Unraveling Anomalous Eutectic Formation in Ni-Sn Alloys During Directional Solidification with Transition Variable...

Area of Science:

• Materials Science
• Solidification Science
• Alloy Development

Background:

• Eutectic alloys exhibit distinct microstructures (lamellar or rod-like) under steady-state directional solidification.
• Understanding transitions between regular and anomalous eutectic morphologies is crucial for tailoring material properties.

Purpose of the Study:

• To investigate eutectic morphology transitions in Ni-Sn alloys under variable solidification speeds.
• To correlate processing parameters with microstructural evolution and mechanical properties.
• To elucidate the mechanisms behind anomalous eutectic formation using simulations.

Main Methods:

• Bridgman directional solidification with controlled velocity transitions.
• Cellular automaton (CA) simulations to model microstructure evolution.
• Microhardness testing to quantify mechanical properties.

Main Results:

• Steady-state solidification yielded regular lamellar/rod-like eutectics across a wide speed range (0.1-2000 μm/s).
• Velocity jumps induced anomalous eutectic morphologies specifically at transition interfaces (0.1-1000 μm/s).
• Increased drawing speed led to decreased lamellar spacing (3 μm to 0.4 μm) and increased microhardness (426 HV to 500 HV).

Conclusions:

• Anomalous eutectic formation in Ni-Sn alloys is triggered by rapid changes in solidification velocity.
• CA simulations confirmed lamellar destabilization and specific phase growth mechanisms during transitions.
• The study establishes a processing window for anomalous eutectics and links solidification dynamics to microstructural outcomes.