Atomic-Resolution EDS Characterization of Ordering in a β–Cu–Zn–Al Alloy

Atomic ordering in single-crystal β –Cu–Zn–Al, relevant to the martensitic transformation and functional properties, is investigated using analytical STEM. Atomic-resolution EDS along the [110] zone axis, where all Wyckoff positions are spatially resolved, reveals three chemically distinct site occupancies. Correlation with HAADF-STEM contrast provides real-space evidence consistent with L2 1 ordering. In agreement with experiments, first-principles calculations show a slight energetic preference for L2 1 over D0 3 , with finite-temperature free-energy calculations indicating that this preference persists at elevated temperatures.