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 fi lms and of the intermediate layers formed at the film/substrate interface. Deposition experiments were performed by hot-filament CVD systematically va rying the deposition temperature (650-850 degrees C) and time (60-360 min). The morphology and structure of the coatings and interfaces were investiga ted by optical and electron microscopy (SEM) and by the combined use of ref lection 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 pr epared transversal sections of the specimen. Only small differences concern ing the mechanical properties have been found for films grown on pure Ti an d Ti-6Al-4V substrates. Adhesion of diamond on the substrate has been deter mined by the scratch test. The analysis of the micrographs of the indenter scratches and of the fracture-correlated acoustic emissions clearly indicat es the occurrence of a multi-step detachment process, leading progressively to effective delamination of the diamond coatings. (C) 1999 Elsevier Scien ce S.A. All rights reserved.