Casting microporosity growth in single-crystal superalloys by a three-dimensional unit cell analysis

Finite element (FE) analysis is employed to investigate casting microporosity growth in nickel-base single-crystal superalloys DD3. Based on a finite deformation rate-dependent crystallographic constitutive equation, the simulation of casting microporosity in a three-dimensional unit cell model was carried out under variation in a range of parameters including triaxiality, Lode parameter and a type of different slip systems activated and loading orientation. The FE results show that the stress triaxiality has profound effects on growth behaviour, volume fraction of casting microporosity and shape transition; the Lode parameter is an important parameter for casting microporosity growth and shape transition as well as triaxiality. Large local cumulative shear strain around casting microporosity plays an important role in driving casting microporosity growth; the high casting microporosity volume fraction corresponds to big cumulative shear strain. The operative slip systems type and loading orientation has a remarkable effect on casting microporosity growth, which is associated with the Schmid Factor and the Young's modulus of orientation.