JPH0816029B2 - Method for manufacturing high-strength ceramic compact sintered body - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for manufacturing a ceramic molded sintered body, and more particularly, by improving the mechanical properties of the product, a gas turbine,
In fields such as transportation machinery such as diesel engines and Stirling engines, energy machinery such as superchargers and heat exchangers, and general industrial machinery such as industrial furnaces and hydraulic pressure equipment, rotating components, sliding components, heat-resistant components The present invention relates to a method for producing a high-strength ceramics sintered compact used as a corrosion-resistant component, a wear-resistant component, or the like.

[Prior Art] In recent years, ceramics such as silicon nitride and silicon carbide have attracted attention because they have high strength at high temperatures.

However, such high strength ceramics were difficult to sinter.

Therefore, the conventional method for producing a high-strength ceramic sintered body is to mix other ceramic powder particles such as aluminum oxide or beryllium oxide as a sintering accelerator with the powder of the ceramic raw material such as silicon nitride or silicon carbide. It was done.

Further, particularly in the case of forming a product having a complicated precise shape, a method of mixing the powder of the ceramic raw material with a melt of an organic substance such as wax or resin and the sintering accelerator and performing injection molding has been adopted. . In this case, after molding the ceramics, it is heated to remove the organic substance as a molding aid,
After that, sintering was performed to densify the ceramic compact.

[Problems to be Solved by the Invention] By the way, the following problems have been encountered in the method for producing a high-strength ceramics sintered compact of this kind.

Since the addition of the above-mentioned sintering promoter to the ceramic raw material such as the above silicon nitride or silicon carbide is made by mixing the powder of the ceramic raw material with the powder particles of other ceramics, uniform mixing is difficult. However, in order to fully exert its sintering promoting effect, it is necessary to add a large amount of several% to several tens% or more. Therefore, in the ceramic molded sintered body manufactured in this way, the material becomes inhomogeneous, and there is a problem that reliability or mechanical properties are low.

Further, in the above injection molding method, it is important to improve the fluidity of the raw material at the time of molding, but in order to improve this fluidity, it is necessary to mix the organic substance in the volume ratio of about 50%. did. Therefore, it becomes difficult to remove the above organic substances without causing defects such as distortion and cracks in the ceramic molded body, the packing density of the ceramic molded body is low, and finally the mechanical properties of the ceramic molded sintered body are also reduced. There was a problem of becoming low.

In view of the above problems, the present invention can reduce the mixing amount of organic substances as a sintering accelerator or a molding aid to a ceramic raw material such as silicon nitride or silicon carbide, and obtain a high quality molded sintered body. An object of the present invention is to provide a method for producing a high-strength ceramics sintered compact that can be manufactured.

[Means for Solving Problems] In order to solve the problems in the prior art, the present invention is to knead a liquid mixture of a fatty acid metal salt and an organic compound compatible with the ceramic raw material, and mix this with a predetermined amount. After being shaped into a shape, the fatty acid metal salt and the organic substance are thermally decomposed by heating, and after that, the ceramic compact is sintered and densified.

The ceramic raw material contains silicon nitride powder, silicon carbide powder, silicon powder or a mixture thereof as a main component.
Use the one containing more than volume%. Other components having a volume of 40% or less may contain a strengthening agent such as zirconium oxide particles for dispersion strengthening or silicon carbide whiskers in order to improve mechanical properties and corrosion resistance.

The fatty acids forming the fatty acid metal salt are stearic acid, oleic acid, lauric acid, caprophosphoric acid, and the like, and the metals are IIa group, III group, and IV group in the periodic table,
V group and VI group.

Further, as the above-mentioned organic substance, for example, oil, wax, hydrocarbon-based polymer, oxygen-containing hydrocarbon-based polymer or a mixture thereof which is compatible with the fatty acid metal salt is used. Compatibility with the fatty acid metal salt may be obtained by heating the organic substance to a temperature of 250 ° C. or lower.

Furthermore, the amount of the fatty acid metal salt added to the ceramic raw material is 0.2 to 5% by weight in terms of metal in the fatty acid salt.
The mixing amount of the liquid mixture of the fatty acid metal salt with respect to the ceramic raw material and the organic material compatible with this is 30 to 60.
Volume%

Then, the molding of these mixtures is carried out by filling the mixture in a mold at a high pressure and producing an intricate precision shape by injection molding, or by extruding the mixture from a die to produce a long product having a complex precision cross section. By law.

Heating of the ceramic molded body molded by the injection molding method or the extrusion molding method is performed in an oxidizing atmosphere or a non-oxidizing atmosphere to thermally decompose the fatty acid metal salt to change it into an oxide and to heat the organic substance. Disassemble or remove.
This organic matter may remain as carbon.

Finally, a ceramic molded body obtained by thermally decomposing a fatty acid metal salt and an organic substance is adjusted to have an atmosphere under normal pressure, or is pressed to sinter and densify the ceramic to obtain high strength, high density and high homogeneity. A molded sintered body is obtained. When silicon powder is included as the ceramic raw material, a nitrogen atmosphere produces silicon nitride, and an inert atmosphere produces silicon carbide.

[Operation] The powder of the above ceramic raw material, which is made as described above,
By sufficiently kneading and dispersing in a liquid mixture of a fatty acid metal salt and an organic material compatible with the fatty acid metal, the organic material imparts fluidity to the ceramic raw material powder, and when the kneaded material is molded into a predetermined shape. Improves moldability. Further, the fatty acid metal salt itself becomes compatible and becomes a part of the liquid, acts to give fluidity to the ceramic raw material powder, and is uniformly mixed with the ceramic raw material powder. Furthermore, since this fatty acid metal salt improves the wettability between the grain surface of the ceramic raw material powder and the organic liquid, it further improves the dispersibility of the ceramic raw material in the kneaded product.

Further, since the above-mentioned kneaded product is in a liquid state, it can be favorably molded by an injection molding method, an extrusion molding method or the like. This molded body is heated in an oxidizing atmosphere or a non-oxidizing atmosphere, and the above-mentioned fatty acid metal salt undergoes thermal decomposition to become a metal oxide or the like. This metal oxide acts as a sintering accelerator for a ceramic raw material such as silicon nitride or silicon carbide when the shaped body is sintered.

The ceramic raw material containing silicon nitride powder or silicon carbide powder as a main component is densified by the above-mentioned sintering and exhibits excellent mechanical properties. When silicon powder is used as a ceramic raw material, silicon nitride is produced by sintering in a nitrogen atmosphere, and silicon carbide is produced by coexistence with carbon if sintered in an inert atmosphere.

Here, the addition amount of the fatty acid metal salt to the ceramic raw material is set to 0.2 to 5% by weight in terms of the metal in the fatty acid salt, if the amount is less than 0.2% by weight, the above-mentioned sintering promoting effect is hardly exhibited, and 5% by weight is added. This is because the characteristics as a sintered body deteriorate if the content exceeds the limit. Further, the mixing amount of the liquid mixture of the fatty acid metal salt and the organic material compatible with the ceramic raw material is set to 30 to 60% by volume because the fluidity of the kneaded product is insufficient when the volume is less than 30% by volume. Not suitable, on the other hand,
This is because if it exceeds 60% by volume, the molded product is likely to be distorted or cracked.

It should be noted that, as the above-mentioned organic substance, it is necessary that the organic substance has compatibility with which a required amount of a fatty acid metal salt can be dissolved,
This compatibility may be obtained by heating to a temperature of 250 ° C. or lower at which the thermal decomposition becomes remarkable. For example, oil, wax or low molecular weight polyethylene, polypropylene,
It is selected from polyethylene glycol, polystyrene, polyethylene vinyl acetate, etc., and if necessary, phthalic acid-based organic matter as a plasticizer, stearic acid for improving the wettability with the ceramic raw material powder, a coupling agent, etc. are added. Also obtains the above-described operation.

[Example] An example of a method for producing a high-strength ceramics sintered body of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is an explanatory view showing a manufacturing process in the method of the present invention. According to this manufacturing process, in the first embodiment, the ceramic raw material 1 has an average particle diameter of 0.8 μm and 1% by weight.
With respect to 100 parts by weight of silicon carbide powder containing free carbon of
Aluminum monostearate 10 as fatty acid metal salt 2
Parts by weight (about 1% by weight based on the above-mentioned silicon carbide in terms of metallic aluminum) and 7 parts by weight of wax as an organic substance 3 having compatibility therewith, and kneading at 180 ° C.,
Disperse. At this time, the aluminum monostearate and the wax are mixed in advance in a liquid form 4 and kneaded 5 with silicon carbide. In this way about 65
A heat-kneaded product containing volume% is obtained. Then, this heat-kneaded product is molded 6 into a predetermined shape such as a pipe shape by an extrusion molding method. Next, this ceramic compact is heated 7 to 800 ° C. in an argon gas stream. By this heating, the aluminum stearate and the wax in the ceramic molded body are thermally decomposed. After that, the ceramic molded body was placed in an argon gas atmosphere at 1 atm for 21
Sinter 8 at 50 ° C. to densify.

The situation from the molding 6 to the sintering 8 of the above-mentioned ceramic molded body shows changes as shown in FIG.

As a result, it was possible to obtain a homogeneous silicon carbide compact sintered body having a density of 97% or more of the theoretical density. And, as a result of measuring the bending strength by the test piece cut out from the silicon carbide molded sintered body thus obtained, 50 kg
It showed a high strength of f / mm ² or more.

Next, in the second embodiment, a powder 1 of a ceramic raw material 1 in which a silicon nitride powder having an average particle diameter of 0.5 μm and a zirconium oxide powder having an average particle diameter of 0.3 μm are mixed at a weight ratio of 60:40
To 100 parts by weight, 3 parts by weight of aluminum monostearate and 3 parts by weight of aluminum laurate were added as the fatty acid metal salt 2, and 12 parts by weight of wax as the organic substance 3 compatible with these, ethylene vinyl acetate resin ( 2 parts by weight of an average molecular weight of 3000) and 1 part by weight of fish oil are added and sufficiently kneaded and dispersed at 170 ° C. At this time, the above-mentioned aluminum monostearate and aluminum laurate, wax, ethylene vinyl acetate resin and fish oil are mixed in advance into a liquid 4, and kneaded 5 with the above silicon nitride and zirconium oxide. This heat-kneaded product is molded 6 into a predetermined shape such as a small rotating disk shape by an injection molding method. Next, this ceramic molded body is placed in an air stream.
Heat to 500 ° C 7. By this heating, the aluminum monostearate and aluminum laurate in the ceramic molded body are changed to aluminum oxide, and the wax, ethylene vinyl acetate resin, etc. are oxidized and removed. After that, this ceramic compact is embedded in boron nitride powder and pressure-sintered at 1700 ° C. and 500 kgf / cm ² to densify it. The zirconium oxide acts as a strengthening agent, and the aluminum oxide acts as a sintering accelerator.

As a result, it was possible to obtain a homogeneous silicon nitride-based sintered compact disc having a density substantially equal to the theoretical density. Then, the test piece cut out from the silicon nitride compact sintered body thus obtained had a 4-point bending strength of 80 kgf / mm ² and a fracture toughness of 7 MPa · m.
It was confirmed that such high characteristics can be obtained.

Next, in the third embodiment, the average particle size is 1.2 μm.
5 parts by weight of aluminum stearate and 5 parts by weight of magnesium stearate as the fatty acid metal salt 2 are mixed with 100 parts by weight of a ceramic raw material 1 in which 30% by weight of silicon carbide whiskers having an average diameter of 1 μm and a length of 50 μm are mixed with the above silicon powder. Organic substances that are compatible with these when added 3
As wax, 3 parts by weight of wax and 5 parts by weight of polyethylene glycol (average molecular weight 5000) are added, and the mixture is sufficiently kneaded at 160 ° C. to disperse.

At this time, the aluminum stearate and magnesium stearate, the wax and the polyethylene glycol are mixed in a liquid form 4 in advance, and kneaded 5 with the silicon and silicon carbide whiskers. This heat-kneaded product is molded 6 by injection molding into a predetermined shape such as a stationary blade shape of a small gas turbine. Next, this molded body is heated to 600 ° C. in the atmosphere. By this heating, the aluminum stearate and magnesium stearate in the ceramic molded body are changed to aluminum oxide and magnesium oxide, respectively, and the wax and polyethylene glycol are oxidized and removed. Then, the compact is heated to 1250 ° C. in a nitrogen stream to carry out nitriding reaction sintering of silicon to obtain a silicon nitride ceramic compact. After that, after forming a capsule containing silica / glass on this ceramic molded body, in a hot isostatic press
Pressure sinter 8 at 1700 ° C. and 2000 atm to densify.

As a result, a high-strength silicon nitride ceramics compact sintered body reinforced by the above-mentioned silicon carbide whiskers could be obtained.

[Effects of the Invention] In summary, according to the present invention, the following excellent effects are exhibited.

(1) Since the ceramic raw material powder is kneaded and molded with a liquid mixture of a fatty acid metal salt and an organic material compatible with the metal raw material, the organic material gives fluidity to the ceramic raw material powder, and the fatty acid itself is also an organic material. The fatty acid metal salt improves the wettability between the surface of the ceramic raw material powder and the above-mentioned organic liquid, so that the ceramic raw material is sufficiently mixed in the kneaded product. And can be homogenized to improve moldability.

(2) As described above, the fatty acid metal salt and the organic compound compatible with the fatty acid salt mutually enhance the fluidity and dispersibility of the ceramic raw material, so that the addition amount thereof can be relatively small.

(3) By heating, the fatty acid metal salt and the organic substance in the ceramic molded body are thermally decomposed to change the fatty acid metal salt to a metal oxide, and the organic substance is oxidized to be removed or carbonized. It is possible to prevent defects such as distortion and cracks from occurring in the ceramic molded body during the thermal decomposition.

(4) Since the fatty acid metal salt that acts as a so-called forming aid changes to a metal oxide by heating, this acts as a sintering accelerator during the sintering of the ceramic formed body, and due to its fluidity as described above. Since it is extremely homogeneously dispersed in the ceramic compact, it is possible to effectively exhibit the sintering promoting effect by adding a small amount.

(5) Good sintering is performed, and the ceramic molded sintered body is densified and becomes homogeneous and high density, and excellent characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a manufacturing process of a method for manufacturing a high-strength ceramics sintered body according to the present invention, and FIG. It is explanatory drawing which shows the condition until a conclusion. In the figure, 1 is a ceramic raw material, 2 is a fatty acid metal salt, 3 is an organic substance, 4 is liquid, 5 is kneading, 6 is molding, 7 is heating, 8
Is sintering.

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Claims (1)

[Claims] 1. A ceramic raw material containing 60% or more of a powder selected from silicon nitride, silicon carbide and silicon is kneaded with a liquid mixture of a fatty acid metal salt and an organic substance compatible therewith, and the mixture is predetermined. After being molded into the shape described above, the fatty acid metal salt and the organic substance are pyrolyzed by heating, and after that, the ceramic molded body is sintered and densified to obtain a high-strength ceramic sintered body. Manufacturing method.