US4524138A
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US
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Substantially pore-free sintered polycrystalline articles of α-silicon carbide, boron carbide and free carbon and process for their manufacture
Assignee: Elektroschmelzwerk Kempten GmbH
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Filing: 1983-05-05
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Granted: 1985-06-18
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Expires: 2003-05-05
Abstract
Abstract The invention provides substantially pore-free sintered polycrystalline articles comprising α-silicon carbide, boron carbide and free carbon, the quantitative proportions of which, in percent by weight, are defined by the trapezoidal area having, in the ternary system B/Si/C of FIG. 1 the corner points a=89.0% B 4 C, 9.9% α-Sic, 1.1% C b=9.9% B 4 C, 89.0% α-SiC, 1.1% C c=9.0% B 4 C, 81.0% α-Sic, 10.0% C d=81.0% B 4 C, 9.0% α-SiC, 10.0% C The articles have a density of at least 99% of the theoretical density, an average structural grain size of less than 20 μm and a 4-point flexural strength of at least 400 N/mm 2 . They are manufactured from fine-grained mixtures of α-silicon carbide, boron carbide, carbon and/or material that can be coked to form carbon, in a two-stage sintering process. In the first stage, green bodies preshaped from the powder are subjected to pressureless sintering to a density of at least 95% TD at from 1950° to 2150° C. In the second stage, the sintered articles are subjected to a post-densification to a density of at least 99% TD, by isostatic hot pressing, without encapsulating, at from 1850° to 2150° C. in a high-pressure autoclave under a gas pressure of at least 10 MPa.
Inventors
- 👤 Karl A. Schwetz
- 👤 Klaus Reinmuth
- 👤 Klaus Hunold
- 👤 Franz Isemann
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-26 20:51
CPC Classifications
C; C04; C04B; C04B35/00; C04B35/515; C04B35/56; C04B35/563; C04B35/565; C04B35/575; C04B35/5755; C04B35/622; C04B35/64; C04B35/645
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
165 words
A substantially pore-free sintered polycrystalline article consisting essentially of α-silicon carbide, boron carbide and free carbon, the proportions in percent by weight, are defined by the trapezoidal area having, in the ternary system B/Si/C of FIG. 1, the corner points a=89.0% B 4 C, 9.9% α-SiC, 1.1% C b=9.9% B 4 C, 89.0% α-SiC, 1.1% C c=9.0% B 4 C, 81.0% α-SiC, 10.0% C d=81.0% B 4 C, 9.0% α-SiC 10.0% C; the article having a homogeneous microstructure and a density of at least 99% of the theoretical density, an average structural grain size of less than 20 μm, and a 4-point flexural strength of at least 400 N/mm 2 said article being produced from fine-grained mixtures of α-silicon carbide, boron carbide, and a carbon source selected from carbon, an organic material that can be coked to form carbon, and mixtures thereof, by pressureless sintering and subsequent post-densification of the resulting sintered article by hot isostatic pressure sintering using an inert gas as pressure-transfer medium.
Claim 2
Dependent Claim
165 words
A substantially pore-free sintered polycrystalline article consisting essentially of α-silicon carbide, boron carbide and free carbon, the proportions in percent by weight, are defined by the trapezoidal area having, in the ternary system B/Si/C of FIG. 1, the corner points a=89.0% B 4 C, 9.9% α-SiC, 1.1% C b=9.9% B 4 C, 89.0% α-SiC, 1.1% C c=9.0% B 4 C, 81.0% α-SiC, 10.0% C d=81.0% B 4 C, 9.0% α-SiC 10.0% C; the article having a homogeneous microstructure and a density of at least 99% of the theoretical density, an average structural grain size of less than 20 μm, and a 4-point flexural strength of at least 400 N/mm 2 said article being produced from fine-grained mixtures of α-silicon carbide, boron carbide, and a carbon source selected from carbon, an organic material that can be coked to form carbon, and mixtures thereof, by pressureless sintering and subsequent post-densification of the resulting sintered article by hot isostatic pressure sintering using an inert gas as pressure-transfer medium.
Claim 3
Dependent Claim
20 words
A sintered article according to claim 1, which contains less than about 1% by weight of metallic and non-metallic impurities.
Claim 4
Dependent Claim
174 words
A process for the manufacture of sintered articles which comprises: mixing homogeneously fine particulate α-silicon carbide and fine particulate boron carbide, in a weight ratio of SiC:B 4 C of from 90:10 to 10:90, with a carbon source selected from fine particulate carbon, an organic material that can be coked at temperatures up to 1000° C. to from carbon and mixtures thereof in an amount corresponding to from 1.5 to 12% by weight of free carbon; shaping the mixture to form green bodies having a density of at least 50% of the theoretical density; pressureless sintering the green bodies at a temperature of from 1950° to 2150° C. in the presence of a protective gas atmosphere or in vacuo, to form sintered articles having a density of at least 95% of the theoretical density; and post-densifying sintered articles to a density of at least 99% of the theoretical density, by isostatic hot pressure sintering, without encapsulating at a temperature of from 1850° to 2150° C. under a gas pressure of at least 10 MPa.
Claim 5
Dependent Claim
174 words
A process for the manufacture of sintered articles which comprises: mixing homogeneously fine particulate α-silicon carbide and fine particulate boron carbide, in a weight ratio of SiC:B 4 C of from 90:10 to 10:90, with a carbon source selected from fine particulate carbon, an organic material that can be coked at temperatures up to 1000° C. to from carbon and mixtures thereof in an amount corresponding to from 1.5 to 12% by weight of free carbon; shaping the mixture to form green bodies having a density of at least 50% of the theoretical density; pressureless sintering the green bodies at a temperature of from 1950° to 2150° C. in the presence of a protective gas atmosphere or in vacuo, to form sintered articles having a density of at least 95% of the theoretical density; and post-densifying sintered articles to a density of at least 99% of the theoretical density, by isostatic hot pressure sintering, without encapsulating at a temperature of from 1850° to 2150° C. under a gas pressure of at least 10 MPa.
Claim 6
Dependent Claim
23 words
A process according to claim 3, wherein the silicon carbide, has a specific surface area of from 2 to 50 m 2 /g.
Claim 7
Dependent Claim
37 words
A process according to claim 3, wherein the boron carbide powder, has a boron:carbon atomic ratio within the range of from 3.8 to 4.2 and a specific surface area of from 3 to 60 m 2 /g.
Claim 8
Dependent Claim
32 words
A process according to claim 3, wherein the carbon source is carbon black or colloidal graphite having a specific surface area within the range of from 10 to 400 m 2 /g.
Claim 9
Dependent Claim
22 words
A process according to claim 3, wherein the carbon source is selected from a phenol-formaldehyde condensation product, coal-tar pitch and mixtures thereof.
Claim 10
Dependent Claim
39 words
A process according to claim 3, wherein, prior to the pressureless sintering, the preshaped green body is preheated in the presence of an inert or reducing atmosphere to a temperature within the range of from 100° to 1500° C.
Claim 11
Dependent Claim
37 words
A process according to claim 3, wherein the preshaped green body is pressureless sintered in a protective gas atmosphere at a pressure of approximately 0.1 MPa or in vacuo at a pressure of less than 5000 Pa.
Claim 12
Dependent Claim
33 words
A process according to claim 3, wherein sintered articles are post-densified, without a capsule at a temperature of less than about 2050° C. under a gas pressure of from 150 to 250 MPa.
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| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
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| 3.5 Years (Year 4) | 1988-06-17 | 1988-12-17 | 1989-06-18 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1992-06-17 | 1992-12-17 | 1993-06-18 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1996-06-17 | 1996-12-17 | 1997-06-18 | $7700.00 | Window Closed / Lapsed |