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Thermoelectric devices are environmentally friendly renewable energy sources that use waste heat to generate electricity. So far, p-type Bi–Sb–Te-based alloys with high thermoelectric properties were fabricated using low-dimensional and single growth methods as small-scale, laboratory-grown samples. However, large-scale fabrication processes are required for commercial applications of thermoelectric devices. In this work, large amounts (2–3 kg) of p-type 20%Bi2Te3–80%Sb2Te3 alloy powders were fabricated using the gas atomization (GA) process under an inert gas atmosphere. Subsequently, a large-scale sample, 64 mm thick and 25 mm in diameter, was consolidated from the as-fabricated GA powders using spark plasma sintering at 673 K. The homogeneity of the microstructure, density, thermoelectric properties, and mechanical properties of the high-thickness sintered bulk were systematically investigated at various positions. The EBSD texture analysis revealed that an almost similar microstructure existed in all positions of the bulk sample, which was comprised of a mixture of coarse grains and fine grains randomly distributed throughout the matrix. The peak electrical conductivity of 1100 Ω−1 cm−1 was obtained from the top position of the thick sample, which had a relatively higher carrier mobility. The maximum power factor of 3.96 mW/mK2 was achieved by the top part of the specimen, because of its higher electrical conductivity. The lowest thermal conductivity of 0.964 W/mK at 350 K was obtained from the bottom part of the specimen. As a result, the maximum figure of merit, ZT of 1.25 was achieved in the bottom position of the high-thickness sample. Homogeneous (within 5% of variation) thermoelectric transport properties were observed throughout the fabricated high-thickness sintered sample, regardless of position. [ABSTRACT FROM AUTHOR]

A single pulse of 0.57–1.1 kJ/0.3 g-spherical Ti-powder in size range of 30–70 μm, using a constant 450 μF capacitor, was applied to produce fully porous Ti- and W-compacts by electro-discharge sintering. Microstructure examination and hardness measurement of the porous Ti-compacts revealed that more stable necks formed with increasing electrical input energy up to 1.1 kJ. On the contrary, W-compacts using rectangular W-powders in size range of 5–15 μm are composed of solid region with micropore and porous layer with weak particle bonding indicating heterogeneous structure. These results suggest that the powder morphology plays a crucial role to control the porous microstructure. [ABSTRACT FROM AUTHOR]

Abstract: This study investigates the mechanical and wear properties of Al92.5Fe2.5Cr2.5Ti2.5 alloys prepared via Magnetic Pulsed Compaction (MPC) starting from elemental powders. The potential of MPC-processed Al92.5Fe2.5Cr2.5Ti2.5 alloy for structural applications at both ambient and elevated temperatures has also been studied. The difficulty with which to form supersaturated Al-based solid solutions depends on alloying elements with Fe being the easiest element and Cr the most difficult one to form supersaturated Al-based solid solutions. After exposure to high temperature (up to 500°C), the MPC-processed Al92.5Fe2.5Cr2.5Ti2.5 alloy exhibits an incremental hardness and reaches the maximum at 400°C with minimum wear loss, due to strengthening of intermetallic precipitation. [Copyright &y& Elsevier]

Abstract: Metallic glass (MG)/metallic glass composites being CuA (Cu-base alloy)/10% NiA (Ni-base alloy) and NiA/10% CuA in weight were newly synthesized using gas atomization and spark plasma sintering (SPS). The composition of MG powders was Cu54Ni6Zr22Ti18 (CuA) and Ni59Zr15Ti13Nb7Si3Sn2Al1 (NiA), which consisted of fully amorphous phases. T g and T x of both the powders were 716K and 765K for CuA, but 836K and 890K for NiA. The resultant phases of composites were Cu crystalline dispersed NiA matrix composites as well as NiA phase dispersed CuA matrix composites, depending on the SPS temperatures. The effect of the second phases embedded in the MG matrix on microstructure and mechanical properties is discussed. [Copyright &y& Elsevier]

A transmission electron microscopy analysis was conducted on the oxide layers of Mg–5.5Al–0.25Mn (AM60) alloys with different levels of CaO content formed in a thermogravimetric analyzer (TGA) system at 450 °C for 7 h. It was found that the oxide layer in AM60 + CaO grew as a columnar structure and, resultantly, that the oxide layers had different thicknesses with different levels of CaO content. The columnar oxide grains that were formed on the Mg + CaO alloy grew on the [1 0 0] MgO , resulting in a more compact and thicker initial oxide layer compared to the normal oxide layer. The columnar growth of the oxide layer in AM60 + CaO formed due to the Ca, which dissolved from CaO. [ABSTRACT FROM AUTHOR]

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]

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]

Abstract: Deformation behavior of a Mg72Cu5Zn23 alloy containing bimodal eutectic structure has been systematically investigated based on microstructural changes upon different amounts of compressive strain. The microstructural evolution of the sample at the early stage of the deformation up to 3% strain reveals that a large number of twins form homogeneously in the α-Mg phase of the coarse eutectic structure. After further deformation to failure, propagation of cracks takes place along the interface between the fine and coarse eutectic structures forming a typical dimple-like morphology on the fracture surface, indicative of the effective dissipation of the stress. [Copyright &y& Elsevier]