Metastable and equilibrium decomposition of the eutectoid β-phase in the Cu-In system

Abstract

The β -phase in the Cu-In system is known to decompose into α and δ below 847 K through a eutectoid transformation controlled by interphase boundary diffusion. The present study with the Cu-20.15 at.% In eutectoid alloy investigates the morphology, identity and origin of a duplex microstructure in the prior β region ahead of the eutectoid reaction front. A detailed investigation through optical, scanning and transmission electron microscopy and X-ray diffraction analysis indicates that the prior β region undergoes a time dependent pre-precipitation of a transient phase through a static boundary mode. The latter precedes/accompanies the moving boundary eutectoid transformation initiated at the prior β grain boundaries.