FORMATION OF FUNCTIONALLY GRADIENT DIAMOND FILMS

To improve the adhesion strength of diamond films, we developed a deposition process for functionally gradient diamond film. The film has an intermediate composition gradient layer consisting of diamond synthesized using d.c. plasma jet chemical vapor deposition and plasma-sprayed material. Diamond film is synthesized by spraying a plasma jet of hydrogen and methane onto a water-cooled substrate. The intermediate layer is formed by feeding powdered materials to the plasma for diamond synthesis. The composition gradient can be controlled by changing the powder feed rate. Tungsten carbide powder and molybdenum powder were plasma-sprayed at the same time during diamond synthesis. The formation of the mixture of diamond and plasma-sprayed materials was observed by electron probe microanalysis. X-ray diffraction and Raman spectroscopic analysis showed that the intermediate layer did not contain graphite. The adhesion strength of the diamond film with an intermediate layer exceeded 150 kg cm-2.