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By using the electron backscattered diffraction (EBSD) technique, pattern selection of twinned growth in Al-4.5 wt% Cu alloy has been studied in Bridgman solidification experiments. Based on the original twin planes formed at 3000 μm/s, the twinned growth was produced till the end of solidification after abruptly decreasing the growth rate to 100, 50, 20, 10, 5, 3, 1 and 0.3 μm/s. The stable twinned growth could be achieved during a wide range of solidification process. For the first time, the so-called twinned cell pattern was observed and prevailed in the solidified structure at 3 and less than 3 μm/s. The twinned growth in aluminum alloy was not limited to dendrite pattern as has previously been reported. The twinned pattern selection map was also revealed. Meanwhile, an interesting orientation rotation phenomenon was elucidated using EBSD technique on both sides of the coherent twin boundary during twinned cell growth. At a lower rate of 0.3 μm/s, the orientation rotation deflection concerning the original Σ3 60° twinning relation was confirmed. Some coincidence site lattice boundaries with higher Σ values served as the preferred states for this orientation deflection during growth. [ABSTRACT FROM AUTHOR]

A single crystal of Sb-doped Mg 2 Si 0.35 Sn 0.65 has been successfully prepared using high temperature-gradient directional solidification. The composition distribution of the crystal is uniform, and the preferred growth direction of the crystal is [111] orientation. The Seebeck coefficient ( S ) of the crystal is anisotropic in different orientations, and the electrical and thermal conductivity are isotropic properties. The S value in the [111] orientation can reach −265 μVK −1 , which is much larger than the reported results. Also, the power factor in the [111] orientation has a value of 5.56 mWm −1 K −2 , which leads to a maximum ZT of 1.3 at 730 K. Results of Hall testing and first principles calculations agree well with the experiment results. [ABSTRACT FROM AUTHOR]

Solid-state cooling based on elastocaloric effect possesses potential for refrigeration. The improvement of elastocaloric effect and thermal cycle stability is beneficial to enhance the refrigeration efficiency and service life of refrigeration equipment. Here, single-crystal Ni 50 Mn 31.6 Ti 18.4 shape-memory alloys were successfully prepared using directional solidification technique. The microstructure, martensitic transformation, isothermal stress-strain responses and elastocaloric effect of the single crystals with different solidification rates have been systematically studied. The single crystal solidified at 10 µm s−1 exhibits lower stress hysteresis Δ σ hy and much more superior adiabatic temperature |Δ T ad | than those of alloys solidified at 100 µm s−1 and 500 µm s−1, with the values of 34 MPa and 24.8 K. In addition, the single crystal at low solidification rate also performs excellent cyclic stability. All these results show that the single crystal with larger austenite primary dendrite arm spacing (PDAS) can effectively enhance the elastocaloric effect and thermal cycling stability in Ni 50 Mn 31.6 Ti 18.4 alloys. This work sheds a bright light on the relationship between the elastocaloric performance and microstructure for shape-memory alloys. • Single-crystal Ni 50 Mn 31.6 Ti 18.4 alloys were successfully prepared by directional solidification. • The alloy with large primary dendrite spacing has the excellent adiabatic temperature of 24.8 K. • Single-crystal prepared with larger primary dendrite spacing can effectively enhance the thermal cycling stability. [ABSTRACT FROM AUTHOR]

Phase selection under far-from-equilibrium condition has been investigated in three Cr 2 Nb-20/30/40Ti (at. %) alloys processed by laser surface melting (LSM) with scanning speeds of 50–200 mm/s. Phase identification was performed by micro-area XRD technique combined with SEM plus EDS methods. The results show that, at all scanning speeds of 50–200 mm/s, the microstructure of Cr 2 Nb-20Ti alloy consisted of single-phase Cr 2 Nb, whereas it evolved to monolithic β-Ti in the Cr 2 Nb-40Ti alloy. Meanwhile, the microstructure of Cr 2 Nb-30Ti alloy solidified with eutectic β-Ti/Cr 2 Nb at 50 mm/s, which transited to monolithic β-Ti as scanning speeds increased to 100–200 mm/s. Microstructures evolution was interpreted based on Trivedi-Magnin-Kurz (TMK) and Kurz-Giovanola-Trivedi (KGT) models incorporating the effect of non-equilibrium solidification. After the process of LSM, the micro-hardness of Cr 2 Nb-20Ti alloy was improved to a level of 9.0 GPa, and the fracture toughness was reduced to about 3.1 MPa m 1/2 ; while for the Cr 2 Nb-30/40Ti alloys, the micro-hardness decreased within a range of 5.5–6.6 GPa, but with a great increase of facture toughness of 21–23 MPa m 1/2 . [ABSTRACT FROM AUTHOR]

• The nanostructured Te-SnTe composites were successfully prepared via a rapid fabrication process. • The eutectic Sn-90at%Te composite exhibits an enhanced thermoelectric performance. • An ultralow lattice thermal conductivity could be obtained for the Sb doped eutectics. • The improved thermoelectric properties for the eutectic system provide a new strategy to explore high-performance materials. The eutectic Te‒SnTe composites were successfully prepared via a melt spinning method combined with a spark plasma sintering technique. The differences in thermoelectric properties for alloys near the eutectic composition were investigated. These composites could benefit from both the higher electrical conductivity of the SnTe phase and the superior Seebeck coefficient of the Te phase. The eutectic Sn-90at%Te composite exhibits an enhanced thermoelectric performance. Its maximum ZT is 1.8–2.1 times higher than that of pristine SnTe and Te materials. Upon doping with the Sb element, the electrical transport behavior could be further improved. Large amounts of grain boundaries and phase interfaces can readily scatter phonons. Combined with the extra scattering from nanoprecipitates, dislocations, and strain fields, an ultralow lattice thermal conductivity of 0.49 W m−1 K−1 could be obtained for the Sn-90at%Te-2.0at%Sb alloy at 633 K. The improved thermoelectric properties for the Te‒SnTe eutectic system provide a new strategy to explore high-performance materials. [ABSTRACT FROM AUTHOR]

SnTe based materials have attracted considerable attention owing to their eco-friendly nature. Here, we employed a melt spinning method combined with spark plasma sintering (MS-SPS) technique to optimize the electrical and thermal transport performance of SnTe based alloys. Doping with Sb optimizes carrier concentration efficiently, leading to an enhanced Seebeck coefficient and power factor. Unlike the original phonon dispersion relation, the introduction of Sb heightens the phonon-phonon interaction and flattens the phonon dispersion, resulting in a significant decline in the phonon group velocity. Combined with the enhanced scattering from lattice distortion, nanoprecipitates and large amounts of grain boundaries, an ultralow lattice thermal conductivity of 0.57 Wm−1K−1 was obtained for Sn 0.91 Sb 0.18 Te 1.18 MS-SPS alloy. An improved ZT value of 0.95 can be realized, which is 2.2 times higher than that of pure SnTe alloy. The enhanced phonon scattering and reinforced phonon-phonon interaction give valuable access to develop high-performance SnTe based thermoelectric materials. • Melt spinning followed by spark plasma sintering technique was employed to prepare nanostructured materials. • Introduction of element Sb changes the phonon dispersion relations of SnTe based materials. • An ultralow lattice thermal conductivity of 0.57 Wm−1K−1 was obtained for Sn 0.91 Sb 0.18 Te 1.18 alloy. • Nanostructuring is effective to enhance the thermoelectric performance. [ABSTRACT FROM AUTHOR]

Bulk NbCr 2 samples with ultra-fine grains have been fabricated by mechanical milling and subsequent spark plasma sintering. The room-temperature fracture toughness of these bulk samples achieves as high as 11.3 ± 0.5 MPa m1/2, which is remarkably improved compared to the as-cast monolithic NbCr 2 Laves phase (1.2 MPa m1/2). The microstructural analysis indicates the presence of abundant non-equilibrium Nb and Cr solid solutions among the grain boundaries. The formation of Nb and Cr solid solutions is attributed to the applied pulsed electric current during spark plasma sintering, which can decrease the critical nucleation undercooling, accelerate the atomic diffusion and enhance the nucleation rate. Based on the microstructural characterization, the enhancement in fracture toughness is ascribed to formation of non-equilibrium Nb and Cr solid solutions toughening and grain boundary toughening mechanisms. Furthermore, strong texture components have been detected in these bulk samples. For the sample sintered with the powder milled for 30 h, the <100> direction of NbCr 2 Laves phase is perpendicular to the compressive axis while the Nb and Cr solid solutions show random orientation. When sintered with the powder milled for 60 h and 90 h, the texture component in NbCr 2 Laves phase transforms into <110> fiber texture, and the Cr solid solution also show strong <100> and <110> texture components perpendicular to the compressive axis. The evolution of texture component is discussed by considering the crystallization behaviour of the milled powders. • Ultra-fine NbCr 2 bulks have been produced by mechanical alloying and spark plasma sintering. • The fracture toughness of the bulks attains 11.3 ± 0.5 MPa m1/2, which is 9.3 times of NbCr 2. • Non-equilibrium Nb and Cr solid solutions are detected among the NbCr 2 grain boundaries. • The NbCr 2 Laves phase and non-equilibrium Cr solid solutions show strong texture. • The texture in NbCr 2 Laves phase transformed from <100> to <110> with the increase of milling time. [ABSTRACT FROM AUTHOR]

A quinary Cr–12Nb–5Ti–5Mo–5Si (at.%) alloy was prepared by arc melting in this study to improve the strength and toughness of Laves phase Cr 2 Nb alloy. The quinary alloy was solidified with full eutectic Cr 2 Nb/Cr, in which the Cr 2 Nb phase exceeded 55 vol % and existed as matrix. The eutectic was developed with an orientation relationship of {001}Cr 2 Nb//{001}Cr, leading to a low lattice mismatch of 15.57% at the eutectic interface. The yield strength and fracture toughness of the quinary alloy reached 1950–1980 MPa and 14.0–14.8 MPa⋅m1/2, respectively, much higher than most reported Cr 2 Nb alloys. The reason for the superior properties is the synergistic effects of solid solution strengthening, alloying toughening, and eutectic strengthening-toughening. • The alloy Cr–12Nb–5Ti–5Mo–5Si was solidified with full eutectic Cr 2 Nb/Cr. • The orientation relationship of the full eutectic was {001}Cr 2 Nb//{001}Cr. • The improved strength and toughness was achieved in the quinary alloy. • Relevant strengthening and toughening mechanisms were discussed. [ABSTRACT FROM AUTHOR]

At different directional solidification rates (10, 20 and 100 μm/s), microstructures and growth orientation variations of Al 2 Cu dendrite in Al-40%Cu alloy were characterized. When solidification rates were ranged from 10 to 100 μm/s, three-dimensional microstructure of Al 2 Cu dendrite changed from faceted L-shaped patterns to non-faceted complex dendrite morphology in transverse section. By the macro and micro orientation analysis characterize methods, [001] growth direction of Al 2 Cu dendrites with different morphologies was determined. The deviation angle between [001] direction and the heat flow direction was increased with solidified rate increasing. The experimental results showed that the regular solidified microstructure and growth orientation along the heat flow direction could be well controlled under lower directional solidification rate. [ABSTRACT FROM AUTHOR]