Surface Modification and Heat Treatment of Ti Rod by Electro Discharge

Single pulse of 2.0 to 3.5 kJ from 150 1sF capacitor was applied 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 and the elongation increased after a discharge due to a slight grain growth. By using more than 3.0 kJ of input energy, the electro discharge made a phase transformation and the hardness at the edge of the cross section increased significantly. The Ti rod before a discharge was lightly oxidized and was primarily in the form of TiO2. However, the surface of the Ti rod has been instantaneously modified by a discharge into the main form of TiN from TiO2. Therefore, the electro discharge can modify its surface chemistry in times as short as 200 mu sec by manipulating the input energy, capacitance, and discharging environment.