Influence of the characteristic of recrystallization grain boundary on the formation of creep cracks in a directionally solidified Ni-base superalloy

Creep tests of a directionally solidified (DS) Ni-base superalloy specimens containing local recrystallization (RX) were carried out at 980 °C/235 MPa and the influence of the characteristic of RX grain boundary on the formation of creep cracks was investigated. The RX grain boundary morphology, misorientation and dislocation pattern at high, low angle and twin boundaries during creep were examined. It was shown that only a few high angle grain boundaries (GBs), but not all of them cracked during creep and even after ruptured. This is associated with the dislocation mobility at GBs or the morphology of GBs. The possibility of crack formation was discussed based on the transmission behavior of dislocations at different GBs.