Adhesion and durability of multi-interlayered diamond-like carbon films deposited on aluminum alloy

Aluminum (Al) alloys are light and have good workability; however their low hardness and poor wear resistance are drawbacks limiting their wide application in the automotive industry. Deposition of diamond-like carbon (DLC) films, which exhibit high hardness and good wear resistance, onto the surface of Al alloy substrates can overcome these drawbacks. Because Al alloys and DLC films have low affinity for each other, adhesion between the two is poor. However, the use of an interlayer can improve adhesion. To investigate the effect of multi-interlayers on the adhesion and durability of DLC films on Al substrates, DLC films with Ti, Si-DLC, or Ti/Si-DLC interlayers were deposited onto A2024 substrates using plasma-enhanced chemical vapor deposition (PECVD). Prior to PECVD, an Ar-bombardment treatment was conducted to clean the surface of the substrate. Subsequently, a Ti interlayer was deposited by sputtering for 15 min, a Si-DLC interlayer was deposited using a tetramethylsilane (TMS) and methane gas mixture for 15 min, and DLC was deposited using methane gas for 90 min. The nanohardness of the Ti/Si-DLC multi-interlayered sample reached 33 GPa more than 8 GPa higher than that of the single-interlayered samples. In addition, the Ti/Si-DLC multi-interlayered sample exhibited higher hardness/Young's modulus (H/E) ratios than the single-interlayered samples. Wear tests showed that the wear volumes for the balls and the multi-interlayered samples were smaller than those for the single-interlayered samples. In addition, the delamination distance of the Ti/Si-DLC multi-interlayer sample was 3300 m, more than 1500 m longer than that of single-interlayered samples. This study demonstrates that improving the wear resistance required high plastic index parameter (H/E) values rather than high H values.