The anisotropy of fracture toughness of an α+β titanium alloy by β forging

Abstract

This study aims to investigate the anisotropic fracture toughness of an α+β titanium alloy processed by β forging. A typical basket-weave microstructure is observed, including the primary α (αp) phase, micron-scaled secondary α (αs) phase and residual β 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 β 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 β grain morphology and two-phase texture on anisotropy of KJIC are summarized.

Keywords

• Titanium alloy
• Mechanical anisotropy
• β forging
• Texture
• J-integral