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Superelasticity associated with martensitic transformation has found a broad range of engineering applications, such as in low-temperature devices in the aerospace industry. Nevertheless, the narrow working temperature range and strong temperature sensitivity of the first-order phase transformation significantly hinder the usage of smart metallic components in many critical areas. Here, we scrutinized the phase transformation behavior and mechanical properties of multicomponent B2-structured intermetallic compounds. Strikingly, the (TiZrHfCuNi)_83.3Co_16.7 high-entropy intermetallics (HEIs) show superelasticity with high critical stress over 500 MPa, high fracture strength of over 2700 MPa, and small temperature sensitivity in a wide range of temperatures over 220 K. Themore » complex sublattice occupation in these HEIs facilitates formation of nano-scaled local chemical fluctuation and then elastic confinement, which leads to an ultra-sluggish martensitic transformation. The thermal activation of the martensitic transformation was fully suppressed while the stress activation is severely retarded with an enhanced threshold stress over a wide temperature range. Moreover, the high configurational entropy also results in a small entropy change during phase transformation, consequently giving rise to the low temperature sensitivity of the superelasticity stress. Furthermore, our findings may provide a new paradigm for the development of advanced superelastic alloys, and shed new insights into understanding of martensitic transformation in general.« less

Monolithic metallic glasses often exhibit work softening induced by high atom mobility in the supercooled liquid region in tension. In this work, we report an unusual viscous flow of the Pd_42.5Ni_42.5P₁₅ metallic glass in its supercooled liquid region, which is characterized by a remarkable hardening behavior with decent plasticity during tension. To unravel the causes of this unusual hardening, we conducted structural and thermodynamic analyses by employing several experiments, including dynamic mechanical analysis, differential scanning calorimetry, high-resolution transmission electron microscopy, and in situ heating synchrotron high-energy x-ray diffraction. It was found that the unusual hardening behavior was attributed to structuralmore » ordering during deformation, rather than nanocrystallization or structural relaxation observed, sometimes, in metallic glasses deformed in supercooled liquid region. We also incorporated an additional work hardening region in the modified deformation map for metallic glasses.« less

The equiatomic CrMnFeCoNi high-entropy alloy (HEA) exhibits outstanding toughness and excellent strength-ductility combination at cryogenic temperatures. However, its strength is relatively low at room temperature. In order to strengthen this HEA, microalloying additions of 0.8 at.% Nb and C were made and its properties and microstructure evaluated. It was found that the microalloying resulted in the formation of carbide precipitates and a reduction of the grain size to ~2.6 μm. As a result, the room-temperature tensile yield strength (732 MPa) of the microalloyed HEA is roughly double that of the base HEA (with a concomitant increase in the ultimate strength)more » while its ductility is maintained at a relatively high level (elongation to fracture of ~32%). The strengthening is due to precipitation hardening from the nanoscale carbide particles and grain refinement.« less

We have researched the crystallization kinetics of Ca₄₀Mg₂₅Cu₃₅ bulk metallic glass under isothermal annealing in the supercooled liquid region, with and without applied stress, by in situ high-energy synchrotron x-ray diffraction. We observed that without stress, crystallization started from the very beginning of isothermal annealing. Yet, when a uniaxial compressive stress was applied during isothermal annealing, no change in atomic order was observed at the beginning. Thereafter, the glassy structure relaxed, but still without noticeable evidence of crystallization. It is proposed that the applied compressive stress restricted the atomic mobility, which suppressed crystallization.

Recent studies indicated that high-entropy alloys (HEAs) possess unusual structural and thermal features, which could greatly affect dislocation motion and contribute to the mechanical performance, however, a HEA matrix alone is insufficiently strong for engineering applications and other strengthening mechanisms are urgently needed to be incorporated. In this work, we demonstrate the possibility to precipitate nanosized coherent reinforcing phase, i.e., L1₂-Ni₃(Ti,Al), in a fcc-FeCoNiCr HEA matrix using minor additions of Ti and Al. Through thermomechanical processing and microstructure controlling, extraordinary balanced tensile properties at room temperature were achieved, which is due to a well combination of various hardening mechanisms, particularlymore » precipitation hardening. The applicability and validity of the conventional strengthening theories are also discussed. In conclusion, the current work is a successful demonstration of using integrated strengthening approaches to manipulate the properties of fcc-HEA systems, and the resulting findings are important not only for understanding the strengthening mechanisms of metallic materials in general, but also for the future development of high-performance HEAs for industrial applications.« less