The Experts below are selected from a list of 252 Experts worldwide ranked by ideXlab platform
Gregory B. Thompson - One of the best experts on this subject based on the ideXlab platform.
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Experimental investigation into the crack propagation in multiphase Tantalum Carbide ceramics
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2017Co-Authors: Bradford C. Schulz, Heedong Lee, Pavel Mogilevsky, Christopher R. Weinberger, Triplicane A. Parthasarathy, Lawrence E. Matson, Chase J. Smith, Gregory B. ThompsonAbstract:Abstract Tantalum Carbide ceramics with high volume fractions of the ζ-Ta4C3 phase have been shown to exhibit high fracture strength and toughness as compared to those in absence of this phase. In this work, we investigated how microcracks propagated in this these high toughness ceramics using Knoop and Vickers microindentation. The Knoop indentations demonstrated that cracking preferentially occurred parallel to the lath structure in ζ-Ta4C3; however shorter cracks did form between the laths when a sufficient driving force was present. The resulting crack path was tortuous providing direct evidence for toughening through crack deflection; however, the microscale nature of the work cannot rule out crack bridging as a toughening mechanism as well. Plasticity is also observed under the indents, but is likely a result of the high confining pressures that occurred during indentation allowing for plastic flow.
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influence of hafnium Carbide on vacuum plasma spray processed Tantalum Carbide microstructures
Journal of The European Ceramic Society, 2013Co-Authors: Bradford C. Schulz, R.a. Morris, Daniel Butts, Billie Wang, Gregory B. ThompsonAbstract:Abstract Five specimens of (TaC) 1− x (HfC) x , where x is 0.0, 0.3, 3.0, 16.5, and 19.8 at.%, were fabricated by vacuum plasma spraying. As HfC content increased, the grain size was reduced and the volume fraction of TaC, Ta 2 C and Ta 4 C 3 changed, with the TaC phase being more dominate. Reduced grain sizes also lead to an increase in Knoop hardness values. The reduction of grain size with increasing HfC content has been explained by the system being driven further into a compositionally lower melting temperature phase field. This increase in liquid fraction caused greater under-cooling and the formation of more nucleation sites that lead to a finer grain size. The changing volume fraction of (TaC) 1− x (HfC) x and sub-stoichiometric Tantalum Carbide phases has been contributed to the loss of carbon intrinsic to vacuum plasma spray processing.
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Quantification of Oxide Inclusions and Porosity Structure in a Tantalum Carbide Microstructure Fabricated From Carbothermal Reduced Tantalum Oxide Precursor Powders
International Journal of Applied Ceramic Technology, 2012Co-Authors: R.a. Morris, Daniel Butts, Gregory B. ThompsonAbstract:The oxide inclusion and porosity defect structures in a Tantalum Carbide specimen fabricated from vacuum plasma spraying with postspraying sintering and hot-isostatic pressing has been characterized. The Tantalum Carbide powders were obtained using a carbothermal reduction process of Tantalum oxide precursors. During its fabrication, oxide-based inclusions formed from intrinsic impurities in the powder. Using serial sectioning and three-dimensional reconstruction techniques, interconnected globular oxide inclusions were revealed to be within the matrix phase and in the grain boundaries. The oxide phase was identified to be z-Ta2O5 through selected area electron diffraction. The two- and three-dimensional porosity size distribution was compared and accounted for ~2% of the volume.
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Variations in Tantalum Carbide Microstructures with Changing Carbon Content
International Journal of Applied Ceramic Technology, 2012Co-Authors: R.a. Morris, Daniel Butts, Billie Wang, Gregory B. ThompsonAbstract:A wide variety of microstructures have been obtained by vacuum plasma spraying (VPS) 39Ta:61C atomic percent feedstock powders. During processing, the powder feed was fed through a high energy VPS plasma plume, where altering nozzle angle changed the overall retained carbon concentration in the deposited material. The samples were subsequently sintered and hot isostatic pressed to homogenize and consolidate the microstructure. The microstructures consisted of grains that were either equiaxed or acicular. In the samples with less carbon loss, the equiaxed grains were either the TaC phase or a TaC matrix that encased fine laths of Ta4C3. In the sample with the most carbon loss, acicular grains were found containing layered and parallel TaC, Ta2C, and Ta4C3 laths along the major-axis of the grains. The phases of the compounds have been determined by using complimentary X-ray diffraction and electron diffraction techniques. Focused ion beam serial sectioning and transmission electron microscopy tilt series tomography were performed to generate three-dimensional reconstructions of the microstructure morphologies. This article addresses how Tantalum Carbide microstructures are controlled by the overall concentration and phase fraction content in each of these samples.
Arjun Maity - One of the best experts on this subject based on the ideXlab platform.
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synthesis and magnetic properties of highly dispersed Tantalum Carbide nanoparticles decorated on carbon spheres
CrystEngComm, 2016Co-Authors: Kaustav Bhattacharjee, Trisita Nandy Chatterjee, Satya Prakash Pati, Gopes Chandra Das, Suprakas Sinha Ray, Arjun MaityAbstract:The decoration of carbon spheres (CS) by highly dispersed Tantalum Carbide nanoparticles (TaC NPs) was achieved, for the first time by a unique carbothermal reduction method at 1350 °C for 30 min under reduced oxygen partial pressure. TaC NPs decorated CS composites were then extensively characterized by powder X-ray diffraction and electron microscopy techniques. The composite spheres were approximately 0.8–1 μm in diameter with an average size of 41 nm for the TaC NPs located at the surface. Transmission electron microscopy and Raman analysis showed the formation of the graphene layer at the outer surface of the TaC NPs. An anomalous ferromagnetic response with a spin-glass like behavior has been observed at low temperature in the dc magnetization study with complete suppression of the superconducting response. For ease of synthesis and high reproducibility, this technique opens a new paradigm in the preparation of carbon sphere supported high melting metal Carbide nanoparticles for various technological purposes.
Arvind Agarwal - One of the best experts on this subject based on the ideXlab platform.
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Graphene Nanoplatelet Reinforced Tantalum Carbide
2015Co-Authors: Benjamin Boesl, Arvind AgarwalAbstract:Abstract : In this study, Graphene nanoplatelet (GNP) reinforced Tantalum Carbide (TaC) composites were studied for their mechanical and thermal properties as they relate to usage as ultra high temperature materials. Samples were fabricated using Spark Plasma Sintering (SPS) and ultrahigh-pressure consolidation. The results of mechanical property testing showed GNP reinforced composites have improved modulus, hardness, damping, and damage resistance over unreinforced TaC. Results of thermal analysis during plasma oxidation testing showed an increase in thermal conductivity in GNP reinforced composites resulting in a reduction of peak sample surface temperature. This study resulted in the publications listed below and attached to this document for additional detail (the support from this grant was acknowledged in each). This award also supported the research of three graduate students (A. Nieto, C. Zhang, S. Rengifo : 1 female, 2 of Hispanic decent) and one undergraduate student (S. Thomas).
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Nanodynamic mechanical behavior of graphene nanoplatelet-reinforced Tantalum Carbide
Scripta Materialia, 2013Co-Authors: Andy Nieto, Debrupa Lahiri, Arvind AgarwalAbstract:Nanodynamic mechanical analysis (nanoDMA) is performed on spark plasma sintered Tantalum Carbide composites reinforced with graphene nanoplatelets (GNPs). The addition of GNPs enhances damping (tanδ) at 25–100 Hz frequencies by up to 300%. It also improves damping behavior through energy-dissipating mechanisms, such as GNP bending, kinking and sliding. A model for correlating improvement in the damping behavior with the fracture toughness is presented. GNP energy-dissipating mechanisms are most effective in improving damping behavior when GNPs are dispersed uniformly.
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graphene nanoplatelets reinforced Tantalum Carbide consolidated by spark plasma sintering
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 2013Co-Authors: Andy Nieto, Debrupa Lahiri, Arvind AgarwalAbstract:Abstract Graphene NanoPlatelets (GNP) reinforced Tantalum Carbide composites are synthesized by spark plasma sintering (SPS) at processing conditions of 1850 °C and 80–100 MPa. The GNP addition enhances the densification of TaC–GNP composites to 99% theoretical density, while reducing the grain size by over 60% through grain wrapping mechanism. Survival and structure retention of GNP is confirmed through scanning electron microscopy and micro-Raman spectroscopy. Nanoindentation and high load (20–30 N) microindentation are utilized to evaluate elastic modulus and hardness. GNP improves fracture toughness of TaC by up to 99% through toughening mechanisms such as GNP bending, sheet sliding, cracking bridging, and crack deflection.
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Graphene-induced strengthening in spark plasma sintered Tantalum Carbide–nanotube composite
Scripta Materialia, 2013Co-Authors: Debrupa Lahiri, Evan Khaleghi, Eugene A. Olevsky, Srinivasa R. Bakshi, Arvind AgarwalAbstract:Transverse rupture strength of spark plasma sintered Tantalum Carbide (TaC) composites reinforced with long and short carbon nanotubes (CNTs) is reported. The rupture strength depends on the transformation behavior of the CNTs during spark plasma sintering, which is dependent on their length. The TaC composite with short nanotubes shows the highest specific rupture strength. Shorter CNTs transform into multi-layered graphene sheets between TaC grains, whereas long ones retain the tubular structure. Two-dimensionsal graphene platelets offer higher resistance to pull-out, resulting in delayed fracture and higher strength.
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graphene induced strengthening in spark plasma sintered Tantalum Carbide nanotube composite
Scripta Materialia, 2013Co-Authors: Debrupa Lahiri, Evan Khaleghi, Eugene A. Olevsky, Srinivasa R. Bakshi, Arvind AgarwalAbstract:Transverse rupture strength of spark plasma sintered Tantalum Carbide (TaC) composites reinforced with long and short carbon nanotubes (CNTs) is reported. The rupture strength depends on the transformation behavior of the CNTs during spark plasma sintering, which is dependent on their length. The TaC composite with short nanotubes shows the highest specific rupture strength. Shorter CNTs transform into multi-layered graphene sheets between TaC grains, whereas long ones retain the tubular structure. Two-dimensionsal graphene platelets offer higher resistance to pull-out, resulting in delayed fracture and higher strength.
Jeffrey T Glass - One of the best experts on this subject based on the ideXlab platform.
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effects of applied substrate bias during reactive sputter deposition of nanocomposite Tantalum Carbide amorphous hydrocarbon thin films
Thin Solid Films, 2007Co-Authors: Ryan D Evans, Gary L Doll, W J Meng, F Mei, Jeffrey T GlassAbstract:Abstract Nanocomposite Tantalum Carbide/amorphous hydrocarbon (TaC/a-C:H) thin film composition, structure, and mechanical properties depend on the direct current bias voltage (Vb) level applied to the substrate during reactive sputter deposition. A set of TaC/a-C:H films was deposited across the range Vb = 0 to − 300 V with all other deposition parameters held constant except substrate temperature, which was allowed to reach its steady state during the depositions. Effects of Vb on film composition and structure were explored, including TaC crystallite size and dispersion using X-ray diffraction and high resolution transmission electron microscopy. In addition, the dependency of stress and hardness on Vb was studied with an emphasis on relationships to a-C:H phase structure.
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mechanical property development in reactively sputtered Tantalum Carbide amorphous hydrocarbon thin films
Journal of Materials Research, 2006Co-Authors: Ryan D Evans, Gary L Doll, Jeffrey T GlassAbstract:Hardness, elastic modulus, and stress directly influence the ability of Tantalum Carbide/amorphous hydrocarbon (TaC/a-C:H) thin films to enhance the wear-resistance of steel tribological component surfaces. Designed factorial experiments enabled an evaluation of the effects of acetylene flow rate ( Q C2H2 ), direct current bias voltage level ( V b ), and substrate rotation rate ( ω Rot ) during deposition on the mechanical properties of reactively sputtered TaC/a-C:H films. Significant relationships were found between compressive stress level and V b , whereas hardness and elastic modulus were dependent primarily on V b and secondarily on Q C2H2 within the studied parameter space. It is proposed that effects of ion bombardment on the a-C:H phase during growth are responsible for property dependencies on V b . Decreases in hardness and elastic modulus with increasing Q C2H2 are attributed to increased hydrogen concentration and a concomitant decreased volume fraction of TaC crystallites in the films.
Ryan D Evans - One of the best experts on this subject based on the ideXlab platform.
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effects of applied substrate bias during reactive sputter deposition of nanocomposite Tantalum Carbide amorphous hydrocarbon thin films
Thin Solid Films, 2007Co-Authors: Ryan D Evans, Gary L Doll, W J Meng, F Mei, Jeffrey T GlassAbstract:Abstract Nanocomposite Tantalum Carbide/amorphous hydrocarbon (TaC/a-C:H) thin film composition, structure, and mechanical properties depend on the direct current bias voltage (Vb) level applied to the substrate during reactive sputter deposition. A set of TaC/a-C:H films was deposited across the range Vb = 0 to − 300 V with all other deposition parameters held constant except substrate temperature, which was allowed to reach its steady state during the depositions. Effects of Vb on film composition and structure were explored, including TaC crystallite size and dispersion using X-ray diffraction and high resolution transmission electron microscopy. In addition, the dependency of stress and hardness on Vb was studied with an emphasis on relationships to a-C:H phase structure.
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mechanical property development in reactively sputtered Tantalum Carbide amorphous hydrocarbon thin films
Journal of Materials Research, 2006Co-Authors: Ryan D Evans, Gary L Doll, Jeffrey T GlassAbstract:Hardness, elastic modulus, and stress directly influence the ability of Tantalum Carbide/amorphous hydrocarbon (TaC/a-C:H) thin films to enhance the wear-resistance of steel tribological component surfaces. Designed factorial experiments enabled an evaluation of the effects of acetylene flow rate ( Q C2H2 ), direct current bias voltage level ( V b ), and substrate rotation rate ( ω Rot ) during deposition on the mechanical properties of reactively sputtered TaC/a-C:H films. Significant relationships were found between compressive stress level and V b , whereas hardness and elastic modulus were dependent primarily on V b and secondarily on Q C2H2 within the studied parameter space. It is proposed that effects of ion bombardment on the a-C:H phase during growth are responsible for property dependencies on V b . Decreases in hardness and elastic modulus with increasing Q C2H2 are attributed to increased hydrogen concentration and a concomitant decreased volume fraction of TaC crystallites in the films.
