Fracture characteristics of γ-TiAl alloy with high Nb content under cyclic loading

This work investigates the isothermal low cycle fatigue (LCF) behavior of a third generation gamma-TiAl-based alloy with duplex microstructure under the various test conditions, including temperature (550-750 degrees C), total strain amplitude (0.3-0.6%) and environment (air and vacuum) in order to clarify the relationships among the fatigue life, plastic deformation character and fracture process. The plastic strain accumulation during cyclic loading has a great contribution to LCF damage. Under the small total strain amplitude (<= 0.4%), the increase of test temperature enforces microstructure resistance to LCF fracture. However, under the large total strain amplitude (>= 0.5%) the increase of test temperature accelerates the microstructural degradation process that behaves the dissolution Of alpha(2) lamellae and coarsening of gamma grains, and results in great LCF damage. Moreover, the environment brittlement during high temperature exposure to air influences the initiation rate of fatigue cracks and shortens LCF life. The paper also discussed the LCF fracture mechanisms of gamma-TiAl alloy at various temperatures. (C) 2008 Elsevier B.V. All rights reserved.