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

• Micro-pillar compression tests were carried on a multiple high-entropy alloy. • Deformation behaviors of FCC , BCC and their interphase pillars were analyzed. • The strain bursts weakened with increasing strain in interphase pillar. • Interphase pillar exhibited better mechanical properties compared with FCC and BCC. • Revealed the relation between small scale deformation and interphase strengthening. 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 Fe 24 Co 25 Ni 24 Cr 23 Al 4 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.