Microstructural characterization and corrosion behavior of AlxCoCrFeNi high entropy alloys

In this study, AlxCoCrFeNi high entropy alloys (x = 0, 0.25, 0.75, 1.25 and 2) with multiprincipal elements were prepared by induction-melting in Ar atmosphere. The microstructural evaluation showed that with increasing aluminum content, the AlxCoCrFeNi alloys change from a single FCC phase to a single BCC phase with a transition duplex FCC/BCC region. Moreover, the increase of aluminum led to dendritic structure in associated with elemental segregation and alloy strengthening. The highest hardness (700 HV) was observed to be achieved for x = 0.75, in which the structure changed from FCC to FCC/BCC dual phase. The potentiodynamic polarization test of the AlxCoCrFeNi alloys showed that the corrosion current densities increased with increment of molar ratio of aluminum element. The FCC structure is a corrosion resistant phase regarding to promotion of polarization resistance values. Also, EIS test demonstrated that with increasing molar ratio of Al and presence of BCC phase, the value of corrosion resistance reduced due to passive layer properties and elemental segregation.