Failure Analysis of a Ti8Al-1Mo-1V Fan Blade

A failed TF34 fan blade failed during flight that caused and in flight emergency. Post flight inspections revealed that only a small portion of the blade tang remained. A failure analysis was requested to learn as much as possible from the remnant evidence. The Metallurgical Analysis Section at Tinker AFB was tasked with this investigation of the Ti-6Al-4V blade fragment. Laboratory analyses of the fracture surface, which included optical and scanning electron microscopy, revealed fatigue as the mode of failure that initiated subsurface and progressed approximately 70% of the fracture surface. Distinct differences in propagation morphologies were found from flat facets, inclined facets, and classic fatigue striations. Chemical analyses confirmed the material to be consistent with the alloy specified. Metallography and Electron Backscatter Diffraction revealed a sub-optimal microstructure that did not receive sufficient forging during manufacturing. It was recommended and pursued to track down other blades from the same lot to be removed form service.