Eutectoid transformation in Au–39 at.-%In

Abstract

The kinetics of the isothermal eutectoid transformation in a eutectoid Au–39 at.-%In alloy has been studied in the temperature range 393–473 K. The maximum extent of growth of the eutectoid colonies and the lamellar spacing were determined through optical and scanning electron microscopy. The analysis of the kinetic data using existing classical and ledge growth models of boundary diffusion controlled eutectoid transformation yielded a low activation energy of 111 kJ mol^-1, indicating that the eutectoid transformation in this alloy is an interface diffusion controlled process. Comparison with interface boundary diffusivity data appears to suggest that the ledge growth model may be valid for the present system. The microscopy observations indicated that the parent ψ phase experiences a continuous precipitation of γ′ phase. This precipitation reaction precedes and accompanies the eutectoid decompos ition of the alloy, and the separate γ′ precipitates become embedded in the eutectoid colonies.