Gas-Phase Phosphate Surface Modification of Iron Powders: Microstructural Evolution and Coating Formation Mechanisms

Surface modification of metallic powders plays a critical role in improving their chemical stability, interfacial characteristics, and processing behavior in powder metallurgy applications. In this study, micron-sized iron powders were treated using a controlled gas-phase phosphating process to investigate surface layer formation and microstructural evolution. The influence of treatment conditions on phase stability, surface morphology, and elemental distribution was systematically analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The results confirm the preservation of the body-centered cubic α-Fe phase within an optimized temperature range, while a conformal phosphate-based surface layer was successfully formed. Increased treatment severity led to partial surface oxidation and localized microstructural heterogeneity. Elemental mapping revealed homogeneous phosphorus distribution under controlled processing conditions, indicating uniform coating development. The study establishes clear correlations between gas-phase processing parameters and surface layer formation mechanisms. These findings provide insight into the controlled surface engineering of iron powders and offer practical guidance for optimizing gas-phase phosphating routes in advanced powder metallurgy and metallurgical applications.