Crack paths in the superalloy IN738 in aged conditions

• Analysis of crack paths of artificial and service cracks in turbine blades at room and elevated temperature.
• Transcrystalline crack extension modes are quite frequent even at elevated temperature.
• Transgranular service cracks exhibit recrystallized layer along crack faces and at the crack tip.

The crack paths are analyzed of fatigue cracks in aged IN738 taken from removed turbine blades. Both artificial cracks initiated from notches and service cracks found in removed blades are taken into consideration. Transgranular crack growth is most common in the virgin material, but can still be found in aged material and in service cracks. Under operating conditions, transgranular crack growth is related to recrystallization of the material along the crack faces. It is suggested that the local plastic deformation plays an important role in this recrystallization process.