Materials Science and Engineering / Malzeme Bilimi ve Mühendisliği

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  • Article
    Citation - WoS: 21
    Citation - Scopus: 22
    Green Function, Quasi-Classical Langevin and Kubo-Greenwood Methods in Quantum Thermal Transport
    (IOP Publishing, 2019) Sevinçli, Haldun; Roche, S.; Cuniberti, G.; Brandbyge, M.; Gutierrez, R.; Sandonas, L. Medrano
    With the advances in fabrication of materials with feature sizes at the order of nanometers, it has been possible to alter their thermal transport properties dramatically. Miniaturization of device size increases the power density in general, hence faster electronics require better thermal transport, whereas better thermoelectric applications require the opposite. Such diverse needs bring new challenges for material design. Shrinkage of length scales has also changed the experimental and theoretical methods to study thermal transport. Unsurprisingly, novel approaches have emerged to control phonon flow. Besides, ever increasing computational power is another driving force for developing new computational methods. In this review, we discuss three methods developed for computing vibrational thermal transport properties of nano-structured systems, namely Green function, quasi-classical Langevin, and Kubo-Green methods. The Green function methods are explained using both nonequilibrium expressions and the Landauer-type formula. The partitioning scheme, decimation techniques and surface Green functions are reviewed, and a simple model for reservoir Green functions is shown. The expressions for the Kubo-Greenwood method are derived, and Lanczos tridiagonalization, continued fraction and Chebyshev polynomial expansion methods are discussed. Additionally, the quasi-classical Langevin approach, which is useful for incorporating phonon-phonon and other scatterings is summarized.
  • Article
    Citation - WoS: 8
    Citation - Scopus: 10
    Microstructures and Mechanical Properties of Graphene Platelets-Reinforced Spark Plasma Sintered Tantalum Diboride-Silicon Carbide Composites
    (IOP Publishing, 2019) Gürcan, Kübra; İnci, Ezgi; Saçkan, İbrahim; Ayaş, Erhan; Gasan, Hakan
    Graphene nanoplates reinforcement (GNPs) TaB2-SiC composites were fabricated with Spark Plazma sintering (SPS) at 1850 degrees C with a-uniaxial pressure of 50 MPa and 10 min dwell time. Systematic investigation on the effect of GNP amount of densification, microstructural and mechanical properties (microhardness and fracture toughness) of the composites were presented. Density and hardness of composites decreased with the addition of GNP, while similar to 35% increase of fracture toughness value was obtained with GNP addition. The microstructural evaluation indicated that overlapped and agglomerated GNPs increased with an increasing amount of GNP in the composites and caused to decrease of density and hardness. On the other hand, GNP was retained in the composite form even with high process temperature (1850 degrees C) and cause toughening of composites with changing the fracture mode from transgranular to transgranular/intergranular fracture. GNP pull out, crack branching, crack bridging and crack deflection were observed as main toughening mechanisms.