Fatigue crack propagation behavior of K40S cobalt-base superalloy at elevated temperature

摘要

Fatigue crack propagation behavior of K40S cobalt-base superalloy under ambient atmosphere at 700℃ and 900℃ was investigated. The detailed fatigue crack propagation and fracture mechanism under the alternating loads were studied. The results show that, there is a defined threshold for K40S alloy at elevated temperatures. The fatigue threshold is 23.9 MPa · m~(1/2) at 700℃ and 12 MPa · m~(1/2) at 900℃. The significant decrease of the threshold with increasing temperature is associated with the oxidation induced embrittlement at crack tip. Observation on the fatigue fracture surfaces indicates a ductile fracture mechanism related to the fatigue crack growth.