Nanoscale Phase Separation in Al0.5CoCrFeNi(Cu) High Entropy Alloys as Studied by Atom Probe Tomography

High entropy alloys (HEAs) typically contain five or more principal elements in nearly equiatomic proportions [1–3]. The most studied HEA systems are the AlCoCrFeNi and AlCoCrFeNiCu alloys, which solidify into dendritic and interdentritic regions with an attendant microsegration of solute species. Within these microscale heterogeneities the material microstructures further segregate into (i) nanoscale modulated structures composed of alternating Al/Ni-rich and Fe/Cr-rich phases formed by spinodal decompostion, and (ii) nanoscale Cu precipitate formation. The microstructures formed during casting and after annealing of an Al0.5CoCrFeNi (atomic fraction) HEA, with and without Cu additions, are studied by atom probe tomography (APT). These microstructures are correlated to the observed strength, as measured by Vickers microhardness and uniaxial tensile tests.