Fatigue crack propagation at elevated temperatures in titanium aluminide intermetallic

The objectives of the present study are to evaluate fatigue crack propagation (FCP) characteristics at elevated temperatures in TiA1 with a fully lamellar microstructure and to make better understanding for the effect of temperature on FCP behavior. FCP experiments have been performed at 600°C and 800°C and the obtained results were compared with the data at ambient temperature. In intermediate and high ΔK regions, FCP rates at 600°C were similar to those at 800°C and they were faster than those at ambient temperature. In low ΔK regions, FCP rates at 800°C decreased rapidly with decreasing ΔK compared with those at 600°C and higher threshold stress intensity factor range was attained at 800°C, which was almost the same as that at ambient temperature. This higher FCP resistance at 800°C in low ΔK region still existed in terms of ΔK normalized by elastic modulus. Based on crack path morphology, fracture surface examination and additional FCP experiments, pronounced crack closure induced by the formation of oxide film was found to be responsible for the higher FCP resistance at 800°C.