Quantifying adhesion of ultra-thin multi-layer DLC coatings to Ni and Si substrates using shear, tension, and nanoscratch molecular dynamics simulations

- Flow reactor platform is employed to separate chemical effects of carbon dioxide.
- New strategies are applied to eliminate thermal and dilution effects.
- Chemical effects of carbon dioxide are due to radical and collision factors.

Ultra-thin diamond-like carbon (DLC) coatings are used in many engineering applications including hard disk drives, automobile engines, and MEMS/NEMS devices to protect delicate substrates against wear and corrosion. However, they are susceptible to brittle cracking and delamination due to high intrinsic stress and poor adhesion to many substrates. Inclusion of an intermediate layer can prevent delamination of the coating. We perform simple shear and tension loading and nanoscratch molecular dynamics simulations to quantify the effect of coating layer thickness and composition on the adhesion of the ultra-thin multi-layer DLC coatings used in hard disk drives to their substrate. We observe that an intermediate Si layer improves adhesion of DLC coatings to Ni substrates compared to coatings without one, and that an optimum thickness of the Si layer exists. We also find that an intermediate DLC layer with sp3 fraction lower than the outermost DLC coating layer protects the substrate from plastic deformation under external loading, and that it improves adhesion to Si but not Ni substrates compared to coatings with no intermediate layer.

488