Surface Modification and Heat Treatment of Ti Rod by Electro Discharge

Single pulse of 2.0 to 3.5 kJ of input energy from 150 μF capacitor was applied in a N2 atmosphere to the cp Ti rod for its surface modification and heat treatment. Under the conditions of using 2.0 and 2.5 kJ of input energy, no phase transformation has been occurred. However, the hardness and tensile strength decreased slightly after a discharge due to a grain growth. Using greater than 3.0 kJ of input energy, the electro discharge process made a phase transformation and the hardness especially at the edge of the cross-section of the Ti rod increased significantly. The Ti rod before the discharge was lightly oxidized and was primarily in the form of TiO2. However, the surface of the Ti rod has been instantaneously modified by the discharge into the major form of TiN from TiO2. The electro discharge process can thus modify the Ti rod’s surface in times as short as 200 μsec by manipulating the input energy, capacitance, and discharging ambience.