A multilayer approach for enhancing the erosive wear resistance of CVD diamond coatings

The erosive wear behavior of mono-, bi- and multilayered diamond composite coatings grown by hot filament chemical vapor deposition (HFCVD) is investigated. The effect of the surface pre-treatment on the silicon nitride substrates was firstly evaluated revealing that flat lapping mechanical treatment combined with chemical CF4 plasma etching is the best surface preparation to achieve high adhesion levels. Multilayers were designed to combine the excellent adhesion of microcrystalline diamond (MCD) with a top nanocrystalline diamond (NCD) layer of reduced surface roughness. Indeed, the multilayered diamond coatings revealed the best erosive resistance, whose damage occurred by gradual loosening of material from the outer layer after longer testing time. The absence of areas with film spallation or substrate exposure is given by the action of the MCD/NCD interfaces in deflecting cracks, thus acting as “energy sinks” to further propagation. An analytical model of the stress field distribution within the coatings based on the von Mises criterion was developed to elucidate the erosive mechanical behavior of the different diamond composites.