Abstract
The recrystallization behavior, grain growth kinetics, and corresponding hardness variation of homogenized and 80% cold-rolled FeCoNiCrPd, FeCoNiCrMn, and their quaternary/ternary FCC-structured high/medium entropy alloys (H/MEAs) annealed under different conditions were investigated. Experimental results indicate that the grain size and hardness of these H/MEAs follow the Hall–Petch equation, with the Hall–Petch coefficient KH value being mainly dominated by the alloy’s stacking fault energy and shear modulus. The FeCoNiCrPd alloy exhibits the highest hardness of the H/MEAs at the same grain size due to the largest Young’s modulus difference between Cr and Pd. The grain growth exponent n, kinetic constant k, and activation energy for grain growth QG of all H/MEAs are calculated. The k can be expressed by the Arrhenius equation with QG, which is attributed to the diffusion rate. The results demonstrate that the QG values of these H/MEAs are much higher than those of conventional alloys; most notable is FeCoNiCrPd HEA, which has an unusually lattice distortion effect that hinders grain growth.
Highlights
High entropy alloys (HEAs) are attracting attention for their promising mechanical properties and intriguing concepts in alloy design [1,2,3,4,5,6,7,8]
Yeh et al hypothesized that HEA contained at least five principal elements with equiatomic or near-equiatomic compositions, which would result in high configurational entropy of this multi-principal-element alloy (MPEA) [1]
high/medium entropy alloys (H/MEAs) were fabricated in a vacuum arc remelter (VAR), and the purity of each constituent element was higher than 99.9 wt %
Summary
High entropy alloys (HEAs) are attracting attention for their promising mechanical properties and intriguing concepts in alloy design [1,2,3,4,5,6,7,8]. The high configurational entropy would favor the formation of solid solutions rather than intermetallics by overwhelming the enthalpy of compound formation; i.e., HEAs would develop a single-phase alloy without precipitation. Recent studies have pointed out that secondary phases or precipitates appear in most HEAs [19,20,21,22]. It seems that the initial concept of high configurational entropy is unlikely to overcome the phase separation
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