Tensile behavior and deformation mechanism of a bimodal microstructure with microtextured region in Ti6242S alloy

In this paper, the tensile behavior and deformation mechanism of two typical bimodal microstructures in Ti6242S alloy were investigated through the in-situ scanning electron microscope (SEM) test and electron backscatter diffraction (EBSD). The results showed that the two microstructures presented different mechanical properties due to the different microscopic slip and fracture behaviors. In the homogeneous microstructure (with homogeneous crystallographic orientation), most of the slip traces were restricted within the grains because the slip transmissions between neighboring grains were blocked. The slip deformation was relatively homogeneous. Therefore, the fracture mechanism was micro-void accumulation fracture. In the inhomogeneous microstructure (with many microtextured regions), there existed many long slip traces directly passing through the microtextured region (the region of α phase with similar crystallographic orientation), the slip behavior was closely related to the same basal slip. The blocked slip aroused a high stress concentration in microtextured region, which was easy to induce the formation of microcrack, and then the microcrack propagated along the slip band. This can be attributed to the fact that slip transmission behavior was closely related not only to the alignment between slip planes and slip directions in two neighboring slip systems , but also to their Schmidt factors (SFs). Thus, the fracture mechanism was the coexistence of micro-void accumulation facture and cleavage fracture.