Effect of grain size and duty ratio on the mechanical behavior of titanium under tension with pulsed current

Abstract

The influence of a high-density pulsed current on the deformation behavior of titanium with different structure refinement is studied. A comparison of the features of the deformation curves has been carried out of coarse-grained and nanostructured commercial pure Ti Grade 4 under tension with the introduction of a pulsed current. A current of various duty ratio and densities was supplied from a pulse generator to a sample in the grips of a tensile testing machine. The microstructure of a coarse-grained titanium in the sample head and near the fracture region in the longitudinal section was studied by optical microscopy. To study the microstructure of nanostructured titanium foils, the transmission electron microscopy was used. The electroplastic effect in the studied materials manifested itself in the tensile curve in the form of separate downward stress jumps. Under the same regimes of high-duty ratio pulsed current, the amplitude of stress jumps in the coarse-grained titanium is higher than in the nanostructured titanium. For a low duty ratio current the stress jumps are the same in the plastic region. A high duty ratio pulsed current in nanostructured titanium led to an anomalous hardening effect, the physical nature of which needs a further investigation. The used modes of the pulsed current did not lead to structural changes noticeable under optical magnification of the tensile samples, except for the disappearance of twins and the separation of impurity particles in the coarse-grained titanium. The fractographic fracture patterns of nanostructured titanium tested with and without current indicate ductile fracture without significant changes, which testified a minimal thermal contribution during the experiments.

Keywords

• tension
• titanium
• nanostructure
• electroplastic effect
• pulsed current
• fractography