Chemical medium-range order in a medium-entropy alloy.

Area of Science:

• Materials Science
• Alloy Design
• Solid-State Chemistry

Background:

• High-/medium-entropy alloys (H/MEA) exhibit inherent local chemical order.
• The existence and stability of chemical medium-range order (CMRO) in MEAs remain largely unexplored.
• Understanding CMRO is crucial for bridging short-range and long-range order phenomena.

Purpose of the Study:

• To provide compelling evidence for the existence of CMRO in an AlCrCoNi medium-entropy alloy.
• To characterize the structural and chemical nature of CMRO.
• To investigate the mechanical stability of CMRO during plastic deformation.

Main Methods:

• Electron diffraction analysis under specific zone axes ([[Formula: see text]] and [[Formula: see text]]).
• Dark-field imaging to visualize CMRO entities.
• Atomic-resolution Energy-Dispersive X-ray Spectroscopy (EDS) mapping for chemical species distribution.

Main Results:

• Definite diffraction spots indicating lattice periodicity of CMRO were observed.
• Direct visualization of medium-sized CMRO entities using dark-field imaging.
• EDS mapping revealed a tendency for like-pair avoidance and unlike-pair preference.

Conclusions:

• This study substantiates the existence of CMRO in AlCrCoNi MEA with a realistic structural picture.
• The findings clarify the role of crystal periodicity and chemical occupation in CMRO formation.
• This research advances the understanding of microstructural links at extended length scales beyond short-range order.