JP2608772B2 - β-type silicon nitride whisker composite material and method for producing the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a β-type silicon nitride whisker composite material and a method for producing the same, and more particularly, to a ceramic-metal composite material or ceramics using a specific β-type silicon nitride whisker molded body. -Ceramic composite materials and methods for their production.

(Prior art and its problems) Ceramic whiskers generally have good heat resistance and abrasion resistance, and are expected to be used as reinforcing materials for providing composite materials having high strength and elastic modulus. One of them is a whisker-reinforced composite material. Among them, β-type silicon nitride whiskers are suitable as a reinforcing material for high melting point metals or ceramics because they are present stably at high temperatures.

In order to use the whiskers as a preform of a composite material, it is common to purify the crude whiskers obtained by firing by a suitable method and remold the powdery whiskers by a suitable method. The preform-like whiskers obtained in this way are shorter in length than when the whiskers are formed, and require a number of steps of processing that requires complicated and sophisticated descriptions before the preform is formed. Reform manufacturing is not economically satisfactory. Further, even when it is used as a preform for various composite materials, there is a problem that it does not have sufficient strength and hardness because it relies on the above-mentioned manufacturing method.

As a method of forming a preform, for example, JP-A-59-226 is known.
As described in Japanese Patent Publication No. 139, whiskers obtained by calcining the raw materials are dispersed in a solvent such as water, a binder is added if necessary, and then the dispersion is put into a mold having a desired shape and added. A method of removing liquid by applying pressure or vacuum has been adopted, but the obtained preform has a problem of low strength.

Next, as a method of producing a composite material using whiskers, for example, first, in the case of compounding with a metal material, several methods have been developed centering on a high pressure casting method and a powder metallurgy method. The high pressure casting method is drawing attention as a practical method. In the high pressure casting method, a whisker reinforced metal composite material (hereinafter, referred to as a whisker preform) is placed in a mold, a molten metal of the base metal is poured into the mold, and the molten metal is solidified while being pressed in the mold.
WRM).

In the case of compounding with a ceramic material, sintering by a hot press method is most common. By filling a mixed powder of ceramic raw material powder and whisker, which is a matrix, and firing at a suitable high temperature and pressure,
It is possible to manufacture whisker-reinforced ceramic composite materials (hereinafter referred to as WRC).

However, WRM and WRC obtained by the above manufacturing method
Is a dense body, and the whiskers are dispersed in the dense body. That is, there is a problem that it is not suitable for producing a porous composite material using a whisker forming body.

(Object of the Invention) The object of the present invention is to use a porous whisker molded article,
An object of the present invention is to provide a β-type silicon nitride whisker composite material that can be used for various applications and a method for producing the same.

(Technical means for solving problems) The present invention has a density of 0.15 to 1.1 g / cm ³ , a bending strength of 25 kg / cm ² or more, a hardness of 45 kg / cm ² or more, a compression strength of 30 kg / cm ² or more. Molded silicon nitride whisker, comprising:
% Or more consists of β-type silicon nitride whiskers, and 80% or more of the whiskers have a diameter of 0.1 to 5 μm and 2 to 1
Metal and / or ceramic coating on the surface of a β-type silicon nitride whisker molded body having a length of 00 μm and in which whiskers are in contact with each other at one or more locations per whisker, and the surface of the whisker inside the molded body The present invention relates to a β-type silicon nitride whisker composite material having a porosity of 0 to 90% formed by forming a layer.

Further, the present invention provides a C-type silicon nitride whisker molded body with a CV
The present invention relates to a method for producing the above-mentioned β-type silicon nitride whisker composite material, wherein the β-type silicon nitride whisker composite material is heated to a deposition temperature range of a D reaction, and a CVD reaction gas is supplied to the molded body to cause a reaction to precipitate a solid phase.

The bending strength, hardness and compressive strength of the β-type silicon nitride whisker molded body used in the present invention are measured according to JIS Z211
3. Measured according to JIS Z2117 and JIS Z2111.

The β-type silicon nitride whisker molded body used in the present invention has a density of 0.15 to 1.1 g / cm ³ , a bending strength of 25 kg / cm ² or more,
The hardness is 45 kg / cm ² or more, the compressive strength is 30 kg / cm ² or more, and 90 wt% or more of the molded product is β-type silicon nitride whiskers, and 80 wt% or more of the whiskers have a diameter of 0.1 to 5 μm, and 2 The whiskers have a length of 100100 μm, and the whiskers are contacted and fixed at one or more locations per whisker.

Such a β-type silicon nitride whisker compact is disclosed in Japanese Patent Application No.
-232010. That is, in 100 parts by weight of amorphous silicon nitride and / or α-type silicon nitride powder, an oxide powder of a rare earth element and / or an alkaline earth metal or a compound powder that can be converted into an oxide during firing is calculated as an oxide. the mixed powder is 0.1 to 20 parts by weight blended, filled with a density of the crucible-type in the range of 0.15~1.1g / cm ³ of a desired shape, under nitrogen Motohi oxidizing gas atmosphere, the highest temperature
Obtained by firing at 1600-1850 ° C.

Here, the amorphous silicon nitride powder can be prepared by a method known per se, for example, by heat-treating a reaction product obtained by reacting silicon tetrahalide and ammonia in a liquid phase or a gas phase, It is a so-called amorphous powder in which a clear diffraction phenomenon does not appear by ordinary X-ray diffraction.

The α-type silicon nitride powder can be manufactured by a known method such as a reduction nitriding method of silica or a direct nitriding method of silicon, in addition to the method of firing the above-mentioned amorphous silicon nitride powder. The specific surface area of the α-type silicon nitride powder is preferably 0.01 to ²⁰ m ² / g, and particularly preferably ^{2 to} 13 m ² / g.

Specific examples of rare earth elements include yttrium, lanthanum, cerium, praseodymium, neodymium, samarium, europium, gadolinium, dysprosium,
Lanthanum series elements such as ytterbium and scandium. In addition, specific examples of the alkaline earth metal include magnesium, calcium, strontium, barium, and the like.

As the compound that can be converted into an oxide of a rare earth element and / or an alkaline earth metal during firing, any compound can be used as long as it is a compound that can be partially or wholly converted into an oxide during β-type silicon nitride whisker growth. And examples thereof include hydroxides and carbonates.

The compounding amount of the compound powder of the rare earth element and / or the alkaline earth metal is 0.1 in terms of oxide per 100 parts by weight of the raw material powder selected from the amorphous silicon nitride and / or the α-type silicon nitride.
~ 20 parts by weight. If the blending amount of these is smaller than the lower limit, the formation of whiskers is insufficient, and if it is larger than the upper limit, a densified sintered body-like product is produced, and it cannot be said to be a molded body made of whiskers. Only unsatisfactory forms can be made.

There is no particular limitation on the method of preparing the mixed powder of the amorphous silicon nitride and / or α-type silicon nitride powder and the compound powder of the rare earth element and / or the alkaline earth metal. A method of dry mixing, a method of wet-mixing both in an inert liquid, and then removing the inert liquid can be employed. A V-type mixer, a ball mill or a vibrating ball mill is preferably used as the mixing device. Another method for preparing the mixed powder is to mix and disperse a compound powder of a rare earth element and / or an alkaline earth metal in a precursor of a non-crystalline silicon nitride powder, for example, silicon diimide or silicon tetraamide, and disperse the dispersion. It is also possible to adopt a method of heat treatment. In the above adjustment method,
When using crystalline silicon nitride or its precursors, they are very sensitive to oxygen or moisture and must be handled under a controlled inert atmosphere.

Specific examples of the nitrogen-containing non-oxidizing gas include nitrogen, argon, ammonia, and a mixed gas thereof. The firing conditions are preferably set so that the mixed powder is heated for 0.1 to 40 hours, particularly 4 to 20 hours on average between 1000 ° C. and the maximum temperature. The maximum temperature during firing is 1850 ° C. or lower, preferably a temperature in the range of 1600 to 1800 ° C. The furnace used for firing is not particularly limited, and for example, a batch furnace, a rotary furnace, a pusher furnace, or the like using a high-frequency induction heating method or a resistance heating method can be used.

In the present invention, a metal and / or ceramic coating layer is formed on the surface of the β-type silicon nitride whiskers and the surface of the whiskers inside the molded body.

Metals and / or ceramics include Ta, W, Mo,
Desirably, at least one selected from SiC, TiC, TiN, TiB ₂ , and BN is used.

In the present invention, a β-type silicon nitride whisker molded body is
A β-type silicon nitride whisker composite material can be manufactured by heating to a deposition temperature region of a CVD reaction and supplying a CVD reaction gas to the compact.

The heating method and the supply method of the reaction gas are not particularly limited as long as the precipitate can be deposited on the surface of the molded body and the whisker surface inside the molded body. In the process of flowing, an isothermal method in which gas diffuses and deposits on the surface and inside of the molded body and can be adopted. In addition, a temperature gradient is provided on the formed body,
A temperature gradient method in which a reaction gas is caused to flow on the surface of the constant temperature side, the reaction gas is diffused to the high temperature side and reacted in the high temperature part, and the reaction gas is sequentially deposited from the high temperature side, or the pressure that causes the reaction gas to flow in the compact by pressure. The difference method can also be adopted.

In the present invention, the precipitate to be deposited on the surface of the β-type silicon nitride whisker molded body and the whisker surface inside the molded body by the CVD reaction is selected from carbides, borides, nitrides and metals that can be deposited by the CVD reaction. Especially SiC, TiC,
At least one selected from TiB ₂ , BN, TiN, Ta, W and Mo is desirable. Producing a β-type silicon nitride whisker composite material having various characteristics by making use of the characteristics of the β-type silicon nitride whisker molded body and further selecting the above-mentioned metals and / or ceramics according to the required characteristics. You can

(Effect of the Invention) The β-type silicon nitride whisker composite material obtained in the present invention is a composite material having completely different properties as compared with known WRM and WRC. By changing the pressure, composite materials having different porosities can be easily manufactured.

(Example) An example is shown below.

Reference Example 1 <Production of Preform Made of β-Type Silicon Nitride Whiskers> 100 parts by weight of amorphous silicon nitride powder obtained by thermally decomposing silicon diimide at 1200 ° C. and 1 part by weight of yttrium oxide having a purity of 99.9% Was placed in a vibrating ball mill under a nitrogen gas atmosphere and mixed for 1 hour.

The mixed powder was filled in a cylindrical carbon container having an inner diameter of 50 mm and a length of 30 mm. This container was set in an electric furnace and fired at 1750 ° C. under a nitrogen gas atmosphere.

After cooling to room temperature, a disk-shaped β with a diameter of 50 mm and a thickness of 10 mm
The silicon nitride whisker preform was removed from the container.

The disk-shaped product had a density of about 0.32 g / cm ^3, flexural strength of 40.5 kg / cm ^2, the compressive strength of the hardness and 46.2kg / cm ² of 69.5kg / cm ^2. Observation of this disk-shaped object with a scanning electron microscope revealed that 80% by weight or more of the whiskers was 0.2-4.
An image having a diameter of μm, a length of 5 to 100 μm, and intricately entangled images in which one whisker was fixed at one or more points was recognized.

Further, when the powder obtained by pulverizing the disk-shaped material was examined by X-ray diffraction, diffraction other than diffraction that can be attributed to β-type silicon nitride was hardly recognized.

Reference Example 2 <Production of Preform Made of β-Type Silicon Nitride Whiskers> 120 parts by weight of α-type silicon nitride powder having a specific surface area of 4.8 m ² / g, 1 part by weight of calcium oxide and 600 parts by weight of ethanol were put into a ball mill and wet-mixed. After that, it was dried under reduced pressure, and the obtained lump was crushed to obtain a mixed powder.

This mixed powder was filled in a cylindrical carbon container having an inner diameter of 50 mm and a height of 30 mm. The container was set in an electric furnace and fired at 1750 ° C. in a nitrogen gas atmosphere to obtain a disk-shaped β-type silicon nitride whisker preform corresponding to the shape of the container.

The cylindrical product had a density of about 0.36 g / cm ^3, flexural strength of 42.0 kg / cm ^2, the compressive strength of the hardness and 50.4 kg / cm ² of 72.3kg / cm ^2. Observation of this disk-shaped object with a scanning electron microscope revealed that 80% by weight or more of the whiskers were 0.5 to 0.7.
An image having a diameter of 10 μm, a length of 10 to 100 μm, and intricately entangled whiskers were fixed at one or more locations per one.

Further, when the powder obtained by pulverizing the disk-shaped material was examined by X-ray diffraction, diffraction other than diffraction that can be attributed to β-type silicon nitride was hardly recognized.

Example 1 The β-type silicon nitride whisker preform obtained in Reference Example 1 was placed in an apparatus as shown in FIG. 1 and was preheated to 1000 ° C. in an argon gas atmosphere. Then, as a reaction gas, a mixed gas of TiCl ₄ , H ₂ and CH ₄ (volume ratio 1: 40: 8) was added to 25
At a flow rate of 00 cc / min, a CVD reaction was caused under the conditions of a heating time of 6 hours and a reaction stress of 50 Torr to obtain a TiC / β-type silicon nitride whisker-based composite material. When the central part of the obtained composite material was cut and observed with a scanning electron microscope, the inside of the composite material was in a state where TiC covered the whiskers, and the coating layer became thicker toward the surface . The surface of the composite material was densely covered with TiC. The porosity was measured to be 70%.

Example 2 One end surface of the β-type silicon nitride whisker preform obtained in Reference Example 2 was placed on a carbon steel plate and preheated to 1000 ° C. in an argon gas atmosphere. Then, as a reaction gas,
A Ta / β-type silicon nitride whisker-based composite material is produced by flowing a mixed gas of TaCl ₂ and H ₂ (volume ratio 1: 2.5) at 800 cc / min, causing a CVD reaction under heating conditions of 6 hours and a reaction pressure of 50 Torr. And

When the central part of the obtained composite material was cut and observed with a scanning electron microscope, the inside of the composite material was in a state where Ta covered the whiskers, and the coating layer became thicker toward the surface. . Further, the surface of the composite material was densely covered with Ta. Also, when the porosity was measured,
70%.

[Brief description of the drawings]

FIG. 1 is a schematic view of the CVD apparatus used in Examples 1 and 2. DESCRIPTION OF SYMBOLS 1 ... beta-type silicon nitride whisker forming body, 2 ... introduction gas, 3 ... reaction furnace, 4 ... heating furnace, 5 ... exhaust device, 6
…… Exhaust gas treatment equipment

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C30B 29/62 C30B 29/62 R

Claims (3)

(57) [Claims] (1) A density of 0.15 to 1.1 g / cm ³ , a bending strength of 25 kg / cm ² or more (JIS Z2113 method), and a hardness of 45 kg / cm ² or more (JIS Z2117
Method), a β-type silicon nitride whisker molded body having a compressive strength of 30 kg / cm ² or more (JIS Z2111 method),
% Or more consists of β-type silicon nitride whiskers, and 80% or more of the whiskers have a diameter of 0.1 to 5 μm and 2 to 1
The surface of the β-type silicon nitride whisker molded body having a length of 00 μm and in which the whiskers are in contact with each other at one or more locations per whisker, and the surface of the whisker inside the molded body is coated with metal and / or ceramics. A β-type silicon nitride whisker composite material having a layer and having a porosity of 0 to 90%. 2. The method according to claim 1, wherein the metal and / or ceramic is Ta, W,
Mo, SiC, TiC, BN, TiN, β -silicon nitride whisker composite material Claims paragraph 1, wherein the at least one selected from TiB _2. 3. A density of 0.15 to 1.1 g / cm ³ , a bending strength of 25 kg / cm ² or more (JIS Z2113 method), a hardness of 45 kg / cm ² or more (JIS Z2117).
Method), a β-type silicon nitride whisker molded article having a compressive strength of 30 kg / cm ² or more (JIS Z2111 method).
At least 80% by weight of the whiskers have a diameter of 0.1 to 5 μm and a weight of 2 to 100%.
It has a length of μm and whiskers are whiskers 1
The β-type silicon nitride whisker compact, which is contact-fixed at one or more locations per book, is heated to a deposition temperature range of a CVD reaction, and a CVD reaction gas is supplied to the compact to react and precipitate a solid phase. The method for producing a β-type silicon nitride whisker composite material according to claim 1, wherein