Microstructural optimization of FexCrNiAl0.5Ti0.5 high entropy alloys toward high ductility

It remains challenging to develop low-cost body-centered cubic (BCC) high-entropy alloys (HEAs) with superior mechanical properties. In this work, we investigated the microstructure and mechanical properties of BCC FexCrNiAl0.5Ti0.5 HEAs containing L21 nanocrystals. With increasing the Fe content from Fe2 to Fe4 and Fe6, the formation of a big blocky L21 phase and a σ phase can be fully suppressed, and the size and fraction of the L21 crystals also decrease. Fe4 and Fe6 HEAs exhibit an optimized dual-phase microstructure with high-density L21 nanocrystals homogeneously distributed in the BCC matrix. Fe4 and Fe6 HEAs show high strength and do not fracture even at a large compressive strain of 70%, exhibiting the best combination of strength and fracture strain among all the reported BCC HEAs with nanocrystals. The superior mechanical properties of Fe4 and Fe6 HEAs are attributed to the optimized microstructure. These findings promote the development of low-cost HEAs with superior mechanical properties.