JPS61201662A - Manufacture of composite ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to a method for manufacturing composite ceramics.

In particular, the present invention relates to a method for manufacturing composite ceramics suitable for manufacturing structural materials that require higher dimensional accuracy, higher strength, thermal shock resistance, and corrosion resistance than conventional reaction sintering methods.

[Background of the invention]

Generally, silicon nitride or silicon carbide is considered as an engineering ceramic suitable for structural materials such as engines and turbines. The sintering technology is the pressureless sintering method.
There are 9 pressure sintering methods and 9 reaction sintering methods. Among these, pressureless sintering method,
Pressure sintering has a firing shrinkage rate of nearly 20%, poor dimensional accuracy, and requires advanced technology.

On the other hand, the one-reaction sintering method has a smaller firing shrinkage rate than other methods, but it is difficult to increase strength and thermal shock resistance.
Although the firing shrinkage rate is small, JP-A-58-14037
As shown in Publication No. 5, it is 1 to 1.5%, and in order to reduce processing costs, it is necessary to further reduce the firing shrinkage rate and achieve high dimensional accuracy.

Therefore, it has been conceived to apply silicon nitride-bonded silicon carbide compositions, which are currently used as refractories, to materials for heat-resistant structures. An example of manufacturing a silicon nitride-bonded silicon carbide composition is disclosed in JP-A-58-88169, but it has insufficient mechanical strength and is unsuitable for use as a material for mechanical structures, and dimensional changes occur. It is also about 1 to 1.5%.

Therefore, it is important to have high strength in order to be compatible with the material for the structure, and it is also important to have high dimensional accuracy. Until now, there is no technology that can deal with this, and there is nothing practical.

[Purpose of the invention]

An object of the present invention is to provide a method for manufacturing composite ceramics that has high dimensional accuracy and increased strength so that it can be used as a structural material.

[Summary of the invention]

To summarize the present invention, the present invention relates to a method for producing composite ceramics, which has an average particle size of 5 to 100 μm and 0.
．． A process of mixing and molding two types of silicon carbide powders of large and small sizes of 3 to 1 μm, metallic silicon powder with an average particle size of 0.25 to 2 μm, and a molding aid, and melting of the metallic silicon in a nitriding gas atmosphere. It is characterized by including each step of firing at a temperature lower than the above temperature.

The present invention uses silicon carbide powders of two types, large and small, with an average particle size of 5 to 100 μm and 0.3 to 1 μm, and a silicon carbide powder with an average particle size of 0.25 to 2 μm.
This material is characterized by the fact that it is formulated with metallic silicon powder, and it not only has excellent thermal shock resistance like conventional products, but also has high strength and high dimensional accuracy so that it can be applied to structural materials. It has particularly effective characteristics.

The general conditions of the method of the present invention will be explained below.

First, as a raw material, preferably 25 to 250 parts by weight of silicon carbide with an average particle size of 5 to 100 μm, and an average particle size of 0.3 to 1
A mixture of preferably 5 to 40 parts by weight of silicon carbide with a diameter of 0.25 to 2 μm and 100 parts by weight of metal silicon with an average particle size of 0.25 to 2 μm is used, and an organic polymer compound such as polyvinyl butyral or polyethylene, or a thermoplastic resin is used. and auxiliary agents such as binders, stabilizers, and lubricants, preferably from 2 to
A mixed portion of 15 parts by weight is formed into a molded product using a mechanical press, an injection molding machine, or the like. There is no particular restriction on the size of the molded body, and commercially available silicon carbide and metal silicon can be used as they are. Alternatively, rounded particles pulverized by a mill or the like may be used.
Heat to a temperature at which the auxiliary agent decomposes and evaporates. Further, it is preferable that the relative density of the molded body is 60% or more.

The molded body is heated in a nitriding gas atmosphere containing nitrogen and/or ammonia and hydrogen, if necessary, at a temperature lower than the melting point of metal silicon to form a sintered body. When heated to a temperature above the melting point of metallic silicon.

This is because metal silicon melts and seeps out onto one surface.

In the present invention, the average particle size of silicon carbide powder is 5 to 100.
The reason why the particle size is set to 0.3 to 1 μm is that within this particle size range, the silicon carbide powder is well dispersed and the relative density of the molded body is improved.

Further, if the particle size is larger than 100 μm, the strength will not be improved. Further, if only fine particles smaller than 5 μm are used, the thermal shock resistance will not be improved. Furthermore, if coarse particles larger than 100 μm are present, it is difficult to mix with the molding aid, and the molding aid and the coarse powder will separate during injection molding, making molding difficult.

In the present invention, the particle size ratio of silicon carbide and metal silicon, which has a larger average particle size, is silicon carbide: metal silicon = 5 to 20.
:1 is preferable, because within this particle size ratio, silicon carbide powder and metal silicon powder are well dispersed, so the relative density of the compact is improved, and the dimensional change due to sintering is reduced to ±0. This is because higher dimensional accuracy than the conventional reaction sintering method, which is within .3%, can be achieved.

In the present invention, as mentioned above, the average particle size is 5 to 100 μm.
m silicon carbide 25-50 parts by weight, average particle size 0.3-1
μm silicon carbide 5-40 parts by weight, average particle size 0.25-
The reason why a mixture of 100 parts by weight of 2 μm metal silicon is preferable is that it improves the relative density of the compact, and it also provides higher dimensional accuracy than the conventional reaction sintering method, which keeps the dimensional change due to sintering within ±0.3%. This is because high strength can be obtained.

According to the present invention, the sintered body of this composition has thermal shock resistance,
It has heat resistance, corrosion resistance, and high strength without dimensional changes due to sintering, so it can be used in structural materials with complex shapes, etc.

[Embodiments of the invention]

Hereinafter, the present invention will be explained more specifically using examples,
The invention is not limited to these examples.

Note that Figures 1 and 2 show the four samples tested using the product of the present invention.
A front view (Fig. 1) and a plan view (Fig.
(Fig. 2), the unit of each numerical value is 1111.

Example 1 60 g of metallic silicon powder with an average particle size of 2 μm and an average particle size of 16
100 cc of a 15% solution of polyvinyl butyral as a molding aid was added to a mixed powder of 30 g of silicon carbide of μm and silicon carbide Log of an average particle size of 0.7 μm, and
The mixture was mixed for 2 hours and then dried at room temperature to provide a test material. This raw material is molded using a mechanical press at a pressure of 250 k.
g-f/Cm” diameter 100mm, thickness 30Il111
I molded it. This was heated at 1100°C for 10 hours in a nitrogen gas atmosphere of 5 kg/am''.

20 hours at 1200℃, 15 hours at 1300℃, 1
After being held at 350°C for 5 hours, it was cooled in a furnace. Here, each temperature increase rate is 10° C./min. The relative density of the sintered body after firing is 85%
, the dimensional change rate was 0.3%. The test results of this sintered body are shown in Table 1. Here, the thermal shock resistance was determined by holding the sintered body at 1200° C. for 30 minutes in nitrogen gas and quenching it in water. The number of repetitions until a crack is found is shown.

Example 2 Table 2 shows the results of sintering in the same manner as in Example 1 by changing the particle size and composition of metallic silicon powder and silicon carbide powder.

As is clear from this, the product of the present invention has excellent thermal shock resistance, heat resistance, and corrosion resistance, as well as high dimensional accuracy.

It can be seen that it has high strength.

Example 3 A molding aid was added to a mixed powder of 80.1 g of silicon metal powder with an average particle size of 0.9 μm, 39.15 g of silicon carbide with an average particle size of 16 μm, and 13.05 g of silicon carbide with an average particle size of 0.5 μm. A raw material was prepared by mixing 3.5 g of polyethylene, 7.1 g of polyethylene wax, 3.5 g of natural wax, and 2.4 g of stearic acid. Using this raw material, an injection molding machine was used to fabricate a four-blade molded article as shown in FIGS. 1 and 2. This was heated to 410°C in nitrogen gas to decompose and volatilize the forming aid, and then heated at 1100°C in a nitrogen gas atmosphere of 5 kg/cI112 for 10 hours.

20 hours at 1200℃, 20 hours at 1300℃, 1
After being held at 350°C for 5 hours, it was cooled in a furnace. Here, each temperature increase rate is 10° C./min. The relative density of the sintered body after firing is 86%
The rate of change in one dimension was 0.27%. In addition, there was no deformation or cracking, and the dimensional accuracy was good.

As is clear from this, the product of the present invention can easily obtain structural materials with complex shapes with good dimensional accuracy without deformation or cracking, and has excellent strength, thermal shock resistance, heat resistance, and corrosion resistance. I understand.

〔Effect of the invention〕

According to the present invention, thermal shock resistance, heat resistance, and corrosion resistance.

In addition to high strength, it is possible to easily obtain a nitrogen-silicon bonded silicon carbide sintered body that has a dimensional change of ±0.3% due to sintering, which is higher dimensional accuracy than that of the conventional reaction sintering method.
This has the remarkable effect of significantly reducing processing costs and expanding the range of applications not only for refractory parts but also for structural materials with complex shapes such as engines and turbines.

[Brief explanation of drawings]

Claims (1)

[Claims] 1. Average particle size of 5 to 100 μm and 0.3 to 1 μm 2.
A step of mixing and molding different types of silicon carbide powder, metallic silicon powder with an average particle size of 0.25 to 2 μm, and a forming aid, and firing the compact at a temperature below the melting temperature of metallic silicon in a nitriding gas atmosphere. A method for producing composite ceramics characterized by including each step of the process. 2. The particle size ratio of silicon carbide with a larger average particle size and the metal silicon is silicon carbide: metal silicon: 5 to 20:1
A method for producing composite ceramics according to claim 1. 3. 25 to 2 silicon carbide with an average particle size of 5 to 100 μm
Claim 1: 50 parts by weight, 5 to 40 parts by weight of silicon carbide having an average particle size of 0.3 to 1 μm, 100 parts by weight of the metallic silicon, and 2 to 15 parts by weight of the molding aid. Method of manufacturing the described composite ceramics. 4. The method for producing composite ceramics according to claim 1, wherein the dimensional change of the molded body upon firing is within ±0.3%.