Stability of ordered L12 and B2 precipitates in face centered cubic based high entropy alloys - Al0.3CoFeCrNi and Al0.3CuFeCrNi2

Adding a small amount of Al to the well-known high entropy alloy (HEA), Al0.1CoCrFeNi, to form Al0.3CoCrFeNi, leads to the precipitation of highly refined ordered L1(2) precipitates, which are stable at 550 C. However, the L12 precipitates (stoichiometry of (Ni,Cr)(3)(Al,Fe,Co)) are de-stabilized and replaced by coarser B2 precipitates on annealing at 700 C. Contrastingly, in the Co-free, Al0.3CuCrFeNi2 high entropy alloy, the L1(2) precipitates are stable at both 550 degrees C (similar to 5 nm) and 700 degrees C (similar to 50 nm), and exhibit a stoichiometry of (NLCu)(3)(ALFe,Cr). These results lead to interesting insights into the stability of ordered phases in HEAs as a function of composition and temperature. (C) 2016 Elsevier Ltd. All rights reserved.