Melting and remelting phenomena

Abstract

Melting processes influence the microstructure evolution in metal alloys during casting and heat treatments. Melting is often treated as 'inverse solidification', which is only appropriate in a limited number of cases. In the present article, asymmetry between solidification and melting is reviewed in detail. The current state of the thermodynamic description of melting under diffusion control is outlined. Kinetic aspects that break the symmetry between solidifi-cation and melting that are discussed are solute partitioning, solute concentration gradients and solute transport in the involved phases. The view on nucleation of liquid and pre-melting phenomena, mostly of pure materials, based on experimental and theoretical work, is given. Emphasis is laid on aspects of melting with technical relevance, i.e. melting of alloys. Particu-larities of thermally and solutally controlled melting are introduced. Mechanisms that involve both melting and solidification simultaneously are capillary driven coarsening, temperature gradient zone melting and liquid film migration. The impact of these processes on microstructural evolution is discussed. Open questions concerning modelling and simulation of melting, namely, the interaction of different melting mechanisms and the role of the solid/liquid inter-face, are identified.

Mushy Zone Coarsening in an AlCu30 Alloy Accelerated by a Rotating Magnetic Field

“…[10] Annealing of a mush in a constant temperature gradient changes the process of morphological modifications by mass transport completely. Rettenmayr [11] points out that a stable temperature gradient along a mush induces a concentration gradient and therefore a species transport from the bottom to the top of the mush, leading ultimately to complete disappearance of the dendritic network. A single-phase crystal with a concentration profile dictated by the solidus line is then the final state of morphological evolution.…”

Inverse Model for the Solute Micro-Field Formation during Self-Propagating High Temperature Reaction

“…However, the current model has almost the same meaning as that which names melting as "inverse solidification", [17]. In fact, solidification is opposed phenomenon in comparison with melting.…”

Modeling and characterization of grain structures and defects in solidification

“…Finally, if growth kinetics models are fairly well established, phenomena related to grain ''birth'' need to be studied in greater depth, sometimes with ''new eyes''. Production of new grains by dendrite fragmentation should consider remelting, for which there are limited studies only [70]. Heterogeneous nucleation on foreign particles such as Al on TiB 2 or TiC particles has been shown to be athermal and thus does not follow standard theories, at least at small undercooling [11].…”