Analysis of the mechanical deformation arising from investment casting of directionally solidified nickel-based superalloys

To provide insight into the factors causing recrystallisation of nickel-based single crystal superalloys, analysis of the thermal-mechanical deformation caused by investment casting of these components is presented. Three-dimensional thermal-mechanical finite element analysis is first used to demonstrate that the reaction of the casting and mould-at least in the aerofoil section-can be approximated as one-dimensional. One-dimensional models are then built based upon static equilibrium for plasticity on the microscale caused by differential thermal contraction of metal, mould and core, using temperature dependent material properties. The models take various forms to study the mechanical response under different situations relevant to practical applications. The results indicate that the plastic strain causing recrystallisation is likely to be induced during cooling at temperatures above 1000°C. The relative importance of thicker and stiffer ceramic shells is studied. Our analysis indicates that it is important to account for creep deformation for such applications.