Rapid recrystallisation and surface modification of titanium by electro discharge

Abstract

2·0 to 3·5 kJ of input energy as a single pulse from a 150 μF capacitor was applied to a 50% cold rolled Ti to induce rapid recrystallisation and surface modification. Using an input energy of 2·0 kJ, complete recrystallisation occurred over a period of 96 μs and the resulting microstructure was identical to that of a Ti before cold rolling. With an input energy of 2·5 kJ or higher, thermal oxycarburisation progressed by the formation of a titanium oxycarbide layer and the activation energy for the associated diffusion process was calculated to be 231 kJ mol⁻¹. A much higher value of hardness that was observed at the edge of the cross section was attributed to oxygen and carbon induced solid solution hardening. Both the recrystallisation and surface modification processes depended on the amount of heat generated during an electro discharge, which could be manipulated by input energy and capacitance.

Keywords:

• Discharge
• Titanium
• Microstructure
• Hardness
• XPS

Acknowledgement

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2013R1A1A2010207).