The Occurrence and Periodicity of Oscillation Peritectic Microstructures Developed during Directional Solidification

摘要

The layered microstructures that can form duringplane-front directional solidification in peritectic systems werecharacterized quantitatively as a function of growth velocity usinga Sn-CD alloy .Layers were formed for an alloy compositionoutside of the two-phase peritectic region in the absence oflongitudinal macrosegregation .The layers did not extent over theentire sample cross sections ,so that the layered regions had adifferent composition than the alloy .Each of the two solids wasfound to be interconnected and continuous in threedimensions .The layer lengths and individual layer compositionsdid not vary with solidification distance .The average layercompositions were not a function of growth velocity and wereapproximately those at the peritectic temperature .This researchwas compared to the current model by Trivedi ,which is basedupon cyclic accumulation and depletion of solute in the liquidahead of the interface linked to repeated nucleation events .Thedependence of layer length on growth velocity predicted by themodel was not obtained experimen-tally .The differences betweenresults and predictions are related to the continuity of the twosolids and the nonuniform cross-sectional composition in the Sn-Cd samples ,which contradict assumptions of the model .Aformation mechanism involving competitive lateral growthbetween the two solids at the solid-liquid interface would be moreconsistent with the current research .