Cryogenic-deformation-induced phase transformation in an FeCoCrNi high-entropy alloy

Abstract

An FeCoCrNi high-entropy alloy (HEA) was deformed at ambient temperature and cryogenic temperatures down to 4.2 K. Phase transformation from a face-centered cubic (FCC) structure to a hexagonal close-packed (HCP) structure occurred during cryogenic deformation. Lowering the temperature promotes the transformation. Atomic-scale structural characterisation suggested that the formation of the HCP structure was achieved via the glide of Shockley partial dislocations on every other {111} FCC plane. Due to the kinetic limitation, the occurrence of this transformation was limited even though theoretical investigations predicted lower free energy of the HCP phase than that of the FCC phase in the HEA. IMPACT STATEMENT Atomic-scale FCC-to-HCP transformation was revealed in an FeCoCrNi high-entropy alloy during cryogenic-temperature deformation. The transformation was restricted due to the kinetic limitation.

Microstructure, Texture, and Strength Development during High-Pressure Torsion of CrMnFeCoNi High-Entropy Alloy

“…Unfortunately, the HCP diffraction spots cannot be selected separately to locally identify the HCP phase by dark-field imaging. However, in comparison with high resolution TEM images of CrFeCoNi and CrCoNi medium-entropy alloys (MEAs) [21,22] tensile tested at cryogenic temperatures the lamellar features observed may be reasonably attributed to the HCP phase. The spotty TEM diffraction pattern for HPT at LNT in comparison to that at RT [4] indicates that with decreasing temperature deformation becomes more heterogeneous.…”

Twinning-induced strain hardening in dual-phase FeCoCrNiAl0.5 at room and cryogenic temperature

“…While slip is the most common deformation mode in fcc and bcc materials there are now several high and medium entropy alloys that benefit from deformation twinning and from strain- or pressure-induced martensitic transformation 3 , 4 , 10 , 11 , 24 , 38 – 44 . Especially, the damage tolerance (toughness) profits substantially from these effects.…”

Fundamental understanding of mechanical behavior of high-entropy alloys at low temperatures: A review

“…Moreover, the ultimate tensile strength and the work hardening rate are increased due to the interfaces in the grains introduced by twinning during deformation. In the latest study, by Lin et al, 41 the authors observed the phase transformation from FCC to HCP structure in the FeCoCrNi HEA during cryogenic deformation at a low temperature, i.e., 4.2 K. They confirmed that the phase transformation is associated with the glide of Shockley partial dislocation on the {111} plane of the FCC phase. However, the effect of the phase transformation on the cryogenic mechanical properties of the FeCoCrNi HEA is not clear.…”