Implications of Microstructure in Helium-Implanted Nanocrystalline Metals.

Area of Science:

• Materials Science
• Nuclear Engineering
• Nanotechnology

Background:

• Helium bubbles form in nuclear reactor materials due to radiation damage, causing swelling and embrittlement.
• Nanocrystalline (NC) metals are promising for radiation resistance due to high defect sink densities.
• Mechanisms of defect evolution in NC metals under extreme conditions require further investigation.

Purpose of the Study:

• To investigate the performance of NC nickel (Ni) and iron (Fe) under helium bombardment.
• To understand the mechanisms of helium bubble formation and evolution in NC metals.
• To compare the radiation resistance of NC Ni and NC Fe.

Main Methods:

• Helium bombardment of NC Ni and Fe specimens.
• Transmission electron microscopy (TEM) for bubble density analysis.
• Rate theory modeling to study helium diffusion and trapping kinetics.

Main Results:

• Bubble density increased with saturation in both NC Ni and Fe.
• Fe exhibited over 300% greater bubble density than Ni.
• Helium is preferentially trapped in NC Fe grains, while it migrates to grain boundaries in NC Ni.

Conclusions:

• Grain boundaries significantly influence bubble swelling and can dominate over crystal structure.
• NC Ni demonstrates superior resistance to helium bubble growth compared to NC Fe.
• NC Ni shows high potential for applications in extreme environments susceptible to helium bubble formation.