Revealing mechanical and structural properties of Si-doped nanodiamond composite films through applied biasing voltages on WC- Co substrates

Silicon-doped nanodiamond composite (Si-NDC) films hold significant promise for advancing cutting tool performance in demanding applications. These films, created through coaxial arc plasma deposition from 1 at.% silicon blended graphite targets, eliminate the need for external heating, chemical reactions, Co etching, or nanodiamond seeding on cemented carbide substrates. This study explores the influence of biasing voltages (0 V,-50 V, and -100 V) during Si-NDC film deposition on their mechanical properties. As biasing voltage increased from 0 to-100 V, Si-NDC films displayed remarkable improvements in hardness (from 56 to 65 GPa) and Young's modulus (from 535 to 655 GPa). These enhancements stem from the presence of nanodiamonds, C -Si sp3 bonds, and unique features within the amorphous carbon matrix. Nevertheless, this transformation introduced higher internal stress levels (0.88 to 3.75 GPa), adversely affecting film-substrate adhesion, which decreased from a critical load of 31 N to 16.6 N for unbiased and -100 V biased films, respectively. Intriguingly, unbiased films exhibited enhanced adhesion attributed to the formation of intermetallic compounds like CoSi2 and SiC. Surface roughness increased from 90 nm to 180 nm with-100 V biasing, attributed to droplet attraction. Biasing improved film hardness but aggravated internal stress, impacting adhesion and surface roughness.