Microstructure and mechanical behavior of the directionally solidified AlCoCrFeNi2.1 eutectic high-entropy alloy

Obtaining in-situ composites through the solidification of eutectic alloys is an interesting approach to overcome the trade-off between mechanical strength and ductility. A notable example is the AlCoCrFeNi2.1 eutectic high-entropy alloy composed of the hard NiAl-rich (B2) and soft CoCrFeNi-rich (L12) phases. In this study, the directional solidification of the AlCoCrFeNi2.1 alloy was investigated using a vertical Bridgman setup. Aspects such as conditions for growth at very low rates, regular and anomalous eutectic growth, and mechanical behavior were evaluated. The directionally solidified samples exhibited a well-aligned microstructure with a lamellar morphology, regardless of the growth rate employed. The lamellar spacing followed the Jackson and Hunt model, whereas the growth rate did not induce any significant variations in the phase fraction, chemical composition, phase lattice parameter, and hardness. The mechanical behavior of the AlCoCrFeNi2.1 alloy, evaluated through compression tests, was improved in comparison to materials similar to its constituent phases, namely the NiAl (B2) and CoCrFeNi (FCC) alloys.