Atomistic mechanism of phase transformation between topologically close-packed complex intermetallics

Area of Science:

• Solid-state transformations
• Materials science
• Physical metallurgy

Background:

• Topologically close-packed phases (TCPs) are crucial in nickel-based superalloys.
• Understanding TCP phase transformations is a significant challenge in materials science.

Purpose of the Study:

• To elucidate the atomic-level mechanisms governing the transformation between TCP phases, specifically the μ and P phases.
• To investigate the role of lattice defects in facilitating these solid-state transformations.

Main Methods:

• Utilized atomic-resolution techniques to observe phase transitions.
• Employed first-principles calculations to determine the energy of specific crystallographic defects.
• Analyzed the role of dislocation loops and their Burgers vectors in atomic rearrangement.

Main Results:

• Identified intrinsic (110) faulted twin boundaries (FTBs) as the origin of the P phase.
• Demonstrated that FTBs possess exceptionally low energy, promoting phase stability.
• Revealed that FTBs facilitate the diffusion of smaller 3d transition metals, forming Frank interstitial dislocation loops.
• Showcased dislocation climb with an unusual Burgers vector as the key mechanism for structural transformation.

Conclusions:

• Established an intrinsic link between different TCP configurations through lattice defects.
• Highlighted the critical role of internal lattice defects, such as FTBs, in mediating phase transitions.
• Provided insights for designing alloys with improved properties by controlling complex phase formation.