Compositional Dependence of Phase Selection in CoCrCu0.1FeMoNi-Based High-Entropy Alloys.

Ning Liu,Pengjie Zhou,Chen Chen,Xiaojing Wang,Isaac Chang

doi:10.3390/ma11081290

Ning Liu, Pengjie Zhou + Show 3 more

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https://doi.org/10.3390/ma11081290

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Abstract

To study the effect of alloy composition on phase selection in the CoCrCu0.1FeMoNi high-entropy alloy (HEA), Mo was partially replaced by Co, Cr, Fe, and Ni. The microstructures and phase selection behaviors of the CoCrCu0.1FeMoNi HEA system were investigated. Dendritic, inter-dendritic, and eutectic microstructures were observed in the as-solidified HEAs. A simple face centered cubic (FCC) single-phase solid solution was obtained when the molar ratio of Fe, Co, and Ni was increased to 1.7 at the expense of Mo, indicating that Fe, Co, and Ni stabilized the FCC structure. The FCC structure was favored at the atomic radius ratio δ ≤ 2.8, valence electron concentration (VEC) ≥ 8.27, mixing entropy ΔS ≤ 13.037, local lattice distortion parameter α2 ≤ 0.0051, and ΔS/δ2 > 1.7. Mixed FCC + body centered cubic (BCC) structures occurred for 4.1 ≤ δ ≤ 4.3 and 7.71 ≤ VEC ≤ 7.86; FCC or/and BCC + intermetallic (IM) mixtures were favored at 2.8 ≤ δ ≤ 4.1 or δ > 4.3 and 7.39 < VEC ≤ 8.27. The IM phase is favored at electronegativity differences greater than 0.133. However, ΔS, α2, and ΔS/δ2 were inefficient in identifying the (FCC or/and BCC + IM)/(FCC + BCC) transition. Moreover, the mixing enthalpy cannot predict phase structures in this system.

Highlights

High-entropy alloys (HEAs) represent a new class of materials that have attracted extensive attention since 2004 [1,2,3,4,5,6,7,8]
HEAs are defined as alloys containing at least five major elements wherein every major element has an atomic fraction between 5% and 35% [9]
A typical eutectic structure is found in the inter-dendritic region, and the volume fraction of the eutectic mixture is decreased with increasing Co and decreasing Mo

Summary

Introduction

High-entropy alloys (HEAs) represent a new class of materials that have attracted extensive attention since 2004 [1,2,3,4,5,6,7,8]. Various studies on HEAs, including composition, processing, crystal structure and microstructure, and physical and mechanical properties, have been performed in the past years [5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23]. The microstructures and crystalline phases present in HEAs are very sensitive to the alloy composition. An α phase appears when the molar ratio of Mo in AlCoCrFeNiMox alloys exceeds 0.1 [17]. Changes in the molar ratio of Fe, Co, and Cr in AlCoCrFeMo0.5 Ni alloys affect the crystalline phases and mechanical properties. As the Mo content increases, the volume fraction of the σ phase increases in Ni2 CrFeMox alloys [18]. The volume fraction of the σ phase is increased with increasing

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