Anodic and chrome coatings for firearm barrels: Microstructural and phase analysis

The study employs X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS) and metallographic analysis to assess the phase composition and microstructural features of anodic and chrome coatings. In response to increasing demands for enhanced durability and corrosion resistance in defence applications, surface treatments have become an integral part of the barrel manufacturing process. Aluminium barrels were anodised, while steel barrels were hard chrome plated. The electrochemical rifling (ECR) process was conducted under optimised conditions: current ≈ 950 A, voltage ≈ 7 V, pressure ≈ 2.2 MPa and duration ≈ 176 s. Before coating deposition, the inner bore surface roughness was controlled at Ra = 0.8 µm, ensuring reliable adhesion of the subsequent layers. The XRD and EDS results confirmed near-stoichiometric compositions for both coating types. The anodised layers revealed aluminium and γ-Al2O3 phases, accompanied by minor intermetallic compounds, such as S (Al2CuMg), T (Al2Mg3Zn3) and η (MgZn2). Chrome-plated steel sample exhibited the presence of elemental chromium and goethite (β-FeOOH). These findings support the suitability of the ECR method as a foundation for high-performance coating systems in military applications.