Fatigue crack propagation at elevated temperatures in titanium aluminide intermetallic

The objectives of the present study an to evaluate fatigue crack propagation (FCP) characteristics at elevated temperatures in TiAl 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 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 were similar to those at 800 degrees C and they were faster than those at ambient temperature. In low Delta K regions, FCP rates at 800 degrees C decreased rapidly with decreasing Delta K compared with those at 600 degrees C and higher threshold stress intensity factor range was attained at 800 degrees C, which was almost the same as that at ambient temperature. This higher FCP resistance at 800 degrees C in low Delta K region still existed in terms of Delta K 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 degrees C. (C) 1999 Elsevier Science S.A. All rights reserved.