Evolution of the Solidification Microstructures in Directionally Solidified CM247LC Rod

Directional solidification of CM247LC was performed at a constant growth velocity (300 mm/h) using a Bridgman type furnace. Microstructural features, including the number of grains, PDAS, and EBSD IPF map, were investigated with progressive positions from the starter block. As directional solidification proceeded, the number of grains decreased and PDAS increased. These results indicate that the thermal gradient decreases with distance from the starter block. Thermal gradient changes were estimated by dendrite spacing change in the directionally solidified rod. The EBSD IPF map showed that almost all of the grains were close to the <001> preferred direction, but with heights of about 300 mm from the starter block, some grains at the center of the specimen exhibited quite different crystallographic directions near the gate instead of the preferred direction.