Abstract: Abstract: Diamond films were synthesized by electron enhanced CVD and hot cathode DC-PCVD, and the corrosive action of transition-metals Fe, Ni and Co on the surface was investigated using hot-filament heating under vacuum. The metals and the corroded surface of the diamond films were characterized by X-ray diffraction (XRD) and Raman spectroscopy. The corrosive effect of these transition-metals on the diamond films can be seen, with Fe having the largest effect. A non-diamond carbon phase was formed on the corroded surface of the diamond films and on the transition-metals, but transition-metal carbides were not found.