In Situ SEM Investigation of Local Deformation and Failure Behavior of Ti6Al4V under Tensile and Shear Loading

The local deformation and fracture behaviors have been studied for titanium alloy Ti6Al4V using in situ scanning electron microscope (SEM). Uniaxial tensile and shear samples are used to study the deformation and damage processes during the testing up to final failure. The evolution of strain fields on the samples is measured by digital image correlation (DIC) technique. The DIC results show that strain localization develops for samples both uniaxial tensile and shear, which is along the direction of the maximum shear stress. The fracture surfaces for tension and shear samples are observed by the SEM to investigate the coalescence of voids as well as void shapes in different stress states. A large number of dimples which indicate ductile fracture are present at the central region of uniaxial tensile sample while elongated dimples are observed on the edge of fracture surface. In shear test, equiaxial dimples are also observed on the center of the fracture surface and shear dimples elongate along the direction of the maximum shear stress. It is suggested that nucleation and growth of microvoids are the dominant failure mechanism which induced the microcrack initiation, and the effect of the maximum shear stress must be considered both in tensile and shear stress state.