Thermochemistry and Kinetics

Weimer, Alan W.

doi:10.1007/978-94-009-0071-4_3

Cited by 54 publications

(53 citation statements)

References 61 publications

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“…22,23 B 4 C bodies are produced from powders that are densified by pressure-assisted sintering techniques such as hot-pressing or spark-plasma sintering. [24][25][26][27] Metallic impurities are common in B 4 C because the powders are produced by grinding and milling B 4 C "ingots" (formed by reacting B 2 O 3 and C in an arc-melting furnace) using steel implements. 27 Even with acid washing, metallic impurities remain.…”

Section: Introductionmentioning

confidence: 99%

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Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Yang

Coleman

LaSalvia

et al. 2018

ACS Appl. Mater. Interfaces

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Abstract:The role that grain boundaries (GB) can play on mechanical properties has been studied extensively for metals and alloys. However, for covalent solids such as boron carbide (B 4 C), the role of GB on the inelastic response to applied stresses is not well established. We consider here the unusual ceramic, boron carbide (B 4 C), which is very hard and lightweight but exhibits brittle impact behavior. We used quantum mechanics (QM) simulations to examine the mechanical response in atomistic structures that model GBs in B 4 C under pure shear and also with biaxial shear deformation that mimics indentation stress conditions. We carried out these studies for two simple GB models including also the effect of adding Fe atoms (possible sintering aid and/or impurity) to the GB. We found that the critical shear stresses of these GB models are much lower than for crystalline and twinned B 4 C. The two GB models lead to different interfacial energies. The higher interfacial energy at the GB only slightly decreases the critical shear stress but dramatically increases the critical failure strain. Doping the GB with Fe decreases the critical shear stress of at the boundary by 14% under pure shear deformation. In all GBs studied here, failure arises from deconstructing the icosahedra within the GB region under shear deformation. We find that Fe dopant interacts with icosahedra at the GB to facilitate this deconstruction of icosahedra. These results provide significant insight for designing polycrystalline B 4 C with improved strength and ductility.

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Section: Introductionmentioning

confidence: 99%

“…28 In addition, B 4 C is usually experimentally synthesized using steel implements. [24][25][26][27] Finally, we used quantum mechanics (QM) simulations to examine the mechanical response of all three GB models under both pure shear and biaxial shear deformation.…”

Section: Introductionmentioning

confidence: 99%

Shear-Induced Brittle Failure along Grain Boundaries in Boron Carbide

Yang

Coleman

LaSalvia

et al. 2018

ACS Appl. Mater. Interfaces

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“…They include porous amorphous carbon films, silicon carbide (SiC), silicon nitride, and aluminum nitride and have many important applications. 1 SiC, for example, 2 has high fracture toughness and withstands high temperatures and has many applications, ranging from electronic devices and sensors, to structural materials, automobile parts, and thin filament pyrometry. Biocompatibility, resistance to acidic and alkali environments, and chemical inertness have also made SiC a promising material for fabrication of nanoporous membranes 3 for separation of gas and liquid mixtures in harsh environments.…”

Section: Introductionmentioning

confidence: 99%

First principles-based multiparadigm, multiscale strategy for simulating complex materials processes with applications to amorphous SiC films

Naserifar

Goddard

Tsotsis

et al. 2015

The Journal of Chemical Physics

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Progress has recently been made in developing reactive force fields to describe chemical reactions in systems too large for quantum mechanical (QM) methods. In particular, ReaxFF, a force field with parameters that are obtained solely from fitting QM reaction data, has been used to predict structures and properties of many materials. Important applications require, however, determination of the final structures produced by such complex processes as chemical vapor deposition, atomic layer deposition, and formation of ceramic films by pyrolysis of polymers. This requires the force field to properly describe the formation of other products of the process, in addition to yielding the final structure of the material. We describe a strategy for accomplishing this and present an example of its use for forming amorphous SiC films that have a wide variety of applications. Extensive reactive molecular dynamics (MD) simulations have been carried out to simulate the pyrolysis of hydridopolycarbosilane. The reaction products all agree with the experimental data. After removing the reaction products, the system is cooled down to room temperature at which it produces amorphous SiC film, for which the computed radial distribution function, x-ray diffraction pattern, and the equation of state describing the three main SiC polytypes agree with the data and with the QM calculations. Extensive MD simulations have also been carried out to compute other structural properties, as well the effective diffusivities of light gases in the amorphous SiC film. C 2015 AIP Publishing LLC. [http://dx

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“…The carburizing parameters may have significant effects on the thickness, adhesion, density and chemical composition of carburized layer formed on the titanium substrate. Studies on titanium carbide powder synthesis by carbothermal method in argon environment requires high temperature in the range of 1700-2100 °C (Weimer, 1997) and long reaction time (10-24 h) (Gotoh et al, 2001). Other workers tried to synthesize TiC powder at lower temperatures and shorter time with success.…”

Section: Thermal Carburizationmentioning

confidence: 99%