EFFECTS OF SUPERHEAT ON THE MICROSEGREGATION AND FLUID FLOW TENDENCY DURING DIRECTIONAL SOLIDIFICATION OF SUPERALLOY In718

Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDAX) have been used to study the microstructure and interdendritic segregation along mushy zones in samples of superalloy Inconel 718. These samples had been directionally solidified at remelting temperatures of 1600 degrees C and 1700 degrees C. Concentration profiles, liquid density, and relative Rayleigh number profiles of the mushy zones have been presented. It was found that when superheat increases, alloy segregation decreases; although the final increase in the liquid density difference is small, it increases quickly and to a great extent in the initial stages of solidification; at the same time, permeability increases through the mushy zone and the maximal relative Rayleigh number rises markedly, suggesting a larger tendency for fluid flow.