"Influence of stacking fault energy on tensile properties and plastic deformation mechanisms in CrMnFeCoNi high-entropy alloys"
This presentation focuses on one of the most studied high-entropy alloy systems, namely, fcc CrMnFeCoNi alloys. They have been shown to exhibit exciting mechanical properties, including increasing strength and tensile ductility with decreasing temperature, with composition having a strong effect. In this presentation, I will talk about the tensile properties and deformation mechanisms at room and cryogenic temperatures of single-phase, face-centered-cubic (FCC) CrxMn20Fe20Co20Ni40-x (0 ≤ x ≤ 26 at.%) high-entropy alloys (HEAs) with different grain sizes (6 ≤ d ≤ 283 µm). An interesting characteristic of these alloys is that their stacking fault energy (SFE) strongly decreases as the Cr/Ni ratio increases, while other strength-influencing parameters (solute misfit volumes and elastic constants) remain constant [1, 2]. Therefore, these alloys can be considered model alloys to study the influence of SFE on the tensile properties and deformation mechanisms of FCC HEAs. The intrinsic lattice strength is found to be roughly independent of composition at room temperature, but at 77 K, it increases significantly as the Cr/Ni ratio increases and SFE decreases. In contrast, grain boundary strengthening is almost independent of SFE and temperature. Regarding the deformation mechanisms, nanotwinning occurs at room temperature when x ≥ 20 at.% (SFE ≤ 35 mJ/m2) and for all alloys at 77 K. In addition to nanotwinning, an FCC-to-HCP (hexagonal close-packed) martensitic transformation was observed at 77 K in the Cr26Mn20Fe20Co20Ni14 HEA, which causes early rupture in coarse-grained alloys. Finally, the effect of a grain size reduction on nanotwinning will be addressed in the case of the equiatomic CrMnFeCoNi alloy [3]. Wherever possible, our data will be compared to those of single-crystalline alloys determined experimentally and theoretically.
