The effect of Si addition on the structure and mechanical properties of equiatomic CoCrFeMnNi high entropy alloy by experiment and simulation

The effect of Si addition on the mechanical properties and deformation behaviour of the Cantor alloy in varying compositions from 1 to 5 atomic % has been investigated by experiments and first principle calculations. All alloy compositions exhibit single-phase FCC crystal structures with average grain size ranges from 125–140 μm. Cantor alloy with 1 and 2 atomic % of Si shows an excellent combination of strength and ductility while 5 atomic % Si exhibits the lowest strength and highest ductility (⁓100 %). Detailed TEM analysis of deformed samples revealed the formation of high densities of closely spaced deformation twins in 1 and 2 atomic % Si at room temperature which was observed in Cantor alloy at cryogenic temperatures, while 5 atomic % Si shows the slip-mediated deformation with no observations of the twins. The dependency of the generalized stacking fault energy as a function of Si concentration was investigated by the first principle calculation for Si-containing alloys. The change in deformation mode from twinning for low Si content ( < 4 atomic %) to the dislocation-mediated slip for high Si content ( ≥ 4 atomic %) can be explained based on effective energy barrier, average interlayer distance, and interlayer distance distortion, which is in good agreement with experiments. The study showcases the unique contribution of Si in triggering multiple strengthening and strain hardening mechanisms by stacking fault mediated plasticity in Cantor alloy, thus highlighting the potency of minor alloying additions to single phase HEAs to achieve a large spectrum of strength-ductility paradigm.