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The FexCoNiCuCr ( x = 0·2, 0·5, 0·8, 1 and 2) high entropy alloys were prepared by arc melting in an argon atmosphere. The effects of the Fe content and heat treatments on the microstructure and hardness of the alloys were investigated using X-ray diffraction, scanning electron microscope, and hardness tests. The as cast alloys consist of two FCC solid solution structures, and display a typical dendrite microstructure with Cu-rich in the interdendrite (ID) region. The heat treatment has no obvious effect on the phase constituents of the alloys, meaning that the alloys have very good thermal stability. At the annealing temperature of 1000°C, the submicrometre-size particles were observed in the dendrite region, while a further high annealing temperature of 1200°C results in the formation of the discontinuous ID phase and ball shape Cu-rich particles. The hardness of the alloys become smaller after being heated at the temperature from 400-1000°C for 5 h. [ABSTRACT FROM AUTHOR]