Now showing 1 - 6 of 6
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    Low frequency dielectric behavior and AC conductivity of polymer derived SiC(O)/HfCxN1-x ceramic nanocomposites
    (15-02-2021)
    Awin, Eranezhuth Wasan
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    Sridar, Soumya
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    Kousaalya, Adhimoolam Bakthavachalam
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    Vendra, S. S.Lokesh
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    Koroleva, Ekaterina
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    Filimonov, Alexey
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    Vakhrushev, Sergey
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    The dielectric behavior of spark plasma sintered SiC(O)/HfCxN1-x nanocomposites synthesized through polymer derived ceramic route was investigated in the frequency range of 1 kHz to 1 MHz at room temperature. The nanostructural features revealed HfCxN1-x nanocrystals encapsulated in a nanometric thin layer of carbon dispersed uniformly in a SiC(O) matrix with segregated free carbon. The nanocomposites exhibited colossal permittivity values in the order of 103 at 1 kHz which reduced to 646 at 1 MHz. The interfacial polarization mechanism existing between complex nanostructural interfaces and the percolation of HfCxN1-x nanocrystals are believed to be responsible for the high permittivity values observed in the measured frequency range. The AC conductivity exemplified a frequency independent behavior at lower frequencies while at higher frequencies, the conductivity exhibited frequency dependence, indicating the existence of hopping type mechanism.
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    Publication
    Structural, functional and mechanical properties of spark plasma sintered gadolinia (Gd2O3)
    (01-01-2016)
    Awin, Eranezhuth Wasan
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    Sridar, Soumya
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    Shabadi, Rajashekhar
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    Powder particles of gadolinia were spark plasma sintered at varied temperatures between 1400 °C and 1600 °C. High-density samples free of any sintering additives were obtained at the highest sintering temperature and the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) including density measurements. The contact angle measurements and translucence studies implied the sintered samples to be hydrophobic and translucent respectively. The nanohardness values enhanced up to ∼88% with increase in sintering temperature from 1400 °C to 1600 °C. Young's modulii determined using nanoindentation varied from 126 GPa to 169 GPa for the samples sintered at the lowest and highest temperatures respectively. The theoretical Young's modulus was also determined using first principle calculations which were eventually used for fracture toughness calculations. The fracture toughness values of the sintered samples were calculated using the indentation crack length method (ICL) and compared with the crack opening displacement (COD) method.
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    Publication
    Mechanical characterization of spark plasma sintered titania-silicon oxycarbide (TiO2/SiOC) nanocomposites
    (01-02-2022)
    Awin, E. W.
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    Kumar, K. C.H.
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    Bernard, S.
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    In this work, titania-silicon oxycarbide nanocomposites synthesized via the polymer derived ceramics route have been sintered into crack-free monoliths using spark plasma sintering and their mechanical properties as well as their apparent density have been characterized. The x-ray diffractogram clearly showed the stabilization of anatase phase of size less than 10 nm size in an amorphous silicon oxycarbide matrix at 1200 °C. The hardness and elastic modulus determined using nanoindentation were found to be 9 GPa and 82 GPa, respectively, and the fracture toughness calculated using indentation crack length method was found to be 2.34 MPa m1/2. In addition to this, ball-on-three ball technique was used to evaluate the biaxial flexural strength and fractographic studies were carried out to understand the fracture mechanisms.
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    Publication
    Ablation resistance of precursor derived Si-Hf-C-N(O) ceramics
    (01-11-2016)
    Eranezhuth, Wasan Awin
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    Sridar, Soumya
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    Adhimoolam, Bakthavachalam Kousaalya
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    Polymer derived Si-Hf-C-N(O) foams were produced by the pyrolysis of polysilazane containing varying amounts of hafnium tetra n-butoxide. X-ray tomography was used to determine the cell size distribution. The ablation resistance of the foams was studied by subjecting it to different oxyacetylene flame temperatures. After ablation, fragmentation was not observed and the mass ablation rate was found to be minimal for the foams produced from highest vol% of hafnium tetra n-butoxide. The foams remained X-ray amorphous after ablation and the presence of [Formula presented] and [Formula presented] bonds were confirmed using ATR spectroscopy. For comparison, a reasonably dense spark plasma sintered pellet was also ablated and the evolution of monoclinic hafnia was confirmed using X-ray diffraction. The microstructural characterization exhibited three different zones on the ablated surface for sintered sample and the ablation mechanisms were understood using thermodynamic calculations.
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    Influence of spark plasma sintering temperature on the densification, microstructure and mechanical properties of Al-4.5 wt.%Cu alloy
    (01-12-2013)
    Devaraj, S.
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    The effect of sintering temperature on the densification mechanisms, microstructural evolution and mechanical properties of spark plasma sintered (SPS) compacts of a gas atomized Al-4.5 wt.%Cu alloy was investigated. The powder particles whose size varied between 10 to 500 μm was subjected to SPS at 400, 450 and 500 °C at a pressure of 30 MPa. The compact sintered at 500 °C exhibited fully dense microstructure which was characterized by a uniform distribution of the secondary phase, free of dendrites and micro-porosity. Microscopy and the SPS data reveal that the events such as particle rearrangement, localized deformation and bulk deformation appear to be the sequence of sintering mechanisms depending on the size range of powder particles used for consolidation. The compact sintered at 500 °C exhibited the highest hardness and compression strength since the microstructure was characterized by fine distribution of precipitates, large fraction of submicron grains and complete metallurgical bonding. © The Chinese Society for Metals and Springer-Verlag Berlin Heidelberg.
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    Electric erosion induced microstructure and mechanical properties in spark plasma sintered Al-4.5 wt. % Cu alloy
    (01-01-2016)
    Devaraj, S.
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    The Al-4.5 wt.% Cu powder was compacted by spark plasma sintering at three compaction pressures namely 30, 40, and 50 MPa maintaining temperature constant at 500°C. Porosity seems to be closed in all the 3 cases. Relative density of S-50 is decreased due to increase in electrical erosion holes. Transmission electron microscopy studies reveal the presence of dislocations in all the compacts and shear bands observed only in the compact sintered at 50 MPa. A power law creep mechanism involving dislocations is found to be observed in all the compacts sintered at all pressures, which is evident from the TEM micrographs as well. The dissolution of Al2Cu precipitates in the aluminum matrix, and the increase in electric erosion holes were noticed with increase in pressure from 30 to 50 MPa. The decrease in the volume fraction of Al2Cu phase and the increase in the formation of electric erosion holes resulted in reduced hardness and compression strengths of the compacts.