Simulation of Transport Phenomena in Directionally Solidified Castings

摘要

Critical components in modern aircraftengines are manufactured by a casting process known asdirectional solidification (DS). In order to arrive ata set of production parameters consistent withdefect-free castings, in the past casting engineersdevised empirical methodologies that involved expensivetrial-and-error prototype production runs. With theadvent of simulation software, the empirical approachis being replaced by applying models of the transportphenomena and materials science during solidification.A mathematical model of the dendritic solidification ofmulticomponent alloys, that includes includesthermosolutal convection and macrosegregation, ispresented. The model is an extension of porous mediatheory applied to dendritic solidification, a topicpublished by Julian Szekely as early as 1978. Numericalsimulations are given for multicomponent Ni-base alloys,and the evolution of macrosegregation duringsolidification is studied. The results show thatsegregation patterns vary greatly with coolingconditions, adopting several shapes and levels ofintensity. Calculations of segregation in castings ofsimple shapes and in ceramic shell molds exhibitsignificant differences in the distribution ofmacrosegregation because of the nonadiabatic conditionalong the side walls of the mold as it is withdrawn from a radiation hot zone.