Fatigue testing of thin CoNiCr wire up to 1010Â cycles

Crack initiation occurs at Al2O3-inclusions at the surface, where the interfaces between particles and matrix fail. Sizes of the crack initiating inclusions, areainc. are between 1.9 μm and 3.5 μm. Fatigue lifetimes can be approximated with a single S-N curve between 104 and 1010 cycles. No change of crack-initiation mode into the interior is observed when lifetimes extend into the VHCF regime. Inclusions can be considered as initial cracks, and a fracture mechanics concept is used to describe fatigue lifetimes. On average a stress intensity range as low as 1.0 MPam can propagate the crack to fracture at lifetimes above 108 cycles.