Faceted crack induced failure behavior and micro-crack growth based strength evaluation of titanium alloys under very high cycle fatigue

Very high cycle fatigue properties of titanium alloys under symmetrical and asymmetrical loads were experimentally examined to clarify the failure behavior. An inhomogeneous microstructure zone (IMZ) containing facets is observable. By focused ion beam testing, the interior micro-crack extends along the maximum shear stress plane and the facet plane is about 45 degrees. By the modeling of growth rate and the definition of controlling line, a strength evaluation approach with the failure behavior was well proposed. This reflects that the microcrack growth rate in IMZ stage is below one Burger's vector.