Direct visualization of the existence of surface local chemical order in a high-entropy CoCrFeMnNi alloy.

Abstract

The impacts of local chemical order (LCO) on the physical properties of high-entropy alloys (HEAs) have been widely discussed. However, the difficulty in unambiguously observing LCO with high precision poses a great challenge in establishing microscopic mechanisms regarding the impacts of LCO on physical properties. Furthermore, it is still unclear whether the LCO extends to HEA surfaces, which may impact surface-based properties, such as corrosion, oxidation, and catalytic activities. Through the utilization of scanning tunneling microscopy (STM), two surface LCO domains with corresponding <math xmlns="http://www.w3.org/1998/Math/MathML"><msqrt><mrow><mn>5</mn></mrow></msqrt><mo>×</mo><msqrt><mrow><mn>5</mn></mrow></msqrt><mi>R</mi><mo>±</mo><mn>26</mn><mo>.</mo><msup><mrow><mn>6</mn></mrow><mrow><mo>∘</mo></mrow></msup></math> quasi-long-range orderings (QLRO) are directly observed on a CoCrFeMnNi surface. Density functional theory (DFT) calculations identify the LCO within QLRO supercells. The findings provide evidence of the existence of the surface LCO and demonstrate a method to directly observe the surface LCO of HEAs. With the ability to unambiguously resolve elemental configuration at atomic scale, the understanding of how LCO influences surface-based properties can be achieved, facilitating the design of HEAs with tailored functionalities.