Effect of Zr on phase separation, mechanical and corrosion behavior of heterogeneous CoCrFeNiZrx high-entropy alloy

CoCrFeNi high entropy alloy (HEA) has attracted extensive attention due to its excellent corrosion resistance, but the low strength limits its engineering application prospects. In order to develop CoCrFeNi based HEAs with high strength, ductility and corrosion resistance, the effects of Zr content on the microstructure, mechanical properties and corrosion resistance of heterogeneous CoCrFeNiZrx (x = 0, 0.25, 0.5 and 1) HEAs were investigated in this work. The results indicate that the increase of Zr content can significantly affect the phase stability of the alloy, and promote the formation of intermetallic compounds (Ni7Zr2 and/or Laves phase) and the transformation of solid solution from face-centered cubic (FCC) structure (x = 0, 0.25 and 0.5) to body-centered cubic (BCC) structure (x = 1). Reasonable control of the Zr content can endow the alloy excellent comprehensive properties. Especially, for CoCrFeNiZr0.25 alloy, composed of FCC matrix and a small amount of Ni7Zr2 phases, the yield strength (similar to 655 MPa) is increased by nearly four times higher than that of Zr-free alloy, and it also has good ductility (fracture stain > 50%). Meanwhile, the corrosion resistance of CoCrFeNiZr0.25 alloy is better than that of SS304. The EIS results show that the addition of Zr reduces the stability of the passive film on the alloy, which can be related to the content of the beneficial oxide in the passive film and the thickness of the passive film through XPS analysis. Moreover, the work functions of different phases in CoCrFeNiZrx alloys were obtained by first-principles calculations, which further confirmed the selective corrosion mechanism of the CoCrFeNiZrx alloy combining the experimental results. (C) 2021 Published by Elsevier Ltd on behalf of Chinese Society for Metals.

Automated summary

The effects of Zr content on the microstructure, mechanical properties, and corrosion resistance of CoCrFeNi high entropy alloy were investigated. Reasonable control of Zr content can enhance the alloy's comprehensive properties, especially CoCrFeNiZr0.25 alloy, which has higher yield strength, good ductility, and better corrosion resistance compared to SS304.