Structural and electronic performance of Zn–HAP/hBN composite coatings investigated through experimental and first-principles approaches

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Zinc (Zn)-based composite coatings are emerging as advanced surface materials for aerospace, automotive, energy storage and biomedical applications, yet their development is often hindered by weak interfacial bonding and limited multifunctionality. In this study, reinforcement phases of hexagonal boron nitride (h-BN) and hydroxyapatite (HAP) were integrated into Zn matrices (0.2–0.6 wt.%) via electrodeposition to address these limitations. Among all tested formulations, the Zn–hBN0.2 composite coating demonstrated the most superior multifunctional performance, characterised by the highest microhardness (218 HV) and improved adhesion strength (38.1 ± 1.5 MPa). The combined experimental and computational analyses revealed that the synergistic effect between the inherent solid lubrication of hBN and the strong interfacial bonding between Zn and hBN significantly enhanced the tribological performance. Consequently, the Zn–hBN0.2 coating exhibited a reduced coefficient of friction (0.56), substantially lower wear volume (4.35 × 10 −3 mm 3 ), and the minimum wear rate (2.47 × 10 −3 mm 3 N −1 m −1 ) compared to bare Zn and Zn–HAP coatings. The combination of these features underscores the excellent wear resistance and mechanical stability of the Zn–hBN0.2 coating, confirming its potential as a multifunctional protective material for advanced surface engineering applications. These enhancements stem from h-BN's solid-lubricating nature, uniform dispersion, and strong interfacial bonding with Zn, unlike agglomerated higher-loading hBN or Zn-HAP coatings, which are constrained by weaker Zn···O interactions. To elucidate the underlying mechanisms, density functional theory (DFT) simulations quantified interfacial energetics and electronic properties. The Zn-hBN composite model (BE: −14.0 kcal/mol, E gap : 2.214 eV) demonstrated greater stability than Zn-HAP (BE: −9.3 kcal/mol, E gap : 1.521 eV), including BSSE-corrected binding energy, consistent with experimental hardness and roughness outcomes. By integrating experimental validation with first-principles insights, this work establishes a mechanistic framework for interface-engineered Zn-based coatings, advancing the design of multifunctional, structurally robust, and electronically stable surfaces for demanding applications such as energy storage, aerospace, automotive and other high-performance engineering sectors.

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