Cost-effective and facile route to ultrafine-microstructure high-entropy alloy for cryogenic applications

Industry applications of the current cryogenic high entropy alloys (HEAs) are limited by their prohibitive costs, relatively low yield strength and unknown corrosion resistance. Here, we present a cost-effective and facile approach to produce cryogenic HEAs with lower cost, exceptional mechanical properties and corrosion resistance. The key is to design a cost-effective Fe35Ni35Cr20Mo5Al5 HEA and introduce ultrafine microstructure (UFM), including ultrafine grains (∼693 nm), high density of annealing twins and nanoprecipitates, into the alloy by manipulating the concurrent precipitation and recrystallization at 940 °C within 2 min. The cost-effective UFM-HEA exhibits a temperature-dependent strain-hardening capacity and a superior strength-ductility synergy at 77 K with a yield strength of ∼1165 MPa, a tensile strength of ∼1412 MPa and a uniform elongation over 20%. The superior tensile properties at cryogenic temperature are attributed to the twining-dominated multiple deformation mechanisms and the integrated strengthening effects, including grain refinement strengthening, twin strengthening and second-phase strengthening. At the fracture strain of ∼20%, extensive microcracks formed within the nanoprecipitates without propagating into the face-cantered-cubic matrix, suggesting a high crack tolerance of the UFM-HEA at both room and cryogenic temperatures. Moreover, the UFM-HEA has a superior corrosion resistance compared to the 316L stainless steel due to the larger passivity region and higher charge transfer resistance. Such outstanding cryogenic mechanical properties and corrosion resistance together with the lower cost make the UFM-HEA superior to most cryogenic HEAs. This strategy not only sheds light on the development of new-generation cryogenic HEAs but also significantly enhances their industrial application potential.