Diamond coatings deposited on tool materials with a 915 MHz scaled up surface-wave-sustained plasma

An essential difficulty in coating tool materials with polycrystalline diam ond is the film poor adhesion. To solve this problem we have developed a ge neric pretreatment method for the substrate surface, prior to diamond depos ition which essentially consists of submitting it to ion bombardment by car bon species through plasma immersion in a methane d.c, glow discharge. This procedure leads to carbon supersaturation of the substrate surface. Under diamond deposition conditions, it ensures carbon saturation of the substrat e surface with respect to the gas phase and provides a diffusion barrier pr eventing migration, from the substrate bulk to the surface, of species whic h exert a catalytic effect on sp(2) carbon phases. thereby enhancing diamon d nucleation and ensuring good adhesion of the diamond film. The diamond fi lms were deposited with a 915 MHz surface-wave-sustained plasma scaled up f rom a 2.45 GHz system, enabling us to eventually coat large areas (100 mm i n diameter) of cobalt sintered WC. With such a material, as shown by second ary ion mass spectroscopy, the diffusion barrier obtained through carbon su persaturation is effective in preventing cobalt atoms from migrating to the surface where they would favor the formation of non-diamond phases. Raman spectroscopy and scanning electron microscopy measurements confirmed the go od quality of the obtained diamond films. A scratch test analysis was used to demonstrate the improved adhesion strength resulting from this novel pre treatment method. (C) 2000 Elsevier Science S.A. All rights reserved.