On the mechanical behavior and microstructural evolution of CoCrFeMnNi high entropy alloy in energy-efficient deformation by cyclic-ultrasonic loading

Z Li and LC Zhang and J Ma and AK Gain, JOURNAL OF ALLOYS AND COMPOUNDS, 1048, 185294 (2025).

DOI: 10.1016/j.jallcom.2025.185294

High-entropy alloys (HEAs) exhibit excellent mechanical properties due to the solid solution effect of their multi-principal elements. However, their mechanical behavior under extreme loading conditions remains poorly understood. This study explores the dynamic deformation mechanisms of a CoCrFeMnNi HEA under ultrasonic compressive loading, characterized by an ultra-high strain rate (similar to 10 (3) s(-)(1)) and a cyclic frequency of 20 kHz. Results show that the required deformation stress drops to just 1/13 of that under conventional uniaxial loading, while the deformation energy is reduced to 1/15, indicating a highly energy-efficient deformation mode. This pronounced softening deformation behavior is attributed to the distinct microstructural evolutions activated by ultrasonic vibration. Stress wave concentration near surface layers produces gradient grain refinement from the surface to the core of the HEA sample, along with dense dislocations and nano-twins. Moreover, dislocations dynamic rearrangement and coarse grains rotation have been evoked in the deformation areas under ultrasonic loading. These microstructural evolutions facilitate the rapid release of crystal distortions and the coordinated deformation between coarse grains, thus leading to a remarkable reduction of strain-hardening rate and deformation resistance. In addition, the dislocation density and residual compressive stress after ultrasonic loading are lower than those resulted from uniaxial loading. Based on this, the dynamic deformation mechanisms have been proposed through phenomenological analysis to correlate the microstructural evolutions with the macroscopic mechanical behaviors under ultrasonic loading. These findings offer valuable insights for developing high-efficient processing techniques for HEAs.

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