The pronounced grain size refinement at the edge position of the diamond-coated WC–Co inserts under microwave plasma with negative bias

Abstract

The effect of negative direct current (DC) bias on the deposition of diamond on WC–Co insert was investigated. Diamond was deposited by microwave plasma assisted chemical vapor deposition (MW PACVD) on the SPGN type of WC–Co insert at 30 Torr with H 2-2%CH 4 mixed gas. During the deposition process, 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 was observed to decrease with the negative bias voltage. Furthermore, its tendency was more pronounced near the edge than at the center of the insert. The ion impact on the growth surface during deposition was considered to induce surface defects, which resulted in the renucleation of diamond crystals and grain size refinement.