Achieving Single Solid Solution in Equimolar AlCrCuFeNi via Rapid Solidification

Abstract

This study investigates the effect of cooling rate on the equimolar AlCrCuFeNi High-Entropy Alloy (HEA) using a 6.5m-tall drop-tube facility. It is found that as-cast AlCrCuFeNi comprises an FCC phase and a B2 phase. However, the AlCrCuFeNi alloy is found to attain a single B2 structure at cooling rates of 10² K/s and above. The cooling rates achieved in this work are estimated to vary between 112 K/s and 1.13×10⁶ K/s. Phase separation within the dendrites is observed in the as-cast alloy. This phase separation occurs via spinodal decomposition and is inhibited only at the highest achieved cooling rate of around 1.13×10⁶ K/s. As such, with higher cooling rates, simpler microstructures are obtained, extending the solid-solution of the system. This is one of the primary objectives in employing rapid-solidification techniques in HEAs. Finally, the microhardness of the rapidly cooled samples is probed and found to increase with cooling rate. Notable jumps in microhardness are noted and related to changes in morphology.