Diffusionless (chemically partitionless) crystallization and subsequent decomposition of supersaturated solid...

Area of Science:

• Materials Science
• Metallurgy
• Solidification Science

Background:

• Eutectic alloys like Sn-Bi exhibit complex microstructural evolution.
• Understanding solidification mechanisms is crucial for tailoring material properties.

Purpose of the Study:

• Investigate the microstructural evolution of eutectic Sn-57 wt.% Bi under varying cooling rates.
• Compare solidification mechanisms between eutectic and hypoeutectic Sn-Bi alloys.

Main Methods:

• Processing Sn-Bi alloys at cooling rates of 10⁻², 1, and ~10⁵ K s⁻¹.
• Comparative analysis of microstructures across different alloy compositions and cooling rates.

Main Results:

• Coupled eutectic growth and lamellar structures observed at lower cooling rates (10⁻² and 1 K s⁻¹).
• Partitionless solidification forming a supersaturated solid solution occurred at rapid quenching (~10⁵ K s⁻¹).
• Microstructure in rapidly solidified alloys results from the decomposition of the supersaturated solid solution.

Conclusions:

• Cooling rate significantly dictates the solidification pathway and resulting microstructure in Sn-Bi alloys.
• Partitionless solidification is a key mechanism at high cooling rates, leading to metastable phases.
• The decomposition of supersaturated solid solutions governs the final microstructure after rapid solidification.