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

► Crack was observed at some of the high angle RX GBs with the misorientation angle more than 20°. ► Not all of high angle RX GBs cracked. ► It is difficult for cracks to form at low angle RX GBs and twin boundary. ► Crack formation is related to the dislocation mobility at GB. 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.