Kinetics of cellular dissolution in a CuIn alloy

Abstract

The dissolution of lamellar precipitates by cell boundary migration has been studied in a Cu-15 wt.% In alloy in the temperature range 778–853 K, primarily by optical microscopy. Microstructural observations indicated that the process of dissolution in this alloy is a cellular mode of transformation. By approximating the tip radius at the α-δ interface as equal to half the width of a δ lamella, the interface composition during dissolution was determined using the Gibbs-Thomson relation. The boundary diffusivities were calculated using the theories of Tu and Turnbull and of Petermann and Hornbogen modified for dissolution and a formulation applying balance of fluxes at the edge of a receding cell boundary similar to the formulation of Aaronson and Liu for the cellular precipitation reaction. The diffusivity values calculated from the experimental data fall within a range of two orders of magnitude for these theories but in all cases are four to five orders of magnitude higher than the volume diffusivity. For this alloy, there exists a critical temperature at which the driving forces for cellular precipitation and dissolution are equal. The value lies approximately 23 K below the equilibrium solvus temperature. An activation energy in the range 148–159 kJ mol −1 for different models has been obtained which agrees well with the Q values reported for cellular precipitation in CuIn alloys.