JPH06116045A - Silicon nitride sintered compact and its production - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a method for producing a silicon nitride sintered body which is capable of reliably nitriding the inside of a formed body containing silicon powder as a main component in a short time and is excellent in strength. [Constitution] (a) Silicon powder 82.0-98.4% by weight (Si ₃
And N ₄ converted _{value), (b) Y 2 O} 3 powder 1.5 to 10.0 wt%
And (c) Al ₂ O ₃ powder 5.0% by weight or less, and (d) a metal having a valence different from that of Si, an ionic radius of 0.3 to 1.0 angstrom, and a melting point of the silicide of 579 to 1450 ° C. A powder or a powder of the metal oxide 0.1 to 3.0% by weight (elemental conversion value) is used to prepare a molded body, which is heated in a nitrogen-containing atmosphere for nitriding, and further at 1900 ° C.
This is the method of firing.

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 and a method for manufacturing the same, and more particularly to a method for manufacturing a silicon nitride sintered body capable of reliably nitriding the inside of a molded body containing silicon as a main component. .

[0002]

2. Description of the Related Art A silicon nitride ceramic sintered body is a gas turbine member because of its high strength, high heat resistance, high thermal shock resistance, high wear resistance, oxidation resistance and the like. Etc., it is expected to be used as a structural ceramic used under severe conditions.

By the way, as a method for producing a silicon nitride ceramic sintered body, there is a method in which a compact having a desired shape is produced by using silicon nitride powder and a sintering aid, and this is sintered. As another method, there is a so-called reactive sintering method in which a compact is produced using silicon powder and the compact is nitrided to obtain a silicon nitride sintered body. According to the latter method, the shrinkage observed during sintering can be suppressed to a low level, and a sintered body with relatively high dimensional accuracy can be obtained. Also, because it is low cost (raw materials are cheap),
Attempts have been made to apply it to the production of various engineering ceramic members.

As a method for obtaining a silicon nitride sintered body by the reaction sintering method, Japanese Patent Laid-Open No. 59-88374 discloses that (a) silicon, (b) Mg,
Y, Cr, Mo, Fe, Mn, W, Co, V, U, Ni, Ti, Hf, Z
nitriding a compact containing one or more oxide sintering aids selected from the group consisting of r, Nb, and Ta oxides;
A method of sintering is disclosed.

However, according to the study by the present inventors, simply by randomly selecting one or more oxides from the above-mentioned metal oxides according to the above method, and using them as sintering aids, If a compact is manufactured from this and silicon powder to nitrid it, it takes a long time to reliably nitride the compact. The long-time nitriding treatment is not preferable in terms of an increase in manufacturing time and consumption of a large amount of energy. Also, especially
If the molded product is not a thin product, the inside of the molded product may not be easily nitrided. If the molded body is not uniformly nitrided and sintered (if it does not become a sintered body having a uniform structure), the strength of the sintered body is naturally low and the range of use as a ceramic member is greatly narrowed. To be

Therefore, an object of the present invention is to provide a silicon nitride sintered body having good strength.

Another object of the present invention is to provide a method for producing a silicon nitride sintered body which can nitrid the interior of the compact satisfactorily and thus has good strength.

[0008]

As a result of earnest research in view of the above object, the present inventors have found that (a) silicon powder contains a predetermined amount of (b) Y ₂ O ₃ and (c) as a sintering aid. ) Al ₂ O ₃ is further added, and (d) a metal having a valence different from that of Si and a specific ionic radius, and the melting point of the silicide is within a predetermined range, or an oxide of this metal. It has been discovered that the addition of strontium can greatly accelerate the nitriding reaction of silicon, so that the compact can be reliably nitrided in a short time.
The present invention has been completed.

That is, the silicon nitride sintered body of the present invention is
(a) Silicon powder 82.0-98.4% by weight (Si ₃ N ₄ conversion value), (b) Y ₂ O ₃ powder 1.5-10.0% by weight, (c) Al
₂ O ₃ powder 5.0% by weight or less, (d) a metal powder having a valence different from that of Si, an ionic radius of 0.3 to 1.0 angstrom, and a melting point of the silicide of 579 to 1450 ° C., or A molded body containing 0.1 to 3.0% by weight of oxide powder (elemental conversion value) is heated and fired in a nitrogen-containing atmosphere.

Further, the method of the present invention for producing a silicon nitride sintered body is (a) 82.0 to 98.4% by weight of silicon powder (provided that Si ₃ N is used).
₄ conversion value), and (b) Y ₂ O ₃ powder 1.5 to 10.0% by weight,
(c) Al ₂ O ₃ powder 5.0% by weight or less, and (d) a metal powder having a valence different from that of Si, an ionic radius of 0.3 to 1.0 angstrom, and a melting point of the silicide of 579 to 1450 ° C., Or 0.1 to 3.0% by weight of oxide powder of the above metal
(Elemental conversion value) is produced, the formed body is heated to 1250 to 1450 ° C. in a nitrogen-containing atmosphere to be nitrided, and further fired at 1900 ° C. or higher.

The present invention will be described in detail below. The silicon nitride sintered body of the present invention has a valence different from (a) silicon powder, (b) Y ₂ O ₃ powder, (c) Al ₂ O ₃ powder, and (d) Si, and has an ionic radius A metal of 0.3 to 1.0 angstrom and the silicide of which has a melting point of 579 to 1450 ° C., or a powder formed of an oxide of this metal is heated in a nitrogen-containing atmosphere to be nitrided. It is formed by firing at a predetermined high temperature. Here, among the components (b) to (d), the component
(b) and (c) will be referred to as sintering aids, and the component (d) will be referred to as "nitriding reaction accelerator".

(A) The average particle size of the silicon powder used to manufacture the silicon powder compact is 5 to 300.
It is preferably μm. If an average particle size of less than 5 μm is used, the density of the molded product is reduced and the shrinkage rate due to sintering increases, so that good dimensional accuracy cannot be obtained. Further, the strength and toughness of the obtained sintered body are also reduced. On the other hand, the use of silicon powder having an average particle size of more than 300 μm is not preferable because Si is eluted and nitriding requires a long time. More preferably, the average particle size of the silicon powder is 5 to 50 μm.

By using the silicon powder having the above-mentioned average particle diameter, the density of the molded body can be increased, and as a result, the degree of shrinkage of the molded body during firing can be reduced.

The maximum particle size of the silicon powder used is 50 to 50.
It is preferably in the range of 600 μm. Maximum particle size is 50
If a silicon powder having a particle size of less than μm is used, the density of the compact tends to decrease, and shrinkage due to sintering tends to increase. On the other hand, if silicon powder with a maximum particle size exceeding 600 μm is used,
Is less likely to elute and nitrid, which is not preferable. The more preferable range of the maximum particle size of the silicon powder is 50 to 100 μm.
m.

Sintering Aid (Components (b) and (c) ) In the present invention, Y ₂ O ₃ and Al ₂ O ₃ are used as a sintering aid. These sintering aids are used in powder form. The average particle size of the sintering aid is 0.1 to 5 μ for both Y ₂ O ₃ and Al ₂ O _3.
It is preferably about m.

Nitriding reaction accelerator (component (d)) A metal having a valence different from Si and an ionic radius of 0.3 to 1.0 angstrom for promoting the nitriding reaction of silicon, and the melting point of the silicide. Is 579 ~ 1450 ℃
Or a powder of its oxide. Less than,
The reason for adding the nitriding reaction accelerator and the conditions that can be the nitriding reaction accelerator will be described.

In the reaction of nitriding silicon, first, at least the surface portion of the silicon particles is melted, the Si melt and nitrogen react with each other to produce Si ₃ N ₄ , and the nitriding gradually progresses to the inside of the silicon particles. It is thought to do. Here, diffusion of nitrogen (N) in Si ₃ N ₄ generated on the surface portion of the silicon particles in the initial stage of the nitriding treatment is the rate-determining step of the nitriding reaction. Therefore, in order to promote the nitriding reaction of silicon, it is necessary to increase the diffusion rate of N in Si ₃ N ₄ .

By the way, it is known that the diffusion of nitrogen (N) in Si ₃ N ₄ is so-called vacancy diffusion. Therefore, in order to accelerate the nitriding reaction of silicon, N in Si ₃ N ₄ should be accelerated. It is preferable to add an element that generates vacancies.

In order to generate vacancies, a metal having a valence different from Si and substituting Si in the Si ₃ N ₄ crystal lattice (a metal that is a so-called solid substitution metal with Si) must be used. That is, it has a valence other than +4 and an ionic radius of 0.3 to 1.0.
Angstrom metals are used as reaction promoters. The preferred valence is +3. When the ionic radius is larger than 1.0 angstrom, the metal does not form a substitutional solid solution with Si but forms a so-called interstitial solid solution, and Si ₃
No vacancies are formed in N ₄ . On the other hand, the ion radius is 0.
If it is less than 3 angstroms, no vacancy is formed because there is substantially no metal ion. The preferred ionic radius is 0.64 to 0.67 angstroms.

As described above, it is considered that the Si melt and nitrogen react with each other to produce Si ₃ N _4. Therefore, the metal element serving as the nitriding reaction accelerator is a compound with silicon (silicide). The melting point of is 579 to 1450 ° C. If the melting point of the silicide is less than 579 ° C, at the temperature of the nitriding treatment, the metal evaporates from the liquid phase containing Si and the metal element serving as the nitriding reaction promoter, and the metal was added as the nitriding reaction promoter. No effect. On the other hand, when a metal having a melting point of silicide higher than 1450 ° C. is used, at the temperature of the nitriding treatment, a liquid phase in which Si and the metal of the nitriding reaction promoter coexist is not formed, and the nitriding reaction does not proceed well. . The metal silicide generally exhibits the properties of an intermetallic compound.

Fe and C are metals that satisfy the above conditions.
r, or Co.

The nitriding reaction accelerator can actually be added to the above components (a) to (c) as a metal powder, but it may be used in the form of an oxide. In either case of metal powder or metal oxide powder, the average particle size is 0.5 to 5μ.
It is preferably m.

The compounding ratio of each component is as follows. (a) Silicon powder (however, the weight of the silicon powder is a Si ₃ N ₄ conversion value. Here, the Si ₃ N ₄ conversion value is the case where all the existing Si is changed to Si ₃ N ₄ . and Si ₃ by weight of N _4.), and (b) Y ₂ O _3, and (c) Al ₂ O _3,
(d) Total 10 with nitriding reaction accelerator (metal element conversion value)
0% by weight, (a) silicon powder 82.0-98.4% by weight (Si ₃
N ₄ converted _{value), (b) Y 2 O} 3 powder 1.5 to 10.0 wt%,
(c) Al ₂ O ₃ powder is 5.0% by weight or less, and (d) nitriding reaction accelerator is 0.1 to 3.0% by weight (elemental conversion value).

If the amount of the sintering aid component (b) is less than the above lower limit value, the densification of the sintered body does not proceed, and the strength and toughness of the sintered body deteriorate. On the other hand, when the amounts of the components (b) and (c) exceed the upper limits, the high temperature strength of the obtained sintered body decreases.

Regarding the nitriding reaction accelerator (d),
If it is less than 1% by weight, the effect of adding the nitriding reaction accelerator does not appear and the nitriding reaction is not promoted. On the other hand, 3.0% by weight
If the blending amount exceeds, the high temperature strength of the obtained sintered body will decrease.

The preferred blending amount is (b) Y ₂ O ₃ powder 2.5
~ 7.5 wt%, (c) Al ₂ O ₃ powder 2 wt% or less, and
(d) Nitriding reaction accelerator is 0.3 to 1.0% by weight (elemental conversion value), and the balance (a) is silicon powder.

Next, a method for manufacturing the silicon nitride sintered body of the present invention will be described. (A) Preparation of molded body First, the above-mentioned components (a) to (d) are mixed in the above-mentioned mixing ratio to prepare a molded body. In the production of this molded body, in addition to the above-mentioned essential components, various organic binders that are usually used in the production of ceramic molded bodies can be added. Examples of such a binder include ethyl silicate, polyethylene glycol, polyvinyl alcohol (PVA) and the like.
Also, an inorganic binder can be added.

The raw materials (components (a) to (d), additives, etc.) can be mixed by a known method such as a ball mill or a disperser. When mixing with a ball mill,
It is preferable to add a dispersion medium such as water, ethanol or butanol to the mixed powder.

For the production of the molded body, conventionally known methods, for example, casting molding such as slip casting method, injection molding and the like can be adopted, but it is important to increase the density of the molded body as much as possible. It is preferable to adopt a die press or a cold isostatic press (CIP).

(B) Nitriding treatment Next, the molded body is heated in a nitrogen-containing atmosphere, preferably in a nitrogen gas atmosphere to nitride silicon in the molded body.

In the nitriding treatment, preferably, 90% or more, more preferably 95% or more, of the silicon in the compact is nitrided to form silicon nitride, and the treatment temperature, the nitrogen-containing atmosphere pressure,
Set the processing time. In the present invention, the degree of nitriding is expressed as a percentage, which is calculated from the ratio of the peak heights of the chart in X-ray diffraction.

The various conditions of the nitriding treatment need to be changed to some extent depending on the thickness of the molded body, but the treatment temperature is 1250 to 1
The temperature is 450 ° C. Also, the nitrogen-containing atmosphere pressure is 1 kg / cm ²
The above is preferable. If the temperature is lower than 1250 ° C. or the nitrogen-containing atmosphere pressure is lower than 1 kg / cm ² , nitriding of silicon in the molded body does not proceed well. On the other hand, when the heating temperature is higher than 1450 ° C, Si in the molded body may elute or Si
It is not preferable because it causes vaporization. The nitriding time varies depending on the thickness of the compact, the nitriding temperature, etc., but is generally about 1 to 10 hours. More preferably, the nitriding temperature is 1350 to 1450 ° C., and the nitrogen-containing atmosphere pressure is 5 to 2000 kg / cm ² .

When the nitriding treatment is performed under the above conditions, the silicon particles in the compact are nitrided to produce Si ₃ N ₄ containing α-Si ₃ N ₄ . When silicon particles are nitrided and silicon nitride is generated, the particles in the compact expand, and as a result, the pores existing in the structure of the compact before nitriding (the voids between the powder particles) that solidifies the powder. Is greatly reduced

(C) High-Temperature Firing In the present invention, the molded body after the nitriding treatment is further fired at 1900 ° C. or higher, preferably 1900 to 2000 ° C. When the firing temperature is lower than 1900 ° C, the strength and toughness of the sintered body decrease. Firing in a non-oxidizing atmosphere,
It is preferably performed under a nitrogen gas atmosphere. At this time, the atmospheric gas pressure is preferably about 5 to 2000 kg / cm ² . Also, firing time (time to hold at 1900 ° C or higher)
Is preferably about 1 to 5 hours.

By firing within the above temperature range, the α-Si ₃ N ₄ particles produced by the above nitriding treatment are partially melted, and the needle-shaped β-Si ₃ N ₄ crystal particles are changed into dense particles. To generate. When the acicular β-Si ₃ N ₄ crystal particles are densely formed in this manner, the strength and toughness of the sintered body are significantly improved.

[0036]

EXAMPLES The present invention will now be described in more detail with reference to specific examples, but the present invention is not limited thereto. Example 1 (a) 95.5% by weight of silicon powder having an average particle size of 20 μm (Si ₃ N
₄ conversion value) and (b) Y ₂ O ₃ (average particle size 1 μm, maximum particle size 5 μm, manufactured by Japan Yttrium Co., Ltd.) as a sintering aid.
2.5% by weight and (c) Al ₂ O ₃ (average particle size 0.8 μm, maximum particle size 5 μm, manufactured by Sumitomo Chemical Co., Ltd.) 1% by weight, and (d) component 1% by weight Co metal powder. The mixture was put into a 2 liter polyethylene pot, and 80 parts by weight of ethanol was added to 100 parts by weight of the above components, and the mixture was ball-milled for 18 hours.

The obtained mixture was dried by a rotary evaporator, and CIP (pressure of 3000 kg / cm ² ) was used to produce a molded body having a size of 30 mm × 50 mm × 5 mm.
145 in a nitrogen gas pressure of 9 kg / cm ² for this compact
Nitriding was performed by heating at 0 ° C. for 4 hours.

The X-ray diffraction of the sintered body (referred to as a calcined body) immediately after the nitriding treatment was measured to obtain the nitriding degree after the nitriding treatment. The results are shown in Table 1.

Further, the calcined body is subjected to a nitrogen gas pressure of 9 kg / cm.
Baking in ² at 1950 ° C. for 4 hours. When the nitriding degree of the thus obtained sintered body was examined in the same manner, the nitriding degree was 100%.

Example 2 A molded body was manufactured in the same manner as in Example 1 except that the Co metal powder of the component (d) was 3% by weight and the silicon powder was reduced by that amount. , Nitriding treatment was performed.
The nitriding degree of the calcined body was obtained in the same manner as in Example 1. The results are shown in Table 1. Further, it was fired in the same manner as in Example 1.
The nitriding degree of the obtained sintered body was 100%.

Example 3 Example 1 was repeated except that Cr ₂ O ₃ powder (1% by weight, oxide% by weight) was used as the component (d) in the production of the molded body.
A molded body was produced in the same manner as in 1. and was nitrided. The nitriding degree of the calcined body was obtained in the same manner as in Example 1. The results are shown in Table 1.
Shown in. Further, this calcined body was fired in the same manner as in Example 1. The nitriding degree of the obtained sintered body was 100%.

Example 4 A molded product was prepared in the same manner as in Example 1 except that Cr ₂ O ₃ powder was 3% by weight as the component (d) and the silicon powder was reduced by that amount. It was produced and nitrided. The nitriding degree of the calcined body was obtained in the same manner as in Example 1. The results are shown in Table 1. Furthermore, this calcined body was used in Example 1.
It baked like the above. The nitriding degree of the obtained sintered body is 10
It was 0%.

Comparative Example 1 A molded product was prepared in the same manner as in Example 1 except that the component (d) was not added and the amount of the component (a) was increased. It was The nitriding degree of the calcined body was obtained in the same manner as in Example 1. The results are shown in Table 1. further,
This calcined body was fired in the same manner as in Example 1. The nitriding degree of the finally obtained sintered body was 94.8%.

Comparative Example 2 A molded product was produced in the same manner as in Example 1 except that the component (d) was not added and the amount of the component (b) was increased accordingly. Then, the nitriding treatment was performed in the same manner as in Example 1 to determine the nitriding degree of the obtained calcined body. The results are shown in Table 1. Further, this calcined body was fired in the same manner as in Example 1. The nitriding degree of the obtained sintered body was 94.5%.

Table 1 Example No. Nitriding degree of calcined body ⁽¹⁾ Nitriding degree after firing ⁽²⁾ Example 1 95.3 100 Example 2 96.1 100 Example 3 97.2 100 Example 4 100 100 Comparative Example 1 93.9 94.8 Comparative Example 2 92.7 94.5 Table 1 Note: (1) and (2) are both degrees (%) calculated from the peak height of the X-ray diffraction chart.

Comparative Example 3 In the production of a molded body, 1% by weight of an oxide powder of a metal (Mn or Hf) having a valence of +4 was used as the component (d), and the same components as in Example 1 were used, A molded body was prepared and nitrided in the same manner as in Example 1 to obtain a calcined body. The nitriding degree of the calcined body was as follows.

[0047] Table 2 Note (1): Only the metal elements of the oxides used are shown.

[0048]

As described above in detail, according to the method of the present invention, a compact containing silicon powder can be reliably nitrided in a short time.

Further, in the method of the present invention, high temperature firing is carried out after the nitriding treatment, so that the obtained sintered body has a structure in which acicular β-silicon nitride particles are densely present, and has mechanical strength and toughness. Is also excellent. The silicon nitride sintered body produced by the method of the present invention can be widely used as various engineering ceramic members.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunobu Kawakami 1-4-1, Chuo, Wako-shi, Saitama Stock Research Institute Honda Technical Research Institute

Claims (3)

[Claims] 1. A silicon powder 82.0-98.4% by weight (however,
(Si ₃ N ₄ conversion value), (b) Y ₂ O ₃ powder 1.5 to 10.0% by weight, (c) Al ₂ O ₃ powder 5.0% by weight or less, and (d) having a valence different from Si and ion Nitrogen-containing compacts containing a metal powder having a radius of 0.3 to 1.0 angstrom and a melting point of the silicide of 579 to 1450 ° C, or an oxide powder of the metal of 0.1 to 3.0% by weight (element conversion value). A silicon nitride sintered body, characterized by being heated and fired in an atmosphere. 2. The silicon nitride sintered body according to claim 1, wherein the (d) metal powder or its oxide powder is Fe or C.
A silicon nitride sintered body characterized by comprising r, Co or any of these oxides. 3. (a) Silicon powder 82.0-98.4% by weight (however
(Si ₃ N ₄ conversion value), (b) Y ₂ O ₃ powder 1.5 to 10.0% by weight, (c) Al ₂ O ₃ powder 5.0% by weight or less, and (d) having a valence different from Si and ion A molded body containing a metal powder having a radius of 0.3 to 1.0 angstrom and a melting point of the silicide of 579 to 1450 ° C, or an oxide powder of the metal of 0.1 to 3.0% by weight (elemental conversion value) is prepared. A method for producing a silicon nitride sintered body, comprising: heating the molded body under a nitrogen-containing atmosphere at 1250 to 1450 ° C. for nitriding, and further firing at 1900 ° C. or higher.