Self-organized Sr leads to solid state twinning in nano-scaled eutectic Si phase.

Area of Science:

• Materials Science
• Metallurgy
• Computational Materials Science

Background:

• Twin nucleation is critical in controlling the microstructure and properties of eutectic aluminum-silicon (Al-Si) alloys.
• The established mechanism for twin formation in Al-Si alloys involves growth-dependent processes.
• The role of trace impurities, such as strontium (Sr), in modifying nucleation pathways remains incompletely understood.

Purpose of the Study:

• To elucidate a novel mechanism for twin nucleation in eutectic Al-Si alloys.
• To investigate the influence of trace strontium (Sr) impurities on twin nucleation.
• To provide a new perspective on twin formation in Al-Si alloys.

Main Methods:

• Sub-angstrom resolution scanning transmission electron microscopy (STEM) for atomic-scale imaging.
• X-ray probing techniques to identify elemental distributions and bonding.
• Density functional theory (DFT) simulations for atomic interactions and energy calculations.

Main Results:

• Direct observation of <110> strontium (Sr) columns preferentially located at twin boundaries.
• DFT simulations revealed Sr atoms bind along the <110> direction in the silicon (Si) lattice.
• Energetic favorability of twin nucleation at Sr columns was confirmed through DFT total energy calculations.

Conclusions:

• A new mechanism for twin nucleation in Al-Si alloys involving Sr impurities is proposed.
• Twin nucleation is suggested to occur in Si precipitates post-solidification, facilitated by Sr columns.
• This finding challenges the conventional understanding of twin formation during precipitate growth.