JPH05330919A - Silicon nitride-based sintered compact and its production - Google Patents

Abstract

PURPOSE:To provide a silicon nitride sintered compact involving a grain boundary phase having a high solid phase temperature, therefore, low in reduction of strength at high temperatures and exhibiting a high density, heat resistance and a high strength and to provide its production method. CONSTITUTION:In the silicon nitride sintered compact, the gaps between silicon nitride grains are characteristically filled with an Al-Yb-Si-O-N-based or an Al-Er-Si-O-N-based oxynitride glass phase, with that oxynitride glass phase and its crystallites or with a crystallized glass phase of that oxynitride. Its production method is also provided.

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 heat resistance and abrasion resistance, and a method for producing the same.

[0002]

2. Description of the Related Art A silicon nitride sintered body is expected as a high temperature structural material and a wear resistant material which are required to have heat resistance, but since it is a hardly sinterable substance, it is Al ₂ O ₃ as a sintering aid. , Y ₂ O
₃ , the method of adding MgO and sintering is adopted. However, since the solid phase temperature of the grain boundary glass phase (the temperature at which the liquid phase begins to appear by heating) is as low as about 1300 ° C., the sintered body produced by this method has a temperature of 1300 ° C. when heated to a high temperature.
There was a problem that a liquid phase began to appear at the grain boundaries in the front and rear temperature regions, and the strength of the sintered body gradually decreased.

[0003]

Therefore, according to the present invention,
It is an object of the present invention to solve the above problems and provide a silicon nitride sintered body having a grain boundary phase having a high temperature at which a liquid phase appears in the grain boundary phase, that is, a solid phase temperature, and a method for producing the same.

[0004]

The present invention is a silicon nitride sintered body and a method for producing the same as described below. (1) The gap between the silicon nitride particles is Al-Yb-Si-O-.
An N-based or Al-Er-Si-O-N-based oxynitride glass phase, or a silicon nitride sintered body characterized by being filled with the oxynitride glass phase and microcrystals thereof. ,
(2) For silicon nitride particles having an average particle size of 10 μm or less,
Both are oxides with an average particle size of 10 μm or less,
Alumina was used as the additive, ytterbium oxide or erbium oxide was used as the second additive, and silica was used as the third additive, if necessary, so that the total addition amount was 3 to 30% by weight. A method for producing a silicon nitride sintered body, which comprises uniformly mixing with a dispersant, drying and molding, degreasing, and then sintering at a temperature of 1600 to 1950 ° C. in a nitrogen pressure atmosphere, ( 3) In the method for producing a silicon nitride sintered body according to the above (2), the weight ratio of rare earth oxide to alumina in the additive is maintained in the range of 0.5 to 7, and silica is added as needed. A method for producing a silicon nitride-based sintered body, characterized by adding not more than wt%, (4)
A silicon nitride sintered material characterized in that the gaps between the silicon nitride particles are filled with a crystallized glass phase of an Al—Yb—Si—O—N-based or Al—Er—Si—O—N-based oxynitride. (5) The silicon nitride sintered body obtained by the manufacturing method according to (5) above (2) is heat-treated in a temperature range of 850 to 1050 ° C. in a nitrogen gas atmosphere to form crystal nuclei in the grain boundary glass phase. A method for producing a silicon nitride sintered body, which is characterized in that it is formed and then heat-treated at a temperature of 1100 to 1500 ° C. in a nitrogen pressure atmosphere to grow a crystal, and a grain boundary glass phase becomes a crystallized glass phase. .. In addition, when exemplifying the microcrystals filled between the silicon nitride particles of the above (1), Yb ₂ Si ₂ O ₇ and Er ₂ S are given.
i ₂ O ₇ , Si ₂ N ₂ O and the like.

[0005]

The present invention is based on silicon nitride (Si₃N_Four) 2 for powder
~ 3 kinds of oxide powder (Al₂O ₃-Yb₂O₃, Al₂
O₃-Er₂O₃, Al₂O₃-Yb₂O₃-Si
O₂, Al₂O₃-Er₂O₃-SiO₂) 3 to 30
Wt%, add a dispersant in an organic solvent and mix evenly.
In this case, silicon nitride is obtained by drying, molding, degreasing and firing.
Al-Yb-Si or A, which has a high solid phase temperature, is placed in the gap between the particles.
1-Er-Si oxynitride glass or its crystal is filled.
It is intended to provide a filled silicon nitride sintered body.
It By the way, silicon nitride (Si₃N_Four) Sintered in liquid phase
Since it is a sintering process, the additives used in the raw material powder of silicon nitride cannot be added.
Silica contained as a pure substance and added as an auxiliary agent
It is necessary to generate a liquid phase with silica.

The present inventors have found that Al ₂ O ₃ --Yb ₂ O _3-
Examination of the vitrification range of the SiO ₂ system revealed that
It turns out that the range is surrounded by the solid line. Also, A
The vitrification range of the l ₂ O ₃ —Er ₂ O ₃ —SiO ₂ system is also A
It was found to be almost the same as the 1 ₂ O ₃ —Yb ₂ O ₃ —SiO ₂ system. That is, in order to make the grain boundary a glass phase,
The weight ratio of Yb ₂ O ₃ (Er ₂ O ₃ ) and Al ₂ O ₃ is adjusted to the range of 0.5 to 7, and the SiO ₂ concentration in the total oxide is adjusted to the range of 18 to 50% by weight. Is desirable.
In order to keep the SiO ₂ concentration in the grain boundary phase within this range,
When the SiO ₂ component in the grain boundary phase is entirely derived from impurities in the Si ₃ N ₄ raw material, the amount of the auxiliary agent added needs to be 3 to 15% by weight.

FIG. 2 shows Yb₂O₃/ Al₂O₃Molar ratio of
To 3/5 (Al_1.25Yb_0.75O ₃Is 5Al₂O₃・
3Yb₂O₃Equivalent to), Si₃N_FourConcentration and SiO₂
Heat treatment at 1600 ° C for 20 hours by changing the concentration ratio with the concentration.
It is a diagram showing the crystal structure of the sintered body obtained by
Degree of less than 30% Si₃N_FourOther than (indicated by SN in the figure)
To Yb₂Si₂O₇Crystals such as (indicated by D in the figure) precipitate
In the exposed area (SN + D + L area), oxide particles are deposited.
By the effect of the
Be done. However, if the additive amount exceeds 30% by weight, S
i₃N_FourThe amount of
Problems such as₃N_FourThe excellent properties of the sintered body are damaged.
Be struck. In FIG. 2, Si₃N_Four70% or more
SN + L region and SN + D + L region are mainly preferred in
This is a region where a new silicon nitride sintered body is produced.

Al ₂ O ₃ --Yb ₂ O ₃ --SiO ₂
The solid phase temperature of the sintered system is about 1500 ° C, Al ₂ O ₃ -Er
The solid phase temperature of the ₂ O ₃ —SiO ₂ system sintered body is about 1450 ° C., and about 100 ° C. or more from the solid phase temperature 1350 ° C. of the conventional Al ₂ O ₃ —Y ₂ O ₃ —SiO ₂ system sintered body. Also has a high solidus temperature. Therefore, the temperature at which the liquid phase begins to appear in the sintered body of the present invention is higher than that of the conventional sintered body by about 100 ° C. or more, and the heat resistance can be improved.

In the present invention, polyethyleneamine, polyvinyl alcohol, or the like can be used as a dispersant for dispersing raw material powders such as Si ₃ N ₄ and an auxiliary agent, and the amount thereof is 100 parts by weight of the ceramic raw material. However, the range of 1 to 10 parts by weight is preferable. When the amount of the dispersant used is less than 1 part by weight, there is no effect of dispersing the raw material powder,
If it exceeds 10 parts by weight, the time required for degreasing becomes long, which is not suitable. Further, as the organic solvent, ethanol,
Butanol and the like can be mentioned, and the amount thereof is preferably in the range of 50 to 150 parts by weight with respect to 100 parts by weight of the ceramic raw material.

The obtained homogeneously mixed and dispersed powder is 1 to 5 t / c.
Mold by pressurizing with a hydrostatic pressure of m ² . The dispersant can be degreased by heating the molded body to 300 to 700 ° C. in a vacuum prior to sintering. The degreased compact can be heat-treated under nitrogen gas pressure at a temperature of 1600 to 1950 ° C. to obtain a dense sintered compact. Since the sintering aid of the present invention is added, the temperature at which the grain boundary phase becomes a liquid phase becomes high, and when the sintering temperature is lower than 1600 ° C., there is no deposition shrinkage associated with the sintering and the sintering does not proceed. If the temperature exceeds 1950 ° C., the density does not increase due to decomposition or the like, and there arises a problem that a good quality sintered body cannot be obtained. The pressurizing condition is preferably nitrogen gas at about 3 atm or more.

The average particle size of the raw material fine powder is required to be 10 μm or less in order to produce a ceramic having a uniform composition. Particularly, by using the fine powder having a particle size of about 1 μm, It is possible to produce a good quality sintered body in a relatively short time.

In order to crystallize the glass phase at the grain boundaries, it is necessary to generate crystal nuclei in the glass phase. As a result of various studies on the formation rate of crystal nuclei, the temperature range of 850 to 1050 ° C. is the fastest, and the temperature becomes higher or lower than this temperature range. That is, in order to form crystal nuclei,
It is sufficient to perform heat treatment in the temperature range of 1050 ° C. for 0.5 to 3 hours. Then, to grow crystals, 1100-
It is necessary to perform heat treatment in a temperature range of 1500 ° C. for 0.5 to 48 hours. When the temperature is lower than 1100 ° C., the crystal growth rate is slow, and when it exceeds 1500 ° C., a liquid phase starts to appear at the grain boundary. Melt the grown crystals. Then, 11
It is sufficient to perform the heat treatment in the temperature range of 00 to 1500 ° C. for 0.5 to 48 hours.

[0013]

【Example】

Example 1 Si ₃ N _{4 having} an average particle size of 0.3 μm, and Al ₂ O ₃ having an average particle size of 0.8 to 1 μm as an auxiliary agent,
Alumina ball mill was prepared by mixing Yb ₂ O ₃ , Er ₂ O ₃ and SiO ₂ in the mixing ratio shown in Table 1, and adding 3 parts by weight of a dispersant polyethyleneamine and 120 parts by weight of solvent ethanol to 100 parts by weight of raw material powder. After being uniformly mixed with, the mixture was dried, pressed into a disk shape having a diameter of 60 mm and a thickness of about 6 mm, and a molded body was obtained by a hydrostatic pressure press of 4 t / cm ² . The compact was heated to 500 ° C. in vacuum, held for 1 hour to be degreased, pressurized with nitrogen gas at 10 atm and heat-treated under the heat treatment conditions shown in Table 2 to obtain a silicon nitride sintered body.

[0014]

[Table 1]

[0015]

[Table 2]

Table 2 shows the relationship between the heat treatment conditions and the relative density and bending strength of the obtained sintered body. As is clear from Table 2, the sintered body of the present invention has a ratio of the room temperature bending strength to the bending strength at 1300 ° C. of about 0.7, which is in comparison with the conventional sintered body of about 0.5. And shows a large value. this is,
This indicates that the rate of decrease in strength at high temperatures is small, and in the sintered body of the present invention, the temperature at which the liquid phase begins to appear at the grain boundaries is 100 ° C. or more higher than that in the conventional sintered body. It is considered that this characteristic was obtained.

Further, regarding the above-mentioned composition, 16
When the relationship between the crystal structure of the sintered body obtained by heat treatment at 00 ° C. for 20 hours and the composition of the additive (wt%) was examined, it was as shown in the schematic FIG. Al _1.25 Y _0.75 O among auxiliary additives
_{When the amount of 3} (5Al ₂ O ₃ · 3Yb ₂ O ₃ abbreviated as G phase) increases, Yb ₂ Si ₂ O is added in addition to Si ₃ N ₄ (SN phase).
Precipitation of ₇ crystals (D phase) was observed, and when the amount of SiO _{2 was} increased, precipitation of Si ₂ N ₂ O crystals (Ox phase) was observed.
A composite sintered body in which ₃ N ₄ and another crystal phase are composite is obtained. The C phase means SiO ₂ crystal (cristobalite). Further, even such a silicon nitride sintered body can be used as a practical material.

(Example 2) Sample numbers Y1, Y3 in Table 1
The mixed composition of Y7, E1, and E4 was heat-treated at 1800 ° C. for 4 hours, the obtained sintered body was heat-treated at 950 ° C. for 1 hour to form crystal nuclei, and then heat-treated at 1350 ° C. for 20 hours to obtain grain boundaries. When the phase was crystallized and the bending strength at 1300 ° C. was measured, it was as shown in Table 3. Further, when the crystal structure produced by crystallizing the glass phase was examined by X-ray diffraction, Yb ₂ Si ₂ O ₇ crystal (D phase), Al _1.25
It was estimated to be Y _0.75 O ₃ (G phase) and Al ₆ Si ₂ O ₁₃ (M phase). From this result, it was confirmed that the strength is improved by the crystallization of the grain boundary glass phase.

[0019]

[Table 3]

(Example 3) 93Si ₃ N ₄ -2Al ₂ O
₃ -5Yb ₂ O ₃ composition (Example 3) and 93Si ₃ N
_A sintered body obtained by heat-treating a raw material of 4-2Al ₂ O ₃ -5Y ₂ O ₃ composition (conventional example) at 1800 ° C. for 4 hours in a nitrogen pressure atmosphere at 1350 ° C. for 20 hours in the air Oxidation and increase in oxidative weight were measured with a thermobalance, and the results are shown in Table 4. In the conventional example, since a liquid phase appears in the grain boundary phase at around 1300 ° C., the diffusion of Y ions and Al ions in the grain boundaries is fast, and the oxidation rate at high temperature is also fast. On the other hand, in Example 3, the temperature at which the liquid phase appears is about 150 ° C. higher than that in the conventional example, so that the grain boundary phase remains a solid phase at the above-mentioned oxidation temperature of 1350 ° C. Therefore, the diffusion rate of metal ions is much slower than that in the liquid phase. Therefore, it can be seen that the oxidation rate of the sintered body of Example 3 is slower than that of the conventional example and the oxidation resistance is excellent.

[0021]

[Table 4]

[0022]

EFFECTS OF THE INVENTION By adopting the above constitution, the present invention can provide a dense, heat-resistant, high-strength silicon nitride sintered body with a low rate of decrease in strength at high temperatures. It was

[Brief description of drawings]

FIG. 1 is a diagram showing a vitrification range of an Al ₂ O ₃ —Yb ₂ O ₃ —SiO ₂ based oxide forming a grain boundary phase of a sintered body according to an example of the present invention.

FIG. 2 is a crystal structure of a sintered body obtained by heat treatment at 1600 ° C. for 20 hours and a compounding composition (5Al ₂ O ₃ ·.
It is a diagram showing the relationship between 3Yb ₂ O _3).

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsunori Akiyama 1-8-8, Koura, Kanazawa-ku, Yokohama-shi, Kanagawa Mitsubishi Heavy Industries, Ltd.

Claims (5)

[Claims] 1. The gap between the silicon nitride particles is Al—Yb—S.
i-O-N-based or Al-Er-Si-O-N-based oxynitride glass phase, or silicon nitride filled with the oxynitride glass phase and microcrystals thereof. Quality sintered body. 2. An oxide having an average particle size of 10 μm or less, with respect to silicon nitride particles having an average particle size of 10 μm or less, wherein alumina is the first additive and ytterbium oxide or erbium oxide is the second additive. If necessary, silica as a third additive is added and adjusted so that the total addition amount is 3 to 30% by weight, and the mixture is uniformly mixed with a dispersant in an organic solvent, then dried and molded, and degreased. And then sintering at a temperature of 1600 to 1950 ° C. in a nitrogen pressure atmosphere, the method for producing a silicon nitride sintered body. 3. The method for producing a silicon nitride sintered body according to claim 2, wherein the weight ratio of the rare earth oxide and the alumina in the additive is kept in the range of 0.5 to 7, and silica is added if necessary. 27% by weight or less is added to the silicon nitride sintered body. 4. The gap between the silicon nitride particles is Al—Yb—S.
A silicon nitride-based sintered body characterized by being filled with a crystallized glass phase of an i-O-N-based or Al-Er-Si-O-N-based oxynitride. 5. The silicon nitride sintered body obtained by the manufacturing method according to claim 2 is heat-treated in a temperature range of 850 to 1050 ° C. in a nitrogen gas atmosphere to form crystal nuclei in a grain boundary glass phase. Then, a method for producing a silicon nitride sintered body, characterized by heat-treating at a temperature of 1100 to 1500 ° C. in a nitrogen pressure atmosphere to grow a crystal, and a grain boundary glass phase into a crystallized glass phase.