Microsegregation and Solidification Reactions in Ni-Cr-Mo AlloysProf. Matthew John M. Krane
School of Materials Engineering
Nickel based alloys are used in high temperature and corrosive environments, such as gas turbine engines, chemical plants, flue gas desulfurization equipment, and heat exchangers. We are interested in the solidification behavior of several Ni-Cr-Mo alloys which have application in non-rotating parts in gas turbine engines. During the solidification of these alloys, defects arise which lead to severe degradation of the mechanical or corrosive properties of the final product. The purpose of this work is to improve models to predict the formation of such defects. The approach is to simulate the physical mechanisms which cause the defects, particularly the interactions of microscopic solidification behavior and macroscopic transport phenomena in Ni alloys during electroslag remelting and other refining processes. The partitioning of alloying elements during solidification leads to their nonuniform distribution and increased amounts of secondary solid phases. The redistribution of solute occurs at different lengths scales; this project is concerned with microsegregation, or compositional inhomogeneities on the scale of dendrite arm spacings, which arise from the preferential rejection of solute into the liquid during solidification. The approach is centered on a numerical model of a multicomponent alloy which accounts for a changing overall composition of the liquid-solid mixture and for remelting due to those compositional changes. The model is being validated and improved by experimental analysis, which is necessary due to the paucity of phase diagram information on these alloys. When complete, this model will become part of a larger simulation of the multi-scale phenomena in the electroslag remelting process.