TABLE OF CONTENTS Solidification processes taking place in shape castings, ingots, or welding joints are always non-equilibrium. An important consequence of this fact is dendritic liquation (microsegregation) a direct result of the suppression of diffusion processes in liquid and in solid phases.
Microsegregation develops in alloys that solidify in a certain temperature range. It results in the formation of concentration micro-inhomogeneity and non-uniform distribution of alloying elements and impurities across the volume of solid solution crystallites. Additionally, under certain conditions it may also result in the precipitation of excessive phases and/or structural features (in aluminum alloys typically of eutectic or peritectic origin).
Today we have a significant number of studies on different aspects of non-equilibrium solidification (see e.g., [71, 80 82]). In particular, Pikunov [82] consider the whole solidification process as decomposition of liquid phase and interaction of precipitating crystals with the liquid that surrounds them. Decomposition takes place due to mass transfer between liquid and crystals, and also inside crystals. Under the conditions of non-equilibrium solidification this latter process is suppressed, which, in turn, results in the suppression of mass transfer between liquid and crystals.
We will adopt a somewhat different approach described below. To analyze the nature and extent of microsegregation we will consider three types of diffusion processes [83]. Firstly, the formation of crystals of equilibrium composition from the melt requires that atomic redistribution processes on the solidification front take place. This results in the equilibrium concentration difference, which can be determined...
