Influence of structure on adhesion of grains in CVD diamond films

Abstract

Diamond thin films of different structures were prepared by using chemical vapor deposition on WC(6%Co) substrates under different conditions.Reman spectroscopy was used for the quality evaluation of the diamond films.The cracking size in indentation tests was used for the evaluation of adhesion strength,and the influence of structure of diamond films on the adhesion was studied.Results obtained show that: (1) The buffer role of sp2_carbon between grain boundaries greatly affect the residual stress of the film,hence the cracking size decreases steadily with increasing sp2 content.(2) The increase of nucleation density is mainlyh due to the contribution of the diamond seed grains left. In this case,the increase of nucleation density cannot effectively improve the chemical adhesioe force between the film and the WC substrate,and cannot improve the adhesion between the film and the substrate.(3)For thinner films there is no compressive stress among diamond grains,hence the cracking size does n t increase apparently with increasing deposition time.Strong compressive stress emerges only after the thickness increases to a certain value,and then the cracking size increases rapidly with increasing deposition time.