5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

The columnar growth of Ti-48Al-2Nb-2Cr alloy was investigated using power down directional solidification experiments under various gravity conditions, ranging from micro-gravity to 20 g. The g-vector always pointed in direction opposite to the growth direction. The columnar dendrite morphology and primary spacing was analyzed in longitudinal and transverse sections and for selected experiments in 1g and 15g also by X-Ray tomography. The results show that the primary dendrite arm spacing decreases with increasing gravity from an average value of 790 µm at µg down to 370 µm at 20g. Furthermore, the spacing evolution along the entire solidification length depends not only on the temperature gradient and velocity but also on the magnitude of the applied gravity. The experimental analysis was complemented by numerical simulations using among other an OpenFOAM code to couple solidification and fluid flow. We will present and discuss the observed spacing refinement and the associated refinement mechanisms based on current models of dendrite growth under the action of upward flow in the mushy zone. Key observations form phase-field modeling are presented in a second contribution.