Grain size refinement of the diamond film deposited on the WC–Co cutting inserts using direct current biasing

The effect of negative direct current (DC) bias has been investigated in the deposited diamond on WC–Co insert. SPGN type of WC–Co was used as a substrate where diamond was deposited by hot filament chemical vapor deposition at 60 Torr with H2–3%CH4 gas. DC bias was applied to the insert with the range between 0 and −120 V. The grain size of diamond film deposited on WC–Co insert decreased with the increase in negative bias voltage. The grain size was more refined near the edge than the center of the insert. Compared to other processing parameters such as pressure, temperature and carbon concentration, the biasing is a very effective way to reduce the grain size of diamond film, especially at the edge region where workpiece contacts during machining process.