Multiphysics modelling of dendritic thermo-mechanical deformation during directional solidification of nickel-based single-crystal superalloys

Nickel-based single-crystal (SX) superalloys are the key metallic materials of aero-engine. However, thermo-mechanical deformation always occurs during directional solidification of SX superalloy, which has a negative influence on the SX structure. While casting deformation is simulated in most of the previous studies, the direct simulation of dendritic thermo-mechanical deformation has been largely ignored, resulting in a lack of comprehensive understanding of this process. In this work, we systematically study the dendritic thermo-mechanical deformation using a model coupled with the dendrite growth, fluid flow and thermo-mechanical deformation behaviours. Results reveal that the dendritic thermo-mechanical deformation-induced dendrite bending is not randomly distributed but mainly concentrated on the casting surface. The dendritic thermal stress increases as dendrite grows and is built up after dendrite bridging. The transverse thermal contraction is mainly at the edge of casting in the corner, and the axial thermal contraction is larger than the transverse contraction. The high stress region of the primary dendrite trunk is mainly distributed below the dendrite bridging near the solidified part, while the stress along the transverse direction reaches maximum on the casting surface. The stress concentrated on the casting surface is mainly attributed to the variations of transverse temperature gradients caused by the heat dissipation on the lateral mould wall, and inconsistent constraints in the lateral mould walls.