The influence of grain boundary angle on the hot cracking of single crystal superalloy DD6

• Hot cracking formation is misorientation angle dependent.
• The critical boundary angle for hot cracking formation is 16 for DD6.
• The liquid film at grain boundary is more fatal than that inside grain in intradendritic region.

Grain boundary is found to be the most vulnerable place to produce hot cracking during casting and welding processes. Understanding the underlying mechanism of it is helpful to prevent the crack for the repair of aerospace and automotive parts. By producing bi-crystal with pure tilt grain boundary, the effect of boundary misorientation on hot cracking susceptibility was studied for Ni-based superalloy DD6. It is found that the crack takes place when the grain boundary angle is larger than 16° under the present processing conditions. The experimental results are discussed by the theory of coalescence at the last stage of solidification. Furthermore, the calculated temperature interval corresponding to the vulnerable regime in the intradendritic region is much smaller than the coalescence undercooling for the residual liquid film at the boundary, indicating that if the grain boundary exists, the key factor to the hot cracking is the liquid film but not those in the intradendritic region.