Interfacial Enthalpy Engineering in Nanostructured Ti/TiN Multilayer Coatings: Linking Surface Thermodynamics to Hardness, Friction, and Self-Healing Corrosion Protection
Year: 2026
Type: article
Abstract: Metallic Ti interlayers in reactively sputtered TiN films offer a quantifiable handle on interfacial energetics, with measurable consequences for hardness, friction, and corrosion behaviour. Interlayer-driven re-nucleation refines the crystallite size from 42.5±1.5 to 24.3±0.9 nm and simultaneously roughens the surface (Rq from 10.0 ± 0.7 to 14.0 ± 0.8 nm), so the two structural changes cannot be separated: the modest decrease in water contact angle from 89 ± 1.4° to 87.2 ± 1.6°, is largely topographic in origin, and only after Wenzel correction does it yield a physically meaningful effective surface energy, rising from 2.76 ±0.05 to 2.91 ±0.07 J·m⁻². Because the excess enthalpy term 6γV m /d responds to both γ and d, grain refinement alone does not account for the observed energetics; the calculated ΔH f ° shifts from −331.57 ±0.10 to −328.13 ±0.17 kJ·mol⁻¹, i.e. 3.47 ±0.20 kJ·mol⁻¹ above the bulk benchmark of −336 kJ·mol⁻¹, which we interpret as enthalpy stored in a denser boundary network rather than as a loss of stability. This interpretation is supported on three independent fronts. Nanoindentation gives 22.5 ± 0.5 GPa against 19.7 ± 0.6 GPa, with discrete pop-in events pointing to dislocation nucleation at boundary triple junctions. Reciprocating sliding lowers the steady-state friction coefficient from about 0.50 ±0.02 to 0.44 ±0.02 and the track depth from 2.7 ±0.1 to 2.2 ±0.1 µm, sustained by a self-organised TiO x /TiN x tribofilm whose stability tracks boundary density. In Hank’s solution, EIS resolves a near-threefold gain in total polarisation resistance and an additional corrosion-product term R cp about 411,925 ± 24,000 Ω·cm² absent from the monolithic circuit, consistent with TiO₂ sealing defects at exposed Ti sites. Grain size, roughness, and surface energy therefore act as one coupled set of variables governing both the thermodynamics and the durability of nanostructured nitride coatings.
Source: Materials Today Communications
Language: English
Subfield: Mechanics of Materials
Field: Engineering
Domain: Physical Sciences
Open Access status: hybrid
Estimated APC paid: $2,830
OpenAlex ID: W7225414036