Laves phase assisted the passive behaviors of Co-free non-equiatomic Cr-Fe-Ni-Nb eutectic high-entropy alloys

Abstract

A novel Co-free non-equiatomic Cr-Fe-Ni-Nb eutectic high entropy alloys (EHEAs) were developed, and the microstructures, corrosion behaviors, and mechanism of as-cast EHEAs were explored in 3.5 wt% NaCl solution. The quaternary EHEAs demonstrated the typical lamellar microstructure, evidencing that a dual-phase microstructure composed of FCC (Nb-lean) and Laves (Nb-rich) phases. With increase of Nb, the volume fraction of the Laves phase increased, while the interlayer distance decreased from 340 nm to 150 nm, leading to significantly improvement of corrosion resistance. The Co-free EHEAs displayed the distinguished combination of a wide passive region (approximately 1300 mV), a low corrosion current density of 6.31 × 10−8 A cm−2, and a superior repassivation ability, with preeminent corrosion resistance compared to the established anticorrosion alloys. Reasonable control of the Nb content could reduce of the point-defect density in the passive films. Especially, for Cr8Fe8Ni13Nb5 EHEAs, the critical pitting potential (1148 mV) was increased by nearly three times higher than that of SS304. The outcome of our study enriched the designing system of the eutectic high entropy alloys with excellent corrosion resistance.