Study of the diamond deposition on cemented carbides containing 10% Co with a tungsten intermediate layer

Abstract

CVD diamond coatings are expected to increase significantly the lifetime of cemented carbide tools. The preparation of such coatings is, however, hindered by the presence of the Co binder phase. Because of its catalyst function, Co promotes the formation of a poorly adhering non-diamond phase at the interface between the diamond and the hard metal substrate. Different methods have been used to solve this problem, such as selective Co etching of the substrate or deposition of intermediate layers.

In the present study, intermediate W layers were sputter deposited on 10 wt.% Co-containing cemented carbide prior to the deposition of the diamond layer, to act as a buffer layer for Co diffusion. Diamond films have been deposited by microwave plasma-enhanced CVD. The thickness of the W layer has been varied to influence the amount of Co which diffuses to the surface. The phase transformation at the diamond-intermediate layer interface has been studied by means of transmission electron microscopy, secondary-ion mass spectroscopy and glancing-angle X-ray diffraction.

The results with the intermediate layer have been compared with the results obtained with Co etching of the surface.