Fatigue Crack Propagation Behavior of Cast Ni -based Superalloy under Two-Step Variable Amplitude Stresses above and below Fatigue Limit

Abstract

This study investigated fatigue crack propagation behavior and the number of cycles to fatigue crack arrest of cast Ni based superalloy 246 below its fatigue limit. Fatigue tests were performed under two-step variable amplitude stresses above and below the fatigue limit under load controlled condition. Low level stresses σ_Low below the fatigue limit are set as 91.4 MPa and 68.6 MPa. As the result of the observation of the micro cracks and they progresses under σ_Low = 91.4 MPa. Also in the case of σ_Low = 68.6 MPa, the micro crack progresses. In comparison between the number of cycles to stop fatigue crack propagation under σ_Low = 91.4 MPa and 68.6 MPa, the number of cycles under σ_Low = 68.6 MPa is less than σ_Low = 91.4 MPa.