Adhesion improvement of diamond coating on silicon nitride substrate

Adherent diamond coating on sintered silicon nitride substrate was prepared by a microwave plasma enhanced chemical vapor deposition (CVD) in the CO a nd H-2 reactant system. The substrate was pretreated in a hot and strong ac id solution and microflawed ultrasonically with diamond grains suspended in ethanol. The effects of diamond-like carbon (DLC) interlayer on the adhesi on strength of diamond film was investigated in relation to the formation o f the graded texture and characteristic C-C bonding varied from substrate s ide to diamond film. The DLC interlayer was grown by RF plasma enhanced CVD in the CH4-H-2 system. Adhesion strength of the diamond film were evaluate d by a compression topple test and the subsequent observation of the fractu red surface. Adhesion was found to increase considerably by the insertion o f DLC layer, which would relax the residual stress in the interfacial regio n between diamond film and substrate. Actual cutting test by milling the Al -20 wt%Si alloy work revealed an excellent long tool life in using a thick diamond coated specimen inserted with DLC interlayer. (C) 1999 Elsevier Sci ence S.A. All rights reserved.