Ultrahigh cryogenic strength and ductility in a duplex metastable ferrous medium-entropy alloy

This work presents a unique low-cost Fe6(2)Co(5)Ni(10)Cr(13)Si(7)Al(3) (at%) medium-entropy alloy (MEA) with ultra-high strength and ductility. A duplex partially recrystallized microstructure consisting of face-centered cubic (FCC) and body-centered cubic (BCC) phases was produced by cold-rolling and short-time annealing in the MEA. In the non-recrystallized area, there are high density dislocations, and the ultra-fine grained matrix has lots of nano-precipitates. This MEA has excellent yield strength (1237 MPa and 1640 MPa) and uniform elongation (12.7% and 29.1%) at 298 K and 77 K. Additionally, due to the high multi-stage strain hardening behavior, the ultimate tensile strength of -2109 MPa is obtained at 77K. The excellent cryogenic mechanical properties are mainly attributed to high density dislocations, ultra-fine grains, nano-precipitates, huge Luders deformation, hetero-deformation-induced hardening, and deformation-induced martensitic transformation.

Automated summary

This work presents a unique low-cost medium-entropy alloy (MEA) with ultra-high strength and ductility. The MEA exhibits a duplex partially recrystallized microstructure consisting of FCC and BCC phases, along with high density dislocations and nano-precipitates. It shows excellent yield strength and uniform elongation at both room temperature and cryogenic temperatures, as well as a high ultimate tensile strength at 77K. The excellent cryogenic mechanical properties can be attributed to various factors including high density dislocations, ultra-fine grains, nano-precipitates, Luders deformation, hetero-deformation-induced hardening, and deformation-induced martensitic transformation.