Rapid forming of high-entropy alloy under extreme low temperature via ultrasonic vibration

Low-temperature forming technology has a wide range of applications, particularly in aerospace and polar exploration. However, its application often confined by the low-temperature brittleness of metallic materials. This study proposes a simple and efficient route to form high-entropy alloys at a low temperature (77 K) using ultrasonic vibration, termed ultrasonic-assisted plastic forming. Our findings demonstrate that this ultra-fast processing technology can achieves a macroscopic high strain rate of 1.25 x 10- 1 s- 1 with significantly lower stress compared to conventional compression methods. The reduction in stress is attributed to the deformation twin and large angle grain rotation induced by ultrasonic vibration, which activate additional slip systems and facilitates deformation. The Vickers hardness in the processed surface increases by 39.1 % compared to the as- cast sample, suggesting the method enables simultaneous surface modification and forming. Furthermore, fine multi-scale structures and with small parts of special shapes are fabricated successfully using the proposed method. The detailed structure characterization of the formed sample and the proposed forming mechanism provide valuable insight into deformation under dynamic loading. Owing to its high efficiency and lightweight equipment requirements resulting from low forming stress, ultrasonic-assisted plastic forming holds potential for engineering applications in forming metal alloys, even in extreme environments.