JPH01282154A - Production of fiber-reinforced silicon oxynitride sintered compact - Google Patents

Abstract

PURPOSE:To obtain the title fiber-reinforced silicon oxynitride sintered compact having high toughness by compacting the raw material powder contg. SiC whiskers or beta-Si3N4 whiskers, a specified amt. of a sintering assistant, and the balance silicon component consisting of Si and SiO2, nitriding, and sintering the compact. CONSTITUTION:The raw powder consists essentially of 5-40wt.% of the SiC and/or beta-Si3N4 whiskers contg. SiC whiskers in total, 0.5-30wt.% of one or >=2 kinds of oxides selected from Al, Sc, Y, and rare-earth elements in total, and the balance silicon component consisting of Si and SiO2. The content of the SiC whiskers and/or beta-Si3N4 whiskers is controlled to >=5wt.%. The powder is treated in the following stages a-d to obtain a sintered compact. Namely, (a) the raw powder is compacted, (b) the compact is nitrided at 1300-1500 deg.C in a nitrogen atmosphere, (c) the nitrided compact is calcined in a nonoxidizing atmosphere at 1550-1900 deg.C and 1-10atm, and (d) the calcined product is sintered and densified in a nonoxidizing atmosphere at 1600-2000 deg.C and 30-2000 atm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for manufacturing fiber-reinforced ceramics based on silicon oxynitride (S i21'ho) reinforced by whiskers.

[Prior art] In recent years, high strength, high toughness, wear resistance, chipping resistance, oxidation resistance, and heat resistance are being used in cutting tools, automobile engine parts such as ceramic valves, and heat engine parts such as gas turbine rotors. There is a need for excellent ceramic materials.

Silicon oxynitride (S 12N20) is known as one of the ceramic materials with excellent heat resistance and oxidation resistance.

Silicon oxynitride is 1988 Ceramics Association Annual Meeting Proceedings 3A25
In addition, as seen in the 25th Ceramics Basics Conference Lecture Abstracts IA18, there is a method of manufacturing by adding metal oxide powder as a sintering aid to 5j3N4 and Si02 and sintering, and 49-115999 and Ceramics Association Journal 75 (4)
, 111-119 (1967), a method is known in which a mixture of silicon and silicon dioxide is nitrided to obtain acicular crystals or powder of silicon oxynitride.

In addition, Si
It is known that SiC powder is added to 3N4 and 5i(h) and sintered to obtain a silicon oxynitride sintered body with high high-temperature strength.

[Problems to be Solved by the Invention] However, conventional silicon oxynitride sintered bodies have excellent heat resistance and oxidation resistance, and have relatively high strength, but do not have sufficient toughness.

Also, S i 3N4+ S i 02-+2 S i
2N20C7) Since the reaction is slow, unreacted α-9i
3N4 and SiO2 tend to remain in the sintered body, especially Si
Remaining 02 tends to adversely affect the hot properties of the sintered body.

On the other hand, if the reaction sintering time is increased in order to promote the reaction, the strength is likely to decrease due to bores caused by decomposition and volatilization of silicon oxynitride and silicon oxynitride grains that have grown too much.

[Means for Solving the Problems] The present invention employs the following means to solve the above problems.

That is, the gist of the present application is to provide SiC and/or β-Si 31 containing SiC whiskers.
'L4 whiskers totaling 5 to 40% by weight, kQ, Sc
, Y, and rare earth elements in a total of 0.5 to 30% by weight, and the remainder of the silicon component consisting of Sl and 5iOp; SiC whiskers and/or β-Si 3
A method for producing an m-fiber-reinforced silicon oxynitride sintered body using a compact made of raw material powder having a total content of Na whiskers of 5% by weight or more, the method comprising nitriding the compact in a nitrogen atmosphere at 1300 to 1500°C. A nitriding step of
a pre-sintering step of forming a pre-sintered body in a non-oxidizing atmosphere containing nitrogen at 0 atm;
The present invention provides a method for producing a fiber-reinforced silicon oxynitride sintered body, comprising a step of sintering in a non-oxidizing atmosphere containing nitrogen at atmospheric pressure.

Here, as the SiC whiskers and β-5i3N4 whiskers, those that are normally commercially available can be used, and their typical shape is an average diameter of 0.2 to 5 μm and an average length of 2 to 5 μm.
It is 200am. : Especially AQ, Ca, Mg, Ni,
It is preferable that the crystal has a small amount of cationic components such as Fe, Co, Mn, Cr, Y, etc., and has a small amount of constrictions, branching, and surface defects.

Furthermore, the surface of the whisker may be coated with BN, carbon, or the like.

Note that the Si3N4 voicer contains β-3 used in the present invention.
In addition to i3N4 whiskers, α-9L3N4 whiskers exist. However, when α-9i3Nt whiskers are used, they undergo a melting and precipitation process during sintering of the present fiber-reinforced ceramic and transform into β-513NA. Therefore, no voice force exists after sintering. Therefore, α-913Na whiskers cannot be used in the present invention.

In the present invention, if this voice force is less than 5% by weight of the raw material powder, the resulting fiber-reinforced silicon oxynitride sintered body will not have sufficient toughness.

Additionally, SiC containing SiC whiskers and/or β-9i
If the total amount of iN4 whiskers is less than 5% by weight, it is impossible to suppress the decomposition of silicon oxynitride during sintering, and there is almost no effect on increasing the strength of the sintered body by suppressing grain growth.

On the other hand, if the content exceeds 40% by weight, sinterability deteriorates, making it impossible to obtain the desired fiber-reinforced silicon oxynitride sintered body.

In particular, it is preferable that these components be contained in an amount of 10 to 30% by weight because the toughness is high and the sinterability is good.

Furthermore, if the total amount of one or more oxides selected from AQ, Sc, Y, and rare earth elements is less than 0.5% by weight, sinterability will deteriorate and the desired fiber-reinforced silicon oxynitride It is not possible to obtain a sintered body. On the other hand, this oxide
If it exceeds 0% by weight, the glass component in the fiber-reinforced silicon oxynitride sintered body becomes too large, resulting in a decrease in strength, heat resistance, and oxidation resistance.

For Si and S i 02, it is recommended to use as high purity and fine powder as possible, and to set the mixing ratio of Si and 5iCh to a molar ratio of about 3: 1 to obtain a thorough and high-performance acid. This is desirable for obtaining a silicon nitride sintered body.

The kQ-, Sc, Y and rare earth element oxides, S
i02 may be added in powder form from the beginning, but it can also be mixed in the form of a metal alkoxide solution and colloidal silica (silica sol), respectively, and then calcined after hydrolysis, etc., and then used as the raw material powder of the present invention. good.

The raw material powder obtained as described above is formed into a molded body by a method commonly used for molding such as press molding, with the addition of a binder if necessary.

The nitriding step is a step in which Si, SiO2 in the molded body and nitrogen gas in the nitrogen atmosphere are reacted to form silicon oxynitride.

If the treatment temperature in this nitriding step is lower than 1300° C., nitriding will not proceed sufficiently, making it impossible to obtain a fiber-reinforced silicon oxynitride sintered body with sufficient performance.

On the other hand, if the treatment temperature in the nitriding step exceeds 1500° C., Si in the raw material powder will melt, making it impossible to maintain the shape of the molded product.

Further, the pressure of the nitrogen atmosphere in the nitriding step is not particularly limited, but is preferably about 1 atmosphere.

The preliminary sintering process makes the sintered body containing silicon oxynitride produced in the nitriding process about 70% or more in terms of theoretical density ratio, and allows for stricter densification in the subsequent densification process.

Note that the theoretical density is the sum of the products of the volume ratio of each component and the true density of each component, assuming that each component of the sintered body occupies a volume corresponding to its molar ratio. The theoretical density ratio is the ratio of the actual density of the sintered body to the theoretical density calculated in this way, expressed as a percentage.

In this pre-sintering step, sintering is carried out in the range of 1550 to 1900 °C, but if the sintering temperature is lower than this temperature range, the sintering temperature will not be as strict as required, and if it is higher than this temperature range, conversely The silicon oxynitride in the molded body will decompose.

Further, the non-oxidizing atmosphere in the preliminary sintering step needs to contain nitrogen to prevent decomposition of silicon oxynitride.

By sintering in a non-oxidizing atmosphere with a pressure in the range of 1 to 10 atmospheres, it is possible to obtain a desired theoretical density and to prevent decomposition of silicon oxynitride.

In the densification step, the pre-via sintered body obtained in the pre-sintering step is further heated at 1600-2000°C and 30-2000°C.
By sintering in a non-oxidizing atmosphere containing nitrogen at atmospheric pressure, a fiber-reinforced silicon oxynitride sintered body having a theoretical density ratio of 97% or more is obtained.

If the temperature and pressure of this densification step are outside the range, a fiber-reinforced silicon oxynitride sintered body with desired characteristics cannot be obtained.

Note that as the non-oxidizing atmosphere used in the preliminary sintering step and the densification step, only nitrogen gas or a mixed gas of nitrogen and argon may be used.

Further, the nitriding step, the preliminary sintering step, and the densification step may be performed independently, or may be performed continuously without cooling while changing the sintering conditions such as temperature and pressure.

Furthermore, when AQ203 is selected as the oxide, part or all of AQ2o3 becomes a solid solution in S12N20 of the sintered body, forming 0'-sialon represented by S12-xk Q*0l-xN2-x. It's okay to stay.

In addition, Y2S 12 to the extent that it does not affect the properties of the sintered body
07, Ce5i207, Ce4. ay (S i O4
) 30 etc. may be included.

[Operations/Effects] In the method for producing a fiber-reinforced silicon oxynitride sintered body of the present invention, S ich +35 j+2N2→2S 12N20
Due to the chemical reaction shown, Si, 5i (h
This produces more silicon oxynitride.

Therefore, silicon oxynitride, AQ, Sc, Y
and one or more oxides selected from rare earth elements are in sufficient contact with each other to promote sintering of silicon oxynitride, and a sufficiently dense fiber-reinforced silicon oxynitride sintered body can be obtained. .

In addition, silicon oxynitride is 3512N at temperatures exceeding 1700℃.
20→S i: Rapidly decomposes by the reaction of qN4+3s io+N2.

However, in the present invention, the decomposition of 512N20 is suppressed by the voice force in the compact and the pressurized non-oxidizing atmosphere containing nitrogen.

Furthermore, the voice force component suppresses grain growth of silicon oxynitride grains during sintering, contributing to higher strength.

The fiber-reinforced silicon oxynitride sintered body produced according to the present invention has high toughness due to the crack deflection and pullout effect of the SiC whiskers or β-913Ns whiskers.

Note that the pull-out effect is an effect that, in the stress field at the tip of a crack generated in the matrix, whiskers are pulled out of the matrix, thereby significantly reducing stress concentration at the tip of the crack and improving toughness.

With the above structure, the present invention is made of fiber-reinforced silicon oxynitride sintered material, which is a ceramic material with high strength, high toughness, and excellent wear resistance, chipping resistance, oxidation resistance, heat resistance, corrosion resistance, and electrical insulation. This made it possible to produce solids.

[Example code] Examples of the present invention will be described.

The raw materials listed below were blended in the proportions shown in the first batch, uniformly dispersed and mixed in ethanol for 16 hours using a ball mill, and then 5% by weight of an acrylic binder was added and dried.
Granulation was performed to obtain a base powder.

5iyJ powder: Average particle size 2um Purity 99.9% S j 02 powder: Average particle size 15%m Purity 99.9% Apparent specific gravity Approx. 50g/Q Oxides of AQ, Sc, Y and rare earth elements: Average particle size 2
SiC powder below LLm: Average particle size 1.6L1. m ・Purity 96% SiC whisker: Average diameter 0.6 am Length 1(] ~ 80 LLm β-5i3N4 Whisker: Average diameter 1 um, length 5 ~ 50 μm.

The above base powder was uniaxial press molded into a size of 50 x 50 x 7 mm at a molding pressure of 1°5t/ctn', and then
Degreased in a nitrogen atmosphere for an hour.

Then, as a nitriding treatment, 14
It was held at 20°C for 20 hours.

Subsequently, as a preliminary sintering step, sintering was performed for 4 hours at the atmosphere, pressure, and sintering temperature shown in Table 1 to obtain a preliminary sintered body.

Further, as a densification step, this preliminary sintered body was sintered for 2 hours at the atmosphere, pressure, and sintering temperature shown in Table 1 to obtain a final sintered body.

The size of the obtained sintered body is 4 mm x 3 mm x 40 m
A sample was prepared by grinding to a size of m.

For this sample, the bending strength at room temperature was determined by JIS-R
According to JIS-R1604, the fracture toughness at a load of 10 kg is determined according to JIS-R1604.
Fracture toughness was measured by the dentition microfracture method, and the results are shown in Table 1.

In addition, in this example, in order to include voice force in the raw material,
-Voice force is oriented in the molded product by shaft bushing molding.

In order to investigate the influence, the fracture toughness in the pressurizing direction of press forming (denoted as pressurization in Table 1) and the fracture toughness in the direction perpendicular to it (denoted as vertical in Table 1) were determined. Examined.

The crystal phase in the sample was identified using X-ray diffraction, and the results are also listed in Table 1.

Regarding the voice force in each sample, as a result of XvA diffraction and observation using an optical microscope and a scanning electron microscope, it was found that there was almost no voice force, and it did not react with other components - remained in the sintered body.
It turned out to be dispersed.

Furthermore, the theoretical density ratios of samples NnA-1 to A-10 of this example were all 98.5% or more.

Note that the theoretical density ratios of the samples described as "not densified" in the table are all 90% or less.

From Table 1, the following was found.

■ If SiC and/or β-5i3N4 voices containing sintering aids and SiC whiskers are not included, as in sample NnB-1, the compact will decompose and volatilize during the preliminary sintering process, resulting in poor quality. It is not possible to obtain a sintered body.

■As in samples NnB-2 to B-5, SiC and/or β-Si3N4 whiskers, including SiC whiskers,
If it is outside the scope of the present application, it may decompose and volatilize in the preliminary sintering step, or it will not be sufficiently densified in the densification step, making it impossible to obtain a good sintered body.

■ As in samples NnB-6 to B-8, if the sintering aid component is outside the range specified in this application, densification may not be achieved or the bending strength at high temperatures will be significantly reduced, making it impossible to obtain a good sintered body. It is not possible.

(2) If the amount of voice force is outside the range specified in the present application, as in samples NnB-10 to B-11, sufficient toughness will not be exhibited and a good sintered body cannot be obtained.

■ As in samples NαC-1 to C-3, if the pressure and sintering temperature in the densification process are outside the range specified in this application, it may decompose and volatilize during sintering, or densification may not occur, resulting in poor sintering. You can't get a body.

■ As in Samples NnD-1 to D-3, if the pressure and sintering temperature in the preliminary sintering step are outside the range specified in this application, it may decompose and volatilize during sintering, or it may not be densified, resulting in poor sintering. You can't get a body.

(2) As in samples NnA-1 to A-10, it was confirmed that a good sintered body could be obtained by keeping the compounding composition and each sintering condition within the range of the present application.

Agent: Patent attorney Tsutomu Sadatsu (2 Sen)

Claims (1)

[Claims] SiC and/or β-Si_3N containing SiC whiskers
_4 Whiskers totaling 5 to 40% by weight, Al, Sc,
The main components are a total of 0.5 to 30% by weight of one or more oxides selected from Y and rare earth elements, and the remainder of the silicon component consists of Si and SiO_2, SiC whiskers and/or β-Si_3N
_4 A method for producing a fiber-reinforced silicon oxynitride sintered body using a compact made of raw material powder containing 5% by weight or more of whiskers in total, the method comprising nitriding the compact in a nitrogen atmosphere at 1300 to 1500°C. Step: The nitrided molded body is heated at 1550 to 1900°C for 1 to 1
a pre-sintering step of forming a pre-sintered body in a non-oxidizing atmosphere containing nitrogen at 0 atm;
1. A method for producing a fiber-reinforced silicon oxynitride sintered body, comprising a densification step of sintering in a non-oxidizing atmosphere containing nitrogen at atmospheric pressure.