Processing-structure-adhesion relationship in CVD diamond films on titanium substrates

The hardness and adhesion properties of diamond films deposited on pure Ti and Ti-6Al-4V alloy are related to the structural characteristics of the films and of the intermediate layers formed at the film/substrate interface. Deposition experiments were performed by hot-filament CVD systematically varying the deposition temperature (650-850 degrees C) and time (60-360 min). The morphology and structure of the coatings and interfaces were investigated by optical and electron microscopy (SEM) and by the combined use of reflection diffraction (RHEED) and X-ray powder diffraction (XRPD), used also in the GID (Grazing Incidence Diffraction) mode. Hardness measurements (HV) of the deposits were made at a constant loading of 25 g on specifically prepared transversal sections of the specimen. Only small differences concerning the mechanical properties have been found for films grown on pure Ti and Ti-6Al-4V substrates. Adhesion of diamond on the substrate has been determined by the scratch test. The analysis of the micrographs of the indenter scratches and of the fracture-correlated acoustic emissions clearly indicates the occurrence of a multi-step detachment process, leading progressively to effective delamination of the diamond coatings. (C) 1999 Elsevier Science S.A. All rights reserved.