JP2539968B2 - Silicon nitride-based 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 silicon nitride-based sintered body which has excellent mechanical strength at room temperature and is excellent in productivity and cost.

[0002]

2. Description of the Related Art Conventionally, various researches and developments have been carried out for the purpose of improving the strength of silicon nitride-based materials, such as sintering methods, sintering aids, and limiting the contained crystal phases. For example, regarding the sintering method, in the hot press sintering method, Am. Ceram.
Soc. Bull. , 52 (1973) pp560
100 kg / mm ² (flexural strength) has been achieved, and the hot isostatic pressing method (HIP
Law) has also been developed. Although such a technique provides excellent strength characteristics of the sintered body, it cannot be said to be an excellent technique in terms of productivity and cost. On the other hand, there is a gas pressure sintering method (for example, Sanyu, Powder and Kogyo, Vol. 12, No. 12, pp27, 1989) for such a problem. However, in this method, the final densification of the sintered body is β -Since it is accompanied by the grain growth of silicon nitride crystals, there is a high possibility that it may cause strength deterioration due to the precipitation of coarse crystal grains.
Since N ₂ gas pressure above atmospheric pressure is applied to carry out sintering, the size of the sintering equipment becomes large as in the hot press method and HIP method.
It cannot be said that this method is excellent in characteristics and production. On the other hand,
For the sintering _{aid, Si 3 N 4 -Al 2 O} 3 -Y 2 O 3 system of silicon nitride sintered body is Japanese Patent Publication No. 49-21091 using Y ₂ O ₃ as a main aid, JP-B No. 48-38448. As described in the patent specification, these improve the strength and toughness because the β-type silicon nitride crystal grains form a fibrous structure in the sintered body and are dispersed in the matrix. It is considered to be profitable.
That is, this is a positive use of the fact that the crystal form of β-type silicon nitride is a hexagonal crystal and that the crystal grows anisotropically in the C-axis direction. In particular, Japanese Patent Publication No. 48-38448 and Journal of the Ceramic Society of Japan. , 94, pp96, 1986, the fibrous β-silicon nitride crystal grains are 10 in the C-axis direction.
It may grow to several μm or more. However,
In the present technology, this grain growth may lead to abnormal growth and generation of pores, and may lead to strength deterioration.In the sintered body using only the sintering aid in this method, the sintering temperature is If the temperature is not raised to 1700 to 1900 ° C., sufficient densification cannot be achieved, and in N ₂ gas pressure sintering near atmospheric pressure, sublimation decomposition of silicon nitride may occur and a stable sintered body may not be obtained. For this reason, similarly, it cannot be said that both the properties of the sintered body and the productivity are sufficiently excellent. On the other hand, in the methods described above, the strength of the obtained sintered body is, for example, J
Three-point bending strength based on IS-R1601 at most 1
It is around 00 kg / mm ² , and when considering the application of various silicon nitride-based materials, sufficient characteristics are not always obtained.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of satisfying both the productivity and the mechanical properties of a sintered body in the prior art.

[0004]

The present invention comprises α-silicon nitride and β'-sialon, the average crystal grain size of α-silicon nitride is 0.5 μm or less, the long axis of β'-sialon,
The average crystal grain size in the minor axis direction is 2.5 μm or less,
It was found that a silicon nitride sintered body characterized by having a thickness of 0.5 μm or less easily has a three-point bending strength of 130 kg / mm ² or more according to JISR-1601. The effect of the sintered body of the present invention to obtain excellent strength characteristics is that by combining both crystalline phases of α-silicon nitride of fine grains and equiaxed crystal and β′-sialon columnarized with fine grains, conventional columnar In comparison with a sintered body composed only of a crystallized β'-sialon (including β-silicon nitride) crystal phase,
Young's modulus and hardness are improved. This is a physical property value that indicates the deformation resistance of the material.In brittle materials such as ceramic materials,
This is because improving this value leads to an increase in the strength of the material in a broad sense. Further, according to Griffith's theory, which is the basic concept of fracture of brittle materials, the fracture strength σ _f of the sintered body is given by the following equation.

Σ _f = E · γs / 4a, E; Young's modulus, γ
s: surface energy of fracture, a: pre-existing crack length Since γs is considered to depend on the composition and thickness of the grain boundary phase, grain refinement that improves the existing density of crystal grains particularly in terms of thickness. It is advantageous to combine the crystalline phase with Further, according to this formula, it is important to increase E and decrease a in order to improve the fracture strength. Since the value of a depends on the crystal grain size if the defect size inevitable in the process is excluded, the present invention in which the filling property is improved by fine crystal grains is effective for improving the strength in terms of E and γs.

The concept of combining both α-type silicon nitride and columnar β-type silicon nitride crystal phases is disclosed in, for example, JP-A-61-191065 and JP-A-2-44066. Also α'-sialon (general formula M
_X (Si, Al) ₁₂ (O, N) ₁₆ , M: Mg, Ca, L
i and rare earth elements) and β′-sialon (including β-type silicon nitride) in the combination of crystalline phases, and compositionally Si
₃ N ₄ -AlN-MO (M; MgO, Y ₂ O ₃ , CaO, etc.)
The three-component system is mainly used, and the range of the addition ratio of AlN and MO is a limited range of 1: 9 in mol%, and α′-sialon and β′-sialon (including β-silicon nitride) are included. This shows that the mechanical properties such as strength were improved by producing a composite crystal phase, and as is clear from the examples, the strength properties of each sintered body were 100 kg in terms of bending strength.
All of the methods for producing a sintered body that stably exceed / mm ² are based on the hot pressing method, and industrially stable and high strength properties have not yet been achieved. In addition, these sintered bodies have a large difference in thermal expansion coefficient between α'-sialon and β'-sialon (including β-silicon nitride), which causes tensile residual stress in the sintered body. May cause deterioration of strength. An object of the present invention is to provide a high-strength sintered body that is industrially stable without being limited to such conditions.

In order to obtain the sintered body of the present invention, the sintering aid is SiO ₂ present on the surface of silicon nitride and an aid which forms a liquid phase at a temperature as low as possible, such as MgO, CeO ₂ , Ca.
It is desirable to sinter at a sintering temperature of 1650 ° C. or lower using O and La ₂ O ₃ . This low-temperature sintering can prevent deterioration of the characteristics of the sintered body due to abnormal grain growth. Further, since silicon nitride is sublimated decomposed at a temperature range of not lower than 1700 ° C. under N ₂ atmosphere at atmospheric pressure, must be sintered under pressure N ₂ atmosphere, using a batch-type sintering furnace in terms of facilities Was there. However, if it becomes possible to sinter at such a low temperature, an open continuous sintering furnace such as a pusher type or a belt type can be used as a sintering method, and at the same time, it becomes possible to perform high productivity sintering. In addition to this detailed description, gas pressure sintering using a so-called batch type sintering furnace is mainly used as a method for sintering silicon nitride-based materials generally having excellent strength characteristics. Therefore, it is not sufficient as a manufacturing method for stably supplying ceramic materials for use in mass-produced parts and the like because variations in conditions and variations in conditions between lots always occur. From this point as well, the present invention is industrially important in that its productivity is improved at the same time.

In order to make the effect of the present invention more remarkable, the precipitation ratio of the crystal phases of α-silicon nitride and β'-sialon in the sintered body is 0% <, which is the peak intensity ratio by X-ray diffraction.
α-silicon nitride ≦ 30%, 70% ≦ β′-silicon nitride <
It is preferably 100%. If the precipitation ratio of α-silicon nitride exceeds 30% and shifts to the high α-Si ₃ N ₄ side, β
The effect of the ???-sialon columnar crystal structure is reduced, the effect of compounding the crystal phase is not sufficiently exhibited, and the effect of improving the strength is not sufficient.

Further, in this composition range, the Z value of β'-sialon (general formula: Si ₆ -Z Al _Z O _Z N _8-Z ) in the sintered body is 0.
When the grain boundary phase is controlled within the range of <Z <1.0, high strength is stabilized.

[0010]

EXAMPLE A silicon nitride raw material powder having an average particle size of 0.4 μm, an α crystallization rate of 96% and an oxygen content of 1.4% by weight, and an average particle size of 0.8 μm, 0.4 μm, 0.5 μm, 0.5 μm. Each powder of Y ₂ O ₃ , Al ₂ O ₃ , AlN, and MgO in ethanol was wet-mixed for 100 hours in a nylon ball mill, and then dried to obtain a mixed powder of 3000 kg /
CIP molding was carried out at a pressure of ₂ cm ² , and this molded body was subjected to primary sintering at ˜1650 ° C. for 5 to 10 hours in 1 atm of N ₂ gas. The obtained sintered body was subjected to 1 at 1650 ° C. and 100 atm N ₂ gas atmosphere.
Time, secondary sintering. JISR1601 from this sintered body
After cutting a bending test piece corresponding to 3 mm x 4 mm x 40 mm in conformity with JIS, it was ground and finished with a # 800 diamond grindstone, and then the tensile surface was lapped with a diamond paste of # 3000 and then JI.
Fifteen three-point bending strengths were performed in accordance with SR1601. Table 1 shows the average crystal grain size, the ratio of crystal phases, and the bending strength. For the measurement of the average crystal grain size, an arbitrary two-dimensional cross section of the obtained sintered body was mirror-finished to have a surface roughness of 0.1 μm or less with a ten-point average roughness (R _Z ), and then Ar The grain boundary phase was etched by ions, and this surface was observed in a scanning electron microscope (SEM) at a magnification of 5,000 times, and α-Si ₃ N ₄ was observed in a granular form from an arbitrary visual field of 30 μm × 30 μm. The crystal grains and β′-sialon crystal grains observed in a hexagonal shape or a columnar shape may be arbitrarily selected as 1
The average crystal diameter was calculated by sampling 0 to 20 pieces each. The grain size of α-Si ₃ N ₄ and the minor axis and major axis diameters of β′-sialon are defined as shown in enlarged views I, B, and C in the model diagram of the sintered body structure shown in FIG. It shall be.

The ratio of crystal phases was calculated from the peak height ratio of each crystal phase obtained by the X-ray diffraction method shown in FIGS.

[0012]

[Table 1]

[0013]

According to the present invention, it is possible to obtain a silicon nitride-based sintered body which has excellent mechanical strength especially at room temperature and is excellent in productivity and cost.

[Brief description of drawings]

FIG. 1 is an X-ray diffraction diagram of a sintered body of Example 7.

FIG. 2 is an X-ray diffraction diagram of a sintered body of Comparative Example No. 16.

FIG. 3 is an explanatory diagram of definitions of particle diameter, minor axis and major axis diameter in a model diagram of a sintered body structure.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Yamakawa 1-1-1 Kunyo Kita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works (56) Reference JP-A-3-141163 (JP, A) ) JP-A-2-55263 (JP, A) JP-A-2-22173 (JP, A) JP-A-4-202060 (JP, A)

Claims (3)

(57) [Claims] 1. A silicon nitride sintered body composed of α-silicon nitride and β′-sialon, wherein α-silicon nitride has an average crystal grain size of 0.5 μm or less, and a long axis of β′-sialon,
The average crystal grain size in the minor axis direction is 2.5 μm or less,
A silicon nitride-based sintered body characterized by being 0.5 μm or less. 2. The crystal phase of α-silicon nitride and β′-sialon in the sintered body has a peak intensity ratio by X-ray diffraction of 0% <.
α-silicon nitride ≦ 30%, 70% ≦ β′-sialon <
The silicon nitride-based sintered body according to claim 1, which is 100%. 3. A β'-sialon (general formula:
The silicon nitride sintered body according to claim 1, wherein Si _6-Z Al _Z O _Z N _8-Z ) is in the range of 0 <Z <1.0.