NCD by HFCVD on a Si3N4-bioglass composite for biomechanical applications

A biocompatible Si3N4-bioglass composite was coated with nanocrystalline diamond (NCD) by the hot filament chemical vapour deposition technique (HFCVD) using a H2/Ar/CH4 gas mixture. The advantages of the biocomposite are combined with a hard, smooth and low friction coating, making it a potential material for biotribological applications. Very low intrinsic surface roughness in the range 5 to 15 nm was determined by AFM and crystallite sizes of 1 to 30 nm were measured by TEM. The substrate temperature, Ar / H2 ratio, starting roughness and cooling rate after deposition are key factors in determining the uniformity and adhesion of the NCD film to the biocomposite. To avoid blistering and guarantee high adhesion levels, depositions must be conducted below the bioglass crystallization temperature (637 °C). The highest growth rate (1 μm h− 1) was reached with a Ar / H2 = 0.1 ratio. Brale indentation tests with 200 N showed that flat lapped substrates give a better adhesion relatively to smoother ones pre-polished in soft cloths. Slow cooling rates after deposition (2 °C min− 1) prevented film delamination under this applied load.