Surface and tribological characterization of anodic aluminum oxide coating containing diamond-like carbon flakes

Abstract

The incorporation of carbonaceous material like graphite into anodic aluminum oxide coatings offers excellent mechanical properties and low friction due to its self-lubricating behavior. However, the coating containing graphite has poor durability and surface quality, such as the formation of submicron cracks on the surface, which limit its use in a load-bearing application. These limitations encouraged the study of diamond-like carbon (DLC) performance in the aluminum oxide matrix since DLC consists of sp2-bonded carbon of graphite-like structure and sp3-bonded carbon of diamond-like structure. Since DLC usually exists as a thin film, it was deposited on copper particles that act as a carrier. As an effective approach to improve sliding properties, annealing heat treatments were conducted at temperatures ranging from 100 °C to 500 °C for 1 min holding time. AA2017-T4 aluminum alloy was anodized with 1 g/L of untreated and hear-treated DLC deposited on copper (Cu) particles, respectively, at a constant current density of (15 A/dm2) and fluctuant voltage (±15 V). Then, morphological, chemical composition, surface hardness, and tribological properties were evaluated. Results showed that the incorporation of DLC showed a significant reduction in porosity and microcracks and increase surface hardness compared to conventional oxide coating. The oxide coating with heat-treated DLC showed better sliding properties than untreated DLC due to more sp2 graphite phase formed as a lubricating layer and helped to reduce friction and wear at sliding contact interfaces.