Abstract
Polycrystalline diamond thin films have been deposited onto titanium and chromium substrates using a conventional microwave plasma chemical vapour deposition (MPCVD) system. The coatings deposited were ∼1·5 μm in thickness. A modified scratch tester was employed to perform indentations on the coated substrates in order to evaluate the adhesion of the coatings to the substrates at 95 and 180 N loads. Complementary Raman spectroscopy studies were performed to investigate the film stress levels along the section across the indentation zone. Analysis of the results obtained suggests that the coating on the chromium substrate was under greater stress than the diamond coating on the titanium substrate. Both coatings remained attached to their substrates after a 95 N load indentation test. Interestingly, a 180 N load indentation was sufficient to delaminate the coating on the chromium substrate, whereas, the coating on the titanium substrate remained attached to its substrate. This may be attributed to titanium forming a stronger carbide bond than chromium, which plays the role of an adhesive, sticking the film to the substrate. A newly proposed adhesion characterisation method, which couples indentation loading with acoustic emissions, was used throughout this study to measure the coating adhesion quantitatively and reliably.
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