"Conjugate channeling" effect in dislocation core diffusion: carbon transport in dislocated BCC iron

Area of Science:

• Materials Science
• Solid-State Physics
• Physical Chemistry

Background:

• Dislocation pipe diffusion is a known mechanism for atomic migration along crystal defects.
• The directionality and mechanisms governing interstitial diffusion in metals require further elucidation.

Purpose of the Study:

• To investigate the unexpected diffusion behavior of interstitials, specifically carbon in iron.
• To explore the role of crystallographic channeling in accelerating interstitial migration.
• To characterize the temperature-dependent activation enthalpy of dislocation-core-coupled diffusion.

Main Methods:

• Molecular dynamics simulations.
• Accelerated dynamics simulations.
• Analysis of interstitial migration pathways in iron.

Main Results:

• Interstitial carbon diffusion in iron is accelerated in a conjugate direction, not along the dislocation line.
• A crystallographic channeling effect drives this accelerated random walk.
• Dislocation-core-coupled carbon diffusion exhibits a temperature-dependent activation enthalpy, similar to fragile glasses.
• Straightforward pipe diffusion, independent of dislocation mobility, was observed only for the 71° mixed dislocation.

Conclusions:

• Interstitial diffusion in metals can be significantly influenced by crystallographic channeling effects.
• The observed diffusion behavior challenges conventional understanding of dislocation pipe diffusion.
• Dislocation mobility is not always the primary factor governing interstitial diffusion rates in certain configurations.