers were added, the shape of crack growth from the Vickers indentation was linear. On the other hand, in the case where SiC particles and whiskers were added, a remarkable curved surface was observed in the shape of crack growth, which was thought to be due to the occurrence of diffraction. It is thought that the occurrence of this diffraction improved the toughness and, as a result, the strength.

[Effect of SiC addition on high-temperature bending strength vg] Figure 6 shows the bending strength in a high-temperature oxidizing atmosphere of an MgO sintered body produced at a sintering temperature of 1900°C and containing 10% by volume of each of SiC particles and whiskers. This is a graph showing the results.

It is known that a significant decrease in strength occurs in M g Orlt bodies at high temperatures. In the case where SiC particles and whiskers were added, no decrease in strength was observed from room temperature to 1400°C, and the strength was maintained at the same level as room temperature. And Si
In the case where the amount of C added was 10% by volume, a remarkable increase in strength was observed at around 1000°C. In particular, the surface of the sample heated to around 1400° C. turned white. This is thought to be caused by the oxidation of SiC, and the occurrence of this oxidation causes the strength paper F. Therefore, Si
It has been shown that the strength at high temperatures can be significantly improved by adding C.

[Effects of the Invention] The SiC-added MgO matrix according to the present invention provides the following remarkable technical effects.

First, as is clear from the above description, it is possible to provide an MgO/SiC composite material that has utility as a structural material that can be used at high temperatures.

Second, the MgO matrix ceramic composite obtained by the manufacturing method of the present invention can have significantly improved properties and high strength.

Thirdly, the ceramic composite of the present invention makes use of the characteristics of MgO and can provide a material having high strength and high toughness.

FIG. 1 is an explanatory diagram schematically showing the structure of the ceramic composite of the present invention.

FIG. 2 shows the relationship between the densification of the MgO matrix sintered body according to the present invention and the amount of SIC whiskers added.
This is a graph.

FIG. 3 is a graph in which the measured bending strength is plotted against the content of SiC whiskers, in order to show the relationship between the bending strength of the MgO matrix/customer sintered body according to the present invention and the amount of SiC whiskers added. .

FIG. 4 is a graph in which the measured Vickers hardness is plotted against the SiC whisker content in order to show the relationship between the Vickers hardness of the MgO matrix sintered body according to the present invention and the amount of SiC whiskers added.

FIG. 5 is a graph in which the measured fracture toughness is plotted against the SiC whisker content in order to show the relationship between the fracture toughness of the MgO matrix sintered body according to the present invention and the amount of SiC whisker added.

FIG. 6 is a graph plotting the measured high temperature bending strength against temperature to show the bending strength at high temperatures of the sintered body of the MgO matrix and SiC whisker composite according to the present invention.

Patent applicant: 3FFF, Gyo Cement Co., Ltd. (1 other person)
Attorney Hiroshi Kuramochi Figure 3 Figure 4

Claims (2)

[Claims] (1) Mg with crystal grains of 0.5 μm to 100 μm
S with a particle size of 1.0 μm or less in the crystal grains of the O matrix
A ceramic composite material characterized by dispersing iC fine particles and SiC whiskers with a diameter of 3 μm or less. (2) MgO finely ground to a particle size of 5 μm or less and 1.
SiC finely ground to a particle size of 0 μm or less and a diameter of 3 μm
The method for producing a ceramic composite material according to claim 1, characterized in that the following SiC whiskers are mixed and fired.