Effect of annealing treatment on microstructures and mechanical properties of FeCoNiCuAl high entropy alloys

As-cast FeCoNiCuAl high entropy alloys were annealed at various temperatures for a given time. The microstructure and mechanical properties of the annealed FeCoNiCuAl high entropy alloys were investigated using optical microscopy, scanning electron microscopy, X-ray diffraction, compressive and hardness tests. It has been found that the FeCoNiCuAl has high thermal stability. A needle-like Cu-rich FCC phase has been precipitated from the BCC dendrite region when the annealing temperature is higher than 973 K. The higher temperature treatment greatly enhances the plasticity of the alloys, and reduces the hardness of the alloys. The annealing induced change in microstructure and properties could be attributed to a solid phase transformation, which consists of the dissolution of the FCC interdendrite phase into the matrix and the concomitant precipitation of the needle-like shape FCC phase from dendrite region.