JPH0474770A - High-strength ceramics and production thereof - Google Patents

Abstract

PURPOSE:To easily obtain high-strength, high-toughness polycrystalline ceramics by heat treatment of a ceramic sintered compact, a solid solution comprising plural components to effect phase separation, i.e. precipitation of a phase differing in elastic constant from those of the surroundings inside each grain and grain boundaries making up the sintered compact. CONSTITUTION:Firstly, a mixture of plural kinds of raw material 20 (e.g. silicon carbide, aluminum nitride) is formed and sintered into a ceramic sintered compact or calcined form made up of plural components (at least part of it being a solid solution). Thence, this sintered compact or calcined form is heat-treated to effect phase separation, i.e. precipitation of a phase such as grains 16 or 18 differing in elastic constant from those of the surroundings inside each grain 22 and/or grain boundaries making up the sintered compact, thus obtaining the objective high-strength polycrystalline ceramics.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for manufacturing ceramics and high-strength ceramics, and more particularly to a method for producing polycrystalline ceramics characterized by a strengthening mechanism.

(Prior Art) Polycrystalline ceramics, particularly structural ceramics, have been strengthened by various methods. Typical examples are (a) a method by controlling the starting material such as atomization or high purity of the raw material, (a) a method by selecting or controlling the sintering aid, and (c) a method by controlling the sintering aid.
Fine particles are dispersed in a ceramic matrix, or as shown in FIG.
A method of compositing a reinforcing material 102 such as whiskers, fibers, metal, etc. therein.

(Problems to be Solved by the Invention) However, in the case of the method (a) above, the pure material properties of the starting material are the limit, and it is difficult to improve the properties beyond those of the pure material.

On the other hand, in the case of the method (a) using an auxiliary agent, there is a drawback that the effectiveness is low if the fracture in the ceramic is based on internal fracture of particles constituting the sintered body.

Furthermore, in the method (c) of compositing reinforcing materials such as whiskers and fibers, it may be difficult to mold or it may not be possible to obtain a dense sintered body due to problems such as the affinity between these reinforcing materials and the matrix. However, there is a problem in that the strength may actually decrease in some cases.

The present invention has been made against the background of the above-mentioned circumstances, and its purpose is to provide a method for manufacturing ceramics that is reinforced by a novel mechanism that is completely different from conventional ones, and a method for manufacturing ceramics that is strengthened by this method. The purpose is to provide a ceramic sintered body or a calcined body consisting of a plurality of components that are at least partially dissolved in solid solution, and to heat-treat the ceramic sintered body or calcined body to phase separate the particles constituting the sintered body. The purpose is to precipitate phases with different elastic constants within the grains and/or at the grain boundaries.

(Operations and Effects of the Invention) As described above, the present invention phase-separates (phase-separates) a solid solution consisting of at least a partially homogeneous phase by heat treatment, and provides elasticity within the grains and/or grain boundaries constituting the sintered body. This method precipitates phases with different constants.

Here, there are several modes of phase separation, and accordingly, different compositions can be obtained.

This point will be specifically explained based on the phase diagram shown in FIG. In this figure, the horizontal axis shows the component ratio of substances A and B, and the vertical axis shows the temperature. In the figure, the solid line 10 is a heinodal line, and the broken line 12 is a spinol line, and from this pinodal line 10. In the γ region on the first side, A,! =B
It is in a solid solution with , forming a physically and chemically homogeneous phase.

On the other hand, the inner region surrounded by the solid pinodal line 10 is a region separated into an α phase containing a large amount of A and a β phase containing a large amount of B. The area surrounded by the spinodal line 12 is the area where nuclei are generated and
This is a phase separation region due to growth, and the region surrounded by the spinodal line 12 is a phase separation region due to so-called spinodal decomposition due to only diffusion without the generation and growth of nuclei. Phase separation occurs in a typical 1 degree fluctuation pattern.

Therefore, a mixture of components A and B is heated to the γ region to form a single phase (solid solution) (a1 in the figure), and when this solid solution is held at temperature Tz for a predetermined time (a2 in the figure), spinodal decomposition occurs. Phase separation occurs, and as shown in Fig. M42 (A), the grains 14, which were initially uniform, become grains 16 whose phase is separated to form a wavy (or lattice) pattern on the entire surface (the grain size is generally luLm or less) (see Example 1).

On the other hand, when a γ-phase solid solution having the composition indicated by b1 in the figure is kept at temperature T3 for a predetermined period of time, phase separation occurs due to nucleation and growth, and as shown in Figure 2 (B), it is initially uniform. The inside of the ceramic grains 14, which were previously present, become grains 18 in which different phases due to nucleation and growth are separated and precipitated in scattered dots (see Example 2).

Similar phase separation/precipitation reactions also occur in material systems having the phase relationship shown in FIG. That is, in the figure, when a solid solution of CO is subjected to phase separation precipitation at temperature T1, the phase separation shown in Fig. 2 (A) occurs, and when a solid solution of CI is subjected to phase separation precipitation at temperature T2, the phase separation shown in the same figure (B) occurs The phase separation shown occurs (see Example 5).

Now, according to the present invention, as shown in FIG. 4, the raw material powder 20 is shaped and sintered, and the sintered body (or calcined body) is subjected to phase separation precipitation treatment to form a ceramic polycrystalline body. When a phase separation as shown by grains 16 (grains 16 include those having a lattice-like phase separation) or 18 is produced in each grain 22, the toughness and strength of the ceramic sintered body are effectively improved. This has been confirmed. The reason is considered to be due to the following points. In other words, when separated phases are precipitated within grains by the above treatment, phases with different elastic constants are generated adjacent to each other within the grains. The cracks that occurred and progressed hit the phase separation boundary area and were bent in their direction of propagation.
This is thought to be due to the absorption of fracture energy at that time.

The same can be said when phase separation is produced at grain boundaries, and this improves the toughness and strength of the ceramic.

The above phenomenon of phase separation is used in certain fields of glass and metals (age hardening), but the present invention utilizes this phase separation for a completely different object and for a different purpose. Therefore, according to the present invention, a ceramic having high toughness and high strength can be obtained.

In the method of the present invention, a sintered body (or calcined body) is obtained in the same manner as a normal ceramic manufacturing method, and then a strengthening mechanism is developed by heat treatment. Unlike the above case, there are no particular problems in terms of formability and compactness of the sintered body, and it is possible to obtain a sintered body with a desired density and shape. However, the present invention can also be applied to ceramics made of a composite of reinforcing materials, and in this case, both the reinforcing effect of the reinforcing material and the strengthening of the matrix and particle particles themselves can be obtained. It will be done.

(Example) Next, in order to further clarify the characteristics of the present invention, examples thereof will be described in detail below.

[Example 1] 50 parts of commercially available fine grain silicon carbide and 50 parts of commercially available fine grain aluminum nitride were thoroughly mixed using Improper Tool as a dispersion medium. A mixed powder consisting of this was heated at 2200°C for 12 hours in a non-oxidizing atmosphere using a graphite die with an inner diameter of 40 x 30 mm.
Hot pressed for an hour. The pressure at that time is 100 kg/
cm2. When this sample was subjected to X-ray diffraction (XRD), it was confirmed that it was a complete solid solution.

The above sample was subjected to phase separation reaction treatment at 1800° C. for 50 hours in a non-oxidizing atmosphere. After finishing the process and cooling, the surface is polished.
Fracture toughness values were measured by the indentation method (IF method). In addition, the sample was processed into a size of 4 × 3 × 40 layers, and 3
A bending strength test was conducted using point bending. As a result, the fracture toughness value of solid solution ceramic/gloss without phase separation precipitation treatment was 3.4 MN/m3/2, and the bending strength was 420 M.
By performing the same treatment, the fracture toughness value was 4.5 MN/m312. Transverse bending strength is 490M
Pa had improved.

When X-ray diffraction was performed on the sample subjected to the phase separation precipitation treatment, phase separation into a 5iC-AIN solid solution phase containing a large amount of silicon carbide and a 5iC-^IN solid solution phase containing a large amount of aluminum nitride was detected. Ta. This phase separation is a1 in Figure 1.
→This is due to the phase separation precipitation reaction of a2. Further, the water absorption rate of the treated body was within 0.05%, and it was a dense body.

[Example 2] 80 parts of commercially available fine grain silicon carbide and 20 parts of commercially available fine grain aluminum nitride were mixed and hot pressed in the same manner as in Example 1 to synthesize a solid solution. This sample is x
It was confirmed by m-diffraction (XRD) that it was a complete solid solution.

This sample was subjected to a separation phase precipitation reaction treatment at 1800° C. for 50 minutes in a non-oxidizing atmosphere. After completion of the treatment and cooling, the surface was polished and the fracture toughness value was measured by the indentation method (IF method). In addition, the sample was processed into a size of 4 x 3 x 40 ms,
A bending strength test was conducted using three-point bending.

As a result, the fracture strength value of solid solution ceramics with the same composition but not subjected to phase separation precipitation treatment was 3.3 MN/m3/2.
, the bending strength was 430 MPa, but by performing the same treatment, the fracture toughness value was 4.8 MN/m"7,
The bending strength was improved to 510 MPa.

When X-ray diffraction was performed on the sample subjected to phase separation precipitation treatment, it was found that a SiC-AIN solid solution phase containing a large amount of silicon carbide,
Phase separation into a 5iC-AIN solid solution phase containing a large amount of aluminum nitride was observed. This phase separation is b1→ in Figure 1.
This is due to the phase separation precipitation reaction shown in b2. Moreover, the water absorption rate of the treated body was within 0.05%, and it was a dense body.

[Example 3] A mixed powder of 55 parts of commercially available fine-grain alumina and 45 parts of commercially available fine-grain chromia was molded into It/c layer 2 in one machine, and then fired in the atmosphere at 1650°C for 20 hours.

It was confirmed by X-ray diffraction (XRD) that this sample was a complete solid solution.

This sample was subjected to phase separation precipitation reaction treatment at 800° C. for 60 hours in the air. After the process is completed and cooled, the surface is polished and the indentation method (
The fracture toughness value was measured using the IF method. In addition, the sample was processed to a size of 4×3×40 cm, and a bending strength test was conducted by three-point bending. As a result, the fracture toughness value of solid solution ceramics with the same composition but not subjected to phase separation precipitation reaction is 2.
2MN/+n3/2, the bending strength was 220MPa, but by performing the same treatment, the fracture toughness value was 3.
．． 3MN/m3/2, and the bending strength was improved to 290MPa.

[Example 4] A mixed powder of 70 parts of commercially available fine alumina and 30 parts of commercially available fine chromia was molded and fired in the same manner as in Example 3 to synthesize a solid solution. This sample was subjected to X-ray diffraction (XR
It was confirmed that a complete solid solution was formed in D).

This sample was subjected to phase separation precipitation reaction treatment at 700° C. for 80 hours in the air. After completion of the treatment and cooling, the surface was polished and the fracture toughness value was measured by the indentation method (IF method). In addition, the sample was processed into a size of 4×3×40, and a bending strength test was conducted by three-point bending. As a result, the fracture toughness value of solid solution ceramics with the same composition but not subjected to phase separation precipitation treatment was 2.3 MN/m3/2. While the bending strength was 210 MPa, the fracture toughness value was reduced to 3 by performing the same treatment.
．． At 5 MN/m3, the bending strength was improved to 300 MPa.

[Example 5] Synthesis was performed using a solution method. 35 parts magnesia and 65 parts alumina
The amorphous raw material in solid solution containing 30% of the total weight was calcined at about 1250°C. This powder was uniaxially molded at It/c 2 and then fired at 1650° C. for 2 hours in the air. This sample was confirmed to have a spinel single phase by X-ray diffraction (XRD).

This sample was subjected to phase separation precipitation reaction treatment at 1000° C. for 20 hours in the air. After completion of the treatment and cooling, the surface was polished and the fracture toughness value was measured by the indentation method (IF method). Further, the sample was processed into a size of 4×3×4 Om, and a bending strength test was conducted by three-point bending. As a result, the fracture toughness value of spinel ceramics with the same composition but not subjected to split phase precipitation treatment was 1.1 MN/m" and the bending strength was 80 MPa, whereas The value is 1.
9MN/m312, and the bending strength was improved to 100MPa.

Although the embodiments of the present invention have been described in detail above, these are merely examples, and the present invention can be implemented with various modifications based on the knowledge of those skilled in the art without departing from the spirit thereof.

[Brief explanation of the drawing]

FIG. 1 is a phase diagram shown to explain the aspect of phase separation in the present invention, FIG. phase diagram of material systems,
FIG. 4 is an explanatory diagram of a ceramic manufacturing method according to an embodiment of the present invention, and FIG. 5 is an explanatory diagram of a conventional ceramic manufacturing method. Figure 1 Composition 14.16. ．． 18: Grain diagram

Claims (2)

[Claims] (1) A ceramic sintered body or calcined body consisting of multiple components that are at least partially dissolved in solid solution is heat-treated to cause phase separation, so that the elastic constants are different within each grain and/or at the grain boundary constituting the sintered body. A method for producing polycrystalline high-strength ceramics characterized by precipitating a phase. (2) A ceramic sintered body or calcined body consisting of multiple components that are at least partially dissolved in solid solution is heat-treated to cause phase separation, so that the elastic constants are different within each grain and/or at the grain boundary making up the sintered body. A polycrystalline high-strength ceramic made of precipitated phases.