Grain boundary structures in silicon carbide: Verification of the extended boundary concept

Tsurekawa, Sadahiro; Nitta, S.; Nakashima, Hideharu; Yoshinaga, Hideo

doi:10.1007/bf00203983

Cited by 16 publications

(3 citation statements)

References 10 publications

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“…Identification of GB atoms is not unique and the centrosymmetry analysis provides an approximate upper bound for GB thickness. Typical experimental values of GB thickness of SiC range from 0.5 to 3 nm . Figure shows the nc‐SiC sample along with the grain size distribution.…”

Section: Methodsmentioning

confidence: 99%

Plasticity‐Controlled Friction and Wear in Nanocrystalline SiC

2014

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Wear resistance of ceramics can be improved by suppressing fracture, which can be accomplished either by decreasing the grain size or by reducing the size of the deformation zone. We have combined these two strategies with the goal of understanding the atomistic mechanisms underlying the plasticity-controlled friction and wear in nanocrystalline (nc) silicon carbide (SiC). We have performed molecular dynamics simulations of nanoscale wear on nc-SiC with 5 nm grain diameter with a nanoscale cutting tool. We find that grain-boundary (GB) sliding is the primary deformation mechanism during wear and that it is accommodated by heterogeneous nucleation of partial dislocations, formation of voids at the triple junctions, and grain pull-out. We estimate the stresses required for heterogeneous nucleation of partial dislocations at triple junctions and shear strength of GBs. Pile up in nc-SiC consists of grains that were pulled out during deformation. We compare the wear response of nc-SiC to single-crystal (sc) SiC and show that scratch hardness of nc-SiC is lower than that of sc-SiC. Our results demonstrate that the higher scratch hardness in sc-SiC originates from nucleation and motion of dislocations, whereas nc-SiC is more pliable due to additional mechanism of deformation via GB sliding.

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Section: Methodsmentioning

confidence: 99%

Plasticity‐Controlled Friction and Wear in Nanocrystalline SiC

2014

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“…However, the arrows stop ϳ0.3-0.5 nm before they intersect observed disordered structure at the interface is thought to provide an easy diffusion path during sintering, and the densithe interface, suggesting the presence of an extended grain boundary, as observed in sintered, BϩC-doped SiC. 37 This fication of pure OHAp is believed to be governed by grainboundary diffusion. Studying the influence of the initial particle means that commonly, at least in this low-temperature-sintered OHAp material, no interface was found where both adjacent size on the densification rate yielded that grain-boundary diffusion is the limiting factor for OHAp densification.…”

Section: (1) Convergent-beam Electron Diffraction (Cbed) Studiesmentioning

confidence: 95%

High‐Resolution Electron Microscopy and Convergent‐Beam Electron Diffraction of Sintered Undoped Hydroxyapatite

Kleebe

Brs

Bernache-Assolant

et al. 1997

Journal of the American Ceramic Society

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Transmission electron microscopy (TEM) was used toreported to decompose to tricalcium phosphate, Ca 3 (PO 4 ) 2 , and tetracalcium phosphate, Ca 4 O(PO 4 ) 2 , according to 16-21 characterize the microstructure of sintered undoped hydroxyapatite (OHAp). Conventional TEM observations were accomCa 10 (PO 4 ) 6 (OH) 2 → 2Ca 3 (PO 4 ) 2 ϩ Ca 4 O(PO 4 ) 2 ϩ H 2 O panied by high-resolution electron microscopy (HREM) and convergent-beam electron diffraction (CBED) studies. CBEDWhen sintering under moisture, OHAp also can be stable at analysis enabled the determination of the space group of the temperatures Ͼ1300ЊC, indicating that the sintering atmoOHAp, P6 3 /m. Densification of the material was performed sphere has a strong influence on the decomposition temperaby pressureless sintering at 1250؇C for 30 min. The undoped ture. 21 According to van Landuyt et al., 16 temperatures even sample was comprised of apatite as the only crystalline higher than 1300ЊC can be used during densification without phase, in addition to a small volume fraction (4%) of closed the decomposition of OHAp when the holding time is mainporosity. In general, the observed microstructure was tained below the incubation time for decomposition. The maxihomogeneous and consisted of equiaxed apatite grains with mum temperature-time cycle applicable without an appreciable an average grain diameter of }1-2 m. No indication of a amount of phase transformation is 1450ЊC for 3 h; at 1500ЊC, residual amorphous phase, which may have formed during the decomposition of OHAp has been shown to start after ϳ1 h. sintering, was observed at multigrain junctions. HREMGrain boundaries in different ceramic materials, 22-27 as studies on grain boundaries also revealed that no intergranwell as ceramic-metal interfaces, 28 have been studied by highular glass film was present along two-grain junctions, indiresolution electron microscopy (HREM). Using the same techcating that densification proceeded without a liquid phase.nique, several structural defects have been recently detected A slightly disordered region at the interfaces was observed, inside human-tooth-enamel OHAp crystals. 29,30 In this paper, suggesting an extended grain-boundary structure.the nanostructure of an undoped (without the addition of sintering aids) sintered OHAp material also is characterized by HREM and convergent-beam electron diffraction (CBED). The

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“…SiC that has been doped with boron and carbon (B,C-SiC) and fabricated using solid-phase sintering 15 is known to have no intergranular glassy phase. [16][17][18] However, fabrication of a nanocrystalline SiC via solid-phase sintering is difficult, because solid-phase sintering requires a higher sintering temperature than does liquid-phase sintering. To fabricate a nanocrystalline SiC, we must keep the sintering temperature as low as possible and inhibit grain growth during sintering.…”

Section: Introductionmentioning

confidence: 99%

Superplasticity of Silicon Carbide

Shinoda

Nagano²,

Gu³

et al. 1999

Journal of the American Ceramic Society

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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.

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Grain boundary structures in silicon carbide: Verification of the extended boundary concept

Cited by 16 publications

References 10 publications

Plasticity‐Controlled Friction and Wear in Nanocrystalline SiC

Plasticity‐Controlled Friction and Wear in Nanocrystalline SiC

High‐Resolution Electron Microscopy and Convergent‐Beam Electron Diffraction of Sintered Undoped Hydroxyapatite

Superplasticity of Silicon Carbide

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