FATIGUE CRACK GROWTH RETARDATION IN TITANIUM ALLOY

The gas turbine components undergo fatigue load spectrum of variable amplitude loading. In this study, fatigue crack growth rate after multiple cycles of tensile overload has been investigated in Ti-2.77Sn-0.48Cu-1.15Fe-6.61V alloy. The overload at the crack tip produces the plastic zone at the vicinity, which retards the crack growth. Crack growth retardation effect has been studied at 15% and 25% overload percentages to observe its retardation effect. The multiple overloads applied after fixed interval of cycles produces a plastic region around the crack. After reloading the specimen further with constant loading, the crack growth rate is retarded thus causing increase in the fatigue life, which is observed in the graph of crack length vs number of cycles. The microstructure study has been carried out using Scanning Electron Microscope (SEM) and Electron Back Scatter Diffraction (EBSD), which gives qualitative information of strain to characterize the fatigue crack growth. The slope of crack length vs number of cycles before and after tensile peak overload was compared to evaluate the retardation effect at varying overload percentages.