• • At a modulation period of 186 nm, TiAlN/VN multilayers achieved a maximum hardness of 25.46 ± 0.69 GPa and a minimum residual compressive stress of 0.88 GPa, surpassing the rule-of-mixtures hardness of monolithic TiAlN and VN films. This hardness-stress combination is critical for connecting rods subjected to cyclic loading, where stress-induced cracking would otherwise accelerate fatigue failure.
• • The multilayer with Λ = 280 nm delivered the highest H/E and H³/E² ratios, correlating with superior fracture toughness and film-substrate adhesion, and maintained a stable friction coefficient of 0.5 with optimal wear resistance. These metrics indicate that a moderate interface density balances hardness and toughness, preventing premature delamination under sliding contact.
• • The Λ = 186 nm multilayer exhibited increased self-corrosion potential and reduced corrosion current density compared to the TC4 substrate, owing to a higher interface count and lower porosity that effectively sealed micro-pores and micro-cracks. This barrier effect impedes corrosive media diffusion, directly extending the service life of titanium alloy connecting rods in chloride-rich or acidic environments.
• • Decreasing the modulation period while holding total film thickness constant increased the number of interfaces, which absorbed energy from TiAlN layers and relaxed their strain fields, producing lower residual stress. This interface engineering strategy offers a scalable route to tailor residual stress and mechanical properties without altering chemical composition.