Thermomechanical fatigue behaviours of a third generation γ-TiAl based alloy

In order to clarify the behaviours of thermomechanical fatigue (TMF) of a third generation gamma-TiAl based alloy, the influence of related microstructural instability during TMF process on stress-strain response, fatigue life and fracture way under in-phase (IP) and out-of-phase (OP) loading mode was investigated. Cyclic softening at high temperature (>700 degrees C) arises from the dissolution of alpha(2) lamellae and recrystallization of gamma phase. Cyclic hardening at low temperature (<550 degrees C) is caused by strong interaction between dislocations. As temperature increases, the mean stress and remained plastic strain range increase, leading to severe TMF damage. Owing to the formation of superfine gamma grains in IP condition, a superimposed effect of creep and fatigue damage contributes to the TMF failure. OP loading mode brings about the coarsening of primary equiaxed gamma grains. Fatigue damage displays the intergranular fracture and transgranular cleavage fracture ways of coarse gamma grains. (C) 2006 Elsevier Ltd. All rights reserved.