Adhesion
analysis of polycrystalline diamond films on molybdenum by means of
scratch, indentation and sand abrasion testing
Buijnsters JG, Shankar P, van Enckevort WJP, Schermer JJ, ter Meulen JJ
Thin Solid Films 474 (2005) 186-196
Abstract:
Diamond films have been grown by hot-filament chemical vapour
deposition (CVD) on molybdenum substrates under different growth
conditions. The films grown with increasing substrate temperatures show
a higher interconnection of diamond grains, whereas increasing methane
concentrations in the 0.5-4.0% range lead to a transition from micro-
towards nanocrystalline films. X-ray diffraction analysis shows Mo2C
interlayer formation. Indentation, scratch and sand erosion tests are
used to evaluate the adhesion strength of the diamond films. Using
steel ball indenters (circle divide 750 mum), indentation and scratch
adhesion tests are performed up to final loads of 200 N. Upon
indentation, the load values at which diamond film failure such as
flaking and detachment is first observed, increase for increasing
temperatures in the deposition temperature range of 450-850 degreesC.
The scratch adhesion tests show critical load values in the range of
16-40 N normal load for films grown for 4 h. In contrast, diamond films
grown for 24 h at a methane concentration of 0.5% do not show any
failure at all upon scratching up to 75 N. Film failure upon indenting
and scratching is also found to decrease for increasing methane
concentration in the CVD gas mixture. The sand abrasion tests show
significant differences in coating failure for films grown at varying
CH4/H-2 ratios. In contrast to the other tests, here best coating
performance is observed for the films deposited with a methane
concentration of 4%. (C) 2004 Elsevier B.V. All rights reserved.