JP2001122665A - Method for manufacturing boron carbide atmospheric sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a boron carbide atmospheric sintered compact which is highly dense, has high bending strength and dies not allow sintering assistant components to remain. SOLUTION: This method for manufacturing the boron carbide atmospheric sintered compact consists in heating up the preform of boron carbide powder at a heating up temperature of 5 to l00 deg.C/hr from 2,150 to 2,200 deg.C in atmospheric sintering of the preform in a nonoxidizing atmosphere, and then raising the temperature up to the final sintering temperature exceeding 2,200 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a high-density and high-flexural strength boron carbide atmospheric pressure sintered body.

[0002]

2. Description of the Related Art Boron carbide sintered bodies are high hardness and light weight, and are used for blast nozzles, brushing materials (grinding stones), wear-resistant machine parts, etc. by taking advantage of their excellent wear resistance. ing.

Conventionally, to produce a boron carbide sintered body,
Although the hot press method is widely used, it is not suitable for production of large-sized or complicated-shaped products or continuous production. One example is described in JP-A-8-12434 and JP-A-11-11.
157935. However, in these normal pressure sintering methods, since a sintering aid such as aluminum is used, the sintering aid component remains in the troublesome mixing operation and the obtained normal pressure sintered body, In addition, there is a problem that the homogeneity of bending strength is poor.

Further, when a boron carbide atmospheric pressure sintered body is manufactured in accordance with the above-mentioned prior art embodiment, a relatively good densified product is manufactured, but the outer skin (outer peripheral portion) is first made dense. Therefore, the internal pores could not be completely removed, and a sufficiently high densified product could not be obtained.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above, and an object of the present invention is to provide a high-density and high-flexural strength boron carbide sintered body without using a sintering aid. It is manufactured by normal pressure sintering.

[0006]

That is, the present invention provides a method for sintering a preformed body of boron carbide powder at normal pressure in a non-oxidizing atmosphere at a temperature rising rate between 2150 ° C and 2200 ° C. A method for producing a normal-pressure boron carbide sintered body, characterized in that after raising the temperature at 5 to 100 ° C./hr, the temperature is further raised to a final sintering temperature exceeding 2200 ° C.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail.

As the boron carbide powder used in the present invention, commercially available products are sufficient, but among others, the average particle size is 0.5 to 2 μm,
In particular, it is 1.0 μm or less, and the specific surface area is 5 m ² / g.
As described above, it is particularly preferable that the powder is a fine powder of 15 m ² / g or more. As a commercial product, Stark Co., Ltd. (HCS
“HS grade” manufactured by Starck Corporation.

The preformed body of the boron carbide powder is preferably formed by first forming the boron carbide powder in a mold and then performing CIP (cold isostatic pressing). The primary molding is performed at a pressure sufficient to maintain the shape, and is usually 4 to 10 MPa. Further, the CIP molding is preferably performed under a high pressure, and an example is 150 to 300 MPa. It is enough.

The sintering is performed by using a rare gas such as argon or helium,
This is performed in a non-oxidizing atmosphere such as carbon monoxide and hydrogen. Among them, an argon atmosphere is preferable from the viewpoint of handling properties and safety.

In the present invention, in a non-oxidizing atmosphere,
Sintering is performed at a final sintering temperature exceeding 200 ° C., but it is important that when the ambient temperature is between 2150 ° C. and 2200 ° C., the heating rate is 5 to 100 ° C./hr, preferably 10 to 75 ° C. / Hr. Heating rate is 5 ℃
If it is less than / hr, it takes too much time to produce a sufficiently high densified product, and if it exceeds 100 ° C / hr, the above-mentioned sintering preceding sintering becomes remarkable, and a sufficiently high densified product is produced. You will not be able to do it. Temperature 2150 ° C to 2200
It is particularly preferred that the temperature rise between ℃ is carried out at a constant speed.

In the present invention, there are no particular restrictions on the rate of temperature rise until the temperature reaches 2150 ° C. and the rate of temperature rise until the final sintering temperature exceeds 2200 ° C. For example, for the former, 400 to 1200 ° C./h
r, the latter can be heated at a rate of 5 to 100 ° C./hr.

The final sintering temperature in the present invention is 2
It is preferable that the temperature be any temperature from 200 ° C. to 2300 ° C., and particularly preferably 2220 to 2250 ° C.
If the final sintering temperature exceeds 2300 ° C., abnormal grain growth is likely to occur, which may cause a decrease in strength.

[0014]

The present invention will be described more specifically with reference to examples and comparative examples.

Examples 1 to 3 Comparative Examples 1 to 3 60 g of boron carbide powder ("HS grade" manufactured by H. C. Starck) was placed in a cylinder having a diameter of 52 mm, and pressurized with a cylinder at 4.9 MPa to perform primary press. A molded body was manufactured. Next, the resultant was subjected to a surface pressure of 265 MPa by CIP (cold isostatic press) to form a cylindrical preform. This was put in a graphite crucible, and a sintering furnace (FVS-R-80 / 80, manufactured by Fuji Electric Co., Ltd.) was placed in an argon atmosphere at normal pressure.
Sintering was performed under the conditions shown in Table 1 by FRET-20).
After the temperature reached the final sintering temperature, the temperature control power was turned off and the product was naturally cooled in an argon atmosphere.

The density of the obtained sintered body under normal pressure was measured by Archimedes method, and 3 × 4 × 36 mm
Was cut out, and the three-point bending strength was measured in accordance with JISR1601. Table 1 shows the results.

[0017]

[Table 1]

[0018]

According to the present invention, a normal-pressure sintered body of boron carbide having high density and high bending strength and having no sintering aid component remaining can be obtained.

Claims (1)

[Claims] When sintering a preformed body of boron carbide powder at normal pressure in a non-oxidizing atmosphere, the temperature was raised between 2150 ° C. and 2200 ° C. at a rate of 5-100 ° C./hr. Thereafter, the temperature is further increased to a final sintering temperature exceeding 2200 ° C., thereby producing a boron carbide normal pressure sintered body.