JPH06271358A - Silicon nitride-based sintered compact - Google Patents

Abstract

PURPOSE:To provide a silicon nitride-based sintered compact excellent in mechanical characteristics and relatively easy to produce. CONSTITUTION:This silicon nitride-based sintered compact contains columnar grains and isometric grains of Si3N4 and sialon and fine dispersed grains dispersed in a grain boundary phase in voids. The average minor axis size of the columnar grains is <=0.3mum and the average major axis size is <=5mum. The average grain diameter of the isometric grain is <=0.5mum and that of the fine dispersed grains is <=0.03mum.

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.

[0002]

2. Description of the Related Art Conventionally, various methods have been tried in order to improve the strength of silicon nitride.

For example, as a silicon nitride single-phase material, Japanese Patent Laid-Open No.
As disclosed in JP-A-1-91065 and JP-A-2-44066, a uniform grain size of α'-sialon [general formula M _x (S
i, Al) ₁₂ (O, N) ₁₆ , M: Mg, Ca, Li and rare earth elements] and a columnar β′-sialon (including β-type silicon nitride) in a combination of crystal phases, and a composite crystal phase Some of them have been shown to have improved mechanical properties such as strength. However, as is apparent from the examples, all the sintered body manufacturing methods in which the strength characteristics of each sintered body stably exceed 100 kg / mm ² in terms of bending strength are hot pressing methods, and are industrially stable and high. It has not yet reached the strength characteristics.

In the case of a composite material, for example, Japanese Patent Laid-Open No. 4-20
2059, silicon nitride having a minor axis diameter of 0.05 to 3 μm and an aspect ratio of 3 to 20 and 1 to 50 for sialon.
There is an example in which fine particles of 0 nm are dispersed. Although the strength of the example is 167 kg / mm ² at the maximum, it may contain coarse silicon nitride, which may cause strength deterioration, and the Weibull coefficient is about 9, so that stable high strength characteristics cannot be obtained. .

There is also an example in which different kinds of particles are dispersed in a grain boundary phase of silicon nitride having a columnar structure as disclosed in Japanese Patent Laid-Open No. 4-295056. In the case of this sintered body, the maximum particle diameter is from 2 μm to 3.5 μm for minor axis diameter and 10 μm for length,
Since the matrix itself is a source of destruction due to the presence of m, the maximum strength of the example is 158 kg / mm ² , and the firing temperature is 1800 ° C. or higher, which is not sufficient in terms of productivity and cost.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to provide a silicon nitride-based sintered body which has excellent mechanical properties and is relatively easy to produce.

[0007]

In order to solve the above-mentioned problems, the present invention provides a sintered body having columnar particles made of at least one of Si ₃ N ₄ and sialon, equiaxed particles, and a gap. The grain boundary phase contains finely dispersed particles, for example, a Ti compound, and the average particle diameter of the minor axis of the columnar particles of the sintered body is 0.3 μm or less,
The major axis diameter is 5.0 μm or less on average, the equiaxed particles have an average particle diameter of 0.5 μm or less, and the dispersed particles have an average particle diameter of 0.03 μm.
The following is a silicon nitride-based sintered body characterized by the following.

According to the present invention, the three-point bending strength in accordance with JISR-1601 can be easily obtained with stable strength having a characteristic of 170 kg / mm ² or more, and high impact value and fatigue characteristics can be obtained. It is to provide silicon nitride excellent in mechanical properties such as cost and productivity.

Generally, one of the causes of the deterioration of the strength of silicon nitride is the problem of the grain boundary phase existing inside the structure. This grain boundary phase is made of a glassy material containing a sintering aid which is inevitable when obtained by sintering silicon nitride ceramics, and is generally more brittle than a silicon nitride matrix. Therefore, when stress concentration is applied to such a grain boundary phase, it has been a cause of lowering the strength of the sintered body.

In the present invention, when the above problems were examined in detail, three columnar fine grains, equiaxed grains and a Ti compound dispersed in the grain boundary phase of the interstices between the grains were developed. By doing so, the grain boundary phase area increases and the relative amount of the glass phase decreases, so brittleness at the grain boundaries can be reduced, and it is possible to obtain a sintered body with high strength, fatigue properties, and impact resistance. Got knowledge that can be obtained.

One of the methods for reducing the thickness of the grain boundary phase is to reduce the thickness by producing a fine structure composed of columnar grains and equiaxed grains as disclosed in JP-A-2-70715. There is a method to achieve high strength. However, in order to make the α grains fine, it is necessary to use a fine powder having a high α ratio as the raw material powder, and since the strength property cannot be obtained unless the β ratio is increased during sintering, Since the β-grain size also becomes 2.0 μm or more during sintering, there is a limit in reducing the thickness of the grain boundary phase by refining only silicon nitride.

However, in the sintered body of the present invention, not only the fine equiaxed and columnar grains are packed as described above, but also a finer Ti compound is dispersed in the grain boundary phase to reduce the thickness of the glass phase. In addition to the above, the Ti compound also controls the size of the equiaxed and columnar grains, and it is considered that a sintered body having excellent mechanical properties was obtained.

Further, in order to exert the above effects, sintering is performed in which the short axis of the columnar grains has an average grain size of 0.3 μm or less, the long axis diameter has an average grain size of 5.0 μm or less, and the equiaxed grains have an average grain size of 0.5 μm or less. It must consist of the body. In both cases, if the respective upper limit values are exceeded, the structure becomes non-uniform, and the particles themselves may become the source of destruction and reduce the strength, as well as lead to a decrease in packing density and an increase in the thickness of the grain boundary phase. , There is a possibility of causing a decrease in strength.

The Ti compound, which is the dispersed particles, has an average particle size of 0.03 μm or less. When it is larger than this, the amount of the triplet or the same size as the equiaxed grain exists in addition to the grain boundary phase existing in the gap between the grains, and the relative amount of the glass phase of the grain boundary phase decreases. Cannot be obtained and high strength cannot be obtained. Further, by controlling the Ti compound to have a grain size not more than this, it plays a role of suppressing grain growth of the entire structure,
A fine and uniform tissue can be expressed.

In the present invention, the Ti compound is TiN.
It is necessary to be present in an amount of 0.05 to 2% by volume in terms of the structure of the sintered body. If it is less than 0.05% by volume, the high strength effect is not exhibited, and the strength is not improved,
If it exceeds 2.0% by volume, the Ti compounds aggregate with each other to form defects, and the presence of the Ti compound significantly deteriorates the sinterability, so that a non-uniform portion is generated in the silicon nitride structure, which is an excellent mechanical property. The characteristics cannot be obtained. In addition, these Ti compounds are considered to contain at least TiN by X-ray diffraction measurement.

As the silicon nitride powder for obtaining the sintered body of the present invention, it is not always necessary to use a powder having a high α ratio and a fine grain size due to the presence of the Ti compound, and the Ti compound is commercially available such as titanium oxide. It is possible to obtain a Ti compound during sintering from powders that have been used as starting materials. When titanium oxide is used, the titanium oxide powder preferably has a primary particle size of 0.05 μm or less in order to form a Ti compound having the above size.

In order to obtain the structure of the present invention, SiO ₂ present on the surface of silicon nitride and an auxiliary agent which forms a liquid phase at a temperature as low as possible, such as MgO, CeO ₂ , CaO, etc.
It can be obtained by sintering using spinel or the like at a temperature of 1600 ° C. or lower in a non-oxidizing atmosphere. At this temperature, it is not necessary to perform sintering in a pressurized atmosphere used to suppress sublimation decomposition of silicon nitride. In terms of equipment, it is not necessary to use a pressurized atmosphere furnace such as a batch furnace sintering furnace, and a furnace suitable for mass production such as a pusher type or belt type continuous sintering furnace can be used. Furthermore, since a high-strength sintered body can be easily obtained without using a hot isostatic press (HIP) or the like, the present invention can provide a sintered body excellent in cost and productivity.

[0018]

EXAMPLES The present invention will be specifically described below with reference to examples. Example 1 Commercially available Si ₃ N ₄ having an average particle size of 0.7 μm and Y, A
Compounds having the elements of 1 and Mg are respectively occupied by the oxide weight conversion ratio, and each powder of titanium oxide having a primary particle diameter of 15 nm as a raw material of the dispersed particles is occupied by the whole sintered body structure in the TiN volume conversion ratio. The mixture was blended as shown in Table 1 in a volume ratio with a ratio of 1, and wet-mixed in ethanol for 100 hours using a nylon ball mill, and then CIP was performed at 3000 kg / cm ² .
Molded.

[0019]

[Table 1]

The compacts obtained in Table 1 were subjected to primary sintering at 1500 ° C. for 4 hours in 1 atm of N ₂ gas, and then N
Secondary sintering was performed at 1575 ° C. for 1 hour in 1000 atm of ₂ gases. The obtained sintered body was cut into an anti-segregation test piece of 3 × 4 × 40 mm, cut and finished with a # 800 diamond grindstone, and then subjected to 15-point three-point bending strength in accordance with JIS R1601. The crystal phase was calculated from the peak height of each crystal phase ratio by the X-ray diffraction method, and the crystal average grain was 8 after lapping an arbitrary cross section of the sintered body.
30 at 0 ° C HF: HNO ₃ = 2: 1 etching solution
After minute etching processing, it was observed with a scanning electron microscope at a magnification of 5000 times. The dispersed particles were observed by a transmission electron microscope at an arbitrary position to obtain the average particle size.

Table 2 shows the density of the secondary sintering of the obtained sintered body, the α-β crystal phase ratio after the secondary sintering, the average bending strength and the Weibull coefficient. Columnar shape obtained at the same time, average particle size of equiaxed grains,
The average particle size of the dispersed particles is shown.

[0022]

[Table 2]

[0023]

[Table 3]

Example 2 Using the same powder as used in Example 1, the composition shown in Table 3 was first sintered in N ₂ gas under the conditions shown in Table 4, and then the secondary powder was also produced under the conditions shown in Table 4. Sintering was performed. The secondary sintering may be performed under the condition of secondary sintering after the primary sintering, or the sample that has reached room temperature after the primary sintering may be sintered under the condition of secondary sintering. . For the obtained sintered body, the secondary sintering density, the three-point bending strength, the α-β ratio, the Weibull coefficient, the columnar shape, the average particle diameter of equiaxed particles, and the average particle diameter of dispersed particles were obtained in the same manner as in Example 1. It was
The results are shown in Table 5.

[0025]

[Table 4]

[0026]

[Table 5]

[0027]

[Table 6]

[0028]

[Table 7]

Example 3 Next, among the three compositions shown in Table 6, the composition was kept constant and only the primary particle diameter of titanium oxide was changed, and primary sintering was performed at 1500 ° C., 1600 ° C., and N ₂ gas was 500 atm. Secondary sintering was performed therein. For the obtained sintered body, the secondary sintering density, the three-point bending strength, the α-β ratio, the Weibull coefficient, the columnar shape, the average particle diameter of equiaxed particles, and the average particle diameter of dispersed particles were obtained in the same manner as in Example 1. It was
The results are shown in Table 7.

[0030]

[Table 8]

[0031]

[Table 9]

[0032]

[Table 10]

Example 4 Materials having the compositions shown in Table 8 were subjected to atmospheric pressure sintering at 1500 ° C., and then secondary sintering was performed at 1575 ° C. and 1000 atm of N ₂ gas. This sintered body was subjected to a Charby impact test and a fatigue strength test.

The Charpy impact test uses JIS 1601, a grooveless test piece, and has a Charpy capacity of 1.5 kgfc.
m and an impact velocity of 0.76 m / sec. An Ono-type rotary bending fatigue (evaluation part = φ6 mm, both ends fixed part = φ8 mm, gauge length = 12 mm) test was performed for fatigue measurement. The dimensions of the sample are shown in FIG. 2, and the concept of the tester is shown in FIG. The results of the Charpy impact test are shown in Table 12, and the results of the fatigue test are shown in FIG.

[0035]

[Table 11]

[0036]

[Table 12]

From these results, it is understood that the material of the present invention has higher impact value and fatigue strength than the conventional materials.

[0038]

As described above, according to the present invention, a silicon nitride-based sintered body having excellent mechanical strength, especially at room temperature, can be obtained.

[Brief description of drawings]

FIG. 1 is a graph showing rotational bending fatigue strength.

FIG. 2 is an explanatory view of the shape of a rotating bending fatigue test piece.

[Fig. 3] Conceptual diagram of rotary bending fatigue tester

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

Claims (3)

[Claims] 1. A sintered body comprising columnar particles made of at least one of Si ₃ N ₄ and sialon, equiaxed particles and finely dispersed particles dispersed in a grain boundary phase in a gap, The average particle diameter of the minor axis diameter of the columnar particles is 0.3 μm or less, the average diameter of the major axis diameter is 5 μm or less, and the average particle diameter of the equiaxed particles is 0.5 μm.
Hereinafter, the average particle diameter of dispersed particles is 0.03 μm or less, a silicon nitride-based sintered body. 2. The silicon nitride based sintered body according to claim 1, wherein the finely dispersed particles are a Ti compound. 3. The silicon nitride-based firing according to claim 2, wherein the Ti compound is 0.05 to 2% by volume when the volume of the other sintered body structure is converted to TiN to 1. Union.