Adhesion improvement of the diamond film in diamond-coated WC–Co insert prepared with AC substrate bias

The grain size of diamond film deposited on WC–Co insert can be reduced by AC substrate bias during deposition, which enables a smooth surface finish of a workpiece during machining process. However, the adhesion of diamond film deposited on WC–Co insert became poor due to AC bias application, which was attributed to the increased surface Co content. To maintain adhesion strength while achieving grain size refinement by AC-biased growth, a certain thickness of diamond layer grown without bias was introduced as a buffer layer. The AC bias was applied after diamond deposition of 8 and 15 μm in thickness without bias and the total thickness of the diamond film was controlled to be around 20 μm. The adhesion strength of diamond film for the diamond-coated WC–Co insert prepared with AC bias, measured by indentation technique, was greatly improved by the adoption of diamond buffer layer deposited without bias.