The effect of microstructure on tensile properties, deformation mechanisms and fracture models of TG6 high temperature titanium alloy

The tensile properties at room temperature and 600°C of TG6 titanium alloy with different microstructures {bi-modal microstructures with thick α lamella (BTL) and fine α lamella (BFL), and a mixed microstructure with different morphologies of α phase} were obtained. It was found that the BFL microstructure possessed the highest tensile strength, and the elongations of the BTL and BFL microstructures were almost the same of about 13% at room temperature and 17% at 600°C, respectively. In addition, the mixed microstructure had the lowest plasticity. The tensile deformation mechanisms of α lamella (α_L), primary α phase (α_p), equiaxed α phase (α_e) and α colonies were researched by the analysis of respective dislocation morphologies. Notably, the accommodative deformations through grain/phase boundaries sliding determined the deformation models of α_L, α_p, and α_e. Compared to the thick α_L and α colony, the fine α_L and α colony activated more slip systems due to their excellent accommodative deformation capability. Furthermore the deformation mechanisms at room temperature and 600°C were different from each other. Scanning electron microscope (SEM), energy-dispersive spectrometer (EDS) and transmission electron microscopy (TEM) were used to research the crack propagation paths and fracture models. Crack propagation path crossing α colonies and α_p were discussed, respectively. The colonies boundaries, α_p/colonies boundaries, α_e/α_e boundaries and silicide were found to be the stress concentration locations. The micro-plasticity of tensile specimens determined the fracture morphologies and fracture models.