Thermal analysis of the Bridgman and liquid-metal-cooled directional solidification investment casting processes

Thermal profiles obtained during directional solidification of Ni-base superalloy castings by the Bridgman and liquid-metal-cooled (LMC) techniques have been used to develop and validate the finite-element models of these processes. Models of the directional solidification processes for the columnar-grain alloy GTD-444 are used to evaluate the various heat-transfer steps and heat extraction modes within each process. This analysis highlights the similarities and the fundamental differences in heat-transfer modes between the two solidification approaches. Ultimately, the unique limiting heat-transfer step of each process is identified. For the stepped plate configuration investigated, heat extraction is limited by radiation from the exterior mold surface in the Bridgman process. Heat transfer between the casting and the interior mold surface is the primary resistance in the LMC process, and heat extraction is enhanced by the lowering coolant temperatures in this process.