On the use of CrN/Cr and CrN interlayers in hot filament chemical vapour deposition (HF-CVD) of diamond films onto WC-Co substrates

CrN/Cr-based films were deposited using PVD-arc technique onto Co-cemented tungsten carbide (WC-Co) substrates and, then, seeded with diamond powder suspension or mechanically treated by Fluidized Bed Peening (FBP) of brittle diamond powders. Multilayered coatings were obtained from the superimposition of 4 µm-thick diamond coatings, deposited on the PVD interlayer using hot filament chemical vapour deposition (HFCVD). The effectiveness of fluidized bed peened CrN/Cr interlayers on the adhesion enhancement of diamond on WC-Co substrates was studied and compared to diamond coated WC-Co substrates with unpeened CrN/Cr or CrN interlayers, or pre-treated with two-step chemical etching (Murakami's reagent and Caro's acid, MC-treatment).In particular, growth, morphology, wear endurance and adhesion of the CVD deposited diamond films onto peened CrN/Cr interlayer were looked into. Diamond coatings on peened CrN/Cr interlayers exhibited a rougher surface morphology than as-prepared CrN/Cr films as a result of the surface roughening of the ductile Cr layer produced by the repeated impacts on it of the diamond powders during FBP. FBP was found to be a necessary step in improving the scarce adhesion of CVD diamond onto CrN/Cr-interlayer.However, the use of FB peened CrN/Cr interlayer did not represent the best way to pre-treat WC-Co substrates, as the unpeened single-layer CrN, or the use of MC pretreatment, was found to ensure better adhesion and wear endurance.