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Coherency Strain induced Ordering in Substitutional Alloys
Lee, J . K .,Hiratani, M .,Kalaitzidou, K .,Shyam, A . 대한금속재료학회(대한금속학회) 1999 METALS AND MATERIALS International Vol.5 No.6
It has been well known that one of the driving forces for ordering is the relaxation of elastic strain energy due to difference in atomic size, a clear evidence being the change in lattice parameter between ordered and disordered states. Because of mathematical complexity, however, only a few strain models have been presented for substitutional alloys. This work reports coherency-induced ordering in a simple model with a two-dimensional square lattice. At an equi-atom composition, a square lattice displays two elementary, ordered structures, S1_0 and S1_1 similar to L1_0(CuAul) and L1_1(CuPt) in fcc. The stability of two superlattices at the ground state depends strongly on elastic anisotropy. For a homogeneous system, Zener's anisotropy ratio is sufficient to measure the stability of one structure against the other. If the elastic constants are different, however, the stability depends not only on the elastic moduli of both elements but also on the solvent-solute bond length. The order-to-disorder transition is studied via the Discrete Atom Method, which is predicated upon statistical mechanics and linear elasticity. When both elastic and chemical interactions join together for ordering, the transition temperature is raised to a value greater than the sum of the two individual casesan indication of a coupling between the two driving forces.
Shaun Eshraghi,Suman Das,Mehdi Karevan,Kyriaki Kalaitzidou 한국정밀공학회 2013 International Journal of Precision Engineering and Vol. No.
Electrically conductive polymer nanocomposites were prepared through selective laser sintering (SLS) of polyamide-12 (PA) powder coated with graphite nanoplatelets (GNP) using sonication. The SLS process parameters were optimized in order to maximize the tensile modulus at 3 and 5 wt% GNP. The highest tensile modulus (2.1 GPa) was achieved at 3 wt%. A slight decrease in flexural modulus and strength was observed at 3 and 5 wt% GNP compared with the neat polymer. Morphological observation of the graphitecoated PA powder showed fairly homogeneous dispersion. The SLS processed parts were nearly fully dense and the highest density (99.5%) was found at 3 wt% GNP. The bulk electrical conductivity of the SLS-processed nanocomposites was found to be 3.8×10-11 and 6.4×10-8 S/cm for 3 and 5 wt% GNP respectively.
Mehdi Karevan,Raghuram V. Pucha,Md.A. Bhuiyan,Kyriaki Kalaitzidou 한국탄소학회 2010 Carbon Letters Vol.11 No.4
This study investigates the effect of filler content (wt%), presence of interphase and agglomerates on the effective Young's modulus of polypropylene (PP) based nanocomposites reinforced with exfoliated graphite nanoplatelets (xGnPTM) and carbon nanotubes (CNTs). The Young's modulus of the composites is determined using tensile testing based on ASTM D638. The reinforcement/polymer interphase is characterized in terms of width and mechanical properties using atomic force microscopy which is also used to investigate the presence and size of agglomerates. It is found that the interphase has an average width of ~30 nm and modulus in the range of 5 to 12 GPa. The Halpin-Tsai micromechanical model is modified to account for the effect of interphase and filler agglomerates and the model predictions for the effective modulus of the composites are compared to the experimental data. The presented results highlight the need of considering various experimentally observed filler characteristics such as agglomerate size and aspect ratio and presence and properties of interphase in the micromechanical models in order to develop better design tools to fabricate multifunctional polymer nanocomposites with engineered properties.