Nonbasal Slip Systems Enable a Strong and Ductile Hexagonal-Close-Packed High-Entropy Phase

Area of Science:

• Materials Science
• Metallurgy
• Crystallography

Background:

• Dislocations govern mechanical properties in crystalline alloys.
• Deformation mechanisms in traditional alloys are understood, but less so in high-entropy alloys (HEAs).
• Hexagonal close-packed (hcp) HEAs often exhibit brittleness due to limited slip systems.

Purpose of the Study:

• Investigate the deformation mechanisms and formability of a novel hcp high-entropy phase.
• Understand the role of dislocations in the mechanical behavior of complex HEAs.
• Identify design principles for enhancing ductility in hcp HEAs.

Main Methods:

• In situ tensile testing to observe deformation under load.
• Transmission electron microscopy for postmortem microstructural analysis.
• Analysis of dislocation types and their line fractions.

Main Results:

• A novel hcp phase in a dual-phase HEA (Fe50Mn30Co10Cr10) exhibits high formability.
• Three types of dislocations (⟨a⟩, ⟨c⟩, and ⟨c+a⟩) were activated in the hcp phase.
• A high fraction (∼31%) of nonbasal ⟨c+a⟩ dislocations facilitates double cross slip, explaining the enhanced deformability.

Conclusions:

• The c/a ratio of 1.616 in the hcp structure promotes nonbasal ⟨c+a⟩ slip.
• Ductile hcp HEAs can be designed by tuning the c/a ratio to activate nonbasal slip.
• This design principle is well-suited for HEAs due to their compositional flexibility.