Electro-thermo-mechanical characterization of microscale Ti-6Al-4V wires using an innovative experimental method

The deformation behavior of Ti-6Al-4V (at.%) wires under direct electric current was investigated. To minimize thermal effects due to Joule heating on plastic deformation, fine Ti-6Al-4V wires with 100 μm diameter were tested by developing and utilizing an innovative electro-thermo-mechanical tensile tester. The force-controlled tensile tester consists of an electronic balance, piezo actuator, optical camera, infrared thermometer, and electric power supply. To characterize the state of Joule heating in the fine wire, the temperatures at the wire and load frame junction were measured with a non-contact infrared thermometer and then a finite element analysis was conducted using the measured temperatures as boundary conditions. For validation of our experimental approach, we have carried out uniaxial tensile testing of Ti-6Al-4V wires under 0, 10, and 20 A/mm² current densities, respectively, and the results were compared with previous reported values. In our specimen, the change of mechanical properties including the reduction of elastic modulus and strength and the increase of ductility and failure strain was observed with increasing the applied current. However, the level of change was not severe compared to other research. It could therefore be concluded that the thermal effect was minimized by using fine Ti-6Al-4V wires with a large surface-to-volume ratio. In the analysis of fracture surface, the transition from brittle to ductile fracture mode was clearly observed with increasing current density.