Micro/nano-mechanical behaviors of individual FCC, BCC and FCC/BCC interphase in a high-entropy alloy

Here, a systematic investigation was made on the interphase strengthening effects induced superior mechanical performances of multiphase high-entropy alloys (HEAs) at micro/nano-scale, compared with single phase HEAs. A pillar compression test under a scanning electron microscope (SEM) was performed on the individual face centered cubic (FCC), body centered cubic (BCC), and mixed-phases with different diameters in a Fe24Co25Ni24Cr23Al4 HEA using focused ion beam (FIB) milling and a nanoindenter equipped with a flat punch. The stress-strain response of pillar underneath the indenter was selected to explore the diameter/phase-dependent size effect, the periodically fluctuation of local stress, and strain hardening. It was revealed that the pillars at the interphase exhibited significantly higher strength, compared with the FCC and BCC pillars. An experiment also verified the coincident mechanical size effects independent with the type of phases. The stress responses in the mixed-phase pillars manifested as a distinct transition from the dramatic drop to the minor fluctuation during the post-yield stages with the increasing strain, indicating the propagation of Al-Ni enriched solid solution phase (BCC1) under compression. Except the BCC1 phase, numerous dislocations were observed in the post-deformed pillars, particularly serving as the major source to enhance the strain hardening of BCC pillars. (C) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.