Fatigue failure analyses on a Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy at different temperatures

The fatigue micro crack initiation and propagation tests of a TiAl alloy with 8% Nb content were carried out by using scanning electron microscopy in situ technology at room temperature and at 750 degrees C. These results indicated that the fatigue micro crack initiation was mainly caused by the stress concentration at room temperature, but at an elevated temperature (750 degrees C) the multi-cracks were caused by the coupled factors of both lamellar microstructure and stress concentration. Therefore, fatigue micro crack initiation behavior is much more dependent on the lamellar structure at an elevated temperature. One of the reasons is that the elevated temperature degrades the interface strength between the lamellar of the TiAl alloy with 8% Nb content. Therefore, the small fatigue crack propagation behavior of the alloy exhibited a mixture damage model of interlamellar and translamellar at a micro scale. The crack growth path and fracture characteristics provided a proof of crack deflection, branching and/or bridging induced either by interlamellar or by translamellar failure mode.