Fatigue crack propagation at elevated temperatures in titanium aluminide intermetallic

This paper describes fatigue crack propagation (FCP) characteristics at elevated temperatures in titanium aluminide TiAl with a fully lamellar microstructure. The effect of temperature on FCP behaviour and FCP mechanisms were studied. FCP experiments have been performed at 600 degrees C and 800 degrees C and the obtained results were compared with the data at ambient temperature. In intermediate and high Delta K regions, FCP rates at 600 degrees C and 800 degrees C were similar and faster than these at ambient tem perature. In low Delta K region, the FCP resistance at 600 degrees C was the lowest and FCP rates at 800 degrees C decreased rapidly and higher threshold stress intensity factor range was attained, which was almost the same as that at ambient temperature. This tendency still existed in FCP behaviour characterized in terms of Delta K normalized by elastic modulus. Based on crack path morphology, fracture surface examination and additional FCP experiments, less crack tip shielding and pronounced crack closure induced by the oxide film formation were found to be responsible for the lowest FCP resistance at 600 degrees C and the higher FCP resis tance at 800 degrees C, respectively.