Superplasticity of Silicon Carbide

Abstract

Nanocrystalline silicon carbide that was doped with boron and carbon (B,C-SiC) and contained 1 wt% boron additive and 3.5 wt% free carbon was fabricated using hot isostatic pressing under an ultrahigh pressure of 980 MPa and a temperature of 1600°C. The average grain size of the material was 200 nm. The tensile deformation behavior of this material at elevated temperature was investigated. The nanocrystalline B,C-SiC exhibited superplastic elongation of >140% at a temperature of 1800°C. High-resolution transmission electron microscopy observation and electron energy-loss spectroscopy analysis revealed that this nanocrystalline SiC did not have a secondary glassy phase at the grain boundary and the grain boundary had a strong covalent nature, which means that an intergranular glassy phase was not necessary to obtain superplasticity of covalent materials.

Development of Creep-Resistant Tungsten Carbide Copper Cemented Carbide

“…14) We have also shown that segregation of boron at grain boundaries in SiC promoted grain growth and/or deformation at elevated temperatures. [15][16][17] This was due to the fact that grainboundary diffusion of silicon is significantly enhanced in the B 4 C-like local structure of the grain boundary in borondoped SiC, because the diffusion coefficient of silicon atoms in B 4 C is three orders of magnitude higher than that in SiC. In the same way, the diffusion of tungsten and carbon at the WC/WC grain boundaries is thought to be enhanced by the intergranular segregation of cobalt.…”

Electron Energy-loss Spectroscopy Characterization of ∼1 nm-thick Amorphous Film at Grain Boundary in Si-based Ceramics

“…Boron-doped SiC nano-crystalline material is such an example, which exhibited superplasticity without the help of amorphous films. 21,22,27) Nevertheless, amorphous films were found in liquid-phase sintered (LPS) -SiC ceramics, and they did contribute to high temperature deformation by promoting the grain sliding. 23,28) These films are not as stable as in Si 3 N 4 since they change substantially and may even disappear after deformation at high temperatures.…”

“…This is in strong contrast with B-doped nano-crystalline SiC ceramics where the deformation times were 1-2 orders longer. 23,27) By measuring excess of additive segregation before and after the tensile and compressive deformations using EELS, 11) changes in the amorphous films can be understood. As shown in Fig.…”

Nanostructured silicon carbide ceramics fabricated through liquid-phase sintering by spark plasma sintering

“…Additionally, nanostructured SiC ceramics are expected to enhance creep and superplastic characteristics in the application to structural applications. 15) To fabricate fully dense nanostructured SiC ceramics, nanosized or nanocrystalline SiC powders should be densified with appropriate sintering additives to minimize the grain growth during sintering. 16)18) The sintering temperature to densify SiC powder compact can be decreased in the presence of a liquid phase formed from oxide additives.…”