A comparison study of diamond adhesion on ductile metals

Thin films of polycrystalline diamond have been deposited on chromium and t itanium substrates using microwave plasma chemical vapour deposition (MPCVD ) system. Indentation tests were combined with acoustic emission signals du ring loading in order to compare the coating adhesion. Optical microscopic images of the indented surfaces showed that indentations carried out at loa ds lower than 95 N did not produce significant cracking, detachment and/or propagation of delamination in the coatings. However, a 180-N load indentat ion was sufficient to delaminate the diamond film from the chromium substra te. Interestingly, the diamond film remained on the titanium substrate even after the indentation test. Acoustic emission (AE) signals emitted during the indentation process were found to be effective in determining the criti cal load, under which the film begins to crack and/or break off the substra te. Our results indicate that better adhesion can be achieved with titanium substrates, which can find potential usage as interlayer materials for enh ancing diamond adhesion on some non-carbon affinity substrates. Possible re asons for the difference in the adhesion of diamond coatings on Cr and Ti a re discussed in terms of the strength of carbide bonds and residual stresse s. (C) 2000 Published by Elsevier Science B.V. All rights reserved.