Fracture mechanism of electrically-assisted micro-tension in nanostructured titanium using synchrotron radiation X-ray tomography

A coarse-grained (CG) Ti with an average grain size of ∼50 μm was processed by high-pressure torsion (HPT) under a pressure of 6.0 GPa through 10 turns at room temperature (RT) to produce nanostructured titanium (Nano-Ti) with an average grain size of ∼95 nm. Electrically-assisted (EA) micro-tensions of CG-Ti and Nano-Ti were performed using pulsed unidirectional current with a current density of 750 A/mm2, pulse width of 10−4 s. The stress drop is higher for Nano-Ti compared with CG-Ti. The results of fractograph observations show many cleavage steps in Nano-Ti while the CG-Ti is dominated by dimples. The spatial distribution of voids in tensile specimens was revealed after testing using synchrotron radiation X-ray tomography. The results demonstrate that applying a pulse current can effectively reduce the number and volume of voids before fracture. A model is presented describing the fracture mechanism of CG-Ti and Nano-Ti during EA micro-tension. [Display omitted]