Simulation of transport phenomena in directionally solidified castings

摘要

Critical components in modern aircraft engines are manufactured by a casting process known as directional solidification (DS). In order to arrive at a set of production parameters consistent with defect-free castings,in the past casting engineers devised empirical methodologies that involved expensive trial-and-error prototype production runs.With the advent of simulation software,the empirical approach is being replaced by applying models of the transport phenomena and materials science during solidification.A mathematical model of the dendritic solidification of multicomponent alloys,that includes thermosolutal convection and macrosegregation,is presented.The model is an extension of porous media theory applied to dendritic solidification,a topic prblished by Julian Szekely as early as 1978.Numerical simulations are given for multicomponent Ni-base alloys,and the evolution of macrosegregation during solidification is studied.The results show that segregation patterns vary greatly with cooling conditions,adopting several shapes and levels of intensity.Calculations of segregation in casitings of simple shapes and in ceramic shell molds exhibit significant differences in the distribution of macrosegregation because of the nonadiabatic condition along the side walls of the mold as it is withdrawn from a radiation hot zone.