The anisotropy of fracture toughness of an -F titanium alloy by forging

This study aims to investigate the anisotropic fracture toughness of an alpha-F beta titanium alloy processed by beta forging. A typical basket-weave microstructure is observed, including the primary alpha (alpha p) phase, micron-scaled secondary alpha (alpha s) phase and residual beta phase. The tensile test results show that the anisotropic strength results from the fine grain strengthening as well as the texture strengthening, and the plasticity difference is determined by the normal stress acting on the main crack in the fracture process. The orientation of the specimen also has a significant impact on fracture toughness. The corresponding toughening models of underlying damage mechanism with different orientations are proposed and discussed. It is found that the internal toughening mechanism is dominant, and external toughening mechanism also plays an important role in fracture toughness, including delamination and crack deflection caused by elongated beta grains arrangement. Finally, the differences of J-integral resistance curves with different orientations are investigated in detail. The strength and fracture toughness values, KJIC (crack-initiation toughness) and KSS (growth toughness), are both highest when loading along radial direction (RD), and the positive effects of beta grain morphology and two-phase texture on anisotropy of KJIC are summarized.