Directional solidification of Ni-based superalloy castings: Thermal analysis

The method of temperature measurement in directionally solidified (DS) Ni-based CMSX-4 superalloy castings manufactured using withdrawal rates of 3 and 5 mm/min in the Bridgman furnace with graphite heaters, was successfully improved. The numerical simulation of directional solidification process was performed with the use of ProCAST software, for withdrawal rates of 1, 3 and 5 mm/min in order to predict cooling rate, axial and transverse temperature gradients, solidification rate, height of mushy zone, shape of liquidus isotherm and its location relative to thermal baffle along the casting height. The critical distance from chill plate, above which of the steady-state solidification process starts, was established. The liquidus isotherm attained the concave, convex or flat shape, in dependence on withdrawal rate of casting and the distance from chill plate. The relationship between the shape of liquidus isotherm and grain structure was found for castings withdrawn at 1 and 5 mm/min. Grains grew in the direction of the rod axis and that of casting surface for the concave and convex isotherm shape, respectively. The flat shape of liquidus isotherm induced grain growth in the direction which was the most parallel to axis of casting.