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• The crystal structure evolutions of the Pb m Bi 2 S 3+ m (m = 1–10) compounds with increasing m values are revealed. • The origin of the intrinsically low lattice thermal conductivities of PbBi 2 S 4 , Pb 3 Bi 2 S 6 , and Pb 6 Bi 2 S 9 is systematically explored from both theoretical and experimental perspectives. • Strong lattice anharmonicity leads to the extremely low lattice thermal conductivities 0.57, 0.56, and 0.80 W m−1 K−1 in PbBi 2 S 4 , Pb 3 Bi 2 S 6 , and Pb 6 Bi 2 S 9 compounds at room temperature. Ternary Pb-Bi-S compounds emerge as potential thermoelectric materials owing to low thermal conductivity, but the origin of their intrinsic low lattice thermal conductivities lacks further investigation. Herein, a series of ternary Pb m Bi 2 S 3+ m (m = 1–10) compounds are synthesized and their crystal structure evolutions with increasing m values are clearly unclosed. The room-temperature lattice thermal conductivities in PbBi 2 S 4 , Pb 3 Bi 2 S 6 and Pb 6 Bi 2 S 9 can reach at 0.57, 0.56 and 0.80 W m−1 K−1, respectively, outperforming other ternary sulfur-based compounds. Theoretical calculations show that the low lattice thermal conductivities in Pb m Bi 2 S 3+ m (m = 1–10) mainly originate from soft phonon dispersion caused by strong lattice anharmonicity, and both asymmetric chemical bond and lone pair electrons (Pb 6 s 2 and Bi 6 s 2) can favorably block phonon propagation. Furthermore, the elastic measurements also confirm relatively low sound velocities and shear modulus, and the Grüneisen parameter (γ) calculated by sound velocities can reach at 1.67, 1.85 and 1.94 in PbBi 2 S 4 , Pb 3 Bi 2 S 6 and Pb 6 Bi 2 S 9 , respectively. Finally, the intrinsic low lattice thermal conductivities in Pb m Bi 2 S 3+ m (m = 1–10) contribute to promising thermoelectric performance, and the maximum ZT values of 0.47, 0.38 and 0.45 can be achieved in undoped PbBi 2 S 4 , Pb 3 Bi 2 S 6 and Pb 6 Bi 2 S 9 , respectively. [Display omitted] [ABSTRACT FROM AUTHOR]

• A facile method of gradient rolling is provided to attain inverse gradient nanostructure (iGNS). • The iGNS is firstly demonstrated in a Ti-Ni shape memory alloy (SMA) wire. • The iGNS leads to a reversible gradient martensitic transformation upon stressing. • The iGNS SMA exhibits quasi-linear superelasticity in a wide temperature range with improved SE strain and efficiency. Gradient nanostructured (GNS) metallic materials are commonly achieved by gradient severe plastic deformation with a gradient of nano- to micro-sized structural units from the surface/boundaries to the center. Certainly, such GNS can be inversely positioned, which however has not yet been reported. The present work reports a facile method in deformation gradient control to attain inverse gradient nanostructured (iGNS), i.e., tailoring the cross-section shape, successfully demonstrated in Ti-50.3Ni shape memory alloy (SMA) wire through cold rolling. The microstructure of the rolled wire is characterized by a macroscopic inverse gradient from boundaries to the center—the average sizes of grain and martensite domain evolve from micrometer to nanometer scale. The iGNS leads to a gradient martensitic transformation upon stress, which has been proved to be effectively reversible via in-situ bending scanning electron microscopy (SEM) observations. The iGNS Ti-50.3Ni SMA exhibits quasi-linear superelasticity (SE) in a wide temperature range from 173 to 423 K. Compared to uniform cold rolling, the gradient cold rolling with less overall plasticity further improves SE strain (up to 4.8 %) and SE efficiency. In-situ tensiling synchrotron X-ray diffraction (SXRD) analysis reveals the underlying mechanisms of the unique SE in the iGNS SMAs. It provides a new design strategy to realize excellent SE in SMAs and sheds light on the advanced GNS metallic materials. [Display omitted] [ABSTRACT FROM AUTHOR]

• To choose the best seed alloy and suitable dopants, the assumed screening criteria include small anisotropy, high specific modulus, high dynamical stability, and high ductility. • As compared to a traditional trial-and-error concept, our proposed multi-principal element alloy design strategy and screening criteria can substantially reduce the exploration of alloy space and thus accelerate alloy design. • We find a shortcut to design U-based high-entropy alloy from typical binary (UTi and UNb) to ternary (UTiNb), quaternary (UTiNbTa), and quinary (UTiNbTaFe). The dynamical stability and mechanical properties of candidates are greatly enhanced with increasing the number of multi-principal element, indicating the feasibility and effectiveness of adopted alloying strategy. • As compared to the empirical strength-hardness relationship, improved strength prediction can be achieved using a parameter-free theory considering volume mismatch and temperature effect on yield strength. It is found that larger volume mismatch corresponds to higher yield strength. Reducing the exploration of multi-principal element alloy space is a key challenge to design high-performance U-based high-entropy alloy (UHEA). Here, the best combination of multi-principal element can be efficiently acquired because proposed alloying strategy and screening criteria can substantially reduce the space of alloy and thus accelerate alloy design, rather than enormous random combinations through a trial-and-error approach. To choose the best seed alloy and suitable dopants, the screening criteria include small anisotropy, high specific modulus, high dynamical stability, and high ductility. We therefore find a shortcut to design UHEA from typical binary (UTi and UNb) to ternary (UTiNb), quaternary (UTiNbTa), and quinary (UTiNbTaFe). Finally, we find a best bcc senary UHEA (UTiNbTaFeMo), which has highest hardness and yield strength, while maintains good ductility among all the candidates. Compared to overestimation from empirical strength-hardness relationship, improved strength prediction can be achieved using a parameter-free theory considering volume mismatch and temperature effect on yield strength. This finding indicates that larger volume mismatch corresponds to higher yield strength, agreeing with the available measurements. Moreover, the dynamical stability and mechanical properties of candidates are greatly enhanced with increasing the number of multi-principal element, indicating the feasibility and effectiveness of adopted alloying strategy. The increasing of multi-principal element corresponds to the increasing valence electron concentration (VEC). Alternatively, the mechanical properties significantly improve as increasing VEC, agreeing with measurements for other various bcc HEAs. This work can speed up research and development of advanced UHEA by greatly reducing the space of alloy composition. [ABSTRACT FROM AUTHOR]

• Fine equiaxed grains strengthened by coherent Laves nanoprecipitates were successfully prepared in FeCrAl alloy using a novel processing method. • The novel FeCrAl alloys exhibit a ultrahigh yield strength over ∼992 MPa, excellent uniform elongation of ∼7.6% at room temperature, and superior thermal stability at temperature ∼1200 °C. • The enrichment of Si element in Laves precipitates not only decreases their stacking fault energy but also improves their thermal stability. • The advantage of nanoprecipitation engineering in this paper is also applicable to other precipitate-strengthened alloys. Designing microstructurally stable FeCrAl alloys with excellent strength-ductility synergy is highly desirable for their engineering applications. However, due to the preference nucleation of precipitates at grain boundaries (GBs), the improved precipitation strengthening of these alloys is usually accompanied by intergranular embrittlement. Here, we propose a novel thermomechanical processing route coupled with the Si alloying strategy via precipitation of coherent deformable Laves precipitates inside equiaxed fine-grains to achieve FeCrAl alloys with ultrahigh yield strength over ∼992 MPa, excellent uniform elongation of ∼7.6% at room temperature, and superior thermal stability at temperature ∼1200 °C. The Si alloying not only decreases the stacking fault energy of Laves precipitates favorable for their stacking-fault-mediated deformation but also hinders grain coarsening at 1200 °C due to the Si-enrichment favorable for GB pinning effects. Our results prove the possibility of achieving the collaborative enhancement of mutually exclusive properties in alloys, such as strength-ductility-thermal stability via nanoprecipitation engineering, and offer a promising route to prepare dispersion-strengthened materials. [Display omitted] [ABSTRACT FROM AUTHOR]