Investigation of Heat Transfer Coefficients Effects in Directional Solidification of GTD111 Super-alloy

The purpose of this study was evaluation of the directional solidification of GTD111 super alloy bars by Bridgman method, and then, to determine numerically the effect of the heat transfer boundary conditions on the directional solidification rate and the resulting microstructure and grains. For this purpose, in the first step, the heat transfer boundary conditions at the intersection of melt-mold and melt-chill-plate in the Bridgman furnace during solidification of a cluster, consisting of GTD111 rods, were determined, and then the grain structure of the rods after the metallography operation, in both longitudinal and transverse sections, appeared. In the second step, the intended boundary conditions were introduced into the Pro-Cast software and the solidification process was simulated. The grain growth pattern in both longitudinal and transverse sections was achieved and the results of both virtual and real metallography compared. After assuring the accuracy of the simulation results, the effect of the temperature gradient on the pattern of columnar grain growth with the change of the thermal conditions was modeled and its effect on the secondary dendrite arm spacing were obtained. The results show that at a growth rate of about 4mm/min, and a temperature gradient of 80-100°C/mm, the mean secondary dendrite arm spacing will be approximately 100- 120 microns