A Dual Scale Model of Segregation Phenomena

Abstract Segregation processes in solidifying metal alloys occur at two distinct length scales; microsegregation (controlled by mass diffusion in the dendritic arm spaces) and macrosegregation (controlled by convection over the scale of the casting). In modeling macrosegregation, microsegregation effects are accounted for on assuming limiting mass diffusion behavior. In modeling microsegregation, the macro scale effects are accounted for on prescribing the cooling rate and concentration history. The aim in this paper is to develop a dual length scale model of segregation which attempts to couple the micro- and macro-segregation processes more closely. In the first place, the development of separate macro- and micro-segregation models are described. On defining a dual scale numerical grid, consisting of a single macro scale mesh and a set of distinct micro scale meshes (each associated with a macro scale node point), the macro and micro models are coupled and a dual scale segregation model is developed. Initial results indicate that the choice of microsegregation model does affect the macrosegregation results, in particular the level of macrosegregation achieved is proportional to the amount of eutectic formed at the micro scale.