JP2597774B2 - Silicon nitride based sintered body and method for producing the same - 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 sintered body having excellent mechanical strength, especially at room temperature, and excellent in productivity and cost, and a method for producing the same .

[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) is realized, and hot isostatic pressing (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, for such a problem, there is a gas pressure sintering method (for example, Sanyu, Powder and Industry, Vol. 12, No. 12, pp. 27, 1989). -Si ₃ N ₄ is accompanied by grain growth, so that in addition to the possibility that the strength is deteriorated due to precipitation of coarse crystal grains,
Since sintering is performed by applying N ₂ gas pressure higher than atmospheric pressure, the sintering equipment becomes large as in the case of the hot press method or the HIP method.
It cannot be said that this method is excellent in characteristics and production. On the other hand,
Regarding the sintering aid, Si ₃ N ₄ —Al ₂ O ₃ —Y ₂ O ₃ based silicon nitride based sintered body using Y ₂ O ₃ as a main aid is disclosed in Japanese Patent Publication No. 49-21091 and Japanese Patent Publication No. No. 48-38448. These, as shown in the patent specification, improve the strength and toughness because β-Si ₃ N ₄ crystal grains form a fibrous structure in a sintered body and this is dispersed in a matrix. It is considered possible. In other words, this is an active use of the fact that the β-Si ₃ N ₄ crystal form is hexagonal and the crystal grows anisotropically in the C-axis direction. Journal, Vol. 94, pp. 96, 1986, fibrous β-Si ₃ N ₄ crystal grains may grow to more than 10 μm or more in the C-axis direction. However, in the present technology, the grain growth also leads to abnormal growth and generation of pores, which may lead to deterioration in strength.In the case of a sintered body using only the sintering aid in the present method, sintering is not possible. Temperature 1700
Unless the temperature is increased to about 1900 ° C., densification cannot be sufficiently 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. 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, JIS-
At most 100k with 3-point bending strength according to R1601
g / mm ² , which means that sufficient characteristics are not necessarily obtained when various silicon nitride-based materials are applied.
In addition, Nagoya Industrial Technology Laboratory Report, Vol. 40, No. 1 (1
991), PP45 includes Si ₃ N ₄ —Y ₂ O ₃ —Al ₂
In an O ₃ —MgO-based sintered body, α-Si ₃ N ₄ and β
Although a sintered body having a composite crystal phase of —Si ₃ N ₄ is disclosed, it is considered that the sintering temperature is 1700 ° C. or higher, a sufficiently fine composite structure is not achieved, 100 kg / mm in bending strength depending on the knotting method
² or more have not been stably maintained.

[0003]

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

[0004]

According to the present invention, there is provided a ternary composition diagram of Si ₃ N ₄ -first auxiliary agent-second auxiliary agent, wherein the first auxiliary agent is Y
₂ O ₃ and made of a combination consisting of two MgO, whereas it consists combinations second aid consisting of two Al ₂ O ₃ and AlN, range range of the composition is shown in Figure 1, i.e. Si ₃ The additive composition ratio of N ₄ and the first auxiliary agent is 85:15 in mol%.
1 to 95: 5, and points A, B, C, and C in FIG. 1 in which the additive composition ratio of Si ₃ N ₄ and the second auxiliary is in the range of 90:10 to 98: 2 in mol%. D and the addition ratio of Al ₂ O ₃ and AlN as the second auxiliary agent
But 25 to a molar ratio _{{AlN / (Al 2 O 3} + AlN)}
In the range of 75%, and the crystal phase in the obtained sintered body is α
-Containing both Si ₃ N ₄ and β'-sialon, the relative density of the sintered body is 98% or more, and the sintered body is JISR-
The three-point bending strength according to 1601 is easily 100 kg /
A silicon nitride-based sintered body having characteristics of not less than mm ² .

In the present invention, the sintering temperature and atmosphere conditions of the sintered body are adjusted so that the relative density of the sintered body becomes 96% or more in an N ₂ gas atmosphere at 1500 to 1700 ° C. and 1.1 atm or less. After sintering, 1500-170
Since the secondary sintering is performed 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, a sintered body excellent in productivity is obtained. At the same time, since the sintering temperature is low, the characteristics of the sintered body do not deteriorate due to abnormal grain growth.

[0006] The effect of the sintered body of the present invention to obtain excellent strength characteristics is that fine particles of equiaxed α-Si ₃ N ₄ and β′-
By combining both crystal phases of sialon, the Young's modulus and hardness are improved as compared with a conventional sintered body composed of only a columnarized β'-sialon crystal phase. This is a physical property value indicating the deformation resistance of the material, and in 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 a basic concept of fracture of a brittle material, the fracture strength σf of a sintered body is given by the following equation.

Σf = E · γs / 4a, E: Young's modulus, γs: Surface energy of fracture, a: Preexisting crack length Here, γs is considered to depend on the composition and thickness of the grain boundary phase. It is advantageous to combine crystal phases to increase the 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 breaking 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. Such α-Si ₃ N ₄ and β′-Si ₃ N ₄ columnarized
The idea of compounding both crystal phases is described in, for example, JP-A-61-91065 and JP-A-2-440.
No. 66, all of which are composed of 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 limited to 1: 9 in terms of mol%, showing improvement of mechanical properties such as strength. As is clear from the examples, the strength characteristics of each sintered body are 100% in bending strength.
Any method for producing a sintered body stably exceeding kg / mm ² is based on a hot press method, and has not yet achieved industrially stable high strength characteristics. In addition, these sintered bodies have a large difference in coefficient of thermal expansion between α'-sialon and β'-sialon, which may cause tensile residual stress in the sintered body, which may lead to deterioration in strength. There is.
An object of the present invention is to provide a high-strength sintered body that is industrially stable without being limited to such conditions.

To explain 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
When the additive composition ratio of the auxiliaries 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 auxiliaries is in the range of 90:10 to 98: 2 in mol%. 1 is a range surrounded by points A, B, C, and D in FIG .
The addition ratio of the assistants Al ₂ O ₃ and AlN is the molar ratio ΔA
1N / (Al ₂ O ₃ + AlN)} is 25 to 75%.
It shall be within the box .

The composition range is set such that when the additive composition ratio of Si ₃ N ₄ to the first auxiliary agent is 85% in mole% and shifts to the first auxiliary agent side, the content of α-Si ₃ N ₄ becomes higher. This is because it causes deterioration of the strength of the sintered body, and is also affected by the atmosphere during sintering, so that a surface layer is formed on the surface of the sintered body that deteriorates properties such as strength. When the composition ratio is 95: 5, Si
₃ N deviates from the sintering property is lowered to ₄ side unless a pressure sintering method such as hot press method because it is not possible to obtain a sufficiently dense sintered body. On the other hand, if the additive composition ratio of Si ₃ N ₄ and the second auxiliary exceeds 90:10 in mol% and shifts to the second auxiliary side, coarse crystals of β′-sialon are selectively generated, leading to strength deterioration. At the same time, a surface layer which is also affected by the atmosphere during sintering and deteriorates properties such as strength on the surface of the sintered body is generated. If the composition ratio is shifted 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 press method is used. It is. Under such auxiliary composition conditions
In addition, the addition ratio of Al ₂ O ₃ and AlN of the second auxiliary agent
The rate is an important condition for achieving the effects of the present invention.
That is, the addition ratio of Al ₂ O ₃ and AlN of the second auxiliary is
Molar ratio _{{AlN / (Al 2 O 3} + AlN)} 25~75
% Range. If this molar ratio is less than 25%, β ′
-Grain growth of sialon is remarkable, and the strength of the sintered body is deteriorated.
On the other hand, if it exceeds 75%, α-Si ₃ N ₄
Compound ratio increases, and the effect of compounding the crystal phase is sufficient
It does not appear and the effect of improving strength is not sufficient. In order to make the effect of the present invention more remarkable, the precipitation ratio of the crystal phases of α-Si ₃ N ₄ and β′-sialon in the sintered body should be such that the peak intensity ratio of X-ray diffraction is 0 <α− Si ₃ N ₄ ≦ 30 %, 30 % ≦ β′−
It is desirable that Sialon <100%. If this precipitation ratio shifts to the 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. Further, in the present invention, the effect of the crystal grain size of both α-Si ₃ N ₄ and β′-sialon crystal phases in the sintered body is great. That is, the average particle size of α-Si ₃ N _{4 in} the sintered body is 0.5 μm.
Hereinafter, it is preferable that the average crystal grain size in the major axis and minor axis directions of β′-sialon be 2.5 μm and 0.5 μm, respectively, in order to stably obtain a bending strength of 100 kg / mm ² or more. . As for β'-sialon, β'-sialon in the sintered body (general formula Si _6-Z Al _Z O
_Z N _8-Z ) is preferably in the range of 0 <Z <1.0. When the Z value exceeds 1.0, the effect of compounding the crystal phase does not sufficiently appear, and the effect of improving the strength is not sufficient.

In the present invention, the conditions for producing the sintered body are also important. That is, the α ratio is 93% or more and the average particle size is 0.7 μm.
m or less, and satisfying the composition range shown in FIG. 1 and the composition ratio of Al ₂ O ₃ and AlN described above.
The auxiliary powder is mixed, and the green compact made of the mixed powder is subjected to primary firing in an N ₂ gas atmosphere at 1500 to 1700 ° C. and 1.1 atm or less so that the relative density of the sintered body becomes 96% or more. After sintering, secondary sintering is performed in an N ₂ gas atmosphere at 1500 to 1700 ° C. and 10 atm or more so that the relative density of the sintered body becomes 99% or more. Here, the reason that the silicon nitride raw material powder is required to have an α ratio of 93% or more and an average particle size of 0.7 μm or less is to improve the sinterability in a low temperature range. Further, by selecting the range of the composition of the present invention, the sintering conditions are as follows.
This is possible in a low temperature range in an N ₂ gas atmosphere of 0 ° C. and 1.1 atm or less. For this reason, the composite of crystal grains is constituted by finer crystal grains, and the effect is remarkable.
An open type continuous sintering furnace such as a pusher type or a belt type for the next sintering enables sintering with excellent productivity at the same time. 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.
Silicon nitride is 1700 ° C. in an N ₂ atmosphere at atmospheric pressure.
In order to perform sublimation decomposition in the above temperature range, it is necessary to perform sintering under a pressurized N ₂ atmosphere, and a batch type sintering furnace is used in terms of equipment. Thus, the present invention is industrially important in that its productivity has been improved at the same time. Here, the sintering temperature is 1500
The reason why the temperature is set to １1700 ° C. is that it is 1500
If the temperature is lower than 0 ° C., the sintered body cannot be sufficiently densified. If the temperature exceeds 1700 ° C., the crystal grains become remarkably coarse, which causes deterioration and variation in the strength characteristics. The reason why the relative density of the primary sintered body is sintered to 96% or more is to sufficiently achieve the 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.
If the temperature is lower than 500 ° C., the sintered body cannot be sufficiently densified.
If the temperature exceeds 0 ° C., the crystal grains become remarkably coarse, which causes deterioration or variation in strength characteristics. When the secondary sintering is performed in an N ₂ atmosphere of less than 10 atm, the final sintered body is not sufficiently densified, so that the pressure is set to 10 atm or more. On the other hand, when the relative density of the sintered body obtained is less than 99%, because the variation in the strength characteristics. Further, the above-mentioned conditions are preferable when the method for producing the silicon nitride raw material powder is based on the imide decomposition method for further improving the strength characteristics of the sintered body. Since the silicon nitride raw material powder obtained by the imide decomposition method has a high α ratio and a narrow particle size distribution of the crystal grain size, the combination of the composition and the sintering method of the present invention makes the effect of compounding the crystal phase remarkable. . That is, the average particle diameter of the α-Si ₃ N ₄ crystal grains is 0.5 μm or less, and the average particle diameters of the long axis and the short axis of the β′-sialon crystal grains are 2.5 m and 0.5 μm, respectively.
This is because both crystal phases are combined in a very fine form of not more than μm. The strength of the sintered body in which the crystal grains are compounded in this range not only easily exceeds 100 kg / mm ² in bending strength, but also has very little variation. From the above, it became clear that the sintered body of the present invention was excellent in strength characteristics, productivity, and cost.

[0011]

【Example】

Example 1 Average particle size 0.4 μm, α crystallization ratio 96%, oxygen content 1.4
Wt% silicon nitride raw material powder produced by an imide decomposition method, and an average particle diameter of 0.8 μm, 0.4 μm, 0.5 μm
m, 0.5 μm of each powder of Y ₂ O ₃ , Al ₂ O ₃ , AlN, and MgO were wet-mixed with ethanol in a nylon ball mill for 100 hours in ethanol with the composition shown in Table 1, and then dried. CIP at 3000 kg / cm ²
The molded body was subjected to primary sintering at 1450 ° C. for 6 hours and 1550 ° C. for 3 hours in 1 atmosphere of N ₂ gas. The resulting sintered body 1600 ° C., 1 in 1000 atm N ₂ gas atmosphere
Time, secondary sintering. JISR1601 from this sintered body
A 3 mm x 4 mm x 40 mm equivalent bending test piece was cut out and polished with a # 800 diamond grindstone. The tensile surface was wrapped with a # 3000 diamond paste, and then subjected to JI.
Fifteen three-point bending strengths were performed in accordance with SR1601. Table 2 shows the relative density of the primary sintered body, the relative density of the secondary sintered body, the ratio of the crystal phase, the bending strength, and the Weibull coefficient. The ratio of the crystal phases was calculated from the peak height ratio of each crystal phase obtained by the X-ray diffraction method.

[0012]

[Table 1]

[0013]

[Table 2]

Example 2 Example 1 was applied to a commercially available silicon nitride raw material powder (average particle size = 0.7 μm, α crystallization ratio = 93%, oxygen content = 1.5% by weight) obtained by a commercial direct nitriding method. The same auxiliary powder was mixed, dried and molded in the same manner as in Example 1 so as to obtain compositions 1 to 5 of Example 1. 5 hours at 1480 ° C. The molded body in a N ₂ gas 1 atm, after 2 hours primary sintering at 1600 ° C., 1600 ° C., 1 hour at 1000 atm N ₂ gas atmosphere and secondary sintering. A bending test piece based on JISR1601 was processed from this sintered body in the same manner as in Example 1 and subjected to the same evaluation. Table 3 shows the results.

[0015]

[Table 3]

Example 3 The same raw material powder as in Example 1 was prepared by using the composition 1 shown in Example 1
-5 were mixed, dried and molded in the same manner. The obtained molded body was placed at 1450 ° C. for 6 hours under one atmosphere of N ₂ gas,
After primary sintering at 1550 ° C. for 3 hours, 1600
Secondary sintering was performed in a N ₂ gas atmosphere at 80 ° C. and 80 atm for 2 hours. JI was obtained from the obtained sintered body in the same manner as in Example 1.
A bending test piece conforming to SR1601 was cut out and evaluated in the same manner as in Example 1. Table 4 shows the results.

[0017]

[Table 4]

Example 4 The same raw material powder as in Example 2 was mixed, dried, and molded in the same manner as in Example 1 for the compositions 2, 4, 5, and 9 shown in Example 1. After the obtained compact was primarily sintered under the conditions shown in Table 5, it was sintered at 1600 ° C. in a 50 atm N ₂ gas atmosphere for 2 hours. Example 1 was obtained from the obtained sintered body.
A bending test piece in accordance with JISR1601 was cut out in the same manner as described above, and evaluated in the same manner as in Example 1. Table 5 shows the results of evaluating the microstructure of each sintered body by TEM observation and determining the crystal grain size.

[0019]

[Table 5]

[0020]

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

[Brief description of the drawings]

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

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Akira Yamakawa 1-1-1, Kunyokita, Itami-shi, Itami-shi, Hyogo Sumitomo Electric Industries, Ltd. Itami Works (56) References JP-A-2-22173 (JP, A JP-A-2-167861 (JP, A) JP-A-57-123865 (JP, A) JP-A-63-218584 (JP, A) JP-A-63-139057 (JP, A) 156070 (JP, A)

Claims (5)

(57) [Claims] In the ternary composition diagram of Si ₃ N ₄ -first auxiliary agent-second auxiliary agent, the first auxiliary agent is composed of a combination of two kinds of Y ₂ O ₃ and MgO, while the second auxiliary agent is composed of the second auxiliary agent. Aids are Al ₂ O ₃ and A
consists combination consisting of two l N, the range where the range of compositions is shown in Figure 1, i.e. Si ₃ N ₄ and the first addition composition ratio of aid to 85:15 in mol% 95: 5 range 1, and the addition composition ratio of Si ₃ N ₄ and the second auxiliary is in the range of 90:10 to 98: 2 in mol%, and is within the range surrounded by points A, B, C, and D in FIG. And the addition ratio of Al ₂ O ₃ and AlN of the second auxiliary is molar ratio ｛AlN /
(Al ₂ O ₃ + AlN)} in the range of 25 to 75%,
The crystal phase in the obtained sintered body contains both α-Si ₃ N ₄ and β′-sialon, the relative density of the sintered body is 98% or more, and the bending strength thereof conforms to JISR1601. A silicon nitride-based sintered body having an average point bending strength of 100 kg / mm ² or more. 2. A precipitation ratio of α-Si ₃ N ₄ in the sintered body β'- sialon crystal phase is X-ray diffraction peak - click intensity ratio, 0
2. The silicon nitride-based sintered body according to claim 1, wherein% <α-Si ₃ N ₄ ≦ 30% and 70% ≦ β′-sialon <100%. 3. The average grain size of α-Si ₃ N ₄ crystal grains in the sintered body is 0.5 μm or less, and the average grain size of β′-sialon in the major axis and minor axis directions is 2.5 μm and 0 μm, respectively. 2. The silicon nitride-based sintered body according to claim 1, wherein the thickness is 0.5 μm or less. 4. A β′-sialon in a sintered body (general formula S
2. The silicon nitride sintered body according to claim 1, wherein i _6-Z Al _Z O _Z N _8-Z ) is in the range of 0 <Z <1.0. 5. An α ratio of at least 93% and an average particle size of 0.7 μm.
The following silicon nitride raw material powder was used as an auxiliary having the composition range shown in FIG. 1, and the addition ratio of Al ₂ O ₃ and AlN of the auxiliary was a molar ratio {AlN / (Al ₂ O ₃ + AlN)}. From the mixed powder having a range of 25 to 75%,
After primary sintering in a N ₂ gas atmosphere at 0 to 1700 ° C. and 1.1 atm or less so that the relative density of the sintered body becomes 96% or more, N _{2 at} 1500 to 1700 ° C. and 10 atm or more is applied.
A method for producing a silicon nitride-based sintered body, comprising performing secondary sintering so that the relative density of the sintered body becomes 99% or more in a gas atmosphere.