Thin films of polycrystalline diamond have been deposited on chromium and titanium substrates using microwave plasma chemical vapour deposition (MPCVD) system. Indentation tests were combined with acoustic emission signals during loading in order to compare the coating adhesion. Optical microscopic images of the indented surfaces showed that indentations carried out at loads lower than 95 N did not produce significant cracking, detachment and/or propagation of delamination in the coatings. However, a 180-N load indentation was sufficient to delaminate the diamond film from the chromium substrate. 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 critical load, under which the film begins to crack and/or break off the substrate. Our results indicate that better adhesion can be achieved with titanium substrates, which can find potential usage as interlayer materials for enhancing diamond adhesion on some non-carbon affinity substrates. Possible reasons for the difference in the adhesion of diamond coatings on Cr and Ti are discussed in terms of the strength of carbide bonds and residual stresses.