Quantitative and well-targeted design of modern alloys is extremely challenging due to their immense compositional space. When considering only 50 elements for compositional blending the number of possible alloys is practically infinite, as is the associated unexplored property realm. In this paper, we present a simple property-targeted quantitative design approach for atomic-level complexity in complex concentrated and high-entropy alloys, based on quantum-mechanically derived atomic-level pressure approximation. It allows identification of the best suited element mix for high solid-solution strengthening using the simple electronegativity difference among the constituent elements. This approach can be used for designing alloys with customized properties, such as a simple binary NiV solid solution whose yield strength exceeds that of the Cantor high-entropy alloy by nearly a factor of two. This study provides general design rules that enable effective utilization of atomic level information to reduce the immense degrees of freedom in compositional space without sacrificing physics-related plausibility.
The formation of a single phase is an important requirement for high-entropy ceramics (HECs) because precipitation of unwanted phases generally degrades their functional properties. This paper provides a useful guideline for the single-phase formation of HECs. First, metal elements constituting HECs can be divided into two groups: elements that have a parent phase as a stable phase and elements that have a phase with the same stoichiometry as the parent phase but a different crystal structure. Second, even when the latter elements are added in an HEC, we can stabilize the parent phase if stabilizing energy by configurational entropy is larger than the difference in formation energy due to their stable phase, which can be quantitatively calculated through first-principles calculation. Interestingly, based on these guidelines, (CrMnFeCoNi)Si HE silicide with a single B20 structure was sequentially developed from mono-silicide. In particular, the HEC with maximized configurational entropy was searched in our HEC system by adding NiSi to (CrMnFeCo)Si, which is stable in B31 and B20 structures. This study offers a chance to increase the structural and compositional complexity in HECs, enabling the expansion of the single-phase region in HECs.
Herein, we carefully investigate the effect of nitrogen doping in the equiatomic CoCrFeMnNi high-entropy alloy (HEA) on the microstructure evolution and mechanical properties. After homogenization (1100 °C for 20 h), cold-rolling (reduction ratio of 60%) and subsequent annealing (800 °C for 1 h), a unique complex heterogeneous microstructure consisting of fine recrystallized grains, large non-recrystallized grains, and nanoscale Cr2N precipitates, were obtained in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA. The yield strength and ultimate tensile strength can be significantly improved in nitrogen-doped (0.3 wt.%) CoCrFeMnNi HEA with a complex heterogeneous microstructure, which shows more than two times higher than those compared to CoCrFeMnNi HEA under the identical process condition. It is achieved by the simultaneous operation of various strengthening mechanisms from the complex heterogeneous microstructure. Although it still has not solved the problem of ductility reduction, as the strength increases because the microstructure optimization is not yet complete, it is expected that precise control of the unique complex heterogeneous structure in nitrogen-doped CoCrFeMnNi HEA can open a new era in overcoming the strength–ductility trade-off, one of the oldest dilemmas of structural materials.
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