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Shape memory alloys (SMAs) that exhibit superelasticity with large recoverable strain and small hysteresis are in demand for practical applications, although their synthesis remains a challenge. We introduce metastable engineering to dope conventional SMA solid-solution atoms of relatively high concentration with "weak" local lattice distortion to realize ultralow hysteretic superelasticity. Large-scale molecular dynamic (MD) simulations of NiTi-based SMAs are performed to demonstrate how the presence of 2 ∼ 4 at.% Nb dopants lead to a stress-induced transition from a metastable pretransitional state to a strain-glass state. This is facilitated by a macroscopically homogeneous and continuous phase transformation in the course of superelastic loading and unloading. This spinodal decomposition-like phase transformation process endows SMAs with anhysteretic superelasticity that is insensitive to loading direction and grain size (below 15 nm). These findings show promise of achieving ultralow hysteretic superelasticity with large recoverable strain for SMAs. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] Large-scale applications of elastocaloric cooling demand bulk materials showing both large adiabatic temperature change (Δ T a d ) and low-fatigue characteristics at room temperature. Using cold-rolling and aging treatment, we synthesize a bulk Ti 49.2 Ni 40.8 Cu 10 polycrystalline alloy that has microstructural features of nanocrystallinity and epitaxially related Ti(Ni,Cu) 2 nanoprecipitates. It exhibits a large Δ T a d of 13.8 K and a coefficient of performance of 13 at room temperature. Moreover, the degradation of Δ T a d is only 0.3 K after 450 tensile cycles. We attribute the favorable properties to the enhanced reversibility of martensitic transformation during stress cycling, aided by the internal epitaxy-generated stress at the interface between the Ti(Ni,Cu) 2 nanoprecipitates and matrix, together with grain refinement. The results indicate that the alloy offers a good balance of multiple objectives, holding promise for solid-state refrigeration applications. [ABSTRACT FROM AUTHOR]