Topological grain boundary segregation transitions

Area of Science:

• Materials Science
• Metallurgy
• Nanotechnology

Background:

• Tailoring polycrystalline material properties via grain boundary (GB) engineering is crucial.
• Solute segregation at GBs can induce phase transitions, theoretically offering interface design pathways.
• The atomistic mechanisms of solute-induced GB phase transitions remain poorly understood.

Purpose of the Study:

• To investigate the atomistic nature of solute segregation triggering phase transitions at GBs.
• To elucidate the role of iron segregation in stabilizing specific GB structures in titanium.
• To explore the formation and characteristics of novel GB phases induced by solute segregation.

Main Methods:

• Atomic resolution electron microscopy for direct imaging of GB structures.
• Atomistic simulations to model solute segregation and phase formation.
• Advanced GB structure prediction algorithms to validate observed phases.

Main Results:

• Iron segregation to GBs in titanium stabilizes icosahedral units ('cages').
• These icosahedral cages act as building blocks for distinct GB phases with five-fold symmetry.
• Hierarchical GB phases assemble through clustering of these cages, exhibiting varied structures.
• Observed phases and high iron excess at GBs are validated by simulations.

Conclusions:

• Iron segregation drives the formation of novel, hierarchical GB phases in titanium.
• Icosahedral cages are key structural units in these solute-stabilized GB phases.
• Understanding these atomistic mechanisms enables precise engineering of GB properties for advanced materials.