High temperature tribological performance and thermal conductivity of thick Ti/Ti-DLC multilayer coatings with the application potential for Al alloy pistons

Abstract To improve the mechanical and tribological performance of Al alloy for pistons, a ~ 17 μm thick Ti-DLC multilayer coating composed of alternating Ti and Ti-DLC layers was designed and prepared on the Al alloy substrate by FCVA technology. The microstructure, mechanical properties, high temperature tribological properties and thermal conductivity of the coating were evaluated. The results showed that the added Ti atoms were embedded in the amorphous carbon structure in the form of TiC crystals to form a nanocrystalline amorphous composite structure. The tribological test demonstrated that the multilayer Ti-DLC coating exhibited excellent wear resistance at room temperature, benefiting from the high hardness, high toughness and superior plastic deformation resistance, namely hardness H (~18.1 GPa), Young's modulus E (~168.2 GPa), H/E (~0.11), H3/E2 (~0.21 GPa), and elastic recovery We (~61.5%) values. At a high temperature test of 300 °C, the coating can maintain outstanding tribological properties with a low friction coefficient of ~0.12 and a low wear rate of ~2.69 × 10−7 mm3/Nm. The thermal conductivity of the multilayer Ti-DLC coating Al alloy substrate was about 30 W/(m∙K) lower than that of the untreated substrate under above 300 °C, which indicated that the multilayer Ti-DLC coating could reduce heat loss and improve fuel, and had the potential to be used as a protective coating for Al alloy pistons.