Analysis on the key role in corrosion behavior of CoCrNiAlTi-based high entropy alloy

Abstract

In this study, CoCr2Ni2AlTi, Co2Cr2Ni2AlTi and CoCr2Ni3AlTi alloys are prepared using vacuum arc melting furnace. The morphology, microstructure, compositions and corrosion behavior in 3.5 wt% NaCl solution or 0.5 M H2SO4 solution are investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive spectrometer (EDS) and electro-chemical workstation, respectively. The results show that all high entropy alloys (HEAs) display analogous petal-like equi-axed dendrite and the dendrite arms are thin-like strip. The BCC1 phase is mainly rich in Al–Ni–Ti elements, the BCC2 is rich in Cr element and the FCC phase is composed of Co–Ti elements. Besides, the high contents of Co can promote distribution of Cr into inter-dendrite and can promote the formation of the nano-particles. In addition, all HEAs have better corrosion resistance than 304 stainless steel or other corrosion resistant HEAs and Co2Cr2Ni2AlTi has the best corrosion resistance in three HEAs under NaCl solution or H2SO4 solution. Cr element can form the passivation film Cr2O3, which has an important role in improving corrosion resistance. Co element can increase the stability of the passivation film and attenuates the hydrolysis of Cr3+. Ni element cannot increase the stability of the passivation film and promote the hydrolysis of Cr3+ in H2SO4 solution.