Abstract
The generalized stacking fault energy (GSFE) is a material property that can provide invaluable insights into describing nanoscale plasticity phenomena in crystalline materials. Lattice strains have been suggested to influence such phenomena. Here, the GSFE curves for sequential faulting pathways in dual phase [face-centered cubic (fcc) and hexagonal close-packed (hcp)] ${\mathrm{Cr}}_{20}{\mathrm{Mn}}_{20}{\mathrm{Fe}}_{20}{\mathrm{Co}}_{20}{\mathrm{Ni}}_{20}, {\mathrm{Cr}}_{25}{\mathrm{Fe}}_{25}{\mathrm{Co}}_{25}{\mathrm{Ni}}_{25}, {\mathrm{Cr}}_{20}{\mathrm{Mn}}_{20}{\mathrm{Fe}}_{34}{\mathrm{Co}}_{20}{\mathrm{Ni}}_{6}, {\mathrm{Cr}}_{20}{\mathrm{Mn}}_{20}{\mathrm{Fe}}_{30}{\mathrm{Co}}_{20}{\mathrm{Ni}}_{10}$, and ${\mathrm{Cr}}_{10}{\mathrm{Mn}}_{30}{\mathrm{Fe}}_{50}{\mathrm{Co}}_{10}$ high-entropy alloys are investigated on ${{111}}_{\text{fcc}}$ and ${(0002)}_{\text{hcp}}$ close-packed planes using density-functional calculations. The dependence of GSFEs on imposed volumetric and longitudinal lattice strains is studied in detail for ${\mathrm{Cr}}_{20}{\mathrm{Mn}}_{20}{\mathrm{Fe}}_{20}{\mathrm{Co}}_{20}{\mathrm{Ni}}_{20}$ and ${\mathrm{Cr}}_{10}{\mathrm{Mn}}_{30}{\mathrm{Fe}}_{50}{\mathrm{Co}}_{10}$. The competition between various plastic deformation modes is discussed for both phases based on effective energy barriers determined from the calculated GSFEs and compared with experimentally observed deformation mechanisms. The intrinsic stacking fault energy, unstable stacking fault energy, and unstable twinning fault energy are found to be closely related in how they are affected by applied strain. The ratio of two of these planar fault energies can thus serve as characteristic material property. An inverse relationship between the intrinsic stacking fault energy in the hcp phase and the axial ratio ${(c/a)}_{\text{hcp}}$ is revealed and explained via band theory.
Highlights
The research field of high-entropy alloys (HEAs) has attracted significant attention since these were proposed by Yeh et al [1] and Cantor et al [2]
We found that the strain derivatives of γisf, γusf, and γutf evaluated at zero strain closely satisfy the following relation, d γutf dγusf + 1 dγisf
We presented a density-functional theory (DFT) investigation of generalized stacking fault energy (GSFE) in five polymorphic, four- and five-component HEAs composed of Cr, Mn, Fe, Co, and Ni in their compositionally equivalent fcc and hcp phases
Summary
The research field of high-entropy alloys (HEAs) has attracted significant attention since these were proposed by Yeh et al [1] and Cantor et al [2]. Tailoring phase stability in HEAs towards exhibiting a transformation-induced fcc to hcp phase transition resulted in the development of Cr20Mn20Fe34Co20Ni6 and Cr10Mn30Fe50Co10 [5,11] Both two-phase HEAs show superior strength-ductility combinations than mono-phase counterparts owing to several active hardening mechanisms. These recent experimental progresses motivate to explore and understand the fundamental deformation mechanisms underlying crystal plasticity in advanced polymorphic HEAs. The intrinsic stacking fault (ISF) energy is an experimentally and theoretically accessible material property often claimed to be correlated with the predominantly active plastic deformation mode in the fcc phase of metals and alloys.
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