Abstract
Microstructures are the strategic link between materials processing and materials behavior. A dendritic structure is the most frequently observed pattern of solidified alloys. The microstructural scales of dendrites, such as primary and secondary arm spacings, control the segregation profiles and the formation of secondary phases within interdendritic regions, determine the properties of cast structures. In this work, the influence of thermosolutal convection on dendrite arm spacings is experimentally examined in the downward vertical unsteady-state directional solidification of Sn-Pb hypoeutectic alloys. The experimental observations are compared not only with the main predictive theoretical models for dendritic spacings but also with experimental results obtained for Sn-Pb alloys solidified vertically upwards. Primary dendritic arm spacings have been affected by the direction of growth, decreasing in conditions of downward vertical solidification when compared with those grown vertically upwards. Further, the unsteady-state l1 predictive models did not generate the experimental observations.
Highlights
The fundamental understanding of the relationship between solidification variables and the resulting structure is essential for the development of improved methods for quality castings
Several theoretical models have been proposed in the literature to describe the dependence of primary and secondary dendrite arm spacings on solidification variables such as initial alloy composition, growth rate and thermal gradient[1,2,3,4,5,6,7,8]
It can be seen that a same power law can represent the variation of secondary spacings with tip growth rate for the 5 and 15wt.%Pb alloys
Summary
The fundamental understanding of the relationship between solidification variables and the resulting structure is essential for the development of improved methods for quality castings. Fluid flow and the transport of solute, which influence the development of both the macrostructure and the microstructure. The prediction of these structures is of great interest for the evaluation and design of mechanical properties of castings. Several theoretical models have been proposed in the literature to describe the dependence of primary and secondary dendrite arm spacings on solidification variables such as initial alloy composition, growth rate and thermal gradient[1,2,3,4,5,6,7,8]. Recent articles on cellular[9,10] and primary dendritic[11] growth under unsteady-state solidification conditions have shown that the predictive theoretical models existing in the literature did not generate the experimental observations
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