Unveiling the durability, friction, and wear behaviour of nanodiamond composite films deposited on biased cemented carbide with varying Al interlayer thickness

Nanodiamond composite (NDC) films were deposited on biased cemented carbide (WC−6 wt. % Co) substrates using a coaxial arc plasma deposition technique, incorporating sputtered aluminium (Al) interlayers with varying thicknesses (0,50, 100, 300, and 500 nm). This study systematically investigates the durability, friction, and wear behaviour of NDC films, focusing on optimizing Al interlayer thickness to enhance performance in dry and harsh machining conditions. The primary objective was to mitigate interfacial catalytic reactions, particularly Co-induced graphitization, which adversely affect adhesion and mechanical integrity. Experimental findings identified a 100 nm Al interlayer as the optimal configuration, forming a protective Al₂O₃ layer that effectively suppressed graphitization. This resulted in significant improvements in coating performance, including a 79 % increase in adhesion strength, as indicated by a critical load of 17 N for full spallation during scratch testing, and a 62 % enhancement in wear resistance, yielding a wear rate of 7.85 × 10 −8 mm³/N.m. Simultaneously, the coefficient of friction (COF) decreased by 71 % compared to the uncoated substrate, maintaining a stable value of 0.09 during dry sliding tests against a rough Al₂O₃ counterpart. The exceptional tribological performance of the optimized NDC coatings is attributed to multiple factors. The refined nanostructure, featuring a dense grain boundary network, facilitated the formation of a lubricating graphitic layer, contributing to low and stable friction. Additionally, the high hardness (75 GPa) and Young's modulus (724 GPa) provided superior wear resistance and load-bearing capacity. These results underscore the potential of Al interlayers to significantly enhance the tribological performance of NDC coatings. However, the improvements in durability remain limited by the low adhesion strength, which remains a critical factor for cutting tools operating under dry machining conditions.