Self-supporting nanocrystalline diamond foils: Influence of template morphologies on the mechanical properties measured by ball on three balls testing

The mechanical characterization of self-supporting nanocrystalline diamond foils (NCDFs) using the “ball on three balls test” is introduced. This mechanical testing method is validated for the measurement of fracture strengths of NCDFs of a thickness down to 50 μm. NCDFs manufactured by a hot-filament chemical vapor deposition (HFCVD) process on rolled copper sheets, oxidized and polished silicon wafers as templates, were characterized in regards to their surface morphology by scanning electron microscopy, 3-D surface imaging and atomic force microscopy. The effects of the different template materials on the mechanical properties of the NCDFs are presented by means of a statistical Weibull approach. Thus a mechanical characterization method is provided to measure the impact of different manufacturing parameters on the fracture strength of self-supporting NCDFs. This is a crucial milestone on the way to applying NCDFs on substrate materials which cannot sustain the HFCVD environment, thus exploiting the excellent properties of diamond for protection against friction and wear. In comparison with state-of-the-art ceramic foils it could be shown that NCDFs can be manufactured with high reliability, and offer fracture strengths far greater than those of conventional technical ceramics.

► Mechanical characterization of self-supporting nanocrystalline diamond foils. ► Synthesis by hot-filament chemical vapor deposition on selected templates. ► Statistical evaluation of ball-on-three-balls test results by Weibull approach. ► Model of morphologies for template-dependent growth of nanocrystalline diamond. ► Smooth template surface states crucial factor for reliable mechanical properties.