Adhesion of diamond coatings on steel and copper with a titanium interlayer

Adherent diamond coatings on steel and copper were obtained by using a tita nium interlayer. The adhesion of the coatings was evaluated by scratch test s and micro-indentation tests. The diamond coating on steel exhibited a muc h higher critical load than on copper, as revealed by the scratch tests. Ho wever, an observation on the back of the scratch-delaminated film and on th e corresponding substrate surface showed that the detachment occurred betwe en the diamond film and the titanium interlayer. Therefore, the difference in the critical scratch load is due mainly to a substrate effect, making it difficult to compare the adhesion of different coatings. On the other hand, Knoop indentation tests showed interesting results: a sm all indentation load causes round spallation in the film with no observable crack. An exponential sink-in deformation under the indentation is propose d, y = -a exp(-bx). The coating adhesion is considered to be equivalent to the deformation stress at the edge of the spallation zone. The adhesion of diamond coatings on steel and copper with a titanium interlayer is evaluate d quantitatively using this model. Furthermore, a thermal quench method is proposed to estimate the coating adhesion. The results found are in agreeme nt with the indentation model. (C) 1999 Elsevier Science S.A. All rights re served.