Direct Observation of Short-Range Order in High Entropy Alloys—Impacts on Corrosion and Phase Transformation

High entropy alloys (HEAs) have garnered significant attention due to their unique mechanical and structural properties. The local chemical ordering (LCO) within these alloys significantly influences their thermal and electrical conductivity, as well as aspects like diffusion and passivity. In this study, we investigated how LCO impacts several alloy characteristics, including corrosion resistance, magnetic properties, and phase transformation. Initially, we utilized Extended X-ray Absorption Fine Structure (EXAFS) technique to analyze short-range order (SRO) at the micrometer scale. Subsequently, we employed Extended energy loss fine structure (EXELFS) , a high spatial resolution technique in transmission electron microscopy (TEM), to quantify fluctuations in local chemical order over length scales ranging from 50 to 200 nm in CoCrNi medium entropy alloys. Our findings revealed that the bond lengths of Cr, Co, and Ni decreased after aging treatment, indicating variations in their bonding environments. Simulation analysis showed an increased preference for Cr-Cr bonding in the second shell after aging. Furthermore, we demonstrated that clustered Cr-Cr in CoCrNi alloys provides distinct advantages in both short-term and long-term passivation and breakdown regimes. Through this exploration, we aim to uncover the fundamental principles governing the atomic-scale behavior of these materials, thereby laying the groundwork for further advancements in alloy design