Damage Analysis of High Temperature Isothermal and Thermomechanical Fatigue on a TZM Alloy

摘要

High temperature isothermal fatigue and in-phase thermomechanical fatigue (TMF) tests in stress control were performed on a molybdenum-based alloy, one of the best known of the refractory alloys, TZM. Two temperature levels of 350 deg C and 500 deg C were chosen for isothermal fatigue tests and a temperature interval of 350deg - 500 deg C was applied to thermomechanical fatigue tests. The stress-strain response and the cyclic life of the material were measured. The fatigue lives obtained in the in-phase TMF tests is lower than the ones obtained in the isothermal tests at the same stress range. Continuous cyclic creep represented by ratcheting occurred during the tests with an increasing creep rate which is dependent on temperature and stress range. The analysis of microstructure of the damaged specimens demonstrated that the fracture of the alloy was on the whole a brittle process under higher cyclic stress conditions. The cracks seemed to propagate along the inclusions and across the grain.