Effects of oxygen content on Charpy impact properties and crack resistance of α titanium alloys

Abstract Charpy impact properties and crack resistance of commercial pure (CP) Ti and Ti-6Al alloy with different oxygen contents were systematically investigated by using the instrumented Charpy impact testing machine. The scanning electron microscope (SEM) equipped with electron backscatter diffraction (EBSD) detector and transmission electron microscope were employed to detect the deformation mechanisms. The experimental results showed that decreasing the oxygen content significantly improved the impact toughness of CP Ti and Ti-6Al alloy. Furthermore, decreasing the oxygen content simultaneously strengthened the resistance to crack initiation and propagation of CP Ti while only improved the resistance to crack propagation of Ti-6Al alloy. EBSD analysis demonstrated the significant effects of oxygen content on dislocation activities and deformation twinning behaviors in CP Ti and Ti-6Al. Decreasing the oxygen content significantly increased the dislocation activities and deformation twinning behaviors in CP Ti and Ti-6Al alloy which were mainly responsible for the improved impact properties and the strong crack resistance of CP Ti and Ti-6Al alloy. A mathematical model was introduced for the first time to uncover the interactions between oxygen atoms and dislocation as well as the deformation twinning on the view of valence electron by employing the Yu Rui-huang electron theory. By conducting the systematically experimental and theoretical investigations, we are aiming to provide deep insights into the relationships between interstitial oxygen and impact toughness as well as the crack resistance of titanium alloys and promote the production of titanium alloys with excellent impact properties.