Grain Boundary Segregation Suppresses Local Short-Range Ordering in Nanocrystalline High-Entropy Alloys

Area of Science:

• Materials Science
• Metallurgy
• Nanotechnology

Background:

• High-entropy alloys (HEAs) exhibit unique properties but tend to form short-range ordering (SRO).
• Controlling SRO evolution is crucial for optimizing HEA performance.
• Nanocrystalline (NC) structures and grain boundary (GB) phenomena can influence atomic ordering.

Purpose of the Study:

• To investigate the effect of nanocrystalline structure and Zr addition on SRO in AlCoCrFe-based HEAs.
• To understand the mechanisms suppressing SRO in NC-HEAs.
• To explore the role of grain boundaries in atomic arrangement.

Main Methods:

• Advanced characterization: Transmission electron microscopy (TEM), high-energy synchrotron X-ray diffraction/pair distribution function (PDF), and atom probe tomography (APT).
• Computational analysis: Warren-Cowley coefficient calculations.
• Alloy composition variation: NC-(AlCoCrFe)100-xZrx (x = 0-1.5 atomic %).

Main Results:

• SRO was suppressed in as-milled and GB-decorated NC-(AlCoCrFe)100-xZrx alloys.
• GB segregation of Cr, Fe, and Zr was observed, altering matrix chemistry and disfavoring SRO.
• Calculations validated SRO suppression.
• Despite GB segregation, matrices and GBs maintained random solid solutions.

Conclusions:

• Nanocrystalline architecture and grain boundary segregation effectively suppress short-range ordering in AlCoCrFeZr HEAs.
• This suppression mechanism offers a pathway to control atomic arrangement and maintain random solid solutions in HEAs.
• The findings highlight the importance of nanostructuring for tailoring HEA properties.