Effect of rare earth La2O3 on the microstructure and corrosion resistance of CoCrFeNiMoSi high entropy alloys

This study systematically investigated the effect of incorporating trace amounts of La2O3 into the CoCrFeNiMoSi high-entropy alloy (HEA) system on its corrosion resistance in neutral chloride ionic salt solutions. The CoCrFeNiMoSi HEA coatings and CoCrFeNiMoSi-0.5 % La2O3 HEA coatings were prepared using the laser melting technique. The microstructure, phase composition, and electrochemical corrosion performance were characterized using X-ray diffraction, scanning electron microscopy, electrochemical workstation, and X-ray photoelectron spectroscopy. The experimental results revealed that the microstructure primarily comprised face-centered cubic structure (FCC), body-centered cubic structure (BCC), and Si-rich intermetallic compounds. Notably, the addition of La2O3 facilitated the formation of the FCC phase. Electrochemical tests demonstrated that the CoCrFeNiMoSi-0.5 % La2O3 HEA coating exhibited an elevated corrosion potential and a reduced self-corrosion current density when compared to the CoCrFeNiMoSi HEA coating. The X-ray photoelectron spectroscopy (XPS) data revealed a notable increase in the Cr content and oxide content of the passive film when La2O3 was present in the HEA. This resulted in the formation of a more protective passivated film. Consequently, the potential utilization of rare earth lanthanum oxide to enhance the corrosion resistance of HEA coatings is promising.