Phase formation in mechanically alloyed AlxCoCrCuFeNi (x = 0.45, 1, 2.5, 5 mol) high entropy alloys

► Homogeneous HEA of AlxCoCrCuFeNi (x = 0.45 - 5 mol) are made by mechanical alloying. ► Increase in Al results in microstructural change from three phases to single phase. ► B2 compound is the stable phase in alloy with highest Al content, Al5CoCrCuFeNi. ► Nanocrystallinity is retained even after exposure to high temperature of 1480 °C. ► Existing criteria of phase formation in HEA are deficient to explain our results.