Fatigue properties and fracture mechanism of Stellite12 cobalt-based alloy

The three-point bending fatigue method was used to determine the S-N fatigue curves of smooth specimens and straight-notched specimens to study the fatigue properties of Stellite12 cobalt-based alloy, and the fatigue fracture processes of the cobalt-based alloy were investigated by the observation of fracture morphology.The results show that the fatigue limit of the smooth specimen is 545 MPa, which is about 25.4% of the original bending strength of 1552 MPa. The fatigue limit of the straight-notched specimen is about 101 MPa, which is about 19.1% of static bending strength of 517.6 MPa. The fatigue sensitivity of smooth specimens and straight-notched specimens is 397 and 31, respectively. In addition, it is found that the fatigue cracks can initiate in the carbides aggregated regions in the near surface. Surface defects can also induce the initiation of fatigue cracks. The transgranular fracture of the carbides dominates in the crack propagation. The cobalt base metal presents a lot of tearing ridges under the condition of stress ratio R=0.1, but it also shows a certain degree brittle fracture mode, so the fatigue crack propagation mode is a mixed mode of true fatigue and static fatigue.