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Boron carbide based sintered compact and method for preparation thereof

a boron carbide and compact technology, applied in the field of boron carbide based sintered bodies, can solve the problems of low strength, drawbacks and the inability to obtain a flexural strength of at least 600 mpa of boron carbide sintered bodies

Inactive Publication Date: 2005-03-17
NAT INST OF ADVANCED IND SCI & TECH +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

However, on the other hand, such a boron carbide sintered body has a drawback that it has low strength.
For example, K. A. Schwetz, J. Solid State Chemistry, 133, 177-81 (1997) discloses preparation of boron carbide sintered bodies by HIP treatment under various sintering conditions, but a boron carbide sintered body having a flexural strength of at least 600 MPa has not yet been obtained.
However, as mentioned above, according to the conventional methods, a boron carbide based sintered body having a high four-point flexural strength exceeding 621 MPa has not yet been obtained.
Further, a boron carbide based sintered body is hardly sinterable and accordingly, it is usually prepared by a hot press method.
This production method hinders a common application of a boron carbide based sintered body, since its production cost is high.
However, such a method is not practically preferred, since it is necessary to carry out sintering at an extremely high temperature of at least 2150° C.
Further, a boron carbide sintered body has an extremely high hardness, whereby it can hardly be processed by a usual grinding / polishing method, and further, the electric conductivity of the boron carbide sintered body is low at a level of from 10 to 300 S / m, whereby there has been a problem that the discharge processing is difficult.
As mentioned above, a boron carbide sintered body is hardly sinterable and hardly processable, and at present, it is practically used only in an extremely limited application.

Method used

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Examples

Experimental program
Comparison scheme
Effect test

examples 1 to 40

[0068] As boron carbide powders, specific boron carbide powders A, B and C having the physical properties as identified in Table 1, were employed. As a submicron-size titanium dioxide powder, one having an average particle diameter (D50 as measured by a laser diffraction scattering analyzer) of 0.3 μm and a crystal phase of rutile type, was used. Further, as a nano-size titanium dioxide powder, a spherical powder prepared by a gas phase method and having a specific surface area (BET) of 48.5 m2 / g, an average particle diameter (BET method) of 31 nm and a crystal phase of 80% anatase and 20% rutile, was used. As a carbon powder, carbon black having a specific surface area (BET) of 88.1 m2 / g and an average particle diameter (BET method) of 30 nm, was used.

TABLE 1Physical properties of boron carbide powdersB4C startingAverageMaximummaterialparticleparticleBETpowderdiameter μmdiameter μmm2 / gA0.502.421.5B0.443.315.5C0.412.322.5D0.555.718.7E1.205.98.6

[0069] To the boron carbide powder, 1...

example 5

[0075] To a boron carbide powder I having the physical properties as identified in Table 3, 20 mol% of a chromium diboride powder having an average particle diameter (D50) of 3.5 μm was blended, and using a methanol solvent, the blend was mixed by a planetary ball mill made of SiC at a rotational speed of 275 rpm for 1 hour. The slurry was dried by an evaporator and further dried at 150° C. for 24 hours, and then it was sieved through a sieve of 250 mesh to obtain a boron carbide-chromium diboride mixed powder.

[0076] This powder was molded in a mold under 20 MPa, followed by CIP molding under 200 MPa to obtain a molded product. The molded product was put into a graphite container and placed in a resistance heating type firing furnace. Heating was carried out at a temperature-raising rate of 40° C. / min while vacuuming to a pressure of from 2.0×10−1 to 2.0×10−2 Pa by means of a diffusion pump. When the temperature reached 1000° C., vacuuming was terminated, and Ar gas was introduced,...

example 6

[0079] To a boron carbide powder II having the physical properties as identified in Table 3, 20 mol% of a chromium diboride powder having an average particle diameter (D50) of 3.5 μm was blended, and using a methanol solvent, the blend was mixed by a planetary ball mill made of SiC at a rotational speed of 275 rpm for 1 hour. The slurry was dried by an evaporator and further dried at 150° C. for 24 hours, whereupon it was sieved through a sieve of 250 mesh to obtain a boron carbide-chronium diboride mixed powder.

[0080] This powder was molded in a mold under 20 MPa, followed by CIP molding under 200 MPa to obtain a molded product. The molded product was put into a graphite container and placed in a resistance heating type firing furnace. Heating was carried out at a temperature-raising rate of 40° C. / min while vacuuming to a pressure of from 2.0×10−1 to 2.0×10−2 Pa by means of a diffusion pump. When the temperature reached 1000° C., vacuuming was terminated, and Ar gas was introduce...

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Abstract

A boron carbide based sintered body having a four-point flexural strength of at least 400 MPa and a fracture toughness of at least 2.8 MPa·m1 / 2, which has the following two preferred embodiments. (1) A boron carbide-titanium diboride sintered body obtained by sintering a mixed powder of a B4C powder, a TiO2 powder and a C powder while reacting them under a pressurized condition and comprising from 95 to 70 mol % of boron carbide and from 5 to 30 mol % of titanium diboride, wherein the boron carbide has a maximum particle diameter of at most 5 μm. (2) A boron carbide-chromium diboride sintered body containing from 10 to 25 mol % of CrB2 in B4C, wherein the sintered body has a relative density of at least 90%, boron carbide particles in the sintered body have a maximum particle diameter of at most 100 μm, and the abundance ratio (area ratio) of boron carbide particles of from 10 to 100 μm to boron carbide particles having a particle diameter of at most 5 μm, is from 0.02 to 0.6.

Description

TECHNICAL FIELD [0001] The present invention relates to a boron carbide based sintered body, such as a boron carbide-titanium diboride sintered body or a boron carbide-chromium diboride sintered body, having high density, four-point flexural strength and fracture toughness, and a process for its production. BACKGROUND ART [0002] In general, a boron carbide sintered body is expected to have a wide range of applications as a material having a light weight and high hardness and being excellent in abrasion resistance or corrosion resistance. At present, it is used, for example, for a sandblast nozzle, a wire drawing die or an extrusion die. However, on the other hand, such a boron carbide sintered body has a drawback that it has low strength. For example, K. A. Schwetz, J. Solid State Chemistry, 133, 177-81 (1997) discloses preparation of boron carbide sintered bodies by HIP treatment under various sintering conditions, but a boron carbide sintered body having a flexural strength of at ...

Claims

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Application Information

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IPC IPC(8): C04B35/563
CPCB82Y30/00C04B2235/96C04B35/64C04B35/645C04B2235/3231C04B2235/3232C04B2235/3813C04B2235/3821C04B2235/422C04B2235/424C04B2235/528C04B2235/5409C04B2235/5436C04B2235/5445C04B2235/5454C04B2235/604C04B2235/656C04B2235/6562C04B2235/658C04B2235/6581C04B2235/661C04B2235/77C04B2235/786C04B2235/80C04B2235/94C04B35/563
Inventor HIRAO, KIYOSHISAKAGUCHI, SHUJIYAMAUCHI, YUKIHIKOKANZAKI, SHUZOYAMADA, SUZUYA
Owner NAT INST OF ADVANCED IND SCI & TECH
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