Hydrogenated vacancies lock dislocations in aluminium

Area of Science:

• Materials Science
• Physical Metallurgy
• Hydrogen Embrittlement

Background:

• Hydrogen's role in metal plasticity is complex, often considered a weak inhibitor or promoter of dislocation movement.
• Understanding hydrogen-metal interactions is crucial for predicting material behavior in hydrogen-rich environments.

Purpose of the Study:

• To investigate the impact of hydrogen exposure on dislocation mobility in aluminum.
• To elucidate the mechanisms behind hydrogen-induced dislocation locking and unlocking.
• To identify the role of vacancies in hydrogen-assisted plasticity.

Main Methods:

• Quantitative mechanical testing using an environmental transmission electron microscope (ETEM).
• In-situ observation of dislocation behavior during hydrogen exposure and degassing.
• Atomistic calculations to verify proposed mechanisms.

Main Results:

• Hydrogen exposure significantly reduces dislocation mobility in aluminum, more than doubling the activating stress.
• Degassed, locked dislocations exhibit stick-slip motion under cyclic loading.
• Dislocation relocking occurs over a surprisingly long timescale (∼10^3 s), inconsistent with interstitial diffusion.

Conclusions:

• Superabundant hydrogenated vacancies are responsible for the strong dislocation locking and slow relocking kinetics.
• Vacancies act as crucial agents for plastic flow localization and damage in hydrogen environments.
• The findings challenge conventional models of hydrogen-dislocation interactions.