CYCLIC STRESS-STRAIN RESPONSE OF HIGH-TEMPERATURE TITANIUM ALLOY IMI 834 UNDER THERMOMECHANICAL FATIGUE CONDITIONS

摘要

Cyclic stress-strain response of high-temperature titanium alloy IMI 834 was studied under isothermal and thermomechanical fatigue (TMF) conditions, respectively. Transmission electron microscopy revealed that identical microstructures are formed irrespective of the actual loading mode if the maximum test temperature (T_(max)) does not exceed 600°C. Consequently, deformation behaviour observed in TMF tests was found to be predictable quite accurately from isothermal test data. By contrast, an unique microstructure was observed in TMF tests conducted with T_(max)= 650°C, and stress-strain response was significantly different from any isothermal test performed in the respective temperature range. The observed influence of T_(max) on deformation behaviour is shown to be correlated with a change from planar to more wavy dislocation slip. The implications of this change in dislocation slip mode on modelling of stress-strain response will be addressed.