JPH05124867A - Silicon nitride-based sintered body - Google Patents

Abstract

(57) [Summary] [Purpose] It has excellent mechanical strength, especially at room temperature.
It is an object of the present invention to provide a silicon nitride-based sintered body which is excellent in productivity and cost. 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 β′-sialon has long-axis and short-axis directions. The average crystal grain size is 2.0 to 5.0 μm,
The peak intensity ratio by crystallographic X-ray diffraction is 20% ≦ α-silicon nitride ≦ 50
%, 50% ≦ β′-sialon ≦ 80%.

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 having excellent mechanical strength at room temperature, and excellent productivity and cost.

[0002]

2. Description of the Related Art Conventionally, various researches and developments such as a sintering method, a sintering aid, and a limitation of contained crystal phases have been carried out for the purpose of improving the strength of silicon nitride materials. For example, regarding the sintering method, in the hot press sintering method, Am. Ceram.
Soc. Bull. , 52 (1973) pp560-
100 kg / mm ² (bending strength) has been realized, and the hot isostatic pressing method (HIP
Law) is also being developed. Although such a method has obtained excellent characteristics in terms of strength characteristics of the sintered body, it cannot be said to be an excellent method 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, but in this method, the final densification of the sintered body is β -Since it is accompanied by grain growth of silicon nitride crystals, there is a high possibility that strength deterioration due to the precipitation of coarse crystal grains will occur.
Since sintering is performed by applying N ₂ gas pressure of atmospheric pressure or more, the sintering equipment becomes large like the hot press method and the HIP method,
It cannot be said that it is a sufficiently excellent method in terms of 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 shown 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 hexagonal and that the crystal grows anisotropically in the C-axis direction. In particular, Japanese Patent Publication No. 48-38448 and Journal of Ceramic Industry , 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 addition, in the sintered body using only the sintering aid in this method, the sintering temperature is Unless the temperature is 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 occurs, and a stable sintered body may not be obtained in some cases. Therefore, similarly, it cannot be said that the sintered body is sufficiently excellent in both characteristics and productivity. On the other hand, in the methods described above, the strength of the obtained sintered body is, for example, J
Three-point bending strength in accordance with IS-R1601 at most 1
It is around 00 kg / mm ² , and when considering applications of various silicon nitride 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 the 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 major axis of β'-sialon,
The average crystal grain size in the minor axis direction is 2.0 to 5.0 μ, respectively.
It was obtained that the silicon nitride sintered body characterized by m and 0.5 μm or less easily has a three-point bending strength of 130 kg / mm ² or more in accordance with 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 finely columnarized, The Young's modulus and hardness are improved as compared with the sintered body composed only of the crystallized β'-sialon (including β-silicon nitride) crystal phase. This is because it is a physical property value indicating the deformation resistance of a material, and in the case of a brittle material such as a ceramic material, improving this value leads to an improvement 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. 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 unavoidable in the process is excluded, the present invention in which the filling property is improved by fine crystal grains is effective in improving the strength in terms of E and γs.

The concept of compounding both the crystal phases of α-type silicon nitride and columnar β-type silicon nitride 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 crystal 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 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 have not reached industrially stable and high strength characteristics. 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 in strength. The present invention is to provide an industrially stable and high-strength sintered body that is not 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, it becomes possible at the same time to perform sintering with excellent productivity by using an open continuous sintering furnace such as a pusher type or a belt type. Adding this detailed description, gas pressure sintering in a so-called batch-type sintering furnace is generally the main sintering method for silicon nitride-based materials with excellent strength characteristics. It is not sufficient as a manufacturing method for stably supplying a ceramic material for use in mass-produced parts or the like, because variations in manufacturing conditions, variations in conditions between lots, and the like will always occur. From this point as well, the present invention is industrially important in that the productivity is improved at the same time.

Further, in order to make the effect of the present invention remarkable, the average grain size of the crystal grains of α-silicon nitride and β'-sialon in the sintered body is important. That is, the average particle size of α-silicon nitride is 0.5 μm or less, and the average particle size of the long axis of β′-sialon is 2.0 to 5.0 μm and the average particle size of the short axis is 0.5 μm or less. It is necessary. If the average crystal grain size of α-silicon nitride exceeds 0.5 μm, the packing density of the crystal grains when the crystal phases are compounded decreases, and the effect of the α-silicon nitride crystal phase on the strength cannot be expected sufficiently. On the other hand, when the average crystal grain size of the long axis of β'-sialon is less than 2.0 μm, the strengthening effect due to the dispersion of the columnar β'-sialon crystal grains cannot be expected sufficiently, which leads to the deterioration of strength. . On the other hand, when the thickness exceeds 5.0 μm, the β′-sialon crystal grains act as coarse grains to cause the deterioration of the strength and also the packing density of the crystal grains to decrease, which also deteriorates the strength.
Further, when the minor axis diameter exceeds 0.5 μm, the strengthening effect due to the dispersion of the columnar β′-sialon crystal grains cannot be sufficiently expected, and the strength is deteriorated.
In order to sufficiently improve the effect of the present invention, the precipitation ratio of the crystal phases of α-silicon nitride and β′-sialon is a peak intensity ratio by X-ray diffraction, and 20% ≦ α-silicon nitride ≦ 50.
%, 50% ≦ β′-silicon nitride ≦ 80%. If the deposition ratio of α-silicon nitride exceeds 50% and shifts to the high α-Si ₃ N ₄ side, the effect of β'-sialon columnar crystal structure decreases, and the effect of compounding the crystal phase does not sufficiently appear. If it is less than 20%, the density of the crystal grains filling the space between the crystal grains of β'-sialon decreases and the grain growth of β'-sialon occurs, so that the effect of improving the strength is not sufficient.

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.
If 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 0.5 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, 0.2 μm. Each powder of Y ₂ O ₃ , Al ₂ O ₃ , AlN, and MgO was wet-mixed in ethanol for 100 hours in a nylon ball mill, and then dried to obtain a mixed powder of 3000 kg /
and CIP molded at cm ^2, the molded body was 5 to 10 hours primary sintering at to 1650 ° C. in a N ₂ gas 1 atm. The obtained sintered body was subjected to secondary sintering for 1 hour at ˜1650 ° C. and 1000 atmospheric pressure N ₂ gas atmosphere. From this sintered body JIS R160
A bending test piece corresponding to 3 mm × 4 mm × 40 mm according to 1 was cut out and ground by a # 800 diamond grindstone, and then the tensile surface was lapped by a diamond paste of # 3000.
In accordance with ISR1601, 15 3-point bending strengths were carried out. Table 1 shows the average crystal grain size, the ratio of crystal phases, and the bending strength.

The crystal phase ratio 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 9.

FIG. 2 is an X-ray diffraction diagram of a sintered body of Comparative Example No. 13.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akira Yamakawa 1-1-1 Kunyo Kita, Itami City, Hyogo Prefecture Sumitomo Electric Industries, Ltd. Itami Works

Claims (4)

[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 2.0 μm to 5.0, respectively.
A silicon nitride-based sintered body characterized by having a size of less than or equal to 0.5 μm. 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 20%.
The silicon nitride-based sintered body according to claim 1, wherein ≦ α-silicon nitride ≦ 50% and 50% ≦ β′-sialon ≦ 80%. 3. A β'-sialon (general formula:
The silicon nitride-based 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. 4. The α-silicon nitride in the sintered body is substantially J
The silicon nitride sintered body according to claim 1, which is identified as α-silicon nitride of CPDS (09-0250).