Comparison of diffusion kinetics during isothermal solidification and homogenisation stages of transient liquid phase bonding

Abstract

ABSTRACTA numerical model that incorporates variable diffusion coefficient is used to study and compare the kinetics of solute penetration during diffusion-controlled isothermal solidification and homogenisation stages of transient liquid phase (TLP) bonding in planar and non-planar (cylindrical and spherical) systems. The study reveals new information regarding key differences between the two stages, depending on whether the diffusion coefficient is constant or varies with composition. Notwithstanding the fact that non-planar solid–liquid interfaces cause the solute penetration to depart from a linear relationship with , known as parabolic-law behaviour, during isothermal solidification, the penetration kinetics in all the systems follow the parabolic-law during the homogenisation stage, when the diffusivity is constant. Moreover, in the planar system, while a variation of diffusivity with concentration does not alter the solute penetration kinetics through deviation from the parabolic-law behaviour during the isothermal solidification, it causes a deviation during the homogenisation stage.