High temperature isothermal and thermomechanical fatigue on a molybdenum-based alloy

High temperature isothermaI fatigue and in-phase thermomechanical fatigue (TMF) tests in stress control were performed on a molybdenum-based alloy, TZM. Two temperature levels of 350 and 500 degrees C were chosen for isothermal fatigue tests and a temperature interval of 350-500 degrees C was applied to thermomechanical fatigue tests.The stress-strain response and the hfe cycle of the material were measured during the tests. It appears that temperature variations influence the fatigue life of the alloy and the material is further damaged with combined stress and temperature cycles. The analysis of the hysteresis loops showed that a ratcheting phenomenon and a cyclic softening behavior of the material occurred during each kind of the fatigue tests. The observations of the microstructure of the damaged specimens demonstrated that the fracture of the alloy was, on the whole, a brittle process under higher cyclic stress conditions. (C) 1998 Elsevier Science S.A. All rights reserved.