JP2557548B2 - Method for producing SiC whisker reinforced Si3N4 composite material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a high-strength and high-toughness SiC whisker-reinforced Si ₃ suitable for use as automobile engine parts and various structural materials.
The present invention relates to an N ₄ composite material and a manufacturing method thereof.

[Conventional technology]

Si ₃ N ₄ ceramics, which contains silicon nitride (Si ₃ N ₄ ) as the main component, has excellent properties such as strength at room temperature, oxidation resistance, wear resistance, thermal shock resistance, corrosion resistance, etc., and is suitable for cutting tools and automobile parts. It has been put to practical use.

Further, recently, in order to develop a high-efficiency engine, it has been attempted to use Si ₃ N ₄ as a high temperature material for an engine. For that purpose, it is possible to further improve toughness and high temperature strength at 1200 ° C or higher. is necessary.

As a method of improving the toughness of Si ₃ N ₄ , JP-A-62-2651
As shown in Japanese Patent Publication No. 73, etc., there is an attempt to disperse SiC whiskers as a reinforcing material in a Si ₃ N ₄ matrix to form a composite.

However, in the whisker reinforced composite material by the conventional method, no remarkable improvement in toughness due to the composite of whiskers is seen, and even at high temperature strength, it is improved as compared with a single body containing no whiskers, but still higher than room temperature strength. The situation is declining.

[Problems to be Solved by the Invention]

In view of such conventional circumstances, it is an object of the present invention to provide a highly reliable SiC whisker reinforced Si ₃ N ₄ composite material having high toughness, excellent strength, and particularly high temperature strength. .

[Means for solving the problem]

To achieve the above object, the SiC whisker reinforced Si ₃ N ₄ composite material of the present invention is composed of a sintered body containing SiC whiskers in the matrix of Si ₃ N ₄ , and the SiC whiskers are uniaxially oriented. It is characterized by

Further, the method for producing the SiC whisker reinforced Si ₃ N ₄ composite material, a slurry containing Si ₃ N ₄ powder and SiC whiskers is made into a sheet with a doctor blade to form a green sheet having a thickness of 0.05 to 0.5 mm, and this green A plurality of sheets are laminated by aligning the orientation direction of the SiC whiskers, and the laminated compact is hot-pressed or pressure-sintered in nitrogen gas.

[Action]

One of the reasons why the conventional SiC whisker reinforced Si ₃ N ₄ composite material is not yet satisfactory in toughness and high temperature strength is considered to be the whisker dispersion orientation. That is, in the conventional SiC whisker reinforced Si ₃ N ₄ composite material, since the SiC whiskers were randomly dispersed in the matrix,
It could not be a great resistance against the crack surface that develops at the time of destruction. In addition, it is difficult to completely eliminate the agglomeration due to the entanglement of the whiskers by a normal molding method such as press molding or CIP molding, so that the densification is hindered, or the whisker agglomerates easily become the starting point of the fracture. It was

On the other hand, in the method of the present invention, a slurry containing Si ₃ N ₄ powder and SiC whiskers was made to have a thickness of 0.05 by a doctor blade.
By making a sheet of ~ 0.5 mm, the whiskers in the slurry can be uniaxially oriented in the pull-out direction. Therefore, the obtained green sheets are laminated by aligning the orientation direction of the whiskers, and sintered to obtain a SiC whisker-reinforced Si ₃ N ₄ composite material in which the whiskers are uniaxially oriented.

SiC whisker-reinforced S with whiskers uniaxially oriented
The i ₃ N ₄ composite material has great resistance to the development of the crack surface perpendicular to the orientation direction of the whiskers. Therefore, the SiC of the present invention should be oriented so that the orientation direction of the whiskers is orthogonal to the direction in which the crack surface progresses as a structural material.
If you place and use whisker reinforced Si ₃ N ₄ composite material,
It becomes possible to remarkably improve the high temperature strength at which the pinning effect of the whiskers becomes remarkable, and the fracture toughness, which largely contributes to the crack deflection effect and the pullout effect.

In the method of the present invention, the slurry normally contains an organic binder together with Si ₃ N ₄ powder and SiC whiskers, and the content thereof is preferably 10 to 30% by weight. After adjusting the viscosity of this slurry using a defoaming machine or the like, it is formed into a sheet by the doctor blade method. The viscosity of the slurry is preferably in the range of 500 to 10,000 cP, more preferably in the range of 800 to 3000 cP. If the viscosity of the slurry is outside the above range of 500 to 10,000 cP, it is difficult to form a sheet. That is, if it is less than 500 cP, it is difficult to control the uniformity of the sheet and the sheet thickness.
This is because if it is 0 cP or more, the fluidity is poor and the moldability is poor.

The thickness of the green sheet produced by making the slurry into a sheet by the doctor blade method depends on the diameter of the whiskers, but in the case of the most commonly obtained ordinary SiC whiskers, it is in the range of 0.05 to 0.5 mm. understood. When the thickness of the green sheet exceeds 0.5 mm, the degree of freedom of the whiskers in the thickness direction increases, so the one-dimensional binding force becomes weaker, and the whisker directions are three-dimensionally randomized.
A uniaxial orientation along the pulling direction cannot be obtained. or,
When the thickness of the green sheet is less than 0.05 mm, it is difficult to handle, and the whiskers cause bridging in the thickness direction to form a non-uniform portion, which makes it difficult to produce a uniform green sheet.

Laminate a plurality of green sheets prepared as above,
The laminated compact is heat-treated at 500 to 900 ° C. in the atmosphere to remove the organic binder, and then hot-pressed or pressure-sintered in nitrogen gas. Preferred sintering conditions are a temperature of 1600 to 1950 ° C. and a hot press pressure of 100 to 400 kg / cm ² . Further, the laminated green sheets are laminated by a press, preferably at a temperature of 40 to 80 ° C. and a pressure of 20 to 50 kg / cm ² ,
Thermocompression bonding may be performed under the condition of time of 2 to 8 minutes.

The SiC whiskers have a diameter of 10 μm or less and a length of 150 μm.
The most common size is m or less, but as the diameter and length of whiskers increase, holes easily form between the whiskers and the whiskers bridging as the green sheet becomes thinner. Inhomogeneous portions are likely to occur, and they become defects, resulting in a decrease in strength. Therefore, it is generally preferable that the SiC whiskers have a diameter of 0.1 to 3.0 μm and a length of 2 to 200 μm, and the amount of the whiskers mixed with the powder is 1.0 to 60 parts by weight.

〔Example〕

Example 1 8.4 wt% Y ₂ O ₃ and 2.0 wt% Al ₂ O ₃ as sintering aids
480g of Si ₃ N ₄ powder containing Si with 0.5μm in diameter and 15μm in length
120 g of C whiskers (sieved with 200 mesh sieve) were added and mixed in 1.5 l of ethanol for 2 hours, and 60 g of polyvinyl butyral and 40 g of di-n-butyl phthalate as an organic binder were added and further mixed for 4 hours. After adjusting the viscosity of the obtained slurry to 850 cP with a defoaming machine, a green sheet having a thickness of 0.3 mm was produced using a doctor blade device. When the green sheet was observed with a scanning electron microscope after evaporating ethanol by natural drying, the SiC whiskers were uniaxially oriented in the drawing direction of the doctor blade.

Cut out this green sheet into a 100 x 100 mm square and stack 50 sheets so that the whiskers in each 100 x 100 mm sheet have the same orientation direction.
The laminated sheet was pressure-bonded by a laminating press under the conditions of kg / cm ² and 3 minutes. This laminated compact was heat-treated in the air at 600 ° C. for 2 hours to remove the organic binder, and then 1700 in N ₂ gas.
Sintering was performed by hot pressing at a temperature of ° C and a pressing pressure of 200 kg / cm ² for 2 hours.

The obtained sintered body was cut into a JIS size test piece, and the room temperature strength (σrt) and the strength at 1250 ° C. in N ₂ (σ1250) and
Fracture toughness (K _IC ) measured by SENB method was σrt = 110 kg / mm ² , σ1250 = 120 kg / mm ² and K _IC = 9.6 MPa, respectively.
^It was found to be ^1/2, which has high strength and high toughness, and is particularly excellent in strength at high temperatures. Also, the observation of the sintered body by a scanning electron microscope revealed that the SiC whiskers were uniaxially oriented in the Si ₃ N ₄ matrix.

Example 2 A sintered body was manufactured in the same manner as in Example 1, except that the diameter and length of the SiC whiskers, the compounding amount with respect to the powder, and the thickness of the green sheet were changed as shown in the following table. The room temperature strength (σrt), the strength at 1250 ° C. in N ₂ (σ1250) and the fracture toughness (K _IC ) by the SENB method were measured, and the results are shown in the table below.

[Effects of the Invention] According to the present invention, the SiC whiskers in the Si ₃ N ₄ matrix are uniaxially oriented, and have excellent toughness and excellent strength,
It is possible to provide a highly reliable SiC whisker reinforced Si ₃ N ₄ composite material having particularly excellent high temperature strength.

Therefore, the SiC whisker-reinforced Si ₃ N ₄ composite material of the present invention can be expected as a high-temperature material for gas turbine engines, automobile engines, and the like.

Claims (1)

(57) [Claims] 1. A slurry containing Si ₃ N ₄ powder and SiC whiskers is formed into a sheet with a doctor blade and has a thickness of 0.05 to 0.5 m.
We made a green sheet of m and
A method for producing a SiC whisker-reinforced Si ₃ N ₄ composite material, which comprises laminating a plurality of whiskers in the same orientation direction and hot pressing or press-sintering the laminated compact in a nitrogen gas.