Influence of the cooling rate on the solidification path and microstructure of a AlCoCrFeNi2.1 alloy

Abstract

The AlCoCrFeNi2.1 alloy is a promising eutectic high entropy alloy which may act as an in-situ composite, showing a trade-off between mechanical properties and ductility. Controlling the microstructure formation is crucial for achieving the best balance since it is closely related to the cooling rates during solidification. Hence, the present study determined the relationship between different cooling rates and the formed microstructures. As such, the AlCoCrFeNi2.1 alloy was subjected to a directional solidification process so that samples solidified at different cooling rates could be generated. The examined samples corresponded to a range from 1 to 6 °C/s, which resulted in microstructures composed of primary dendrites and uncoupled eutectic, with varying secondary dendritic spacings from 18 to 54 μm and eutectic spacings from 4.5 to 10 μm. The use of CALPHAD, XRD, SEM-EDS, and EBSD phase mapping enabled to determine that the primary FCC dendrites formed in all samples enveloped by the FCC + B2 eutectic. Moreover, the solidification cooling rate affected both dendritic (primary phase) and eutectic length-scales. Finally, the solidification sequence path was able to be changed, and the primary FCC dendrites were also able to form, due to the non-equilibrium nature of the solidification process, which imposed particular segregation and growth conditions.