Compositional Dependence of Phase Selection in CoCrCu_0.1FeMoNi-Based High-Entropy Alloys

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• High-entropy alloys (HEAs) offer unique properties due to their complex multi-element compositions.
• Understanding phase selection in HEAs is crucial for tailoring their microstructure and performance.
• The CoCrCu_0.1FeMoNi HEA system is a promising candidate for various applications.

Purpose of the Study:

• To investigate the effect of substituting Mo with other elements (Co, Cr, Fe, Ni) on phase selection in CoCrCu_0.1FeMoNi HEAs.
• To correlate microstructural features with key physical parameters governing phase stability.

Main Methods:

• Systematic variation of alloy composition by partially replacing Mo with Co, Cr, Fe, and Ni.
• Microstructural characterization using techniques to identify dendritic, inter-dendritic, and eutectic phases.
• Analysis of phase selection based on atomic radius ratio (δ), valence electron concentration (VEC), mixing entropy (ΔS), local lattice distortion (α₂), and electronegativity differences.

Main Results:

• A single-phase face-centered cubic (FCC) solid solution was achieved by increasing the molar ratio of Fe, Co, and Ni, stabilizing the FCC structure.
• Specific ranges of δ, VEC, ΔS, α₂, and ΔS/δ² were identified for FCC, FCC + body-centered cubic (BCC), and FCC/BCC + intermetallic (IM) phase formations.
• Electronegativity differences were found to favor the formation of the IM phase.

Conclusions:

• Fe, Co, and Ni act as FCC stabilizers in the CoCrCu_0.1FeMoNi HEA system.
• While several parameters correlate with phase formation, ΔS, α₂, and ΔS/δ² were insufficient for predicting the transition between IM and BCC phases.
• Mixing enthalpy was not a reliable predictor of phase structures in this specific HEA system.