Thermal Stability Study of Vacancy-Type Defects in Commercial Pure Titanium Using Positron Annihilation Spectroscopy

Commercially pure (CP) titanium has been subjected to hydrostatic extrusion at room temperature at true strains ranging from 0.70 to 3.24. Isochronal thermal treatments, from room temperature to 1200 degrees C, have been performed and the thermal stability of the deformation-induced defects has been studied by positron annihilation spectroscopy (PAS). In non-annealed samples, vacancy-type defects are formed and interact with iron impurities. These defects are not stable near room temperature. Saturation of the positron annihilation parameters is not observed for cumulative true strains as large as 3.24, due to dynamic recovery during the extrusion process. TEM experiments confirm the formation of iron-rich precipitates. Vacancy-type defects and vacancy-impurity complexes anneal out at temperatures approximate to 700 degrees C.