JP2001039772A - High strength silicon carbide sintered body and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high strength silicon carbide sintered body which is obtained by adding a non-oxide sintering aid capable of accelerating the densification even at a low temp. to be sintered while lowering the sintering temp. of the silicon carbide sintered body and to provide a method for producing the same in a short time by a pulse electric current sintering method. SOLUTION: The high strength silicon carbide sintered body is obtained by adding 1.5 to 10.0 wt.% of a non-oxide sintering aid, in which aluminum carbide and boron carbide are mixed in such a ratio that the most preferable molar ratio of the former to the latter is 2:1, to a fine silicon carbide powder produced by a CVD method or from an organic raw material and having an average particle size of about several tens of nanometer and then sintering the obtained mixture by applying electric pulses. The method for producing the high strength silicon carbide sintered body comprises adding 1.5 to 10.0 wt.% of the non-oxide sintering aid to the fine silicon carbide powder produced by a CVD method or from an organic raw material and having the average particle size of about several tens of nanometer and then sintering the obtained mixture by applying electric pulses at 1,500 to 1,750 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength silicon carbide sintered body and a method for producing the same, and more particularly, to a high-strength and wear-resistant heat engine such as a gasoline engine or a diesel engine or a drawing die. TECHNICAL FIELD The present invention relates to a silicon carbide ceramic which is a member for a mechanical structure requiring a property and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, silicon carbide ceramics have been sintered at, for example, a temperature of 2100 ° C. or more in an argon atmosphere by adding a sintering aid consisting of boron and carbon to silicon carbide powder. Silicon carbide ceramics are structural materials that are excellent in chemical stability, wear resistance, and high-temperature strength, and are used for materials such as gas turbines for power generation.
Since silicon carbide ceramics have a strong covalent bond, a small diffusion coefficient, and are difficult to sinter, they hardly sinter even when a molded body of pure silicon carbide powder is heated. Therefore, a sintering aid is generally added during sintering. By adding the sintering aid, the sintered body is densified and the strength can be improved. Normal,
Although sintering is performed by hot pressing, sintering without pressure has also been studied. Examples of pressureless sintering include solid phase sintering in which boron and carbon are added as assistants, and liquid phase sintering in which alumina and rare earth oxides are added as assistants.

There have been many attempts to introduce a metal or metal oxide into the skeleton or side chain of an organosilicon compound and then produce ceramics such as silicon carbide or silicon nitride. For example, Japanese Patent Publication No. 56-13645 proposes a method for producing a silicon carbide sintered body from an organosilicon polymer having Si, B and O as main skeleton components and having a group containing C in a side chain. I have. In addition, Japanese Patent Publication No. 57-3854
In No. 9, a method of producing a silicon carbide ceramic from a material in which at least one element selected from B, Al, Fe, or Ti or a compound containing the same is chemically bonded to polycarbosilane, which is a kind of an organosilicon compound, Has been proposed. JP-A-57-22169 proposes a method for producing a heat-resistant ceramic sintered body by mixing a polycarbosilane partially containing a vanadio-siloxane bond (VO-Si) with a non-oxide ceramic powder. ing. In Japanese Patent Publication No. 59-10945, a semi-inorganic polymer containing Si, B and O is mixed with a ceramic powder such as oxide, carbide, nitride, boride and silicide to form a heat-resistant ceramic sintered compact. How to get it has been proposed. Japanese Patent Application Laid-Open No. S60-151276 proposes a method for obtaining a silicon carbide sintered body from a homogeneously dispersed mixture of silicon carbide powder and an organometallic polymer containing silicon, carbon, boron and nitrogen as main components.

In the above-mentioned conventional techniques, sintering by hot pressing effectively applies pressure together with heat, but sintering occurs effectively, but there is a problem that the shape of ceramics is limited. In this regard, pressureless solid-phase sintering does not have a problem of shape limitation and can be said to be a versatile technique. However, among pressureless sintering, solid-phase sintering by adding boron and carbon as assistants has a very narrow temperature range for obtaining a dense sintered body, and the conditions must be strictly controlled. Is a problem. On the other hand, alumina and rare earth oxides,
Pressureless liquid phase sintering by the addition of a complex oxide such as YAG (Y ₃ Al ₅ O ₁₂ ) or a combination of two or more oxides is relatively more sintering than pressureless solid phase sintering. The result is wide.
However, in order to obtain a dense sintered body, it is necessary to add a certain amount or more of an auxiliary agent. At this time, there is a problem that the auxiliary component forms a second phase at the grain boundary, and this grain boundary phase causes grain boundary slip due to viscous flow at a high temperature. Grain boundary slip is a kind of plastic deformation, but it is a non-uniform deformation, so it causes stress concentration and causes a decrease in strength. Auxiliary components segregated at the grain boundary triple point pose a serious problem from the viewpoint of oxidation resistance.

[0005]

In order to lower the sintering temperature and to reduce the production equipment and production cost, the search for a sintering aid that produces a liquid phase at a low temperature and the use of ultrafine silicon carbide powder have been studied. However, a dense sintered body sufficient to maintain high mechanical strength could not be produced. An object of the present invention is to reduce the sintering temperature of a silicon carbide sintered body and to add a non-oxide sintering aid that promotes densification even at a low temperature. An object of the present invention is to provide a short-time manufacturing method of a silicon carbide sintered body by a pulse electric current sintering method.

[0006]

Means for Solving the Problems The present inventors have found that low-temperature sintering suitable for pulse current heating is based on the discovery that the densification temperature of silicon carbide is lowered by pulse current heating. The search for agents resulted in the completion of the present invention.
That is, instead of a solid-phase sintering aid composed of boron and carbon, which are general sintering aids of silicon carbide, a liquid phase having excellent wettability to silicon carbide at a comparatively low temperature is used as a sintering aid. The resulting mixed powder of aluminum carbide and boron carbide is added to ultra-fine silicon carbide powder having an average particle size of several tens of nanometers manufactured by a method such as a CVD method suitable for lowering the sintering temperature, and pulse current is applied. Has found a method of sintering silicon carbide ceramics having high strength despite the sintering temperature being lower by 300 to 550 ° C. than the conventional method.

The present invention for solving the above problems comprises the following technical means. (1) Aluminum carbide and boron carbide in a molar ratio of 2: 1
Non-oxide sintering aids mixed at the optimum ratio
1.5 to 10.0 fine silicon carbide powder having an average particle size of several tens of nanometers produced by CVD or organic raw materials.
A high-strength silicon carbide sintered body formed by sintering by pulse current in addition to weight%. (2) 1.5 to 10.0% by weight of the non-oxide sintering aid of (1) is added to fine silicon carbide powder having an average particle diameter of several tens of nanometers synthesized from a CVD method or an organic raw material. ,
A method for producing a high-strength silicon carbide sintered body, characterized by sintering at a temperature of 1500 to 1750 ° C. by pulse current.

[0008]

Next, the present invention will be described in more detail.
explain. CVD method and organic material used in the present invention
Fine particles with an average particle size of tens of nanometers
Specific examples of the silicon carbide powder include, for example, SiH
_Four Gas and C_Two H_Four Thermal plasma CVD using gas as raw material
Silicon carbide powder with an average particle diameter of 30 nm synthesized by
The end (CH_Three )_Two SiCl_Two By pyrolysis of gas
Preferred is a silicon carbide powder having an average particle size of 50 nm to be synthesized.
Suitable examples include, but are not limited to,
Use the appropriate fine silicon carbide powder if it has the same effect as
can do. Next, aluminum carbide-boron carbide
In general, non-oxide sintering aids composed of elemental
High purity such as aluminum carbide and boron carbide sold
Can be prepared by mixing a predetermined amount of fine powder.
You. In this case, a mixture of aluminum carbide and boron carbide
In the case, the molar ratio is optimally 2: 1 but is not limited to this.
Not something.

In the present invention, the above-mentioned aluminum carbide
A non-oxide sintering aid composed of boron carbide is added in an amount of 1.5 to 10% by weight based on the fine silicon carbide powder.
In this case, if the sintering temperature is increased to 1.5% by weight or less, a sintered body having a sintering density of 90% or more cannot be produced. Although a high sintered body can be obtained, it is not preferable because the high-temperature strength and creep resistance of the manufactured sintered body are significantly reduced due to an increase in the number of amorphous grain boundary phases filling the silicon carbide crystal grain boundaries.

Next, the above raw material is sintered at a temperature of 1500 to 1750 ° C. by pulse current heating. In this case, 15
If the temperature is lower than 00 ° C., a liquid phase melted from the sintering aid is not generated, so that a dense sintered body cannot be produced.
When the temperature is 1750 ° C. or more, abnormal grain growth of silicon carbide occurs, so that the strength is remarkably reduced. The conditions of the pulse current heating include, for example, heating in an argon gas atmosphere by adjusting the pulse current so that the rate of temperature rise is 100 to 400 ° C./min.

By the above process, the conventional method is 30 times less than the conventional method.
0 to 550 ° C lower sintering temperature, shorter time (2 minutes)
A high-strength silicon carbide sintered body having a relative density of 99.5% or more and a strength of 800 MPa or more is obtained. FIG. 1 shows an electron micrograph of the structure of the silicon carbide sintered body of the present invention obtained by adding a non-oxide liquid phase sintering aid and sintering by a pulsed current method (sintering conditions: sintering temperature; Setting time: 5 minutes, heating rate: 200 ° C./min, in an argon atmosphere). A structure suitable for improving the strength and toughness is obtained by mixing a silicon carbide crystal which has grown into a plate shape (which looks like a column in the photograph) and a fine silicon carbide crystal.

According to the method of the present invention, not only the energy cost required for sintering is reduced by lowering the sintering temperature, but also the time required for sintering is reduced to about 2 minutes. It is a sintering technology with high production efficiency and a silicon carbide sintered body with high mechanical strength because it is a sintered body consisting of fine crystal grains with grain growth of silicon carbide suppressed by low-temperature short-time sintering .

[0013]

Next, the present invention will be specifically described based on examples, but the present invention is not limited to the examples. Example 1 2.04 wt% of aluminum carbide and 0.4 wt% of boron carbide were added to fine silicon carbide powder having an average particle diameter of 30 nm produced by a CVD method, and a molded product was formed under an argon gas atmosphere. Sintering was performed at 1600 ° C. for 2 minutes by a pulse current method while applying a load of 47 MPa. It has a relative density of 99.5% and a strength of 807MP.
a was obtained.

Example 2 A compact produced in the same manner as in Example 1 was sintered at 1600 ° C. for 5 minutes by a pulse current method while applying a load of 47 MPa under an argon gas atmosphere. This was a silicon carbide sintered body having a relative density of 99.9% and a strength of 731 MPa.

Reference Example 1 A compact produced in the same manner as in Example 1 was sintered at 1800 ° C. for 1 hour by a hot press method under an argon gas atmosphere while applying a load of 40 MPa. This one is
A porous silicon carbide sintered body having pores with a relative density of 94.9% remained.

REFERENCE EXAMPLE 2 To a fine silicon carbide powder having an average particle diameter of 30 nm produced by the CVD method, 2.64 wt% of aluminum oxide and 1.76 wt% of yttrium oxide were added, and the molded article was formed in an argon gas atmosphere. Under a load of 47 MPa, sintering was performed at 1700 ° C. for 5 minutes by a pulse current method. It has a relative density of 89.4% and a strength of 408
A silicon carbide sintered body of MPa was obtained.

[0017]

According to the present invention, a non-oxide sintering aid composed of aluminum carbide and boron carbide is added to fine silicon carbide powder having an average particle size of several tens of nanometers, and pulse current is applied to heat the mixture to obtain high-strength silicon carbide. According to the present invention, a sintered body is manufactured. 1) 300 to 55 times compared with the conventional method.
High strength silicon carbide ceramics can be manufactured at 0 ° C lower sintering temperature. 2) The time required for sintering (1-2 hours in the case of the conventional resistance heating type atmosphere sintering furnace) is about 2 minutes. 3) By sintering at a low temperature for a short time, it is possible to obtain a sintered body composed of fine crystal grains in which grain growth of silicon carbide is suppressed. 4) It is possible to reduce the energy cost required for sintering. 5) It is possible to produce silicon carbide ceramics having high strength and abrasion resistance by a simple process with high production efficiency.

[Brief description of the drawings]

FIG. 1 shows an electron micrograph of a structure of a silicon carbide sintered body of the present invention obtained by adding a non-oxide liquid phase sintering aid and sintering by a pulsed current method.

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motohiro Toriyama 6-3, Chuodai, Kasugai-shi, Aichi 1 (72) Inventor Kiyoji Hirao 2-2-2 Meijo, Kita-ku, Nagoya-shi, Aichi 6-36 (72 ) Inventor Hidehiko Tanaka 1-chome, Azuma 3-chome, Tsukuba-shi, Ibaraki Pref.

Claims (2)

[Claims] 1. A non-oxide sintering aid in which aluminum carbide and boron carbide are mixed at an optimum molar ratio of 2: 1 is mixed with a non-oxide sintering aid having an average particle diameter produced by a CVD method or an organic raw material. A high-strength silicon carbide sintered body obtained by adding 1.5 to 10.0% by weight to a fine silicon carbide powder of 10 nanometers and sintering by pulse current. 2. The method according to claim 1, wherein the non-oxide-based sintering aid is added to a fine silicon carbide powder having an average particle diameter of several tens of nanometers synthesized from a CVD method or an organic raw material.
A method for producing a high-strength silicon carbide sintered body, characterized by adding 0% by weight and sintering at a temperature of 1500 to 1750 ° C. by pulse current.