JP3315483B2 - Ceramic composite sintered body - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic composite sintered body having significantly improved and improved fracture toughness and high-temperature characteristics of ceramics.

[0002]

2. Description of the Related Art Ceramics have excellent characteristics such as high mechanical strength, excellent chemical stability and abrasion resistance, and low specific gravity. Oxide-based aluminum oxide (Al)
₂ O ₃ ), zirconium oxide (ZrO ₂ ), nitride silicon nitride (Si ₃ N ₄ ) and aluminum nitride (Al
N), and in the carbide system, sintered bodies such as silicon carbide (SiC) are widely used.

[0003] Recently, research on applying these ceramic materials to high-temperature structural members such as various parts of an automobile engine has been advanced. How to overcome and improve brittleness. For this reason, many attempts have been made to improve the strength and toughness of ceramic materials, and toughness and high strength by compounding with whiskers and long fibers and controlling the composition have been proposed.

For example, JP-A-2-141466 discloses a ceramic composite material in which strength at room temperature or high temperature is improved by dispersing SiC particles of 1.0 μm or less in crystal grains of an MgO matrix. Have been. Japanese Unexamined Patent Publication (Kokai) No. 4-202059 discloses that Si ₃ N is dispersed by dispersing particles of 1 to 500 nm in columnar silicon nitride or sialon having a minor axis diameter of 0.05 to 3 μm and an aspect ratio of 3 to 20. ₍₄ ) A method for improving the strength of a sintered body is disclosed.

[0005] As described above, ceramic composite materials in which nanometer-sized fine particles are dispersed and compounded in ceramic crystal particles to improve strength and toughness are known, and are referred to as nanocomposites or nanocomposites. Is.
However, even ceramic composites (hereinafter referred to as nanocomposites) in which these nanometer-sized particles are dispersed provide high fracture toughness and fracture energy, as well as excellent high-temperature properties such as creep resistance. In that respect, it is not sufficient, and further improvement in characteristics has been desired.

[0006]

SUMMARY OF THE INVENTION In view of the above circumstances, the present invention provides a ceramic which has sufficient strength as a structural material and has improved and improved high-temperature properties such as fracture toughness and creep resistance at room temperature and high temperature. An object is to provide a composite sintered body.

[0007]

Means for Solving the Problems To achieve the above object, a ceramic composite sintered body provided by the present invention comprises a matrix having ceramic crystal particles,
A matrix dispersed in the crystal grains of the matrix and / or in the grain boundary phase thereof and a spherical particle of another type of nanometer-sized ceramic;
A matrix in the range of 30 μm and having a thickness of 6 μm or less and plate-like particles of another type of ceramics,
The content of the plate-like particles is 0.5 to 20% by volume of the whole.

[0008]

The ceramic composite sintered body of the present invention not only disperses conventional nanometer-sized particles (hereinafter referred to as nanoparticles), but also disperses slightly larger micron-sized plate-like particles in the grain boundary phase. Then, by performing the hybridization with the crystal grains and the grain boundary phase of the matrix, the fracture toughness and the high-temperature characteristics can be remarkably improved as compared with the conventional nanocomposite.

That is, in the ceramic composite sintered body of the present invention, by dispersing the plate-like particles in the grain boundary phase, a pull-out effect for preventing the propagation of cracks in the ceramic,
The bridging effect, the deflection effect at the crack tip, and the like are induced, and the toughness and fracture energy of the ceramic composite sintered body can be significantly improved. In particular, since flat plate-like particles are used in the present invention, it is considered that they exert an effect on the deflection effect at the crack tip.

[0010] Furthermore, the nanoparticle present in the intragranular and / or grain boundary phase enhances the effect of pulling out and bridging the plate-like particle, and the nanoparticle itself also exerts an effect on crack deflection and the like, so that the crack progresses. Therefore, it is considered that the toughness and fracture energy of the ceramic composite sintered body are further improved.

In particular, when the crystal grains of the matrix are oxide and the nanoparticles dispersed in the grains are non-oxide, residual stress due to the difference in the coefficient of thermal expansion often occurs in the matrix. So that intragranular fracture is induced,
Therefore, the crack does not pass through the grain boundary portion having a weak bonding force, which leads to an improvement in the characteristics. In addition, there is often a large difference in the coefficient of thermal expansion between the plate-like particles and the crystal grains of the matrix, which results in small cracks that improve stress concentration and increase toughness and fracture energy. It is effective.

Also, the ceramic composite sintered body of the present invention
The creep characteristics at high temperatures can be significantly improved as compared with the conventional nanocomposite. This is because, in addition to the flat plate-like particles dispersed at the grain boundaries, grain boundary slip is suppressed, and the movement, diffusion, and grain boundary slip of the transition are suppressed by nanoparticles present in the grains and / or at the grain boundaries. It is thought to be because.

In the ceramic composite sintered body of the present invention, the ceramic constituting the crystal grains of the matrix is not particularly limited, and may be any of oxide-based and non-oxide-based materials conventionally used as structural materials. , Al
Preferred are ₂ O ₃ , ZrO ₂ , Si ₃ N ₄ , SiC or AlN. Further, ceramic constituting the spherical particles and / or plate-like particles are dispersed is a different kind of ceramic matrix may be similar to those which have been conventionally used as nanoparticles. Among these Al ₂ O ₃ , ZrO ₂ ,
Si ₃ N ₄ or SiC is preferred.

The size of the plate-like particles in the present invention must be such that the diameter of the flat particles is in the range of 5 to 30 μm. When the diameter is less than 5 μm, the contribution of the drawing effect and the crack deflecting effect is reduced, so that sufficient characteristics cannot be obtained.
If it exceeds 30 μm, the sinterability is reduced, and especially when the matrix is an oxide, many microcracks and the like are generated around the plate-like particles, so that an improvement in characteristics cannot be expected. Further, in order to sufficiently exert the effect of the above-mentioned plate-like particles, it is desirable that the thickness of the flat plate-like particles is 6 μm or less, preferably 3 μm or less.

Further, in order to exert the above-mentioned effects of improving the fracture toughness and high-temperature characteristics, the amount of the plate-like particles needs to be 0.5 to 20% by volume of the entire composite sintered body.
The reason is that if it is less than 0.5% by volume, the effect of improving the fracture toughness and high temperature properties does not appear, and if it exceeds 20% by volume, the densification of the composite sintered body is hindered, and the mechanical properties are greatly reduced. is there.

On the other hand, the spherical particles are the same as the nanoparticles used in the conventional nanocomposite, but the average particle diameter is preferably 100 nm or less. Further, the content of the spherical particles is preferably in the range of 5 to 30% by volume of the entire composite sintered body. The reason is that the content of the spherical particles is 5% of the whole.
If it is less than 3% by volume, the effect of the present invention cannot be obtained, and
If the content exceeds 0% by volume, the particles form aggregates and deteriorate the properties of the composite sintered body.

Incidentally, the production of the ceramic composite sintered body of the present invention comprises the steps of:
Nanometer-sized spherical particle powder and 5-30 diameter
The powder of micron-sized plate-like particles having a thickness of 6 μm or less and a thickness of 6 μm or less may be mixed, a suitable sintering aid may be added as needed, and sintering may be performed in a suitable atmosphere. The spherical particle powder and the plate-like particle powder are both publicly known, and can be obtained as powders having different shapes due to a difference in crystal system or the like by changing the method of producing the powder and the production conditions.

[0018]

EXAMPLE 1 An average particle size of 10 was added to γ-Al ₂ O ₃ powder having an average particle size of 25 nm.
Β-SiC (spherical particle) powder of 0 nm or less
Volume% and α of 10 to 20 μm in diameter and 3 to 6 μm in thickness
-SiC (plate-like particles) powder was added in an amount of 20% by volume of the whole, and after sufficient mixing, pressure sintering was performed at 1850 ° C and 30 MPa in a nitrogen gas atmosphere.

In the obtained composite sintered body material of the present invention, spherical particles of SiC having an average particle diameter of 100 nm or less are contained in the intragranular phase and the grain boundary phase of Al ₂ O ₃ crystal grains as a matrix, and in the grain boundary phase. Had a structure in which plate-like particles of SiC having a diameter of 10 to 20 μm and a thickness of 3 to 6 μm were dispersed.

Various evaluation tests were performed on the composite sintered body material. As a result, the crack propagation resistance is shown in FIG.
2 and the results of the creep test at 1300 ° C. are shown in FIG. Table 1 shows the breaking energy measured by the CN (Chevron Notch) method and the three-point bending strength measured according to JISR1601.

[0021] For comparison, Al ₂ as Al ₂ O ₃ sintered body
O ₃ powder at 1500 ° C., and Al ₂ O ₃ + as SiC nanocomposite Al ₂ O ₃ powder and 5 vol% beta-SiC powder at 1600 ° C., others were pressure sintering under the same conditions as above. The obtained conventional Al ₂ O ₃ sintered body and Al ₂ O ₃ + SiC
For the nanocomposite, the same evaluation test as above was performed.
The results are shown in FIG. 1, FIG. 2, and Table 1.

[0022]

Table 1 Sintered material fracture energy Г (J / m ² ) Three-point bending strength (MPa) Composite sintered body of the present invention 82.2 800 Al ₂ O ₃ sintered body 11.2 350 Al ₂ O ₃ + SiC nano composite 15.2 1000

From these results, it can be seen that Al ₂ O ₃ + S of the present invention is used.
Although the iC-based ceramic composite sintered body has a three-point bending strength slightly lower than that of the Al ₂ O ₃ + SiC nano composite compared to the conventional Al ₂ O ₃ sintered body and Al ₂ O ₃ + SiC nano composite. It can be seen that the Al ₂ O ₃ ceramic has sufficiently high strength, and at the same time, has very high fracture toughness and fracture energy, as well as extremely excellent creep resistance.

Example 2 The powders constituting the matrix, spherical particles and plate-like particles shown in Table 2 below were blended and sintered according to the conditions shown in Table 2. Each of the spherical particles had an average particle size of 1
Powder having a diameter of 5 nm or less, and
Those having a thickness of ３０30 μm and a thickness of 3 μm or less were used.

[0025]

TABLE 2 spherical particles shaped particles sintering temperature N ₂ pressure sample matrix vol% vol% (℃) ( atm) 1 Al 2 O 3 SiC 5 SiC 10 1900 1 2 Al 2 O 3 Si 3 N 4 10 SiC 10 1900 13 Al ₂ O ₃ SiC 10 ZrO ₂ 20 1850 14 Al ₂ O ₃ ZrO ₂ 20 ZrO ₂ 10 1900 15 * Al ₂ O ₃ − − SiC 10 1900 16 * Al ₂ O ₃ SiC 5 SiC 25 2000 17 * Al ₂ O ₃ SiC 5 SiC 0.1 1800 18 * Al ₂ O ₃ SiC 5 − 1600 19 * Al ₂ O ₃ ZrO ₂ 10 − 1600 1 10 * Al ₂ O ₃ − − 1500 1 11 Si ₃ N ₄ SiC 10 SiC 15 1900 5 12 Si ₃ N ₄ SiC 20 SiC 5 1900 5 13 * Si ₃ N ₄ SiC 20 − 1850 5 14 * Si ₃ N ₄ − − 1800 5 15 ZrO ₂ SiC 15 SiC 15 1800 1 16 ZrO ₂ Si ₃ N ₄ 5 SiC 10 1800 1 17 ZrO ₂ Al ₂ O ₃ 20 Al ₂ O ₃ 10 1800 1 18 * ZrO ₂ SiC 10 − 1800 1 19 * ZrO ₂ − − 1600 1 20 AlN SiC 10 SiC 15 1950 1 _{21 AlN Si 3 N 4 10 SiC} 20 1950 1 22 * AlN - - 1800 1 23 SiC Si 3 N 4 10 SiC 15 2000 5 24 * iC - - 2000 5 (Note) samples * in the table are comparative examples.

For each of the obtained sintered compact samples, the relative density, the fracture toughness value by the SEPB test (pre-crack introduction test) in accordance with JIS R1607, and the room temperature and 1200 ° C. in a vacuum using a high-temperature microscope hardness meter. Were measured for Vickers hardness, and the results are shown in Table 3.

[0027]

[Table 3] (Note) Samples marked with * in the table are comparative examples.

From the above results, when comparing the conventional single sintered body and the nanocomposite with the composite sintered body of the present invention having the same matrix as the matrix, the nanoparticles were placed in the intragranular and grain boundary phases and the plate-like particles. It is understood that the composite sintered body of the present invention in which is dispersed in the grain boundary phase has remarkably high fracture toughness and has improved high-temperature hardness.

[0029]

According to the present invention, a ceramic having a sufficient strength as a structural material and having significantly higher high-temperature properties such as fracture toughness and creep resistance at room temperature and high temperature than conventional nanocomposites. A composite sintered body can be provided. Therefore, the ceramic composite sintered body of the present invention is particularly useful as a high-temperature structural material for automobile engine parts and the like.

[Brief description of the drawings]

FIG. 1 is a graph showing crack propagation resistance in an Al ₂ O ₃ + SiC-based composite sintered body of the present invention, a conventional nanocomposite of the same type, and an Al ₂ O ₃ sintered body.

[Figure 2] Al ₂ O ₃ + 130 in the conventional nanocomposite and Al ₂ O ₃ sintered body of the present invention composite sintered body and syngeneic SiC-based
It is a graph which shows a stress-strain straight line in a 0 degreeC area.

────────────────────────────────────────────────── ─── front page continued (51) Int.Cl. ⁷ identifications FI C04B 35/584 C04B 35/58 104K (56 ) references Patent Rights 2-160669 (JP, a) Patent Rights 2-289470 ( JP, A) JP-A-5-58751 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/00-35/84

Claims (5)

(57) [Claims] 1. A matrix having crystal grains of ceramics, a matrix dispersed within the grains of the crystal grains of the matrix and / or a grain boundary phase thereof, and spherical particles of a nanometer-sized ceramic of a different kind, and dispersed in a grain boundary phase. A matrix having a diameter in the range of 5 to 30 μm and a thickness of 6 μm or less and plate-like particles of another type of ceramic, and the content of the plate-like particles is 0.5 to 20
A ceramic composite sintered body characterized by volume%. 2. The ceramic composite sintered body according to claim 1, wherein the spherical particles have an average particle diameter of 100 nm or less and the content thereof is 5 to 30% by volume of the whole. 3. The ceramic composite sintered body according to claim 1, wherein the thickness of the plate-like particles is 3 μm or less. 4. The ceramic constituting the crystal grains of the matrix is Al ₂ O ₃ , ZrO ₂ , Si ₃ N ₄ , SiC or AlN, and the ceramic constituting the spherical particles and / or the plate-like particles is Al ₂ O ₃ , ZrO ₂ , Si ₃ N ₄ or Si
The ceramic composite sintered body according to any one of claims 1 to 3, wherein C is C. 5. The ceramic constituting the crystal grains of the matrix is an oxide, and the ceramic constituting the spherical particles and the plate-like particles is a non-oxide.
The ceramic composite sintered body according to claim 1.