Microstructural evolution and phase transformation in the liquid-solid Al/Ni diffusion couple

ABSTRACT

The liquid-solid Al/Ni diffusion couple was successfully fabricated by annealing at 1373 K for 48 h followed by water-quenching. Cross-sectional scanning and transmission electron microscopic analyses show that the multilayered diffusion zones comprise the following sequence of layers: γ-Ni(Al) | γ′-Ni₃Al | β′-NiAl | Ni-rich β-NiAl | β-NiAl. The Ni-rich β-NiAl upon quenching undergoes a martensitic transformation from β (B2) to β′ (L1₀). The β′ martensite is found to be internally twinned on the {111}<112>system. The volume changes and strains due to martensitic phase transformation, the precipitation of γ′-Ni₃Al from γ-Ni(Al) and lattice mismatch between Ni-rich β-NiAl and β-NiAl in the Al/Ni diffusion couple are quantitatively determined. The cuboidal γ′ phase coherently precipitates cube-on-cube in γ-Ni(Al). Composition fluctuations existing in the supersaturated solid solution γ-Ni(Al), provide sufficient driving force for the precipitation and facilitate nucleation and growth of the γ′ phase under isothermal annealing.

KEYWORDS:

• Nickel aluminides
• diffusion
• microstructure
• phase transformation
• transmission electron microscopy (TEM)

Acknowledgments

This work was supported by the Shanghai Committee of Science and Technology, China under grant number 16520721700, the Network for Functional Nanostructures funded by the Baden-Württemberg Foundation and the Alexander von Humboldt Foundation for a renewed research stay.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Shanghai Science and Technology Committee, China under [grant number 16520721700], the Network for Functional Nanostructures funded by the Baden-Württemberg Foundation and the Alexander von Humboldt Foundation for a renewed research stay.