Tuning superelasticity in high entropy alloy via a hidden strain order.

Superelasticity - exhibiting either Hookean (linear) or non-Hookean (nonlinear) recoverable strain beyond 2% - has been realized in distinct material systems such as metallic glasses, shape memory alloys, strain glass alloys and Gum metals, enabling diverse technological applications. Here we demonstrate that, through compositional tuning in a high-entropy alloy, the elastic behavior can be continuously and reversibly modulated between Hookean superelasticity, non-Hookean superelasticity with an ultrahigh recoverable strain of ~8%, and back to the Hookean regime. By combining atomic-scale strain mapping and extensive first-principles calculations, we reveal that this tunability is governed by a hidden strain order, arising from frustrated crystallization of two competing phases. As a result, local lattice distortion arises, producing a heterogeneous strain landscape that modulates phase stability, phase transformation propensity, and elastic response. Our findings establish a materials design strategy for programming Hookean and non-Hookean elasticity behavior on demand, with promising applications in microelectromechanical systems, high-precision actuators, and adaptive damping devices.