Grain refinement and FCC phase formation in AlCoCrFeNi high entropy alloys by the addition of carbon

To refine grains and improve the mechanical properties of the AlCoCrFeNi HEA (high entropy alloy), a series of (AlCoCrFeNi)(100)C--x(x) (x = 0-8, atomic ratio) HEAs were prepared, the alloying effects of C (carbon) on the microstructure and mechanical properties of the HEA were investigated. The results showed that C addition had potential in refining grains; the grains size decreased with increasing C content until 2%. When the C content was more than 1.5%, the second phase (FCC phase) was generated, its fraction increased with the increase of C content. During solidification, C atoms accumulated on the grains surface and inhibited grains growth, which contributed to the refinement of grains size. When the C content was more than 2%, the second phases (FCC phase) were formed. The compressive strength and fracture strain reached the maximum value respectively (3.3 GPa and 35%) when the C content was 1.5%. The grains size decreased with the increase of C content from 0% to 1.5%, which contributed to the increase in compressive strength and fracture strain.