Qualitative Evaluation of Ultra-thin Multi-layer Diamond-Like Carbon Coatings Using Molecular Dynamics Nanoindentation Simulations

Ultra-thin diamond-like carbon (DLC) coatings are used in hard disk drives to protect the intricate magnetic structures from wear and corrosion. The coating on the recording head consists of a hard DLC layer and a silicon (Si) layer that improves adhesion between the DLC layer and the substrate. Damage to this protective coating can expose the magnetic structures to corrosion and compromise the reliability and functionality of the hard disk drive. Hence, it is critical to understand how coating design parameters affect the mechanical properties of these protective DLC coatings. We have used molecular dynamics simulations to determine the hardness and Young's modulus of the ultra-thin multi-layer protective DLC coating of a recording head as a function of coating design parameters. We have found that hardness and Young's modulus of the multi-layer coating increase with increasing DLC layer and decreasing Si layer thickness. Furthermore, hardness and Young's modulus of the multi-layer coating are a function of the sp(3) fraction and, thus, the hardness of the DLC layer. In addition, the mismatch between the hardness of the DLC layer and the substrate determines whether plastic deformation occurs in the coating or the substrate, and significantly affects the hardness of the multi-layer protective coating.