Date of Award

2010

Degree Type

Thesis

Department

Chemical and Biomedical Engineering

First Advisor

Tewari, Surendra

Subject Headings

Directional solidification, Aluminum alloys, Silicon alloys, Succinonitrile, Dendritic crystals, Directional solidification, Primary dendrite spacing, Primary dendrite trunk diameter

Abstract

Al - 7 wt Si alloy has been directionally solidified from an aluminum single crystal seed with its [100] orientation parallel to the growth direction with a positive thermal gradient of 40 K/cm and over the range of growth speeds. Growth speed dependence of primary Dendrite Spacing and Primary Dendrite trunk Diameter has been analyzed during the step increase and step decrease in the growth speeds. Frequency distribution of Nearest Neighbor dendrites obtained from the statistical analysis shows the hexagonal distribution of dendrites. The interdendritic convection was present in the form of transverse macrosegregation and non uniform distribution of dendrites at low growth speeds, 4 and 5 μm/s. The samples grown at higher growth speed of 22 and 72 μ/s did not show the microstructure inhomogeneity. An increase in the growth speed shows decrease in primary dendrite arm spacing which is in agreement with theoretical models. One unanticipated finding was that the primary dendrite spacing predicted by the Hunt-Lu model is small when compared with the experimental Spacing. The Current investigation showed that steady state distribution is achieved after a solidification distance of 3 mushy zone lengths after the change in speed

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