Ni基鋳造材246合金の片振り疲労強度評価と微小き裂進展挙動

抄録

The purpose of this study is to investigate low cycle fatigue (LCF) and high cycle fatigue (HCF) strength, crack initiation and growth behavior of Ni based castalloy 246. LCF and HCF tests are conducted under load controlled conditions. As the result of the observation of etched specimen, grain size is from 3 mm to 5 mm. And microstructure is composed of dendritic structure. Growth orientation of dendritic structure varies in every grains. The results of LCF test show that small cracks initiate at the first cycle, followed by the crack growth along slip direction. Observation of fracture surface reveals that small cracks are originated at casting defect or dendritic boundary. The results of HCF, on the other hand, show that small crack initiates from subsurface casting defect under Δσ ≦ 600 MPa, while under Δσ > 600 MPa, fracture origin becomes surface. As the result of EBSD, crack growth direction is along slip plane.