Deformation modes investigation during ex-situ dwell fatigue testing in a bimodal near-α titanium alloy

In this paper, quasi-cleavage facet formation and deformation mechanisms in dwell fatigue have been studied on specimens from a Ti834 compressor disc alloy with a bimodal microstructure by ex-situ dwell fatigue testing at temperatures between 80 °C and 200 °C. Basal <a> slip was observed in grains with their c-axis near parallel the loading direction, while colonies similarly oriented accommodate deformation by tensile twins 101¯2<112¯0>. This type of slip in basal planes is the most critical damage mode leading to failure during dwell fatigue loading. A Rogue colony-grain combination is presented and a possible criterion for slip transfer in bimodal titanium alloys is introduced. The requirements cited for quasi-cleavage facet formation leading to dwell fatigue failure have been experimentally observed in agreement with the suggested hypothesis in previously presented crystal plasticity models.