Influence of stress state on cavitation during hot working of Ti-6Al-4V

Abstract

Notched-tension tests were conducted on Ti-6Al-4V samples with a colony-alpha microstructure to determine the effect of the stress state on cavitation during hot working of alpha/beta titanium alloys. The experiments were complemented by finite-element-method analyses to establish the local stress state, strain, and damage factor for different areas within each sample. A critical damage factor, defined by a modified Cockcroft-and-Latham criterion, was found to be applicable for the prediction of cavity initiation for the different notch geometries. Measured cavity growth rates were also correlated to the stress state (i.e., ratio of mean-to-effective stress, σ _M /σ _e ) and compared to predictions of prior models. Model predictions showed reasonable agreement with measurements at low levels of stress triaxiality, but exhibited some deviations at higher values of σ _M /σ _e . The differences were attributed to differences in the properties of the present material and those assumed in deriving the models as well as the neglect of cavity interaction in one of the models. The results were summarized in terms of a processing map, which delineates the initiation of cavities and their size as a function of the stress state and effective strain.