Dislocation Multijunction-Driven Plasticity in HfNbTiZr High-Entropy Alloys.

Area of Science:

• Materials Science
• Metallurgy
• Solid Mechanics

Background:

• Refractory body-centered cubic (BCC) high-entropy alloys (HEAs) are promising for extreme environments.
• A key limitation is the lack of room-temperature ductility in BCC-HEAs.
• The HfNbTiZr alloy shows exceptional room-temperature tensile plasticity, but the underlying mechanisms are unclear.

Purpose of the Study:

• To elucidate the mechanisms responsible for the superior room-temperature ductility of the HfNbTiZr alloy.
• To understand how atomic structure influences plastic deformation in BCC-HEAs.

Main Methods:

• Integrated experimental characterization techniques.
• Atomistic simulations (e.g., molecular dynamics).

Main Results:

• Pronounced atomic size mismatch in HfNbTiZr induces significant lattice distortions.
• These distortions promote the formation of grid-like dislocation multijunctions.
• Dislocation multijunctions act as nucleation sites, enabling massive, autocatalytic dislocation multiplication.

Conclusions:

• An autocatalytic dislocation multiplication mechanism, driven by dislocation multijunctions, underpins the intrinsic plasticity of HfNbTiZr.
• This mechanism operates across a wide temperature range, overcoming inherent dislocation mobility limitations in BCC-HEAs.
• Findings offer insights into designing ductile refractory HEAs for demanding applications.