JPH07277835A - Method for manufacturing composite sintered body - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for producing a composite sintered body having high hardness. [Constitution] α-type silicon nitride powder, yttria powder,
By mixing aluminum nitride powder and silicon carbide powder having an oxygen content of 0.8 to 5% by weight and sintering the mixture, α-sialon, β-sialon, and silicon carbide are main components. A composite sintered body is manufactured.

Description

Detailed Description of the Invention

[0001]

The present invention relates to α-sialon and β-sialon.
The present invention relates to a method for producing a composite sintered body containing sialon and silicon carbide as main components.

[0002]

2. Description of the Related Art A sintered body made of sialon in which yttrium or aluminum is substituted in silicon nitride has a high hardness, and particularly, a sintered body containing both α-sialon and β-sialon having different crystal forms is It has extremely high hardness and is used as a wear resistant material for ball mills and balls. Sliding wear of ceramic materials is governed by hardness, toughness, strength, grain size, etc.
In particular, it is largely controlled by hardness.

However, since the hardness of α-type silicon nitride and silicon carbide is higher than the hardness of the sintered body containing both α-sialon and β-sialon, both α-sialon and β-sialon are present. When the powder of α-type silicon nitride or silicon carbide is pulverized by a ball mill or balls made of a sintered body contained therein, the ball mill or the balls, especially the balls are often abraded and mixed in the powder as impurities.

As described above, as a method for further improving the hardness of a sintered body containing both α-sialon and β-sialon, it has been proposed to add silicon carbide to the sintered body.

As an example, there is the following method.

An α-sialon containing yttrium (Y) is produced by nitriding a raw material composed of amorphous silicon nitride, yttria and aluminum. This α
-By adding silicon nitride and silicon carbide to sialon and sintering, α-sialon and β-sialon,
And a sintered body made of silicon carbide is obtained (Japanese Patent Application Laid-Open No. HEI-1)
No. 179766).

Further, as a similar method, there is the following method.

Using α-type silicon nitride, silicon carbide, oxides of Group 3a elements of the periodic table such as yttria and silicon oxide as raw materials, the raw materials are sintered by hot pressing or HIP (hot isostatic pressing). There is a method (JP-A-5-2017)
No. 68).

[0009]

However, the above-mentioned Japanese Unexamined Patent Application Publication No.
The method described in JP-A-179766 has the following problems.

It is necessary to use amorphous silicon nitride as a raw material, but this amorphous silicon nitride is difficult to manufacture and is not a general material. In addition, from this amorphous silicon nitride
-Since it is necessary to manufacture sialon, the number of processes is three (amorphous silicon nitride manufacturing process, α-sialon manufacturing process, and mixing and sintering processes), which is very complicated in the industry.

Further, the method described in Japanese Patent Laid-Open No. 5-201768 has the following problems.

The crystal phase of the obtained sintered body is composed of β-type silicon nitride and silicon carbide. The hardness of silicon carbide is about 28
High as GPa, but hardness of β-type silicon nitride is about 15 GPa
And α-sialon (hardness 24 GPa) and β-
Since it is lower than Sialon (hardness 18 GPa), the sintered body made of β-type silicon nitride and silicon carbide is not hard enough for practical use. Further, the sintering must be performed by a hot press or HIP, which requires complicated equipment and work.

The present invention has been made in view of the problems of the prior art, and an object thereof is to provide a method for producing a composite sintered body having a high hardness.

[0014]

According to the present invention, a step of mixing silicon carbide powder, α-type silicon nitride powder, yttria powder, and aluminum nitride powder, and sintering the mixture to obtain α- In a method for producing a composite sintered body, which comprises a step of obtaining a composite sintered body containing sialon, β-sialon, and silicon carbide as main components, the silicon carbide powder contains 0.8 to 5% by weight of oxygen. Is a method for manufacturing a composite sintered body.

[0015]

In the present invention, a composite sintered body having a high hardness can be obtained. The reason for this is not clear, but it is assumed as follows.

A dense sintered body is obtained by adding yttria, aluminum nitride and silicon carbide to α-type silicon nitride and sintering. Further, aluminum nitride and oxygen are solid-dissolved in α-type silicon nitride, and α-sialon is precipitated by the reaction with yttria, and β-sialon is formed by solid-solution of aluminum nitride and oxygen in α-type silicon nitride. Is deposited. Moreover, silicon carbide is precipitated as it is as a crystal phase. Therefore, a sintered body is obtained in which the respective crystal phases of α-sialon, β-sialon and silicon carbide are deposited.

At this time, the α-type silicon nitride and oxygen in the silicon carbide powder (this oxygen is considered to be present as silicon oxide on the surface of the silicon carbide powder) reacts with yttria to form glass and is burned. Promotes connectivity. In particular, oxygen in the silicon carbide powder promotes the reactivity with the surface of the silicon nitride particles and greatly contributes to the sinterability.

In the present invention, the amount of oxygen contained in the silicon carbide powder is in the range of 0.8 to 5% by weight. If the amount of oxygen is less than 0.8% by weight, the sinterability is poor and dense sintering cannot be performed, and if it exceeds 5% by weight, the production of α-sialon is suppressed and the hardness of the sintered body decreases. To do.

As described above, in the present invention, a dense sintered body can be obtained by producing a composite sintered body by improving the sinterability, and particularly, α-sialon and silicon carbide have extremely high hardness. Since it has a high crystal phase, the sintered body has a high hardness.

Further, according to the present invention, a sintered body can be manufactured by a simple process.

[0021]

According to the present invention, a composite sintered body having a high hardness can be manufactured.

[0022]

EXAMPLES The inventions (other inventions) that make the present invention more specific will be described below.

(Explanation of Other Inventions) In the present invention, powders of silicon carbide powder, α-type silicon nitride powder, yttria powder, and aluminum nitride powder are used as raw materials, which are mixed and sintered. Is the way to do it.

The amount of oxygen contained in the silicon carbide (SiC) powder is in the range of 0.8 to 5% by weight. Further, it is desirable that the amount of oxygen be in the range of 1 to 3% by weight. Within this range, the hardness is further improved.

The amount of oxygen in the silicon carbide powder is measured by the melting in inert gas-thermal conductivity method.

The particles of silicon carbide powder have an average particle size of 0.8 μm or less, preferably 0.5 μm or less.
This is because finer particles are easier to sinter. Further, there is no difference in sinterability or hardness whether the crystal phase is α or β.

The silicon nitride (Si ₃ N ₄ ) is of α type. Note that β-type silicon nitride may also be included. Therefore, the content of the α phase contained in the silicon nitride powder is 70% or more, more preferably 90% or more. β
This is because if there are many phases, the production of α-sialon is inhibited.

The particles of silicon nitride powder have an average particle diameter of 0.
It is 8 μm or less, preferably 0.5 μm or less. This is because finer particles are easier to sinter.

The yttria (Y ₂ O ₃ ) powder particles have an average particle size of 1.0 μm or less, preferably 0.5 μm or less. This is because finer particles are easier to sinter.

The particles of aluminum nitride (AlN) powder have an average particle size of 1.0 μm or less, preferably 0.5 μm.
The following is good. This is because finer particles are easier to sinter.

Regarding the compounding ratio of the raw materials, the abundance of α-sialon in the manufactured composite sintered body is 20 to 40% by weight based on the whole sintered body, and the abundance of β-sialon in the entire sintered body is. It is desirable to mix α-type silicon nitride, yttria, and aluminum nitride so as to be 40 to 60% by weight. By setting the amount of β-sialon to be 40 wt% or more, the toughness of the sintered body is further improved, and 60 wt%
By the following, the hardness of the sintered body is further improved and the wear resistance is further improved. In order to set the abundance of α-sialon and β-sialon in the range, for example, when the ratio of yttria to aluminum nitride is yttria: aluminum nitride = 1: 9 (molar ratio), α-type silicon nitride and yttria are added. If the total amount of aluminum nitride is 100 parts by weight, the total amount of yttria and aluminum nitride is 10 parts.
-18 parts by weight is desirable, and 15 parts by weight is most suitable.

The blending ratio of silicon carbide in the raw material is
It is preferable to set it in the range of 10 to 30% by weight with respect to the entire raw material. When it is 10% by weight or more, the hardness of the sintered body is further improved, and when it is 30% by weight or less, the sintered body is densely sintered to further improve the wear resistance of the sintered body.

In addition, the total amount of α-sialon and silicon carbide in the composite sintered body produced is 40 to 6 in total.
It is preferable that the range is 0% by weight. This total is 40% by weight
By the above, the hardness of the sintered body is further improved, and 60
When the content is less than or equal to wt%, the toughness is further improved and the wear resistance of the sintered body is further improved.

The raw material powders may be mixed by a commonly used mixing method using a ball mill or the like.

The mixture obtained by mixing the raw material powders may be shaped into a desired shape before sintering.

As a method for sintering the above mixture, normal pressure sintering, gas pressure sintering, hot pressing, or other conventional method for sintering silicon nitride can be used. Gas pressure sintering of 0.95 MPa or less is industrially desirable.

In the case of normal pressure sintering or gas pressure sintering, the sintering temperature is preferably in the range of 1700 to 1900 ° C, and more preferably 1750 to 1850 ° C. By setting the temperature to 1700 ° C. or higher, a dense sintered body can be obtained. By setting the temperature to 1900 ° C. or less, silicon nitride is less likely to be decomposed, and generation of pores in the sintered body can be suppressed.

The sintering time is about 2 to 6 hours, preferably 3 to 4 hours. By setting the time to 2 hours or more, the sinterability is further improved and the sintered body can be made dense. By setting the time to 6 hours or less, it is possible to suppress the grain growth of the crystal of the sintered body and suppress the strength reduction of the sintered body.

The sintering atmosphere is preferably in the range of 0.1 to 0.9 MPa under nitrogen gas pressure. 0.1 MPa
By the above, silicon nitride is hard to decompose, and generation of pores in the sintered body can be suppressed. By setting the gas pressure to 0.9 MPa or less, an increase in the amount of gas is suppressed, and it is not necessary to use an expensive device such as a type 1 pressure vessel.

The composite sintered body obtained according to the present invention has the same toughness, strength and crystal grain size as the conventional composite sintered body, but has high hardness and 2-3 times higher wear resistance. Improve. Therefore, it can be used as a wear resistant member such as a ball mill and its balls. For example, when it is used for a ball mill or its balls, it is possible to reduce the mixing of impurities into the powder due to abrasion.

Examples of the present invention will be described below.

Example 1 As raw material powder, 76.5% by weight of silicon nitride powder having an average particle size of 0.4 μm and α phase of 95%, and 5.0% by weight of yttria powder having an average particle size of 0.6 μm, Aluminum nitride powder having an average particle size of 0.5 μm 8.
To 5% by weight, 10% by weight of silicon carbide powder having an average particle size of 0.4 μm and various oxygen contents were added, and mixed in a ball mill for 72 hours in ethanol. The obtained slurry was dried, crushed, and then press-molded at a pressure of 200 MPa. The obtained molded body is 1 at 0.9 MPa in a nitrogen atmosphere.
Sintered at 800 ° C. for 4 hours. The relative density, the amount of α-sialon, and the hardness of the obtained sintered body were measured and shown in Table 1 (* in Table 1 indicates a sample in which the amount of oxygen in the silicon carbide powder is outside the range of the present invention. (Comparative example).

[0043]

[Table 1]

As shown in Table 1, the oxygen content is 0.8 to
The sintered body to which 5.0% by weight (wt%) of silicon carbide powder was added was a dense sintered body having a relative density of 96% or more and had high hardness. However, a sintered body to which a silicon carbide powder having an oxygen content of less than 0.8 wt% is not densely sintered and has low hardness, and a sintered body having an oxygen content of more than 5.0 wt% is α-sialon. The amount produced was small and the hardness was low.

Example 2 The same silicon nitride powder, yttria powder and aluminum nitride powder as in Example 1 were used,
Sintered bodies were produced under the same conditions as in Example 1, with the compounding amounts thereof being constant, various kinds of silicon carbide powder having an average particle size of 0.4 μm and an oxygen content of 1.2 wt% being added. The relative density, crystal phase, and hardness of the obtained sintered body were measured and shown in Table 2 (* in Table 2 is a sample without silicon carbide added (comparative example)).

[0046]

[Table 2]

As shown in Table 2, the sintered body to which silicon carbide was added became a dense sintered body and had high hardness. But,
The sintered body containing no silicon carbide had low hardness because there was no high-hardness silicon carbide.

(Example 3) The same powder as in Example 2 was used, and the addition amount of silicon nitride, yttria, and aluminum nitride was changed to 20% by weight of silicon carbide powder as shown in Table 3 to obtain Example 1. A sintered body was produced under the same conditions. The relative density, crystal phase, hardness and toughness of the obtained sintered body were measured,
The results are shown in Table 3.

[0049]

[Table 3]

As shown in Table 3, by adjusting the amounts of silicon nitride, yttria, and aluminum aluminum nitrogen added to the silicon carbide, the amount of α-sialon produced was adjusted to Sample No. It can be seen that the toughness is increased by setting the value to 10 or 12.

Example 4 Sample No. With the same blending amount as in 10, the average particle size of each powder was changed as shown in Table 4, and a sintered body was produced under the same conditions as in Example 1. The relative density, crystal phase, hardness and toughness of the obtained sintered body were measured,
The results are shown in Table 4.

[0052]

[Table 4]

As shown in Table 4, the finer the particle size of the powder, the denser the sintering and the higher the hardness, which is preferable.
In particular, it can be seen that the particle sizes of the silicon nitride powder and the silicon carbide powder have a great influence on the sinterability.

Example 5 Sample No. With the same blending amount and molding method as in 10, the sintering conditions were changed as shown in Table 5,
A sintered body was produced. The relative density, crystal phase, hardness and toughness of the obtained sintered body were measured and shown in Table 5.

[0055]

[Table 5]

As shown in Table 5, the sintering temperature is 1800 ° C.
Is optimum, the density is higher than that at the low sintering temperature, and the amount of α-sialon is increased and the hardness is higher than that at the high sintering temperature. Also, the sintering time and the sintering pressure were the same, and the optimum values were 4 hours and 0.9 MPa.

Claims (1)

[Claims] 1. A step of mixing silicon carbide powder, α-type silicon nitride powder, yttria powder, and aluminum nitride powder, and sintering the mixture to obtain α-sialon and β-sialon.
In the method for producing a composite sintered body, which comprises the step of obtaining a composite sintered body containing sialon and silicon carbide as main components, the silicon carbide powder contains 0.8 to 5% by weight of oxygen. And a method for producing a composite sintered body.