Re-Examination of the Microstructural Evolution in Undercooled Co-18.5at.%B Eutectic Alloy

Area of Science:

• Materials Science
• Metallurgy
• Phase Transformations

Background:

• Understanding solidification in undercooled alloys is crucial for materials design.
• Cobalt-Boron (Co-B) alloys exhibit complex phase behavior under non-equilibrium conditions.

Purpose of the Study:

• To systematically explore the impact of undercooling on solidification pathways, microstructure, and recalescence in Co-18.5at.%B eutectic alloys.
• To elucidate the mechanisms governing microstructural evolution and phase selection during rapid solidification.

Main Methods:

• Experimental investigation of undercooled Co-18.5at.%B eutectic alloys.
• Analysis of solidification pathways, microstructural evolution, and recalescence behaviors at varying undercooling levels (ΔT).

Main Results:

• Identified four distinct solidification pathways dependent on undercooling levels.
• Observed phase selection including FCC-Co, Co3B, Co2B, and metastable Co23B6 phases.
• Detected prenucleation of the primary FCC-Co phase through recalescence analysis.

Conclusions:

• Undercooling significantly dictates the solidification route and resulting microstructure in Co-B alloys.
• Mechanisms like solute trapping and strain-induced transformation influence phase selection.
• Findings provide insights for controlling microstructure and properties in undercooled Co-B systems.