Unusual activated processes controlling dislocation motion in body-centered-cubic high-entropy alloys

Area of Science:

• Materials Science
• Solid Mechanics
• Computational Materials Science

Background:

• Body-centered cubic (BCC) metals are known for distinct dislocation behaviors.
• High-entropy alloys (HEAs) present unique material compositions with inherent fluctuations.
• Understanding dislocation mobility is crucial for predicting material strength and deformation.

Purpose of the Study:

• To investigate the atomistic mechanisms governing dislocation mobility in BCC high-entropy alloys (HEAs).
• To compare dislocation behavior in HEAs with traditional BCC metals.
• To elucidate the role of composition fluctuations and inhomogeneities in HEAs on dislocation dynamics.

Main Methods:

• Atomistic simulations were employed to model dislocation movement at the atomic scale.
• The simulations focused on screw and edge dislocations within the BCC HEA lattice.
• Analysis involved identifying energy barriers for dislocation nucleation, propagation, and detrapping.

Main Results:

• Compositional inhomogeneities in HEAs locally promote kink nucleation but significantly impede dislocation propagation.
• Dislocation trapping by inhomogeneities becomes the rate-limiting mechanism, overriding kink nucleation.
• Edge dislocations exhibit an activated process of nanoscale segment detrapping with an activation barrier comparable to screw dislocations.
• The mobility of edge dislocations becomes similar to that of screw dislocations in HEAs.

Conclusions:

• Dislocation mobility in BCC HEAs is fundamentally different from traditional BCC metals due to composition-induced inhomogeneities.
• Inhomogeneities play a critical role in controlling dislocation behavior and, consequently, the mechanical properties of HEAs.
• The comparable mobility of edge and screw dislocations suggests a unified mechanism of strength contribution in these alloys.