Phase evolution, mechanical properties, and corrosion behavior of FeCoNiCu-based high-entropy alloys
M. Shirali, Kh. Gheisari, M. Reihanian
Abstract
This study comprehensively investigates the phase microstructure, mechanical properties, and corrosion behavior of FeCoNiCu and its Mo, Si, Cr, and Nb-substituted high-entropy alloys (HEAs). X-ray diffraction (XRD) revealed a single FCC phase in FeCoNiCu and FeCoNiCuMo, while FeCoNiCuSi exhibited a complex multiphase structure (BCC + FCC + intermetallics), FeCoNiCuCr a dual-FCC phase, and FeCoNiCuNb an FCC phase with a Co 2 Nb intermetallic. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) confirmed these phase distributions and revealed elemental segregation in Mo, Si, Cr, and Nb-containing alloys. Mechanical compression tests showed ductile behavior for FeCoNiCu (yield strength 170 MPa), FeCoNiCuMo (330 MPa), and FeCoNiCuCr (165 MPa), while FeCoNiCuSi (fracture strength 116 MPa) and FeCoNiCuNb (458 MPa) exhibited brittle fracture, correlating with their complex microstructures and high hardness (863 HV and 414 HV, respectively). Electrochemical corrosion studies in NaCl solution showed that FeCoNiCuNb exhibited the lowest corrosion current density, attributed to a semi-passive Nb 2 O 5 -rich layer confirmed by electrochemical impedance spectroscopy (EIS). The EIS evaluation revealed a total corrosion resistance of 45.666 kΩ cm 2 for FeCoNiCuNb, significantly higher than FeCoNiCu (17.701 kΩ cm 2 ), FeCoNiCuMo (1.582 kΩ cm 2 ), FeCoNiCuCr (1.738 kΩ cm 2 ), and FeCoNiCuSi (4.234 kΩ cm 2 ), indicating less developed passive films and more active corrosion behavior in the other compositions. The interplay between phase microstructure, mechanical response, and corrosion resistance highlights the critical role of alloying additions in tailoring the overall performance of these high-entropy alloys.