Effect of surface pretreatment on nanocrystalline diamond ballas morphology

Abstract

Nanocrystalline diamonds are grown in ballas morphology is deposited on tungsten carbide substrates using Hot Filament Chemical Vapour Deposition (HFCVD) technique. The diamond ballas however exhibits its' own formations and arrangements. These arrangements are analysed using Field Emission Scanning Electron Microscope (FESEM) and optical microscope. This is due to the tungsten carbide substrates undergo various sectioning processes and pretreatments to prepare and ensure nanocrystalline diamonds is deposited. Sectioning involve using precision diamond cutting, Electrical Discharge Machining-Wire Cut (EDM-wire cut) and Electrical Discharge Machining (EDM). The three different forms of sectioning influences preference of sites where new ballas are to nucleate and grow. For precision cut substrates, ballas nucleate evenly across the surface. However EDM cuts give a grain-like formation where ballas does not nucleate well on the boundaries. This is caused by the heat effect of EDM cuts that involves high temperature on the tungsten carbide substrates. It is also shown that the diamond coating manages to accommodate large scratches, giving an even coating of diamond ballast on the floor and walls of the scratches which in turn could be applied to micro channels. Finally untreated samples have similar ballas arrangement to that of precision cut except there is voids and cavities under the diamond layer causing the planar view to show an uneven surface.