Mechanisms of chemical-reaction-induced tensile deformation of an Fe/Ni/Cr alloy revealed by reactive atomistic simulations

Abstract

High entropy alloys (HEAs) have demonstrated excellent potential in various applications owing to the unique properties. One of the most critical issues of HEAs is the stress corrosion cracking (SCC) which limits its reliability in practical applications. However, the SCC mechanisms have not been fully understood yet because of the difficulty of experimental measuring of atomic-scale deformation mechanisms and surface reactions. In this work, we conduct atomistic uniaxial tensile simulations using an FCC-type Fe₄₀Ni₄₀Cr₂₀ alloy as a typical simplification of normal HEAs, in order to reveal how a corrosive environment such as high-temperature/pressure water affects the tensile behaviors and deformation mechanisms. In a vacuum, we observe the generation of layered HCP phases in an FCC matrix during tensile simulation induced by the formation of Shockley partial dislocations from surface and grain boundaries. While, in the corrosive environment of high-temperature/pressure water, the alloy surface is oxidized by chemical reactions with water and this oxide surface layer can suppress the formation of Shockley partial dislocation as well as the resulting FCC-to-HCP phase transition; instead, a BCC phase is preferred to generate in the FCC matrix for releasing the tensile stress and stored elastic energy, leading to a reduced ductility as the BCC phase is typically more brittle than the FCC and HCP. Overall, the deformation mechanism of the FeNiCr alloy is changed by the presence of a high-temperature/pressure water environment—from FCC-to-HCP phase transition in vacuum to FCC-to-BCC phase transition in water. This theoretical fundamental study may contribute to the further improvement of HEAs with high resistance to SCC in experiments.