Search

Abstract: This work describes the role of temperature and rolling method on density and microstructure changes in Cu–15% In (wt%) alloy powder during normal and cross-roll rolling. The rolled specimen consisted of two distinct microstructures: α-Cu and Cu7In3 intermetallic compounds. The specimen obtained with 5° of cross rolling degree and 60% of rolling reduction ratio at 600°C has the highest density of 8.812g/cm3. A detailed analysis of these results in terms of the microstructural changes and densification mechanisms is also presented. [Copyright &y& Elsevier]

The importance of ZT in thermoelectric (TE) materials is critical for green power generation and cooling applications. Therefore, tremendous efforts were underway to improve ZT, in which we proposed a layer structured approach by successively arranging of coarse Bi 0.5 Sb 1.5 Te 3 (BST) and fine BST/0.07Cu microstructure materials and investigated their transportation mechanism. The dual bulk microstructure was well-bonded and confirmed by analyzing the microstructure through scanning electron microscope (SEM), electron backscatter diffraction analysis (EBSD) and simulated the electrical potential and temperature distribution during spark plasma sintering with COMSOL software. The results indicate that the highest power factor of 3.8 mW/m-K2 was attained in the layer structured sample, which is significantly higher than other samples due to its synergistically optimized electrical conductivity and Seebeck coefficient. Through the varied microstructure, the κ was decreased at 400 K and consequently the ZT was improved to 1.25 at 400 K for the layer structure samples. Therefore, it is suggested that layered arrangement of different microstructure material could improve the thermoelectric properties of materials. [Display omitted] • Novel fabrication of hierarchical structured material with successive arrangement of two different microstructures. • Successful consolidation of well-bonded hierarchical material and confirming by simulating results from COMSOL software. • Highest power factor of 3.8 * 10−3 W/m-K2 obtained by transportation of charge carriers through two different energy levels. • Hierarchical structured sample show highest figure of merit of 1.25 at 400 K which is highest among all reported samples. [ABSTRACT FROM AUTHOR]

Tantalum nitride nanoparticles were produced from a (K2TaF7 +5NaN3) exothermic mixture under the combustion regime. The effects of the K2TaF7/NaN3 ratio and KF and NH4F concentrations on the combustion parameters, product composition, and size of the tantalum nitride particles were studied. Depending on the synthesis conditions, the combustion temperature was maintained in the 700–1200°C range, resulting in hexagonal ε-TaN, TaN0.8, and Ta2N phases. The dominant phases were TaN and TaN0.8 in the 1000–1200°C range, whereas only the Ta2N phase was present in the 700–100°C range. Pure-phase cubic tantalum nitride (δ-TaN) was produced with 4.0mol of NH4F at a combustion temperature of ~800°C. Under controlled reaction conditions, the size of the tantalum nitride particles was about 10–50nm. We also found that during the synthesis, the stainless steel tube located inside of the reaction mixture was partially coated with fine TaN crystals. The mechanism of the combustion process is discussed in regards to the experimental results. [ABSTRACT FROM AUTHOR]

Abstract: Quasi-aligned, high-aspect-ratio AlN micro- and nanostructures were synthesized under high nitrogen pressure by the exothermic reaction of an Al+0.015mol (C2F4) n mixture. Structurally uniform AlN micro- and nanofibers with hexagonal and cylindrical morphologies were obtained when the system temperature was maintained within the range of 1600–1700°C. The fibers had aspect ratios as high as 2000, diameters in the range of ∼0.05–20μm, and were ∼100–1000μm in length. High-resolution transmission electron microscopic and selected area diffraction analyses indicated that the as-synthesized AlN micro- and nanostructures are perfectly single crystalline with preferential growth along the [001] direction. Branching was also observed in some of the micro-fibers, giving rise to randomized, two-dimensional comb textures. Based on the results obtained in the present study, a mechanism for the formation of AlN micro- and nanostructures under combustion conditions was proposed. [Copyright &y& Elsevier]

Abstract: An experimental study on the preparation of zirconium silicides was conducted using ZrSiO4–Mg, ZrSiO4–SiO2–Mg and ZrSiO4–ZrO2–Mg powder mixtures by the combustion synthesis (CS) technique. Test specimens having different composition ratios including Zr:Si=1:2, 1:1, 5:4, 5:3, 2:1, and 3:1 were employed in this study. Temperature profiles relative to all the starting compositions were measured using thermocouples, and the values of the combustion parameters (combustion temperature and wave velocity) were estimated using the same. The formation of ZrSi, ZrSi2, Zr5Si3, and Zr3Si2 phases was confirmed by X-ray analysis; however, only ZrSi was produced as a single-phase product. The proposed method was also extended to synthesize spherical ZrSi particles having mean diameters of 0.2–3.0μm. A comprehensive chemical pathway to describe the sequence of chemical reactions in the combustion wave was also proposed. [ABSTRACT FROM AUTHOR]

The analyses of phase composition, microstructure and the mechanical properties were conducted for as-cast Ta x Al 0.7 CoCrFeNi 2.1 (x = 0.3, 0.5, 0.6 and 0.7) eutectic high entropy composites (EHECs). With the x value increases from 0.3 to 0.6, the phases of dendrite changed from L1 2 to B2 and volume fraction of ultrafine-eutectic matrix consisting of Face-centered cubic and Laves phases increased. When x = 0.7, the Laves phase appears as the primary dendrite and the matrix region changed into the bimodal eutectic structure (L1 2 + Laves and B2 + Laves). Thermo-physical parameters could be used for understanding phase formation in EHECs. Experimental and theoretical comparison using thermo-physical parameters shows a reasonable consistency. Depending on the microstructural variation, the yield strength increased from 1304 MPa (x = 0.3) to 2154 MPa (x = 0.6) and plasticity decreased from 17% (x = 0.5) to 4% (x = 0.6). In order to understand the nano-to-micronscale deformation mechanisms depending on the microstructural variations, the systematic investigations of post-deformed samples (x = 0.5 and 0.6) were carried out by multi-scale SEM, TEM, and AFM analyses. [Display omitted] [ABSTRACT FROM AUTHOR]