Diffusion in the liquid Al–In alloy when approaching the miscibility gap

Abstract Monotectic alloys offer the potential to produce materials with exceptional functional properties due to their demixing behavior. To understand and control the formation of the final microstructure, knowledge of the dynamics near the miscibility gap is required. We measured interdiffusion in liquid Al–In using a combination of X-ray radiography and a shear cell furnace, which allows in situ observation of the diffusion process. While the temperature dependence of interdiffusion can be described by an Arrhenius function, its concentration dependence is unexpectedly weak. From thermodynamics, a steep decrease of interdiffusion close to the miscibility gap is expected. However, the kinetic behavior of the liquid alloy, mainly determined by the self-diffusion coefficients, seems to largely compensate for this decrease. This finding is supported by additional density measurements. Studying the density in liquid Al–In up to a concentration of 20 at% In at temperatures between 850 and 1400 K shows that the temperature dependence of density, as well as the thermal expansion, for each alloy composition under consideration is the same inside and outside the miscibility gap. Significant deviation from ideality is obtained for the concentration dependences of density. This is reflected in a negative excess volume.