High-temperature radiation resistance of NiCoFe medium-entropy alloy enabled by stable nanostructures and defect evolution mechanisms

ST Nori and A Esfandiarpour and D Kalita and M Zielinski and K Mulewska and R Bjorge and PE Vullum and PA Ferreirós and W Chrominski and MY Li and YQ Chang and YW Zhang and R Diduszko and N Macha and SRK Malladi and DR Mason and R Holmestad and M Alava and L Kurpaska, JOURNAL OF MATERIALS RESEARCH AND TECHNOLOGY-JMR&T, 37, 5448-5464 (2025).

DOI: 10.1016/j.jmrt.2025.07.079

The study innovatively examined a nano oxide dispersion-strengthened (ODS) NiCoFe medium-entropy alloy with nanosized grains to address the challenge of discovering structural materials for high-temperature irradiation applications, such as in advanced nuclear reactors. The ODS- NiCoFe alloy exhibited a nanoindentation hardness of 4.3 +/- 0.9 GPa, representing a two-fold enhancement over the 2.0 +/- 0.1 GPa of single- crystal NiCoFe. Dislocations were identified as the primary defect structures. Following irradiation (Ni2+, 580 degrees C), the average dislocation length density increased from similar to 2.6 x 10(13) m(-2) to similar to 6.1 x 10(13) m(-2), while the mean dislocation length decreased from 249 nm to 104 nm, contributing to a relative irradiation hardening of 25 %. Additionally, the study demonstrated the stability of various nanostructures, with only minor changes in the average sizes of nanoprecipitates and grains-from 6.7 +/- 1.7 nm to 6.4 +/- 1.7 nm, and from 73 +/- 2 nm to 76 +/- 2 nm, respectively, upon irradiation, suggesting effective defect annihilation at interfaces and grain boundaries. The alloy exhibited no observable irradiation-induced voids. Molecular dynamics simulations revealed irradiation resistance of the alloy through the absorption of vacancy clusters at grain boundaries and Shockley-dominant-dislocation chains and the absorption of interstitial clusters at grain boundaries, aided by the high mobility and three- dimensional motion of interstitial clusters. Thus, the findings demonstrate the high-temperature radiation resistance of the novel ODS- NiCoFe alloy, surpassing that of well-known ODS steels, using a correlative approach that combines experiments and simulations.

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