Effects of casting process variables on the residual stress in Ni-base superalloys

Quality of castings is partly affected by the type and extent of residual stresses, which may lead to undesirable distortions and dimensional changes in critical parts and components. The effect of pouring temperature on residual stress in Ni-base superalloys, IN713C and U500, was investigated using a cutting technique, followed by measurements of the change in the distance between prescribed markings. For this purpose, rectangular and triangular shape samples were cast under vacuum using investment casting process. It was found that increasing melt superheat temperature leads to higher levels of casting residual stresses. The extent of residual stresses were also found to depend on the casting shape, being higher in the triangular sample due to local variations in casting modulus. Furthermore, it was found that higher levels of residual stresses are developed in U500 compared to IN713C, at constant melt superheat temperatures. The differences are explained in terms of variations in the freezing range and thermo-mechanical properties with alloy chemical composition.