JPH0558739A - Silicon nitride sintered body and its production - Google Patents

Abstract

PURPOSE:To provide a silicon nitride sintered body having excellent mechanical strength especially at room temp. and advatages in productivity and cost. CONSTITUTION:This silicon nitride sintered body has the compsn. of Si3N4-first aid (Y2O3+MgO)-second aid (one or two of Al2O3 and AlN) in the range defined by ABCD in fig. 1. The sintered body has >=98% relative density and contains body of alpha'-sialon (including alpha-Si3N4) and beta'-sialon (beta-Si3N4) in the crystalline phase. The silicon nitride sintered body is produced by subjecting a compacted body of the source material described above to first sintering at 1500-1700 deg.C in N2 gas of <=1.1 atm. to obtain a body having >=96% relative density, and then subjecting it to second sintering at 1500-1700 deg.C in N2 gas of >=10 atm. to obtain the objective body having >=98% relative density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body which has excellent mechanical strength at room temperature and is excellent in productivity and cost, and a method for producing the same.

[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 accompanying the grain growth of -Si ₃ N ₄ crystal, in addition to it is likely to lead to deterioration in strength due to coarse grain precipitation, in general, 10
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 β-Si ₃ N ₄ crystal grains form a fibrous structure in the sintered body and are dispersed in the matrix. It is considered possible. That is, this is a positive use of the fact that the β-Si ₃ N ₄ crystal form is a hexagonal crystal and the crystal anisotropically grows in the C-axis direction. In particular, Japanese Examined Patent Publication No. 48-38448 and the Ceramic Society of Japan As shown in the magazine, Vol. 94, pp96, 1986, fibrous β-Si ₃ N ₄ crystal grains may grow to 10 and several μm or more in the C-axis direction. However, in the present technology, this grain growth may lead to abnormal growth and generation of pores, and may lead to strength deterioration, and in the sintered body using only the sintering aid in this method, Temperature 1700
Unless the temperature is raised 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. 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, JIS-
3-point bending strength conforming to R1601 at most 100k
It is around g / mm ² , and when considering the application 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]

According to the present invention, in the ternary composition diagram of Si ₃ N ₄ -first auxiliary agent-second auxiliary agent, the first auxiliary agent is Y.
₂ O ₃ and MgO, and the second auxiliary agent is a combination selected from one or two of AlN, and the composition range thereof is the range shown in FIG. 1, that is, Si ₃ The composition ratio of N ₄ and the first auxiliary added is 85: 1 in mol%.
5 to 95: 5 and the addition composition ratio of Si ₃ N ₄ and the second auxiliary agent is in the range of 90:10 to 98: 2 in mol%, and points A, B and C in FIG. , D, and the crystal phase in the obtained sintered body has α′-sialon (including α-Si ₃ N ₄ ) and β′-sialon (β-Si).
₍ Including ₃ N ₄ ) and the relative density of the sintered body is 9
It is a silicon nitride-based sintered body characterized by being 8% or more.

In the present invention, such a sintered body is a JISR-
3-point bending strength according to 1601 is easily 100 kg /
The knowledge obtained has characteristics of mm ² or more.

The present invention uses a raw material powder of silicon nitride having an α ratio of 93% or more and an average particle size of 0.7 μm or less, and a mixed powder prepared by mixing an auxiliary agent having a composition range shown in FIG. A green compact is formed, which is 1500 to 1700 ° C.
After performing primary sintering in a N ₂ gas atmosphere of 1.1 atm or less so that the relative density of the sintered body is 96% or more, 150
This is a method for producing a silicon nitride-based sintered body, which comprises performing secondary sintering so that the relative density of the sintered body becomes 99% or more in an N ₂ gas atmosphere of 0 to 1700 ° C. and 10 atm or more. This manufacturing method is a method for obtaining a sintered body having excellent productivity, and at the same time, since the sintering temperature is low, the characteristics of the sintered body are not deteriorated due to abnormal grain growth. The effect of the sintered body of the present invention to obtain excellent strength characteristics is that fine particles of equiaxed α′-sialon (including α-Si ₃ N ₄ ) and columnar β′-sialon (β-Si ₃ N) are used. (Including ₄ ), the conventional columnarized β'-
The Young's modulus and hardness are improved as compared with the sintered body composed only of the sialon (including β-Si ₃ N ₄ ) 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 σf of the sintered body is given by the following equation.

Σf = E · γs / 4a, E; Young's modulus, γ
s; surface energy of fracture, a; pre-existing crack length where γ
Since s is considered to depend on the composition and thickness of the grain boundary phase,
In particular, it is advantageous to combine the crystal phases to improve the existing density of crystal grains in terms of thickness. 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 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 combining both α′-sialon (including α-Si ₃ N ₄ ) and columnar β′-sialon (including β-Si ₃ N ₄ ) crystal phases is disclosed in, for example, Japanese Patent Laid-Open No. 61- 9106
No. 5 and JP-A No. 2-44066, both of which are compositionally Si ₃ N ₄ -AlN-MO (M; Mg).
O, Y ₂ O ₃ , CaO, etc.) is mainly used as a three-component system, and in that range, the mechanical properties such as strength are improved in a limited range where the addition ratio of AlN and MO is mol% of 1: 9. As is clear from the examples, the sintered body manufacturing method in which the strength characteristics of each sintered body stably exceeds 100 kg / mm ² in bending strength is based on the hot pressing method. It has not reached the point of obtaining industrially stable and high strength characteristics. The present invention is to provide an industrially stable and high-strength sintered body that is not limited to such conditions.

Explaining the detailed operation of the present invention, the composition range is as shown in FIG. 1, that is, Si ₃ N ₄ and the first range.
When the additive composition ratio of the auxiliary agent is in the range of 85:15 to 95: 5 in mol%, and the additive composition ratio of Si ₃ N ₄ and the second auxiliary agent is in the range of 90:10 to 98: 2 in the case of mol%. The range surrounded by points A, B, C and D in FIG. 1 is Si ₃
If the additive composition ratio of N ₄ and the first auxiliary is mol% and shifts from 85:15 to the first auxiliary side, α′-sialon (α-Si ₃ N ₄
Content is high, which causes deterioration of the strength of the sintered body, and produces a surface layer that deteriorates the properties such as strength on the surface of the sintered body under the influence of the atmosphere during sintering. Is. Further, if the composition ratio deviates from 95: 5 to the Si ₃ N ₄ side, the sinterability deteriorates, and a sufficiently dense sintered body cannot be obtained unless a pressure sintering method such as a hot pressing method is used. is there. On the other hand, when the additive composition ratio of Si ₃ N ₄ and the second auxiliary exceeds 90:10 in mol% and shifts toward the second auxiliary, coarse crystals of β′-sialon (including β-Si ₃ N ₄ ) are formed. This is because the strength is deteriorated because it is selectively generated, and the surface layer that deteriorates characteristics such as strength is also generated on the surface of the sintered body due to the influence of the atmosphere during sintering. Further, if the composition ratio deviates from 98: 2 to the Si ₃ N ₄ side, the sinterability deteriorates and a sufficiently dense sintered body cannot be obtained unless a pressure sintering method such as a hot pressing method is used. Is. Further, in order to make the effect of the present invention remarkable, α'-sialon (including α-Si ₃ N ₄ ) and β'-sialon (β- in the sintered body.
The precipitation ratio of the crystal phase of (including Si ₃ N ₄ ) is preferably in the range of 5:95 to 30:70 as the peak intensity ratio of X-ray diffraction. This precipitation ratio exceeds 5:95 and low α '
-If it shifts to the sialon (including α-Si ₃ N ₄ ) side, the effect of compounding the crystal phase does not sufficiently appear and the effect of improving the strength is not sufficient. If the precipitation ratio exceeds 30:70 and shifts to the high α'-sialon (including α-Si ₃ N ₄ ) side, the effect of the columnar crystal structure of β'-sialon (including β-Si ₃ N ₄ ) is obtained. As a result, the effect of compounding the crystal phase is not sufficiently exhibited and the effect of improving the strength is not sufficient.

Further, the effect of the present invention is also important in the manufacturing conditions of the sintered body. That is, using a silicon nitride raw material powder having an α ratio of 93% or more and an average particle size of 0.7 μm or less, a green compact made of a mixed powder that serves as an auxiliary agent in the composition range shown in FIG. After performing primary sintering in a N ₂ gas atmosphere of 1 atm or less so that the relative density of the sintered body becomes 96% or more, 1500 to 1700 ° C., relative to the sintered body in an N ₂ gas atmosphere of 10 atm or more Secondary sintering is preferably performed so that the density becomes 99% or more. The reason why the silicon nitride raw material powder having an α ratio of 93% or more and an average particle diameter of 0.7 μm or less is required as the silicon nitride raw material is to improve the sinterability in the low temperature range. Further, by selecting the composition range of the present invention, the sintering conditions are as follows:
It became possible in a low temperature range of 0 to 1700 ° C. and N ₂ gas atmosphere of 1.1 atm or less. For this reason, the compounding of crystal grains is made up of finer crystal grains, which makes the effect remarkable, and the primary sintering is performed simultaneously by the open type continuous sintering furnace such as the pusher type or the belt type, which is excellent in productivity. Sintering becomes possible. 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. Also, silicon nitride has a value of 1 in an N ₂ atmosphere at atmospheric pressure.
Since it decomposes by sublimation in a temperature range of 700 ° C. or higher, it is necessary to sinter under a pressurized N ₂ atmosphere, and a batch-type sintering furnace was used in terms of equipment. From this point as well, the present invention is industrially important in that the productivity is improved at the same time. The reason why the sintering temperature is set to 1500 to 1700 ° C. is that the sintered body cannot be sufficiently densified if the temperature is less than 1500 ° C.
If the temperature exceeds 700 ° C., coarsening of crystal grains becomes remarkable, which causes deterioration or variation in strength characteristics. Further, the reason why the relative density of the primary sintered body is sintered to 96% or more is to achieve sufficient densification of the sintered body in the secondary sintering. On the other hand, the reason why the sintering temperature under the secondary sintering condition is 1500 to 1700 ° C. is that
This is also because if the temperature is lower than 1500 ° C., the sintered body cannot be sufficiently densified, and if the temperature exceeds 1700 ° C., the coarsening of the sintered grains becomes remarkable, which causes deterioration or variation in strength characteristics. Particularly, regarding the secondary sintering temperature, the primary sintering temperature or less is preferable from the above point. If the secondary sintering is carried out in an N ₂ atmosphere of less than 10 atm, the final sintered body will not be sufficiently densified, so 10 atm or more is preferable. On the other hand, if the relative density of the obtained sintered body is less than 99%, the strength characteristics vary, which is not preferable. Further, the above-mentioned conditions are that the production method of the silicon nitride raw material powder is an imide decomposition method, and α′-sialon (including α-Si ₃ N ₄ ) in the obtained sintered body is used.
The average grain size of the crystal grains is 0.5 μm or less, and the average grain size of the β′-sialon (including β-Si ₃ N ₄ ) crystal grains is 5 μm.
The following is preferable for further improving the strength characteristics of the sintered body. The silicon nitride raw material powder obtained by the imide decomposition method has a high α ratio and a narrow grain size distribution of the crystal grain size.
By the combination of the composition and the sintering method of the present invention, the effect of compounding the crystal phase becomes remarkable. That is, α'-sialon (α
-Si ₃ N ₄ ) average grain size is 0.5 μm or less, and β′-sialon (including β-Si ₃ N ₄ ) grain size is 5 μm or less, which is a very fine form. This is because both crystal phases are combined with each other. The strength of the sintered body in which the crystal grains are compounded in this range has a bending strength of 100 kg / mm ²
This is because not only it easily crosses, but also its variation is extremely small. From the above, it became clear that the sintered body of the present invention is excellent in strength characteristics, productivity and cost.

[0010]

【Example】

Example 1 Average particle size 0.4 μm, α crystallization rate 96%, oxygen amount 1.4
Raw material powder of silicon nitride produced by the imide decomposition method with weight% and average particle diameters of 0.8 μm, 0.4 μm and 0.5 μm
Y ₂ O ₃ , Al ₂ O ₃ , AlN, and MgO powders having the composition shown in Table 1 were wet-mixed in ethanol for 100 hours in a nylon ball mill, and then dried to obtain a mixed powder. CIP molding was performed at 3000 kg / cm ² , and this molded body was subjected to 1650 at 1500 ° C. for 6 hours in 1 atmosphere of N ₂ gas.
Primary sintering was performed at ℃ for 3 hours. The obtained sintered body is 1600
Secondary sintering was carried out in an atmosphere of N ₂ gas at 1000 ° C. for 1 hour. 3m from this sintered body according to JISR1601
Cut a bending test piece equivalent to mx 4 mm x 40 mm,
After cutting and finishing with 800 diamond grindstone,
The tensile surface was lapped with # 3000 diamond paste, and then subjected to 15-point three-point bending strength according to JIS R1601. Table 2 shows the relative density of the primary sintered body, the relative density of the secondary sintered body, the ratio of the crystal phases, the bending strength, and the Weibull coefficient. In addition,
The crystal phase ratio was calculated from the peak height ratio of each crystal phase obtained by the X-ray diffraction method.

[0011]

[Table 1]

[0012]

[Table 2]

Example 2 A silicon nitride raw material powder (average particle size = 0.7 μm, α crystallization rate = 93%, oxygen amount = 1.5% by weight) obtained by a commercially available direct nitriding method was used. The same auxiliary agent powders were mixed, dried and molded in the same manner as in Example 1 so as to have the compositions 1 to 5 of Example 1. 5 hours at 1550 ° C. The molded body in a N ₂ gas 1 atm, after 2 hours primary sintering at 1650 ° C., 1600 ° C., 1 hour at 1000 atm N ₂ gas atmosphere and secondary sintering. A bending test piece according to JIS R1601 was processed from this sintered body by the same method as in Example 1, and subjected to the same evaluation. The results are shown in Table 3.

[0014]

[Table 3]

Example 3 A raw material powder similar to that of Example 1 was used as the composition 1 shown in Example 1.
About 5 to 5 were mixed, dried and molded by the same method. Got
The molded body₂6 hours at 1500 ℃ in 1 atmosphere of gas,
After primary sintering at 1650 ° C for 3 hours, continuous 1600
℃, 80 bar N ₂Secondary sintering for 2 hours in gas atmosphere
It was From the obtained sintered body, a JI was prepared in the same manner as in Example 1.
A bending test piece conforming to SR1601 was cut out and used as an example.
Evaluation was performed in the same manner as in 1. The results are shown in Table 4.

[0016]

[Table 4]

[0017]

According to the present invention, a silicon nitride-based sintered body having excellent mechanical strength, particularly at room temperature, can be produced
It is advantageously provided in terms of cost.

[Brief description of drawings]

FIG. 1 is a ternary composition diagram showing a composition range in the present invention.

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

Claims (5)

[Claims] 1. In a ternary composition diagram of Si ₃ N ₄ -first auxiliary agent-second auxiliary agent, the first auxiliary agent is a combination of two kinds of Y ₂ O ₃ and MgO, while the second auxiliary agent is the _second auxiliary agent. Auxiliary agents are Al ₂ O ₃ and A
1N or a combination selected from 2 types,
The composition range is shown in FIG. 1, that is, Si ₃
The additive composition ratio of N ₄ and the first auxiliary agent is in the range of 85:15 to 95: 5 in mol%, and the additive composition ratio of Si ₃ N ₄ and the second auxiliary agent is in the range of 90:10 to 98% in mol%. : In a range surrounded by points A, B, C, and D in FIG.
Α′-sialon (α-S) was added to the crystal phase in the obtained sintered body.
i ₃ N ₄ ) and β′-sialon (including β-Si ₃ N ₄ ), and the relative density of the sintered body is 98% or more. body. 2. An α'-sialon (α-Si in a sintered body.
₃ N ₄ included) and β′-sialon (including β-Si ₃ N ₄ ) crystal phase precipitation ratio is a peak intensity ratio of X-ray diffraction,
The silicon nitride-based sintered body according to claim 1, which is in the range of 5:95 to 30:70. 3. An α'-sialon (α-Si in a sintered body.
₍ Including ₃ N ₄ ) the average grain size of the crystal grains is 0.5 μm or less, and
The average particle diameter of β'-sialon (including β-Si ₃ N ₄ ) crystal grains is 5 μm or less, and the silicon nitride based sintered body according to claim 1 or 2. 4. The α ratio is 93% or more, and the average particle size is 0.7 μm.
The following silicon nitride raw material powder was used, and a powder compact was formed from a mixed powder obtained by mixing an auxiliary agent having a composition range shown in FIG. 1 with the powder at 1500 to 1700 ° C. and 1.1 atm or less. After performing primary sintering in a N ₂ gas atmosphere so that the relative density of the sintered body is 96% or more, 1500 to 170
A method for producing a silicon nitride-based sintered body, which comprises performing secondary sintering so that the relative density of the sintered body becomes 99% or more in an N ₂ gas atmosphere at 0 ° C. and 10 atm or more. 5. The method for producing a silicon nitride-based sintered body according to claim 4, wherein the silicon nitride raw material powder is obtained by an imide decomposition method.