Synthesis of multilayer diamond film and evaluation of its mechanical properties

When diamond is used as a wear-resistant material for tools, its unique wear resistance cannot be fully exploited due to the possibility of brittle fracture. In general, diamond films synthesized by the vapor phase method are polycrystalline exhibiting columnar crystal growth. In the polycrystalline structure, once cracks occur on the surface of the film, they tend to propagate through the columnar particles, leading to a decrease in toughness. In this study, using the hot-filament chemical vapor deposition (CVD) method, diamond secondary nuclei are grown on a substrate by applying bias current to the substrate repeatedly and intermittently; multilayer diamond films, in which the continuity of grain growth is suppressed, are synthesized. The interfaces formed by the multilayer structure are expected to prevent crack propagation. To confirm this effect, mechanical characteristics, such as the bending strength of the multilayer diamond film are evaluated. The results indicate that the bending strength of the multilayer diamond film is approximately 30% higher than that of a conventionally-produced diamond film.