Ultrastrong and ductile high-entropy alloy with minimal serration at liquid helium temperature via coherent nanoprecipitate

초록

The concept of high-entropy alloys (HEAs) introduces a promising approach to designing cryogenic alloys. However, assessment of their mechanical behavior is mostly limited to liquid nitrogen temperature. Additionally, tailoring discontinuous plastic flow (DPF) at near 0 K is essential for preventing inhomogeneous localized deformation and premature failure. Here, we show that precipitation strengthening via coherent nanoprecipitates introduces a synergetic effect in improving mechanical properties and governing DPF at liquid helium temperature (4.2 K). A direct-aged Cr18Fe18Co28Ni28Al4Ti4 alloy exhibits exceptional strength-ductility synergy (2186 MPa-16.2 %) at 4.2 K, with remarkably low stress-drop amplitude, despite its considerably high strength. Micro-plasticity mechanisms, facilitated by nanoprecipitates and their short-range interaction with dislocations, improve the strain-hardening rate and reduce the size of dislocation avalanches, leading to insignificant stress drop. These findings demonstrate that employing coherent precipitates can be a promising design strategy for cryogenic alloys, even in extreme environments close to absolute zero.

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