Low-Cycle Fatigue Crack Initiation Behavior of Nickel-Based Single Crystal Superalloy
Low-cycle fatigue crack initiation behavior of nickel-based single crystal superalloy at 530 ℃ was investigated.Results show that the behavior of crack initiation is closely related to the maximum strain.When the maximum strain is 2.0％,the fatigue crack is originated at the position of persistent slip bands on the surface of specimen,which is located on the {111} slip plane.No defects are observed at the crack initiation position.When the maximum strain is lower than 1.6％,the cracks are initiated at the casting defects on sub-surface or at interior of the specimen.The casting defects are located on the {100} slip plane vertical to the axial force.The crack is initiated along the {100} slip plane and then expanded along different {111} slip planes after a short stage of expansion.As the maximum strain decreases,the position of crack initiation gradually changes from the surface to the interior.Moreover,the secondary cracks extending inward along the fracture surface appear in the crack initiation area,and there is obvious stress concentration near the secondary cracks.The dislocation density is high near the fracture surface in the crack initiation zone,where a lot of dislocations cutting into the γ'phase exist.An oxide layer of 50-100 nm is presented on the fracture surface,and Ni,Al,Cr and Co elements are mainly segregated into the oxide layer of the surface.
crack initiationlow-cycle fatiguesingle crystal superalloycasting defectsdislocation density
NETL
NSTL
万方数据
