Densification and characterization of rapid carbothermal synthesized boron carbide

Toksoy, Muhammet Fatih; Rafaniello, William; Xie, Kelvin Y.; Ma, Luoning; Hemker, Kevin J.; Haber, Richard A.

doi:10.1111/ijac.12654

Cited by 16 publications

(9 citation statements)

References 46 publications

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“…Twins were placed on the grain edges, as seen in Figure , which indicated modification generated twins around the particles. This is an agreement from previous work which showed RCR synthesized powders has higher twin density and existed twins increased the hardness of boron carbide . Modification of commercial boron carbide improved hardness results by removing free carbon, changing the morphology and introducing more twin structures to dense samples, despite increased particle size.…”

Section: Resultssupporting

confidence: 91%

Modification of commercial boron carbide powder using Rapid Carbothermal Reduction

Toksoy

Haber

2018

Int J Applied Ceramic Tech

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Non‐uniform morphology and existence of free carbon are two main problems for commercial boron carbide powders. This work proposes a method for eliminating free carbon and changing the morphology of commercial powders using Rapid Carbothermal Reduction (RCR) process. Free carbon is eliminated from commercial boron carbide powders and morphology is evolved to less angular shapes with limited particle size growth. Commercial and modified powders were densified by Spark Plasma Sintering at 1900°C with 0, 5, and 20 minutes dwell. Despite the particle size growth, modified boron carbide powders reached >99% TD with shorter dwell times compared with commercial starting powders. Improved microhardness observed with dense modified samples as a result of enhanced morphology and increased twinning.

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Section: Resultssupporting

confidence: 91%

Modification of commercial boron carbide powder using Rapid Carbothermal Reduction

Toksoy

Haber

2018

Int J Applied Ceramic Tech

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“…Binary powder mixtures of boron carbide and SiB 6 with various ratios (Table 1) were studied in order to densify and dope boron carbide with maximum Si concentration (at sintering temperature) in a single step. In house synthesized boron carbide powder [16,17] was mixed with SiB 6 powder and densified at 1600 °C for 4 hours. The reaction of the precursor powders resulted in a densified material comprised of phases consistent with those predicted from the phase equilibria in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…Boron carbide was synthesized by using rapid carbothermal reduction (RCR) process discussed in previous studies [16,17]. This process aided in synthesizing fine particles of boron carbide free of particulate carbon.…”

Section: Methodsmentioning

confidence: 99%

“…B 12 icosahedra serve as a signature to this class of compounds. Boron carbide is one of the most important members of this class, owing to its extremely high hardness (30 GPa), high Hugoniot elastic limit (15)(16)(17)(18)(19)(20), and still a low theoretical density (~ 2.52 g/cm 3 ) [1]. It consists of a three-atom chain, typically a C-B-C chain in addition to B 12 or B 11 C p icosahedra [1,2].…”

Section: Introductionmentioning

confidence: 99%

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Locating Si atoms in Si-doped boron carbide: A route to understand amorphization mitigation mechanism

et al. 2018

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The well-documented formation of amorphous bands in boron carbide (B 4 C) under contact loading has been identified in the literature as one of the possible mechanisms for its catastrophic failure. To mitigate amorphization, Si-doping was suggested by an earlier computational work, which was further substantiated by an experimental study. However, there have been discrepancies between theoretical and experimental studies, about Si replacing atom/s in B 12 icosahedra or the C-B-C chain. Dense single phase Si-doped boron carbide is produced through a conventional scalable route. A powder mixture of SiB 6 , B 4 C, and amorphous boron is reactively sintered, yielding a dense Si-doped boron carbide material.A combined analysis of Rietveld refinement on XRD pattern coupled with electron density difference Fourier maps and DFT simulations were performed in order to investigate the location of Si atoms in boron carbide lattice. Si atoms occupy an interstitial position, between the icosahedra and the chain. These Si atoms are bonded to the chain end C atoms and result in a kinked chain. Additionally, these Si atoms are also bonded to the neighboring equatorial M A N U S C R I P T A C C E P T E D ACCEPTED MANUSCRIPT2 B atom of the icosahedra, which is already bonded to the C atom of the chain, forming a bridge like geometry. Si atoms are found to reside around the chain, resulting in a kinked chain. These Si atoms lie close to boron atom of the neighboring icosahedra. Owing to this bonding, distance suggests weak bonding and Si is anticipated to stabilize the icosahedra through electron donation, which is expected to help in mitigating stress-induced amorphization. Possible supercell structures are suggested along with the most plausible structure for Si-doped boron carbide.

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“…The B 12 C 3 (i.e., B 4 C) samples were produced at Rutgers University by consolidating B 4 C powders (previously synthesized by a rapid carbothermal reduction method) via spark plasma sintering under 50 MPa for 5 min at nominal temperatures exceeding 1900°C, as described in [9]. The B-rich B 13 C 2 sample was produced at Ceradyne by hot-pressing H. C. Starck grade C amorphous boron and ESK Tetrabor grade 10 μm B 4 C powders at 1900-2200°C and 13.8 MPa for approximately an hour [10].…”

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confidence: 99%

Atomic-Level Understanding of “Asymmetric Twins” in Boron Carbide

Xie

Toksoy

et al. 2015

Phys. Rev. Lett.

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Recent observations of planar defects in boron carbide have been shown to deviate from perfect mirror symmetry and are referred to as "asymmetric twins." Here, we demonstrate that these asymmetric twins are really phase boundaries that form in stoichiometric B 4 C (i.e., B 12 C 3 ) but not in B 13 C 2 . TEM observations and ab initio simulations have been coupled to show that these planar defects result from an interplay of stoichiometry, atomic positioning, icosahedral twinning, and structural hierarchy. The composition of icosahedra in B 4 C is B 11 C and translation of the carbon atom from a polar to equatorial site leads to a shift in bonding and a slight distortion of the lattice. No such distortion is observed in boron-rich B 13 C 2 because the icosahedra do not contain carbon. Implications for tailoring boron carbide with stoichiometry and extrapolations to other hierarchical crystalline materials are discussed. DOI: 10.1103/PhysRevLett.115.175501 PACS numbers: 61.72.Nn, 61.50.Ah, 61.50.Nw In crystalline materials the formation of twin boundaries, which separate adjacent crystallographic regions whose lattices are related by mirror symmetry, have been associated with both crystal growth and deformation processes. Because of their inherent symmetry, twin boundaries are usually coherent, have low interfacial energy, and are relatively stable as compared to general grain boundaries of random misorientation [1]. The formation of twins and the presence of twin boundaries can significantly affect the plasticity and strength of materials. The latter is demonstrated by the development of twinning-induced steels [2], recent observations that nanotwinned Cu is ten times stronger than coarse-grained Cu [3], and by reports that nanotwinned cubic BN is harder than diamond [4,5]. In this light, understanding how twins are formed and developing effective strategies for incorporating twin boundaries into polycrystalline microstructures offer an attractive approach for enhancing the mechanical response of metals and ceramics.Twin boundaries in relatively simple systems, such as fcc, bcc, and hcp, can be easily identified with the unambiguous twin planes and misorientation angles. However, as the crystal structure becomes more complicated and exhibits secondary and tertiary structural hierarchy (e.g., boron carbide [6]), the matrix-twin relationship can be complex. Recently, Fujita et al. discovered a new type of planar defect in boron carbide and characterized it with spherical-aberration-corrected scanning transmission electron microscopy (STEM) [7]. At first glance their highresolution STEM images suggest that the planar defects are conventional twin boundaries, but closer investigation reveals that the lattices do not mirror each other exactly, the angle between the (100) and (010) planes differs by ∼2°o n either side of the boundary. Upon realizing the loss of mirror symmetry, the authors named these planar defects "asymmetric twins" and stated that their formation mechanisms were not fully understood. At this poi...

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Densification and characterization of rapid carbothermal synthesized boron carbide

Cited by 16 publications

References 46 publications

Modification of commercial boron carbide powder using Rapid Carbothermal Reduction

Modification of commercial boron carbide powder using Rapid Carbothermal Reduction

Locating Si atoms in Si-doped boron carbide: A route to understand amorphization mitigation mechanism

Atomic-Level Understanding of “Asymmetric Twins” in Boron Carbide

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