Mechanisms of TiC layer formation on high speed steel by a single pulse in electrical discharge machining

Abstract

Mechanisms of the Titanium carbide (TiC) layer formation in electrical discharge coating (EDC) using TiC powder electrodes were investigated. We have observed and analyzed the migration and adhesion of TiC powder in single pulse discharges in electrical discharge machining (EDM) as the first step towards elucidating the adhesion mechanism of TiC with the use of TiC powder and high speed steel as the electrodes and workpiece, respectively. The adhesion mechanism of TiC powder was discussed from the shape and composition distribution of the discharge crater and the voltage and current waveforms at the time of discharge. TiC is directly supplied from the electrode to the surface of the workpiece by single pulse discharge without the presence of TiC between the electrodes. When the voltage remains constant during discharge, the melted and resolidified TiC is localized in the crater. When a temporary voltage drop occurs during discharge, the clustered TiC that has maintained its powder form is present in the crater. The temporary voltage drop during discharge occurred by existing the large clustered TiC powder between the electrodes and by the bulge of the crater. The amount of TiC provided from TiC electrodes to TiC layer is smaller than that to high speed steel. The thickness of TiC layer on high speed steel increases and converges some constant value with increasing EDC process time because of the balance of TiC removal and adhesion by a single pulse discharge.