Vapor Deposited Nanostructured Diamond Films with Tailored Hardness and Adhesion Properties

The ability to tailor the mechanical properties of vapor deposited hard carbon films to suit a particular application’s requirements is very important. The combined influence and interdependence of film properties such as hardness, toughness, adhesion, and elastic modulus should be considered when designing the film. In this study, we investigate the effect of changing the N_2/CH₄ feedgas ratio on the structure and mechanical properties of microwave plasma chemical vapor deposited diamond films grown on Ti-6Al-4V substrates. The relative concentration of CH₄ and N₂ (in a balance of H_2) is shown to strongly influence film structure, hardness, and adhesion. Smooth nanostructured diamond films with good adhesion and high hardness are obtainable. We find a distinct correlation between the nanoindentation hardness of the deposited film and the N_2/CH₄ ratio in the plasma as well as correlation of hardness to features in the Raman spectra. Our results suggest that nanostructured diamond films can be tailored on metallic surfaces with hardness ranging from 10 GPa (medium-hard) to 100 GPa (superhard) for wear resistant applications.