JPH05170541A - Silicon nitride sintered product - Google Patents

Abstract

PURPOSE:To provide a silicon nitride sintered product having an excellent mechanical strength, etc., specially at the ordinary temperature and excellent on the aspects of productivity and cost. CONSTITUTION:A silicon nitride sintered product comprising alpha-silicon nitride and beta'-sialon is characterized in that the average crystal particle diameter of the alpha-silicon nitride is <=0.5mum and that the average crystal particle diameters of the beta'-sialon in the long and short axial directions are <=5mum and <=0.5mum, respectively. The crystal phases of the alpha-silicon nitride and the beta'-sialon have peak strength ratios represented by 0% < alpha-silicon nitride <=50% and 50% <=beta'-sialon <100% by an X-ray diffraction method.

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 based on 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 sizes in the minor axis direction are 5 μm or less and 0.5, respectively.
A silicon nitride sintered body characterized in that
3 point bending strength based on JIS R-1601 is easily 1
The knowledge obtained has characteristics of 30 kg / mm ² or more. The effect of the sintered body of the present invention to obtain excellent strength characteristics is
Fine-grained equiaxed α-silicon nitride and fine-grained columnar β '
-By combining both crystalline phases of Sialon,
The Young's modulus and hardness are improved as compared with the conventional sintered body composed only of the columnar 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. G, which is the basic concept of fracture of brittle materials
According to the riffith theory, the fracture strength σ _{f of the} sintered body
Is given by

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, Y and lanthanide metal elements other than Ce and La)
And β'-sialon (including β-type silicon nitride) in a crystalline phase, and compositionally, Si ₃ N ₄ -AlN-MO.
(M; MgO, Y ₂ O ₃ , CaO, etc.) is mainly used as a three-component system, and the range thereof is 1: 9 when the addition ratio of AlN and MO is mol%.
In a limited range of, by forming a composite crystal phase of α'-sialon and β'-sialon (including β-silicon nitride), it is shown that the mechanical properties such as strength are improved. As is clear from the examples, the method for producing a sintered body in which the strength characteristics of each sintered body stably exceeds 100 kg / mm ² in bending strength is all by the hot pressing method, which is industrially stable and high. It has not yet reached the strength characteristics. 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 existing on the surface of silicon nitride and an aid that forms a liquid phase at a temperature as low as possible, such as MgO, CeO ₂ , CaO, La ₂ O ₃ , Mg
Oxides such as Al ₂ O ₄ or Mg, Ce, Ca, La,
It is desirable to sinter at a sintering temperature of 1650 ° C. or lower using an oxide composed of Al element or a combination thereof. This low-temperature sintering can prevent deterioration of the characteristics of the sintered body due to abnormal grain growth. Furthermore, silicon nitride is N at atmospheric pressure.
_Since it decomposes by sublimation in a temperature range of 1700 ° C. or higher under ₂ atmospheres, it is necessary to sinter under a pressurized N ₂ atmosphere, and a batch-type sintering furnace was used in terms of equipment. 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.

In order to make the effect of the present invention more remarkable, the precipitation ratio of α-silicon nitride and β'-sialon crystal phase in the sintered body is 0% <α as a peak intensity ratio by X-ray diffraction.
-Silicon nitride ≤ 50%, 50% ≤ β'-Silicon nitride <1
It is preferably 00%. If the deposition ratio of α-silicon nitride exceeds 50% and shifts to the high α-Si ₃ N ₄ side, β '
-The effect of the sialon columnar structure is reduced, the effect of compounding the crystal phase does not sufficiently appear, and β'-only the sialon does not exhibit the compound effect of filling between the crystal grains of the present invention, and β'-
Since sialon causes grain growth, the effect of improving strength is not sufficient.

On the other hand, a method for producing a preform for obtaining the present sintered body is a known technique such as a powder pressing method, an injection molding method,
Although any technique such as a slip casting method can be used, a molding method by which a high density body having a relative density of 50% or more can be obtained is desirable.

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 0.4 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. Powder of Y ₂ O ₃ , Al ₂ O ₃ , AlN, and MgO of 6 mm ×
It was molded into 8 mm × 60 mm, and this molded body was subjected to primary sintering in N ₂ gas at 1 atm at ˜1650 ° C. for 5 to 10 hours. The obtained sintered body was subjected to secondary sintering for 1 hour at ˜1650 ° C. and 1000 atmospheric pressure N ₂ gas atmosphere. JISR from this sintered body
A bending test piece equivalent to 3 mm x 4 mm x 40 mm according to 1601 is cut out and ground by a # 800 diamond grindstone, and then a tensile surface is lapped by a # 3000 diamond paste, and then according to JISR1601. Three-point bending strength was carried out for each of 15 pieces. 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 8.

FIG. 2 is an X-ray diffraction diagram of a sintered body of Comparative Example No. 14.

 ─────────────────────────────────────────────────── ─── 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,
A silicon nitride-based sintered body, characterized in that the average crystal grain size in the minor axis direction is 5 μm or less and 0.5 μm or less, respectively. 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 ≦ 50%, 50% ≦ β′-sialon <
The silicon nitride-based sintered body according to claim 1, which is 100%. 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).