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 (αL), primary α phase (αp), equiaxed α phase (αe) 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 αL, αp, and αe. Compared to the thick αL and α colony, the fine αL 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 αp were discussed, respectively. The colonies boundaries, αp/colonies boundaries, αe/αe boundaries and silicide were found to be the stress concentration locations. The micro-plasticity of tensile specimens determined the fracture morphologies and fracture models.